The role of prostaglandin I2 and biliary lipids during evolving cholecystitis in the rabbit

Cholecystokinin (CCK) down regulates PGE2 and PGI2 release in inflamed Guinea pig gallbladder smooth muscle cell cultures

This study examines the hypothesis that cholecystitis down-regulates Guinea pig gallbladder (GPGB) smooth muscle cholecystokinin (CCK)-stimulated prostaglandin (PG) release. Guinea pig gallbladder from Control and 48 h bile duct ligated (BDL) animals were placed in cell culture and grown to confluence. The cultures underwent Western Blot analysis for smooth muscle cell content of COX-1, COX-2, Prostacyclin Synthase (PS), or were incubated with CCK at 10(-8)M or 10(-6)M with and without indomethacin for 1h and analyzed for release of 6-keto-PGF1alpha, PGE2 and TxB2 by EIA. BDL increased Guinea pig gallbladder cell culture basal PGE2 and PGI2 release which was in part due to increased COX-2 content. CCK incubation down-regulated BDL Guinea pig gallbladder cell culture release of 6-keto-PGF1alpha and PGE2 and down-regulated COX-2 content but did not alter the Control group. The decrease in CCK-mediated BDL cell Guinea pig gallbladder release may be an endogenous mechanism to limit physiologic derangements induced by increased endogenous gallbladder PG synthesis during early acute cholecystitis.

Bile duct ligation induced acute inflammation up-regulates cyclooxygenase-2 content and PGE2 release in guinea pig gallbladder smooth muscle cell cultures

INTRODUCTION

This study examines hypotheses that BDL induces increased guinea pig gallbladder smooth muscle PGE2 release by up-regulation of COX-2.

METHODS

BDL, Sham and Control Hartley guinea pig gallbladders were placed in cell culture, grown to confluence and underwent Western Blot analysis for smooth muscle cell content of COX-1, COX-2, Prostacylin Synthase, actin, caldesmon, vinculin, meta-vinculin and tropomyosin and were assayed for basal release of 6-keto-PGF(1alpha), PGE2 and TxB2 by EIA.

RESULTS

BDL did not alter content of smooth muscle cytoskeletal proteins. BDL for 48 h increased smooth muscle cell release of PGE2 and 6-keto-PGF(1alpha) by 3-fold or more when compared to the Control and Sham groups. Western Blot analysis showed increased content of COX-2 in the BDL group.

CONCLUSIONS

BDL for 48 h markedly increased endogenous guinea pig smooth muscle cell PG release, which was due to increased COX-2 synthesis.

[Increased bile lithogenicity after simultaneous total parenteral nutrition and octrotide. A model of calcium palmitate Gallstones]

Gallbladder stasis and gallstone formation are well-known complications of both fasting-associated total parenteral nutrition (TPN) and long-term treatment with octreotide. Additive noxious effects to hepatobiliary function may develop when both therapies are given together as treatment of enteric fistulae. The aim of this study was to assess the risk of gallstone formation during treatment with TPN and octreotide separately and in combination. We studied four groups of New Zealand rabbits (n = 32) during a 2-week intervention period: 14 chow-fed controls; 6 fasted and TPN-fed; 6 chow-fed and administered octreotide, and 6 fasted and treated with both TPN and octreotide. After treatment, the bile duct was cannulated and the gallbladder and liver tissue were obtained for histological analysis. Hepatic and gallbladder bile were retrieved for microscopic examination and measurement of biliary lipids, bilirubin, calcium, total protein, and cholesterol nucleation time. The chemical composition of gallstones was also analyzed. The results of the study suggest that simultaneous administration of these two therapies in rabbits has additive effects on gallbladder stasis and bile lithogenicity. The administration of both treatments can play an important role in the formation of calcium palmitate gallstones in these animals.

Effect of indomethacin on gallbladder inflammation and contractility during acute cholecystitis

OBJECTIVE

The aim of this study was to determine whether the prostaglandin synthase inhibitor indomethacin reverses the inflammation and abnormal gallbladder contractility that occur after common bile duct ligation (CBDL), a model of acute cholecystitis.

