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Recently, we demonstrated that chronic blockade of the renin-angiotensin system (RAS) lowered the blood pressure (BP) of adult Ren-2 transgenic rats (TGR) mainly through the attenuation of central sympathoexcitation. However, the participation of central and peripheral mechanisms in the development of high BP in immature TGR remains unclear. In the present study, 6-week-old heterozygous TGR males were chronically treated with intracerebroventricular (ICV) or intraperitoneal (IP) infusions of the AT1 receptor inhibitor losartan (1 or 2 mg/kg/day) for 4 weeks. The influence of these treatments on sympathetic- and angiotensin II-dependent BP components (BP response to pentolinium or captopril, respectively) as well as on BP response to exogenous angiotensin II were determined to evaluate the participation of central and peripheral RAS in hypertension development. Chronic IP losartan administration (1 or 2 mg/kg/day) lowered the BP of immature TGR by reducing both sympathetic and angiotensin II-dependent BP components. The central action of IP-administered losartan was indicated by a reduced BP response to acute ICV angiotensin II injection. Chronic ICV administration of a lower losartan dose (1 mg/kg/day) reduced only the sympathetic BP component, whereas a higher ICV administered dose (2 mg/kg/day) was required to influence the angiotensin II-dependent BP component. Accordingly, chronic ICV losartan administration of 2 mg/kg/day (but not 1 mg/kg/day) attenuated the BP response to acute intravenous angiotensin II application. In conclusion, central sympathoexcitation seems to play an important role in hypertension development in immature TGR. Central sympathoexcitation is highly susceptible to inhibition by low doses of RAS-blocking agents, whereas higher doses also affect peripheral angiotensin II-dependent vasoconstriction.

Salt hypertensive Dahl rats are characterized by sympathoexcitation and relative NO deficiency. We tested the hypothesis that the increased blood pressure (BP) response to fasudil in salt hypertensive Dahl rats is due to augmented calcium sensitization in the salt-sensitive strain and/or due to their decreased baroreflex efficiency. BP reduction after acute administration of nifedipine (an L-type voltage-dependent calcium channel blocker) or fasudil (a Rho kinase inhibitor) was studied in conscious intact rats and in rats subjected to acute NO synthase inhibition or combined blockade of the renin-angiotensin system (captopril), sympathetic nervous system (pentolinium), and NO synthase (L-NAME). Intact salt-sensitive (SS) Dahl rats fed a low-salt diet had greater BP responses to nifedipine (-31 ± 6 mmHg) or fasudil (-34 ± 7 mmHg) than salt-resistant (SR) Dahl rats (-16 ± 4 and -17 ± 2 mmHg, respectively), and a high-salt intake augmented the BP response only in SS rats. These BP responses were doubled after acute NO synthase inhibition, indicating that endogenous NO attenuates both calcium entry and calcium sensitization. Additional pentolinium administration, which minimized sympathetic compensation for the drug-induced BP reduction, magnified the BP responses to nifedipine or fasudil in all groups except for salt hypertensive SS rats due to their lower baroreflex efficiency. The BP response to the calcium channel blocker nifedipine can distinguish SS and SR rats even after calcium sensitization inhibition by fasudil, which was not seen when fasudil was administered to nifedipine-pretreated rats. Thus, enhanced calcium entry (potentiated by sympathoexcitation) in salt hypertensive Dahl rats is the abnormality that is essential for their BP increase, which was further augmented by increased calcium sensitization in salt-sensitive Dahl rats.

Glucocorticoids (GCS) are known to modulate cardiovascular response during stress conditions. The present study was aimed to test the hypothesis that permissive and/or stimulating effect of GCs is essential for the maintenance of peripheral vascular resistance and for the adequate response of cardiovascular system to stressor exposure. The effects of acute pharmacological adrenalectomy (PhADX) on humoral and cardiovascular parameters were studied in adult Wistar rats under the basal conditions and during the acute restraint stress. Acute PhADX was performed by the administration of metyrapone and aminoglutethimide (100 mg/kg s.c. of each drug) resulting in a suppression of endogenous glucocorticoid synthesis. Blood pressure (BP), heart rate (HR) and core body temperature were measured using radiotelemetry. BP responses to administration of vasoactive agents were determined in pentobarbital-anesthetized animals. PhADX considerably attenuated stress-induced increase of BP, HR and core body temperature. PhADX did not abolish BP and HR lowering effects of ganglionic blocker pentolinium indicating preserved sympathetic function in PhADX rats. BP response to exogenous norepinephrine administration was attenuated in PhADX rats, suggesting reduced sensitivity of cardiovascular system. Suppression of corticosterone synthesis by PhADX increased basal plasma levels of ACTH, aldosterone and plasma renin activity in unstressed animals but there was no further increase of these hormones following stressor exposure. In conclusion, PhADX attenuated stress-induced rise of blood pressure, heart rate and core body temperature indicating an important permissive and/or stimulating role of glucocorticoids in the maintenance of the adequate response of cardiovascular system and thermoregulation to several stimuli including acute exposure to stressor.

Mecamylamine is a non-competitive nicotinic acetylcholine receptor (nAChR) antagonist that has been prescribed for hypertension and as an off-label smoking cessation aid. Here, we examined pharmacological mechanisms underlying the interoceptive effects (i.e., discriminative stimulus effects) of mecamylamine (5.6 mg/kg s.c.) and compared the effects of nAChR antagonists in this discrimination assay to their capacity to block a nicotine discriminative stimulus (1.78 mg/kg s.c.) in rhesus monkeys. Central (pempidine) and peripherally restricted nAChR antagonists (pentolinium and chlorisondamine) dose-dependently substituted for the mecamylamine discriminative stimulus in the following rank order potency (pentolinium > pempidine > chlorisondamine > mecamylamine). In contrast, at equi-effective doses based on substitution for mecamylamine, only mecamylamine antagonized the discriminative stimulus effects of nicotine, i.e., pentolinium, chlorisondamine, and pempidine did not. NMDA receptor antagonists produced dose-dependent substitution for mecamylamine with the following rank order potency (MK-801 > phencyclidine > ketamine). In contrast, behaviorally active doses of smoking cessation aids including nAChR agonists (nicotine, varenicline, and cytisine), the smoking cessation aid and antidepressant bupropion, and the benzodiazepine midazolam did not substitute for the discriminative stimulus effects of mecamylamine. These data suggest that peripheral nAChRs and NMDA receptors may contribute to the interoceptive stimulus effects produced by mecamylamine. Based on the current results, the therapeutic use of mecamylamine (i.e., for smoking or to alleviate green tobacco sickness) should be weighed against the potential for mecamylamine to produce interoceptive effects that overlap with another class of abused drugs (i.e., NMDA receptor agonists).

Schlager mice (BPH/2J) are hypertensive due to a greater contribution of the sympathetic nervous system (SNS) and renin-angiotensin system (RAS). The kidneys of BPH/2J are hyper-innervated suggesting renal nerves may contribute to the hypertension. We therefore determined the effect of bilateral renal denervation (RD) on hypertension in BPH/2J. Mean arterial pressure (MAP) was measured by radiotelemetry before and for 3 weeks after RD in BPH/2J and BPN/3J. The effects of pentolinium and enalaprilat were examined to determine the contribution of the SNS and RAS, respectively. After 3 weeks, MAP was -10.9 ± 2.1 mmHg lower in RD BPH/2J compared to baseline and -2.1 ± 2.2 mmHg in sham BPH/2J (P 0.001, n = 8-10). RD had no effect in BPN/3J (P 0.1). The depressor response to pentolinium was greater in BPH/2J than BPN/3J, but in both cases the response in RD mice was similar to sham. Enalaprilat decreased MAP more in RD BPH/2J compared to sham (-12 vs -3 mmHg, P 0.001) but had no effect in BPN/3J. RD reduced renal noradrenaline in both strains but more so in BPH/2J. RD reduced renin mRNA and protein, but not plasma renin in BPH/2J to levels comparable with BPN/3J mice. We conclude that renal nerves contribute to hypertension in BPH mice as RD induced a sustained fall in MAP, which was associated with a reduction of intrarenal renin expression. The lack of inhibition of the depressor effects of pentolinium and enalaprilat by RD suggests that vasoconstrictor effects of the SNS or RAS are not involved.

Ligands of auxiliary α 2 δ subunit of voltage-dependent calcium channels (VDCCs) decrease elevated L-type VDCCs surface expression in arterial myocytes and arterial constriction in spontaneously hypertensive rats (SHR). However, their effect on blood pressure (BP) is unclear. In this study, we investigated the hemodynamic response to acute and chronic administration of gabapentin, a ligand of auxiliary α 2 δ subunit of VDCCs, in adult SHR with established neurogenic hypertension. The acute gabapentin administration lowered BP and heart rate more in conscious SHR than Wistar-Kyoto rats. Both nifedipine (L-type VDCCs blocker) and ω-conotoxin GVIA (N-type VDCCs blocker) also decreased BP more in SHR, but only gabapentin and ω-conotoxin GVIA abolished the nitroprusside-induced reflex tachycardia of baroreceptor-heart rate control. Hypotensive effect of gabapentin was accompanied by a reduction of (1) plasma norepinephrine level, (2) depressor response to ganglionic blocker pentolinium, (3) power of low frequency component of systolic BP variability, and (4) pressor response of mesenteric vascular bed to periarterial nerve stimulation, suggesting the decrease of peripheral sympathetic nerve transmission. Moreover, gabapentin effects on BP and baroreflex were absent in sympathectomized rats. In conclusion, the acute (but not chronic) administration of gabapentin lowered BP more in SHR than in Wistar-Kyoto rats. Besides the known L-type VDCCs involvement in the vascular effect of gabapentin, our data revealed the important role of N-type VDCCs in acute gabapentin effect on sympathetic control of BP. Gabapentin-induced changes of sympathetic nerve transmission indicated major hemodynamic mechanism of the acute response to this drug.

