Control Of Pancreatic Enzyme Secretion Research Articles

Nutrient control of release of pancreatic enzymes in yellowtail ( Seriola quinqueradiata): Involvement of CCK and PY in the regulatory loop

Cholecystokinin (CCK) and neuropeptide Y (NPY)-related peptides are key regulators of pancreatic enzyme secretion in vertebrates. CCK stimulates enzyme secretion whereas peptide Y (PY), a NPY-related peptide, plays an antagonistic role to that of CCK. In fish, very little is known about how different nutrients affect the synthesis of CCK and PY in the digestive tract, and the mechanism by which CCK and PY actually regulate digestive enzyme secretion is not well understood. In order to determine how different nutrients stimulate the synthesis of CCK and PY in yellowtail ( Seriola quinqueradiata), CCK and PY mRNA levels in the digestive tract were measured after oral administration of a single bolus of either phosphate-buffered saline (PBS: control), starch (carbohydrate), casein (protein), oleic acid (fatty acid) or tri-olein (triglyceride). In addition, in order to confirm the synthesis and secretion of digestive enzymes, the mRNA levels and enzymatic activities of three digestive enzymes (lipase, trypsin and amylase) were also analyzed. Casein, oleic acid and tri-olein increased the synthesis of lipase, trypsin and amylase, while starch and PBS did not affect the activity of any of these enzymes. CCK mRNA levels rose, while PY mRNA levels were reduced in fish administered casein, oleic acid and tri-olein. These results suggest that in yellowtail, CCK and PY maintain antagonistic control of pancreatic enzyme secretion after intake of protein and/or fat.

Influence of chronic ethanol consumption on the muscarinic cholinergic control of rat pancreatic acinar cells.

There are a number of hypothetical explanations for the actions of ethanol on the exocrine pancreas; among them, the cholinergic hypothesis has received special attention. According to this hypothesis, chronic alcohol consumption induces alterations in the control of exocrine pancreatic function resulting in cholinergic hyperstimulation of pancreatic acinar cells and their muscarinic receptors. Our aim was to investigate the cholinergic control of pancreatic enzyme secretion and the number and affinity of muscarinic receptors in the pancreatic acinar cells of rats subjected to chronic ethanol ingestion. We also investigated whether a high-fibre diet modifies the actions of ethanol on these aspects of the exocrine pancreatic function. Four groups of rats received either a standard or a high fibre diet, and either water or 20% (v/v) ethanol. After 6 months of treatment, isolated pancreatic acini were used for the determination of carbachol-stimulated amylase secretion and for the analysis of muscarinic receptors, using 1-[N-methyl-3H]scopolamine as a radioligand. Neither chronic ethanol intake nor a high fibre diet caused any apparent alteration in pancreatic histology, neither did them modify plasmatic amylase levels. Chronic alcoholization resulted in a significant increase in the amylase released from pancreatic acini in response to carbachol stimulation, but it did not affect either the number or the affinity of pancreatic acinar muscarinic receptors. The actions of ethanol are not significantly modified by the simultaneous consumption of a high fibre diet.

Agonists and Antagonists of Regulatory Peptides as Tools to Study Regulation of Pancreatic Exocrine Secretion, Cell Proliferation and Gene Expression

For more than two decades, our research group has been studying the pancreatic actions of three groups of regulatory peptides: members of the cholecystokinin/gastrin family, bombesin-like peptides and somatostatin. Investigating these peptides, our work has focused on three particularly interesting aspects: peptidergic regulation of pancreatic enzyme secretion and growth in adult rats, peptidergic control of pancreatic enzyme secretion and growth during postnatal development in rats, and peptidergic regulation of proliferation and differential gene expression in pancreatic adenocarcinoma cells. Our data confirmed that the control of the exocrine function of the pancreas is complex, and that it involves peptides such as the cholecystokinin/gastrin-like peptides, bombesin-like peptides and somatostatin. In these investigations, it became evident that selective peptide receptor agonists, antagonists and monoclonal antibodies raised against peptides are useful tools to identify the role of these bioactive peptides in pancreatic exocrine secretion and cell proliferation.

