Circulating hematopoietic progenitor cells in runners.

Because endurance exercise causes release of mediators and growth factors
activeon the bone marrow, we asked whether it might affect circulating
hematopoietic progenitor cells (HPCs) in amateur runners [n = 16, age:
41.8 +/- 13.5 (SD) yr, training: 93.8 +/- 31.8 km/wk] compared with
sedentary controls (n = 9, age: 39.4 +/- 10.2 yr). HPCs, plasma cortisol,
interleukin (IL)-6, granulocyte colony-stimulating factor (G-CSF), and the
growth factor fms-like tyrosinekinase-3 (flt3)-ligand were measured at
rest and after a marathon (M; n = 8) or half-marathon (HM; n = 8).
Circulating HPC counts (i.e., CD34(+) cells and their subpopulations) were
three- to fourfold higher in runners than in controls at baseline. They
were unaffected by HM or M acutely but decreased the morning postrace.
Baseline cortisol, flt3-ligand, IL-6, and G-CSF levels were similar in
runners and controls. IL-6 and G-CSF increased to higher levels after M
compared with HM, whereas cortisol and flt3-ligand increased similarly
postrace. Our data suggest that increased HPCs reflect an adaptation
response to recurrent, exercise-associated release of neutrophils and
stress and inflammatory mediators, indicating modulation of bone marrow
activity by habitual running.