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Introduction: Hypertension is highly prevalent in patients with chronic kidney disease and hypervolemia is one of the principal causes., Objective: To evaluate the influence of the reduction of volemia on blood pressure as well as on echocardiographic parameters in patients on continuous ambulatory peritoneal dialysis., Methods: Twelve patients with no clinical evidence of hypervolemia were submitted to an increase in the rate of the dialysis with the purpose of reducing body weight by 5%. The volemia was evaluated by electrical bioimpedance and by ultrasound of the inferior cava vena (ICV). Blood pressure was measured by ambulatory blood pressure monitoring and cardiac function was evaluated by echocardiography both at baseline and 5 weeks after the intervention period., Results: After the increase in the ultrafiltration, body weight, extracellular water and the inspiratory diameter of the ICV decreased significantly in parallel with a non-significant increase in the collapsing ICV index. Despite the reduction of anti-hypertensive drugs, systolic blood pressure during the sleep period decreased from 138.4 ± 18.6 to 126.7 ± 18.0 mmHg, the nocturnal blood pressure drop increased and the final systolic left ventricular diameter decreased significantly., Conclusion: Reduction of the volemia of patients on peritoneal dialysis, with no signs of hypervolemia, was associated with a better blood pressure control and with a decrease of the final systolic left ventricular diameter.

Multiple cell membrane alterations have been reported to be the cause of various forms of hypertension. The present study focuses on the lipid portion of the membranes, characterizing the microviscosity of membranes reconstituted with lipids extracted from the aorta and mesenteric arteries of spontaneously hypertensive (SHR) and normotensive control rat strains (WKY and NWR). Membrane-incorporated phospholipid spin labels were used to monitor the bilayer structure at different depths. The packing of lipids extracted from both aorta and mesenteric arteries of normotensive and hypertensive rats was similar. Lipid extract analysis showed similar phospholipid composition for all membranes. However, cholesterol content was lower in SHR arteries than in normotensive animal arteries. These findings contrast with the fact that the SHR aorta is hyporeactive while the SHR mesenteric artery is hyperreactive to vasopressor agents when compared to the vessels of normotensive animal strains. Hence, factors other than microviscosity of bulk lipids contribute to the vascular smooth muscle reactivity and hypertension of SHR. The excess cholesterol in the arteries of normotensive animal strains apparently is not dissolved in bulk lipids and is not directly related to vascular reactivity since it is present in both the aorta and mesenteric arteries. The lower cholesterol concentrations in SHR arteries may in fact result from metabolic differences due to the hypertensive state or to genes that co-segregate with those that determine hypertension during the process of strain selection.

Introduction: Acute renal failure (ARF) remains highly prevalent with a high rate of morbidity and mortality., Objective: of this study was to compare use of the APACHE II scoring prognosis with that of the ATN-ISS to determine whether the APACHE II could be used for patients with ARF outside the ICU., Methods: For this purpose, 205 patients with ARF were accompanied in a prospective cohort. Demographic data, preexisting conditions, organ failure and characteristics of ARF were analyzed. The prognostic scores were performed with the assessment of a nephrologist., Results: The mean age was 52 +/- 18 years, 50% were male, 69% were white, 45% were treated in ICU and 55% in other units. Mortality in the ICU group was 85% and in the non-ICU group 18%. Factors that correlated with higher mortality were more prevalent in the ICU group: age, male, hospitalization with ARF, organ failure, sepsis, septic IRA, oliguria and need of dialysis. Overall, the prognostic markers were the same for both the ICU and non-ICU groups. The discrimination with the APACHE II was similar in both, ICU and non-ICU groups and calibration was better in the non-ICU group. The ATN-ISS achieved good discrimination in both the ICU and non-ICU groups, but, regarding calibration, there was a discreet over estimating of mortality in the non-ICU group. The ATN-ISS showed a greater capacity for discrimination than the APACHE II in both the ICU and non-ICU groups., Conclusion: It was concluded that the APACHE II and ATN-ISS scores could be used for stratification of risk in patients with ARF treated outside of the ICU in Brazil.

Although rat aorta smooth muscle cells in culture constitutively express bradykinin B1 receptors, the normotensive rat aorta does not respond to the bradykinin B1 receptor agonist des-Arg9-bradykinin, whereas vessels from the spontaneously hypertensive rat (SHR) respond to bradykinin B1 receptor agonists with cell membrane hyperpolarization and relaxation. Bacterial lipopolysaccharide also is inactive on the normotensive rat but hyperpolarizes the SHR aorta. To determine whether this could be due to the increased intracellular Ca2+ concentration ([Ca2+]i) in the SHR, we raised [Ca2+]i in normotensive rats by treatment with thapsigargin. In the thapsigargin-treated aorta, both lipopolysaccharide and des-Arg9-bradykinin induced hyperpolarization, which was reversed by the Ca2+-dependent K+ channel inhibitor iberiotoxin and by the bradykinin B1 receptor antagonists Lys-[Leu8]-des-Arg9-bradykinin and [Leu8]-des-Arg9-bradykinin. Thus the bradykinin B1 receptor, as well as lipopolysaccharide, needs activated Ca2+-dependent K+ channels for functional expression. The two bradykinin B1 receptor inhibitors, however, have effects on Ca2+-dependent K+ channels which are not mediated by bradykinin B1 receptors.

The mediators involved in the hyperpolarizing effects of lipopolysaccharide and of the bradykinin B1 receptor agonist des-Arg9-bradykinin on the rat aorta were investigated by comparing the responses of aortic rings of spontaneously hypertensive and normotensive Wistar rats. Endothelized rings from hypertensive rats were hyperpolarized by des-Arg9-bradykinin and lipopolysaccharide, whereas de-endothelized rings responded to lipopolysaccharide but not to des-Arg9-bradykinin. In endothelized preparations, the responses to des-Arg9-bradykinin were inhibited by Nomega-nitro-L-arginine and iberiotoxin. De-endothelized ring responses to lipopolysaccharide were inhibited by iberiotoxin, glibenclamide and B1 antagonist Lys-[Leu8,des-Arg9]-bradykinin. This antagonist also inhibited hyperpolarization by des-Arg9-bradykinin and by the á2-adrenoceptor agonist, brimonidine. Our results indicate that Ca(2+)-sensitive K+ channels are the final mediators of the responses to des-Arg9-bradykinin, whereas both Ca(2+)- and ATP-sensitive K+ channels mediate the responses to lipopolysaccharide. The inhibitory effects of Lys-[Leu8,des-Arg9]-bradykinin is due to a direct action on Ca(2+)- and ATP-sensitive potassium channels.

