Pharmacologic characterization of excitatory and inhibitory cholecystokinin receptors of the cat gallbladder and sphincter of Oddi

Evolution of the restorative proctocolectomy and its effects on gastrointestinal hormones

Gastrointestinal (GI) peptide hormones are chemical messengers that regulate secretory, mechanical, metabolic, and trophic functions of the gut. Restorative proctocolectomy (RPC) or resection of the colon and rectum with maintenance of intestinal continuity through the construction of an ileal pouch reservoir and preservation of the anal sphincters has become the standard of care for the surgical treatment of ulcerative colitis and familial adenomatous polyposis. The manipulation of the digestive system to create the ileal pouch involves altering gut-associated lymphoid tissue among other anatomic changes that lead to changes in GI peptides. In addition, the ileal pouch epithelium responds to a wide variety of stimuli by adjusting its cellularity and function. These adaptive mechanisms involve systemic factors, such as humoral and neural stimuli, as well as local factors, such as changes in intestinal peristalsis and intraluminal nutrients. There have been conflicting reports as to whether the alterations in GI hormones after RPC have actual clinical implications. What the studies on alterations of GI peptides' response and behavior after RPC have contributed, however, is a window into the possible etiology of complications after pouch surgery, such as pouchitis and malabsorption. Given the possibility of pharmacologically modifying GI peptides or select components of adaptation as a therapeutic strategy for patients with ileal pouch dysfunction or pouchitis, a clear understanding of human pouch mucosal adaptation is of paramount importance. In this review, we summarize the evolution of the RPC and its effects on the GI hormones as well as their possible clinical implications.

Does topical GTN on the sphincter of Oddi facilitate ERCP? A double-blind randomized control trial

BACKGROUND

Endoscopic retrograde cholangio pancreatography (ERCP) is a technically challenging procedure. Glyceryl trinitrate (GTN) has been shown to reduce tone in the sphincter of Oddi (SO), cannulation of which is a rate-limiting factor. A double-blind randomized control trial was performed to assess whether topical GTN on the SO would facilitate cholangiography and/or bile duct cannulation.

METHODS

104 patients requiring ERCP for biliary symptoms were randomized into two groups, 52 controls pretreated with 5 ml 0.9% normal saline (NS) and 52 pretreated with 5 ml GTN (concentration 1 mg/ml).

RESULTS

There was no significant between the control group and the GTN group in primary cannulation rate (p = 0.76), time taken to cholangiography (p = 0.58), or time to cannulation (p = 0.43).

CONCLUSION

Topically administered GTN to the SO does not aid in obtaining a cholangiogram or cannulation during an ERCP.

Nitroester drug’s effects and their antagonistic effects against morphine on human sphincter of Oddi motility

AIM: To evaluate the effects of nitroester drugs on human sphincter of Oddi (SO) motility and their antagonistic effects against morphine which shows excitatory effect on Oddi’s sphincter motility.

METHODS: The effects of these drugs on SO were evaluated by means of choledochofiberoscopy manometry. A total of 67 patients having T-tubes after cholecystectomy and choledochotomy were involved in the study, they were randomly divided into glyceryl trinitrate (GTN) group, isosorbide dinitrate (ISDN) group, pentaerythritol tetranitrate (PTN) group, morphine associated with GTN group, morphine associated with ISDN group and morphine associated with PTN group. Basal pressure of Oddi’s sphincter (BPOS), amplitude of phasic contractions (SOCA), frequency of phasic contractions (SOF), duration of phasic contractions (SOD), duodenal pressure (DP) and common bile duct pressure (CBDP) were scored and analyzed. Morphine was given intramuscularly while nitroester drugs were applied sublingually.

RESULTS: BPOS and SOCA decreased significantly after administration of ISDN and GTN, BPOS reduced from 10.95±7.49 mmHg to 5.92±4.04 mmHg (P<0.05) evidently after application of PTN. BPOS increased from 7.37±5.58 mmHg to 16.60±13.87 mmHg, SOCA increased from 54.09±38.37 mmHg to 100.70±43.51 mmHg, SOF increased from 7.15±3.20 mmHg to 10.38±2.93 mmHg and CBDP increased 3.75±1.95 mmHg to 10.49±8.21 mmHg (P<0.01) evidently after injection of morphine. After associated application of ISDN and GTN, the four indications above decreased obviously. As for application associated with PTN, SOCA and SOF decreased separately from 100.64±44.99 mmHg to 66.17±35.88 mmHg and from 10.70±2.76 mmHg to 9.04±1.71 mmHg (P<0.05) markedly.

CONCLUSION: The regular dose of GTN, ISDN and PTN showed inhibitory effect on SO motility, morphine showed excitatory effect on SO while GTN, ISDN and PTN could antagonize the effect of morphine. Among the three nitroester drugs, the effect of ISDN on SO was most significant.

Oxytocin and cholecystokinin secretion in women with colectomy

Background

Cholecystokinin (CCK) concentrations in plasma have been shown to be significantly higher in colectomised subjects compared to healthy controls. This has been ascribed to reduced inhibition of CCK release from colon. In an earlier study CCK in all but one woman who was colectomised, induced release of oxytocin, a peptide present throughout the gastrointestinal (GI) tract. The aim of this study was thus to examine if colectomised women had a different oxytocin response to CCK compared to healthy controls.

Methods

Eleven women, mean age 34.4 ± 2.3 years, who had undergone colectomy because of ulcerative colitis or constipation were studied. Eleven age-matched healthy women served as controls. All subjects were fasted overnight and given 0.2 μg/kg body weight of CCK-8 i.v. in the morning. Samples were taken ten minutes and immediately before the injection, and 10, 20, 30, 45, 60, 90 and 120 min afterwards. Plasma was collected for measurement of CCK and oxytocin concentrations.

