Are all "cytoprotective" drugs gastroprotective?

The effect of three--structurally different--groups of compounds was compared against gastric mucosal damages induced by ethanol or prostaglandin (PG) synthesis inhibitors, as well as against carrageenan-induced inflammation. All the compounds studied--SH-compounds (cysteamine, 2,3-dimercaptosuccinic acid, D,L-penicillamine), SH-blocking N-ethylmaleimide (NEM) and morphine-exerted dose-dependent inhibition on carrageenan edema test and against ethanol-induced gastric damage. Mucosal lesions induced by PG synthesis inhibitors (indomethacin 20 mg/kg, naproxen 75 mg/kg, piroxicam 60 mg/kg) were inhibited by drugs studied when the compounds were given before the damaging agents. However, when the drugs were injected 1 h after the inhibitors of PG synthesis opposite actions were observed; SH-compounds exerted protective, while NEM (2 mg/kg p.o.) and morphine (5 mg/kg p.o.) aggravating action. The results suggest that: 1. SH-compounds might have therapeutic importance in the treatment of gastric damage induced by prostaglandin synthesis inhibitors. 2. Reconsideration of the use of the term "cytoprotection" is necessary, since "cytoprotective" agents may aggravate mucosal damage in other ulcer model.     

Solanum paniculatum L. (Jurubeba): potent inhibitor of gastric acid secretion in mice.

Solanum paniculatum L. is used commonly in Brazilian folk medicine for the treatment of liver and gastrointestinal disorders. The freeze-dried aqueous extracts (WEs) obtained from distinct parts of the plant (flowers, fruits, leaves, stems and roots) were tested to determine their antiulcer and antisecretory gastric acid activities using mice. The aqueous extracts of roots, stems and flowers inhibited gastric acid secretion in pylorus-ligated mice with ED50 values of 418, 777 and 820 mg/kg body wt. (i.d.), respectively. Extracts of leaves (0.5-2 g/kg body wt., i.d.) did not affect gastric secretion, whereas fruit extracts (0.5-2 g/kg body wt., i.d.) stimulated gastric acid secretion. The stimulatory effect of the fruit extract was inhibited by pretreatment with atropine (5 mg/kg body wt., i.m.) but not with ranitidine (80 mg/kg body wt., i.p.) suggesting that the fruit extract activates the muscarinic pathway of gastric acid secretion. In contrast, administration of the root extract into the duodenal lumen inhibited histamine- and bethanechol-induced gastric secretion in pylorus-ligated mice. In addition, the aqueous extract of roots (ED50 value, 1.2 g/kg body wt., p.o.) protected the animals against production of gastric lesions subsequent to the hypersecretion induced in mice by stress following cold restraint. This effect was not reproduced when the lesions were induced by blockade of prostaglandins synthesis via subcutaneous injection of indomethacin. Thus, antiulcer activity of the plant extracts appears to be related directly to a potent anti-secretory activity. No toxic signs were observed following administration of different extracts up to 2 g/kg body wt., p.o. Collectively, the results validate folk use of Solanum paniculatum L. plant to treat gastric disorders.     

Quebrachitol-induced gastroprotection against acute gastric lesions: Role of prostaglandins, nitric oxide and KATP channels

The effect of Quebrachitol (2-O-methyl-l-inositol), a bioactive component from Magonia glabrata fruit extract was investigated against gastric damage induced by absolute ethanol (96%, 0.2 ml/animal) and indomethacin (30 mg/kg, p.o.), in mice. Quebrachitol at oral doses of 12.5, 25, and 50 mg/kg markedly attenuated the gastric lesions induced by ethanol to the extent of 69%, 64%, and 53% and against indomethacin by 55%, 59%, and 26%, respectively. While pretreatment with TRPV1 antagonist capsazepine (5 mg/kg, i.p.) failed to block effectively the gastroprotective effect of quebrachitol (25 mg/kg) against ethanol damage, the non-selective cyclooxygenase inhibitor indomethacin (10 mg/kg, p.o.), almost abolished it. Furthermore, quebrachitol effect was significantly reduced in mice pretreated with l-NAME, or glibenclamide, the respective inhibitors of nitric oxide synthase and K⁺_ATP channel activation. Thus we provide the first evidence that quebrachitol reduces the gastric damage induced by ethanol and indomethacin, at least in part, by mechanisms that involve endogenous prostaglandins, nitric oxide release, and or the activation of K⁺_ATP channels.     

