Structure of the adduct of glutathione and activated 3-methylindole.

3-Methylindole (3MI) is a pneumotoxic metabolite of tryptophan fermentation in ruminants. The toxicity of 3MI is organ, cell, and species specific. In ruminants and horses, the most susceptible species, the lung is the target organ. Type I alveolar epithelial and nonciliated bronchiolar epithelial (Clara) cells are the most susceptible targets within the lungs of ruminants, 2,3 while Clara cells only are primarily damaged by 3MI in horses.4 Exposure of man to 3MI is through intestinal absorption and by cigarette smoke although the toxic manifestations of this exposure have not yet been assessed.5–7