Atorvastatin reduces oxidative stress in the rostral ventrolateral medulla of stroke-prone spontaneously hypertensive rats

Previously, we demonstrated that atorvastatin has sympatho-inhibitory effects with the upregulation of nitric oxide synthase in the brain in stroke-prone spontaneously hypertensive rats (SHRSP), and that reactive oxygen species in the rostral ventrolateral medulla (RVLM), where the vasomotor center is located, mediate the sympatho-excitatory effect. The aim of the present study was to determine if atorvastatin reduces oxidative stress in the RVLM of SHRSP along with the sympatho-inhibitory effect. SHRSP and Wistar-Kyoto (WKY) rats received standard feed with atorvastatin (50mg/kg per day) or standard feed for 30 days. Systolic blood pressure and heart rate were evaluated using the tail-cuff method. Urinary norepinephrine excretion was measured for 24 hours. After 30 days in SHRSP, blood pressure and urinary norepinephrine excretion were significantly lower in the atorvastatin group than in the control group. Thiobarbituric acid-reactive substance (TBARS) levels in the RVLM tissue obtained using the micropunch technique were used as measures of oxidative stress. Prior to the treatment, TBARS levels in the RVLM of SHRSP were significantly higher than those of WKY. After 30 days, TBARS levels in the RVLM of SHRSP were significantly lower in the atorvastatin group than in the control group. After 30 days in WKY, however, there were no differences in blood pressure, urinary norepinephrine excretion, and TBARS levels between the atorvastatin and control groups. These results suggest that atorvastatin reduces oxidative stress in the RVLM of SHRSP, which might contribute to the sympatho-inhibitory effects of atorvastatin in SHRSP.     

Long-acting calcium channel blocker, azelnidipine, increases endothelial nitric oxide synthase in the brain and inhibits sympathetic nerve activity

Nitric oxide (NO) in the central nervous system inhibits sympathetic nerve activity, thereby decreasing blood pressure. It is unknown, however, whether orally administered antihypertensive treatment alters NO synthase (NOS) expression, particularly in the brain, and how changes in NOS expression affects sympathetic nerve activity. Azelnidipine, a recently developed long-acting dihydropyridine calcium channel blocker, does not cause baroreflex-induced tachycardia. The aim of the present study was to determine whether antihypertensive treatment with azelnidipine alters endothelial NOS (eNOS), neuronal NOS (nNOS), or inducible NOS (iNOS) expression in the brain, and how changes in NOS affect sympathetic nerve activity. Azelnidipine (20 mg/kg/day) or hydralazine (20 mg/kg/day) was orally administered for 30 days in stroke-prone spontaneously hypertensive rats (SHRSP). Blood pressure and heart rate were measured by the tail cuff method. Urinary norepinephrine excretion was measured as a marker of sympathetic nerve activity. Western blot analysis was performed to examine eNOS, nNOS, or iNOS expression levels in the brain (cortex, cerebellum, hypothalamus, and the brain stem), heart, and aorta. The extent of blood pressure reduction was similar between the two groups. Heart rate increased in the hydralazine-treated group but did not change in the azelnidipine-treated group. Urinary norepinephrine excretion was significantly increased only in the hydralazine-treated group. Treatment with azelnidipine significantly increased eNOS expression levels in the brain, heart, and aorta, but did not alter nNOS or iNOS expression levels. Treatment with hydralazine did not change any of the NOS expression levels. These results suggest that antihypertensive treatment with azelnidipine attenuates reflex-induced sympathetic activation and enhances eNOS expression levels in the brain as well as in the heart and aorta.     

Long-Acting Calcium Channel Blocker,Azelnidipine, Increases Endothelial Nitric Oxide Synthase in the Brain and Inhibits Sympathetic Nerve Activity

