Blood Pressure In Wistar-Kyoto Research Articles

Interaction between Angiotensinase Activities in Pituitary and Adrenal Glands of Wistar-Kyoto and Spontaneously Hypertensive Rats under Hypotensive or Hypertensive Treatments.

In the present study, we analyzed the activity of several aminopeptidases (angiotensinases) involved in the metabolism of various angiotensin peptides, in pituitary and adrenal glands of untreated Wistar–Kyoto (WKY) and spontaneously hypertensive rats (SHR) or treated with the antihypertensive drugs captopril and propranolol or with the L-Arginine hypertensive analogue L-NG-Nitroarginine Methyl Ester (L-NAME). Intra- and inter-gland correlations between angiotensinase activities were also calculated. Membrane-bound alanyl-, cystinyl-, and glutamyl-aminopeptidase activities were determined fluorometrically using aminoacyl-β-naphthylamide as substrates. Depending on the type of angiotensinase analyzed, the results reflect a complex picture showing substantial differences between glands, strains, and treatments. Alanyl-aminopeptidase responsible for the metabolism of Ang III to Ang IV appears to be the most active angiotensinase in both pituitary and adrenals of WKY and particularly in SHR. Independently of treatment, most positive correlations are observed in the pituitary gland of WKY whereas such positive correlations are predominant in adrenals of SHR. Negative inter-gland correlations were observed in control SHR and L-NAME treated WKY. Positive inter-gland correlations were observed in captopril-treated SHR and propranolol-treated WKY. These results may reflect additional mechanisms for increasing or decreasing systolic blood pressure in WKY or SHR.

Effects of Prehypertensive Losartan Treatment on Resistance Vessel Remodeling and Angiotensin II Type 1 Receptor Expression in Spontaneously Hypertensive Rats

Abstract Background To study the effects of prehypertensive losartan treatment on blood pressure, resistance vessel remodeling, and angiotensin II type 1 receptor (AT1R) expression in adult spontaneously hypertensive rats (SHRs). Methods Four-week-old SHR and Wistar-Kyoto rats were randomly divided into losartan-treated and untreated groups. Losartan was administrated by gavage from 4 to 10 weeks old. Blood pressure was monitored by the tail-cuff method till 26 weeks old. The third grade mesenteric arteries were then isolated. Vessel structure, relaxation reactivity, angiotensin II type 1 receptor expression, and angiotensin II levels were analyzed. Results Losartan treatment from 4 to 10 weeks of age significantly lowered systolic blood pressure from 10 to 26 weeks in SHR. At 26 weeks old, wall thickness to lumen radius and wall area to lumen area of mesenteric arteries were significantly lower in losartan-treated than untreated SHR (P < 0.01). Maximum relaxation to acetylcholine and its pD2 were increased in losartan-treated compared to untreated SHR (P < 0.01). Angiotensin II type 1 receptor mRNA and protein levels were significantly reduced in losartan-treated SHR (P < 0.01). However, angiotensin II levels in plasma and mesenteric arteries of losartan-treated SHR were higher than those of untreated SHR (P < 0.05). Losartan treatment lowered systolic blood pressure in Wistar-Kyoto at the age of 10 weeks (P < 0.05), but had no significant effect on blood pressure after 14 weeks or mesenteric arteries at 26 weeks. Conclusions Blood pressure reduction induced by prehypertensive losartan treatment ameliorates resistance vessel remodeling and downregulates angiotensin II type 1 receptor expression in adult SHR.

Endothelial Dysfunction in Femoral Artery of the Hypertensive Rats Is Nitric Oxide Independent

