Ethyl acrylate-induced gastric toxicity. III. Development and recovery of lesions

Rats receiving 14 daily gavage doses of 100 or 200 mg/kg ethyl acrylate (EtAc) and killed at varying times following the end of dosing exhibited dose-dependent lesions and recovery from lesions in the forestomach. The glandular stomach which was previously shown to be affected by acute exposure to EtAc appeared to have adapted to resist EtAc toxicity with repeat exposure and appeared normal in all animals. Adaptation of the forestomach was characterized by increased papillomatous thickening with dose. Lesions observed in acute exposure to EtAc were still present with repeat dosing and were more pronounced at the high dose. Forestomachs of rats which received 100 mg/kg EtAc for 14 days were recovered to normal within 2 weeks following the last dose. Forestomachs of rats receiving 200 mg/kg EtAc still exhibited numerous lesions 2 weeks following the last dose, and mucosal hyperplasia was present in the forestomachs at 4 weeks postexposure. Two lesions, submucosal fibrosis and foreign body reaction, became more prevalent in high-dose animals with time. Foreign body reaction, which was present in all animals 4 weeks postexposure, appeared to have resulted from entrapment of hair and/or feed particles in forestomach lesions in the course of healing. It is speculated that the increased cell proliferation and the induced foreign body reactions may contribute to the previously demonstrated carcinogenic effect of EtAc on the rat forestomach.     

Ethyl Acrylate Distribution, Maromoleular Binding, Excretion, and Metabolism in Male Fisher 344 Rats

We have demonstrated previously that ethyl acrylate causes severeacute forestomach (nonglandular portion of the stomach) toxicityin rats. Ethyl acrylate was also shown to cause forestomachtumors when administered to rats chronically by gavage. Thecurrent studies were designed to investigate ethyl acrylatedistribution, excretion, and metabolism, as well as the macromolecularinteractions of ethyl acrylate (EtAc) in the forestomach (targetorgan) and liver (nontarget organ). 2,3-[¹⁴C]Ethyl acrylatewas administered in corn oil at 100, 200, or 400 mg/kg by gavage.Data presented here show that the radioactivity derived fromEtAc is rapidly absorbed after gavage administration and distributedinto all major tissues of male F344 rats. The highest concentrationof EtAc-derived radioactivity was detected in the forestom ach,glandular stomach, intestine, liver, and kidney at 4 and 24hr after dosing. The highest percentage of EtAc-derived radioactivitywas found in the lipid fraction of the liver. In the forestomach,the highest percentage of EtAc-derived radioactivity was foundin the protein fraction. The major route of EtAc excretion wasCO₂ exhalation (approximately 70% of the administered dose in24 hr) followed by the urinary excretion. Two metabolites wereidentified in the unne, namely, N-acetyl-s-(2-carboxyethyl)cysteineand N-acetyl-s-(2-carboxyethyl)cysteine ethyl ester. This suggeststhat Michael-like addition of sulfhydryls to acrylate is a pathwayof EtAc metabolism. Hydrolysis of the ethyl ester may occurbefore or after conjugation. Further degra dation of the GSHconjugates resulted in the formation of the mercapturic acidsdetected in the urine of EtAc-treated rats.     

Effects of sulfhydryl modulation on ethyl acrylate-induced forestomach toxicity

Acute administration of a single dose of ethyl acrylate (EA) to F344 rats by gavage caused time- and dose-dependent forestomach edema. Evidence from our laboratory and others suggested that EA is hydrolyzed to acrylic acid (AA) and ethanol both in vivo and in vitro. The major metabolites detected in teh urine of rats treated with EA were derivatives of the glutathione conjugates of EA and AA. The current work was undertaken to investigate the effects of sulfhydryl-depleting agents (diethylmaleate and fasting) and sulfhydryl-containing agents (cysteine and cysteamine) on EA-induced forestomach edema. Results presented in this report revealed that pretreatment of rats with sulfhydryl-containing chemicals such as cysteine or cysteamine has potentiated EA-induced forestomach edema. In contrast, depletion of indigenous sulfhydryls by fasting of rats or pretreatment with diethylmaleate (DEM) protected against EA-induced forestomach edema. Furthermore, repetitive daily administration of EA by gavage induced mucosal forestomach hyperplasia. Co-administration of cysteamine and EA resulted in a significant enhancement of the severity of EA-induced forestomach mucosal hyperplasia. In conclusion, current data suggest that modulation of indigenous sulfhydryls play a role in EA-induced forestomach toxicity; however, the exact mechanism underlying this role remains to be characterized.     