1. The effects of balloon injury on the reactivity of ipsilateral and contralateral carotid arteries were compared to those observed in arteries from intact animals (control arteries). 2. Carotid arteries were obtained from Wistar rats 2, 4, 7, 15, 30 or 45 days after injury and mounted in an isolated organ bath. Reactivity to angiotensin II (Ang II), phenylephrine (Phe) and bradykinin (BK) was studied. Curves were constructed in the absence or presence of endothelium or after incubation with 10 microm indomethacin, 500 microm valeryl salicylate or 0.1 microm celecoxib. 3. Phe, Ang II and BK maximum effects (Emax) were decreased in ipsilateral arteries when compared to control arteries. No differences were observed among pD2 or Hill coefficient. 4. Emax to Phe (4 and 7 days) and to Ang II (15 and 30 days) increased in the contralateral artery. In addition, Phe or Ang II reactivity was not significantly different in aorta rings from control or carotid-injured animals. 5. The increased responsiveness of contralateral artery was not due to changes in carotid blood flow or resting membrane potential. The endothelium-dependent inhibitory component is not present in the contraction of contralateral arteries and it is not related to superoxide anion production. 6. Indomethacin decreased contralateral artery responsiveness to Phe and Ang II. Valeryl salicylate reduced the Ang II response in contralateral and control arteries. Celecoxib decreased the Phe Emax of contralateral artery. 7. In conclusion, decreased endothelium-derived factors and increased prostanoids appear to be responsible for the increased reactivity of contralateral arteries after injury.

We examined the roles played by impaired K+ channels, diminished nitric oxide (NO) production, endothelin release, and smooth muscle membrane potential in the increased restenosis observed in spontaneously hypertensive rat (SHR) carotid arteries after angioplasty. The SHR carotid was found to be less polarized than that of normotensive Wistar rats (NWR), and it was further depolarized by the alpha2 agonist UK 14,304. This response was blocked by iberiotoxin, indicating that calcium-dependent K+ channels operate normally in the SHR carotid. Acetylcholine caused a hyperpolarization that was significantly smaller in SHR than in NWR carotids, indicating a deficient release of NO in the SHR. After angioplasty, SHR and NWR vessels were depolarized, returning to baseline after 10 days. In the SHR but not in the NWR the contralateral carotid was also depolarized, and this was prevented by the endothelin A/B receptor antagonist bosentan. After angioplasty, endothelin-1 plasma levels increased in both SHR and NWR, but the increase was significantly more prolonged in SHR. We found that the more pronounced restenosis observed in the SHR carotid after angioplasty is not due to impairment of calcium-dependent K+ channels but is related to the relatively depolarized vascular smooth muscles, involving endothelin release caused by reduced NO levels in that strain.

Background: We investigated the effects of amitriptyline in the urinary tract smooth muscle and urolithiasis., Methods: Cats presenting with obstructive acute renal failure (ARF) received amitriptyline, and renal function and survival rates were analyzed. Isometric contractions and membrane potentials of rat, pig, or human isolated urinary tract smooth muscle were recorded in the presence or absence of amitriptyline., Results: Twenty cats with obstructive ARF caused by urethral plugs received amitriptyline. In all cases, plugs were completely eliminated, and renal function returned to normal, with a 100% survival rate in the follow-up. Amitriptyline produced potent relaxations in rat urethral strips, accompanied by significant reductions in urethral ring membrane potential. This effect was prevented by pretreatment of urethral rings with 4-aminopyridine (4-AP), a voltage-dependent potassium channel blocker. Amitriptyline abolished in a reversible manner acetylcholine-, bradykinin-, and KCl-induced contractions in rat isolated bladder, and this effect was also prevented by 4-AP. Of interest, spontaneous and KCl-induced contractions of pig and human isolated ureter were also blocked by amitriptyline., Conclusion: Our results indicate that amitriptyline is an effective and potent relaxant of urinary tract smooth muscle and this effect is mediated by opening of voltage dependent-potassium channels. We suggest that amitriptyline administration may help to promote elimination of urinary calculi.

Previous works have shown that the alpha(2)-adrenoceptor agonist UK 14,304 induced the relaxation and hyperpolarization of the rat aorta, mediated by alpha(2)-adrenoceptors present in the smooth muscles, through small-conductance, ATP-sensitive K(+) channels. We now report that in spontaneously hypertensive rat (SHR) aortic rings, UK 14,304 induced concentration-dependent hyperpolarizing responses, which were inhibited by yohimbine, an alpha(2)-adrenoceptor inhibitor, and by glibenclamide, a specific inhibitor of small-conductance, ATP-sensitive K(+) channels. The responses were also partially inhibited by iberiotoxin and by apamin. Treatment with N(omega)-nitro-L-arginine (L-NNA) did not affect the response to UK 14,304. These results indicate that alpha(2)-adrenoceptors are present in SHR aortic smooth muscle cell membranes, but differ from those of normotensive animals regarding the K(+) channels involved in their responses. Moreover, the resting membrane potential (RMP) was significantly more negative in SHR than in normotensive rats. This relative hyperpolarized state is probably due to Ca(2+)-dependent K(+) channels being constitutively open in SHR, since the addition of iberiotoxin caused a significant depolarization of the aortic smooth muscle membranes in this strain.

1. The direct and endothelium-dependent effects of lipopolysaccharide (LPS) were investigated on resistance and conductance arteries from normotensive Wistar (NWR) and spontaneously hypertensive (SHR) rats. 2. In both NWR and SHR, LPS induced dose-dependent relaxations of the mesenteric vascular bed, which were inhibited by L-NNA in SHR but not in NWR. Iberiotoxin (IBTX) inhibited the responses to LPS in both groups, indicating the participation of high conductance Ca(2+)-dependent K(+) channels. 3. In mesenteric artery rings, the resting membrane potentials and the hyperpolarizing responses of NWR to LPS did not differ in endothelized and denuded preparations but L-NNA inhibited the responses only in endothelized rings. These responses were reduced by bosentan, suggesting that endothelin release may mask a possible hyperpolarizing response to LPS. The hyperpolarizing responses to LPS were blocked by IBTX in both endothelized and de-endothelized NWR rings. In the SHR only intact rings showed hyperpolarization to LPS, which was inhibited by IBTX and byL-NNA. 4. In SHR aortic endothelized or denuded rings, LPS induced hyperpolarizing responses which, in endothelized rings, were partially blocked by L-NNA, by IBTX or by glibenclamide, but totally abolished by IBTX plus glibenclamide. No response to LPS was observed in NWR aortic rings. 5. Our results indicate that LPS activates large conductance Ca(2+)-sensitive K(+) channels located in the smooth muscle cell membrane both directly and indirectly, through NO release from the endothelium in NWR, whereas NO is the major mediator of the LPS responses in SHR resistance vessels.

