EFFECT OF CARBENOXOLONE ON THE GASTRIC MUCOSAL BARRIER IN MAN AFTER ADMINISTRATION OF TAUROCHOLIC ACID

Transcription

1 GASTROENTEROLOGY 64: , 1973 Copyright 1973 by The Williams & Wilkins Co. Vol. 64 No.6 Printed in U.S.A. EFFECT OF CARBENOXOLONE ON THE GASTRIC MUCOSAL BARRIER IN MAN AFTER ADMINISTRATION OF TAUROCHOLIC ACID KEVIN J. IVEY, M.D., AND C. GRAY A. W. Morrow Department of Gastroenterology, Royal Prince Alfred Hospital, and the Division of Computing Research, Commonwealth Scientific Industrial Research Organisation, Sydney, Australia The mechanism of action of carbenoxolone in healing gastric ulcers is unknown. It has recently been postulated that it acts by preventing increased back diffusion of H+ ions due to intra gastric bile reflux. We studied the ability of carbenoxolone to prevent increased back diffusion of H+ ions after intra gastric instillation of a 10 mm solution of taurocholic acid in five healthy human volunteers. In control studies taurocholic acid produced a net loss of H+ ions of -3.8 meq per 15 min and Na + gain of 3.6 meq per 15 min. With prior intra gastric instillation of 100 mg of carbenoxolone, the net H+ loss was -2.8 meq per 15 min and Na+ gain was 3.1 meq per 15 min. These differences were not significant. Studies repeated in 3 subjects after a 3-week course of oral carbenoxolone showed similar results. We conclude that the mechanism of action of carbenoxolone in healing gastric ulcers is unlikely to occur by preventing back diffusion of H+ ions after bile reflux. Cross and Rhodes l have recently reported that carbenoxolone administered intragastrically significantly reduced back diffusion of H + ions across Heidenhain pouches in dogs after instillation of human bile. They postulated that since there is an increased reflux of bile into the stomach of patients with gastric ulcer, this might be the mechanism of action of carbenoxolone in healing gastric ulcers. We have previously shown that the bile acid, taurocholic acid, causes increased back diffusion of H+ ions across human gastric mucosa. 2, 3 In this study, we tested the effect of carbenoxolone on electrolyte fluxes across the human stomach when it Received September 26, Accepted December 21, Address requests for reprints to: Dr. Kevin J. Ivey, A. W. Morrow Department of Gastroenterology, Royal Prince Alfred Hospital, Camperdown, 2050, New South Wales, Australia. This study was supported in part by the National Health and Medical Research Council of Australia, and the New South Wales State Cancer Council was administered immediately before taurocholic acid. Because patients with gastric ulcer are given a course of carbenoxolone we repeated our studies with taurocholic acid in the same subjects after a 3-week course of oral carbenoxolone. Subjects and Methods A total of 16 studies was carried out in five healthy volunteers (four male, one female), aged 21 to 23 years. Three subjects (two male, one female) were restudied after oral therapy with carbenoxolone, 300 mg per day, in three divided doses for three weeks. Test solutions. The test solution in control studies was 160 meq per liter of HCI, 307 milliosomoles per kg containing 25 J.Lc per liter of 5lCrCl a as nonabsorbable indicator. A wash solution contained 160 meq per liter of HCI only. The carbenoxolone test solution contained 100 mg of carbenoxolone (two tablets) dissolved in 200 ml of the control test solution. The taurocholic acid test solution contained 10 mm taurocholic acid (Maybridge Chemicals, Tintagel, Cornwall, United Kingdom, pure reagent grade) dissolved in 200 ml of the control test