Nitric oxide (NO) in the central nervous system inhibits sympathetic nerve activity, thereby decreasing blood pressure. It is unknown, however, whether orally administered antihypertensive treatment alters NO synthase (NOS) expression, particularly in the brain, and how changes in NOS expression affects sympathetic nerve activity. Azelnidipine, a recently developed long-acting dihydropyridine calcium channel blocker, does not cause baroreflex-induced tachycardia. The aim of the present study was to determine whether antihypertensive treatment with azelnidipine alters endothelial NOS (eNOS), neuronal NOS (nNOS), or inducible NOS (iNOS) expression in the brain, and how changes in NOS affect sympathetic nerve activity. Azelnidipine (20 mg/kg/day) or hydralazine (20 mg/kg/day) was orally administered for 30 days in stroke-prone spontaneously hypertensive rats (SHRSP). Blood pressure and heart rate were measured by the tail cuff method. Urinary norepinephrine excretion was measured as a marker of sympathetic nerve activity. Western blot analysis was performed to examine eNOS, nNOS, or iNOS expression levels in the brain (cortex, cerebellum, hypothalamus, and the brain stem), heart, and aorta. The extent of blood pressure reduction was similar between the two groups. Heart rate increased in the hydralazine-treated group but did not change in the azelnidipine-treated group. Urinary norepinephrine excretion was significantly increased only in the hydralazine-treated group. Treatment with azelnidipine significantly increased eNOS expression levels in the brain, heart, and aorta, but did not alter nNOS or iNOS expression levels. Treatment with hydralazine did not change any of the NOS expression levels. These results suggest that antihypertensive treatment with azelnidipine attenuates reflex-induced sympathetic activation and enhances eNOS expression levels in the brain as well as in the heart and aorta.     

Atorvastatin causes depressor and sympatho-inhibitory effects with upregulation of nitric oxide synthases in stroke-prone spontaneously hypertensive rats

OBJECTIVE: Recent studies have suggested that statins decrease blood pressure in hypertensive animals and upregulate endothelial nitric oxide synthase (eNOS) expression. However, the effects of statins on the expression of nitric oxide synthase (NOS) in the brain and the sympathetic nervous system remain to be elucidated. The aim of this study was thus to examine the effects of atorvastatin on blood pressure, sympathetic nerve activity, and the expression of NOS in stroke-prone spontaneously hypertensive rats (SHRSP) as well as in Wistar-Kyoto (WKY) rats. METHODS: The animals received atorvastatin (50 mg/kg per day) for 30 days. Systolic blood pressure and heart rate were evaluated using the tail-cuff method. Urinary norepinephrine excretion was measured for 24 h. The expression of eNOS, neuronal NOS (nNOS), and inducible NOS (iNOS) in the brain (cortex, cerebellum, hypothalamus and brainstem), aorta and heart were determined by Western blot analysis. RESULTS: Systolic blood pressure and 24-h urinary norepinephrine excretion were significantly decreased in SHRSP, but not in WKY, after the treatment with atorvastatin. The eNOS and iNOS expression in the brain and aorta was significantly increased in atorvastatin-treated SHRSP and WKY. However, the nNOS expression in the brain was not altered in the atorvastatin-treated group. CONCLUSIONS: These results suggest that atorvastatin decreases blood pressure, at least in part via the reduction of sympathetic nervous system activity in SHRSP. They also suggest that this sympatho-inhibitory effect may be mediated by an increase in NO production, with the upregulation of eNOS expression in the brain.     

Effect of Antihypertensive Therapy on a Vascular Change in Genetically Hypertensive Rats

Isolated tail arteries from stroke-prone spontaneously hypertensive rats (SHRSP), but not normotensive Wistar-Kyoto (WKY) rats, exhibit oscillatory contractions in response to norepinephrine. To establish whether this vascular abnormality is secondary to elevated arterial pressure, SHRSP and WKY were treated with hydralazine and hydrochlorothiazide from weaning to 4 months of age. Hydralazine and hydrochlorothiazide treatment significantly attenuated hypertension development in SHRSP (systolic blood pressure: control SHRSP = 219 ± 9 mmHg; treated SHRSP = 143 ± 5 mmHg at 15 weeks of age). Helically-cut tail artery strips from all rats were mounted in tissue baths for isometric force recording and exposed to norepinephrine (6×10^?10 - 6×10^?6M) 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 NE incubation. There was no significant difference in the magnitude of oscillatory activity between hydralazine/hydro-clorothiazide-treated SHRSP and control SHRSP. From these results we conclude that norepinephrine-induced oscillatory activity in SHRSP is a primary vascular abnormality that is not secondary to high blood pressure.     

Assessment of oxidative stress in the spontaneously hypertensive rat brain using electron spin resonance (ESR) imaging and in vivo L-Band ESR.

