Studies on Natural and Racemic Amino Acids With Rats

We have previously reported that glycine, nL-phenylalanine, and Lproline inhibit the growth of young rats when added to an adequate diet at a 5 per cent level (1).Toxicity of amino acids has been reported by other workers (2-6).We have extended these studies to a number of other amino acids and have shown differences, in some cases, between the growth-inhibiting effects of natural isomers and racemic mixtures.In the case of aspartic acid a more thorough study has been made. EXPERIMENTALIn the preliminary experiments 21 day-old male albino rats weighing 40 f 2 gm.were divided into groups of five each and fed the experimental diets ad libitum.The diets contained 20 per cent Labco casein and other ingredients, as previously reported (1).The amino acids were fed at a 2 or 5 per cent level of the diet.Subsequently, the effects of feeding L-and nL-aspartic acids at a 5 per cent level were similarly studied on groups of ten rats each.After 2 weeks on this diet, the animals were kept in metabolism cages for 5 days