Mechanisms involved in the gastroprotective activity of esculin on acute gastric lesions in mice

This work describes the gastroprotective actions of esculin (6,7-dihydroxycoumarin-6-o-glucoside) against indomethacin- or ethanol-induced lesions and verifies the role of nitric oxide, ATP-dependent K⁺ channels, prostaglandins, transient receptor potential vanilloid 1 and antioxidant effects in the gastroprotective mechanism of esculin in the ethanol-induced gastric lesion model. The intragastric administration of esculin at doses of 12.5, 25 and 50 mg/kg was able to protect the gastric mucosa against ethanol (0.2 mL/animal p.o.), and esculin at doses of 25 and 50 mg/kg protected against indomethacin-induced lesions (20 mg/kg p.o.). Administration of l-NAME (10 mg/kg i.p.), glibenclamide (10 mg/kg i.p.) or indomethacin (10 mg/kg p.o.), but not capsazepine (5 mg/kg p.o.), was able to reduce the gastroprotection promoted by esculin (25 mg/kg) on the ethanol-induced lesions. Measurements of nitrite, a NO metabolite, were increased in the group that was pretreated with esculin. In terms of antioxidant activity as a gastroprotective mechanism of esculin, the results show that pre-treatment with esculin decreased the amount of GSH, increased SOD activity, did not interfere with the CAT activity and decreased both the MPO activity and the MDA amount. In conclusion, pre-treatment with esculin confers significant gastroprotective and antioxidant activity and leads to a reduction in gastric injury; the mechanisms underlying these effects include stimulation of endogenous prostaglandins, nitric oxide synthesis, opening of K_ATP channels and reduction of free radicals or modulation of antioxidant enzyme systems.     

5-Hydroxytryptamine3-receptor blockade protects against gastric mucosal damage in rats.

Ondansetron, a specific 5-hydroxytryptamine3 (5-HT3)-blocker, injected s.c. (0.038, 0.075, 0.15 or 0.3 mg/kg) every 12 h with the fourth dose given 0.5 h before restraint at 4 degrees C (stress) or oral administration (p.o.) of 1 ml 80% ethanol, dose-dependently prevented gastric mucosal damage in female Sprague-Dawley rats (160-180 g); the animals were killed 2 or 1 h after stress or ethanol p.o., respectively. A similar pretreatment regimen with cyproheptadine (0.1, 0.25 or 0.5 mg/kg) or ketanserin (15, 30, or 75 micrograms/kg), both being 5HT2-receptor antagonists, also dose-dependently lowered the severity of stress- or ethanol-induced mucosal lesions. Only the higher doses of phenobarbitone (25 or 50 mg/kg given s.c. in a single dose 0.5 h beforehand) inhibited stress-induced gastric ulcers; however, even the lowest non-antinuclear dose (12.5 mg/kg), effectively produced CNS depression. These preliminary findings suggest that 5HT3-receptor blockade not only can antagonise stress- or ethanol-evoked gastric mucosal damage, but also may act through a peripheral mechanism.     

Roles of capsaicin-sensitive sensory nerves, endogenous nitric oxide, sulfhydryls, and prostaglandins in gastroprotection by momordin Ic, an oleanolic acid oligoglycoside, on ethanol-induced gastric mucosal lesions in rats.