This study examined nitric oxide (NO) production, oxidative load and endothelium-dependent relaxation (NO-dependent and NO-independent) in adult male borderline hypertensive (BHR) and spontaneously hypertensive (SHR) rats as compared to normotensive Wistar-Kyoto (WKY) rats. Systolic blood pressure (BP) was determined by tail-cuff. NO production was determined by conversion of [(3)H]-L-arginine. Conjugated dienes (CD) and concentrations of thiobarbituric acid-reactive substances (TBARS) were measured for assessment of oxidative load. Vascular function was investigated in rings of the femoral artery (FA) using a wire myograph. BP of WKY, BHR and SHR was 106+/-2, 143+/-3 and 191+/-3 mm Hg, respectively (p<0.01 for each). Significant left ventricle (LV) hypertrophy and elevated levels of CD and TBARS in the LV were present in BHR and SHR as compared to WKY. NO production was elevated significantly in the aorta of BHR and SHR vs. WKY as well as in the LV of SHR vs. WKY. Acetylcholine (ACh)-induced relaxation of the FA was reduced significantly in both BHR and SHR vs. WKY. The NO-dependent component of ACh-induced relaxation had increasing tendency in hypertensive groups and it correlated positively with BP. The NO-independent component of vasorelaxation was reduced significantly in BHR and SHR vs. WKY and it correlated negatively with BP. In conclusion, the results showed that endothelial dysfunction in the experimental model of borderline hypertensive and hypertensive rats is NO-independent. The results suggest that borderline hypertension represents a risk of other cardiovascular disorders which is qualitatively similar to that of fully developed hypertension.

2,4,3′,5′‐Tetramethoxystilbene Reduces Blood Pressure and Associated Cardiac Fibrosis Via Inhibition of Cytochrome P450 1B1 and Decreased Oxidative Stress in SHR

Previously, we reported that inhibition of cytochrome P450 (CYP) 1B1 activity with 2,4,3′,5′‐tetramethoxystilbene (TMS) reversed angiotensin II‐ and deoxycoticosterone acetate salt‐induced hypertension and associated pathophysiology in rats. This study was conducted to investigate the effect of TMS on blood pressure (BP), and associated cardiac fibrosis and oxidative stress in male, normotensive Wistar Kyoto (WKY) and spontaneously hypertensive rats (SHR). TMS (600 μg/kg, i.p. daily for 6 weeks) beginning at 8 weeks of age, did not alter systolic BP in WKY, but decreased it in SHR (207 ± 7 mmHg vehicle, vs. 129 ± 2 mmHg TMS, P &lt; 0.05). Cardiac CYP1B1 activity that was increased in SHR was reduced by TMS treatment. Cardiac fibrosis, as indicated by increased collagen deposition and myofibroblast accumulation, was observed in SHR, which was prevented by TMS. SHR had increased cardiac levels of reactive oxygen species, increased NADPH oxidase activity, and increased plasma levels of H2O2, NOx, and TBARS that were prevented by TMS, suggesting that in addition to inhibiting CYP1B1 activity and limiting cardiac damage, TMS regulates cardiac oxidative stress in SHR. These data suggest that CYP1B1 contributes to increased BP, cardiac damage, and associated oxidative stress in SHR. Moreover, CYP1B1 could serve as a novel target for the development of drugs such as TMS to treat cardiac disease associated with hypertension.

Diesel exhaust induced pulmonary and cardiovascular impairment: The role of hypertension intervention

Exposure to diesel exhaust (DE) and associated gases is linked to cardiovascular impairments; however, the susceptibility of hypertensive individuals is poorly understood. The objectives of this study were (1) to determine cardiopulmonary effects of gas-phase versus whole-DE and (2) to examine the contribution of systemic hypertension in pulmonary and cardiovascular effects. Male Wistar Kyoto (WKY) rats were treated with hydralazine to reduce blood pressure (BP) or l-NAME to increase BP. Spontaneously hypertensive (SH) rats were treated with hydralazine to reduce BP. Control and drug-pretreated rats were exposed to air, particle-filtered exhaust (gas), or whole DE (1500μg/m3), 4h/day for 2days or 5days/week for 4weeks. Acute and 4-week gas and DE exposures increased neutrophils and γ-glutamyl transferase (γ-GT) activity in lavage fluid of WKY and SH rats. DE (4weeks) caused pulmonary albumin leakage and inflammation in SH rats. Two-day DE increased serum fatty acid binding protein-3 (FABP-3) in WKY. Marked increases occurred in aortic mRNA after 4-week DE in SH (eNOS, TF, tPA, TNF-α, MMP-2, RAGE, and HMGB-1). Hydralazine decreased BP in SH while l-NAME tended to increase BP in WKY; however, neither changed inflammation nor BALF γ-GT. DE-induced and baseline BALF albumin leakage was reduced by hydralazine in SH rats and increased by l-NAME in WKY rats. Hydralazine pretreatment reversed DE-induced TF, tPA, TNF-α, and MMP-2 expression but not eNOS, RAGE, and HMGB-1. ET-1 was decreased by HYD. In conclusion, antihypertensive drug treatment reduces gas and DE-induced pulmonary protein leakage and expression of vascular atherogenic markers.

