Bitter Melon Extracts in Diabetic and Normal Rats Favorably Influence Blood Glucose and Blood Pressure Regulation

Abstract

Bitter melon (BM) was tested in normal and streptozotocin (STZ)-induced diabetic rats. First, normal and diabetic Wistar rats were given four test extracts (EX-1–EX-4) of a wild-genotype BM or metformin by intubation. Second, normal Sprague–Dawley rats were divided into control and three test groups given for 52 days one of three BM preparations in food: Chinese or Indian commercial preparations or EX-4 from experiment I. In experiment I, extracts of BM administered at 50 mg/kg of body weight in normal rats reduced blood sugar for 4 hours without, unlike metformin, inducing hypoglycemia. In STZ-induced diabetic rats, two extracts administered at 250 mg/kg decreased glucose levels to values comparable to metformin at 150 mg/kg. At 4 hours, EX-1 and EX-4 significantly reduced blood glucose 67% and 63%, respectively, compared with metformin's 54%. In experiment II, all test groups had lowered systolic, but not diastolic, blood pressure. The China and EX-4 arms had significantly lowered serum glucose levels compared with the control. In the glucose tolerance test, only EX-4 had significantly lowered glucose levels. Only EX-4 had significantly lowered angiotensin converting enzyme (ACE) activity. All active arms showed significance in the losartan challenge (the renin–angiotensin system [RAS]), with the greatest effect in the EX-4 group. In the N ^ω-nitro-l-arginine-methyl ester challenge, only EX-4 exhibited a significant impact on the nitric oxide system, suggesting higher activity in this group. In the STZ-induced diabetic rat model, wild-type BM powerfully lowered glucose levels, and, in healthy adult rats, wild-type BM exhibited beneficial effects in the regulation of blood glucose, in RAS and ACE inhibition, and in nitric oxide generation.