Gluconeogenesis in non-obese diabetic (NOD) mice: In vivo effects of vanadate treatment on hepatic glucose-6-phosphatase and phosphoenolpyruvate carboxykinase

The contribution of gluconeogenesis to hyperglycemia in non-obese diabetic (NOD) mice has been investigated using oral vanadate administration. Vanada te compounds have been shown to mimic many actions of insulin; however, the exact mechanism is poorly understood. The aims of the present study were ( 1) to elucidate vanadate's action In vivo, and to assess the possibility th at its glucose-reducing effect is dependent on the presence of a minimal co ncentration of insulin; and (2) to evaluate the effects of vanadate adminis tration on the key hepatic gluconeogenesis enzymes, glucose-6-phosphatase ( G-6-Pase) and phosphoenolpyruvate carboxykinase (PEPCK), as well as glucose -6-phosphate dehydrogenase (G-6-PDH). Vanadate caused a significant reducti on in blood glucose but failed to normalize it, despite effective serum van adate concentrations (26.2 +/- 1.6 mu mol/L). Two weeks after initiation of treatment, blood glucose levels were 26.0 +/- 1.8, 21.7 +/- 3.0, 16.0 +/- 1.6, and 14.3 +/- 2.3 mmol/L in the control (C), insulin (I), vanadate (V), and combined vanadate and insulin (V + I) groups, respectively(P < .001), G-6-Pase activity was significantly reduced by vanadate (622 +/- 134 v365 /- 83 nmol/min/mg protein in C vV, P < .05). PEPCK activity was also signif icantly reduced (844 +/- 370, 623 +/- 36, 337 +/- 43, and 317 +/- 75 nmol/m in/mg in the C, I, V, and V + I groups, respectively, P < .001). No signifi cant differences in the hepatic glycogen stores and G-6-PDH activity were n oted between treatment groups. Our study suggests that the inhibition of he patic G-6-Pase and PEPCK activity by vanadate plays an important role in re ducing blood glucose levels in NOD mice. Copyright (C) 2000 by W.B. Saunder s Company.