Search

Significance: It has been reported that children with attention-deficit hyperactivity disorder (ADHD) have impairment in the recognition of angry but not of happy facial expressions, and they show atypical cortical activation patterns in response to facial expressions. However, little is known about neural mechanisms underlying the impaired recognition of facial expressions in school-aged children with ADHD and the effects of acute medication on their processing of facial expressions. Aim: We aimed to investigate the possibility that acute administration of methylphenidate (MPH) affects processing of facial expressions in ADHD children. Approach: We measured the hemodynamic changes in the bilateral temporo-occipital areas of ADHD children observing the happy and angry facial expressions before and 1.5 h after MPH or placebo administration in a randomized, double-blind, placebo-controlled, crossover design study. Results: We found that, regardless of medication, happy expressions induced increased oxyhemoglobin (oxy-Hb) responses in the right inferior occipital region but not in the superior temporal region. For angry expressions, oxy-Hb responses increased after MPH administration, but not after placebo administration, in the left inferior occipital area, whereas there was no significant activation before MPH administration. Conclusions: Our results suggest that (1) ADHD children consistently recruit the right inferior occipital regions to process happy expressions and (2) MPH administration to ADHD children enhances cortical activation in the left inferior occipital regions when they process angry expressions.

Objective: We aimed to clarify the validity of fNIRS measurement for assessing the methylphenidate (MPH) induced neuropharmacological effect in medication-naive children with attention deficit hyperactivity disorder (ADHD) with or without comorbid autism spectrum disorder (ASD), thereby providing the first evidence for differing neurofunctional pathology between the two groups. Methods: We monitored the effects of a single acute clinical dose of MPH on the cortical hemodynamics of 32 medication-naive ADHD children (ADHD with ASD n=11 and ADHD without ASD n=21) performing a go/no-go task before and 1.5 h after MPH or placebo administration, using a randomized, double-blind, placebo-controlled, crossover design. In addition, all subjects’ symptoms were monitored using the Japanese version of the ADHD Rating Scale-IV (ADHDRS- IV-J) before and one month after MPH administration. Results: Medication-naive ADHD children without ASD exhibited reduced right prefrontal activation. MPH medication elicited significant right prefrontal activation except in comparative conditions associated with the placebo effect. Medication-naive ADHD children with ASD exhibited marginal activation before the first day of medication and reduced activation after MPH medication in the right prefrontal area. While the neuropharmacological effects of MPH were different, ADHD-RS-IV-J scores were significantly improved one month after MPH administration in ADHD groups both with and without ASD. Conclusion: Taken together, these results suggest that ADHD with ASD is characterized by a different underlying neurofunctional pathology for inhibition control than that without ASD. To our knowledge, this is the first comparative neuroimaging study between ADHD patients with and without comorbid ASD.

Gender differences in psychiatric disorders are considered to be associated with the serotonergic (5-HTergic) system; however the underlying mechanisms have not been clearly elucidated. In this study, possible involvement of the median raphe nucleus (MRN)-hippocampus 5-HTergic system in gender-specific emotional regulation was investigated, focusing on synaptic plasticity in rats. A behavioral study using a contextual fear conditioning (CFC) paradigm showed that the females exhibited low anxiety-like behavior. Extracellular 5-HT levels in the hippocampus were increased by CFC only in the males. Long-term potentiation (LTP) in the hippocampal CA1 field was suppressed after CFC in the males, which was mimicked by the synaptic response to MRN electrical stimulation. In the MRN, 5-HT immunoreactive cells significantly increased in the females compared with those in the males. Pretreatment with the 5-HT1A receptor agonists tandospirone (10 mg/kg, i.p.) and 8-OH DPAT (3 mg/kg, i.p.) significantly suppressed LTP induction in the males. Synaptic responses to CFC and 5-HT1A receptor interventions were not observed in the females. These results suggest that the metaplastic 5-HTergic mechanism via 5-HT1A receptors in the MRN-hippocampus pathway is a key component for gender-specific emotional regulation and may be a cause of psychiatric disorders associated with vulnerability or resistance to emotional stress. Keywords:: gender difference, serotonin, hippocampus, long-term potentiation, serotonin 5-HT1A receptor

The present study elucidated the functional role of modulatory effects of basolateral amygdala (BLA) on synaptic transmission in the rat hippocampus–medial prefrontal cortex (mPFC) pathway, compared with the hippocampal dentate gyrus (DG). Exposure to conditioned fear stress (CFS) or prior BLA activation enhanced tetanus-induced long-term potentiation (LTP) in DG. A similar synaptic response was found by low frequency stimulation (LFS) prior to tetanus. In mPFC, they did not affect LTP, but prior BLA activation, as well as pretreatment with the N-methyl-d-aspartate (NMDA)-receptor antagonist MK-801 (0.1 mg/kg, i.p.), suppressed LFS-primed LTP. This BLA-mediated synaptic pattern was mimicked by synaptic changes observed in the fear extinction process; prior BLA activation suppressed the synaptic potentiation responsible for extinction retrieval and attenuated decreases in fear-related freezing behavior. These data suggest that LFS-primed LTP in mPFC is related to the neural basis of extinction. Extinction-related synaptic potentiation did not occur in a juvenile stress model that exhibited extinction deficit. In addition, LFS-primed LTP was suppressed in this model, which was reversed by the NMDA-receptor agonist d-cycloserine (15 mg/kg, i.p.). These findings suggest that modulatory effects of BLA on synaptic function in the hippocampus–mPFC pathway play a significant role in fear extinction in rats. Keywords:: basolateral amygdala, synaptic potentiation, medial prefrontal cortex, extinction retrieval, low frequency stimulation

