Utilization of Injected and Orally Administered Amino Acids by the Rat. ∗

Abstract

Summary

Rats fed a lysine-deficient diet ad libitum and injected subcutaneously twice daily with a lysine solution grew at about half the rate of rats receiving lysine in the diet. Rats fed ad libitum an isoleucine-de-ficient diet failed to respond when they were injected twice daily with an isoleucine solution. If rats were fed the isoleucine-deficient diet for a period of only 2 hours daily and were given subcutaneous injections of isoleucine at the end of feeding period their rate of growth was about one-third that of rats receiving isoleucine in the diet. Under the same conditions, injection of rats fed a diet high in leucine with isoleucine and valine resulted in a comparable improvement of growth. These observations indicate that the rate of catabolism of isoleucine is much faster than that of lysine in the rat and that the amount of an amino acid catabolized depends upon mode of administration.