Structural and functional consequence of neonatal sympathectomy on the blood vessels of spontaneously hypertensive rats

Neonatal sympathectomy of spontaneously hypertensive rats (SHR) and control Wistar-Kyoto rats (WKY) was performed by a combined treatment with antiserum to nerve growth factor and guanethidine during the first 4 weeks after birth. The development of hypertension was completely prevented in the treated SHR: at 28 to 30 weeks of age, systolic blood pressure of treated SHR was 139 +/- 2 mm Hg as compared with 195 +/- 8 mm Hg in untreated SHR. The extent of sympathectomy was verified by histofluorescence. Fluorescence histochemistry for catecholamine-containing nerves showed a complete absence of adrenergic nerves in the mesenteric arteries of treated rats. A supersensitivity to norepinephrine was exhibited by mesenteric arteries, anococcygeus muscle, and tail arteries from the treated SHR and WKY. In the mesenteric vascular bed, maximal response to norepinephrine was significantly reduced by sympathectomy. Sympathectomy also abolished the responses (e.g., generation of excitatory junctional potentials) of tail arteries to electrical stimulation of perivascular nerves. Morphometric measurements of three categories of mesenteric arteries showed that sympathectomy had no effect on the hypertrophic change of smooth muscle cells in the conducting vessels, but it prevented the hyperplastic changes of the muscle cells from reactive, muscular arteries and small resistance vessels. These results suggest that one of the primary roles of the overactive sympathetic nervous system in the development of hypertension in SHR is manifested through its trophic effect on the arteries of SHR. This trophic effect appears to cause a hyperplastic change in the smooth muscle cells in the reactive and resistance vessels, thereby contributing to the development of hypertension in older SHR.     

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.     

Thromboxane synthesis and blood pressure in spontaneously hypertensive rats

The present study examines effects of administration of OKY 046, an inhibitor of thromboxane synthesis, for 100 days on systemic blood pressure and renal function in spontaneously hypertensive rats and in normotensive control rats. Untreated spontaneously hypertensive rats had higher values for thromboxane excretion in the urine and higher values for blood pressure than did normotensive control rats. Administration of OKY 046 decreased systolic and mean arterial blood pressure and urinary excretion of thromboxane and protein in spontaneously hypertensive rats. Administration of OKY 046 decreased thromboxane excretion in the urine of normotensive control rats but had no effect on blood pressure or protein excretion. Renal function, as assessed by the clearances of inulin and p-aminohippuric acid, was greater in spontaneously hypertensive rats treated with OKY 046 than in those receiving vehicle alone. In normotensive control rats, OKY 046 administration did not affect renal function. These results suggest that increased renal synthesis of thromboxane may play a role in the pathogenesis of the elevated blood pressure of spontaneously hypertensive rats.     

长期抑制大麻素受体-1对自发性高血压大鼠血压及血管功能的作用

目的观察长期应用内源性大麻素受体-1(CB1)抑制剂利莫那班对自发性高血压大鼠(SHR)血压及血管功能的作用。方法16只2月龄雄性SHR随机分为对照组(8只)和利莫那班组(8只)。每月测体重,无创法测鼠尾动脉收缩压;6个月后行颈动脉插管测颈动脉血压。检测大鼠胸主动脉对血管紧张素Ⅱ(AngⅡ)、去甲肾上腺素、乙酰胆碱和硝酸甘油的反应。Westernblot法检测胸主动脉内皮型一氧化氮合酶(eNOS)的表达。结果6个月后,利莫那班组体重明显低于对照组(P<0.05);鼠尾动脉和颈动脉收缩压低于对照组(P<0.05)。利莫那班组体外胸主动脉对AngⅡ诱导的收缩反应明显低于对照组(P<0.01),对乙酰胆碱及硝酸甘油诱导的舒张反应高于对照组(P<0.05)。利莫那班组胸主动脉eNOS的表达明显高于对照组(P<0.01)。结论长期抑制CB1受体能有效降低SHR血压,改善血管对AngⅡ的收缩反应及舒张功能,其机制为促进动脉eNOS的表达。     

