Rise and fall of agonist-evoked platelet Ca2+ in hypertensive rats.

We previously reported an enhanced peak response of intracellular free Ca2+ to thrombin in platelets of spontaneously hypertensive rats in comparison with normotensive Wistar-Kyoto rats. In the present study, we compared the platelet intracellular Ca2+ response to the receptor-linked agonist thrombin with the response to the Ca2+ ionophore ionomycin. Basal intracellular Ca2+ was higher in hypertensive platelets as was leakage of fura-2. We confirmed the previous finding that the thrombin-induced intracellular Ca2+ peak is greater in platelets of hypertensive rats and noted that the rate of recovery from peak intracellular Ca2+ is significantly greater in this model. In contrast, the peak platelet intracellular Ca2+ response to ionomycin (50 nM and 5 microM) was not different between the two strains, and the rate of recovery from the peak response was only slightly depressed in hypertensive rats after the low dose of ionomycin. Internal Ca2+ discharge capacity, assessed by the intracellular Ca2+ response to a maximal dose of ionomycin in Ca(2+)-free medium, was not different between platelets of the two strains. Thus, activated platelet intracellular Ca2+ is not altered in the hypertensive rat when the nonphysiological ionophore ionomycin is used as agonist. However, a heightened intracellular Ca2+ response is observed when the receptor-mediated agonist thrombin is used. These results are consistent with the hypothesis that differences in receptor-linked second messenger pathways underlie the altered intracellular Ca2+ response in platelets of genetically hypertensive rats and may contribute to differences both in the mobilization of Ca2+ and in its fall.     

Abnormal Ca2+ handling and increased Mg2+ permeability in platelets of hypertensive rats.

In order to test the hypothesis that intracellular Na+ accumulation and cellular Mg2+ deficiency may be involved in the abnormalities in Ca2+ handling and reactivity in spontaneously hypertensive rats (SHR) platelets, the metabolism of Na+, Ca2+ and Mg2+ was determined in fluorescent dye loaded platelets from 15 SHR and 15 Wistar-Kyoto rats (WKY) at 12 weeks of age. Mg2+ leak was estimated as the Mg2+ influx induced by an increase in extracellular [Mg2+] (from 1 to 5 mmol/l) and Mg2+/Na+ exchange activity was estimated as the Mg2+ influx induced by a decrease in extracellular [Na+] (from 140 to 50 mmol/l). Cellular metabolism of the fluorescent dye was similar in the two groups. Mean platelet [Ca2+]i was significantly increased under basal and thrombin (0.1 U/ml)-stimulated conditions in SHR compared to WKY, both in the presence and absence of extracellular Ca2+. Mean Ca2+ discharge capacity was similar between the two groups. There was no difference in mean [Na+]i between the two groups. Basal [Mg2+]i was also increased in SHR platelets. Mg2+ leak was higher in SHR than in WKY, while Mg2+/Na+ exchange activity was similar in the two groups. There was no difference in serum Mg2+ concentration between SHR and WKY. These data suggest that abnormal Ca2+ handling is accompanied by elevation in [Mg2+]i via increased permeability of platelet cell membranes to Mg2+ in SHR without any alteration in [Na+]i, and do not support the Mg2+ deficiency hypothesis in genetically hypertensive rats.     

Effects of cilazapril on the cerebral circulation in spontaneously hypertensive rats

Chronic hypertension is associated with a lower cerebral vascular reserve due to thickening of the media of cerebral vessels. The goal of the present study was to determine if long-term inhibition of angiotensin converting enzyme with cilazapril, a new long-acting angiotensin converting enzyme inhibitor, could improve cerebral vascular reserve. For this purpose, two groups of 12 spontaneously hypertensive rats were compared. One group was treated with 10 mg/kg/day cilazapril from 14 weeks to 33 weeks of age and was compared with a group treated with placebo. A third group of 12 Wistar-Kyoto rats treated with placebo was used as reference. At the end of the treatment period, cerebral vascular reserve was evaluated by measuring cerebral blood flow (radioactive microspheres) at rest and during maximal vasodilation induced by seizures provoked by bicuculline. Then, the rats were perfusion-fixed, and morphometry of the cerebral vasculature was performed. Cerebral vascular reserve was severely impaired in the spontaneously hypertensive rats since their maximal cerebral blood flow was decreased by 52% compared with the Wistar-Kyoto rats. Cilazapril normalized cerebral blood flow reserve. This normalization was associated with a decreased thickness of the medial layer in the carotid artery, the middle cerebral artery, and in the pial arteries larger than 100 microns. Further studies are required to determine whether this decreased medial thickness is due to the normalization of blood pressure induced by cilazapril or to the reduction of trophic factors such as angiotensin II.     

