AN IMPROVED EVERTED GUT SAC AS A SIMPLE AND ACCURATE TECHNIQUE TO MEASURE PARACELLULAR TRANSPORT ACROSS THE SMALL-INTESTINE

An improved everted gut sac system has been developed in which the sac s were carefully prepared from rat small intestine and incubated in ti ssue culture medium. Under these conditions, the tissue showed good mo rphology at the electron microscope level, and was metabolically activ e for up to 2 h at 37 degrees C. Mannitol, an established probe of par acellular transport, was transported from the mucosal to the serosal s ide of the sac tissue. Excellent kinetic data showed that transport wa s linear up to 75 min and over a wide range of concentrations (0.025 - (10 mM). Mannitol was not detected in the tissue and transport was en hanced by EGTA, confirming the paracellular route of passage. Sacs pre pared from colon also showed mannitol transport, but at a slower rate. Comparisons with Caco-2 cell monolayers showed that the everted sacs exhibited higher levels of paracellular transport than the cultured ce ll line. The improved everted gut sac system is an inexpensive and rel atively simple technique with considerable potential as an in vitro to ol to study the mechanisms, kinetics and enhancement of drug absorptio n across the small intestine at different sites and in the colon.