Arterial pressure after chronic reductions in suprarenal aortic flow in fetal lambs.

Experiments were performed on 13 fetal lambs of 126 days gestational age. Seven days after surgery, suprarenal aortic blood flow was reduced to 70% of control with an inflatable occluder for a period of at least 4 days. This produced an almost constant aortic pressure difference of 35 mmHg across the occluder. Plasma renin activity (PRA) rose in the next hour from 6 to 42 ng.ml-1.h-1 (P less than 0.01) but decreased to a level that was statistically insignificantly above normal by the next day. PRA as a function of lower body arterial blood pressure showed rapid adaptation. Upper body arterial blood pressure was statistically significantly elevated by 5 mmHg within 5 min and continued to rise while plasma renin activity was falling. Femoral artery blood pressure dropped immediately but returned to near normal within 1 h and remained there. The long-term upper body hypertension was irreversible with a 30-min infusion of saralasin. Subrenal aortic flow reduction caused none of these changes. We conclude that the fetal kidneys can regulate arterial blood pressure upward but that the long-term effect does not depend solely on a direct vasoconstrictive action of angiotensin.