Water and enzyme secretion are tightly coupled in pancreatic secretion stimulated by food or CCK-58 but not by CCK-8

The feeding responses evoked by endogenous cholecystokinin are regulated by different gastrointestinal sites

The current study tested the hypothesis that cholecystokinin (CCK) A receptor (CCKAR) in areas supplied by the celiac artery (CA), stomach and upper duodenum, and the cranial mesenteric artery (CMA), small and parts of the large intestine, is necessary for reduction of meal size, prolongation of the intermeal interval (time between first and second meal) and increased satiety ratio (intermeal interval/meal size or amount of food consumed during any given unit of time) by the non-nutrient stimulator of endogenous CCK release camostat. Consistent with our previous findings camostat reduced meal size, prolonged the intermeal interval and increased the satiety ratio. Here, we report that blocking CCKAR in the area supplied by the celiac artery attenuated reduction of meal size by camostat more so than the cranial mesenteric artery route. Blocking CCKAR in the area supplied by the cranial mesenteric artery attenuated prolongation of the intermeal interval length and increased satiety ratio by camostat more so than the celiac artery route. Blocking CCKAR in the areas supplied by the femoral artery (control) failed to alter the feeding responses evoked by camostat. These results support the hypothesis that CCKAR in the area supplied by the CA is necessary for reduction of meal size by camostat whereas CCKAR in the area supplied by the CMA is necessary for prolongation of the intermeal interval and increased satiety ratio by this substance. Our results demonstrate that meal size and intermeal interval length by camostat are regulated through different gastrointestinal sites.

The role of antisecretory factor in pancreatic exocrine secretion: studies in vivo and in vitro

NEW FINDINGS

What is the central question of this study? Antisecretory factor, an endogenous protein detected in many tissues of the body, is known as an inhibitor of intestinal secretion, but its role in pancreatic exocrine secretory function has not yet been investigated. What is the main finding and its importance? In a rodent model, we show that antisecretory factor reduces pancreatic exocrine secretion, probably via its direct action on the pancreatic acini and via modulation of the enteropancreatic reflexes involving cholecystokinin and sensory nerves. Antisecretory factor (AF) regulates ion and water transport through the intestinal cell membrane. Antisecretory factor inhibits intestinal secretion, but its effect on the exocrine pancreas has not yet been shown. We investigated the effect of AF on pancreatic amylase secretion in vivo and in vitro using pancreatic acini isolated by collagenase digestion. For the in vivo study, Wistar rats were surgically equipped with silicone catheters, inserted into the pancreaticobiliary duct and into the duodenum. Capsaicin was used to deactivate the sensory nerves in turn to assess their involvement in the effects of AF on the exocrine pancreas. Antisecretory factor (1, 3 or 10 μg kg(-1) i.p.) was given in basal conditions or following stimulation of pancreatic secretion with diversion of pancreaticobiliary juice. For the in vitro study, rat pancreatic acini were incubated in the presence of increasing doses of AF (from 10(-8) to 10(-5)  m) alone or in combination with caerulein (10(-12)  m). Cytoplasmic cholecystokinin 1 (CCK1 ) receptor protein was detected by Western blot and immunoprecipitation studies. Antisecretory factor markedly reduced the output of pancreatic amylase both in basal conditions and when stimulated by diversion of pancreaticobiliary juice. Deactivation of the sensory nerves with capsaicin completely reversed the inhibitory effects of AF on the exocrine pancreas. Caerulein-induced enzyme secretion from the pancreatic acini was inhibited by AF, whereas basal secretion was unaffected. Administration of AF to the rats significantly diminished the synthesis of CCK1 receptor protein. We conclude that AF inhibits pancreatic exocrine secretion indirectly via sensory nerves and directly decreases amylase release from isolated pancreatic acini. The direct inhibitory action of AF on the exocrine pancreas could be related, at least in part, to a reduction of CCK1 receptors on pancreatic acinar cells.

