Effects of octapeptide-cholecystokinin,secretin, and glucagon on intestinal mucosal growth in parenterally nourished rats

Nutrients in the lumen of the small intestine may cause the release of enteric hormones which directly or indirectly stimulate intestinal mucosal growth. Male Sprague-Dawley rats with either an intact small bowel or following jejunal resection were maintained on total parenteral nutrition (TPN). C-terminal octapeptide-cholecystokinin alone or combined with secretin, or glucagon alone were added to the intravenous nutrient solution and continuously infused. Control rats received only TPN or gastric infusion of isocaloric amounts of TPN solution. After 7 days, intestinal hypoplasia was noted in rats with an intact bowel maintained on TPN alone compared with the gastrically infused group. TPN did not maintain the proximal-distal gradient of mucosal mass. Continuous intravenous infusion of octapeptide-cholecystokinin alone and together with secretin in rats maintained on TPN significantly stimulated small bowel mucosal growth, partially restoring the proximal-distal gradient. Glucagon infusion did not stimulate mucosal growth. Rats with a jejunal resection and maintained on TPN for 7 or 14 days failed to develop mucosal hyperplasia of the ileum in contrast to rats given the TPN solution intragastrically. Continuous intravenous infusion of octapeptide-cholecystokinin in rats maintained on TPN after jejunal resection caused significant mucosal growth in the ileum compared with the rats maintained on TPN alone, but not to the extent seen in gastrically fed animals. Intravenous infusion of octapeptide-cholecystokinin stimulates small-bowel mucosal growth. Secretin appears to have an additional effect when given together with octapeptide-CCK. Although a direct trophic action by these hormones on the intestinal mucosa is possible, this effect is more likely mediated via stimulation of pancreaticobiliary secretions.This work was supported by the Morrison Trust of San Antonio. SQ 19,844 was generously provided by Dr. Miguel Ondetti of the Squibb Institute for Medical Research.     

Pancreatic,Hepatic, and Duodenal Mucosal Bicarbonate Secretion during Infusion of Secretin and Cholecystokinin: Evidence of the Importance of Hepatic Bicarbonate in the Neutralization of Acid in the Duodenum of Anaesthetized Pigs

The effect of infusion of secretin alone or in combination with cholecystokinin (CCK) on pancreatic, hepatic, and duodenal mucosal bicarbonate secretion was studied in anaesthetized pigs. After laparotomy, catheters were inserted into the common bile duct, the pancreatic duct, and both ends of the duodenum. Pancreatic, hepatic, and duodenal mucosal secretions were collected during intraportal infusion of increasing doses of secretin, either alone or in combination with CCK. During infusion of secretin in doses that caused physiologic increases in plasma secretin concentrations the liver produced significantly more bicarbonate than the pancreas. A physiologic dose of CCK augmented the effect of secretin on both hepatic and pancreatic bicarbonate secretion, but the hepatic production of bicarbonate was still larger than the pancreatic production. Neither secretin alone nor secretin combined with CCK caused any changes in duodenal mucosal bicarbonate secretion. These results suggest that the liver plays an important role in the neutralization of acid in the duodenum.     

Pancreatic, hepatic, and duodenal mucosal bicarbonate secretion during infusion of secretin and cholecystokinin. Evidence of the importance of hepatic bicarbonate in the neutralization of acid in the duodenum of anaesthetized pigs

The effect of infusion of secretin alone or in combination with cholecystokinin (CCK) on pancreatic, hepatic, and duodenal mucosal bicarbonate secretion was studied in anaesthetized pigs. After laparotomy, catheters were inserted into the common bile duct, the pancreatic duct, and both ends of the duodenum. Pancreatic, hepatic, and duodenal mucosal secretions were collected during intraportal infusion of increasing doses of secretin, either alone or in combination with CCK. During infusion of secretin in doses that caused physiologic increases in plasma secretin concentrations the liver produced significantly more bicarbonate than the pancreas. A physiologic dose of CCK augmented the effect of secretin on both hepatic and pancreatic bicarbonate secretion, but the hepatic production of bicarbonate was still larger than the pancreatic production. Neither secretin alone nor secretin combined with CCK caused any changes in duodenal mucosal bicarbonate secretion. These results suggest that the liver plays an important role in the neutralization of acid in the duodenum.     

