Increased urinary excretion of tryptophan metabolites in rats exposed to nitrogen dioxide

Nitrogen dioxide (NO 2) is widely distributed in nature, and human exposure to it is extensive. It is abundant in all burnt organic materials, including automobile exhaust and cigarette smoke. In the lung of animals exposed to NOo, some subtle changes will occur and they include inflammation (Gardner et al. 1969), emphysema (Freeman and Haydon 1964) and reduced phagocytic or bactericidal activity of the alveolar macrophages (Suzuki et ai.1986). In epidemiological study, Yanagisawa et al. (1986) reported the increased urinary hydroxyproline excretion of residents living in areas of high NO 2 levels. Moreover, in experimental study using animals, exposure to NO o induced the alteration of collagen synthesis and/or ~ degradation in lung (Kleinerman 1979) and accelerated collagen degradation in lung by NOo exposure was responsible for the increase in the excretion of urinary hydroxyproline (Kosmider et al. 1973). From these findings on the increased excretion of urinary hydroxyproline by NO2, Yanagisawa et al. (1986) suggest that urinary hydroxyproline could be used as a personal biochemical indicator of the effects of NO 2 on human health prior to manifestation of respiratory symptoms. Moreover, Ripperton and Johnston (1959) reported that urinary content of aspartic acid increased in rats exposed to NO 9. Exposure to NO 2 may influence the metabolism of amin8 acids to induce their excessive urinary excretion. Since the maximum permissible limit for NOo in working environments in Japan is 5 ppm, in this wo2k, we have studied the changes of urinary excretion of tryptophan metabolites in rats exposed to 5 ppm NO 2 in order to find a new urinary biochemical indicator of the effects of NO 2 exposure on human health.