The role of neurotensin in human gallbladder motility

New Avenues in the Regulation of Gallbladder Motility-Implications for the Use of Glucagon-Like Peptide-Derived Drugs

CONTEXT

Several cases of cholelithiasis and cholecystitis have been reported in patients treated with glucagon-like peptide 1 (GLP-1) receptor agonists (GLP-1RAs) and GLP-2 receptor agonists (GLP-2RAs), respectively. Thus, the effects of GLP-1 and GLP-2 on gallbladder motility have been investigated. We have provided an overview of the mechanisms regulating gallbladder motility and highlight novel findings on the effects of bile acids and glucagon-like peptides on gallbladder motility.

EVIDENCE ACQUISITION

The articles included in the present review were identified using electronic literature searches. The search results were narrowed to data reporting the effects of bile acids and GLPs on gallbladder motility.

EVIDENCE SYNTHESIS

Bile acids negate the effect of postprandial cholecystokinin-mediated gallbladder contraction. Two bile acid receptors seem to be involved in this feedback mechanism, the transmembrane Takeda G protein-coupled receptor 5 (TGR5) and the nuclear farnesoid X receptor. Furthermore, activation of TGR5 in enteroendocrine L cells leads to release of GLP-1 and, possibly, GLP-2. Recent findings have pointed to the existence of a bile acid-TGR5-L cell-GLP-2 axis that serves to terminate meal-induced gallbladder contraction and thereby initiate gallbladder refilling. GLP-2 might play a dominant role in this axis by directly relaxing the gallbladder. Moreover, recent findings have suggested GLP-1RA treatment prolongs the refilling phase of the gallbladder.

CONCLUSIONS

GLP-2 receptor activation in rodents acutely increases the volume of the gallbladder, which might explain the risk of gallbladder diseases associated with GLP-2RA treatment observed in humans. GLP-1RA-induced prolongation of human gallbladder refilling may explain the gallbladder events observed in GLP-1RA clinical trials.

Functions of the Gallbladder

The gallbladder stores and concentrates bile between meals. Gallbladder motor function is regulated by bile acids via the membrane bile acid receptor, TGR5, and by neurohormonal signals linked to digestion, for example, cholecystokinin and FGF15/19 intestinal hormones, which trigger gallbladder emptying and refilling, respectively. The cycle of gallbladder filling and emptying controls the flow of bile into the intestine and thereby the enterohepatic circulation of bile acids. The gallbladder also largely contributes to the regulation of bile composition by unique absorptive and secretory capacities. The gallbladder epithelium secretes bicarbonate and mucins, which both provide cytoprotection against bile acids. The reversal of fluid transport from absorption to secretion occurs together with bicarbonate secretion after feeding, predominantly in response to an adenosine 3',5'-cyclic monophosphate (cAMP)-dependent pathway triggered by neurohormonal factors, such as vasoactive intestinal peptide. Mucin secretion in the gallbladder is stimulated predominantly by calcium-dependent pathways that are activated by ATP present in bile, and bile acids. The gallbladder epithelium has the capacity to absorb cholesterol and provides a cholecystohepatic shunt pathway for bile acids. Changes in gallbladder motor function not only can contribute to gallstone disease, but also subserve protective functions in multiple pathological settings through the sequestration of bile acids and changes in the bile acid composition. Cholecystectomy increases the enterohepatic recirculation rates of bile acids leading to metabolic effects and an increased risk of nonalcoholic fatty liver disease, cirrhosis, and small-intestine carcinoid, independently of cholelithiasis. Among subjects with gallstones, cholecystectomy remains a priority in those at risk of gallbladder cancer, while others could benefit from gallbladder-preserving strategies. © 2016 American Physiological Society. Compr Physiol 6:1549-1577, 2016.

