Effect of exhaustive exercise on membrane estradiol concentration, intracellular calcium, and oxidative damage in mouse thymic lymphocytes

Early Ca2+ signaling events in cells of the immune system after exhaustive exercise challenge (8% slope, 32 m/min−1 speed) of female C57BL/6 mice, and their effects on oxidative reactions in thymus were studied. Intracellular Ca2+ and the oscillation of free extracellular Ca2+ were imaged with cell permeant cell and cell impermeant Fluo 3 calcium indicator in thymocytes. The role of estradiol was assessed by RIA for levels of membrane bound estradiol. Oxidative product release and membrane lipid peroxide were also evaluated. Intracellular Ca2+ levels were significantly higher in thymocytes of exercised compared with control mice (p < .001). There was a continuous flux of Ca2+ after exercise when cells were monitored in Ca2+ rich medium, with a significant influx between 160 and 200 sec (p < .001). Membrane bound estradiol was elevated in thymocytes of exercised compared to control mice (p < .05). Immediately after exercise there was a greater release of oxidative products by thymocytes in exhaustively exercised compared with control animals. There was also significant generation of lipid peroxide in thymus of exercised mice (p < .001). The findings suggest that exhaustive exercise may stimulate estradiol uptake by receptors on thymocytes, with a possible opening up of estradiol-receptor operated channels for Ca2+ entry into cells. This may have damaging effects on thymic lymphocytes by the triggering of oxidative reactions as determined by higher oxidative product release and greater generation of lipid peroxide.