Beta-adrenergic receptors in chronic alcoholic rat hearts

Properties of cardiac beta-adrenergic receptors from chronic alcoholic and control rats were studied to determine whether alterations in the receptor contribute to the decreased responsiveness of isolated working alcoholic rat hearts to beta-adrenergic stimulation. The receptors, assessed in crude membrane fractions by the binding of (-)[3H]dihydroalprenolol, did not differ significantly in either number or affinity in alcoholic rats (22.5 +/- 1.9 fmol . mg protein-1; Kd = 0.49 +/- 0.03 nmol . litre-1; n = 7) compared with control rats (25.9 +/- 1.3 fmol . mg protein-1; Kd = 0.55 +/-0.04 nmol . litre-1; n = 7). Competition experiments indicated that there was no difference in the binding affinity of (-)isoprenaline for the alcoholic and control rat heart receptors, nor in the affinity of (-)propranolol for he alcoholic and control rat heart receptors. In the presence of 5' -guanylylimidodiphosphate, the affinity of (-)isoprenaline for the receptors was decreased the same amount in the alcoholic and control rat hearts. These results suggest that the beta-adrenergic subsensitivity of chronic alcoholic rat hearts is mediated by a biochemical mechanism other than a direct alteration of the beta-adrenergic receptor or coupling between the receptor and adenylate cyclase.