缬沙坦对自发性高血压大鼠血压和肾素-血管紧张素水平的对照研究

目的:动物实验观察缬沙坦的降压效果及其对血浆肾素活性和血管紧张素Ⅱ的影响.方法:24只雄性14周龄的SHR分为生理盐水组、苯那普利组、小剂量缬沙坦和大剂量缬沙坦组,另用6 只同龄雄性WKY大鼠对照.观察用药4周前后的血压、肾素活性和血管紧张素Ⅱ水平.结果:与生理盐水组、苯那普利组比较,缬沙坦的降压效果明确;大剂量缬沙坦平均下降41.7±4.93 mmHg,明显大于小剂量组的降压幅度27.7±4.46 mmHg,(P <0.01).SHR与WKY大鼠比较,血浆肾素活性仅在大剂量缬沙坦组明显升高;血管紧张素Ⅱ水平,大剂量缬沙坦组更为明显升高,而苯那普利组有所下降.结论:缬沙坦的降压效果优于苯那普利,苯那普利使血浆AngⅡ水平减低,而缬沙坦使血浆AngⅡ水平升高.在长期用药过程中,较高的血浆AngⅡ水平对人体的影响或对器官的影响如何,尚待进一步研究.     

缬沙坦对自发性高血压大鼠血压和肾素—血管紧张素水平的对照研究

目的：动物实验观察缬沙坦的降压效果及其对血浆肾素活性和血管紧张素Ⅱ的影响。方法：２４只雄性１４周龄的ＳＨＲ分为生理盐水组、苯那普利组、小剂量缬沙坦和大剂量缬沙坦组,另用６只同龄雄性ＷＫＹ大鼠对照。观察用药４周前后的血压、肾素活性和血管紧张素对水平。结果：与生理盐水组、苯那普利组比较,缬沙坦的降压效果明确;大剂量缬沙坦平均下降 ４１． ７±４． ９３ ｍｍＨｇ,明显大于小剂量组的降压幅度 ２７． ７±４． ４６ ｍｍＨｇ,（Ｐ＜０．０１）。 ＳＨＲ与ＷＫＹ大鼠比较,血浆肾素活性仅在大剂量缬沙坦组明显升高;血管紧张素Ⅱ水平,大剂量缬沙坦组更为明显升高,而苯那普利组有所下降。结论：缬沙坦的降压效果优于苯那普利,苯那普利使血浆ＡｎｇⅡ水平减低,而缬沙坦使血浆ＡｎｇⅡ水平升高。在长期用药过程中,较高的血浆 Ａｎｇ Ⅱ水平对人体的影响或对器官的影响如何,尚待进一步研究。     

Protein kinase inhibitors and blood pressure control in spontaneously hypertensive rats

Considerable evidence suggests that protein kinase C activation participates in the regulation of vascular smooth muscle tone. The objective of the current study was to examine the relations between inhibition of protein kinase C (PKC) and myosin light-chain kinase (MLCK) and vasorelaxation and blood pressure regulation in spontaneously hypertensive rats (SHR). Putative PKC inhibitors from two chemical classes, staurosporinelike (staurosporine and K252A) and isoquinolinesulfonamides (H7 and HA1004), were tested for their ability to 1) inhibit PKC and MLCK from SHR aorta, 2) relax isolated SHR aorta, and 3) lower blood pressure in conscious SHR. A rank order of potency for the inhibition of PKC and MLCK was established, with the staurosporinelike compounds (staurosporine PKC IC50 = 54 nM) clearly more potent than the isoquinolinesulfonamides (H7 PKC IC50 = 128 microM). The rank order of potency for inhibition of PKC was retained for inhibition of MLCK for all compounds. Staurosporine (EC50 = 75 nM) and H7 (EC50 = 2 microM) caused concentration-dependent relaxation of SHR aorta, but only staurosporine produced vasorelaxation at concentrations consistent with the inhibition of PKC or MLCK. Dose-dependent reductions in arterial pressure of SHR were demonstrated after intravenous injection of staurosporine and HA1004. A single intravenous injection of staurosporine (0.3 mg/kg) lowered blood pressure for more than 10 hours. Staurosporine also lowered blood pressure after oral administration. The depressor response to staurosporine was unaffected by sympathetic beta-adrenergic blockade. In conclusion, the vasorelaxant and antihypertensive actions of staurosporine in SHR are consistent with the inhibition of PKC but could also be equally related to inhibition of MLCK. Not all PKC inhibitors produce vasorelaxation and lower blood pressure. Moreover, the lack of correlation between in vitro vasodilation and PKC or MLCK inhibition for the isoquinolinesulfonamide protein kinase inhibitors H7 and HA1004 suggests that these agents do not cause vasorelaxation in SHR by inhibition of these enzymes.     