BPH/2J mice are recognized as a neurogenic model of hypertension primarily based on overactivity of the sympathetic nervous system and greater neuronal activity in key autonomic cardiovascular regulatory brain regions. The medial amygdala (MeAm) is a forebrain region that integrates the autonomic response to stress and is the only region found to have greater Fos during the night and daytime in BPH/2J compared with BPN/3J mice. To determine the contribution of the MeAm to hypertension, the effect of neuronal ablation on blood pressure (BP) was assessed in BPH/2J (n=7) and normotensive BPN/3J mice (n=7). Mice were preimplanted with radiotelemetry devices to measure 24-hour BP and cardiovascular responses to stress, before and 1 to 3 weeks after bilateral lesions of the MeAm. Baseline BP was 121±4 mm Hg in BPH/2J and 101±2 mm Hg in BPN/3J mice ( P strain P lesion P lesion P lesion

OBJECTIVE Excessive opening of the adenosine triphosphate-sensitive potassium channel in vascular smooth muscle is implicated in the vasodilation and vascular hyporeactivity underlying septic shock. Therapeutic channel inhibition using sulfonylurea agents has proved disappointing, although agents acting on its pore appear more promising. We thus investigated the hemodynamic effects of adenosine triphosphate-sensitive potassium channel pore inhibition in awake, fluid-resuscitated septic rats, and the extent to which these responses are modulated by the high sympathetic tone present in sepsis. Temporal changes in ex-vivo channel activity and subunit gene expression were also investigated. DESIGN In vivo and ex vivo animal study. SETTING University research laboratory. SUBJECTS Male adult Wistar rats. INTERVENTIONS AND MEASUREMENTS Fecal peritonitis was induced in conscious, fluid-resuscitated rats. Pressor responses to norepinephrine and PNU-37883A (a vascular adenosine triphosphate-sensitive potassium channel inhibitor acting on the Kir6.1 pore-forming subunit) were measured at 6 or 24 hrs, in the absence or presence of the autonomic ganglion blocker, pentolinium. The aorta and mesenteric artery were examined ex vivo for rubidium efflux as a marker of adenosine triphosphate-sensitive potassium channel activity, and for adenosine triphosphate-sensitive potassium channel subunit gene expression using quantitative reverse transcription-polymerase chain reaction. MAIN RESULTS A total of 120 rats (50 sham-operated controls, 70 septic) were included. Septic rats became hypotensive after 12 hrs, with a 24-hr mortality of 51.7% (0% in controls). At 6 hrs, there was an attenuated pressor response to norepinephrine (p < .01) despite blood pressure being elevated (p < .01). PNU-37883A had no pressor effect, except in the presence of pentolinium (p < .01). Kir6.1 subunit mRNA increased significantly in the mesenteric artery while rubidium efflux was increased in both the aorta and mesenteric artery at 24 hrs. CONCLUSIONS Despite evidence of increased adenosine triphosphate-sensitive potassium channel activity in sepsis, it appears to be inhibited in vivo by high sympathetic tone. This may explain, at least in part, the reduced efficacy of adenosine triphosphate-sensitive potassium channel blockers in human septic shock.

Hypertension is associated with the imbalance of vasoconstrictor and vasodilator systems. Vasodilation is usually evaluated in isolated blood vessels, but except for nitric oxide (NO), relatively little attention is given to the in vivo efficiency of particular vasodilator mechanisms. The aim of our study was to evaluate the contribution of endogenous vasodilator prostanoids, Ca2+-activated K+ channels and NO to blood pressure (BP) maintenance in rats with three different forms of experimental hypertension. Both principal vasopressor systems (the renin–angiotensin system and the sympathetic nervous system) were blocked by captopril and pentolinium in conscious spontaneously hypertensive rats (SHRs), Dahl salt-hypertensive (DS-HS) rats and rats with NO-deficient hypertension, as well as in their normotensive controls. Thereafter, we monitored BP changes in rats subjected to either a sequential or an isolated blockade of prostanoid synthesis by the non-selective cyclooxygenase inhibitor, indomethacin, of Ca2+-activated K+ channels by tetraethylammonium and of NO formation by NG-nitro-L-arginine methyl ester. All three forms of experimental hypertension were characterized by augmented sympathetic vasoconstriction. The vasodilatation exerted by endogenous prostanoids and Ca2+-activated K+ channels was enhanced in all forms of hypertension, almost proportionally to BP elevation. On the contrary, NO-dependent vasodilatation was not enhanced in any form of experimental hypertension, and there was a severe relative NO deficiency in both, SHRs and DS-HS rats. In conclusion, our data suggested that there is a compensatory activation of vasodilator prostanoids and Ca2+-activated K+ channels in rats with experimental hypertension, whereas NO-dependent vasodilatation is not augmented. Thus, the overall activity of vasodilator systems failed to compensate for augmented sympathetic vasoconstriction in hypertensive animals.

The medial amygdaloid nucleus (MeA) is involved in the modulation of physiological and behavioral processes, as well as regulation of the autonomic nervous system. Moreover, MeA electrical stimulation evokes cardiovascular responses. Thus, as noradrenergic receptors are present in this structure, the present study tested the effects of local noradrenaline (NA) microinjection into the MeA on cardiovascular responses in conscious rats. Moreover, we describe the types of adrenoceptor involved and the peripheral mechanisms involved in the cardiovascular responses. Increasing doses of NA (3, 9, 27 or 45 nmol/100 nL) microinjected into the MeA of conscious rats caused dose-related pressor and bradycardic responses. The NA cardiovascular effects were abolished by local pretreatment of the MeA with 10 nmol/100 nL of the specific α₂-receptor antagonist RX821002, but were not affected by local pretreatment with 10 nmol/100 nL of the specific α₁-receptor antagonist WB4101. The magnitude of pressor response evoked by NA microinjected into the MeA was potentiated by intravenous pretreatment with the ganglion blocker pentolinium (5 mg/kg), and blocked by intravenous pretreatment with the selective V₁-vasopressin antagonist dTyr(CH₂)₅ (Me)AVP (50 μg/kg). In conclusion, our results show that microinjection of NA into the MeA of conscious rats activates local α₂-adrenoceptors, evoking pressor and bradycardic responses, which are mediated by vasopressin release.

Whole body hematocrit/large vessel hematocrit (WBH/LVH ratio) has been examined in 21 normotensive and 35 hypertensive subjects and found to be the same, presumably as an expression of a uniform distribution of the blood volume in the two groups. Moderate renal impairment, the degree of the retinopathy, or the height of the diastolic blood pressure do not seem to influence the ratio figures. The WBH/LVH ratio was examined during treatment with various hypotensive drugs. A significant increase in the ratio was demonstrated during the influence of a single effective intravenous dose of pentolinium. Similar results were obtained during short-term treatment with guanethidine alone and during long-term treatment with guanethidine and hydrochlorothiazide. Treatment with hydrochlorothiazide alone caused an increase in ratio after one week and after three months, but these increases were not significant. The possible causes of these alterations in the WBH/LVH ratio are discussed. The advantage of employing a double isotope technique in preference to a quicker single isotope technique has been analyzed in relation to the determination of the total blood volume in patients during treatment with hypotensive drugs.

Background: Determinants of plasma norepinephrine (NE) and epinephrine concentrations are well known; those of the third endogenous catecholamine, dopamine (DA), remain poorly understood. We tested in humans whether DA enters the plasma after corelease with NE during exocytosis from sympathetic noradrenergic nerves. Methods: We reviewed plasma catecholamine data from patients referred for autonomic testing and control subjects under the following experimental conditions: during supine rest and in response to orthostasis; intravenous yohimbine (YOH), isoproterenol (ISO), or glucagon (GLU), which augment exocytotic release of NE from sympathetic nerves; intravenous trimethaphan (TRI) or pentolinium (PEN), which decrease exocytotic NE release; or intravenous tyramine (TYR), which releases NE by nonexocytotic means. We included groups of patients with pure autonomic failure (PAF), bilateral thoracic sympathectomies (SNS-x), or multiple system atrophy (MSA), since PAF and SNS-x are associated with noradrenergic denervation and MSA is not. Results: Orthostasis, YOH, ISO, and TYR increased and TRI/PEN decreased plasma DA concentrations. Individual values for changes in plasma DA concentrations correlated positively with changes in NE in response to orthostasis (r = 0.72, P < 0.0001), YOH (r = 0.75, P < 0.0001), ISO (r = 0.71, P < 0.0001), GLU (r = 0.47, P = 0.01), and TYR (r = 0.67, P < 0.0001). PAF and SNS-x patients had low plasma DA concentrations. We estimated that DA constitutes 2%–4% of the catecholamine released by exocytosis from sympathetic nerves and that 50%–90% of plasma DA has a sympathoneural source. Conclusions: Plasma DA is derived substantially from sympathetic noradrenergic nerves.

The present study is designed to screen the effect of syringin, an active principle purified from the rhizome and root parts of Eleutherococcus senticosus (Araliaceae), on the plasma glucose and investigate the possible mechanisms. Plasma glucose decreased in a dose-dependent manner 60 min after intravenous injection of syringin into fasting Wistar rats. In parallel to the decrease of plasma glucose, increases of plasma insulin level as well as the plasma C-peptide was also observed in rats receiving same treatment. Both the plasma glucose lowering action and the raised plasma levels of insulin and C-peptide induced by syringin were also inhibited by 4-diphenylacetoxy-N-methylpiperdine methiodide (4-DAMP), the antagonist of the muscarinic M3 receptors, but not affected by the ganglionic nicotinic antagonist, pentolinium or hexamethonium. Moreover, disruption of synaptic available acetylcholine (ACh) using an inhibitor of choline uptake, hemicholinium-3, or vesicular acetylcholine transport, vesamicol, abolished these actions of syringin. Also, physostigmine at concentration sufficient to inhibit acetylcholinesterase enhanced the actions of syringin. Mediation of ACh release from the nerve terminals to enhance insulin secretion by syringin can thus be considered. The results suggest that syringin has an ability to raise the release of ACh from nerve terminals, which in turn to stimulate muscarinic M3 receptors in pancreatic cells and augment the insulin release to result in plasma glucose lowering action.

