ENDOGENOUS PROSTANOIDS MODULATE THE ACTH AND AVP RESPONSES TO HYPOTENSION IN LATE-GESTATION FETAL SHEEP

We have previously reported that prostaglandin E-2 and thromboxane A(2 ) stimulate endocrine and cardiovascular responses similar to the resp onses to arterial hypotension. The present experiments were designed t o test the hypothesis that prostanoids are involved in the generation of responses to hypotension induced by vena cava occlusion. Fetal shee p were either intact or subjected to a prior carotid sinus denervation and bilateral vagosympathetic nerve section. Indomethacin or vehicle was injected intravenously 90 min before the start of arterial hypoten sion. In intact fetuses treated with phosphate buffer, ACTH increased significantly from 83 +/- 39 to 3,611 +/- 774 pg/ml, arginine vasopres sin (AVP) increased from 3.9 +/- 0.5 to 1,079 +/- 549 pg/ml, and corti sol increased from 4.7 +/- 0.8 to 9.5 +/- 1.7 ng/ml. Indomethacin trea tment significantly reduced the magnitudes of the hormonal responses. Baroreceptor and chemoreceptor denervation attenuated the ACTH and AVP responses, but these responses were not further inhibited by indometh acin. We conclude that endogenous prostanoids partially mediate the re flex hormonal and hemodynamic responses to arterial hypotension in lat e-gestation fetal sheep.