Effects of chronic nitric oxide synthase inhibition on cerebral arterioles in Wistar-Kyoto rats

OBJECTIVE: Cerebral arterioles in stroke-prone spontaneously hypertensive rats (SHRSP), but not in Sprague-Dawley rats with hypertension induced by nitric oxide (NO) synthase inhibition, undergo inward remodeling. The goal of this study was to determine whether development of vascular inward remodeling may depend on genetic factors. DESIGN: We examined effects of NO synthase inhibition on the structure of cerebral arterioles in Wistar-Kyoto rats (WKY), a rat strain genetically distinct from Sprague-Dawley. METHODS: Pressure (servonull), diameter (cranial window) and cross-sectional area of the vessel wall (CSA, histologically) were measured in maximally dilated (EDTA) cerebral arterioles in WKY, untreated (n = 8) or treated for 3 months with the NO synthase inhibitor N-nitro-L-arginine methyl ester (L-NAME) (10 mg/kg per day, n = 10) in the drinking water, and in untreated SHRSP (n = 7). RESULTS: Treatment with L-NAME in WKY increased mean cerebral arteriolar pressure (69 +/- 7 versus 47 +/- 7 mmHg, P < 0.05) and pulse pressure (30 +/- 3 versus 17 +/- 1 mmHg, P < 0.05) to levels significantly lower than in SHRSP (98 +/- 5 and 35 +/- 1 mmHg respectively, P < 0.05). CSA was significantly greater in L-NAME-treated WKY and SHRSP than in untreated WKY (1692 +/- 50 and 1525 +/- 98 microm respectively, versus 1224 +/- 85, P < 0.05). External diameter was significantly less in L-NAME-treated WKY than in untreated WKY (119 +/- 5 versus 135 +/- 4 microm, P < 0.05) but significantly greater than in SHRSP (98 +/- 1 microm, P < 0.05). CONCLUSION: Cerebral arterioles undergo hypertrophy and remodeling in WKY with L-NAME-induced hypertension. These findings suggest that genetic factors present in WKY and SHRSP may play a role in the development of vascular inward remodeling during chronic hypertension in rats.     

Responses of cerebral arterioles to adenosine 5'-diphosphate, serotonin, and the thromboxane analogue U-46619 during chronic hypertension

The goal of this study was to determine whether responses of cerebral arterioles to products released by platelets are impaired in stroke-prone spontaneously hypertensive rats (SHRSP). The diameter of pial arterioles was measured during suffusion with adenosine 5'-diphosphate (ADP), serotonin, and the thromboxane analogue U-46619, using intravital microscopy in normotensive Wistar-Kyoto rats (WKY) and SHRSP (7-10 months old). Responses of cerebral arterioles to ADP and serotonin were profoundly impaired in SHRSP. ADP (10(-5) M) increased pial arteriolar diameter 17 +/- 3% (mean +/- SE) in WKY and only 4 +/- 1% in SHRSP. Serotonin (10(-5) M) increased pial arteriolar diameter 15 +/- 2% in WKY and, in contrast, reduced the diameter 13 +/- 1% in SHRSP. Nitroglycerin produced a similar dilatation of cerebral arterioles in WKY and SHRSP, suggesting that impairment of dilatation in SHRSP in response to ADP and serotonin was not related to nonspecific impairment of vasodilatation in SHRSP. The thromboxane analogue U-46619 produced a similar constriction of arterioles in WKY and SHRSP. We also examined the possibility that impaired dilator responses of cerebral arterioles in SHRSP in response to ADP and serotonin may be related to production of a cyclooxygenase vasoconstrictor substance. Indomethacin (10 mg/kg i.v.) partially restored dilator responses to ADP and serotonin in SHRSP, without altering responses in WKY. Thus, we speculate that vasoactive substances released by platelets may release a prostanoid constrictor substance from cerebral vessels of SHRSP and thereby predispose SHRSP to cerebral ischemia and, perhaps, stroke.     

