Gluconeogenic and Lipogenic Enzyme Activities in Growing Chicks Fed High Fat and High Carbohydrate Diets

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Abstract
The activities of key gluconeogenic and lipogenic enzymes of liver were examined in growing chicks fed either a high carbohydrate or a carbohydrate-free high fat diet for 29 days. A large initial increase in the activities of pyruvate carboxylase and fructose-1,6-diphosphatase was observed in high-fat-fed chicks; however, these activities returned to the initial level in about 3 weeks. The activities of phosphoenolpyruvate carboxykinase, malic enzyme and citrate cleavage enzyme were not affected when compared to the activities in 1-day-old chicks. When the chicks were fed the high carbohydrate diet there was a large decrease in the activities of all gluconeogenic enzymes measured. Pyruvate carboxylase, fructose-1,6-diphosphatase and glucose-6-phosphatase activities increased to their initial levels after about 3 weeks, while the activity of phosphoenolpyruvate carboxykinase remained lower. The increase in the activities of malic enzyme and citrate cleavage enzyme was very noticeable. The activities of isocitrate dehydrogenase and total hexose monophosphate shunt dehydrogenases were not altered significantly by feeding either diet. This study shows: 1) both the hepatic gluconeogenic and lipogenic enzyme activities of the chick respond to the dietary energy source as has been demonstrated in the laboratory rat and, 2) isocitrate dehydrogenase and hexose monophosphate shunt dehydrogenases may not play a major role in lipogenesis in the chick.

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