Effect of Dietary Protein on Hepatic Lipogenesis in the Growing Chick

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Abstract
The influence of dietary protein on hepatic lipogenesis in growing chicks has been investigated. Both in vitro and in vivo studies demonstrated that the incorporation of glucose-U-14C, pyruvate-2-14C and acetate-1-14C into liver fatty acids was depressed by elevating the dietary protein level. Liver cholesterol content, however, as well as synthesis, was increased as the dietary protein increased. The data suggest that hepatic lipogenesis and cholesterogenesis are altered by dietary protein per se regardless of its quality or its growth-stimulation effect. The plasma free fatty acid level was decreased by increasing dietary protein and was positively related to the rate of hepatic lipogenesis. Incorporation of DL-lactate-2-14C and pyruvate-2-14C into blood glucose appeared to be increased as the dietary protein level increased. The activity of malic enzyme was positively correlated with the rate of lipogenesis. Increasing dietary protein from 15 to 35% depressed both in vitro fatty acid synthesis and malic enzyme activity by about 75%. The possible regulatory mechanisms responsible for the depression of hepatic lipogenesis in chicks fed a high protein diet are discussed. It is suggested that a limitation in the availability of cytoplasmic reducing equivalents may initiate the reduction in hepatic fatty acid synthesis of chicks fed a high protein diet.