GLUCOCORTICOID RESPONSE TO FORCED EXERCISE IN LABORATORY HOUSE MICE (MUS-DOMESTICUS)

We examined the time course and sex differences of the glucocorticoid response to forced, moderate-intensity treadmill exercise in outbred l aboratory house mice. Mice (n = 64 total) were divided into eight grou ps, each of four males and four females, which were run on a motorized treadmill at 1.0 km/h for either 0, 2, 5, 10, 15, 25, 40, or 60 min. Serum samples were taken immediately after exercise and corticosterone (CORT) concentration was determined by radioimmunoassay. Resting CORT levels ranged between 11.6 and 29.5 ng/mL for both sexes. CORT levels increased with length of exercise and then exhibited a plateau by 25 min in females and by 40 min in males. Females displayed a significant ly more rapid increase in serum CORT levels and attained higher maxima l CORT levels than males. Females also had significantly larger adrena l glands, both in absolute terms and relative to body mass. (C) 1998 E lsevier Science Inc.