Glucocorticoid receptor mRNA expression in peripheral blood mononuclear cells in high trained compared to low trained athletes and untrained subjects

Background: Physiological needs during prolonged exercise are a potent stimulus for the hypothalamic-pituitary-adrenal (HPA) axis. Hence, athletes undergoing daily endurance training sessions may have frequent and prolonged phases of endogenous hypercortisolism. Since chronic glucocorticoids treatment leads to down-regulation of glucocorticoid receptor α (GR-α) mRNA expression, endurance training could lead to modulation of GR expression. Aim: The aim of the study was to evaluate GR-α and GR-β mRNA expressions in peripheral blood mononuclear cells and plasma cortisol, ACTH and cortisol binding globulin (CBG) concentrations at rest in subjects undergoing different training regimes. Subjects and methods: Nine high trained (HT) swimmers (training volume: 21.6±1.7 hours/week in 10-12 sessions) were compared with two age-matched control groups represented by 8 low trained (LT) runners (training volume: 6.4±2.6 h/week in 3-5 sessions) and 9 untrained subjects. Expression of GR was determined by RT-PCR of total RNA. Hormone levels were determined by radioimmunoassay methods. Results: HT athletes showed 10 times less GR-α mRNA expression than the untrained subjects, while LT athletes exhibited values about two-fold less than the untrained subjects. GR-β mRNA expression was undetectable in all subjects. No differences were observed among the three groups in hormone levels. Conclusions: GR-α mRNA expression is repressed in proportion to the amount and frequency of the stressful stimuli due to training. Hence, this down-regulation may be a consequence of the frequent and prolonged exposure to cortisol acute elevations induced by training. GR-β did not play an important role in inducing the down-regulation of GR-α mRNA expression observed.