The role of apelin in the modulation of gastric and pancreatic enzymes activity in adult rats.

Apelin is considered as important gut regulatory peptide ligand of APJ receptor with a potential physiological role in gastrointestinal cytoprotection, regulation of food intake and drinking behavior. Circulating apelin inhibits secretion of pancreatic juice through vagal- cholecystokinin-dependent mechanism and reduces local blood flow. Our study was aimed to determine the effect of fundectomy and intraperitoneal or intragastric administration of apelin-13 on pancreatic and gastric enzymes activities in adult rats. Fundectomy is a surgical removal of stomach fundus - maine site apelin synthesis. Three independent experiments were carried out on Wistar rats. In the first and second experiment apelin-13 was given by intragastric or intraperitoneal way twice a day for 10 days (100 nmol/kg b.w.). Control groups received the physiological saline respectively. In the third experiment the group of rats after fundectomy were used. Fundectomized rats did not receive apelin and the rats from control group were 'sham operated'. At the end of experiment rats were sacrificed and blood from rats was withdrawn for apelin and CCK (cholecystokinin) radioimmunoassay analysis and pancreas and stomach tissues were collected for enzyme activity analyses. Intragastric and intraperitoneal administrations of apelin-13 increased basal plasma CCK level and stimulated gastric and pancreatic enzymes activity in rats. In animals after fundectomy decreased activity of studied enzymes was observed, as well as basal plasma apelin and CCK levels. In conclusion, apelin can effects on CCK release and stimulates some gastric and pancreatic enzymes activity in adult rats while fudectomy suppresses those processes. Changes in the level of pancreatic lipase activity point out that apelin may occurs as a regulator of lipase secretion.

Early-effect of bariatric surgery (Scopinaro method) on intestinal hormones and adipokines in insulin resistant Wistar rat.

Bariatric surgery consists in duodenal exclusion from the food passage in obese patients with coexistent type 2 diabetes. Nowadays bariatric surgery is considered the most effective method of glycemic index normalization and insulin resistance reduction. Recent results on obese and non-obese rats showed remission of type 2 diabetes symptoms within few days after the surgery. The aim of the present work was to analyze the mechanisms of neuro-hormonal regulation responsible for early normalization of metabolic syndrome after bariatric surgery. In present study the concentration of selected intestinal hormones and adipokines in blood plasma and gastrointestinal tissues were analyzed. Study was conducted on Wistar rats. Animals were divided into three groups (each n=6): control (SH) shame-operated rats; animals in which visceral fat tissue was extracted (LP); and rats in which Scopinaro bariatric surgery was performed (BPD). Immunochemistry analysis of blood plasma showed decrease of insulin concentration in BPD and LP and increase of polypeptide YY (PYY) in BPD group as compared to the control. In duodenal mucosa homogenates the tendency to reduce insulin in LP and BPD group, and increase PYY and visfatin in BPD group was observed. Histometry analysis showed reduction of mucosa thickness in excluded segments of gastrointestinal tract in BPD group as compared to the SH and LP. Concluding, model studies on rats allowed better understanding of mechanisms important for early normalization of glycemic index and insulin resistance reduction in rats.

Influence of fundectomy and intraperitoneal or intragastric administration of apelin on apoptosis, mitosis, and DNA repair enzyme OGG1,2 expression in adult rats gastrointestinal tract and pancreas.

Apelin, endogenous ligand of G protein-coupled apelin receptor (APJ), is released into the gastrointestinal lumen, however, local effect of luminal apelin on gut epithelium has not been elucidated so far. The present study aimed to determine the effects of fundectomy, and intraperitoneal or intragastric administration of apelin on pancreatic, gastric and intestinal epithelium apoptosis, mitosis and DNA repair enzyme OGG1,2 expression in adult Wistar rats. Apelin-13 was given by intraperitoneal or gastric gavage twice a day for 10 days (100 nmol/kg b. wt./day). Fundectomized rats did not receive apelin. Control groups received saline as placebo. At the end of the experiment the rats were sacrificed and the pancreas, gastric fundus, duodenum, middle jejunum and colon tissue samples were harvested for immunofluorescence studies. Intraperitoneal and intragastric apelin-13 reduced apoptosis, mitosis and number of DNA damages in rats gastrointestinal tract (p≤0.001) as compared to control. In fundectomized rats, the apoptotic index in the pancreas and colon was decreased (p<0.001), and in the stomach and jejunum was increased (p<0.001). Mitotic index was decreased in all gastrointestinal tissues. Number of DNA damages (p≤0.001) in fundectomized rats was reduced except stomach where OGG1,2 expression was increased (p≤0.001) as compared to control. In conclusion, circulating and luminal exogenous apelin-13 caused similar effects on intestinal epithelium. Endogenous (gastric) apelin is important for renewal of intestinal epithelium in adult rats. Pharmacological doses of apelin-13 may reduce the cell turnover in the upper gastrointestinal tract epithelium and pancreas, and improve the overall gut health.

