Involvement of beta3-adrenergic receptors in relaxation mediated by nitric oxide in chicken basilar artery

The response of basilar arteries to noradrenaline varies among many animal species, but remains little studied in poultry. Accordingly, we aimed to characterize the adrenergic receptor (AR) subtypes that modulate vascular response in basilar arteries in the chicken, with isometric recording of arterial ring tension using an organ bath. We demonstrated the presence of both alpha and beta (α and β) receptor subtypes through evaluating the response to noradrenaline, with and without a range of β-AR and α-AR antagonists. The concentration-dependent relaxations then induced by a range of β-AR agonists indicated a potency ranking of isoproterenol > noradrenaline > adrenaline > procaterol. We then investigated the effects of β-AR antagonists that attenuate the effect of isoproterenol (propranolol for β1,2,3-ARs, atenolol for β1-ARs, butoxamine for β2-ARs, and SR 59230A for β3-ARs), with Schild regression analysis, ascertaining multiple β-AR subtypes, with neither the β1-AR nor the β2-AR as the dominant subtype. SR 59230A was the only antagonist to yield a pA2value (7.52) close to the reported equivalent for the relevant receptor subtype. Furthermore, treatment with SR 58611 (a β3-AR agonist) induced relaxation, which was inhibited (P< 0.01) by L-NNA and SR 59230A. Additionally, treating basilar arterial strips (containing endothelium) with SR 58611 induced nitric oxide (NO) production, which was inhibited (P< 0.01) by L-NNA and SR 59230A. Based on this first characterization of AR subtypes in chicken basilar arteries (to our knowledge), we suggest that α- and β-ARs are involved in contraction and relaxation, and that β3-ARs, especially those on the endothelium, may play an important role in vasodilation via NO release.