Selective inhibition of pentagastrin- and cholecystokinin-stimulated exocrine secretion by proglumide

Effect of intravenous infusion of proglumide on ruminal motility in conscious sheep (Ovis aries)

The effects of intravenous infusion of proglumide on regular ruminal contractions were examined in conscious sheep using doses that inhibit pancreatic exocrine secretion. After a control period of 20 min, proglumide was infused intravenously for 40 min at a dose of 15, 30 or 60 micromol/kg per min and venous blood was collected. The intravenous infusion of proglumide significantly increased the frequency of ruminal contractions at 15 micromol/kg per min without altering the amplitude, while it significantly decreased the frequency and amplitude of ruminal contractions at 30 and 60 micromol/kg per min in a dose-dependent manner. Proglumide did not increase contractile activity of the omasum, abomasum and duodenum or the plasma concentration of immunoreactive cholecystokinin (CCK). Application of proglumide at 1-30 mmol/L inhibited bethanechol-induced contraction in both longitudinal and circular muscle strips of the dorsal sac of the rumen. These results suggest that proglumide at a low dose acts indirectly on the rumen as a CCK receptor antagonist to increase the frequency of contractions, whereas at higher doses it inhibits cholinergic-induced contraction of the ruminal muscles or acts as an agonist to inhibit contractions in sheep. Hence, proglumide at high doses seems unsuitable for research or therapeutic use as a CCK receptor blockade in sheep.

Gastrin inhibits secretin-induced ductal secretion by interaction with specific receptors on rat cholangiocytes

We assessed the effect of gastrin on ductal secretion in normal and bile duct-ligated (BDL) rats. The effect of gastrin on ductal secretion was examined in the presence of proglumide, a specific antagonist for gastrin receptor (GR). We isolated pure cholangiocytes from normal and BDL rats and assessed gastrin effects on secretin receptor (SR) gene expression and intracellular adenosine 3',5'-cyclic monophosphate (cAMP) levels. We examined the presence of GR mRNA in cholangiocytes by reverse transcription polymerase chain reaction (RT-PCR). In normal or BDL rats, gastrin produced no changes in spontaneous bile secretion. Simultaneous infusion of gastrin inhibited secretin-induced choleresis and bicarbonate output in BDL rats. In the presence of proglumide gastrin did not inhibit secretin-induced choleresis in BDL rats. Gastrin decreased in cholangiocytes from BDL rats 1) SR gene expression and 2) secretin-induced cAMP levels. With the use of RT-PCR, GR mRNA was detected in cholangiocytes. Similar to what is shown for secretin and somatostatin, we propose that the opposing effects of secretin and gastrin on cholangiocyte secretory activity regulate ductal secretion in rats.

Role of endogenous CCK in regulation of interdigestive pancreatic exocrine secretion in sheep (Ovis aries)

The role of endogenous cholecystokinin (CCK) in the regulation of pancreatic exocrine secretion during the interdigestive period was studied in conscious sheep. Intravenous infusion of proglumide (15, 30 and 60 mumol/kg/min) for 70 min significantly decreased flow rate, protein and amylase output in pancreatic juice by 80% at the maximum dose, as well as atropine (10 micrograms/kg/min), without a significant decrease in plasma concentration of immunoreactive CCK. Intravenous injection of CCK (114 pmol/kg) increased the pancreatic secretion during atropine infusion, but not during proglumide infusion. These results suggest that the regulation of interdigestive pancreatic exocrine secretion in sheep depends greatly on endogenous CCK as well as on the cholinergic mechanism.

Perspectives of CCK antagonists in pancreatic research. Part II. Experimental studies

In this article, the effects of different classes of cholecystokinin (CCK) receptor antagonists in CCK-related physiological processes of the pancreas have been discussed. Both glutaramic acid derivatives and natural (benzodiazepine) analogs are potent, competitive antagonists of peripheral CCK receptors. These compounds thus provide a powerful tool for investigating the physiological and pharmacological actions of CCK in the gastrointestinal system, and have already clarified the role of CCK in pancreatic secretion and trophism or growth.