The effect of exogenous apelin on the secretion of pancreatic juice in anaesthetized rats.

Apelin is known to stimulate cholecystokinin (CCK) and inhibit insulin release, however the mechanisms on pancreatic secretion remain unclear. The present study aimed to determine the expression of apelin and apelin receptor in the pancreas by immunofluorescence studies and the effect of exogenous apelin on the secretion of pancreatic juice in anesthetized rats. Pancreatic-biliary juice (P-BJ) was collected from Wistar rats treated with apelin (10, 20 and 50 nmol/kg b.w., boluses given every 30 min intravenously or intraduodenaly). The same apelin doses were administered to rats subjected to intraduodenal tarazapide, capsaicin or vagotomy. Pancreatic blood flow was measured by a laser doppler flowmeter. Direct effects of apelin were tested on dispersed acinar cells. Apelin receptor was expressed on acinar cells, pancreatic duct and islets cells, whereas apelin in pancreatic acini, but not in the islets. Intravenous apelin decreased P-BJ volume, protein and trypsin outputs in a dose-dependent manner. In contrast, intraduodenal apelin stimulated P-BJ secretion. Pharmacological block of mucosal CCK(1) receptor by tarazepide, vagotomy and capsaicin pretreatment abolished the effects of intravenous and intraduodenal apelin on P-BJ volume, protein and tryspin outputs. Apelin decreased the pancreatic blood flow. Apelin at 10(-6) M increased the release of amylase from non-stimulated and CCK-8-stimulated acinar cells. In conclusion, apelin can affect the exocrine pancreas through a complex mechanism involving local blood flow regulation and is driven by vagal nerves.

Role of feed-regulating peptides on pancreatic exocrine secretion.

In recent two decades a group of feed intake-regulating peptides (i.e., leptin, apelin, ghrelin, obestatin and orexins) have been discovered. Besides the central nervous system these regulatory peptides are produced and released by the gastrointestinal (GI) endocrine cells and neurons, and functional receptors were found in the GI tract and the pancreas. High expression of feed intake-regulating peptides was found in the stomach; however, they may be expressed in other GI tissues too. The peptides control gastrointestinal functions, modulate orexigenic drive and energy metabolism via different mechanisms. Basal leptin, apelin, ghrelin and obestatin plasma concentrations correlated with BMI, and we observed significant reduction of ghrelin and leptin concentrations following fundectomy in rats. We have shown previously that exogenous leptin and ghrelin (a peptide derived from the same preprohormone as obestatin) inhibit the secretion of rat pancreatic juice through a neurohormonal mechanism. Intravenous obestatin was found to stimulate pancreatic protein output in anaesthetized rat via a CCK-vagal-dependent mechanism, whilst a direct action of obestatin on rat pancreatic acini in vitro resulted in opposite effect. Intravenous boluses of apelin reduced the juice volume, protein and trypsin outputs in a dose-dependent manner. However, apelin administered into the duodenal lumen significantly increased pancreatic protein and trypsin outputs through a vagal mechanism. Orexin A and B were found to stimulate insulin release, though on the rat exocrine pancreas orexin A had no effect, and the effect of orexin B was weak. Concluding, feed intake-regulating peptides participate in controlling the exocrine pancreas.

Plasma concentration of leptin and ghrelin in Standardbred foals as related to the age, sex, exercise and training.

The effect of acute exercise was studied in a group of 42 clinically healthy young Standardbred trotters. These trotters had been divided into four groups according to their age. Their ages were from 1.5 to 3 years. Three jugular venous blood samples were collected via venipuncture from each horse. These samples were collected while (1) at rest, (2) after the end of the exercise and (3) 30 min after the end of the exercise. Exercise showed a significant increase in plasma leptin concentration (3.8 ± 0.31 at rest v. 4.3 ± 0.37 just after exercise and 4.4 ± 0.47 ng/ml after a 30-min rest; ANOVA P < 0.05). The difference between values obtained 30 min after exercise and at rest was significantly greater in 1.5-year-old horses than in those aged 2.5 years (+1.3 ± 0.43 v. +0.1 ± 0.15 ng/ml; ANOVA P < 0.05). The mean plasma leptin concentration was higher in fillies than in colts (4.9 ± 0.47 v. 3.5 ± 0.36 ng/ml; ANOVA P < 0.05). A positive correlation between the plasma concentrations of leptin and triacylglycerides measured just after exercise was detected (r = 0.65). The acute exercise significantly increased the plasma concentration of ghrelin that was measured just after exercise (1255 ± 55.9 v. 1127 ± 54.2 pg/ml; ANOVA P < 0.05). The exercise-induced age-related changes in the plasma ghrelin concentration were significantly lower in 2.5-year-old trotters than in 1.5-year olds. To sum up, the changes in plasma leptin and ghrelin concentrations during bouts of exertion tend to decrease with age and/or training of Standardbred foals.

