The kinetics of amino acid absorption and alteration of plasma composition of free amino acids after intestinal perfusion of amino acid mixtures

is believed to be facilitated by three carrier-mediated transport systems (1) which are stereospecific for the neutral, basic, and acidic groups of amino acids. The active process of absorption has been demonstrated for the neutral and basic amino acids only (2, 3). Although all the neutral amino acids (except cystine, which is transported with the basic amino acids) seem to share the same transport system (4), the presence of several transport sites with different affinities for the neutral amino acids has been postulated (5). Present knowledge concerning the ab-sorption and transport of amino acids from the intestine stems almost entirely from animal experiments utilizing the in vitro (everted sac) and in vivo techniques. Data Ofl the intestinal absorption of amino acids in the human are meager, since studies have been limited to one experimental subject with a blind 1001) (Thiry) of the ileum open-ing through the abdominal wall (6). Th