Effects of local reduction in pressure on distensibility and composition of cerebral arterioles

This study examined effects of local reductions in mean and pulse pressures on cerebral arterioles in normotensive Wistar-Kyoto rats (WKY) and stroke-prone spontaneously hypertensive rats (SHRSP). WKY and SHRSP underwent clipping of one carotid artery at 1 month of age. At 10-12 months of age, mechanics of pial arterioles were examined in vivo in anesthetized rats. Bilateral craniotomies were performed to expose pial arterioles in the sham and clipped cerebral hemispheres. Stress-strain relations were calculated from measurements of pial arteriolar pressure (servo null), diameter, and cross-sectional area of the arteriolar wall. Point counting stereology was used to quantitate individual components in the arteriolar wall. Before deactivation of smooth muscle with EDTA, mean (Pm) and pulse (Pp) pressures were significantly less (p less than 0.05) in clipped than in sham arterioles in WKY (Pm, 63 +/- 2 versus 73 +/- 2 mm Hg; Pp, 23 +/- 3 versus 30 +/- 3 mm Hg) and SHRSP (Pm, 94 +/- 4 versus 110 +/- 4 mm Hg; Pp, 27 +/- 2 versus 38 +/- 3 mm Hg). Cross-sectional area of the arteriolar wall was less (p less than 0.05) in clipped than in sham arterioles in both groups of rats (1,403 +/- 125 versus 1,683 +/- 125 microns2 in WKY; 1,436 +/- 72 versus 1,926 +/- 134 microns2 in SHRSP). There was a correlation between cross-sectional area of the vessel wall and pulse pressure (r2 = 0.66), but not mean pressure (r2 = 0.09). During maximal dilatation with EDTA, the stress-strain curve was shifted to the left in clipped arterioles of SHRSP, but not of WKY, which indicates that carotid clipping in SHRSP reduces passive distensibility of cerebral arterioles. The proportion of distensible components in the vessel wall (smooth muscle, elastin, and endothelium) was reduced in clipped arterioles in SHRSP, but not in WKY. These findings suggest that 1) vascular hypertrophy of cerebral arterioles is related more closely to pulse pressure than to mean pressure, and 2) reduction of pial arteriolar pressure completely prevents cerebral vascular hypertrophy and attenuates increases in passive distensibility of cerebral arterioles in SHRSP.     

Effects of antihypertensive therapy on mechanics of cerebral arterioles in rats.

The purpose of this study was to examine effects of antihypertensive treatment on structure and mechanics of cerebral arterioles and the incidence of stroke in stroke-prone spontaneously hypertensive rats (SHRSP). Treatment of hypertension was begun at 3 months of age with cilazapril (45 mg/kg/day), an angiotensin converting enzyme (ACE) inhibitor, or with hydralazine (18 mg/kg/day). Cilazapril and hydralazine reduced systolic arterial pressure (from 195 +/- 8 to 125 +/- 5 and 148 +/- 3 mm Hg, respectively [mean +/- SEM]; p less than 0.05). To examine structure and mechanics of cerebral arterioles, we measured pressure (servonull), external diameter, and cross-sectional area of the vessel wall (histologically) in pial arterioles of normotensive Wistar-Kyoto (WKY) rats and SHRSP that were untreated or that were treated for 3 months with cilazapril or with hydralazine. Arterioles were maximally dilated with EDTA. In WKY rats, cilazapril and hydralazine did not alter pial arteriolar pressure, external diameter, or cross-sectional area of the vessel wall. In SHRSP, both cilazapril and hydralazine reduced cross-sectional area of the vessel wall to levels not significantly different from WKY rats (from 1,911 +/- 155 to 1,244 +/- 101 and 1,388 +/- 59 microns 2, respectively, compared with 1,405 +/- 95 microns 2 for untreated WKY rats). Cilazapril was more effective than hydralazine in reducing pial arteriolar pressure (from 110 +/- 6 to 62 +/- 2 mm Hg with cilazapril versus 79 +/- 5 mm Hg for hydralazine compared with 60 +/- 4 mm Hg for untreated WKY rats). Cilazapril, but not hydralazine, attenuated reductions in external diameter of pial arterioles (from 91 +/- 4 to 100 +/- 4 microns for cilazapril versus 91 +/- 3 microns for hydralazine compared with 107 +/- 3 microns for untreated WKY rats).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of an angiotensin-converting enzyme inhibitor and a beta-blocker on cerebral arterioles in rats

