Ultrastructural changes in type I and type II alveolar epithelial cells in isolated perfused dog lungs after production of moderate and severe hydrostatic edema.

Volume densities of type-I and type-II alveolar cell cytoplasmic organelles were estimated by established stereologic procedures. The measurements were obtained from isolated-perfused dog lungs after the onset of acute hydrostatic edema. The isolated lungs provided three successive lobar preparations: control, moderately edematous, and severely edematous. The type-II cell lamellar body volume densities were decreased in both stages of edema. Volume density of the granular endoplasmic reticulum (including polyribosome clusters) was increased after progression to severely edematous conditions. Concomitant increases in vesicular volume densities were recorded in type-I cells after both moderate and severe edema. In addition, the relative percentages of vesicles directly attached to the luminal and abluminal plasma membranes were increased in the edematous lungs. These marked ultrastructural changes in the alveolar epithelium are consistent with the interpretation that both the release of lamellar bodies from type-II cells and the number of type-I cell pinocytotic vesicles are increased in isolated dog lungs after production of edema.