Meal-stimulated cholecystokinin release and exocrine pancreatic secretion in dogs

To confirm the role of cholecystokinin (CCK) and secretin in digestion, exocrine pancreatic secretion, plasma CCK, and secretin were measured simultaneously in six dogs prepared with gastric and pancreatic fistulas after feeding a solid meal. Plasma CCK concentration determined by radioimmunoassay increased significantly from the basal level, reached a peak 35 min after meal ingestion, and after a dip it further increased toward the end of the 3-h observation. Pancreatic protein output increased significantly, peaked at the fifth 10-min period, and then declined progressively. Plasma CCK concentration and pancreatic protein output correlated significantly during the first postprandial hour. Plasma secretion demonstrated significant elevation at 15 min and a peak at 25 min after a meal. Plasma secretin correlated significantly with both bicarbonate output and flow rate during the 3 h. Simultaneous measurements of plasma CCK and secretin and of pancreatic secretion suggested that postprandial pancreatic secretion is primarily mediated by releases of CCK and secretin, but these hormones do not seem to be the only factors responsible for the secretion.     

Effect of cholestyramine on plasma cholecystokinin and pancreatic polypeptide levels, and exocrine pancreatic secretion

The effect of acute and long-term administration of cholestyramine, a non-absorbable bile salt binding resin, on exocrine pancreatic secretion, plasma-cholecystokinin (CCK) and plasma-pancreatic polypeptide (PP) was investigated in 10 healthy volunteers. Oral ingestion of 12 g cholestyramine augmented the stimulatory effect of a liquid test meal on plasma-CCK (3.5-fold) and plasma-PP (2-fold). During prolonged treatment with 3 x 12 g cholestyramine daily for 4 weeks, the most pronounced increase in basal hormone levels was observed after 1 day, but progressively decreased during treatment and had normalized after 4 weeks. However, the stimulated plasma-CCK output was still significantly elevated after cessation of treatment, compared with pretreatment values. After acute and chronic cholestyramine administration only stimulated lipase secretion was elevated, whereas trypsin and amylase remained unchanged. It is suggested that removal of bile salts enhances CCK and thereby PP release and pancreatic lipase secretion.     

The effect of selective sympathetic denervation on pancreatic exocrine secretion

The purpose of this study was to investigate the influence of selective sympathetic denervation of the rat pancreas on exocrine secretion and to study whether the observed effects were due to pancreatic trophism. Sprague-Dawley rats were divided into two groups. One group underwent selective sympathetic denervation by skeletonizing the superior and inferior pancreaticoduodenal and splenic arteries. The other group underwent simple laparotomy and served as controls. One week after the operation a catheter was introduced into the bile-pancreatic duct and pancreatic juice was collected at 30-min intervals for 4 h. The output of bicarbonate, total protein, amylase, trypsin, chymotrypsin, lipase, colipase and carboxyesterlipase were determined. Following denervation secretion of pancreatic enzymes was significantly enhanced compared with sham-operated animals. We did not find any signs of pancreatic trophism 1 week after denervation.     

CRL41405: a drug with a new pharmacological profile on pancreatic exocrine secretion in the rat

The recently described compound CRL41405 displays central effects suggesting possible antidepressive and awakening properties. In order to further analyze the pharmacology of this compound, its effects were studied on basal and stimulated pancreatic secretion in anaesthetized rats. CRL41405 alone (7-20 mg/kg, sc) had no effect on basal pancreatic secretion. Larger doses (67-200 mg/kg) increased basal secretion through the stimulation of cholinergic muscarinic receptors, the effect being antagonized by atropine. CRL41405 (20 mg/kg) suppressed the 2-deoxyglucose-induced (but not the acetylcholine-induced) stimulation of pancreatic secretion through an alpha-2 adrenoceptor inhibitory mechanism that was blocked by idazoxan (0.3 mg/kg, sc). In addition, a beta adrenoceptor mediated stimulation of sodium and bicarbonate excretion (blocked by propranolol) was evidenced when the alpha-2 inhibition was suppressed by idazoxan. Under alpha-2 adrenoceptor blockade, water and electrolyte stimulation by CRL41405 could be demonstrated on basal, 2-deoxyglucose-induced and acetylcholine-induced pancreatic secretion. This original profile makes CRL41405 a unique drug in pancreatic pharmacology.     

