Maitake (Grifola frondosa) improve glucose tolerance of experimental diabetic rats

We have previously reported that rats with diabetes induced by injecting streptozotocin into neonates showed remarkably lower blood glucose, urine volume, and glucosuria after administration of Maitake (Grifola frondosa). In the present study, we investigated the effects of Maitake on insulin concentration, organ weight, serum composition, and islets of Langerhans in streptozotocin-induced diabetic rats using the same method. The diabetic rats were produced by injecting 80 mg/kg B.W. streptozotocin into 2-d-old neonates. From the age of 9 wk, the rats were given experimental diets for 100 d. The diabetes and control groups were given either diets containing 20% Maitake (DM and CM groups) or control diets (D and C groups). During administration of the experimental diets, we measured body weight, food intake, amount of feces, and serum insulin concentration at glucose loading. The glucose tolerance test was performed at the 10th week after the start of the experimental diets. The D group had an initial fasting blood glucose of 225+/-49 mg/dL, and a maximum blood glucose of 419+/-55 mg/dL at 60 min. In the DM group, however, the initial fasting blood glucose was 170+/-23 mg/dL, and the maximum blood glucose was 250+/-41 mg/dL at 15 min. Both values were markedly lower than those in the D group (p<0.05). The insulin concentration at 15 min. after glucose loading in the DM group was 41+/-16 microU/mL, which was significantly higher than that in the D group (15+/-7 microU/mL) (p<0.05). After the 100-d experimental period, blood samples were collected. The fructosamine level was significantly lower in the DM group (152+/-21 mmol/L) than in the D group (185+/-13 mmol/L). The concentration of 1.5-A.G. (1.5-anhydro glucitol) was significantly higher in the DM group (9.33+/-2.42 microg/mL) than in the D group (1.33+/-0.52 microg/mL). Observation of insulin antibody stain in the Langerhans cells of the pancreas using ABC method showed a decrease insulin antibody stain in the D group. The cells of the DM group were stained more darkly than those of the D group. From these results, we postulated that the bioactive substances present in Maitake can ameliorate the symptoms of diabetes.