Insulin-like growth factors prevent apoptosis in cortical neurons isolated from stroke-prone spontaneously hypertensive rats

Cerebral ischemia induces a massive efflux of glutamate causing delayed neuronal death in stroke-prone spontaneously hypertensive rats (SHRSP) but not in Wistar Kyoto rats (WKY). It is obvious that L-N-nitroarginine (L-NNA; NO synthase (NOS) inhibitor), benzamide (poly(ADP-ribose) synthetase inhibitor), and growth factors are involved in reducing neuronal cell death due to toxic conditions, especially phosphatidylinositol 3 (PI3)-kinase activity; however, no studies have clarified whether genetic vulnerability to neurotoxic states is present in cortical neurons isolated from SHRSP. For this purpose, we prepared cortical neurons from WKY and SHRSP (15 weeks of gestation) to test the genetic vulnerability involved in the pathogenesis of stroke as well as apoptosis of cortical neurons isolated from SHRSP. We also examined the mechanisms necessary to reduce apoptosis under neurotoxic states using ultrastructural and biochemical techniques. Cortical neurons from SHRSP were in fact found to be more vulnerable than neurons from WKY and resulted in apoptosis when treated with nitric oxide (NO)- and N-methyl-D-aspartate (NMDA)-mediated neurotoxic agents. Growth factors, especially insulin-like growth factor (IGF), rescued neurons from NO- and NMDA-mediated neurotoxicity, particularly those from SHRSP. Conversely, benzamide and L-NNA reduced NMDA-mediated neurotoxicity but not NO-mediated toxicity. The ability to protect neurons from neurotoxicity was as follows: IGF-->nerve growth factor epidermal growth factor-->L-NNA-->benzamide. In addition, it was demonstrated that wortmannin, a PI3-kinase inhibitor, lessened the protective effects of these growth factors against NO-mediated toxicity. The data thus indicate that genetic factors related to neuronal vulnerability to apoptosis are involved in the pathogenesis of stroke lesions in SHRSP. PI3-kinase activity, which is stimulated by growth factors, is closely related to protective effects against NO- and NMDA-mediated toxicity in cortical neurons, especially those isolated from SHRSP. Moreover, the genetic vulnerability observed in SHRSP neurons is possibly linked to the inadequate activation of signaling pathways in the downstream of protein tyrosine kinases.     

Impaired endothelium-dependent relaxation in isolated resistance arteries of spontaneously diabetic rats

