Effects of excess leucine on growth and tryptophan and niacin metabolism in rats.

Abstract

SummaryThe effects of an excess intake of leucine, for a short period (3 to 4 weeks) and a long period (12 weeks), on growth and excretion of tryptophan and niacin metabolites in rats were studied. Excess intake of leucine (4 or 5%) for a short period did not affect increase in body weight or organ weight (liver, kidney and heart) compared with those of rats fed the control diet. Excess intake of leucine for a long period resulted in a decrease in body weight, and an increase in the relative weight of the liver and kidney. Urinary excretions of N1 methyl nicotinamide (N-MNA), N1-methyl-2-pyridone-5-carboxamide (2 Py), niacin, quinolinic acid and 5-hydroxyindole acetic acid did not differ in rats fed an excess-leucine diet and rats fed a control diet. In niacin deficiency, the excretions of N-MNA, 2-Py and NiA decreased. Excess leucine intake increased the plasma levels of leucine and alanine and decreased those of valine, isoleucine, tryptophan and cystine. Excess leucine intake decreased the levels of valine, isoleucine, methionine and leucine in the liver, but these changes were not observed in niacin deficient rats. Changes in the levels of nicotinamide mononucleotide (NMN), nicotinamide adenine dinucleotide (NAD), nicotinamide adenine dinucleotide phosphate (NADP) in erythrocytes, suggested to occur in pellagra, were not observed. These findings do not support the idea that an excess intake of leucine results in changes in metabolism similar to those observed in pellagra.

Effects of leucine/isoleucine ratio in amino acid mixture-diets simulating normal and high-lysine maize proteins on growth, nitrogen balance, and tryptophan-niacin metabolism in rats.

“…Later, they found that isoleucine supplementation could reverse and correct the abnormalities induced by excess leucine in diet, and indicated that ratios of leucine to isoleucine in diet might be etiologically related to pellagra (7). Though these problems have been studied repeatedly by many investigators, all of their results cannot support the findings of Gopalan et al (8)(9)(10)(11)(12)(13). To resolve this discrepancy and to re-examine the action of excess leucine, we paid attention to differences of leucine/isoleucine ratios seen in normal maize and its mutants.…”

“…Raghuramulu et al reported that NMN and quinolinic acid in urine of rats fed 1.5% leucine supplemented casein diet increased significantly(5). However , other investigators could not reproduce their results and reversely could find a decrease in these compounds (9,12). Furthermore, considering our results, it could be concluded that leucine supplementation failed to affect tryptophan and niacin metabolism.…”

“…The plasma tryptophan level was unchanged by dietary excess leucine in this study. It has been reported that plasma tryptophan level decreased in rats fed on maize diet (26) and leucine added maize diet (9,27) or in pellagrins (8). However, there is the report that the plasma tryptophan level did not change in pellagrins (28 Vol.…”