Effects of exercise on hematological parameters, circulating side population cells, and cytokines

To determine the effects of exercise and/or training on hematologic indices, circulating side population (SP) cells, and cytokines. Specifically hemoglobin (Hgb), hematocrit (Hct), white blood cell (WBC) and platelet (Plt) numbers, SP cells and plasma vascular endothelial growth factor (VEGF) and interleukin-6 (IL-6) levels were analyzed before and following exercise to maximal fatigue.

Thirty-seven nonsmoking subjects, aged 19 to 35 years, free of cardiopulmonary disease were enrolled and characterized as "trained" or "untrained." Standard hematologic indices were measured. Blood cells were stained with Hoechst 33342 vital dye and analyzed using flow cytometry for enumeration of SP cells. The levels of IL-6 and VEGF were determined by enzyme-linked immunosorbent assay.

Trained individuals had higher oxygen utilization and significantly longer exercise times than untrained individuals. Following exercise, significant increases were observed in Hgb, Hct, Plt, SP cell numbers, and IL-6 levels. These changes occurred in both trained and untrained individuals of both genders. No significant change in WBC numbers or VEGF levels was observed. Although circulating SP cell numbers were significantly increased, the "quality" of SP cells, defined by the ratio of lower SP to upper SP cells, was unchanged. Increases in SP cells did not correlate with cytokine levels.

Exercise increased Hgb, Hct, and Plt numbers, circulating SP cell numbers and IL-6 levels in young, healthy individuals of both genders and all fitness levels. These changes in hematologic, hematopoietic, and cytokine parameters, suggest that exercise can have a physiologic impact by potentially mobilizing stem cells and thereby enhancing tissue repair mechanisms.