Acrylic microspheres in vivo VII: morphological studies on mice and cultured macrophages.

Intravenously injected microparticles of polyacrylamide were cleared from the circulatory system in mice predominantly in liver, spleen, and bone marrow in mice by macrophages belonging to the reticuloendothelial system. In these cells, particles were found in dilated secondary lysosomes. The lysosomotropic character of the particles was further demonstrated using cultured peritoneal mouse macrophages. Histological changes of the liver, spleen, and bone marrow detectable by light and electron microscopy could only be seen after administration of massive doses of microparticles corresponding to 160 mg/kg body weight. In such cases, a medium-coarse vacuolization of liver parenchymal cells could be seen 1-2 days after particle administration. After 3-5 days, degeneration and necrotic cellular alteration occurred in the liver, spleen, and bone marrow. One week after particle administration, regeneration started under formation of granulomas which replaced the necrotic areas. The tissues later became normalized (after 2-3 weeks), but small granulomas remained for several weeks. The damage was parallelled by changes in the liver and spleen weights. Electron microscopy of the liver revealed that the initiated vacuolization of the parenchymal cells was due to mitochondrial swelling with rupture of the mitochondrial cristae.