| Abstract: | Intestinal absorption of amino acids in the chicken occurs by way of processes which are concentrative, Na+-dependent and dependent upon metabolic energy in the form of ATP. Intestinal transport is carrier-mediated, subject to exchange transport (trans-membrane effects) and is inhibitable by sugars, reagents which inactivate sulfhydryl groups, potassium ion, and by deoxpyridoxine, an anti-vitamin B6 agent. It is stimulated by phlorizin, a potent inhibitor of sugar transport, and in Na+-leached tissue by modifiers of tissue cyclic AMP levels, e.g. theophylline, histamine, carbachol and secretin. Separate transport sites with broad, overlapping specificities function in the intestinal absorption of the various classes of common amino acids. A simple model for these sites includes one for leucine and other neutral amino acids, one for proline, beta-alanine and related imino and amino acids, one for basic amino acids, and one for acidic amino acids. Absorption of amino acids appears to be widespread in occurrence in the digestive tract of the domestic fowl; transport has been reported to be present in the crop, gizzard, proventriculus, small intestine and in the colon. By the end of the first week of life post-hatch, the caecum loses its ability to transport. Similarly, the yolk sac loses its ability by the second day post-hatch. Intestinal transport was noted before hatch and was found to be maximal immediately post-hatch. A requirement for Ca2+ appears to be lost after the first week of life post-hatch. The cationic amino acids appear to be reabsorbed by a common mechanism in the kidney. Transport rates of leucine measured in the intestine or in the erythrocyte were found to cluster about discrete values when many individual chickens were surveyed; such patterns may be an expression of gene differences between individuals. Two lines of chickens have been developed, one high and the other low uptake, through selective breeding based on the ability of individual birds to absorb leucine in erythrocytes. High leucine absorbing chickens were found to be more effective in absorbing lysine and glycine, were more effectively stimulated by Na+, had greater erythrocyte Na+, K+-ATPase activity, and their erythrocytes contained about 20% less Na+ than low line erythrocytes. The underlying genetic difference between these lines may reside at the level of the Na+, K+-ATPase and (or) with a regulatory gene determining carrier copies. Amino acid transport in erythrocytes was noted to be highest in pre-hatch chicks and to diminish during post-hatch development.(ABSTRACT TRUNCATED AT 400 WORDS) |
