MICROPARTICULATE ABSORPTION FROM THE RAT INTESTINE

A range of fluorescent polystyrene microparticles (0.15, 0.5, 1.0, 3.0 and 10.0 mu m) were administered intraduodenally to Wistar rats to provide an assessment of the levels of absorption of microparticles. Coupling a surgical procedure for the cannulation of the superior mesenteric lymph duct and the removal of Peyer's patches and mesenteric lymph nodes, with a sensitive flow cytometric assay it was possible to quantify microparticle absorption across the intestine. Absorption occurred after 5 min and was temporally variable, for all sizes of microparticles, over the time period studied. The 0.5-mu m microparticles were found to be absorbed in significantly greater numbers to the Fever's patches (P<0.01) and the mesenteric lymph (P<0.05) than other sizes and the 3.0-mu m microparticles were found to be retained in the mesenteric lymph nodes in greater numbers than particles of other sizes. The 10.0-mu m microparticles were retained in the mesenteric lymph nodes in low numbers. The levels of absorption, retention and extravasation of some sizes of microparticles suggests that the delivery of microencapsulated vaccines may allow the controlled delivery of antigens to the gut-associated lymphoid tissue (GALT) and their subsequent systemic dissemination.