Fat Metabolism in Three Forms of Experimental Obesity

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Abstract
The retention of C14 in carcass and liver lipids 30 minutes after an intraperitoneal injection of C14-carboxyl-labeled acetate was measured in 3 types of obese animals; animals with the hereditary obese-hyperglycemic syndrome, mice made obese with an LD50 injection of goldthioglucose and rats with hypothalamic lesions and their controls when in a fed condition and after a fast of 24 hours. The bulk of synthesis appeared to occur in the adipose tissue. In the control mice this amounted to 60-70% of the total synthesis, in the rats to 80%. When the animals were fasted, lipogenesis was more markedly affected in the liver than in peripheral tissues being decreased to about 15% of the fed values in the liver of the control animals, while peripheral synthesis is decreased only to about 70% of the fed value. This would indicate that hepatic lipogenesis is more dependent upon the nutritional status of the animals than is peripheral synthesis. When all animals were fed "ad libitum" the 3 types of obese animals synthesized more fat both in liver and carcass than did their controls. Under fasting conditions the obese-hyperglycemic mice still synthesized more fat than their controls, while the goldthioglucose obese mice and the hypothalamic rats did not synthesize more fat than their controls. The possible relation of these differences in fat synthesis to the etiology of the various forms of obesity is discussed.