Naloxone attenuates development of hypertension in two-kidney one-clip Goldblatt rats

The present experiments were designed to determine if an opiate antagonist affects blood pressure in two-kidney one-clip Goldblatt rats. Male Sprague-Dawley rats were divided into three groups. Group 1 received an infusion of saline intraperitoneally via an osmotic pump and left renal artery constriction (RAC). In group 2, rats were treated the same as group 1, except that they received an intraperitoneal infusion of naloxone (100 micrograms/h). Group 3 received the same infusion of naloxone without RAC. Naloxone-infused Goldblatt rats showed a significantly lower systolic blood pressure (SBP) than saline-infused Goldblatt rats (132 +/- 7 vs. 160 +/- 9 mmHg at day 14), but a higher SBP than control (132 +/- 7 vs. 106 +/- 1 mmHg). Infusion of naloxone did not significantly change SBP in normotensive rats. Renal renin activity in the clipped kidney was higher than in the nonclipped kidney in groups 1 and 2. Plasma renin activity (PRA) in both groups of Goldblatt rats was higher than in group 3, but no significant difference was found between the two groups of Goldblatt rats (groups 1 and 2). Naloxone (1.5 microM) did not affect the basal secretion of renin by isolated cortical slices from untreated rats. The present data demonstrate that naloxone significantly attenuates the development of hypertension in two-kidney one-clip rats. The attenuation of blood pressure was not associated with the changes in PRA, renal renin activity, or plasma aldosterone concentrations. The data support the hypothesis that the endogenous opioid system may be involved in the development of renovascular hypertension.