The roles of capsaicin-sensitive sensory nerves (CPSN), endogenous nitric oxide (NO), sulfhydryls (SHs), prostaglandins (PGs) in the gastroprotection by momordin Ic, an oleanolic acid oligoglycoside isolated from the fruit of Kochia scoparia (L.) SCHRAD., on ethanol-induced gastric mucosal lesions were investigated in rats. Momordin Ic (10 mg/kg, p.o.) potentially inhibited ethanol-induced gastric mucosal lesions. The effect of momordin Ic was markedly attenuated by the pretreatment with capsaicin (125 mg/kg in total, s.c., an ablater of CPSN), N(G)-nitro-L-arginine methyl ester (L-NAME, 70 mg/kg, i.p., an inhibitor of NO synthase), N-ethylmaleimide (NEM, 10 mg/kg, s.c., a blocker of SHs), or indomethacin (10 mg/kg, s.c., an inhibitor of PGs biosynthesis). The attenuation of L-NAME was abolished by L-arginine (300 mg/kg, i.v., a substrate of NO synthase), but not by D-arginine (300 mg/kg, i.v., the enatiomer of L-arginine). The effect of the combination of capsaicin with indomethacin, NEM, or L-NAME was not more potent than that of capsaicin alone. The combination of indomethacin and NEM, indomethacin and L-NAME, or indomethacin and NEM and L-NAME increased the attenuation of each alone. These results suggest that CPSN play an important role in the gastroprotection by momordin Ic on ethanol-induced gastric mucosal lesions, and endogenous PGs, NO, and SHs interactively participate, in rats.     

Ulcerogenic and healing impairing actions of monochloramine in rat stomachs: effects of zinc L-carnosine, polaprezinc.

Effects of a novel zinc compound (polaprezinc), N-(3-aminopropionyl)-L-histidinato zinc, on the mucosal ulcerogenic and healing impairing responses induced by monochloramine (NH2Cl) were examined in rat stomach. Oral administration of NH2Cl (> 60 mM) produced severe hemorrhagic lesions in unanesthetized rat stomachs with a marked increase of thiobarbituric acid reactants (TBAR). Pretreatment of the animals with polaprezinc (3 approximately 30 mg/kg, p.o.) showed a dose-dependent inhibition against gastric ulcerogenic and TBAR responses induced by NH2Cl (120 mM). Likewise, mucosal exposure to NH4OH (60 mM) in urethane anesthetized stomachs made ischemic by bleeding from the carotid artery (1 ml per 100 g body w.t.) resulted in severe gastric lesions. This ulcerogenic response caused NH4OH plus ischemia was also attenuated by prior application of polaprezinc as well as taurine (25 mg/ml, 1 ml). On the other hand, the healing of gastric mucosal lesions induced by NH2Cl occurred more slowly than of ethanol-induced lesions, and the latter was significantly delayed by the repeated administration of NH2Cl. Polaprezinc (> 10 mg/kg, p.o.) given twice daily for 7 days not only accelerated the healing of NH2Cl-induced gastric lesions but also antagonized the delayed healing of ethanol-induced lesions in the presence of NH2Cl as well. Polaprezinc showed a scavenging action against NH2Cl in vitro. These results suggest that NH2Cl caused deleterious action on the healing of pre-existing acute lesions as well as irritating action to the mucosa in the rat stomach. Polaprezinc not only protects the stomach against injury caused by NH2Cl but also promotes healing of NH2Cl-induced gastric lesions as well as the delayed healing of ethanol-induced lesions caused by NH2Cl. Although the detailed mechanisms underlying these actions of polaprezinc remain unknown, they may be partly attributable to a scavenging action of this agent against NH2Cl.     

Evaluation of the antiulcerogenic activity of violacein and its modulation by the inclusion complexation with beta-cyclodextrin

The effects of beta-cyclodextrin (betaCD) inclusion complexation on the ability of violacein to prevent gastric ulceration in mice were studied. Violacein-betaCD inclusion complexes were prepared in 1:1 and 1:2 molar ratios and analysed by differential scanning calorimetry and powder X-ray diffractometry. Violacein previously administered orally at 10 mg/kg significantly reduced indomethacin-induced gastric lesions, as well as 100 mg/kg of cimetidine (positive control). However, betaCD complexation in both molar ratios significantly potentiated the protective action of violacein. In the HCl--ethanol-induced gastric ulcer model, violacein and the 1:2 inclusion complex (10 mg/kg, p.o.) inhibited gastric damage by almost 85%, whereas a 63% reduction was observed for the positive control, lansoprazole, at 30 mg/kg. In contrast, treatment with the 1:1 inclusion complex resulted in almost total disappearance of the antiulcer activity in this model. No significant changes in stress-induced gastric injury were found. In addition, the 1:2 inclusion complex improved the antilipoperoxidant activity of violacein in rat liver cells exposed to t-butyl hydroperoxide, whereas the 1:1 complex was less active than violacein. In summary, the 1:2 betaCD inclusion complex has gastroprotective properties similar to or higher than that of violacein. An increase in mucosal defensive mechanisms and protection against peroxidative damage might be involved.     

