Change Of The Entero-insular Axis In The Rat Model Of Catch-up Growth After Food Restriction And Possible Mechanisms

Objective:To determine the impact of catch-up growth after food restriction (CUGFR) on the entero-insular axis and the possible mechanism leading to metabolic disorder.Methods:The study was conducted in rats. Compared against the control group, which consisted of age-matched rats, some rats were food-restricted for 4 weeks, and then refed for 0,2,4 weeks respectively. In all rats, general physiological parameters, pancreatic morphometry, pancreaticαandβcell relative area and mass, insulin content as well as plasma glucose, insulin and GLP-1 level during OGTT were measured. And the intestinal mucosa morphology, L cell number, gastric emptying rate of barium swallow, incretin effect and GLP-1 receptor (GLP-1R) gene expression in the islet were also analyzed.Results:1. Change of general physiological parametersRats which were food-restricted at 60% of their spontaneous standard chow intake had lighter body weight, shorter body length, smaller body fat content, lower serum triglyceride and free fatty acid than NC group. However, catch-up growth rats whose food intake was suddenly increased possesed faster increase in body weight, body length and body fat content after refeeding, and accordingly their plasma lipids increased except HDL-C. However, although the body fat content and plasma lipids increased except HDL-C had exceeded those in NC group, the body weight, body length of these rats was consistently lower than that of the control group, even after refeeding for four weeks.2. Quantification of pancreticα-andβ-cell relative area and massCompared with NC group, food-restriction in rats was characterized by remarkably decrease in the relative area and mass of P-cell, accordingly by increase in the relativeα-cell area excepting the a-cell mass. After refeeding, morphometric analysis revealed that there was gradually increase in the relative area and mass ofβ-cell with the extension of time to catch up. Although the experimental data over the course of the catch-up growth revealed that there was remarkably increase in the relative a-cell area in comparison with NC group, there was no significent difference between both groups in the a-cell mass.3. Pancreatic insulin contentFood-restriction made pancreatic insulin content decreased remarkablly in CUGFR group and refeeding had improved this. However, pancreatic insulin content in CUGFR group didn't return to normal levels untill catch-up growth for 4 weeks.4. Beta cell functionPlasma glucose and insulin levels at the end of food-restriction were all significantly lower than or similar to NC group when fasting,15,30 and 60 min after glucose gavage. At 2 weeks'catch up, plasma glucose remained lower in the refed group than in the NC group whereas plasma insulin was higher than control at 15 min post-gavage. After 4 weeks'catch up, plasma glucose was still lower in the CUGFR group than in NC group. However, plasma insulin levels were higher than control at all time points of the OGTT, especially at 30 min post-gavage.The insulin/glucose incremental area ratio (ΔAUCI/ΔAUCG) expresses the overall ability of the beta cell to increase its release rate in response to the total glycaemic stimulus presented. It was significantly reduced in the CUGFR group when food restriction for 4 weeks. But refeeding for two weeks made this index rebounced to normal level even higher than NC group. At the end of the 4-week period of refeeding, the insulin/glucose incremental area ratio was not significantly different between both groups.Insulinogenic index at 15 min (I15min/G15min) expresses the early insulin secretion closely related to dietary changes. It was higher in the CUGFR group when food restriction for 4 weeks, and then it decreased with the extention of catch up growth. At the end of the 4-week period of refeeding, the insulinogenic index was lower in CUGFR group than that in NC group. 