Effect of enalapril treatment on the pressure-natriuresis curve in spontaneously hypertensive rats.

The effect of chronic angiotensin I converting enzyme inhibition on the pressure-natriuresis relation was studied in Wistar-Kyoto and spontaneously hypertensive rats. Enalapril maleate (25 mg.kg-1.day-1 in drinking water) was started at 4-5 weeks of age. At 7-9 weeks of age, the pressure-natriuresis relation was studied while the rats were under Inactin anesthesia 1 week after the right kidney and adrenal gland were removed. Neural and hormonal influences on the remaining kidney were fixed by surgical renal denervation, adrenalectomy, and infusion of a hormone cocktail (330 microliters.kg-1.min-1) containing high levels of aldosterone, arginine vasopressin, hydrocortisone, and norepinephrine dissolved in 0.9% NaCl containing 1% albumin. Changes in renal function resulting from alterations in renal artery pressure were compared between enalapril-treated and control rats. Mean arterial pressure (+/- SEM) under anesthesia was 118 +/- 5, 94 +/- 4, 175 +/- 3, and 124 +/- 2 mm Hg for control Wistar-Kyoto (n = 10), enalapril-treated Wistar-Kyoto (n = 10), control spontaneously hypertensive (n = 9), and enalapril-treated spontaneously hypertensive (n = 9) rats, respectively. When renal artery pressure was set at values above approximately 125 mm Hg, control spontaneously hypertensive rats excreted less sodium and water than control Wistar-Kyoto rats. Enalapril treatment resulted in a significant and similar shift to the left of the pressure-natriuresis relation in both strains of rats so that a lower renal artery pressure was required to excrete a similar amount of sodium when compared with their respective untreated controls.(ABSTRACT TRUNCATED AT 250 WORDS)