Anti-hyperglycaemic activity of H. rosa-sinensis leaves is partly mediated by inhibition of carbohydrate digestion and absorption, and enhancement of insulin secretion.

Hibiscus rosa-sinensis (HRS) is a tropical flowery plant, widely distributed in Asian region and an important traditional medicine used in many diseases including cough, diarrhoea and diabetes.Hibiscus rosa-sinensis (HRS) leaves have been reported to possess anti-hyperglycaemic activity, but little is known concerning the underlying mechanism. This study investigated effects of ethanol extract of HRS on insulin release and glucose homeostasis in a type 2 diabetic rat model.Effects of ethanol extract of grinded H. rosa-sinensis (HRS) leaves on insulin release, membrane potential and intracellular calcium were determined using rat clonal β-cells (BRIN-BD11 cells) and isolated mouse pancreatic islets. Effects on DPP-IV enzyme activity were investigated in vitro. Acute effects of HRS on glucose tolerance, gut perfusion in situ, sucrose content, intestinal disaccharidase activity and gut motility were measured. Streptozotocin induced type 2 diabetic rats treated for 28 days with ethanol extract of HRS leaf (250 and 500 mg/kg) were used to assess glucose homeostasis.

HRS, significantly increased insulin release from clonal rat BRIN-BD11 cells and this action was confirmed using isolated mouse pancreas islets with stimulatory effects equivalent to GLP-1. HRS induced membrane depolarization and increased intracellular Ca²⁺ in BRIN BD11 cells and significantly inhibited DPP-IV enzyme activity in vitro. HRS administration in vivo improved glucose tolerance in type 2 diabetic rats, inhibited both glucose absorption during gut perfusion and postprandial hyperglycaemia and it reversibly increased unabsorbed sucrose passage through the gut following sucrose ingestion. HRS decreased intestinal disaccharidase activity and increased gastrointestinal motility in non-diabetic rats. In a chronic 28-day study with type 2 diabetic rats, HRS, at 250 or 500 mg/kg, significantly decreased serum glucose, cholesterol, triglycerides and increased circulating insulin, HDL cholesterol and hepatic glycogen without increasing body weight.

These data suggest the antihyperglycaemic activity of HRS is mediated by inhibiting carbohydrate digestion and absorption, while significantly enhancing insulin secretion in a dose dependent manner. This suggests that HRS has potential as a novel antidiabetic therapy or a dietary supplement for the treatment of type 2 diabetes.