Effect of 70% oxygen on postresectional lung growth in rats

We tested the hypothesis that exposure to hyperoxia could inhibit postresectional compensatory lung growth to the same degree that it inhibits newborn lung growth. We removed the 3 upper lobes of the right lung of rats, allowed them to breathe either air or 70% oxygen after surgery, and performed electron microscopy and morphometry on the left lung at 14 d postresection. Rats that had a thoracotomy without removal of lung were used as controls. Resection of lung tissue resulted in increases of about 100-200% (relative to controls) in the total volume per left lung of alveolar type 1 and type 2 epithelial cells, capillary endothelial cells, interstitial cells, and interstitial matrix; the total capillary and type 1 epithelial surface areas each increased about 40%. Exposure to 70% oxygen did not significantly inhibit postresectional growth, although there was a trend toward a lesser increase in capillary surface area. However, 70% oxygen did result in a 78% greater (relative to the nonexposed resected group) alveolar type 2 cell volume density and a 54% greater interstitial cell volume density; this suggested that increased proliferation of type 2 cells and interstitial cells occurred. Qualitative ultrastructural assessment confirmed that the type 2 cells and fibroblasts appeared increased and that interstitial edema and neutrophil accumulation were also present. We conclude that although 70% oxygen exposure is not entirely innocuous, it does not inhibit postresectional lung growth.