| Objective: In the past few years,along with the extending of a lot of tumor patients lives, more and more investigations were done to prevent the side effect of antitumor drugs. Many researchers have demonstrated that there are more and more new diabetes mellitus during or after chemotherapy. They pointed that the damage of islet cell by antitumor drugs may induce the direct impairment of glucose tolerance or diabetes mellitus. But by now,most of the researches are restricted at retrospective analysis. Tumor patients have hyperalimentation and high fat diet during chemotherapy intermission. But hyperalimentation and high fat diet reduces the insulin secretion and sensitivity. It is important to study the influence of chemotherapy and a short term high fat diet on blood glucose and insulin secretion.Mitomycin(MMC) is one of the antibiotic antitumor drugs.In its chemical constitution,there are ethylene-imine and carboxamide group.They have alkanisation.These groups can inhibit duplication of DNA by cross-linking with double strands of DNA.They also break part of DNA. MMC that has a wide anti-tumor spectra is no cycle specific drug.Its t1/2 is one hour.The main adverse effects are obvious and lasting marrow depression and gastrointestinal tract reaction.Sometimes it causes mesenchymal pneumonia. In this research,rats were given the high fat diet and intravenous injection with MMC, the effects of high fat diet and MMC on glucose tolerance and insulin secretion were examined.Methods: Male Wistar rats(n=48),six-weeks old,after adaptive being acclimated for one week, were randomly divided into 4 groups:normal control,MMC group, HF group(high fat diet),and HF +MMC group(high fat diet and MMC),12 in each group.On the 6th day, MMC were administered via intravenous injection at 1.67mg/kg in MMC group and HF+MMC group. Saline were injected into the tail vein(1.67mg/kg in NC and HF group). On the second day after administration (48 hours later),intraperitoneal glucose tolerance test (IPGTT) was performed. The rats were fasted for 10 hours before IPGTT, and the blood samples were taken from the tail vein.Pancreas were removed and weighed with water absorbed away by filter paper after rats were sacrificed the third day after admistration.The pancreas were stored in 10% formalin solution.1 FeedingThe Wistar rats were kept in an airconditioned room(temperature22±2℃, relative humidity55%~65%, lightness 12/24 hours).They were kept individually. Normal control and group MMC received standard laboratory chow diet(11% fat, 60% carbohydrates and 29% protein). Group HF and group HF +MMC were fed with high fat diet (65% fat, 25% carbohydrates and 10% protein).2 The intraperitoneal glucose tolerance test (IPGTT)All rats were fasted for 10 hours (from 06:00 to 16:00 of the same day).Around 16:00,fasting blood was collected from the tail vein,then rats were administered 20% glucose solution intraperitoneally,the dose was 2.0g/kg.Blood was collected from the tail vein at 20 min,60min,120min after glucose loading. The plasma was separated immediately.3 The measurements of glucose and insulin levelsGlucose oxidase method was used for the determination of glucose and radioimmunoassay method for the the determina- tion of insulin levels.4 The measurements of FFA levelsFFA were measured by the ratio of Cu2+ chrom.5 The morphological examination of pancreaThe paraffin section was made by routine method,it was stained with the method of immunohistochemistry to examine the expression of insulin protein and bcl-2 protein in islet cell,and to measure the area of pancreatic beta cells with anti-insulin antibody.6 Statistical methodsResults are expresssed as the values±SD.The data were subjected to ANOVA using SPSS13.0. Student's t-test was used when there was a significant difference amang groups.The 0.05 level of prebability was used as the criterion of significance. Results:1 The weight of ratsThere was no significant difference in weight among each group at the beginning of the experiment, before intravenous injection and before the intraperitoneal glucose tolerance test(P>0.05).2 Plasma glucose levels during IPGTTThe fasting plasma glucose (FPG) levels were much higher in the HF group and the HF+MMC group than in the normal control group(P<0.05); but there was no significant difference in FPG between the MMC group and the normal control group(P>0.05); there was no significant difference in FPG among the MMC group,the HF group and the HF+MMC group(P>0.05).The 20-min, 60-min, 120-min postload glucose levels in the MMC group, the HF group and the HF+MMC group were much higher than in the normal control group(P<0.05); The 20-min, 60-min, 120-min postload glucose levels in the HF+MMC group were much higher than in the MMC group and the HF group(P <0.05);but there was no significant difference between the MMC group and the HF group(P> 0.05).3 Insulin levels during IPGTTThe fasting plasma insulin(FIN) levels in the HF+MMC group were much lower than others group(P<0.05); but there were no significant difference among the normal control group,the MMC group and the HF group (P>0.05). The 20-min postload insulin levels in the MMC group, the HF group and the HF+MMC group were much lower than that of the normal control group(P<0.05); the 20-min postload insulin levels in the HF+MMC group was much lower than in the MMC group and the HF group(P <0.05);but there was no significant difference between the MMC group and the HF group(P> 0.05).The 60-min postload insulin levels in the MMC group and the HF+MMC group were much lower than the normal control group(P<0.05); but there was no significant difference between the HF group and the normal control group(P>0.05). The 60-min postload insulin levels in the HF group was much lower than the HF+MMC group(P> 0.05),but much higher than the MMC group(P> 0.05).The 120-min postload insulin levels in the HF+MMC group were much lower than that of the normal control group and the HF group(P<0.05); but there was no significant difference among the normal control group,the MMC group and the HF group(P> 0.05).The plasma insulin of each group rats reached the peak at 20 minutes after intraperitoneal injection, the 20-min plasma insulin levels in the normal control group was about 3.80 times FIN,the MMC group 2.60 times FIN, the HF group 2.77 times FIN, and the HF+MMC group 2.22 times FIN.4 FFA levelsThe FFA levels of the HF group and the HF+MMC group were much lower than that of the normal control group and the MMC group(P<0.05); but there was no significant difference between the normal control groupand the MMC group (P> 0.05); and there was no significant difference between the HF group and the HF+MMC group (P> 0.05).5 The effects on the pancrea weight of ratsThe pancrea weights and the ratio of pancrea/body weight in the MMC group, the HF group and the HF+MMC group were lower than the normal control group ( P <0.050).6 The mean area of pancreatic beta cellsThere was no significant difference in the area of pancreatic beta cells among the MMC group, the HF group,the HF+MMC group and the normal control group(P>0.05)7 The expression of insulin and bcl-2 in the islet cellsThere was no significant difference in the expression of insulin among each group( P> 0.05). The expression of bcl-2 in the MMC group and the HF+MMC group were lower than the normal control group (P<0.050); but there was no significant difference between the HF group and the normal control group( P>0.050).The expression of bcl-2 in the HF+MMC group was lower than the MMC group(P<0.050).Conclusion:1 The glucose tolerance and insulin secretion in rats were impaired 48 hours after administration of mitomycin.2 The glucose tolerance and insulin secretion in rats were impaired after administration of short-term high-fat diet. 3 MMC has a direct toxic effect on the pancreatic beta-cell. MMC reduced the anti-apoptotic gene Bcl-2 expression to promote pancreatic beta-cell apoptosis, while high-fat diet can further promotes the toxic effects of MMC. |
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