We examined the effects of an angiotensin-converting enzyme inhibitor, perindopril, and a beta-blocker, propranolol, on cerebral arterioles in stroke-prone spontaneously hypertensive rats (SHRSP). The structure and mechanics of cerebral arterioles were examined in untreated Wistar-Kyoto rats (WKY) and SHRSP that were untreated or treated for 3 months with a high (2 mg/kg per day) or a low (0.3 mg/kg per day) dose of perindopril or propranolol (250 mg/kg per day) alone or in combination with the low dose of perindopril. We measured pressure, external diameter, and cross-sectional area of the vessel wall (CSA) in maximally dilated (with EDTA) cerebral arterioles. Treatment of SHRSP with the high dose of perindopril or the combination of propranolol and the low dose of perindopril normalized cerebral arteriolar mean pressure (50+/-1 [mean+/-SEM] and 43+/-2 mm Hg vs 50+/-1 mm Hg in WKY and 94+/-3 mm Hg in untreated SHRSP; P<0.05), pulse pressure (15+/-1 and 16+/-1 mm Hg vs 13+/-1 mm Hg in WKY and 35+/-1 mm Hg in untreated SHRSP; P<0.05), and CSA (1103+/-53 and 1099+/-51 microm2, respectively, vs 1057+/-49 microm2 in WKY and 1281+/-62 microm2 in untreated SHRSP; P<0.05). In contrast, treatment of SHRSP with the low dose of perindopril or propranolol alone did not normalize arteriolar pulse pressure (24+/-1 and 21+/-1 mm Hg) and failed to prevent increases in CSA (1282+/-77 and 1267+/-94 microm2). Treatment with either dose of perindopril or the combination of propranolol and perindopril significantly increased external diameter in cerebral arterioles of SHRSP (99+/-3, 103+/-2, and 98+/-3 microm vs 87+/-2 microm in untreated SHRSP; P<0.05), whereas propranolol alone did not (94+/-3 microm; P>0.05). These findings suggest that effects of angiotensin-converting enzyme inhibitors on cerebral arteriolar hypertrophy in SHRSP may depend primarily on their effects on arterial pressure, particularly pulse pressure, whereas their effects on cerebral arteriolar remodeling (defined as a reduction in external diameter) may be pressure independent.     

Reduction of the soluble cyclic GMP vasorelaxing system in the vascular wall of stroke-prone spontaneously hypertensive rats: effect of the alpha1 -receptor blocker doxazosin

OBJECTIVE : The aim of the present study was to analyse the nitric oxide (NO)/cyclic GMP (cGMP) relaxing system in spontaneously hypertensive rats of the stroke-prone substrain (SHRSP). DESIGN : The study was performed in 20-week-old SHRSP rats. A group of normotensive Wistar-Kyoto (WKY) rats was used as control. RESULTS : The endothelium-dependent relaxation to acetylcholine was reduced in SHRSP rats (n = 15). No modifications in the expression of the endothelial nitric oxide synthase were found in the vascular wall of WKY rats (n = 15) and SHRSP rats. SHRSP rats demonstrated an impaired relaxing response to the NO-donor sodium nitroprusside that was accompanied by a reduction in the level of the main second messenger of NO, cyclic GMP. The expression of the soluble guanylate cyclase (sGC) beta1-subunit was markedly reduced in the vascular wall of SHRSP rats. In the experimental model of SHRSP, an increased concentration of catecholamines has been reported. Therefore, we evaluated the effect of an alpha1-receptor blocker, doxazosin, on the NO/cGMP system. Doxazosin [10 mg/kg body weight (bw) per day for 15 days, n = 15] reduced mean arterial pressure (MAP) in SHRSP rats. Treatment with doxazosin preserved the endothelium-independent relaxation response to sodium nitroprusside in aortic segments from SHRSP rats which was associated with an increased expression of the sGC beta1-subunit. A dose of doxazosin (1 mg/kg bw per day, n = 15) that did not modify MAP partially prevented sGC protein expression in the vascular wall. CONCLUSIONS : Independently of the endothelial NO-generating system, impaired vasorelaxation could also result from vascular smooth muscle cell layer dysfunction. Doxazosin treatment improved the endothelial-independent relaxation and preserved the cGMP generating system in the vascular wall of SHRSP rats.     

Effect of felodipine on blood pressure and vascular reactivity in stroke-prone spontaneously hypertensive rats

