Expressions Of GnRH MRNA In Pancreas And Its Relationship With Glucose Metabolism In Different Age Rats

In recent years, the prevalence of diabetes among old-aged groupscontinues to increase which is positively related with age. According to statistics,the incidence of diabetes between 60 and 70-year-old age group may be as highas 20%, showing an upward trend with age. So, it is worth to study theproceeding of the occuring of abnormal glucose metabolism with age. Clinicaldata showed that application of GnRH analogue treatment for reproductivesystem diseases can increase the risk of metabolic diseases, such as osteoporosis,type 2 diabetes (T2DM), insulin resistance (IR), cardiovascular disease. Thissuggests that there is some relationship between GnRH and abnormal glucosemetabolism. Meanwhile, it is reported that the expression of GnRH gene of therat becomes lower in the hypothalamus-pituitary-gonadal axis with age, theelectrophysiological activity and the function of synthesis and transport proteinsof GnRH neurons significantly decreased. Our previous work proved that thereare GnRH and its receptor in the pancreatic system, but their expression changeswith age in the pancreas have not been reported. Whether there is the samechange and whether this change is related to the age-related abnormality of the glucose metabolism, which is the focus of this experiment.Objective:To observe the change of the expression of GnRH mRNA in pancreas of ratsin different age, and to analyze the relationship between the change and thechanges of glucose metabolism.Methods:24 rats were divided into young group(1m, n=8), middle-aged group (7m,n=8), old group (14-16m, n=8) respectively. Oral glucose tolerance test (OGTT)and Intravenous glucose tolerance test (IVGTT) were carried out, and theexpressions of GnRH mRNA in rats was detected with Real-time quantitativePCR (SYBR Green) .Results:1．OGTT:In aged rats, the levels of the blood glucose and insulin (60min,120min) of this group are higher than that in other two groups (P <0.01); therelated indexs HOMA-IR,△I30/△G30,△I120/△G120, AUCI/AUCG arehigher in aged group (P <0.01).2. IVGTT: In aged rats, the level of the blood glucose(5, 30, 60, 120min) arehigher than that of the other two groups(P <0.01); the levels of the insulin(5, 10,15min) are lower than that of the other two groups(P <0.01), Ins(120min) ishigher than the other two groups(P <0.05); the index of the first-phase secretion△I5/△G5, AUCI(0-10min), AUCI(0-30min), AUCI(0-120min), AIR are lowerthan the other two groups (P <0.01); AUCG(0- 30min), AUCG(0- 120min) arehigher in aged group (P <0.05); the level of glucose(5min) and insulin(5min) arenegative related (r = -0.751). This showed that the first-phase secretion of insulinof the old rats is insufficient, and the peak of insulin is delayed. 3. Immunohistochemistry: The distributiones of GnRH, GnRH-R-positive cells ofthree groups of rats are similar, but GnRH, GnRH-R-positive cells of old ratdecreased (Fig. 5-6), while its islets are smaller.4. RT-PCR:The aged group had the lowest level of the expressions of GnRHmRNA compared with the other two groups (P <0.01).5. The analyze of correlation.5.1 The expression level of GnRH mRNA and the index of OGTT. There isnegative correlation between the level of the blood glucose and insulin(0min)andthe expression level of GnRH mRNA(r =-0.628 and r =-0.636,P<0.05). There isalso negative correlation between the level of the blood glucose andinsulin(120min)and the expression level of GnRH mRNA(r = -0.889 and r = -0.874,P <0.05).△I30/△G30 and GnRH mRNA (r = -0.573, P<0.05),△I120/△G120( r = -0.67, P<0.05), HOMA-IR(r =-0.718,P <0.05), n=21.5.2 The expression level of GnRH mRNA and the index of IVGTT: theexpression level of GnRH mRNA and the level of glucose(5min) are negativerelated (r =-0.782, P<0.05); Positive related are the level of insulin(5min) (r=0.869, P<0.05) and△I5/△G5(r = 0.863, P<0.05).Conclusion:In aged rat group, the average level of the blood glucose are higher, and thefirst-phase secretion of insulin is insufficient, the peak of insulin is delayed;Meanwhile, the expression of GnRH mRNA in pancreas is lower, there aresignificantly negtive correlations with the level of glucose(0min,120min) andinsulin(0min,120min), positive related is the level of the first-phase secretion ofinsulin. So we can conclude that the expression change of GnRH mRNA inpancreas in old rats may be related to the age-relataed abnormality of the glucosemetabolism. The mechanisms need futher researches.