Acute Urinary Tract Toxicity of Tetraethylorthosilicate in Rats

Acute stomach, kidney, and bladder toxicity was evaluated inF344 rats after gastric gavage of tetraethylorthosilicate (TES)at daily doses of 0, 0.111, 0.223, and 0.333 g. Five rats ofeach sex at each dose were sacrificed after 1, 2, and 4 days.In TES-treated groups, silicate accumulated in the stomach glandsand the muscle layer of the forestomach and glandular stomach.Serum chemistries demonstrated acute onset of renal failure.In the kidneys, acute tubular necrosis, accumulation of silicates,and superficial necrotizing papillitis were observed. In therenal pelvis and bladder, there was urothelial simple hyperplasia,focal erosion of the mucosa, edema, and inflammation. Theseacute toxic changes were dose and time dependent, but significantsex differences were not observed. The microscopic changes inthe urothelium were similar to those observed following administrationof high doses of sodium saccharin to male rats in which urinarysilicate precipitate and crystals form.     

14-Week toxicity and cell proliferation of methyleugenol administered by gavage to F344 rats and B6C3F1 mice.

Methyleugenol, a food flavor and fragrance agent, was tested for toxicity in male and female F344/N rats and B6C3F1 mice. Groups of 10 males and 10 females per sex per species were administered 0, 10, 30, 100, 300 or 1000 mg methyleugenol/kg body weight in 0.5% aqueous methylcellulose by gavage, 5 days per week for 14 weeks. Additional groups of rats and mice of each sex were dosed similarly and used for hematology and clinical chemistry studies. Groups of 10 male and 10 female rats and mice received the vehicle by gavage on the same dosing schedule and served as vehicle controls. For serum gastrin, gastric pH and cell proliferation studies groups of 10 female rats were given 0, 37, 75 or 150 mg/kg, once daily 5 days per week for 30 or 90 days or 300 or 1000 mg/kg for 30 days; male mice were given 0, 9, 18.5, 37, 75, 150 or 300 mg/kg for 30 or 90 days. For the gastrin, pH and cell proliferation studies, groups of 10 female rats and 10 male mice were given the vehicle for 30 or 90 days and served as controls. Methyleugenol administration to rats induced erythrocyte microcytosis and thrombocytosis in male and female rats. It also caused an increase in serum alanine aminotransferase and sorbitol dehydrogenase activities and bile acid concentration, suggesting hepatocellular injury, cholestasis or altered hepatic function. Additionally, methyleugenol induced hypoproteinemia and hypoalbuminemia, evidenced by decreased total protein and albumin concentrations in both male and female rats, suggesting in inefficiency of dietary protein utilization due to methyleugenol-induced toxic effects on the liver and glandular stomach of rats and mice. The increase in gastrin and gastric pH of rats and mice given methyleugenol suggests that gastrin feedback was impaired and resulted in conditions not conducive to protein digestion. In rats, methyleugenol caused an increase in the incidences of hepatocyte cytologic alteration, cytomegaly, Kupffer cell pigmentation, mixed foci of cellular alteration and bile duct hyperplasia of the liver and atrophy and chronic inflammation of the mucosa of the glandular stomach. In mice, it caused an increase in the incidence of cytologic alteration, necrosis, bile duct hyperplasia and subacute inflammation of the liver and atrophy, degeneration, necrosis, edema, mitotic alteration, and cystic glands of the fundic region of the glandular stomach. The increased incidences of adrenal gland cortical hypertrophy and/or cytoplasmic alteration in the submandibular salivary glands, adrenal glands, testis and uterus of rats were considered secondary to the chemical-related effects observed in the liver and glandular stomach. Based on mortality, body weight gain, clinical chemistry and gross and microscopic evaluation of tissues of rats and mice, the no-observed-effect level (NOEL) of methyleugenol for both species was estimated at 10 mg/kg.     

