The permeability of the plasma-lymph barrier of the small intestine of various species to macromolecules.

The filtration coefficients of polyvinylpyrrolidone (PVP) of molecular weight 10,000-110,000 were measured at the plasma-lymph barrier of the upper small intestine of rabbits, rats and cats. For this purpose the animals were given intravenous injections or infusions of PVP in such a way as to produce a constant blood level; PVP concentrations were measured in lymph obtained by cannulating the mesenteric duct and also in the plasma. In these species low molecular weight PVP had a filtration coefficient of 0.85-0.64, while high molecular weight PVP (MW 110,000) either had a very low filtration coefficient - 0.22 - or was not detectable in the intestinal lymph. The three species, representing herbivores, omnivores and carnivores, showed no differences in the penetration behavior of PVP, i.e., in the permeability of the plasma-lymph barrier to macromolecules.