Glucagon inhibition of cerulein-induced hypertrophy of the exocrine pancreas

Glucagon is structurally related to secretin but inhibits the effects of secretin and cholecystokinin (CCK) on pancreatic secretion in vivo. Because secretin is a weak stimulant of pancreatic growth and potentiates the trophic effects of CCK, we hypothesized that glucagon might inhibit CCK-induced pancreatic growth. Four groups of 10 rats were injected with saline, glucagon (30 micrograms/kg, equimolar to a known trophic dose of secretin), cerulein (0.67 microgram/kg), or glucagon plus cerulein every 8 h for 5 days. The pancreas was excised, weighed, and assayed for total content of DNA, protein, amylase, chymotrypsinogen, and lipase. In control and glucagon-alone groups, the small intestine was also removed, weighed, and assayed for DNA, protein, and disaccharidase content. Glucagon alone decreased pancreatic DNA and increased lipase content. Compared with cerulein-treated animals, animals treated with glucagon and cerulein showed significant decreases in pancreatic weight and content of protein, amylase, and chymotrypsinogen. Although glucagon had significant effects on intestinal protein, maltase, and sucrase contents in certain segments, there was no clear pattern of response. The data suggest that glucagon may be an inhibitory regulator of pancreatic growth, acting to block the effects of CCK on pancreatic hypertrophy.     

The trophic effect on the pancreas of long-term continuous intravenous infusion of secretin and a cholecystokinin-like peptide in rats

Rats were treated for 5 days with continuous intravenous infusion of different doses of secretin and Thr28Nle31CCK25-33 (CCK-LP) alone and combined. The trophic effect on the pancreas was evaluated by means of pancreatic weight and contents of DNA, RNA, and protein. The acute effects on pancreatic protein secretion were studied in anesthetized rats. The findings generally confirmed the trophic effects of secretin and CCK-like peptides on the pancreas. No convincing evidence of potentiation was found between small doses of secretin and CCK-LP for either pancreatic growth or protein secretion. The maximal dose of CCK-LP was the same for pancreatic growth and for protein secretion (2.5 micrograms/kg-h). Potentiation was demonstrated between secretin and the maximal dose of CCK-LP for protein secretion. The maximal effect of CCK-LP on pancreatic growth, however, was not enhanced by secretin.     

Study on the trophic effect of camostate mesilate on ethionine-induced pancreatic injury rat

Pancreatic injury was induced to rats with intraperitoneal injection of ethionine 60 mg per 100 g BW twice or three times weekly for 6 weeks. These rats were given 100 mg/kg of Camostate mesilate (CM) via a gastric tube daily for 14 days. CM administration resulted in an increase of pancreatic wet weight, hypertrophy and hyperplasia of acinar cells, and an increase of exocrine pancreatic function. Acini prepared from CM and ethionine-treated rats exhibited increased response to caerulein, but decreased sensitivity to caerulein. The plasma CCK level in rats with CM administration 24 hours later was higher than that without CM administration. However, there were no significant changes in plasma CCK and secretin level thereafter. We concluded that CM had a trophic effect on the pancrease with ethionine-induced pancreatic injury, and CCK was considered playing the same role in injured pancreas as the normal rat pancreas. Studies using CCK receptor antagonist are needed for further clarification.     

Endogenous somatostatin inhibits interaction of insulin and cholecystokinin on exocrine secretion of isolated, perfused rat pancreas

