glutaminase and Diabetic-Ketoacidosis

The intestine is capable of shifting its major fuel source from glutamine in the fed animal to ketone bodies in the fasted animal. Glutaminase (EC 3.5.1.2), the entry enzyme of glutamine oxidation, was examined for its function as a determinant in the utilization of jejunal fuel during diabetes and fasting. Male Sprague-Dawley rats were made ketotic to varied degrees by either fasting or the induction of diabetes with graded doses of streptozotocin (SZ). Specific activity of glutaminase was decreased in the diabetic animals to 64% (p less than 0.05) of controls in the group receiving 110 mg/kg SZ and 82% of controls in the group receiving 65 mg/kg SZ and to 78% (p less than 0.05) of controls in the fasted animals. The activity of glutaminase in the small intestine was negatively correlated to the concentration of beta-hydroxybutyrate in the plasma (r = -0.97, p less than 0.025) and jejunum (r = -0.92, p less than 0.05) for the four groups of animals. Specific activity of glutaminase was decreased in all cell types isolated along the villus-crypt axis of the small intestine from diabetic and fasted rats compared with control rats. The quantity of glutaminase-protein was determined by a dot immunobinding assay using an antibody to purified glutaminase. The activity of glutaminase relative to immunoreactive glutaminase-protein was significantly decreased (p less than 0.05) to 53% of control values in the 110 mg/kg SZ group, 77% in the 65 mg/kg SZ group, and 70% in the fasted group. These data indicate that an inactivation of glutaminase-protein may play a role in the ability of the intestine to shift its fuel source from glutamine to ketone bodies during diabetes and fasting.

Topics: 3-Hydroxybutyric Acid; Animals; Diabetes Mellitus, Experimental; Diabetic Ketoacidosis; Fasting; Glutaminase; Glutamine; Hydroxybutyrates; Jejunum; Male; Rats; Rats, Inbred Strains

The activities of various ammoniagenic, gluconeogenic, and glycolytic enzymes were measured in the renal cortex and also in the liver of rats made diabetic with streptozotocin. Five groups of animals were studied: normal, normoglycemic diabetic (insulin therapy), hyperglycemic, ketoacidotic, and ammonium chloride treated rats. Glutaminase I, glutamate dehydrogenase, glutamine synthetase, phosphoenolpyruvate carboxykinase (PEPCK), hexokinase, phosphofructokinase, fructose-1,6-diphosphatase, malate dehydrogenase, malic enzyme, and lactate dehydrogenase were measured. Renal glutaminase I activity rose during ketoacidosis and ammonium chloride acidosis. Glutamate dehydrogenase in the kidney rose only in ammonium chloride treated animals. Glutamine synthetase showed no particular variation. PEPCK rose in diabetic hyperglycemic animals and more so during ketoacidosis and ammonium chloride acidosis. It also rose in the liver of the diabetic animals. Hexokinase activity in the kidney rose in diabetic insulin-treated normoglycemic rats and also during ketoacidosis. The same pattern was observed in the liver of these diabetic rats. Renal and hepatic phosphofructokinase activities were elevated in all groups of experimental animals. Fructose-1,6-diphosphatase and malate dehydrogenase did not vary significantly in the kidney and the liver. Malic enzyme was lower in the kidney and liver of the hyperglycemic diabetic animals and also in the liver of the ketoacidotic rats. Lactate dehydrogenase fell slightly in the liver of diabetic hyperglycemic and NH4Cl acidotic animals. The present study indicates that glutaminase I is associated with the first step of increased renal ammoniagenesis during ketoacidosis. PEPCK activity is influenced both by hyperglycemia and ketoacidosis, acidosis playing an additional role. Insulin appears to prevent renal gluconeogenesis and to favour glycolysis. The latter would seem to remain operative in hyperglycemic and ketoacidotic diabetic animals.

Topics: Animals; Carbohydrate Metabolism; Diabetes Mellitus, Experimental; Diabetic Ketoacidosis; Glutaminase; Hexokinase; Insulin; Kidney; Liver; Phosphoenolpyruvate Carboxykinase (GTP); Phosphofructokinase-1; Rats; Rats, Inbred Strains