The vasodilation and hyperpolarization induced by bradykinin (BK) in the mesenteric vascular bed and mesenteric arteries from spontaneously hypertensive rats (SHR) and from normotensive Wistar rats (NWR), as well as Wistar Kyoto rats (WKY), was investigated before and after prolonged oral treatment with cholecalciferol (125 mg kg(-1) body weight per day) for 3 weeks. The cholecalciferol treatment caused a decrease in the SHR blood pressure, as well as a normalization in the resting potential of the smooth muscle cell membrane of mesenteric arteries and restored their hyperpolarizing response to BK. The concentration-response curves for the vasodilator effect of BK on the mesenteric vascular bed were significantly decreased in SHR and in WKY when compared with NWR. Cholecalciferol treatment improved the maximum responses of the SHR preparation, bringing them to levels similar to those of the NWR preparations, which themselves were unaffected by the treatment. In the presence of apamin, a Ca(2+)-dependent K(+) channel inhibitor, the maximum responses to BK in preparations from NWR or cholecalciferol-treated SHR decreased to values similar to those observed in untreated SHR. Our results indicate that the low responsivity of the SHR resistance vessels to the relaxant effect of BK is due to impaired Ca(2+)-dependent K(+) channels and that reversion of this impairment contributes to the blood pressure reduction caused by the cholecalciferol treatment. However, the mechanism of the low responsivity in WKY remains to be investigated.

The involvement of AT1 and AT2 receptor subtypes in the response of the isolated rat uterus to angiotensin II (AngII) was studied throughout the estrous cycle. The AngII potency varied during the different estrous cycle phases, as indicated by significantly different pD2 values. No significant differences were observed in AngII metabolism among different estrous phases. Morphological analysis indicated that external and internal myometrium layers were thicker during estrus. In addition, the highest resting membrane potential was also observed during this phase, when compared with the proestrus and diestrus phases. The AngII-induced uterine contractions were blocked by losartan. Different losartan pD2 values were observed. PD123319 had no effect on the contractile response to AngII. The results also indicate that estrous cycle-dependent changes in AngII potency are correlated with uterine morphological and/or membrane potential changes., (Copyright 2002 S. Karger AG, Basel)

There is little information regarding the time of hypolipidemic treatment of changes in atherosclerotic plaque, tissue cholesterol content, and also for the recovery of endothelial function. To assess the early effects of lipid-lowering treatment on these parameters, six groups of New Zealand male rabbits were studied. Animals in groups I and II were fed regular chow; groups III and IV received a 12-week 0.5% cholesterol diet followed by 12 weeks of 0.05% cholesterol diet. Finally, groups V and VI were fed a 12-week 0.5% cholesterol diet and were then shifted to a regular diet for 12 weeks. During the last four weeks, the rabbits in groups I, III, and V received low-dose pravastatin (2 mg/day), added to the diet. Group IV animals had the highest cholesterol plasma levels (vs. groups I, II, III, and V, p < 0.01) and presented atherosclerotic plaques in a more advanced stage. Nonatherogenic diet was insufficient to restore endothelial function in animals previously fed cholesterol-enriched diets (groups IV and VI). Conversely, pravastatin treatment promoted significant improvement in endothelial function and reduced the progression of atherosclerosis. Marked increase in cholesterol content was seen in aorta and liver in response to the atherogenic diet. However, neither treatment with pravastatin nor nonatherogenic diet was capable of modifying the tissue cholesterol content. Our study supports the hypothesis that the early use of statins can attenuate the progression of atherosclerosis and ameliorate endothelial function. In addition, significant changes in the tissue cholesterol pool probably need a longer period of treatment.

Angiotensin II (AngII) and bradykinin (BK) derivatives containing the TOAC (2,2,6,6-tetramethylpiperidine-N-oxyl-4-amino-4-carboxylic acid) spin label were synthesized by solid phase methodology. Ammonium hydroxide (pH 10, 50 degrees C, l h) was the best means for reverting nitroxide protonation occurring during peptide cleavage. EPR spectra yielded rotational correlation times for internally labeled analogs that were nearly twice as large as those of N-terminally labeled analogs. Except for TOAC(1)-AngII and TOAC(0)-BK, which showed high intrinsic activities, other derivatives were inactive in smooth muscle preparations. These active paramagnetic analogs may be useful for conformational studies in solution and in the presence of model and biological membranes.

Based on observations that vascular smooth muscle cells (VSMC) from spontaneously hypertensive rats (SHR) have altered resting potentials as well as abnormal cell proliferation rates, neointima formation after controlled balloon injury was compared in arteries from SHR and Wistar Kyoto rats (WKY). SHR aortic VSMC showed hyperpolarized resting membrane potentials (-93+/-8 mV) when compared to those from WKY (-61+/-6 mV). Histomorphometric analysis of cross sections from aortic segments submitted to balloon injury showed reduced neointima formation in SHR (neointima/media ratio: 0.04+/-0.03) as compared to WKY (0.2+/-0.1). On the other hand, in injured carotid arteries, neointima formation was more extensive in SHR (neointima/media ratio 5.0+/-0.9) than in WKY (0.8+/-0.7), leading in most cases to luminal occlusion. Measurements of VSMC resting potential showed that carotid artery cells from SHR were depolarized with respect to those from WKY (-46+/-4 vs. -69+/-5 mV, respectively). The results demonstrate an inverse relationship between VSMC membrane polarization and neointima formation in SHR arteries, suggesting that genetic modifications in SHR determine a dysfunctional cellular physiology that may influence cell proliferation subsequent to injury.

The role of alpha(2)-adrenoceptors in the response of aorta smooth muscle rings to the alpha(2)-adrenoceptors agonists UK 14,304 and clonidine was studied. Stimulation by 1 - 10 nM UK 14,304 caused dose-dependent relaxant responses in BaCl(2)-contracted endothelium-denuded aorta rings, and hyperpolarization in rings with or without endothelium, which were inhibited by yohimbine and glibenclamide, but not affected by prazosin, propranolol, apamin or iberiotoxin. At higher concentrations (10 nM - 10 microM) UK 14,304 also induced a depolarizing effect which was potentiated by yohimbine and inhibited by prazosin. These results indicate that UK 14,304 acts on alpha(2)-adrenoceptors at lower concentrations and on both alpha(1)- and alpha(2)-adrenoceptors above 10 nM. In rings, with or without endothelium, noradrenaline had a depolarizing effect which was inhibited by prazosin. Adrenaline did not affect the membrane potential but in the presence of prazosin caused hyperpolarization, which was inhibited by yohimbine and glibenclamide. These results indicate that noradrenaline is more selective for alpha(1)-, whereas adrenaline has similar affinities for alpha(1)- and alpha(2)-adrenoceptors. In aortae with endothelium, L-NNA caused a small depolarization but did not affect the hyperpolarization induced by UK 14,304, indicating that NO is not involved in that response. Glibenclamide induced a small depolarization in aortae, with or without endothelium, indicating that ATP-sensitive K(+) channels may play a role in maintaining the smooth muscle's membrane potential. Our results indicate that, in rat aorta, alpha(2)-adrenoceptors are also present in the smooth muscle, and that these receptors act through small-conductance ATP-sensitive K(+) channels.

