| Gonadotropin-releasing hormone (GnRH) is a deca-peptide synthesized by hypothalamus and released in a pulsatile manner into the hypophysial-portal circulation, stimulating gonadotropin target cells in anterior pituitary. GnRH promotes the release of luteinizing hormone (LH) and follicle stimulating hormone (FSH) and plays a central role in the control of production of gamete and development of gonads. More and more studies showed that GnRH and its receptor not only play a role in hypothalamus-pituitary-gonads axis, but also have functions in other human tissues (such as pancreas, ovary and placenta) .carcinomas (liver cancer, pancreas cancer, ovary tumor ) and immune system (T and B lymphocytes). It regulates the growth of normal tissues and involves the tumor formations. A series of researches published by our university showed that GnRH immunoreactive cells and its receptor mRNA were distributed in rat gastrointestinal tract. In rat stomach, GnRH had animportant role in the modulation of gastric acid production in autocrine or paracrine way. GnRH analogue can greatly promote the secretion of never growth factor (NGF) in submaxillary gland.On the other hand, glucagon is initially from proglucagon, and the molecular sequence of 33-61 amino acid of proglucagon is glucagon. The hormone that is similar to glucagon and secreted by gastrointestinal epithelia (EG cells or L cells) is called enteroglucagon. So the common immunoassay method can bind three forms of immunoreactive substances, which are glucagon^ proglucagon> enteroglucagon. Glucagon is a hormone which is secreted by pancreatic A cells into blood to stimulate catabolism. It has potent effect on promoting glycogenolysis and gluconeogenesis to increase blood glucose. Insulin secreted from pancreatic B cells has an effect against glucagon. Glucagon is modulated by glucose and lots of other factors. Previous experiment had disclosed that GnRH immunoreactive cells were found in the exocrine pancreas, while GnRH receptor immunoreactive cells were located in endocrine pancreas. The number and distribution of the latter coincide with that of glucagon immunoreactive cells. Glucagon cells in islets of pancreas may be the target cells of GnRH which was synthesized in the exocrine. From this point, we hypothesize that there is a relationship between GnRH and enteroglucagon, which may have a role in the regulation of blood glucose.To understand the relationship between GnRH and enteroglucagon, we studied the distribution of L cells inrat gastrointestinal tract and coexistence of glucagon immunoreactive substance and GnRH receptor (GnRHR) in rat ileum by immunohistochemistry method. Also radioimmunoassay was used to evaluate the influence of GnRH analogue (Alarelin) in different concentration on glucagon immunoreactive substance secreted from rat ileum in vitro and the influence of Alarelin at 1.0X10~4mol/L on glucagon immunoreactive substance secretion in vivo. The results are as follows:(1)Glucagon immunoreactive cells showed with immunohistochemistry of ABC method were distributed in rat ileum and colon (EG cells or L cells). Double labeling immunohisto-chemical method showed that glucagon immunoreactive cells in rat ileum also had GnRHR immunoreactivity. It suggests that EG cells only distributed in rat ileum and colon, and GnRHR was expressed in these cells. It indicates GnRH may regulate glucagon immunoreactive substance which secreted from EG cells in autocrine or paracrine mechanism.(2)When GnRH analogue Alarelin(from 1. 0X10-8mol/L to 1. 0X 10-6mol/L) was added to the culture medium of ileum tissue, the level of glucagon immunoreactive substance in the medium was increased with the increment of GnRH analogue concentration. After it reached the peak, the level of glucagon immunoreactive substance in medium was decreased with the increment of GnRH analogue. It suggests that in rat ileum within the certain extent of GnRH, the secretion of glucagon immunoreactive subtance may be regulated by GnRH in two-way.(3)When GnRH analogue Alarelin (1.0 X 10-4mol...
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