The ventral medial prefrontal cortex (vMPFC) is involved in central cardiovascular control. In the present study, we studied the cardiovascular effects of injections of L-glutamate into the vMPFC of unanaesthetized rats and the mechanisms of these effects. Male Wistar rats were used and L-glutamate was microinjected in the vMPFC in a final volume of 200 nL. Microinjections of L-glutamate (9, 27, 81, 150 or 300 nmol) caused long-lasting, dose-related pressor and tachycardic responses in unanaesthetized rats. No differences were observed among cardiovascular responses when L-glutamate was injected into the three sub-areas that comprise the vMPFC, namely the prelimbic, the infralimbic and the dorsal peduncular cortices. No responses were observed when the dose of 81 nmol of L-glutamate was microinjected into surrounding structures such as the cingulate cortex area 1, the corpus callosum and the tenia tecta, indicating a predominant action on the vMPFC. The cardiovascular response to L-glutamate into the vMPFC was blocked by intravenous pretreatment with the ganglion blocker pentolinium (10 mg/kg, i.v.) or the beta 1 -adrenoceptor antagonist atenolol (1.5 mg/kg, i.v.), supporting the involvement of the cardiac sympathetic nervous system in the response to L-glutamate. Pretreatment with the muscarinic antagonist homatropine methyl bromide (1 mg/kg, i.v.) reduced the latency to the onset of the pressor and tachycardic responses to L-glutamate injected into the vMPFC without significant effects on response duration or maximum effect. We conclude that stimulation of the vMPFC with L-glutamate caused pressor and tachycardic responses in unanaesthetized rats, responses which were dependent on cardiac sympathetic nerve activation and were potentiated by blockade of peripheral muscarinic receptors.

Acute pharmacogenetic analysis was carried out in an intercross F2 population derived from Prague hypertensive-hypertriglyceridemic and Lewis rats. Quantitative trait loci (QTL) mapping was performed for baseline blood pressure (BP) and for BP after blockade of the renin-angiotensin system by losartan, of the sympathetic nervous system (SNS) by pentolinium, and of the nitric oxide system by N(G)-nitro- L-arginine methyl ester. Two significant loci for baseline BP were found on chromosome (Chr) 3 (logarithm of likelihood, LOD, 3.8) and Chr 5 (LOD 3.6), and one suggestive locus on Chr 1 (LOD 2.7). The QTL on Chr 3 persisted after treatment with the three agents while the QTL on Chr 5 and Chr 1 disappeared after pentolinium administration. This suggests independence of the locus on Chr 3 from each acute BP regulatory system examined, whereas the loci on Chr 5 and Chr 1 appeared to be controlled mainly by the SNS. Although not apparent at baseline, a significant locus appeared on Chr 8 (LOD 7.0) after blockade of the SNS, and NO system blockade led to the appearance of a new QTL on Chr 1 (LOD 3.6), indicating the contribution of the inhibited systems to these loci. Pharmacogenetic dissection of the BP trait is a powerful tool to unravel the underlying physiological mechanisms of QTL affecting baseline BP and to identify specific QTL for the response to drugs. This pharmocogenetic approach enabled us to determine the main causative acute BP regulatory systems and should lead to better selection of suitable antihypertensive drugs for individual patients.

BACKGROUND Our previous experiments demonstrated that selective endothelin A (ETA) receptor blockade had antihypertensive effects in Ren-2 transgenic rats (TGRs), but the mechanisms responsible for this change of blood pressure (BP) have not been explored yet. METHOD Four-week-old male heterozygous TGRs and their normotensive controls--Hannover Sprague-Dawley (HanSD) rats--were fed high-salt diet (2% NaCl) and were treated with selective ETA receptor blocker atrasentan (5 mg/kg per day) for 8 weeks. At the end of the study, the contribution of principle vasoactive systems was evaluated by the sequential blockade of the renin-angiotensin system (captopril), sympathetic nervous system (pentolinium) and nitric oxide synthase [N-nitro-L-arginine methyl ester (L-NAME)]. The role of calcium influx through L-type voltage-dependent calcium channels in BP maintenance was evaluated using nifedipine. In a separate group of animals, the efficiency of distinct vasodilator systems--prostanoids (blocked by nonselective cyclooxygenase inhibitor indomethacin) and Ca-activated K channels (inhibited by tetraethylammonium)--was also analyzed. RESULTS Atrasentan attenuated the development of hypertension in heterozygous TGRs, but had no effects in Hannover Sprague-Dawley rats. Moreover, atrasentan moderately attenuated renin-angiotensin system-dependent vasoconstriction, whereas it had no effect on sympathetic vasoconstriction. The nifedipine-sensitive BP component was markedly decreased by atrasentan treatment. In contrast, vasodilatation mediated by nitric oxide, endogenous prostanoids or Ca-activated K channels was reduced in atrasentan-treated TGRs, indicating the absence of compensatory augmentation of endothelin B receptor-mediated vasodilation in these animals. CONCLUSION BP-lowering effect of chronic atrasentan treatment in TGRs was mainly caused by reduced Ca influx through L-type voltage-dependent calcium channels due to missing ETA receptor-dependent vasoconstriction and attenuated angiotensin II-dependent vasoconstriction.

Hypertension provoked since the beginning of the 19th century a medical debate between physicians. The early antihypertensive agents were poorly tolerated. Progress towards more effective drugs, appeared after the 2nd World War. Thiocyanates, dehydrogenated alkaloids of ergot, barbiturates, bismuth and bromides, were soon replaced by phenoxbenzamine, hexamethonium, pentolinium, and mecamylamine. Thiazide diuretics were the biggest breakthrough during the early 1960's. Then Beta(β)-blockers and angiotensin-converting enzyme inhibitors heralded a new era, until 1995, when losartan, the first non-peptide anti-hypertensive drug, was introduced. The plethora of the antihypertensive drugs changed the relationship between physicians and patients, pushed medicine towards prevention, and altered the medical marketing forever.

Regional haemodynamic responses to the cannabinoid agonist, WIN 55212-2 (5 – 250 μg kg−1 i.v.) were assessed in conscious, normotensive, Hannover, Sprague-Dawley (HSD) rats, and in hypertensive, transgenic ((mRen-2)27) (abbreviated to TG) rats. In HSD rats, WIN 55212-2 caused pressor, and renal and mesenteric vasoconstrictor effects, with a hindquarters vasodilator effect occurring only at the highest dose. In TG rats, the effects of the cannabinoid agonist were qualitatively similar to those seen in HSD rats, except there was no hindquarters vasodilatation. In both strains of rat, in the presence of losartan, pentolinium and a vasopressin (V1-receptor) antagonist, the pressor and vasoconstrictor effects of WIN 55212-2 were abolished, but the hindquarters vasodilator response was enhanced (HSD rats) or was seen only in that circumstance (TG rats). Under these conditions, both strains of rat showed a modest fall in blood pressure, together with mesenteric vasodilatation. In additional experiments in normotensive SD rats from Charles River (CRSD), it was shown that, in the presence of the V1-receptor antagonist alone, or losartan alone, or the two antagonists together, the cardiovascular effects of WIN 55212-2 (50 or 150 μg kg−1) were not attenuated. Hence, the effects described above were likely due to pentolinium. There were no consistent differences between HSD and TG rats in their haemodynamic responses to methoxamine or noradrenaline, indicating the two strains were not likely to differ markedly in their responsiveness to any putative sympathetic activation induced by WIN 55212-2. Collectively, the results indicate that the predominant cardiovascular effects of WIN 55212-2 in conscious HSD and TG rats (i.e., pressor and vasoconstrictor actions) can be attributed largely to indirect, pentolinium-sensitive mechanisms, which appear to differ little in the normotensive and hypertensive state, at least in conscious animals. Under the conditions of our experiments, signs of cannabinoid-induced vasodilatation were modest. Keywords: WIN 55212-2, cannabinoids, transgenic rats, hypertension, vasodilatation Introduction The discovery of the existence of endogenous cannabinoids (see Mechoulam et al., 1994; 1998 for review), and specific receptors for them (see Pertwee, 1997 for review), has stimulated renewed interest in the possible biological role, and therapeutic potential, of drugs derived from these compounds. However, the literature to date amply illustrates the complexity of this area of research, particularly in the context of cardiovascular function (see Compton et al., 1996 for review). For example, the effects of the cannabinoids may be influenced by the nature of the experiment (in vitro vs in vivo), the type of in vitro preparation (e.g., isolated mesenteric vessel vs perfused mesenteric vascular bed), and, for in vivo studies, the state of the experimental animals (pithed, anaesthetized, or conscious), their strain, and the route of administration (central vs peripheral) of the compounds. Further complexity is added by recent observations indicating that endogenous cannabinoids, such as anandamide, may exert effects by interacting, not only with cannabinoid receptors, but also with vanilloid receptors (Zygmunt et al., 1999; see Szallasi & Di Marzo, 2000 for review). Thus, some of the reported differences between anandamide and other cannabinoids could be due to such additional actions of anandamide. However, even synthetic cannabinoids, such as WIN 55212-2 (an aminoalkylindole with affinity for CB1 and CB2 receptors (see Pertwee, 1997)), have complex influences on cardiovascular function. In that context, a recent, elegant study by Niederhoffer & Szabo (1999), identified at least four cardiovascular regulatory mechanisms influenced by WIN 55212-2 in rabbits, namely: prejunctional inhibition of noradrenaline release from postganglionic sympathetic neurones (pithed animals), central sympathoexcitation, and vagal cardiac efferent activation (both at the level of the brain stem following central administration to conscious rabbits), and central sympathoinhibition (following high systemic doses in conscious rabbits). Interestingly, Niederhoffer & Szabo (1999) could find no evidence for cannabinoid-mediated vasodilatation (Randall et al., 1996), as judged by a lack of depressor effect of WIN 55212-2 in pithed, noradrenaline-supported, rabbits, although no direct measures of vascular tone were made in any of their experiments. Furthermore, the question of whether or not cannabinoids have vasodilator actions in other species in vivo is unresolved. With these various observations as a backdrop, our present objectives were to evaluate the regional haemodynamic actions of a range of systemic doses of WIN 55212-2 in conscious rats. We studied normotensive, Hannover Sprague-Dawley (HSD) rats, and transgenic ((mRen-2)-27) hypertensive (TG) rats (Mullins et al., 1990), our hypothesis being that the altered sympathetic control mechanisms in the latter (Averill et al., 1996) might influence the cardiovascular responses to WIN 55212-2. This seemed feasible, since Lake et al. (1997b) have reported that the cardiovascular effects of anandamide in conscious spontaneously hypertensive rats (SHRs) differed from those seen in the normotensive control rats, and they attributed the difference to the level of pre-existing sympathetic tone. Our experiments were performed before and after inhibition of the major neurohumoral vasoconstrictor systems (sympathoadrenal, renin-angiotensin and vasopressin), using ganglion blockade, and angiotensin (AT1), and vasopressin (V1) receptor antagonism. We did this in an attempt to determine whether or not, in the absence of the major pressor systems, vasodilator effects of the cannabinoid could be demonstrated. Since we observed some differences between the responses to WIN 55212-2 in the HSD and TG rats in the intact state, in a final experiment we compared regional haemodynamic responses to noradrenaline and methoxamine, to discern whether or not the differential effects of WIN 55212-2 might be attributable to differences in responsiveness to sympathoexcitation in the two strains of rat. Some of the results have been presented to the British Pharmacological Society (Gardiner et al., 1999a; 2000a).