This study examined the blood brain barrier (BBB)-permeable nitroxyl compound, 3-methoxycarbonyl-2,2,5,5-tetramethylpyrrolidine-1-oxyl (MC-PROXYL), as a spin probe for the assessment of oxidative stress in the brain by electron spin resonance (ESR) imaging and in vivo L-band ESR. Preliminary comparisons were made by ESR imaging of MC-PROXYL in the isolated brains of normal Wistar-Kyoto rats (WKY), spontaneously hypertensive rats (SHR), and stroke prone SHR (SHRSP). The decay of the ESR images of MC-PROXYL in the isolated brains was faster in SHR than in normal WKY, but was only moderate in SHRSP. In addition, the decay rate of MC-PROXYL in the heads of live rats, as measured noninvasively by L-band ESR, was faster in SHR than in WKY, and was slower in SHR than in SHRSP. Taken together, our data suggest that the oxidative stress of SHR is not as high as that in high oxidative stress animal models such as SHRSP. This is the first study to present reconstructed 3D images of the distribution of MC-PROXYL in the isolated SHR brain. The ESR technique employed herein appears to be a powerful tool for evaluating oxidative stress and for detecting the region of oxidative stress in the brain of SHR.     

Vascular reactivity in the spontaneously hypertensive stroke-prone rat. Effect of antihypertensive treatment

This study investigated vascular responsiveness in stroke-prone spontaneously hypertensive rats (SHRSP) and the effect of antihypertensive treatment on this responsiveness. Weanling (4-week-old) male and female SHRSP and Wistar-Kyoto rats (WKY) received either the antihypertensive combination treatment of hydralazine plus hydrochlorothiazide in drinking water or tap water alone (controls) for 15 weeks. Whereas the antihypertensive combination prevented the development of hypertension in treated SHRSP (SHRSP-T), blood pressure remained unchanged in treated WKY (WKY-T). Femoral arterial smooth muscle responsiveness to KCl, norepinephrine, and calcium (in the presence of either 40 mM KCl or 1 microM norepinephrine) was not altered in SHRSP when compared with WKY. A significant increase in the sensitivity of femoral arteries to KCl and calcium (in the presence of 40 mM KCl) was seen, however, in SHRSP-T and WKY-T. An increased sensitivity to norepinephrine and calcium (in the presence of 1 microM norepinephrine) was seen only in SHRSP-T. Isoproterenol-induced relaxation was significantly attenuated in both SHRSP and SHRSP-T. Relaxation induced by sodium nitroprusside and calcium (membrane stabilization) was not different between the four groups. These results show that femoral arterial smooth muscle responsiveness to vasoconstrictor stimuli is not altered in SHRSP but that beta-adrenergic-mediated relaxation is attenuated. Antihypertensive treatment resulted in an enhanced responsiveness to these vasoconstrictor stimuli but had no effect on the relaxation properties of femoral arterial smooth muscle.     

Increased renal fatty acid binding protein in spontaneously hypertensive rats

The level of renal fatty acid binding protein (FABP) was quantified by a specific radial immunodiffusion method using an antibody to cytosolic FABP in stroke-prone spontaneously hypertensive rats (SHRSP) and normotensive Wistar-Kyoto rats (WKY) at 5, 10, 20 and 40 weeks of age. Increased levels were found in the SHRSP medulla, but not in the WKY medulla. The increase occurred in the hypertension development period, reaching a peak at 20 weeks of age. This increase was confirmed by immunoblotting. There was no significant change of FABP in the cortex. To elucidate the mechanism responsible for these changes in the FABP level, three antihypertensive drugs (nicardipine, hydralazine and enalapril) were given to SHRSP at 20 weeks of age for a period of four weeks. Antihypertensive treatment significantly inhibited the development of hypertension and the increase in the medullary FABP level. The differential response of FABP in SHRSP and WKY suggests that this protein may play an important role in the cellular metabolism of fatty acids under the pathological condition of high blood pressure.     

Calcium antagonist reduces oxidative stress by upregulating Cu/Zn superoxide dismutase in stroke-prone spontaneously hypertensive rats.

