Retention of Glass Fibers in the Rat Trachea Following Administration by Intratracheal Instillation

Abstract

Three experimental glass fiber samples, with different chemical compositions but with similar dimensions, were administered to rats by intratracheal instillation. Groups of animals were killed at predetermined time points following administration. The lungs were excised and the tracheas and extrapulmonary bronchi removed and lavaged with physiological saline solution. The lavage fluid and the lavaged airways were digested with commercial bleach solution and the resulting digests filtered. The numbers and length distributions of lavaged fibers, and of fibers remaining in the airways, were determined by phase-contrast optical microscopy. At 2 days after instillation the number of fibers recovered by tracheal lavage varied from 0.1 to 1% of the number of fibers initially retained in the respiratory tract. The number of fibers recovered by lavage declined rapidly and after 14 days was only about 0.01% of the number of fibers retained initially. The numbers and length distributions of lavaged fibers indicated that clearance of fibers deposited in the conducting airways at the time of administration was essentially complete by about 4 days after instiltation. The mean lengths of fibers recovered by tracheal lavage after this time were generally shorter than those of either the administered material or fibers recovered from lung at the same time. It was found that about 0.1–0.2% of the instilled fibers was retained in the lavaged airways and that the numbers retained at this site only declined slowly, if at all.