Effects of prolonged heat exposure on the cellular metabolism of the hamster

Abstract

Studies were made on mitochondrial and soluble fractions of livers from hamsters exposed to 35 C for 60 days and from controls (at 23 C) to see if oxidative enzymatic activity is affected. Mitochondrial respiration with succinate, isocitrate, glutamate, [beta]-hydroxybutyrate, [alpha]-ketoglutarate, or reduced cytochrome c of the heat-acclimated animals all are lower (38-52%) than control values. P/O ratios (moles of phosphate estrified per gram atom of O2 consume) are equal in the 2 groups. With succinate, metabolic control by adenosine diphosphate (ADP) is greater after heat acclimation. Glucose 6-phosphate dehydrogenase activity does not change. Liver, kidney, heart, testis, and testis fat-pad weights are lower after heat acclimation. Heat-acclimated animals cannot maintain homeothermy in a 5 C room for more than an hour but appear to survive 39.5[long dash]40.5 C better than controls. Comparison between these results and those reported on enzymatic and organ weight changes in cold acclimation indicates that some changes are temperature dependent, not responses to nonspecific stress. Contrary to nonshivering thermogenesis in cold acclimation, in heat-acclimated animals cellular metabolic changes should favor decreased body thermogenesis.