Genetic association of hypertension and vascular changes in stroke-prone spontaneously hypertensive rats

Isolated tail arteries from stroke-prone spontaneously hypertensive rats (SHRSP) exhibit oscillatory contractile activity in response to norepinephrine, whereas those from normotensive Wistar-Kyoto rats (WKY) do not. To determine whether the norepinephrine-induced oscillations are related to high blood pressure or to separable genetic differences between strains, the response to norepinephrine was studied in adult SHRSP, WKY, and progeny of genetic crosses of SHRSP and WKY (F1, F2, F1 X SHRSP, F1 X WKY). Helical tail artery strips were mounted in a tissue bath for isometric force recording. Rats were classified as responders if oscillatory activity in the presence of 1.8 X 10(-7) M norepinephrine exceeded 250 mg/10 min (milligrams of force amplitude during a 10-minute interval). The blood pressures (mm Hg +/- SEM; tail cuff method) and percentage of rats exhibiting norepinephrine-induced oscillations were as follows: WKY: 109 +/- 3, 0%; F1: 129 +/- 4, 0%; F2: 150 +/- 4, 38%; F1 X WKY: 137 +/- 3, 9%; F1 X SHRSP: 188 +/- 7, 71%; SHRSP: 207 +/- 7, 100%. The distribution of the frequency of animals with oscillatory activity among the progenies was consistent with the hypothesis that a single gene locus determines the observed difference in oscillatory activity between the WKY and SHRSP strains. The allele from the SHRSP that determines the activity phenotype is recessive to the allele contributed by the normotensive WKY strain. In the segregating F2 progeny, the blood pressure of the responders was higher than that of the nonresponders (161 +/- 6 vs 144 +/- 4 mm Hg; p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Genetic analysis of blood pressure and sodium balance in spontaneously hypertensive rats

Blood pressure and parameters of sodium balance were measured during the first 16 weeks of life in male Okamoto spontaneously hypertensive rats (SHR, n = 22), Wistar-Kyoto rats (WKY, n = 25), and the F1 (n = 27) and F2 (n = 81) hybrids of the SHR and WKY. Genetic analysis revealed that blood pressure in SHR was controlled by approximately four independent genetic loci and the degree of genetic determination was 64.5%. No difference in blood pressure was discernible before 12 weeks of age between those F2 rats that at 16 weeks had blood pressures either higher or lower than one standard deviation from the mean. Exchangeable sodium was measured sequentially in individual rats of all populations by determining their whole-body radioactivity while receiving 37.5 mM 22Na/23NaCl drinking fluid of constant specific activity as their sole source of sodium. The SHR had consistently higher exchangeable sodium levels than WKY and showed evidence of relative sodium retention during the early developmental phase of hypertension. Sodium intake was higher in SHR than WKY from 4 to 16 weeks of age, although saline preference was the same in both strains. None of these parameters of sodium balance were found to correlate with blood pressure in the F2 population. It is concluded that the heritable abnormalities of sodium balance in SHR appear to represent coincidental inbred characteristics controlled by genetic loci that are unrelated to those loci responsible for the expression of hypertension in this model.     

