Inositol Phosphate Metabolism and Nitric-Oxide Synthase Activity in Endothelial Cells Are Involved in the Vasorelaxant Activity of Nebivolol1

Abstract

Nebivolol is a recently developed β-blocker provided with vasodilator properties. Because the mechanism of the putative endothelium-dependent effect of this β-adrenoceptor blocker has not been completely elucidated, the aim of this study was to investigate the effects of nebivolol on an isolated resistance vascular bed and on cell messengers and constitutive nitric-oxide synthase activity (cNOS) in endothelial cells. Experiments were carried out using the rat mesenteric vascular bed and cultured bovine coronary postcapillary venular endothelial cells from bovine heart (CVEC). In mesenteric vascular bed preconstricted by 30 μM noradrenaline and 0.3 μM U46619, dl-nebivolol induced a concentration-dependent relaxing effect at concentrations between 3 and 30 μM; this effect was changed to a concentration-dependent vasoconstrictor response either in endothelium-denuded preparations or in intact preparations pretreated with 100 μMN^ω-nitro-l-arginine methyl ester plus 3 μM indomethacin. The vasorelaxant effect ofdl-nebivolol in preconstricted preparations was completely blocked by pretreatment either with the phospholipase C inhibitor U73122 (1 μM) or with the endoplasmic reticulum Ca²⁺-ATPase inhibitor thapsigargin (1 μM) for 30 min. The cellular level of the inositol trisphosphate metabolite inositol monophosphate in coronary postcapillary venular endothelial cells was not affected by dl-nebivolol in the concentration range 100 nM to 1 μM, but it was concentration dependently increased after exposure for 15 min to 10 and 30 μMdl-nebivolol. The activity of cNOS was almost doubled after a 5-min exposure to 10 μM dl-nebivolol and was significantly impaired by thapsigargin andN^ω-nitro-l-arginine methyl ester treatment, although it was unaffected byN^ω-nitro-d-arginine methyl ester. These findings demonstrate that nebivolol, in micromolar concentrations, induces vasorelaxation through activation of inositol phosphate metabolism and stimulation of cNOS activity in endothelial cells.