The Characteristic And Mechanism Of Glucose-related Insulin-secretion Impairment In Natural Aging Rats

Backgroud and Objective To evaluate the age-related changes of metabolic profile, the morphology and secretary function ofβ-cell.Materials and methods Natural aging SD rats with different age (6, 12, 20-24mon) was used in this. experiment. After the BW were measured, rats were anesthetizd with sodium pentobarbital (30mg/kg BW, ip), blood were drawn for detecting fasting blood glucose, lipid profile and FFA as basal metabolic parameters. Pancreases were isolated quickly, fixated and embed. Then islet population, size and the insulin secretary granule withinβ-cell from different age groups were assessed by using immunohistochemistry and electron microscope (EM), respectively. Moreover, isolated rats islets from different age were purified and cultured with two culture medium containing 5.6mmol/l and 16.7mmol/l glucose over 24 hours, respectively. The static secretion of insulin levels at 2, 4, 6, 12, 24hours was measured by RIA.Findings 1) The significantly higher concentration of FFA was found in 12, 20-24 months groups (386.02±88.08; 349.43±93.47 vs. 263.93±68.77 mmol/l, respectively, p＜0.05), with no difference in WT, FBG, lipid profile among three groups; 2) Glucose stimulated insulin secretion in old rats showed lower peak value than in their younger counterparts (6.4±2.7 vs. 13.97±1.23 (6 mon.) & 12.08±0.76(12mon.) mU/l/30islets). 3) Theβ-cell mass to islet ratio were sligtly larger in old rats than in younger rats (72.99± 29.65% vs. 67.76±23.48% (12mon.) & 61.69±30.12% (6mon.), p＞0.05); The express of insulin measured by insulin immunohistochemistry in old rat islet was found dramatically decreased compared with 6, 12months rats (242.71±95.37(24mon.), 309±83.99 (12mon.) vs. 558±69.94 (6mon.), P＜0.05).Conclusion and interpretation Older rats showed higher FFA and age-related impairment of insulin secretion with or without the glucose stimulation. These findings suggest that insulin therapy should be taken into account for elder earlier once type 2 diabetes was diagnosed. Backgroud and Objective Autophagy is a non-apoptotic programmed cell death. It has been implicated in a variety of physiological and pathological conditions. whether autophagy and apoptosis occure inβ-cell in ageing rats are not yet known. Thus, the present study was to observe the phenomena of autophagy, apoptosis and age-related ultrastructural changes inβ-cell of different age rats.Materials and methods Isolated pancreas from age of 6, 12, 20-24month SD rats were paraffin embedding, fixation and then went to these two next steps: 1) Autophagolysosme and apoptotic bodies were observed by EM, for EM has been the only reliable method for monitoring autophagy; 2) Apoptosis rate was also tested by the method of Tunel immunohistochemical staining.Findings Autophagic vacuoles (AV) was charectaristic by the autophagsome which is a double membrane structure containling undigested cytolpasmic material including organelles, or the cytolysosome which is a singal memberance structure containing cytoplasmic components at various stages of degradation. Various of AV were found inβ-cells of 20-24mon. age rats; as well as initial autophagic vacuoles in theβ-cell of 12mon. age rats; whereas no any similar change in 6mon. rats. Meanwhile there was no any evidence of apoptosis by both ways of EM and Tunel immunohistochemical staining inβ-cell. Furthermore, swelling and vacuolar degeneration were found in both mitochondrion and endoplasmic reticulum inβ-cell of the oldest rats.Conclusion and interpretation These findings indicated that under physical conditions, it was autophagy not apoptosis that was activated inβ-cell of old rat. And the age-related change inβ-cell was obviously different from high carloric diet-induced diabetic rats we studied before, which involved two ways of programed cell death - autophagy and apoptosis. Activated autophagy inβ-cell of aged rat might be a possible explanation for insulin secretion impairment in rodents. Further study should be considered to make sure the relationship between atuopahgy and insulin secretion impairment inβ-cell of old rats. Objective Aging is associated with glucose tolerance impairment, but the mechanisms underline it is not yet well known. Insulin receptor substrate-1 (IRS-1) proved to play an important role as an early intermediary between the insulin and IGF receptors, which might relevent to both aging and insulin resistance. The expression of IRS-1 and its downstream signal p-Akt were investgated in this study to figuer out changes that occur with aging.Materials and methods Three groups (6, 12, 20-24months) SD rats were used in the experiments. Food was withdrawn 12-14 h before the experiments. Histological section of livers, muscle, and pancreas were made by the method described before. Immunohistochemical staining was used to test the expression of IRS-1 and p-Akt according to corresponding method.Findings 1) IRS-1 was expressed in three tissue of all age groups. The value of MOD showed slightly decreased not only in islet (240.70±77.14 vs. 266.92±54.92(12mon.) & 360.73±23.89(6mon.))but also in liver (3905.09±579.04 vs. 4045.60±974.79(12mon.) & 5004.71±552.70(6mon.)) and muscle (1571.07±748.50 vs. 1605.80±829.60 (12mon.) & 2356.80±875.85 (6mon.)). 2) A significantly decreased of p-Akt expression in liver was found in old rat than their younger counterparts (2911.06±268.13 vs. 4683.72±582.29 (12mon.) & 4903.06±688.44 (6mon.), P＜0.05), while no difference was found in muscule among three age groups. Conclusion and interpretation Glucose intolerance with aging might be attributed at least in part to the defects of Akt phosphorylation in liver, which was one of the major insulin-responsive impairment tissues. Furthermore, research might be done to detect the expression of p-Akt inβ-cell.