Isolated tail arteries from stroke-prone spontaneously hypertensive rats (SHRSP), but not from normotensive Wistar-Kyoto rats (WKY), exhibit oscillatory contractions in response to norepinephrine. Previous studies indicate that the mechanism for these oscillations involves altered membrane calcium and/or potassium handling, and that this vascular change is a genetic defect associated with hypertension in SHRSP. The purpose of this experiment was to determine whether treatment of SHRSP with the calcium entry blocker felodipine would alter oscillatory activity. Adult SHRSP and WKY rats were treated orally with felodipine for 8 weeks. Felodipine treatment produced a significant decrease in blood pressure in SHRSP (control SHRSP: 240 +/- 7 mmHg, n = 6; felodipine-treated SHRSP: 164 +/- 8 mmHg, n = 5, P less than 0.05; tail-cuff method). Helically-cut tail artery strips from all rats were mounted in tissue baths for isometric force recording and exposed to norepinephrine (6 x 10(-9) to 6 x 10(-6) mol/l) for 20 min at each concentration. Oscillatory activity was defined as the sum of the magnitudes of all phasic contractions occurring during the final 10 min of norepinephrine incubation. Oscillatory activity was markedly reduced in tail arteries from felodipine-treated SHRSP when compared with control SHRSP. Felodipine also inhibited oscillatory activity when added directly to the tissue bath. It seems, therefore, that felodipine may lower blood pressure in SHRSP, at least in part, by correcting the genetic defect responsible for oscillatory activity.     

维生素E对糖尿病大鼠肾脏的保护作用

目的探讨维生素E对糖尿病大鼠肾脏保护作用及其可能机制。方法实验动物分为正常对照组、链脲佐菌素诱导的糖尿病未治疗组、糖尿病给予维生素E（20mg.kg-1.d-1）治疗组,共观察8周。测定尿白蛋白排泄量(UAE),内生肌酐清除率（Ccr）、血浆及肾脏组织一氧化氮（NO）、一氧化氮合成酶（NOS）、内皮素（ET）和肾小球蛋白激酶C（PKC）。结果2周时糖尿病未治疗组Ccr［(6.47±1.51)ml·min-1·kg-1］、尿白蛋白排泄量［(15.60±1.64)μg/24h］、NO［(37.30±3.77)μmol/L］、NOS［(34.89±3.83)U/L］及肾小球细胞膜PKC［(86.85±11.37)pmol·min-1·mgprotein-1］明显高于对照组,ET低于对照组。8周时糖尿病大鼠肾小球细胞膜PKC［(84.18±12.14)pmol·min-1·mgprotein-1］仍明显高于对照组,但NO［(22.75±2.89)μmol/L］及NOS［(21.34±1.92)U/L］低于对照组,ET高于对照组。给予维生素E治疗组8周时,Ccr［(4.46±0.49)ml·min-1·kg-1］及尿白蛋白量［(16.31±1.12)μg/24h］显著低于未治疗组,8周时肾小球细胞膜PKC［(65.19±8.83)pmol·min-1·mgprotein-1］,2周时NO［(33.13±3.77)μmol/L］及NOS［(30.16±2.89)U/L］明显低于未治疗组,维生素E治疗组2周时与8周时的NO及NOS下降幅度明显小于未治疗组。结论维生素E通过抑制蛋白激酶C可以纠正糖尿病早期的肾脏高滤过、高灌注,并与抑制肾脏NO合成有关,抑制蛋白激酶C活性对糖尿病肾病防治尤为重要。     

Genetic and gender influences on sensitivity to focal cerebral ischemia in the stroke-prone spontaneously hypertensive rat

We have investigated genetic transmission of increased sensitivity to focal cerebral ischemia and the influence of gender in the stroke-prone spontaneously hypertensive rat (SHRSP). Halothane-anesthetized, 3- to 5-month-old male and female Wistar-Kyoto rats (WKY), SHRSP, and the first filial generation rats (F1 crosses 1 and 2) underwent distal (2 mm) permanent middle cerebral artery occlusion (MCAO) by electrocoagulation. Infarct volume was measured by using hematoxylin-eosin-stained sections and image analysis 24 hours after ischemia and expressed as a percentage of the volume of the ipsilateral hemisphere. Infarct volume in males and females grouped together were significantly larger in SHRSP, F1 cross 1 (SHRSP father), and F1 cross 2 (WKY father), at 36.6+/-2.3% (mean+/-SEM, P<0.001, n=15), 25.4+/-2.4% (P<0.01, n=14), and 33. 9+/-1.6% (P<0.001, n=18), respectively, compared with WKY (14+/-2%, n=17). Male F1 cross 1 (18.9+/-2.4%, n=6) developed significantly smaller infarcts than male F1 cross 2 (32.8+/-2%, n=8, P<0.005). Females, which underwent ischemia during metestrus, developed larger infarcts than respective males. A group of females in which the cycle was not controlled for developed significantly smaller infarcts than females in metestrus. Thus, the increased sensitivity to MCAO in SHRSP is retained in both F1 cross 1 and cross 2 hybrids, suggesting a dominant or codominant trait; response to cerebral ischemia appears to be affected by gender and stage in the estrous cycle. In addition, the male progenitor of the cross (ie, SHRSP versus WKY) influences stroke sensitivity in male F1 cohorts.     

