Effect of sexual maturation and exhaustive exercise on myocardial glycogen metabolism

Prepubertal, pubertal, and postpubertal (28, 45, and 60 days old, respectively) rats of both sexes were run to exhaustion on a motor-driven treadmill to determine whether sexual maturation was involved in the glycogen sparing phenomenon previously reported in the myocardium of female rats receiving high doses of estrogen. Positive work was calculated and was not different in the male and female age-paired rats. Liver glycogen was significantly depleted by 92-98% in male and 96-97% in female exercising rats of all ages. The exercise bout resulted in significant depletion of glycogen in the red and white portions of the vastus lateralis muscle of male and female animals. At 45 and 60 days of age female animals had significantly more glycogen in the red muscle at exhaustion than age-paired males. Myocardial glycogen was significantly depleted by 32, 38, and 41% in prepubertal and pubertal males and prepubertal females, respectively. Pubertal females depleted myocardial glycogen by 19% (P less than 0.05). Postpubertal male animals exhibited a 46% depletion of myocardial glycogen (P less than 0.01), while myocardial glycogen in sexually mature females was not decreased at exhaustion. These data indicate that a myocardial glycogen sparing phenomenon exists in vivo in sexually mature female rats. These data further suggest that the glycogen sparing phenomenon develops in association with sexual maturation.