Intestinal absorption of amino acids in the Pacific bluefin tuna (Thunnus orientalis): In vitro uptake of amino acids using hydrolyzed sardine muscle at three different concentrations

The absorption rates of different amino acids (AAs) were compared using the everted intestine technique with fresh proximal intestinal sections from the Pacific bluefin tuna (Thunnus orientalis). Sardine muscle was hydrolyzed in two steps; first with porcine pepsin, followed by an alkaline pancreatic bluefin tuna extract. The hydrolyzed extract was tested in triplicate samples at three concentrations (0.14, 0.09, and 0.06 mg of soluble protein mL− 1). In general, the non-essential amino acids (NEAAs; mainly Ala, Glu, and Gly) were assimilated in preference to the essential amino acids (EAAs). It was observed that certain AAs, such as Arg and Lys, had more affinity with the cationic transporters than did His. The glucogenic AA Glu always displayed double the absorption rate observed for Asp, probably to satisfy an energy requirement of the cells. The neutral AAs, Ala and Gly, showed the highest absorption rates at all concentrations. Other AA relations are also discussed. This is the first study that evaluates the use of this gastrointestinal system to estimate AA absorption and kinetics from a natural pool of AAs obtained from sardine muscle hydrolyzed with bluefin tuna digestive enzymes.