Endothelium-dependent responses of cerebral blood vessels during chronic hypertension

Acetylcholine produces less dilatation of pial arterioles in stroke-prone spontaneously hypertensive rats (SHRSP) than in normotensive (WKY) rats. Responses of cerebral vessels to acetylcholine and bradykinin appear to involve different mechanisms. Our first goal was to determine whether responses of pial arterioles to bradykinin are impaired in SHRSP. Diameter of pial arterioles (20-60 microns) was measured using intravital microscopy in WKY rats and SHRSP (9-12 months old). Superfusion of bradykinin (3 x 10(-7) M) dilated pial arterioles by 35 +/- 6% (mean +/- SEM) in WKY rats, but only 21 +/- 3% in SHRSP (p less than 0.05 versus WKY rats). Both nitric oxide (5 x 10(-7) M) and nitroglycerin (10(-5) M) produced similar vasodilatation in WKY rats and SHRSP. Our second goal was to determine whether alteration of postreceptor mechanisms contributes to impairment of endothelium-dependent cerebral vasodilatation in SHRSP. Calcium ionophore A23187 (10(-5) M) produced more vasodilatation in WKY rats than in SHRSP (32 +/- 8% versus 9 +/- 4%, p less than 0.05). Responses to A23187 (10(-5) M) were inhibited by indomethacin (46 +/- 13% versus 15 +/- 5%, p less than 0.05) in WKY rats, whereas responses to A23187 (10(-6) M) were potentiated modestly by indomethacin (-3 +/- 2% versus 4 +/- 2%, p less than 0.05) in SHRSP.(ABSTRACT TRUNCATED AT 250 WORDS)     

Development of collaterals in the cerebral circulation

Sudden occlusion of the middle cerebral artery (MCA) in normotensive rats increases blood flow through anastomosing branches into the territory of the occluded artery. Three weeks after MCA occlusion, anastomoses to anterior cerebral branches are increased by more than 50% in luminal diameter. One month after MCA occlusion, blood flow and blood flow reserve to the territory of the occluded MCA are returned to normal levels. In stroke-prone spontaneously hypertensive rats (SHRSP), the anastomoses are significantly narrower and blood flow through the anastomoses is less than in normotensive rats. Tissue infarction invariably develops in the territory of the occluded MCA in SHRSP. We propose that the luminal width of the anastomosis is a major determinant of blood flow into the territory of the occluded artery and of the amount of tissue protected from infarction by collateral circulation.     

Stroke-prone spontaneously hypertensive rats as a model for toxemia of pregnancy and aggravating and preventive effects of maternal modifications during pregnancy on offspring's growth

Genetical differences in changes in blood pressure (BP) were chronologically investigated during pregnancy in stroke-prone spontaneously hypertensive rats (SHRSP), Wistar-Kyoto rats (WKY) and Sprague-Dawley (SD) rats. Especially, the early stages were carefully studied. Maternal conditions in SHRSP were modified by the treatments with NaCl and taurine, respectively. BP in SHRSP and WKY rose significantly at the early stage of pregnancy compared to prepregnancy levels (SHRSP; 208 +/- 2 mmHg vs 197 +/- 5 mmHg, WKY; 133 +/- 2 mmHg vs 126 +/- 1 mmHg) (p less than 0.05). In contrast, no such changes were observed in SD rats. Differences in 24-hour urinary epinephrine excretion before and during pregnancy ran parallel with such BP changes among these strains. NaCl-loaded SHRSP died during pregnancy with severe pathohistological changes in their kidneys and severe proteinuria. Taurine treatment had a marked prophylactic effect on these maternal pathological changes during pregnancy, resulting in better growth in offsprings. These results suggest that SHRSP could be one of the suitable animal models for the studies on toxemia of pregnancy and also suggest an important role of hypertensive genetical disposition in the development of toxemia of pregnancy.     

