Adrenocortical activity and urinary cyclic AMP levels: effects of hypobaric hypoxia

Six highly motivated and trained military test subjects were exposed to a simulated altitude of 4267 m (477 torr) for 48 hours, prededed and followed by sea level runs lasting 32 hours. During each scenario tests subjects were required to perform their respective military tasks on a continual basis with sporadic rest not exceeding several hours. Extremely high levels of plasma cortisol prior to the start of each session and persistently elevated concentrations of urinary 17-OH corticosteroids at sea level were consistently observed. (This observation probably explains the relatively minor changes in adrenocortical output noted during acute exposure to hypobaric hypoxia. Analogous results were obtained for urinary cyclic AMP, i.e. elevated baseline levels and minimal response to high altitude. The results indicate an attenuated response as well as an association between urinary measures of adrenocortical activity and cyclic AMP excretion.