Kinetics of D-histidine diffusion across rat intestine in vitro.

A five-compartment linear model for diffusion in vitro across rat jejunum has been proposed for the study of the kinetic constants of D-histidine transport. Once preliminary experiments using 2,4-dinitrophenol and L-methionine have proved that D-histidine gives rise to passive transport only, the validity of the model was tested and its parameters estimated through a best-fitting procedure by using experimental data concerning D-histidine transport. D-Histidine diffusion was studied in everted and unreverted loops mounted in an oxygenated bath system. Both mucosa to serosa and seroa to mucosa movements of D-histidine (3-30 mM) were evaluated by measuring chemically the amount of D-histidine transported into intestinal lumen every 5 min for 60 min. Results obtained proved that D-histidine transport in each direction (mucosa to seroa or seroa to mucosa) was dependent-concentration process. Nevertheless different values of gain and time constants were estimated for the transport in the two directions.