Hypertension is one of the major precursors of atherosclerotic vascular disease, and vascular smooth muscle abnormal cell replication is a key feature of plaque formation. The present study was conducted to examine the relationship between hypertension and smooth muscle cell proliferation after balloon injury and to correlate neointima formation with resting membrane potential of uninjured smooth muscle cells, since it has been suggested that altered vascular function in hypertension may be related to the resetting of the resting membrane potential in spontaneously hypertensive rats (SHR). Neointima formation was induced by balloon injury to the carotid arteries of SHR and renovascular hypertensive rats (1K-1C), as well as in their normotensive controls, i.e., Wistar Kyoto (WKY) and normal Wistar (NWR) rats. After 14 days the animals were killed and the carotid arteries were submitted to histomorphometric and immunohistochemical analyses. Resting membrane potential measurements showed that uninjured carotid arteries from SHR smooth muscle cells were significantly depolarized (-46.5 +/- 1.9 mV) compared to NWR (-69 +/- 1.4 mV), NWR 1K-1C (-60.8 +/- 1.6 mV), WKY (-67.1 +/- 3.2 mV) and WKY 1K-1C (-56.9 +/- 1.2 mV). The SHR arteries responded to balloon injury with an enhanced neointima formation (neo/media = 3.97 +/- 0.86) when compared to arteries of all the other groups (NWR 0.93 +/- 0.65, NWR 1K-1C 1.24 +/- 0.45, WKY 1.22 +/- 0.32, WKY 1K-1C 1.15 +/- 0.74). Our results indicate that the increased fibroproliferative response observed in SHR is not related to the hypertensive state but could be associated with the resetting of the carotid smooth muscle cell resting membrane potential to a more depolarized state.

RMP-7 is a bradykinin (BK) agonist designed to be resistant to kininases such as angiotensin-converting enzyme (ACE). Pharmacological assays were performed with RMP-7 in isolated guinea-pig ileum and rat mesenteric artery. RMP-7 induced contractile responses in the guinea-pig ileum, where the apparent affinity of the peptide (pD2) was significantly lower than that determined for BK (7.3 +/- 0.07 vs. 8.3 +/- 0.05, respectively). HOE-140 blocked this effect indicating that B2 receptor was involved. Captopril (1 microM) had no potentiating effect on RMP-7 but increased pD2 value determined for BK (8.8 +/- 0.1), confirming a high resistance of RMP-7 to the ACE. In rat mesenteric artery, RMP-7 induced endothelium-dependent relaxation (7.8 +/- 0.4), with a higher affinity than that of BK which induced vasodilatation only in the presence of 1 microM captopril (6.9 +/- 0.36). Nevertheless, the maximum effect induced by RMP-7 was lower than that of BK in contrast to that observed in guinea-pig ileum although B2 receptor was involved in both cases. We concluded that: RMP-7 is greatly resistant to the ACE and that the receptor sites activated by RMP-7 and BK show important differences in vascular and non-vascular preparations probably due to the different sensitivity of the B2 receptor to RMP-7.

We studied the effect of oral cholecalciferol treatment on the endothelium-dependent vascular relaxation and hyperpolarization induced by acetylcholine (ACh), which is impaired in spontaneously hypertensive rats (SHR). Adult female SHR and normotensive Wistar-Kyoto rat (WKY) controls received 125 microg of cholecalciferol per kilogram body weight per day for 6 weeks. The responses to ACh of the isolated mesenteric vascular bed and mesenteric artery rings were measured, as well as the smooth muscle cell membrane potential. After cholecalciferol treatment, the systolic blood pressure and basal perfusion pressure of the mesenteric vascular bed of the SHR fell to control levels. The relaxant and hyperpolarizing effects of ACh, which are reduced in SHR, were also brought to control levels after cholecalciferol treatment. These effects of ACh were inhibited by N(omega)-nitro-L-arginine in SHR and by apamin in WKY. After cholecalciferol treatment, SHR hyperpolarizing responses showed the same inhibition pattern as those of WKY. This indicates that, after cholecalciferol treatment, SHR vascular mesenteric preparation responses to ACh are mediated by endothelium-derived hyperpolarizing factor, which induces activation of Ca(2+)-dependent K(+) channels, as in WKY. In untreated SHR, the ACh-mediated response is entirely due to ACh acting via the release of nitric oxide.

1. The mechanism responsible for blood pressure reduction in spontaneously hypertensive rats (SHR) after prolonged cholecalciferol treatment was studied. Two-week treatment of SHR with 0.125 mg cholecalciferol kg-1 body weight per day orally caused significant reductions of systolic blood pressure and of the resting perfusion pressure of the mesenteric vascular bed at constant flow. 2. In addition, the treated animals presented a normalization of the maximum vasoconstriction response to noradrenaline and a reduction of the maximum effect of the adrenaline concentration-response curves. This latter effect probably was due to recovery of the impaired Ca(2+)-dependent K+ channels coupled to alpha 2-adrenoceptors since it was prevented by apamin. 3. The treatment with cholecalciferol also normalized the smooth muscle cell membrane potential of de-endothelialized mesenteric arteries of SHR and their hyperpolarizing responses to alpha 2-adrenergic agonists, which were depressed in untreated SHR. 4. In mesenteric rings with endothelium, alpha 2-adrenergic agonists caused similar hyperpolarizing responses in the SHR and in normotensive Wistar (NWR) and Wistar Kyoto (WKY). In non cholecalciferol-treated SHR the hyperpolarizing mediator involved in this effect was NO, while in NWR it was the endothelium-derived hyperpolarizing factor (EDHF). After cholecalciferol treatment, the hyperpolarization induced by alpha 2-adrenergic agonists in SHR smooth muscle cells was mediated by EDHF, as in NWR. 5. Our results indicate that the hypotensive effect of cholecalciferol in the SHR is probably due to the normalization of vascular reactivity, by restoring the functioning of apamin- and ATP-sensitive K+ channels located in the vascular smooth muscle cell membrane, which are impaired in the SHR.