Neurotensin and cholecystokinin contract gallbladder circular muscle in chickens

The contractile effects of neurotensin (NT) and cholecystokinin octapeptide (CCK-8) on isolated circular smooth muscle strips of chicken gallbladder were investigated. The NT (0.25-300 nM) produced concentration-dependent contractions on smooth muscle with an EC50 of 8.5 nM (95% confidence limits = 5.3-13.6 nM). In comparison, CCK-8 produced concentration-dependent contractions with an EC50 of 13 nM (95% confidence limits of 9-20 nM). There were no statistical differences in contractile responses when comparing NT and CCK-8 at equimolar concentrations. The NT appears to act directly on smooth muscle tissue in the chicken; the contractile responses were not blocked by 10 µM atropine or tetrodotoxin. A portion of the activity is mediated by extracellular calcium as 100 nM nifedipine inhibited 30% of peptide-induced muscle tension. The NT receptor (NTR) type 1 antagonist SR 48692 (0.1 µM) did not significantly reduce NT potency. The contractile effects of CCK-8 remained unaltered in tissues pretreated with atropine, TTX, or nifedipine. The CCK-A antagonist lorglumide, at a concentration of 1 µM, reduced the contractile potency of CCK-8 by one-half. Avian receptors for NT and CCK may differ pharmacologically from their mammalian counterparts, but their contractile actions on the gallbladder resulting in increased biliary output by flow are further evidence of their role in the postprandial regulation of lipid digestion in chickens.

Effect of enteral feeding on gallbladder function in dogs

Nutritional support in critically ill patients is a fundamental principle of patient care. Little is known about gallbladder motility during the interdigestive phase and in response to enteral feeding. The objective of this study was to investigate the effect of enteral feeding on gallbladder function in dogs. The cholagogue meal (Lipofundin infusion) was applied in four anatomical positions (jejunum, duodenojejunal junction, descending duodenum, stomach) in five healthy Beagle dogs. Gallbladder volume (GBV) was monitored by ultrasonography. Lipofundin infusion given through the feeding tube caused a maximal gallbladder contraction of 9.2% (range 3.7-13.9%) in the jejunum, 16.5% (9.1-22.1%) at the duodenojejunal junction and 26.3% (22.8-29.5%) in the descending duodenum. When the cholagogue meal was given through the mouth, it caused a mean 33.8% (28.6-46.5%) maximum gallbladder contraction in the same animals. In conclusion, we can establish that the ultrasound-guided gallbladder emptying method proved to be a useful technique for monitoring the cholagogue effect of Lipofundin meal applied in different anatomical positions of the intestine. The deeper the position of application, the smaller and shorter gallbladder contraction was evoked.

Stimulation of oval cell and hepatocyte proliferation by exogenous bombesin and neurotensin in partially hepatectomized rats

AIM: To investigate the effect of the neuropeptides bombesin (BBS) and neurotensin (NT) on oval cell proliferation in partially hepatectomized rats not pretreated with a known hepatocyte inhibitor.

METHODS: Seventy male Wistar rats were randomly divided into five groups: I = controls, II = sham operated, III = partial hepatectomy 70% (PHx), IV = PHx + BBS (30 μg/kg per day), V = PHx + NT (300 μg/kg per day). Forty eight hours after liver resection, portal endotoxin levels and hepatic glutathione redox state were determined. α-fetoprotein (AFP) mRNA (in situ hybridisation), cytokeratin-19 and Ki67 antigen expression (immunohistochemistry) and apoptosis (TUNEL) were evaluated on liver tissue samples. Cells with morphological features of oval cells that were cytokeratin-19 (+) and AFP mRNA (+) were scored in morphometric analysis and their proliferation was recorded. In addition, the proliferation and apoptotic rates of hepatocytes were determined.

RESULTS: In the control and sham operated groups, oval cells were significantly less compared to groups III, IV and V (P < 0.001). The neuropeptides BBS and NT significantly increased the proliferation of oval cells compared to group III (P < 0.001). In addition, BBS and NT induced a significant increase of hepatocyte proliferation (P < 0.001), whereas it decreased their apoptotic activity (P < 0.001) compared to group III. BBS and NT significantly decreased portal endotoxemia (P < 0.001) and increased the hepatic GSH: GSSG ratio (P < 0.05 and P < 0.001, respectively) compared to group III.

CONCLUSION: BBS and NT stimulated oval cell proliferation in a model of liver regeneration, without use of concomitant suppression of hepatocyte proliferation as oval cell activation stimuli, and improved the hepatocyte regenerative response. This peptides-induced combined stimulation of oval cell and hepatocyte proliferation might serve as a possible treatment modality for several liver diseases.

