Adaptations of the beta-adrenoceptor-adenylyl cyclase system in rat skeletal muscle to endurance physical training

beta-Adrenergic mechanisms may be important in the adaptation of skeletal muscle to endurance training. beta-Adrenergic signal transduction was examined in the gastrocnemius muscle of mts submitted to a progressive, 12-week treadmill running program and compared with sedentary controls. beta-Adrenoceptor density was significantly lower in exercised rats than in controls. The affinity constant for [I-125]-(-) iodocyanopindolol binding was not different among the various groups. Adenosine cyclic monophosphate formation was significantly decreased in trained animals when isoproterenol plus gua nosine triphosphate or forskolin plus Mn2+ were used to stimulate adenylyl cyclase. Immunoblot analyses revealed that the amount of the alpha-subunit of stimulatory guanine nucleotide-binding protein (G(s,alpha)), both the small and the large isoforms, also decreased with physical exercise. Thus, the present report shows that endurance training results in alterations in beta-adrenergic receptor density, adenylyl cyclase activity and G(s) protein level in rat gastrocnemius muscle.