1. Previous studies have shown that endothelium-dependent relaxation in the aorta of spontaneously diabetic bio bred rats (BB) is impaired. 2. We have investigated noradrenaline (NA) contractility, endothelium-dependent acetylcholine (ACh) and bradykinin (BK) relaxation, and endothelium-independent sodium nitroprusside (SNP) relaxation in mesenteric resistance arteries of recent onset BB rats and established insulin treated BB rats, compared to their age-matched non diabetic controls. 3. There was no significant difference in the maximum contractile response or sensitivity to noradrenaline in either of the diabetic groups compared to their age-matched controls. 4. Incubation with the nitric oxide synthetase inhibitor NG-nitro-L-arginine (L-NOARG) resulted in a significant increase in maximum contractile response to noradrenaline in the recent onset age-matched control group (P < 0.05). Analysis of the whole dose-response curve (using ANOVA for repeated measures with paired t test) showed a significant left-ward shift following the addition of L-NOARG (P < 0.001). A similar but less marked shift (P < 0.01) was evident in vessels from recent onset diabetics. An overall shift in both sensitivity and maximum response was also evident in the age-matched non diabetic controls of the insulin-treated group (P < 0.05). However, by contrast, there was no significant change in sensitivity in the insulin-treated diabetic rats. 5. ACh-induced endothelium-dependent relaxation was significantly impaired in the recent onset diabetic rats compared to their age-matched controls (47 +/- 11% versus 92 +/- 2%, P < 0.05, n = 6), and in the insulin treated diabetic rats (34 +/- 5% versus 75 +/- 6%, P < 0.05, n = 6). The relaxation responses to BK also were significantly impaired in the diabetic rats compared to their age-matched controls (recent onset: 20 +/- 3% versus 72 +/- 7%, P < 0.05, n = 6; insulin treated: 12 +/- 9% versus 68 +/- 7%, P < 0.05, n = 7). 6. Incubation with either the nitric oxide synthetase substrate, U-arginine, or the free radical scavenging enzyme superoxide dismutase (150 mu ml-1) failed to improve the attenuated response of acetylcholine-induced relaxation in the diabetic vessels. 7. Endothelium-dependent relaxation mediated by ACh and BK was significantly attenuated in both the diabetic and control vessels after incubation with L-NOARG. 8. Pretreatment with a cyclo-oxygenase inhibitor, indomethacin, significantly enhanced the relaxation to ACh in both the recent onset and insulin treated diabetic rats (42 +/- 10%, n = 7 versus 64 +/- 7%, n = 7, P < 0.05, and 40 +/- 5%, n = 7 versus 65 +/- 9%, n = 6, P < 0.05). 9. Following endothelium removal, there was a marked impairment in endothelium-dependent relaxation responses to ACh and BK in both the diabetic and control vessels. 10. Incubation with the thromboxane A2 receptor antagonist SQ29548, did not significantly improve the ACh endothelium-dependent relaxation response in the diabetic vessels. 11. Endothelium-independent relaxation to sodium nitroprusside was significantly impaired in the first group of diabetic vessels studied; however, subsequent studies showed no impairment of the sodium nitroprusside response in the diabetic vessels. 12. In conclusion, the ability of the endothelium to regulate vascular contractility is reduced in recent onset diabetic vessels, and significantly impaired in established insulin treated diabetics. Relaxation to the endothelium-dependent vasodilators ACh and BK was impaired in both the recent onset and the established insulin treated diabetics, and the ACh response was significantly improved following pretreatment with indomethacin, suggesting a role for a cyclo-oxygenase-derived vasoconstrictor. Preliminary studies with a thromboxane A2, receptor antagonist, SQ29548 did not significantly improve the impaired relaxation to ACh, indicating that the vasoconstrictor prostanoid is not thromboxane A2.     

Noradrenergic hyperinnervation in the heart of stroke-prone spontaneously hypertensive rats

1. Noradrenergic (NA) nerve fibre distribution was investigated in the epicardium and myocardium of the heart in stroke-prone spontaneously hypertensive rats (SHRSP) and was compared to that in normotensive Wistar-Kyoto (WKY) rats. Fluorescent NA nerve fibres in the left and right epicardium of both strains aged 10, 30, 60, 90 and 180 days, and in the myocardium of left and right ventricles and the ventricular septum of both strains aged 30, 90 and 180 days were examined by the glyoxylic acid method. The distribution densities of NA nerve fibres were measured by quantitative image analysis. 2. The distribution pattern of NA nerve fibres in the epicardium of both strains showed a constant meshwork pattern throughout the entire examination period. 3. In the myocardium, NA nerve fibres were distributed irregularly between myocytes of both strains in all ages examined. 4. The densities of NA nerve fibres in the epicardium of SHRSP were significantly higher (P < 0.01 and 0.05; Student's t-test, 6 d.f.) than those of WKY at all ages examined except left epicardium at 90 days of age. 5. The densities in the right myocardium in 30 and 90 day old SHRSP were significantly higher (P < 0.05; Student's t-test, 6 d.f.) than those of WKY. 6. NA hyperinnervation in the epicardium and the myocardium of SHRSP may be assumed to be caused by the hyperfunction of the stellate ganglia which innervate the heart and may give rise to hypertrophy of the heart in SHRSP by a trophic effect of NA nerve fibre.     