Metabolism of 2- and 3-tert-butyl-4-hydroxyanisole (2- and 3-BHA) in the rat. (II): Metabolism in forestomach and covalent binding to tissue macromolecules

The mechanism of action of 2(3)-tert-butyl-4-hydroxyanisole (2-BHA or 3-BHA) on rat forestomach epithelium was studied by examining the metabolites of BHA in the stomach and the covalent binding of BHA to macromolecules in the forestomach epithelium. Male F344 rats 6 weeks old were given a single intragastric injection of 1 g/kg body wt of [tert-14C]-3-BHA (Bu-3-BHA) or [methyl-14C]-3-BHA (Me-3-BHA), and 6 h later BHA metabolites in the forestomach, glandular stomach and stomach contents were examined by thin-layer chromatography. No significant amounts of metabolites were detected in the forestomach or glandular stomach epithelium and almost all the radioactivity in these tissues was extracted with organic solvents. In in vitro experiments also, no significant amounts of metabolites were detected when the 9000 g supernatant of the forestomach or glandular stomach epithelium, or gastric juice was incubated with Bu-3-BHA in the absence or presence of NADPH. In binding studies, rats were given Bu-3-BHA, [tert-14C]-2-BHA (Bu-2-BHA), Me-3-BHA or [methyl-14C] butylated hydroxytoluene (Me-BHT) intragastrically at a dose of 1 g/kg body wt with or without pretreatment with unlabelled 1% 3-BHA or BHT in the diet for 6 days. Six hours after treatment with a labelled compound, the rats were sacrificed and the DNA, RNA and protein of their forestomach, glandular stomach, liver and kidney were isolated. Bu-3-BHA, Bu-2-BHA and Me-3-BHA did not bind covalently to forestomach DNA or RNA, and the amounts of radioactivity of these compounds bound to proteins in the 4 tissues were similar. These findings suggest that BHA acts on the forestomach epithelium directly without metabolic activation, and that its action is not related to its binding to DNA or RNA.     

Pathological and Biochemical Effects of Dimethyl Hydrogen Phosphite in Fischer 344 Rats

Pathological and Biochemical Effects of Dimethyl Hydrogen Phosphitein Fischer 344 Rats. NOMEIR, A. A., AND URAIH, L. C. (1988).Fundam. Appl. Toxicol 10, 114–124. In a chronic studyby the National Toxicology Program (NTP), dimethyl hydrogenphosphite (DMHP) caused neoplastic and nonneoplastic changesin the lungs and forestomach of F344/N rats following gavageadministration for 2 years. The current investigation was designedto study the effect of a short-term exposure on a series ofbiochemical systems in target and nontarget tissues which maybe involved in the metabolism and/or the manifestation of DMHPtoxicity. Rats were treated daily with a dose similar to thatused in the NTP study (200 mgkg) for 4, 5, or 6 weeks. Two groupsof animals were also treated /for 4 weeks and then treatmentwas discontinued and the rats were allowed to recover for 1or 2 weeks. An equal number of animals was treated similarlywith the vehicle and used as control. The microsomal and solublefractions were separated from liver, lungs, kidneys, forestomach,and glandular stomach from the 6-week treatment group. Anothergroup of rats treated for 6 weeks was prepared for pathologyexamination of the lungs, forestomach, and glandular stomach.There was a significant increase in the weight of the forestomachof rats treated for 4, 5, or 6 weeks relative to control animals,while no significant difference was observed in the weight ofliver, lungs, kidneys, and glandular stomach. The forestomachweight of rats treated for 4 weeks returned to the control valueafter 1 week of recovery. Microscopic examination of the forestomachof rats treated for 6 weeks revealed a thickened stratifiedsquamous epithelium characterized by hyperplasia, hyperkeratosis,and subepithelial inflammation and edema. There were no microscopicchanges in the lungs or glandular stomach of animals treatedfor 6 weeks. The activity of angiotensin converting enzyme inthe serum of rats treated for 4, 5, or 6 weeks was significantlyincreased over that of control animals. The activity of thisenzyme returned to near levels seen in the control animals after1 week of recovery following 4 weeks of treatment. No treatment-relatedeffect was observed in the activities of the microsomal p-nitroanisoledemethylase, soluble glutathione S-transferase, and solublesuperox-ide dismutase in the five tissues studied. There wasa significant increase in the level of nonpro-tein soluble sulfhydrylsin the forestomach but in no other tissue of rats treated for6 weeks. Also the activity of soluble carboxylesterase was significantlyreduced in the lungs and forestomach, but not in any other tissueof the 6-week-treated rats. Results of this study indicate thatearly pathological and biochemical changes are detected in targettissues of rats exposed to.     