METHODS

Gallbladder muscle contractility was studied in vitro in normal, CBDL, and sham-operated guinea pigs. Animals were treated with saline or indomethacin in vivo. Acetylcholine (ACh) was used to directly contract the muscle and electric field stimulation (EFS) to activate intrinsic nerves. Hematoxylin and eosin-stained slides of muscle strips were scored for inflammation.

RESULTS

CBDL in saline-treated animals increased the inflammation score and decreased gallbladder muscle contractility to ACh and EFS. Indomethacin decreased the inflammation score and partly reversed the smooth muscle contractile response to ACh 6 and 24 h after CBDL, but not at 48 h. Indomethacin did not reverse the CBDL-induced decrease in nerve-evoked contractions.

CONCLUSION

Gallbladder inflammation and contractile dysfunction after CBDL are partly reversed with indomethacin at 6 and 24 h, but not at 48 h. This suggests that, early in the course of CBDL, the inflammation and contractile dysfunction are, in part, prostaglandin-mediated.

Effect of acalculous cholecystitis on gallbladder neuromuscular transmission and contractility

BACKGROUND

Impaired smooth muscle contractility is important in the pathophysiology of acalculous cholecystitis. Common bile duct ligation (CBDL) is a model of acalculous cholecystitis, producing acute inflammatory changes and decrease in gallbladder smooth muscle contractility. The aim of this study was to determine whether there is coexistent dysfunction of neural efferent motor pathways of the gallbladder after CBDL.

MATERIALS AND METHODS

Gallbladder muscle contractility was studied in vitro in normal, CBDL, and sham-operated guinea pigs. Electric field stimulation (EFS; 2-16 Hz) was used to activate intrinsic nerves and exogenous acetylcholine (ACh) was used to directly stimulate the muscle. H&E-stained slides of muscle strips were scored for inflammatory changes.

RESULTS

After CBDL, there was a progressive increase in the inflammation score and decrease in gallbladder muscle contractility to ACh. There was also a progressive decline in EFS-induced contractility when expressed as absolute force or normalized to the maximal muscle contractile response to ACh. The nitric oxide synthase inhibitor l-NNA (10 microM) increased EFS-induced contractions by 50 +/- 25% (P = 0.05) in CBDL animals but had no effect in sham surgical controls.

CONCLUSIONS

CBDL with its acute gallbladder inflammation affects gallbladder contractility by two mechanisms: (1) decreased smooth muscle contractility, and (2) decreased neurally mediated contractions. The neurally mediated alterations result from dysfunction of cholinergic excitatory nerves and upregulation of nitric-oxide-mediated inhibition of smooth muscle contractility.

Effect of experimental acalculous cholecystitis on gallbladder smooth muscle contractility

Gallbladder motility is impaired in chronic cholelithiasis but has not been studied in acute acalculous cholecystitis. The aim of this study was to determine the effects of acute acalculous inflammation on gallbladder contractility using the common bile duct ligation (CBDL) model in guinea pigs. Three groups of guinea pigs were studied: CBDL, normal, and sham surgical controls. Gallbladder dimensions were measured, and muscle strips were used for histology and in vitro contractility studies. CBDL resulted in progressive gallbladder distension, increased serum bilirubin, and gallbladder inflammation. There was a progressive decline in muscle contractility in the CBDL group as evidenced by a decrease in the contractile response to potassium and bethanechol with the duration of CBDL. In conclusion, CBDL in the guinea pig produces acute gallbladder inflammation and decreased gallbladder muscle contractility. Direct inhibition of muscle function is indicated by impaired contractile responses to potassium depolarization and bethanechol stimulation. Although the mechanism of the decrease in contractility with CBDL is unknown, we speculate that impaired muscle contractility is secondary to inflammation and may play a role in the clinicopathology of acute acalculous cholecystitis.

Enhanced bradykinin-stimulated prostaglandin release in the acutely inflamed guinea pig gallbladder is due to new synthesis of cyclooxygenase 1 and prostacyclin synthase

BACKGROUND

Our previous studies have shown that acute gallbladder (GB) inflammation increases endogenous bradykinin (BK)-stimulated prostaglandin (PG) release and inhibits guinea pig (GP) GB contractility. This study examines the hypothesis that exaggerated PG release following BK stimulation in the inflamed guinea pig GB is due to new protein synthesis of cyclooxygenase 1 (COX-1) and prostacyclin synthase (PS).

