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Tryptophan and Nitrogen Metabolism and Pregnancy of the Rat as Affected by Dietary Supplementations with Leucine and with Amino Acid Mixtures^1,2,

Department of Nutrition and Food, University of Massachusetts, Amherst, Massachusetts 01002

Niacin-free, low tryptophan diets of rats were supplemented by either L-leucine; a combination of L-leucine, L-isoleucine and L-valine; a tryptophan-free mixture of essential amino acids; or a mixture of nonessential amino acids. Determinations were made of the effects produced by these supplementations on N¹-methylnicotinamide excretion, hepatic pyridine nucleotide concentration, nitrogen balance, nitrogen content of carcasses and on the condition and viability of fetuses. Supplementation with 5% leucine resulted in depression of values of the tryptophan metabolites which could not be attributed to decreased food intake. It also produced lowering in nitrogen retention, impairment in fetal condition, a small decrease in the percentage nitrogen in the fetuses, but no significant changes in the percentage of nitrogen in the carcasses. At the 2.5% level leucine was less effective in producing these changes. The adverse effect of leucine supplementation on tryptophan and nitrogen metabolism and on fetuses was decreased but not completely alleviated by addition of isoleucine and valine to the leucine diet. The amino acid imbalance created by supplementation of low tryptophan diets with a tryptophan-free essential amino acid mixture produced greater depression of tryptophan metabolism and impairment of the fetuses than did supplementation with an isonitrogenous mixture of nonessential amino acids.

² Preliminary results of this investigation were presented at the 52nd annual meeting of the Federation of American Societies for Experimental Biology, Atlantic City, New Jersey, 1968.

Manuscript received 8 August 1969.