Nitric oxide-mediated beta 2-adrenoceptor relaxation is impaired in mesenteric veins from portal-hypertensive rats.

Abstract BACKGROUND & AIMS: beta-Adrenergic relaxation seems to be mediated by nitric oxide. The aim of this study was to evaluate changes induced by portal hypertension in beta 2-adrenergic vasorelaxation. METHODS: Isolated rat mesenteric veins were relaxed by salbutamol, and nerve- mediated vasocontractions were induced by electrical field stimulation. Responses were evaluated in the presence of NG-nitro-L-arginine methyl ester (L-NAME) or tetrodotoxin. Immunocytochemical techniques were used for localization of neuronal NO synthase. RESULTS: Salbutamol-induced relaxations were decreased in rings from portal-hypertensive animals. L- NAME reduced these relaxations, but its effects were mor…