Effect of digested protein on pancreatic exocrine secretion and gut hormone release in the dog

The hormonal mechanisms mediating protein-stimulated pancreatic exocrine secretion were investigated in four conscious dogs with gastric cannulas and Thomas duodenal cannulas. Pancreatic juice was collected by direct cannulation of the main pancreatic duct in response to intraduodenal infusates prepared with cooked beef liver. When the homogenized liver was administered intraduodenally, cholecystokinin (CCK) in plasma significantly increased. This increase was accompanied by a significant increase in pancreatic exocrine secretion, including volume, bicarbonate, and protein output. The liver homogenate incubated with pancreatic enzymes further increased both plasma CCK and exocrine pancreatic secretion. However, plasma secretin was not affected by the protein digests. Intravenous administration of loxiglumide at the rate of 5.0 and 10.0 mg/kg/h resulted in a significant decrease in the stimulated pancreatic secretion of fluid, bicarbonate, and protein. The study indicates that endogenous CCK released by protein digests exerts not only enzyme secretion but also bicarbonate secretion in dogs.

Effect of [(CH2NH)4,5]secretin on pancreatic exocrine secretion in guinea pigs and rats

[psi 4,5]Secretin was shown to be a secretin receptor antagonist that inhibits secretin-stimulated increase in adenosine 3',5'-cyclic monophosphate in isolated pancreatic acini of the guinea pig. To determine whether it inhibits pancreatic exocrine secretion in vivo, we have studied the effect of [psi 4,5]secretin on the pancreatic secretion stimulated by secretin in anesthetized guinea pigs and rats. In basal state, [psi 4,5]secretin given intravenously for 2 or 3 h in varying doses of 1.6-32.7 nmol.kg-1.h-1 dose dependently increased pancreatic secretion of both fluid and bicarbonate during the 1st h, but it returned gradually to basal level within 2 or 3 h. On the other hand, [psi 4,5]secretin significantly inhibited the pancreatic secretion stimulated by either exogenous or endogenous secretin in a dose-related manner. The inhibitory effect of [psi 4,5]secretin in guinea pigs was greater than that in rats. However, it did not completely block the secretin-stimulated pancreatic secretion, whereas a rabbit antisecretin serum suppressed it completely. We conclude that 1) in the unstimulated state, [psi 4,5]secretin is a partial agonist of pancreatic exocrine secretion of both fluid and bicarbonate; and 2) when pancreatic secretion is stimulated by secretin, unlike an antisecretin serum, it is a partial inhibitor in intact guinea pigs and rats.

Role of secretin in negative feedback regulation of postprandial pancreatic secretion in dogs

BACKGROUND

A negative feedback regulation of pancreatic exocrine secretion has been observed in fasting rats, pigs, and humans, but this phenomenon could not be found in fasting dogs. The aims of the present study were to investigate whether or not postprandial pancreatic secretion is regulated by a negative feedback mechanism and to determine if the mechanism is mediated by secretion and/or cholecystokinin (CCK) in dogs.

METHODS

In eight dogs prepared with gastric and Herrera's pancreatic cannulas, pancreatic juice was collected for 3 hours after feeding a mixed meal to measure volume, bicarbonate, and trypsin output. Peripheral venous blood was obtained to determine plasma immunoreactive secretin and CCK levels. Four groups of experiments were performed while pancreatic juice was diverted from the duodenum: (1) diversion of pancreatic juice alone, (2) intraduodenal infusion of fresh pancreatic juice while pancreatic juice was diverted, (3) intraduodenal infusion of 150 mg/h of trypsin and 300 mg/h of chymotrypsin, and (4) intraduodenal infusion of 0.1 mol/L NaHCO3.

RESULTS

Pancreatic secretion during diversion of pancreatic juice was significantly greater than that obtained while pancreatic juice was returned. Diversion-induced pancreatic hypersecretion was significantly suppressed by intraduodenal administration of pancreatic proteases, but it was not influenced significantly by 0.1 mol/L NaHCO3. The suppression by either pancreatic juice or proteases paralleled the decrease in plasma secretin response, whereas the CCK response remained unchanged. The inhibitory effect of pancreatic proteases on pancreatic secretion was blocked by a physiological dose of exogenous secretin, 0.06 clinical U.kg-1.h-1.

CONCLUSIONS

In dogs, postprandial pancreatic secretion is controlled by a negative feedback mechanism mediated mainly by the release of secretin, but not by CCK.

