Oxygen and lung fibrosis.

Young adult rats were continuously exposed to environments containing 9% to 10%, 20% and 80% oxygen for 41 and 84 days. Animals exposed to both extreme oxygen concentrations demonstrated a noticeably slowed body growth, and the weight of the lungs was proportionally lower. Total amount and density of hydroxyproline in the lungs of both groups was markedly higher than in rats exposed to an ambient atmosphere. At both extreme oxygen concentrations, the content of lactate in the lung and total lactate dehydrogenase (LDH) activity were markedly higher, as was the activity of prolyl hydroxylase. The finding of enhanced peroxidizability of lipids in the lungs (examined by determination of malonaldehyde and change in the profile of fatty acids) indicates that both extreme oxygen concentrations represent an injury to lung constituents. We propose that under chronic exposure to low (9% to 10%) or high (80%) oxygen, the lung tissue was damaged (enhanced peroxidizability of lipids). It also developed inflammatory changes (increased lactate and LDH activity) that resulted in the enhancement of fibroplasia (increased activity of prolyl hydroxylase and collagen content). It is also possible that the content of tissue lactate in vivo situations may control the activity of prolyl hydroxylase.