We developed a new model of psychological "open-field" stress in freely moving rats. Blood pressure and heart rate of the rats were measured by radiotelemetry and behavior analyzed by video tracking software. Open-field exposure induced marked increases in blood pressure and heart rate. Repeated daily exposure induced pressor responses that were slightly higher on Day 4 when compared to Day 1. Pretreatment with the beta1-adrenoceptor antagonist atenolol inhibited the tachycardia whereas the ganglion blocker pentolinium inhibited the pressor response, indicating involvement of the sympathetic nervous system. Pretreatment with diazepam prevented the novelty stress-induced pressor response and reduced the tachycardia. These results show that the psychological stress of exposing rats to an open field induces marked cardiovascular effects that are mediated by sympathetic hyperactivity. This model is unique in that it focuses on psychological stress and allows concomitant measurement of blood pressure, heart rate, and behavior in freely moving rats.

A muscarinic alkaloid with a quaternary nitrogen was isolated from Trophis racemosa. Aqueous solutions (0.5%-2%) of the chloride salt of the alkaloid produced dose-dependent reductions of intra-ocular pressure ranging from 6.6 +/- 0.7 mmHg to 15.7 +/- 0.3 mmHg, (p < 0. 001, n = 5) in dogs. Atropine (0.1 mL of a 1% solution) and pirenzepine at a non selective antagonist dose (0.1 mL of 0.5% solution) for M(1) and M(3) receptors blocked the reduction of intra-ocular pressure, but alpha-adrenoceptor blockade with phenoxybenzamine (0.1 mL of a 1% solution) did not block the reduction of intra-ocular pressure. On the isolated guinea-pig ileum and trachea, the alkaloid produced contractions which were inhibited by atropine (6 x 10(-7) M or 0.4 microg/mL) and by pirenzepine at a non-selective antagonist dose (3.1 x 10(-6) M or 1.3 microg/mL) for M(1) and M(3) receptors. But neither selective blockade of M(2) receptors with gallamine (1.7 x 10(-6) M or 1.5 microg/mL) nor selective blockade of M(1) receptors with pirenzepine (7 x 10(-9) M or 3 ng/mL) inhibited the alkaloid-induced contractions. There was also no inhibition of the alkaloid-induced contractions in the presence of ganglionic nicotinic receptor blockade with pentolinium (5.6 x 10(-7) M or 0.3 microg/mL) and hexamethonium (1.7 x 10(-6) M or 0.6 microg/mL), but nicotine-induced contractions were inhibited by these ganglionic blockers. These results suggest that a muscarinic alkaloid from Trophis racemosa produced ocular hypotension via M(3) receptor stimulation in dogs.

1. Microinjection of the cholinergic agonist carbachol (3.3, 5.5 and 13.2 nmol) into the posterior hypothalamic nucleus of conscious rats evokes a dose-dependent increase in blood pressure. The pressor response evoked by the lower doses of carbachol was attenuated by pretreatment with the ganglionic nicotinic receptor antagonist pentolinium (10 mg kg(-1), i.v.) while blockade of V1-vasopressin receptors with [d(CH2)5Tyr(Me)]AVP (20 microg kg(-1), i.v.) reduced the pressor response evoked by the highest dose. 2. The combination of pentolinium and the muscarinic receptor antagonist methylatropine (2 mg kg(-1), i.v.) completely blocked the response evoked by the lower doses while the addition of [d(CH2)5Tyr(Me)]AVP to these two antagonists was required for further inhibition of the pressor response to the highest dose of carbachol. Bilateral adrenal demedullation did not affect the pressor response evoked by 5.5 or 13.2 nmol of carbachol. 3. Treatment of intact and adrenal demedullated rats with pentolinium after the pressor response to 13.2 nmol of carbachol was underway reversed the pressor response, but not to the same degree as that provided by the combination of pentolinium and methylatropine, or pentolinium and [d(CH2)5Tyr(Me)]AVP. 4. Methylatropine or [d(CH2)5Tyr(Me)]AVP caused a slight reversal of the carbachol-induced pressor response once it was underway in intact rats. Methylatropine given before or after pentolinium worked with the pentolinium to completely reverse the response. Methylatropine given alone reversed the bradycardia evoked by carbachol to a tachycardia which itself was antagonized by subsequent treatment with pentolinium. 5. These results suggest that the pressor response evoked by carbachol microinjection into the posterior hypothalamic nucleus of conscious rats involves sympathoexcitation and vasopressin release. The sympathoexcitation involves nicotinic and muscarinic receptors in autonomic ganglia.

We examined the role of central nitric oxide (NO) in the baroreceptor reflex in conscious rabbits. Intracerebroventricular infusion of 20 μmol of N ω-nitro-l-arginine methyl ester (l-NAME) to block central NO resulted in increases in arterial pressure, renal sympathetic nerve activity (RSNA), and plasma catecholamine levels, and the pressor response was suppressed by pretreatment with pentolinium (5 mg/kg iv). On the other hand, a subpressor dose of intracerebroventricular l-NAME (10 μmol/h) caused significant increases in baroreflex sensitivities assessed by RSNA and heart rate compared with vehicle infusion [maximum gain: −18.2 ± 0.9 vs. −9.6 ± 0.9%/mmHg ( P < 0.001) and −14.3 ± 2.3 vs. −5.7 ± 0.4 beats ⋅ min−1 ⋅ mmHg−1( P < 0.05), respectively]. Conversely, an intracerebroventricular infusion of Et2N[N(O)NO]Na, an NO donor (1 μmol/h) significantly attenuated the baroreflex sensitivities. However, intracerebroventricular infusion of N ω-nitro-d-arginine methyl ester (10 μmol/h), an enantiomer ofl-NAME, failed to alter the baroreflex sensitivities. These results suggest that 1) the pressor response induced by inhibition of central NO synthesis is mainly mediated by the enhanced sympathetic outflow and 2) central NO attenuates the baroreflex control of RSNA and heart rate in conscious rabbits.

Restraint stress (RS) is an experimental model to study stress-related cardiovascular responses, characterized by sustained pressor and tachycardiac responses. We used pharmacologic and surgical procedures to investigate the role played by sympathetic nervous system (SNS) and parasympathetic nervous system (PSNS) in the mediation of stress-evoked cardiovascular responses. Ganglionic blockade with pentolinium significantly reduced RS-evoked pressor and tachycardiac responses. Intravenous treatment with homatropine methyl bromide did not affect the pressor response but increased tachycardia. Pretreatment with prazosin reduced the pressor and increased the tachycardiac response. Pretreatment with atenolol did not affect the pressor response but reduced tachycardia. The combined treatment with atenolol and prazosin reduced both pressor and tachycardiac responses. Adrenal demedullation reduced the pressor response without affecting tachycardia. Sinoaortic denervation increased pressor and tachycardiac responses. The results indicate that: (1) the RS-evoked cardiovascular response is mediated by the autonomic nervous system without an important involvement of humoral factors; (2) hypertension results primarily from sympathovascular and sympathoadrenal activation, without a significant involvement of the cardiac sympathetic component (CSNS); (3) the abrupt initial peak in the hypertensive response to restraint is sympathovascular-mediated, whereas the less intense but sustained hypertensive response observed throughout the remaining restraint session is mainly mediated by sympathoadrenal activation and epinephrine release; (4) tachycardia results from CSNS activation, and not from PSNS inhibition; (5) RS evokes simultaneous CSNS and PSNS activation, and heart rate changes are a vector of both influences; (6) the baroreflex is functional during restraint, and modulates both the vascular and cardiac responses to restraint.

The pressor and vasoconstrictor action of angiotensin II (ANG II) is considered to be caused by a combination of its direct and indirect vascular effects, the latter mediated by the sympathetic nervous system. The purpose of this study was to determine the extent to which the direct and indirect actions of ANG II contribute to its pressor and vascular effects. Blood pressure, cutaneous vascular, and plasma norepinephrine responses to intravenous ANG II were measured in conscious rabbits before and after inhibition of central sympathetic outflow with intravenous and intracisternal clonidine and after ganglionic blockade with intravenous pentolinium. Intravenous ANG II caused a similar dose-related rise in blood pressure before and after sympathetic blockade with intravenous clonidine, intracisternal clonidine, and intravenous pentolinium. In contrast, the dose-related fall in cutaneous ear blood flow and cutaneous ear temperature and rise in cutaneous ear vascular resistance induced by intravenous ANG II were abolished after intravenous clonidine, intracisternal clonidine, and intravenous pentolinium. Heart rate was unchanged after ANG II. There were no changes in back skin or rectal temperature. There was a nonsignificant fall in plasma norepinephrine and no change in epinephrine after ANG II. These results demonstrate that the acute pressor response to intravenous ANG II is mediated by its direct vascular effects and is not dependent on central or ganglionic stimulation of the sympathetic nervous system, in contrast to the effect of ANG II on cutaneous ear vasoconstriction, which is predominantly caused by a centrally mediated increase in sympathetic nervous activity. Our results separate, in conscious rabbits, the direct vascular effects of ANG II from its indirect vascular actions, which are mediated by central sympathetic stimulation in the brain.