Dietary phytosterols and phytostanols decrease cholesterol levels but increase blood pressure in WKY inbred rats in the absence of salt-loading

BackgroundThere are safety concerns regarding widespread consumption of phytosterol and phytostanol supplemented food products. The aim of this study was to determine, in the absence of excess dietary salt, the individual effects of excess accumulation of dietary phytosterols and phytostanols on blood pressure in Wistar Kyoto (WKY) inbred rats that have a mutation in the Abcg5 gene and thus over absorb phytosterols and phytostanols.MethodsThirty 35-day old male WKY inbred rats (10/group) were fed a control diet or a diet containing phytosterols or phytostanols (2.0 g/kg diet) for 5 weeks. The sterol composition of the diets, plasma and tissues were analysed by gas chromatography. Blood pressure was measured by the tail cuff method. mRNA levels of several renal blood pressure regulatory genes were measured by real-time quantitative PCR.ResultsCompared to the control diet, the phytosterol diet resulted in 3- to 4-fold increases in the levels of phytosterols in plasma, red blood cells, liver, aorta and kidney of WKY inbred rats (P < 0.05). The phytostanol diet dramatically increased (> 9-fold) the levels of phytostanols in plasma, red blood cells, liver, aorta and kidney of these rats (P < 0.05). The phytosterol diet decreased cholesterol levels by 40%, 31%, and 19% in liver, aorta and kidney, respectively (P < 0.05). The phytostanol diet decreased cholesterol levels by 15%, 16%, 20% and 14% in plasma, liver, aorta and kidney, respectively (P < 0.05). The phytostanol diet also decreased phytosterol levels by 29% to 54% in plasma and tissues (P < 0.05). Both the phytosterol and phytostanol diets produced significant decreases in the ratios of cholesterol to phytosterols and phytostanols in plasma, red blood cells, liver, aorta and kidney. Rats that consumed the phytosterol or phytostanol diets displayed significant increases in systolic and diastolic blood pressure compared to rats that consumed the control diet (P < 0.05). The phytosterol diet increased renal angiotensinogen mRNA levels of these rats.ConclusionThese data suggest that excessive accumulation of dietary phytosterols and phytostanols in plasma and tissues may contribute to the increased blood pressure in WKY inbred rats in the absence of excess dietary salt. Therefore, even though phytosterols and phytostanols lower cholesterol levels, prospective clinical studies testing the net beneficial effects of dietary phytosterols and phytostanols on cardiovascular events for subgroups of individuals that have an increased incorporation of these substances are needed.

Effects of deep-frying oil on blood pressure and oxidative stress in spontaneously hypertensive and normotensive rats

Objective Ingestion of deep-frying oil has been reported to cause physiologic and histologic changes in experimental animals' tissue, increase the oxidative stress, and possibly lead to death. The purpose of this study was to investigate the effect of deep-frying oil on oxidative stress and blood pressure in spontaneously hypertensive (SHR) and Wistar Kyoto (WKY) rats. Methods Deep-frying oil was prepared by frying fresh soybean oil at 180 ± 5°C for 8 h each day, for 4 consecutive days. Male SHR and WKY rats were fed diets containing 15% fresh soybean oil or deep-frying oil (DO) for 10 wk. Results Rats ingesting the DO diet had lower feed efficiency and higher relative liver and kidney weights but deep frying had no significant influence on blood pressure in WKY or SHR rats. The DO diet had no effect on plasma renin activity, aldosterone content, or tissue angiotension-I–converting enzyme activity. WKY rats fed the DO diet showed significantly increased urinary thromboxane B 2 and 8-iso-prostaglandin F 2α excretion, but not urinary 6-keto-prostaglandin F 1α excretion. Diets containing deep-frying oil resulted in increased plasma thiobarbituric acid-reactive substances and nitric oxide contents and decreased plasma total antioxidant capacity in SHR and WKY rats. Conclusion The ingestion of deep-frying oil seemed not to influence blood pressure or its related parameters, but altered eicosanoid metabolism and elevated oxidative stress in SHR and WKY rats.

