Inositol phosphate metabolism and nitric-oxide synthase activity in endothelial cells are involved in the vasorelaxant activity of nebivolol

Nebivolol is a recently developed beta-blocker provided with vasodilator pr operties. Because the mechanism of the putative endothelium-dependent effec t of this beta-adrenoceptor blocker has not been completely elucidated, the aim of this study was to investigate the effects of nebivolol on an isolat ed resistance vascular bed and on cell messengers and constitutive nitric-o xide synthase activity (cNOS) in endothelial cells. Experiments were carrie d out using the rat mesenteric vascular bed and cultured bovine coronary po stcapillary venular endothelial cells from bovine heart (CVEC). In mesenter ic vascular bed preconstricted by 30 mu M noradrenaline and 0.3 mu M U46619 , dl-nebivolol induced a concentration-dependent relaxing effect at concent rations between 3 and 30 mu M; this effect was changed to a concentration-d ependent vasoconstrictor response either in endothelium-denuded preparation s or in intact preparations pretreated with 100 mM N-omega-nitro-L-arginine methyl ester plus 3 mu M indomethacin. The vasorelaxant effect of dl-nebiv olol in preconstricted preparations was completely blocked by pretreatment either with the phospholipase C inhibitor U73122 (1 mu M) or with the endop lasmic reticulum Ca2+-ATPase inhibitor thapsigargin (1 mu M) for 30 min. Th e cellular level of the inositol trisphosphate metabolite inositol monophos phate in coronary postcapillary venular endothelial cells was not affected by dl-nebivolol in the concentration range 100 nM to 1 mu M, but it was con centration dependently increased after exposure for 15 min to 10 and 30 mu M dl-nebivolol. The activity of cNOS was almost doubled after a 5-min expos ure to 10 mu M dl-nebivolol and was significantly impaired by thapsigargin and N-omega-nitro-L-arginine methyl ester treatment, although it was unaffe cted by N-omega-nitro-D-arginine methyl ester. These findings demonstrate t hat nebivolol, in micromolar concentrations, induces vasorelaxation through activation of inositol phosphate metabolism and stimulation of cNOS activi ty in endothelial cells.