Ca2+ pathways activated by angiotensin II and carbachol were evaluated in the circular muscle of the guinea-pig ileum by recording mechanical and electrical activities. Transient contractions induced by angiotensin II were greatly reduced by Ca2+ removal from the medium whereas carbachol-induced responses were not significantly altered. Nifedipine had no effect on the responses to both agonists. A high concentration of tetrodotoxin (0.1 microM) inhibited angiotensin II-induced contractile responses without affecting the depolarization, whereas 1 mM Ni2+ inhibited the mechanical and electrical effects. Neither tetrodotoxin nor Ni2+ affected carbachol-induced effects. These results indicate that angiotensin II-induced phasic contractions depend on extracellular Ca2+ but not on voltage-dependent L-type Ca2+ channels. It is suggested that angiotensin II activates Ni2+-sensitive Na+ and non-specific cationic channels, whereas the responses to carbachol are dependent on receptor-activated Ca2+ release. Furthermore the different response of the longitudinal and circular muscles to the inhibitory effects of tetrodotoxin and Ni2+ on the angiotensin II- and carbachol-induced contractions indicates that these agonists exert their own myogenic effects on each layer and are able to trigger different Ca2+ mobilization pathways.

The alpha2-adrenoceptor function in mesenteric arteries of spontaneously hypertensive rats (SHR) was investigated by comparing membrane potential changes in response to adrenergic agonists in preparations from female SHR, Wistar-Kyoto (WKY) and normotensive Wistar rats (NWR). Resting membrane potential was found to be less negative in mesenteric arteries from SHR than in those from NWR and WKY. Apamin induced a decrease in the membrane potential of mesenteric artery rings without endothelium from NWR and WKY, but had no effects in those from SHR. Both UK 14,304 and adrenaline, in the presence of prazosin, induced a hyperpolarization that was significantly lower in de-endothelialized mesenteric rings from SHR than in those from NWR and WKY. In mesenteric rings with endothelium, however, similar hyperpolarization was observed in the three strains. In NWR mesenteric rings with endothelium the hyperpolarization induced by activation of alpha2-adrenoceptors was abolished by apamin, whereas in intact SHR mesenteric rings this hyperpolarization was slightly reduced by apamin and more efficiently reduced by Nomega-nitro-L-arginine. It is concluded that the activity of potassium channels coupled to alpha2-adrenoceptors is altered in the smooth muscle cells of SHR mesenteric arteries, contributing to their less negative membrane potential. On the other hand, the endothelial alpha2-receptors are functioning in mesenteric vessels from SHR and their stimulation induces a hyperpolarization mainly through the release of nitric oxide.

The purpose of the present study was to examine the importance of magnesium in endothelial function after arterial balloon injury. Male Wistar rats were fed normal, high or low concentrations of magnesium. Three weeks later the animals underwent endothelial injury of the thoracic aorta by a balloon catheter or a sham operation. Biochemical, histological and endothelial function analysis were performed 15 days after the surgical treatment. The animals fed a low magnesium diet presented the lowest level of serum magnesium and the highest ionized blood calcium levels. Histomorphometric analysis revealed no differences among groups neither regarding the magnitude of intimal thickening nor the recovery of endothelial coverage. However, when vasoreactivity responses were compared in the balloon-injured group, those animals fed a high magnesium diet had the better endothelium-dependent vascular relaxation. In conclusion, a higher magnesium level in the diet was beneficial to vessels that underwent endothelial injury by balloon catheter.

1. The diet of spontaneously hypertensive rats (SHR) and normotensive Wistar rats (NWR) was supplemented with 12.5 micrograms cholecalciferol per 100 g body weight daily, by gavage, for 4 weeks. 2. The amplitude of the contractile responses of aortic rings from SHR to potassium and adrenaline, which was smaller than in NWR aortae, was increased after treatment with cholecalciferol. No further changes were observed in the responses of NWR and SHR aortae in the presence of 100 nM apamin. 3. The membrane potentials of aortae from SHR, which were higher than those of aortae from NWR, decreased after treatment with cholecalciferol. Further depolarization was observed in aortic rings from NWR, but not in aortic rings from SHR, after their preincubation with 100 nM apamin. 4. It is concluded that cholecalciferol normalizes the membrane potential and contractility of aortae from SHR, probably through an effect on lipid composition and structure of the plasma membrane.

The effect of clonidine on the mesenteric vascular bed and the isolated mesenteric artery was examined in preparations in which tonus was induced by norepinephrine or endothelin. In preparations precontracted by norepinephrine, clonidine caused a relaxation which was not inhibited by the alpha-2 antagonists yohimbine and idazoxan or by the K+ channel blockers apamine, tetraethylammonium and glibenclamide. In preparations precontracted with endothelin, clonidine increased the depolarization and induced a contraction. Both these effects were inhibited by prazosin. In isolated mesenteric arteries, norepinephrine cause a significant depolarization that was inhibited by clonidine or prazosin. On the other hand, clonidine caused a hyperpolarization which was inhibited by idazoxan or yohimbine, but not by prazosin. This hyperpolarization was also abolished by apamine, tetraethylammonium and glibenclamide. It is concluded that clonidine acts on alpha-1 adrenoceptors as a partial agonist, causing relaxation of the mesenteric artery precontracted with norepinephrine or contraction of preparations precontracted with endothelin. Moreover, clonidine can open K+ channels and hyperpolarize the plasma membrane of mesenteric artery by acting on alpha-2 adrenoceptors.

Angiotensin II (AII) tachyphylaxis occurs in the guinea pig ileum, but is not induced by analogs lacking the N-terminal amino group or the Arg2 guanidino group. Both AII and Lys2AII increased cell inositol trisphoshate content in cultured intestinal smooth muscle cells. Protein kinase C inhibition by staurosporine or downregulation by prolonged incubation with phorbol reverted tachyphylaxis of the inositol trisphoshate response, but not that of the Na+ uptake response, indicating that the uncoupling of the phosphoinositide signal system by protein kinase C did not involve all processes distal to receptor activation. Tachyphylaxis of the Na+ uptake response was prevented when receptor internalization was blocked by reduction of the temperature (4 degrees C) or by pretreatment of the cells with phenylarsine oxide. Acid washings, which prevented tachyphylaxis of the 24Na+ influx response, also prevented tachyphylaxis of the contractile response of the guinea pig ileum to AII. Although these findings suggest that sequestration or internalization of the AII receptor might be involved in AII tachyphylaxis, binding of [125I]AII and of [125I]Lys2AII to the cells was equally unaffected by repeated administrations of the peptides. The results suggest that conformational change of the AII-receptor complex within the plasma membrane, but not internalization, is the most important factor responsible for tachyphylaxis.

