Inhibitory Effects of Mulberry Fruit on Intestinal Disaccharidase Activity and Hyperglycemia in Streptozotocin-Induced Diabetic Rats

The current study examined the effects of freeze-dried mulberry fruit on disaccharidase activity in the small intestine and the lowering of blood glucose in streptozotocin (STZ)-induced diabetic rats. Sprague-Dawley male rats were randomly assigned to one normal and three streptozotocin (STZ)-induced diabetic groups. The diabetic groups were fed a mulberry fruit-free diet (DM-group), 0.3% mulberry fruit diet (DM-F group) or 0.6% mulberry fruit diet (DM-2F group). After they were fed the experimental diets for three weeks, diabetes was induced with an intraperitoneal injection of streptozotocin 50 mg/kg b.w before sacrificing 9 days later using the same experimental treatments. Analyses of anthocyanins, flavonoid and 1-deoxynojirimycin (DNJ) of lyophilized mulberry fruit were carried out and the major anthocyanins were rutin (142.5 mg), isoquercitrin (10.3 mg), quercetin (5.8 mg), morin (1.6 mg) dihydroquercetin (3.83 mg), cy-3-O-glucopyranoside (230.45 mg) and cy-3-O-rutinoside (131.5 mg) on the basis of 100 g dry weight. Total DNJ content was 2.39 mg/g dry weight of lyophilized mulberry fruit. Blood glucose level decreased in the diabetic mts fed the mulberry fruit supplement. The content of the liver glycogen increased in the diabetic mts fed the mulberry fruit supplement. Disaccharidase activity in the proximal part of the intestine, such as that of maltase, sucrase and lactase in the mulberry fruit supplementation groups, were lower than that of the DM group. These results suggest that mulberry fruit possess a suppressive effect on hyperglycemia, possibly by inhibiting the activity of disaccharidase in the small intestine of rats.