Effects of the selective cyclooxygenase-2 inhibitor nimesulide on vascular contractions in endothelium-denuded rat aorta

Abstract

We have examined the effects of the selective cyclooxygenase-2 inhibitor nimesulide and the non-selective cyclooxygenase inhibitor indomethacin on vascular responsiveness of endothelium-denuded rat aorta. Isometric contractions were obtained to the α-adrenoceptor agonists phenylephrine (full agonist) and clonidine (partial agonist relative to phenylephrine) and to endothelin-1 and KCl. Maximum contractile responses to the partial agonist clonidine were significantly reduced by nimesulide (10 μM) and by indomethacin (10 μM) to 60.8±8.5% ( n=8) and 69.0±9.6% ( n=12) of control, respectively, as compared with the effects of vehicle (99.0±5.8%; n=17). The inhibitors had lesser effects against contractions to phenylephrine: nimesulide had no significant effect, whereas indomethacin caused a small but significant reduction in the maximum contraction to phenylephrine to 90.3±5.0% ( n=12) of control (vehicle: 108.0±5.2%, n=15 nimesulide: 111.8±5.9%, n=5). Neither nimesulide nor indomethacin had any effect on contractions to endothelin-1 or KCl. These actions differed from the effects of the Ca 2+ entry blocker nifedipine, which significantly reduced contractions to clonidine and KCl to a similar extent. The maximum contraction to clonidine was also significantly reduced by the thromboxane receptor antagonist SQ 29548 (1 μM) to 83.4±6.4% of control ( n=7) (vehicle 115.5±7.5%, n=7). It is concluded that the cyclooxygenase inhibitors nimesulide or indomethacin reduce vascular responsiveness to α-adrenoceptor agonists in endothelium-denuded rat aorta, presumably by preventing the formation of vasoconstrictor prostaglandins in aortic smooth muscle by cyclooxygenase-2. This reduced vascular responsiveness was most clearly seen with the partial agonist clonidine.