5. Plasma GLP-1 concentration and GLP-1R mRNA expression in islets Food-restriction resulted in a significant decrease in plasma GLP-1 level. Following refeeding, GLP-1 increased but not to the level of that in NC group, even after 4-week catch-up.GLP-1R expression ratio increased remarkably in the CUGFR group compared with NC group during food restriction. However, catch-up growth blunted this trend, and GLP-1R expression ratio declined with time and was even less than NC group after 4-week catch-up.6. Gastric emptying rate of barium swallowThere was a significant decrease in gastric emptying rate of barium swallow in CUGFR rats during 4-week food restriction. However, more rapid gastric emptying rate can be detected in CUGFR group, especially when catch up for 2 weeks.7. Incretin effectThe glucose concentrations were well matched between the OGTT and isoglycemic IV glucose test (IsoG IVGT) in all groups. However the insulin response was greater after oral than iv glucose before or after refeeding, known as the so-called incretin effect. The incretin effect was decreased significantly by food restriction compared with NC group. After refeeding, the incretin effect remained consistently lower in the refed group until the end of the study.8. The morphology of intestinal mucosa and number of glucagon positive cells in the ileumVillus height and villus height-to-crypt depth ratio decreased during food restriction period. However, catch-up growth increased villus height and decreased the crypt depth, accordingly leading to a higher villus height to crypt depth ratio as compared to NC group. Nevertheless, this trend weakened as the time of catch-up growth extended.There were fewer glucagon positive cells in CUGFR group than in NC group at the end of food restriction. Although catch-up growth moderated this trend partly, the number of glucagon positive cells in CUGFR group still had not caught up with the corresponding NC group after 4-week catch-up.Conclusion:CUGFR decreases incretin effect and leads to disturbance in the entero-insular axis partly due to the decrease in GLP-1 concentration, potentially providing a mechanism for the increased risk of metabolic disorder in those with CUGFR. Objective:To explore general characters of the aninal model which undergone catch-up growth after food restriction.Methods:The study was conducted in rats. Compared against the control group, which consisted of age-matched rats, some rats were food-restricted for 4 weeks, and then refed for 0,2,4 weeks respectively. In all rats, general physiological parameters, including food intake, body weight, body length, body fat content, plasma triglyceride (TG), plasma free fatty acid (FFA), plasma high density lipoprotein cholesterol (HDL-C) and plasma low density lipoprotein cholesterol (LDL-C) would be measured.Results:Rats which were food-restricted at 60% of their spontaneous standard chow intake had lighter body weight, shorter body length, smaller body fat content, lower serum triglyceride and free fatty acid than NC group. However, catch-up growth rats whose food intake was suddenly increased possesed faster increase in body weight, body length and body fat content after refeeding, and accordingly their plasma lipids increased except HDL-C. However, although the body fat content and plasma lipids increased except HDL-C had exceeded those in NC group, the body weight, body length of these rats was consistently lower than that of the control group, even after refeeding for four weeks.Conclusion:The animal model of catch-up growth setted by refeeding after food restriction bears the character of stunted-obese and dyslipidemia. Objective:To investigate the gastrointestinal morphology and functional change in the rat model of catch-up growth after food restriction.Methods:Animal model was established as chapterⅠ. All rats were received an OGTT test before decapitation and then plasma GLP-1 level during OGTT were measured. The general morphology of gastrointestinal tract, gastric emptying rate of barium swallow, intestinal mucosa morphology, L cell number were also analyzed.Results:1. The weight of remaining food in stomchThere was more remaining food in the stomch of CUGFR rats during 4-week food restriction. Following refeeding, the remaining food in stomch decreased, especially when catch up for 2 weeks. There was less remaining food in the stomch of CUGFR rats when this study finished.2. The wet weight of intestinThere was lighter weight of intestin in CUGFR rats during 4-week food restriction. There was little increase of intestinal wet weight during the whole process of catch-up growth.3. The total length of intestinFood-restriction resulted in a significant increase in the total length of intestine. However, it remained almost unchanged after refeeding. Due to constantly increase of the total length of intestine in NC group, there was smaller length of intestine in CUGFR group than in NC group when this study finished.4. The weight of mesenteric fatThere was less mesenteric fat in CUGFR rats during 4-week food restriction. After refeeding, it increased rapidly so as to exceed that of the control group when catch up for 4 wekks.5. Intestinal mucosa morphologyVillus height and villus height-to-crypt depth ratio decreased during food restriction