INTRODUCTION: Although somatostatin inhibits pancreatic exocrine secretion, the inhibitory mechanism of endogenous somatostatin is not clearly understood. AIM: To investigate the effect of endogenous somatostatin on the interaction between endogenous insulin and exogenous cholecystokinin (CCK) in exocrine secretion of the totally isolated, perfused rat pancreas. METHODOLOGY: Endogenous releases of somatostatin and insulin were induced by 18 mM glucose. Streptozotocin (75 mg/kg) or cysteamine (300 mg/kg) was injected into rats 24 hours before the experiment to deplete insulin or somatostatin in the pancreas. RESULTS: Glucose (18 mM) enhanced CCK (10 pM)-stimulated secretions of fluid and amylase in the normal pancreas, which was further elevated by a somatostatin antagonist. Exogenous insulin (100 nM) also enhanced CCK-stimulated secretions in the streptozotocin-treated pancreas, which was also markedly increased by the somatostatin antagonist. The glucose (18 mM)-enhanced CCK-stimulated secretions were much higher in the cysteamine-treated pancreas than in the normal pancreas, which was dose-dependently reduced by exogenous somatostatin (30, 100 pM). However, endogenous or exogenous somatostatin did not modify the pancreatic responses to CCK alone. CONCLUSION: Endogenous somatostatin inhibits the interaction of endogenous insulin and CCK on pancreatic exocrine secretion in the rat rather than reducing the action of CCK alone or endogenous release of insulin.     

Effects of intraluminal trypsin and bile on the exocrine and endocrine pancreas after pancreaticobiliary diversion and biliodigestive shunt

Pancreaticobiliary diversion (PBD) and biliodigestive shunt (BDS) cause long-standing hypercholecystokininemia followed by pancreatic hyperplasia. These changes have been suggested to be due to the lack of intraluminal trypsin and bile, respectively, in the upper small intestine. The aim of these experiments was to study the effect of restoration of intraluminal trypsin and bile on plasma levels of cholecystokinin (CCK) and the changes found in exocrine and endocrine pancreas after PBD and BDS. Male Sprague-Dawley rats were used. PBD was done in 16 rats, eight of which had trypsin dissolved in 50 mM sodium bicarbonate (SB), and eight had SB only by gastric intubation twice daily. BDS was done in another 16 rats, eight of which had bile dissolved in SB, and eight had SB in a similar manner. Sham-operated rats had SB and served as controls. After 4 weeks, the rats were killed, and the concentrations of circulating CCK, gastrin, glucose, glucagon, and insulin were determined. The pancreas was removed, weighed, and analyzed for contents of water, protein, and DNA. In another study, PBD-operated rats got trypsin in varying dosages or trypsin and taurocholate in combination for 2 weeks before death. The concentrations of plasma CCK and glucagon were elevated after both PBD and BDS. PBD decreased the concentration of gastrin in plasma. PBD caused an increase of pancreatic weight and the contents of protein and DNA. Trypsin substitution to PBD-operated rats did not affect plasma CCK or glucagon levels, but the PBD-induced increases in weight and DNA content were counteracted by trypsin. Higher dosages of trypsin did not further influence the effects seen after PBD. Pancreatic weight and DNA content were increased after BDS. Bile administration completely abolished the increase in plasma CCK and glucagon, as well as the gain in pancreatic weight, and reduced the increase in pancreatic DNA. Substitution with bile to BDS-operated rats abolished the increase in the plasma levels of CCK and glucagon, as well as the trophic effects on the pancreas. Trypsin substitution to PBD-operated rats partly reversed the trophic effects on the pancreas but not the hormonal changes in plasma. Thus the trophic effects on the pancreas exerted by BDS seem to be dependent on the lack of bile in the upper small intestine, whereas the effects of PBD only partly are a consequence of the absence of intraluminal trypsin.     

The significance of plasma CCK and secretin in the oleate-stimulated pancreatico-biliary secretion in man

In eight normal persons the plasma levels of secretin and cholecystokinin (CCK) measured after intraduodenal oleate were reproduced by intravenous (i.v.) infusion of synthetic secretin (3.4 pmol.kg-1.h-1) and CCK-8 (17.5 pmol.kg-1.h-1), either alone or in combination. Using an indicator dilution technique, the combined infusions of the two hormones were found to account for all the pancreatico-biliary secretion of amylase, bicarbonate, bile salts and volume elicited in response to intraduodenal oleate, pH 6. Furthermore, the bicarbonate secretion and the flow rate elicited by secretin were augmented by CCK, whereas no augmentation was found with regard to the CCK-stimulated enzyme and bile salts output.     