1. Intravenous administration of the ganglionic nicotinic receptor agonist DMPP (1,1-dimethyl-4-phenylpiperazinium iodide) into urethane-anaesthetized rats evoked dose-dependent increases in mean arterial pressure (MAP) and renal sympathetic nerve activity (RSNA). 2. The ganglionic nicotinic receptor antagonists pentolinium and hexamethonium either alone or combined did not inhibit the increase in RSNA and MAP evoked by 50 to 200 micrograms kg-1 doses of DMPP. The increase in renal sympathetic nerve activity evoked by DMPP occurred as a brief burst in firing. 3. The increase in MAP, but not RSNA, evoked by DMPP in the presence of pentolinium was inhibited by the selective alpha 1-adrenergic receptor antagonist prazosin. 4. The non-selective alpha-adrenoceptor and NPY receptor antagonist benextramine also inhibited the increase in MAP without inhibiting the increase in RSNA. Surprisingly, the combination of benextramine and pentolinium, or benextramine and hexamethonium, completely blocked the DMPP-evoked increase in RSNA and thus the increase in MAP. 5. The uptake1 antagonist desipramine combined with pentolinium did not affect the DMPP-evoked increases in MAP or RSNA when compared to the responses evoked in the presence of pentolinium alone. 6. Adding the selective M1 muscarinic receptor antagonist telenzepine to pentolinium and prazosin did not inhibit the increase in RSNA evoked by a 100 micrograms kg-1 dose of DMPP. 7. While the DMPP-evoked increase in MAP in the presence of ganglionic nicotinic receptor antagonists is primarily dependent upon activation of alpha 1-adrenoceptors, the increase in RSNA occurs via activation of ganglionic nicotinic receptors and activation of a mechanism susceptible to blockade by benextramine.

Most anesthetics induce characteristic hemodynamic changes leading to blood pressure (BP) reduction but the role of renin-angiotensin system (RAS), sympathetic nervous system (SNS) and nitric oxide (NO) synthesis in this BP reduction is unknown. We therefore studied the influence of four widely used anesthetics – pentobarbital (P), isoflurane (ISO), ketamine-xylazine (KX) and chloralose-urethane (CU) – on the participation of these vasoactive systems in BP maintenance. BP effects elicited by the acute sequential blockade of RAS (captopril), SNS (pentolinium) and NO synthase (L-NAME) were compared in conscious and anesthetized Wistar or spontaneously hypertensive rats (SHR). Except for pentobarbital all studied anesthetics evidenced by diminished BP responses to pentolinium. The absolute pentolinium-induced BP changes were always greater in SHR than Wistar rats. KX anesthesia eliminated BP response to pentolinium and considerably enhanced BP response to NO synthase inhibition in SHR. In both rat strains the anesthesia with ISO or CU augmented BP response to captopril, decreased BP response to pentolinium and attenuated BP response to NO synthase inhibition. In conclusion, pentobarbital anesthesia had a modest influence on BP level and its maintenance by the above vasoactive systems. Isoflurane and chloralose-urethane anesthesia may be used in cardiovascular experiments if substantial BP decrease due to altered contribution of RAS, SNS and NO to BP regulation does not interfere with the respective research aim. Major BP reduction (namely in SHR) due to a complete SNS absence is a major drawback of ketamine-xylazine anesthesia.

Genetically hypertensive mice (BPH/2J) are hypertensive because of an exaggerated contribution of the sympathetic nervous system to blood pressure. We hypothesize that an additional contribution to elevated blood pressure is via sympathetically mediated activation of the intrarenal renin–angiotensin system. Our aim was to determine the contribution of the renin–angiotensin system and sympathetic nervous system to hypertension in BPH/2J mice. BPH/2J and normotensive BPN/3J mice were preimplanted with radiotelemetry devices to measure blood pressure. Depressor responses to ganglion blocker pentolinium (5 mg/kg IP) in mice pretreated with the angiotensin-converting enzyme inhibitor enalaprilat (1.5 mg/kg IP) revealed a 2-fold greater sympathetic contribution to blood pressure in BPH/2J mice during the active and inactive period. However, the depressor response to enalaprilat was 4-fold greater in BPH/2J compared with BPN/3J mice, but only during the active period ( P =0.01). This was associated with 1.6-fold higher renal renin messenger RNA (mRNA; P =0.02) and 0.8-fold lower abundance of micro-RNA-181a ( P =0.03), identified previously as regulating human renin mRNA. Renin mRNA levels correlated positively with depressor responses to pentolinium ( r =0.99; P =0.001), and BPH/2J mice had greater renal sympathetic innervation density as identified by tyrosine hydroxylase staining of cortical tubules. Although there is a major sympathetic contribution to hypertension in BPH/2J mice, the renin–angiotensin system also contributes, doing so to a greater extent during the active period and less during the inactive period. This is the opposite of the normal renin–angiotensin system circadian pattern. We suggest that renal hyperinnervation and enhanced sympathetically induced renin synthesis mediated by lower micro-RNA-181a contributes to hypertension in BPH/2J mice.

A conditioned stimulus previously paired with electric footshock produced an increase in blood pressure in conscious, freely moving rats. The conditioned pressor response was reproducible. Intracerebroventricular injection of the nicotinic receptor antagonists hexamethonium (1-10 micrograms) or pentolinium (10 micrograms) but not the muscarinic receptor antagonist methylatropine (3 micrograms) produced an inhibition of the conditioned pressor response, whereas intraarterial injection of hexamethonium (10 micrograms) did not affect the response. Intraventricular injection of the cholinesterase inhibitor physostigmine (3-10 micrograms) produced an enhancement of the conditioned pressor response. These results are consistent with the possibility that central nicotinic receptors play a role in the expression of the emotionally conditioned pressor response in rats.

Treatment with dopamine receptor agonists has been shown to induce centrally mediated effects on cardiovascular regulation. We have investigated the effect on blood pressure and heart rate of stimulating the release of endogenous dopamine in the brain from the mesolimbic/mesocortical (A10) dopaminergic system of conscious Sprague-Dawley rats. Stimulation of the region of origin of the A10 dopaminergic system, the ventral tegmental area (VTA), with local micro-injection of the substance P analogue DiMe-C7, produced a dose-dependent increase in blood pressure and heart rate. The injection of 10 nmol of DiMe-C7 produced a maximum increase in blood pressure of 15-20 mmHg at 10 min following administration and a maximum tachycardia of 70-80 B/min. Intravenous pretreatment with the dopamine D-1 receptor antagonist SCH 23390 (0.1 mg/kg) or the dopamine D-2 receptor antagonist raclopride (0.5 mg/kg) markedly inhibited the pressor response and revealed a bradycardia. Furthermore, the pressor response and tachycardia were completely blocked by pretreatment with the vasopressin V-1 receptor antagonist, Pmp1,O-Me-Tyr2-[Arg8]vasopressin (10 micrograms/kg). Pretreatment with the ganglion blocker, pentolinium (10 mg/kg), had little effect on the blood pressure response, however it attenuated the tachycardia. Micro-injection of 10 nmol of DiMe-C7 into a region 2 mm dorsal to the VTA had little effect on blood pressure yet produced a marked bradycardia. The administration of DiMe-C7 into the region of origin of the nigrostriatal A9 dopaminergic system, the substantia nigra, produced a slight but significant increase in blood pressure with little effect on heart rate. Intracerebroventricular administration of DiMe-C7 also produced a pressor response with a more pronounced tachycardia. The blood pressure responses produced by intranigral or i.c.v. injection of DiMe-C7 were not inhibited by pretreating the rats with raclopride. These results suggest an involvement of the mesolimbic A10 dopaminergic system in the regulation of blood pressure and heart rate through the activation of dopamine D-1 and D-2 receptors and vasopressin release.

1. The aim of this study was to clarify the extent to which vascular nitric oxide contributes to basal blood pressure in conscious spontaneously hypertensive rats and normotensive Wistar Kyoto rats. 2. The contribution of vascular nitric oxide to maintenance of blood pressure was estimated by measuring the pressor response to an intravenous injection of nitric oxide synthase inhibitor, Nω-l-arginine methyl ester, given after serial injections of captopril, vasopressin V1-receptor antagonist (V1-antagonist) and ganglion blocker (pentolinium) in conscious spontaneously hypertensive and Wistar Kyoto rats aged 20–28 weeks. To estimate the ‘amplifier property’ of hypertrophied vasculature in spontaneously hypertensive rats, which is known to modulate pressor responses, the lower blood pressure plateau after serial injections of captopril, V1-antagonist and pentolinium and the maximum blood pressure elicited by subsequent injection of increasing doses of phenylephrine were also measured. 3. The serial injections of captopril, V1-antagonist and pentolinium decreased mean arterial pressure from 164 ± 9 mmHg to 67 ± 2 mmHg and from 117 ± 2 mmHg to 49 ± 1 mmHg in spontaneously hypertensive and Wistar Kyoto rats respectively. The subsequent injection of Nω-l-arginine methyl ester restored mean arterial pressure almost to its control levels in both spontaneously hypertensive and Wistar Kyoto rats. The absolute changes in mean arterial pressure elicited by Nω-l-arginine methyl ester were significantly greater in spontaneously hypertensive than in Wistar Kyoto rats (P < 0.01), but there was no significant difference in the responses to Nω-l-arginine methyl ester when they were expressed as percentages of either the lower blood pressure plateau or maximum blood pressure. 4. These results indicate that basal blood pressure in both spontaneous hypertensive and Wistar Kyoto rats is maintained by a balance between vascular nitric oxide and major pressor systems. They also suggest that the vasodilatory effect of vascular nitric oxide does not differ between spontaneously hypertensive and Wistar Kyoto rats, and that the increased pressor effect of Nω-l-arginine methyl ester in spontaneously hypertensive rats is due to a vascular amplifier mechanism.

