Lactate dehydrogenase isoenzyme pattern and total LDH activity in the lung and liver of rats chronically exposed to low and high oxygen concentrations.

Young adult rats were continuously exposed for 44 and 84 days to environments containing 9–11%, 20%, and 80% oxygen. Low and high oxygen atmospheres were achieved by using boxes laminated with silicone rubber membranes which have a differing permeability for oxygen on one side and for carbon dioxide and nitrogen on the other. Animals exposed to both extreme concentrations significantly slowed body growth, and the weight of the lungs was proportionally less. The pattern of LDH isoenzymes in the lung showed the presence of all five characteristically changing isoenzymes in relation to oxygen concentration. A marked increase of M subunits in the LDH in lungs of rats exposed to low oxygen indicated a higher tissue concentration of lactate. Thus, the percentage of M subunits was significantly higher in low oxygen and significantly lower in lungs of rats exposed to high oxygen as compared to controls. Under the same experimental conditions there were no changes in the liver LDH isoenzyme pattern. Total LDH activity in the lungs of rats exposed to either extreme oxygen atmosphere was significantly elevated as compared to controls kept at an ambient atmosphere. It is concluded that chronic exposure of rats to low as well as to high oxygen was injurious to the lung tissue, as evidenced by total LDH activity. Thus, LDH isoenzyme pattern in the lung reflected the actual gas exposure (pO₂), rather than local tissue metabolism.