A physiological role of peptide YY on exocrine pancreatic secretion in rats

BACKGROUND

Peptide YY (PYY) given intravenously was shown to inhibit pancreatic exocrine secretion both in the dog and the rat. However, a possible physiological role of PYY on the pancreatic secretion has not been clarified. The present study was undertaken to investigate its physiological role on the exocrine pancreas.

METHODS

In conscious rats, plasma PYY was determined in response to oral ingestion of a 6-mL meal and intravenous infusion of PYY; small intestinal transit time was measured by phenol red as a nonabsorbable marker, and pancreatic secretory studies were performed in rats with pancreatic fistulas and jugular vein catheters.

RESULTS

Oral ingestion of the meal (containing phenol red, 1.6 mg/100 mL) significantly increased plasma PYY within 30 minutes. During this period, most (97%) of the phenol red was detected in the proximal two-thirds of the small intestine. Intravenous infusion of PYY in 25, 50, and 100 pmol.kg-1 x h-1 produced a dose-dependent increase in plasma PYY. The dose of PYY that simulated the peak postprandial level was 50 pmol.kg-1 x h-1, and this dose of PYY significantly inhibited the pancreatic secretion stimulated by physiological doses of secretin and cholecystokinin-8 (CCK-8). After the meal, pancreatic secretion of bicarbonate and protein significantly increased in rats pretreated with normal rabbit serum, whereas this increase was significantly augmented in rats pretreated with an anti-PYY serum because the postprandial increase in plasma PYY was abolished.

CONCLUSIONS

PYY plays a regulatory role in the postprandial pancreatic exocrine secretion in rats.

Multistage enhancement of surface recordings of canine gastric electrical signals

This article describes a multistage signal processing scheme to enhance the quality of canine gastric signals recorded from the abdominal surface. The scheme involves a cascade application of linear prediction followed by a nonlinear processing known as alpha-TM filtering. The linear prediction is used to separate, in the minimum mean square error sense, the slow wave from other uncorrelated interference signals. We make novel use of the order versus frequency response characteristics of linear predictors to achieve this separation. The nonlinear filtering is used to suppress the residual wide band impulsive noise. Our studies have indicated that such an optimized signal enhancement scheme produces a clean time domain signal, which is easy to interpret visually. It not only preserves the periodicity of the slow wave, but also seems to track any irregularities in the periods. We believe that this last feature, namely the potential to track nonstationarities in the signal, is the main contribution of our approach.

Characterization of secretin release in secretin cell-enriched preparation isolated from canine duodenal mucosa

The release of secretin was studied in secretin cell-enriched preparations isolated from canine duodenal mucosa. The crude enterocytes were isolated by treating the duodenal mucosa sequentially with collagenase and ethylenediaminetetraacetic acid. Secretin cell-enriched fraction was prepared by centrifugation of the crude enterocytes in a counterflow elutriation rotor to obtain a final preparation containing 3.2 +/- 0.3 pmol/10(6) cell of immunoreactive secretin, which was 13-fold greater than the crude cell preparation (N = 5). The cells were incubated in Hanks' balanced salt solution for 20 min at 37 degrees C under 95% O2/5% CO2 before adding various agents and further incubated for various periods of time. The amounts of secretin released into the medium and retained by the cells were then determined by a specific radioimmunoassay. The release of immunoreactive secretin was increased dose-dependently over the control by dibutyryl cyclic-3',5'-adenosine monophosphate, forskolin, 4 beta-12-O-tetradecanoylphorbol-13-acetate, the synthetic serine protease inhibitor, camostat, and the calcium ionophore, A23187. The effects of forskolin, the phorbol ester, and A23187 were time-dependent and not observed at 4 degrees C. The release of immunoreactive secretin was also stimulated by KCl in high concentration and by sodium oleate. The effect of A23187 was abolished in a Ca(2+)-free medium, while those of dibutyryl cyclic-3',5'-adenosine monophosphate and forskolin were potentiated by 3-isobutyl-1-methylxanthine, which did not have a significant effect when added alone. These results indicate that the release of secretin is regulated by both Ca(2+)- and cyclic-3',5'-adenosine monophosphate-dependent mechanisms.2+ release.

