Acute cholecystitis potentiates bradykinin stimulated fibroblast prostanoid release 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.

Role of prostaglandin E(2) and Ca(2+) in bradykinin induced contractions of guinea-pig gallbladder in vitro

In this study, we investigated the contribution of prostaglandin E(2) to bradykinin induced contractions of guinea-pig gallbladder in vitro and characterized the sources of activator Ca(2+) for the bradykinin mediated contractions. Contractions induced by bradykinin in guinea-pig gallbladder smooth muscle strips were significantly attenuated by the cyclooxygenase inhibitor piroxicam (10 microM). In the presence of piroxicam, a threshold concentration of prostaglandin E(2) (1 nM) significantly enhanced the contractile response to subsequent challenge with bradykinin. Contractile responses to bradykinin were abolished in a Ca(2+)-free medium plus EDTA. The inhibitor of receptor mediated Ca(2+) entry, SK&F 96365 (1-[beta-[3-(4-methoxyphenyl)-propoxy]-4-methoxyphenethyl]-1H-imidazole hydrochloride, 10-50 microM) dose dependently abolished the response to bradykinin, while this response was only partially attenuated by nifedipine (10-50 microM; a voltage-operated Ca(2+) channel antagonist). Thapsigargin (an inhibitor of the sarcoplasmic reticulum calcium ATP-ase pump, 1 microM) produced sustained contractions of guinea-pig gallbladder strips that were dependent on extracellular Ca(2+). After incubation of strips in a Ca(2+)-free medium with thapsigargin, replacement of Ca(2+) caused a large sustained contraction. We conclude that the contractile response of guinea-pig gallbladder to bradykinin is modulated by prostaglandin E(2). Bradykinin induced contractions of guinea-pig gallbladder are highly dependent on extracellular Ca(2+) which enters through store-operated Ca(2+) channels and partially through voltage-operated Ca(2+) channels.

Bradykinin and electrical stimulation increase prostaglandin production in the rat vas deferens

The epididymal portion of the rat vas deferens produced prostaglandins (PG) E(2), F(2alpha)and 6-keto F(1alpha). Electrical stimulation (ES, 0.1 Hz, 1 ms) increased such production by 100%, and similar results were obtained in the presence of 1.0 microM bradykinin (Bk). When both stimuli were applied simultaneously, the increases in PG production were 1100% for PGE(2), 800% for PGF(2alpha)and 400% for PG6-keto F(1alpha). Prazosin abolished the effect of ES on PG production. A selective Bk B(2)-receptor antagonist abolished the increase in PG production induced by Bk, both in non-stimulated and in ES tissues. Bk (1.0 microM) elicited contractile responses in non-stimulated as well as in ES tissues, responses that were not modified in the presence of 10 microM indomethacin. In conclusion, the effects of Bk on prostaglandin production appears to depend on the activation of B(2) receptors, while the increase in prostaglandin release induced by ES, and the effects observed with both stimuli simultaneously, should be mediated by the release of noradrenaline and the subsequent activation of alpha(1) adrenoceptors.

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.

Induction of human B2 bradykinin receptor mRNA and membrane receptors by IFNgamma

A potential mechanism for the increased sensitivity of inflamed tissues to bradykinin is the upregulation of bradykinin receptor expression. We report that recombinant human IFNgamma stimulated a concentration-dependent increase in cell surface bradykinin receptor expression in intact T24 human epithelial-like cells, determined by radioligand binding analysis. Analysis of specific [3H]-bradykinin binding revealed that IFNgamma-treated cells had a two- to threefold increase in bradykinin receptor number compared to the controls with no effect on receptor affinity. The ability of IFNgamma to stimulate increased bradykinin receptor expression was abrogated by treatment with either the transcription inhibitor actinomycin D or the protein synthesis inhibitor cycloheximide. IFNgamma enhanced steady-state human B2 bradykinin receptor mRNA expression in the T24 cells in a dose-dependent manner. B2 bradykinin receptor mRNA expression was increased as early as 1 h following IFNgamma stimulation, and continued to accumulate for 24 h. Bradykinin-stimulated intracellular calcium mobilization was also increased in IFNgamma-treated T24 cells compared to controls. The ability of IFNgamma to upregulate B2 bradykinin receptors in primary epithelial cells was demonstrated using cultured human airway epithelial cells. These observations suggest that increasing IFNgamma levels during inflammation may upregulate the expression of B2 bradykinin receptors, leading to increased sensitivity to bradykinin.