In our previous report, we showed that L-arginine induced depolarization of smooth muscle cells of the rat portal vein with an increased contraction. To clarify the ionic mechanism of the membrane depolarization, the effect of L-arginine on the holding current was studied in freshly isolated smooth muscle cells of the rat portal vein. The whole-cell patch-clamp technique was used, with the membrane potential held at -60 mV. In the presence of Na+ in the perfusate, L-arginine 10 mM induced an inward current in about 50% of the cells. In Na+-deficient perfusate, L-arginine 10 mM increased the amplitude of the inward current in a Na+ concentration-dependent manner. BCH, an inhibitor of the Na+-dependent amino acid transporter, ceased the L-arginine-induced current. These results indicate that L-arginine induces an inward current via Na +-dependent mechanisms in rat portal venous smooth muscle cells.

The purpose of the present study was to evaluate the salivary Chromogranin-A (CgA) response to the psychological stress induced by a cognitive test battery. The subjects were 14 healthy volunteers administered the cognitive test battery CogScreen Aeromedical Edition (CogScreen-AE). CogScreen-AE is a test of reaction time and fundamental cognitive ability in the assessment of aeroplane pilots. The subjects were given five batteries of the test (1st approximately 5th) on separate days with 2 week intervals. Saliva samples were collected at 20 min before the test (BASE), immediately before the test (PRE), in the middle of the test (MID), and 5 min after the test (POS) for each subject. The concentration of CgA was determined by enzyme-linked immunosorbent assay. ANOVA revealed a significant by time interaction (BASE, PRE, MID and POS) without a significant effect of battery interaction (1st, 2nd, 3rd, 4th and 5th). The CgA concentration increased at PRE (2.46 +/- 0.24 pmol.mg protein- 1) from BASE (1.19 +/- 0.10 pmol.mg protein- 1). CgA level remained increased in the MID (2.90 +/- 0.26 pmol.mg protein- 1) and remained high in the POS samples (2.81 +/- 0.23 pmol.mg protein- 1). Salivary CgA remained at basal levels during a control study over the same time course without exposure to CogScreen-AE. The changes in salivary CgA secretion as a result of exposure to a cognitive task may indicate psychological stress in humans.

Clonidine, an alpha2-agonist, has been shown to be useful in the treatment of hepatic portal hypertension in cirrhosis. The mechanism has been attributed to a clonidine-induced decrease in sympathetic activity. While clonidine has been shown to stimulate the alpha2-adrenoceptors of blood vessels, there is limited knowledge of the effects of clonidine on the circular muscle of the hepatic portal vein which regulates its blood flow. To investigate clonidine-induced contraction of the circular muscle of the hepatic portal vein and to clarify the possible role of the endothelium in the contraction, we examined the effects of clonidine on the isometric contraction of endothelium-intact and -removed ring preparations of the rat hepatic portal vein. In endothelium-intact preparations, clonidine caused a concentration-dependent increase in the amplitude of contractions. Inhibition of NO synthesis with Nomega-nitro-L-arginine (L-NNA) elevated the resting tone, and increased the amplitude of the clonidine-induced contractions. Inhibition of cyclooxygenase by diclofenac did not change the amplitude of the clonidine-induced contractions observed both in the presence and absence of L-NNA. Application of a single concentration of clonidine induced a clear increase in amplitude of both twitch and tonic contractions. Twitch and tonic contractions induced by clonidine were inhibited by yohimbine. When the endothelium was damaged by sodium deoxycholate, tonic contractions induced by clonidine were completely suppressed, whereas the increase in twitch contractions was not influenced by chemical damage of the endothelium. Neither SKF-96365, a nonselective cation channel blocker, nor superoxide dismutase, a free radical scavenger, in the presence of catalase, changed the tonic contraction induced by clonidine. These results indicate that stimulation of alpha2-adrenoceptors enhanced twitch contractions and induced tonic contractions in the circular muscle of the rat hepatic portal vein, especially in the absence of NO. The latter, but not the former, occurs through an endothelium-dependent pathway.