Results

The basal oxytocin and CCK concentrations in plasma were similar in the two groups. Intravenous injection of CCK increased the release of oxytocin from 1.31 ± 0.12 and 1.64 ± 0.19 pmol/l to 2.82 ± 0.35 and 3.26 ± 0.50 pmol/l in controls and colectomised women, respectively (p < 0.001). Given the short half-life of CCK-8 in plasma, the increased concentration following injection could not be demonstrated in the controls. On the other hand, in colectomised women, an increase of CCK in plasma was observed for up to 20 minutes after the injection, concentrations increasing from 1.00 ± 0.21 to a maximum of 1.81 ± 0.26 pmol/l (p < 0.002).

Conclusion

CCK stimulates the release of oxytocin in women. There is no difference in plasma concentrations between colectomised and controls. However, colectomy seems to reduce the metabolic clearance of CCK. The hyperCCKemia in patients who had undergone colectomy is consequently not only dependent on CCK release, but may also depend on reduced clearance.

Oddi sphincter function after canine auto-pancreas transplantation with bladder drainage

AIM: Several neural and hormonal factors are known to affect motility of sphincter of Oddi (SO). The major roles of SO are to regulate the flow of bile and pancreatic juice into the duodenum and to prevent the reflux of duodenal contents into the biliary and pancreatic duct. After pancreas transplantation, graft SO was denervated and graft pancreatitis might have relations to SO motility. The motility of SO after canine pancreas transplantation with bladder drainage was investigated.

METHODS: Normal canine SO manometry and pancreas graft SO manometry after pancreas transplantation with bladder drainage were performed in seven dogs respectively before and after cholecystokinin (CCK) administration. Data of SO basal pressure, contraction frequency, amplitude and motility index after transplantation and CCK administration were compared with that in controls and before CCK administration.

RESULTS: SO showed regular contractions with a certain basal pressure in control dogs. After transplantation, the graft SO basal pressure and contraction frequency were higher than that in controls, but the amplitude decreased (P < 0.01). There was no great difference in SO motility index. CCK administration could relax normal SO but stimulate graft SO after pancreas transplantation with bladder drainage. After CCK administration, SO basal pressure, frequency and motility index were increased significantly (P < 0.05), in comparison with that before administration. The amplitude remained unchanged (P > 0.05), in comparison with that before CCK administration.

CONCLUSION: After auto-pancreas transplantation with bladder drainage, canine SO motility was inhibited. Basal pressure and frequency increased but amplitude decreased. CCK administration after transplantation had an inhibitory effect on canine SO instead of a relaxation effect observed in normal canine SO. This will increase the resistance of SO to the pancreatic juice flow and induce pancreatic juice stagnation and can not prevent reflux of urine and duodenal contents when the bladder pressure is increased to a certain extent, which may cause graft pancreatitis.

Cholecystokinin activates both A- and C-type vagal afferent neurons

Patch-clamp electrophysiological methods were used on dissociated rat nodose neurons maintained in culture to determine whether responses to cholecystokinin (CCK) were associated with capsaicin-resistant (A type) or capsaicin-sensitive (C type) neurons. Nodose neurons were classified as A or C type on the basis of the characteristics of the Na+ current, a hyperpolarization-activated current, and sensitivity to a low concentration of capsaicin to ascertain the presence of vanilloid receptor 1 that has been associated with C-type neurons in sensory ganglia. It was expected that only capsaicin-sensitive C-type neurons would respond to CCK, because most vagally mediated actions of CCK are blocked by capsaicin treatment. However, we found that subpopulations of both A- and C-type neurons responded to CCK (24 and 38%, respectively). Thus some vagally mediated actions of CCK may be mediated by capsaicin insensitive A-type neurons.

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Review article: in vitro studies of gall-bladder smooth muscle function. Relevance in cholesterol gallstone disease

The interplay between contraction and relaxation in the gall-bladder muscularis leads to appropriate gall-bladder emptying and refilling during fasting and in the postprandial state in vivo. Several studies in both human and animal models have focused on cellular and molecular events in the gall-bladder wall in health and disease in vitro. Principal methods to study gall-bladder smooth muscle function include receptor binding studies (at the level of plasmamembranes or histological sections), phase contrast microscopy (at the level of isolated smooth muscle cells), and tensiometry (at the level of smooth muscle strips or the whole gall-bladder). At a very early stage, cholesterol gallstone disease is characterized by exposure of the gall-bladder wall to excess of biliary cholesterol and the cytotoxic effect of the bile salt deoxycholate. On a long-term basis, a form of gall-bladder leiomyopathy develops with defects involving the mechanisms of signal transduction at the level of plasmamembranes. The end-stage result is pathological contraction and/or relaxation of smooth musculature, impaired gall-bladder motility and gall-bladder stasis, all key factors in the pathogenesis of biliary cholesterol crystallization and gallstones.

Direct neuronal interactions between the duodenum and the sphincter of Oddi

The sphincter of Oddi (SO) is a complex structure that must function in coordination with the motor activities of the gallbladder and the duodenum. It is now clear that a neural circuit exists between the duodenum and the SO, and it is likely that this network is largely responsible for the regulation of SO motility. Recent studies have demonstrated that this circuit provides excitatory cholinergic input to SO ganglia that can be activated by electrical stimulation of the duodenal mucosa, distention of the duodenum, and increased motor activity of the duodenum.

