The Preliminary Exploration On Mechanism Of Insulin Concentration Increased For Experimental Rat Diabetes

Objective：Insulin resistance and hyposecretion of insulin are two majorfeatures in the pathogenesis of type2diabetes. Recent studies done in animalmodels of diabetes have suggested that the β-cell mass is a critical factor inthe onset of overt diabetes. In our previous research, we found a phenomenonthat the concentration of insulin increased in the process of type2diabetic inrats model.so we try to develop a rat model would closely mimic the naturalhistory of human type2diabetes. The successful establishment of such amodel would be used to study the mechanism insulin concentrationincreased.As a result,we can get a new idea for the treatment of type2diabetes.Method: The rat model of type2diabetes was developed by feeding theanimal with high-fat diet following a single intraperitoneal injection of30mg/kg of streptozoficin (STZ). All the rats were kept under conventionalconditions and provided with a12:12h light-dark cycle. After1week of STZinjection, the rats with the fasting blood glucose of≥11.1mmol/L wereconsidered diabetic（group4），the other rats were divided into3groups:control group (group1), regular chow-STZ (group2), and high-fat diet(group3);On the day of treatment and72h,4weeks,8weeks,12weeks,16weeks,18weeks and28weeks after treatment, The concentration of INS wasmeasured quantitatively by ELISA kit and animals were then killed byoverdose of anesthesia（2%Pentobarbital sodium，30mg/kg body weight).Pancreases were collected immediately and fixed to be ready forimmunohistochemistry.cell proliferation with Brdu immunohistochemistry;label amount of β-cell with insuline immune-histochemistry staing. All theexperiment data was tested by the normality test to clear the generaldistribution types. The normal distribution data was with mean±standarddeviation said (x±s) and the comparison between groups used the t test; Non-normal distribution data was with median (quarterback spacing)[Md(Interquartile Range)] and the comparison between groups used Wilcoxontest. When P <0.05, we think that it is as a statistical significance.Results:⑴plasma glucose concentration:Compared with day0（6.8±0.5）,the plasma glucose concentration increased sharply on day3with astatistical significance in model (16.7±2.6) and regular-chow (14.4±2.7)groups,(P=0.00<0.05; P=0.00<0.05). From now on, the plasma glucoseconcentration showed not statistically significant,(P>0.05).The other twogroups showed not statistically significant at any time，(P>0.05).⑵insulinconcentration: Compared with day3(30.393±2.038) and0(28.061±1.963),the concentration of insulin at4weeks （31.321±2.467）with astatistical significance,it increased obviously,(P=0.00<0.05). however, at4weeks,8weeks,12weeks,16weeks and18weeks the concentration of insulinshowed not statistically significant,(P>0.05).At12weeks the concentration ofinsulin reached the highest level（37.071±5.537）. Compared with day0(28.061±1.963),the concentration of insulin at28weeks（30.854±3.420）back down to lower levels, with no statistical significance,(P>0.05).⑶hematoxylin-eosin staining：Different pathology change appeared in islets ofmodel group. β-cells showed normal,edema,decline in mass,vacuolesdegeneration and necrosis,⑷insulin-positive cells: The IOD value on day3and at12weeks were190.2491±29.923,1113.367±14.684.The value at12weeks was higher than on day3(P=0.000<0.05).It descriped thatinsulin-positive cells and insulin concentration increased.while Diameter valuewere11.670±0.658、14,235±0.968. The value at12weeks was higher thanon day3, with a statistical significance (P=0.009<0.05).⑸Brdu-positivecells:The number of Brdu-positive cells on day3,at4weeks and12weekswere3.5±1.048、4.0±0.894、7.2±1.169respectively. the number on day3and at12weeks was not statistical significance (P>0.05). The number at12weeks was higher than on day3, with a statistical significance (P=0.001<0.05)The number at4weeks was higher than on day3, with a statisticalsignificance (P=0.001<0.05). Conclusisons:In our study,The peak of insulin secretion appeared in theprocess of type2diabetic in rats model,which was caused by the regenerationof β-cells.however,resulting from dedifferentiation,the plasma glucoseconcentration didn`t show significantly lower at this time.