Endothelium-removed carotid artery strips from stroke-prone spontaneously hypertensive rats spontaneously developed a tonic myogenic contraction. Flufenamic acid reduced the resting tone observed during superfusion with Tyrode's solution, in a concentration-dependent manner. Flufenamic acid also inhibited contractions produced by high-K solutions in a concentration-dependent manner. The resting membrane potential of smooth muscle cells in the artery was around -32 mV, with occasional oscillatory potentials. Flufenamic acid hyperpolarized the membrane in a concentration-dependent manner. The voltage-dependent outward currents recorded in isolated cells with micropipettes filled with high-K+ solution (holding potential, -60 mV) were enhanced by flufenamic acid and inhibited by tetraethylammonium. When the recording micropipette was filled with high Cs to inhibit the K+-current, depolarizing step pulses evoked nifedipine-sensitive inward currents. Flufenamic acid inhibited the inward currents. These results indicate that flufenamic acid inhibits the spontaneous active tone of the carotid artery by inhibiting L-type Ca2+-channels and possibly by membrane hyperpolarization through activation of the voltage-dependent K+-channels.

Effects of chronic treatment of normotensive Wistar rats with N(omega)-nitro-L-arginine methyl ester (L-NAME) on blood pressure and on endothelium-dependent relaxation of the aorta, carotid and iliac arteries were studied. The endothelium-dependent relaxation was compared in arteries from normotensive Wistar Kyoto rats (WKY) and genetically hypertensive rats (stroke-prone spontaneously hypertensive rats, SHRSP). Chronic treatment of normotensive Wistar rats with L-NAME caused an elevation of blood pressure. The elevated blood pressure at 15 weeks of age was significantly higher in these animals than that of untreated Wistar rats, but lower than that of SHRSP. Endothelium-dependent relaxation of the arteries induced by acetylcholine (ACh) was almost abolished by chronic treatment with L-NAME. The remaining small relaxation in arteries from L-NAME-treated rats was completely inhibited by application of L-NAME (10(-4) M). In such preparations, higher concentrations of ACh induced a contraction, which was abolished by removal of the endothelium or by an application of indomethacin (10(-5) M). Endothelium-independent relaxation induced by sodium nitroprusside was similar between preparations from untreated and L-NAME-treated Wistar rats. Endothelium-dependent relaxation was significantly impaired in preparations from SHRSP, when compared with that in those from WKY. However, the impairment was less prominent in preparations from SHRSP than in those from L-NAME-treated rats. These results suggest that the impairment of endothelium-dependent relaxation in the arteries from L-NAME-treated rats is not due to the elevated blood pressure resulting from the chronic treatment, and that impairment of NO synthesis by the endothelium does not play a major role in the initiation of hypertension in SHRSP.

Effects of isoproterenol on contraction and membrane potential of gastric smooth muscle were studied in stroke prone spontaneously hypertensive rats (SHRSP) and normotensive Wistar Kyoto rats (WKY). Circular muscle preparation from the gastric fundus developed tonic contraction by re administration of Ca2+ to a nominally Ca2+-free solution. The contraction was inhibited by nifedipine or nicardipine. Isoproterenol induced relaxation when it was applied to the Ca2+-induced contraction. The amplitude of isoproterenol induced relaxation was concentration-dependent. Propranolol 10(-6) M abolished the relaxation induced by isoproterenol 10(-7) M. In the preparation from SHRSP, the amplitude of isoproterenol induced relaxation was smaller than that from WKY between 3 x 10(-9) and 10(-7) M. Forskolin, an adenylate cyclase activator, induced concentration-dependent relaxation. There was no difference in the relaxation induced by forskolin between preparations from WKY and SHRSP. Dibutilyl cyclic AMP, a membrane permeable analogue of cyclic AMP, also induced similar relaxation in preparations from WKY and SHRSP. Resting membrane potential of smooth muscle cell was not different between preparations from WKY and SHRSP. Isoproterenol hyperpolarized the membrane concentration-dependently. Isoproterenol-induced hyperpolarization in the preparation from SHRSP was smaller than that from WKY between 10(-8) and 10(-6) M. When the membrane was depolarized by Tyrode's solution containing 40 mM K+, isoproterenol-induced hyperpolarization was almost abolished. In this condition, the isoproterenol-induced relaxation was inhibited partly, however, there was no difference in the amplitude of relaxation between preparations from WKY and SHRSP. Therefore, isoproterenol-induced hyperpolarization contributed at least partly to the relaxation. Forskolin hyperpolarized the membrane by the same amplitude in the preparations from WKY and SHRSP. These results indicate that a decrease in hyperpolarization may contribute to the decreased relaxation by isoproterenol in the preparation from SHRSP.