Spironolactone improves structure and increases tone in the cerebral vasculature of male spontaneously hypertensive stroke-prone rats

BACKGROUND: Previous studies show that ischemic cerebral infarct size is related to cerebral vessel structure. Spironolactone, a mineralocorticoid receptor antagonist, decreases ischemic cerebral infarct size in male spontaneously hypertensive stroke-prone rats (SHRSP). Therefore, we hypothesized that chronic spironolactone treatment would improve cerebral artery structure in the SHRSP. METHODS: Six-week-old male SHRSP were treated with spironolactone (2.5 mg/day) for 6 weeks and were compared to untreated control SHRSP and normotensive Wistar Kyoto (WKY) rats. Using a pressurized arteriograph, structural measurements of the middle cerebral artery (MCA) were taken under passive (calcium-free), zero-flow conditions. Myogenic tone was calculated from active and passive measurements taken at 75 and 125 mmHg. Mean arterial pressure was measured using radiotelemetry. RESULTS: Myogenic tone was increased only at 75 mmHg in the spironolactone-treated SHRSP compared to control rats. The MCA lumen and outer diameters were increased in the spironolactone-treated SHRSP compared to control SHRSP, but were not different from WKY rats, indicating a decrease in vascular remodeling. There was no effect of spironolactone on blood pressure, suggesting that this is a blood pressure-independent effect. CONCLUSION: Increased myogenic tone and lumen diameter in the spironolactone-treated SHRSP may be responsible for the protective role of spironolactone in ischemic stroke.     

Increased susceptibility to osmotic disruption of the blood-brain barrier in chronic hypertension

We examined the effects of chronic hypertension and acute reduction of arterial pressure on the susceptibility of the blood-brain barrier (BBB) to disruption. The BBB was disrupted with an intracarotid injection of 1.6 M arabinose in spontaneously hypertensive rats (SHR), stroke-prone SHR (SHRSP), and normotensive Wistar-Kyoto (WKY) rats. Permeability of the BBB was determined from the ratio of 125I-albumin in brain to 125I-albumin in blood. When the BBB was intact, permeability was less than 0.4%. After hypertonic arabinose, permeability of the BBB was greater (mean +/- SE) in SHRSP (17.6% +/- 1.6%) and in SHR (21.1% +/- 3.1%) than in WKY (10.3% +/- 2.4%) (p less than 0.05). When arterial pressure of SHRSP was reduced acutely with nitroprusside before arabinose, the BBB permeability to albumin was not reduced (21.5% +/- 1.5%). In other rats, we examined survival after osmotic disruption. In SHRSP, 14 of 15 rats died within 1 day after osmotic disruption with marked cerebral edema. In WKY, four of 15 rats died (p less than 0.05 vs SHRSP). When arterial pressure of SHRSP was reduced before arabinose, mortality was reduced to six of 15 (p less than 0.05 vs untreated SHRSP). We conclude that the BBB in SHRSP has enhanced vulnerability that is detrimental to survival. Reduction of arterial pressure improves survival in SHRSP without affecting BBB permeability to albumin.(ABSTRACT TRUNCATED AT 250 WORDS)     

Superoxide anion production is increased in a model of genetic hypertension: role of the endothelium.

The hypothesis that the decreased nitric oxide (NO) availability observed in spontaneously hypertensive stroke-prone rats (SHRSP) is due to excess superoxide (O2-) was examined. O2- generation, measured by lucigenin chemiluminescence, was studied in 12- to 16-week male and female Wistar-Kyoto rats (WKY) and SHRSP. In addition, expression of the gene encoding endothelial NO synthase, the enzyme involved in NO generation, was investigated. O2- generation was increased in male and female SHRSP (4.11+/-0.24 and 3. 84+/-0.28 nmol O2-. min-1. mg-1 respectively) compared with their WKY counterparts and was significantly higher in male than female WKY (1.22+/-0.08 in males and 0.8+/-0.08 nmol O2-. min-1. mg-1 respectively) (SHRSP versus WKY P<0.0001, 95% CI -3.39, -2.51; male versus female WKY P=0.0029, 95% CI -0.67, -0.17). Removal of the endothelium by rubbing or addition of NO synthase inhibitors attenuated O2- generation in SHRSP but not WKY. In males, removal of the endothelium reduced O2- generation from 3.86+/-0.12 to 1.35+/-0. 08 nmol. min-1. mg-1 (P<0.0001, 95% CI 2.29, 2.81), whereas addition of L-NAME caused a reduction from 4.13+/-0.17 to 1.32+/-0.16 nmol. min-1. mg-1 (P<0.0001, 95% CI 2.36, 2.83). Similar reductions were observed in females. L-arginine had no significant effect, but tetrahydrobiopterin significantly decreased O2- generation in SHRSP from 4.04+/-0.11 to 2.36+/-0.40 nmol. min-1. mg-1 (P=0.0026, 95% CI 0.89, 2.44). Endothelial NO synthase mRNA expression was significantly greater in SHRSP than in WKY and in WKY males than in WKY females. These results show that O2- generation is increased in SHRSP and that the tissue and enzymatic sources of this excess O2- appear to be the endothelium and eNOS, respectively. The increase in O2- generation could explain the decreased availability of basal NO observed in this model of genetic hypertension.     