Possible involvement that the pressor and positive chronotropic effects of endothelin-3 (ET-3) administered intracerebroventricularly (i.c.v.) participate in the central beta-adrenoceptor has been studied in urethane anesthetized rats. ET-3 administered i.c.v. at dose of 50 pmol elicited the increase in blood pressure and heart rate over a long duration, but a dose of 30 pmol had a minimal effect. These cardiovascular responses to ET-3 were significantly reduced by intravenous pretreatment with pentolinium, ganglionic blocking agent, and phentolamine, alpha-blocker. Also pressor responses to ET-3 were abolished dose-dependently by i.c.v. pretreatment with propranolol at a dose of 1 mumol, nonselective beta-blocker and ICI 118551, beta 2-selective adrenoceptor blocker, but not by i.c.v. pretreatment with metoprolol, atenolol, beta 1-selective blocker, procaine and phentolamine. These results suggest that ET-3 may play a role in cardiovascular regulation through the activation of the sympathetic nervous system involved in the central beta 2-adrenoceptor system.

Punicalagain, an active principle isolated from the leaves of Lumnitzera racemosa (Combretaceae), reversed the fall in arterial blood pressure in conscious Wistar rats with orthostatic hypotension induced by injection of hexamethonium into animals subjected to 90° head-up tilts for 60 s. Punicalagin was found to be less effective on prazosin-induced orthostatic hypotension. Plasma norepinephrine (NE) was elevated by intravenous injection of punicalagin in a dose-dependent manner from 0.5 to 15 mg/kg, both in normotensive rats and the orthostatic hypotensive animals. An increase of mean blood pressure was also found in rats that received the injection of punicalagin; this increase in blood pressure was totally abolished by prazosin. Failure of hexamethonium or pentolinium, antagonists of ganglionic nicotinic receptors, to influence the NE releasing action of punicalagin ruled out the participation of ganglionic stimulation. This NE-releasing action of punicalagin was, however, totally blocked by the inhibitors of noradrenergic nerve terminals, guanethidine or bretylium. Also, the activity of punicalagin was not modified by adrenalectomy. Thus, a direct release of NE from the noradrenergic nerve terminals by punicalagin seems responsible for the reversal of orthostatic hypotension.

OBJECTIVE Schlager hypertensive (BPH/2J) mice have been suggested to have high blood pressure (BP) due to an overactive sympathetic nervous system (SNS), but the contribution of the renin-angiotensin system (RAS) is unclear. In the present study, we examined the cardiovascular effects of chronically blocking the RAS in BPH/2J mice. METHODS Schlager normotensive (BPN/3J, n = 6) and BPH/2J mice (n = 8) received the angiotensin AT 1A-receptor antagonist losartan (150 mg/kg per day) in drinking water for 2 weeks. Pre-implanted telemetry devices were used to record mean arterial pressure (MAP), heart rate (HR) and locomotor activity. RESULTS MAP was reduced by losartan treatment in BPN/3J (-23 mmHg, P < 0.01) and in BPH/2J mice (-25 mmHg, P < 0.001), whereas HR was increased. Losartan had little effect on initial pressor responses to feeding or to stress, but did attenuate the sustained pressor response to cage-switch stress. During the active period, the hypotension to sympathetic blockade with pentolinium was greater in BPH/2J than BPN/3J (suggesting neurogenic hypertension), but was not affected by losartan. During the inactive period, a greater depressor response to pentolinium was observed in losartan-treated animals. CONCLUSION The hypotensive actions of losartan suggest that although the RAS provides an important contribution to BP, it contributes little, if at all, to the hypertension-induced or the greater stress-induced pressor responses in Schlager mice. The effects of pentolinium suggest that the SNS is mainly responsible for hypertension in BPH/2J mice. However, the RAS inhibits sympathetic vasomotor tone during inactivity and prolongs sympathetic activation during periods of adverse stress, indicating an important sympatho-modulatory role.

Editorial Comment: The authors review the current state of medical information referable to pheochromocytoma. Urinary catecholamine levels are often positive when a pheochromocytoma is present. Platelet catecholamine levels may also be helpful in the diagnosis. Rarely, pharmacological tests, such as pentolinium suppression, clonidine suppression and glucagon provocation, are in order when the aforementioned levels are negative. Computerized tomography, magnetic resonance imaging and metaiodobenzylguanidine scanning are the imaging modalities that are most appropriate. All but 2% of pheochromocytomas are abdominal. Associated conditions, such as adrenal cortical stimulation by adrenocorticotropic hormone produced by the pheochromocytoma, renal artery stenosis, cholelithiasis and cardiac myopathy may also be present. Of course, surgical extraction is generally curative. W. Scott McDougal, M.D.

The discriminative stimulus effects of the nicotine antagonist mecamylamine have been investigated to characterize further its behavioural effects and its interactions with (–)-nicotine. Rats were trained to discriminate the effects of mecamylamine from saline in a two-bar operant conditioning procedure with food reinforcers presented on a tandem schedule of reinforcement. Mecamylamine (3.5 mg/kg s.c.) acquired strong stimulus control over behaviour and there was only a small reduction in overall rates of responding. The mecamylamine stimulus generalized completely to some ganglion-blocking drugs (order of relative potency: pentolinium > mecamylamine > pempidine) but it did not generalize to other ganglion-blockers (hexamethonium, trimetaphan and chlorisondamine). The mecamylamine stimulus also failed to generalize to (–)-nicotine, to muscarinic antagonists (atropine and scopolamine) or to excitatory amino acid antagonists (dizocilpine, phencyclidine and D-CPPene). Mecamylamine, pempidine, hexamethonium, trimetaphan, (–)-nicotine, scopolamine, phencyclidine, dizocilpine and D-CPPene were tested up to doses that reduced overall rates of responding. Tests also showed that (–)-nicotine did not antagonize the response to mecamylamine. The discriminative stimulus produced by mecamylamine may originate at nicotinic receptors but whether these are located centrally or peripherally is unclear. There was no evidence that either muscarinic or excitatory amino acid receptors were involved in mediating the effect.

Made available in DSpace on 2013-09-27T14:53:45Z (GMT). No. of bitstreams: 1 WOS000287989000014.pdf: 589964 bytes, checksum: 81671d7c36ff2c929dbef4f3ea5bcd5f (MD5) Previous issue date: 2011-02-24 Made available in DSpace on 2013-09-30T18:08:02Z (GMT). No. of bitstreams: 1 WOS000287989000014.pdf: 589964 bytes, checksum: 81671d7c36ff2c929dbef4f3ea5bcd5f (MD5) Previous issue date: 2011-02-24 Submitted by Vitor Silverio Rodrigues (vitorsrodrigues@reitoria.unesp.br) on 2014-05-20T13:25:36Z No. of bitstreams: 1 WOS000287989000014.pdf: 589964 bytes, checksum: 81671d7c36ff2c929dbef4f3ea5bcd5f (MD5) Made available in DSpace on 2014-05-20T13:25:36Z (GMT). No. of bitstreams: 1 WOS000287989000014.pdf: 589964 bytes, checksum: 81671d7c36ff2c929dbef4f3ea5bcd5f (MD5) Previous issue date: 2011-02-24 Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Fundação de Apoio ao Ensino, Pesquisa e Assistência do Hospital das Clínicas da Faculdade de Medicina de Ribeirão Preto da USP (FAEPA) The insular cortex (IC) has been reported to be involved in central cardiovascular control. In the present study, we investigated the cardiovascular responses evoked by microinjection of noradrenaline into the IC as well as the central and peripheral mechanisms involved in their mediation. Microinjection of noradrenaline into the IC (3, 7, 10, 15,30 and 45 nmol/100 nL) caused long-lasting dose-related pressor and bradycardiac responses. The cardiovascular responses evoked by 15 nmol of noradrenaline were blocked by IC pretreatment with WB4101 or 5-methyl-urapidil, selective alpha(1)-adrenoceptor antagonists. IC pretreatment with either the selective alpha(2)-adrenoceptor antagonists RX821002 or the beta-adrenoceptor antagonist propranolol did not affect noradrenaline cardiovascular responses. Noradrenaline cardiovascular responses were mimicked by microinjection of the selective alpha(1)-adrenoceptor agonist phenylephrine into the IC, thus reinforcing the idea that alpha(1)-adrenoceptors mediate cardiovascular responses to noradrenaline microinjected into the IC. The pressor response to noradrenaline microinjection was potentiated by i.v. pretreatment with the ganglion blocker pentolinium and inhibited by i.v. pretreatment with the selective V(1)-vasopressin receptor antagonist dTyr(CH(2))(5)(Me)AVP. The bradycardiac response to noradrenaline microinjection into the IC was abolished by pretreatment with either pentolinium or the V(1)-vasopressin receptor antagonist, indicating its reflex origin. In conclusion, our results suggest that pressor response evoked by microinjection of noradrenaline into the IC involve the activation of IC alpha(1)-adrenoceptors to cause the release of vasopressin into the circulation. (C) 2010 Elsevier B.V. All rights reserved. USP, Sch Med Ribeirao Preto, Dept Pharmacol, BR-14049900 Ribeirao Preto, SP, Brazil São Paulo State Univ, Sch Pharmaceut Sci, Dept Nat Act Principles & Toxicol, UNESP, BR-14801902 Araraquara, SP, Brazil São Paulo State Univ, Sch Pharmaceut Sci, Dept Nat Act Principles & Toxicol, UNESP, BR-14801902 Araraquara, SP, Brazil CNPq: 870307/1997-5 CNPq: 306381/2003-6 CNPq: 505394/2003-0 FAPESP: 06/57670-4