Calcimimetic NPS R-568 induces hypotensive effect in spontaneously hypertensive rats

The discovery of calcium receptors and calcimimetics created the possibility of "pharmacologic parathyroidectomy" (phPTX), which decreased secretion of parathormone (PTH). Parathyroid glands of spontaneously hypertensive rats (SHR) and of patients with primary hyperparathyroidism and hypertension secrete parathyroid hypertensive factor (PHF). Parathyroidectomy decreases blood pressure in these rats and in patients. The present study determined whether phPTX induced by calcimimetics decreases mean arterial blood pressure (MAP) in hypertensive rats. Hypertensive SHR and normotensive Wistar Kyoto (WKY) rats were used. Clearance experiments were performed and the effect of 1 mg/kg body weight (given intravenously) synthesized NPS R-568 (NPS) on MAP in the presence or absence of thyroparathyroidectomy (TPTX) was monitored. The success phPTX and TPTX were proven by a significant decrease in plasma Ca(2+) concentration and a decrease in urinary fractional phosphate excretion (FE Pi). The administration of NPS significantly decreased blood pressure in SHR versus SHR/control: Delta(0-50 min of experiment) MAP -16.5 +/- 2.5 mm Hg v -3.2 +/- 1.5 mm Hg (P < .002). The TPTX decreased blood pressure in SHR versus SHR/control and was not different versus SHR/TPTX/NPS (DeltaMAP: -10.2 +/- 1.6 mm Hg v -3.2 +/- 1.5 mm Hg (P < .01) and v -8.3 +/- 2.2 mm Hg (P = not significant). In normotensive WKY rats application of NPS did not reach significance in DeltaMAP: -6.7 +/- 1.8 mm Hg v -2.6 +/- 2.8 mm Hg (P = not significant) in WKY/control. The TPTX lowered blood pressure in WKY versus WKY/control and remained unchanged versus WKY/TPTX/NPS (DeltaMAP: -11.3 +/- 1.7 mm Hg v -2.6 +/- 2.8 mm Hg (P < .04) and v -11.4 +/- 2.6 mm Hg (P = not significant). We conclude that phPTX with NPS R-568 is responsible for a decrease of MAP in SHR.

Opposite effect of methionine-supplemented diet, a model of hyperhomocysteinemia, on plasma and liver antioxidant status in normotensive and spontaneously hypertensive rats

Hyperhomocysteinemia is often associated with an increase in blood pressure. However our previous study has shown that methionine supplementation induced an increase in blood pressure in Wistar-Kyoto (WKY) rats and a decrease in blood pressure in spontaneously hypertensive rats (SHR) with significant differences in plasma homocysteine (Hcy) metabolites levels. Previously liver antioxidant status has been shown to be decreased in SHR compared to WKY rats. It has been suggested that oxidative stress may predispose to a decrease in NO bioavailability and induce the flux of Hcy through the liver transsulfuration pathway. Thus the aim of this study was 1) to investigate the effect of methionine supplementation on NO-derived metabolites in plasma and urine 2) to investigate whether abnormalities in Hcy metabolism may be responsible for the discrepancies observed between WKY rats and SHR concerning blood pressure and 3) to investigate whether a methionine-enriched diet, differently modified plasma and liver antioxidant status in WKY rats an SHR. We conclude that the increase in blood pressure in WKY rats is related to high plasma cysteine levels and is not due to a decrease in NO bioavailability and that the decrease in blood pressure in SHR is associated with high plasma GSH levels after methionine supplementation. So GSH synthesis appears to be stimulated by liver oxidative stress and GSH is redistributed into blood in SHR. So the great GSH synthesis can be rationalized as an autocorrective response that leads to a decreased blood pressure in SHR.

