Gut 1995; 36: 511-515 511 Misoprostol inhibits gastric mucosal release of endogenous prostaglandin E2 and thromboxane B2 in healthy volunteers Gut: first published as 10.1136/gut.36.4.511 on 1 April 1995. Downloaded from A Mertz-Nielsen, 0 Eskerod, K Bukhave, J Rask-Madsen Abstract they seemed equal to or even less effective than Prostaglandin analogues of the E-series histamine H2 receptor antagonists in prevent- theoretically offer the ideal antiulcer ing ulcer relapse.4-6 These findings would drugs. Peptic ulcer healing with prosta- imply that the so called cytoprotective proper- glandin analogues is, however, no better ties of prostaglandins, shown in animal experi- than would be predicted from their ability ments8 and clinically by a significant reduction to inhibit gastric acid secretion and they in the incidence of the gastric or duodenal are less effective than histamine H2 ulcers associated with the use of non-steroidal receptor antagonists in preventing ulcer anti-inflammatory drugs (NSAIDs),9 10 play relapse. It could be that prostaglandin no major part in ulcer healing and prevention. analogues inhibit gastric mucosal synthe- Despite enormous interest in the cytoprotec- sis or release of endogenous eicosanoids, tive phenomenon, the mechanism by which thereby abrogating their own effects. This prostaglandins produce this effect is still study, therefore, examined how a single unclear. On the other hand, a role for various therapeutic dose (200 Kug) of misoprostol, inflammatory mediators in the pathogenesis of a synthetic analogue of prostaglandin E,, ulcer disease has been supported by both influences gastric mucosal release of experimental models and clinical studies."1 endogenous prostaglandin E2 (PGE2), For example, platelet activating factor,'2 13 thromboxane B2 (TXB2), and chemotactic histamine,'4 15 and tumour necrosis factor leukotriene B4 (LTB4) during basal condi- alpha,'6-'8 in addition to leukotrienes,'3 have tions and in response to gastric luminal been implicated as mediators of gastro- acidification (0.1 M HCI; 5 mI/min for 10 intestinal injury. Potent inhibitory effects of minutes). Nine healthy volunteers were E-type prostaglandins and the prostaglandin http://gut.bmj.com/ studied in a single blind, cross over analogue, misoprostol, on the release of pro- design. In each subject misoprostol or inflammatory mediators from, for example, placebo was instilled in randomised order mast cells have also been shown.'9 On theor- into the stomach, which was subsequently etical grounds such effects might be beneficial perfused with isotonic mannitol. in ulcer treatment and for prevention of Misoprostol significantly decreased basal NSAID induced gastroduodenal damage, but as well as acid stimulated output of PGE2 the administration of a synthetic prostaglandin on September 30, 2021 by guest. Protected copyright. and TXB2, without affecting output of analogue might also inhibit the synthesis or the LTB4. These data show that misoprostol release of endogenous eicosanoids, or both, inhibits gastric mucosal synthesis of thereby abrogating its own effects. We have, prostanoids. Decreased concentrations, therefore, examined the acute effects of miso- or even a changed profile, of native prostol, a synthetic analogue of prostaglandin eicosanoids modulating the release of E,, on gastric release of prostaglandin E2 inflammatory mediators from immune (PGE2), thromboxane B2 (TXB2), and cells might explain why prostaglandin leukotriene B4 (LTB4), in addition to fluid and analogues have a comparatively poor acid output, during 'steady state' gastric perfu- clinical performance in ulcer healing and sions of the unstimulated and acid stimulated prevention. stomach in healthy subjects. (Gut 1995; 36: 511-515) Departments of Medical Gastroenterology, Keywords: misoprostol, prostaglandins, thromboxanes, Methods Hvidovre and Herlev leukotrienes. Hospitals, University of Copenhagen and SUBJECTS Technical University Ten healthy volunteers (six males and four of Denmark, Denmark Synthetic prostaglandin analogues of the E- females, median age 27 years, range 21-46) A Mertz-Nielsen series, in doses recommended for ulcer heal- with no history of peptic ulcer disease con- O Eskerod K Bukhave ing, combine acid inhibitory effects and sented to the protocol. The study was carried J Rask-Madsen cytoprotective properties with an ability to out according to the Helsinki II Declaration inhibit -7 Correspondence to: meal stimulated gastrin release. This and approved by the ethics committee of Dr J Rask-Madsen, triade of effects was originally considered to Copenhagen and Frederiksberg. Department of Medical Gastroenterology 26 1, offer the ideal antiulcer drug. Surprisingly, Hvidovre Hospital, prostaglandin analogues were shown to