| Objective:Diabetes (diabetes mellitus, DM) is a series of metabolicdisorder syndrome which is caused by relative or absolute lack of insulinsecretion. In clinic, an abnormal rise of the level of blood sugar is the mainfeature of this syndrome. In the world, diabetes can be divided into four types-type1, type2, gestational diabetes and special type of diabetes. More than95%of diabetic patients suffering type2diabetes mellitus. As the onlyhormone which can reduce the level of blood sugar, the synthesis process ofinsulin in cell has been explained clearly. But the extracellular transit pathwayof insulin under physiological conditions has not been so cleared. Mostscientists always believe that the hormones produced by endocrine cells of thebody are transported to the target organ by blood circulation. However, somescholars have observed that there were affluent lymphatic capillariesdistributed around the islets, and the relationship between the islets andlymphatic vessels is much closer than the relationship between the islets andthe blood vessels of the same class as the lymphatic capillaries. At the sametime, the permeability of lymphatic capillaries is much larger than that of thecapillaries, which make it easier for macromolecular protein to pass throughthe lymphatic vessels. With the deepening of research, some scholars havediscovered the presence of insulin in the lymphatic system, which suggeststhat lymphatic system may be an important transit pathway of insulin underphysiological conditions. This pathway has important physiological andpathological significance. As macromolecular, insulin and amylin aresynthesized and secreted according to a certain proportion synchronously byislet cells. There is a close relationship between the two kinds ofpeptides. Some researches have discovered that the deposition of amylinaround the islets is a typical pathological feature of pancreas in patients with type2diabetes in their early stage. This experiment will give somemorphological basis to the investigation of the transport pathway of insulinand other peptide hormone and the mechanism of the deposition of amylinaround the islets.Obesity, which means overweight obviously and excessive thick of fatlayer, is a pathological state caused by the fat (especially triglycerides)accumulate excessively in the body. Because of excessive intake of food ordisorders of body's metabolize, one's body weight grows excessively, whichresult in excessive accumulation of fat and a series of physiological andpathological changes. Obesity, especially obesity in splanchna, is a clearindependent risk factor of type2diabetes, but the pathogenesis is still notclear now. Lipid, especially the lipid absorbed by the intestinal, is mostlyabsorbed by lymphatic capillaries in the intestinal villi or the central lacteal(about80%to90%). The excessive accumulation of fat can certainly increasethe load of lymphatic system. This experiment will further investigate theeffect of lymphatic stasis on the structure of the pancreas in obese rat on thebase of the transport mechanism of lipid and protein.Methods:1Grouping of experimental animal and preparation of model401-month-old healthy SD rats of either sex were selected. Each one wasabout100g weight, and12cm length. All the animals were provided by theExperimental Animal Center of Hebei Medical University. All the rats weredivided into two groups randomly: normal diet group (20) which named groupA, high-fat diet group (20) which named group B. Then rats in group A weregiven feed normally, and rats in group B were given high fat diet.10weekslater, rats in group A were randomly divided into A1sham group (10) and theA2surgery group (10); group B were randomly divided into B1sham group(10) and B2surgery group (10).2Light microscope sample preparation and observationPart of the pancreas in rats was frozen and paraffin-embedded and sliced.Then HE stained, amylin immunohistochemical stained and observed by light microscopy to compare the subtle differences of the structure of thepancreases.3TEM sample preparation and observationPart of the pancreas specimens were used to make TEM sample. Thetissues were resin-embedded, blue stained and then semi-thin sliced. Weobserved the tissues by light microscopy to determine the presence of the islet.After that we observed the tissue by electron microscopy to compare theultrastructural differences of the pancreas, especially the islets.4Scanning electron microscopy sample preparation and observationPart of the pancreas specimens fixed by aldehydes fixative. After aconventional process of conducted, fixed, dehydrated, and vacuum dried, thesamples were fixed in sample care of electron microscopy. Then thecharacteristics of the structural of the pancreatic surface were observed.Results:1A general observation of the pancreasThe obese group (group B) compared with the normal group (A):abdominal wall and mesentery showed slight lipid deposition, greasy feeling.The color of pancreatic tissue is slightly lighter, and there is a minor adhesionaround the tissue.The surgery group compared with the sham group: abdominal organs,mesentery, etc. lipid deposited obviously. There is a significant lipid coveragearound the pancreatic tissue and adhered with liver.2An observation under light microscopeRoutine HE staining of tissue sections (1) Varying degrees of isletamyloid change appeared at all the pancreatic tissue except the normal controlgroup (A1). We saw the derangement, swelling and even apoptosis of isletcells in the remaining three groups of experimental groups. We also saw thatthe stromal among cells was loosed, connective tissue hyperplasiaed, thelymphatic-like pipeline expanded and lipid tissue accumulated.(2) On thepancreatic tissue sections with amylin immunohistochemical staining, islets ofthe normal control group (A1) were lightly stained, and the islets of the remaining three groups of experimental animals pancreatic tissue as well as itssurrounding showed amylin positive immune response with brown color.3TEM observations of thin tissue sectionsThe pancreatic tissue of high-fat diet sham operation group (group B1)and thoracic duct ligation group (group A2, B2) showed that the gap amongislet cells was widened and expanded, where large amount of lipid andamyloid accumulated. In addition, inflammatory cells often can be seen in theislet area.4Observation of pancreatic tissue surface with electron microscopePancreas is one of the intraperitoneal organs and the surface was coveredby peritoneum which was consisted by flat epithelial cells. Compared withnormal sham operation group, the thoracic duct ligation group we can see themicrovillis at surface and the edge parts of pancreatic peritoneal epithelialcells were increased significantly, and the gap between two cells increasedsignificantly.5Comparative and analysis of body weight and the levels of blood sugar andinsulinDiet for10weeks, the rats' weight and the level of blood sugar of thehigh fat diet group (group B) were significantly higher than normal diet group(A), statistical analysis had significant differences (P <0.05).6months after surgery, the level of blood glucose did not changesignificantly in sham operation group; the level of blood glucose in thethoracic duct ligation group was significantly increased. The statisticalanalysis had significant difference (P <0.05) among the three groups, bloodsugar level showing B2> A2> B1Conclusion:1Fatty diet can cause elevate of rats' weight and LEE index and lead toobesity; the high-fat diet is one of the ideal methods of preparation ofnutritional obese animal models.2Thoracic duct ligated can cause abdominal organs including the pancreas,lymphatic flow disorders; pancreatic lymph stases can change the structure and function of rat pancreatic tissue.3Obesity is similar with the structure and function changes of the pancreatictissue caused by thoracic duct ligation, so obesity may be related to abnormalfat deposition in the pancreas, lymphatic flow disorders, and pancreatic amylinpeptide hormone transporter. |
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