Low-dose angiotensin II reduces urinary cyclic AMP excretion in spontaneously hypertensive, but not normotensive, rats: independence from hypertension and renal hemodynamic effects of angiotensin.
Chronic daily administration of cilazapril (1 X 10 mg/kg/day p.o., from age 4 to 14 weeks) to young spontaneously hypertensive rats (SHR) prevented the development of hypertension. The antihypertensive effect of a single dose of cilazapril persisted greater than 24 h. Discontinuation of long-term treatment resulted in an increase of systolic arterial blood pressure (SAP) to control hypertensive levels within 4 days. Following 10 weeks of drug administration, comparative hemodynamic studies were carried out on age-matched (14 weeks) control SHR and cilazapril-treated SHR. Cilazapril-treated SHR had a significantly lower mean arterial blood pressure (MAP) and total peripheral vascular resistance than did control SHR. The antihypertensive effect of cilazapril was not associated with changes in heart rate (HR). The myocardial performance parameters, cardiac output, and stroke volume, were similar in treated and control SHR, suggesting that the antihypertensive effect of cilazapril following chronic administration to SHR is mainly due to a reduction in peripheral vascular resistance. Vasopressor responses to angiotensin I were significantly lower in cilazapril-treated SHR than in control SHR. By contrast, pressor responses to angiotensin II and a high dose of norepinephrine (1.0 microgram/kg i.v.) were significantly enhanced. Isoproterenol elicited a fall in blood pressure in both groups, the extent of which was dependent upon the magnitude of basal blood pressure levels. Chronic cilazapril treatment resulted in a reduction of heart weight, suggesting that the drug may prevent development of cardiac hypertrophy in SHR. Kidney and adrenal weights were unaffected by the chronic treatment. Specific renin activities (SRA) in tissues of SHR were increased by factors of 20 (plasma) or 2 (kidney and adrenal) following cilazapril administration.(ABSTRACT TRUNCATED AT 250 WORDS)