Celiac and the cranial mesenteric arteries supply gastrointestinal sites that regulate meal size and intermeal interval length via cholecystokinin-58 in male rats

The site(s) of action that control meal size and intermeal interval (IMI) length by cholecystokinin-58 (CCK-58), the only detectable endocrine form of CCK in the rat, are not known. To test the hypothesis that the gastrointestinal tract may contain such sites, we infused low doses of CCK-58 (0.01, 0.05, 0.15 and 0.25nmol/kg) into the celiac artery (CA, supplying stomach and upper duodenum), the cranial mesenteric artery (CMA, supplying small and most of the large intestines), the femoral artery (FA, control) and the portal vein (PV, draining the gastrointestinal tract) prior to the onset of the dark cycle in freely fed male rats. We measured the first meal size (chow), second meal size, IMI and satiety ratio (SR, IMI/meal size). We found that (1) all doses of CCK-58 given in the CA and the highest dose given in the CMA reduced the first meal size, (2) all doses of CCK-58 given in the CA reduced the second meal size, (3) a CCK-58 dose of 0.15nmol/kg given in the CA and 0.15 and 0.25nmol/kg given in the CMA prolonged the IMI, (4) CCK-58 (0.05, 0.15, 0.25nmol/kg) given in the CA and 0.25nmol/kg given in the CMA increased the SR, and (5) CCK-58 given in the FA and PV had no effect on the meal size or intermeal interval. These results support our hypothesis that the gastrointestinal tract contains sites of action that regulate meal size and IMI length via CCK-58. The stomach and upper duodenum may contain sites regulating meal size, whereas the small intestine and part of the large intestine may contain sites regulating the IMI.

CCK-58 prolongs the intermeal interval, whereas CCK-8 reduces this interval: not all forms of cholecystokinin have equal bioactivity

It has been accepted for decades that "all forms of cholecystokinin (CCK) have equal bioactivity," despite accumulating evidence to the contrary. To challenge this concept, we compared two feeding responses, meal size (MS, 10% sucrose) and intermeal interval (IMI), in response to CCK-58, which is the major endocrine form of CCK, and CCK-8, which is the most abundantly utilized form. Doses (0, 0.1, 0.5, 0.75, 1, 3 and 5 nmol/kg) were administered intraperitoneally over a 210-min test to Sprague Dawley rats that had been food-deprived overnight. We found that (1) all doses of CCK-58, except the lowest dose, and all doses of CCK-8, except the lowest two doses, reduced food intake more than vehicle did; (2) at two doses, 0.75 and 3 nmol/kg, CCK-58 increased the IMI, while CCK-8 failed to alter this feeding response; and (3) CCK-58, at all but the lowest two doses, increased the satiety ratio (IMI between first and second meals (min) divided by first MS (ml)) relative to vehicle, while CCK-8 did not affect this value. These findings demonstrate that the only circulating form of CCK in rats, CCK-58, prolongs the IMI more than CCK-8, the peptide generally utilized in feeding studies. Taken together, these results add to a growing list of functions where CCK-8 and CCK-58 express qualitatively different bioactivities. In conclusion, the hypothesis that "all forms of cholecystokinin (CCK) have equal bioactivity" is not supported.

CCK-58 elicits both satiety and satiation in rats while CCK-8 elicits only satiation

Reduction of food intake by exogenous cholecystokinin (CCK) has been demonstrated primarily for its short molecular form, CCK-8. Mounting evidence, however, implicates CCK-58 as a major physiologically active CCK form, with different neural and exocrine response profiles than CCK-8. In three studies, we compared meal-pattern effects of intraperitoneal injections CCK-8 vs. CCK-58 in undeprived male Sprague-Dawley rats consuming sweetened condensed milk. In study 1, rats (N=10) received CCK-8, CCK-58 (0.45, 0.9, 1.8 and 3.6 nmol/kg) or vehicle before a 4-h test-food presentation. At most doses, both CCK-8 and CCK-58 similarly reduced meal size relative to vehicle. Meal-size reduction prompted a compensatory shortening of the intermeal interval (IMI) after CCK-8, but not after CCK-58, which uniquely increased the satiety ratio (IMI/size of the preceding meal). In the second study, lick patterns were monitored after administration of 0.9 nmol/kg CCK-58, CCK-8 or vehicle. Lick cluster size, lick efficiency and interlick-interval distribution remained unaltered compared to vehicle, implying natural satiation, rather than illness, following both CCK forms. In study 3, threshold satiating doses of the two CCK forms were given at 5 and 30 min after meal termination, respectively. CCK 58, but not CCK-8 increased the intermeal interval and satiety ratio compared to vehicle. In conclusion, while CCK 58 and CCK-8 both stimulate satiation, thereby reducing meal size, CCK-58 consistently exerts a satiety effect, prolonging IMI. Given the physiological prominence of CCK-58, these results suggest that CCK's role in food intake regulation may require re-examination.

