Involvement of the β3 adrenoceptor in nebivolol-induced vasorelaxation in the rat aorta

Nebivolol is a highly selective beta(1) adrenoceptor blocker with additional vasodilating properties. Although it has been shown that the nebivolol-induced vasorelaxation is nitric oxide (NO) and cGMP dependent, the receptor that mediates these actions remains controversial, and scrotonergic as well as beta-adrenergic pathways may be involved. Therefore, functional experiments investigating the receptor involved in nebivolol-induced vasorelaxation were performed in the rat aorta. Isolated aortic rings were exposed to cumulative concentrations of nebivolol. Nebivolol concentrations of 3 mumol/L and higher caused vasorelaxation, which was inhibited by the presence of the NO synthase inhibitor L-NNA (100 mumol/L), or by mechanical removal of the endothelium. Exposure of the vessel rings to the selective 5-HT1A antagonist NAN-190 (1 mumol/L) or the 5-HT1/2 antagonist methysergide (1 mumol/L) did not influence nebivolol-induced vasorelaxation. Similarly, the incubation with the beta(2)-adrenoceptor antagonist butoxamine (50 mumol/L) did not prevent vasorelaxation. The selective beta(3)-adrenoceptor antagonist S-(-)-cyanopindolol (1 mumol/L), however, significantly counteracted the nebivolol-induced vasorelaxation. Furthermore, exposure of the aortic rings to cumulative concentrations of the beta(3) selective adrenoceptor agonist BRL37344 caused, like nebivolol, NO-dependent vasorelaxation that was antagonized by S-(-)-cyanopindolol. The results suggest that nebivolol-induced NO-dependent vasorelaxation is, at least in part, caused by a beta(2)-adrenoceptor agonistic effect.