period. However, catch-up growth increased villus height and decreased the crypt depth, accordingly leading to a higher villus height to crypt depth ratio as compared to NC group. Nevertheless, this trend weakened as the time of catch-up growth extended.6. Glucagon-positive cells number in lleumThere were fewer glucagon positive cells in CUGFR group than in NC group at the end of food restriction. Although catch-up growth moderated this trend partly, the number of glucagon positive cells in CUGFR group still had not caught up with the corresponding NC group after 4-week catch-up.7. Gastric emptying rate of barium swallowThere was a significant decrease in gastric emptying rate of barium swallow in CUGFR rats during 4-week food restriction. However, more rapid gastric emptying rate can be detected in CUGFR group, especially when catch up for 2 weeks.8. Plasma GLP-1 level during OGTTFood-restriction resulted in a significant decrease in plasma GLP-1 level. Following refeeding, GLP-1 increased but not to the level of that in NC group, even after 4-week catch-up.Conclusion:The gastrointestinal morphology and functional change in the rat model of catch-up growth after food restriction, potentially providing a mechanism for the disturbance in entero-insular axis. Objective:To investigate the incretin effect and pancreatic islet function in rat model of catch-up growth after food restriction.Methods:Animal model was established as chapterⅠ. All rats were received an OGTT test before decapitation and an IVGTT test which plasma glucose profile was varied to match the glucose concentrations during the OGTT then plasma glucose and insulin level during OGTT and IVGTT were measured, and the incretin effect was calculated. The quantification of pancreticα-andβ-cell relative area and mass, pancreatic insulin content, islet function were also analyzed.Results:1. Incretin effect The incretin effect was decreased significantly by food restriction compared with NC group. After refeeding, the incretin effect remained consistently lower in the refed group until the end of the study.2. Quantification of pancreticα-andβ-cell relative area and mass Compared with NC group, food-restriction in rats was characterized by remarkably decrease in the relative area and mass ofβ-cell, accordingly by increase in the relativeα-cell area excepting the a-cell mass. After refeeding, morphometric analysis revealed that there was gradually increase in the relative area and mass ofβ-cell with the extension of time to catch up. Although the experimental data over the course of the catch-up growth revealed that there was remarkably increase in the relative a-cell area in comparison with NC group, there was no significent difference between both groups in the a-cell mass.3. Pancreatic insulin content Food-restriction made pancreatic insulin content decreased remarkablly in CUGFR group and refeeding had improved this. However, pancreatic insulin content in CUGFR group didn't return to normal levels untill catch-up growth for 4 weeks.4. Beta cell functionPlasma glucose and insulin levels at the end of food-restriction were all significantly lower than or similar to NC group when fasting,15,30 and 60 min after glucose gavage. At 2 weeks'catch up, plasma glucose remained lower in the refed group than in the NC group whereas plasma insulin was higher than control at 15 min post-gavage. After 4 weeks'catch up, plasma glucose was still lower in the CUGFR group than in NC group. However, plasma insulin levels were higher than control at all time points of the OGTT, especially at 30 min post-gavage.The insulin/glucose incremental area ratio (ΔAUCI/ΔAUCG) expresses the overall ability of the beta cell to increase its release rate in response to the total glycaemic stimulus presented. It was significantly reduced in the CUGFR group when food restriction for 4 weeks. But refeeding for two weeks made this index rebounced to normal level even higher than NC group. At the end of the 4-week period of refeeding, the insulin/glucose incremental area ratio was not significantly different between both groups.Insulinogenic index at 15 min (I15min/G15min) expresses the early insulin secretion closely related to dietary changes. It was higher in the CUGFR group when food restriction for 4 weeks, and then it decreased with the extention of catch up growth. At the end of the 4-week period of refeeding, the insulinogenic index was lower in CUGFR group than that in NC group.Conclusion:CUGFR decreases incretin effect and leads to disturbance in the entero-insular axis, potentially providing a mechanism for the increased risk of metabolic disorder in those with CUGFR.