BACKGROUND We investigated the contribution of the sympathetic tone to the hypertension induced by chronic administration of buthionine sulfoximine (BSO) and characterized this model in mice. METHODS Three experiments were performed. In experiment I, four groups of CBA-C57 male mice were used: controls and three groups that received oral BSO at 5, 10, or 20 mmol/l. In experiment II, the alpha(1)-adrenergic blocker prazosin was orally administered (10 mg/100 ml) to control and BSO-treated mice. All treatments were maintained for 5 weeks. Body weight (BW), tail blood pressure (BP), and heart rate (HR) were measured weekly. Direct mean arterial pressure (MAP) and morphological, metabolic, plasma, and renal variables were measured at the end of the experiments. In experiment III, the acute response of MAP and HR to the ganglionic blocker pentolinium (10 mg/kg intravenous) was used to further evaluate the sympathetic contribution to BP and HR in control and BSO-treated mice. RESULTS BSO produced dose-related increases in BP (control, 115 +/- 0.5; BSO-5, 141 +/- 0.5; BSO-10, 151 +/- 0.9; BSO-20, 163 +/- 1.1 mm Hg) and HR and augmented plasma noradrenaline, brainstem isoprostane levels, and total urinary isoprostane excretion. BSO did not produce cardiac hypertrophy and did not modify metabolic or plasma variables, or creatinine clearance, proteinuria, or renal morphology. Chronic prazosin markedly reduced MAP (control, 101 +/- 4.7; prazosin, 95 +/- 1.29; BSO-10, 130 +/- 2.9; BSO-10 +/- prazosin, 98 +/- 0.9) and HR. Acute pentolinium produced a greater percentage MAP (control, 43 +/- 4.2; BSO-10, 66 +/- 4.5) and HR decrease in BSO-treated mice vs. controls. CONCLUSION Sympathetic tone plays a major role in the increased BP and HR of BSO hypertensive mice.

The superior colliculus (SC) is a mesencephalic area involved in the mediation of defensive movements associated with cardiovascular changes. Noradrenaline (NA) is a neurotransmitter with an important role in central cardiovascular regulation exerted by several structures of the central nervous system. Although noradrenergic nerve terminals have been observed in the SC, there are no reports on the effects of local NA injection into this area. Taking this into consideration, we studied the cardiovascular effects of NA microinjection into the SC of unanesthetized rats. Microinjection of NA into the SC evoked a dose-dependent blood pressure increase and a heart rate decrease in unanesthetized rats. The pressor response to NA was not modified by intravenous pretreatment with the vasopressin v(1)-receptor antagonist dTyr(CH(2))(5)(Me)AVP, indicating a lack of vasopressin involvement in the response mediation. The effect of NA microinjection into the SC was blocked by intravenous pretreatment with the ganglionic blocker pentolinium, indicating its mediation by the sympathetic nervous system. Although the pressor response to NA was not affected by adrenal demedullation, the accompanying bradycardia was potentiated, suggesting some involvement of the sympathoadrenal system in the cardiovascular response to NA microinjection into the SC. In summary, results indicate that stimulation of noradrenergic receptors in the SC causes cardiovascular responses which are mediated by activation of both neural and adrenal sympathetic nervous system components.

Background Human ‘new pressor protein' (NPP), related to coagulation beta-factor XIIa (β-FXIIa), potently releases sympathoadrenal catecholamines in bioassay rats, with concurrent elevation of systolic and diastolic blood pressure (SBP/DBP) and heart rate (HR). Elevated plasma NPP/β-FXIIa levels in hypertensive anephric pediatric patients on hemodialysis associated with fluid status and blood pressure changes were previously reported, suggesting that NPP/β-FXIIa contributed to their hypertension. Objective To investigate the mechanism of action of NPP/β-FXIIa. Methods Hemodynamic and sympathoadrenal responses to NPP (20μL plasma equivalent/rat) or coagulation β-FXIIa (300ng/kg intravenously) were measured in rats treated with pentolinium (ganglion blockade [+GB]) and/or captopril (+CAP; angiotensin converting enzyme [ACE] inhibition). Results In controls not receiving GB or CAP (–GB–CAP), NPP/ β-FXIIa raised plasma epinephrine (E) sixfold, SBP/DBP by 14/8mmHg and HR by 15 beats/min. With blockade of the cholinergic pathway to the sympathoadrenal system (+GB), basal E, norepinephrine (NE), SBP, DBP and HR all dropped. However NPP/β-FXIIa remained capable of raising E 20-fold, NE fourfold, SBP/DBP by 27/11mmHg and HR by 20 beats/min, suggesting that it acted through a ‘noncholinergic' mechanism. With +CAP alone, NPP/β-FXIIa raised plasma E 18-fold, NE threefold, SBP/DBP by 29/8mmHg and HR by 73 beats/min, implicating an ACE-regulated ‘peptidergic' mechanism. Combining +GB with +CAP potentiated NPP/β-FXIIa actions further by raising E 50-fold, NE sevenfold, SBP/DBP by 55/20mmHg and HR by 87 beats/min, strengthening the efficacy of this alternate pathway. Conclusions The cardiovascular effects of NPP/β-FXIIa are considerably mediated by a noncholinergic (peptidergic) ACE-regulated mechanism for sympathoadrenal catecholamine release that is enhanced by +GB and/or +CAP. Under inflammatory procoagulant conditions, endogenously produced NPP/β-FXIIa may interfere with the antihypertensive effects of ACE inhibition therapy.

Forty-eight anesthetized and artificially ventilated rats were pretreated with the ganglion blocking agent, pentolinium (5 mg/kg, i.v.), followed by continuous phenylephrine infusion for maintenance of normotension. The rats were subjected to mock treatment (16 rats), to sudden exposure to thermoneutral water (34-36 degrees C, 16 rats), or to cold water (16 degrees C, 16 rats). The latter treatment lowered the cutaneous temperature to 25-30 degrees C. Neither one of these treatments produced any significant changes in arterial pressure or heart rate. Exposure to cold elicited hyperperfusion (microsphere method) in each of the brain regions studied. The increase in cerebral cortical blood flow (by 59 +/- 8%, mean +/- SEM) was most significant. The cerebral cortical metabolic rate for oxygen was increased by 46 +/- 10%. During the cold exposure, excellent tight coupling between the metabolic rate and blood flow was observed in the cerebral cortex. Mock treatment and exposure to thermoneutral water resulted in only trivial increases in blood flow and in metabolic rate. Thus, during cold exposure, an enhanced metabolic state of the brain represented the primary determinant increasing the brain blood flow, provided that normotension was maintained.

Study objective — The aim was to provide meaningful information on the function of the sympathetic system soon after an increased pressure overload on the heart. Design — Noradrenaline storage, turnover, uptake, and synthesis were investigated at 3, 14, and 28 d after aortic banding in rats. Sham operated rats without aortic banding were used as control group. Experimental material — Left ventricle, spleen, and kidney from male Sprague-Dawley rats (175-200 g) were used in this study. Measurements and main results — Cardiac noradrenaline concentration was decreased at 3 d and 28 d after banding and increased at 14 d; left ventricular mass was increased from 14 d onwards. The rate of change in the specific activity of myocardial noradrenaline (noradrenaline turnover) as well as dopamine β hydroxylase, an enzyme for noradrenaline synthesis, was unaltered at 3 d, increased at 14 d, and decreased at 28 d after aortic banding. Myocardial [3H]noradrenaline uptake, on the other hand, was decreased at all time points studied. The changes observed in the myocardium at day 14 were specific since noradrenaline turnover rate was unaltered in other peripheral organs such as spleen and kidney. Furthermore, after ganglionic blockade with pentolinium, both sham operated control and banded animals had identical, low noradrenaline turnover rate constants, and significant restoration of cardiac weight and noradrenaline stores was observed in the hearts from banded animals. Conclusions — Noradrenaline turnover and metabolism are altered soon after imposing increased workload on heart. Whether or not the changes in the sympathetic activity are a prerequisites for hypertrophy still remains to be seen.

We report on the cardiovascular effects of noradrenaline (NA) microinjection into the hypothalamic supraoptic nucleus (SON) as well as the central and peripheral mechanisms involved in their mediation. Microinjections of NA 1, 3, 10, 30 or 45 nmol/100 nL into the SON caused dose-related pressor and bradycardiac response in unanesthetized rats. The response to NA 10 nmol was blocked by SON pretreatment with 15 nmol of the alpha(2)-adrenoceptor antagonist RX821002 and not affected by pretreatment with equimolar dose of the selective alpha(1)-adrenoceptor antagonist WB4101, suggesting that local alpha(2)-adrenoceptors mediate these responses. Pretreatment of the SON with the nonselective beta-adrenoceptor antagonist propranolol 15 nmol did not affect the pressor response to NA microinjection of into the SON. Moreover, the microinjection of the 100 nmol of the selective alpha(1)-adrenoceptor agonist methoxamine (MET) into the SON did not cause cardiovascular response while the microinjection of the selective alpha(2)-adrenoceptor agonists BHT920 (BHT, 100 nmol) or clonidine (CLO, 5 nmol) caused pressor and bradycardiac responses, similar to that observed after the microinjection of NA. The pressor response to NA was potentiated by intravenous pretreatment with the ganglion blocker pentolinium and was blocked by intravenous pretreatment with the V(1)-vasopressin receptor antagonist dTyr(CH2)5(Me)AVP, suggesting an involvement of circulating vasopressin in this response. In conclusion, our results suggest that pressor responses caused by microinjections of NA into the SON involve activation of local alpha(2)-adrenoceptor receptors and are mediated by vasopressin release into circulation.

