Effects of prostaglandin E2 on salicylate-induced damage to the rat gastric mucosa: ... PG pretreatment did not produce a reduction in the effects of topical ...
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Effects of prostaglandin E2 on salicylate-induced damage to the rat gastric mucosa: cytoprotection is not associated with preservation of the gastric mucosal barrier GERALDP. MORRIS,"^ JOHNL. WALLACE, AND PATKICIA L. HAKDING Department ($Biology, Queen's University, Kingston. Ont., Canada K7L 3NG Received August 2, 1983
MORRIS.G. P., J. L. WALL,ACE, and P. L. WARDING. 1984. Effects of prostaglandin E2 on salicylate-induced damage to the rat gastric mucosa: cytoprotection is not associated with preservation of the gastric mucosal barrier. Can. 9. Physiol. Phamacol. 62: 1065- 1069. The effects of pretreatment with prostaglandin E2 (PGE,) on salicylate-induced gastric damage in the rat were studied with a gastric chamber model. Transmural potential difference (PD) and net potassium ion (K') efflux were monitored as indices of gastric mucosal barrier integrity. Topical application of 20 mM salicylate for 10 inin produced an abrupt drop in PD, an increase in net K+ flux, and the formation of hemorrhagic erosions covering approximately 24% of the glandular mucosa. Prior topical application of PGE, at doses of 25, 75, and 300 pg/kg significantly reduced the extent of hemowhagic erosions. However. PG pretreatment did not produce a reduction in the effects of topical salicylate on either PD or net K' efflux. Rather. the drop in PD was initially accelerated and the net K' efflux was increased by PGEz pretreatment. Subsequently, in PGE2-pretreated mucosae, both parameters showed more rapid recovery toward control values. These results suggest that the mechanism of "cytoprotection" by PGEz against salicylate-induced gastric damage is not a consequence of preservation of the gastric mucosal barrier. MORRIS,@. P., J. L. WALLACEet P. L. WARDING. 1984. Effects of prostaglandin E2 on salicylate-induced damage to the rat gastric mucosa: cytoprotection is not associated with preservation of the gastric mucosal barrier. Can. J . Physiol. Pharmacol. 62: 1065- 1069. On a utilisC un modkle de chambre gastrique pour examiner les effets d'un pretraitement avec la prostaglandine E2 (PGE2) sur une lesion gastrique induite par du salicylate. On a considere la difference de potentiel (BP) transmural et l'efflux net d'ions potassium (K') comme des indices d'intkgrite de la barrikre muquese. L,'application topique de 20 mM de salicylate pendant 20 min provoqua une chute abrupte de PD, une augmentation de l'efflux net de Kf et la formation d'erusions hCmorragiques couvrant approximativement 24% de la muqueuse glandulaire. Une application topique anterieure de doses de 25, 75 et 300 pg/kg de PGE, reduisit significativement l'entendue des erosions hemorragiques. Toutefois, un pretraitement avec la PG ne reduisit des effets du salicylate topique ni sur la PB ni sur l'efflux net de K'. Au contraire, la chute de la PD ni fut accCl6ree au debut et le traitement i la P@E2augmenta l'efilux net de K'. Ultkrieurement, dans les muqueuses prktraitees avec la PGE,. les deux paramktres montrkent un retour plus rapide aux valeurs temoins. Ces rksultats suggkrent que le mecanisme de "cytoprotection" de la PGE2 contre la lesion gastrique induite par le salicylate n'est pas le r6sultat d'une preservation de la barrikre muqueuse. [Traduit par le journal]
Introduction
Pretreatment with PG at "cytoprotective" doses has also been reported to reduce the magnitlide of the drop in transmural potential difference (PD) and in net ion fluxes following luminal infusion of barrier breakers (Cohcn and Pollett 1976; Dajani et al. 1978; Chaudhury and Jacobsen 1978). In this study we describe the short-term changes in transmural PD and K' efflux following topical application of salicylic acid. We have previously found these two parameters to be the most sensitive predictors of the extent of hemorrhagic n~ucosaldamage induced by necrotizing agents (Morris et al. 1984). Pretreatment with P@E2 reduced the extent of salicylate-induced hemorrhagic erosions but did not initially produce changes which can be readily associated with preservation of gastric ~nucosalbarrier integrity.
The phenomenon of "cytoprotection" has elicited great interest because of the apparent ability of a wide variety of agents and procedures to prevent the development of acute hemorrhagic erosions in the gastrointestinal tract (see Robert 1981 , for review). In the most simple and widely known experiments, topical or systemic administration of various prostaglandins (PG) at intervals of 1-30 ~ninprior to luminal infusion of necrotizing agents prevented the subsequent development of hemorrhagic erosions. It can be reasonably stated that the mechanism by which these agents confer this protection is unknown. The implicit assumption in most studies of cytoprotection is that the surface epithelium is protected against the effects of luminal '.barrier bieakers." It is-now apparent that this is not the case. Recent studies have shown that PG-mediated protection against ethanol does not involve preservrition of surface epithelial cell (SEC) integrity (Lacy and Ito 1982; Wallace et al. 1982). We have also established that PGE2 does not protect SEC against salicylic acid, even though the extent of gross mucosal damage is significantly reduced (Morris and Harding 1984).