MATERIALS AND METHODS

Male Hartley GPs (450-550 g) were anesthetized and underwent common bile duct ligation (BDL, a model of acute inflammation). GBs were harvested after 3 days from BDL and control groups. Tissue slices were prepared and placed in oxygenated tissue culture medium at 37 degrees C for 1 h (basal) and for a second hour in medium alone (carrier, Car), medium plus 10(-6) M BK, or medium plus 10(-6) M BK plus cycloheximide 100 microgram/ml (BK + CX). The medium was assayed for net release of 6-keto-PGF1alpha (PGI2 metabolite), thromboxane B2 (TxB2), PGE2, leukotriene B4 (LTB4), and C4 (LTC4) by enzyme immunoassay and data are reported as nanograms per milligram of protein. GB tissue from control and BDL groups was examined for COX-1, COX-2, PS, and inducible nitric oxide synthase (iNOS) content by Western blot analysis, analyzed by densitometry, and reported as densitometry units.

RESULTS

All data were analyzed by ANOVA and t test and reported as means +/- SEM, N >/= 5.BK increased the release of PGI2 and PGE2 from the control group and markedly exaggerated release of PGI2 and PGE2 from the BDL GP gallbladder. This exaggerated PGI2 and PGE2 release was greatly diminished by inhibition of new protein synthesis with cycloheximide. TxB2, LTB4, and LTC4 showed no significant differences between any groups. COX-1 and PS contents were significantly elevated in the BDL group compared with control. COX-2 and iNOS were not present in control or BDL GBs.

CONCLUSIONS

These data suggest that the enhanced BK-stimulated PG release seen in the acutely inflamed GP gallbladder is due to the synthesis of new COX-1 and PS enzymes.

Chemopreventive effects of taurine on diethylnitrosamine and phenobarbital-induced hepatocarcinogenesis in male F344 rats

Modifying effects of taurine, a naturally occurring organosulfur compound, on diethylnitrosamine (DEN) and phenobarbital (PB)-induced hepatocarcinogenesis were examined in rats. Male F344 rats, 5 weeks old, were divided into 8 groups. Rats of groups 1 through 5 were given i.p. injections of DEN (100 mg/kg body weight) once a week for 3 weeks from one week after the start of the experiment. Of them, animals of group 2 received taurine mixed in a basal diet at a concentration of 2000 ppm for the initial 4 weeks, and those of groups 3 and 5 were given the agent starting 4 weeks after the beginning of the experiment until the end (24 weeks). Rats in groups 1, 4, 7 and 8 were kept on the basal diet throughout the experiment (24 weeks). Group 6 was given taurine throughout the experiment and group 8 was treated as a vehicle control. Animals of groups 1,2, 3 and 7 received PB in drinking water at a dose of 500 ppm from one week after the end of carcinogen or vehicle treatment. Liver neoplasms were recognized only in DEN-treated groups. The incidence and average number of liver neoplasms of group 3 were significantly lower than those of group 1. The number of glutathione S-transferase placental form (GST-P)-positive foci of group 2 or 3 was significantly smaller than that of group 1 (P < 0.01 or P < 0.005). The average and unit areas of GST-P-positive foci in groups 2 and 3 were also significantly smaller than those in group 1 (P < 0.005 and P < 0.0001 and P < 0.0001, respectively). In this study, the level of ornithine decarboxylase activity in non-neoplastic liver tissue was reduced by taurine treatment in both the initiation and postinitiation phases. These results suggest that taurine could be a chemopreventive agent for liver neoplasia.