CCK-8 and CCK-58 differ in their effects on nocturnal solid meal pattern in undisturbed rats

Various molecular forms of CCK reduce food intake in rats. Although CCK-8 is the most studied form, we reported that CCK-58 is the only detectable endocrine peptide form in rats. We investigated the dark-phase rat chow intake pattern following injection of CCK-8 and CCK-58. Ad libitum-fed male Sprague-Dawley rats were intraperitoneally injected with CCK-8, CCK-58 (0.6, 1.8, and 5.2 nmol/kg), or vehicle. Food intake pattern was assessed during the dark phase using an automated weighing system that allowed continuous undisturbed monitoring of physiological eating behavior. Both CCK-8 and CCK-58 dose dependently reduced 1-h, dark-phase food intake, with an equimolar dose of 1.8 nmol being similarly effective (-49% and -44%). CCK-58 increased the latency to the first meal, whereas CCK-8 did not. The intermeal interval was reduced after CCK-8 (1.8 nmol/kg, -41%) but not after CCK-58. At this dose, CCK-8 increased the satiety ratio by 80% and CCK-58 by 160%, respectively, compared with vehicle. When behavior was assessed manually, CCK-8 reduced locomotor activity (-31%), whereas grooming behavior was increased (+59%). CCK-58 affected neither grooming nor locomotor activity. In conclusion, reduction of food intake by CCK-8 and CCK-58 is achieved by differential modulation of food intake microstructure and behavior. These data highlight the importance of studying the molecular forms of peptides that exist in vivo in tissue and circulation of the animal being studied.

Molecular mechanism of pancreatic and salivary gland fluid and HCO3 secretion

Fluid and HCO(3)(-) secretion is a vital function of all epithelia and is required for the survival of the tissue. Aberrant fluid and HCO(3)(-) secretion is associated with many epithelial diseases, such as cystic fibrosis, pancreatitis, Sjögren's syndrome, and other epithelial inflammatory and autoimmune diseases. Significant progress has been made over the last 20 years in our understanding of epithelial fluid and HCO(3)(-) secretion, in particular by secretory glands. Fluid and HCO(3)(-) secretion by secretory glands is a two-step process. Acinar cells secrete isotonic fluid in which the major salt is NaCl. Subsequently, the duct modifies the volume and electrolyte composition of the fluid to absorb the Cl(-) and secrete HCO(3)(-). The relative volume secreted by acinar and duct cells and modification of electrolyte composition of the secreted fluids varies among secretory glands to meet their physiological functions. In the pancreas, acinar cells secrete a small amount of NaCl-rich fluid, while the duct absorbs the Cl(-) and secretes HCO(3)(-) and the bulk of the fluid in the pancreatic juice. Fluid secretion appears to be driven by active HCO(3)(-) secretion. In the salivary glands, acinar cells secrete the bulk of the fluid in the saliva that is driven by active Cl(-) secretion and contains high concentrations of Na(+) and Cl(-). The salivary glands duct absorbs both the Na(+) and Cl(-) and secretes K(+) and HCO(3)(-). In this review, we focus on the molecular mechanism of fluid and HCO(3)(-) secretion by the pancreas and salivary glands, to highlight the similarities of the fundamental mechanisms of acinar and duct cell functions, and to point out the differences to meet gland-specific secretions.