Taurine accelerates the regression of hypercholesterolemia in stroke-prone spontaneously hypertensive rats

The effects of taurine on the regression of pre-established hypercholesterolemia were examined in stroke-prone spontaneously hypertensive rats (SHRSP). Hypercholesterolemia was induced by feeding a hypercholesterolemic diet to SHRSP for 30 days. Then, the diet was switched to normal chow with or without 3% taurine, and the effects were followed up for another 30 days. During regression serum cholesterol level was rapidly decreased, and was accelerated by taurine. A similar accelerated decrease in cholesterol content by taurine was seen also in tissues including the liver, intestine, and aorta. In the liver, acyl-CoA:cholesterol acyltransferase (ACAT) activity was significantly low in the taurine-supplemented group, parallel with the hepatic cholesteryl ester content. On the other hand, hepatic cholesterol 7 alpha-hydoxylase activity maintained a higher level in the taurine-supplemented group. These results showed that taurine accelerates the regression of hypercholesterolemia, and suggested that this effect is related to the increase in cholesterol catabolism to bile acid through the enhancement of 7 alpha-hydoxylase activity.     

Effects of amino acids on alcohol intake in stroke-prone spontaneously hypertensive rats

The concentration-dependent effects of several PCB, PCDD, and PCDF congeners and several commercial PCB preparations as antiestrogens were determined in the aryl hydrocarbon (Ah)-responsive MCF-7 human breast cancer cell lines. The inhibition of the 17 beta-estradiol-induced secretion of the 52-kDa protein (procathepsin D) was measured using a combination of polyacrylamide gel electrophoresis, double-staining of the protein bands with ISS ProBlue and silver stain, and quantitation by densitometric analysis. For the PCBs, the order of antiestrogenic potency was 3,3',4,4',5-pentachlorobiphenyl > 3,3',4,4',5,5'-hexachlorobiphenyl approximately 3,3',4,4'-tetrachlorobiphenyl > 2,3,3',4,4',5'-hexa, 2,3,3',4,4'- and 2,3,4,4',5-pentachlorobiphenyl > Aroclors 1221, 1232, 1248, 1254, and 1260 were inactive as antiestrogens at the highest concentrations used in this study (10(-6) M). For the PCDDs and PCDFs, the order of antiestrogenic potency was 2,3,7,8-tetrachlorodibenzo-p-dioxin > 2,3,7,8-tetrachlorodibenzofuran > 2,3,4,7,8-pentachlorodibenzofuran > 1,2,3,7,9-pentachlorodibenzofuran > 1,3,6,8-tetrachlorodibenzofuran. With few exceptions, the order of potency for all these congeners and mixtures paralleled their relative activities as agonists for other Ah receptor-mediated responses and their competitive binding affinities for the Ah receptor. The results of this study support the role for the Ah receptor in mediating the inhibition of the 17 beta-estradiol-induced secretion of the 52-kDa protein in MCF-7 cells and also points out the utility of this technique as a bioassay for this class of compounds.     

Protective effects of valsartan and benazeprilat in salt-loaded stroke-prone spontaneously hypertensive rats

These experiments examined the effectiveness of chronic blockade of the renin angiotensin system with either valsartan or benazeprilat on survival, blood pressure and end-organ damage in salt-loaded stroke-prone SHR. Valsartan or benazeprilat given continuously by subcutaneous osmotic minipump beginning at 10.5 weeks of age lowered blood pressure, as determined by radiotelemetry, prevented proteinuria, prolonged survival and decreased the severity of histopathological changes in the heart and kidney. These results indicate that angiotensin receptor blockade affords a similar degree of protection as inhibition of angiotensin converting enzyme in salt-loaded stroke-prone SHR. Furthermore, our results are consistent with a primary contribution of angiotensin II to the maintenance of blood pressure and support a principal role for angiotensin II-dependent mechanisms in the development of end-organ damage in the salt-loaded stroke-prone SHR.     

Renal nerve responses to somatic nerve activation in stroke-prone spontaneously hypertensive rats

Antidepressant-induced adverse sexual effects are becoming more frequently reported by patients who require pharmacotherapy. A MED-LINE search was conducted to generate articles reporting such events. We report here on the sexual side effects associated with tricyclics, monoamine oxidase inhibitors including moclobemide, selective serotonin reuptake inhibitors, bupropion, and on the newer antidepressants venlafaxine and nefazadone. We conclude that adverse sexual effects are an increasingly important side effect of antidepressant medications, and patients must be routinely asked about their occurrence.     

