Reduced cortisol potentiates the exercise-induced increase in corticotropin to a greater extent in trained compared with untrained men

We examined the effect of acute exercise and reduced cortisol on pituitary and adrenal responsiveness and the impact of reduced plasma cortisol on max imal oxygen consumption ((V) over dot O(2)max) in eight trained (T) and eig ht untrained (UT) males. Subjects completed two graded maximal exercise tes ts (GXT), each preceded by either overnight metyrapone (MET) or placebo (PL A) administration. Blood samples were collected before and after GXT. With PLA, resting corticotropin (ACTH) levels were higher in T versus UT men; ho wever, cortisol and 11-deoxycortisol were similar between groups. Following GXT on PLA, cortisol was unchanged but 11-deoxycortisol increased in both groups; however, ACTH increased only in UT men. For both groups, cortisol. 11-deoxycortisol, and ACTH were different post-GXT with MET versus PLA. Fur thermore, following GXT with MET, the ACTH response was greater in T versus UT subjects, (V) over dot O(2)max was not altered by MET in either group. We conclude that (1) at: rest, only ACTH levels differed between T and UT m en; (2) individually, the GXT and MET provide a similar ACTH response in UT but not in T subjects; (3) when GXT and MET are superimposed, they provide a stronger stimulus to pituitary and adrenal reserve than either test alon e; (4) the combination of MET and GXT elicits a greater ACTH response in T compared, with UT men; and (5) an acute reduction in plasma cortisol does n ot alter (V) over dot O(2)max. Copyright (C) 1999 by W.B. Saunders Company.