Effects of endogenous and exogenous cholecystokinin and of infusion with the cholecystokinin antagonist L-364,718 on pancreatic and gastrointestinal growth

Continuous subcutaneous infusion of cholecystokinin (CCK-8; 5 micrograms/kg/h) to rats for 7 weeks raised the plasma CCK concentration almost fivefold and increased the pancreatic weight by about 50% but was without effect on the gastrointestinal tract. Continuous subcutaneous infusion of the CCK antagonist L-364,718 (200 micrograms/kg/h) for 7 weeks reduced the weight of the pancreas by about 30% but was without effect on the gastrointestinal tract. The effect of continuous subcutaneous infusion of CCK-8 and L-364,718 in combination was very similar to that of L-364,718 alone. Pancreaticobiliary diversion (PBD) induced a nearly 10-fold increase in the plasma CCK concentration 3 and 7 weeks after the operation. The serum gastrin values were unaffected. The weight of the pancreas was more than doubled after 7 weeks. At the same time the small intestine had gained weight, but the colon was unaffected. Continuous subcutaneous infusion of L-364,718 prevented the effect of PBD on the pancreas. On the basis of the assumption that L-364,718 is a specific antagonist of CCK, we conclude that endogenous CCK has a trophic effect on the pancreas but not on the gastrointestinal tract and that it is essential for normal pancreatic growth.     

Neurotensin and the exocrine pancreas

It has been postulated that neurotensin (NT) has a physiological role in the regulation of the exocrine pancreas, but this is controversial. Using the Thomas cannula canine model, the effect of intravenous NT, in physiological and pharmacological doses on exocrine pancreatic secretion, and on plasma pancreatic polypeptide, secretin and cholecystokinin (CCK) levels is reported. The infusion of physiological doses of NT alone (0.2 pmol/kg per min) did not stimulate pancreatic secretion; however, in conjunction with secretin, NT stimulated protein and bicarbonate output, the latter synergistically. Higher doses of NT (20 and 100 pmol/kg per min) resulted in a dose-dependent stimulation of pancreatic volume, bicarbonate and protein secretion. Cholinergic blockade with atropine reduced pancreatic secretion stimulated by low doses of NT (2–20 pmol/kg per min), but at higher doses (100 pmol/kg per min) protein secretion was reduced whilst bicarbonate secretion was enhanced. The infusion of graded doses of NT had no effect on plasma secretin or CCK levels. In contrast, NT did release pancreatic polypeptide in a dose-dependent manner, but only at pharmacological infusion levels. NT, acting synergistically with other hormones, may thus play a role in exocrine pancreatic stimulation.     

Effect of partial versus complete pancreatic denervation on pancreatic secretion

The aim of this study is to compare the effect of various stimuli on pancreatic secretion in two groups of dogs, one undergoing interruption of the cholinergic and adrenergic branches to the pancreas (long arc reflexes), and the second group undergoing total denervation of the pancreas by its isolation from stomach and duodenum (short arc reflexes). Stimulation of pancreatic secretion was accomplished by (a) hormonal, by i.v. secretin and CCK/PZ and (b) reflex stimulation by intraduodenal administration of fat (Na oleate) or amino acids (Aminosyn). After a few weeks of collected data in stimulated controls, the dogs were divided into two groups: (A) Four dogs underwent proximal truncal vagotomy, celiac ganglionectomy, and stripping of the common hepatic and gastroduodenal arteries for 2-3 cm. (B) Four dogs underwent the same procedures, but in addition the pancreas was dissected away from its vascular and nervous attachments to the duodenal wall and pyloric region, as well as from its mesenteric and peritoneal attachments. All animals were then tested with secretin, Cholecystokinin/pancreozymin (CCK/PZ), intraduodenal fat, and intraduodenal amino acids. The data obtained indicate that secretion of pancreatic bicarbonate is dependent on intact local duodeno-pancreatic nervous reflexes. Fat and amino acids stimulate the secretion of bicarbonate only when the attachments of the pancreas to the stomach and duodenum are intact. Stimulation by secretion or CCK, being humoral-hormonal mediators, appears not to be affected by the local denervation.     