Recent studies have suggested that the calcium antagonists have an antiatherogenic antioxidant property. The effects of the calcium antagonists on reactive oxygen species (ROS)-related enzymes, however, remain unknown. We hypothesized that the calcium antagonists inhibit oxidative stress in the hearts of stroke-prone spontaneously hypertensive rats (SHRSP) through the ROS-scavenging enzymes known as superoxide dismutases (SODs). Male 12-week-old Wister-Kyoto rats (WKY) and SHRSP were used for the study. SHRSP were randomized and treated for 6 weeks with a vehicle, amlodipine (5 mg/kg/day), or enalapril (10 mg/kg/day). NAD(P)H oxidase activity was measured by a luminescence assay, and SOD activity was measured spectrophotometrically. Protein expressions were analyzed by immunoblots. Both drugs showed equipotent effects on systolic blood pressure, left ventricular hypertrophy and fibrosis, the wall-to-lumen ratio, the manganese SOD activity, ROS, and the endothelial NO synthase expression in the SHRSP hearts. Furthermore, amlodipine significantly restored copper/zinc-containing SOD (Cu/ZnSOD) expression and its activity in SHRSP hearts to a level equal to that of WKY more effectively than did enalapril (p <0.05), whereas enalapril downregulated NAD(P)H oxidase activity more than did amlodipine (p <0.05) in the SHRSP hearts. Furthermore, amlodipine restored Cu/ZnSOD expression and its activity in SHRSP hearts to a level equal to that in WKY hearts, and this restoration was significantly more effective than that by enalapril (p <0.05); on the other hand, enalapril induced a greater downregulation of NAD(P)H oxidase activity in SHRSP hearts than did amlodipine (p <0.05). Thus, amlodipine may inhibit vascular remodeling and oxidative stress in the SHRSP heart by efficiently upregulating Cu/ZnSOD, suggesting that the calcium antagonist may exhibit an antiatherogenic antioxidative action beyond blood-pressure lowering through the restoration of Cu/ZnSOD activity in the heart in cases of hypertension.     

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)     

Influence of captopril treatment on angiotensin II receptors and angiotensinogen in the brain of spontaneously hypertensive rats

The brain renin-angiotensin system (RAS) has been suggested as contributing to the pathogenesis of spontaneous hypertension in rats. Brain angiotensinogen- and angiotensin II (AII)-sensitive neurons were therefore investigated in stroke-prone spontaneously hypertensive rats (SHR-sp) and in Wistar-Kyoto (WKY) rats with and without treatment by captopril (CAP). Angiotensinogen was decreased in the anterior hypothalamus but increased in the cortex, the hippocampus, and cerebellum of SHR-sp. There were no differences between SHR-sp and WKY rats concerning the angiotensinogen content of posterior hypothalamus, brain stem, and septum. The sensitivity of the septal neurons to microiontophoretically applied AII was elevated, however, in SHR-sp as compared to WKY rats with regard to threshold and maximal response for AII-evoked neuronal discharges. The excitation characteristics did not change with the age of animals in both WKY rats and SHR-sp. The treatment of SHR-sp with CAP (50 mg/kg/day per os) starting in weanlings kept animals normotensive and reduced the high sensitivity of septal neurons to AII. Simultaneously angiotensinogen content was increased in the anterior hypothalamus and suppressed in the hippocampus. The same treatment of WKY rats reduced blood pressure somewhat and increased the angiotensinogen content in the anterior hypothalamus without affecting the neuronal sensitivity to AII. Thus, malfunction of the brain RAS may participate in the hypertension of SHR-sp, since converting enzyme blockade with CAP inhibited the blood pressure rise, augmented the angiotensinogen content of the anterior hypothalamus, and decreased the sensitivity of AII receptors in the brains of these rats.     

Different effects of amlodipine and enalapril on the mitogen-activated protein kinase/extracellular signal-regulated kinase kinase-extracellular signal-regulated kinase pathway for induction of vascular smooth muscle cell differentiation in vivo.

