Biochemistry of brown fat and liver of cold-acclimated hamsters

Abstract

Studies were made of the effects of cold acclimation on the weight, the total protein content, and the enzymatic activity of brown fat of hamsters. For comparison, some enzymatic assays were also conducted on liver preparations. The mass of the brown fat doubled, as did the per cent protein, and there was a large increase in its mitochondrial and microsomal content. Brown fat mitochondria of cold-acclimated hamsters show striking increases in respiration associated with both ß-hydroxybutyrate and α-glycerophosphate, which indicates that there may be an enhanced capacity to degrade fats. On the other hand there was no change in succinoxidase, and a lowered respiration associated with isocitrate. Thus the mitochondrial catabolic activity involving the citric acid cycle may not be enhanced. Brown fat microsomal NADPH- and NADH-cytochrome c reductases were both increased in response to cold exposure which should be of significance in increasing heat production. Brown fat mitochondria show a respiration rate associated with α-glycerophosphate and isocitrate which is about 300– 400% higher than that of liver mitochondria. It is concluded that there is an increase in thermogenic capacity of the brown fat of the hamster during cold acclimation.