Age-related changes in cerebral and peripheral monoamine contents in stroke-prone spontaneously hypertensive rats

1. We examined monoamine contents in various regions of the brain and catecholamine contents in the heart and the adrenal gland of stroke-prone spontaneously hypertensive rats (SHRSP) and Wistar-Kyoto (WKY) rats aged 1.5, 3 and 6 months. 2. The noradrenaline (NA) content and the 5-hydroxytryptamine (5-HT) content in the brainstem were larger in 1.5 month old SHRSP than in the age-matched WKY. In addition, at age 6 months the brainstem 5-HT content was higher in SHRSP than in WKY. 3. The NA and 5-HT contents in basal ganglia, thalamus, hypothalamus, septum and anterior and lateral cerebral cortex showed no significant difference between SHRSP and WKY at any age. 4. The dopamine (DA) contents in all brain regions examined did not differ between WKY and SHRSP at any age. 5. The NA contents in left and right ventricles were larger in 3 month old SHRSP than in the age-matched WKY, but were lower in 6 month old SHRSP than in the age-matched WKY. The cardiac DA contents did not differ between the two rat strains of any age. 6. The adrenal NA and adrenaline (A) contents in 6 month old SHRSP were significantly larger than those in the corresponding WKY. 7. These findings suggest that the increased NA and 5-HT contents in the brainstem may be related to the onset of hypertension, and that the altered cardiac NA contents and adrenal NA and A contents change as a result of the onset or persistence of hypertension.     

Trandolapril's protective effects in stroke-prone spontaneously hypertensive rats persist long after treatment withdrawal

The effects of long-term oral administration of the angiotensin-converting enzyme (ACE) inhibitor trandolapril (0.01 mg/kg [T0.01] and 1 mg/kg [T1]) on the occurrence of stroke and on mortality were investigated in young salt-loaded stroke-prone spontaneously hypertensive rats during the treatment period (5-20 weeks of age) and up to 8 weeks thereafter. During the treatment period T1, but not T0.01, limited the increase in blood pressure. However, both doses of trandolapril prevented stroke and mortality and strongly opposed (T0.01) or abolished (T1) the increases in saline intake, diuresis, and proteinuria observed in control animals. Simultaneously, trandolapril markedly prevented (T0.01) or abolished (T1) vascular fibrinoid necrosis formation in the brain, kidney, and heart. Finally, trandolapril dose-dependently reduced arterial thickening and glomerular and tubulointerstitial lesions in the kidney, as well as arterial thickening, infarction, and fibrosis in the myocardium. At 8 weeks after treatment withdrawal, the antihypertensive effect of T1 had disappeared, but stroke-related mortality and fibrinoid necrosis remained completely suppressed. Further, no additional cerebral, renal, or cardiac lesions developed, and no increase in proteinuria occurred. In the T0.01 group, 17% of the animals died, fibrinoid necrosis tended to develop, organ lesions worsened, and proteinuria strongly increased. We conclude that (1) early ACE inhibition with trandolapril affords a long-lasting protection versus stroke and mortality both during and after the treatment period; and (2) that this beneficial effect is due to the suppression of fibrinoid necrosis formation and not to the drug's antihypertensive action. In contrast, both properties appear to contribute to trandolapril's renal and cardiac protective effects.     

