Hepatic Gluconeogenesis and Glycolysis in Chickens Fed “Carbohydrate-free” Diets

Abstract

One-day-old chickens were fed either a glucose control diet or diets in which all nonprotein calories were supplied by either soybean oil or soybean oil fatty acids. After 3 weeks, hepatic gluconeogenic and glycolytic enzyme activities and metabolite content were compared. Feeding the “carbohydrate-free” diets tended to decrease glycolytic and increase gluconeogenic enzyme activity which would increase the net production of glucose by the liver. Alterations in enzyme activity and metabolite concentration in response to the soybean oil diet occurred primarily at the hexose phosphate and triose phosphate levels. Feeding the soybean oil fatty acid diet resulted in enzymatic activity and metabolite concentration changes at the pyruvate-phosphoenolpyruvate level as well, which would allow increased utilization of amino acids and lactate for glucose synthesis. Evidence is presented indicating that hepatic glucose-6-phosphatase activity plays a major role in controlling blood glucose concentration under gluconeogenic conditions and that the activity of this enzyme is directly related to glycerol metabolism. On this basis it is suggested that, under gluconeogenic conditions, there is competition for the available carbon sources for glucose and glyceride-glycerol synthesis, especially when soybean oil fatty acids provide all nonprotein calories. Further, it is suggested that these synthetic processes deplete the available supply of amino acids provided by the diet and thereby limit growth.