Effects Of Fluctuant High Blood Glucose On Islet β-cell Function And β-cell Apoptosis In Gk Rats

Objectives:1. Compare the effect of fluctuant high blood glucose and consistent high blood glucose on pancreatic isletsβ-cell function.2. Compare the effect of fluctuant high blood glucose and consistent high blood glucose on isletsβ-cell apoptosis.Methods:1. Twenty-two male GK (Goto-kakisaki) rats were randomly divided into consistent high blood glucose group (HG) and fluctuant high blood glucose group (FG). Eleven male wistar rats were used as normal blood glucose group (NG). The FG animal model was induced by intraperitoneal injection of insulin and glucose at different times.2. After introperitoneal injection, glucose tolerance test (IPGTT) and insulin releasing test (IRT) were performed. Serum insulin was detected by radio- immunoassay.3. Pancreatic islets of GK rats and non-diabetic male Wistar rats were isolated and purified respectively.4. Glucose-stimulated insulin secretion test (GSIS) was carried out. Supernatant insulin was measured by radioimmunoassay.5. Immuohistochemical study was carried out and quantitative evaluation ofβ-cell mass of each group was performed using computer-assisted image analysis procedure.6. The apoptoticβ-cell in islets was detected by the TUNEL technology (labeling of DNA strand breaks) andβ-cell apoptosis rate was calculated.7. Expression of genes INS-1, INS-2, PDX-1, BAX and BCL-2 were studied by RT-PCR.Results:1. After 6 weeks, there was no difference in the body weight between FG and HG group.2. Fasting glucose level was higher in FG group than that in HG group. After glucose load, glucose levels of FG group at 15min, 30min, 60min and 120min were significantly higher than those of HG group; the area under curve of glucose was also higher compared with that of HG group. Insulin levels of FG group at 15min, 30min, 60min and 120min were lower significantly than those of HG group. Moreover, the area under curve of insulin to the area under curve of glucose (AUCi/AUCg) and the ratio of insulin increment to blood glucose increment 15-min after glucose load (ΔI15′/ΔG15′) were decreased significantly in FG group compared with those in HG group.3. The stimulating index of islets in vitro of HG group was significantly higher than that of FG group.4. Image analysis of pancreatic islets showed that the insulin staining positive area, area ratio and total density of insulin positive cells per islet were significantly lower in FG group than that in HG group.5. The frequency ofβ-cell apoptosis in FG group was statistically higher than that in HG group. The expression of BAX mRNA of FG group was stronger than that in HG group, while the expression of BCL-2/BAX was lower in FG group compared with HG group.6. Gene expression of INS-1, INS-2 and PDX-1 of FG group decreased compared with that of HG group. Conclusions:1. Fluctuant high blood glucose could lead to further impairedβ-cell function than consistent high blood glucose.2. Fluctuant high blood glucose could increaseβ-cell apoptosis, which may partially contribute to the degeneration ofβ-cell function.