Although recent clinical trials have shown that amlodipine exerts antiatherogenic effects, the mechanism of these effects remains unknown. This study was designed to examine which signal transduction pathway might be important for the antiatherogenic property of amlodipine, as assessed by aortic smooth muscle cell (SMC) phenotypes in hypertension in vivo. Stroke-prone spontaneously hypertensive rats (SHRSP) were randomly treated with a vehicle, amlodipine, or enalapril while Wistar-Kyoto rats (WKY) used as controls were treated with only the vehicle. Both drugs were equally effective at reducing systolic blood pressure, and inhibiting the progression of aortic remodeling and fibrosis in comparison to those of vehicle-treated SHRSP. In the aortas of vehicle-treated SHRSP, the level of contractile-type smooth muscle (SM) myosin heavy chain (MHC) SM2 was significantly lower, whereas the level of synthetic-type MHC NMHC-B/SMemb was significantly higher compared with those in the WKY aortas. Compared to the vehicle-treated SHRSP group, both drugs significantly and equally shifted the aortic SMC phenotype in SHRSP toward the differentiated state by reducing NMHC-B/SMemb and increasing SM2. The levels of MKK6, p38 MAPK, MEK1 and p-42/44 ERK were significantly higher in the vehicle-treated SHRSP than in the WKY. Both drugs significantly reduced these values in the SHRSP aorta. Furthermore, the levels of MEK1 and p-42/44 ERK were significantly lower in the amlodipine- than in the enalapril-treated SHRSP group, whereas enalapril was more effective than amlodipine at increasing p-Akt and endothelial NO synthase in SHRSP aortas, which were significantly lower in the vehicle SHRSP group than in the WKY group. Thus, the MEK-ERK pathway might be one of the crucial determinants of the aortic SMC phenotype activated by amlodipine treatment of hypertension in vivo.     

Extracellular calcium, contractile activity and membrane potential in tail arteries from genetically hypertensive rats.

OBJECTIVE AND DESIGN: This study compares the effect of extracellular calcium on contractile responsiveness and membrane potential (E(m)) in arteries from stroke-prone spontaneously hypertensive rats (SHRSP) and Wistar-Kyoto normotensive (WKY) rats. METHODS: Isometric force and E(m) were measured in isolated tail artery strips using standard muscle bath and microelectrode techniques, respectively. RESULTS: The resting contractile force in SHRSP and WKY arteries was not influenced by the extracellular calcium concentration. However, the rate of force development in response to norepinephrine (3 x 10(-8) mol/l) was slowed when calcium was elevated and increased when calcium was reduced. Compared with WKY rats, this stabilizing action of calcium on contractions to norepinephrine was reduced in SHRSP. In 1.6 mmol/l calcium, resting E(m) in SHRSP did not differ from that in WKY rats. Calcium-free buffer caused depolarization in SHRSP and WKY rats. Reductions in calcium below physiological levels resulted in depolarization, whereas elevations in calcium caused hyperpolarization. Regardless of the calcium concentration, E(m) values in SHRSP did not differ from those in WKY rats. Norepinephrine (3 x 10(-8) mol/l) caused a depolarization in WKY rat and SHRSP arteries, and the magnitude of this depolarization was not influenced by calcium. Endothelium removal did not alter the stabilizing effects of calcium on the membrane potential or contractile activity in WKY rats or SHRSP. CONCLUSIONS: The reduced stabilizing effect of calcium on the contractile activity in SHRSP arteries is not due to an alteration in the general effect of the cation on the membrane potential.     

Treatment with nicardipine protects brain in an animal model of hypertension-induced damage

Control of blood pressure protects from the development of cerebrovascular lesions and vascular dementia (VaD). This study has assessed the influence of treatment with the dihydropyridine-type Ca2+ antagonist nicardipine on brain microanatomical changes in spontaneously hypertensive rats (SHR). SHR were treated from 16th to 26th week of age with hypotensive (3 mg/Kg/day) or non-hypotensive (0.1 mg/Kg/day) doses of nicardipine, with the non-dihydropyridine-type vasodilator hydralazine (10 mg/kg/day) or with vehicle (control group). Untreated age-matched Wistar Kyoto (WKY) rats were used as a normotensive reference group. Brain volume, number of neurons, glial fibrillary-acidic protein (GFAP)-immunoreactive astrocytes and neurofilament 200 KDa (NFP)-immunoreactivity (IR) were assessed in frontal and occipital cortex, hippocampus and striatum. A decrease of volume and number of nerve cells and a loss of NFP-IR was found in the frontal and occipital cortex and in the CA1 subfield of hippocampus and in the striatum of SHR. Treatment with nicardipine countered microanatomical changes occurring in SHR, whereas hydralazine displayed a less pronounced effect. Comparatively, the non-hypotensive dose of nicardipine was less active than the hypotensive one. The observation that equihypotensive doses of nicardipine or hydralazine did not protect brain in the same way from hypertensive brain damage suggests that lowering blood pressure is per se not enough for affording neuroprotection. The demonstration of neuroprotective effect of nicardipine suggests an use of the compound in situations in which hypertension is accompanied by the risk of brain damage.     