Insulin Mediated Hemodynamic Responses in Spontaneous Hypertensive Rats (SHRs): Effect of Chromosome 4 Gene Transfer

The spontaneous hypertensive rat (SHR) is a widely studied model of essential hypertension and has been reported to exhibit alterations in carbohydrate and lipid metabolism. Genetic linkage studies implicated that SHR carries deletion variant of Cd36 gene of chromosome 4, the gene that encodes fatty acid transporter. Thus it could be possible that primary genetic defect in SHR is compromised tissue utilization of fatty acid that would form the basis for the pathogenesis of hyperinsulinemia, insulin resistance and insulin‐mediated responses. We measured both the hemodynamic and metabolic responses to insulin in SHR in comparison with the chromosome congenic spontaneous hypertensive rats (cSHRs) (rats in which piece of chromosome 4 containing wild type Cd36 was integrated into the SHR genome). A bolus infusion of insulin increased iliac conductance and decreased blood pressure in Wistar Kyoto (WKY) rats. However, in SHR insulin did not reduce blood pressure as in WKY but after about 15 min it significantly enhanced blood pressure and reduced iliac conductance. Whereas in cSHR insulin did not reduce blood pressure as in WKY rats. However, pressor responses to insulin were eliminated by chromosome 4 gene transfer. Glucose clearance was significantly slower in both SHR and cSHR. Glucose tolerance test revealed that SHR are hyperinsulinemic and insulin resistant. These findings indicate that transfer of segment of chromosome 4 from Brown Norway rats onto spontaneous hypertensive background eliminates hyperinsulinemia and pressor effects of insulin.

Dietary borage oil alters plasma, hepatic and vascular tissue fatty acid composition in spontaneously hypertensive rats

Dietary borage oil rich in gamma-linolenic acid (GLA) has been shown to lower blood pressure in Wistar Kyoto (WKY) and spontaneously hypertensive rats (SHR). A potential mechanism for this effect may be attributed to changes in metabolism of GLA to dihomogamma-linolenic (DGLA) and arachidonic acids (AA). We investigated the effects of dietary borage oil on fatty acid composition in the plasma, liver and vascular tissue in WKY and SHR. The diet significantly increased the levels of omega-6 polyunsaturated fatty acids. GLA and DGLA levels in the plasma, liver, aorta and renal artery tissues increased in SHR ( P < 0.001) and WKY ( P < 0.001). AA levels were also increased in both plasma and liver of SHR ( P < 0.05) and WKY ( P < 0.05) fed the borage oil enriched diet. The results demonstrate that dietary borage oil produces marked changes in the metabolism of GLA which may contribute to its blood pressure lowering effect in WKY and SHR.

Left ventricular hypertrophy and its relation to the cardiac kinin-forming system in hypertensive and diabetic rats

We investigated the cardiac tissue kallikrein and kininogen levels, left ventricular wall thickness and mean arterial blood pressure of Wistar Kyoto and spontaneously hypertensive rats with and without streptozotocin-induced diabetes. The mean arterial blood pressure was highly elevated ( P<0.001) in Wistar Kyoto diabetic and spontaneously hypertensive diabetic rats as compared with their respective controls. The cardiac tissue kallikrein and kininogen levels were reduced significantly ( P<0.001) in diabetic Wistar Kyoto, spontaneously hypertensive and diabetic spontaneously hypertensive compared with Wistar Kyoto control rats. In addition, the left ventricular thickness was found to be increased ( P<0.001) in diabetic Wistar Kyoto and spontaneously hypertensive rats in the presence and in the absence of diabetes. Our results indicate that reduced activity of the kinin-forming system may be responsible for inducing left ventricular hypertrophy in the presence of raised mean arterial blood pressure in diabetic and hypertensive rats. Thus, the kinin-forming components might have a protective role against the development of left ventricular hypertrophy. The possible significance of these findings is discussed.

