Diuresis and natriuresis produced by long term administration of a selective Angiotensin-(1-7) antagonist in normotensive and hypertensive rats

In this study we evaluated the renal effects of chronic administration of the selective Angiotensin-(1-7) [Ang-(1-7)] antagonist, A-779, in normotensive and spontaneously hypertensive rats (SHR). Male adult SHR and Wistar rats were housed in metabolic cages with tap water and standard chow, for three-five days before starting infusion (Alzet osmotic mini-pumps) of A-779 (Wistar: 1 mu g/h, n = 9; 2.5 mu g/h, n = 6; SHR: 2.5 mu g/h, n = 6) or vehicle (0.9% NaCl - 1 mu l/h, n = 7 and n = 10 for SHR and Wistar rats, respectively). Urine volume, water and food intake and urinary Na+ were measured daily. On the last day of infusions mean arterial pressure (MAP) was recorded and urine and blood samples were collected to determine renal function parameters. Chronic infusion of A-779 produced a sustained increase in diuresis in normotensive rats [seventh day values: 0.75+/-0.08 ml/h (1 mu g/h) and 0.94+/-0.13 ml/h (2.5 mu g/h) vs. 0.42 + 0.03 ml/h for the control group, P < 0.05] associated to a dose-dependent increase in the creatinine clearance. In SHR, diuresis increased significantly after chronic infusion of A-779 (fifth day values: 0.44 + 0.06 ml/h vs. 0.25+/-0.04 ml/h for the control group, P < 0.05), without changes in creatinine clearance. Infusion of A-779 in normotensive rats produced a decrease in water reabsorption. A-779 infusion also produced a dose-dependent increase in urinary Na+ excretion (1.49 + 0.14 mEq, 1 mu g/h vs. 2.37+/-0.22 mEq, 2.5 mu g/h, P < 0.05), in Wistar rats, without modifying the fractional excretion of Na+. In SHR, urinary Na+ excretion was also increased by A-779 (2.21+/-0.46 mEq vs. 0.94 +/- 0.22 mEq for the control group, P < 0.05). No significant changes in blood pressure were observed. These findings suggest that endogenous Ang-(1-7) participates in the control of hydroelectrolyte balance by modulating water excretion, acting at tubular and glomerular sites. (C) 1998 Elsevier Science B.V.