Work performance of trained rats as affected by corticoadrenal steroids and by adrenalectomy

¹ Merck Institute for Therapeutic Research, West Point, Pennsylvania

Fasted rats trained to climb a rope for a food reward were capable of carrying added weights approximately equal to their own body weights. The logclimbing time in seconds was linearly related to the total weight of the animal plus added load within a narrow range of body weight. When correction was made for skeletal muscle mass, the rate of work performance in gram-meters per long second per gram muscle was essentially the same over a wide range of body weights and of added load. Work performance as measured by this preparation was sensitive to changes in glucocorticoid levels, and was increased by cortisone or hydrocortisone in either intact or adrenalectomized animals, and was decreased by adrenal insufficiency.