2 1102 lveyand GRAY Vol. 64,No. 6 solution. In the control study, test solutions were instilled for four consecutive 15-min periods in the following order: control, taurocholic acid, taurocholic acid, taurocholic. acid. In the carbenoxolone studies the order was: control, carbenoxolone, taurocholic acid, taurocholic acid. Experimental technique, laboratory methods, and calculations. The technique was performed by a well established method previously described,2-4 using the modification of rinsing the stomach with control test solution for 10 to 15 min before beginning the first period. Since the manufacturers of carbenoxolone specifically state that the concurrent use of anticholinergics with carbenoxolone is contraindicated in the treatment of gastric ulcer, atropine was not used to reduce gastric H+ secretion and emptying in these studies. Volumes, H+, Na+, K+, and CI- concentrations, osmolality, and radioactivity were measured, and volumes secreted and emptied, and net ionic fluxes were calculated by methods previously described.' Statistics. Data were analyzed by Student's t-test for paired observations. A P value of < 0.05 was considered significant. Results Ionic fluxes, volumes secreted and emptied. Details of net ionic fluxes, and volumes secreted and emptied after intragastric instillation of taurocholic acid in 5 subjects are given in table 1. There was a significant loss of H+ ions and gain of Na+ between control period 1 and the taurocholic acid periods 2, 3, and 4, respectively. The effect of intra gastric instillation of carbenoxolone before instillation of taurocholic acid is shown in table 2. Again there was a significant loss of H + ions and gain of Na + ions after instillation of taurocholic acid compared with the control period 1. Carbenoxolone itself (period 2) produced no alteration of ionic fluxes compared with control period 1. Electrolyte concentrations and osmolality. Alterations in mean electrolyte concentrations and osmolality in the study of taurocholic acid instillation alone are shown in table 3. There was a significant fall in H+ concentration and rise in Na+ concentration in the taurocholic acid instillation periods compared with the control period. This significant fall in H+ concentration and rise in Na+ concentration was not prevented by prior intragastric instillation of carbenoxolone (table 4). There were no alterations of electrolyte concentrations between the control and carbenoxolone periods. Effect of course of carbenoxolone. The results in 3 subjects who participated in a 3-week course of carbenoxolone, 100 mg three times a day, on net ionic fluxes are shown in figure 1. The failure of the course of carbenoxolone to alter significantly net losses of H+ ions or gain in Na+ with or without prior intra gastric instillation of carbenoxolone is readily apparent. Similarly, there were insignificant changes in TABLE 1. Effect of taurocholic acid on net ionic fluxes and volumes of gastric secretion and emptying Period Net flux Volume H+ Na+ K+ Cl - Secreted Emptied meq/15 min ml/15 min Mean SE ,..,'.. '".. ' (taurocholic acid) Mean , " 3.55" SE Mean..., " 3.56" SE Mean " 3.64" SE..... ' Ql "p < 0.05 for paired t-test between period 1 and other periods. Minus signs, lumen to mucosa flux.

3 June 1973 CARBENOXOLONE AND THE GASTRIC MUCOSAL BARRIER 1103 TABLE 2. Effect of prior intragastric instillation of carbenoxolone on net ionic fluxes and volumes of gastric secretion and emptying after taurocholic acid Period Net flux Volume H+ Na+ K+ Cl- Secreted Emptied meq/15 min ml/15 min Mean SE..., (carbenoxolone) Mean... ' SE Mean, a 3.08 a SE... ' Mean a 2.83 a SE a p < 0.05 for paired t-test between period 1 and other periods. Minus sign, lumen to mucosa flux. TABLE 3. Changes in electrolyte concentration and osmolality in the 15 min after intragastric instillation of taurocholic acid Period H+ Cl- Na+ K+ Osmolality meq/liter milliosmoles/kg Mean SE (taurocholic acid) Mean a a SE (ta urocholicacid) Mean, a a a SE Mean, a a a SE ap < 0.05 for paired t-test period 1 and other periods. Minus values represent decrease in electrolyte concentration or osmolality. electrolyte concentrations and osmolality in studies done after the carbenoxolone course compared with those done before. Effect of mixing taurocholic acid and carbenoxolone in vitro. In 1 subject 100 mg of carbenoxolone and 10 mm taurocholic acid were mixed in vitro and instilled into the stomach. The results were compared with a control study done on a separate day in which 10 mm taurocholic acid alone was instilled. In the control study, the final concentrations of H+ and Na+ ions were 124 meq per liter and 22 meq per liter after instillation of taurocholic acid, compared with 125 meq per liter and 28 meq per liter when taurocholic acid mixed with carbenoxolone was instilled. Discussion These studies confirm previous studies2, 3 that the bile acid, taurocholic acid, significantly alters ionic permeability across the human stomach. The 10 mm concentration of taurocholic acid used in these studies was twice that of 5 mm used in previous human studies,2, 3 yet the mean ± SE net H + loss was almost identical in both studies. Net H+ losses in the first