Dietary calcium decreases blood pressure without decreasing renal vascular resistance or altering the response to NO blockade

Many vasoactive elements are involved in the elevation of blood pressure in spontaneously hypertensive rats (SHR). Elevated dietary calcium has been observed to reduce blood pressure in SHR. This study investigates interactions among dietary calcium, renal vascular resistance (RVR), elevation of blood pressure and effects of norepinephrine and nitric oxide synthesis. We completed a series of experiments on two groups each (fed low, 0.1% and high, 2.0% dietary calcium, respectively) of 9-week-old Wistar Kyoto (WKY), 9-week-old and 6-week-old SHR. Although 9-week-old SHR had elevated baseline blood pressure compared to 9-week-old WKY and also compared to 6 week-old SHR, there was no corresponding elevation in baseline RVR. All SHR fed high calcium diets had lower blood pressure compared to low calcium diets, and there was no corresponding reduction in RVR. WKY controls' blood pressure and RVR were unaffected by dietary calcium levels. In all hypertensive rats the blood pressure and renal vascular resistance were elevated by N G-nitro- l-arginine methylester ( l-NAME), but the dietary differences were sustained. Blood pressure of WKY was unaffected by the low dose of l-NAME. The increase in RVR to l-NAME was greater in SHR than in controls. The renal vascular response to norepinephrine was related to diet in older SHR, but smaller and unrelated to diet in younger SHR. Following l-NAME, WKY had greater responses to norepinephrine than 9-week-old SHR. We conclude that noradrenergic vasoconstriction is enhanced in the adult SHR, especially in the absence of high calcium diet. Alterations in NO synthesis may effect the norepinephrine response.

Antisense to Thyrotropin Releasing Hormone Receptor Reduces Arterial Blood Pressure in Spontaneously Hypertensive Rats

We report in the present study the effect of intrathecal treatment with antisense oligonucleotides complementary to thyrotropin releasing hormone (TRH) receptor mRNA on the pressor response to intrathecal administration of TRH and on resting arterial blood pressure in Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR). In 16-week-old male WKY rats, 18-base phosphodiester antisense or mismatch oligonucleotides to TRH receptor mRNA (100 micrograms per day) were injected intrathecally for 3 days. Twenty-four hours after the last injection, the magnitude of the pressor response to intrathecal TRH (10 micrograms) was significantly smaller in the antisense-treated group (n = 7) compared with mismatch-treated controls (n = 7) (change in mean arterial pressure, +20.3 +/- 3.0 versus +32.6 +/- 2.5 mm Hg, P < .01). No differences were observed in the pressor responses to injection of N-methyl-D-aspartic acid. Resting arterial blood pressure was unaffected by antisense treatment in WKY rats. In separate experiments, 16-week-old male SHR were treated with antisense (n = 7) or mismatch (n = 6) oligonucleotides for 3 days. Mean resting arterial blood pressure was significantly reduced by treatment with antisense oligonucleotides (from 157 +/- 4.8 to 119 +/- 8.8 mm Hg, P < .01), but no significant changes were observed in mismatch-treated animals. Our results suggest that the expression of TRH receptors in spinal sympathetic preganglionic neurons can be selectively reduced by intrathecal treatment with antisense oligonucleotides and that TRH projections to sympathetic preganglionic neurons play an important role in the elevation of arterial blood pressure in SHR.

Dependence of elevated mesenteric arteriolar tone on glucocorticoids in spontaneously hypertensive rats.

This study is designed to explore the effect of adrenal glucocorticoids on arteriolar behavior under steady state conditions in spontaneously hypertensive rats (SHR) compared with their normotensive controls, the Wistar Kyoto (WKY) rats. Mesenteric arterioles were observed by intravital microscopy under general anesthesia and arteriolar diameters were measured. At the end of each experiment, papaverine was topically applied to determine maximum diameter of the vessels for which arteriolar tone was computed. The adrenal contribution to the atypical arteriolar tone in SHR was explored by subjecting them to bilateral adrenalectomy with or without glucocorticoid replacement therapy. Adrenalectomy led to a reduction in the elevated blood pressure in SHR to normotensive levels, which could be restored to its hypertensive level by treatment with dexamethasone. Adrenalectomy had so significant effect on blood pressure in WKY rats, although administration of dexamethasone but not aldosterone did lead to an elevation of the blood pressure in sham-operated WKY. Arteriolar tone in SHR was set at a higher steady state level than in WKY rats. In adrenalectomized SHR, tone fell to the levels observed in WKY rats. This decrease in arteriolar tone in the adrenalectomized SHR could in turn be restored to the hypertensive levels with dexamethasone but not aldosterone. Our results suggest that the enhancement of arteriolar tone, as well as the high blood pressure in SHR, may be related to the above normal levels of adrenal glucocorticoids present in the bloodstream.

