Charge selectivity of rat intestinal capillaries. Influence of polycations

The role of fixed anionic sites on the intestinal capillary wall in transvascular protein exchange was assessed by neutralizing the negative charges with polycations. The studies were performed in anesthetized rats with an intestinal lymph cannula. Intestinal lymph flow and lymph and plasma total protein concentrations were measured at regular intervals before and after intravenous infusion of either protamine sulfate, poly-L-lysine, or poly-ethyleneimine. Protamine sulfate infusion produced an eightfold increase in lymph flow and a fivefold increase in lymph protein clearance. Lymph flow increased 4.6-fold and lymph protein clearance increased 3.6 times over control in rats receiving the poly-L-lysine infusion. Polyethyleneimine infusion produced results comparable in magnitude to protamine sulfate; however, the animals were unable to tolerate this agent. The enhanced transcapillary protein fluxes produced by the polycation infusions suggest that fixed anionic sites normally impede the egress of proteins from the intestinal vasculature.