Effect of chronic inhibition of nitricoxide synthase on the production ofendothelium

Abstract

Endothelial dysfunction is generally associated with a reduced nitricoxide (NO)-mediated responses and an increased production ofendothelium-derived contracting factor (EDCF). NO has been shownto modulate EDCF acutely. However the relationship between theproduction of EDCF and chronic NO inhibition has not been fullyelucidated. This present study is designed to investigate the mechanismand the signaling pathway involved in the modulation of EDCF bychronic inhibition of NO. Eighteen weeks old male Sprague Dawley ratswere treated with the nitric oxide synthase (NOS) inhibitor L-NAME for6 weeks, and sacrificed for isometric tension analysis. Comparisonswere made with a parallel group of vehicle-treated animals. COX-1,COX-2, eNOS and TP receptor expressions were studied by Westernblotting and the level of NO was quantified using a colorimetric assay.Chronic eNOS inhibition increased systolic blood pressure and reducedacetylcholine-induced relaxations in aortic rings. This reduction wasreversed by 1 mM L-arginine. In quiescent aortic rings, A23187 causedcontractions, with greater effect on rings with endothelium and thepresence of L-NAME. These contractions were abolished by the COX-2inhibitor, NS-398 (10 lM) and thromboxane receptor antagonist,S18886 (1 lM), but not by a COX-1 inhibitor (SC-560, 1 lM). In thechronic L-NAME treated group, COX-1 and COX-2 expressions wereamplified; TP receptor expression remained unaffected; eNOS expres-sion and NO level decreased. In summary, chronic NOS inhibition in ratsenhances EDCF responses by altering its production and the COX-2rather than COX-1 signaling pathway is involved.