Protective effects of CD-832 on organ damage in stroke-prone spontaneously hypertensive rats

Effects of a newly developed Ca2+ channel antagonist, (4R)-(-)-2-(nicotinoylamino)ethyl 3 nitrooxypropyl 1,4-dihydro-2,6-dimethyl-4-(3-nitrophenyl) 3,5-pyridine-dicarboxylate (CD-832), on hypertensive complications in stroke-prone spontaneously hypertensive rats (SHRSPs) were compared with effects of diltiazem. We examined changes in histological and hematological parameters in SHRSPs given the following treatments at 8 to 20 weeks of age: (a) CD-832; (b) diltiazem; (c) no treatment. CD-832 and diltiazem were added to the diet, in doses of 0.05 and 0.15% (approximately 30 and 100 mg/kg per day), respectively, throughout the experimental period. In untreated control SHRSPs, systolic blood pressure increased and severe renal lesions such as fibrinoid necrosis, smooth muscle proliferation, glomerular and tubular lesions and some cardiac fibrosis were observed at age 20 weeks. 12-week repeated-administration of CD-832 and diltiazem led to a comparable hypotension and decreased heart rate. CD-832 and diltiazem decreased the ratios of weights of kidney and heart to body weight and the concentration of blood urea nitrogen and creatinine in serum, compared to values in controls. In SHRSPs treated with CD-832 and diltiazem, the incidence of renal lesions and myocardial fibrosis was significantly reduced when compared with control SHRSPs. These results suggest that 12-week repeated-administration of CD-832 prevents the development of hypertension and the incidence of organ damage in SHRSPs. CD-832 and diltiazem were equally efficacious in preventing organ damage but this organ-protective effect was obtained at a lower dose for CD-832 (30 mg/kg per day) than that of diltiazem (100 mg/kg per day).     

Characterization of endothelium-dependent vasodilation and vasoconstriction in coronary arteries from spontaneously hypertensive rats

Coronary artery disease often occurs in patients with hypertension. The present study was designed to evaluate coronary vascular function in isolated coronary arteries of spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats and to determine the effect of antihypertensive treatment on coronary vascular responsiveness. Male SHR and WKY rats (12 to 14 weeks old) were divided into control and hydralazine-treated (120 mg/L drinking water for 10 days) groups. After 10 days, arterial pressure and heart rate were recorded while rats were conscious and unrestrained. Left ventricular coronary arteries (200 to 300 microns diameter) were isolated and intraluminal diameter was continuously recorded while vessels were maintained at a constant intraluminal pressure of 40 mm Hg. Relaxation of coronary arteries to both acetylcholine and nitroprusside was slightly, but significantly, enhanced in vessels from SHR compared to WKY rats. The enhanced relaxation was a specific effect, since isoproterenol induced similar relaxation in coronary arteries from SHR and WKY rats. Contraction to phenylephrine, but not endothelin-1, was augmented in coronary arteries from SHR compared to WKY rats. Treatment with hydralazine significantly lowered arterial pressure in SHR and WKY rats, but did not alter the enhanced contraction to phenylephrine or the enhanced relaxation to acetylcholine and nitroprusside in coronary arteris from SHR. These results indicate that coronary arteries of 12 to 14 week-old SHR do not have impaired endothelium-dependent relaxation, but to exhibit enhanced alpha-adrenoceptor-mediated contraction that is not reduced by lowering arterial pressure.     

Endothelin-induced activation of mitogen-activated protein kinases in glomerular mesangial cells from normotensive and stroke-prone spontaneously hypertensive rats

1. Kinase assay in myelin basic protein (MBP) containing polyacrylamide gels revealed that endothelin-1 (ET-1) and ET-3 increased MBP kinase activities in glomerular mesangial cells (MC) from Wistar-Kyoto (WKY) rats and spontaneously hypertensive rat (SHRSP). ET-1 stimulated MBP kinase activities more potently than ET-3. 2. Immunoprecipitation with anti-41-kDa MAPK antiserum showed that the MBP kinases activated by ET-1 correspond to 43- and 41-kDa MAPK. 3. Since Phorbol 12-myristate 13-acetate, a direct activator of protein kinase C, also activated MAPK, protein kinase C was suggested to mediate ET-induced activation of MAPK. 4. These results suggest that MAPK may mediate the ET actions in glomerular mesangial cells from normotensive rats as well as spontaneously hypertensive rats. Since ET is produced by vascular endothelial cells of the kidney and glomerular mesangial cells, the ET signalling pathway may have some physiological and pathophysiological significance in vivo glomerulus.     