Bombesin and neurotensin exert antiproliferative effects on oval cells and augment the regenerative response of the cholestatic rat liver

The regenerative capacity of the cholestatic liver is significantly attenuated. Oval cells are hepatic stem cells involved in liver's regeneration following diverse types of injury. The present study investigated the effect of the neuropeptides bombesin (BBS) and neurotensin (NT) on oval cell proliferation as well as on hepatocyte and cholangiocyte proliferation and apoptosis in the cholestatic rat liver. Seventy male Wistar rats were randomly divided into five groups: controls, sham operated, bile duct ligated (BDL), BDL+BBS (30 μg/kg/d), BDL+NT (300 μg/kg/d). Ten days later, alpha-fetoprotein (AFP) mRNA (in situ hybridization), cytokeratin-19 and Ki67 antigen expression (immunohistochemistry) and apoptosis (TUNEL) were evaluated on liver tissue samples. Cells with morphologic features of oval cells that were cytokeratin-19(+) and AFP mRNA(+) were scored in morphometric analysis and their proliferation was recorded. In addition, the proliferation and apoptotic rates of hepatocytes and cholangiocytes were determined. Alanine aminotransferase (ALT) levels and hepatic oxidative stress (lipid peroxidation and glutathione redox state) were also estimated. The neuropeptides BBS and NT significantly reduced ALT levels and hepatic oxidative stress. Both agents exerted similar and cell type-specific effects on oval cells, hepatocytes and cholangiocytes: (a) oval cell proliferation and accumulation in the cholestatic liver was attenuated, (b) hepatocyte proliferation was increased along with a decreased rate of their apoptosis and (c) cholangiocyte proliferation was attenuated and their apoptosis was increased. These observations might be of potential value in patients with extrahepatic cholestasis.

Ileal brake: a sensible food target for appetite control. A review

With the rising prevalence of obesity and related health problems increases, there is increased interest in the gastrointestinal system as a possible target for pharmacological or food-based approaches to weight management. Recent studies have shown that under normal physiological situations undigested nutrients can reach the ileum, and induce activation of the so-called "ileal brake", a combination of effects influencing digestive process and ingestive behaviour. The relevance of the ileal brake as a potential target for weight management is based on several findings: First, activation of the ileal brake has been shown to reduce food intake and increase satiety levels. Second, surgical procedures that increase exposure of the ileum to nutrients produce weight loss and improved glycaemic control. Third, the appetite-reducing effect of chronic ileal brake activation appears to be maintained over time. Together, this evidence suggests that activation of the ileal brake is an excellent long-term target to achieve sustainable reductions in food intake. This review addresses the role of the ileal brake in gut function, and considers the possible involvement of several peptide hormone mediators. Attention is given to the ability of macronutrients to activate the ileal brake, and particularly variation attributable to the physicochemical properties of fats. The emphasis is on implications of ileal brake stimulation on food intake and satiety, accompanied by evidence of effects on glycaemic control and weight loss.

The peptide hormone xenin induces gallbladder contractions in conscious dogs

Xenin is a 25-amino acid peptide isolated from human gastric mucosa. The biological activities of xenin include modulating intestinal motility and affecting exocrine pancreatic secretion and gastric acid secretion. The physiological effect of xenin on the gastrointestinal tract, however, is incomplete. The objective of this study is to investigate the effects of xenin on the gastrointestinal tract motility of conscious dogs. Gastrointestinal tract and gallbladder contractions were monitored by chronically implanted force transducers. Synthetic xenin was injected intravenously during the interdigestive state with or without pretreatment with cholinergic blockers. The effects of xenin following cholecystectomy and truncal vagotomy were also investigated. Xenin induced gallbladder and jejunal contractions, although a dose-dependent response was shown only with gallbladder contractions. These effects were inhibited by pretreatment with cholinergic blockers, but were not enhanced by truncal vagotomy. The jejunal contractions were completely inhibited by cholecystectomy. The only direct effect of xenin in terms of gastrointestinal motility was to induce gallbladder contractions in conscious dogs. The neural pathway mediating xenin's action was cholinergic, but not the vagal. This novel finding indicates a new role of xenin.

Ursodeoxycholic acid improves gastrointestinal motility defects in gallstone patients

AIM: To simultaneously evaluate the presence of defects in gallbladder and gastric emptying, as well as in intestinal transit in gallstone patients (GS) and the effect of chronic ursodeoxycholic acid (UDCA) administration on these parameters and on serum bile acids and clinical outcome in GS and controls (CTR).

METHODS: After a standard liquid test meal, gallbla-dder and gastric emptying (by ultrasound), oroileal transit time (OITT) (by an immunoenzymatic technique) and serum bile acids (by HPLC) were evaluated before and after 3 mo of UDCA (12 mg/kg bw/d) or placebo administration in 10 symptomatic GS and 10 matched healthy CTR.

