Influence of Dietary Fat and Protein on Metabolic and Enzymatic Activities in Adipose Tissue of Meal-fed Rats

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Abstract
The influence of dietary protein and fat on the response of adipose tissue to meal-feeding (a single daily 2-hour meal) has been investigated in the rat. Meal-feeding stimulated the incorporation of pyruvate carbon into fatty acids and the oxidation of pyruvate by isolated adipose tissue. This response to meal-feeding was completely abolished by feeding a high fat diet. The activities of glucose 6-phosphate dehydrogenase and malic enzyme were higher in adipose tissue and liver of meal-fed rats consuming a high carbohydrate diet, but were unchanged in tissue of rats meal-fed a high fat diet. The activities of glucose 6-phosphate dehydrogenase and malic enzyme were depressed in adipose tissue of rats fed the high fat diet, whereas only glucose 6-phosphate dehydrogenase activity was depressed in liver of nibbling rats consuming the high fat diet. Adipose tissue from rats fed the high fat diet was able to convert significantly more pyruvate-2-14C to glyceride-glycerol than tissue from rats fed the high carbohydrate diet. The possible significance of this observation is discussed. Dietary protein did not influence the response of adipose tissue to meal-feeding. Increasing the dietary protein level did increase hepatic glutamic-oxaloacetic (GOT) and glutamic-pyruvic (GPT) transaminase activities and decreased the ability of isolated adipose tissue to oxidize glucose-14C and leucine-14C and to incorporate these substrates into fatty acids. Adipose tissue from rats mealfed diets containing 9, 18 or 36% casein oxidized and incorporated into fatty acids significantly more glucose and leucine than tissue from animals fed the same diets ad libitum.