Molecular Pharmacology, Vol 15, 1-15, Copyright © 1979 by the American Society for Pharmacology and Experimental Therapeutics

Identity of [³H]-Dihydroalprenolol Binding Sites and -Adrenergic Receptors Coupled with Adenylate Cyclase in the Central Nervous System: Pharmacological Properties, Distribution and Adaptive Responsiveness

¹ Laboratoire de Physiologie Cellulaire and Groupe NB INSERM U 114, Collège de France, 75231 Paris, and Unité de Recherches Neurophysiologiques, INSERM U. 3. 47, Bd de l’Hôpital 75013, Paris, France

The binding of (-)-[³H]-dihydroalprenolol and -adrenergic-sensitive adenylate cyclase were measured in particulate fractions prepared from cat and rat brain. [³H]-Dihydroalprenolol interacted with a single class of rat cortical sites, having an affinity of 7 ± 0.5 nM (n = 12) and a concentration of 169 ± 8 fmole/mg protein (n = 12). [³H]-Dihydroalprenolol inhibited competitively the (-)-isoproterenol-sensitive adenylate cyclase with an apparent K_I of 10 nM. The K_Dapp of [³H]-dihydroalprenolol and the total number of specific binding sites were identical whether or not the determinations were made under conditions of adenylate cyclase assay. The apparent affinities of -adrenergic agonists and antagonists for adenylate cyclase stimulation or inhibition were highly correlated with their apparent affinities for [³H]-dihydroalprenolol binding sites, whether determined under adenylate cyclase incubation conditions (r = 0.98) or not (r = 0.95). Both processes were stereospecific for agonists and antagonists and showed the characteristics of a -adrenergic receptor. Salbutamol, a ₂-adrenergic agonist in peripheral tissues, appeared to be an antagonist of the ₁-adrenergic receptor coupled to an adenylate cyclase in the cerebral cortex. The topographical distribution of [³H]-dihydroalprenolol binding sites in rat frontal cerebral cortex was parallel to that of (-)-isoproterenol sensitive adenylate cyclase but not to that of dopamine sensitive adenylate cyclase. Similarly, the topographical distribution of [³H]-dihydroalprenolol binding sites in different areas of cat brain was highly correlated with that of (-)-isoproterenol sensitive adenylate cyclase (r = 0.93), but not with endogenous norepinephrine content. Intraventricular administration of 6-hydroxydopamine to five-day old cats resulted in an increase both in [³H]-dihydroalprenolol binding sites and in adenylate cyclase stimulation by (-)-isoproterenol. The augmentation in binding sites increased with time after the lesion, whereas the increase observed in (-)-isoproterenol-sensitive adenylate cyclase activity did not. Chronic treatment of rats with reserpine produced a 50% increase in [³H]-dihydroalprenolol binding sites and 43% increase in (-)-isoproterenol-sensitive adenylate cyclase. Chronic propranolol treatment also resulted in a significant increase in the concentration of [³H]-dihydroalprenolol binding sites (31%), which was more pronounced than that observed in the (-)-isoproterenol-sensitive adenylate cyclase (17%). Chronic treatment with either chlorpromazine or phenoxybenzamine had no effect on either process. The affinity of [³H]-dihydroalprenolol for its binding sites or of (-)-isoproterenol for adenylate cyclase stimulation was not affected by any of the treatments. Thus, the similarities between the pharmacological characteristics, the topographical distribution and the homeostatic regulation of the binding sites for [³H]-dihydroalprenolol and of the -adrenergic receptor coupled with an adenylate cyclase leads to the conclusion that these two components are identical in the central nervous system.

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ACKNOWLEDGMENTS We would like to thank Michèle Perez and Mina Cherif for excellent technical assistance, and Anne du Parc for manuscript preparation.

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