Obestatin stimulates the secretion of pancreatic juice enzymes through a vagal pathway in anaesthetized rats - preliminary results.

Obestatin is a 23 amino acid peptide derived from the preproghrelin precursor, and originally purified from the rat stomach mucosa. It was shown that obestatin may counteract the effects of its sister peptide, ghrelin, on food intake and gastrointestinal motility but the other roles in controlling the gastrointestinal function remain unknown. The aim of the present study was to determine the influence of exogenous obestatin on the secretion of pancreatic juice. In anesthetized male Wistar rats the external jugular vein was catheterized, and the common biliary-pancreatic duct was cannulated with polyethylene tubing for collection of pancreatic-biliary juice (P-BJ). Obestatin boluses (30, 100 and 300 nmol/kg b. wt.) were injected intravenously or intraduodenally every 30 min. Obestatin was also administered in vagotomized (subdiaphragmatic vagotomy) rats. In the examined rats, obestatin intravenous and intraduodenal boluses did not affect the P-BJ volume. On the other hand, obestatin boluses increased the protein output and trypsin activity. Vagotomy abolished the effects of exogenous obestatin administration. In conclusion, the present study demonstrates for the first time that exogenous obestatin may stimulate the secretion of pancreatic juice enzymes. The effect is dose-dependent and requires intact vagal supply.

The ghrelin pentapeptide inhibits the secretion of pancreatic juice in rats.

Ghrelin, a 28 amino acids polypeptide was recognized as an endogenous ligand for the growth hormone secretagogue receptor. It turned out that the entire sequence of ghrelin is not necessary for performing the above-mentioned functions. It was suggested that 5 residues (Gly-Ser-Ser(n-octanoyl)-Phe, pentaghrelin) constituted functionally active part of the full-length polypeptide. Ghrelin-28 was found to inhibit pancreatic enzyme output in rats, though the effect of pentaghrelin was not studied so far. The study aimed to determine the involvement of pentaghrelin in pancreatic juice secretion in anaesthetized rats. Male Wistar rats (220 +/- 20 g body weight, b. wt.) were anesthetized, the external jugular vein and common biliary-pancreatic duct were cannulated. Pentaghrelin boluses (i.v., 1.2, 12, and 50 nmol kg(-1) b. wt.) were injected every 30 min with or without CCK-8 infusion, duodenal mucosal CCK(1) receptor blockade with tarazepide, vagotomy and capsaicin pretreatment. Pentaghrelin boluses reduced the volume of pancreatic-biliary juice, protein and trypsin outputs both under basal and CCK-8-stimulated conditions in a dose-dependent manner. However, exogenous pentaghrelin failed to affect the pancreatic secretion in rats subjected to vagotomy, capsaicin deactivation of afferents or pretreatment with Tarazepide. In conclusion, pentaghrelin may control exocrine pancreas secretion by affecting duodenal neurohormonal mechanism(s) involving CCK and vagal nerves in rats.

The effect of fundectomy on pancreatic secretion in anaesthetized rats.

The aim of present study was to evaluate the influence of surgical fundectomy and exogenous leptin on the secretion of pancreatic juice in anesthetized rats. In male Wistar rats major part of the gastric fundus was surgically removed, and 60 days afterwards the external jugular vein and the pancreatic-biliary duct were catheterized under general anesthesia. The pancreatic-biliary juice (PBJ) was collected in 15 min intervals without introducing it into the duodenum. Intravenous leptin infusions (0.1, 1.0 and 10 microg/kg body weight) were made every 30 min. The same protocol was used in control non operated rats. The PBJ volume was significantly lower in fundectomized rats as compared to control rats and showed no significant effect to exogenous leptin. The PBJ protein output but not trypsin activity was lower in fundectomized rats as compared to control. Leptin reduced the PBJ protein and trypsin outputs in a dose-related manner in the control and experimental group. The inhibition was, however, more evident in the fundectomized rats. Plasma gastrin was higher in fundectomized rats, while plasma leptin and ghrelin were lower. In conclusion, fundectomy seems to reduce the non stimulated pancreatic secretion and modifies the response to leptin in anesthetized rats.