钩藤总碱与天麻素联用对自发性高血压大鼠血压和血压变异性的影响

背景钩藤和天麻是治疗高血压的传统中药,常联合应用。目的研究钩藤、天麻的活性成分钩藤总碱及天麻素抗高血压和改善血压变异性的协同作用。方法 60只自发性高血压大鼠随机分为11组,分别是:对照组、钩藤总碱4组(25、50、100、200mg/kg)、天麻素3组(8、80、800mg/kg)、钩藤总碱+天麻素3组[(50+8)、(50+80)、(50+800)mg/kg],腹腔给药。采用清醒自由活动大鼠血压测定系统监测给药前后大鼠的血压和血压变异性。用两因素多水平析因设计、概率和法和q检验方法评价钩藤总碱和天麻素降压以及改善血压变异性的协同作用。结果在25～200mg/kg剂量范围内,钩藤总碱给药量与血压降低幅度有量效关系。其中,200mg/kg剂量组给药前后收缩压分别为(182±16)和(142±12)mmHg,舒张压分别为(133±21)和(100±19)mmHg,给药前后血压平均值的差异有统计学意义(P<0.01)。天麻素单独注射剂量达到800mg/kg也没有降低自发性高血压大鼠的血压。而钩藤总碱+天麻素组[(50+8)、(50+80)、(50+800)mg/kg]有降压作用,钩藤总碱和天麻素联用具有协同降压作用,对血压变异性没有不良影响。结论钩藤总碱具有确切的降压作用,但对血压变异性没有影响。天麻素本身不降低血压,但与钩藤总碱联用具有协同降压作用。     

Polymorphism in soluble epoxide hydrolase and blood pressure in spontaneously hypertensive rats

We measured soluble epoxide hydrolase (sEH) renal gene expression in prehypertensive (4 to 5 weeks old) spontaneously hypertensive rats of the Heidelberg SP substrain (SHR [Heid]) and when blood pressure levels entered the hypertensive plateau (17 to 18 weeks old) and compared expression with matched Wistar-Kyoto (WKY [Heid]) rats. Less expression of the gene encoding sEH (EPHX2) was observed in SHR (Heid) than in WKY (Heid). Analysis of sEH protein abundance showed a similar difference. However, no correlation between sEH abundance and blood pressure was observed in the F(2) progeny of a parental strain cross. Measurement of protein abundance in SHR and WKY obtained from Charles River confirmed a recent report that abundance of sEH was greater in SHR (CRiv) than WKY (CRiv) strains. Polymorphisms were detected in EPHX2. Resequencing revealed that 2 alleles of EPHX2 exist in these 4 rat strains, differing by 4 single nucleotide polymorphisms, of which 3 produce nonsynonymous amino acid substitutions. The ancestral allele was shared by SHR (Heid) and WKY (CRiv), and the variant allele was shared by WKY (Heid) and SHR (CRiv). Activity of sEH was greater in animals carrying the variant allele. However, inheritance of this allele was not correlated with blood pressure in the F(2) progeny of a cross between SHR (Heid) and WKY (Heid). These data indicate that sequence variation determining functional alterations in EPHX2 is not likely to contribute to blood pressure levels in SHR.     

Subacute and long term effect of swimming training on blood pressure in young and old spontaneously hypertensive rats

The effects of swimming training (three weeks' training with the duration increasing up to a maximum of 180 min per day, at a water temperature of 36 degrees C) on arterial blood pressure were studied in 4, 11, and 18 month old spontaneously hypertensive rats. In addition, in the 11 month old rats the change in blood pressure after individual exercise was determined. The significance of a training induced loss of body weight in lowering blood pressure was assessed by pair feeding of sedentary age matched spontaneously hypertensive rats. Blood pressure was reduced by approximately 50 mmHg within 8-10 days, except in the oldest rats, which tolerated the physical activity poorly and had, if any, only a moderate fall in blood pressure. It was possible to distinguish between subacute transient effects lasting for not more than one day and long term effects. Blood pressures were 20-25 mmHg lower after individual swimming routines than those before exercise when measured on the ninth day of the training programme. On cessation of training, blood pressures approached those of sedentary rats within two weeks. It seems that the loss of body weight was of minor importance in lowering blood pressure under these experimental conditions.     

Does vasopressin sustain blood pressure in conscious spontaneously hypertensive rats?

