EFFECTS OF NALOXONE OPIATE BLOCKADE ON THE IMMUNOMODULATION INDUCED BY EXERCISE IN RATS

The purpose of this study was to examine the possible involvement of the endogenous opiate system in the changes in immune competence induced by isolated exercise. Male untrained rats were subjected to a 2.5 hours swimming exercise bout. Animals were killed 15 min after the end of the exercise. The concentration of leukocytes, lymphocytes, monocytes and granulocytes and T4 (T-helper), T8 (T-suppressor/cytotoxic), interleukin-2 receptor (IL-2R) and transferrin receptor (TrfR) positive lymphocytes were determined both in peripheral blood and spleen by flow cytometric analysis. Exercise resulted in a significant decrease in 1) blood lymphocyte and splenic granulocyte number (p<0.05), 2) blood and splenic T4 positive lymphocytes and T4/T8 ratio (p<0.05), and 3) blood and splenic IL-2R and TrfR positive lymphocytes (p<0.05). The injection of the opiate blocker naloxone to exercising rats induced a decrease in the concentration and proportion of T8 positive lymphocytes, thereby restoring a normal T4/T8 ratio both in peripheral blood and spleen. Naloxone had no effect in control animals. The concentration and proportion of IL-2R and TrfR positive lymphocytes were not affected by naloxone. The mechanisms of the immunomodulation induced by isolated intense exercise are unclear. These data suggest that endogenous opiates participate in the alteration of cell-mediated immunity associated with exercise by modulating the T8 (suppressor/cytotoxic)-cell activity.