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 impo rtant factor in P-adrenergic signal transduction and in the decline in signal transduction with age, we hypothesized that some of the effect s of exercise training may be mediated by changes in postreceptor acti vation of adenylyl cyclase. To this end, we assessed isoproterenol-, G protein-, and forskolin-mediated activation of adenylyl cyclase as we ll as G protein immunoreactivity in the myocardium from young and sene scent F-344 rats with and without prior exercise training by treadmill running. Isoproterenol, beta-gamma-imidoguanosine 5'-triphosphate, an d forskolin stimulation of adenylyl cyclase activity declined by simil ar to 50% with age. Training increased the stimulation in the senescen t rats and decreased the stimulation in the young rats such that the a ge-related decline in signal transduction was no longer significant. G s alpha protein immunoreactivity was unchanged by age or training. The se data suggest that in young rats exercise training decreases beta-ad renergic signal transduction, whereas in older rats training increases signal transduction, partially offsetting the decline in signal trans duction with age.