Exocrine function of the heterotopic transplanted pancreas segment: influence of denervation in dogs

We investigated the effect of denervation after heterotopic segmental pancreas autotransplantation on the exocrine function of the graft. The weight of the pancreas segment was determined, and secretory volume, bicarbonate output, and amylase activity were measured before and after i.v. infusion of secretin and cholecystokinin (CCK)-8. The studies were performed in untreated normal dogs, at 2 months postoperatively in partially pancreatectomized dogs with an innervated segment left in situ, and in totally pancreatectomized recipients of denervated heterotopic autotransplanted segments (approximately 30% of whole pancreas). The weight of the pancreas segment was similar in innervated and denervated dogs. Basal pancreatic secretory volume, bicarbonate output, and amylase activity were largely independent of cholinergic control. The secretory volume and bicarbonate output response to i.v. gut hormones (mainly secretin) were slightly modulated by cholinergic activity, whereas amylase response to gut hormones (mainly CCK-8) was quite independent of cholinergic control. We conclude that, after pancreas transplants, the effect of denervation on graft exocrine function is negligible--a finding that is reassuring if preserving of the exocrine tissue is important for optimal endocrine function of the graft.     

Relationship between enteral glucose load and adaptive mucosal growth in the small bowel

Infusion of hyperosmolar glucose solutions into small bowel will prevent mucosal atrophy or stimulate mucosal growth in rats otherwise maintained on total parenteral nutrition (TPN). It is not certain whether this growth effect is related to the osmolarity of the solution or its total molecular load. Therefore, various concentrations of glucose and sodium salt solutions were studied for comparative effects on growth of small bowel mucosa. Male Sprague-Dawley rats (240 g) were maintained on TPN and infused continuously with either glucose or sodium chloride (2 and 0.6 ml/hr) or sodium sulfate (0.6 ml/hr) via a catheter placed in the mid-small intestine. Concentrations of infusion solutions ranged in osmotic pressure from 300 to 1500 mosmol/liter. Controls were TPN rats without infusion of any solution. Over a seven-day period, TPN rats receiving mid-gut infusions of 300 mosM saline gained 18.4 g in body weight. In TPN rats receiving mid-gut infusions of progressively greater concentrations of glucose, the additional total kilocalories per day resulted in greater body weight gain compared with the saline controls. After seven days, rats were killed, the small bowel removed, and divided into eight equal segments (segment 1, duodenum; segment 8, terminal ileum). Segment weight, mucosal weight, DNA, and protein concentration per segment were measured. Mid-gut infusions of 900 and 1500 mosM glucose solutions progressively increased mucosal mass in segments downstream from the site of infusion compared with 300 mosM glucose in water or 600 mosM glucose in saline which did not differ from any of the salt solutions or TPN alone.(ABSTRACT TRUNCATED AT 250 WORDS)     

The action of synthetic secretin, cholecystokinin-octapeptide and combinations of these hormones on the secretion of the isolated perfused rat pancreas

Determinations of dose-response curves for synthetic secretin and for the octapeptide of cholecystokinin (CCK-8) in the isolated perfused rat pancreas reveal that both secretin and CCK stimulate the pancreatic secretory flow and enzyme secretion. The maximal secretory flow evoked by CCK-8 (1.75 +/- 0.24 microliter/min) equals that evoked by secretin, while the protein output (57.1 +/- 6.3 microgram/min) is approximately twice as high. Stimulation by secretin combined with CCK-8 results in summation of the hydrokinetic action and potentiation of the ecbolic action of these hormones. Since the secretory parameters decrease by supramaximal stimulation, the dose-response curves are biphasic. The secretion of pancreatic enzymes correlates significantly (p less than 0.0005) with the protein output. However, the ratio of amylase, lipase and chymotrypsinogen to protein depends on the degree of pancreatic stimulation in so far as amylase secretion increases significantly (p less than 0.01) more markedly than that of both other enzymes.     

The significance of plasma CCK and secretin in the oleate-stimulated pancreatico-biliary secretion in man

Summary In eight normal persons the plasma levels of secretin and cholecystokinin (CCK) measured after intraduodenal oleate were reproduced by intravenous (i.v.) infusion of synthethic secretin (3.4 pmol · kg^-1 · h^-1) and CCK-8 (17.5 pmol · kg^-1 · h^-1), either alone or in combination. Using an indicator dilution technique, the combined infusions of the two hormones were found to account for all the pancreatico-biliary secretion of amylase, bicarbonate, bile salts and volumen elicited in response to intraduodenal oleate, pH 6. Furthermore, the bicarbonate secretion and the flow rate elicited by secretin were augmented by CCK, whereas no augmentation was found with regard to the CCK-stimulated enzyme and bile salts output.     