Enterohepatic circulation is essential for regular cycling of duodenal migrating motor complexes in dogs

The role of enterohepatic circulation and specific bile acids in the initiation and caudad migration of duodenal migrating motor complexes (MMCs) was investigated in conscious dogs. All dogs had spontaneous duodenal MMCs that migrated to the terminal ileum when bile flow was intact. During the first 3 days after total external biliary diversion, no MMCs originated in the duodenum. Instead, all MMCs originated in the jejunum and migrated to the ileum. During the next 4 days of total external biliary diversion, 81% of the MMCs originated in the jejunum and 19% in the duodenum. When normal bile flow was restored after 9 days of total external biliary diversion, regular duodenal MMCs resumed after a delay of 126 +/- 27 minutes. Perfusion of individual bile acids or dogs' own bile, but not saline or alkaline solution, into the duodenum or perfusion of dogs' own bile directly into the ileum during total external biliary diversion restarted duodenal MMCs with a time lag of about 2 hours. The authors conclude that intact enterohepatic circulation is essential for the initiation of regular duodenal MMCs.

Identification of a transcriptional enhancer important for enteroendocrine and pancreatic islet cell-specific expression of the secretin gene

It is well established that the gene encoding the hormone secretin is expressed in a specific enteroendocrine cell, the S cell. We now show that the secretin gene is transiently expressed in insulin-producing B cells of the developing pancreatic islets in addition to the intestine. Furthermore, secretin is produced by most established islet cell lines. In order to identify and characterize the regulatory elements within the secretin gene that control tissue-specific expression, we have introduced secretin reporter gene constructions into the secretin-producing HIT and STC-1 cell lines as well as the nonexpressing INR1-G9 glucagonoma line. Analysis of deletion mutants revealed that sequences between 174 and 53 bp upstream from the transcriptional start site are required for maximal expression in secretin-producing cells. This positive element functioned independently of position and orientation. Further deletions into the enhancer resulted in a stepwise loss of transcriptional activity, suggesting the presence of several discrete control elements. The sequence CAGCTG within the secretin enhancer closely resembles that of the core of the B-cell-specific enhancer in the insulin gene. Point mutations introduced into this putative element led to greater than 85% reduction in transcriptional activity. Gel mobility shift assays suggested that a factor in B cells closely related or identical to proteins that bind to the insulin enhancer interacts with the CAGCTG motif in the secretin gene.

Neurohormonal mechanism of pancreatic exocrine secretion stimulated by sodium oleate and L-tryptophan in dogs

In the present investigation, we have studied the effect of atropine on the pancreatic secretion stimulated by intraduodenal administration of either sodium oleate or exogenous cholecystokinin (CCK). In four dogs prepared with gastric and Thomas duodenal cannulas, pancreatic juice was collected for measurement of volume, bicarbonate, and protein output, and peripheral venous blood samples were obtained for radioimmunoassay of both secretin and CCK. Volume, bicarbonate, and protein output of the pancreatic juice increased significantly in response to sodium oleate (1-4 mmol/h) in a dose-dependent manner. The increase in pancreatic secretion paralleled the increments in both plasma CCK and secretin. Atropine given intravenously suppressed completely both pancreatic secretion and release of CCK stimulated by sodium oleate, whereas the release of secretin was not affected. Pancreatic secretion was significantly increased in a dose-dependent manner by exogenous CCK octapeptide (CCK-8) at 16, 32, and 64 micrograms (14, 28, and 56 pmol).kg-1.h-1. Atropine inhibited protein output only partially, but it did not influence bicarbonate output. In five additional dogs, the effect of atropine on L-tryptophan-stimulated pancreatic secretion was studied. Interestingly, atropine failed to influence the CCK release and pancreatic secretion of volume and bicarbonate, except for protein secretion, which was significantly inhibited. It was shown previously that atropine inhibited significantly the pancreatic secretion of bicarbonate stimulated by secretin in physiological doses. Thus we conclude that the inhibition by atropine of the pancreatic exocrine secretion stimulated by sodium oleate is mediated by both suppression of CCK release and inhibition of action of secretin on the exocrine pancreas.(ABSTRACT TRUNCATED AT 250 WORDS)

Mediation of trypsin inhibitor-induced pancreatic hypersecretion by secretin and cholecystokinin in rats

We investigated a hormonal mechanism in a trypsin inhibitor-induced pancreatic hypersecretion in rats. Intraduodenal administration of a synthetic trypsin inhibitor, camostat, resulted in significant increases in plasma concentration of both secretin and cholecystokinin in a dose-related manner that paralleled a significant increase in exocrine pancreatic secretion. To eliminate the effect of circulating secretin in rats, a rabbit antisecretin serum was given IV that resulted in a 77% reduction in bicarbonate secretion stimulated by intraduodenal camostat. A cholecystokinin receptor antagonist, MK-329, also inhibited significantly the camostat-induced increase in pancreatic secretion; volume and bicarbonate output were reduced by 35% each and amylase output by 73%. The combined administration of antisecretin serum and MK-329 completely abolished the pancreatic exocrine secretion stimulated by camostat. These observations indicate that the camostat-stimulated pancreatic exocrine secretion is mediated by the increased release of both secretin and cholecystokinin in rats.

