Discipline of Pharmaceutical Sciences, Department of Pharmacology, School of Health Sciences, University of KwaZulu-Natal, Private Bag X54001, Durban, 4000, South Africa.
Eur J Nutr. 2016 Mar;55(2):631-638. doi: 10.1007/s00394-015-0883-4. Epub 2015 Mar 20.
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.
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.
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.
These findings show that GFJ is not insulinotropic but improves glucose intolerance in diabetic rats by suppressing hepatic gluconeogenesis.
葡萄柚汁（GFJ）的降血糖作用已得到广泛认可，但 GFJ 降低血糖水平的机制尚未得到研究。
将 Wistar 大鼠[体重 250-300 克（BW）]分为 8 组（n = 7）。第 1 组动物口服 3.0 ml/kg BW 蒸馏水 60 天，第 3、4、5、6 组动物同样口服 3.0 ml/kg BW GFJ。第 4 组和第 7 组以及第 2、5、6 组和第 8 组分别给予 45.0 和 60.0 mg/kg BW 腹腔注射链脲佐菌素，而第 2 组和第 6 组动物分别额外注射胰岛素（4.0 单位/kg，皮下注射，每天两次）。进行空腹血糖（FBG）和葡萄糖耐量试验。测量肝组织匀浆中的肝糖原含量以及葡萄糖激酶、葡萄糖-6-磷酸酶（G6Pase）和磷酸烯醇丙酮酸羧激酶（PEPCK）活性。
糖尿病大鼠，第 2 组和第 4-8 组与对照组相比，体重增加明显减少，但多饮增加。与对照组相比，糖尿病大鼠的 FBG 显著升高，但与未治疗的糖尿病大鼠相比，GFJ 治疗组的 FBG 显著降低。同样，与对照组相比，糖尿病大鼠的葡萄糖耐量明显降低，但 GFJ 治疗组得到改善。GFJ 治疗并未改善糖尿病大鼠的空腹血浆胰岛素。GFJ 治疗显著提高了糖尿病动物的葡萄糖激酶活性和肝糖原浓度，但分别抑制了 G6Pase 和 PEPCK 的活性。
这些发现表明，GFJ 不是胰岛素增敏剂，但通过抑制肝糖异生改善糖尿病大鼠的葡萄糖耐量。
