Decreased pituitary sensitivity to glucocorticoids in endurance-trained men

Objective: Muscular exercise induces hypothalamo-pituitary-adrenal (HPA) ax is activation and when regularly repeated, as in endurance training, leads to HPA axis adaptation. To assess whether nonprofessional endurance-trained (ET) men with a substantial training load and no clinical or biological fe atures of HPA axis overactivity can present subtle alterations of HPA axis sensitivity to glucocorticoid negative feedback, nine ET men were subjected to HPA axis testing using the dexamethasone-corticotrophin-releasing hormo ne (CRH) test. Design: Nine endurance-trained men and eight healthy age-matched sedentary men were studied, Morning plasma cortisol and 24 h urinary free cortisol (U FC) were determined and a low dose dexamethasone suppression test (LDDST) w as performed followed by CRH stimulation (dexamethasone-CRH test), Results: After a day without physical exercise, at 0800 h, plasma ACTH and cortisol concentrations, and the 24 h UFC and UFC/urinary creatinine (UC) r atio were similar in ET and sedentary men, By contrast, clear differences b etween the groups were seen in cortisol and ACTH responses to the dexametha sone-CRH test. In eight ET subjects, after LDDST basal ACTH and cortisol le vels were similar to those of sedentary men, whereas one ET subject display ed a poor suppression of cortisol level (131 nmol/l), After injection of CR H, however, three of nine ET men's cortisol levels were not suppressed by d examethasone but instead displayed significant CRH-induced increase (peak c ortisol: 88, 125 and 362 nmol/l), No sedentary subject exhibited any increa se in cortisol levels, Conclusion: Three of nine ET men with a mean maximum rate of O-2 uptake (V- O2,V-max) of 61 ml/kg per min, running 50-70 km per week, were resistant to glucocorticoid suppression during the combined dexamethasone-CRH test.