CCK receptor dysfunction in muscle membranes from human gallbladders with cholesterol stones

Human gallbladders with cholesterol stones exhibit impaired muscle contraction induced by agonists that act on transmembrane receptors, increased membrane cholesterol content, and abnormal cholesterol-to-phospholipid ratio compared with those with pigment stones. The present study was designed to investigate the functions of the CCK receptor of gallbladder muscle membranes by radioreceptor assay and cross-linking. 125I-labeled CCK-8 binding was time-dependent, competitive, and specific. Scatchard analysis showed that the maximum specific binding (Bmax) was significantly decreased in cholesterol compared with pigment stone gallbladders (0.18 +/- 0. 07 vs. 0.38 +/- 0.05 pmol/mg protein, P < 0.05). In contrast, the affinity for CCK was higher in cholesterol than pigment stone gallbladders (0.18 +/- 0.06 vs. 1.2 +/- 0.23 nM). Similar results were observed in binding studies with the CCK-A receptor antagonist [3H]L-364,718. Cross-linking and saturation binding studies also showed significantly less CCK binding in gallbladders with cholesterol stones. These abnormalities were reversible after incubation with cholesterol-free liposomes. The Bmax increased (P < 0.01) and the dissociation constant decreased (P < 0.001) after incubation with cholesterol-free liposomes. In conclusion, human gallbladders with cholesterol stones have impaired CCK receptor binding compared with those with pigment stones. These changes are reversed by removal of the excess membrane cholesterol. These receptor alterations may contribute to the defective contractility of the gallbladder muscle in patients with cholesterol stones.

Humoral mechanisms and clinical aspects of biliary tract motility

This review is intended to summarize current information on neurohumoral regulation of the gallbladder and sphincter of Oddi motility under both physiological and pathological circumstances with emphasis on Hungarian contributions to today's knowledge. The mechanism of action of neurohumoral agents that interact on these segments of the biliary tract, and the explored details of the stimulation-contraction/relaxation coupling process of these substances, will be discussed. A modified classification of biliary tract motility disorders with new diagnostic and therapeutic approaches will also be provided. This information will aid understanding of the pathogenesis of motor disorders of the gallbladder and sphincter of Oddi, and will indicate possibilities for pharmacological exploitation in the treatment of diseases resulting from biliary tract motility abnormalities.

Duodenal sensory neurons project to sphincter of Oddi ganglia in guinea pig

Retrograde labeling of duodenum-sphincter of Oddi (SO) preparations in vitro with the carbocyanine dye DiI revealed that duodenal neurons project to the SO. The duodenum-SO-projecting neurons were immunoreactive (IR) for choline acetyltransferase but not nitric oxide synthase or calretinin, indicating that this is a cholinergic projection and that this pathway is distinct from the circuitry involved in the ascending limb of the peristaltic reflex. Approximately 20% of the duodenum-SO projection neurons were IR for calbindin. Calbindin-IR nerves within SO ganglia degenerated when the SO was maintained in organ culture alone, but persisted when the SO was cultured with the duodenum intact. Therefore, SO ganglia are a target of the calbindin-positive duodenum-SO projection. Because calbindin is a marker of intrinsic sensory neurons that have processes that pass to the mucosa, these neurons are in position to detect the release of a compound from the mucosa and signal its release to SO ganglia. When applied to retrogradely labeled neurons, cholecystokinin (CCK) elicited a prolonged depolarization, indicating that duodenum-SO-projecting neurons could be capable of detecting CCK released from the mucosa. It is proposed that the role of the intrinsic sensory neurons that project to the SO may be to signal the postprandial release of CCK, thus providing an instruction to decrease SO resistance and facilitate the flow of bile into the duodenum.

CCK regulates nonselective cation channels in guinea pig gastric smooth muscle cells

CCK has widespread effects in the gastrointestinal tract, stimulating pancreatic secretion and contraction of smooth muscles. The cellular mechanisms by which CCK causes smooth muscle contraction are poorly understood. We investigated the effects of CCK on guinea pig gastric smooth muscle cells using patch-clamp techniques. CCK caused contraction of cells accompanied by inward current. The conductance activated by CCK was nonselective for cations and showed little voltage dependence. Because ACh also activates nonselective cation current, we examined interactions between CCK and ACh. When CCK activated inward current, ACh caused no further effect. When CCK failed to activate current, subsequent ACh-activated current was larger and no longer exhibited its characteristic voltage dependence. Intracellular dialysis with guanosine 5'-O-(3-thiotriphosphate) caused similar changes in the voltage dependence of the ACh-activated current, suggesting a role for G proteins in regulation of the current. Activation of nonselective cation current would depolarize muscle and may contribute to the excitation mediated by CCK in tissues. These findings provide evidence that multiple types of receptors converge to regulate nonselective cation current.

Innervation of the gallbladder: structure, neurochemical coding, and physiological properties of guinea pig gallbladder ganglia

The muscle and epithelial tissues of the gallbladder are regulated by a ganglionated plexus that lies within the wall of the organ. Although these ganglia are derived from the same set of precursor neural crest cells that colonize the gut, they exhibit structural, neurochemical and physiological characteristics that are distinct from the myenteric and submucous plexuses of the enteric nervous system. Structurally, the ganglionated plexus of the guinea pig gallbladder is comprised of small clusters of neurons that are located in the outer wall of the organ, between the serosa and underlying smooth muscle. The ganglia are encapsulated by a shell of fibroblasts and a basal lamina, and are devoid of collagen. Gallbladder neurons are rather simple in structure, consisting of a soma, a few short dendritic processes and one or two long axons. Results reported here indicate that all gallbladder neurons are probably cholinergic since they all express immunoreactivity for choline acetyltransferase. The majority of these neurons also express substance P, neuropeptide Y, and somatostatin, and a small remaining population of neurons express vasoactive intestinal peptide (VIP) immunoreactivity and NADPH-diaphorase enzymatic activity. We report here that NADPH-diaphorase activity, nitric oxide synthase immunoreactivity, and VIP immunoreactivity are expressed by the same neurons in the gallbladder. Physiological studies indicate that the ganglia of the gallbladder are the site of action of the following neurohumoral inputs: 1) all neurons receive nicotinic input from vagal preganglionic fibers; 2) norepinephrine released from sympathetic postganglionic fibers acts presynaptically on vagal terminals within gallbladder ganglia to decrease the release of acetylcholine from vagal terminals; 3) substance P and calcitonin gene-related peptide, which are co-expressed in sensory fibers, cause prolonged depolarizations of gallbladder neurons that resemble slow EPSPs; and 4) cholecystokinin (CCK) acts presynaptically within gallbladder ganglia to increase the release of acetylcholine from vagal terminals. Results reported here indicate that hormonal CCK can readily access gallbladder ganglia, since there is no evidence for a blood-ganglionic barrier in the gallbladder. Taken together, these results indicate that gallbladder ganglia are not simple relay stations, but rather sites of complex modulatory interactions that ultimately influence the functions of muscle and epithelial cells in the organ.

