Pathologic changes in the lungs of mice following injection of human albumin microspheres.

Mice injected with 131I-human albumin microspheres equivalent to 10-20 or 200 human doses were sequentially killed over a 12-day period. About 90% of the microspheres initially lodged in the precapillary arterioles and capillaries of the lungs. Their pulmonary clearance was essentially complete after 3 days. Occlusion of the vessels always led to focal hyperemia of the surrounding tissue and to slight hemorrhage into the alveoli. This was followed, though less frequently, by perivascular nodular inflammtion. Hemorrhagic infarcts were quite uncommon and occurred only after the massive doses. Some emboli underwent organization, but most were resolved. Circulatory disturbances and perivascular inflammation receded in about 1 week and seldom led to obliteration of the involved vessels. Hemorrhagic infarcts were converted into minute scars. Twelve days after injection of microspheres in massive doses, the only findings were post-inarct scars and obliterated vessels, which were sparse and difficult to detect. The lower doses of microspheres did not leave any detectable residues.