THE EFFECTS 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 cigare tte smoke. The present study was designed to measure the effect of cig arette smoke inhalation on the rate of production and release of polym orphonuclear leukocytes (PMN) from the bone marrow into the peripheral blood. The thymidine analogue 5'-bromo-2'-deoxyuridine (BrdU) was use d 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. Com parison of animals exposed to 2 wk of cigarette smoke (n = 8) with sha m-exposed controls (n = 9) showed that smoking decreased the mean tran sit time of PMN(BrdU) through the bone marrow from 97.3 +/- 3.0 h to 8 9.6 +/- 5.8 h (p < 0.001) by reducing the transit time of PMN in the p ostmitotic pool from 66.7 +/- 3.9 h to 53.7 +/- 0.7 h (P < 0.001). Bot h the mitotic (p < 0.05) and postmitotic (p < 0.05) pools of PMN incre ased in size following cigarette-smoke exposure. We conclude that chro nic cigarette smoking stimulates the bone marrow, increases the size o f the mitotic and postmitotic pools of PMN, and reduces the time PMN s pend in the postmitotic pool in the marrow. These changes may contribu te to the leukocytosis seen in cigarette smokers.