1. Contractile responses to KCl and membrane potentials were determined in aortic rings from spontaneously hypertensive rats (SHR), normotensive Wistar rats (NWR) and Wistar Kyoto rats (WKY) both in the absence and in the presence of the Ca(2+)-dependent K-channel blockers, apamin and tetraethylammonium (TEA). 2. Compared to NWR, aortic rings from WKY and SHR were less reactive and their Ca2+ uptake after stimulation with K+ was decreased. 3. Smooth muscle cell membrane potentials were higher in aortae from SHR and WKY than in NWR aortae, whereas SHR had higher K+ and lower Na+ intracellular activities than WKY and NWR, suggesting overactivity of the Na+/K+ pump in the hypertensive animals. 4. Treatment with apamin caused depolarization of WKY and SHR aortae, and increased their contractile responses to the same level as those of the NWR. Treatment with TEA also caused depolarization of aortae from WKY and SHR, but in the SHR the depolarization induced by TEA was smaller than that produced by apamin and the contractile responses to KCl did not reach the level of those of aortae from NWR. 5. It is concluded that overactivity of Ca(2+)-dependent K-channels in aortae of WKY and SHR contributes to their higher membrane potentials and lower responsiveness to vasoconstrictor stimuli. In SHR, an overactive Na+/K+ pump is also present, and the contribution of apamin-sensitive Ca(2+)-dependent K-channels to the membrane potential and reactivity appears to be more relevant than that of TEA-sensitive channels.

The increase in sensitivity of guinea pig preparations to bradykinin (BK) due to stretching occurring with time after mounting was studied by determining the time course of changes in the cell membrane potential, measured with intracellular microelectrodes. A sustained hyperpolarizing effect of BK, which was observed in recently mounted preparations, became transient after 120 min, when it was followed by depolarization, which was much more evident after 4 h of stretching. As a consequence, a parallel increase in the contractile response to BK was also observed. The hyperpolarizing effect was due to the opening of Ca(2+)-dependent K+ channels sensitive to apamin, since BK dose-response curves done within 1 h of mounting were shifted to the left, becoming similar to dose-response curves obtained 4 h after mounting of the guinea pig ileum preparation. These results were specific for BK, since the potentiating effect of apamin was not observed for acetylcholine. Our results show that the activation of B2 receptors by BK in the isolated guinea pig ileum induce a dual effect--hyperpolarization and depolarization--and that the increase in the contractile response consequent to stretching is probably due to the inactivation of apamin-sensitive Ca(2+)-dependent K+ channels.

Sodium taurocholate (NaTC), at concentrations below the critical micellar concentration, caused a transient relaxation of isolated guinea-pig ileum smooth muscle strips. The relaxation was not inhibited by previous incubation with either 10 microM ouabain, 0.4 mM d-tubocurarine or 0.5 microM apamin, ruling out the participation of hyperpolarization of the plasma membrane induced by either stimulation of Na+/K+ ATPase or by opening of Ca(++)-dependent K+ channels. In guinea-pig ileum smooth muscle cultured cells, addition of NaTC (1 mM) stimulated Na+ uptake and Ca++ efflux. The relaxation induced by NaTC was inhibited by 3',4'-dichlorobenzamil, a blocker of the Na+/Ca++ exchanger. Preincubation with NaTC, or its addition during the early stage of the tonic response of the ileum to acetylcholine, enhanced that response, whereas a relaxation was observed when NaTC was added at the late stage of the acetylcholine response. In cultured cells, NaTC potentiated the stimulation of Ca2+ influx by acetylcholine. Our results suggest that NaTC acts on the smooth muscle cell membrane causing a stimulation of the Na+/Ca++ exchange mechanism.

Simultaneous recordings of the tension and intracellular Ca2+ concentration of guinea-pig ileum longitudinal smooth muscle strips, as well as 24Na+ and 45Ca2+ influx measurements in cultured myocytes from the same tissue, were used to investigate the mechanisms underlying angiotensin-induced desensitization and tachyphylaxis. Angiotensin II and [2-lysine]-angiotensin II (Lys2All), incubated for prolonged periods (10 min) with muscle strips, induced fading of the contractile response (desensitization) and reappearance of the intracellular Ca2+ concentration oscillations, which were inhibited during the initial increase in cytosolic Ca2+. The desensitization was paralleled, in cultured myocytes, by inhibition of the 45Ca2+ but not of the 24Na+ influxes which were initially stimulated by the peptides. On the other hand, repeated administrations of angiotensin II (but not of Lys2All) caused gradual reduction of the contractile response and of the 24Na+ influx stimulation evoked by the agonist (tachyphylaxis). Treatment with phorbol 12-13 dibutyrate accelerated the desensitization induced by both angiotensin II and by Lys2All and aggravated the tachyphylaxis to angiotensin II. The results support the hypothesis that activation of protein kinase C is responsible for the desensitization and that tachyphylaxis is due to the slow dissociation of angiotensin II from a postulated Na(+)-dependent regulatory site on the receptor.

1. The dual action of bradykinin (relaxation and contraction) on the rat duodenum was investigated by studying its effect on adenosine 3':5'-cyclic monophosphate (cyclic AMP) levels in cultured duodenal smooth muscle cells, and the effects of apamin on the isolated muscle responses to agonists and antagonists of BK1 and BK2 receptors. 2. No change was observed in the cyclic AMP content of cultured cells incubated with up to 100 nM bradykinin. 3. Apamin (100-500 nM) inhibited the relaxant component and enhanced the contractile component of the responses to bradykinin and to the BK2-specific analogue [Thi5,8,D-Phe7]-bradykinin. 4. Apamin (100-500 nM) did not affect the contractile response of stretched duodenum preparation to the BK1-specific agonist des-Arg9-bradykinin. 5. The BK2 antagonist, [D-Arg0Hyp3Thi5,8,D-Phe7]-bradykinin, at a concentration which completely inhibited the relaxant response to bradykinin and to [Thi5,8,D-Phe7]-bradykinin, also prevented the contraction in response to either agonist in the presence of apamin. 6. Our results demonstrate two populations of bradykinin receptors in rat duodenum: a BK2 subtype responsible for the biphasic response of the non-stretched duodenum, and a BK1 subtype responsible for the contractile effect on the stretched tissue.

1. The diet of spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) and Wistar (NWR) rats was supplemented with either 2% calcium lactate in the drinking water or 12.5 micrograms vitamin D3 100 g-1 body weight daily by gavage, for 14 days. 2. The blood pressure of the SHR treated with either calcium or vitamin D decreased to the same levels as that of WKY and NWR. 3. The response to bradykinin of the SHR isolated duodenum, which is predominantly contractile, upon treatment with vitamin D (but not with calcium), became predominantly relaxant, approaching the normal behavior of the WKY and NWR duodenum. 4. The relaxant responses of the SHR and WKY duodenum to potassium were smaller than those of NWR, but treatment with vitamin D increased the response in all three rat strains. 5. It is concluded that, besides sharing the hypotensive effect of calcium, vitamin D treatment of SHR has an effect on the duodenum smooth muscle which might be due to calmodulin-dependent activation of calcium-dependent potassium channels.

