Endocrine and metabolic responses to extreme altitude and physical exercise in climbers

Context: Chronic hypoxia induces complex metabolic and endocrine adaptations. High-altitude (HA) exposure is a physiological model of hypoxia. Objective: To further investigate the endocrine and metabolic responses to extreme HA. Methods: We studied nine male elite climbers at sea level and at 5200 rn after climbing Mt. Everest. Results: After 7 weeks at HA, body weight was reduced (P<0.05); regarding endocrine variables we observed: a) an increase of 2-h mean GH concentration (P<0.05) as well as of total IGF-I and IGF binding protein-3 levels (P<0.05 for both); b) a prolactin increase (P<0.05) coupled with testosterone decrease (P<0.01) and progesterone increase (P<0.05) without any change in estradiol levels: e) no change in cortisol, ACTH, and dehydroepiandrosterone sulfate (DHEAS) levels; d) an increase in free thyroxine (P<0.05) and free tri-iodothyronine (T3) decrease (P<0.05) but no change in TSH levels; e) a plasma glucose decrease (P<0.05) without any change in insulin levels; 0 an increase in mean free fatty acid levels (P < 0. 0 5); g) despite body weight loss, leptin levels showed non-significant trend toward decrease, while ghrelin levels did not change at all. Conclusions: The results of the present study in a unique experimental human model of maximal exposure to altitude and physical exercise demonstrate that extreme HA and strenuous physical exercise are coupled with specific endocrine adaptations. These include increased activity of the GH/IGF-I axis and a low T₃ syndrome but no change in ghrelin and leptin that was expected taking into account body weight decrease. These findings would contribute to better understanding human endocrine and metabolic physiology in hypoxic conditions.