Abstract: Oral glucose tolerances and blood insulin levels of diabetic rats were observed after the intake of sucrose or starch with green tea extract. The inhibitory activities of green tea extract against alpha-glucosidase (EC 3.2.1.20) and alpha-amylase (EC 3.2.1.1) were then assayed by colorimetric method, while the glucose uptake into brush border membrane vehicles was determined by rapid filtration method. The results showed that the green tea extract significantly improves the glucose tolerance after sucrose or starch intake in diabetic rats. Green tea extract administration showed that the potent alpha-glucosidase inhibitory activity with IC50 value is 0.13 g/L; but the inhibition effect of green tea extract on alpha-amylase is rather low, with the inhibitory activity about 21% at the concentration of 1 g/L. Green tea extract also significantly decreases glucose transport potency of brush border membrane vehicle of rabbit small intestine with IC50 value as 3.5 g/L. It is suggested that the green tea in general, would inhibit carbohydrate digestion and absorption into small intestine, so as to be physiologically useful for suppressing postprandial hyperglycemia.

Key words: green tea； &alpha, -glucosidase； &alpha, -amylase； glucose transporter；