TRAINED VERSUS UNTRAINED MEN - DIFFERENT IMMEDIATE POSTEXERCISE RESPONSES OF PITUITARY-ADRENAL AXIS - A PRELIMINARY-STUDY

The hypothalamo-pituitary-adrenal axis is involved throughout the exer cise-recovery cycle. Nevertheless, differences in hormone responses du ring early recovery between sedentary and endurance trained subjects a re not well known. The aim of this preliminary study was to monitor pl asma cortisol and adrenocorticotropic hormone (ACTH) concentrations bo th during and after the end of running exercise performed by four endu rance trained adults (marathon men) compared to four sedentary subject s. Two parameters, i.e. intensity and duration, were changed on 4 cons ecutive days. The 1(st) day (D-0) was spent in the laboratory: all blo od samples were obtained at rest to determine diurnal variations of ea ch hormone. On the following days (D-1-D-4) the subjects exercised: D1 and D2 brief (20 min), light (50% maximal heart rate HRmax, D-1) or s trenuous (80% HRmax, D-2), D-3 and D-4 prolonged (120 min), light (D-3 ) or strenuous (D-4) In both groups, neither brief (D-1, D-2) nor prol onged light exercise (D-3) induced any significant variation in plasma ACTH or cortisol concentrations. Plasma ACTH and cortisol concentrati ons increased only if the exercise was intense and prolonged (D-4) The training factor did not modify the intensity or duration thresholds f or the activation of the pituitary-adrenocortical response to exercise in the conditions of our experiment. However, during immediate recove ry from the four exercise regimens, the plasma ACTH concentrations of the marathon men were constantly above the values of the sedentary sub jects, although plasma cortisol concentration remained similar in both groups. As an indirect means of evaluating the relationships between ACTH and cortisol we compared the areas under the cortisol and ACTH cu rves (AUG) from 0.5 to 3.5h during recovery from D-1 to D-4 compared t o D-0 at the same time. Cortisol AUC were similar in the sedentary sub jects and marathon men although the ACTH AUC were different in the sed entary subjects and marathon men, suggesting a change in the pituitary -adrenal relationship at some yet indeterminate level. During the imme diate recovery from exercise whatever its intensity, the magnitude of the ACTH response was increased in the trained subjects but with a red uced effect upon its target, the adrenal glands. This phenomenon has n ot been described in the literature. Two non-exclusive phenomena may b e involved, i.e. a decreased adrenal sensitivity to ACTH stimulation, and/or a decreased hypothalamo-pituitary axis sensitivity to cortisol negative feedback.