IDENTIFICATION OF ALPHA-2-ADRENERGIC RECEPTORS IN CHICKEN PINEAL-GLAND USING [H-3] RAUWOLSCINE

The norepinephrine-induced inhibition of avian pineal N-acetyltransferase activity appears to be mediated by .alpha.2-adrenergic receptors. In this study, .alpha.2-adrenergic receptors in the chicken pineal gland were directly identified by radioligand binding. Membrane preparations of pineal glands from chickens from 1 to 6 weeks of age were examined using [3H]rauwolscine, a selective .alpha.2-adrenergic receptor antagonist, to characterize the binding sites. The results indicate no ontological change in either the affinity (KD) or density of receptor binding sites (Bmax) during the time span examined. The binding was saturable and of high affinity with a mean KD of 0.27 .+-. 0.01 nM and a mean Bmax of 242 .+-. 12 fmol/mg protein Further characterization of these binding sites indicated that the .alpha.2-adrenergic receptor is of the .alpha.2A subtype, since prazosin and ARC-239 bound with low affinities and oxymetazoline bound with high affinity.