Cholinergic and adrenergic control of enzyme secretion in isolated rat pancreas

While cholinergic nervous control of pancreatic enzyme secretion is well documented, data concerning adrenergic regulation of the exocrine pancreas are contradictory. In the present study we attempted to elucidate the direct action of adrenergic stimulation on pancreatic enzyme secretion. Rat pancreatic segments were set up in an organ bath and superfused with modified Krebs-Henseleit solution. Electrical field stimulation (EFS) stimulated amylase release from the segments. This stimulation was subject to inhibition with atropine up to 80%. Atropine-resistant enzyme discharge in response to EFS could be blocked by propranolol. Cholinergic agonist urecholine-induced amylase release was completely blocked by atropine. Noradrenaline (NA) exhibited a biphasic effect on amylase release. It inhibited the urecholine-induced amylase release in lower concentrations (10(-8)-10(-7) M), while it stimulated basal enzyme secretion in higher concentrations (10(-5)-10(-4) M). The inhibitory effect was mimicked by phenylephrine and completely prevented by prazosin. Isoprenaline concentration dependently enhanced, while clonidine and guanfacine did not affect amylase discharge. In conclusion, in rat pancreatic acinar tissue it seems likely that acetylcholine is the main neurotransmitter. Adrenergic action can be dual, inhibitory via alpha 1-adrenoceptors or stimulatory via beta-adrenoceptors on amylase secretion.

Role of gastrin-releasing peptide in neural control of pancreatic exocrine secretion.

We studied the effect of electrical stimulation of the vagus nerves on the exocrine secretion of isolated perfused porcine pancreas before and after procedures that almost completely blocked the effects elicited by infusions of gastrin-releasing peptide (GRP): desensitization of the pancreas for GRP (by perfusion with high concentrations of GRP); administration of an antagonist of GRP action [D-Arg1, D-Pro2, D-Trp7,9, Leu11)-substance P]; and perfusion with Fab fragments of antibodies against GRP. Both desensitization and antagonist administration significantly (p less than 0.01) inhibited the effect of vagus stimulation on pancreatic protein secretion (by 42.1 and 33%). The inhibitory effect of anti-GRP perfusion was less pronounced (22% inhibition, 0.05 greater than p less than 0.1). The results support the notion that pancreatic, GRP-producing nerve fibers are involved in the neural control of pancreatic enzyme secretion.

Role of cholecystokinin in the negative feedback control of pancreatic enzyme secretion in conscious rats

Using a specific radioimmunoassay for cholecystokinin (CCK) we have studied the relation between circulating CCK concentrations and the feedback regulation of pancreatic enzyme secretion in conscious rats. Recirculation of diverted bile-pancreatic juice into the duodenum or intraduodenal perfusion of trypsin during biliary-pancreatic juice diversion produced basal output of amylase and trypsin and low portal CCK levels (<10 pmol/L). Biliary-pancreatic juice diversion or inactivation of trypsin caused increased CCK concentrations (peak values 50–100 pmol/L) and enzyme outputs. During biliary-pancreatic juice diversion, infusion of the CCK receptor antagonist proglumide suppressed the enzyme response without altering the increase in CCK. Measurement of portal and peripheral CCK during biliary-pancreatic juice diversion yielded values of 131 ± 37 and 32 ± 5 pmol/L, respectively. The peripheral CCK levels corresponded to concentrations achieved during exogenous CCK-8 infusion which resulted in similar enzyme outputs. Gel chromatography of portal plasma during diversion of biliary-pancreatic juice revealed one peak of CCK corresponding to CCK-8, and a larger peak eluted between CCK-33 and CCK-8, probably representing CCK-22. Similar CCK components were found in water extracts of jejunal mucosa, whereas the acetic acid extracts mainly contained CCK-33/39. We conclude that the negative feedback regulation of pancreatic enzyme secretion in rats is mediated by the release of CCK from the intestine and that the major molecular form of CCK in plasma is probably CCK-22.

Contraindication for osmotic mini-pump in the abdominal cavity to study muscarinic cholinergic control of pancreatic enzyme secretion and muscarinic receptors

Alzet mini-pumps were used to study modulation of rat pancreatic muscarinic receptors and the acinic secretory response to long-term N-methylscopolamine (NMS) treatment. Infused intraperitoneally (i.p.), NMS, 25 mg.kg-1.day-1 for 14 days, resulted in a shift to the left in the amylase dose-response curve to carbamylcholine (Cch) and an increase in receptor concentration compared to saline-infused group. Compared to previously published control data [4,5] the saline-infused group exhibited desensitization with increased EC50 for secretion. An alternative mode of saline treatment, subcutaneous (s.c.) infusion showed normal pancreatic secretory response. Desensitization by i.p. saline infusion was prevented by NMS infusion. In conclusion, a foreign body such as a mini-pump in the abdominal cavity can cause desensitization of the pancreatic secretory function under neural cholinergic control.

