Effect of α-Aminoisobutyric Acid on Arginine Metabolism in Chicks

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Abstract
The addition of 0.5% α-aminoisobutyric acid (AIB), a presumably nonmetabolizable amino acid, to a casein basal diet supplemented with graded levels of L-arginine·HCl caused an accumulation of free arginine and a depression of free ornithine in both plasma and muscle of chicks, and also altered the levels of some other amino acids. The differential effect on free amino acids was more pronounced in muscle than in plasma. Injection of AIB into the breast muscle of chicks fed the casein diet supplemented with 3% L-arginine·HCl gave an effect on arginine, ornithine and other amino acids similar to that given by oral feeding of AIB. Further observations of significance were that the weight gain and feed efficiency of chicks fed the casein basal diet were improvd by supplementation with AIB, and that kidney arginase activity was greatly depressed when AIB was fed. Arginine metabolism was also affected by AIB in chicks fed a basal diet based on wheat gluten supplemented with arginine, but the growth response to AIB supplementation found with the casein diet was not observed. Possible mechanisms of the influence of AIB on arginine metabolism are discussed in relation to the experimental findings.