摘要:

No. Abstract

ISSN:0194-911X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

In inbred dogs with neonataiiy induced coarctation hypertension, prior serial studies during the first year after aortic banding showed extracellular volume excess with normal plasma renin activity (PRA). The present studies test the hypothesis that slowly evolving aortic constriction in this model will yield intrarenal angiotensin II excess, peripherally undetectable, with continuous slightly positive sodium balance, and thus that chronic blockade of angiotensin II formation will prevent generation of hypertension. Accordingly, we used MK421 (enalapril, mg/kg twice daily), a long-acting angiotensin converting enzyme inhibitor, or placebo, administered orally, from the time of banding through 4 months after banding in sex-matched littermates randomly assigned to one of four groups: coarcted/MK421; control/MK421; coarcted/placebo; control/placebo. Results indicate that MK421 caused identical lowering of absolute forelimb systolic blood pressure in coarcted and control pups but failed to modify evolution of a significant (p< 0.005) systolic blood pressure difference hi coarcted versus control dogs. Thus, neither temporal course nor final magnitude of relative hypertension was altered by MK421. Efficacy of MK421 was documented by 83% inhibition of the pressor response to angiotensin I at nadir of drug effect and by sustained increases in angiotensin I and renin concentration throughout the period of study. Coarcted and control pups responded similarly to MK421 for all measured variables. Glomerular nitration rate and extracellular volume (measured by [MC]inulin disappearance) did not differ among groups. Thus, chronic administration of MK421 failed to prevent hypertension and did not impair maintenance of normal renal function in the evolving phase of neonataiiy induced coarctation hypertension. We conclude that, although angiotensin II may participate in the untreated model, it does not appear essential to generation of hypertension. We propose that the renal pressure-natriuresis mechanism regulates distal pressure, that stenosis-related resistance independently determines the proximal-distal difference, and that chronic converting enzyme inhibition lowers the set point of the former without influencing stenosis evolution, thus secondarily lowering proximal pressure by an equal degree.

ISSN:0194-911X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

Carotid arteries from control and deoxycorticosterone acetate (DOCA) hypertensive swine were examined for alterations in structure and in contractile properties. Vessels were excised 7 weeks after subcutaneous implantation of the steroid and subsequent elevation in mean arterial pressure from 102 to 133 mm Hg. The carotid media was 1.8 times thicker in arteries from hypertensive animals than in arteries from control animals. This enlargement was associated with an increase in muscle mass, as the fraction of the media composed of smooth muscle cells remained unchanged. Maximal active stress induced by several agonists normalized for cell cross-sectional area was unaltered. No change was observed in sensitivity or maximal response to norepinephrine, histamine, or KC1 depolarization. Isotonic shortening rates were also comparable, as was the time course of shortening velocity to a constant afterload during tonic contractions. It is concluded that an enlargement of the carotid media develops in this model of hypertension. However, this response is not associated with detectable alterations in contractile system function.

ISSN:0194-911X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

The objective of these studies was to investigate the role of arterial baroreceptors in the control of neurohypophyseal secretion. The effect of sinoaortic denervation on basal and osmoticinduced release of oxytocin and vasopressin and on blood pressure was determined. Hypertonic or isotonic saline was infused intravenously into sham-operated or denervated rats 3 days after surgery. Plasma oxytocin and vasopressin were measured at 5 and 15 minutes after the infusion. The control levels of oxytocin were increased in the denervated rats, but vasopressin levels were not significantly altered. The vasopressin and oxytocin responses to hypertonic saline were greater after baroreceptor denervation. Plasma oxytocin was increased from 4.7±0.9 to 72.2±8.7 pg/ml in the denervated rats and from 1.8±0.3 to 39.9±6.7 pg/ml in the shamoperated control group at 5 minutes after the infusion (p< 0.01). The plasma vasopressin response to hypertonic saline was 7.1 ±0.6 pg/ml in the sham-operated versus 11.1±1.6 pg/ml in the denervated rats (p< 0.05). There was no difference between sham-operated and denervated rats hi the effect of hypertonic saline on plasma sodium and hematocrit. Mean arterial blood pressure was increased after sinoaortic denervation (116.3±4.2 mm Hg in the sham-operated vs. 138.2±8.3 mm Hg in the denervated rats,p< 0.05); however, there was no difference in the pressor response to hypertonic saline. These results show that the baroreceptor system influences the secretion of both oxytocin and vasopressin, with effects on basal secretion as well as the response to an osmotic stimulus. These changes may be important in the regulation of cardiovascular and fluid balance under conditions of baroreceptor deficiency.

