Surface tension, metabolic activity, and lipid composition of alveolar cells in washings from normal dog lungs and after pulmonary artery ligation. Importance of a highly surface-active acellular layer.

Lung-washings from mammalian species are a rich source of surfactant and of cells, predominantly alveolar macrophages, that could be important in the metabolism of the surfactant. We obtained washings from normal dogs, and from dogs that had had one pulmonary artery (PA) ligated 1 or 2 days earlier. Centrifugation of wash (400 x g for 20 min) separated a sediment, made up of cells at the bottom and a white layer, largely acellular, from the supernatant. The volume of sediment averaged 2.1 +/- 1.4 ml,. 75% of which was white layer. The cells resembled the large alveolar (type II) cells found in the lung; however they differed by at least one major histochemical reaction. The white layer had greater surface activity than the cells or the supernate, and was richest in phospholipids and lecithin. The cells lost their surface activity when rinsed and resuspended. These observations suggest that surfactant is normally present, mainly in an acellular fraction and possibly at the surface of the alveolar cells. The alveolar macrophages may either store surfactant, rather than synthesize it, or simply acquire a coat of surfactant during sedimentation. After PA ligation, the earliest abnormality was a decrease in the white layer; the cells were fewer, smaller, and weaker in metabolic activity.