Lung tissue volume changes induced by hypertonic NaCl: morphometric evaluation.

Lung tissue was examined to determine how the volumes of alveolar septum components change when NaCl is added to the vascular perfusate, increasing the osmolarity by 70 mosM. Isolated rabbit lungs were perfused with Ringer solution containing dextran, either with or without added NaCl, and fixed by vascular perfusion. Tissue samples from both "control" and "hypertonic" lungs, prepared for electron microscopy, were examined using established morphometric procedures. Volumes of septal cells, interstitial space, capillary lumen, surface-lining layer, and endothelial and epithelial areas were measured, all normalized against the endothelium basement-membrane area. Results showed that hypertonic NaCl caused a reduction in total cell and surface-lining layer volumes but no change in interstitial or capillary lumen volumes. This supports the hypothesis that small molecules have no osmotic effect across the pulmonary capillary endothelium but do cause a fluid flux from cells and across the alveolar epithelium. Areas and volume measurements for different septal cell types suggest a heterogeneous response: epithelial cells showed significant decreases and endothelial cells changed little, if at all.