Studies On The Expression Of GnRH And GnRH-R In Jejunum And Pancreas Of Rats After Ingestion Or Castration

Some studies showed that GnRH analogues could lead to disorders of glucoregulation. GnRH and GnRH receptor widely distribute in digestive system and pancreas, which is highly related to glucoregulation .Whether GnRH secreted by intestine and pancreas is related to glucoregulation, Whether they could have a role on glucoregulation by acting on GnRH recteptor in intestine and pancreas to influence intestinal absorption and motor function, or to regulate other gastrointestinal hormones secretion such as glucagon, glucagon-like peptid-1, these issues are needed to be investigated.PART ONE: Distributions of GnRH and its receptor in jejunum and pancreas of rats after gonadectomy or GnRH analogue administration.OBJECTIVE:To observe if there is distribution change in rat jejunum and pancreas at the 12th week after gonadectomy or GnRH analogue administration, and to lay foundation for further studies on the mechanism of glucoregulation disorders caused by GnRH analogues.METHOD:Distributions of GnRH, GnRH receptor were observed immunohistochemically in jejunum and pancreas in rats at the 12th week after gonadectomy or GnRH analogue administration (Leuprorelin, 100ug/Kg).RESULTS:1. Immunohistochemical staining showed GnRH and GnRH receptor expression in rats after gonadectomy or GnRH analogue administration has the same distribution characteristics as in contol rats.CONCLUSION:The distribution of GnRH and its receptor in rats jejunum and pancreas may not be influenced by gonadectomy or GnRH administration.PART TWO:The effect of intragastrical administration of glucose on the expression of GnRH and GnRH receptor mRNA in rat jejunum and pancreasOBJECTIVE:To observe the effect of intragastrical administration of glucose on the expression of GnRH and its receptor mRNA in jejunum and pancreas of rats and to lay foundation for further studies on the relationship between glucoregulation and GnRH and its receptor in jejunum and pancreas.METHOD:Real-time quantitative PCR was used to detect the changes of the mRNA expression of GnRH, GnRH receptor mRNA at the time of 0 min, 15min, 30min after intragastrical administration of glucose(2 g/Kg). RESULTS:1. The relative mRNA levels of GnRH in jejunum were lower at the time of 15min, 30min after intragastrical administration of glucose than that in fasting group(P<0.05). There were no statistical differences of the relative expression level of GnRH receptor mRNA in jejunum among different groups.2. The relative mRNA levels of GnRH in pancreas were decreased at the time of 15min after intragastrical administration of glucose compared with fasting group(P<0.05). There were no statistical differences of the relative level of GnRH receptor mRNA in pancreas among different groups.CONCLUSION:Here we first report the change of relative mRNA level of GnRH and its receptor in jejunum and pancreas after intragastrical glucose administration at different time-points. The data showed that the relative mRNA levels of GnRH in jejunum and pancreas were decreased in the early stage of intragastrical administration of glucose, it suggestes that GnRH secreted by jejunum and pancreas may be related to glucoregulation, but its mechanism should be explored further.PART THREE: The effect of gonadectomy on the expression of GnRH and GnRH receptor mRNA in rat jejunum and pancreasOBJECTIVE:To observe the effect of gonadectomy on the expression of GnRH and its receptor mRNA in jejunum and pancreas of male rats and to lay foundation for further study of the mechanism of glucoregulation disorders caused by GnRH analogues in clinical practice. METHOD:Real-time quantitative PCR was used to observe the effect of gonadectomy on the change of the mRNA expression of GnRH and its receptor mRNA at the time of 3h after intragastrical administration of glucose (2 g/Kg).RESULTS:There were no statistical differences of the relative level of GnRH and its receptor mRNA in jejunum and pancreas between gonadectomy group and control.CONCLUSION:The expression of GnRH and its receptor mRNA in jejunum and pancreas of rats may not be influenced by gonadectomy greatly.PART FOUR: The effect of subcutaneous injection of GnRH analogue on the expression of GnRH and its receptor mRNA in rat jejunum and pancreasOBJECTIVE:To study the effect of subcutaneous injection of GnRH analogue on the change of the expression of GnRH, GnRH receptor, proglucagon and GLP-1 receptor in jejunum and pancreas of male rats and to understand the role of GnRH analogues in glucoregulation disorders.METHOD:Real-time quantitative PCR was used and male rats (n=5) were subcutaneously injected GnRH analogue (Leuprorelin, 100ug/Kg) for 12 weeks, the expression of GnRH, GnRH receptor, proglucagon and GLP-1 receptor in jejunum and pancreas of rats were observed at the time of 3h after intragastrical administration of glucose (2 g/Kg).RESULTS:1. The fasting serum glucose were higher in rats injected subcutaneously GnRH analogue than those in control rats (P<0.05), the serum insulin concentrations at the time of 0 h and 0.5h during OGTT were higher in rats injected subcutaneously GnRH analogue than those in control rats. There were no statistical differences of serum glucose and insulin concentration at the rest time points during OGTT between subcutaneous injection group and control group.2. There were no statistical differences of the relative mRNA level of GnRH, GnRH receptor, proglucagon and GLP-1 receptor in jejunum and pancreas between subcutaneous injection group and control group.3. A significant positive correlation between the expression of GnRH mRNA and proglucagaon mRNA was observed in jejunum of rats inclulding subcutaneous injection group and control group (r=0.959, P<0.01).CONCLUSION:After GnRH analogue was subcutaneously injected for 12 weeks, the fasting serum glucose and insulin concentration was increased, and the early stage of postprandial insulin secretion was augmented. The result also showed that the expression of GnRH mRNA and proglucagaon mRNA was positively correlated. These data suggested that GnRH secreted by jejunum and pancreas may be related to the mechanism of glucoregulation disorders caused by GnRH analogues in clinical practice, further research should be done to explore its mechanism.SUMMARY:Our studies showed that the relative mRNA levels of GnRH in jejunum and pancreas were decreased in the early stage of intragastrical administration of glucose; after GnRH analogue was injected subcutaneously for 12 weeks, the fasting serum glucose and fasting insulin concentration was increased and the early stage of postprandial insulin secretion was augmented, but in gonadectomized rats, there was no change in serum glucose and serum insulin concentration. With that a significant positive correlation between the expression of GnRH mRNA and proglucagaon mRNA was observed in rat jejunum inclulding subcutaneous injection group and control group, our data showed that GnRH in intestine and pancreas may be related to glucoregulation, and maybe contributes to the mechanism of glucoregulation disorders caused by GnRH analogue. There are more mechanisms should be explored further.