Release of cholecystokinin and secretin by sodium oleate in dogs: molecular form and bioactivity

The release of cholecystokinin (CCK) and secretin into both circulation and duodenal lumen, after intraduodenal perfusion with sodium oleate or oral ingestion of fat, was studied in anesthetized and conscious dogs, respectively. Intraduodenal infusion with sodium oleate (4 mmol.kg.-1.h-1, pH 9.5) in anesthetized dogs with diversion of bile and pancreatic juice stimulated the release of both CCK and secretin not only into the circulation but also into the duodenal lumen. The concentration of CCK and secretin in the luminal perfusate increased from 0.2 +/- 0.1 to 2.1 +/- 0.4 nM and 0.34 +/- 0.16 to 2.59 +/- 0.63 nM, respectively. Intraduodenal infusion of NaHCO3 solution at pH 9.5 did not result in release of either hormone. Luminal release of both hormones was also observed by intraduodenal infusion of sodium oleate in the dogs without diversion of bile and pancreatic juice, albeit at lower concentrations than those released in the dogs with diversion. Analysis of the molecular form of luminal secretin by gel filtration, ion-exchange chromatography, and high-performance liquid chromatography showed only a single form of secretin with molecular size, hydrophobicity, and charge similar to those of natural porcine secretin. In contrast, multiple forms of CCK were released into both circulation and duodenal lumen with CCK-58 as the predominant form. In conscious dogs, CCK-58 was also found to be the predominant form of CCK released into the circulation after oral ingestion of fat.(ABSTRACT TRUNCATED AT 250 WORDS)

The secretin gene: evolutionary history, alternative splicing, and developmental regulation

The gene encoding the hormone secretin has been isolated and structurally characterized. The transcriptional unit is divided into four exons spanning 813 nucleotides. Comparison of the rat secretin gene to the other members of the glucagon-secretin gene family reveals that similarities are restricted to the exons encoding the biologically active peptides. Analysis of RNA from porcine intestine indicates that at least two transcripts are generated from the porcine secretin gene as a result of differential splicing. The longer and more abundant transcript appears to be identical to a previously isolated cDNA, which encodes a precursor that includes a 72-amino acid C-terminal extension peptide. The shorter transcript does not contain the third exon and, as a result, encodes only 44 residues beyond the C terminus of secretin. The amino acid sequence deduced from the shorter transcript is identical to a precursor form of secretin recently isolated from porcine duodenum [Gafvelin, G., Jornvall, H. & Mutt, V. (1990) Proc. Natl. Acad. Sci. USA 87, 6781-6785]. Developmental studies reveal that both secretin mRNA and peptide levels in the intestine are highest just before birth, prior to the onset of gastric acid secretion and feeding. This observation implies that secretin biosynthesis in developing animals is controlled independently of the principal factors known to regulate secretin release in adult animals.

[Ulcerous disease of endocrinal origin caused by a non-gastric substance]

The purpose of this paper is to report on a form of duodenal ulceration associated with a major hypersecretion that we described in 1984. This entity belongs to the group of endocrine duodenal ulcer diatheses of which the Zollinger-Ellison Syndrome (ZES) is the prototype. We have recently in 1989 reported a series of patients with clinical and pathologic features indistinguishable from those of the Zollinger-Ellison syndrome but without hypergastrinemia. We have also found that the plasma and the tumor tissues of these patients contains a potent non-gastrin secretagogue.

Regulation of pancreatic exocrine secretion

The exocrine pancreas secretes throughout 24 hours. In both interdigestive and postprandial states, pancreatic secretion is regulated by neural and hormonal actions, and neurohormonal interactions. At the turn of this century, the prevailing theory of Pavlov (1) that pancreatic exocrine secretion was exclusively regulated by secretory fibers in both vagi and splanchnic nerves was refuted by Bayliss and Starling in 1902, who put forward their hypothesis that pancreatic secretion was stimulated by a circulating hormone, "secretin," which was released by hydrochloric acid from the duodenal mucosa (2). Soon, Pavlov conceded to the hypothesis of Bayliss and Starling. Pavlov adopted the theory of a dual mechanism--nervous and hormonal--of the regulation of pancreatic secretion. In recent decades, explosions of new information about old and newly discovered gut hormones or peptides and neuropeptides have resulted in a better understanding of the regulatory mechanism of the exocrine pancreas, and also opened new, exciting frontiers in the investigations of the physiology and pathophysiology of pancreatic secretion.