Postprandial release of cholecystokinin after duodenum-preserving total pancreatectomy is independent of intraluminal pancreatic protease activity in dogs

The effect of meal stimulation, with and without the intraduodenal presence of pancreatic enzymes, on plasma cholecystokinin (CCK) release was studied in order to investigate the role of CCK in the putative feedback mechanism between intraduodenal pancreatic proteases and pancreatic enzyme secretion. Plasma CCK concentrations in response to a semiliquid meal, with and without the supplementation of exocrine pancreatic enzymes, were measured in 8 dogs after duodenum preserving pancreatectomy. With a well-balanced endocrine and exocrine substitution regimen all dogs were kept in good clinical condition, without steatorrhea or significant weight loss, and fasting plasma glucose levels within the normal range. Exocrine supplementation was stopped at least 3 days prior to tests. Basal plasma CCK levels after 3 days without exocrine supplementation (2.5 +/- 0.3 pM) did not significantly differ from the results with supplementation (3.0 +/- 0.5 pM) nor from the preoperative levels (2.3 +/- 0.3 pM). In addition, integrated plasma CCK responses to the meal without exocrine supplementation (330 +/- 37 pM.90 min) were not significantly different from the responses to the meal with exocrine supplementation (303 +/- 49 pM.90 min), or from the postprandial CCK response in the dogs with an intact pancreas preoperatively (390 +/- 100 pM.90 min). It is concluded that the release of CCK in dogs after total pancreatectomy is independent of intraluminal protease activity. It is therefore not likely that CCK mediates the putative feedback mechanism between intraluminal protease activity and pancreatic enzyme secretion in dogs.     

Influence of an absorbable alpha-glucosidase inhibitor (Bay o 1248) on the endocrine and exocrine pancreas of the rat

The influence of an absorbable glucosidase inhibitor (Bay o 1248) on the endocrine and exocrine rat pancreas was evaluated. Rats fed a standard diet containing Bay o 1248 over 10 days consumed less food, gained about 30% less body weight than controls and showed meteorism. In these animals postprandial plasma insulin and glucose levels were decreased, but the total pancreatic insulin content was not different versus controls. The early insulin secretory response studied by pancreas perfusions was found reduced after a stimulatory glucose load (10 mM). Addition of the glucosidase inhibitor (1 mM) to the incubation medium diminished the glucose-induced insulin release from isolated islets of rats fed a standard diet. The compound added to the perfusion medium (10 microM) induced a slight reduction of half-maximal glucose-induced (10 mM) insulin release from the perfused pancreas. This inhibitory effect disappeared during maximal stimulation (20 mM glucose) of insulin secretion. The compound neither altered basal nor arginine-induced (15 mM) insulin release from the perfused organ. The exocrine pancreas was studied after feeding a Bay o 1248-enriched standard diet over 10 days. Amylase and trypsin concentration and total output into the biliary-pancreatic juice in response to CCK and secretin (20 IU or CU/kg body weight each) were diminished. The pancreatic enzyme content did not differ compared to controls. A significant role of carbohydrate maldigestion, systemic effects of the glucosidase inhibitor, and endocrine-exocrine pancreatic interrelations are discussed to account for the effects of the compound on the rat pancreas.     

Effect of a new cholecystokinin antagonist (FK 480) on gene expression of cholecystokinin and secretin in rat intestine

The effects of a new cholecystokinin (CCK) antagonist (FK 480; 0.1 mg/kg per day given by intragastric administration to rats for 3 days) on the expression of the CCK and secretin genes, plasma CCK immunoreactivity, and CCK content in the intestinal mucosa were examined. FK 480 increased the level of CCK mRNA in the intestine to 1.7 times the level in control rats, but did not affect the level of secretin mRNA. It did not increase plasma CCK immunoreactivity or CCK content in the intestinal mucosa. These results suggest that the ingested FK 480 directly increased CCK mRNA level in the intestine and produced a dissociation between the synthesis and release of CCK.