Introduction: To investigate preventive effect of Tribulus terrestris extract (TT) on exercise-related immunosuppression in rats and explore the mechanisms- the role of Glucocorticoid (GC), Glucocorticoid Receptor (GR) and NF-kB inhibitor protein alpha (IkBa). Methods: Thirty male SD rats were randomly divided into control group, over-trained group and over-trained plus TT group. The last two groups were trained on a motor-driven treadmill with a progressively increased load for 6 weeks. The over-trained plus TT rats took the medicine by gastric irrigation while the others ingested the same amount of saline. The numbers of CD3+, CD4+ and CD8+ T cells and natural killing (NK) and NKT cells were detected by Flow Cytometry. The plasma levels of testosterone and corticosterone and the protein levels of GR and IkBa in livers of rats were determined by ELISA and Western blot, respectively. Results: ①Distinct decreases of body weigh, testosterone/corticosterone (T/C) ratio, the numbers of CD3+T and NK cells were found in over-trained rats compared with that of control rats, indicating successful establishement of exercise-related immunosuppression. ②Supplement of TT lead to significant increases of T/C ratio, CD4+/CD8+ ratio and the amounts of CD8+ cells, NK and NKT cells in the over-trained rats. ③The plasma levels of GC in over-trained rats kept unchanged compared to control rats, while obvious decrease (about 50% of over-trained rats) was observed in over-trained plus TT rats. ④The protein levels of GR decreased in the livers of over-trained rats, while obvious increases of protein expression of GR were observed in over-trained plus TT rats. ⑤The protein levels of IkBa raised significantly in the livers of over-trained rats, while reduced protein levels of IkBa were shown in over-trained plus TT rats. Conclusions: These results indicated that: ①supplement of TT improved the suppressed immune function resulted from over-training in rats. ②TT decreased the plasma levels of GC and the protein levels of IkBa in livers of over-trained rats and increased the protein levels of GR in livers of over-trained rats, which might be related to the preventive effect of TT on exercise-related immunosuppression.



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