1. The effects of cyclopiazonic acid (CPA), a selective inhibitor of sarcoplasmic reticulum (SR) Ca2+-ATPase, on twitch contraction and on the resting state of tension and intracellular Ca2+ level ([Ca2+]i) of the oesophageal striated muscle of stroke-prone spontaneously hypertensive rats (SHRSP) and normotensive Wistar Kyoto rats (WKY) were compared. 2. CPA (10 micronM) augmented the twitch contraction of oesophageal striated muscle preparations from both SHRSP and WKY, reducing the rate of relaxation (-dT/dt), and thus resulting in the prolongation of the time to 80% relaxation. The effect was significantly smaller in the SHRSP preparations. 3. In the resting state, CPA caused a sustained elevation of [Ca2+]i. The elevation was greater in the WKY preparations. Tension development accompanied by the elevation was observed in WKY preparations, but not in SHRSP preparations. 4. The sustained elevation of [Ca2+]i induced by CPA was eliminated by the removal of extracellular Ca2+. Both the elevated [Ca2+]i and tension in the preparations from WKY were reduced by flufenamic acid (100 micronM), mefenamic acid (100 micronM), lanthanum (La3+, 100 micronM), gadolinium (Gd3+, 100 micronM) and SK&F 96365 (100 micronM) but not by verapamil (10 micronM). 5. Thapsigargin (3 micronM), another SR Ca2+-ATPase inhibitor, produced similar effects on basal tension to those of CPA, although it reduced the amplitude of twitch contraction. 6. These results suggest that in the rat oesophageal striated muscle, (1) CPA extends the sequestrating time of Ca2+ into the SR, (2) CPA induces a Ca2+ influx mediated through verapamil-insensitive pathways, possibly nonselective cation channels, and (3) the mechanism of [Ca2+](i) modulation due to CPA-sensitive SR Ca2+-ATPase is deteriorated in the oesophageal striated muscle from SHRSP as compared with WKY preparations.

Differences in the acetylcholine (ACh)-induced endothelium-dependent relaxation and hyperpolarization of the mesenteric arteries of Wistar Kyoto rats (WKY) and stroke-prone spontaneously hypertensive rats (SHRSP) were studied. Relaxation was impaired in preparations from SHRSP and tendency to reverse the relaxation was observed at high concentrations of ACh in these preparations. Relaxation was partly blocked by NG-nitro-L-arginine (L-NOARG, 100 μM) and, in the presence of L-NOARG, tendency to reverse the relaxation was observed in response to higher concentrations of ACh, even in preparations from WKY. The relaxation remaining in the presence of L-NOARG was also smaller in preparations from SHRSP. The tendency to reverse the relaxation observed at higher concentrations of ACh in preparations from SHRSP or WKY in the presence of L-NOARG were abolished by indomethacin (10 μM). Elevating the K+ concentration of the incubation medium decreased relaxation in the presence of both indomethacin and L-NOARG. Relaxation in the presence of L-NOARG and indomethacin was reduced by the application of both apamin (5 μM) and charybdotoxin (0.1 μM). This suggests that the relaxation induced by ACh is brought about by both endothelium-derived relaxing factor (EDRF, nitric oxide (NO)) and hyperpolarizing factor (EDHF), which activates Ca2+-sensitive K+ channels. Electrophysiological measurement revealed that ACh induced endothelium-dependent hyperpolarization of the smooth muscle of both preparations in the presence of L-NOARG and indomethacin; the hyperpolarization being smaller in the preparation from SHRSP than that from WKY. These results suggest that the release of both NO and EDHF is reduced in preparations from SHRSP. In addition, indomethacin-sensitive endothelium-derived contracting factor (EDCF) is released from both preparations; the release being increased in preparations from SHRSP. British Journal of Pharmacology (1999) 126, 709–716; doi:10.1038/sj.bjp.0702355

Contractile sensitivity to Ca2+ was studied in rat portal vein circular muscle isolated from normotensive Wistar Kyoto rats (WKY) and stroke-prone spontaneously hypertensive rats (SHRSP). There was no difference in resting membrane potential between WKY and SHRSP. Elevation of extracellular K+ concentration induced similar increase in tension in preparations from WKY and SHRSP. High K(+)-depolarized preparation developed tension increase when extracellular Ca2+ concentration was increased. The sensitivity to extracellular Ca2+ was similar in preparations from WKY and SHRSP. Permeabilized preparation contracted when free Ca2+ concentration was increased. Sensitivity of permeabilized preparation to Ca2+ was similar in preparations from WKY and SHRSP. These results indicate that regulation of contraction by Ca2+ was similar between WKY and SHRSP. Since there was no change in high K-induced contraction in intact preparations or Ca-induced contraction in permeabilized preparations, there seemed to be no difference in Ca2+ influx via voltage-dependent channels in portal vein circular muscle from WKY and SHRSP.

Control of the active tone by endothelium in aortae from various strains of spontaneously hypertensive rats was studied. The active tone was negligibly observed in endothelium-intact preparation. The application of N(G)-nitro-L-arginine (L-NNA, 10(-4) M) induced slowly developed active tone in the preparations from hypertensive rats but no active tone was induced in the preparation from normotensive Wistar Kyoto rats (WKY). The developed tension was stronger in preparations from rats with higher blood pressure as observed in endothelium denuded preparations. The developed active tone in the presence of L-NNA was greater than that observed in endothelium denuded preparations. The active tone was abolished by the removal of extracellular Ca2+ or by the application of Ca-antagonists. L-arginine counteracted the effects of L-NNA and depressed the developed active tone in the presence of the latter drug. The application of indomethacin (10(-5) M) depressed the active tone of the preparations from SHRSP by 25.5+/-5.2%. Increasing extracellular K+ concentration or application of tetraethylammonium (TEA) could not be used to observe the effect of endothelium-derived factors on the active tone, because of their strong contractile effect. Simultaneous application of apamin and charybdotoxin induced an elevation of tension which was often associated with spontaneous tension oscillation. It is concluded that the active tone, which is smooth muscle origin, is depressed by endothelium-derived nitric oxide (NO) strongly and potentiated by a product of arachidonic acid cascade through cyclooxygenase pathway. The involvement of endothelium-derived hyperpolarizing factor (EDHF) in the depressing effect of endothelium is thought to be small.