Actions of L- And D-Arginine and NG-Monomethyl-l-Arginine on the Blood Pressure of Pithed Normotensive and Spontaneously Hypertensive Rats

We have examined the depressor effects of L- and D-arginine on the diastolic blood pressure of pithed normotensive Wistar (NW), Wistar-Kyoto (WKY) and spontaneously hypertensive (SH) rats after the administration of a single bolus injection of the nitric oxide synthase inhibitor, NG-monomethyl-L-arginine (L-NMMA). A single bolus intravenous injection of L-NMMA, 30 mg/kg, produced an increase in both the systolic and diastolic blood pressure of pithed rats. Injections of bolus doses, 1-300 mg/kg, of D-arginine did not lead to sustained reductions of the blood pressure in pithed NW rats although slight decreases in the blood pressure of WKY and SH rats were observed, and these transient effects of D-arginine appeared to be more pronounced in the WKY strain. Immediately following the bolus injections of the higher doses of D-arginine a transient decrease in both the systolic and diastolic pressure occurred. In contrast to the actions of D-arginine single bolus injections of L-arginine, 1-300 mg/kg, produced a dose-dependent sustained reduction in both the systolic and diastolic blood pressures of all rats. The threshold for the depressor actions of L-arginine was the same for NW, WKY and SH rats. The final dose of L-arginine (300 mg/kg), produced a significantly greater depressor effect in WKY and SH rats as compared to NW rats. The blood pressure remained elevated after the dose-response curve to D-arginine and, in order to determine whether D-arginine-treated rats are sensitive to the effects of other vasodilators and whether differences in vasoactive actions exist for vasodilators acting other than via nitric oxide synthesis, a dose-response curve to the calcium channel antagonist verapamil was constructed. Injections of verapamil, 0.1-1000 micrograms/kg, produced a dose-dependent reduction in blood pressure with no difference in either threshold or sensitivity to the actions of verapamil among the three strains of rats. Our results suggest that strain differences exist between the depressor actions of L-arginine and that it is possible that these differences may be due to an alteration in the endogenous levels of nitric oxide synthase and/or the activity of guanylate cyclase, however, no relationship to the hypertensive state of the spontaneously hypertensive rats was apparent.

Brain kinins are responsible for the pressor effect of intracerebroventricular captopril in spontaneously hypertensive rats.

The role of the brain kallikrein-kinin system in the regulation of arterial blood pressure of normotensive and spontaneously hypertensive rats was evaluated. Intracerebroventricular administration of the kinin antagonist [DArg0]Hyp3-Thi5,8[DPhe7]bradykinin caused no change in mean blood pressure in Wistar-Kyoto, Sprague-Dawley, or spontaneously hypertensive rats. The antagonist proved to be very potent in blocking the pressor effect of intracerebroventricular bradykinin (32 +/- 3 vs. 3 +/- 1 mm Hg, p less than 0.01). It was specific, as the pressor effect induced by other unrelated peptides was similar during the infusion of either vehicle or kinin antagonist (angiotensin II, 25 +/- 4 vs. 26 +/- 2 mm Hg; prostaglandin E2, 48 +/- 3 vs. 47 +/- 8 mm Hg; norepinephrine, 17 +/- 2 vs. 18 +/- 2 mm Hg; leucine-enkephaline, 15 +/- 2 vs. 16 +/- 1 mm Hg; neurotensin, 18 +/- 2 vs. 19 +/- 1 mm Hg; substance P, 19 +/- 2 vs. 19 +/- 2 mm Hg). Intracerebroventricular administration of 1 mg captopril, an inhibitor of kininase II (one of the enzymes responsible for kinin degradation), caused no change in mean blood pressure in normotensive rats, whereas it increased mean blood pressure by 44 +/- 9 mm Hg (p less than 0.01) in spontaneously hypertensive rats. This increase in mean blood pressure was blocked and then reversed into a hypotensive effect (22 +/- 6 mm Hg, p less than 0.05) during the infusion of kinin antagonist. Our data suggest that the pressor effect induced by intracerebroventricular captopril is due to a transient elevation in endogenous brain kinin levels, supporting the hypothesis that the brain kallikrein-kinin system plays a role in the central regulation of blood pressure in spontaneously hypertensive rats.