Effects of limonene and essential oil from Citrus aurantium on gastric mucosa: Role of prostaglandins and gastric mucus secretion

Essential oil from Citrus aurantium and the monoterpene limonene are widely used flavoring agents that are found in some common food items. This specie is also used medicinally throughout the world to treat gastritis and gastric disorders. Therefore, biological assays were performed in vivo on essential oil of C. aurantium (OEC) and its majority compound limonene (LIM) to evaluate their effect on gastric mucosa. The OEC (250 mg/kg, p.o.) and LIM (245 mg/kg, p.o.) provided effective (99%) gastroprotection against lesions induced by absolute ethanol and NSAID (non-steroidal anti-inflammatory drug) in rats. OEC and LIM do not interfere with gastric H⁺ secretion, serum gastrin or glutathione (GSH) level in gastric mucosa. But the gastroprotective action of OEC and LIM occurs due to an increase in the gastric mucus production induced by conserving the basal PGE₂ levels after challenge by agents harmful to the gastric mucosa. Given that LIM and OEC are excellent flavoring agents and also present gastroprotective actions, they can be regarded as a promising target for the development of a new drug for the prevention of gastric damage.     

Gastroprotective effect of aparisthman, a diterpene isolated from Aparisthmium cordatum, on experimental gastric ulcer models in rats and mice.

Aparisthmium cordatum (Juss.) Bail. (Euphorbiaceae), known in the State of Pará, Brazil as "ariquena queimosa", is a medium-sized tree which is native to the North Brazilian coastal region. Previous phytochemical studies of the bark of A. cordatum yielded a furan diterpenoid with a clerodane skeleton, called aparisthman. Recently, we reported the antiulcerogenic activity of trans-dehydrocrotonin (DHC), a furan diterpene isolated from Croton cajucara bark, in different ulcerogenic models in mice and rats. The aim of the present study was to assess the possible antiulcerogenic activity of aparisthman. When previously administered (p.o.) at the dose of 100 mg/kg(-1), aparisthman reduced significantly (p < 0.01) gastric injury induced by the indomethacin/bethanechol (71%), ethanol (71%), pylorus ligature, (59%) and hypothermic restraint-stress models (50%), in mice and rats. In the HCl/ethanol-induced gastric ulcer model in mice, at oral doses of 100 and 250 mg/kg(-1), aparisthman from A. cordatum reduced significantly (p < 0.001) the formation of gastric lesions by 59% and 66%, respectively, as compared with control. In the pylorus-ligature model, aparisthman (p.o.) decreased the volume of gastric juice as compared with control (p < 0.001). When aparisthman (100 mg/kg(-1)) was administered intraduodenally to mice, significant modifications were found, such as a decrease in gastric acidity as compared with control. In the animals pre-treated with aparisthman, free mucus production increased by 19% in the gastric mucosa (p < 0.05). The results suggest that aparisthman from A. cordatum presents a significant anti-ulcer effect when assessed in these induced ulcer models. Although the mechanism underlying this antiulcerogenic effect remains unknown, it seems to be related to an increase of the defensive mechanisms of the stomach such as prostaglandin synthesis and mucus production. The good yield of aparisthman obtained from A. cordatum, as well as its antiulcerogenic activity, suggest that this compound should be submitted to pharmacological research as a potential new antiulcerogenic drug.     