Comparative toxicity of ethylene dichloride in F344/N, Sprague-Dawley and Osborne-Mendel rats

Studies were conducted to compare the toxicity of ethylene dichloride (EDC) in F344/N rats, Sprague-Dawley rats, and Osborne-Mendel rats. Ten rats/sex/group were exposed to EDC in drinking-water at 0, 500, 1000, 2000, 4000 and 8000 ppm for 13 wk. The highest concentration was limited by the maximum solubility of EDC in water (about 9000 ppm). In addition, F344/N rats (10/sex/group) were administered EDC in corn oil by gavage to compare toxicity resulting from bolus administration with that of continuous exposure in drinking-water. Gavage doses of EDC were within the range of total daily doses (in mg/kg body weight/day) resulting from exposure in drinking-water. EDC administered by gavage resulted in greater toxicity to F344/N rats than did administration of similar doses in drinking-water. All males receiving 240 and 480 mg/kg body weight and 9/10 females receiving 300 mg/kg body weight by gavage died before the end of the study. Necrosis of the cerebellum was observed in the brains of 3 males receiving 240 mg/kg body weight and 3 females receiving 300 mg/kg body weight. Hyperplasia and inflammation of the forestomach mucosa were observed in 8 male and 3 female rats that died or were killed in moribund condition. EDC caused minimal toxicity to F344/N, Sprague-Dawley and Osborne-Mendel rats at the drinking-water concentrations used in these studies; only female F344/N rats had EDC-related renal lesions. Based on mortality and EDC-related lesions, the no-effect levels for EDC administered by gavage to F344/N rats were 120 mg/kg body weight for males and 150 mg/kg body weight for females.     

Chronic toxicology and carcinogenesis studies of Telone II by gavage in Fischer-344 rats and B6C3F1 mice

Telone II (technical grade, 1,3-dichloropropene), a soil fumigant, was evaluated in chronic toxicology/carcinogenicity studies using Fischer-344 (F344) rats and B6C3F1 mice of both sexes. Doses administered were 0, 25, or 50 mg/kg to rats and 0, 50, or 100 mg/kg to mice. Telone II was given in corn oil by gavage 3 times per week for 104 wk. Ancillary studies were conducted to determine time-related effects, in which dose groups containing 5 male and 5 females rats were killed after receiving Telone II for 9, 16, 21, 24, or 27 mo. The primary organs affected were the forestomach (rats and mice), urinary bladder (mice), lung (mice), and liver (rats). Compound-related non-neoplastic lesions included basal-cell or epithelial hyperplasia of the forestomach (rats and mice), epithelial hyperplasia of the urinary bladder (mice), and hydronephrosis (mice). Neoplastic lesions associated with administration of Telone II included squamous-cell papillomas of the forestomach (male and female rats, female mice), squamous-cell carcinomas of the forestomach (Male rats, female mice), transitional-cell carcinomas of the urinary bladder (female mice), alveolar/bronchiolar adenomas (female mice), and neoplastic nodules of the liver (male rats). Although cis- and trans-1,3-dichloropropene are the principal components of Telone II, the presence of 1% epichlorohydrin, a direct-acting mutagen and carcinogen added as stabilizer, may have influenced the development of forestomach lesions. The results of the ancillary studies supported the findings of the carcinogenesis studies and demonstrated the time-dependent development of lesions in the forestomach (basal-cell hyperplasia and squamous-cell papilloma). Under the conditions of these gavage studies, Telone II was shown to be carcinogenic in male and female F344 rats and female B6C3F1 mice. Although the study in male B6C3F1 mice was considered inadequate because of the low survival resulting from suppurative inflammation of the heart (myocarditis) in the control group, there was some indication of Telone II-related increases of transitional-cell carcinomas of the urinary bladder, squamous-cell papillomas of the forestomach, and alveolar/bronchiolar adenomas and carcinomas of the lung.     

Gastric mucosal damage induced by endotoxin shock and its prevention by naloxone and anti-ulcer drugs in rats

Administration of endotoxin (20 mg/kg i.p.) produced a moderate degree of gastric mucosal damage in rats. The lesions remained confined to the glandular mucosa and consisted of small punctiform lesions, erosions and petechial hemorrhage. The characteristic feature of these lesions was a typical submucosal ecchymosis in the glandular stomach observed in about 30% of the animals. Pretreatment with ranitidine, pirenzepine, proglumide, sucralfate and naloxone produced varying degrees of protection. The ulcerogenic effect of endotoxin shock is apparently mediated through the release of endorphins.     