The short term satiety peptide cholecystokinin reduces meal size and prolongs intermeal interval

Camostat mesilate (or mesylate) releases endogenous cholecystokinin (CCK) or CCK-58, the only detectable endocrine form of CCK in the rat, and reduces cumulative food intake by activating CCK(1) receptor. However, the literature lacks meal pattern analysis and an appropriate dose-response curve for this peptide. Therefore, the current study determines meal size (MS), intermeal interval (IMI) and satiety ratio (SR) by orogastric gavage of camostat (0, 12.5, 25, 50, 100, 200, 300, 400, 800mg/kg) and compares them to those previously reported by a single dose of CCK-8 (1nmol/kg, i.p), the most utilized form of CCK. We found that camostat (200, 300, 400 and 800mg/kg) and CCK-8 reduced cumulative food intake and the size of the first meal, but only camostat prolonged IMI and increased SR. There was no change in the duration of the first two meals or in rated behaviors such as feeding, grooming, standing and resting in response to camostat and CCK-8, but there was more resting during the IMI in response to camostat. This study provides meal pattern analysis and an appropriate dose-response curve for camostat and CCK-8. Camostat reduces food intake by decreasing MS and prolonging IMI, whereas CCK-8 reduces food intake by reducing only meal size.

Interaction between gastric and upper small intestinal hormones in the regulation of hunger and satiety: ghrelin and cholecystokinin take the central stage

Several peptides are produced and released from endocrine cells scattered within the gastric oxyntic and the small intestinal mucosa. These peptide hormones are crucially involved in the regulation of gastrointestinal functions and food intake by conveying their information to central regulatory sites located in the brainstem as well as in the forebrain, such as hypothalamic nuclei. So far, ghrelin is the only known hormone that is peripherally produced in gastric X/A-like cells and centrally acting to stimulate food intake, whereas the suppression of feeding seems to be much more redundantly controlled by a number of gut peptides. Cholecystokinin produced in the duodenum is a well established anorexigenic hormone that interacts with ghrelin to modulate food intake indicating a regulatory network located at the first site of contact with nutrients in the stomach and upper small intestine. In addition, a number of peptides including leptin, urocortin 2, amylin and glucagon-like peptide 1 interact synergistically with CCK to potentiate its satiety signaling effect. New developments have led to the identification of additional peptides in X/A-like cells either derived from the pro-ghrelin gene by alternative splicing and posttranslational processing (obestatin) or a distinct gene (nucleobindin2/nesfatin-1) which have been investigated for their influence on food intake.

Cholecystokinin-58 and cholecystokinin-8 exhibit similar actions on calcium signaling, zymogen secretion, and cell fate in murine pancreatic acinar cells

The gastrointestinal hormone CCK exists in various molecular forms, with differences in bioactivity between the well-characterized CCK-8 and larger CCK-58 previously reported. We have compared the effects of these peptides on cytosolic calcium concentration ([Ca(2+)](c)), mitochondrial metabolism, enzyme secretion, and cell fate in murine isolated pancreatic acinar cells using fluorescence confocal microscopy and patch-clamp electrophysiology. CCK-58 (1-10 pM) induced transient, oscillatory increases of [Ca(2+)](c), which showed apical to basolateral progression and were associated with a rise of mitochondrial NAD(P)H. CCK-58 (10 pM) induced zymogen exocytosis in isolated cells and amylase secretion from isolated cells and whole tissues. Hyperstimulation with supraphysiological CCK-58 (5 nM) induced a single large increase of [Ca(2+)](c) that declined to a plateau, which remained above the basal level 20 min after application and was dependent on external Ca(2+) entry. In cells dispersed from the same tissues, CCK-8 induced similar patterns of responses to those of CCK-58, with oscillatory increases of [Ca(2+)](c) at lower (pM) concentrations and sustained responses at 5 nM. CCK-58 and CCK-8 exhibited similar profiles of action on cell death, with increases in necrosis at high CCK-58 and CCK-8 (10 nM) that were not significantly different between peptides. The present experiments indicate that CCK-8 and CCK-58 have essentially identical actions on the acinar cell at high and low agonist concentrations, suggesting an action via the same receptor and that the differences observed in an intact rat model may result from indirect effects of the peptides. Our data strengthen the argument that CCK-58 is an important physiological form of this gastrointestinal hormone.