RESULTS: OITT was longer in GS than in CTR (P < 0.0001); UDCA significantly reduced OITT in GS (P < 0.0001), but not in CTR. GS had longer gastric half-emptying time (t_1/2) than CTR (P < 0.0044) at baseline; after UDCA, t_1/2 significantly decreased (P < 0.006) in GS but not in CTR. Placebo administration had no effect on gastric emptying and intestinal transit in both GS and CTR.

CONCLUSION: The gallstone patient has simultaneous multiple impairments of gallbladder and gastric emptying, as well as of intestinal transit. UDCA administration restores these defects in GS, without any effect in CTR. These results confirm the pathogenetic role of gastrointestinal motility in gallstone disease and suggest an additional mechanism of action for UDCA in reducing bile cholesterol supersaturation.

Rho kinase expression and its central role in ovine gallbladder contractions elicited by a variety of excitatory stimuli

Rho kinase has contractile activity, which induces Ca2+ sensitization in various cells. Several receptors are linked to the Rho/Rho-kinase pathway. Therefore, in this study we aimed to demonstrate the central importance of this novel pathway for diverse excitatory stimuli in the smooth muscle of the sheep gallbladder. Accordingly, the effects of a Rho kinase inhibitor, (+)-(R)-trans-4-(1-aminoethyl)-N-(4-pyridyl) cyclohexanecarboxamide dihydrochloride monohydrate (Y-27632, 10(-8)-3 x 10(-5) M), were investigated on cholecystokinin-8 (CCK-8, 10(-8) M), endothelin-1 (10(-8) M), carbachol (10(-6)-10(-5) M), 5-hydroxytryptamine (5-HT, 10(-6)-10(-5) M), histamine (10(-6)-10(-5) M), phenylephrine (10(-5)-10(-4) M), neurokinin A (10(-7)-10(-6) M), electrical field stimulation (40 V, 0.5 ms, 2, 4, 8, 16, 32 Hz, 15 s, 3 min intervals) and potassium chloride (KCl, 25-50 mM)-induced contractions as well as spontaneous contractile activity. Electrical field stimulation evoked tetrodotoxin (3 x 10(-6) M)-sensitive reproducible contractions, which were inhibited by atropine (2 x 10(-6) M) and potentiated by eserine (5 x 10(-7) M). EFS-induced contraction was significantly inhibited by Y-27632 (10(-5) M). In addition, spontaneous contractile activity was suppressed in the presence of the compound (10(-6)-10(-5) M). This Rho kinase inhibitor also dramatically decreased the contractions elicited by 5-HT, neurokinin A and carbachol. KCl-induced contraction, which was not atropine-sensitive, was also conspicuously attenuated by Y-27632. Moreover, Y-27632 (10(-8)-3 x 10(-5) M) relaxed gallbladder strips that were contracted by histamine, endothelin-1, CCK-8 and phenylephrine in a concentration-dependent manner. pEC50 values for Y-27632 were 6.25+/-0.10, 5.79+/-0.12, 5.83+/-0.09 and 5.70+/-0.13 for the contraction elicited by histamine, CCK-8, endothelin-1 and phenylephrine, respectively. Furthermore, we also demonstrated Rho kinase protein expression (ROCK-1 and ROCK-2) by Western blot analysis. In conclusion, ROCK is expressed in the smooth muscle of the ovine gallbladder, and it has a central role in the contractile activity induced by diverse excitatory stimuli.

SR 48692, a specific neurotensin receptor antagonist, has no effect on oesophageal motility in humans

BACKGROUND

The administration of exogenous neurotensin can reduce the lower oesophageal sphincter pressure, but it is unclear whether this effect is pharmacological or physiological.

AIM

A specific neurotensin receptor antagonist (SR 48692) was used to assess the effect of endogenous neurotensin on lower oesophageal sphincter function.

METHODS

Twenty-four healthy male subjects were included in a double-blind, placebo-controlled, randomized, cross-over study designed to determine the effects of two single doses (90 and 300 mg, preceded by a loading dose) of SR 48692 on the resting lower oesophageal sphincter pressure, transient lower oesophageal sphincter relaxations, primary oesophageal peristalsis and oesophageal acid exposure. Oesophageal pH and motility recordings were performed during 1 h of fasting and 3 h post-prandially. Plasma neurotensin-like immunoreactivity release was determined by radioimmunoassay.

RESULTS

During fasting, the lower oesophageal sphincter pressure, transient lower oesophageal sphincter relaxation rate and reflux episodes were similar with the two doses of SR 48692 and placebo. Meal ingestion induced a rise in plasma neurotensin-like immunoreactivity, a decrease in lower oesophageal sphincter pressure and an increase in both the transient lower oesophageal sphincter relaxation rate and the number of reflux episodes, which were not significantly modified by SR 48692. SR 48692 did not affect oesophageal primary peristalsis.

