Endocrine response to high-intensity exercise: dose-dependent effects of dexamethasone

We recently reported that in 30-50% of healthy men and women the release of ACTH and cortisol stimulated by exercise is not suppressed by prior administration of a 4-mg dose of dexamethasone (DEX). We now explore other potential differences between these subjects and those whose exercise response was suppressed by examining the effect of a smaller, 1-mg, dose of DEX on exercise-stimulated ACTH and cortisol. Men (n = 15) and women (n = 9) were studied during three high intensity exercise tests: one after taking placebo, one after taking 1 mg DEX, and one after taking 4 mg DEX. Before participation, subjects underwent a test for classification as either a high (HR; n = 10) or low (LR; n = 14) reactor and a maximal exercise test to assess maximal aerobic capacity. Distinct dose-related reductions in plasma concentrations of ACTH, cortisol, and dehydroepiandrosterone (DHEA) were noted for HR under the treatment conditions, whereas both doses of DEX blocked ACTH, cortisol, and DHEA release in LR. Furthermore, basal plasma cortisol, DHEA, and DHEA sulfate were significantly higher in HR compared to LR. Thus, there are inherent basal and stress-reactive differences in HR and LR, and these differences may be useful in constructing a model for the mechanisms and physiological regulation of hypothalamic-pituitary-adrenal axis activation. The question of whether these differences in reactivity of the ACTH-cortisol axis between the HR and LR groups have implications for individual short term function or long term health remains to be answered.