Altered pressure-natriuresis in obese Zucker rats.

It has not been examined whether the pressure-natriuresis response is altered in the insulin-resistant condition. Furthermore, despite an important role of nitric oxide (NO) in modulating pressure-natriuresis, no investigations have been conducted assessing the renal interstitial NO production in insulin resistance. The present study examined whether pressure-natriuresis was altered in insulin-resistant obese Zucker rats (OZ) and assessed the cortical and medullary nitrate/nitrite (NOx) levels with the use of the renal microdialysis technique. In OZ, serum insulin/glucose ratio (23.0+/-4.0x10(-8), n=9) and blood pressure (119+/-3 mm Hg) were greater than those in lean Zucker rats (LZ; 7.0+/-1.9x10(-8) and 103+/-4 mm Hg, n=9). The pressure-natriuresis curve in OZ was shifted to higher renal perfusion pressure (RPP), and the slope was blunted compared with that in LZ (0.073+/-0.015 vs 0.217+/-0.047 microEq/min kidney weight/mm Hg, P<0.05). The basal renal NOx level was reduced in OZ (cortex, 4.032+/-0.331 micromol/L; medulla, 4. 329+/-0.515 micromol/L) compared with that in LZ (cortex, 7.315+/-1. 102 micromol/L; medulla: 7.698+/-0.964 micromol/L). Furthermore, elevating RPP increased the medullary NOx in LZ, but this pressure-induced response was lost in OZ. Four-week treatment with troglitazone, an insulin-sensitizing agent, improved hyperinsulinemia, systemic hypertension, and basal renal NOx levels (cortex, 5.639+/-0.286 micromol/L; medulla, 5.978+/-0.284 micromol/L), and partially ameliorated the pressure-natriuresis curves; the slope of pressure-natriuresis curves and elevated RPP-induced NOx, however, were not corrected. In conclusion, our study suggests that insulin resistance is closely associated with abnormal pressure-natriuresis and hypertension. These deranged renal responses to insulin resistance are most likely attributed to impaired medullary NO production within the medulla.     

Effect of ACE/NEP inhibition on cardiac and vascular collagen in stroke-prone spontaneously hypertensive rats.

Left ventricular remodeling in hypertension is associated with cardiac interstitial and perivascular collagen deposition. The dual angiotensin I converting enzyme/neutral endopeptidase inhibitor omapatrilat (also called vasopeptidase inhibitor) improves left ventricular remodeling in experimental heart failure. We hypothesized that omapatrilat would induce regression of cardiac and vascular fibrosis in hypertension. We, therefore, investigated the effect of omapatrilat on collagen deposition in heart and aorta of stroke-prone spontaneously hypertensive rats (SHRSP). Twenty-week-old normotensive Wistar-Kyoto (WKY) rats, untreated SHRSP, and SHRSP treated with omapatrilat (40 mg/kg per day, orally) for 10 weeks were investigated. Collagen in the heart and the descending thoracic aorta was stained with Sirius red. After 10 weeks, systolic blood pressure (BP) was significantly (P < .01) reduced in omapatrilat-treated versus untreated SHRSP. Interstitial collagen density was significantly decreased in the subendocardial myocardium (to 2.71 +/- 0.24% v 4.12 +/- 0.30%, respectively, P < .05) and in the midmyocardium of omapatrilat-treated versus untreated SHRSP (to 3.01 +/- 0.25 v 4.19 +/- 0.17% respectively, P < .05). Perivascular collagen was significantly (P < .05) decreased in the subepicardial, mid-myocardial and, subendocardial regions of the myocardium of omapatrilat-treated versus untreated SHRSP. Aortic collagen content decreased in omapatrilat-treated versus untreated SHRSP (to 36.1 +/- 2.8 v 58.8 +/- 6.1 x 10(3) microm2/mm section, respectively, P < .05). In conclusion, in addition to being a potent antihypertensive agent, omapatrilat significantly improves cardiac and vascular fibrosis in SHRSP.     

