NO2 REACTIVE ABSORPTION SUBSTRATES IN RAT PULMONARY SURFACE LINING FLUIDS

Inhaled (NO2)-N-. is absorbed by a free radical-dependent reaction mec hanism that localizes the initial oxidative events to the extracellula r space of the pulmonary surface lining layer (SLL). Because (NO2)-N-. per se is eliminated upon absorption, most likely the SLL-derived rea ction products are critical to the genesis of (NO2)-N-.-induced lung i njury. We utilized analysis of the rate of (NO2)-N-. disappearance fro m the gas phase to determine the preferential absorption substrates wi thin rat SLL. SLL was obtained via bronchoalveolar lavage and was used either as the cell-free composite or after constituent manipulation [ (i) dialysis, treatment with (ii) N-ethylmaleimide, (iii) ascorbate ox idase, (iv) uricase, or (v) combined ii + iii]. Specific SLL constitue nts were studied in pure chemical systems. Exposures were conducted un der conditions where (NO2)-N-. is the limiting reagent and disappears with first-order kinetics ([NO2](0) less than or equal to 10 ppm). Red uced glutathione and ascorbate were the principle rat SLL absorption s ubstrates. Nonsulfhydryl amino acids and dipalmitoyl phosphatidylcholi ne exhibited negligible absorption activity. Whereas uric acid and vit amins A and E displayed rapid absorption kinetics, their low SLL conce ntrations preclude appreciable direct interaction, Unsaturated fatty a cids may account for less than or equal to 20% of absorption. The resu lts suggest that water soluble, low molecular weight antioxidants are the preferential substrates driving (NO2)-N-. absorption. Consequently , their free radicals, produced as a consequence of (NO2)-N-. exposure , may participate in initiating the (NO2)-N-.-induced cascade, which r esults in epithelial injury.