Adaptive Changes in the Serum LDH Isoenzymes of Monkey During Chronic Exposure to Simulated High Altitude

Abstract

There are several reports in the literature of adaptive changes in tissue lactic dehydrogenase (LDH) in response to environmental alteration. Serum LDH has also been reported to be elevated by hypoxia, however, mechanismus and implications of the enzyme elevation are not well defined. In this experiment, effects of chronic hypoxia on serum LDH and isoenzyme pattern in monkeys were examined.
Japanese monkeys weighing 7.5-12.0 kg were exposed to a simulated altitude of 18, 000 f t for 30 days in an air ventilated hypobaric chamber at 24 ±1°C. Ascent from sea level to altitude was accomplished at a rate of approximately 3, 000 ft/min. Blood samples were taken from cepharic vein under light anesthesia with ketamine hydrochloride (20 mg/kg) . The blood was allowed to clot, and the serum removed immediately. Serum LDH activity was determined according to the method of Wrbblewski, and LDH isoenzymes were separated by electrophoresis using the cellulose acetate membrane (TAITAN III) . Quantitative measurements of each isoenzyme were made by densitometric scanning of the stained isozymes.
Total LDH activity was increased gradually, and reached its maximum at 14th day of hypoxic exposure, which remained elevated for the rest of exposure period. The maximum enzyme activity was three times higher than the original pre-exposure level. After the decent from altitude to sea level, the enzyme activity was gradually recovered to the original level in 7 days. The percentages of LDH-1 and -2 in the total LDH sample were decreased after two weeks of hypoxic exposure. On the contrary, those of LDH-3, -4 and -5 were increased. LDH isoenzyme pattern shifted to anaerobic form in 2 weeks exposure, which probably corresponded to the period of altitude acclimatization, since monkeys recovered their appetite and physical activities at 14th day of hypoxic exposure.
From these results, it was suggested that changes in LDH activity and isoenzyme pattern might reflect the degree of adaptive changes in chronic hypoxia.