Passage of molecules through the wall of the gastrointestinal tract. I. A simple experimental model

We describe here a simple experimental model for studying how the structural integrity of the intestinal wall is related to the transmural passage of molecules into the circulation. The model is based on the deposition of fluorescently labeled dextran in the intestine and its eventual recovery in the portal blood and mesenteric lymph. The fluorescent compound can be determined with sensitivity and ease by using fluorescence spectrometry. As judged from chromatography on Sephadex G-100, the compound was not degraded or otherwise chemically altered on its route of passage. The rate of passage was inversely proportional to the molecular size. The model may prove useful for studying factors that influence the transmission of macromolecules across the intestinal wall. Such a transmission probably underlies the pathogenesis of a variety of diseases.