Stimulation of Pancreatic Enzyme Secretion by a Peptide Purified from Rat Bile-Pancreatic Juice

We purified a peptide from rat pancreatic juice that enhances pancreatic enzyme secretion in a manner different from that of exogenous trypsin inhibitors, such as soybean trypsin inhibitor, when it is infused into the rat intestine. In this paper, we present evidence for the release of gut hormone(s) into the blood of rats after intestinal administration of the peptide. In the presence of atropine, an anesthetized rat small intestine was washed out with saline containing soybean trypsin inhibitor (Kunitz type) to eliminate proteases. Under these conditions, the rat small intestine was divided into four equal parts by ligation. Administration of the peptide into the first quarter of the small intestine stimulated pancreatic enzyme secretion. However, administrations into the more distal parts did not stimulate the enzyme secretion. Moreover, intravenous injection of 1 mL of plasma from rats in which the peptide had been infused into the duodenum caused stimulation of pancreatic enzyme secretion in the recipient rats. It was suggested that the purified peptide acts in the proximal small intestine and that it stimulates the release of gut hormone(s) into the blood to enhance pancreatic enzyme secretion. These findings support the hypothesis that the peptide we purified is responsible in part for the humoral control of pancreatic enzyme secretion in the response to food intake.

Elevated plasma cholecystokinin concentrations in exocrine pancreatic atrophy in the rat.

Rats were fed with a copper-deficient diet combined with penicillamine to produce an atrophy of the exocrine pancreas by selective destruction of the acinar cells, which are replaced by fat cells. Plasma cholecystokinin (CCK) concentrations in animals with exocrine pancreatic atrophy were 250% higher compared to control animals (21.7 +/- 7.8 vs. 6.1 +/- 1.07 pmol/l; p less than 0.001). Plasma concentrations of gastrin were significantly decreased by 44% and of gastric inhibitory polypeptide (GIP) significantly increased by 24%, while the decrease of the plasma insulin did not reach the level of significance. In the proximal duodenum a significant decrease of the CCK concentration could be observed, whereas tissue concentrations of GIP in duodenum and jejunum and gastrin in the gastric antrum remained unaltered. These data suggest that the negative feedback control of pancreatic enzyme secretion is mediated by the release of CCK.

Progress and future needs for research in soya protein utilization and nutrition

AbstractAlthough soya protein was clearly recognized as an essential part of the diet in the Orient centuries ago, its acceptance in the western world has been slow and recent. Progress in utilization has revolved around solving problems of flavor, nutrition and functionality, and has resulted in commercial development of flours and grits, concentrates, isolates, textured products, cereal‐soya blends and beef‐soya blends. Among the latter two developments, cereal‐soya blends established the principle of using soya to increase protein content and quality of cereal diets consumed in many countries, and beef‐soya blends demonstrated the usefulness of soya in extending expensive meat supplies. Governmental actions such as approval of soya in school lunches and in military diets in the U.S. have also contributed to progress in utilizing soya protein in foods. Future research needed to increase food uses of soya protein includes: further improvement in flavor, greater versatility in functional properties, development of new foods rather than simulation of traditional items, and elaboration of adequate methods for determining soya proteins in regulated products. Highlights in soya protein nutrition research include: discovery of the need for moist heat treatment to develop maximal nutritive value; establishment of methionine as the first limiting amino acid; isolation and characterization of trypsin inhibitors; determination that trypsin inhibitor retards growth and causes pancreatic hypertrophy; discovery of negative feedback control of pancreatic enzyme secretion; and demonstration of apparent adequacy of soya proteins in meeting protein requirements of young children and adults. Further nutritional research is needed in the following areas: long‐term studies with humans to determine protein quality as well as possible needs for fortification with vitamins and minerals; establishment of need or lack of need for supplementation with methionine; mechanism of action trypsin inhibitors when ingested from soya and other sources; and development of rapid methods for measuring protein quality.