Diazepam-binding inhibitor mediates feedback regulation of pancreatic secretion and postprandial release of cholecystokinin

Recently, we isolated a trypsin-sensitive cholecystokinin-releasing peptide (CCK-RP) from porcine and rat intestinal mucosa. The amino acid sequence of this peptide was determined to be identical to that of the diazepam-binding inhibitor (DBI). To test the role of DBI in pancreatic secretion and responses to feeding, we used pancreaticobiliary and intestinal cannula to divert bile-pancreatic juice from anesthetized rats. Within 2 hours, this treatment caused a 2-fold increase in pancreatic protein output and a >10-fold increase in plasma CCK. Luminal DBI levels increased 4-fold. At 5 hours after diversion of bile-pancreatic juice, each of these measures returned to basal levels. Intraduodenal infusion of peptone evoked a 5-fold increase in the concentration of luminal DBI. In separate studies, we demonstrated that intraduodenal administration of antiserum to a DBI peptide specifically abolished pancreatic secretion and the increase in plasma CCK levels after diversion of bile-pancreatic juice. To demonstrate that DBI mediates the postprandial rise in plasma CCK levels, we showed that intraduodenal administration of 5% peptone induced dramatic increases in pancreatic secretion and plasma CCK, effects that could be blocked by intraduodenal administration of anti-DBI antiserum. Hence, DBI, a trypsin-sensitive CCK-RP secreted from the proximal small bowel, mediates the feedback regulation of pancreatic secretion and the postprandial release of CCK.     

Interactions of calcium, magnesium and atropine on exocrine pancreatic secretion in man

Abstract. The effects of the intravenous administration of atropine or magnesium on pancreatic secretion which has been stimulated by secretin and induced hypercal-caemia have been studied in man.
In the presence of secretin (0.5 CU/kg.h) the infusion of Ca²⁺ (0.3 mmol/kg.105 min) resulted in an increase in secretion of enzymes by 100–200%, and in that of Ca²⁺ and Mg²⁺ by 50–100% without affecting fluid and bicarbonate secretion.
The additional injection of atropine (0.5 mg i.v. and 0.5 mg s.c.) were followed by a prompt fall in enzymes but not in Ca²⁺ and Mg²⁺ to the secretin-stimulated values.
The additional infusion of Mg²⁺ (0.12 mmol/kg.45 min) to the Ca²⁺-infusion did not alter the secretion of enzymes, Ca²⁺ or Mg²⁺ compared with the calcium infusion alone.
It is suggested that the hypercalcaemic stimulus depends on an intact innervation of the acinar cells.
In these experiments the secretion of Ca²⁺ and Mg²⁺ seem to originate mainly from extracellular fluxes.     

Subtypes of adenosine receptors on pancreatic exocrine secretion in anaesthetized dogs

Characterization of adenosine receptor subtypes was examined on the canine exocrine pancreas using selective adenosine receptor agonists and antagonists in the isolated and blood-perfused pancreas of anaesthetized dogs. Each drug was injected intra-arterially in a single bolus fashion. Graded doses of CGS21680 (1-300 nmol/kg), a selective adenosine A2A receptor agonist, produced dose-dependent increases in the secretory rate of pancreatic juice, with a maximum effect at approximately 30 nmol/kg. However, CPA (1-300 nmol/kg), a selective adenosine A1 receptor agonist, did not cause the pancreatic secretion. CGS21680 (3-30 nmol/kg) and secretin (0.01-0.03 pmol/kg) increased the bicarbonate concentration in pancreatic juice and decreased the protein concentration. CCK-8 (0.1-0.3 pmol/kg) increased the protein concentration but did not alter the bicarbonate concentration. DMPX (5-50 nmol/kg), a weak adenosine A2A receptor antagonist, caused a progressive parallel shift to the right in the dose response curve for CGS21680-induced pancreatic secretion without changes in the maximal response. DPCPX (100 nmol/kg), a selective A1 adenosine receptor antagonist, did not antagonize the CGS21680-induced pancreatic secretion. Schild analysis of the data indicated that the apparent pA2 value for DMPX was 8.3 using CGS21680 as the agonist. The slope of the Schild regression line was not different from 1. When a phosphodiesterase IV inhibitor rolipram (0.1 nmol/kg) was added, pancreatic secretion induced by CGS21680 (10 nmol/kg) and secretin (0.03 pmol/kg) were potentiated, but not that of CCK-8 (0.3 pmol/kg). These results suggest the existence of adenosine A2A receptors in the exocrine cells of the dog pancreas involved in the water and bicarbonate secretory response.     