Gastro-protective effect of methanol extract of Ficus asperifolia bark on indomethacin-induced gastric ulcer in rats

The gastro-protective and antioxidant effects of methanol extract of Ficus asperifolia bark on indomethacin induced gastric ulcer were investigated in male rats. Thirty two male rats divided into 4 equal groups and were treated as follows: group1 (control), 0.5ml of 5% tween 80 (vehicle for the extract), groups 2 and 3, 100 and 500mg/kg of Ficus asperifolia extract respectively and group 4, cimetidine (100mg/kg). After two weeks of daily oral administration of vehicle, extract or cimetidine, gastric ulcer was induced in all rats with indomethacin (40 mg/kg, p.o). Gastric juice pH, gastric acid concentration, gastric ulcer score, percentage gastric ulcer inhibition, activity levels of superoxide dismutase (SOD), catalase and malondiadehyde (MDA) were determined. Ficus asperifolia extract significantly increased gastric pH (p.     

A novel method to produce extensive gastric antral ulcer in rats: pharmacological factors involved in the etiology of antral ulceration.

Gastric antral area is the most susceptible region to gastric ulceration in man. However, only limited information is available on animal models. In the present paper, we have developed an improved method for inducing gastric antral ulcers by the administration of 1.0 M HCl after refeeding for 1 h in rats. On day 4, the severe ulcer was found covering extensively the whole area of the antrum, and penetrated through the muscularis mucosae. The incidence of ulceration was 100% and the mean ulcer index was 37.1 +/- 16.6 mm2. In contrast, none of the erosive lesions were observed in the corpus area. Before 24 h, only slight hyperemia was observed in the antral region, suggesting that some submucosal mechanisms are involved in the ulceration processes other than the direct erosive action of HCl on the mucosal surface. Additional treatment with diethyldithiocarbamate (125 mg x kg(-1), s.c.), superoxide dismutase inhibitor, significantly aggravated this antral ulcer, and the ulcer index was 66.0 +/- 13.6 mm2. Allopurinol (50 mg x kg(-1), p.o.) significantly prevented ulcer formation induced by HCl plus DDC. GSH (150 mg x kg(-1), i.p.) also markedly prevented the ulceration. However, DMSO (0.5%, 5 mL x kg(-1), p.o.) was found not to affect ulcer formation. Famotidine (20 mg x kg(-1), p.o.) almost completely inhibited ulcer formation. From the above results, it was concluded that gastric antral ulcer can be induced by the simple treatment of 1.0 M HCl in refed rats, and the antrum has a different defensive mechanism from that in the corpus area. In addition. oxygen derived radicals, especially superoxide anion and endogenous acid secretion were found to be involved in the etiology of the aggravation of the gastric antral ulcer induced by DDC.     

Effects of tepoxalin, a dual inhibitor of cyclooxygenase/5-lipoxygenase, on events associated with NSAID-induced gastrointestinal inflammation

Prostaglandins and thromboxanes are products of arachidonic acid metabolism via the cyclooxygenase (CO) enzyme and are responsible for the pain and swelling common to sites of inflammation. Non-steroidal anti-inflammatory drugs (NSAIDs) inhibit the production of these substances and are used in the treatment of inflammatory diseases such as arthritis. However, one of the major side-effects of NSAID therapy is gastric ulceration. It is possible that inhibition of prostaglandin production and a related increase in the formation of leukotrienes via the 5-lipoxygenase (5-LO) enzymatic pathway are responsible for attracting inflammatory cells, causing local sites of inflammation and producing ulceration. To determine the effects of 5-LO inhibition on this hypothesis, studies were performed in rats to evaluate the effects of tepoxalin, a dual CO/LO inhibitor on leukotriene B₄ levels in gastric mucosa and neutrophil adhesion in mesenteric venules. In rats, chronic oral administration of an NSAID, indomethacin (2 mg/kg daily over 4 days), resulted in 40% mortality, accompanied by intestinal adhesions and perforations when evaluated 24 h after the fourth dose of drug. Additionally, neutrophil adhesion was increased in the mesenteric venules and cell infiltration was evident in the mesenteric interstitium. These gastrointestinal side-effects were inhibited in a separate group of rats administered tepoxalin (20 mg/kg, p.o) 30 min prior to each daily indomethacin treatment. Further studies were performed to determine tepoxalin's effects on early events associated with NSAID-induced gastrointestinal inflammation, including neutrophil adhesion, lipid peroxide generation and LTB₄ production. Indomethacin (100 mg/kg, p.o.) produced elevated levels of LTB₄ in rat gastric mucosa 90 min after administration. Additionally, neutrophil adhesion in mesenteric venules was increased at this dose and with the administration of another NSAID, naproxen. No generation of lipid peroxides was evident in the gastric mucosa at this timepoint. Tepoxalin (up to 400 mg/kg, p.o.) did not have an effects on gastric mucosal LTB₄ generation and lipid peroxide levels. A decrease in neutrophil adhesion was observed at the highest dose. In another study, pretreatment with tepoxalin (ED₅₀=7.5 mg/kg, p.o.) or the selective 5-LO inhibitor zileuton (100 mg/kg, p.o.) prevented the increases in gastric mucosal LTB₄ levels and neutrophil adhesion induced by indomethacin (100 mg/kg, p.o.). These data suggest that LO inhibition may play a vital role in the prevention of NSAID-induced gastric inflammation, providing insight into the lack of ulcerogenicity with tepoxalin and new approaches to anti-inflammatory therapy which may prevent gastric side effects.     

