Decrease in ventricular beta-adrenergic receptors in trained diabetic rats

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Abstract
The effects of physical training on beta-adrenergic receptors were evaluated in heart ventricular tissue of diabetic rats. Mild diabetes mellitus was induced in rats with streptozotocin (45 mg/kg, iv). They were then submitted to a progressive 10-week running programme on a treadmill. Binding studies were done at six different concentrations of (−) [3H] dihydroalprenolol (0.5 to 14.4 nM) with ventricular membrane preparations from control (n=13), sedentary diabetic (n=9) and trained diabetic rats (n=10). Direct linear plot analysis of the data revealed that the total number of beta-adrenoceptors was reduced in sedentary diabetic rats as compared to control (2231±207 vs 2922±211 fmol/ventricules; P0.05). On the other hand, the beta-adrenergic binding sites were decreased in trained diabetic rats, either expressed as the total number of receptors (1920±179 vs 2922±211; PD) of these receptors between groups (KD=4.08±0.51, 4.69±0.93 and 2.88±0.39 nM respectively for control, sedentary diabetic and diabetic trained animals). The basal epinephrine concentration was significantly increased in trained diabetic rats (102±21 pg/ml vs 47±7 for control (P<0.05) and vs 49±9 for sedentary diabetic (P<0.05). These data indicate that a programme of physical training in diabetic rats can reduce both the total number and the density of beta-adrenoceptors in heart ventricular tissue, possibly by increasing the basal epinephrine secretion.