We reported that the growth promoting activity of di-n-butylphthalate (DBP)
was observed when rats were fed with a niacin-free and tryptophan-limiting
diet (Shibata et al., 1982. J Nutr Sci Vitaminol 28, 173-177). The present
experiment was performed to investigate whether this phenomenon is attribu
table to the increase in the conversion ratio of tryptophan to niacin. The
weaning rats were fed with a 10% (low protein diet) or 20% protein (convent
ional protein diet) diet with or without adding 1% DBP The conversion ratio
of tryptophan to niacin was significantly higher in the DBP group than in
the control group; for 10%, casein diets, it increased two-fold and for 20%
casein diet, about five-fold. From these results, the previous finding is
possibly explained by DBP increasing the conversion ratio of tryptophan to
niacin.