Contribution of constrictor prostanoids to the calcium-dependent basal tone in the aorta from rats with aortic coarctation-induced hypertension: relationship to nitric oxide.

Rings of thoracic aortae taken from rats made hypertensive by aortic coarctation express a calcium-dependent basal tone. We investigated whether this basal tone is mediated by prostanoids. To this end, we contrasted the effects of indomethacin, an inhibitor of cyclooxygenase, and of ifetroban, an antagonist of thromboxane A2/prostaglandin endoperoxide H2 receptors, on basal tone in aortic rings taken from normotensive and hypertensive rats. Rings with endothelium from normotensive rats were unaffected by indomethacin and ifetroban. However, in endothelium-intact rings from hypertensive rats, the basal tone was reduced 65 to 75% by indomethacin and ifetroban, but not by CGS13080, an inhibitor of thromboxane synthase. The reductions in tone elicited by indomethacin and ifetroban in rings from hypertensive rats were eliminated upon removal of the endothelium and were attenuated when the rings were pretreated with an inhibitor of nitric oxide synthase (N omega-nitro-L-arginine methyl ester or N omega-nitro-L-arginine) or an inhibitor of soluble guanylate cyclase. Neither indomethacin nor ifetroban affected tissue cGMP levels or nitrite release in aortic rings taken from hypertensive rats. However, sodium nitroprusside offset the inhibitory effects of N omega-nitro-L-arginine methyl ester, on the relaxant responses to indomethacin and ifetroban. These data suggest that a constrictor prostanoid other than thromboxane A2, presumably prostaglandin endoperoxide H2 contributes to the implementation of the basal tone in rings from hypertensive rats and that part of the relaxant response to indomethacin and ifetroban is linked to nitric oxide.