CONCLUSION

This study shows that SR 48692, a specific neurotensin 1 receptor antagonist, has no effect on oesophageal motility in humans.

Effect of somatostatin on postprandial gallbladder relaxation

Although the inhibitory effect of somatostatin (SST) on gallbladder contraction is well known, the influence of SST on gallbladder motility during the late postprandial or relaxation phase has not been studied. We therefore investigated the effect of SST on gallbladder relaxation and gut hormone release during the late postprandial phase. Eight healthy volunteers participated in two experiments performed in random order during continuous infusion of either SST or saline (placebo) starting 2 h after meal ingestion. At regular intervals, gallbladder volumes were measured (ultrasonography) and blood samples were taken for determination of plasma cholecystokinin (CCK), pancreatic polypeptide (PP), peptide YY (PYY) and neurotensin levels (radioimmunoassay). Postprandial gallbladder contraction was similar in both experiments: 68 +/- 4% vs. 66 +/- 4%. During SST infusion, postprandial gallbladder contraction was significantly (P<0.01) reduced (2874 +/- 813% *240 min) compared with saline (9391 +/- 1595% *240 min). Plasma CCK, PP, PYY and neurotensin levels were in the same range in the early postprandial phase but were significantly reduced during SST infusion compared with placebo (late postprandial phase). Plasma levels of CCK correlated with gallbladder volumes during both the contraction and relaxation phase (r=0.68, P=0.01 and r=0.61, P=0.008, respectively). SST enhances gallbladder relaxation and reduces hormone secretion in the late postprandial phase. The results point to an association between CCK and gallbladder volume not only during the postprandial contraction phase but also during the relaxation phase.

Exercise and gall bladder function

Epidemiological research has demonstrated protective effects of varying strength from physical activity against the risk for several chronic diseases such as coronary heart disease, hypertension, non-insulin-dependent diabetes mellitus and osteoporosis. Epidemiological studies have been supported by experimental research showing that exercise training improves coronary heart disease risk factors and other health-related factors. In contrast, the association between physical activity, exercise and gall stone disease has not yet been firmly established. This paper presents the theoretical role of aerobic exercise: (i) in the primary prevention of gall stone disease; and (ii) as a potential prokinetic agent in high risk gall stone disease groups. Primary risk factors in the pathogenesis of gall stone formation include cholesterol supersaturation in the solutes that precipitate from bile, hypernucleation (measured as "crystal appearance time') and finally hypomotility of the gall bladder which allows bile stasis and crystal formation. While the results of epidemiological studies suggest that physical activity may be inversely associated with gall stone disease, the mechanisms by which exercise may influence gall stone disease pathogeneses are poorly understood. In this paper the association between physical activity and exercise to gall bladder function and gall stone disease will be examined. Recommendations for future research and the implications for the primary prevention of gall stone disease will also be discussed.

Gallbladder motility, gallstones, and the surgeon

Cholecystectomy is one of the commonest surgical procedures in the Western world, with more than half a million procedures performed annually in the United States alone. In recent years, studies of gallstone pathogenesis and gallbladder disease have increasingly focused on abnormal gallbladder motility in the pathogenesis of some, if not all, gallbladder conditions. The control of gallbladder motility is complex and depends on an intricate interplay of neural and hormonal factors. An understanding of the control of gallbladder motility is crucial to the understanding of the mechanisms of gallstone formation and may help to explain the failure to cure symptoms after cholecystectomy in up to one third of patients. The purpose of this article is to outline mechanisms controlling gallbladder motility, examine recent developments in our understanding of this complex process, and relate changes in motility to common disease conditions of the gallbladder. The role of altered motility in the pathogenesis of gallstones is discussed and the effects of commonly performed surgical procedures such as truncal vagotomy and cholecystectomy on upper gut physiology are reviewed.

Intestinal intraluminal continuity is a prerequisite for the distal bowel motility response to feeding

BACKGROUND

We wanted to elucidate further the regulation of the intestinal motility response to feeding.

METHODS

After intraduodenal administration of an oleate solution, mimicking a meal, the distal bowel motility and the plasma levels of bile acids, cholecystokinin (CCK), and neurotensin were monitored in patients operated on with restorative proctocolectomy (n = 4) or low anterior resection of the rectum (n = 4). Investigations were performed both with and without a diverting loop ileostomy.