The effects of perindopril on vascular smooth muscle polyploidy in stroke-prone spontaneously hypertensive rats

OBJECTIVE: To quantify vascular smooth muscle polyploidy and growth kinetics in aortic cells from stroke-prone spontaneously hypertensive rats (SHRSP) and from normotensive Wistar-Kyoto (WKY) rats, and to examine the effects of treatment with the angiotensin converting enzyme (ACE) inhibitor perindopril on these parameters. DESIGN: The following experimental groups were used: young (age < 20 weeks) and old (age > 20 weeks) untreated WKY rats and untreated SHRSP; SHRSP treated with perindopril, and age- and sex-matched control SHRSP; and SHRSP treated with hydralazine and hydrochlorothiazide and age- and sex-matched control SHRSP. The effects of treatment of the SHRSP with perindopril for 30 days on vascular smooth muscle polyploidy and growth kinetics were measured and compared with the effects of equivalent antihypertensive doses of hydralazine and hydrochlorothiazide. METHODS: Vascular smooth muscle polyploidy was measured using flow-cytometry DNA analysis of freshly harvested cells. Growth curves were performed on cultured aortic cells. Plasma renin activity was measured by an antibody-trapping method, plasma angiotensin II (Ang II) by radioimmunoassay and plasma ACE activity by a colorimetric method. Cardiac hypertrophy was evaluated by measuring the heart weight:body weight and left ventricle + septum weight:body weight ratios. RESULTS: The SHRSP had markedly and significantly elevated G2 + M phase of the cell cycle. Treatment with perindopril resulted in a significant reduction in polyploidy in the SHRSP, whereas treatment with hydralazine and hydrochlorothiazide had no effect on the percentage of cells in the G2 + M phase of the cell cycle. The regression of polyploidy after treatment with perindopril was associated with a significant reduction in the concentration of Ang II and ACE activity, and with a significant regression of cardiac hypertrophy. Increased mitogenesis of cultured vascular smooth muscle cells from the SHRSP was not altered by treatment with perindopril. CONCLUSIONS: ACE inhibition reduces vascular smooth muscle polyploidy in large conduit arteries. This type of vascular protection is mediated by the reduced Ang II and possibly by increased kinins level, rather than by the hypotensive effect alone.     

Evidence from comparative investigations that impaired platelet activation is not specific for stroke-prone spontaneously hypertensive rats

BACKGROUND AND PURPOSE: Platelet behavior of Sprague Dawley (SD), Wistar (WI), Wistar-Kyoto (WKY), spontaneously hypertensive (SHR), and stroke-prone spontaneously hypertensive rats (SHRSP) was studied in vivo to evaluate the importance of hypertension-related hemostatic disorders. METHODS: The study was based on the model of stimulus-induced pulmonary microembolization of labeled platelets. After injection of 51Cr-labeled homologous platelets into urethane-anesthetized rats, the organ distribution of the platelets was continuously monitored by gamma detectors. Count rates of two detectors--one placed above the animals' thoraxes (C1), the other above their abdomens (C2)-and the ratio of C1:C2 were calculated. The following platelet activators were applied intravenously: adenosine diphosphate (ADP; 50 micrograms/kg), collagen (100 micrograms/kg), and thrombin (50 IU/kg). RESULTS: All three substances caused a reversible pulmonary accumulation of the labeled platelets and hence an increase in C1/C2 (delta C1/C2%). ADP induced a shift of 75% in SD, 52% in WI, 32% in WKY, 30% in SHR, and 31% in SHRSP. Thrombin-mediated shift was 79% in SD, 64% in WI, 58% in WKY, 48% in SHR, and 54% in SHRSP. Collagen induced a shift of 85% in SD, 96% in WI, 84% in WKY, 56% in SHR, and 62% in SHRSP. CONCLUSIONS: Because indistinguishable results were observed in both hypertensive strains, we conclude that impaired platelet aggregation is not specific for SHRSP. Hence, it may not primarily be responsible for the increased occurrence of stroke in these animals.     

