| Objective: It has been demonstrated that type 2 diabetes mellitus (T2DM) has obviously heredity heterogeneity and is influenced by many environmental factors. Insulin resistance (IR) and pancreatic islet dysfunction are the dominant mechanisms in the pathogenesis of T2DM. Disorders of lipid metabolism are often the early-stage incidents in the pathogenesis of T2DM and also a symbol of IR. Pancreatic islet β cells proliferate with compensatory hypertrophy under higher metabolism burden, on the other hand, hypertrophic β cells are prone to apoptosis and dysfunction, and finally result in severe lack of insulin-secreting cells. In clinical T2DM stage, apoptosis β cells are remarkably increased. Islet β cell apoptosis is an important factor contributing to β -cell loss, and recent studies show it is also one of the early stage incidents in the pathogenesis of T2DM. There is a theory of " shen xu xue yu " on the pathogenesis of DM in traditional Chinese medicine and DM is sorted to "xiao ke symptom" . We improved the traditional compound herbal medicine —"yu ye tang" which is used to treat "xiao ke symptom" , and got a new compound herbal medicine prescription —"yu ye tang hua cai". The newcompound herbal medicine has the efficacy of "yi qi zi yin, gu shen xiao ke, shu xue tong luo ". So the aims of this study are as follows: Firstly, through long-term high-fat feeding normal SD male rats, to observe the changes of oral glucose stimulated insulin secretion (GSIS), apoptosis rate of pancreatic islet ￡ cells and mass of 3 cells, and to explore the role of lipotoxicity in the pathogenesis of T2DM. Secondly, through observing the effects of compound herbal medicine —"yu ye tang hua cai" on the GSIS, pancreatic islet P cells apoptosis and mass of ￡ cells in the long-term high-fat feeding SD rats, to explore the protective action of compound herbal medicine from the lipotoxicity to pancreatic islet ￡ cells.Methods: Sixty healthy male Sprague-Dawley rats, 8 weeks of age, weighing 208±20g, were provided by HeBei province experimental animal center. They were randomly divided into 4 groups and fifteen rats in each group. Normal control group (NC) rats were fed with common chow ( 13% of calories as fat); high fat chow group (HF) rats were fed with high fat chow (55% of calories as fat); herbal medicine group (HM) rats were fed with both high fat chow and compound herbal medicine; metformin group (MT) rats were fed with both high fat and metformin. They were housed 5 animals per cage in a room 12/12-hour light/dark cycle for six months.Body weight was measured regularly and blood samples were taken at the beginning and end of the experiment. After 12h fast, blood samples were taken from the medial canthus ofeyes, and serum was stored at -20 °C for measurement. The animals in each group were subjected to an oral glucose tolerance test (OGTT) at the end of the experiment, pancreatic tissues were isolated and fixed in 4% neutral paraformaldehyde for the observing pancreatic morphology.1 Measurement of blood glucose and insulin: The levels of blood glucose and insulin were determined respectively with glucose oxidase assay and radioimmoassay. Triglyceride (TG)n total cholesterol (TC)^ high density lipoprotein cholesterol (HDL-C) were measured with an enzyme colorimetric method. Lower density lipoprotein cholesterol (LDL-C) was calculated with Friedewald equation (LDL-C=TC-HDL-TG/2.2). FFAs was measured by the ratio of Cu2+ chrom.2 The epiploon fat and epididymal fat pads were isolated and weighed as visceral fat mass.3 The pancreatic islet morphological and ￡ cells apoptosis were evaluated by HE staining > immunohistochemistry and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) in five rats of each treatment group.4 Statistical analysis: All of data were treated with SPSS 11.0. and continuous variables were expressed as mean+SD. The statistical significance between two groups was determined by T-test. One-way ANOVA were used to compare continuous variables among groups.Results 1 The effects of high-fat diets on body weightThere were no significantly differences of body weights in each treatment groups at the beginning of the experiment. At the end of the experiment, the body weight in HF group(490± 28g )was significantly higher than that in NC group (428+ 37g)(P<0.01). The body weights in HM group( 406±32g) and MT group( 403±22g) were clearly decreased, compared with that in HF group(separately P < 0.01). The percentage of visceral fat weight / body weight was significantly higher in HF group (5.0% ± 0.7% ) than that in NC group(2.8% ± 0.2%)(P<0.01). The percentages of visceral fat weight / body weight in HM group (4.5% ±0.3% ) and MT group( 4.7% ± 0.4%) were not significantly decrease than that in HF group.2 Results of OGTT at the end of the experimentThere were no significantly differences in fast blood glucose (FBG) between four groups. The blood glucose concentrations at 30min(8.3 ± 0.4mmol/L) > 60min(8.6 ± 0.2mmol/L) and 120min(7.2 ± 1.3mmol/L) after oral administration of glucose in HF group were significantly higher than those in NC group (PO.05~0.01) . The blood glucose concentrations at 30mhK 60min and 120min time points in HM group and MT group were significantly lower than those in HF group(P<0.05~0.01).3 Results of GSIS at the end of the experimentThe fasting blood insulin concentration in HF group (26.5±6.2mIU/L) was significantly higher than that in NC group(17.7±2.3mIU/L ) (P<0.01). The blood insulin concentrationat 30min after oral administration of glucose in HF group (31.1±3.3mIU/L) was significantly lower than those in NC group( 45.3 ± 4.8mIU/L ) and HM group ( 39.8 ± 4.5mIU/L )(separately P<0.01) . But the blood insulin concentration at120min in HF group (28.5 ±5.3mIU/L) was clearly higher thanthose in NC group (17.2±1.6mIU/L)> HM group (21.9+6.2mIU/L) and MT group (17.9±3.2mIU/L) (separately P<0.05) .4 Serum lipid levels at the end of the experimentThe serum TG . TC and LDL-C concentrations of HF group were significantly higher than those of NC group (separately P < 0.01). The serum TG , TC and LDL-C concentrations in HM group and MT group were significantly decreased than those in HF group. FFAs concentrations in HF group ( 454 ± 53 mmol/L ) was significantly higher than that in NC group (409+26 mmol/L) (P < 0.01), although there were decreasing trend of FFAs concentrations in HM group and MT groups compared with that in HF group, but there were not significant differences(P>0.05). There were also no significant differences in serum HDL-C concentrations between four groups.5 The apoptosis of pancreatic islet cells and P cell insulin-positive areasThe percentage of islet P cells apoptosis in HF group(12.3%±0.8%) was significantly higher than that in NC group(2.1%±0.9%) (PO.001) . The percentage of islet 0 cells...
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