Prostaglandin endoperoxide-dependent vasospasm in bovine coronary arteriesafter nitration of prostacyclin synthase

In the present study we used a bioassay to study the effects of peroxynitri te (ONOO-) on angiotensin II (A-II)-triggered tension in isolated bovine co ronary arteries in order to show the consequences of the previously reporte d PGI(2)-synthase inhibition by ONOO- in this model. The following results were obtained: 1 mu mol L-1 ONOO- impaired A-II-induced vasorelaxation and caused a second long lasting constriction phase. Indomethacin (10(-5)M) prevented both eff ects. U51605, a dual blocker of PGI(2)-synthase and thromboxane (TX)A(2)-sy nthase mimicked the effects of ONOO-. 2 The selective TXA(2)/prostaglandin endoperoxide (PGH(2)) receptor antagon ist SQ29548 antagonized the second vasoconstriction phase after ONOO--treat ment. Since a generation of TXA(2) and 8-iso-prostaglandin F-2 alpha could be excluded a direct action of unmetabolized PGH(2) on the TXA(2)/PGH(2) re ceptor was postulated. 3 ONOO- dose-dependently inhibited the conversion of C-14-PGH(2) into 6-ket o-PGF(1 alpha) in isolated bovine coronary arteries with an IC50-value of 1 00 nM. 4 Immunoprecipitation of 3-nitrotyrosine-containing proteins with a monoclo nal antibody revealed PGI(2)-synthase as the only nitrated protein in bovin e coronary arteries treated with 1 mu mol l(-1) ONOO-. 5 Using immunohistochemistry a co-localization of PGI(2)-synthase and nitro tyrosine-containing proteins was clearly visible in both endothelial and v ascular smooth muscle cells. We concluded that ONOO- not only eliminated th e vasodilatory, growth-inhibiting, antithrombotic and antiadhesive effects of PGI(2) but also allowed and promoted an action of the potent vasoconstri ctor, prothrombotic agent, growth promoter, and leukocyte adherer, PGH(2).