Anti-diabetic and anti-dyslipidaemic effects of grapefruit juice.
Background Hypoglycaemic effects of grapefruit juice in diabetic rats have been previously reported. The mechanisms by which grapefruit juice lowers blood glucose are not known. This study aimed to investigate the hypoglycaemic and anti-dyslipidaemic effects of grapefruit juice, as well as to elucidate the possible mechanism/s of action of this juice. Materials and Methods Male Wistar Rats (Rattusnovergicus) of 200-300 g body weight (BW) were randomly divided into five groups (n=6). Animals in group 1 were treated with 3.0 ml/kg of water for 60 days, by oral gavage. Groups 2, 4 and 5 were rendered diabetic by a single intraperitoneal injection of 60 mg/kg BW of streptozotocin. Group 5 was further treated with 4.0 U/kg of insulin (subcutaneously, twice daily), while groups 3 and 4 were orally treated with 3.0 ml/kg of GFJ. Fasting blood glucose and glucose tolerance tests were done in all the groups. Plasma insulin levels were also measured. Hepatic glycogen content, glucokinase and glucose-6-phosphatase (G6Pase) activities were measured in homogenised liver tissues. Plasma lipid levels were measured and hepatic enzymes (Acetyl-Coenzyme Aacetyl Transferase (ACAT) and 3-Hydroxy-3-Methyl-Glutaryl-CoA (HMG-CoA reductase) expression was determined. Results Diabetic rats showed significantly reduced weight gain, but higher water consumption in comparison to the controls. Fasting blood glucose was significantly higher in the diabetic group compared to controls, but were significantly (p<0.05) attenuated in GFJ-treated diabetic group, compared to the control. Diabetic rats exhibited significantly impaired glucose tolerance compared to controls, which was, however, improved in GFJ-treated groups in comparison to the diabetic non-treated group. GFJ treatment did not improve fasting plasma insulin in diabetic animals. Glucokinase activity and hepatic glycogen concentrations were significantly increased by GJF treatment, but G6Pase was alternatively suppressed by GFJ treatment. HDL-C levels were significantly increased in GFJ treated diabetic animals. Liver ACAT and HMG-CoA reductase enzyme expression were significantly suppressed in GFJ treated diabetic animals in comparison to the non-treated diabetic animals. Conclusion The findings show that GFJ has both hypoglycaemic and anti-dyslipidaemic effects. Although it not insulinotrophic, GFJ improves glucose intolerance in diabetic animals by supressing hepatic gluconeogenesis. Furthermore, GFJ improved plasma lipid profiles and supressed the liver expression of ACAT and HMG-CoA reductase enzymes.