Retention of microspheres in the rat lung after intratracheal instillation.

Abstract This 106-day study examined lung retention of 3-, 9-, and 15-μm polystyrene microspheres in Fischer 344 rats after intratracheal instillation. A mixture of microspheres, each size labeled with a different γ-emitting radionuclide, was instilled intratracheally into each rat. Three micrometer microspheres were retained in a manner similar to inhaled particles of a similar size; half of the microspheres were retained with a biological half-time of 12 days, the other half with a biological half-time of 69 days. Twenty-four and seventy-six percent of the 9-μm microspheres cleared with biological half-times of 17 and 580 days, respectively. Fourteen percent of the 15-μm microspheres cleared with a biological half-time of 2.3 days, the other microspheres were retained in the lung with a half-time which was not measurable over 106 days. Feces content of radionuclides paralleled lung clearance. The 3-μm microspheres translocated to the lung-associated lymph nodes; the 9- and 15-μm microspheres were not translocated to lymph nodes. Tissue data showed a fairly uniform dispersion of the three microsphere sizes in the lung. Results indicated that large particles which lodge in the deep lung could be retained indefinitely and yield unique chemical or radiation dose patterns to surrounding tissue.