Eugenol (> or = 0.1 mM) inhibited the contractions induced by various stimulants, such as 90 mM extracellular K+ solution ([K+]0), histamine and noradrenaline in the rabbit ear artery. Inhibitory actions of eugenol occurred in a concentration-dependent manner, however, eugenol more dominantly inhibited the histamine-induced contraction than those induced by either 90 mM [K+]0 solution or noradrenaline. Removal of both endothelium and adventitia did not change the inhibitory actions of eugenol on the 90 mM [K+]0- and noradrenaline-induced contractions, however, attenuated those on the histamine-induced contraction. Chlorphenylamine abolished the histamine-induced contraction, but neither cimetidine, ranitidine nor thioperamide modified the eugenol actions on the contractions induced by histamine. Pretreatment with nitric oxide syntheses inhibitor NG-nitro-L-arginine (LNNA; 100 microM), but not soluble guanylate cyclase inhibitor methylene blue (MB; 10 microM), prevented endothelium/adventitia-dependent augmentation of the eugenol-induced relaxation on the histamine-induced contraction. When an intact tissue, but not an endothelium/adventitia-denuded tissue, was placed at the up-stream close to the other denuded preparation (test preparation), histamine-induced contraction observed in the test preparation tended to be augmented. Similarly, eugenol-induced relaxation was also augmented by the same treatment. Eugenol (0.3 mM) inhibited the excitatory junction potentials (EJPs) without hyperpolarization of the membrane. However, a high concentration of eugenol (1 mM) slightly hyperpolarized the membrane (ca. 5 mV). No transient enhancement of amplitude of EJP was recorded. These results suggest that eugenol may inhibit the histamine-induced muscle contraction directly, and the inhibition is augmented by the adventitia and endothelium partly by vasoactive substances, which were released from the adventitia/endothelium-derived substances in rabbit ear artery.

Oscillatory contractions of arteries in vitro are frequently induced by receptor stimulation with agonists. In certain arteries, the membrane potential and cytoplasmic intracellular free Ca2+ concentration in smooth muscle cells oscillate in the presence of agonists. The oscillatory changes are related to the Ca2+ release from store sites as well as Ca2+ influx. Gap junctions between smooth muscle cells play important roles in the synchronization of Ca2+ concentration in arterial tissues. Some of the agonist-induced oscillatory contractions are dependent on endothelium. Endothelial cells or endothelium-derived substances may modulate the tension oscillation of smooth muscle cells. In arteries from hypertensive animals, oscillatory contraction has been induced by agonists more frequently than that from normotensive animals. Abnormalities in membrane excitability of smooth muscle cells, gap junctions and endothelium may influence the tension oscillation in arteries from hypertensive rats.

The membrane hyperpolarization produced by endothelium-derived hyperpolarizing factor (EDHF) is one of the components in the endothelium-dependent relaxations. Different subtype of endothelium receptor is involved in the release of EDHF from that for nitric oxide. Although EDHF has not been identified, it may be related to cytochrome P450. The responses mediated by EDHF have been studied by observation of membrane potential or relaxation which is resistant to inhibitors of nitric oxide synthase and cyclooxygenase. The responses are dependent on potassium gradient across cell membrane, therefore, the response is mediated by potassium channels. The EDHF-mediated hyperpolarization or relaxation is sensitive to charybdotoxin plus apamin, inhibitors of calcium activated potassium channels. The EDHF-mediated response is more remarkable in small resistant arteries than large arteries, therefore, EDHF may play an important role in the regulation of vascular resistance. The EDHF-mediated response is decreased in hypertensive or aged animals. Understanding of EDHF-mediated response will promote development of a new strategy for the treatment of pathophysiological conditions.

Differences in alpha(2)-adrenoceptor-induced relaxation of the aorta between stroke-prone spontaneously hypertensive rats (SHRSP) and control normotensive Wistar Kyoto rats (WKY) were studied. Changes in the tension of ring preparations of the aortas were measured isometrically. Relaxation was observed in the preparations precontracted in the presence of ONO-11113, a thromboxane A(2) analogue. The alpha(2)-agonist clonidine and UK-14304 induced dose-dependent relaxation in both the WKY and SHRSP preparations. The relaxation was impaired in the SHRSP preparation. A modified sandwich experiment showed that the relaxing substance from the SHRSP endothelium was decreased. Acetylcholine (ACh) also induced dose-dependent relaxation, and the relaxation was impaired in the SHRSP preparations. alpha(2)-Agonists induced a greater degree of impairment in the relaxation than did ACh. The relaxation induced by alpha(2)-agonists and by ACh was blocked by N G-nitro-L-arginine (L-NNA). Indomethacin improved the relaxation induced by ACh but not that induced by alpha(2)-agonists in the SHRSP aortas. These results suggest that the impairment of relaxation by alpha(2)-agonists in SHRSP is not caused by the increase in the release of endothelium-derived contracting factor (EDCF) but by the reduction in the release of nitric oxide (NO). Alteration of the alpha(2)-adrenoceptors and/or the intracellular mechanism through which NO is synthesized by stimulation of the alpha(2)-adrenoceptors may be the cause of the reduction in relaxation.