RESULTS

Intraduodenal sodium oleate elicited a prompt and significant increase in distal bowel motility. The motility response failed to appear when the luminal flow was diverted by a loop ileostomy. An increase in plasma CCK preceded the motility increase, but CCK was increased also in patients with a loop ileostomy. Whereas plasma bile acid levels were significantly increased after 30-45 min (p < 0.05), both with and without a loop ileostomy, neurotensin levels were not affected.

CONCLUSION

Intestinal continuity is a prerequisite for the distal bowel motility response, indicating that apart from other possible mechanisms, luminal factors are involved in the regulation of intestinal motility.

Cholesterol gallstone formation in man and potential treatments of the gallbladder motility defect

Cholelithiasis affects 10-15% of the adult population in Western society, and about 75% of gallstones are of cholesterol type. Hepatic hypersecretion of cholesterol with the formation of instable cholesterol-rich vesicles in bile, an imbalance between nucleation-inhibiting and nucleation-promoting proteins with further aggregation of cholesterol crystals in a gallbladder with a motility defect (stasis), all play a role in the pathogenesis of cholesterol gallstones. Experimental animal models suggest that gallstone formation can be prevented by improving gallbladder emptying. Thus, a better understanding of the causes underlying the impaired gallbladder motor function in patients with gallstones might lead to the selection of therapeutic approaches for those individuals who are at increased risk for the formation or recurrence of gallstones. The present article focuses on current concepts and theories on the pathogenesis of cholesterol gallstones with emphasis on the gallbladder motility defect. Several treatment strategies for the correction of gallbladder hypomotility are also discussed.

Effect of endogenous cholecystokinin on postprandial gallbladder refilling. Ultrasonographic study in healthy subjects and in gallstone patients

The postprandial release of cholecystokinin (CCK) regulates gallbladder (GB) contraction but little is known about the role, if any, of the still-elevated CCK blood levels on subsequent GB refilling. To assess the role of CCK in GB refilling, a CCK-receptor antagonist, loxiglumide, or saline were infused intravenously in a random double-blind fashion after the ingestion of a liquid test meal in 16 healthy subjects. An identical study protocol was performed in 10 GB "contractor" patient with radiolucent stones to ascertain whether the reported reduced CCK effect on GB emptying also affects GB refilling. GB volumes were assessed ultrasonographically in the fasting state and for 150 min at 15-min intervals after meal ingestion. GB volumes during postprandial refilling were significantly greater during loxiglumide than placebo infusion (P < 0.01), but they did not differ between gallstone and control subjects. In conclusion, postprandial endogenous CCK has a relevant role in delaying GB refilling, and this effect is not altered in patients with radiolucent gallstones.

Physiology and pathophysiology of gallbladder motility

Most significant gallbladder disease is associated with gallbladder stasis. Gallbladder motility is controlled by a complex interplay of hormonal and neural factors. Experimental and clinical studies have demonstrated impaired motility in gallstone disease, and experimental evidence indicates that motility disturbances precede gallstone formation. The ability to measure gallbladder motility clinically has also resulted in better diagnosis and treatment for patients with chronic acalculous cholecystitis.

Effect of neurotensin on the canine gallbladder motility: in vivo and in vitro experiments

Neurotensin (NT) (10(-8)-10(-6)) exerted a dose-dependent increase in the tone and release of [3H]ACh in the guinea-pig gallbladder muscle strips but was inefficient in the canine gallbladder muscle strips. However, in conscious dogs NT (2.5-20 ng/kg intravenously (i.v.)) dose-dependently increased the gallbladder pressure. Similar was the effect of CCK8 (1-10 ng/kg i.v.) and carbachol (0.5-2 micrograms/kg i.v.). The NT- or CCK8-induced gallbladder pressure was inhibited by atropine (10-50 micrograms/kg i.v.) or hexamethonium (0.5-3 mg/kg i.v.). Somatostatin (1-2 micrograms/kg i.v.) or VIP (0.5-1 microgram/kg i.v.) also reduced or even abolished the NT- or CCK8-induced gallbladder pressure. The NT-induced increase of the tone of guinea-pig gallbladder preparations was accompanied by an increase of [3H]ACh release, suggesting the involvement of cholinergic innervation.