Bradykinin (BK) did not increase cyclic AMP production in cultured rat duodenum smooth muscle cells. Its relaxant effect on the tissue was inhibited by apamin and potentiated by phorbol dibutyrate (PDBU). PDBU also caused a relaxation which was inhibited by apamin. BK's relaxant effect, and its potentiation by PDBU, are due to activation of Ca(2+)-dependent K+ channels.

Tachyphylaxis to both angiotensin II (ANG II) and Sar1-ANG II is observed in normal rabbit aorta rings, but helical strips show tachyphylaxis only to Sar1-ANG II, whereas everted rings are not tachyphylactic to either analogue. In normal rings, a good correlation was observed between intraluminal pH and degree of tachyphylaxis to both analogues, suggesting that rate-limiting access of the agonists to their site of action may enhance tachyphylaxis in this preparation. Membrane potential and intracellular Na+ activity measurements, as well as the relaxation by K+ of norepinephrine-contracted preparations in K(+)-free medium, indicated that helical strips are more depolarized than everted rings due to Na+ leakage into the smooth muscle cells. These results suggest that the differences in the degree of tachyphylaxis induced by angiotensin in different rabbit aorta preparations are due to a less accessible site of action in normal rings and to the higher intracellular Na+ and more depolarized state of helical strips relative to everted rings.

The effects of angiotensin II (ANG) on Na+ and Ca++ fluxes in cultured intestinal smooth muscle cells from the guinea pig ileum were studied and correlated with the contraction and desensitization observed in whole muscles. The effects of ANG were compared with those of acetylcholine (ACh), an agonist that acts at muscarinic receptors in the intestinal smooth muscle and which does not induce desensitization. Both ANG and ACh stimulated 24Na+ influx upon addition to the cells, and this stimulation persisted for at least 30 min. Both agonists also stimulated 45Ca++ uptake but ANG's effect was transient, whereas that of ACh was persistent. Short-term (30 min) treatment with PMA (phorbol-12-myristate-13-acetate) caused a fade of the tonic response of the whole muscle to ANG, and also blocked this hormone's stimulating effect on 45Ca++, but not on 24Na+ influx. Long-term (7 hr) treatment with PMA, which suppresses protein kinase C activity, restored ANG's ability to stimulate 45Ca++ influx. The stimulating effects of ACh on 24Na+ and 45Ca++ influxes were not affected by short- or long-term treatment of the cells with PMA. Our results suggest that ANG desensitization involves protein kinase C inhibition of a step in the stimulus-response chain that is subsequent to phospholipase C-activation.

The isometric responses of the longitudinal smooth muscle of the guinea-pig ileum to acetylcholine and to histamine consist of a phasic contraction followed by a fade and a tonic contraction. At high agonist concentrations the fade is more pronounced and a period of lower tonus is observed in the early stage of the tonic component of the response. Experiments done in Ca2+-free medium indicate that the events responsible for the shape of the response take place in the absence of Ca2+ and of contraction. The phasic contraction was inhibited by hyperpolarization in low-Na+ medium. Small decreases in the external Na+ concentration caused a diminution of the fade. Reduction of the Na+ concentration during the early stages of the tonic response caused contraction whereas relaxation was observed at the late stages. It is proposed that the fade is dependent on a Na+-sensitive mechanism that is predominant at early but not at late stages of the responses to agonists.

The belief that the smooth muscle contracting activity of angiotensin II (angiotensin) in the guinea pig ileum is partly mediated by release of acetylcholine was reexamined, with the following results. 1. Atropine did not reduce the maximum contraction produced by angiotensin, although it caused a shift to the right of the log dose-response curve (dose ratio = 2.2). A similar shift was observed with histamine, bradykinin and BaCl2. 2. A moderate potentiation of angiotensin by eserine was also observed, which was similarly found for the other agonists. 3. A previous report that atropine blocks the fast (phasic) component of the isometric response of the ileum to angiotensin was not confirmed. The disappearance of the phasic component was found to be due to a tachyphylactic change in the response. 4. Depolarization by high doses of nicotine, and inhibition of acetylcholine synthesis by hemicholinium, did not affect the response to angiotensin. 5. Ilei in which the intramural ganglia had been destroyed by incubation at 4 degrees 48-56 h responed maximally to angiotensin, without loss of the phasic component of the response. It is concluded that the available evidence does not support the participation of a cholinergic mechanism in the effect of angiotensin upon the guinea pig ileum.

The ability of angiotensin II (AII) and of seven N-terminally modified peptide analogs to induce tachyphylaxis in isolated preparations of the rat uterus and the guinea-pig ileum was found to correlate well with the degree of amino group protonation. No correlation was found between tachyphylaxis and the affinity for the rat uterus receptors, as measured by the reciprocals of ED50 values. Dissociation between the tachyphylactic property and receptor affinity in the rat uterus was also evident by lowering the calcium concentration in the medium, which resulted in increased tachyphylaxis without significant changes in ED50 values. In the guinea-pig ileum, tachyphylaxis correlated with the reciprocal of ED50, but there was a better correlation with amino group protonation. [6-Pyrazolylalanine] AII was approximately as tachyphylactic as AII in both smooth muscles studied, indicating that protonation of the histidine side-chain may not be important for the manifestation of tachyphylaxis. The recovery of the guinea-pig ileum for AII tachyphylaxis was not affected by repeated treatments with BaCl2, but it was partially impaired by [Suc1]AII, des-Asp-AII, bradykinin and histamine.

The role of Ca++ in the stimulus-contraction coupling of the response of the isolated rabbit aorta to angiotensin II was investigated. Angiotensin was found to have lower intrinsic activity than epinephrine and to be more sensitive to acute exposure of the organ to Ca++-free medium. Two minutes after removal of Ca++, the maximal responses to angiotensin and epinephrine were reduced by 40% +/- 8% and 7% +/- 5%, respectively. Further loss of response for the two agonists followed parallel time courses. In another series of experiments, angiotensin tachyphylaxis was obtained in the rabbit aorta by administration of either [1-sarcosine]angiotensin or betainyl-angiotensin. The intrinsic activity of [1-sarcosine]angiotensin was lower than that of angiotensin and was not affected by removal of Ca++. It is concluded that the low intrinsic activity and the tachyphylaxis may be dependent on a strong binding of the molecule's positively charged N-terminus to sites responsible for release of Ca++ into the cell.