1. Conscious Long Evans rats, chronically instrumented for cardiovascular measurements, were challenged with i.v. bolus doses of glyceryl trinitrate (40 nmol kg-1), acetylcholine (1.2 nmol kg-1), bradykinin (3.2 nmol kg-1), or endothelin-1 (0.25 nmol kg-1). Under control conditions these doses produced similar falls in mean arterial blood pressure (glyceryl trinitrate, -20 +/- 3 mmHg; acetylcholine, -24 +/- 2 mmHg: bradykinin, -21 +/- 3 mmHg; endothelin-1, -25 +/- 3 mmHg), associated with renal, mesenteric and hindquarters vasodilatations (except for endothelin-1 which caused mesenteric vasoconstriction). 2. In the presence of NG-nitro-L-arginine methyl ester (L-NAME, 10 mgkg-1), a potent inhibitor of nitric oxide biosynthesis and endothelium-dependent vasorelaxation in vitro, the hypotensive responses to glyceryl trinitrate, acetylcholine, and endothelin-1 were increased, although that to bradykinin was not. However, comparing the differences between the response to glyceryl trinitrate and that to any other agonist in the absence and presence of L-NAME showed that there were relative attenuations of the hypotensive responses to bradykinin and endothelin-1, but not to acetylcholine, in the presence of L-NAME. 3. This comparative analysis showed that the renal and hindquarters vasodilator responses to bradykinin and endothelin-1 were attenuated in the presence of L-NAME, but the renal, mesenteric and hindquarters vasodilator responses to acetylcholine were not. However, when L-NAME was administered in the presence of pentolinium, captopril and the vasopressin V1-receptor antagonist, d(CH2)5[Tyr-(Et)]DAVP, (to abolish baroreflex and neurohumoral mechanisms), there was attenuation of the renal and mesenteric vasodilator effects of acetylcholine relative to those seen with glyceryl trinitrate. Under those conditions only the renal vasodilator effects of bradykinin and endothelin-1 were attenuated. 4. In separate experiments in conscious Long Evans rats, direct measurement of cardiac haemodynamics showed that the hypotensive responses to glyceryl trinitrate, acetylcholine, bradykinin and endothelin-l were entirely attributable to rises in total peripheral conductance since both in the absence and presence of L-NAME there were no reductions in cardiac index in response to these substances. 5. The results indicate that measurement of systemic arterial blood pressure alone in conscious rats does not permit reliable quantitation of the influence of L-NAME on regional vasodilator responses to glyceryl trinitrate, acetylcholine, bradykinin or endothelin-1. Furthermore, these substances exert effects in different vascular beds that may be differentially influenced by baroreflex mechanisms, neurohumoral mechanisms, or both. Moreover, except in the case of the renal vasodilator response to endothelin-1 (which was abolished in the presence of L-NAME), even when L-NAME caused attenuation of the vasodilator effects of acetylcholine or bradykinin (relative to glyceryl trinitrate), substantial responses remained. It is feasible that such responses in vivo are nitric oxide-independent.

The mechanisms of action of tachykinin peptides thought to be involved in central cardiovascular regulation were examined. Intracerebroventricular injections (i.c.v.) of tachykinin peptides caused dose-dependent increases in blood pressure and heart rate. The pressor responses to substance P (SP) (10 micrograms, i.c.v.) and neurokinin A (NKA) (10 micrograms, i.c.v.) were blocked by peripheral administration of pentolinium or phentolamine, and partially attenuated by adrenalectomy. In contrast, the only initial pressor response to the neurokinin B (NKB) analogue senktide (10 micrograms, i.c.v.) was blocked by pentolinium or phentolamine. The pressor response to senktide was inhibited by pretreatment with a vasopressin V1 receptor antagonist (d(CH2)5OMe(Tyr)AVP) (10 micrograms/kg, i.v.), and senktide (10 micrograms, i.c.v.) caused an increase in plasma vasopressin level. However, the vasopressin antagonist did not influence the SP- and NKA-induced pressor responses. These results suggest that central SP and NKA increase the blood pressure and heart rate via sympathetic nerve activity, whereas central NKB increases the blood pressure mainly via release of vasopressin from the hypothalamus.

The diabetogenic agent streptozotocin (STZ) was injected intraperitoneally in Long-Evans and arginine vasopressin (AVP)-deficient Brattleboro rats. Twenty-eight days later both strains had a bradycardia and systolic hypotension; STZ-treated Brattleboro rats also had diastolic hypotension. The vasopressin (V1-receptor) antagonist, d(CH2)5[Tyr(Et)]DAVP, had no effect on resting blood pressure (BP) or heart rate (HR) in either strain of rat, indicating the relative maintenance of diastolic BP in STZ-treated Long-Evans rats was not dependent on acute vascular actions of AVP. Captopril caused a modest hypotension in all groups of rats, indicating that BP was not differentially dependent on the renin-angiotensin system in the different groups. In the presence of captopril and the ganglion blocker, pentolinium tartrate, the AVP-mediated recovery in BP was impaired in STZ-treated Long-Evans rats. During administration of d(CH2)5[Tyr(Et)]DAVP and pentolinium, the angiotensin II (ANG II)-mediated BP recovery was smaller in both groups of STZ-treated rats, indicating that this abnormality was not likely to be caused by inhibition of renin release by AVP. The abnormalities in ANG II- and AVP-mediated recovery were prevented by insulin treatment.

Osmotic minipumps were used to infuse hypertonic saline intracerebroventricularly into conscious rats fed high-salt diets to determine if combining high-salt intake with ICV saline infusion would elevate blood pressure more than either procedure alone. Mean aortic pressures became progressively elevated in all rats infused with saline and the magnitude of the elevation was significantly larger in those fed high-salt diets instead of the regular chow. Added pressor effects of high-salt feeding were unaffected by pharmacologic vasopressin or angiotensin blockade thereby indicating that humoral mediation by either peptide was not involved. A general increase in cardiovascular reactivity also seemed unlikely since pressor responsiveness to injected norepinephrine did not differ between rat groups. Sympathetic hyperactivity was considered to be a logical explanation because enhancement by high-salt feeding was abolished following either ganglion blockade with pentolinium or chemical sympathectomy with 6-hydroxydopamine. These findings are compatible with the interpretation that high-salt feeding enhanced pressor responses to centrally-infused saline by increasing sympathetic vasomotor tone.

The periaqueductal gray area (PAG) is a mesencephalic area involved in cardiovascular modulation. Noradrenaline (NA), a neurotransmitter involved in central blood pressure control, is present in the rat PAG. We report here on the cardiovascular effects caused by NA microinjection into the ventrolateral PAG (vlPAG) of unanesthetized rats and the peripheral mechanism involved in their mediation. NA microinjection in the vlPAG of unanesthetized rats evoked dose-related pressor and bradycardiac responses. No significant cardiovascular responses were observed in urethane-anesthetized rats. The pressor response was potentiated by pretreatment with the ganglion blocker pentolinium (5 or 10 mg/kg, intravenously). Pretreatment with the vasopressin antagonist dTyr(CH2)5 (Me)AVP (50 microg/kg, intravenously) blocked the pressor response evoked by the NA microinjection into the vlPAG. Additionally, circulating vasopressin content was found to be significantly increased after NA microinjection in the vlPAG. The results suggest that activation of noradrenergic synapses within the vlPAG modulates vasopressin release in unanesthetized rats.

Hypertension due to chronic inhibition of NO synthase (NOS) by Nomega-nitro-L-arginine methyl ester (L-NAME) administration is characterized by both impaired NO-dependent vasodilation and enhanced sympathetic vasoconstriction. The aim of our study was to evaluate changes in the participation of major vasoactive systems in L-NAME-treated rats which were subjected to simultaneous antihypertensive (captopril) or antioxidant (N-acetylcysteine, NAC) treatment. Three-month-old Wistar males treated with L-NAME (60 mg/kg/day) for 5 weeks were compared to rats in which L-NAME treatment was combined with simultaneous chronic administration of captopril or NAC. Basal blood pressure (BP) and its acute responses to consecutive i.v. injections of captopril (10 mg/kg), pentolinium (5 mg/kg), L-NAME (30 mg/kg), tetraethylammonium (TEA, 16 mg/kg) and nitroprusside (NP, 20 microg/kg) were determined in conscious rats at the end of the study. The development of L-NAME hypertension was prevented by captopril treatment, whereas NAC treatment caused only a moderate BP reduction. Captopril treatment normalized the sympathetic BP component and significantly reduced residual BP (measured at full NP-induced vasodilation). In contrast, chronic NAC treatment did not modify the sympathetic BP component or residual BP, but significantly enhanced NO-dependent vasodilation. Neither captopril nor NAC treatment influenced the compensatory increase of TEA-sensitive vasodilation mediated by endothelium-derived hyperpolarizing factor in L-NAME-treated rats. Chronic captopril treatment prevented L-NAME hypertension by lowering of sympathetic tone, whereas chronic NAC treatment attenuated L-NAME hypertension by reduction in the vasodilator deficit due to enhanced NO-dependent vasodilation.

The lateral septal area (LSA) is involved in central cardiovascular control. In the present study, we report on the cardiovascular effects of noradrenaline (NA) injection into the LSA of unanesthetized rats, as well as on local receptors and peripheral mechanisms involved in their mediation. Microinjections of NA (9, 15, 21, 27 or 45 nmol) caused long-lasting, dose-related pressor and bradycardic responses in unanesthetized rats. No responses were observed when the dose of 21 nmol of NA was microinjected into medial septal area or lateral ventricle suggesting a main action at the LSA. No changes were observed in arterial pressure and heart rate when NA was injected in the LSA of anesthetized rats. The effects of 21 nmol of NA were abolished by local pretreatment with 10 nmol of the specific α 1 -receptor antagonist WB 4101, but were not affected by pretreatment with 10 nmol of the specific α 2 -receptor antagonist RX 821002. The magnitude of pressor response to NA in the LSA was increased by i.v. pretreatment with the ganglion blocker pentolinium (10 mg/kg) and significantly reduced by i.v. pretreatment with the V 1 -vasopressin receptor antagonist dTyr (CH2)5(Me) AVP (50 μg/kg). No pressor response to NA was observed in hypophysectomized rats. The present observation of α 1 -adrenoceptor-mediated pressor responses after local injection of NA confirms earlier evidence of a LSA involvement in central cardiovascular control. Pretreatment with the α 1 -adrenoceptor antagonist WB-4101 did not affect baseline blood pressure or heart rate suggesting no tonic involvement of septal adrenergic mechanisms suggesting a modulatory LSA influence on cardiovascular control. Additionally, the blockade of the pressor response by the i.v. pretreatment with a V 1 -vasopressin antagonist indicates that noradrenergic LSA mechanisms modulate vasopressin release.