RETENTION OF GLASS-FIBERS IN THE RAT TRACHEA FOLLOWING ADMINISTRATIONBY INTRATRACHEAL INSTILLATION

Three experimental glass fiber samples, with different chemical compos itions but with similar dimensions, were administered to rats by intra tracheal instillation. Groups of animals were killed at predetermined time points following administration. The lungs were excised and the t racheas and extrapulmonary bronchi removed and lavaged with physiologi cal saline solution. The lavage fluid and the lavaged airways were dig ested with commercial bleach solution and the resulting digests filter ed. The numbers and length distributions of lavaged fibers, and of fib ers remaining in the airways, were determined by phase-contrast optica l microscopy. At 2 days after instillation the number of fibers recove red by tracheal lavage varied from 0.1 to 1% of the number of fibers i nitially retained in the respiratory tract. The number of fibers recov ered by lavage declined rapidly and after 14 days was only about 0.01% of the number of fibers retained initially. The numbers and length di stributions of lavaged fibers indicated that clearance of fibers depos ited in the conducting airways at the time of administration was essen tially complete by about 4 days after instillation. The mean lengths o f fibers recovered by tracheal lavage after this time were generally s horter than those of either the administered material or fibers recove red from lung at the same time. It was found that about 0.1-0.2 % of t he instilled fibers was retained in the lavaged airways and that the n umbers retained at this site only declined slowly, if at all.