The RAPID method for blood processing yields new insight in plasma concentrations and molecular forms of circulating gut peptides

The correct identification of circulating molecular forms and measurement of peptide levels in blood entails that the endocrine peptide being studied is stable and recovered in good yields during blood processing. However, it is not clear whether this is achieved in studies using standard blood processing. Therefore, we compared peptide concentration and form of 12 (125)I-labeled peptides using the standard procedure (EDTA-blood on ice) and a new method employing Reduced temperatures, Acidification, Protease inhibition, Isotopic exogenous controls, and Dilution (RAPID). During standard processing there was at least 80% loss for calcitonin-gene-related peptide and cholecystokinin-58 (CCK-58) and more than 35% loss for amylin, insulin, peptide YY forms (PYY((1-36)) and PYY((3-36))), and somatostatin-28. In contrast, the RAPID method significantly improved the recovery for 11 of 12 peptides (P < 0.05) and eliminated the breakdown of endocrine peptides occurring after standard processing as reflected in radically changed molecular forms for CCK-58, gastrin-releasing peptide, somatostatin-28, and ghrelin. For endogenous ghrelin, this led to an acyl/total ghrelin ratio of 1:5 instead of 1:19 by the standard method. These results show that the RAPID method enables accurate assessment of circulating gut peptide concentrations and forms such as CCK-58, acylated ghrelin, and somatostatin-28. Therefore, the RAPID method represents an efficacious means to detect circulating variations in peptide concentrations and form relevant to the understanding of physiological function of endocrine peptides.

Effects of cholecystokinin-58 on type 1 cholecystokinin receptor function and regulation

Cholecystokinin, like many peptide hormones, is present as multiple molecular forms. CCK-58 has been identified as the dominant form in the circulation, whereas most of the studies of CCK-receptor interactions have been performed with CCK-8. Despite both sharing the pharmacophoric region of CCK, representing its carboxy terminal heptapeptide amide, studies in vivo have demonstrated biological diversity of action of the two peptides, with CCK-58, but not CCK-8, stimulating pancreatic fluid secretion and lengthening the interval between meals. Here, we have directly studied the ability of these two CCK peptides to bind to the type 1 CCK receptor and to stimulate it to elicit an intracellular calcium response. The calcium response relative to receptor occupation was identical for CCK-58 and CCK-8, with the longer peptide binding with approximately fivefold lower affinity. We also examined the ability of the two peptides to elicit receptor internalization using morphological techniques and to disrupt the constitutive oligomerization of the CCK receptor using receptor bioluminescence resonance energy transfer. Here, both full agonist peptides had similar effects on these regulatory processes. These data suggest that both molecular forms of CCK act at the CCK1 receptor quite similarly and elicit similar regulatory processes for that receptor, suggesting that the differences in biological activity observed in vivo most likely reflect differences in the clearance and/or metabolism of these long and short forms of CCK peptides.

Direct activation of cytosolic Ca2+ signaling and enzyme secretion by cholecystokinin in human pancreatic acinar cells

BACKGROUND & AIMS

Cholecystokinin (CCK) has been thought to act only indirectly on human pancreatic acinar cells via vagal nerve stimulation, rather than by direct CCK receptor activation as on rodent pancreatic acinar cells. We tested whether CCK (CCK-8 and human CCK-58) can act directly on human pancreatic acinar cells.

METHODS

Human acinar cells were freshly isolated from pancreatic transection line samples, loaded with Fluo4-AM or quinacrine, and examined for Ca(2+), metabolic and secretory responses to CCK-8, human CCK-58, or acetylcholine with confocal microscopy.