4 1104 IVEY AND GRAY Vol. 64, No.6 period of taurocholic acid instillation were ± 0.63 meq per 15 min with 10 mm solution, and -4.0 ± 0.1 meq per 15 min with 5 mm solution. 2 Intragastric instillation of carbenoxolone did not by itself alter ionic permeability when measured either immediately after intragastric instillation or after a 3-week course of oral therapy. This confirms previous studies (unpublished observations) which we have carried out on the effect of repeated intra gastric instillation of carbenoxolone before and after a course of oral therapy. The dose of carbenoxolone, 100 mg, used in this study is the dose shown to increase significantly the healing rate of gastric ulcer in man. 6 We were unable to confirm in man the findings of Cross and Rhodes 1 in Heidenhain pouch preparations in the dog. These authors reported that pretreatment with 100 mg of carbenoxolone for either 5 days or 1 hr significantly reduced back diffusion of H+ ions after intragastric administration of a 10 mm solution of human bile. 1 Cross and Rhodes were unable to show a corresponding decrease in N a + gain in the bile studies done after carbenoxolone. Since nearly all investigators have found a reciprocal relationship between H+ and Na+ fluxes this finding is hard to explain. 7 Second, Cross and Rhodes found that carbenoxolone-rich human bile obtained from patients with T tubes receiving carbenoxolone was as equally damaging to mucosal pouches as bile not containing carbenoxolone. 1 We also found, in an additional study, that carbenoxolone mixed in vitro with 10 mm taurocholic solution produced a similar alteration in ionic permeability to that of taurocholic acid alone. These results make it doubtful that carbenoxolone could prevent back diffusion of H+ ions due to bile regurgitation in man throughout the day. The difference between our findings and those of Cross and Rhodes may be partially explained by the considerably higher dose of carbenoxolone achieved locally in the Heidenhain pouch preparation. A dose of 100 mg daily instilled into the pouch, from which it can all be absorbed, will produce a considerably larger concentration per unit area than the same dose administered to the intact stomach of man, from which most of the drug will be removed by gastric emptying. The same principle applies to the studies of Cross and Rhodes 1 in which the dose (presumably 100 mg) was instilled into the pouch for 1 hr prior to study, compared with our study in which 100 mg (diluted in 200 cc of fluid) were left in the intact stomach for only 15 min. Therefore, while a larger dose TABLE 4. Effect of prior intragastric instillation of carbenoxolone on changes in electrolyte concentration and osmolality after taurocholic acid Period H+ Cl- Na+ K+ Osmolality meq/liter milliosmoles/kg Mean.,.... ", SE (carbenoxolone) Mean SE Mean..,..,.. " " " " SE , Mean " " " SE "p < 0.05 for paired t-test between period 1 and other periods. Minus values represent decrease in electrolyte concentration and osmolality.

5 June 1973 CARBENOXOLONE AND THE GASTRIC MUCOSAL BARRIER 1105 Na + + H Em ~ C. B.L ~ Eil T. C.A. De Control NET FLUX 4 3 meql15-1, 0 -t~-t~ ~~~--&-~~~r-~~~~~l-~~--~~--~~~~~~~~~ PRE -O RAL C. B. E. POST - ORAL C. B. E. COURSE COURSE FIG. 1. Effect of taurocholic acid (T.C.A.) on mean ± SE net H+ and Na+ fluxes prior to and after intragastric instillation of carbenoxolone (C.B.E.). The first half of the figure represents studies in 5 subjects without a prior course of carbenoxolone (PRE-ORAL C.B.E. COURSE). The other half represents studies repeated in 3 of these subjects after a 3-week course of carbenoxolone 300 mg per day. A positive flux indicates a gain of ions by the lumen; a negative flux indicates a loss of ions from the lumen. might reduce back diffusion of hydrogen ions in man, it is unlikely to be of practical value since the dose of 100 mg of carbenoxolone three times daily is associated with a considerable incidence of side effects (hyp6kalemia, and peripheral edema and hypertension due to salt retention), so that the risks of additional dose increases would, in general, not be acceptable clinically. In our studies, the mean net H+ loss and Na+ gain after instillation of taurocholic acid in the stomach, treated immediately beforehand with intragastric carbenoxolone, were less than those untreated. The differences were not statistically significant, and even if they had been, the magnitude of the differences were such that they would be of little meaning in the clinical setting of patients with gastric ulcer. In the preliminary report by Cross and Rhodes,l actual amounts of H+ loss were not stated. It is our conclusion that the mechanism of action of carbenoxolone in healing gastric ulcers in man is unlikely to occur by preventing back diffusion of H+ ions after bile reflux. REFERENCES 1. Cross S, Rhodes J : Carbenoxolone: its protective action against bile damage to gastric mucosa in canine pouches. Gastroenterology 62:737, Ivey KJ, Den Besten L, Clifton JA: Effect of bile salts on ionic movement across the human gastric mucosa. Gastroenterology 59: , Ivey KJ, Clifton JA, Den Besten L: Effect of bile salts and atropine on ionic movement across human gastric mucosa. Gut 12: , Ivey KJ, Clifton JA: Ionic movement across the gastric mucosa of man: reproductibility and effect of intravenous atropine. J Lab Clin Med 78: , Ivey KJ, Morrison S, Gray C: Effect of salicylates on the gastric mucosal barrier in man. J Appl Physiol 33: Doll R, Hill ID, Hutton C, et al: Clinical trial of a triterpenoid liquorice compound in gastric and duodenal ulcer. Lancet 2: , Ivey KJ: The gastric mucosal barrier. Gastroenterology 61 : , 1971