Factors regulating the exchange of nutrients and drugs between lymph and blood in the small intestine.

An experimental design was developed to study the factors regulating the absorption of nutrients and drugs into the intestinal lymphatic system in normal and cirrhotic rats. Test compounds given via in situ jejunal luminal perfusion or systemic intravenous infusion were measured simultaneously in intestinal lymph, portal venous plasma and intestinal perfusate. Steady-state lymph plasma concentration ratios were used to compare the permeability characteristics of the intestinal mucosal-lymph and blood-lymph barriers. The absorption of compounds from the interstitial space into the intestinal lymphatic system is determined primarily by their permeability through the capillary of the portal circulation and by their lipid solubility; if a compound is too large to be absorbed into the portal circulation it is absorbed into the intestinal lymphatics.