The effect of cigarette smoking on the bone marrow.

Chronic cigarette smoking produces a 20 to 25% increase in the number of peripheral blood leukocytes, and there is increasing evidence that these leukocytes are activated in the lung by the inhalation of cigarette smoke. The present study was designed to measure the effect of cigarette smoke inhalation on the rate of production and release of polymorphonuclear leukocytes (PMN) from the bone marrow into the peripheral blood. The thymidine analogue 5'-bromo-2'-deoxyuridine (BrdU) was used to pulse-label the dividing cells in the marrow of rabbits, measure their appearance in the peripheral blood, and calculate the time that PMN spend in the mitotic and postmitotic pools of the bone marrow. Comparison of animals exposed to 2 wk of cigarette smoke (n = 8) with sham-exposed controls (n = 9) showed that smoking decreased the mean transit time of PMNBrdU through the bone marrow from 97.3 +/- 3.0 h to 89.6 +/- 5.8 h (p < 0.001) by reducing the transit time of PMN in the postmitotic pool from 66.7 +/- 3.9 h to 53.7 +/- 0.7 h (p < 0.001). Both the mitotic (p < 0.05) and postmitotic (p < 0.05) pools of PMN increased in size following cigarette-smoke exposure. We conclude that chronic cigarette smoking stimulates the bone marrow, increases the size of the mitotic and postmitotic pools of PMN, and reduces the time PMN spend in the postmitotic pool in the marrow. These changes may contribute to the leukocytosis seen in cigarette smokers.