Characterization of β-adrenergic receptors in duck cerebral cortex

Abstract

β-Adrenoceptor binding sites were characterized in duck cerebral cortex by an in vitro binding technique, using [3H]dihydroalprenolol ([3H]DHA) as a receptor-specific radioligand. The specific binding of [3H]DHA 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 (K(d) = 1.18 nM) and high capacity (B(max) = 162 fmol/mg protein). Competition studies showed the following relative rank order of potency of various compounds to inhibit the [3H]DHA binding: Antagonists - ICI 118,551 > S(-)-propranolol >> betaxolol, yohimbine, WB-4101, prazosin, mianserine; agonists - isoprenaline ≃ fenoterol > salbutamol >> clonidine, phenylephrine. The obtained data suggest that in duck cerebral cortex β-adrenergic receptors (like those described in brains of chick and pigeon) are of the β2 subtype. This is in contrast to what has been reported for the mammalian brain, where - among β-adrenoceptors - the β1 subtype is predominant.