Effect of losartan and enalapril on renal adaptation sodium restriction in rat.

The influence of losartan (10 or 30 mg.kg-1.day-1), enalapril (10 mg.kg-1.day-1), and combined treatment by losartan and enalapril on the renal adaptation to dietary sodium withdrawal was assessed in normal rats. Treatments were given by gavage for 3 days before and during the 6-day period of low-sodium (LS) diet. Cumulative sodium excretion during LS was similar in untreated and low-dose losartan groups (0.62 +/- 0.07 and 0.75 +/- 0.07 mmol/6 days), whereas it was significantly increased in groups treated by the high dose of losartan and enalapril alone or combined with both doses of losartan (1.38 +/- 0.16, 1.50 +/- 0.10, 1.37 +/- 0.16, and 1.12 +/- 0.03 mmol/6 days, respectively). A decrease in conscious systolic arterial pressure was observed in all treated groups in response to LS. At the end of LS, conscious renal blood flow (microsphere method) was similarly increased in all treated groups. Creatinine clearance decreased to a similar extent with both doses of losartan, whereas a further reduction was observed with enalapril given alone or combined with losartan. These results demonstrate that the enalapril-induced disturbance in the response of renal sodium excretion to LS is mainly related to angiotensin-mediated mechanisms. However, non-angiotensin-related actions of enalapril may contribute to the deterioration of renal function in sodium-restricted animals. In addition, a high dose of losartan is required to impair renal sodium conservation, thus suggesting that the tubular renin-angiotensin system may play a crucial role in the renal adaptation to dietary sodium withdrawal.