Ten-week-old Zucker diabetic fatty (ZDF) rats at an early stage of diabetes embody metabolic characteristics of obese human patients with
type 2 diabetes, such as severe
insulin and
glucose intolerance in muscle and the liver, excessive postprandial excursion of plasma
glucose and
insulin, and a loss of metabolic flexibility with decreased
lipid oxidation. Metabolic flexibility and
glucose flux were examined in ZDF rats during fasting and near-normal postprandial insulinemia and glycemia after correcting excessive
postprandial hyperglycemia using treatment with a
sodium-glucose cotransporter 2 inhibitor (SGLT2-I) for 7 days. Preprandial
lipid oxidation was normalized, and with fasting, endogenous
glucose production (EGP) increased by 30% and endogenous
glucose disposal (E-Rd) decreased by 40%. During a postprandial hyperglycemic-hyperinsulinemic clamp after SGLT2-I treatment, E-Rd increased by normalizing
glucose effectiveness to suppress EGP and stimulate hepatic
glucose uptake; activation of
glucokinase was restored and
insulin action was improved, stimulating muscle
glucose uptake in association with decreased intracellular
triglyceride content. In conclusion, SGLT2-I treatment improves impaired
glucose effectiveness in the liver and
insulin sensitivity in muscle by eliminating glucotoxicity, which reinstates metabolic flexibility with restored preprandial
lipid oxidation and postprandial
glucose flux in ZDF rats.