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

Abstract

Background - The therapeutic effects of nonspecific β-blockers are limited by vasoconstriction, thus justifying the interest in molecules with ancillary vasodilating properties. Nebivolol is a selective β3- adrenoreceptor antagonist that releases nitric oxide (NO) through incompletely characterized mechanisms. We identified endothelial β3- adrenoreceptors in human coronary microarteries that mediate endothelium- and NO-dependent relaxation and hypothesized that nebivolol activates these β3-adrenoreceptors. Methods and Results - Nebivolol dose-dependently relaxed rodent coronary resistance microarteries studied by videomicroscopy (10 μmol/L, -86±6% of prostaglandin F2α contraction); this was sensitive to NO synthase (NOS) inhibition, unaffected by the β1-2-blocker nadolol, and prevented by the β1-2-3-blocker bupranolol (P<0.05; n = 3 to 8). Importantly, nebivolol failed to relax microarteries from β3-adrenoreceptor- deficient mice. Nebivolol (10 μmol/L) also relaxed human coronary microvessels (-71±5% of KCl contraction); this was dependent on a functional endothelium and NO synthase but insensitive to β1-2- 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 β3-adrenoreceptor- or endothelial NOS-deficient mice. In cultured endothelial cells, 10 μmol/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 threonine495, and fura-2 calcium fluorescence increased by 91.8±23.7%; this effect was unaffected by β1-2-blockade but abrogated by β1-2-3-blockade (all P<0.05). Conclusions - Nebivolol dilates human and rodent coronary resistance microarteries through an agonist effect on endothelial β3-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. © 2005 American Heart Association, Inc.