Exercise increases the frequency of circulating hematopoietic progenitor cells, but reduces hematopoietic colony-forming capacity.

Circulating hematopoietic progenitor cells (CPCs) may be triggered by physical exercise and/or normobaric hypoxia from the bone marrow. The aim of the study was to investigate the influence of physical exercise and normobaric hypoxia on CPC number and functionality in the peripheral blood as well as the involvement of oxidative stress parameters as possibly active agents. Ten healthy male subjects (25.3±4.4 years) underwent a standardized cycle incremental exercise test protocol (40 W+20 W/min) under either normoxic (FiO2 ∼0.21) or hypoxic conditions (FiO2<0.15, equals 3,500 m, 3 h xposure) within a time span of at least 1 week. Blood was drawn from the cubital vein before and 10, 30, 60, and 120 min after exercise. The number of CPCs in the peripheral blood was analyzed by flow cytometry (CD34/CD45-positive cells). The functionality of cells present was addressed by secondary colony-forming unit-granulocyte macrophage (CFU-GM) assays. To determine a possible correlation between the mobilization of CPCs and reactive oxygen species, parameters for oxidative stress such as malondialdehyde (MDA) and myeloperoxidase (MPO) were obtained. Data showed a significant increase of CPC release under normoxic as well as hypoxic conditions after 10 min of recovery (P<0.01). Most interestingly, although CD34+/CD45dim cells increased in number, the proliferative capacity of CPCs decreased significantly 10 min after cessation of exercise (P<0.05). A positive correlation between CPCs and MDA/MPO levels turned out to be significant for both normoxic and hypoxic conditions (P<0.05/P<0.01). Hypoxia did not provoke an additional effect. Although the CPC frequency increased, the functionality of CPCs decreased significantly after exercise, possibly due to the influence of increased oxidative stress levels.