The role of Ang (1-7) in mediating the chronic hypotensive effects of losartan in normal rats

Hypothesis. The following studies were designed to test the hypothesis that Ang (1-7) contributes to the chronic hypotensive effects of the angiotensin II AT₁-receptor antagonist, losartan, in normal rats. Introduction. We have previously shown a chronic, hypotensive response to the AT₁-receptor antagonist, losartan, in normotensive rats. The mechanism of this response is not completely understood. Previous studies by others have demonstrated a role for Ang (1-7) in the beneficial antihypertensive effects of angiotensin-converting enzyme (ACE) inhibition. This is thought to be due to vasodilatory effects of increased levels of Ang (1-7) during ACE inhibition. Since it has now been shown that Ang (1-7) levels are also increased during AT₁ antagonism, we designed experiments to test the hypothesis above. Materials and methods. Sprague-Dawley rats were instrumented with venous catheters and radiotelemetric pressure transducers and commenced on a normal (0.4%) NaCl diet. Arterial pressure responses were measured in rats treated with losartan (10 mg/kg/day) (LOS rats, n=8) and compared with those treated with losartan and the Ang (1-7) antagonist, A779 (24 μg/kg/hour) (A779/LOS rats, n=11) for 10 days. Results. By day 7 of treatment, mean arterial pressure had dropped by 27±1 mmHg in LOS rats, in contrast with a decrease of only 21±2 mmHg in A779/LOS rats. This attenuated response in rats treated with A779 became more prominent and continued through day 10 of losartan treatment. Conclusion. These results support the hypothesis that the chronic hypotensive effects of losartan in normal rats are mediated in part through the actions of Ang (1-7).