Estrogen receptor-mediated vascular responsiveness to nebivolol:: a novel endothelium-related mechanism of therapeutic Vasorelaxation

Nebivolol is a highly selective and lipophilic beta(1)-adrenergic receptor antagonist with vasodilating characteristics attributed mainly to endothelial generation of nitric oxide (NO). Coincidently, rapid vascular vasodilating effects of estradiol are also widely reported and membrane- initiated signaling by estrogen receptor (ER), leading to generation of NO, parallels the vasodilating effects observed for nebivolol. Thus, we hypothesized that the NO-dependent vasodilating effect attributed to nebivolol may be partially mediated through its interaction with the membrane-associated form of ER. The objective of this study was to examine the ER-mediated/endothelium-dependent vascular responses to nebivolol and the specific binding properties of nebivolol to ER. In isolated rat aortic rings, the endothelium-dependent vasodilating effect of nebivolol was significantly blocked by the use of the potent ER antagonist, ICI 182,780. In contrast, in the absence of intact endotbelium, nebivolol-induced vasorelaxation was not blocked by ICI 182,780, strongly suggesting that nebivolol-elicited vasorelaxation is partially dependent on ER-mediated pathways. Further, we examined the binding of nebivolol to ER (MCF-7 cells) by radioligand binding assay and revealed specific binding kinetics with an estimated DC50 of 5 x 10(-4) M, coinciding with the approximate EC50 of nebivolol as a vasorelaxant. In conclusion, the endothelium-dependent vascular response to nebivolol is attributed partially to its interaction with ER.