Effects of ionophore A23187 on calcium flux and amylase release in isolated mouse pancreatic acini

The divalent cation ionophore A23187 has been used extensively to demonstrate the importance of Ca 2+ in the control of pancreatic enzyme secretion. The relative importance, however, of the ability of the ionophore to facilitate Ca 2+ movement across plasma and intracellular membranes in the stimulation of amylase release is not clear. We therefore studied these relationships in isolated pancreatic acini, a preparation in which it is possible to precisely measure both 45Ca 2+ fluxes, Ca 2+ content and amylase release. A23187 increased the initial rates of both 45Ca 2+ uptake and washout. In addition, the content of both exchangeable 45Ca 2+ and total Ca 2+ were reduced. These results indicated, therefore, that A23187 increases Ca 2+ fluxes across both plasma and intracellular membranes. Consistent with this observation, the initial stimulation of amylase release by A23187 was independent of extracellular Ca 2+. In the absence of extracellular Ca 2+, however, A23187 caused a rapid fall in acinar Ca 2+ and subsequent amylase release was abolished. Depletion of intracellular Ca 2+ by the ionophore also blocked the subsequent stimulation by cholecystokinin (CCK). The results indicate certain similarities in the actions of A23187 and CCK on pancreatic acini; both the agonists have striking effects on intracellular Ca 2+ which in turn mediates their actions.

Muscarinic Receptors of the Pancreas: a Correlation between Displacement of (&lt;sup&gt;3&lt;/sup&gt;H)-Quinuclidinyl Benzilate Binding and Amylase Secretion

(3H)-quinuclidinyl benzilate [(3H)-QNB], A potent muscarinic antagonist, was used as a tool to reveal the presence of muscarinic receptors in rat pancreas. Binding assays were performed on a 49,000 g pellet. Known muscarinic antagonists and agonists were used for competition assays on (3N)-QNB binding and studies on amylase secretion in vitro. A correlation was established between the binding assays and the studies on amylase release which suggests that the binding sites and those involved in the cholinergic control of pancreatic enzyme secretion are similar.

Control of pancreatic enzyme secretion: A critique on the role of calcium

Secretion of digestive enzymes by the exocrine pancreas is thought to be initiated by a rise in cytosol Ca 2+ activity. It is not yet clear whether influx of extracellular calcium or release of calcium from an intracellular site is responsible for this event. Review of the literature provides evidence that both extracellular and intracellular calcium regulate secretion and that under different circumstances each may be an important source of ‘messenger’ calcium.

Chronic and acute studies indicating absence of exocrine pancreatic feedback inhibition in dogs.

Chronic administration of raw soybean flour containing active trypsin inhibitor to dogs reduced the pancreatic output of trypsin and chymotrypsin in response to cholecystokinin. Dogs stimulated by a meat meal showed no consistent alteration in the output of trypsin and chymotrypsin when given additional duodenal infusions of trypsin and chymotrypsin, or canine pancreatic juice, or ovalbumin trypsin inhibitor. Two dogs, whose pancreas was stimulated by intraduodenal infusion of amino acids, showed no consistent change when trypsin, or trypsin together with trypsin inhibitors, or trypsin together with canine pancreatic juice was infused concurrently into the duodenum. These results indicate that feedback control of pancreatic enzyme secretion, of the type proposed on the basis of studies similar to the present in rats, does not exist in dogs.

Protein, as a regulator of pancreatic enzyme secretion in the rat.

SummaryPancreatic enzyme secretion was studied in conscious, recovered rats with bile-pancreatic juice collected directly via a cannula. When bile-pancreatic juice was collected and continuously returned to the intestine, introduction of protein evoked a marked increase in enzyme secretion, while protein hydrolysates were not effective stimulants. Diversion of bile-pancreatic juice, or introduction of soybean trypsin inhibitor, resulted in very large increases in enzyme secretion. The results support the concept of negative feedback control of pancreatic enzyme secretion, and it is proposed that protein stimulates increased pancreatic enzyme secretion by reducing feedback inhibition produced by trypsin and chymotrypsin in the intestine.The authors express their thanks to Raul Reyes for his technical assistance.

Effect of insulin on pancreatic amylase and chymotrypsinogen

This review article has primary objective to summarize pancreatic research which has been done in our laboratory since 1965, the first year of the author's registration in the Ph.D. program at the University of Sherbrooke (Canada). It covers the following major topics of pancreatic physiology: controls of pancreatic adaptation to diet, control of pancreatic enzyme secretion, control of pancreatic enzyme synthesis, control of pancreatic growth, intracellular events stimulated during pancreatic growth, pancreas regeneration after pancreatitis and pancreatectomy, the pancreatic cholecystokinin receptor types 1 and 2, growth control and cell signaling in pancreatic cancer cells and finally, cystic fibrosis.