Control of gallbladder contractions by cholecystokinin through cholecystokinin-A receptors in the vagal pathway and gallbladder in the dog

The mechanism of CCK action on gallbladder contractions in the physiological condition is unclear. Gallbladder contractions were monitored by means of chronically implanted force transducers in conscious dogs. Postprandial gallbladder contractions were partially inhibited by atropine and hexamethonium, and completely inhibited by devazepide. In vitro contractile response of canine gallbladder muscle strips to CCK-8 was also studied. CCK-8-induced muscle strip contraction was atropine and tetrodotoxin resistant, but was completely eliminated by devazepide. The existence of CCK receptors in the vagal nerve and gallbladder was examined by means of autoradiography. Forty-eight hours after ligation of the abdominal vagus, CCK-8 binding sites were found to accumulate in the subdiaphragmatic vagal nerve immediately proximal to the ligature, and similar binding sites were also found in the gallbladder smooth muscle layer. These binding sites were displaced by the addition of 10(-7) mol/1 unlabeled CCK-8 and devazepide, but L-365,260 had no effect. In conclusion, it is considerable that postprandial CCK-induced gallbladder contractions are controlled through CCK-A receptors both on the vagal nerve in stimulating endogenous release of acetylcholine and on the gallbladder directly to stimulate muscle contraction in the dog.

Functional role and histological demonstration of nitric-oxide-mediated inhibitory nerves in dog sphincter of Oddi

Nitric oxide (NO) plays an important physiological role in regulating gastrointestinal motility. Involvement of endogenous NO was evaluated in the response to non-adrenergic, non-cholinergic (NANC) nerve stimulation of the dog sphincter muscle of Oddi. Transmural electrical stimulation (TES), nicotine (10(-5) M) and K+ (10 mM) produced only a relaxation in the sphincter muscle strips contracted with substance P, which was not potentiated by atropine. The TES-induced relaxation was abolished by tetrodotoxin (3 x 10(-7) M) and oxyhaemoglobin (1.6 x 10(-5) M), but not affected by atropine (10(-7) M), propranolol (10(-7) M), phentolamine (10(-7) M), indomethacin (10(-6) M), cholecystokinin (CCK, 10(-8) M) and vasoactive intestinal polypeptide (VIP, 10(-8) M). The relaxation was also abolished by treatment with NG-nitro-L-arginine (L-NA, 10(-5) M), an NO synthase inhibitor. Nicotine produced a transient relaxation, which was abolished by tetrodotoxin, hexamethonium (10(-5) M) and L-NA, but not affected by atropine and NG-nitro-D-arginine (D-NA, 10(-5) M). The addition of K+ elicited a transient relaxation, which was abolished by tetrodotoxin and L-NA. The inhibitory effects of L-NA were antagonized by L-arginine (10(-3) M). The presence of neurons containing nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase was histochemically demonstrated in the sphincter of Oddi. These findings may indicate that TES, nicotine and K+ liberate NO from NANC inhibitory nerve which is involved in the relaxation of the dog sphincter of Oddi. The muscular tone does not seem to be regulated by cholinergic nerves under the experimental conditions used.

Role of nitric oxide in motility and secretion of the feline hepatobiliary tract

BACKGROUND

Nitric oxide (NO) mediates inhibition of gastrointestinal smooth-muscle cells via nonadrenergic, non-cholinergic (NANC) nervous pathways. The effect of NO on the absorption and secretion by the mucosa of the gastrointestinal and hepatobiliary tracts is less well known. The aim of this study was to evaluate the effects of a pharmacologic blockade of NO synthase on sphincter of Oddi activity, gallbladder function, and bile secretion and to demonstrate the presence of NO synthase-positive neurons in this region.

METHODS

Experiments were conducted on anesthetized cats after blockage of noradrenergic and cholinergic neurotransmission. Flow resistance in the sphincter of Oddi, gallbladder fluid absorption and motility, bile outflow from the liver, and bile salt secretion were registered.

RESULTS

Flow resistance exerted by the sphincter of Oddi increased dose-dependently in response to the NO synthase blocker NG-nitro-L-arginine. The increase in flow resistance was reversed stereospecifically by L-arginine, the substrate for NO synthesis. No significant effects on bile secretion, gallbladder fluid transport, or gallbladder motility were observed. NO synthase-positive neurons were identified close to the sphincter of Oddi and in the gallbladder mucosa.

CONCLUSIONS

This tonically active inhibitory NANC innervation of the sphincter of Oddi may be important in the physiologic regulation of the bile duct pressure.

Signal transduction pathway of the muscarinic receptors mediating gallbladder contraction

In gallbladder smooth muscle, carbachol interacts with M3 receptors to mediate contraction. To examine components of the intracellular second messenger system that is coupled to these receptors we have tested whether carbachol stimulates the formation of inositol phosphates (IP) to cause contraction. Guinea pig gallbladder muscle strips were prelabeled with [3H]inositol and were incubated with 0.1 mmol/l carbachol, a concentration causing maximal contraction. [3H]inositol monophosphates, [3H]inositol bisphosphates and [3H]inositol trisphosphates and contraction were measured at various times (0-90 s). To examine whether a pertussis toxin-sensitive guanine nucleotide binding protein is coupled to the muscarinic receptors, guinea pigs were pretreated with pertussis toxin (180 micrograms/kg i.v./24 h). The effectiveness of pertussis toxin treatment was determined by measuring [32P]ADP-ribosylation of a approximately 40/41 kDa protein from gallbladder homogenates. Carbachol caused a significant time-dependent increase in the formation of [3H]inositol monophosphates, [3H]inositol bisphosphates and [3H]inositol trisphosphates. The time course of [3H]inositol trisphosphate turnover caused by carbachol was biphasic, and was detectable at 15 s and maximal at 60 s; at 75 s and 90 s formation of [3H]inositol trisphosphates decreased, whereas the time course of carbachol-induced contraction of the gallbladder smooth muscle strips reached a plateau after 90 s. The effects of carbachol on [3H]inositol trisphosphates and on contraction were abolished by atropine.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of CCK on pancreatic function and morphology