Neuromodulation of guinea pig intestinal electrolyte transport by cholecystokinin octapeptide

We examined the effect of cholecystokinin octapeptide on electrolyte transport across isolated guinea pig mucosa. Segments of distal ileum stripped of longitudinal muscle and bathed on both sides with a Krebs'-bicarbonate buffer responded to cholecystokinin octapeptide when studied under short-circuited conditions. Cholecystokinin octapeptide (0.5-50 nmol/L) evoked a transient (4-10-minute) increase in transepithelial potential difference and short-circuit current upon application to the serosal side. Maximal increases in short-circuit current, achieved at 50-500 nmol/L, were 67 +/- 11 microA/cm2, whereas half-maximal effects occurred at a concentration of 0.7 +/- 0.2 nmol/L. Pretreatment of the tissues with 0.5 mumol/L atropine reduced the maximal short-circuit response to cholecystokinin octapeptide by 53%. The change in short-circuit current due to cholecystokinin octapeptide was nearly abolished by pretreatment with 0.5 mumol/L tetrodotoxin, suggesting neuronal involvement. Cholecystokinin octapeptide-induced increases in short-circuit current were halved by removal of serosal buffer Ca2+ and were abolished in Cl(-)- and HCO3(-)-free buffer. The cholecystokin-receptor antagonists proglumide and lorglumide shifted the concentration-response curve for cholecystokinin octapeptide competitively to the right, having antagonists potencies of 130 and 0.03 mumol/L, respectively. Cerulein (0.1-500 nmol/L) also increased short-circuit current, whereas nonsulfated cholecystokinin octapeptide was ineffective. In conclusion, cholecystokinin octapeptide seems to act at neuronal cholecystokinin receptors to stimulate mucosal anion secretion, in part, by releasing acetylcholine.

Early acinar cell changes in caerulein-induced interstitial acute pancreatitis in the rat

Early ultrastructural and immunohistochemical changes caused by supramaximal secretory stimulation with caerulein were studied in the rat pancreas. The morphological basis for the earlier reported decrease of pancreatic juice secretion after supramaximal caerulein was the appearance of swollen and irregular zymogen-like material containing structures with short segments of budding bristle-coated membranes in the apical parts of acinar cells. Images of exocytosis of zymogen granules were only few. Later, marked vacuolization and signs of autophagocytosis are seen in the basal cytoplasm. Immunohistochemistry showed that the large zymogen containing structures were intensively labelled for trypsin at the early stages of the experiment (4-30 min). Later (1-2 h), the vacuoles were empty or contained occasional, small-labelled granules only. The pancreozymin-receptor antagonist proglumide as well as cycloleucine that inhibits protein synthesis by inhibiting the synthesis of S-adenosylmethionine, effectively prevented the caerulein induced acinar cell changes. The irregular zymogen containing structures with coated pits on their surface indicate disturbed zymogen granule formation leading to the accumulation of large lakes of zymogen material and finally to marked autophagocytosis in acinar cells. The effects of caerulein are receptor-mediated and depend on the process of methylation in the formation of zymogen granules.

Effects of a cholecystokinin receptor antagonist on intestinal phase of pancreatic and biliary responses in man

The present study was designed (a) to characterize the activity of loxiglumide as a peripheral cholecystokinin (CCK) antagonist in healthy human subjects, and (b) to determine whether CCK is a physiologic regulator of the intestinal phase of meal-stimulated exocrine pancreatic and biliary secretions in man. Intravenous loxiglumide (22 mumol/kg per h) was highly potent in antagonizing CCK8-induced pancreatic enzyme and bile acid secretion as well as pancreatic polypeptide release. The potency and selectivity of loxiglumide as an antagonist of CCK provides the tool for evaluating the role of CCK as a physiological mediator of meal-induced pancreatic and biliary responses in humans. Infusion of a liquid test meal into the duodenum evoked an immediate response of pancreatic enzyme and bilirubin outputs, respectively. Intravenous loxiglumide significantly inhibited the meal-induced pancreatic amylase output by 63% (P less than 0.05), lipase output by 43% (P less than 0.05), and bilirubin output by 59% (P less than 0.05). These data suggest that CCK is a physiological mediator of the intestinal phase of meal-stimulated pancreatic and biliary responses.

