To test the hypothesis that prostanoids contribute to angiotensin H-induced vascular contraction, we compared the effect of angiotensin II on isometric tension development by rings of descending thoracic aorta bathed in Krebs' bicarbonate buffer with and without indomethacin (10 fiM) to inhibit cyclooxygenase, CGS13080 (10 fiM) to inhibit thromboxane A2 synthesis, or SQ29548 (1 fiM) to block thromboxane A2/prostaglandin endoperoxide receptors. The comparisons were made in rings of aorta taken from nonnotensive rats and from rats with aortic coarctation-induced hypertension at 12 days and 90-113 days after coarctation. These rings released thromboxane B2, which was found to be endothelium dependent, increased in hypertensive rats, and stimulated by angiotensin II (10~6 M) in normotensive rats and in hypertensive rats at 12 days after coarctation. The angiotensin II (10~6 to 10~5M)-induced contraction of aortic rings was increased by about 30% at 12 days after coarctation and decreased at 90-113 days after coarctation. Removal of the endothelium increased the contractile effect of angiotensin II (10"' M) in aortic rings of normotensive rats and hypertensive rats at 90-113 days after coarctation but decreased the effect in aortic rings of hypertensive rats at 12 days after coarctation. In rats at 12 days after coarctation, the angiotensin II (10~6 M)-induced contraction of aortic rings with endothelium was attenuated by indomethacin and SQ29548 but not by CGS13080. These data suggest that a prostanoidmediated and endothelium-dependent mechanism of vasoconstriction contributes to the constrictor effect of angiotensin II in aortic rings of rats in the early phase of aortic coarctation-induced hypertension.