Correlation between gall bladder fasting volume and postprandial emptying in patients with gall stones and healthy controls

To evaluate whether the extent of postprandial gall bladder emptying is correlated with gall bladder fasting volume, gall bladder motility was studied in 56 patients with cholesterol gall stone and 19 control patients. Gall bladder volumes were determined sonographically, while cholecystokinin plasma values were measured radioimmunologically. Twenty three per cent of gall stone patients were classified as pathological contractors (residual fraction > mean +2SD of controls) and 77% as normal contractors. Normal but not pathological contractor patients exhibited larger gall bladder fasting volumes (mean (SEM)) (24.7 (1.7) ml) than controls (15.3 (1.2) ml, p < 0.001). In normal contractor patients and controls fasting volume was closely related with ejection volume (r = 0.97, p < 0.001) and residual volume (r = 0.80, p < 0.001). Although ejection volume was enlarged in normal contractor patients it did not compensate the increase in fasting volume. Thus, residual volumes were considerably increased not only in pathological contractors (12.7 (2.5) ml, p < 0.001) but also in normal contractor patients (7.0 (0.5) v 4.6 (0.6) ml, p < 0.001). Postprandial cholecystokinin secretion did not differ between patients and controls. It is concluded, that in normal contractor patients gall bladder fasting volume is closely correlated with ejection and residual volume. Thus, fasting volume may be an essential factor affecting postprandial gall bladder emptying. Large fasting volumes in cholesterol gall stone disease could thereby contribute to bile retention, which facilitates gall stone growth.

Gallbladder dysfunction in diabetes mellitus

To further elucidate the mechanism of impaired gallbladder emptying in diabetics with and without neuropathy, gallbladder function was assessed by ultrasonography following a medium-chain triglyceride (lipomul, 1.5 mg/kg) infusion into the duodenum and compared to that during intravenous infusion of cholecystokinin in diabetic women. Results were compared with five healthy control women. Mean (+/- SD) maximal percent gallbladder volume in diabetics following lipomul was reduced to 49 +/- 8% and after intravenous cholecystokinin to 47 +/- 9%, which was less than those in controls, 21 +/- 9% and 24 +/- 6%, respectively, but not significantly different. Further analysis of gallbladder emptying to lipomul differentiated two subgroups of diabetics: one subgroup (N = 5) had emptying comparable to controls (responders), while the other (N = 5) had very modest emptying (nonresponders). Two of the patients in the latter group had normal gallbladder emptying during exogenous cholecystokinin and their response would be compatible with visceral neuropathy. Blood levels of cholecystokinin, measured by bioassay, following lipomul and exogenous cholecystokinin were similar in controls and diabetics. Presence of diabetic neuropathy did not correlate with impaired gallbladder emptying. Follow up at 6 and 12 months of the three nonresponder diabetics revealed that no gallstones had developed and that two of them became responders to exogenous cholecystokinin.(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptation of biliary response to dietary olive oil and sunflower-seed oil in dogs

The effects of adaptation to dietary fat of different degrees of unsaturation (olive oil and sunflower oil) on bile secretion were studied in dogs at rest and after food intake. The animals were prepared with a bidirectional biliary cannula and a duodenal cannula to provide bile return. The two experimental groups were fed on diets containing 150 g fat/kg in the form of either olive oil (O) or sunflower-seed oil (S). The flow-rate under resting conditions and the patterns of response to food were similar in both experimental groups, although postprandial hypersection were significantly greater in volume and more prolonged in group O. No appreciable differences in concentration and output of biliary cholesterol or phospholipids were noted between the two groups. In contrast, the concentration and output of bile acids differed significantly both at rest and after food: concentration and output of bile acids were greater at rest in group S. However, after food intake, these responses were increased only in group O. The results suggest that the type of dietary fat affects biliary response to food, probably through differences in the contribution of the gall bladder in the two experimental groups.

Gallbladder contraction after hormonal manipulations in normal subjects and patients under total parenteral nutrition

Total parenteral nutrition (TPN) induces biliary dilatation, sludge and formation of gallstones. Cholecystokinin (CCK) induces gallbladder (GB) contraction. During thyrotropin-releasing hormone (TRH) testing for thyroid function, we observed that patients felt a strong micturition reflex attributable to smooth muscle contraction of the bladder. The possibility of GB contraction after TRH administration was studied compared to cholecystokinin-octapeptide (CCK-OP) and/or fatty meal administration. The effect of intravenous (IV) CCK-OP, TRH and a combination of the two on GB volume was studied in normal volunteers without GB or liver disease and in patients receiving TPN for greater than 2 weeks. Subjects included six normal volunteers who received an oral fatty meal only, 18 other normal volunteers (Group A) and 18 TPN patients (Group B). Gallbladder contraction was estimated by ultrasound prior to and after administration of the fatty meal; in the other 36 subjects, GB contraction was calculated prior to and after administration of CCK-OP, TRH, or both. Results are expressed as a percentage of the GB basal volume using each subject as his or her own control. Group A and Group B were each divided into three equal subgroups receiving IV CCK-OP (A1, B1), TRH (A2, B2), or both (A3, B3).(ABSTRACT TRUNCATED AT 250 WORDS)

