Binding characteristics of (3H)dihydroalprenolol to .BETA.-adrenergic receptors of rat brain: Comparison with those of rat heart treated with neuraminidase.

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Abstract
Binding characteristics of the .beta.-antagonists and agonists with the .beta.-adrenoceptors were investigated in [3H]dihydroalprenolol ([3H]DHA) binding to rat brain membranes and the results were compared with those for rat heart membranes treated with neuraminidase. In this study, an improved automatic cell harvester LM-101 (Labo Science, Tokyo) was also used for filtration and washing of GF/C glass fiber filters. The use of this instrument allowed a large number of tubes to be assayed. The ranking order of inhibition of .beta.-antagonists or agonists was: pindolol > alprenolol > dl-propranolol > labetalol > YM-09538 > oxprenolol > K-351 > S-596 > N-696 > dichloroisoproterenol > metoprolol > acebutolol > sotalol > butoxamine > atenolol > practolol as antagonists or l-isoproterenolol > l-epinephrine = l-norepinephrine > salbutamol as agonists. Although lower IC50 (concentration of drug which inhibits [3H]DHA binding by 50%) values in the heart than in the brain were observed, a good correlation (r = 0.86, p < 0.001) was found between IC50 values in the binding assay with rat brain membranes and with rat heart membranes treated with neuraminidase. Thus, the radioligand binding assay method using rat brain can be useful for assessment of the relative potencies of newly synthesized chemicals as .beta.-blockers.

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