In vivo increase of passive intestinal absorption by cotransporter activation in rat.

The effect of the luminal exposure to 25 mmol/L galactose, alanine, tryptophan or sorbitol on the passive absorption of 10 mmol/L galactose, mannitol and 2-deoxyglucose has been studied in in vivo perfused rat jejunum. Absorption of mannitol or 2-deoxyglucose is markedly enhanced by the presence of any of the three cotransported substrates, but not by that of the non transportable sorbitol. Furthermore the passive absorption of galactose (measured in the presence of 2 mmol/L phloridzin) increases after alanine active transport, while it remains unmodified after sorbitol exposure. The stimulatory effect on mannitol or 2-deoxyglucose absorption can be observed 5 min after addition of galactose and it is not significantly modified during the 50 min period that followed. The passive absorption increase observed with alanine and especially with galactose seems to be easily reversed by washing with saline solution. With tryptophan, the effect remains after washing but some mucosa desquamation is observed. These results with direct measures confirm the passive absorption stimulation by the activation of Na(+)-substrate cotransporters. The passive absorption may take place by the paracellular way through the tight junctions.