Abnormal contractile response of aortas from spontaneously hypertensive rats to Ca2+ after depletion of Ca2+ in Ca2+-free medium

Vascular responses of aortic rings from spontaneously hypertensive rats (SHR) were compared to those of the normotensive Wistar-Kyoto rats (WKY) in three sets of experimental protocols. The responses to cumulative doses of KCl indicated that SHR aortic rings were hyperresponsive to low but not high doses of KCl compared to WKY aortic rings. After Ca depletion by prolonged incubation of the rat aortic rings with Ca2+-free, EGTA containing solution, Ca repletion resulted in contraction. The magnitude of such a contraction was dependent on the period of Ca depletion and was highly sensitive to dihydropyridine Ca channel blocker, nifedipine. Although the Ca-depleted aortic rings eventually developed to the same level of maximum tension development upon Ca repletion, it took a considerably shorter period of Ca depletion for SHR than for WKY aortic rings to reach the maximum contraction upon Ca repletion. Our findings support the view that cell membranes of vascular smooth muscle in hypertension are more excitable and more susceptible to membrane destabilization by Ca removal.     

Effect of ageing on Ca2+ uptake via NMDA receptors into barrel cortex slices of spontaneously hypertensive rats

In the normal ageing cortex of the brain there is a group of dying neurons with shrinking dendritic trees and a group of surviving neurons with expanding dendritic trees. The ageing process affects neurotransmitter systems, including glutamate neurons and NMDA receptors. Calcium is an important signaling molecule. It enters brain cells through NMDA receptors and voltage-gated calcium channels. Since NMDA receptors play an important role in brain plasticity, calcium uptake through NMDA receptors can be used as a measure of brain activity. This study therefore sought to determine the effect of ageing on NMDA-stimulated Ca²⁺ uptake into barrel cortex slices of Spontaneously Hypertensive Rats (SHR) compared to control Wistar-Kyoto rats (WKY). Young rats (prepuberty, 4–6 weeks) and adult rats (14–16 weeks) were used in the study. The results show a significant decrease in NMDA-stimulated Ca²⁺ uptake in adult rats compared to their young litter-mates. It can be concluded that ageing negatively affects NMDA-stimulated Ca²⁺ uptake into barrel cortex slices of SHR and WKY.     

Increased Ca2+ buffering function of sarcoplasmic reticulum in small mesenteric arteries from spontaneously hypertensive rats.

We compared the Ca2+ buffering function of the superficial sarcoplasmic reticulum (SR) during rest and during contraction in endothelium-denuded strips of small mesenteric arteries from 13-week-old spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY). The addition of caffeine (1-20 mM) caused a transient contraction in both strains, and the contraction was significantly larger in SHR. When the SR Ca2+ buffering function was eliminated by cyclopiazonic acid (CPA; 10 microM) or thapsigargin (100 nM), both of which inhibit SR Ca2+-ATPase, or by ryanodine (10 microM), which depletes the SR Ca2+, there was a larger contraction in SHR than in WKY, suggesting that the Ca2+ buffering function of the SR during rest is more important in SHR than in WKY. Judging from the augmenting effects of these three agents on the contractile responses to Bay k 8644 (1-300 nM), an agonist of L-type Ca2+ channels, or norepinephrine (10(-9)-10(-4) M), an alpha-adrenoceptor agonist, the effects were significantly greater in SHR than in WKY. We conclude that 1) the Ca2+ influx during rest and during stimulation with Bay k 8644 or norepinephrine is strongly buffered by Ca2+ uptake into the superficial SR in the small mesenteric arteries from SHR and WKY; and 2) these Ca2+ buffering functions are increased in SHR because of the larger capacity of SR for Ca2+ storage.     