ISSN:0194-911X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

The influence of chronic treatment with the angiotensin I converting enzyme (ACE) inhibitor enalapril on blood pressure, kidney function, and survival was examined in stroke-prone spontaneously hypertensive rats (SHRSP). Male SHRSP that were fed a Japanese rat chow plus a 1% NaCl drinking solution beginning at 7–8 weeks of age developed severe hypertension and stroke; 14 of 18 untreated control SHRSP died by 14 weeks of age and exhibited evidence of cerebrovascular lesions. When enalapril (15 mg/kg/day) was included in the drinking solution of 15 SHRSP, blood pressure was initially reduced by only a slight degree, whereas survival unproved markedly; only one of 10 SHRSP died before the rest were killed at 18 to 21 weeks. The remaining five enalapril-treated SHRSP lived beyond 36 weeks and on histological examination exhibited no evidence of cerebrovascular lesions. Chronic enalapril treatment also prevented the greater urinary excretion of protein and severe renal lesions observed in untreated SHRSP but did not affect urinary salt and water excretion. In anesthetized rats, glomerular filtration rate and tubular reabsorption of water were lower hi untreated control SHRSP when compared with enalapril-treated SHRSP. Mean arterial pressure was comparable in both groups. These data support a possible role for ACE inhibition in the prevention of stroke and maintenance of kidney function independent of any marked change in blood pressure of SHRSP. Whether the protective effects of ACE inhibition relate to reduced angiotensin H formation, increased tissue kinins, or another mechanism remains to be determined.

ISSN:0194-911X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

A high salt diet has been shown to increase renal mass of intact rats, although the mechanism by which this occurs has not been investigated. We used Dahl rats that are sensitive (DS) or resistant (DR) to the hypertensinogenic effect of salt to examine changes in renal size and composition caused by a high salt diet. Renal index, deoxyribonudeic add (DNA), protein, water content, protein/DNA ratio, and cell number and size were measured in age-matched DR and DS on a high salt diet for 7,14, or 28 days. The results were compared with those obtained from respective rats on a low salt diet. High salt diet elevated renal index and protein hi DR and DS rats at each time point. After 7 days of a high salt diet, DNA increased in DS only. Protein/DNA ratio was progressively decreased by a high salt diet in DS and remained unchanged in DR rats. Cell number was increased 35% in DS versus only 13% in DR rats at 4 weeks. Cell size decreased 24% in DS and only 11% in DR rats. These results indicate that renal growth due to hyperplasia accompanies ingestion of a high salt diet in both DR and DS rats, but the rate of growth and the mechanism through which it occurs differ between strains. This difference may be important in delineating salt sensitivity and future development of hypertension.

ISSN:0194-911X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

The objectives of this study were to determine the hemodynamic and microcirculatory changes that occur during reduced renal mass hypertension in rats. In conscious animals with 75% reduction of total renal mass, mean arterial pressure was initially (4–8 hours) elevated by 15–20 mm Hg during intravenous infusion with isonatremic (145.4 mM) NaCl. Cardiac index was elevated by 15–20%, and total peripheral resistance index was normal or reduced. Cardiac index subsequently returned toward normal, but mean arterial pressure remained elevated (20–40 mm Hg), presumably because of an elevated total peripheral resistance. Cremasteric arterioles were actively constricted (35–50%) in rats with short-term (36 hours), but not chronic (5–6 weeks) reduced renal mass hypertension. Total microvessel density was approximately 15% lower in maximally dilated cremaster muscles of chronically hypertensive rats versus sham-operated controls, which suggests that arterioles are lost during sustained reduced renal mass hypertension. Arteriolar constriction in response to increased superfusate Po2(0% to 5% O2) was 2–4 times greater in rats with both short-term and chronic reduced renal mass hypertension than in normotensive controls, which suggests that oxygen-dependent autoregulatory mechanisms are altered. The hemodynamic and microcirculatory alterations observed in these experiments suggest that classic short-term autoregulatory mechanisms and an enhanced response of arterioles to increased oxygen availability contribute to the elevated total peripheral resistance in short-term reduced renal mass hypertension, whereas structural changes and altered vascular oxygen responses contribute to an elevated microvascular resistance in chronic reduced renal mass hypertension.

