2-micron latex particles accumulated in macrophages in intestinal Peyer's patches of mice given latex suspensions as drinking fluid for 2 months. The number of particles accumulating was a direct (but nonlinear) function of the number ingested. Some of the latex particles were still present in Peyer's patches 6 weeks after the cessation of latex feeding.
Intestinal barrier function in mice was assessed after acute or chronic oral administration of 15.8- and 5.7-micron synthetic spherical particles. The results failed to confirm previous reports that ingested particles rapidly appear in blood. Furthermore, 15.8-micron particles did not accumulate in intestinal Peyer's patches, mesenteric lymph nodes, or other organs of the reticuloendothelial system, even after the maximum dosage of 8 X 10(6) particles per day for 60 d. However, the 5.7-micron particles were demonstrated in Peyer's patches, mesenteric lymph nodes, and lungs after the maximum dosage of 4.5 X 10(8) particles per day for 60 d. At 77 d after the termination of ingestion, 5.7-micron particles were still present in these tissues. The 5.7-micron particles were not found in spleen; retention in liver was equivocal. The site of uptake of particles capable of penetrating the intestinal mucosa appears to be the Peyer's patches. It is suggested that most absorbed particles are sequestered in Peyer's patch macrophages. Particles that escape sequestration are transported by lymph rather than by portal blood. The findings indicate that hazards associated with intestinal uptake of large (> 5 micron) particulates exist, but that the frequency of such penetration is still unclear.
Single doses of 7Be-labeled carbon particles prepared by proton bombardment of carbon black were administered by gavage to weanling (4 weeks) and aged (18 months) mice. Body distribution of 7Be radioactivity was determined 4 hr and 1, 2, 5, and 14 days later. The results were compared with those obtained after administration of a solution of 7BeC12. 7Be radioactivity in nonintestinal tissues was 17-58 times greater in mice gavaged with the soluble salt than in those gavaged with the particles, indicating that particle-bound 7Be was well confined to
the gastrointestinal tract. Upper limits of the amount of labeled carbon remaining in intestinalPeyer's patches were as follows: 1 day: weanling, 1.8 X old, 5.5 X lop3%; 15 days: weanling, 3.3 X lop5%, old, 8.4 X lo-'%. The particles are potentially useful as models for diesel emissions Or other particulate pOllUtantS.
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