Site and rate of active transport of L-lysine in the intestine of the fowl.

A study was made to determine whether the avian small intestine was capable of actively transporting L-lysine from the mucosal to the serosal surface against a concentration gradient; and if it was, whether the rate of transport varied along the length of the intestine. The rate of active transport of L-lysine across the intestinal wall of the fowl was determined at 6 levels of the small intestine; the upper and lower halves of the duodenum, of the jejunum and of the ileum. Transport rates were calculated both as the amount of lysine transported per unit weight of dried intestine and per length of live intestine. These data indicated no active transport of lysine by the duodenum but active transport by the jejunum and ileum. Based on weight, the jejunal and ileal levels transported 7.0 AmÃ3les of lysine/g of dried intestine per hour. Based on length, the rate of active transport progressively de creased significantly from the upper jejunal to lower ileal regions of the small intes tine. It was concluded that rates of L-lysine transported across the intestinal wall based on unit length represented true physiological differences between the various intestinal segments studied. Kratzer (l) concluded that all amino acids were absorbed by simple diffusion. He measured the rate of absorption of 15 amino acids (including L-lysine) from the intestinal tract of White Leghorn chicks using the Cori method. In this pro cedure a measured volume of solution was introduced into the crop of an unanesthetized chicken, and at the end of the experimental period the animal was killed, and the unabsorbed gastrointes tinal tract contents were analyzed. Hagihira et al. (2), using everted sacs of intestine and an initial 1 HIM amino acid concentration in the mucosal and serosal fluids, successfully demonstrated that L-lysine is actively transported across the intestinal wall of the hamster against a concentration gradient. According to Wilson (3), Hagihira showed that the rate of active L-lysine transport is approxi mately the same in the upper, mid, and lower small intestine of the hamster. Larsen et al. (4) obtained similar results using everted sacs of rat small intestine. Since the Kratzer study, Paine and Newman (5), and Lin and Wilson (6) have found evidence that the L-isomers of methionine and histidine, and the Lisomer of tyrosine, respectively, are trans ported across the intestinal wall of the chick by a selective process. Imondi and Bird (7) investigated the site of nitrogen absorption in the fowl and found that the percentage of dietary nitro gen which disappeared from each intes tine level progressively decreased from the upper jejunum to the lower ileum. The present investigation was under taken to gain a more thorough understand ing of the physiology of absorption in the avian intestine. The specific aims of the investigation were to determine whether the avian intestine was capable of actively transporting L-lysine from the mucosal to the serosal surface against a concentration gradient; and if it was, at what rate the lysine was transported across the various levels of the intestine (upper and lower halves of the duodenum, of the jejunum, and of the ileum). EXPERIMENTAL PROCEDURE