11 beta-Hydroxysteroid dehydrogenase activity in mesenteric arteries of spontaneously hypertensive rats

1. 11 beta-Hydroxysteroid dehydrogenase (11-HSD) activity in mesenteric arteries of spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats was determined and expressed as the percentage conversion of [3H]-corticosterone to [3H]-11-dehydrocorticosterone. 2. 11-HSD activity was significantly decreased in mesenteric arteries of both 4 and 9 week old SHR (8.4 +/- 0.8%, 5.0 +/- 1.5%, respectively) compared with WKY rats (12.4 +/- 0.6%, 15.8 +/- 0.7%, respectively; P < 0.05). 3. Total RNA from rat vascular smooth muscle cells (VSMC) and endothelial cells (EC) were prepared with selective precipitation in 3 mol/L LiCl/6 mol/L urea. The expression of 11-HSD mRNA was confirmed in the rat VSMC but its mRNA expression was not detected in EC, using northern blot analysis. 4. The results in this study indicate that 11-HSD in the vascular wall may play a role in the pathogenesis of hypertension in SHR.     

Lipid-regulating action of gemfibrozil in the stroke-prone spontaneously hypertensive rat

1. Gemfibrozil (Lopid) is extensively used as lipid-regulating agent in the Western World, and its beneficial effect is demonstrated in human studies such as the Helsinki Heart Study. However, the mechanism of its hypolipidaemic action is not fully understood. In the present paper, to elucidate the hypolipidaemic mechanism, we examined the effects of gemfibrozil on lipid metabolism in the normocholesterolaemic and hypercholesterolaemic stroke-prone spontaneously hypersensitive rat (SHRSP). 2. Gemfibrozil effectively increased high density lipoprotein (HDL) subfraction rich in apoE (apoE-HDL) and significantly decreased very low density lipoprotein (VLDL) in normocholesterolaemic SHRSP. In the liver of normocholesterolaemic SHRSP, gemfibrozil significantly reduced the activity of microsomal acyl-CoA:cholesterol acyltransferase. 3. Gemfibrozil markedly reduced atherogenic beta-very low density lipoprotein (beta-VLDL) and low density lipoprotein (LDL) in hypercholesterolaemic SHRSP fed a high-fat and high-cholesterol diet (HFC diet). On the other hand, it significantly increased the contents of apoA-I, A-IV and E in the HDL fraction compared with the control group, suggesting that gemfibrozil effectively increases anti-atherogenic HDL subfractions rich in apoA-I, A-IV or E. In the liver of hypercholesterolaemic SHRSP, gemfibrozil markedly prevented lipid accumulation.     

Free fatty acid fractions from some vegetable oils exhibit reduced survival time-shortening activity in stroke-prone spontaneously hypertensive rats

Previously, we demonstrated that several vegetable oils that included low-erucic rapeseed oil markedly shortened the survival time (by approximately 40%) of stroke-prone spontaneously hypertensive (SHRSP) rats as compared with perilla oil, soybean oil, and fish oil. We considered that a factor other than fatty acids is toxic to SHRSP rats, because the survival time-shortening activity could not be accounted for by the fatty acid compositions of these oils. In fact, a free fatty acid (FFA) fraction derived from lipase-treated rapeseed oil was found to be essentially devoid of such activity. A high-oleate safflower oil/safflower oil/perilla oil mixture exhibited a survival time-shortening activity comparable to that of rapeseed oil, but the activity of this mixed oil was also reduced by lipase treatment. A partially hydrogenated soybean oil shortened the survival time by approximately 40%, but a FFA fraction derived from lipase-treated partially hydrogenated soybean oil shortened it by 13% compared with soybean oil. Fatty acid compositions of the rapeseed oil and a FFA fraction derived from lipase-treated rapeseed oil were similar, but those of hepatic phospholipids of rats fed the oil and FFA were slightly but significantly different. These results support the interpretation that the survival time-shortening activity exhibited by some vegetable oils is due to minor components other than fatty acids, and that an active component(s) were produced in or contaminated soybean oil during the partial hydrogenation processes.     

