Oxidative stress induced by tert-butyl hydroperoxide causes vasoconstriction in the aorta from hypertensive and aged rats: role of cyclooxygenase-2 isoform.

We analyzed the mechanisms involved in the effect of tert-butyl hydroperoxide (t-BOOH) in isolated aortic rings with and without endothelium from normotensive Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) at 6, 18, and 24 months of age. t-BOOH (1 microM-10 mM) induced concentration-dependent contractions that were scarcely modified by aging and potentiated in SHR and by endothelium removal. The nitric oxide synthase and prostacyclin synthase inhibitors N(G)-nitro-L-arginine methyl ester (100 microM) and tranylcypromine (100 microM), respectively, increased both basal tone and the t-BOOH-induced contractions in intact segments from WKY, with these effects not observed in SHR. Indomethacin (10 microM), a nonspecific cyclooxygenase inhibitor, and SQ 29,548 (10 microM), a prostaglandin H(2)/thromboxane A(2) receptor blocker, abolished the t-BOOH-induced vasoconstriction, independent of age and hypertension. In both strains, these contractile responses were unaltered by the thromboxane synthase inhibitor imidazole (10 microM). The cyclooxygenase-2 inhibitor NS-398 (10 microM) abolished or markedly reduced the t-BOOH-induced contractions in segments with or without endothelium, respectively. In addition, expression of cyclooxygenase-2 protein was detected in aorta from WKY and SHR in either basal condition or after stimulation with t-BOOH. These results suggest that (1) t-BOOH-induced vasoconstriction in the aorta from WKY and SHR is essentially mediated by cyclooxygenase-2 metabolites, different from thromboxane-A(2), probably prostaglandin-H(2), and/or isoprostanes; (2) aging scarcely modifies, whereas endothelium negatively modulates, these contractions in both strains; and (3) nitric oxide and prostacyclin exert a negative modulator role on the t-BOOH-induced vasoconstriction in WKY, with this modulator role lost in SHR.