heal Kettegard All 30, DK-2650 Hvidovre, Denmark. peptic ulcers no better than would be predicted EXPERIMENTAL DESIGN Accepted for publication from their ability to inhibit gastric acid secre- All 10 healthy volunteers were studied twice 15 July 1994 tion2 3 and in equipotent antisecretory doses with an interval of at least one week. Because 512 Mertz-Nielsen, Eskerod, Bukhave, Rask-Madsen misoprostol is a potent inhibitor of gastric acid on microcolumns. Furthermore, addition of secretion the identity of active and placebo pure misoprostol in the range of 002-20 ng experiments could not remain blinded to the per test tube during the final radioimmuno- investigator. Consequently, a randomised, assay caused no other interference with the single blind, cross over design was used. A 200 measurement of PGE2 than a cross reaction of ,ug misoprostol tablet or a placebo tablet of about 0-1%. Gut: first published as 10.1136/gut.36.4.511 on 1 April 1995. Downloaded from similar appearance (kindly provided by Searle TXB2 was measured by radioimmunoassay as Pharmaceuticals, Morpeth, UK) was dissolved previously described in detail.24 The procedure in 10 ml ofwater and instilled into the stomach included addition of 3H-labelled TXB2 one hour before gastric perfusion. Each gastric (Amersham International) as an internal perfusion included a 30 minute equilibration standard, acidification, extraction with dichloro- period followed by a 30 minute basal period methane, and chromatography on micro- and a 45 minute period after acidification of columns of Sephadex LH-20 before performing the stomach. the radioimmunoassay on the eluate fraction.24 LTB4 was determined by the method previ- ously described,24 using another commercially EXPERIMENTAL PROCEDURE available antibody (Advanced Magnetics, Experiments were performed using a double Cambridge, MA, USA). Briefly, the procedure lumen gastric tube (16 French gauge, AN 10 included addition of 3H-labelled LTB4 Anderson Samplers, Atlanta, GA, USA) as (Amersham International) as an internal stan- described previously in detail.20 After an dard, acidification, extraction with dichloro- overnight fast the stomach was intubated. methane:cyclohexane (2:3), and isolation of Under fluoroscopic guidance the tip of the LTB4 by chromatography on microcolumns of tube was placed in the distal antrum. After Sephadex LH-20 before the radioimmuno- instillation of misoprostol or placebo the sub- assay was performed on the eluate fraction. ject rested in a semirecumbent position for one Trypsin was measured in the gastric efflu- hour before start of perfusion. The stomach ents to assess duodenogastric reflux. A was perfused at a rate of 5 ml/min (LKB 2115 microscale modification of the procedure Multiperpex Pump, Bromma, Sweden) with described by Johnson et al was used.25 This an isotonic solution containing mannitol 54 g/l method was based on the rate at which N- (0 3 M) and [51Cr]-EDTA (10 jiCi/l) as a non- benzoyl-L-arginine-p-nitroanilide hydrochlo- absorbable marker. Aspiration was by intermit- ride (Merck, Darmstadt, Germany) was tent suction from the distal port. During the hydrolysed by a standard solution of porcine perfusion saliva was continuously removed by trypsin (Sigma, St Louis, MO, USA). The dental suction. After the 30 minute equilibra- reaction was performed in microtitration plates http://gut.bmj.com/ tion period 15 minute samples were collected (Nunc, Roskilde, Denmark) and quantified consecutively. For acidification of the stomach spectrophotometrically (Bio-Kinetics reader 100 mM HCl plus 54 mM NaCl were infused EL 31 2e, Bio-Tek Instruments, Winooski, VT, for 10 minutes at a rate of 5 ml/min. USA) at 405 nm against a substrate/water blank. ANALYTICAL PROCEDURES on September 30, 2021 by guest. Protected copyright. The volume of the 15 minute effluents was CALCULATIONS AND STATISTICAL ANALYSES read to the nearest millilitre. The acidity was Basal fluid, acid, PGE2, TXB2, and LTB4 out- determined by titration to pH=7-0 with 0.1 M puts were calculated as the means of the results NaOH using an autotitrator (PHM82, obtained during the two basal periods. Similarly, Radiometer, Copenhagen, Denmark). [51Cr] the results obtained during the periods after activity was measured by gammaspectrometry luminal acidification were calculated as the (Model 1185, Searle Nuclear Chicago means of the first two values. Results are Division, Chicago, IL, USA). Samples for expressed as medians (interquartile ranges). determination of PGE2, TXB2, and LTB4 All data were analysed using analysis of were neutralised immediately and frozen to variance techniques (ANOVA) for a two way - 200C with samples for measurements of model with misoprostol and acid stimulation trypsin until analysis.21 as main effects.