To investigate the possible role of arginine vasopressin in maintaining high blood pressure of spontaneously hypertensive rats (SHR), the effect of two arginine vasopressin pressor antagonists on mean arterial pressure and the pressor responsiveness to exogenous arginine vasopressin were studied in conscious, freely moving SHR and in Wistar-Kyoto rats (WKY). Intravenous injections of either d(CH2)5Tyr(Me)arginine vasopressin, 10 micrograms/kg, or dPTyr(Me)arginine vasopressin, 20 micrograms/kg, had no effect on mean arterial pressure or heart rate of normohydrated SHR, although both antagonists almost completely abolished the pressor response to exogenous arginine vasopressin. Furthermore, dPTyr(Me)arginine vasopressin was ineffective in eliciting a depressor response, even after 24 or 48 hours of water deprivation. During converting enzyme inhibition with SQ 20881, mean arterial pressure and heart rate remained unchanged following arginine vasopressin blockade in both normohydrated and fluid-restricted animals. alpha-Adrenergic receptor blockade reduced the blood pressure of normohydrated SHR, from 160 +/- 7 to 81 +/- 8 mm Hg. When dPTyr(Me)arginine vasopressin was given during alpha-adrenergic receptor blockade there was a small, transient fall in mean arterial pressure. The pressor responsiveness to exogenous arginine vasopressin was similar in hypertensive and normotensive rats. These results suggest that arginine vasopressin does not function as an important pressor hormone in conscious SHR.     

Contribution of blood pressure variability to the effect of nitrendipine on end-organ damage in spontaneously hypertensive rats

OBJECTIVE: It has been proposed that blood pressure variability (BPV) is positively related to end-organ damage (EOD) in hypertension. The present work was designed to observe the effects of long-term treatment with nitrendipine and hydralazine on BPV and EOD in spontaneously hypertensive rats (SHR), to examine the hypothesis that lowering BPV with an antihypertensive drug is an important factor in organ protection. DESIGN AND METHODS: Drugs were mixed in rat chow. After 4 months of drug administration, blood pressure was recorded continuously in conscious freely moving rats for 24 h. The heart, kidneys, and brain were then isolated and examined. RESULTS: It was found that nitrendipine significantly decreased blood pressure and BPV, and significantly decreased EOD score in SHR. Hydralazine decreased blood pressure, but did not lower BPV. No effect on EOD was found in hydralazine-treated rats. In control rats (n = 38), EOD score was weakly related to systolic blood pressure (r = 0.331, P < 0.05) and closely related to long-term systolic BPV (r = 0.551, P < 0.01). In nitrendipine-treated rats, EOD score was closely related to long-term systolic BPV (r = 0.602, P < 0.01), but not to BP level (r = 0.174, P > 0.05). CONCLUSION: BPV plays an important role in the organ-protecting effects of nitrendipine.     

Vascular oxidative stress precedes high blood pressure in spontaneously hypertensive rats

This study examines whether longitudinal antioxidant treatment initiated in prehypertensive spontaneously hypertensive rats (SHR) can attenuate vascular oxidant stress and prevent blood pressure elevation during development. Male SHR and age-matched Wistar-Kyoto rats (WKY) were treated from 6 to 11 weeks of age with Tempol (4-hydroxy-2,2,6,6-tetramethylpiperidinoxyl) (1 mmol/l in drinking water), a membrane-permeable superoxide dismutase mimetic. Mean systolic blood pressures (SBPs) were measured by tail-cuff Agonist-induced and basal O2- production was measured in thoracic aortas of 6- and 11-week-old SHR and WKY by lucigenin-derived chemiluminescence and oxidative fluorescent microscopy, respectively. SBP of 6-week-old SHR (131 +/- 5 mmHg) and WKY (130 +/- 4 mmHg) were not different; however, 11-week-old SHR SBP (171 +/- 4 mmHg) was significantly greater (p = .0001) than 11-week-old WKY SBP (143 +/- 5 mmHg). Tempol treatment completely, but reversibly, prevented this age-related rise in SHR SBP (SHR + Tempol: 137 +/- 4 mmHg; p < .0001 versus untreated SHR). Agonist-induced vascular O2- was increased in 6- (p = .03) and 11-week-old SHR (p < .0001) and 11-week-old WKY (p = .03) but not in 6-week-old WKY. Long-term Tempol treatment significantly lowered O2- production in both strains. Basal O2- measurements in both 6- and 11-week-old SHR were qualitatively increased compared with age-matched WKY; this increase in SHR was inhibited with in vitro Tempol treatment. These data show that antioxidant treatment to reduce oxidative stress prevents the age-related development of high blood pressure in an animal model of genetic hypertension.     

