Purpose: To investigate the effects of Tribulus terrestris (TT) on immune function in over-trained rats and explore the mechanisms the role of glucocorticoid (GC) and glucocorticoid receptor (GR).
Methods: Thirty male SD rats were randomly divided into control group, over-trained group and over-trained+TT group. The last two groups were trained on a motor-driven treadmill with a progressively increased load for 6 weeks. The over-trained+TT rats took the medicine by gastric irrigation while the others ingested the same amount of saline. The levels of plasma testosterone and corticosterone were measured by ELISA. The numbers of CD3+, CD4+ and CD8+ T cells and the levels of IFNγ and IL4 were detected by flow cytometry.
Results: Distinct decreases of body weight, testosterone:corticosterone (T:C) ratio, numbers of CD3+T cells and natural killing (NK) cells were found in the over-trained rats compared with that of non-exercise rats, indicating successful establishement of exercise-related immunosuppression; supplement of TT lead to significant increases of T:C ratio, CD4+:CD8+ ratio and the amounts of CD8+ cells, NK cells, NKT cells in the over-trained rats; down-regulation of IFNγ:IL4 ratio was shown in the over-trained rats, which meant Th1/Th2 imbalance (shift to Th2), and supplement of TT increased IFNγ:IL4 ratio; the level of plasma GC in the over-trained+TT rats was decreased obviously (about 50% of over-trained rats); the protein levels of GR in liver decreased obviously in the over-trained rats while TT increased the expression of GR in liver.
Conclusion: These results indicated that: supplement of TT improved the suppressed immune function resulted from over-training in rats, including increases of CD4+:CD8+ ratio and the amounts of NK, NKT cells and retrieval of Th1/Th2 balance; the improved effect of TT on suppressed immune function in over-trained rats might be related to the increase of GR and decrease of GC.