Downstream effects of splanchnic ischemia-reperfusion injury on renal function and eicosanoid release

This study examines the hypothesis that intestinal ischemia-reperfusion (I/R) injury contributes to renal dysfunction by altered renal eicosanoid release. Anesthetized Sprague-Dawley rats underwent 60 min of sham or superior mesenteric artery (SMA) occlusion with 60 min of reperfusion. The I/R groups received either allopurinol, pentoxifylline, 1-benzylimidazole, or carrier before SMA occlusion. In vivo renal artery blood flow was measured by Transonic flow probes, the kidneys were then perfused in vitro for 30 min, and the effluent was analyzed for eicosanoid release and renal function. Intestinal I/R caused a twofold increase in the ratio of renal release of thromboxane B2 to prostaglandin E2 and to 6-ketoprostaglandin F1alpha compared with the sham level, with a corresponding 25% decrease in renal sodium and inulin clearance and renal blood flow. Pentoxifylline or allopurinol pretreatment restored renal eicosanoid release and renal sodium and inulin clearance to the sham level but did not alter renal blood flow. Pretreatment with 1-benzylimidazole restored renal function, eicosanoid release, and renal blood flow to sham levels. These data suggest that severe intestinal I/R contributes to the downregulation of renal function. The decrease in renal function is due in part to toxic oxygen metabolites, which occur in the milieu of altered renal eicosanoid release, reflecting a decrease in vasodilator and an increase in vasoconstrictor eicosanoids.

Estrogen increases male rat aortic endothelial cell (RAEC) PGI2 release

Estrogen has been proposed as a negative risk factor for development of peripheral vascular disease yet mechanisms of this protection are not known. This study examines the hypothesis that estrogen stimulates rat aortic endothelial cell (RAEC) release of PGI2. Male Sprague-Dawley rat abdominal aortic 1-mm rings were placed on 35 mm matrigel plates, and incubated for 1 week. The cells were transferred to a Primaria 60-mm dish and maintained from passage 3 in RAEC complete media and experiments performed between passages 4-10. Cells were incubated with Krebs-Henseleit buffer (pH 7.4) containing carrier or increasing concentrations of beta-estradiol or testosterone for 60 min. The effluent was analyzed for eicosanoid release of 6-keto-PGF1 alpha (6-keto, PGI2 metabolite), PGE2 and thromboxane B2 (TXB2) by EIA (hormone stimulated-basal). Cells were analyzed for total protein by the Bradford method and for cyclooxygenase-1 (COX-1) and prostacyclin synthase (PS) content by Western blot analysis and densitometry. Testosterone did not alter RAEC 6-keto-PGF1 alpha release, whereas estrogen increased RAEC 6-keto-PGF1 alpha release in a dose-related manner. Estrogen preincubation (10 ng/ml) decreased COX-1 and PS content by 40% suggesting that the estrogen-induced increase in male RAEC PGI2 release was not due to increased synthesis of COX-1 or PS. These data support the hypothesis that estrogen stimulation can increase endogenous male RAEC release of PGI2.

Long-term resuscitation of hemorrhage/reperfusion injury (H/R) stimulates renal PGE2 release

This study examines the hypothesis that long-term resuscitation with hyperalimentation (TPN) following acute hemorrhage/reperfusion (H/R) injury stimulates renal release of PGE2. Male Sprague-Dawley rats were anesthetized and subjected to sham or hemorrhage to 30 mmHg for 30 min followed by reperfusion. All rats were placed on TPN for 5 days, then underwent laparotomy for in vivo renal artery and aortic blood flow for 60 min. The kidney was perfused in vitro with Krebs-Henseleit buffer at 3 ml/min (pH 7.4, 37 degrees C) and venous effluent was collected for analysis of PGE2, 6-keto-PGF1 alpha and thromboxane B2 by EIA. Hemorrhage/reperfusion followed by TPN for 5 days increased renal PGE2 2-fold and decreased in vivo renal artery blood flow by 50% compared to the sham group. Hemorrhage/reperfusion followed by TPN did not alter release of the other eicosanoids measured. These data suggest that the kidney has a limited capacity to maintain renal blood flow by increasing release of PGE2 when the animal is subjected to long-term resuscitation with TPN following mild hemorrhage/reperfusion injury.

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.

Acute mesenteric ischemia/reperfusion down regulates renal PGE2 synthesis

This study examines the hypothesis that pentoxifylline protects renal PGE2 synthesis during mesenteric ischemia/reperfusion injury. Anesthetized Sprague-Dawley rats (300 g) were subjected to sham or superior mesenteric artery occlusion for 20 min followed by 30 min of reperfusion. The ischemia/reperfusion groups received either enteral allopurinol (10 mg/kg) daily for 5 d prior to ischemia, pentoxifylline (50 mg/kg) 10 min prior to ischemia or carrier. The kidney was removed and perfused in vitro with oxygenated Krebs buffer and the effluent was assayed for release of 6-keto-PGF1 alpha, PGE2 and thromboxane B2 (TXB2) by enzyme immunoassay. Mesenteric ischemia/reperfusion decreased renal PGE2 release by 50% (compared to sham) but did not alter release of TXB2 or 6-keto-PGF1 alpha. Pentoxifylline pretreatment (not allopurinol) preserved renal PGE2 release at the sham level. These data showed pentoxifylline exerted a protective effect against severe mesenteric ischemia/reperfusion injury by maintaining release of renal PGE2, a potent endogenous renal vasodilator.