Mechanism of oleic acid-induced inhibition on gastric acid secretion in rats

We investigated the existence of an enterogastrone in rats induced by duodenal administration of oleic acid. Acid secretion by the luminally perfused stomach was stimulated in anesthetized rats by intravenous infusion of 0.3 micrograms.kg-1.h-1 pentagastrin. Intraduodenal administration of 3 mmol of oleic acid produced a profound inhibition (94%) of pentagastrin-stimulated acid output in 10 rats (P less than 0.01). Of several peptides in plasma including secretin, neurotensin, somatostatin, and peptide YY, only secretin was found to increase significantly (P less than 0.001). A similar degree of inhibition of acid output (93%) was caused by porcine secretin, 5.6 pmol.kg-1.h-1, given intravenously to mimic the plasma level of secretin produced by oleic acid infusion. The inhibitory effect of oleic acid on the acid secretion was completely reversed by intravenous injection of a rabbit antisecretin serum but not by a normal rabbit serum. These observations strongly suggest that the inhibition was mediated via circulating secretin. The inhibition produced by either oleic acid or secretin was completely blocked by indomethacin. The blocking action was completely reversed by intravenous administration of 48 micrograms.kg-1.h-1 prostaglandin E2. We conclude that endogenous secretin is a major enterogastrone released by oleic acid in anesthetized rats and that the inhibitory action of secretin requires endogenous prostaglandins.

Role of cholecystokinin in pancreatic bicarbonate secretion in dogs

We investigated the effects of endogenous and exogenous cholecystokinin (CCK) on pancreatic exocrine secretion, in particular that of bicarbonate. In six dogs prepared with gastric cannulas and Thomas duodenal cannulas, intraduodenal administration of corn oil (Lipomul) incubated with hog pancreatic enzymes significantly increased pancreatic secretion of both bicarbonate and protein. Increase in pancreatic secretion of both bicarbonate and protein was accompanied by the increase in plasma CCK concentration. However, the increase in bicarbonate as well as protein secretion was blocked by proglumide, a CCK antagonist, given intravenously. In contrast, intraduodenal infusion of undigested Lipomul failed to stimulate the pancreatic exocrine secretion or release of endogenous CCK. These observations indicate that endogenous CCK plays an important role in secretion of both bicarbonate and protein stimulated by digested corn oil. In a group of four dogs with pancreatic fistulas, intravenous infusion of CCK potentiated the stimulatory effect of secretin on pancreatic bicarbonate secretion. The stimulatory effect as well as potentiating effect of CCK on pancreatic bicarbonate secretion was blocked by infusion of proglumide. We conclude that endogenous CCK plays a significant role in fat-stimulated pancreatic secretion, and it is apparent that both endogenous CCK and secretin are equally important for stimulation of pancreatic bicarbonate secretion, which results from potentiation of the action of the two hormones.

Role of secretin in basal and fat-stimulated pancreatic secretion in conscious rats

The role of endogenous secretin in basal and fat-stimulated pancreatic exocrine secretion was investigated in conscious rats. Rats were prepared with chronic fistulas draining bile and pancreatic juice, which was collected and returned to the duodenum at all times. Six days postoperative rats were fasted overnight, and pancreatic protein and fluid secretion were monitored for 3 h under basal conditions (0.15 M NaCl, intraduodenally) and during 2 h of intraduodenal infusion of a 20% triglyceride emulsion (Liposyn). Solutions were infused at 4.6 ml/h. Rats received a single bolus injection of 0.1 ml antisecretin serum or normal rabbit serum starting in the second hour of the basal period, and the effect on basal and fat-stimulated pancreatic protein and fluid secretion was determined. Antisecretin serum significantly inhibited basal interdigestive pancreatic protein and fluid secretion by 43% and 36%, respectively. Infusion of 20% fat emulsion stimulated a 2.1-fold increase in pancreatic protein and fluid secretion. The stimulation of both protein and fluid secretion was significantly inhibited by 60% by antisecretin serum. Plasma secretin after 2 h of fat infusion was 17.7 +/- 1.8 pM and was greatly reduced by the presence of secretin antiserum. The results support the hypothesis that secretin released by fatty acids is an important mediator of the pancreatic protein and fluid secretory response to dietary fat in the rat.

