Exercise-Induced Monocytosis and Modulation of Monocyte Function

Summary

Twenty male volunteers underwent short-term treadmill exercise with stepwise acceleration until exhaustion. Blood samples were analyzed before, during, and after exercise. The number of circulating white blood cells increased (81.6 % increase) resulting in lymphocytosis (131 %) and a minor granulocytosis (56.5 %). The most pronounced increase was observed with B-lymphocytes (225 %) followed by T-lymphocytes (110 %) and monocytes (87 %). The serum levels of immunoreactive insulin (56 % increase), glucagon (42 %), cortisol (62 %), and most pronounced, growth hormone (2340 %) rose substantially. The metabolic activity of circulating monocytes was slightly enhanced after exhaustive exercise: 2-deoxyglucose uptake increased by 12.5 %, glucose oxidation via the pentose phosphate shunt rose by 13.5 %, whereas the anaerobic formation of lactate remained unchanged. Incubation of resting monocytes with insulin alone had the same but more pronounced effects on glucose metabolism (34 % and 36 % increase, respectively). Under the same conditions, dexamethasone decreased glucose oxidation and the anaerobic glucolysis but had no influence on glucose uptake. Exercise as well as insulin and dexamethasone slightly depressed the phagocytotic activity of monocytes when incubated with opsonized zymosan particles.

In conclusion exercise provokes changes in the number and function of circulating monocytes, which correspond to those induced by insulin (and dexamethasone) in resting cells. The increase in circulating hormone concentrations and the enhanced insulin sensitivity of monocytes after exercise may therefore be responsible for some of these changes. It is not known to which extent the results are influenced by the changes in the circulating mononuclear cell pool.

Key words

exercise - leukocytosis - stress hormones - monocyte - phagocytosis - glucose metabolism