Regulation of eicosanoid synthesis in fibroblasts from inflamed gallbladders

Gallbladder cell cultures obtained from rabbits subjected to sham or 72 h of bile duct ligation (72 h BDL, cholecystitis model) were incubated with calcium ionophore (A23187), dibutyryl cAMP (cAMP), and phorbol 12,13-diacetate (phorbol) to determine the intracellular signal transduction mechanisms responsible for increased inflamed gallbladder eicosanoid synthesis. Incubation of sham and 72 h BDL cell cultures with A23187 or phorbol significantly increased, whereas cAMP decreased, release of 6-keto-PGF1 alpha, PGE2, thromboxane B2 (measured by enzyme immunoassay) in a dose-related manner. Seventy-two-hour BDL cell cultures contained a specific 2-fold increased level of prostacyclin synthase compared to sham cell cultures which was not altered by preincubation with A23187, phorbol or cAMP. These findings suggest that increased PGI2 release in the sham and inflamed cell cultures following A23187 and phorbol stimulation was mediated in part via the inositol triphosphate pathway and protein kinase C activation and was not associated with altered cyclooxygenase or prostacyclin synthase content.

Platelet activating factor (PAF) stimulates release of PGI2 from inflamed rabbit gallbladder cell cultures

This study examines the hypothesis that PAF stimulates release of PGI2 from inflamed rabbit gallbladder explant cell cultures. New Zealand white rabbits underwent bile duct ligation for 72 h (72 h BDL), or sham operation, Sham and 72 h BDL gallbladder explants were placed in culture, and the cells grown to 75% confluence. The cells were exposed to increasing concentrations of PAF for 60 min. The media analyzed for eicosanoid release by EIA and the cells analyzed for cyclooxygenase and prostacyclin synthase content by immunoblot analysis. PAF increased release of 6-keto-PGF1 alpha from the 72 h BDL gallbladder cell cultures in a dose-related manner which was inhibited by indomethacin preincubation by 90%. The increased 72 h BDL cell release of 6-keto-PGF1 alpha was not associated with changes in the content of cyclooxygenase or prostacyclin synthase. PAF did not alter eicosanoid release from sham control cell cultures. These data suggest that PAF can only up-regulate endogenous 6-keto-PGF1 alpha release from the 72 h BDL cells that had been previously stimulated by inflammation. PAF may thus contribute to gallbladder distention and injury by chronic stimulation of inflamed gallbladder PGI2 release.

Taurodeoxycholic acid stimulates rabbit gallbladder eicosanoid release

Rabbit common bile duct ligation has been shown to concomitantly increase levels of gallbladder taurodeoxycholic acid and gallbladder eicosanoid release. This study examines the hypothesis that taurodeoxycholic acid, a known chemical mediator of gallbladder inflammation, stimulates endogenous gallbladder eicosanoid release. Male New Zealand white rabbits were anesthetized, gallbladders removed and perfused in vitro with Krebs-Henseleit buffer (pH 7.4, 37 degrees C) at 1 ml/min with increasing doses of taurodeoxycholic acid (0, 10, 30 and 100 mM) added to the perfusate. The effluent was collected at 15, 30, 60 and 120 min of perfusion and assayed for 6-keto-PGF1 alpha (PGI2 metabolite), PGE2, and thromboxane B2 (TXB2) by enzyme immunoassay. Taurodeoxycholic acid increased gallbladder eicosanoid release in a dose-related manner with 6-keto-PGF1 alpha and PGE2 release 10-fold higher than TXB2. Indomethacin (1.5 mM) decreased gallbladder eicosanoid release by 50% in the gallbladders perfused with 30 mM taurodeoxycholic acid, demonstrating that the increased gallbladder eicosanoid release was due to de novo synthesis. These findings suggest that the increased release of gallbladder PGI2 and PGE2 described in animal models of cholecystitis may, in part, be related to increased gallbladder bile levels of taurodeoxycholic acid.

Increased intragallbladder pressure stimulates gallbladder eicosanoid release

The stimulus for increased gallbladder eicosanoid synthesis during cholecystitis is unknown. This study examines the hypothesis that increased intragallbladder pressure stimulates endogenous gallbladder eicosanoid release. Rabbit gallbladders were perfused in vitro at 1 ml/minute with oxygenated Krebs-Henseleit buffer and subjected to 0, 12 or 24 mm Hg of intraluminal gallbladder pressure. Release of 6-keto-PGF1 alpha infinity PGE2 and thromboxane B2 were measured in all groups after 15 and 30 and 60 minutes of perfusion by enzyme immunoassay and gallbladders were examined histologically. Increasing intraluminal gallbladder pressure concomitantly increased gallbladder 6-keto-PGF1 alpha release 2 fold or more at all time of perfusion and altered gallbladder mucosal architecture by increasing basolateral edema in the submucosal space. Infusion of indomethacin (10 micrograms/ml in the perfusion media) decreased 6-keto-PGF1 alpha release from the in vitro perfused gallbladders subjected to 24 mm Hg by 70%. Increased gallbladder eicosanoid release during early cholecystitis may in part be related to the physical force of increased gallbladder intraluminal pressure on the gallbladder mucosa.