Effect of 2-deoxy- -glucose on acetylcholine and histamine levels in gastric juice of pylorus-ligated rats anesthetized with urethane

Acetylcholine (ACh) in gastric juice was detected and measured by pretreatment of acetylcholinesterase inhibitor, 1 mM eserine (1 ml/rat, p.o.), in pylorus-ligated rats, by liquid chromatography with electrochemical detection. In order to elucidate whether or not the ACh level in gastric juice reflects the activity of cholinergic neurons, the effect of 2-deoxy- -glucose (2-DG), a vagus stimulant, on the levels of ACh, histamine and gastric acid in gastric juice was investigated in pylorus-ligated rats anesthetized with urethane (1.25 g/kg, i.p.). Under the non-anesthetic condition, ACh, histamine and gastric acid levels were 100±25 pmol/h, 120±10 ng/h, and 240±32 μequiv./h, respectively. These levels were completely inhibited by urethane anesthesia. Under the anesthetized condition, 2-DG (50–200 mg/kg, i.v.) significantly increased ACh and histamine levels in gastric juice, as well as acid secretion. The 2-DG (200 mg/kg, i.v.)-induced increases in these levels were completely inhibited by vagotomy. These results suggest that ACh level measured in gastric juice reflects the activity of cholinergic transmission. Furthermore, these results also support the conclusion that vagus stimulation facilitates not only cholinergic transmission but also histaminergic transmission related to gastric acid secretion.     

H(2)S-Releasing Aspirin Protects against Aspirin-Induced Gastric Injury via Reducing Oxidative Stress

The aim of this study was to examine the effect of ACS14, a hydrogen sulfide (H₂S)-releasing derivative of aspirin (Asp), on Asp-induced gastric injury. Gastric hemorrhagic lesions were induced by intragastric administration of Asp (200 mg/kg, suspended in 0.5% carboxymethyl cellulose solutions) in a volume of 1 ml/100 g body weight. ACS14 (1, 5 or 10 mg/kg) was given 30 min before the Asp administration. The total area of gastric erosions, H₂S concentration and oxidative stress in gastric tissues were measured three hours after administration of Asp. Treatment with Asp (200 mg/kg), but not ACS14 (430 mg/kg, at equimolar doses to 200 mg/kg Asp), for 3 h significantly increased gastric mucosal injury. The damage caused by Asp was reversed by ACS14 at 1–10 mg/kg in a concentration-dependent manner. ACS14 abrogated Asp-induced upregulation of COX-2 expression, but had no effect on the reduced PGE₂ level. ACS14 reversed the decreased H₂S concentrations and blood flow in the gastric tissue in Asp-treated rats. Moreover, ACS14 attenuated Asp-suppressed superoxide dismutase-1 (SOD-1) expression and GSH activity, suggesting that ACS14 may stimulate antioxidants in the gastric tissue. ACS14 also obviously inhibited Asp-induced upregulation of protein expression of oxidases including XOD, p47^phox and p67^phox. In conclusion, ACS14 protects Asp induced gastric mucosal injury by inhibiting oxidative stress in the gastric tissue.     

