Physical training increases β-adrenoceptor density and adenylate cyclase activity in high-oxidative skeletal muscle of diabetic rats

Abstract

The effects of physical training on β-adrenergic-receptor density (Bmax) and adenylate cyclase (AC) activity in soleus muscles (type I) and the deep red portion (type IIa) and superficial white portion (type IIb) of vastus lateralis muscles in diabetic rats were investigated. Rats were rendered diabetic with streptozotocin ([STZ] 45 mg/kg intravenously [IV]) and were either kept sedentary ([SD] n = 12) or submitted to a progressive 10-week treadmill running program ([TD] n = 13). A group of normal sedentary rats served as controls ([SC] n = 13). Plasma glucose levels were increased in SD rats in comparison with SC rats (21.3 ± 1.4 mmol/L v 7.7 ± 0.2; mean ± SE, P < .001), but levels were partially reversed to normal by training (10.7 ± 1.7; P < .01 v SD). The gastrocnemius nicotinamide adenine dinucleotide (NAD)-isocitrate dehydrogenase (ICDH) activity was significantly increased in TD rats in comparison to SC or SD rats ( P < .001). The Bmax and antagonist affinity ( K d ) determined with 125iodocyanopindolol (ICYP) were not affected by diabetes in any of the three types of muscle. In type I muscle, TD rats showed a significant 67% increase in Bmax compared with that of SD rats (TD 26.7 ± 2.0 v SD 16.0 ± 1.0; P < .001). In type IIa muscle, Bmax was significantly higher by 68% in TD rats as compared with SD rats (TD 16.5 ± 1.7 v SD 9.8 ± 0.9 fmol/mg protein; P < .01). However, in type IIb muscle, Bmax was not significantly modified by physical training (TD 8.3 ± 0.6 v SD 7.2 ± 0.6). K d was unaffected by training in each muscle type. The basal and sodium fluoride-stimulated AC activities were not modified by diabetes or training in each muscle tested. However, in type I muscle of TD rats, a significant 26% ( P < .01) increase in the AC response to 10 −5 mol/L isoproterenol was observed in comparison to that of SD rats. Such an effect of training was not observed in the two other muscle types. These results indicate that physical training induced changes in Bmax and in AC response to 10 −5 mol/L isoproterenol in skeletal muscles with a high oxidative capacity. How such changes may be implicated in the training-induced improvement of experimental diabetes mellitus remains to be established.