EFFECTS OF DECREASED PLASMA GLUTAMINE CONCENTRATIONS ON PERIPHERAL LYMPHOCYTE-PROLIFERATION IN RATS

The relationship between exercise-induced lowering of plasma glutamine concentrations and proliferation of peripheral lymphocytes was invest igated in male Wistar rats. The T-lymphocyte proliferative responses t o the mitogen, concanavalin A, were determined by incorporation of rad iolabelled thymidine into the DNA in vitro. The rats ran 2 h . day(-1) , 6 days . week(-1) for 4 weeks. Analysis immediately after the final period of exercise showed T-lymphocyte proliferation to be significant ly depressed, together with a marked decrease in plasma glutamine conc entrations. There were also significant increases in serum corticoster one concentrations immediately after exercise. However, following 24-h recovery, this exercise-induced immunosuppression was not statistical ly significant when compared with the age-matched control group. In th e second experiment, in order to clarify the importance of glutamine f or immunological function in vivo, methionine sulfoximine, an effectiv e inhibitor of glutamine synthetase was injected intraperitoneally (12 .5 mg . kg body mass(-1)). Plasma glutamine concentrations were decrea sed 4 h after the injection, compared with the placebo control group, and this resulted in a significant decrease in the rate of T-lymphocyt e proliferation. This treatment had no effects on serum corticosterone concentrations. These results would suggest that the chronic exercise -induced reduction in proliferation of peripheral T-lymphocytes is a t ransient reversible phenomenon, which returns to normal levels within 24 h of the final training period. It is also conceivable that this ex ercise-induced immunosuppression is associated with a decrease in circ ulating glutamine concentrations.