Interactions of calcium, magnesium and atropine on exocrine pancreatic secretion in man.

The effects of the intravenous administration of atropine or magnesium on pancreatic secretion which has been stimulated by secretin and induced hypercalcaemia have been studied in man. In the presence of secretin (0.5 CU/kg.h) the infusion of Ca2+ (0.3 mmol/kg.105 min) resulted in an increase in secretion of enzymes by 100-200%, and in that of Ca2+ and Mg2+ by 50-100% without affecting fluid and bicarbonate secretion. The additional injection of atropine (0.5 mg i.v. and 0.5 mg s.c.) were followed by a prompt fall in enzymes but not in Ca2+ and Mg2+ to the secretin-stimulated values. The additional infusion of Mg2+ (0.12 mmol/kg.45 min) to the Ca2+-infusion did not alter the secretion of enzymes, Ca2+ or Mg2+ compared with the calcium infusion alone. It is suggested that the hypercalcaemic stimulus depends on an intact innervation of the acinar cells. In these experiments the secretion of Ca2+ and Mg2+ seem to originate mainly from extracellular fluxes.     

Inhibitory action of antidiuretic hormone on canine pancreatic exocrine flow.

A direct relationship was observed between the percentage inhibition of secretin-stimulated pancreatic exocrine flow and the dose of antidiuretic hormone administered with the minimal effective concentration being 0.75 m units/kg or 0.012 m units/ml. An alteration in the molecular configuration of the antidiuretic hormone modified its ability to inhibit secretin-stimulated pancreatic exocrine secretion.     

Effects of serum from trypsin inhibitor fed rats on enzyme secretion and protein synthesis by exocrine pancreatic cells

Oral feeding of trypsin inhibitor is known to stimulate rat pancreatic enzyme secretion and cause hypertrophy of the pancreas. In an attempt to detect a possible serum factor(s) responsible, the effects of serum from trypsin inhibitor fed rats on enzyme secretion and protein synthesis by isolated exocrine rat pancreatic cells in suspension were studied.

Serum from trypsin inhibitor fed rats stimulated the secretion of pancreatic enzymes significantly more than serum from control rats. The data suggest that a humoral factor or factors may be involved in the stimulation of pancreatic enzyme secretion by oral trypsin inhibitor.

Serum from trypsin inhibitor fed rats as well as serum from control rats stimulated the ³H-leucine incorporation into protein (protein synthesis) to a significant extent. There was, however, no difference in the effects of the two types of sera in this respect.     

Feedback regulation of pancreatic exocrine secretion in animal and man

Abstract. This chapter focuses on studies dealing with the feedback mechanism of pancreatic exocrine secretion in animal and man. Clear evidence is presented that this feedback mechanism is working in the rat and the pig and that this feedback is mediated in the rat by the gastrointestinal hormones pancreozymin (enzyme secretion) and secretin (volume and bicarbonate secretion). Two novel peptides have been described—the 'CCK-releasing peptide' originating from the small intestinal mucosa, and the 'monitor peptide' cose-creted together with the enzymes in the pancreatic juice—to account for the stimulation of pancreatic enzyme secretion by the release of CCK. A similar feedback regulation of pancreatic secretion is working in man. It remains as yet controversial whether the feedback in humans is regulated via hormonal or neural pathways. It is also a matter of debate whether this feedback regulation of pancreatic enzyme secretion could be utilized for therapeutic aims in the treatment of pain in patients with chronic pancreatitis.     

