COMPARATIVE SENSITIVITY OF LACTATING AND VIRGIN FEMALE RATS TO OZONE-INDUCED PULMONARY INFLAMMATION

Studies from this laboratory have shown that lactating rats exhibit a greater inflammatory response to inhaled ozone than age-matched nullig ravidous or postlactating rats. One factor contributing to this enhanc ed response by lactating rats is their greater ventilation, which resu lts in a higher inhaled dose rate. In the study reported here, we inve stigate the concept that lactating rats are predisposed to ozone-induc ed inflammation, not only because of their higher ventilation but also because of the inherently greater sensitivity of their tissues. We fo und that the airways of naive, 13-day postpartum lactating Sprague-Daw ley rats have significantly greater numbers of polymorphonuclear leuko cytes (PMNs), a higher protein concentration, and a lower concentratio n of the antioxidant ascorbic acid than do the airways of virgin femal es. Lactating rats also have a higher PMN concentration in their circu lating blood. These differences in the steady state condition of lacta ting rats, particularly the airways of the respiratory tract, suggest that predisposition of lactating rats to pulmonary inflammation induce d by ozone may be due in part to changes in immunological status durin g lactation and to the greater propensity of the respiratory tract tis sues of lactating rats to respond to stimulation by ozone. We compared the kinetics of airway inflammatory changes detected in bronchoalveol ar lavage fluid following acute exposure of lactating and virgin femal e rats to 0.3 and 0.5 ppm ozone for 6 h, and observed an earlier onset and greater intensity and persistence of the inflammatory response in the lactating animals.