HETEROGENEITY OF CEREBRAL BETA-ADRENOCEPTOR BINDING-SITES IN VARIOUS VERTEBRATE SPECIES

[3H]-Dihydroalprenolol ([3H]-DHA) binds to cerebral membranes of the frog, chick, rat, mouse, rabbit and human with a dissociation equilibrium constant (KD) of about 1 nM and displays binding characteristics indicative of an interaction with β-adrenoceptors. However, the maximum number of specific binding sites labelled by this β-adrenoceptor ligand varies substantially between the species with the click and mouse having the highest, and the frog the lowest density. The structure-activity relationships of adrenergic agents to inhibit specific [3H]-DHA binding suggests that whereas the membrane sites from all the species had similar affinities for non-selective β-adrenergic agents, several drugs that have been reported to show selectivity for β1-adrenoceptors demonstrated considerably higher affinities for mammalian rather than avian or amphibian membrane sites. By this pharmacological criteria it is likely that all the β-adrenoceptor binding sites in frog and chick cerebral tissue have properties resembling β2-adrenoceptors. However, in mammalian cerebral cortex, evidence is presented that β1-and β2-adrenoceptors coexist in a ratio of 70%/30% respectively. © 1978.