Release of neurotensin by selective perfusion of the jejunum with oleic acid in dogs

Plasma neurotensin concentrations are rapidly elevated after oral ingestion or intraduodenal infusion of fat, apparently before fat reaches the ileum where neurotensin is highly concentrated. The purpose of this study was to investigate the site of neurotensin release and to determine whether neurotensin is released by direct luminal stimulation by fat in conscious dogs. Dogs were prepared with isolated jejunal or ileal segments and portal vein catheters. Release of neurotensin into the portal venous blood was examined by selective perfusion of each intestinal segment with sodium oleáte. The results of this study show that selective perfusion of the jejunum, but not the ileum, with sodium oleate, caused a significant release of neurotensin. We speculate that release of ileal neurotensin is not due to direct luminal stimulation, but is mediated by local neural or humoral intermediates.

Species-specific effects of neurotensin on gallbladder contraction in vitro

We have previously shown that an in vivo administration of neurotensin (NT) stimulates contraction of dog gallbladder (GB), but produces dilatation of GB in humans. The objective of this study was to examine the effect of NT on human, dog, guinea pig, and rabbit GB in vitro, in order to delineate direct versus indirect actions of NT in different species and to evaluate the structure-activity relationships of NT. The effect of NT on the canine sphincter of Oddi (SOD) was also examined in vitro. Isolated longitudinal strips of GB from the four species given above and SOD from dogs were suspended in oxygenated Krebs buffer, and the isometric tension responses to various doses of NT, NT 8-13, NT 1-11, and xenopsin (XP) were determined. All the NT homologs, except NT 1-11, stimulated contraction of the dog GB and SOD in a dose-dependent manner. NT also caused dose-related stimulation of GB contraction from guinea pigs but did not stimulate or depress the contractile activity of human and rabbit GB strips. These results suggest that NT action on GB contraction is species-specific. Tetrodotoxin did not modify the contraction of dog GB and SOD in response to NT, indicating that NT mediates its contractile effects directly. The relaxing effect of NT on GB of humans in vivo, as previously reported by us, thus appears to be an indirect action.(ABSTRACT TRUNCATED AT 250 WORDS)

Correlation of cholecystokinin receptors with gallbladder contractility in patients with gallstones

The authors have previously identified two groups of patients with gallstones: those whose gallbladders contract the same as those of normal volunteers and show an increased sensitivity to endogenous cholecystokinin (CCK) ("contractors") and those whose gallbladders are relatively unresponsive ("noncontractors"). To define the mechanism responsible for these differences in contractility, the authors have measured CCK receptors on gallbladder muscle of patients with gallstones. Twenty-three patients with gallstones and 10 healthy volunteers (controls) fasted overnight. Simultaneous plasma samples for radioimmunoassay of CCK release and ultrasonographic measurements of gallbladder volume were obtained before and at intervals for 60 minutes after ingestion of Lipomul. Patients with gallstones had cholecystectomy, and CCK receptors were determined on cell membranes from gallbladder specimens by use of radiolabeled analogs of CCK-8-SO4. Histologic sections were graded for the degree of inflammation and scarring. Thirteen patients with gallstones were identified as contractors and 10 as noncontractors. Basal gallbladder volumes were not significantly different between patients in either group. The total integrated output of CCK for contractors was 1.6 +/- 0.2 ng X min/ml compared with 5.5 +/- 1.2 ng X min/ml for controls, while the integrated output for noncontractors was 11.1 +/- 2.1 ng X min/ml. Contractors had a higher number of CCK-binding sites (27.6 +/- 6.8 fmol/mg protein) than did noncontractors (4.8 +/- 1.0 fmol/mg protein). CCK receptors in gallbladders of all patients with gallstones correlated closely with gallbladder motility (y = 1.149, x = 0.624, r = 0.7, p less than 0.001). Although contractors had more mild inflammation and scarring, 40% of noncontractors had mild inflammation and scarring; there was no correlation. A decrease in CCK receptors may be an early event in the pathogenesis of gallstone formation by causing a decrease in gallbladder motility in some patients.