RESULTS

CCK-8 and human CCK-58 at physiologic concentrations (1-20 pmol/L) elicited rapid, robust, oscillatory increases of the cytosolic Ca(2+) ion concentration, showing apical to basal progression, in acinar cells from 14 patients with unobstructed pancreata. The cytosolic Ca(2+) ion concentration increases were followed by increases in mitochondrial adenosine triphosphate production and secretion. CCK-elicited Ca(2+) signals and exocytosis were not inhibited by atropine (1 mumol/L) or tetrodotoxin (100 nmol/L), showing that CCK was unlikely to have acted via neurotransmitter release. CCK-elicited Ca(2+) signals were inhibited reversibly by caffeine (5-20 mmol/L), indicating involvement of intracellular inositol trisphosphate receptor Ca(2+) release channels. Acetylcholine (50 nmol/L) elicited similar Ca(2+) signals.

CONCLUSIONS

CCK at physiologic concentrations in the presence of atropine and tetrodotoxin elicits cytosolic Ca(2+) signaling, activates mitochondrial function, and stimulates enzyme secretion in isolated human pancreatic acinar cells. We conclude that CCK acts directly on acinar cells in the human pancreas.

Activation of submucosal but not myenteric plexus of the gastrointestinal tract accompanies reduction of food intake by camostat

It has been shown in the rat that endogenous cholecystokinin (CCK), released in response to the non-nutrient trypsin inhibitor camostat, reduces food intake at meals and increases Fos-like immunoreactivity (Fos-LI; a marker for neuronal activation) in the dorsal vagal complex (DVC) of the hindbrain but not the myenteric plexus of the duodenum and jejunum. Experiment 1: We examined Fos-LI in the myenteric and the submucosal plexuses of the gut in response to orogastric gavage of camostat in rats. As we reported previously, camostat failed to increase Fos-LI in the myenteric plexus. We show here that camostat increased Fos-LI in the submucosal plexus of the duodenum and jejunum. Camostat also increased Fos-LI in the DVC. Experiment 2: Pretreatment with devazepide, a specific CCK(1) receptor antagonist abolished camostat-induced Fos-LI in the submucosal plexus and the DVC. Experiment 3: Bilateral subdiaphragmatic vagotomy reduced camostat-induced Fos-LI in the submucosal plexus approximately 40% and abolished it in the DVC.

CONCLUSIONS

Activation of the submucosal plexus by cholecystokinin at the CCK(1) receptor accompanies stimulation of the dorsal vagal complex of the hindbrain and inhibition of food intake. Unlike the submucosal plexus, activation of the myenteric plexus is not necessary for cholecystokinin's influence on the dorsal vagal complex and food intake. The lack of activation in the myenteric plexus after camostat stimulation, in contrast to nutrient releasers of CCK such as oleate, suggests that intestinal stimulants can either release different amounts of CCK or cause release of CCK from I cells with different molecular forms of CCK. This would suggest that CCK-8 is released by camostat and is not able to travel to the myenteric plexus while a more stable form of CCK such as CCK-58 can travel to this site that is further away from the I cell.

Cholecystokinin-58 and cholecystokinin-8 produce similar but not identical activations of myenteric plexus and dorsal vagal complex

The enteric nervous system (ENS: myenteric and submucosal plexuses) of the gastrointestinal tract may have a role in the reduction of food intake by cholecystokinin (CCK). Exogenous cholecystokinin-8 (CCK-8) activates the myenteric plexus and the feeding control areas of the dorsal vagal complex (DVC) of the brainstem. An increasing number of reports, however, have shown that CCK-58 is the sole or the major circulating form of CCK in rat, human and dog, and that it is qualitatively different from CCK-8 in evoking various gastrointestinal physiological responses (e.g., contraction of the gallbladder and exocrine pancreatic secretion). In the current report, we compared the abilities of exogenous CCK-58 to activate the myenteric plexus and the dorsal vagal complex with those of exogenous CCK-8 by quantifying Fos-like immunoreactivity (Fos-LI; a marker for neuronal activation). We report that CCK-58 (1, 3, and 5 nmol/kg) increased Fos-LI in the myenteric plexus (p<0.001) and in the DVC (p<0.001) compared to the saline vehicle. The highest dose of CCK-58 increased Fos-LI more than an equimolar dose of CCK-8 in the myenteric plexus and the area postrema. Thus, CCK-8 and CCK-58 produce the same qualitative pattern of activation of central and peripheral neurons, but do not provoke identical quantitative patterns at higher doses. The different patterns produced by the two peptides at higher doses, in areas open to the circulation (myenteric plexus and area postrema) may reflect endocrine actions not observed at lower doses.