The role of pancreatic innervation and cholecystokinin in the intestinal phase of pancreatic polypeptide release in conscious dogs

Besides vagal cholinergic mechanisms, pancreatic polypeptide (PP) secretion is thought to be mediated by hormones. This study was performed to delineate the role of extrinsic pancreatic innervation and cholecystokinin (CCK) in amino acid- and fat-stimulated PP secretion. In ten mongrel dogs, pancreatic denervation was performed by the method of Debas et al. [3]. Total denervation of the pancreas did not alter PP response to intraduodenal application of amino acids (integrated output 24434±3260 pmol/1×120 min before vs 22797±2470 pmol/1×120 min after operation) and to intraduodenal fat solution (19595±2121 pmol/1×120 min vs 19983±2031 pmol/1×120 min). Also, no significant differences were measured in CCK release (491±71 pmol/1×120 min vs 430±57 pmol/1×120 min for amino acids, 571=63 pmol/1×120 min vs 563±89 pmol/1×120 min for fat solution). Plasma PP and CCK levels were compared by linear regression analysis. Correlations between PP and CCK were high in the intact pancreas (amino acids,r=0.92; fat,r=0.99) as well as in the denervated pancreas (r=0.93 amino acids andr=0.98 fat). These results show that extrinsic pancreatic innervation does not influence PP and CCK release after intraduodenal amino acids or fat solution and that PP secretion seems to be mediated to some extent through the release of CCK.     

Effects of serum from trypsin inhibitor fed rats on enzyme secretion and protein synthesis by exocrine pancreatic cells

Oral feeding of trypsin inhibitor is known to stimulate rat pancreatic enzyme secretion and cause hypertrophy of the pancreas. In an attempt to detect a possible serum factor(s) responsible, the effects of serum from trypsin inhibitor fed rats on enzyme secretion and protein synthesis by isolated exocrine rat pancreatic cells in suspension were studied. Serum from trypsin inhibitor fed rats stimulated the secretion of pancreatic enzymes significantly more than serum from control rats. The data suggest that a humoral factor or factors may be involved in the stimulation of pancreatic enzyme secretion by oral trypsin inhibitor. Serum from trypsin inhibitor fed rats as well as serum from control rats stimulated the 3H-leucine incorporation into protein (protein synthesis) to a significant extent. There was, however, no difference in the effects of the two types of sera in this respect.     

Effect of lipids on insulin, growth hormone and exocrine pancreatic secretion in man.

Influences of fat on release of insulin, growth hormone and pancreatic enzyme secretion were studied in 35 metabolically healthy subjects. A fat solution containing 40 g of soy bean oil was administered, I.V., orally and intraduodenally. In all cases there was a similar increase of insulin but the rise in serum insulin after oral or intraduodenal fat administration was not related to the changes in plasma free fatty acids, free glycerol and triglyceride levels. Blood surgar responded according to insulin secretion. The route of fat administration may possibly influence growth hormone secretion. Following intraduodenal fat administration volume and bicarbonate contents of the duodenal juice rose slightly whereas trypsin and bilirubin content increased considerably. These results suggest that insulin secretion after oral or intraduodenal administration of fat is influenced by intestinal factors. Cholecystokinin-pancroezymin and gastric inhibitory polypeptide are qualified to serve as such factors.     

Postprandial control of gallbladder contraction and exocrine pancreatic secretion in man

To explore the interactions between cholecystokinin (CCK) and the cholinergic system, we compared the effect of cholinergic or peptidergic CCK blockade on gallbladder contraction and pancreatic enzyme secretion using atropine and loxiglumide (a specific CCK antagonist) as pharmacological tools. Gallbladder contraction was measured by sonography and pancreatic secretion by a marker perfusion and aspiration technique. Graded doses of exogenous CCK8 induced dose-dependent contractions of the gallbladder and increasing enzyme outputs. Loxiglumide (10 mg kg-1 h-1) abolished the gallbladder response and prevented an increase in pancreatic enzyme secretion to CCK8. Atropine (5 micrograms kg-1 h-1), however, only reduced gallbladder contraction and enzyme output to CCK8. Gallbladder volumes decreased maximally to 12 +/- 4% after oral food, whereas enzyme output and plasma CCK levels increased 6- to 8-fold. Loxiglumide completely abolished gallbladder contraction and inhibited enzyme secretion by 30%. Atropine caused a small reduction in gallbladder volumes, but essentially blocked postprandial enzyme secretion. The results indicate that CCK is the major regulator of gallbladder contraction with the cholinergic system modulating the response, while the exocrine pancreas is crucially dependent on a cholinergic background with CCK modulating the secretory response.     