This report reviews the effects of CCK on the pancreas and in particular analyzes recent studies in which CCK antagonists were used to evaluate the physiological role of CCK in modulating pancreatic function and morphology. CCK is released from endocrine cells of the small intestine in response to a meal. In various animal species there are CCK receptors on pancreatic acinar cells with two sites; occupation of the high affinity site is thought to mediate pancreatic secretion and growth, whereas occupation of the low affinity site by high CCK concentrations is thought to be responsible for supramaximal inhibition of secretion and pancreatitis. Recently, CCK receptors were also found on postganglionic cholinergic neurons in the gastrointestinal tract. Administration of CCK agonists stimulates pancreatic secretion and growth. Although in some previous studies CCK was given at doses that mimic its postprandial increase in plasma, these studies did not prove that the actions of exogenous CCK were physiologically important. In addition, it was unclear if CCK primarily acts as a true hormone or as a neurotransmitter. The development of specific CCK receptor antagonists made it possible to better evaluate the physiological role of CCK. In humans, CCK-A antagonists like loxiglumide or L-364,718 at doses that completely inhibited the action of supraphysiological doses of exogenous CCK reduced meal-stimulated pancreatic enzyme secretion only by approximately 50%. On the other hand, atropine abolished the postprandial increase in pancreatic secretion and in addition markedly reduced the increase in pancreatic secretion due to infusion of "physiological" doses of CCK (i.e., CCK doses that mimic its postprandial increase in plasma). The increase in pancreatic bicarbonate secretion was only slightly reduced by CCK blockade. CCK antagonists failed to reduce the postprandial increase in plasma insulin, but markedly reduced the postprandial PP release. CCK-A antagonists caused slight hypotrophy and hypoplasia of the exocrine pancreas. However, even after 9 months of effective blockade of the CCK-A-receptor, mice had normal body weight and an almost normal pancreas. CCK antagonists were unable to alter short-term changes in pancreatic growth due to feeding and fasting. In some species, CCK agonists induced development of pancreatic nodules and increased the growth of malignant tumors. Studies about the effects of CCK antagonists on induction and growth of pancreatic tumors showed controversial results. In conclusion, CCK may act on the pancreas by three pathways: (1) At low doses it serves as a neurotransmitter by acting on cholinergic neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Role of CCK in gallbladder function

Cholecystokinin may play a role in regulation of interdigestive motility, but this still remains to be investigated. CCK constitutes the major hormonal stimulus for postprandial gallbladder emptying. CCK exerts its contractile effects mainly through interaction directly with receptors on the gallbladder smooth muscle cells in the muscle layer, but also through interaction with cholinergic nerves extrinsic and/or intrinsic in nature. Furthermore, CCK can enhance ongoing nicotinic ganglionic transmission occurring in the serosal layer by release of acetylcholine. CCK interaction with the gallbladder smooth muscle CCKA receptor was studied in further detail. CCK contracts strips of gallbladder muscle in a concentration-dependent way with a potency in the nanomolar range in all tested species. The potency is 1,000-fold better than that of gastrin; thus, the receptor is of type CCKA. CCK binding to this receptor is specific and of high affinity, 1,000-fold better than that of gastrin with no differences between the tested species including bovine, porcine, and human. Also, CCK binding affinity was independent of age, gender, or weight of the person and pathology of the human gallbladder. The biochemistry of the CCKA receptor varies between the tested species (bovine and human). Both CCKA receptors are heavily glycosylated, but of different size and carbohydrate content. The bovine CCKA receptor is of apparent size M(r) = 70-85 kD with N-linked complex carbohydrates and sialic acids. The human CCKA receptor is of M(r) = 85-95 kD, with N-linked complex carbohydrates, but no sialic acids. They both have a protein core of apparent size M(r) = 43 kD, with almost identically sized fragments after enzymatic cleavage. Probably the protein cores contain the receptor binding region, which seems well preserved between species. CCK and the CCKA gallbladder muscularis receptor are main regulators of postprandial gallbladder emptying. The biochemistry of the CCKA gallbladder smooth muscle receptor is in accord with newly generated data of purification and cloning of the rat pancreatic CCKA receptor.

Physiology of motor function of the sphincter of Oddi

Human and experimental studies of the sphincter of Oddi have established that the sphincter is not a simple and passive smooth muscle portion of the biliary system; rather, it plays an active role in modulating bile flow into the duodenum in both the fasted and the postprandial states. The sphincter of Oddi in the opossum, and likely in man, demonstrates spontaneous phasic and perhaps peristaltic activity that affects bile flow into the duodenum. The sphincter appears to be under the control of a smooth muscle pacemaking-like region in the proximal sphincter that controls the frequency and direction of propagation of the phasic contractions. Immunohistochemical studies have documented the presence of dense concentrations of neuropeptide-containing myenteric nerves in the sphincter of Oddi. Physiologic studies have confirmed that these peptides, in combination with the classic gastrointestinal hormones, exert significant effects on biliary motility. Experimental studies of the motor physiology of the sphincter of Oddi have advanced our understanding of human biliary motility and dysmotility. A subset of patients experiences biliary-like pain after cholecystectomy. This pain may be attributable to either mechanical stenosis of the papilla or dysfunction of the sphincter of Oddi. No definitive test currently exists to establish the diagnosis with adequate sensitivity or specificity. It is hoped that further development of ultrasonographic, scintigraphic, manometric, or electromyographic techniques will allow a clearer definition of patients who truly have sphincter dysfunction and who might benefit from medical, endoscopic, or surgical therapy.

