This investigation examined the role of glutamine in exercise-induced changes in immune function. The investigation focused on whether changes in plasma glutamine concentration following acute exercise might affect glutamine availability to, and the activity of lymphocytes. Measured variables included: 1) circulating cell counts, 2) plasma and peripheral blood mononuclear cell (PBMC) glutamine concentration, 3) mitogen stimulated whole blood and isolated PBMC proliferation, 4) plasma concentration, and intracellular production of interleukin (IL)-2, and 5) the incidence of upper respiratory tract illness (URTI).
The effect of an exercise-induced decrease in plasma glutamine concentration on glutamine availability to PBMC was determined by the enzymatic measurement of plasma and PBMC glutamine concentration, and calculated relative to changes in the number of cells in the circulation. The effect of a decrease in glutamine availability in vitro and in vivo on lymphocyte activity was determined by the measurement of whole blood and isolated PBMC mitogen stimulated proliferation, and IL-2 production and release measured by enzyme-linked immunosorbent assay (ELISA). The effect of chronic supplementation with branched-chain amino acids (BCAA) on acute exercise-induced changes in lymphocyte activity was determined by the measurement of lymphocyte proliferation and IL-2 production as above. In addition, the effect of chronic BCAA supplementation on the incidence of URTI in the four-week period before, and one-week period after acute, exhaustive exercise was determined by self-report procedure.
When expressed relative to cell count, PBMC glutamine concentration was elevated during recovery from high intensity, intermittent exercise, and prolonged exhaustive exercise. This was shown when plasma glutamine concentration both decreased and remained unchanged in response to acute exercise bouts. This finding demonstrated that PBMC glutamine concentration was not compromised by either high intensity, intermittent exercise, or prolonged exercise.
The importance of glutamine to lymphocyte proliferation in vitro was shown by a concentration-dependent increase in Con A stimulated proliferation using a whole blood method. A decrease in plasma glutamine concentration following acute exercise in vivo, however was not reflected in a decrease in lymphocyte proliferation, nor did it attenuate the production and release of IL-2. When expressed relative to changes in the number and distribution of circulating lymphocytes, proliferation was elevated following acute exercise. This finding demonstrated that the magnitude of decrease in plasma glutamine concentration following acute exercise did not compromise lymphocyte proliferation or IL-2 production, using the methodologies and timing of sampling performed in this investigation.
Chronic supplementation with branched-chain amino acids (BCAA) before a competitive marathon event did not affect the acute, exercise-induced changes in lymphocyte proliferation or IL-2 production. However, during the four-week period before, and one-week period after the event, the self-reported incidence of URTI was markedly lower in the BCAA-supplemented, than in the placebo-supplemented group. These findings demonstrated that chronic BCAA supplementation did not alter transient changes in lymphocyte activity measured in this investigation, yet might have had some other type of effect on the immune system that enhanced defence against invading pathogens.