Effect of training on the phagocytic capacity of peritoneal macrophages from rats exposed to swim stress.

Since strenuous effort may affect the immune system, a study was designed to examine the impact of the progressive training of rats exposed to swim stress. Rats (trained swimmers) were forced to swim daily in a water bath for progressively longer periods. At the end of the study, which continued for a total of 6 weeks, the superoxide anion generation and phagocytic capacity of peritoneal macrophages, the mitogen response of splenic cells (splenocytes) and the serum corticosterone level were examined. The results, compared to those of animals taken in and out of their cages (nonswimmers), showed an increase in superoxide anion generation, as well as a decrease in both the percentage of phagocytosing cells and the number of particles internalized by each individual cell. In trained swimmers, the mitogen response to phytohemagglutinin and concanavalin A (Con A), as well as the corticosterone level, did not change significantly from those of nonswimmers. A third group of animals were forced to swim once only for 30 min, until the appearance of signs of marked fatigue (acute swimmers). Their peritoneal macrophages showed an increased superoxide anion generation and a significantly decreased response to Con A compared to those of the nonswimmers. The serum corticosterone level in acute swimmers was found to be increased compared to that of an additional group of animals kept at complete rest. The findings indicate that the progressive training of rats exposed to swim stress does not prevent alterations in certain immune responses, a fact that should be considered by intensive exercisers.