Response of the bronchial mucociliary clearance system in rabbits to inhaled sulfite and sulfuric acid aerosols.

A group of eight rabbits was exposed (orally) for 1 hr to a distilled water aerosol (sham control) or to submicrometer aerosols of either a transition metal sulfite complex (Fe(III)-S(IV], sodium sulfite (Na2SO3), or sulfuric acid (H2SO4). Mucociliary clearance was evaluated by external retention measurements of radioactively tagged tracer particles from the bronchial tree. Fe(III)-S(IV) in the range of 238 to 1227 micrograms/m3 (as SO2-3) produced no significant change from sham control in the mean residence time (MRT) of the tracer, indicating no effect upon mucociliary clearance rate. On the other hand, Na2SO3 at levels greater than or equal to 1200 micrograms/m3 (as SO2-3) resulted in clearance acceleration; the lack of effect of Fe(III)-S(IV) is possibly due to its stability. H2SO4 at 260 to 2155 micrograms/m3 produced a significant dose-related response, indicating clearance acceleration at low concentrations and a depression at higher levels.