Abstract
1. In the fetal lamb, suprarenal aortic blood flow reduction is known to lead to an upper body hypertension. The dependency of this hypertension on the renin-angiotensin system was investigated. 2. Intravenous infusions of saralasin or saline vehicle were begun before suprarenal aortic blood flow reduction and continued for 24 h. 3. In those fetuses receiving saline, upper body arterial blood pressure was significantly elevated both 60 min (P < 0.05) and 24 h (P < 0.05) after blood flow reduction. In those fetuses receiving an infusion of saralasin, upper body arterial blood pressure failed to rise after 60 min of blood flow reduction. However, 24 h later, blood pressure was elevated (P < 0.05), though the increase was not as great as that seen in the saline infused fetuses (P < 0.05). 4. From these results, we conclude that the initial increase in upper body arterial blood pressure seen after suprarenal aortic blood flow reduction is dependent upon the renin-angiotensin system. However, as early as 1 day later, some other mechanism is responsible for sustaining the hypertension.