Effects of different types of diet and sodium saccharin on proliferation at the limiting ridge of the rat forestomach

Sodium saccharin, at high doses in the diet, has been reported to cause hyperplasia of the forestomach (squamous portion of stomach), at the limiting ridge in F344 rats, in addition to its potential to induce proliferative effects on the urinary bladder epithelium. We have characterized this hyperplasia of the squamous epithelium of the forestomach at the limiting ridge in F344 and Sprague-Dawley rats given various doses of sodium saccharin for 4 to 95 wk. With increasing doses of sodium saccharin, the limiting ridge of the forestomach showed dose-related morphological changes: basal-cell hyperplasia, early papillary hyperplasia with basal-cell hyperplasia and papillary hyperplasia. Calcium saccharin in Prolab diet caused hyperplasia of the forestomach at the limiting ridge, similar to that caused by sodium saccharin. The severity of hyperplasia was influenced by the type of diet and by the strain of rats. AIN-76A diet without added sodium saccharin caused basal-cell hyperplasia in F344 rats, whereas Prolab, Purina and NIH-07 diets without added sodium saccharin had little or no effect on the forestomach. The effect of AIN-76A diet alone persisted through 95 wk of feeding without any evidence of tumour formation. In Sprague-Dawley rats, which appeared more sensitive to effects on the forestomach than F344 rats, Prolab 3200 and Purina diets without sodium saccharin caused basal-cell hyperplasia in more than half of the treated rats. The forestomach hyperplasia associated with AIN-76A or saccharin administration appears to be mild, limited in extent to the limiting ridge, and not associated with carcinogenesis.     

Metabolism of 2- and 3-tert-butyl-4-hydroxyanisole (2- and 3-BHA) in the rat (I): Excretion of BHA in urine, feces and expired air and distribution of BHA in the main organs

The mechanism of the carcinogenic or toxic action of BHA on rat forestomach was examined by studies on the excretion and tissue distribution of radioactivity in F344 male rats given tert-butyl- or methoxy-labelled 3-BHA orally. Within 2 days after a single oral dose of labelled BHA at 1 g/kg body wt, 87-96% of the 14C was excreted, mainly in the urine with smaller amounts in the feces and expired air. More 14C was found in the tissues of rats given the methoxy-labelled compounds. The distributions of 14C in the forestomach and the glandular stomach were similar. At 168 h after treatment, more 14C was found in the forestomach of rats given 2-BHA than in that of rats given 3-BHA. These results indicate that excretion of BHA is rapid, that 4-O-methyl demethylation may take place readily and that demethylated methyl group may become distributed non-specifically in tissues. The carcinogenic or toxic action of BHA on the forestomach does not seem to be due accumulation of BHA in the forestomach.     

Evaluation of potential human carcinogenicity of the synthetic monomer ethyl acrylate

Ethyl acrylate (EA) is an acrylic monomer used in the manufacture of a variety of polymers and copolymers as components of many commercially important products. Human exposure to EA occurs primarily in the workplace via inhalation or dermal contact. In F344 rat and B6C3F(1) mouse studies of EA carcinogenicity conducted by the National Toxicology Program [National Toxicology Program, NTP, 1986. Carcinogenesis Studies of Ethyl Acrylate (CAS No. 140-88-5) in F344/N Rats and B6C3F(1) Mice (Gavage Studies) (Tech. Rep. Ser. No. 259; NIH Publication No. 87-2515), Research Triangle Park, NC, USA], the only increased tumor incidences was in squamous cell papillomas and carcinomas of the forestomach, when EA was administered by gavage in corn oil at 100 or 200mg/kg/day (high dose; HD). The neoplasms were preceded by forestomach irritation, inflammation, hyperkeratosis and hyperplasia of the forestomach mucosa. In studies in which rats and mice were exposed at comparable doses to EA in drinking water, by inhalation, or by dermal application, no neoplasms in the forestomach or in any other tissue were reported. EA exhibited clastogenicity and related mutagenicity in vitro, but was non-genotoxic in vivo, including in the forestomach of treated rats. The in vitro clastogenicity response correlates well with cellular toxicity, mediated by non-protein sulfhydryl depletion and mitochondrial impairment. Thus, the carcinogenicity in the forestomach can be ascribed to a non-genotoxic mode of action (MOA). The forestomach mucosal hyperplastic and even dysplastic changes, observed chronically, were reversible, provided the HD exposure was not longer than 6months. This again supports a non-genotoxic MOA. In addition, the route and rate of EA exposure in rodents for forestomach neoplasia are irrelevant to potential human exposure, since humans do not have forestomach and are not exposed to EA by oral bolus. Thus, the weight of evidence indicates that the tumors produced in the rodent carcinogenicity studies arise from conditions that are irrelevant for human risk assessment.     