Neuropeptides in pig sphincter of Oddi, bile duct, gallbladder, and duodenum

To better understand the complex structure and function of the sphincter of Oddi (SO), the occurrence and localization of nine neuropeptides, including vasoactive intestinal polypeptide (VIP), bombesin, neuropeptide Y, peptide histidine-isoleucine (PHI), calcitonin gene-related peptide (CGRP), galanin, substance P, serotonin, and somatostatin, were studied by immunohistochemical methods in the pig SO. The SO innervation was compared to gallbladder, common bile duct, and duodenal innervation. Specimens from the SO, gallbladder, common bile duct, and duodenum demonstrated a rich network of nerves, as suggested by light microscopy and confirmed by a myelin marker S-100. SO demonstrated very strong immunoreactivity for VIP, strong immunoreactivity for neuropeptide Y and galanin, moderate immunoreactivity for PHI and CGRP, and borderline immunoreactivity for bombesin and substance P. Serotonin and somatostatin immunoreactivity was also observed, not in the nerves, but in some of the epithelial cells. The gallbladder innervation was virtually identical to the SO innervation, whereas common bile duct and duodenal innervation were slightly different. To our knowledge this is the first time that galanin- and PHI-like immunoreactivities have been observed in the SO. Our observations suggest that these peptides, along with VIP, neuropeptide Y, and CGRP, might play a role in the neural control of biliary motility.

Involvement of L-arginine-nitric oxide pathways in neural relaxation of the sphincter of Oddi

To evaluate if L-arginine-nitric oxide-pathways are involved in the neural relaxation of the sphincter of Oddi, we studied the effect of nitric oxide synthase inhibition on electrical field stimulation-induced relaxation of the sphincter of Oddi in the guinea pig in vitro. After incubation with atropine (1 microM), phentolamine (1 microM) and propranolol (1 microM), histamine (50 microM) and cholecystokinin-octapeptide (25 nM) produced similar increases in sphincter tone. Subsequent field stimulation induced sphincteric relaxation, that was significantly greater when the initial tone had been raised by cholecystokinin (5 Hz, 59 +/- 9%; 10 Hz, 79 +/- 9%) compared to histamine (5 Hz, 27 +/- 3%; 10 Hz, 40 +/- 7%). N-omega-Nitro-L-arginine methyl ester (L-NAME, 100 microM), which competitively inhibits nitric oxide synthase, markedly suppressed this relaxation. The subsequent addition of L-arginine (1 mM), but not D-arginine (1 mM), restored the relaxation. Hexamethonium (100 microM) did not affect the relaxation, but tetrodotoxin (1 microM) completely abolished it. Sodium nitroprusside caused a dose-dependent relaxation of the sphincter (ED50 13 nM), which was unaffected by L-NAME. In conclusion, endogenous nitric oxide synthase products represent a major transmitter of non-adrenergic non-cholinergic relaxation of the sphincter of Oddi in the guinea pig. This relaxation is partially facilitated by cholecystokinin.

Effect of selective and nonselective muscarinic blockade on cholecystokinin-induced gallbladder emptying in man

In this study we investigated the effect of selective (M1) and non-selective (M1 and M2) pharmacologic blockade of muscarinic receptors on cholecystokinin-induced gallbladder emptying. After validating the method of study, the gallbladder function was evaluated in 15 normal volunteers by quantitative biliary scintigraphy, and the effect of intravenous atropine (0.15 mg/10 kg) and pirenzepine (10 mg) was analyzed in each subject. Atropine significantly reduced the ejection period and the ejection fraction of gallbladder evacuation. Pirenzepine reduced the ejection period, but the ejection fraction remained unchanged. We conclude that the effect of cholecystokinin on gallbladder motility is mediated through muscarinic receptors. Our results suggest that M2 receptors, but not M1 receptors, are involved in this response.

The role of cholecystokinin in ganglionic transmission in the guinea-pig gall-bladder

1. The effects of cholecystokinin (CCK) on intact guinea-pig gall-bladder ganglia were investigated with intracellular, single-electrode current- and voltage-clamp recording techniques. 2. Cholecystokinin octapeptide (CCK-8; 0.01-100 nM) increased the amplitude of the fast excitatory postsynaptic potential (EPSP) that was evoked by stimulation of interganglionic fibre tracts. In most cases, neurones that exhibited subthreshold EPSPs in normal Krebs solution fired action potentials in the presence of CCK-8. In a low Ca2+/high Mg2+ solution, CCK-8 caused a 3-fold increase in the amplitude of fast EPSPs. 3. The amplitude of the evoked excitatory postsynaptic current (EPSC) was increased by CCK-8 (0.01-100 nM) in a concentration-dependent manner. The effect was maximal at 1.0 nM. 4. Cholecystokinin octapeptide caused a 3-fold increase in the quantal content of the EPSP in a low Ca2+/high Mg2+ solution, but had no effect on the quantal size. 5. The specific CCK-A receptor antagonist, MK-329 (formerly L-364,718; 1.0 nM), reversibly blocked the facilitatory effect of CCK-8 on ganglionic transmission. However, the specific CCK-B receptor antagonist, L-365,260 (10 nM), did not alter the presynaptic facilitatory effect of CCK-8. 6. The response of gall-bladder neurones to exogenously applied ACh was not modified by CCK-8. 7. Application of CCK-8, by superfusion (0.001-100 nM) or by pressure microejection (100 microM), had no effect on the membrane potential, membrane conductance, action potential, or threshold of gall-bladder neurones. 8. Immunohistochemistry was employed to determine whether the actions of CCK could be elicited by release of the peptide from nerve terminals within the ganglionated plexus of the gall-bladder. Immunoreactivity for CCK was not detected in the ganglionated plexus of the gall-bladder, but CCK immunoreactivity was plentiful in control preparations of intestinal myenteric and submucosal plexuses. 9. These results show that CCK has a presynaptic facilitatory effect on fast synaptic transmission in guinea-pig gall-bladder ganglia, and that this effect is mediated by presynaptic CCK-A receptors. Furthermore, it appears that such an effect would normally occur in response to hormonal CCK, rather than CCK that is released from nerve terminals.

