Small intestinal permeability in animals and man.

The permeability of the human small intestine has been studied by measuring the clearance from the plasma into the intestinal lumen of substances with molecular weights ranging from 60 to 80 000. A direct relationship has been demonstrated between intestinal loss and plasma concentration and an inverse one between clearance and molecular size.The permeability of the rabbit small intestine has been studied at various levels by measuring the blood-to-lumen clearance of substances of different molecular size ranging from 60 to 40 000. It has been demonstrated that there is a progressive fall in permeability from the duodenum to the terminal ileum for all the substances studied.