Increased norepinephrine sensitive intracellular Ca2+ pool in the caudal artery of spontaneously hypertensive rats

The contractions evoked by norepinephrine (NE) and caffeine in Ca2+-free solution were determined using denervated caudal artery rings from normotensive Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR). The magnitude of contractions produced by different concentrations of NE was significantly greater (P less than 0.05) in SHR caudal artery rings compared to WKY. The contractions evoked by NE in Ca2+-free solution were mediated primarily through the activation of postsynaptic alpha 1-adrenoceptors. In addition to alpha 1-adrenoceptor stimulation, caffeine also evoked significantly greater (P less than 0.05) contractions in Ca2+-free solution in SHR caudal arteries compared to WKY. From these observations it is concluded that intracellular Ca2+ pool (presumably sarcoplasmic reticulum, SR) is increased in SHR caudal arteries which, at least in part, may account for the increased contraction observed in response to NE and caffeine stimulation in the absence of extracellular Ca2+.     

抑郁对自发性高血压大鼠水通道蛋白-2的影响

目的探讨抑郁对自发性高血压大鼠水通道蛋白2（aquaporin2,AQP2）的影响,并探讨AQP2在高血压中的病理生理作用。方法60只SHR大鼠分为对照组（n=30）和抑郁组（n=30）,两组又各分为两个亚组：对照组非药物治疗亚组（n=15）、对照组贝那普利治疗亚组（n=15）;抑郁组非药物治疗亚组（n=15）、抑郁组贝那普利治疗亚组（n=15）。另外,选取Wistar Kyoto（WKY）大鼠20只作为正常组大鼠。药物治疗亚组大鼠予贝那普利10 mg.d-1.kg-1灌胃。抑郁组大鼠采用慢性不可预计温和应激（CUMS）结合行为学指标建立自发性高血压大鼠并抑郁动物模型。对照组、正常组大鼠动物正常饲养。检测并比较各组大鼠间血压的变化及血管加压素和肾脏AQP2表达的差异。结果 （1）抑郁组非药物治疗亚组血压（175±14）mm Hg高于对照组非药物治疗亚组（160±11）mm Hg及正常组（112±9）mm Hg,差异有统计学意义（P〈0.05）;贝那普利治疗后,抑郁组治疗亚组血压（136±15）mm Hg、对照组治疗亚组（113±12）mm Hg均低于各自非药物治疗组（P〈0.05）。（2）抑郁组非药物治疗亚组与正常组、对照组非药物治疗亚组及对照组贝那普利治疗亚组比较,糖水偏爱性均减低（P〈0.05）,体质量和旷场实验评分均明显下降（P〈0.05）,血浆血管加压素浓度升高[（9.31±0.42）pg/mL vs.（1.6±0.67）pg/mL、（3.04±0.97）pg/mL、（2.34±0.91）pg/mL,P〈0.05],AQP2蛋白表达增加（0.95±0.12 vs.0.12±0.07、0.44±0.06、0.24±0.06,P〈0.05）。（3）抑郁组贝那普利治疗亚组与对照组非药物治疗亚组、对照组贝那普利治疗亚组比较,糖水偏爱性均减低（P〈0.05）,体质量和旷场实验评分均明显下降（P〈0.05）,血浆血管加压素浓度升高[（4.55±0.69）pg/mL vs.（3.04±0.97）pg/mL、（2.34±0.91）pg/mL,P〈0.05],AQP2蛋白表达增加（0.62±0.17 vs.0.12±0.07、0.44±0.06,P〈0.05）。（4）对照组贝那普利治疗亚组与抑郁组非药物治疗亚组比较,糖水偏爱性亦增加（P〈0.05）,体质量和旷场实验评分升高（P〈0.05）,血浆AVP浓度下降[（4.55±0.69）pg/mL vs.（9.31±0.42）pg/mL,P〈0.05],AQP2蛋白表达减少（0.62±0.17 vs.0.95±0.12,P〈0.05）。结论抑郁可以促进自发性高血压大鼠血管加压素的分泌及肾脏AQP2的表达。抑郁可能通过促进血管加压素的分泌及肾脏AQP2的表达影响高血压的发展。     

