Pluronic L-81: a potent inhibitor of the transport of intestinal chylomicrons

We have shown previously that the acute administration of 0.5 mg/h of Pluronic L-81 (L-81), a non-ionic hydrophobic surfactant, markedly reduced the lymphatic lipid transport by the rat small intestine. This inhibition is quickly reversible. By studying two other Pluronic surfactants, 25R1 and P84, we assessed the importance of the positioning of the hydrophilic moiety relative to the hydrophobic chain and also the hydrophilic-to-hydrophobic ratio in the action of L-81. In 25R1 the hydrophilic moiety is at the center and the hydrophobic chain is at both ends; in L-81 the reverse is true. P84 has four times more hydrophilic moiety by weight than L-81. Four groups of intestinal lymph fistula rats were infused intraduodenally for 8 h with [3H]triolein, egg lecithin, sodium taurocholate, and 1 mg/h of either L-81, 25R1, or P84. The control group did not have a surfactant added. Both the absorption of lipid by the small intestine and the intestinal transport of the lipid into the lymph were measured. Similar to previous findings, infusion of 1 mg/h of L-81 produced a dramatic reduction in lipid transport by the small bowel. Although infusion of 1 mg/h of either 25R1 or P84 reduced significantly the intestinal lipid transport, both surfactants were markedly less effective than L-81. In conclusion, both the positioning of the hydrophilic moiety and the hydrophilic-to-hydrophobic ratio of L-81 are important for its action.