Quantitation of Cellular and Extracellular Constituents of the Pulmonary Lining in Rats by Using Bronchoalveolar Lavage

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Abstract
The efficacy of bronchoalveolar lavage in the removal of cellular and extracellular components of the lining layer from the lungs of silica-treated and control rats was determined. Exponential functions were fitted to curves generated by plotting the quantity of lining layer constitutent removed from the lungs by bronchoalveolar lavage versus the lavage number. From these exponential functions we determined the total amount of constituent available in the pulmonary extracellular lining and hence the efficacy of the lavage procedure in removing materials from the lungs. With control rats the removal of extracellular phospholipids, soluble protein, alkaline phosphatase, and .beta.-N-acetylglucosaminidase by bronchoalveolar lavage occurred at significantly different rates. Removal of 95% of the total extracellular phospholipid, .beta.-N-acetylglucosaminidase, soluble protein, and alkaline phosphatase from the lungs required 4, 4, 8, and 11 lavages, respectively. Removal of 95% of the total available alveolar macrophages required 18 lavages. The influence of pulmonary inflammation on the efficacy of the lavage procedure was investigated by injecting silica dust intratracheally into the lungs of rats (50 mg/200- to 250-g rat) and after 3 days performing the analyses. Silica caused an inflammatory condition in the lungs resulting in the accumulation of materials in the alveoli. Highly significantly increases in soluble protein (16-fold), alkaline phosphatase (9-fold), and .beta.-N-acetylglucosaminidase (11-fold), polymorphonuclear leukocytes, eosinophils, and lymphocytes were observed. Alveolar macrophages and extracellular phospholipid were not significantly elevated at 3 days after dosing. Silica did not alter the efficacy of the lavage procedure in removing from the lungs any of the extracellular constituents of the lung lining. The efficacy of the lavage procedure in removing alveolar macrophages was improved after treatment of the lungs with silica (11 lavages for removal of 95%), and all of the cell types were removed from the lungs at similar rates. These data demonstrate that the total amount of any given constituent of the extracellular lining may be estimated from the manner in which that particular constituent is removed from the lungs by bronchoalveolar lavage, that not all constituents are removed with equal efficiency, and that inflammation of the lungs induced by silica has very little influence on the efficiency with which extracellular materials are removed from the lungs. However, under inflammatory conditions, removal of alveolar macrophages by pulmonary lavage appears to proceed more readily.