Malignant hypertensive retinopathy in spontaneously hypertensive stroke-prone rats. Effect of treatment with cicletanine

Stroke-Prone spontaneously hypertensive rat strain (SHR-SP) always develops hypertensive retinopathy. The aim of the present work was to study the activity of a new antihypertensive drug, a synthetic furopyridine: cicletanine, in retinal hypertensive morphological lesions. The experiment was performed in 39 rats SHR-SP/A3N Iffa Credo, 11 weeks old, divided into 3 groups: group 1 was the control group, groups 2 and 3 were orally treated with cicletanine (respectively 100 and 150 mg/kg). All the rats had free access to tap water containing 1 p. 100 NaCl. During 6 weeks, blood pressure, body weight and survival were recorded, then all the rats were sacrificed. The eyes were removed, the posterior pole collected and fixed with Trump liquid for transmission election microscopy. In the SHR-SP control group, each layer showed neural body and/or process lesions: in the ganglion cell layer, some ganglion cells realized cytoid bodies corresponding to a lysed cell with nucleus degeneration, most of the axons were destroyed. In the inner and outer plexiform layers, most of the contacts between processes were lost because of fibrinous deposits. Numerous synapses were destroyed in the outer plexiform layer. These findings might explain the numerous dense bodies in the inner rod segment and the vesiculation of the rod outer segment. The capillaries showed markedly hypertensive lesions. Whereas, in both treated groups, rare and animal lesions were observed. The fact that these lesions were so few and so unimportant after 6 weeks of treatment, as well as for the photoreceptors which remained unimpaired, is closely related to cicletanine therapy, since it was so even though the treatment had been started with an already high blood pressure.(ABSTRACT TRUNCATED AT 250 WORDS)     

Dietary Ca2+ increases natriuretic and diuretic responses to volume loading in NaCl-sensitive spontaneously hypertensive rats

The present study tests the hypothesis that dietary Ca2+ supplementation increases acute diuretic and natriuretic responses to volume loading in the NaCl-sensitive spontaneously hypertensive rat (SHR-S). Seven week old male SHR-S and normotensive Wistar-Kyoto rats (WKY) were fed one of the following diets for 2.5 weeks: basal (0.75% NaCl, 0.68% Ca2+); high NaCl (8% NaCl, 0.68% Ca2+); high Ca2+ (0.75% NaCl, 2.0% Ca2+); and high NaCl and Ca2+ (8% NaCl, 2.0% Ca2+). SHR-S on high Ca2+ and on high NaCl and Ca2+ diets for 2 weeks displayed significantly lower systolic arterial pressures (SAP) than SHR-S on basal and high NaCl diets, respectively. WKY displayed no diet-related change in SAP at any time during the study. After 2.5 weeks on the diets, pre-instrumented, conscious SHR-S and WKY received an intravenous infusion (5% body weight) of isotonic NaCl, and urine was collected through a bladder catheter for a period of 90 min. The infusion did not alter the heart rate or the mean arterial pressure in any group. WKY on the high NaCl diet excreted a significantly greater percentage of the volume and Na+ load than WKY on the basal diet. In contrast, SHR-S on the high NaCl (compared to basal) diet did not display significantly enhanced natriuresis or diuresis. SHR-S on the basal diet displayed excretion rates similar to WKY on the basal diet. Dietary Ca2+ supplementation significantly increased the natriuretic and diuretic responses to saline infusion in SHR-S on the high NaCl diet, but not in SHR-S on the basal diet or in WKY on either diet.(ABSTRACT TRUNCATED AT 250 WORDS)     

Vascular angiotensin converting enzyme activity in spontaneously hypertensive rats and its inhibition with cilazapril

