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 pr ovide an assessment of the levels of absorption of microparticles. Cou pling a surgical procedure for the cannulation of the superior mesente ric lymph duct and the removal of Peyer's patches and mesenteric lymph nodes, with a sensitive flow cytometric assay it was possible to quan tify microparticle absorption across the intestine. Absorption occurre d after 5 min and was temporally variable, for all sizes of microparti cles, over the time period studied. The 0.5-mu m microparticles were f ound to be absorbed in significantly greater numbers to the Fever's pa tches (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 mesenteri c 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 microencaps ulated vaccines may allow the controlled delivery of antigens to the g ut-associated lymphoid tissue (GALT) and their subsequent systemic dis semination.