Endogenous bacteria-triggered inducible nitric oxide synthase activation protects the ovariectomized rat stomach

Under experimental circumstances, ovariectomy attenuates gastric mucosal injury where nitric oxide (NO)-mediated pathways are involved. In this study, we have examined the changes in constitutive (cNOS) and inducible NO synthase (iNOS) enzyme activities (assessed by the citrulline assay), and the role of endogenous bacteria in ovariectomy-provoked mucosal defence. Gastric lesions were induced by indomethacin (50 mg/kg, s.c.) over a 4 h period in sham-operated and ovariectomized female Wistar rats. Groups of animals received the wide-spectrum antibiotic ampicillin (800 mg/kg/day, p.o., for 3 days), and others were injected with bacterial endotoxin (E. coli, 3 mg/kg, i.v., 5 h before autopsy). We found that ovariectomy increased iNOS and decreased cNOS activity (resulting an elevated total gastric NOS level), and protected the stomach, effects reversed by ampicillin treatment. In ovary-intact rats, administration of bacterial endotoxin enhanced gastric iNOS activity and reduced lesion-formation. These results suggest that ovariectomy improves gastric mucosal defence perhaps by endogenous bacteria-triggered induction of iNOS.     

Involvement of nitric oxide in the gastroprotective effects of an aqueous extract of Pfaffia glomerata (Spreng) Pedersen, Amaranthaceae, in rats

The plants belonging to Pfaffia genus are used in folk medicine to treat gastric disturbances. This study examined the effects of an aqueous extract of Pfaffia glomerata (Spreng) Pedersen (AEP) on the gastrointestinal tract. Wistar rats were pretreated orally (p.o.) with the AEP (125, 250, 500 and 1000 mg.kg(-1)) before induction of ulcers by hypothermic restraint stress (HRS, 3 h restraint stress at 4 degrees C), ethanol (ET, 70%; 0.5 ml/animal; p.o.) or indomethacin (IND, 20 mg.kg(-1); s.c.). Control animals received water (C) or ranitidine (60 mg.kg(-1)) p.o. The AEP protected rats against HRS and ET-induced ulcers, but was not able to protect the gastric mucosa against IND-induced ulcers. When injected into the duodenal lumen, the AEP reduced total acidity and both basal and histamine-stimulated acid secretion in pylorus-ligated rats. In addition, gastric secretion from AEP-treated animals exhibited increased concentrations of nitrite and nitrate. Treatment of animals with L-NAME (120 mg.kg(-1), p.o.) prevented both the reduction of total acidity and the increase in NOx levels promoted by AEP treatment. In conclusion, AEP effectively protected the gastric mucosa and inhibited gastric acid secretion in rats, probably by involving the histaminergic pathway and an enhanced production of nitric oxide in the stomach.     

The key-role of vagal nerve and adrenals in the cytoprotection and general gastric mucosal integrity.