Interaction of the cholinergic system and cholecystokinin in the regulation of endogenous and exogenous stimulation of pancreatic secretion in humans

Pancreatic enzyme secretion is regulated in humans by the cholinergic system and by cholecystokinin (CCK). The interaction between both regulatory systems in response to exogenous and endogenous stimulation was analyzed in the present study using the cholinergic antagonist atropine and the CCK antagonist loxiglumide. A dose-dependent stimulation of pancreatic enzyme output was achieved either by duodenal perfusion of graded caloric loads or by IV infusion of increasing doses of cerulein. Prestimulated pancreatic secretion was inhibited by atropine and loxiglumide. Atropine furthermore almost completely blocked meal-stimulated pancreatic secretion, whereas loxiglumide caused 60% inhibition. The enzyme response to graded doses of exogenous CCK was significantly inhibited by atropine and loxiglumide. Plasma levels of CCK were not altered by atropine but increased with infusion of loxiglumide. This study supports the concept that pancreatic enzyme secretion is predominantly dependent on a cholinergic tone and that CCK modulates the enzyme-secretory response.

Effects of a new cholecystokinin antagonist (GE 410) on the smooth muscle of the guinea pig ileum

Suc-Tyr-(SE)-Met-Gly-Trp-Met-Asp-beta-phenethylamide (GE 410) competitively antagonized the contractions of smooth muscle strips from guinea pig ileum (pA2 = 7.6, n = 0.95) induced by cholecystokinin-octapeptide (CCK8). GE 410 inhibited the electrically-induced cholinergically mediated contractile responses and the [3H]ACh release in the ileum, as well as the CCK-stimulated electrical contractile responses and the [3H]ACh release in the cholinergic nerve terminals. The results suggest the existence of CCK-receptors not only in the smooth muscles but also on the neurons.

Is the CCK-8 induced relaxation of the feline sphincter of Oddi mediated by VIP neurons?

The regional, intraarterial, injection of CCK-8 elicits reciprocal effects on the motility of the extrahepatic biliary tree in the cat: the contraction of the gallbladder and a relaxation of the sphincter of Oddi as well as of the duodenal wall. After neural blockade with tetrodotoxin the responses of the sphincter to CCK-8 were blocked, and the responses of the gallbladder were markedly reduced. After the regional administration of a VIP antiserum the sphincter relaxation in response to CCK-8 was blocked. Immunocytochemically it was demonstrated that the feline sphincter contains a rich VIP-ergic innervation, while CCK-like immunoreactivity was found only in mucosal endocrine cells. The results indicate that CCK-8 selectively activates inhibitory VIP neurons innervating the sphincter. After the administration of a nonpeptide CCK-receptor antagonist, the CCK-8 induced motor responses of both the sphincter and the gallbladder were markedly reduced. This indicates that blockade of CCK-8 receptors involves muscular as well as neural CCK-receptors.

Pathogenesis of acute cholecystitis after gastrectomy

The increased incidence of gallbladder diseases after gastrectomy is discussed with regard to contractile motility of the gallbladder. Ultrasonographic findings and contraction of the gallbladder in response to egg yolk or caerulein were studied before and after gastrectomy at intervals ranging from 2 weeks to 6 months. Enlargement of the gallbladder with accumulation of biliary sludge and hypomotility were frequently observed within a month of operation for gastric cancer, suggesting that biliary stasis is an important contributing factor in postoperative acute cholecystitis. Within 3 months of operation, contraction had recovered to close to preoperative levels and the incidence of biliary sludge formation gradually decreased. Daily administration of an opiate antagonist, naloxone (0.8 mg), significantly improved gallbladder dyskinesia and decreased the incidence of biliary sludge formation within 1 month of gastrectomy.

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.

Functional and morphological relationships between the feline main pancreatic and bile duct sphincters

To analyze the relationships between the bile duct and main pancreatic duct sphincters, the resistance to flow through these sphincters was studied simultaneously with perfusion techniques in anesthetized cats. Basal flow resistance was higher in the pancreatic sphincter than in the bile duct sphincter. The pressure in one duct system was not affected by the flow in the other. The muscular activities in the sphincters were usually well coordinated. Distention of the upper biliary tract or the pancreatic duct system reduced the flow resistance in both sphincters. Cholecystokinin-8 (0.01 micrograms), duodenal distention, and sublingual glyceryl trinitrate (0.4 mg) also relaxed both sphincters, whereas secretin in a dose that induced pancreatic secretion had no consistent effect. Morphine increased flow resistance in both systems. These functional studies indicate that the 2 sphincters share smooth muscle fibers at the level where the flow resistances arise, and there are thus no grounds for separate control of the sphincters. There was no evidence of a functionally common sphincter ampulla. The conclusions drawn from the manometric results were supported by morphological findings in this study.

