Mucous Cell Metaplasia in the Airways of Rats Exposed to Machining Fluids

Occupational exposure to microbial-contaminated machining fluidsis associated with a variety of adverse pulmonary effects includingchronic bronchitis and increased sputum production. We havepreviously demonstrated in F344 rats that inhaled endotoxincan increase the amount of stored intraepithelial mucosubstances(Vs) in the respiratory tract. The purpose of the present studywas to examine the effect of endotoxin-contaminated machiningfluid aerosols on mucous production. Rats were exposed to aerosolsof pyrogen-free water, 1 or 10 mg/m³ used machining fluid, or10 mg/m³ unused machining fluid for 3 hr/day for 3 days. Twenty-fourhours after the final exposure, right lung lobes were lavagedand the nasal cavity and left lung were fixed in formalin. Theamount of Alcian blue/periodic acid-Schiff-stained mucosubstanceswas determined by morphometry. Exposure to 10 mg/m³ used machiningfluid (equivalent to 0.8 µg/m³ endotoxin) produced a significantincrease in Vs in the epithelial lining of both the nasal septumand intrapulmonary airways. These changes in Vs were accompaniedby a significant increase in total cells and neutrophils inthe lavage fluid. No changes in stored mucosubstances or lavageparameters were found in animals exposed to 1 mg/m³ used machiningfluid aerosols. A significant increase in Vs was observed inthe nasal septum but not in the intrapulmonary airways of animalsexposed to 10 mg/m³ unused machining fluids (no measurable endotoxin).These results suggest that in addition to endotoxin, nonendotoxincomponents of machining fluids may contribute to the increasein sputum and chronic bronchitis reported for workers exposedto machining fluid aerosols.