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Grapefruit juice improves glucose intolerance in streptozotocin-induced diabetes by suppressing hepatic gluconeogenesis

Abstract

Purpose

Hypoglycemic effects of grapefruit juice (GFJ) are widely recognized, but the mechanism(s) by which GFJ lowers blood glucose levels have not previously been investigated.

Methods

Wistar rats [250–300 g body weight (BW)] were divided into eight groups (n = 7). Group 1 animals were orally treated with 3.0 ml/kg BW of distilled water for 60 days, while groups 3, 4, 5, 6 were similarly treated with 3.0 ml/kg BW of GFJ. Groups 4 and 7 as well as 2, 5, 6 and 8 were given 45.0 and 60.0 mg/kg BW intraperitoneal injections streptozotocin, respectively, while groups 2 and 6 animals were additionally injected with insulin (4.0 units/kg, S.C., b.d), respectively. Fasting blood glucose (FBG) and glucose tolerance tests were done. Hepatic glycogen content and glucokinase, glucose-6-phosphatase (G6Pase) and phosphoenolpyruvate carboxykinase (PEPCK) activities were measured in homogenized liver tissues.

Results

Diabetic rats, groups 2 and 4–8 exhibited significantly reduced weight gain but increased polydipsia compared to controls. FBG was significantly increased in diabetic rats compared to controls but were significantly improved in GFJ-treated—compared to non-treated—diabetic rats. Similarly, diabetic rats showed significant glucose intolerance compared to controls which was improved by GFJ treatment. GFJ treatment did not improve fasting plasma insulin in diabetic rats. GFJ treatment significantly elevated glucokinase activity and hepatic glycogen concentrations but suppressed the activities of G6Pase and PEPCK, respectively, in diabetic animals.

Conclusion

These findings show that GFJ is not insulinotropic but improves glucose intolerance in diabetic rats by suppressing hepatic gluconeogenesis.

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Acknowledgments

The study was supported by a grant from the Medical Research Council of South African, and there is no conflict of interest to declare. The authors also wish to thank the Biomedical Resource Unit of the University of KwaZulu-Natal for helping with in vivo animal work as well as the final year BPharm students; Dludlu S, Govender K, Mahomed R, Moola W, Ngcobo L, Prem R, Ramasir S for helping with experimental work.

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None to declare.

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Correspondence to Peter M. O. Owira.

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Hayanga, J.A., Ngubane, S.P., Murunga, A.N. et al. Grapefruit juice improves glucose intolerance in streptozotocin-induced diabetes by suppressing hepatic gluconeogenesis. Eur J Nutr 55, 631–638 (2016). https://doi.org/10.1007/s00394-015-0883-4

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  • DOI: https://doi.org/10.1007/s00394-015-0883-4

Keywords

  • Grapefruit juice
  • Diabetes
  • Insulin
  • Gluconeogenesis