Endothelial β3-adrenoreceptors mediate nitric oxide-dependent vasorelaxation of coronary microvessels in response to the third-generation β-blocker nebivolol

Background - The therapeutic effects of nonspecific beta-blockers are limited by vasoconstriction, thus justifying the interest in molecules with ancillary vasodilating properties. Nebivolol is a selective beta(1)-adrenoreceptor antagonist that releases nitric oxide ( NO) through incompletely characterized mechanisms. We identified endothelial beta(3)-adrenoreceptors in human coronary microarteries that mediate endothelium- and NO-dependent relaxation and hypothesized that nebivolol activates these beta(3)-adrenoreceptors. Methods and Results - Nebivolol dose-dependently relaxed rodent coronary resistance microarteries studied by videomicroscopy (10 mu mol/L, -86 +/- 6% of prostaglandin F2 alpha contraction); this was sensitive to NO synthase ( NOS) inhibition, unaffected by the beta(1-2)-blocker nadolol, and prevented by the beta(1-2-3)-blocker bupranolol (P < 0.05; n = 3 to 8). Importantly, nebivolol failed to relax microarteries from beta(3)-adrenoreceptor-deficient mice. Nebivolol (10 mu mol/L) also relaxed human coronary microvessels (-71 +/- 5% of KCl contraction); this was dependent on a functional endothelium and NO synthase but insensitive to beta(1-2)-blockade ( all P < 0.05). In a mouse aortic ring assay of neoangiogenesis, nebivolol induced neocapillary tube formation in rings from wild-type but not beta(3)-adrenoreceptor - or endothelial NOS - deficient mice. In cultured endothelial cells, 10 mu mol/L nebivolol increased NO release by 200% as measured by electron paramagnetic spin trapping, which was also reversed by NOS inhibition. In parallel, endothelial NOS was dephosphorylated on threonine(495), and fura-2 calcium fluorescence increased by 91.8 +/- 23.7%; this effect was unaffected by beta(1-2)-blockade but abrogated by beta(1-2-3)-blockade ( all P < 0.05). Conclusions - Nebivolol dilates human and rodent coronary resistance microarteries through an agonist effect on endothelial beta(3)-adrenoreceptors to release NO and promote neoangiogenesis. These properties may prove particularly beneficial for the treatment of ischemic and cardiac failure diseases through preservation of coronary reserve.