Glucocorticoid Receptor Expression in Whole Blood Cells of Professional Water Polo Athletes during the Competitive Season: A Pilot Study

ABSTRACT Regular physical exercise plays a role in modulating the hypothalamic–pituitary–adrenal axis in sedentary individuals, but its effects on athletes remain unclear. As athletes depend on inflammation and micronutrient metabolism to improve, glucocorticoids, which interfere with both, may have an impact on their performances. The objective was to describe the characteristics of the HPA axis in athletes during their training season, as well as determine how high-performance training affects this axis. The inclusion criterion for this prospective observational study was participation as a water polo professional athlete since 2017 and the exclusion criteria were the presence of any chronic disease or the use of any kind of drug that affects the HPA axis during the last 6 months or until the end of the study. Nineteen professional water polo athletes were selected for the analysis of glucocorticoid receptor (isoforms α and β) expression and of glucocorticoid receptor polymorphisms (Bcl-I and A3669G). These analyses were carried out at the beginning of the season (T0), when the athletes were less physically prepared, and again at mid-season (T1) during the peak of physical preparation. The results revealed a good adaptive response in athletes during the progressive stress of the season, characterized by lower expression levels of glucocorticoid receptor alpha and glucocorticoid receptor beta and a lower glucocorticoid receptor alpha/glucocorticoid receptor beta ratio, irrespective of the presence of protective polymorphisms. This adaptation decreases sensitivity to the glucocorticoid receptor, reducing hyper-response to stress, and potentially representing a protective mechanism in athletes. This study explores a plausible theory that relates physical fatigue with the HPA axis and its adaptations.