Stimulation of Hepatic Glycogenolysis and Inhibition of Gluconeogenesis are the Mechanisms of Antidiabetic Effect of Centaurea bruguierana ssp belangerana

The aqueous, dichloromethane, ethyl acetate and methanol extracts of dried aerial fruiting parts of Centaurea bruguierana ssp. belangerana were investigated for hypoglycemic mechanism in diabetic rats. Diabetes was induced by intravenous administration of streptozotocin-alloxan. The methanol and ethyl acetate extracts were administered in a single effective dose of 200 mg kg(-1) and dichloromethane and aqueous extracts were administered in a single effective dose of 400 mg kg(-1). Blood glucose was determined every 1 h until 3 h post administration of the extracts. In the second experiment, the liver was surgically removed 3 h post treatment of diabetic rats with various extracts, homogenized and used for measurement of key enzymes of glycogenolysis (glycogen phosphorylase, GP) and gluconeogenesis (phosphoenolpyruvate carboxykinase, PEPCK). Treatment by dichloromethane, ethyl acetate, methanol and aqueous extracts and the glibenclamide, reduced blood glucose to 41.7, 55.0, 45.7, 29.5 and 34.5%, respectively. The aqueous extract showed the best effect in reduction of hepatic PEPCK activity (84.0%) and increased hepatic GP activity (134.5%), while glibenclamide showed 62.5 and 133.0% activity, respectively. None of the extracts affected blood insulin. Presence of sugar in dried aqueous extract could suppress the hypoglycemic effect during the first hour of the experiment. After 1 h, the hepatic mechanism overwhelmed and thus lowering effect in blood glucose appeared. The conclusion is that C. bruguierana ssp. belangerana is able to lower blood glucose via stimulation of hepatic glycogenolysis and inhibition of gluconeogenesis.