Serum enzyme and tissue changes in shaven rabbits exposed to cold

Shaven rabbits were exposed to −5 °C from 6 to 16 hr. With maximum exposure 50% became severely hypothermic, and the rest either became moderately hypothermic or remained normothermic. In severely hypothermic rabbits, marked elevations in serum concentrations of glutamic oxalacetic transaminase, glutamic pyruvic transaminase, aldolase, creatine phosphotransferase, and lactic dehydrogenase developed within 10–16 hr. Serum enzyme concentrations reached peak levels within 1 day after removal from cold and returned to normal within 6 days. Serum levels of isoenzyme lactic dehydrogenase 5 (SLDH 5) greatly increased and SLDH 1 decreased in severely hypothermic rabbits. This indicated that striated muscle tissue contributed to serum concentration of lactic dehydrogenase. About one-half of the rabbits showed foci of cardiac necrosis multiple pulmonary hemorrhages, and fatty changes in the liver, kidney, and striated and heart muscles. It is apparent that serum enzymes reached peak concentrations within the first day after cold exposure at a time when fatty changes and necrosis were found in the heart and other organs. The tissue changes were most frequent and severe in the hypothermic rabbits with the highest serum enzyme concentrations. Within 3–6 days fatty changes had largely disappeared, but the myocardial lesions persisted in the form of granulation and scar tissue.