Unique activities of cholecystokinin-58; physiological and pathological relevance

PURPOSE OF REVIEW

Cholecystokinin, a regulatory peptide found in multiple molecular forms in brain and small intestine, is responsible for integration of functions associated with the intake, digestion and absorption of food. Whether the different molecular forms have identical biological activities is controversial. New information suggests that CCK58, the largest form of cholecystokinin detected in blood and tissue, has unique functions compared with other forms, and may be the predominant, perhaps only, circulating form in mammals.

RECENT FINDINGS

CCK58 has highly distinctive actions compared with shorter forms, most notably the strong stimulation of water secretion from the pancreas, and the lack of induction of pancreatitis by supramaximal doses of the peptide. Because CCK58 may be the main endogenous form of cholecystokinin, these recent findings have far reaching implications because almost all studies carried out with cholecystokinin have been done with shorter forms, predominately CCK8. Conclusions of studies using CCK8 or other shorter forms of cholecystokinin, therefore, may need to be reevaluated.

SUMMARY

There is a compelling reason to reevaluate the role of cholecystokinin in health and disease because the predominant form of cholecystokinin, CCK58, has unique biological activities compared with forms of cholecystokinin used in previous basic and clinical studies.

Supramaximal CCK-58 does not induce pancreatitis in the rat: role of pancreatic water secretion

In contrast to supramaximal CCK-8 or caerulein, acute or prolonged supraphysiological levels of endogenous CCK-58 do not cause pancreatitis. Compared with CCK-8, CCK-58 is a much stronger stimulant of pancreatic chloride and water secretion, equivalent to maximally effective secretin, but with a chloride-to-bicarbonate ratio characteristic of acinar fluid. Because supraphysiological endogenous CCK does not cause pancreatitis and because coadministration of secretin ameliorated caerulein- or CCK-8-induced pancreatitis, coincident with restoring pancreatic water secretion, we hypothesized that supramaximal CCK-58 would not induce pancreatitis. Conscious rats were infused intravenously with 2 or 4 nmol x kg(-1) x h(-1) of CCK-8 or synthetic rat CCK-58 for 6 h, and pancreases were examined for morphological and biochemical indexes of acute pancreatitis. A second group was treated as above while monitoring pancreatic protein and water secretion. CCK-8 at 2 nmol x kg(-1) x h(-1) caused severe edematous pancreatitis as evidenced by morphological and biochemical criteria. CCK-58 at this dose had minimal or no effect on these indexes. CCK-58 at 4 nmol x kg(-1) x h(-1) increased some indexes of pancreatic damage but less than either the 2 or 4 nmol x kg(-1) x h(-1) dose of CCK-8. Pancreatic water and protein secretion were nearly or completely abolished within 3 h of onset of CCK-8 infusion, whereas water and protein secretion were maintained near basal levels in CCK-58-treated rats. We hypothesize that supramaximal CCK-58 does not induce pancreatitis because it maintains pancreatic acinar chloride and water secretion, which are essential for exocytosis of activated zymogens. We conclude that CCK-58 may be a valuable tool for investigating events that trigger pancreatitis.

Endogenous cholecystokinin reduces food intake and increases Fos-like immunoreactivity in the dorsal vagal complex but not in the myenteric plexus by CCK1 receptor in the adult rat

