Long-term endurance training induced changes in glucocorticoid receptors concentrations in rat and in man

Aim. The responsiveness of target cells to glucocorticoids is directly related to the number and the functional state of intracellular glucocorticoid receptors (GR), which mediated the role of glucocorticoids. Although the effects of acute training on GR have been well characterized, less is known about the effects of chronic training on GR. The purpose of the present study was to describe the effects of long-term endurance training on GR. Methods. Male Sprague-Dawley rats were divided into 2 groups at random, 7 as controls and exercisers (swimming 40-50 min/day for 80 days), respectively. All rats were sacrificed 24 hours after their last training session for measurements of the GR in liver and brain cytosol and thymus cells by radioligand binding assay with H-3-dexamethasone. This study was also carried out on 8 trained adult, 8 aged as well as 6 retired athletes, whose GR in peripheral leukocytes were analyzed. Results. GR in hepatic cytosol and intact thymus cells of rats were significantly lower in exercise group than those in the controls. But the apparent dissociation constant (kd) was not changed. The GR in brain cytosol of rats indicated no significant reduction after training. The GR in peripheral leukocytes of the adult and aged athletes were also significantly lower than that in the controls. However, there was no significant difference between the GR in the retired athletes and that in the controls. Conclusion. This study demonstrated that long-term endurance training could lead to a decrease in GR and that the changes in GR were reversible during training. The possible mechanisms and the physiological significance of these changes need to be determined.