NS-398, a selective cyclooxygenase-2 blocker, acutely inhibits receptor-mediated contractions of rat aorta: role of endothelium

NS-398 ( N-(2-cyclohexyloxy-4-nitrophenyl)-methane sulfonamide) is a selective inhibitor of the cyclooxygenase-2 isozyme in vitro and in vivo. This study reports on acute inhibition of receptor-mediated contractions of isolated rat aorta by NS-398 and its modulation by endothelium-derived nitric oxide. NS-398 (1–10 μM) blocked norepinephrine, and 5-hydroxytryptamine (5-HT) evoked contractions and suppressed E max responses for both agonists. E max changes occurred in endothelium-intact vessel rings and in the absence, as well as in the presence of cycloheximide or dexamethasone in the physiological salt solution (PSS) bathing the tissues. NS-398 altered contractions to these receptor agonists in denuded rings only at 10 μM, and did not significantly alter contractions to KCl and sodium fluoride in all situations. NS-398 (3 and 10 μM) reduced aortic contractions initiated by cyclopiazonic acid (CPA), a sarcoplasmic reticulum Ca 2+-ATPase blocker, in endothelium intact rings bathed with PSS with/without nitro- d-arginine methyl ester ( d-NAME;100 μM), but did not alter contractions to the compound in endothelium-denuded aortic rings and in vessel rings bathed with PSS+ l-NAME (100 μM). Western blot analyses reveal significantly denser cyclooxygenase-2 protein expressions in freshly isolated endothelium-intact, compared to, denuded vessel segments. We conclude that: (1) cyclooxygenase-2 is constitutively expressed in rat aortic endothelial and smooth muscle cells, and (2) NS-398 modulates aortic contractions principally through an action on endothelial cyclooxygenase-2. Our data strongly suggest that cyclooxygenase-2 and/or its product(s), in concert with endothelium-derived nitric oxide, regulates the sarcoplasmic reticulum Ca 2+ pump activity in rat aorta.