Prostaglandin endoperoxide‐dependent vasospasm in bovine coronary arteries after nitration of prostacyclin synthase

In the present study we used a bioassay to study the effects of peroxynitrite (ONOO − ) on angiotensin II (A‐II)‐triggered tension in isolated bovine coronary arteries in order to show the consequences of the previously reported PGI 2 ‐synthase inhibition by ONOO − in this model. The following results were obtained:1 μmol L −1 ONOO − impaired A‐II‐induced vasorelaxation and caused a second long lasting constriction phase. Indomethacin (10 −5 M ) prevented both effects. U51605, a dual blocker of PGI 2 ‐synthase and thromboxane (TX)A 2 ‐synthase mimicked the effects of ONOO − . The selective TXA 2 /prostaglandin endoperoxide (PGH 2 ) receptor antagonist SQ29548 antagonized the second vasoconstriction phase after ONOO − ‐treatment. Since a generation of TXA 2 and 8‐iso‐prostaglandin F 2α could be excluded a direct action of unmetabolized PGH 2 on the TXA 2 /PGH 2 receptor was postulated. ONOO − dose‐dependently inhibited the conversion of 14 C‐PGH 2 into 6‐keto‐PGF 1α in isolated bovine coronary arteries with an IC 50 ‐value of 100 n M . Immunoprecipitation of 3‐nitrotyrosine‐containing proteins with a monoclonal antibody revealed PGI 2 ‐synthase as the only nitrated protein in bovine coronary arteries treated with 1 μmol  l −1 ONOO − . Using immunohistochemistry a co‐localization of PGI 2 ‐synthase and nitrotyrosine‐containing proteins was clearly visible in both endothelial and vascular smooth muscle cells. We concluded that ONOO − not only eliminated the vasodilatory, growth‐inhibiting, antithrombotic and antiadhesive effects of PGI 2 but also allowed and promoted an action of the potent vasoconstrictor, prothrombotic agent, growth promoter, and leukocyte adherer, PGH 2 .British Journal of Pharmacology (1999) 126 , 1283–1292; doi: 10.1038/sj.bjp.0702434