Absorption of glucose, amino acids, and dipeptides by the intestines of Atlantic salmon (Salmo salar L.)

Rates of glucose, amino acid and dipeptide absorption by the intestine of A tlantic salmon (Salmo salar L.) were measured in vitro at 10 degrees C as f unctions of concentration and region using intact tissues (everted sleeve m ethod). Salmon (weight range 300-1300 g) fed a commercial, extruded salmon feed, were kept at 12-13 degrees C in freshwater. Maximum rates (V-max) of glucose and dipeptide transport were low compared to most amino acid V-max values. There was a declining proximal-to-distal gradient of absorption alo ng the post-gastric intestinal tract. A saturable component of absorption w as not evident for proline and glycyl-proline in the distal intestine, and glycyl-sarcosine in any region. 'Apparent diffusion', which may include low affinity, high capacity carrier systems and carrier-independent influx, ap pears to account for the majority of total uptake at higher concentrations of amino acids and dipeptides. There was competition between the dipeptides for transporter sites in the pyloric ceca and mid intestine, suggesting a common carrier. There was also indication of hydrolysis of these dipeptides by brush border membrane enzymes.