Abnormal polyamine metabolism in hypertensive cardiac hypertrophy

In order to assess myocardial hypertrophic activity during the process of hypertensive cardiac hypertrophy in the presence and absence of treatment with anti-hypertensive agents, we analyzed myocardial polyamine concentrations in spontaneous hypertensive (SHR) rats and control rats of Wistar Kyoto (WKY) strain. The anti-hypertensive agents studied were diltiazem, hydralazine and captopril, each of which was administered for 5 weeks. In comparison with WKY rats, SHR rats showed elevated blood pressure and enlarged hearts with higher myocardial spermidine concentration. Although blood pressure was lowered in the diltiazem-treated SHR rats, heart weight and myocardial spermidine concentration increased as in untreated SHR rats. In the hydralazine-treated group increases in both blood pressure and myocardial spermidine concentration were suppressed, while an increase in heart weight was not. In the captopril-treated group, increases in blood pressure, heart weight and spermidine concentration were all suppressed. Since spermidine level appears to be a sensitive indicator of hypertrophic activity in the heart, this study suggests that captopril exerts an inhibitory effect on hypertensive cardiac hypertrophy whereas diltiazem does not. It also suggests that hypertrophy may reach a certain plateau level earlier in the hydralazine-treated animals than in others.     

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.     

Increased gene expression of components of the renin-angiotensin system in glomeruli of genetically hypertensive rats

OBJECTIVE: The renin-angiotensin system (RAS) is implicated in the development of hypertensive glomerulosclerosis. However, no experimental evidence exists that clearly demonstrates activation of glomerular RAS in hypertensive nephropathy. We used stroke-prone spontaneously hypertensive rats (SHRSP) to examine whether RAS components are increased in glomeruli of SHRSP and whether this increase leads to an increase in mRNA levels for transforming growth factor-beta1 (TGF-beta1). METHODS: We examined the sequential changes of urinary albumin excretion (UAE), morphology, and glomerular mRNA expression for TGF-beta1 and fibronectin (FN) in relation to glomerular mRNA expression for angiotensinogen (ATN), angiotensin converting enzyme (ACE), angiotensin II type 1a (AT1a), and type 1b (AT1b) receptors, and intervention with angiotensin II type 1 receptor antagonist candesartan and equihypotensive hydralazine. RESULTS: In SHRSP, UAE was normal at 9 weeks of age, but became higher, beginning at 12 weeks of age, than that in the age-matched Wistar-Kyoto (WKY) rats, while SHRSP showed no glomerulosclerosis until 14 weeks of age; it was marked at 24 weeks. Plasma renin activity and plasma angiotensin II level was equivalent in the 9- and 12-week-old SHRSP and the WKY rats; both parameters, however, were elevated in 24-week-old SHRSP as compared with age-matched control. RNase protection assays showed that glomerular levels of ATN, ACE, and AT1a and AT1b receptors mRNA were significantly increased in 9-, 12-, and 14-week-old, but not in 24-week-old SHRSP, compared with age-matched WKY rats. Northern blot analysis showed that glomerular levels of TGF-beta1 and FN mRNA were higher in SHRSP than in WKY rats at all time points. Candesartan reduced UAE to control levels, whereas hydralazine reduced UAE but not to control levels. Candesartan administration for 12 weeks virtually prevented the progression of glomerulosclerosis. While candesartan reduced mRNA levels for RAS components, TGF-beta1, and FN to control levels, hydralazine was not effective in this respect. Conclusion Results suggest that increases in glomerular RAS components that occur independently of circulating RAS alter glomerular permselectivity and increase the glomerular expression of TGF-beta1 and FN in young SHRSP. Findings in old SHRSP suggest that altered glomerular permselectivity and an increased glomerular expression of TGF-beta1 and FN may be associated with the activation of systemic RAS.     