Angiotensin converting enzyme (ACE) activity was examined in large arteries and veins of rats and found to be present in most of the arteries and to a lesser extent in the veins, except for the femoral vessels which showed higher ACE activity in the vein than in the artery. For the aorta and all its branches, ACE activity was higher in the aorta and its branches in spontaneously hypertensive rats (SHR) than in age-matched normotensive Wistar-Kyoto rats (WKY), with the exception of the hepatic, pulmonary and basilar arteries where the levels were similar for SHR and WKY. For the vena cava and brachial vein, ACE activity was also higher in SHR than WKY but for most other veins the activity was the same with the exception of the pulmonary vein where ACE activity was higher in WKY. The acute treatment of SHR with cilazapril, an ACE inhibitor (0.3 and 3 mg/kg orally, for 4h) decreased aortic blood pressure and ACE activity in arterial and venous mesenteric and renal vessels in a dose-dependent fashion. Cilazapril, at the threshold hypotensive dose, markedly decreased ACE activity in each pair of aortic segments, carotid, pulmonary, subclavian, brachial and femoral vessels to a degree which was equivalent to that caused by the high dose. The effect outlasted a fall in blood pressure 24 h later. This was associated with a marked decrease in plasma angiotensin II and III and accumulation of angiotensin 1 at 4 h. No increase in plasma bradykinin or kallidin levels was detected.(ABSTRACT TRUNCATED AT 250 WORDS)     

Dietary Ca2+ prevents NaCl-induced exacerbation of hypertension and increases hypothalamic norepinephrine turnover in spontaneously hypertensive rats

Dietary calcium (Ca2+) supplementation lowers blood pressure in many forms of genetically mediated and experimentally induced hypertension. The present study tested the hypothesis that neuronal mechanisms underlie the blood pressure-lowering effect of dietary Ca2+ in NaCl-sensitive spontaneously hypertensive rats (SHR-S). SHR-S were fed one of the following diets: control (0.75% NaCl/0.68% Ca2+); high NaCl (8.00% NaCl/0.68% Ca2+); high Ca2+ (0.75% NaCl/2.00% Ca2+), and high NaCl/high Ca2+ (8.00% NaCl/2.00% Ca2+). SHR-S on the 8% NaCl diet for 2 weeks displayed significantly elevated blood pressure (161 +/- 4 mmHg) compared with those on the control diet (139 +/- 3 mmHg). Ca2+ supplementation prevented a rise in blood pressure in rats on the high-NaCl diet but did not alter blood pressure in rats consuming 0.75% NaCl. Plasma norepinephrine stores and turnover in the hypothalamus (anterior and posterior regions), brainstem (pons and medulla) and thoracic spinal cord were assessed using the dopamine-beta-hydroxylase inhibitor 1-cyclohexyl-2-mercapto-imidazole. The 8% NaCl diets reduced anterior hypothalamic region norepinephrine stores and turnover. Concomitant Ca2+ supplementation restored norepinephrine turnover to normal, but did not alter norepinephrine stores in the anterior hypothalamic region. In other regions, no significant differences in norepinephrine content or turnover were observed among groups. In SHR that are resistant to high-NaCl diets (SHR-R), the diets did not alter blood pressure, and neither dietary NaCl nor Ca2+ supplementation affected norepinephrine turnover in any brain region studied. These data indicate that in SHR-S on a diet high in NaCl, Ca2+ supplementation may prevent the NaCl-induced exacerbation of hypertension by increasing norepinephrine turnover in the hypothalamus.     

Na+ and Mg2+ contents in smooth muscle cells in spontaneously hypertensive rats.

