EFFECTS OF AGING ON THE ACTIVITIES OF PYRUVATE-DEHYDROGENASE COMPLEX AND ITS KINASE IN RAT-HEART

Effects of aging on the activities of heart pyruvate dehydrogenase com plex and pyruvate dehydrogenase kinase were examined using 7, 35 and 6 0 wk old rats. Aging did not affect the total activity of pyruvate deh ydrogenase complex but decreased the activity state (percentage of act ive form) of the complex in rats under the fed condition(52%, 36% and 26% for 7, 35 and 60 wk old rats, respectively). This decrease in the complex activity with aging was suggested to be associated with an age -related decrease in the brood glucose disposal. Starvation for 24 h d ecreased the activity state to less than 3% in all of the age groups. The activity of pyruvate dehydrogenase kinase associated with the comp lex was not related to the alteration in the activity state of the com plex; the kinase activity was slightly lower in 60 wk old rats than in the younger rats under the fed condition and activation of the kinase by starvation was greater in the younger rats. The mechanism for the decrease in activity of pyruvate dehydrogenase complex was discussed o n the basis of glucose and fatty acid utilization of heart muscle cell s.