Total denervation of the pancreas does not alter the pancreatic polypeptide-induced inhibition of pancreatic exocrine secretion in dogs

Pancreatic polypeptide (PP) is a potent inhibitor of pancreatic exocrine secretion in vivo. The mechanism of pancreatic inhibition by PP is unknown, but the absence of PP receptors on pancreatic exocrine cells makes a direct effect of this hormone on the gland unlikely. In this study, we investigated the hypothesis that PP exerts its inhibitory effect via extrinsic neural pathways. Ten dogs with gastric and pancreatic fistulas were given an intravenous infusion of 250 ng/kg⁻¹ h⁻¹ secretion and 50 ng/kg⁻¹ h⁻¹ caerulein over 3 h. One hour after starting the infusion, 400 pmol kg⁻¹ h⁻¹ porcine PP were administered over 1 h. Pancreatic bicarbonte and protein secretions were measured. Later, the pancreas was extrinsically denervated. PP infusion decreased bicarbonate secretion in the intact gland by 47% and in the denervated pancreas by 57%. Protein secretion was diminished by exogenous PP by 31% in the intact and by 44% in the denervated pancreas. Despite pancreatic denervation, PP still exerted a significant inhibitory effect. Atropine infusion completely blocked the inhibitory effect of PP on caerulein-stimulated pancreatic protein secretion both in the intact and denervated pancreas and of secretion-evoked bicarbonate output in the denervated gland. We conclude that the inhibitory action of the hormone is not mediated via extrinsic neural pathways of the pancreas, but PP may exert its effect via intrinsic atropine-sensitive mechanisms.     

犬胰液外引流模型的制备及胰腺外分泌功能的观察

目的：建立犬的胰液外引流模型，以利于胰腺外分泌功能的研究。方法：健康杂种犬8只，在无菌的条件下行主胰管插管固定，膀胱造瘘。犬禁食，补液，每日收集胰液，测量胰液的量及胰液中的淀粉酶、总蛋白、pH值、HCO3^-、Na^＋、K^＋、Cl^-、Ca^2＋、mg^2＋。结果：成功建立犬的胰液外引流模型。胰液中淀粉酶和总蛋白的含量第2天明显高于其他几天（P〈O，05），胰液量第3天达到最大值，胰液中pH值、HCO3^-、Na^＋、K^＋、Cl^-、Ca^2＋、Mg^2＋在禁食期间均无显著变化（P〉0．05）。结论：本模型适用于对胰腺外分泌功能的研究，有利于长时间动态观察胰腺的外分泌功能，而且可以在此基础上建立水肿型和坏死型胰腺炎胰液外引流模型，适用于胰腺炎外分泌功能的研究。     

Vagal afferent pathway mediates physiological action of cholecystokinin on pancreatic enzyme secretion.

To establish the mechanism(s) and site(s) of action of cholecystokinin (CCK) on pancreatic secretion under physiological conditions, we used an in vivo model using anesthetized rats with pancreaticobiliary cannulas. Infusion of CCK-8 (10-160 pmol/kg per h) produced a dose-dependent increase in plasma CCK levels. CCK-8 infusion at 40 pmol/kg per h produced a plasma CCK level of 7.9 +/- 1.5 pM and an 80% increase in pancreatic protein output over basal. This level was closely approximated by a postprandial peak plasma CCK level by 6.2 +/- 1.1 pM. Pretreatment with atropine or hexamethonium completely abolished pancreatic protein response to low doses of CCK-8 (10-40 pmol/kg per h) but had only partial effect on doses > 40 pmol/kg per h. Bilateral vagotomy also abolished the pancreatic responses to low doses of CCK-8. Similarly perivagal treatment with a sensory neurotoxin, capsaicin, caused a complete inhibition of pancreatic protein secretion in response to CCK-8 infusion. In contrast, pancreatic protein responses to bethanechol were similar in control and capsaicin-treated rats. In separate studies we demonstrated that gastroduodenal but not jejunal application of capsaicin for 30 min abolished pancreatic protein secretion in response to physiological doses of CCK-8. In conclusion, CCK at physiological levels stimulates pancreatic enzyme secretion via a capsaicin-sensitive afferent vagal pathway originating from the gastroduodenal mucosa.