Whereas in blood cells decreased magnesium concentrations and increased sodium concentrations in essential hypertension have often been described, only sparse data exist on cellular magnesium or sodium content and exchange in vascular smooth muscle cells. Therefore in aortic smooth muscle cells from 10 spontaneously hypertensive rats (SHR) of the Münster strain and 10 normotensive Wistar-Kyoto rats (WKY) aged 8 to 10 months, the intracellular magnesium and sodium content was measured. Electron-probe X-ray microanalysis was used to determine intracellular Mg2+ and Na+ concentrations in aortic cryosections 3 microm thick. The magnesium ion content was 0.90 +/- 0.15 g/kg dry weight in SHR versus 1.15 +/- 0.10 g/kg dry weight in WKY (means +/- SD, P < .05). Vascular smooth muscle sodium ion content was 6.66 +/- 0.39 g/kg dry weight in WKY and 12.61 +/- 0.91 g/kg dry weight in SHR (P < .01). Aortic smooth muscle cells from SHR are characterized by markedly lowered intracellular magnesium ion content and increased sodium ion concentrations in animals 8 to 10 months old, compared with normotensive cells. The results may be due to genetically determined disturbances in transmembrane magnesium and sodium ion transport.     

Protein kinase C and platelet reactivity in spontaneously hypertensive rats

Since protein kinase C (PKC) plays an important role in the control of platelet biological responses, we investigated whether it can be involved in the enhanced platelet reactivity to thrombin which is observed in spontaneously hypertensive rats (SHR) in comparison to that observed in controls (WKY). PKC activity was determined by measuring the phosphorylation of P47 protein (the endogenous substrate of PKC in the platelet). Mean effective concentration (EC50) values for phorbol ester and synthetic diacylglycerol (direct activators of PKC) were similar in SHR and WKY, thus revealing similar intrinsic activity of PKC in both rat strains. EC50 values for thrombin were approximately 30% lower in SHR v WKY. Enhanced PKC activity in SHR is likely the result of an increased diacylglycerol formation and release of Ca2+ from intracellular pools, consequent to an increased thrombin-induced phospholipase C activity.     

Ca2+ buffering function of the sarcoplasmic reticulum is increased in the carotid artery from spontaneously hypertensive rats.

To clarify whether the Ca2+ uptake function of the sarcoplasmic reticulum (SR) during arterial contraction is altered in hypertension, the effects of cyclopiazonic acid (CPA) and thapsigargin, which inhibit SR Ca2+-ATPase, on the contractile responses to Bay k 8644, an agonist of L-type Ca2+ channels, were compared in endothelium-denuded strips of carotid arteries from 13-week-old spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY). The addition of Bay k 8644 (1-300 nM) to the strips caused a concentration-dependent contraction that was larger in SHR than in WKY. The contractile responses to Bay k 8644 were augmented by CPA (10 microM) or thapsigargin (100 nM) in both strains. This augmentation was greater in SHR. Each of CPA and thapsigargin induced a relatively transient contraction, and both of these contractions were larger in SHR than in WKY. The basal 45Ca influx in this artery was larger in SHR than in WKY. The addition of caffeine (1-20 mM) caused a transient contraction that was larger in SHR than in WKY. Our results indicate that 1) the large Ca2+ influx during rest in the SHR carotid artery is strongly buffered by Ca2+ uptake into the superficial SR; and 2) the Ca2+ uptake function of the SR during the contraction with Bay k 8644 was increased in SHR compared with WKY. We conclude that the SHR carotid artery has an increased total capacity of SR for Ca2+ storage as an attempt to compensate for the large Ca2+ influx.     

Effect of antihypertensive treatment on peripheral nerve vasculature in spontaneously hypertensive rats

The influence of hypertension and of treatment with the dihydropyridine-type Ca+2 antagonist nicardipine on peripheral nerve vasculature were investigated in spontaneously hypertensive rats (SHR). Male SHR were treated from the 16th to the 26th week of age with vehicle (control group), with nicardipine, at the hypotensive dose of 3 mg/kg/day, or at the nonhypotensive dose of 0.1 mg/kg/day or with an equihypotensive dose (10 mg/kg/day) of the nondihydropyridine-type vasodilator hydralazine. Age-matched normotensive Wistar-Kyoto (WKY) rats were left untreated and used as normotensive reference animals. In SHR a significant increase of systolic pressure values accompanied by sciatic nerve microvascular changes, involving primarily interfascicular arteries and to a lesser extent intrafascicular arteries, was observed. Treatment with the hypotensive dose of nicardipine countered hypertension-dependent microvascular changes occurring in both interfascicular and intrafascicular arteries. The nonhypotensive dose of nicardipine and hydralazine displayed a modest activity on interfascicular arteries, but significantly countered hypertension-related changes involving intrafascicular arteries. The above findings indicate the occurrence of hypertension-related changes of peripheral nerve microvasculature and of positive effects induced by appropriate pharmacological treatment. Further work is in progress to identify the functional relevance of microanatomical observations of the present study.     

