It is known that deaths attributable to
pellagra, which is considered to be a disease caused by the disturbance of
tryptophan metabolism, have been approximately two-fold higher in women than in men. We investigated the effects of the administration of female and male
sex hormones on the contents of
tryptophan and such metabolites as
serotonin,
nicotinamide,
N1-methylnicotinamide, N1-methyl-2-pyridone-5-carboxamide, and N1-methyl-4-pyridone-3-carboxamide, and on the conversion ratio of
tryptophan to
niacin in male rats. Feeding a diet containing
estrone or
testosterone had no effect on the concentrations of
tryptophan and
serotonin in the blood and brain, or on the concentration of 5-hydroxyindole-3-acetic
acid in the brain. On the contrary, feeding a diet containing
estrone caused to a decrease in the urinary excretion of
nicotinamide,
N1-methylnicotinamide, N1-methyl-2-pyridone-5-carboxamide, and N1-methyl-4-pyridone-3-carboxamide, and of the conversion ratio of
tryptophan to
niacin when compared with the control rats. Feeding a diet containing
testosterone had no effect on any parameter. We postulate from these findings that the cause of higher
pellagra deaths in women than in men is attributable to the decrease in the formation of
niacin from
tryptophan, but not in the formation of
serotonin by the female
hormone. It seems likely that female
sex hormones inhibit the synthesis of
niacin from
tryptophan, and that women, especially during pregnancy, will be more at risk to
pellagra than are men.