Characterization of beta-adrenergic receptors in duck cerebral cortex

Abstract

Beta-adrenoceptor binding sites were characterized in duck cerebral cortex by an in vitro binding technique, using 3H-dihydroalprenolol (3HDHA) as a receptor-specific radioligand. The specific binding of 3HDHA to duck cerebral cortical membranes was found to be rapid, stable, saturable, reversible, and of high affinity. Saturation analysis resulted in a linear Scatchard plot suggesting binding to a single class of receptor binding sites with high affinity (Kd = 1.18 nM) and high capacity (Bmax = 162 fmol/mg protein). Competition studies showed the following relative rank order of potency of various compounds to inhibit the 3HDHA binding: antagonists ­ICI 118,551 > S(-)-propranolol >> betaxolol, yohimbine, WB-4101, prazosin, mianserine; agonists - isoprenaline approximately equal to fenoterol> salbutamol >> clonidine, phenylephrine. The obtained data suggest that in duck cerebral cortex beta-adrenergic receptors (like those described in brains of chick and pigeon) are of the beta2 subtype. This is in contrast to what has been reported for the mammalian brain, where - among beta-adrenoceptors - the beta1 subtype is predominant.