Hormonal mechanism of sodium oleate-stimulated pancreatic secretion in rats

We have investigated the role of two intestinal hormones, secretin and cholecystokinin (CCK), on the pancreatic exocrine secretion stimulated by sodium oleate in anesthetized rats. Each rat was prepared with a polyethylene tube in the proximal duodenum and ligation of the pylorus. To collect pancreatic juice, the common bile-pancreatic duct was cannulated near the duodenal wall while bile was diverted to the exterior. Intraduodenal infusion of sodium oleate at doses of 0.03, 0.06, 0.12, and 0.24 mmol/h resulted in significant increases in pancreatic secretion including fluid, bicarbonate, and protein output. The increases of the three parameters were dose dependent and were correlated well with the increases in plasma secretin and CCK concentrations. To further clarify their hormonal roles, we have repeated identical experiments under intravenous administration of a rabbit anti-secretin serum (0.1 ml) or CR 1409 (4 mg.kg-1.h-1), a CCK-receptor antagonist, or a combination of both the antiserum and CR 1409. The antiserum significantly suppressed volume flow and bicarbonate secretion with a minor inhibitory effect on protein secretion, whereas a normal rabbit serum did not. CR 1409 significantly suppressed all three parameters. The combined treatment with both the antiserum and CR 1409 almost completely abolished the pancreatic secretion. Atropine given intravenously significantly inhibited the protein output but did not influence volume flow or bicarbonate output in response to sodium oleate. We thus conclude that, in rats, fat-stimulated pancreatic secretion of volume flow and bicarbonate depends entirely on the circulating endogenous secretin and CCK but that the protein output appears to be under control of both hormonal and cholinergic controls.

Mechanism of acid-induced release of secretin in rats. Presence of a secretin-releasing peptide

In fasting rats, intraduodenal infusion of dilute hydrochloric acid results in significant increases in both pancreatic exocrine secretion and plasma concentration of secretin. To test the hypothesis that acid-induced release of secretin is mediated by a secretin-releasing factor (S-RF), anesthetized rats were prepared with pyloric ligation, duodenal and jejunal cannulas, and pancreatic duct cannulas. Donor rats were infused intraduodenally with 0.01 N HCl, 0.15 M NaCl, or a combination of 0.01 N HCl and 0.05 N NaHCO3 at 0.3 ml/min for 1.5 h, and the perfusates were collected via jejunal cannulas. The perfusates with pH adjusted to 6.0 were concentrated threefold and infused into the duodena of recipient rats. The concentrate of acid perfusate (CAP) significantly increased both pancreatic volume flow and bicarbonate output and plasma concentration of secretin, whereas concentrates of the saline perfusate (CSP) or the perfusate of a combination of 0.01 N HCl and 0.05 N NaHCO3 (CABP) did not influence pancreatic secretion or plasma concentration of secretin. The increased pancreatic secretion by CAP was attributed to increased circulating secretin because when secretin was immunoneutralized by a rabbit antisecretin serum, CAP-stimulated pancreatic secretion was abolished. The bioactivity of CAP was trypsin-sensitive and heat stable. The active substance in CAP had a molecular weight of less than 5,000 and greater than 1,000, as determined by ultrafiltration and bioassay. In conclusion, dilute HCl releases an S-RF into the upper small intestinal lumen to stimulate release of secretin. This substance, with molecular weight of less than 5,000, is heat stable and trypsin sensitive. Thus, the acid-stimulated release of secretin is mediated by a secretin-releasing peptide in the upper small intestinal lumen.

A nongastrin malignant ampullary tumor causing gastric acid and pepsin hypersecretion. A case report

We report a case of multiple duodenal ulcers with gastric hypersecretion due to a nongastrin secretagogue produced by a malignant tumor of the pancreas in a 78-year-old man. The case resembled a Zollinger-Ellison syndrome (ZES) with high acid output (basal acid output 27, sham meal-stimulated 37, maximum acid output 47 mEq/h), but with fasting gastrin 43 pg/ml, nonresponsive to secretin. As in ZES, pepsin output was comparatively low, and secretion was inhibitable by atropine (50% inhibited by 1 microM). The tumor removed at surgery contained less than 1 ng gastrin per gram, but was many times more potent than pentagastrin in stimulating acid from a lumen-perfused rat stomach. The tumor also contained cholecystokinin (CCK-8 and CCK-33), motilin, insulin, and somatostatin, which were also present in adjacent normal pancreas; in addition, the tumor contained pancreatic polypeptide and pancreatic cancer-associated antigen. This case represents a rare syndrome due to an as yet undefined peptide secreted by a (frequently malignant) pancreatic endocrine tumor and masquerading as ZES. This is the first report of studies of pepsin secretion and of the effect of atropine, suggesting that the physiologic effects of the secretagogue resemble that of gastrin.

