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 β_1,2,3-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 pA₂ value (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.