The influence of blood pressure and age of spontaneously hypertensive rats on endothelium-dependent tension oscillation of aortic preparation were studied. Rats with different blood pressures, normotensive Wistar Kyoto rats (WKY), spontaneously hypertensive rats (SHR), stroke-prone SHR (SHRSP) and malignant type of SHRSP (M-SHRSP), were used. The effects of antihypertensive treatment of SHRSP on the tension oscillation were also studied. High doses of noradrenaline induced tension oscillations in endothelium-intact preparations of all strains of young rats. The rate of the occurrence of the tension oscillation decreased age-dependently. The decrease was faster when the blood pressure of the rats was higher. Application of acetylcholine in the presence of noradrenaline induced a relaxation and tension oscillations, both of which were negatively dependent on age and blood pressure. Antihypertensive treatment of hypertensive rats with hydralazine or captopril prevented a decrease in incidence of the tension oscillation. These influences of age and blood pressure as well as antihypertensive treatments on the tension oscillation resembled those on the endothelium-dependent relaxation and are thought to be brought about by functional changes of the endothelium.

Differences in the influences of endothelium-derived nitric oxside (NO) on alpha-agonists-induced contraction in the aortae of spontaneously hypertensive and normotensive rats were studied by blocking NO synthesis with NG-nitro-L-arginine (L-NNA). L-NNA potentiated the contraction induced by noradrenaline. The potentiation was smaller in the preparation from stroke-prone spontaneously hypertensive rats (SHRSP) than in the preparation from Wistar Kyoto rats (WKY). Similar potentiation was observed in the contraction induced by phenylephrine; the potentiation was also smaller in the preparation from SHRSP. alpha 2-agonists, clonidine and UK-14304 induced dose-dependent contraction only in the presence of L-NNA. The dose-response curves for alpha 2-agonists in SHRSP aorta were different from those in WKY aorta; the maximum tension was observed at the concentration of 10(-6) M in the preparation from WKY, while the contraction further increased up to 10(-4) M in the preparation from WKY. Noradrenaline, clonidine and UK-14304 but not phenylephrine induced relaxation which was blocked by L-NNA. The relaxation was impaired in the preparation from SHRSP in greater extent than that by acetylcholine. It is suggested that basic or noradrenaline-stimulated NO release from endothelium decreased in the preparation from SHRSP and that alpha 2-adrenoceptor of both the endothelium and smooth muscle may be altered in the preparation from SHRSP.

Spontaneously developed tension (active tone) and intracellular Ca2+ level of aortae from spontaneously hypertensive rats (SHR), stroke-prone SHR (SHRSP), malignant SHRSP (M-SHRSP) and control Wistar Kyoto rats (WKY) were compared. Systolic blood pressure of WKY, SHR, SHRSP and M-SHRSP was 130 mmHg, 200 mmHg, 250 mmHg and 260 mmHg, respectively. Preparations from all strains of spontaneously hypertensive rats exhibited active tone which was abolished by the removal of extracellular Ca2+ or by the application of verapamil. The active tone was greater in the order of aortae from SHR < SHRSP < M-SHRSP. Intracellular Ca2+ level measured by Fura-2 method decreased by the removal of extracellular Ca2+. The degree of the decrease was greater as the blood pressure of the rats increased, indicating the greater elevation of intracellular Ca2+ level in the pressure of extracellular Ca2+. A correlation was obtained between the active tone, intracellular Ca2+ level and blood pressure. Thus, it was demonstrated that the development of the active tone is brought about by the changes in Ca2+ influx of smooth muscle cell membrane and the degree of the change is positively related to the degree of hypertension.

The effects of chronic treatment with SQ29852, an angiotensin-converting enzyme inhibitor, on spontaneous smooth muscle tone and endothelium-dependent relaxation of aorta from stroke-prone spontaneously hypertensive rats (SHRSP) were studied and compared with those of captopril. Endothelium-removed aorta from 16-week-old SHRSP exhibited a high amplitude of spontaneously developed active tension (active tone), whereas no active tone was observed in the preparation from control normotensive Wistar-Kyoto (WKY) rats. Treatment with SQ29852 or captopril at age 5-16 weeks prevented the development of hypertension. No active tone could be detected in the preparation from SQ29852-treated SHRSP. Endothelium-dependent relaxation was markedly reduced in the preparation from nontreated SHRSP compared with WKY rats. Treatment with SQ29852 prevented the impairment of endothelium-dependent relaxation. It was also shown that norepinephrine-induced contraction was markedly depressed in endothelium-intact aorta from SQ29852-treated rats. The effects of SQ29852 were more prominent than those of hydralazine when blood pressure was maintained at similar levels. It was suggested that SQ29852 exerts an action on both vascular smooth muscle and endothelium that is mediated by the inhibition of angiotension-converting enzyme in addition to indirect actions of SQ29852 that are brought about by blood pressure lowering.

