Influence of diet on glucose tolerance, on the rate of glucose utilization and on gluconeogenic enzyme activities in the dog.

Four diets containing 0 to 62% of energy from carbohydrate and 24% to 48% of energy from protein were fed to young dogs. Two of the diets (diets LPLC and HPLC) were carbohydrate-free and two of the diets (diets HPHC and HPLC) contained 46% to 48% protein. The influence of these diets on several parameters of glucose metabolism was ascertained. Following an intravenous glucose load, plasma glucose levels were higher in dogs fed carbohydrate-free diets (diets LPLC and HPLC) than observed in dogs fed carbohydrate-containing diets (diet LPHC and HPHC). Consumption of high-protein diets (diets HPHC and HPLC) also impaired glucose tolerance. Estimates of glucose utilization were obtained. Dogs fed carbohydrate-containing diets exhibited a higher rate of glucose utilization than did dogs fed the carbohydrate-free diets. Fasting the dogs for 48 hours reduced the glucose replacement rate in dogs fed the carbohydrate-containing diets but did not influence the rate of glucose utilization in dogs fed the carbohydrate-free diets. The activities of phosphoenolpyruvate carboxykinase (PEPCK) and of pyruvate carboxylase (PYCAR) in livers and kidneys of these dogs were influenced by the diets fed. Mitochondrial PEPCK and PYCAR activities in both liver and kidney were increased in dogs fed the carbohydrate-free diets. Consumption of the high-protein diets actually decreased the activities of PEPCK in liver and kidney mitochondria.