Mechanics of cerebral arterioles in hypertensive rats

Chronic hypertension is associated with hypertrophy of cerebral blood vessels. Previous studies of the mechanical properties of cerebral vessels in chronic hypertension have examined large cerebral arteries. The goals of this study were first to develop a method to examine vascular mechanics of cerebral arterioles in vivo and second to determine whether the stiffness of cerebral arterioles is altered in the presence of chronic hypertension. We calculated circumferential stress and strain of pial arterioles in age-matched, anesthetized stroke-prone spontaneously hypertensive rats (SHRSP) and in Wistar Kyoto rats (WKY) from measurements of pial arteriolar pressure, inner diameter, and wall thickness. Pial arteriolar pressure was measured with a servonull system. Smooth muscle of pial arterioles was deactivated with ethylenediaminetetraacetic acid (EDTA), and pressure-diameter relations were examined during step-wise reductions in pressure. Prior to deactivation of smooth muscle in 3-4-month-old rats, pial arteriolar pressure was greater in SHRSP than in WKY (110 +/- 4 versus 75 +/- 2 mm Hg [mean +/- SE]; p less than 0.05). Pial arteriolar diameter, which was measured at prevailing levels of pial arteriolar pressure, was less in SHRSP than in WKY (52 +/- 5 versus 63 +/- 3 microns; p less than 0.05). Following deactivation of smooth muscle, diameter of pial arterioles at 70 mm Hg of pial arteriolar pressure was similar in the two groups: 104 +/- 6 microns in SHRSP and 109 +/- 3 microns in WKY (p greater than 0.05). Wall thickness was 4.5 +/- 0.2 microns in SHRSP and 4.1 +/- 0.1 microns in WKY (p greater than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparison of the effects of omapatrilat and irbesartan/hydrochlorothiazide on endothelial function and cardiac hypertrophy in the stroke-prone spontaneously hypertensive rat: sex differences

OBJECTIVE: The novel antihypertensive agent, omapatrilat, is both an inhibitor of neutral endopeptidase and angiotensin-converting enzyme. This study investigated the effects of omapatrilat in comparison with an angiotensin I-receptor antagonist/diuretic combination on blood pressure, endothelial function and cardiac hypertrophy in stroke-prone spontaneously hypertensive rats (SHRSP). METHODS: Male and female SHRSP were treated orally with omapatrilat or irbesartan plus hydrochlorothiazide (I + H) or vehicle for 8 weeks. Systolic blood pressure was measured weekly by tail-cuff. Cardiac hypertrophy was monitored by echocardiography at 8, 12 and 16 weeks of age. Endothelial function [basal nitric oxide (NO) bioavailability and stimulated NO release] was examined in carotid arteries using organ bath pharmacology and in mesenteric resistance arteries using wire myography. RESULTS: Compared with untreated controls, omapatrilat and I + H significantly attenuated hypertension [male control, 198.3 +/- 6.9 mmHg versus omapatrilat, 149.6 +/- 3.8 mmHg (F = 8.63 P < 0.0001), versus I + H, 145.6 +/- 5.1 mmHg (F = 7.38 P < 0.0001); female control, 170.3 +/-8.3 mmHg versus omapatrilat, 120.0 +/- 4.6 mmHg (F = 8.36, P < 0.0001), versus I + H, 112.2 +/- 2.9 mmHg (F = 9.08, P < 0.0001)] and left ventricular hypertrophy [male + female controls, 3.02 +/- 0.38 mg/g versus omapatrilat, 2.47 +/- 0.26 mg/g (P < 0.0001; 95% confidence interval, 0.27, 0.83), versus I + H, 2.49 +/- 0.21 mg/g (P < 0.0001; 95% confidence interval, 0.25, 0.83)]. Both treatments also significantly increased male carotid artery basal NO bioavailability relative to control [control, 0.62 +/- 0.17 g/g versus omapatrilat, 1.95 +/- 0.17 g/g (P < 0.0001; 95% confidence interval, -1.83, -0.36), versus I + H, 1.57 +/- 0.21 g/g (P < 0.026; 95% confidence interval, -1.31, -0.12)]. However, stimulated NO (EC50) was only improved in omapatrilat-treated males [controls, 0.19 +/- 0.06 micromol/l versus omapatrilat, 0.05 +/- 0.01 micromol/l (P = 0.05; 95% confidence interval, -1.16, -0.03)]. CONCLUSIONS: Omapatrilat treatment significantly reduced left ventricular hypertrophy and improved endothelial function in carotid arteries from male SHRSP by NO-dependent mechanisms. Despite equivalent antihypertensive and antihypertrophic actions, a similar improvement in endothelial function, specifically stimulated NO release, was not observed after treatment with I + H.