Geranyl-geranyl acetone: a novel stimulant of secretin release in the dog

Geranyl-geranyl acetone (GGA), a new acyclic polyisoprenoid, anti-ulcer drug appears to exert its beneficial effect by stimulating bicarbonate secretion from the stomach and pancreas. Its efficacy in stimulating pancreatic bicarbonate is particularly striking, and this study was designed to examine the mechanism for this action. Since it is structurally similar to the side chain of the prostaglandin molecule, its ability to stimulate bicarbonate secretion could be a direct one. On the other hand, the magnitude of pancreatic bicarbonate response (about 50% of maximal response to secretin) suggests it might act by releasing secretin. Two types of experiments were performed in dogs with pancreatic fistulas: first, secretagogue interactions were examined by studying the effect of intraduodenal GGA (8 mg/kg) or its carrier (control) on the dose-response curves to exogenous secretin and cholecystokinin octapeptide (CCK-8); second, the effect of graded doses of intraduodenal GGA on pancreatic bicarbonate and plasma secretin-like immunoreactivity (SLI) responses was tested directly. Pancreatic bicarbonate responses (micromoles per 30 min) were to secretin doses of 32, 125, and 500 ng/kg/h. Without and with GGA, responses were 74 +/- 27, 952 +/- 215, and 2,000 +/- 425 and 599 +/- 110, 1,624 +/- 472, and 2,129 +/- 398 ng/kg/h, respectively. Similarly, the bicarbonate responses to CCK-8 were augmented. Basal plasma SLI was 1.5 +/- 0.6 pM/ml. Peak plasma SLI in response to 2, 4, and 8 mg of GGA intraduodenally were 6.8 +/- 0.7, 8.9 +/- 3.1, and 19.6 +/- 2.7 pM/ml, respectively. It is concluded that GGA is a potent stimulant of pancreatic bicarbonate secretion, and this action appears to be mediated by the release of duodenal secretin.

Effect of pancreatic proteases on plasma cholecystokinin, secretin, and pancreatic exocrine secretion in response to sodium oleate

The effect of pancreatic proteases or juice on the sodium oleate-stimulated pancreatic secretion and plasma concentrations of secretin and cholecystokinin in anesthetized rats was investigated. Each rat received sodium oleate in a dose of 0.12 mmol.h-1 via a duodenal tube. Sodium oleate infusion significantly increased pancreatic secretion (volume and protein output) compared with the saline given the control group. The increase in pancreatic secretion paralleled significant elevations of plasma concentrations of secretin and cholecystokinin. To determine a possible role of pancreatic proteases on the responses induced by sodium oleate, saline, chymotrypsin, and trypsin, a combination of chymotrypsin and trypsin or pancreatic juice was infused into the duodenum. The pancreatic secretion was significantly reduced by pancreatic proteases or pancreatic juice, and the reduction paralleled the decreases in plasma concentrations of the two hormones. These agents suppressed both pancreatic secretion and plasma hormone levels in the following order of magnitude: (pancreatic juice or chymotrypsin + trypsin) greater than (trypsin) greater than (chymotrypsin). The reduction of pancreatic secretion by pancreatic proteases was reversed by intravenous administration of secretin and cholecystokinin in physiological doses. It is concluded that negative-feedback regulation of pancreatic secretion is operative in the intestinal phase in rats and that both secretin and cholecystokinin are involved in the regulation.

Mechanism of cholecystokinin-induced contraction of the opossum gallbladder

The present study evaluated the mechanism of cholecystokinin-induced gallbladder contraction in awake opossums. Each of 19 chronic animal preparations had an indwelling gallbladder cannula for monitoring changes in gallbladder volume and a jugular catheter for administration of cholecystokinin octapeptide and drugs. An intraduodenal catheter allowed intraduodenal infusion of Isocal (Mead Johnson Laboratories, Evansville, Ind.). Bipolar electrodes in the stomach, duodenum, and jejunum enabled monitoring of the duodenal migratory myoelectric complex cycle. One-hour infusions of cholecystokinin octapeptide (10 ng/kg/min), intraduodenal Isocal (0.4 ml/min), or feeding were started 20 min after cessation of phase 3 duodenal migratory myoelectric complex activity. Bolus intravenous doses of potential pharmacological antagonists were given 10 min before and 20 min after the onset of cholecystokinin octapeptide infusion, Isocal infusion, or feeding. Each test challenge induced about 60% gallbladder emptying at 30 min and 70% at 60 min. Cholecystokinin octapeptide-induced gallbladder emptying was converted to filling by hexamethonium and nearly abolished by atropine. Similar results were obtained for gallbladder emptying induced by feeding or duodenal infusion of Isocal. Phentolamine caused a modest decrease of cholecystokinin octapeptide-induced gallbladder contraction at 30 min, whereas postprandial or Isocal-induced gallbladder contraction was unaffected. Cholecystokinin octapeptide-induced gallbladder contraction was not affected by pirenzepine, 4-diphenylacetoxy-N-methylpiperidine methiodide, prazosin, pyrilamine, cimetidine, methysergide, naloxone, or propranolol. In acute studies of anesthetized animals, gallbladder contraction induced by a D100 intravenous bolus of cholecystokinin octapeptide (800 ng/kg) was not antagonized by hexamethonium, atropine, or tetrodotoxin. It is concluded (a) that cholecystokinin-induced physiologic contraction of the opossum gallbladder occurs through neural mechanisms rather than by a direct action of cholecystokinin on gallbladder smooth muscle, and (b) that studies using pharmacologic bolus doses of cholecystokinin octapeptide and tetrodotoxin indicate that cholecystokinin receptors exist on the gallbladder smooth muscle which do not seem to have any physiological role in gallbladder emptying.

