We have previously shown that peroxynitrite (PN) selectively impaired prostacyclin (PGI2)- dependent vasorelaxation by tyrosine nitration of PGI2 synthase in an in situ model (Zou MH, Jendral M and Ullrich V, Br J Pharmacol126: 1283–1292, 1999). By using this established model, we tested whether or not ebselen (2-phenyl-1, 2-benzisoselenazol-3 (2H)-one), which reacts rapidly with the anionic form of PN, affected PN inhibition of PGI2 ...