| Diabetes mellitus is a common metabolic disorder characterized by chronic hyperglycemia which is caused by insufficiency of insulin secretion relatively or absolutely.Chitin is the polymer ofβ(1,4)-linked N-acetyl-2-deoxy-D-glucose which is widely ground in shells of crustaceans, shrimp, crab and insects. Chitosan is the deacetylated product of chitin, which widely exists in Crustacean and Fungi. It is the only alkaline polysaccharide in the nature. Numerous biological activities of chitosan have been found recently, especially the potential of preventing diabetes. The application research of chitosan in functional food is limited because of its acid-solubility. However, chitosan treated by degradation or by chemical modification can dissolve in water of a broad pH range.In this research, Chitooligosaccharides (COS), COS-Cr complexes (CosCr or CC), low molecular chitosan (LMCH), low molecular 50% deacetylated chitosan (LMC), low molecular chitin (LMCT), low molecular carboxymethyl-chitosan (LM-CMC), low molecular carboxymethyl-chitin (LM-CMCT), were prepared by enzymatic degradation and chemical synthesis of high molecular weight chitosan. And the character of them were detected.Type I diabetic rats were successfully induced by single intraperitoneal injection of streptozotocin (STZ). All of the diabetic rats were randomly divided into COS-Cr treating groups which were administered respectively with COS-Cr complexes at dose of 90mg/kg (CC-L),180mg/kg (CC-M) and 360mg/kg (CC-H) of body weight daily for continuous 30 days; the COS-Cr-Astragalus treating groups which were administered respectively with COS-Cr-Astragalus complexes at dose of 90mg/kg (CCA-L),180mg/kg (CCA-M), and 360mg/kg (CCA-H) of body weight daily. The normal control and model control group were fed with the same volume of distilled water at dose of 5ml/kg. Body weight, fasting plasma glucose (FPG), fasting glucose tolerance (FGT) were measured after 30 days, as well as triglyceride (TG), high density lipoprotein cholesterol (HDL), total cholesterol (TC), creatinine (CR) and blood urea nitrogen (BUN). Pancreas, liver and kidney tissue of the rats were exanimated histologically.The research was carried out to detect the hypoglycemic effects of LMC, LM-CMC and LM-CMCT by fed diabetic rats with them at dose of 180mg/kg body weight daily. After 45 days, besides the index listed above, the hepatic glycogen, muscle glycogen, malondialdehyde (MDA), superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) were also measured, and spleen tissue were histopathological observed.The experiment results were as follows:1. Different doses of COS-Cr complex and COS-Cr-Astragalus compound had different effects on improving glucose metabolism.It can be derived from the experiment results that The FGP,, FGT of CC-L treating group had significant differences (P<0.01) compared with DM control group; The FGP of CC-M treating group had significant differences (P<0.05) compared with DM control group; The FGP of CCA-L and CCA-M groups were lower than DM model group, and had significant differences (P<0.01) compared with DM control group, and the FPT of them had significant differences (P<0.01) compared with DM control group.Combined with the result of tissue observation, the research found that COSCr and COS-Cr-Astragalus have effects on hypoglycemic, glucose tolerance improving, pancreas cells impairing, and the low dose of COSCr was better than others.Compared with DM control group, the COS-Cr complex and COSCr-Astragalus compound have effect on increasing HDL, and CC-M (P<0.05), CCA-L (P<0.05), CCA-M (P<0.05),CCA-H (P<0.05) were better than other groups. At the same time, COS-Cr complex and COS-Cr-Astragalus compound decreased CR, BUN of diabetic rats,and the high dose was better than other dose.2. The hypoglycemic effects of LMC, LM-CMC and LM-CMCT on diabetic rats were found after being treated with 45 days. The FGP, FGT of LMC and CM-LMC treating group had significant differences (P<0.01) compared with DM control group; the hepatic glycogen of LMC group was increased, and had significant differences (P<0.01)Compared with DM control group, the low molecular water soluble chitosan with different chemical group decorated have effect on decreasing total cholesterol (P<0.05), increasing HDL (P<0.05), decreasing CR, BUN of diabetic rats,and LMC and CM-LMCT were better than CM-LMC. As well as decreasing MDA and increasing GSH-Px.The result of tissue observation showed that the low molecular water soluble chitosan with different chemical group decorated also had effects on impairing damaged cells of pancreas, kidney, liver and spleen.The conclusion was all of three low molecular water soluble chitosan have effects on adjusting plasma glucose, LMC and CM-LMCT were better than CM-LMC.The deacetylation degree of the three were different, and the experiment showed that acetyl plays a role in glucose regulation. But the mechanisms of these need further study.
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