Animals Virgin female rats of the Sprague-Dawley strain (average weight 250 g) were used in all experiments. Rats were housed in standard, wire-mesh cages with not more than 12 rats per cage. Standard laboratory chow and tap water were available ad libitum. Prior to the experiment the rat was transferred to an individual cage and deprived of food for 18 h. Water remained available ad libiturn during this time.
'Supported by a grant (MA 8143) from the Medical Research Council of Canada. 'Author to whom correspondence should be addressed.
Gastric*chamber jzreparcitbon All experiments conimenced betwcen 0800 and 61830. Each rat was anaesthetized with sodium anlobarbital (130 mg/kg) and an eex vivo gastric chamber was prepared as described previously (Wallace et al.
Materials and methods
CAN. I. PHYSIOL. PI-IAKMACOL. VOL. 62. 1984
TABLE1. Composition sf lkaminal solutions
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Experiment group -
Ti ane I - 10 11-20 21-30 31-40 41 - B 10
MCI HCl HCI 25PG HCl 25PG HCI MCI PIC8 HCl
HCB 75PG 75K HCI HCl
HCI HCI MCI HCI HGB 300PG HCI 25PG TSPG 30OPG 300PG HCI 25PG 75PG 3OOPG SAL SAL SAL HCI SAL HCl HCI HCI HCI WCI
Nure: HCI, 50 mA.I hydrochloric acid in 200 rnM mdnnitol: xxPG, micrograms per kilogram of WE2;SAE, 20 n M salicylic acid. PGE, and saiicylic acid were alwa)1s added to Iurninal solutions ( 1 0 mL) of 50 tn44 HCI and 700 m44 mannitol.
1982). 'This preparation allowed direct observation of the mucosa throughout the I 10-min experiment. The major gastric vascular and nervous supplies werc intact. 'The chambered stomach exposed both the antral and fundic regions. Immediately after the chamber was prepared, the stomach was gently rinsed with warm (37"Cj 200 rM mannitcd to remove any hair or scales ingested during grooming. Protoc*oi kach experiment consisted of I I sequential 10-min periods; the composition of the luminal bathing solution adcisd to the chamber varied among groups (see Table 1). At the staHt of each period a 10-maL aliquot of the appropriate solution (37°C) was weighcd and delivered into the chamber by syringe. While in the charnker the solutions were stirred constantly by a glass paddle (located 1 cm abovc the mucrssal supface) turning at a rate of 200 revoluti~nsper minute. At the end of each period the luminal solution was aspirated by syringe, reweighed to determine changes in volume, and frozen for subsequent determination of potassiu~rlion concentration (by atcxnic absorption spectrophotometry: Unicam). jrrianstaarar(~1pof~rntiu1Cdiflcr~nc'c Transmural potential difference (PD) was measured througimout each experiment by a technique described in detail previously (Morris and Wallace B 98 1). 'The PD was continuously recorded s n a Sanborn physiograph. The mean PD for a 5-min interval was calcuIated by averaging the values recorded at 1-min intervals. Ccsinrt area Subsequent to the final 19-min period in cach experiment the chambered mucosa was photographed on Ektachrome colour slide film. The slides were prs.jccted onto 21.5 X 28.0 crn paper, and were traced and coded to prevent observer bias. Lesion area data were dcrived from these tracings by planirnetry. Both the total arca of glandular mucosa and the area of damaged mucosa were mncasured. Data were expressed as the percent of glandular mucosa showing gross dimage. Test solutbens Salicylate solutions were freshly prepared prior to each experiment. Salicylic acid (20 M B (Sigma) was dissolved in 50 rmW MCI in 200 IIM mannitol f~nannitol - HCI). Prustaglandin E2 (Sigma) was dissolved in deionized water ( 1 mg/mL) and stored at -2Q°C for no more than 1 week. The PGE, solutions were always added to 10 mL of a lurninal solution of mannitol-HCI in the gastric chamber at the start of periods 2 and 3. PGE, was infused at doses of 25 pg/kg (0.625 ~ g / m L ) , 150 ~ g / k g (1.75 ~ g / m L ) , and 300 pg/kg (7.50 pg/mLj. Statb~tic-QI UPICI~~,SPS All data are expressed as means 2 SEM. For PI3 and potassium ion data, Student's two-tailed f-tests for unpaired data were used to conapare each group with its respective control group (i.e., E VS.A, F VS. B, G vs. C. H vs. D). For lesion area data and any multiple group comparisons for other data, one-way analyses of variance (ANOVA) were performed. Subsequently, Duncan's multiple range test\ were performed to detect those groups which differed significantly. Uraless
TABLE2. Summary of lesion area data Group
PI
Lesion area ((;GI
A
I0 5 5
0.820.4 1.520.5 1.8k0.5
B C
NOTE: Additional expesitnents were performed in groups E and Ci (I'm rneasurerneni of PD) and the experiment was termiaratrd after 40 snin. * p