Gastrin is a major mediator of the gastric phase of acid secretion in dogs: proof by monoclonal antibody neutralization

We developed a monoclonal antibody, 28.2, that binds specifically to the amidated carboxyl terminal region common to gastrin and cholecystokinin. This immunoglobulin G1 antibody has high affinity (ID50 = 30-70 pM for gastrin and cholecystokinin peptides), binds labeled gastrin similarly at 37 degrees C and 4 degrees C, and shows minimal inhibition of binding in the presence of 40% canine serum. Antibody 28.2 was used to carry out in vivo immunoneutralization studies in 8 dogs previously prepared with chronic gastric fistulas. Preliminary studies revealed that a single intravenous dose of 0.75 mg of partially purified immunoglobulin G of monoclonal antibody 28.2 completely inhibited the acid stimulatory effect of exogenous gastrin-17 given intravenously at 200 pmol/kg.h, a physiologic dose, and inhibited by 70% the acid response to a supraphysiologic dose, 800 pmol/kg.h. The same dose of antibody decreased the acid secretory response obtained during distention of the stomach with 300 ml of 5.8% glucose solution by 98% and decreased the response to distention with 300 ml of 8% peptone solution by 68%. A 10-fold higher dose of antibody decreased the acid response to peptone by 96%. The gastrin antibody had no effect on the acid response to exogenous histamine. A control antibody, specific for the biologically inactive glycine-extended gastrin/cholecystokinin peptapeptide region, had no significant effect on gastric acid secretion stimulated by gastrin or by gastric distention with nutrients. These studies indicate that circulating gastrin is of major importance in the gastric phase of gastric acid stimulation caused by distention of the stomach with nutrients.

Pancreatic secretory and trophic response to caerulein in rats: effect of proglumide and lorglumide

The effect of proglumide and lorglumide, two CCK-receptor antagonists, on caerulein-induced pancreatic secretion and growth was studied in the rat. In anaesthetised animals, caerulein (1 microgram/kg) significantly increased the volume of pancreatic juice and protein output. Lorglumide (5 and 10 mg/kg), administered intraperitoneally 15 min before stimulation, reduced peptide-induced pancreatic exocrine secretion. By contrast, proglumide (100 and 400 mg/kg) was completely ineffective. In experiments dealing with the trophic effect of caerulein, both drugs were administered alone or combined with the peptide (1 microgram/kg) 3 times daily for 5 d. Saline-treated rats served as controls. At the end of the experiment, rats were sacrificed, and growth and composition of pancreatic tissue were determined. Pretreatment of the animals with either proglumide or lorglumide did not affect pancreatic size and composition. Caerulein increased the weight of the pancreas, the total pancreatic protein, trypsin, amylase, and DNA content. After pretreatment with proglumide, all these parameters were not significantly different from those obtained with caerulein alone. In contrast, when lorglumide was given together with caerulein, it significantly reduced caerulein-induced pancreatic growth and decreased enzymatic protein content of the gland. These results show that lorglumide is a much more potent and effective CCK-receptor antagonist than proglumide. Its ability to antagonize the pancreatic secretory and trophic action of a CCK-analogue (i.e. caerulein) supports the view that these physiological actions of CCK are mediated through an interaction of the hormone with specific receptors.