To evaluate whether the elevated blood pressure induced by chronic treatment with N(omega)-nitro-L-arginine methyl ester (L-NAME) contributes to an impairment of endothelium-dependent relaxation (EDR), the effects of chronic treatment of Wistar rats with L-NAME on systolic blood pressure, pulmonary arterial blood pressure and EDR of the pulmonary arteries were studied and compared with those of stroke-prone spontaneously hypertensive rats (SHRSP). While the systolic blood pressure (SBP) of Wistar rats was increased above that of controls by chronic treatment with L-NAME, it was still significantly lower than that of SHRSP. Chronic treatment with L-NAME did not affect pulmonary arterial blood pressure. On the other hand, the pulmonary arterial blood pressure of SHRSP was slightly but significantly higher than that of the control normotensive Wistar Kyoto rats (WKY). EDR in response to acetylcholine in the pulmonary artery of L-NAME-treated rats was significantly smaller than that in control Wistar rats. The EDR markedly increased in the presence of L-arginine and completely disappeared in the presence of N(omega)-nitro-L-arginine. Indomethacin hardly affected EDR. In preparations from SHRSP, the EDR was not different from that in those from WKY. Relaxation induced by sodium nitroprusside was identical in all preparations. Elevation of SBP and the impairment of EDR observed in L-NAME-treated rats recovered two weeks following cessation of treatment. These results suggest that the impaired EDR in the pulmonary artery of L-NAME-treated rats is not due to an L-NAME-induced increase in blood pressure but due to the inhibition of nitric oxide synthase by the drug remaining in the endothelium.

Difference in effects of stretch tension on endothelium-derived nitric oxide (EDNO)-dependent depression of noradrenaline (NA)- and high-K+-induced contraction between the aortae from normotensive Wistar Kyoto rats (WKY) a nd stroke-pronespontaneously hypertensive rats (SHRSP) was studied. NA-induced contraction in preparations both from WKY and SHRSP was augmented in the presence of N(omega)-nitro-L-arginine (L-NNA). This augmentation was minimized when the spontaneous tone, which was more prominent in preparations from SHRSP, was subtracted and the effects of L-NNA became less prominent in preparations from SHRSP. The effects of L-NNA were maximal at the stretch tension of 15 mN and, then, decreased as stretch tension increased in both preparations when the spontaneous tone was subtracted. The effects of L-NNA were less prominent when the contraction was initiated by high-K+, although the effects of stretch on high-K+-induced contraction were similar to that of NA-induced contraction. These results suggested 1) that both NA- and high-K+-induced contractions are depressed by EDNO, 2) that the release of EDNO induced by high-K+ is less than that by NA, 3) that increase in stretch tension decreases the release of EDNO, and 4) that the depressive effect of EDNO on contraction is impaired in the aorta of SHRSP.

Hepatic arteries are reportedly innervated by vasoconstrictor and vasodilator nerves. Experiments were carried out to investigate the possible involvement of calcitonin gene related peptide (CGRP) and nitric oxide as neurotransmitters during the relaxation of the rat common hepatic artery produced by transmural electrical field stimulation (ES). Common hepatic arteries were excised under ether-anesthesia from 6 weeks-old female rats, and isometric tensions recorded from endothelium-damaged ring preparations. In the presence of atropine and guanethidine, ES relaxed arteries which had been previously contracted with vasopressin. The relaxation response to ES was attenuated by either tetrodotoxin or capsaicin-pretreatment. CGRP induced a concentration-dependent relaxation, which was inhibited by the CGRP antagonist CGRP(8-37). The ES-induced relaxation was attenuated either slightly by the nitric oxide synthesis inhibitor L-nitroarginine (L-NNA) or markedly by CGRP(8-37). The relaxation response was nearly abolished in the presence of both CGRP(8-37) and L-NNA. These results may indicate that the nerve stimulation-induced vasodilatation of the rat common hepatic artery is mediated mainly by CGRP and partly by nitric oxide.

