Change Of Glucocorticoid Receptor In Rat Liver And Spleen After Exercise-related Immunosuppression

Object:Athletes may experience overexercise induced exercise-related immunosuppression, which resulted in the appearance of infectious disease and affected the exercise ability of athletes. After establishing rat treadmill model of exercise-related immunosuppression by progressive increasing load exercise of 8 weeks, the mRNA and protein levels of glucocorticoid receptor (GR) in rat liver and spleen were detected in order to clarify the role of GR on the exercise-related immunosuppression, which provided the basis to explore its mechanisms.Methods:Forty-two healthy SD rats (180 to 200g body weight) were randomly divided into control group (C,n=12), moderate exercise group (M,n=10) and over-trained group (O,n=20). Three days after adaptive training, the last two group rats were trained on a motor-driven treadmill to do moderate and over-trained exercise with different progressive increasing load of 8 weeks. The concentration of hemoglobin (Hb) in peripheral blood and the levels of testosterone (T) and corticosterone (Cort) in plasma were measured by cyanide methemoglobin method and ELISA assay, respectively. Flow Cytometry was used to detect the numbers of CD3+, CD4+ and CD8+ T cells and the levels of Thl specific cytokine IFN-y and Th2 specific cytokinge IL-4. The purpose of detection the above index and the body weight of rats is to demonstrate successful establishment of the rat model of exercise-related immunosuppression. Rats were decapitated to collect liver and spleen after eight weeks of training, and the mRNA and protein expression of GR in liver and spleen were determined by real time PCR and Western blot, respectively.Results:(1)Changes of body weightControl group rats kept increase in body weight in the eight weeks. The body weight of over-trained group rats declined significantly (P<0.05) on the fourth week, and the decrease of body weight became more obvious from the fifth to eighth weeks (P<0.01) compare with that of the control group. When compared with the moderate exercise group rats, the body weight of over-trained group rats decreased dramatically on the eighth week (P<0.05).(2)Changes of Hb, testosterone, corticosterone and T/C ratio①Variation of hemoglobin (Hb)There was no significant change of Hb concentration in moderate and over-trained group rats after five weeks training. While obvious decrease of Hb in over-trained group rats can be seen after eight weeks of training compared with that of control group (P<0.01) and moderate exercise group (P<0.05).②Alteration of testosterone, corticosterone and T/C ratioCompared with the control group, the levels of testosterone and corticosterone in over-trained group rats significantly decreased (P<0.05) and increased (P<0.01) respectively after eight weeks of progressive increasing load training. The T/C ratio was reduced obviously compared with that of moderate exercise group (P<0.05).(3)Variation of CD3+ cells, CD4+/CD8+ ratio and NK cells and NKT cellsCompared with that of control group, the number of CD3+ cells and NK cells declined significantly (P<0.01), while no change of CD4+/CD8+ ratio and NKT cells were found in over-trained group rats.(4)Variation of the secretion of Thl specific cytokines IFN-y and Th2 specific cytokines IL-4 and change of IFN-γ/IL-4 ratioCompared with that of control group, the levels of Th1 type cytokines IFN-γand Th2 type cytokines IL-4 were significantly enhanced (P<0.01), while IFN-γ/IL-4 ratio was dramatically decreased (P<0.05) after eight weeks of progressive increasing load training. IFN-γand IL-4 are Th1 and Th2 specific cytokine respectively, so IFN-γ/IL-4 ratio represents the situation of Th1/Th2 balance.(5) Variation of the mRNA expression of GR in rats liver and spleenAfter eight weeks of progressive increasing load training, the mRNA expression of GR in rats liver and spleen decreased obviously (P<0.05) in over-trained group, while no significant change in the level of mRNA GR was found in moderate exercise group compared with that of control group.(6)Variation of the protein expression of GR in rats liver and spleenCompared with that of control group, the protein expression of GR in rats liver and spleen decreased obviously (P<0.05) in over-trained group, while the protein level of GR in rats liver and spleen in moderate exercise group enhanced significantly (P<0.01, P<0.05 respectively) after eight weeks of progressive increasing load training.Conclusions:(1) After eight weeks of progressive training, over-trained group rats showed chronic fatigue according to the decrease of body weight, Hb, T and T/C ratio and the increase of Cort. Accompany with the above changes, the decrease of CD3+ cells and NK cells and Th1/Th2 imbalance in over-trained group demonstrated that the rat treadmill model of exercise-related immunosuppression was established successfully.(2) The mRNA and protein levels of GR in rat liver and spleen increased significantly in moderate exercise group rats.(3) The mRNA and protein levels of GR in rat liver and spleen decreased significantly in over-trained group rats.(4) Exercise-related immunosuppression may be related to the decrease of GR.