Adrenocortical responses to repeated parachute jumping and subsequent h-CRH challenge in inexperienced healthy subjects

The present study examined the adrenocortical response to 3 consecutive parachute jumps and a poststress h-CRH challenge. Fifteen participants in a parachute-jumping course took saliva samples for later cortisol analysis every 20 min throughout the day, when they accomplished their very first 3 parachute jumps and throughout a control day. The effects of an h-CRH challenge on salivary cortisol were assessed in the evening of the jumping day and on a control day. Parachute jumping induced 3 distinct highly significant adrenocortical responses. The respective cortisol increases for the first, second, and third jump were 39.4 +/- 26.5 nmol/l, 31.4 +/- 21.4 nmol/l, and 16.5 +/- 11.9 nmol/l. Cortisol responses to the first and second jump did not differ but the response to the third jump was significantly reduced [t(13) = 3.11; p = 0.008]. Two groups of subjects were identified, ''decreasers,'' whose response decreased from one to the other jump, and ''increasers,'' whose response remained unchanged or increased. The magnitude of the preceding cortisol response of decreasers exceeded that of increasers significantly by about 30 nmol. The mean adrenocortical effects of the poststress h-CRH challenge and the time-matched challenge on a control day did not differ although, in 4 subjects, the poststress adrenocortical reponse to h-CRH was completely suppressed. (C) 1997 Elsevier Science Inc.