Abnormal Ca2+ signalling in vascular endothelial cells from spontaneously hypertensive rats: role of free radicals

OBJECTIVE: To test the hypothesis that the Ca2+ signal transduction process in endothelial cells from genetically hypertensive rats (SHR) is affected by an overproduction of free radicals. METHODS: The Ca2+ response to the inositol 1,4,5-triphosphate (IP3) mobilizing agonist, ATP, was measured using the fluorescent probe, fura-2, in endothelial cells from Sprague-Dawley rats, and in young and age-matched genetically hypertensive rats (SHR). The effect of free radicals and reducing agents on the intracellular release of Ca2+ and IP3productionwas determined in resting and ATP-stimulated cells. Experiments were also performed to compare the level of expression and enzymatic activity of catalase and superoxide dismutase (SOD) in endothelial cells from SHR and Sprague-Dawley rats. RESULTS: The exposure of aortic endothelial cells from Sprague-Dawley rats to the free-radical generating system, hypoxanthine + xanthine oxidase (HX/XO), caused a time- and concentration-dependent inhibition of the ATP-induced Ca2+ response. A similar HX/XO-dependent inhibition was also observed in Sprague-Dawley cells stimulated with the endoplasmic reticulum Ca2+-ATPase inhibitor, thapsigargin. Incubation with the antioxidative enzymes, catalase and SOD, had no effect on the ATP-induced Ca2+ release in Sprague-Dawley cells, but led to a strong increase in the internal release of Ca2+ in cells from adult (12 weeks old) or young (3 weeks old) SHR. The effect of antioxidants was not related either to an enhancement of the ATP-induced production of IP3, or to a lower expression and activity of SOD and catalase. CONCLUSION: The present work provides evidence that the Ca2+ signalling process in SHR endothelial cells is affected by an overproduction of free radicals, resulting in a depletion of releasable Ca2+ from IP3-sensitive and insensitive Ca2+ pools. These results point towards a beneficial action of antioxidants on Ca2+ signalling in endothelial cells from models of hypertension.     

Sustained contraction to angiotensin II and impaired Ca2+-sequestration in the smooth muscle of stroke-prone spontaneously hypertensive rats.

Contractile response to angiotensin II (AngII) of vascular smooth muscle was compared between 12-week-old, stroke-prone spontaneously hypertensive rats (SHRSP) and Wistar-Kyoto rats (WKY). AngII induced phasic and tonic contraction in denuded aortic ring preparation. The phasic contraction was concentration-dependent (AngII 10(-9) to 10(-6) mol/L) and similar in both strains. However, the relaxation after phasic contraction was significantly attenuated in SHRSP compared with that in WKY. To examine the recovery of contractile responses to the repeated stimulation, AngII was applied three times at 20- and 60-min intervals. The first maximal contraction was similar in both strains, but the response to the second stimulation was significantly reduced in SHRSP, compared with all three responses in WKY. These results suggested that Ca2+-sequestration into the Ca2+ store is delayed in SHRSP. Cyclopiazonic acid (10(-5) mol/L), an intracellular Ca2+-pump inhibitor, decreased spontaneous relaxation and increased the sustained contraction in WKY, whereas it did not affect the contraction in SHRSP. Insulin, which modulates tonic contraction by facilitating Ca2+-extrusion, was applied at peak contraction by AngII. It enhanced relaxation after phasic contraction in a concentration-dependent manner in SHRSP, but it did not affect the relaxation in WKY. These results suggest that increased sustained contraction observed in SHRSP reflects at least partly the impaired Ca2+-pump activity leading to hypertension.