Influence of Dietary Lipid on Lipogenesis and on the Activity of Malic Enzyme and Citrate Cleavage Enzyme in Liver of the Growing Chick

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Abstract
The effects of both acute and chronic fat feeding on hepatic lipogenesis and on the activity of related enzymes have been evaluated in the growing chick. The results clearly show that hepatic fatty acid synthesis is markedly reduced within 1 hour after oral corn oil administration. A similar reduction in fatty acid synthesis by liver slices was observed from acetate-1-14C or glucose-U-14C in spite of the fact that glucose was consistently incorporated to a lesser extent than acetate. Malic enzyme and citrate cleavage enzyme were not altered within 2 hours of corn oil feeding. In chronic fat feeding studies, increasing the level of dietary fat significantly reduced hepatic lipogenesis from acetate-1-14C or glucose-U-14C as measured in vitro or in vivo. Increasing the level of dietary fat from 2 to 10% depressed the specific activity of both malic enzyme and citrate cleavage enzyme by about 50%. A further increase in the dietary fat level to 20% resulted in specific activities of malic enzyme and citrate cleavage enzyme which were only 14 and 28%, respectively, of the activity observed in chicks fed the 2% corn oil diet. Under the conditions of this experiment where both enzymes are responding to alterations in lipogenesis their activities change in a parallel fashion. Chicks either force-fed corn oil or fed diets containing 10 or 20% fat had elevated levels of plasma free fatty acids. Possible mechanisms by which dietary fat depresses hepatic fatty acid synthesis and enzyme activity are discussed.