Studies on the etiology of acute acalculous cholecystitis: the effect of lipopolysaccharide on human gallbladder mucosal cells

Previous studies in animals have shown that lipopolysaccharide produces experimental cholecystitis possibly through a platelet-activating factor-prostanoid mediated process. In this study it was intended to evaluate the effect of LPS on primary cultures of human gallbladder mucosal cells. Gallbladder mucosal cells were isolated from gallbladders removed during routine cholecystectomies or other operations. The cells were cultured for 24 h before treatment. Unstimulated cells produced low levels of prostanoids and significant basal levels of PAF. LPS produced stimulation of eicosanoid and PAF secretion. The increased prostanoid formation was not enhanced when LPS and PAF were administered together. Prostanoid synthesis was inhibited by the administration of a cyclooxygenase inhibitor while administration of a PAF receptor antagonist significantly increased prostanoid formation, suggesting that increased PAF levels function as a negative control mechanism to decrease prostanoid synthesis. The results suggest that endotoxemia may produce a cascade of inflammatory processes in human gallbladder mucosal cells resulting in the development of acute acalculous cholecystitis.

The production of experimental cholecystitis by endotoxin

Acute acalculous cholecystitis (AAC) is a severe inflammatory disorder of the gallbladder. It occurs primarily in patients acutely ill from other disorders and is related to sepsis and shock. We previously found that platelet-activating factor (PAF), a phospholipid autacoid purported to be a mediator of the shock response, produced AAC. This study was performed to determine the effect of intravenous lipopolysaccharide (LPS) on feline gallbladders. Anesthetized cats underwent LPS administration with and without administration of a cyclooxygenase inhibitor and PAF antagonist. Gallbladder inflammation was evaluated by quantitation of luminal water transport and tissue myeloperoxidase levels. In an attempt to understand the mechanisms of the response, gallbladder perfusate and tissue prostanoid and PAF levels were quantitated as were serum PAF levels. LPS administration resulted in alteration of the normal absorptive pattern of the gallbladder mucosa to exsorption of fluid into the gallbladder lumen, increased tissue myeloperoxidase levels and increased serum PAF levels. This was associated with increased gallbladder tissue and perfusate prostanoid levels and increased perfusate PAF levels. Indomethacin prevented the pro-inflammatory changes in the gallbladder produced by LPS. The PAF antagonist, alprazolam, increased gallbladder prostanoid production when administered alone and with LPS. The administration of LPS resulted in the production of acute changes in the gallbladder consistent with cholecystitis. These changes being prevented by a cyclooxygenase inhibitor suggests that development of AAC may be related to the release of systemic and local pro-inflammatory substances.

Acute cholecystitis potentiates bradykinin stimulated fibroblast prostanoid release in the rabbit

Gallbladder explants from control rabbits and rabbits subjected to bile duct ligation (BDL) for 24 and 72 h (cholecystitis model) were placed in cell culture to determine the source for increased gallbladder prostanoid synthesis during cholecystitis. Cultures from control and 24 h BDL gallbladders grew spindle shaped fibroblasts which did not exhibit increased prostanoid synthesis. 72 h BDL gallbladder cell cultures grew large polygonal shaped cells which appeared to be 'stimulated fibroblasts' by light and electron microscopy and were associated with increased basal and bradykinin stimulated 6-keto-PGF1 alpha release and increased content of prostacyclin synthase when measured by enzyme immunoassay and protein immunoblot analysis respectively. Use of bradykinin antagonists showed that the bradykinin BK2 subtype receptor was the most prominent in the 72 h BDL cell cultures. The 'stimulated fibroblasts' were the source of bradykinin stimulated gallbladder 6-keto-PGF1 alpha synthesis in the inflamed rabbit gallbladder which was mediated by the bradykinin B2 subtype receptor.