The Role Of Ghrelin In Diabetic Gastroparesis

BACKGROUND AND AIMSDiabetes mellitus (DM) is caused by many reasons, and is a kind of metabolism disorder which takes chronic hyperglycemia as characteristic. The gastrointestinal tract is one of main systems that diabetes are easy to implicate. Diabetes gastroparesis ( DGP ) refers to the diabetic patients concurrent stomach creeping motion slow-down or lacks and gastric emptying delay, such as nausea, vomitting, fullness, abdominal distention, abdominal pain, anepithymia and so on. According to the reports, the incidence rate of Diabetes Gastroparesis reache as 30～50%, and the majority diabetic has the gastric emptying delay. Its mechanism mainly is that the hyperglycemia and the autonomic nerve affection, the parasecretion of gastrointestinal hormone, denaturation of gastric and intestinal smooth muscle, the capillaries affection and metabolism disorder. Among these factors, hyperglycemia is fundentmental cause of the disease. The acute hyperglycemia may suppress the interdigestive phase's migrating moter complex(MMC), and step down gastric emptying of solid and liquid through inhibit vago-vagal reflex, simultaneously causes the change of gastrointestinal tract's dynamics through the parasecretion of gastrointestinal hormone, such as motilin, somatostatin, vasoactive intestinal peptide. Ghrelin is a 28-amino acid brain-gut peptideand mainly be secreted into the blood by stomach X/A cell. Human amino acid sequence of ghrelin and human motilin is similar, and human ghrelin receptor shows a remarkable 50% overall identity with human motilin receptor, so named it as motilin-related peptide. Ghrelin have many effects on increasing circulating plasma growth hormone, food intaking and controlling energy balance, gastric acid secretion and motility, increasing gastric emptying rate, through binding with GHS-R in central and peripheral of the nervous system. So, we have done this experiment to explore the role of ghrelin in DGP as follows.1. To investigate the relation between ghrelin expression in gastric mucosa, the blood glucose level and the gastric emptying variation in diabetic Gastroparesis patients.2. To investigate the effect of blood glucose variation on gastric emptying and ghrelin expression in diabetic rats, then explore the relation between the delayed gastric emptying and ghrelin expression in different diabetic stage.3. To investigate the effect of tegaserod maleate on gastric emptying and the expression of Ghrelin and Substance P in diabetic rats, then explore the therapeutical effect of tegaserod maleate on diabetic gastroparesis and its possible mechanism.METHODS1. Thirty diabetic gastroparesis patients were collected and divided into two groups: DGP-A and DGP-B by the blood glucose level of last week ( < 9mmol/L and≥9mmol/L) . Twenty functional dyspepsia (FD) patients were collected to be control group according to RomeⅢcriteria. The liquid gastric emptying and ghrelin expression in gastric mucosa were detected by nuclide method and immunohistochemistry separately.2. Sixty Wistar rats were randomly divided into three groups : normal control group(NC group), diabetes mellitus group(DM group) and insulin- treated group (INS group). Diabetes was induced by intraperitoneal injection of streptozotocin (STZ). One week and four weeks after the STZ injection, gastric emptying was measured by intragastric administration of phenol red and the expression of gastric ghrelin and its mRNA were detected by immunohistochemistry and semi-quantitative RT-PCR separately.3. Fifty Wistar rats were randomly divided into five groups : normal control group(NC group), diabetes mellitus group(DM group), low dose tegaserod maleate-treated group(TEG-L group), moderate dose tegaserod maleate-treated group(TEG-M group) and high dose tegaserod maleate-treated group(TEG-H group). Diabetes was induced by intraperitoneal injection of streptozotocin (STZ). After 8 weeks, tegaserod maleate was administrated by intraperitoneal injection at a dose of 0.1mg/kg,0.5mg/kg,1mg/kg in TEG-L,M,H group respectively for 3 days. Gastric emptying was measured by intragastric administration of phenol red .The expression of Ghrelin in gastric mucosa and SP in gastric antrum were detected by immunohistochemistry.RESULTS1. T_1/2 of gastric emptying in DGP-A group was 24. 57min, which was shorter than that of FD group obviously(q=6.32, P<0.01). T_1/2 of gastric emptying in DGP-B group was 41.92min, which was longer than that of FD and DGP-A groups obviously(q=14.58, P<0.01; q=9.22, P<0.01).The ghrelin-immunoreactive staining of gastric mucosa glands in DGP-A,B group was less than that of FD group obviously. A part of glands were empty and its integral optical density decreased significantly compared with FD group(q=8.80, P<0.01; 9=10.25, P<0.01).The most part of gastric mucosa glands in DGP-B group were empty and the ghrelin content decreased significantly compared with DGP-A group.Its integral optical density also decreased compared with DGP-A group, but the difference was not statistically significant(q=2.03 , P>0.05).There was a inverse correlation between the average blood glucose level and ghrelin integral optical density in DGP-A,B group(r=-0.378, P<0.01; r=-0.155, P<0.05).2. One week after the STZ injection , gastric emptying rates, ghrelin integral optical density and ghrelin mRNA expression levels in the stomach of the DM group decreased significantly compared with the NC group and INS group; four weeks after the STZ injection, the body weight ,gastric emptying rates and ghrelin integral optical density in the stomach of the DM group and INS group decreased significantly compared with the NC group, but ghrelin mRNA expression levels increased significantly. The difference between the DM group and INS group was not statistically significant.3. The integral optical density of Ghrelin and SP in TEG groups all decreased compared with the NC group and increased compared with the DM group. The difference was statistically significant. But the difference of Ghrelin integral optical density among TEG groups was not statistically significant. The integral optical density of SP in TEG-L and TEG-M group increased compared with the TEG-H group.CONCLUSIONS1. Most DM has different degree of gastric emptying dysfunctions; Dyspeptic symptoms in DM is related to gastric emptying dysfunctions; The expression and releasing of ghrelin of gastric mucosa in patients of DGP is related to course of diabetes and blood glucose level; The expression and releasing of ghrelin of gastric mucosa in patients of DGP do not have association with dysfunction of gastric emptying; Dysfunction of gastric emptying in DGP is comprehensive etiological result.2. One week after the STZ injection, the delayed gastric emptying recovered while blood glucose decreased after insulin therapy. However, four weeks after the STZ injection, reducing blood glucose could not recover the delayed of gastric emptying; Short-term hyperglycemia may inhibit the production and release of ghrelin to be involved in the delayed gastric emptying in diabetic rats; Long-term hyperglycemia may stimulate body to syntheses and secrete ghrelin and increase ingestion to maintain energy balance.3. 5-HT4 acceptor partial agonist (Tegaserod maleate) improves the function of gastric emptying and can be used for the treatment of diabetic gastroparesis; Tegaserod maleate accelerates delayed gastric emptying of diabetic rats through promoting expression and relasing of ghrelin and SP in stomach tissue; The promoting effect of tegaserod maleate on gastric emptying differ with different dosage. Sutable dosage of tegaserod maleate is obvious for the treatment of diabetic gastroparesis. 5-HT4 acceptor partial agonist provides a new hope for the treatment of DGP.