The protective effects of sulphasalazine against ethanol-induced gastric damage in rats.

1 The inhibitory action of sulphasalazine on ethanol-induced gastric damage was studied in rats. 2 Sulphasalazine (62.5 or 125 mg kg-1, s.c.) did not affect basal gastric acid secretion but increased pepsin output. 3 Ethanol (40% v/v, 10 ml kg-1, p.o.) produced severe gastric glandular mucosal damage and lessened the stomach emptying rate of resin pellets, but it increased the levels of prostaglandin E2 (PGE2)-like activity in the glandular mucosa. 4 Sulphasalazine markedly prevented ethanol-induced damage and significantly elevated gastric wall mucus levels both in basal conditions and in the presence of ethanol. 5 Sulphasalazine caused a small insignificant increase in mucosal PGE2 levels in both control and ethanol-treated rats. The drug significantly increased mucosal PGE2 levels in indomethacin-treated animals, but did not prevent indomethacin-induced mucosal damage. 6 Sulphapyridine but not 5-aminosalicylic acid, constituents of sulphasalazine, showed a similar antilesion action to the parent drug, and prevented gastric wall mucus depletion in ethanol-treated animals. 7 This study elucidates the protective effects of sulphasalazine against ethanol-induced gastric lesions. The antagonistic action appears to be mediated, at least partly, through the preservation of gastric wall mucus by sulphapyridine.     

Two-year drinking-water study of formaldehyde in rats

Formaldehyde was administered in the drinking-water to groups of 70 male and 70 female Wistar rats for up to 24 months. Survivors of subgroups of ten rats/sex/group each were killed after 12 or 18 months. The mean formaldehyde doses administered were 0, 1.2, 15 or 82 mg/kg body weight/day for males, and 0, 1.8, 21 or 109 mg/kg/day for females. There were no adverse effects on general health, survival or haematological or clinical chemistry parameters. Body weight and food intake were decreased in the high-dose group. Liquid intake was decreased by 40% in the high-dose group in both sexes in comparison with the controls. There was a slight temporary increase in the density of urine, whereas there was a tendency towards lower urine production in the high-dose group. The relative kidney weights were increased in the high-dose females. Gross examination at autopsy revealed a raised and thickened limiting ridge of the forestomach in most high-dose rats. In addition, several rats in the high-dose group showed irregular mucosal thickenings in the fore- and/or glandular stomach. Treatment-related histopathological gastric changes seen in most of the animals of the high-dose group included papillary epithelial hyperplasia frequently accompanied by hyperkeratosis and focal ulceration in the forestomach and focal chronic atrophic gastritis, occasionally accompanied by ulceration and/or glandular hyperplasia, in the glandular stomach. A higher incidence and/or degree of renal papillary necrosis occurred in the high-dose rats. From this study it appeared that the 'no-observed-adverse-effect level' of formaldehyde was 15 and 21 mg/kg body weight/day for male and female rats, respectively. Oral administration of formaldehyde at doses of 82 and 109 mg/kg/day to male and female rats, respectively, caused severe damage to the gastric mucosa but did not result in gastric tumours or tumours at other sites. The study did not provide any evidence of carcinogenicity of formaldehyde after oral administration.     

Calcium and ethanol-induced gastric mucosal damage in rats

The effects of graded doses of ethanol on stomach mucosal damage and calcium levels were studied in rats. The influence of verapamil and/or calcium chloride on these changes was also investigated. Orally administered ethanol (20, 50 or 80% v/v) markedly decreased gastric glandular tissue calcium and it concentration dependently produced mucosal lesions. Pretreatment with verapamil (2.5 or 5 mg/kg, i.p.) dose dependently lessened glandular wall calcium levels and worsened ethanol-induced mucosal damage. Calcium chloride (50 mg/kg, i.p.) significantly prevented ethanol-induced gastric calcium depletion; it also dose dependently antagonized the damaging effect of ethanol as well as the lesion-intensifying action of verapamil. The findings that verapamil potentiated, whereas calcium chloride prevented, ethanol-induced glandular mucosal damage and tissue calcium changes indeed suggest that altered gastric cell calcium levels could be closely related to the mucosal lesions produced by ethanol in rats.     