ISSN:0194-911X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

The fluorescent indicator chlortetracycline was used to estimate membrane-bound calcium in mild, untreated hypertensive patients (n=39) and normotensive controls (n=42). All participants were black. After incubation with chlortetracycline, platelet-rich plasma was centrifuged into a pellet and fluorescence was measured with a microspectrofluorometer. At an interval of 45 minutes mean fluorescence values were 11% higher in the hypertensive than in the normotensive group (567±95 vs. 512±100 counts/sec,p< 0.02). With both groups of participants combined, a correlation of borderline statistical significance was noted between diastolic blood pressure and chlortetracycline fluorescence (r=0.213,p=0.056). In parallel experiments, sodium and potassium concentrations were measured in red blood cells. Intracellular sodium was also significantly higher hi the hypertensive group (p< 0.01). These data indicate that the total cell burden of calcium is increased in the platelets of hypertensive individuals, possibly a result of abnormal cell metabolism of calcium, and further suggest that circulating platelets in hypertensive individuals may be hi a hyperaggregable state.

ISSN:0194-911X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

This study employs multivariate normal mixture analysis, a technique for identifying discrete subgroups within populations, to examine the relation of erythrocyte lithium-sodium (RBC Li+-Na+) countertransport and blood pressure in a group of 474 healthy adults. After adjusting for effects of age, gender, race, height, and weight, univariate mixture analysis of the distribution of mean arterial blood pressure (MAP) revealed the presence of only one group, whereas the distribution of RBC Li+-Na+countertransport values was composed of a mixture of two groups (p< 0.00005). When bivariate mixture analysis was applied to the combined distribution of MAP and RBC Li+-Na+countertransport, two commingled subgroups were identified (p< 0.00005). The smaller group (19%) had significantly higher values for both MAP (108.7±16.7 mm Hg, mean±SD) and RBC Li+-Na+countertransport (0.455±0.147 mmol Li+/1 cells · hr) than the larger (81%) group (MAP 93.3±12.2 mm Hg, RBC Li+-Na+countertransport 0.247±0.080 mmol Li+/1 cells · hr,p≤ 0.0001 for both differences). The relation of MAP to RBC Li+-Na+countertransport was distinctly different in these two subgroups. In the larger group, we found a weak positive (r= 0.21,p≤ 0.0001) correlation for unadjusted values, which was not significant after adjustment. The smaller group, with higher levels of MAP and RBC Li+-Na+countertransport, showed significant negative correlations for both unadjusted (r= −0.28,p≤ 0.008) and adjusted (r= −0.41,p≤ 0.0001) values.

ISSN:0194-911X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

We examined the prevalence of left ventricular structural and functional abnormalities in previously untreated subjects by performing echocardiography in 89 normal volunteers, 57 patients with established hypertension, and 38 patients with mild or borderline hypertension. We measured left ventricular mass, wall thickness, internal diameter, and wall thickness/radius ratio. Because of intergroup differences hi body size, we used covariance analysis to index these variables to a common value of 1.8 m2. No adjustment was needed for the wall thickness/radius ratio. Functional variables determined were fractional shortening and transmitral early/late flow velocity ratio (the latter was standardized by analysis of covariance to age 40 years). The prevalence of left ventricular mass index values more than 2 SD above the mean of the normal group was 30% in the patients with established hypertension and 12–15% hi the patients with mild hypertension. Corresponding figures for wall thickness index were 65% and 32% and for the wall thickness/radius ratio 60% and 40%. The prevalence of abnormality in the transmitral flow velocity was 28% in the patients with established hypertension and 12% in the patients with mild hypertension. A multivariate discriminant function that used combined anatomic and functional variables provided the most reliable classification; it was correct in 82% of normal subjects, 65% of patients with established hypertension, and 61% of patients with mild hypertension. The majority of patients with hypertension have cardiac structural or functional abnormalities, or both.

ISSN:0194-911X    

出版商:OVID    

年代:1989

数据来源: OVID