Cholecystokinin-octapeptide constricts guinea-pig and human airways

1. Cholecystokinin-octapeptide (CCK-OP, 10(-10)-3 x 10(-6) M) produced a concentration-dependent contractile response in guinea-pig trachea which was enhanced by both the mechanical removal of the epithelium and by indomethacin (10(-5) M), with an EC50 of 6.18 +/- 0.10 x 10(-8) M. 2. Sub-threshold concentrations of CCK-OP, which did not alter the resting tone of the smooth muscle, did not alter responses produced to electrical field stimulation (EFS) or to vagal nerve stimulation in an intact tracheal tube preparation. Atropine (2 x 10(-6) M) did not alter the concentration-response curve to CCK-OP, indicating that CCK-OP contraction is not mediated by cholinergic mechanisms. 3. The inhibition of neutral endopeptidase (endopeptidase-24.11) by phosphoramidon (10(-5) M) gave a leftward shift in the CCK-OP concentration-response curve in tissues with intact epithelium obtained from normal animals, but had no effect in tissues denuded of epithelium or in tissues obtained from animals which had been actively sensitized and challenged with ovalbumin (OA). 4. CCK-OP-induced contractile responses were antagonized by the CCK-receptor antagonists dibutyryl cyclic guanosine monophosphate (pA2 = 4.3) and L-364,718 (pA2 = 9.6). 5. CCK-OP induced bronchoconstriction in large, but not small, human airways and was antagonized by the CCK-receptor antagonist L-364,718. CCK-OP had no effect on cholinergic neural responses elicited by EFS in human airways.

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.

Effect of cholecystokinin octapeptide and somatostatin on the motility of guinea pig and canine gallbladder

Species differences have been observed in the effect of cholecystokinin octapeptide (CCK OP) on the canine and guinea pig gallbladder smooth muscle motility. 1. CCK OP was more potent stimulant in canine than in guinea pig gallbladder smooth muscles. Its pD2 values were 10 and 9.2, respectively. 2. The acetylcholine (10(-4) M)-induced maximum contractions in canine gallbladder muscle strips were by 50% lower as compared to the CCK OP (10(-8) M) maximum responses while in guinea pig gallbladder muscle strips the acetylcholine (ACh) maximum responses were by 20% lower than the CCK OP maximum responses. 3. CCK OP increased [3H]ACh release by 27% in canine gallbladder and by 40% in guinea pig gallbladder. 4. Somatostatin (SOM) had not any direct myogenic effect in guinea pig and canine gallbladder but it decreased [3H]ACh release from gallbladder intrinsic cholinergic neurons.

Effects and mechanisms of action of motilin on the cat sphincter of Oddi

The effects of motilin on gallbladder and sphincter of Oddi motor activity and transphincteric flow were studied in the cat in vivo. Motilin at doses of up to 1 microgram/kg had no effect on gallbladder motility. Increasing doses of intraarterial motilin (32-256 ng/kg) caused an increase in tonic pressures and in the force of phasic contractions of the sphincter of Oddi (p less than 0.001). Simultaneous measurements of myoelectric activity and transphincteric flow showed that motilin caused an increase in the frequency of spike bursts with a concomitant dose-dependent decrease in flow (p less than 0.001). The action of motilin was unaffected by extrinsic denervation (cervical vagotomy or splanchnicectomy), hexamethonium, and propranolol. Atropine, methysergide, or phentolamine partially blocked the excitatory effect of motilin (p less than 0.05), whereas tetrodotoxin, a combination of atropine and methysergide, or naloxone completely blocked its effects (p less than 0.001). It is concluded that (a) motilin decreases sphincter of Oddi flow by increasing its motor activity and (b) motilin activates an intramural excitatory pathway that appears to consist of opiate, serotonergic, and cholinergic neurons.

Postprandial sphincter of Oddi myoelectric activity and gallbladder emptying

Feeding initiates gallbladder emptying and bile delivery into the duodenum. It is not yet defined how the sphincter of Oddi regulates flow of bile into the duodenum during gallbladder emptying. The aim of this study was to assess postprandial spike burst activity in the sphincter of Oddi, while quantitating gallbladder emptying with noninvasive radioisotope imaging. Six adult opossums were prepared with bipolar electrodes in the sphincter of Oddi. After 2 weeks of recovery the animals were fasted overnight and positioned under a gamma camera, and myoelectric recordings were begun. After two cycles of the migrating motor complex (MMC), 2 mCi 99Tc-HIDA was infused intravenously and permitted to concentrate in the gallbladder for a period of 30 min. Subsequently, a 30-ml liquid meal, containing 0.9 g protein, 3.5 g carbohydrate, and 3.3 g fat, was instilled into the stomach. Sphincter of Oddi myoelectric activity (spike bursts/min) and gallbladder emptying (expressed as percentage of original 99Tc counts in the gallbladder) were measured at intervals for 120 min following feeding. Feeding resulted in prompt gallbladder emptying. Sphincter of Oddi spike burst activity was not altered significantly in the first 30 min after feeding, suggesting that motor activity in the sphincter of Oddi does not initially influence bile flow. Subsequently, spike burst activity increased progressively, suggesting that sphincter of Oddi motor activity may accelerate bile delivery into the duodenum during later phases of gallbladder emptying.

Novel autonomic neurotransmitters and upper gastrointestinal function

The evidence for, and possible roles of, inhibitory and excitatory non-adrenergic, non-cholinergic (NANC) nerves supplying smooth muscle, and the effects of putative transmitter candidates are considered for each of three main regions of the upper gastrointestinal tract: (A) the smooth muscle portion of the oesophagus and the oesophagogastric junction, (B) the stomach (fundus, body and antrum) and gastroduodenal junction and (C) the biliary tract and choledochoduodenal junction. The major points from human tissues are as follows: 1. Inhibitory (NANCI) nerves appear to be present in the muscularis externa of oesophagus, stomach and duodenum, with greater density in the circular than in the longitudinal muscle. 2. NANCI nerves are present in high density at the oesophagogastric and choledochoduodenal junctions. They may also be present at the gastroduodenal junction. The gall-bladder may have a very sparse NANCI innervation. 3. Excitatory (NANCE) nerves appear to be present throughout the upper gastrointestinal tract. 4. Many candidates need at present to be considered for the role of NANCE transmitter(s) in the human upper gastrointestinal tract but substance P still seems a likely contender for this role. 5. Fewer candidates are at present generally available for the role of NANCI transmitter(s), with VIP and ATP being leading contenders. However, in the human upper gastrointestinal tract the evidence for ATP is not good, and VIP still remains the favourite candidate except in the gall-bladder, where its role remains to be elucidated.