Ethyl acrylate-induced gastric toxicity. II. Structure-toxicity relationships and mechanism

Earlier studies conducted in this laboratory demonstrated that gavage administration of ethyl acrylate caused pronounced gastric toxicity in rats given single or repeated doses. The current studies were undertaken to investigate the structural, metabolic, and physical basis of this chemically induced gastric toxicity. Gavage administration of equimolar doses (2 mmol/kg) of methyl or ethyl acrylate in corn oil resulted in profound gastric toxicity in male F344 rats, while acrylic acid and n-butyl acrylate were without effect. Furthermore, gavage administration of equimolar doses of methyl propionate or ethyl propionate (saturated analogues of methyl acrylate and ethyl acrylate, respectively) as well as methacrylic acid esters were without gastric toxicity. These results indicate that structural requirements for acrylate esters to cause gastric lesions include an intact ester moiety, a double bond, and no substitution at carbon number 2. Additional studies indicate that gastric toxicity may be attributed to the intact ester molecule or to metabolite(s) other than products of carboxylesterase-mediated hydrolysis (acrylic acid and alcohol) and that gastric toxicity is dependent upon both acrylate ester concentration in dose vehicle and the lipophilicity of the dose vehicle (corn oil vs water).     

A profile of the rat gastrointestinal toxicity of drugs used to treat inflammatory diseases

The gastrointestinal (GI) toxicity of some immunologic agents (IA) and some nonsteroidal anti-inflammatory agents (NAA) was studied in two rat models. The first model was designed to detect the potential of drugs for producing gastric lesions. Drugs were administered orally to fasted rats and the stomachs were examined 0.5, 1, 2, 4, 8, 16, and 32 hr after dosing. The second model was designed to evaluate the toxic effects on the small intestine. Drugs were administered daily by the oral route for 4 days. Groups of rats were killed at 24-hr intervals and the stomach and small intestine were examined. The results show that the drugs evaluated can be divided into three categories. One category consists of IA, which cause only gastric mucosal bleeding. The second category consisting of acetaminophen, aspirin, and oxaprozin, causes gastric mucosal bleeding and gastric submucosal lesions. The third category, composed of NAA, causes gastric mucosal and submucosal lesions and perforations and/or adhesions of the small bowel.     

Pathology of BHA- and BHT-induced lesions

The pathology lesions from three studies, two with butylated hydroxyanisole (BHA) and one with butylated hydroxytoluene (BHT), are reviewed. When BHA was fed at 0.5 and 2.0% of the diet to F344 rats for two years, there was an increase in epithelial hyperplasia of the forestomach at both treatment levels. Papilloma and squamous-cell carcinoma of the forestomach were increased at the 2.0% level. When BHA was fed to beagle dogs at 1.0 and 1.3% of the diet for 180 days, no lesions/tumours of the distal oesophagus or stomach could be identified either at gross necropsy or by light or electron microscopy. The BHT was fed to Wistar rats at 0, 25, 100 and 250 mg/kg body weight. At the highest dose there was an increase in the number of rats with hepatocellular adenoma and with hepatocellular carcinoma.     

Dual effects of zinc sulphate on ethanol-induced gastric injury in rats: possibly mediated by an action on mucosal blood flow

The present study examines the protective effect of zinc sulphate against ethanol-induced gastric mucosal ulcers in rats. Absolute ethanol decreased the gastric mucosal blood flow and produced haemorrhagic lesions in the glandular mucosa. Zinc sulphate preincubation in an ex-vivo stomach chamber preparation prevented the formation of ethanol-induced lesions and attenuated the decrease of blood flow produced by ethanol. Subcutaneous injection of the same doses of the drug at 15 and 30 min before ethanol exposure, markedly reduced the blood flow and also aggravated ethanol-induced gastric injury; however, when injected at 23 and 24 h before ethanol administration, zinc sulphate protected against lesion formation but had no effect on the vascular changes induced by ethanol in the gastric glandular mucosa. These findings show that the antiulcer effect of zinc sulphate occurs only when the drug is given orally, or injected s.c. 23 and 24 h before ethanol challenge. Furthermore, this protective action is probably not entirely mediated by preservation of the gastric mucosal blood flow.