Relationship between nifedipine sensitivity of aortae and blood pressure of stroke-prone spontaneously hypertensive rats

1. We have previously described an increased sensitivity to inhibition by nifedipine of noradrenaline-induced contractures of blood vessels in hypertension. In this study we have investigated whether changes in blood pressure (BP) change the sensitivity to nifedipine and K+ of aortic rings from normotensive (Wistar-Kyoto rats, WKY) and stroke-prone spontaneously hypertensive rats (SHRSP). 2. SHRSP were treated with: hydralazine plus hydrochlorothiazide; captopril plus hydrochlorothiazide; hydralazine plus guanethidine; or captopril alone. WKY rats were treated with deoxycorticosterone acetate (DOCA) and NaCl. Treatment commenced from 5 weeks of age and continued until 13-15 weeks. 3. The SHRSP treatments produced similar reductions in BP, and the BP of all the treated groups were significantly lower than the mean BP of untreated SHRSP (201.0 +/- 7.7 mmHg). The mean BP of the treated WKY rats (134.2 +/- 7.6 mmHg) was significantly higher than the mean BP of the untreated WKY rats (86.8 +/- 7.4 mmHg). 4. An area-under-curve (AUC) analysis of the inhibitory effects of nifedipine on responses of aortae to noradrenaline showed no differences between treated and untreated SHRSP groups (overall mean 40.6 +/- 1.9% and 43.4 +/- 3.4% inhibition of control AUC, respectively), or between DOCA-salt treated WKY and untreated WKY groups (58.8 +/- 5.9 and 64.8 +/- 2.3, respectively). Noradrenaline-induced contractures of aortae from all SHRSP groups were significantly more sensitive to inhibition by nifedipine than aortae from both WKY groups. 5. The molar concentration of agonist required to evoke 50% of the maximum response (EC50) values for potassium chloride (KCl) were significantly increased in the aortae of all treated SHRSP groups in comparison to those from untreated SHRSP (treated SHRSP groups, 15.53 +/- 0.68 mmol/L vs untreated SHRSP group, 11.36 +/- 1.10 mmol/L). The EC50 values for KCl for the aortae from the DOCA-treated WKY rats were significantly less than those from aortae of the untreated WKY (11.80 +/- 0.80 and 17.08 +/- 1.50 mmol/L, respectively). 6. We conclude that reduction (in SHRSP) or increase (in WKY) of the BP has no effect on the sensitivity of aortic smooth muscle to the inhibitory effects of nifedipine on responses to noradrenaline, suggesting that alterations in voltage-dependent Ca2+ mechanisms may be a primary phenomenon in the SHRSP. In contrast, the fact that sensitivity to KCl changes in the treated SHRSP and WKY aortae suggests such sensitivity is secondary to the BP and thus a separate phenomenon from voltage-dependent Ca2+ mechanisms.     

Single L-type calcium channels in smooth muscle cells from resistance arteries of spontaneously hypertensive rats

The amplitude of the whole-cell L-type Ca2+ channel current recorded from vascular smooth muscle cells is reportedly greater in spontaneously hypertensive rats (SHR) than in Wistar-Kyoto rats (WKY). However, no study has examined properties of single Ca2+ channels in arterial cells from these strains. To further test the hypothesis that activation of L-type Ca2+ channels in arterial smooth muscle cells would be enhanced in SHR, we recorded single Ca2+ channel currents in resistance mesenteric artery cells from SHR and WKY (8 to 9 weeks of age) using a cell-attached patch clamp technique. With 50 mmol/L Ba2+ in the recording pipette, the depolarizing pulse from a holding potential of -40 mV evoked the single L-type Ca2+ channel current. Opening of the single channels was more frequent in cells from SHR than from WKY. Single-channel conductance (20 pS) and open time (1 ms at 0 mV) did not differ in the two strains. The results suggest that an increased amplitude of the whole-cell current can be attributed to the enhanced opening of single Ca2+ channels in the arterial smooth muscle cells from SHR compared with WKY.