CORTICOTROPH AXIS SENSITIVITY AFTER EXERCISE IN ENDURANCE-TRAINED ATHLETES

OBJECTIVE The present study was conducted in order to describe human h ypothalamo-pituitary adrenal (HPA) axis adaptation in a model of repea ted physical stress (endurance training) that causes a moderate increa se in cortisol levels. SUBJECTS We performed the same stimulation test s (adrenal stimulation with ACTH or pituitary stimulation with combine d CRH/LVP) in a population of 8 endurance-trained athletes in two dist inct situations: resting (baseline cortisol values) and 2 h after the end of strenuous exercise (increased cortisol values) to evaluate the HPA axis sensitivity to endogenous sustained increases in cortisol con centrations. MEASUREMENTS During these tests, saliva and plasma cortis ol (Fs and Fp, respectively) were assessed and compared. RESULT Cortis ol values in both plasma and saliva at the end of 2h of exercise were significantly higher than in rested controls: Fs 11.5+/-1.3 vs 6.5+/-0 .8nmol.l(-1) and Fp 428+/-36 vs 279+/-21nmol.l(-1) (post exercise vs p ost rest sessions, respectively, P<0.001 for both). After either hormo ne test (CRH/LVP or ACTH), cortisol levels in plasma and saliva increa sed similarly when rest was compared to post exercise. Saliva variatio ns (Delta%) under exogenous hormone stimulation were dramatically grea ter than plasma variations. For example, under ACTH stimulation, the r elative increments in cortisol were on control day: Delta Fs 980+/-139 vs Delta Fp 218+/-43% (saliva vs plasma, respectively, P<0.05) and on exercise day: Delta fs 605+/-89 vs Delta Fp 102+/-14% (saliva vs plas ma, respectively, P<0.05). CONCLUSIONS In endurance-trained athletes, displaying a moderate but sustained endogenous cortisol increase: (1) ACTH responses following pituitary stimulation are not blunted, (2) co rtisol responses following maximal adrenal stimulation are not blunted . Our results favour the hypothesis of a decreased pituitary sensitivi ty to cortisol negative feedback whereas the hypothesis of a major dec reased adrenal sensitivity to ACTH was discarded. The greater ability of saliva assays to detect a cortisol increase strongly supports its u se in the study of HPA physiology, whether under basal or dynamic cond itions.