Dipeptide metabolism in the isolated perfused rat small intestine

The purpose of the present study was to investigate the utilisation of vascularly administered leucyl-leucine (Leu-Leu), alanyl-glutamine (Ala-Gln) and glycyl-glutamine (Gly-Gln) by the isolated vascularly perfused rat small intestine. Fractional extraction rates were 49%, 35.5%, and 12% for Leu-Leu, Ala-Gln, and Gly-Gln (0.15mM) corresponding to a net uptake of -63.5, -31.5, and -17 nmol/min/g wet weight. Nitrogen metabolism in terms of glutamine uptake and release of alanine and ammonia was not different when perfusion with dipeptides or with free amino-acids were compared. No soluble dipeptidase activity was released into the plasma- and cell-free synthetic vascular perfusate. No dipeptide could be recovered from the luminal perfusate. Considering the high fractional extraction rate for Leu-Leu, it is conceivable that dipeptide assimilation may occur also in extramucosal gut tissue. Although dipeptide transport cannot be excluded, dipeptide assimilation in small intestine may involve membrane bound peptidase(s), as in liver.