Exercise-Induced Ovarian Dysfunction in the Rat

The effect of treadmill running on estrous cycles was studied in the rat. Additional effects of cortisol acetate treatment and adrenalectomy were studied in both exercising and sedentary rats. Sedentary rats given the vehicle or cortisol acetate, or which had been adrenalectomized, all exhibited estrous cycles with diestrous phases that were uniformly less than 4 days. However exercising rats had extended estrous cycles; 50–62% of cycles were incomplete within 11 days and 78% of rats had cycles with diestrous phases that were more than 4 days long. There were no differences in duration of estrous cycles of running rats that received vehicle, received cortisol acetate, or had been adrenalectomized. We conclude that the running regimen resulted in a delay of the normal ovulatory period in rats, and that this effect of running was not affected by the presence or absence of glucocorticoids.