1. Bradykinin produces a biphasic response in the rat duodenum that consists of a relaxation (pD2 = 8.44) followed by a contraction (pD2 = 6.91). 2. The B1 agonist des-Arg9-bradykinin produced a contraction (pD2 = 7.16) but no relaxation. Des-Arg9-[Leu8]-bradykinin, which is a B1 antagonist in other systems produced contraction (pD2 = 7.65) in the rat duodenum. 3. Four bradykinin analogues that are preferential B2 agonists in other tissues had a biphasic effect with pD2 values in the range 7.22-8.68 for relaxation and 6.26-6.91 for contraction. 4. [Thi5,8,D-Phe7]-bradykinin, which is a B2 antagonist in most other systems produced relaxation in the rat duodenum, with a pD2 of 7.49. 5. It is concluded that the contractile component of the response to bradykinin in rat duodenum may be mediated by a subtype of the B1 receptor and the relaxant component by a receptor of the B2 subtype.

The sensitivity of the guinea pig isolated ileum to bradykinin, but not to other agonists, was increased ca. 2-fold during the 3-4 h following mounting of the preparation under 1 g load. Concomitantly, a decrease was observed in the bradykinin potentiating effect of BPP9a, and of potentiator B but not potentiator C. This decrease was observed only with analogues of BPP9a or potentiator B which retained one or both of the basic amino acid residues in these peptides. Similar stretching of the rat isolated uterus did not affect bradykinin sensitivity or the potency of bradykinin potentiating peptides. Kininase activity of the ileum significantly increased during the 4 h period after mounting of the loaded preparation, but was not affected by treatment with BPP9a. It is proposed that bradykinin sensitivity is favoured by the changes in sodium and potassium transport in the cell membrane caused by stretching of the ileum, and that a similar mechanism may be partly responsible for the action of bradykinin potentiating peptides.

The contractile responses of the rabbit isolated coeliac and mesenteric arteries to five agonists (angiotensin, adrenaline, histamine, acetylcholine and 5-hydroxytryptamine), but not to K+, were potentiated by indomethacin (8.4 microM) The potentiation was similar whether indomethacin was added 1 h before or during the response to the agonist. The agonists that were more potentiated by indomethacin were also more dependent on the Ca2+ concentration in the medium, for their contractile action. Prostaglandin E2 in low concentrations (micromolar) did not affect the resting tone but relaxed the agonist-contracted arteries both in normal and in Ca2+-free medium. No prostaglandin E (PGE)-like substances were detected in the perfusate of arteries contracted by angiotensin. Reduction of the external Na+ concentration to 80 mM resulted in potentiation of the responses to agonists (angiotensin and adrenaline), but not to K+, and in this Na+-deficient medium potentiation by indomethacin was greatly reduced. These results suggest that potentiation by indomethacin of the arteries' responses to vasoactive substances may result from that drug's inhibitory action on sodium influx and consequent increase in calcium entry through receptor-operated channels.

The effect of modifications of the N-terminal end of the angiotensin II (AII) molecule on its ability to induce tachyphylaxis in the isolated rabbit aorta was studied by analyzing the effects of several analogs of AII. No tachyphylaxis to AII was observed, but (1-sarcosine)-AII, (1-guanido-acetic)-AII and (1-glycine)-AII induced marked tachyphylaxis. (1-Betaine)-AII, (2-lysine)-AII, (2-ornithine)-AII and (1-sarcosine,2-lysine)-AII were unable to induce tachyphylaxis in the rabbit aorta. A positively charged N terminus and the guanidino group of the Arg2 side chain appear to be needed for the manifestation of the tachyphylactic property, while the Asp1 side chain is responsible for the absence of tachyphylaxis to AII. It is proposed that the analogs that are able to induce tachyphylaxis, after binding to the receptor to produce the agonistic response, induce a slow conversion of the hormone-receptor complex into a tachyphylactic state, and that this conversion is promoted by the interaction of the N terminus and the guanidino group of the analog with their complementary sites.

The biphasic (relaxation-contraction) response of the isolated duodenum was used to study the reactivity of non-vascular smooth muscles in genetic (SHR) and renal hypertensive rats compared to their respective controls (WKY and Wistar). For the contractile component of the response to bradykinin, the duodenum from WKY rats was more sensitive, whereas the duodenum from SHR was both more sensitive and hyperreactive, compared to that from Wistar rats. The relaxant component of the response to bradykinin was present in the duodenum of both WKY rats and SHR, but was concentration-dependent only in the WKY group. The relaxant response to K+ was very small in SHR, and was not concentration-dependent. The concentration-response curves for relaxant responses to adrenaline and for contractile responses to acetylcholine did not differ in the SHR and WKY groups. Ca2+/Mg2+-ATPase activity was found to be markedly reduced in the SHR group. No qualitative or quantitative differences were observed between the responses of the duodenum of renal hypertensive rats and those of their normotensive controls. It is proposed that the altered reactivity of the SHR duodenum is due to changes in ion handling by the smooth muscle cell membrane.

The structural requirements for prolonged residual ("sensitizing") activity in bradykinin-potentiating peptides (BPP's) were investigated through a study of seven synthetic BPP's including three not previously described: [Lys6]-BPP9a, [Gly6]potentiator B, and [Lys6,Gln8]potentiator B. The quantitation of the sensitizing activities in the isolated guinea pig ileum indicated that the structural requirements for bradykinin potentiation and for sensitization were not the same. The most potent sensitizers were potentiator B and [Lys6]-BPP9a.

The response of the rat duodenum to bradykinin (BK) consists of relaxant and contractile components, which have been attributed to different receptor types. To characterize the receptors responsible for this diphasic response we studied the effects of BK analogues known to act on B1 or B2 receptors in other systems. DesArg9-Leu8-BK and Thi5,8DPhe7-BK presented only relaxant and only contractile effects, respectively, whereas DArg0Hyp3Thi5,8DPhe7-BK was a potent antagonist of the relaxation (but not of the contraction) induced by BK. Our results show that the relaxant and contractile components of the rat duodenum's response to BK are due to B2 and B1 receptor subtypes, respectively.

The responses of rabbit mesenteric or coeliac artery rings to angiotensin II or adrenaline (but not to K+) were enhanced by endothelium destruction (by rubbing). Potentiation by indomethacin of the response to the agonists was observed in rubbed rings but not in intact ones. Both angiotensin II and adrenaline (in the presence of propranolol and prazosin) induced endothelium-dependent relaxation of the arteries. Rubbed rings, but not intact ones, contracted when Ca2+ was added to a previously Ca2+-free medium containing angiotensin II or adrenaline. The vasoconstrictor response appears to be modulated by the regulation of receptor-operated Ca2+ channels through EDRF released by the endothelium and by some cyclo-oxygenase product at the level of the smooth muscle cell membrane.