Parathyroid hormone-related protein overexpression decreases blood pressure in spontaneously hypertensive rats

We have recently demonstrated that arterial PTHrP expression and cardiovascular responses to this protein are altered in SHR compared with normotensive animals, Wistar Kyoto (WKY) and Sprague-Dawley (SD) rats. To investigate whether the slightly, but significantly decreased, aortic PTHrP gene expression observed in SHR, compared to that of normotensive animals, may play a causative role in the maintenance of the elevated arterial blood pressure (ABP) of the SHR, we transfected a hepatic lobe with a PTHrP expression vector in a sense and antisense orientation. At 24 and 48 hours, sense pSV2neo-ECE induced a significant five-fold increase in PTHrP mRNA abundance with respect to antisense pSV2neo-ECE and vehicle. This increment in the PTHrP mRNA induced by the sense PTHrP expression vector was totally inhibited by the co-administration of the antisense PTHrP expression vector. At the same time, we observed a significant decrease of mean ABP (MABP) in SHR transfected with the sense pSV2neo-ECE to similar values as those obtained in the normotensive strain. Neither antisense PTHrP expression vector nor vehicle had any significant effect in any strain. Again, the effect of the sense PTHrP expression vector on MABP was blocked by the simultaneous treatment with the antisense PTHrP expression vector. At 48 hours, the hypotensive effect of the sense pSV2neo-ECE in SHR was reverted by the i.v. bolus injection of a specific competitive PTHrP receptor antagonist such as Nle8,18,Tyr34-bPTH(3-34)amide. We propose that a defect of this potent local vasodilator may contribute to the development and/or maintenance of arterial hypertension in SHR. This defect can be ameliorated by transfecting tissues with protein-exporting capabilities, such as the liver. Finally, our work adds additional data to a cumulative body of evidence suggesting that it might be possible to design an effective gene therapy to treat the common polygenic and multifactorial form of hypertension by increasing the activity of potent and physiological vasodilators.     

A high phosphate diet lowers blood pressure in spontaneously hypertensive rats

Plasma phosphate values are significantly lower in spontaneously hypertensive rats (SHR) than in normotensive Wistar-Kyoto rats (WKY). In this study, we increased plasma phosphate in SHR by a dietary phosphate intake and followed the effects on blood pressure. Fifteen male WKY and 15 male SHR were housed from 4 weeks of age up to 26 weeks. At 4 weeks of age all SHR manifested a hypophosphatemia compared with age-matched WKY (F = 62, p less than 0.0003). At 5 weeks of age, the rats were divided into three diet groups: a control group, a group receiving 1.41% (wt/vol) KCl in drinking water, and a group receiving 2% (wt/vol) K2HPO4 X KH2PO4 in drinking water. In the control (F = 16.2, p less than 0.02) and KCl groups, (F = 36.3, p less than 0.03), hypophosphatemia persisted throughout the study. The phosphate-supplemented diet normalized plasma phosphate level in SHR but did not change plasma phosphate level in WKY. As a consequence, no difference in plasma phosphate level between WKY and SHR was present in the group receiving additional phosphate from that time on (F = 1.2, p greater than 0.41). The phosphate-supplemented diet significantly decreased systolic blood pressure in both strains. In phosphate-supplemented SHR, a significant decline in systolic blood pressure was observed from 20 weeks of age on (at 20 weeks of age: 222 +/- 3 mm Hg for control SHR vs 198 +/- 5 mm Hg for phosphate-supplemented SHR; p less than 0.0003).(ABSTRACT TRUNCATED AT 250 WORDS)