Effect of training on beta-adrenergic receptor number in rat heart

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Abstract
Female Sprague-Dawley rats were subjected to endurance-training programs, and the effect of training on myocardial .beta.-adrenergic receptor number, receptor-binding characteristics and adenylate cyclase (AC) activities associated with the receptor were examined. Training produced a 45% (P < 0.01) increase in the succinate dehydrogenase activity of the plantaris muscle. Specific (-)-[3H]dihydroalprenolol (DHA)-binding data were subjected to Scatchard plot analysis to quantify .beta.-adrenergic receptor number and DHA-binding characteristics of myocardial membranes. The DHA concentrations at which 50% of the total binding sites were occupied were similar for membranes from sedentary (1.95 .+-. 0.51) and trained (1.59 .+-. 0.34 nM)groups. Total DHA-binding sites of membranes from control (91.6 .+-. 0.51) and trained (1.59 .+-. 0.34 nM) groups. Total DHA-binding sites of membranes from control (91.6 .+-. 13.3) and trained (83.1 .+-. 7.6 femtomoles/mg) groups were also similar. Basal and maximally stimulated AC activities were also unchanged by endurance training. Fluoride-stimulated AC activities of crude homogenate and 10,000-g fractions decreased 47 and 49%, respectively, with training. No differences were observed in a 40,000-g fraction. The specific activities of a ouabain-sensitive Na+-K+-ATPase (a sacrolemmal membranes marker) of crude homogenate, 10,000-g and 40,000-g membrane fractions were similar. Evidently, training produces no detectable difference in the potential for adrenergic responses at the receptor level.