Hypoglycaemic effects of myrtle oil in normal and alloxan-diabetic rabbits

Myrtus communis L. (Myrtaceae) leaves as well as the volatile oil (Myrtii Oleum; MO) obtained from the leaves are used to lower the blood glucose level in type-2 diabetic patients in Turkish folk medicine. However, little attention has been paid to the therapeutic use of this plant. The present study was designed to investigate the oral hypoglycaemic activity of single and multiple doses of MO in normal and alloxan-diabetic rabbits. MO did not show any effect in normoglycaemic rabbits either in single or multiple dose administrations, but a good hypoglycaemic activity was observed 4 h after the administration to diabetic animals at 50 mg/kg. To investigate the effect of MO on repeated administration in both normal and diabetic rabbits, it was administered in 50 and 100 mg/kg doses once a day for one week. MO significantly lowered blood glucose by 51% in alloxan-diabetic rabbits on the fourth hour and the following days at a dose of 50 mg/kg (P < 0.001). The hypoglycaemic dose (50 mg/kg) was also determined by performing the oral glucose tolerance test (OGTT) in normal rabbits. The hypoglycaemic effect of the MO was 21% higher in rabbits, which received the glucose load orally, when compared with control group. However, MO did not affect serum insulin concentrations in normal and alloxan-diabetic rabbits but reduced the serum triglyceride concentrations by 14% in alloxan-diabetic rabbits. The above observations show that MO exerts hypoglycaemic as well as mild hypotriglyceridemic activity in diabetic animals. The reduction in blood glucose level may be due to the reversible inhibition of alpha-glucosidases present in the brush-border of the small intestinal mucosa, higher rate of glycolysis as envisaged by the higher activity of glucokinase, as one of the key enzymes of glycolysis, and enhanced rate of glycogenesis as evidenced by the higher amount of liver glycogen present after MO administration.