| With the socioeconomic development, the improvement of living standard and the changes of dietary ingredient, diabetes mellitus becomes more prevalence and the incidence of this disease rises year after year. To prevent and remedy diabetes mellitus is a remarkable topic, In our country and Japan, people often use the infusion from old tea leaves to cure diabetes. This study will investigate the suppressive hyperglycemic effect of tea and tea components and discuss the hypoglycemic mechanism in diabetic SD rats induced by alloxan.After establishing a method how to induce SD rats to the diabetic model, we have investigated the suppressive hyperglycemic effect of extracts from different kind of tea (green tea, oolong tea, black tea, pu'er tea) and the hypoglycemic mechanism of tea polyphenol (TP), tea polysaccharides (TPS), theaflavin (TF) by analyzing the activities of glycolytic enzymes (amylase, sucrase, maltase) in small intestine and blood insulin level. Results showed as follows:1. The components were measured including total amino acid (AA), TPS, TP, caffeine and tea pigment in different instant tea used in this study. Results indicated that the highest content of TP was in oolong tea (27.0%), the next one was in green tea (25.5%); the contents in black tea and pu'er tea were 10.9% and 3.3% respectively. The order of TPS according to the content from high to low was pu'er tea, green tea, black tea, and oolong tea. Only little of AA was in pu'er tea while about 4% in others. The changes of tea pigment content were related with fermented degree during tea processing. Among these 4 kind teas, the content of caffeine in pu'er tea was the highest, whereas that in green tea was the lowest, while the levels in oolong and black tea were almost the same. The crude TPS, extracted from green tea in this laboratory, was a kind of powdery and gray material, and contained polysaccharides about 15% by anthrone-vitriol method employed glucose as standard.2. The optimal treatment to induce SD rats to diabetic model by alloxan was asfollows: rats were fasting for seven hours at first, then intraperitoneally injected alloxan diluted by physiological saline at the dose of 150 mg/kg body weight (BW), on the next day rats were re-injected at the dose of 140 mg/kg BW after fasting by the same time. Consequently, the blood glucose in diabetic rats under this treatment was high and the growth was well. The typical symptom, i.e., over-drinking (polydipsia), over-eating (bulimia), polyhydruria and decreasing of BW in diabetic rats was observed in this study. With the experiment getting on, the symptom became alleviation in experimental animals comparing with the diabetic rats consumed basal diet, but the diabetic rats administered with pu'er tea died gradually, which had pathological changes in eyes and feet at the same time.3. The suppressive hyperglycemic effect of different kinds of instant tea: green tea, oolong tea, black tea was studied first. Among these, green tea was the most effective material on the suppressive hyperglycemia, oolong and black tea showed a declining tendency of blood glucose level, but they are not significant compared with the control group. Oolong and black tea can improve glucose tolerance in diabetic rats, while no significant effect was observed in green tea. There are not obvious changes of weight and appetite in diabetic rats fed different kind of tea.4. To test which tea component(s) showing suppressive hyperglycemic effect, TPS, TP, and TF were administered on diabetic rats for 2 weeks. The results showed that TPS and TP suppressed the increase of blood glucose level significantly, while TF did not. In addition, the glucose tolerance in diabetic rats was meliorated in TPS group. Similarly, TPS and TP didn't affect the changes of body weight and appetite of diabetic rats.5. To investigate the hypoglycemic mechanism of TP and TPS, the relationship between postprandial blood glucose, blood insulin and the activities of glycolytic enzymes in small intestine, such as amylase, sucrase and maltase was analyzed. Compared with control group, the activities of sucrase and maltase were decreased obviously and blood insulin level was improved significantly, but the activity of amylase was not affected in TPS group. Almost the same change without significance was observed in the group fed TP while compared with the control... |
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