Response of rat thoracic aortic rings to thromboxane mimetic U-46,619: roles of endothelium-derived relaxing factor and thromboxane A2 release.

Studies were designed to test the role of the endothelium and endogenous release of thromboxane (Tx) A2 in the contractile response of rat thoracic aortic rings to the TxA2/prostaglandin (PG) H2 mimetic, U-46,619. U-46,619 caused a dose-dependent contraction of rings with endothelium (mean ED50 = 6.54 +/- 3.02 x 10(-9) M; n = 13) which was abolished by the TxA2/PGH2 receptor antagonist, SQ-29,548. Removal of endothelium greatly potentiated (P less than .05) the contractile response to U-46,619 (ED50 = 4.78 +/- 2.14 x 10(-10) M; n = 14). On addition to the organ bath, oxyhemoglobin (10(-6) M), an inhibitor of endothelium-derived relaxing factor, increased vascular smooth muscle contraction in response to U-46,619 and abolished the difference in response between rings with endothelium (ED50 = 6.63 +/- 0.38 x 10(-11) M) and those without (ED50 = 5.13 +/- 0.18 x 10(-11) M). Vascular contraction with U-46,619 (10(-7] was associated with release of immunoreactive TxB2 and 6-keto PGF1 alpha as well as increased conversion of [14C]arachidonate to [14C]TxB2 and 6-keto-[14C]PGF1 alpha. To test the role of endogenous TxA2 in response to U-46,619, the TxA2 synthetase inhibitor UK-38,485 (10(-6) M) was added directly to the organ bath; this diminished (P less than .05) the contractile responses to U-46,619 of rings with and without endothelium.(ABSTRACT TRUNCATED AT 250 WORDS)