Increased adipose tissue glyceroneogenesis in rats adapted to a high protein, carbohydrate-free diet

Glyceroneogenesis was assessed in epididymal adipose tissue from rats adapted to a high protein, carbohydrate-free (HP) diet. All experiments were performed in the fed state. Adaptation to the HP diet induced a two-fold increase in the activity of adipose tissue phosphoenolpyruvate carboxykinase (PEPCK). In the absence of glucose, the conversion of 14C-pyruvate (0.2, 1.0 or 5.0 mM) to glyceride-glycerol was significantly higher in adipose tissue from HP-fed rats than in controls. In the presence of glucose, rates of glycerol synthesis in tissues from HP-fed rats did not differ significantly from those in controls. Incorporation of 14C-pyruvate into fatty acids, both in the presence and absence of glucose, was not affected by the diet. The conversion of 14C-glucose (5 mM) into either glyceride-glycerol or fatty acids did not differ in HP-fed and control rats at any of the concentrations of pyruvate utilized. The data provide further evidence for the adaptative nature of adipose tissue PEPCK and suggest that in situations of reduced availability of glucose in the diet, glyceroneogenesis may be important to maintain an adequate supply of alpha-glycerophosphate for esterification of diet-derived fatty acids.