EFFECT OF OZONE ON THE POSTNATAL-DEVELOPMENT OF LAMB MUCOCILIARY APPARATUS

We determined whether exposure to O3 early in the postnatal period impairs the normal development of the mucociliary apparatus in lambs and whether such changes lead to prolonged abnormalities in mucociliary function. Lambs were exposed to air (controls) or to 1 ppm O3 for 4 h/day for 5 days during the 1st wk of life. Tracheal mucus velocity (TMV), a marker of lung mucociliary clearance, was measured in vivo at birth (0 wk) and up to 24 wk later, and tracheal secretory function was measured (in vitro) and the morphology of the tracheal mucosa was determined at 0 and 2 wk in both groups. In the control group, TMV increased 94% from 0 to 2 wk (P < 0.05), continued to increase until reaching a plateau at 8 wk, and then remained constant from 8 to 24 wk. In contrast, O3-exposed lambs showed a 24% decrease in TMV from 0 to 2 wk (P < 0.05 vs. control), and throughout the remaining time TMV remained below (P < 0.05) that observed in control lambs. O3 exposure partially prevented the age-dependent decrease in basal secretion of tracheal macromolecules normally observed between 0 and 2 wk. These changes in secretory function were associated with a significant increase in tissue conductance (37%, P < 0.05 vs. 0 wk), predominantly the results of active chloride secretion. The functional changes induced by O3 were associated with a retardation of the normal morphological development of the tracheal epithelium. In control lambs mucus cell populations declined from 21% at birth to 16% at 2 wk (P < 0.05) and ciliated cell populations rose from 34 to 38% (P < 0.05). In the O3-exposed lambs, however, mucus and ciliated cell percentages remained at newborn levels (22 and 33%, respectively, both P < 0.05 vs. control). These findings indicate that O3 exposure during the 1st wk of life retards the normal development of the mucociliary system in sheep and that such changes may lead to prolonged impairment of lung mucociliary clearance.