Endothelial β 3 -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 β 1 -adrenoreceptor antagonist that releases nitric oxide (NO) through incompletely characterized mechanisms. We identified endothelial β 3 -adrenoreceptors in human coronary microarteries that mediate endothelium- and NO-dependent relaxation and hypothesized that nebivolol activates these β 3 -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 β 1-2 -blocker nadolol, and prevented by the β 1-2-3 -blocker bupranolol ( P <0.05; n=3 to 8). Importantly, nebivolol failed to relax microarteries from β 3 -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 β 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 β 3 -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 threonine 495 , and fura-2 calcium fluorescence increased by 91.8±23.7%; this effect was unaffected by β 1-2 -blockade but abrogated by β 1-2-3 -blockade (all P <0.05). Conclusions— Nebivolol dilates human and rodent coronary resistance microarteries through an agonist effect on endothelial β 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.