Influence of exercise training on myocardial beta-adrenergic signal transduction: differential regulation with age.

Exercise training is known to increase cardiovascular performance and decrease heart rate. Because activation of adenylyl cyclase is an important factor in beta-adrenergic signal transduction and in the decline in signal transduction with age, we hypothesized that some of the effects of exercise training may be mediated by changes in postreceptor activation of adenylyl cyclase. To this end, we assessed isoproterenol-, G protein-, and forskolin-mediated activation of adenylyl cyclase as well as G protein immunoreactivity in the myocardium from young and senescent F-344 rats with and without prior exercise training by treadmill running. Isoproterenol, beta-gamma-imidoguanosine 5'-triphosphate, and forskolin stimulation of adenylyl cyclase activity declined by approximately 50% with age. Training increased the stimulation in the senescent rats and decreased the stimulation in the young rats such that the age-related decline in signal transduction was no longer significant. Gs alpha protein immunoreactivity was unchanged by age or training. These data suggest that in young rats exercise training decreases beta-adrenergic signal transduction, whereas in older rats training increases signal transduction, partially offsetting the decline in signal transduction with age.