Effect of Supplementing Methionine and Threonine to a Non-protein Diet on the Induction of Enzymes by Polychlorinated Biphenyls in Rats

Abstract

The N-sparing action of methionine and threonine in rats fed with a non-protein diet seems to indicate that methionine and threonine are the endogenously most-limiting amino acids. The effect of a dietary supplementation of methionine and threonine to a non-protein diet on enzyme induction by polychlorinated biphenyls (PCB) was investigated. Liver microsomal drug-metabolizing enzymes were further induced by the methionine and threonine supplement to the non-protein diet in PCB-receiving rats. Although feeding with PCB did not increase the urinary ascorbic acid excretion in rats of the non-protein diet group, the supplementation of methionine and threonine to the non-protein diet markedly increased this excretion. From these observations, dietary methionine and threonine might promote the synthesis of drug-metabolizing enzymes and the enzymes related to ascorbic acid biosynthesis in PCB-receiving rats.