Subcellular changes in capillary endothelial cells during repair of hyperoxic lung injury

We studied the changes in subcellular ultrastructure associated with the hypertrophy of capillary endothelial cells during repair of hyperoxic (100% O2) lung injury in rats. We used stereologic-morphometric measurements at different magnifications to determine the absolute volume of each subcellular compartment per average capillary endothelial cell. The increases in this value during the first 3 days of postexposure repair were 118% for cytoplasm, 786% for polyribosomes, 310% for rough endoplasmic reticulum, and 79% for mitochondria; the volume of pinocytotic vesicles did not change. By day 7 of repair, only the polyribosomes and rough endoplasmic reticulum were still increased; by day 14 all values were normal. We conclude that the capillary endothelial cell hypertrophy that develops during repair of hyperoxic lung injury is associated with large and heterogeneous increases in subcellular organelles and is not merely due to increases in the cytosol or to cellular edema. These increases seem to be an integral part of the repair process and may be important in the development of tolerance to subsequent oxygen exposure.