We hypothesized that endogenous CCK reduces food intake by activating the dorsal vagal complex (DVC) and the myenteric neurons of the gut. To test this hypothesis, adult rats were given camostat mesilate; a nonnutrient releaser of endogenous CCK, by orogastric gavage, and Fos-like immunoreactivity (Fos-LI) was quantified in the DVC and the myenteric plexus. The results for endogenous CCK were compared with those for exogenous CCK-8. Exogenous CCK-8 reduced food intake and stimulated Fos-LI in the DVC and in myenteric neurons of the duodenum and jejunum. In comparison, endogenous CCK reduced food intake and increased DVC Fos-LI but did not increase Fos-LI in the myenteric plexus. Similar to CCK-8, devazepide, a specific CCK1 receptor antagonist, and not L365,260, a specific CCK2 receptor antagonist, attenuated the reduction of food intake by camostat. In addition, Fos-LI in the DVC in response to both exogenous CCK-8 and camostat administration was significantly attenuated by vagotomy, as well as by blocking CCK1 receptors. These results demonstrate for the first time that reduction of food intake in adult rats by endogenous CCK released by a nonnutrient mechanism requires CCK1 receptors, the vagus nerve, and activation of the DVC, but not the myenteric plexus.

Cholecystokinin

PURPOSE OF REVIEW

The hormone cholecystokinin was discovered in 1928 because of its ability to induce gallbladder contraction. Since then, cholecystokinin has been shown to possess multiple functions in the gastrointestinal tract and brain. This review discusses several significant developments in cholecystokinin biology that show how it plays a role in gastrointestinal diseases, including control of appetite.

RECENT FINDINGS

Cholecystokinin was shown to induce satiety by interacting through CCK-1 receptors located in specialized regions of the hindbrain. Cholecystokinin also inhibits expression of orexigenic peptides in the hypothalamus and prevents stimulation of specialized neurons by ghrelin. In the pancreas, cholecystokinin increased the proliferation of insulin-producing beta cells and reduced insulin-induced hyperphagia. Elevated cholecystokinin levels decreased appetite and reduced intestinal inflammation caused by parasites and bacterial toxins.

SUMMARY

Understanding the mechanisms by which cholecystokinin regulates orexigenic pathways in the body may lead to strategies for controlling appetite-related disorders such as obesity and bulimia. The reduction of intestinal inflammation by dietary fats (by elevating cholecystokinin) suggests that the hormone plays an integrated role in regulating the ingestion and digestion of food that may be relevant to inflammatory diseases of the gastrointestinal tract.

Crucial role of position 40 for interactions of CCK-58 revealed by sequence of cat CCK-58

Evidence suggests that amino terminal extensions of CCK-8 affect the carboxyl terminal bioactive region of CCK. Cat CCK-58 was purified by low pressure reverse phase and ion-exchange chromatography steps and several reverse phase HPLC steps. The purified peptide and its tryptic fragments were characterized by mass spectral analysis and microsequence analysis. The structure of cat CCK-58 is: AVQKVDGEPRAHLGALLARYIQQARKAPSGRMSVIKNLQSLDPSHRISDRDY(SO3) MGWMDF-amide. Cat and dog CCK-58 are identical except for position 40 which is serine in cat and asparagine in dog. Radioimmunoassay detected cat CCK-58 about 1/10th as well as dog CCK-58, indicating a marked effect on C-terminal immunoreactivity. Cat CCK-58 with a serine at position 40, the same residue found in pig, mouse, cow and rabbit CCK-58, can be used as a unique bioprobe for defining how amino terminal amino acids influence the structure and bioactivity of the carboxyl terminal region of CCK.

Ca2+ signalling and pancreatitis: effects of alcohol, bile and coffee

Ca2+ is a universal intracellular messenger that controls a wide range of cellular processes. In pancreatic acinar cells, acetylcholine and cholecystokinin regulate secretion via generation of repetitive local cytosolic Ca2+ signals in the apical pole. Bile acids and non-oxidative alcohol metabolites can elicit abnormal cytosolic Ca2+ signals that are global and sustained and result in necrosis. Necrosis results from excessive loss of Ca2+ from the endoplasmic reticulum, which is mediated by Ca2+ release through specific channels and inhibition of Ca2+ pumps in intracellular stores, followed by entry of extracellular Ca2+. Reduction of the cellular ATP level has a major role in this process. These abnormal Ca2+ signals, which can be inhibited by caffeine, explain how excessive alcohol intake and biliary disease cause acute pancreatitis, an often-fatal human disease in which the pancreas digests itself and its surroundings.