Increased volume and decreased emptying of the gallbladder in large (morbidly obese, tall normal, and muscular normal) people

Impaired gallbladder emptying has been suggested as a possible factor in the pathogenesis of gallstones. Obese people have an increased incidence of gallstones, but there is no evidence of this in nonobese large people. This study was undertaken to determine if abnormal gallbladder motility is present in obese people. Fasting gallbladder volumes were determined using real-time ultrasound in 18 morbidly obese subjects whose weights were in a steady state [45 kg (100 lb) over ideal weight or twice expected weight for age and height; 9 males, 9 females], 18 age- and sex-matched volunteers of average size, and 18 nonobese large normal males (9 tall, 9 muscular). Gallbladder emptying studies with 99mtechnetium-diisopropyliminodiacetic acid were performed using 200 ml of 10% cream as a stimulus. The small-volume liquid fatty meal contained 113indium-diethylenetriaminepentaacetic acid to control for differences in gastric emptying in obesity. The gallbladder emptying rate in large people, both obese and nonobese, was less than that in normals of average size (p = 0.05). Fasting gallbladder volumes in large people were: obese, 41 ml (37-66 ml) (median; 95% confidence limits); nonobese large normal, 40 ml (27-43 ml). These values were greater than in normals of average size [17 ml (14-21 ml) (p = 0.03)]. Postprandial gallbladder volumes were also greater in large people: obese, 15 ml (8-23 ml); nonobese large normal, 20 ml (13-23 ml) compared with 2 ml (1-5 ml) in normals of average size (p less than 0.05). There were no differences between obese and nonobese large people. There were no differences in gastric emptying rates or in cholecystokinin, gastrin, motilin, and secretin release between obese and normal subjects. Gallbladder volume is crudely proportional to body size. Although fasting and postprandial volumes are greater in obesity, this is also present in nonobese, relatively size-matched controls. These data do not support a role for impaired gallbladder emptying in gallstone formation in obese patients whose weights are in a steady state.

An important role of endogenous insulin on exocrine pancreatic secretion in rats

We have investigated a physiological role of endogenous insulin on exocrine pancreatic secretion stimulated by a liquid meal as well as exogenous secretin and cholecystokinin octapeptide (CCK-8) in conscious rats. Each rat was prepared with a chronic pancreatic fistula and an indwelling catheter in a jugular vein. Oral ingestion of a liquid meal (5 ml) resulted in significant increases in pancreatic secretion, including volume, bicarbonate, and amylase output, in these rats. A rabbit anti-insulin serum (1.0 ml) given intravenously completely blocked the postprandial exocrine pancreatic secretion, whereas a normal rabbit serum did not influence the pancreatic secretion in the same rats. When pancreatic secretion was stimulated by intravenous administration of both secretin and CCK-8 in three different doses, including 0.015, 0.03, and 0.06 clinical unit and microgram.kg-1.h-1, respectively, volume, bicarbonate, and amylase output increased significantly in a dose-dependent manner. This increase in pancreatic secretion was also completely blocked by a rabbit anti-insulin serum, whereas it was not influenced by a normal rabbit serum. The amount of the antiserum employed abolished the postprandial increases in plasma insulin concentration. We conclude that endogenous insulin plays an important role on the regulation of postprandial pancreatic secretion in rats. Furthermore, for the stimulatory action of the two intestinal hormones secretin and CCK-8 on the pancreatic exocrine secretion, endogenous insulin is need.