BACKGROUND: Our laboratory group observed earlier that the gastric mucosal cytoprotective effect of prostacyclin (PGI(2)) disappeared after surgical vagotomy in rats. Similarly to this, the beta-carotene induced gastric cytoprotection disappeared in adrenalectomized rats too. AIMS: In these studies we aimed to investigate the possible role of vagal nerve and adrenals in the development of gastric mucosal lesions induced by exogenously administered chemicals (ethanol, HCl, NaOH, NaCl and indomethacin), and on the effects of cytoprotective and antisecretory drugs (atropine, cimetidine), and scavengers (vitamin A and beta-carotene). METHODS: The observations were carried out in fasted CFY strain rats. The gastric mucosal lesions were produced by intragastric (i.g.) administration of narcotising agents (96% ethanol; 0.6 M HCl; 0.2 M NaOH; 25% NaCl) or subcutaneously (s.c.) administered indomethacin (20 mg/kg) in intact, surgically bilaterally vagatomized, and adrenalectomized rats without or with glucocorticoid supplementation (Oradexon, 0.6 mg/kg given i.m. for 1 week). The gastric mucosal protective effect of antisecretory doses of atropine (0.1-0.5-1.0 mg/kg i.g.) and cimetidine (10-25-50 mg/kg i.g.), and vitamin A and beta-carotene (0.01-0.1-1.0-10 mg/kg i.g.) was studied. The number and severity of mucosal gastric lesions was numerically or semiquantitatively measured. In other series of observations the gastric acid secretion and mucosal damage were studied in 24 h pylorus-ligated rats without and with acute bilateral surgical vagotomy. RESULTS: It was found that: (1) the chemical-induced gastric mucosal damage was enhanced in vagotomized and adrenalectomized rats, meanwhile the endogenous secretion of gastric acid, and the development of mucosal damage can be prevented by surgical vagotomy; (2) the gastric cyto- and general protection produced by the drugs and scavengers disappeared in vagotomized and adrenalectomized rats; (3) the gastric mucosal protective effects of drugs and of scavengers returned after sufficient glucocorticoid supplementation of the rats. CONCLUSION: It has been concluded that the intact vagal nerve and adrenals have a key role in the gastric mucosal integrity, and in drugs- and scavengers-induced gastric cyto- and general mucosal protection.     

A new simple mouse model for the in vivo evaluation of cholecystokinin (CCK) antagonists: comparative potencies and durations of action of nonpeptide antagonists

A new simple mouse assay for the in vivo evaluation of CCK antagonists which is based upon visual determination of the gastric emptying of a charcoal meal is described. CCK-8 (24 micrograms/kg s.c.) but not various other peptide and nonpeptide agents effectively inhibited gastric emptying in this test system. The effect of CCK-8 was antagonized by established peripheral CCK antagonists but not representative agents of various other pharmacological classes. The rank order of potency of the CCK antagonists were: L-364,718 (ED50 = 0.01 mg/kg, i.v.; 0.04 mg/kg, p.o.) greater than Compound 16 (ED50 = 1.5 mg/kg, i.v.; 2.0 mg/kg p.o.) greater than asperlicin (ED50 = 14.8 mg/kg i.v.) greater than proglumide (ED50 = 184 mg/kg i.v.; 890 mg/kg, p.o.). Duration of action studies based upon ED50 values determined at various time intervals after oral administration showed that L-364,718 and proglumide are considerably longer acting than Compound 16. Asperlicin (ED50 greater than 300 mg/kg, p.o.) was ineffective as a CCK antagonist when administered orally. These data provide the first direct comparisons of the in vivo potencies of current CCK antagonists and demonstrate the utility of a new simple mouse assay for the in vivo characterization of peripheral CCK antagonists.     

Salicylic acid blocks indomethacin-induced cyclooxygenase inhibition and lesion formation in rat gastric mucosa

Salicylic acid has been shown to decrease gastric mucosal lesions induced by indomethacin in the rat. In vitro, it has also been shown to counteract the inhibitory effect of indomethacin and aspirin on the cyclooxygenase enzyme system in seminal vesicle microsomes and in platelets and vascular tissue. The hypothesis that the mechanism of salicylic acid "protection" against indomethacin-induced gastric lesions involves interference with indomethacin-induced mucosal cyclooxygenase inhibition was tested. Male, fasted rats were treated with intragastric salicylic acid in doses of 50, 100, 200, 300, or 400 mg/kg concomitantly with a sc injection of 20 mg/kg of indomethacin. Gastric mucosal lesions and mucosal cyclooxygenase activity (as measured by ex vivo prostaglandin F2 alpha synthesis) were examined 3 hr later. Intragastric salicylic acid, 200-400 mg/kg, significantly reduced indomethacin-induced lesion formation, while counteracting significantly indomethacin inhibition of prostaglandin synthesis. Salicylic acid alone did not significantly change cyclooxygenase activity. It is concluded that topical salicylic acid can decrease indomethacin-induced gastric mucosal lesion in the rat, in part, by counteracting the inhibitory effect of indomethacin at the cyclooxygenase level.