Effect of elevated atrial pressure on plasma renin activity in hypotensive fetal lambs

In adults, renin secretion is stimulated by reductions in arterial pressure and inhibited by increases in atrial pressure. In the late gestation fetus, a fall in arterial pressure stimulates renin secretion, but it is unknown whether elevation of atrial pressure will alter such an increase. Therefore we studied the effect of elevated atrial pressure on renin secretion in the presence of nitroprusside-induced arterial hypotension. Thirteen fetal lambs at 127.9 +/- 0.9 days of gestation were prepared 5 days before study with inflatable pulmonary artery occluders and right atrial, vascular, and amniotic catheters. Each fetus underwent two protocols (hypotension and hypotension with occlusion) using a randomized block design. Nitroprusside reduced arterial pressure by 34% in both groups. Right atrial pressure during the course of hypotension was significantly higher in the occlusion group (F = 14.2, P = 0.001). Plasma renin activity increased similarly in both groups during hypotension (F = 6.0, P = 0.003). Elevated right atrial pressure did not alter hypotension-induced renin secretion in the fetus.