Effects of three different cholecystokinin receptor antagonists on basal and stimulated insulin and glucagon secretion in mice

Cholecystokinin (CCK) receptor antagonists may be valuable tools for investigating the physiological role of CCK in islet function. In this study, the effects of the three different CCK receptor antagonists, proglumide, CR 1409 and L-364,718, on basal and stimulated insulin and glucagon secretion were investigated in vivo in the mouse. Each of the CCK antagonists was injected intravenously, either alone or together with one of the secretagogues CCK-8 (5.3 nmol kg-1), carbachol (0.16 mumol kg-1) or glucose (2.8 mmol kg-1). At a low dose level, proglumide (28 mumol kg-1) inhibited selectively CCK-8-induced insulin and glucagon secretion. However, at a higher dose level (280 mumol kg-1), proglumide inhibited also carbachol- and glucose-induced insulin secretion. Furthermore, proglumide elevated basal plasma levels of both glucagon and glucose. CR 1409 inhibited CCK-8-induced insulin secretion at a high (21 mumol kg-1) but not at a low (0.21 mumol kg-1) dose level. In contrast, CCK-8-induced glucagon secretion was not affected by CR 1409. L-364,718 (2.4 mumol kg-1) inhibited both CCK-8-induced insulin and glucagon secretion. In contrast, L-364,718 did not affect basal plasma levels of insulin, glucagon or glucose or those levels after stimulation with carbachol or glucose. We conclude that, of these three CCK antagonists, L-364,718 is the most specific CCK receptor antagonist for studies of both insulin and glucagon secretion in the mouse.

Proglumide antagonizes cholecystokinin effects on plasma glucose and insulin in rats in vivo

Proglumide was shown to possess a low affinity for cholecystokinin (CCK) receptors and to inhibit the synergistic action of CCK8 on glucose-mediated insulin release in vitro. Proglumide (400 mg/kg i.p., given 15 min before an i.v. combination of CCK8 and glucose) reversed the CCK8 (0.5 nmol/kg)-induced increase of plasma insulin levels and decrease of glucose levels. It had no effect on plasma insulin and glucose levels when the glucose bolus was administered alone. Camostate (400 mg/kg p.o.; Foy-305; a trypsin inhibitor acting via endogenously released CCK) increased plasma insulin levels by 10 microU/ml during an oral glucose (500 mg/kg) tolerance test. Pretreatment with proglumide (400 mg/kg i.p.) antagonized this effect. The data indicate that proglumide has an antagonistic effect on either exogenously added or endogenously released CCK with respect to plasma insulin and glucose levels and that it has no effect on plasma insulin and glucose levels when glucose is given alone. Therefore, proglumide and the newly developed, more potent CCK receptor antagonists are able to disturb insulin and glucose homoeostasis.

Effect of cholecystokinin receptor antagonist on pancreatic responses to exogenous gastrin and cholecystokinin and to meal stimuli

Exocrine pancreatic response to food is believed to result from the interaction of neural and hormonal factors, but their contribution in the net postprandial secretion is unknown. Recent description of a highly specific and potent cholecystokinin (CCK)-receptor antagonist permitted the evaluation of the physiologic role of CCK in postprandial pancreatic secretion. In dogs with chronic pancreatic fistula, CCK antagonism caused little alteration in sham feeding- or urecholine-induced pancreatic protein secretion, but reduced by approximately 60% the pancreatic protein response to a gastrointestinal meal and virtually abolished the pancreatic responses to duodenal perfusion with amino acids or oleate and to exogenous CCK, but not to secretin or neurotensin. The pancreatic protein responses, particularly to lower doses of gastrin, were also reduced by CCK-receptor antagonist, but no changes in the responses to secretin or neurotensin were detected. Cholecystokinin antagonism also significantly reduced the pancreatic polypeptide responses to CCK, gastrin, and the gastrointestinal meal, possibly due to removal of the CCK-mediated release of pancreatic polypeptide. We conclude that CCK plays a crucial role in the mediation of the gastrointestinal phase, but not the cephalic phase, of pancreatic secretion.