Food restriction reduces the blood pressure of the spontaneously hypertensive rat

Spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto (WKy) and Sprague-Dawley (S-D) rats were fed a normal diet on an ad libitum basis or the normal diet was reduced by 35 per cent prior to, during, and after high blood pressure became established in SHR. Weight loss occurred in all animals at all ages and was associated with effective inhibition of the acute rise in blood pressure and the exacerbation of pre-existing elevated blood pressure. Weight loss after high blood pressure had become well established also caused reduction in blood pressure. The purported normotensive WKy rats developed high blood pressure. Weight loss was not as effective in reducing blood pressure in WKy as in SHR. These findings are construed to mean that reduced body weight will ameliorate the inexorable rise in the genetically-programmed high blood pressure of SHR if instituted prior to, during, but not after high blood pressure has become well established.

Increased dietary calcium lowers blood pressure in the spontaneously hypertensive rat

The effect of increased dietary calcium on the development of hypertension in spontaneously hypertensive (SH) rats was investigated by feeding lab chow fortified with calcium carbonate (2.5% calcium, hCa) beginning at 4 wk of age. A control SH group was fed regular lab chow (1.2% calcium, rCa). Two groups of age-matched Wistar-Kyoto (WKY) rats were treated in parallel. Systolic blood pressure (BP) was measured weekly until the age of 18 wk using a tail cuff method. The hCa diet significantly attenuated the time course of hypertension in SH rats even though both SH groups eventually developed hypertension. The hCa also lowered BP in WKYs, but to a lesser extent. Urine output (24-hr volumes) was not affected by hCa, but in both SH and WKY groups fed the hCa diet, the excretion of Na +, K + and Ca ++ was markedly elevated at 11, 15, and 19 wk of age. Urine osmolality was also elevated. Plasma Na +, Ca ++ and osmolality were not significantly altered by the diet in either SH or WKY rats; plasma potassium was significantly lower in the SH group fed the hCa diet than in the group given rCa. The hCa diet did not significantly affect the body or heart, kidney, adrenal, or thymus weights. The results suggest that hCa diet may attenuate genetic hypertension by inducing an osmotic diuresis.

Studies on the role of vasopressin in blood pressure control of spontaneously hypertensive rats with established hypertension (SHR, stroke-prone strain).

We investigated the role of arginine-vasopressin (AVP) in maintaining the blood pressure of spontaneously hypertensive (SH) rats (stroke-prone strain) with established hypertension (22--28 weeks of age). In comparison with normotensive Wistar Kyoto (WKY) rats, plasma AVP concentrations of SH rats with benign hypertension (BH) were elevated twofold and in rats with severe or malignant hypertension (S-MH), fourfold. The height of the blood pressure was quantitatively related to plasma AVP in both BH and S-MH rats, the overall correlation coefficient being 0.66 (p less than 0.001). The intravenous injection of a specific AVP antiserum into conscious and unrestrained rats lowered blood pressure in 4 BH rats by 48 +/- 14 mm Hg and in 4 S-MH rats by 78 +/- 10 mm Hg and had only a marginal effect in 4 normotensive WKY rats. Infusion of saralasin did not lower blood pressure in WKY and BH rats and reduced blood pressure in only 2 of 7 S-MH rats tetsted (by 15 and 20 mm Hg). During AVP infusion the blood pressure of SH rats increased more (p less than 0.001) and heart rate fell much less (p less than 0.001) than in WKY rats. It is concluded that in SH rats with established hypertension, plasma AVP plays an important role in the maintenance of high blood pressure, while the renin-angiotensin system plays a minor or no role.