Reduction of hexavalent chromium by ascorbic acid in rat lung lavage fluid

The reduction of hexavalent chromium [chromium(VI)] in lung lavage fluids, microsomal (S-9) fractions of lung and liver tissues, erythrocyte lysates and plasma prepared from adult rats was examined at pH 7.4 (37 degrees C). Specific reducing capacity, which was defined as the amount of chromium(VI) reduced per mg of protein in the test sample, was highest in the lavage fluids. The concomitant trivalent species [chromium(III)] was detected as complexes with some of the lavage components and probably as colloidal hydroxides. By gel filtration analysis and UV spectrometry, ascorbic acid (AsA) was identified as an important reducing factor in the lavage fluids. AsA levels in the lavage fluids were about 38 micrograms/g tissue, corresponding to 12% of total AsA in the intact lungs. The molar ratios of oxidized AsA and reduced chromium(VI) in the lavage samples were about 3:2.3 on an average. On the basis of this molar ratio, the AsA levels in the lavage fluids are equivalent to a reducing capacity of 8.4 micrograms chromium(VI)/g tissue. These results suggest that the lining layers (surfactant layers) of rat lungs provide an AsA-related capacity for protection of the cells against the toxic effects of chromates and probably other oxidants.