Long-term effects of brief antihypertensive treatment on systolic blood pressure and vascular reactivity in young genetically hypertensive rats

Summary Recent studies have shown that angiotensin converting enzyme (ACE) inhibitor treatment in young spontaneously hypertensive rats (SHR) reduces blood pressure into adulthood. This study explored changes in vascular reactivity in adult normotensive (WKY) rats and stroke-prone SHR (SHRSP) receiving the following treatments at 6–10 weeks of age: (a) ACE inhibitor (ramipril); (b) hydralazine/hydrochlorothiazide (hydral/HCTZ); or (c) no treatment. The hypothesis tested was that vascular changes and blood pressure would be reduced in adult SHRSP treated with ramipril during development. At 17 weeks of age, rats were anesthetized and vascular tissue was excised. Isolated experiments in the aorta included characterization of initial phasic and tonic contractions to 0.1 µM angiotensin II (AII). A phenylephrine (PE) concentration-response curve was performed on carotid arteries, and threshold values were determined. All WKY groups showed lower systolic blood pressure (131±4 mmHg) and reduced phasic AII induced contraction (7.4±4.7%) compared with SHRSP (217±4 mmHg; 37.2±4%). Antihypertensive treatment reduced blood pressure (ramipril: 168±2; hydral/HCTZ: 198±6 mmHg) but not phasic AII responses in adult SHRSP; adult WKY rats were unaffected by treatment. Threshold values for PE in carotid arteries were lower in SHRSP than in WKY, indicating increased sensitivity. However, SHRSP treated with ramipril did not demonstrate increased sensitivity to PE. These data support the hypothesis that blood pressure and sensitivity to PE but not contractile responsiveness to AII in adult SHRSP are determined by an AII-sensitive mechanism during development.     

Atorvastatin Improves the Impaired Baroreflex Sensitivity via Anti-Oxidant Effect in the Rostral Ventrolateral Medulla of SHRSP

We have demonstrated that oxidative stress in the rostral ventrolateral medulla (RVLM), a vasomotor center in brainstem, increases sympathetic nerve activity (SNA) and that oral administration of atorvastatin inhibited SNA via anti-oxidant effect in the RVLM of stroke-prone spontaneously hypertensive rats (SHRSPs). The impairment of baroreflex sensitivity (BRS) is known as the predictive factor of mortality in the hypertension and BRS is impaired in SHRSP. The aim of the present study was to determine whether oral administration of atorvastatin improved the impaired BRS via anti-oxidant effect in the RVLM in SHRSP. Atorvastatin (20 mg/kg/day) or vehicle was orally administered for 28 days in SHRSPs. Systolic blood pressure (SBP), heart rate, and 24-h urinary norepinephrine excretion as an indicator of SNA were comparable between atorvastatin- and control-SHRSP. Thiobarbituric acid-reactive substance (TBARS) levels as a marker of oxidative stress was significantly lower in atorvastatin-SHRSP than in control-SHRSP. Baroreflex sensitivity measured by the spontaneous sequence method was significantly higher in atorvastatin-SHRSP than in control-SHRSP. These results suggest that atorvastatin improves the impaired BRS in SHRSP via its anti-oxidant effect in the RVLM of SHRSP.     

Brain nitric oxide synthase activity in spontaneously hypertensive rats during the development of hypertension

OBJECTIVES: Blockade of neuronal nitric oxide synthase (nNOS) in the brain induced an increase in mean arterial pressure of spontaneously hypertensive rats (SHR). We hypothesize that increased nitric oxide (NO) synthesis in the brain compensates for hypertension. Therefore, we measured NOS activity in different brain regions in SHR at prehypertensive, onset and established hypertension, and compared with age-matched Wistar-Kyoto (WKY) rats. METHOD: NOS activity was measured by the ability of tissue homogenate to convert [3H]l-arginine to [3H]l-citrulline in a Ca2+- and NADPH-dependent manner. RESULTS: NOS activity was impaired in the cerebral cortex and brainstem of prehypertensive SHR. At established hypertension, SHR showed an augmentation in NOS activity in hypothalamus and brainstem. Chronic treatment of SHR with the angiotensin-1 converting enzyme (ACE)-inhibitor, enalapril, and the AT(1) receptor antagonist, losartan, normalized NOS activity in the hypothalamus but not in the brainstem. Treatment with a peripheral vasodilator, hydralazine, did not affect NOS activity. CONCLUSION: Attenuated NOS activity in the cortex and brainstem of prehypertensive SHR may play a role in the pathogenesis of hypertension. The upregulated NOS activity in the hypothalamus and brainstem of SHR possibly serves to compensate for hypertension. Hypothalamic, but not brainstem, NO is involved in antihypertensive effects of ACE inhibition and AT(1) receptor blockade. Since a blood pressure decrease per se had no effect on NOS activity, it appears that central sympathetic activity influenced by endogenous angiotensin II, rather than blood pressure, represents the stimulus for the increased NOS activity in the hypothalamus of SHR.