Influence of repeated exposure to elevated environmental temperature on the activity of respiratory enzymes of rat liver mitochondria.

: The paper presents studies of the activity of lipid-dependent enzymes of the respiratory chain of the liver of rats exposed to increased ambient temperature. The animals were heated in a chamber under controlled humidity (45-55% relative humidity), with forcer air flow and regulated temperature of 21 degrees +/- 1 degree C (control group) and 28 degrees +/- 1 degree C or 35 degrees +/- 1 degree C. They were affected by a relevant temperature for 7 or 14 consecutive days, 6 hrs daily. The enzymes activities were determined in a fraction of submitochondrial particles. The studies demonstrated that under the increased ambient temperature (7 X 6 hrs), the activity of the respiratory enzymes is changed. A statistically significant increase in the activity of NADH dehydrogenase, NADH cytochrome c reductase and cytochrome oxidase was found along with a decrease in the activity of succinate cytochrome c reductase and succinate dehydrogenase. On prolongation of thermal exposure (14 X 6 hrs) the activity of succinate dehydrogenase and succinate reductase: cytochrome c was further decreased. The activities of the other test enzymes did not exhibit any statistically significant differences as compared to controls. Kinetic tests of succinate dehydrogenase point to conformational changes of the enzyme when affected by an increased ambient temperature. This confirms the important role of this enzyme in the animals adaptation to thermally varying environmental conditions.