Two proglumide analogues are equipotent antagonists of the inhibition of food intake by CCK-8

The reduction in food intake produced by exogenous CCK-8 (8 micrograms.kg-1, IP) in 18 hr food-deprived rats was significantly reversed by either of two proglumide analogues at doses of 0.44 and 4.4 microM.kg-1. The two glutamic acid derivatives tested were CR-1409 [N-(3,4-dichlorobenzoyl)-L-glutamic acid-1-di-n-pentylamide], effective at doses of 0.2 and 2.0 mg.kg-1, IP, and PGDPA [N-(phenoxyacetyl)-L-glutamic acid-1-di-n-propylamide], effective at the equimolar doses of 0.16 and 1.6 mg.kg-1, IP, as well as at 16 mg.kg-1 (44 microM.kg-1). By comparison, proglumide reversed the inhibition of food intake by CCK-8 at 160 mg.kg-1 (470 microM.kg-1), but not at 16 mg.kg-1 (47 microM.kg-1). At the 0.44 microM.kg-1 dose which antagonized CCK-8-induced satiety, neither PGDPA nor CR-1409 reduced the inhibition of food intake induced by bombesin, supporting the behavioral specificity of these CCK antagonists. Previous in vitro studies have shown that CR-1409 was approximately 4000-fold more potent than proglumide and PGDPA was 100-fold more potent than proglumide as antagonists of CCK-8-induced amylase secretion and binding in pancreatic acinar cells. Here, we found no potency difference between PGDPA and CR-1409; each was more than 1000-fold more potent than proglumide as an antagonist of the inhibition of food intake produced by CCK-8. This nonparallelism between the potencies of these antagonists at CCK receptors located upon pancreatic acinar cells and at CCK receptors involved in CCK-8-induced satiety suggests that the two receptor populations differ pharmacologically.

L364718, a new CCK antagonist, inhibits biological actions of CCK in conscious dogs

The effects of L364718, a new CCK receptor antagonist, on CCK-8 stimulated pancreatic secretion and PP release were examined in three conscious dogs with pancreatic fistulas. L364718 (20 nmol/kg) caused a potent inhibition of CCK-8 stimulated pancreatic protein, amylase and trypsin secretion but not of volume and bicarbonate secretion. Release of PP by CCK was also significantly suppressed by L364718. The degree of inhibition by L364718 was dependent upon the amount of CCK-8 infused. This study demonstrates that L364718 acts as a potent antagonist of CCK's action on pancreatic enzyme secretion and PP release in dogs and suggests that this agent might be a useful tool for studying the physiological role of CCK in conscious animals.

Biological effects of a proglumide derivative as cholecystokinin antagonist in conscious dogs

In conscious dogs we studied the effects of a new cholecystokinin (CCK) antagonist (coded CR 1505) on CCK8-stimulated exocrine pancreatic secretion and release of pancreatic polypeptide (PP). Graded doses of CCK8 (25-400 ng kg-1h-1) were infused i.v. Experiments were repeated against a background infusion of CR 1505 at different doses (0.1, 1 and 10 mg kg-1h-1). The lowest dose of CR 1505 had no biological effects. However, at the upper two doses the compound significantly inhibited the CCK8-stimulated PP release. Furthermore, a significant inhibition of exocrine pancreatic protein secretion was observed with 10 mg kg-1h-1 of CR 1505 (P less than 0.05). The results suggest that CR 1505 could be a useful tool in defining the physiological role of CCK in vivo.

Medical principles for treatment of peptic ulcer

The pathophysiology behind chronic gastric and duodenal ulcer is not fully understood, but may be explained as an imbalance between aggressive and defensive factors acting on or in the mucosa. Medical therapy may aim to reduce the aggressive factors acid and pepsin by compounds that neutralize the acid or inhibit the secretion of acid. Peptic activity is reduced by the high acid pH and also by the inhibition. Another group of compounds increases the mucosal defence by stimulating the secretion of mucus, bicarbonate, and growth of the mucosa, or by forming a protective layer on the ulcer crater. Some compounds affect both the aggressive and defensive factors. All modern compounds heal most ulcers in 4 to 6 weeks, but do not alter the natural history of ulcer disease, as indicated by the high rate of ulcer relapses after cessation of treatment.