Effects of methionine and related compounds on plasma cholesterol level in rats fed a high cholesterol diet

The comparative effects of methionine and its structurally and metabolically related compounds on plasma cholesterol level were investigated with rats fed a high cholesterol diet. The plasma cholesterol level was significantly enhanced by the dietary addition of methyl compounds such as L-methionine, D-methionine, choline and betaine. On the other hand, the intermediary metabolites of methionine such as homocystine, cysteine and 3-methylthiopropionate reduced plasma cho-lesterol. S-Methyl-L-cysteine and dimethylglycine had no significant effect. The plasma cholesterol-elevating effects of methionine, betaine and histi-dine were all prevented, more or less, by the concurrent addition of glycine to the diet, suggesting the existence of a common mechanism for their effects. The results support a possibility that the plasma cholesterol-elevating efficacy of methionine is attributable to its methyl group.