Endothelium-dependent relaxation of aorta and carotid artery from stroke-prone spontaneously hypertensive rats (SHRSP) and the effect of chronic treatment of SHRSP with perindopril, an angiotensin converting enzyme inhibitor, on endothelium-dependent relaxation were studied. Endothelium-dependent relaxation was induced by acetylcholine (ACh) in preparations of SHRSP and normotensive Wistar Kyoto rats (WKY) precontracted with noradrenaline. The ACh-induced relaxation in both preparations was abolished by L-nitroarginine. The ACh-induced relaxation was impaired in preparations from SHRSP and contraction was observed at high concentrations of ACh. In the presence of indomethacin, impairment of endothelium-dependent relaxation in SHRSP was minimized and the contraction was inhibited. The relaxation with sodium nitroprusside did not differ between the preparations from WKY and SHRSP. Treatment of SHRSP with perindopril (2 mg/kg/ day) for 6 weeks decreased systolic blood pressure and improved the ACh-induced relaxation of aorta and carotid artery. The treatment inhibited the contraction by higher concentrations of ACh in the presence of L-nitroarginine. These results indicate that the impairment of endothelium-dependent relaxation in aorta and carotid artery of SHRSP may be caused by the reduced availability of nitric oxide. The perindopril-treatment may prevent these changes in SHRSP.

Influences of endothelium on contraction of aortic smooth muscle by various agents were studied and those in the preparations from Wistar Kyoto rat (WKY) and stroke-prone spontaneously hypertensive rats (SHRSP) were compared. Endothelium depressed the contractions induced by noradrenaline and 5-hydroxytryptamine (5-HT). The time course of the contraction was bi- or tri-phasic in the former and slow rising monophasic in the latter. On the other hand, the depression was weaker in the contraction by prostaglandin F2alpha- and high K+. The depression was blocked by the removal of endothelium or in the presence of Nomega-nitro-L-arginine (L-NNA), indicating that nitric oxide (NO) released from endothelium was responsible for the inhibition. The inhibition was weaker in the preparation from SHRSP when compared to that in the preparation from WKY. Relaxation by acetylcholine (ACh) of the preparation precontracted in the presence of respective contractile agent was impaired in the preparation from SHRSP. It is concluded that mode of inhibition of the contraction varies depending on the agents used to initiate the contraction, i.e. depending on the mode of the release of NO. In the preparation from SHRSP, the influence of endothelium is impaired due to the reduced release of NO.

Effects of chronic treatment of stroke-prone spontaneously hypertensive rats (SHRSP) with carvedilol, an agent which has both alpha and beta-adrenoceptor blocking actions, on spontaneous muscle tone and on structural and functional abnormalities of endothelium were studied. The treatment of SHRSP with the drug of the dose of 30 to 200 mg/kg/day lowered the blood pressure significantly. Spontaneous muscle tone in endothelium-removed preparation disappeared by the treatment. Noradrenaline-induced contraction was depressed by the treatment in endothelium intact preparation but not in endothelium removed preparation. The treatment prevented the structural and functional abnormalities of endothelium. Similar results were obtained by the treatment with propranolol. These results indicate that carvedilol prevented abnormal contraction of SHRSP aorta through protective effects on smooth muscle and endothelium. These effects may play roles in blood pressure lowering effect of carvedilol.

1. The effects of cyclopiazonic acid (CPA) and thapsigargin (TG), both of which are known to inhibit sarcoplasmic reticular Ca(2+)-ATPase, on the mechanical activities, intracellular Ca2+ level and electrical activities of smooth muscle of the carotid artery of stroke-prone spontaneously hypertensive rats (SHRSP) and Wistar Kyoto rats (WKY) were compared. 2. Both CPA and TG induced elevation of tension of the smooth muscle, which was composed of a phasic and a tonic component. The level of tension attained, especially the tonic component, was greater in the preparation from SHRSP. 3. The elevation of tension was associated with an increased intracellular Ca2+ level. Both the elevation of tension and the increase in intracellular Ca2+ were diminished by the removal of extracellular Ca2+ or by the application of verapamil. 4. The resting membrane potential of the preparations from SHRSP were depolarized to a greater extent than those from WKY.CPA depolarized the smooth muscle from both SHRSP and WKY, and the final level was also more depolarized in the preparation from SHRSP. 5. These results indicate that the elevation of tension induced by these drugs is mainly due to increased Ca2+ influx through voltage-dependent Ca2+ channels, and the difference in the action between the preparation from SHRSP and that from WKY can be explained mainly by the changes in the channels. 6. Thus, differences in the action of these drugs on the tension of smooth muscle between preparations from WKY and SHRSP can mainly be explained by the difference in the membrane potential which is related to the difference in voltage-dependent Ca2+ influx.

Contribution of Ca influx from extracellular pool and Ca-release from store sites in caffeine-induced contraction of rat portal vein longitudinal muscle were examined. At 37 degrees C caffeine induced a phasic contraction and the contraction was inhibited by verapamil or in the absence of Ca. Under low temperature, it was not decreased remarkably by verapamil or by the removal of extracellular Ca. Na-removal potentiated caffeine-induced contraction in the absence of Ca. Caffeine-induced contraction was also potentiated by high-K-depolarization. These contractions were at both temperature inhibited greatly by ryanodine. Caffeine induced the burst of the action potential at 37 degrees C but it was not remarkable at 17 degrees C. These results indicate that both extracellular Ca influx and release of stored Ca are involved in the caffeine-induced contraction. However, dependence of the contraction on Ca sources are influenced by temperature, extracellular Na and membrane potential.