Alteration of Serotonin Metabolism in Rats Deficient in Niacin And Tryptophan.

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Abstract
Mechanisms responsible for the dermatitis, dementia, and diarrhea of pellagra remain obscure. Since serotonin affects skin, gut and brain, and tryptophan is a precursor of both niacin and serotonin, levels of this bioamine were measured in niacin-tryptophan deficient rats. Weanling, male rats were randomly fed diets as follows: niacin-poor, tryptophan-deficient; tryptophan-deficient; normal, restricted in volume; and, normal ad libitum. When the rats manifested pellagra, they and their controls were killed and serotonin levels of the brain, intestine, and colon were determined photofluorometrically by the method of Udenfriend. A low-tryptophan diet significantly decreased serotonin concentrations in the intestine, colon, and brain. In contrast, the pellagrogenic niacin-poor tryptophan-deficient diet markedly increased serotonin concentrations of the small intestine while brain and colonic concentrations were unaffected. This suggests that the diarrhea of pellagra may result from motor effects of increased serotonin concentration in the small intestine. The increased serotonin concentration noted in sprue may be, in fact, due to a niacin-tryptophan deficiency. The increased intestinal concentration of serotonin is probably best explained by decreased local destruction of this bioamine.