Comparison Of Glucose Metabolism Capacity And Islet Cell Characteristics Between Cynopterus Sphinx And Hipposideros Armiger

With the rising incidence rate in recent years,diabetes have become a serious threat to human survival and living quality,as well as a major public health problem.It is well known that two key factors result in diabetes:one is the decrease in the number and crock up of function of islet ? cells,another is insulin resistance.Due to the existing problems of inefficient production and mature rates of ? cells in current diabetes models,it is difficult to fully meet the needs for the research,and only a limited number of species is currently available as animal models for obesity research.Thus,establishing new animal model for diabetes is extremely urgent.Chiroptera is numerous,widely distributed and the second largest order of mammals next only to rodent animals,which shows grand ecological and diet diversity.Pteropodidae is usually considered as one of specific taxon within Chiroptera,which prefers high-sugar diet,such as fruit juice or nectar.High-carbohydrate diets have promoted long-term adaptive evolution of old world fruit-eating bats to show phenotypic characteristics of rapidly reducing blood glucose,and it prevents the sustained hyperglycaemia from feeding a lot of carbohydrate.Therefore,high-carbohydrate diets of old world fruit-eating bats is an ideal animal model of blood glucose regulation mechanism.This study chooses Cynopterus sphinx(frugivorous bat)and Hipposideros armiger(insectivorous bat)as subjects to explore the rapid hypoglycemic mechanism after intaking large amount of high-sugar foods in both hormone and physiological anatomical levels,which can help to study and understand glycemic homeostasis of mammals,and provide new insights for curing human Diabetes.At first,we performed glucose tolerance tests(GTT)and insulin tolerance tests(ITT)were performed in the fasting state.The results showed that there were significant differences in the hypoglycemic rate between frugivorous bats and insectivorous bats(P<0.05),but they depend on insulin to reduce blood glucose.Comparing with H.armiger,a sphinx has a higher efficiency of reducing blood glucose.Secondly,we used enzyme-linked immunosorbent assay(ELISA)to measure the serum insulin concentration.In the fasting state(fasting for 12 h),the serum insulin concentration of C.sphinx(Mean±SE,39.10 ± 4.46 mIU/L,n = 9)was significantly higher than that of H.armiger(26.30± 0.74 mIU/L,n=11)(P<0.05).We considered that the high concentration of insulin in the blood of C.Sphinx is consistent with the rapid decrease in postprandial blood glucose levels due to their long-term adaptation to high-sugar diets,which can prevent the damage from high blood glucose.Then,in the process of anatomy,we found that the pancreatic tissue structure of C.sphinx was concentrated,but the pancreatic tissue structure of H.armiger was dispersed.We dissected the pancreases of bats and fixed in Paraformaledehyde fixative for 24 h,then dehydrated and embedded in paraffin.We stained sections with HE and immunohistochemistry.According to the results of immunohistochemical analysis,the percentage of a cell,? cell and 8 cell in the pancreatic islet of C.sphinx(n = 4)was 29.72±2.08%,48.41±4.59%and 14.73±2.04%,respectively.And the percentage of a cell,? cell and ? cell in the pancreatic islet of H.armiger(n=4)was 22.19±3.24%,50.28±5.99%and 21.74±2.85%,respectively.The ratio of islet area to total pancreas area of C.sphinx was 22.77± 0.90%.The ratio of islet area to total pancreas area of H.armiger was 5.28 ± 0.33%.The percentage of islet tissue to pancreatic tissue in C.sphinx was significantly higher than that of H.armiger.Thus,the islet area of C.sphinx was larger than that of H.armiger.Our results indicated that ? cells distributed throughout the whole islet in C.sphinx,while ? cells of H.armiger were mainly located in the islet core.The size of endocrinal grains was larger in C.sphinx than in H.armiger,and the number of ? cell were more in C.sphinx than in H.armiger as well.The changes of these physiological structures have enhanced the production and secretion of insulin of ? cell in C.sphinx,which may implicate why serum insulin concentration of C.sphinx were notablely higher than H.armiger.At last,we detected expression of BrdU and insulin by immunofluorescence assay technique in pancreas slices,and identified the proliferation of islet ? cells in bats.We concluded that number of proliferating islet ? cell in adult C.sphinx(n = 4)was greater than that of adult H.armiger(n = 5)(P<0.05).It indicated that the rate of islet ? cell renewal in C.sphinx was faster than in H.armiger,which related to fully repair the damage of ? cell in response to postprandial hyperglycemia in C.sphinx,to maintain its efficient production and secretion of:insulin.In summary,the quantitative description of the glucose tolerance test proved that the glucose metabolism capability of C.splhinx(frugivorous bat)was significantly grearer than in H.armiger(insectivorous bat).The evidences from serum insulin concentration,structure of pancreatic islets and characteristics of ? cell proliferation also quantitatively reveal C.sphinx's effectiveness of hypoglycemic ability.It implicates that diet differentiation may effectively promotes adaptive evolution of old world fruit bats to obtain fast hypoglycemic phenotype.