Actions of prostacyclin (PGI2) and its product, 6-oxo-PGF1alpha on the rat gastric mucosa in vivo and in vitro

Study of Melatonin as Preventive Agent of Gastrointestinal Damage Induced by Sodium Diclofenac

Safety profile of nonsteroidal anti-inflammatory drugs (NSAIDs) has been widely studied and both therapeutic and side effects at the gastric and cardiovascular level have been generally associated with the inhibitory effect of isoform 1 (COX-1) and 2 (COX-2) cyclooxygenase enzymes. Now there are evidences of the involvement of multiple cellular pathways in the NSAIDs-mediated-gastrointestinal (GI) damage related to enterocyte redox state. In a previous review we summarized the key role of melatonin (MLT), as an antioxidant, in the inhibition of inflammation pathways mediated by oxidative stress in several diseases, which makes us wonder if MLT could minimize GI NSAIDs side effects. So, the aim of this work is to study the effect of MLT as preventive agent of GI injury caused by NSAIDs. With this objective sodium diclofenac (SD) was administered alone and together with MLT in two experimental models, ex vivo studies in pig intestine, using Franz cells, and in vivo studies in mice where stomach and intestine were studied. The histological evaluation of pig intestine samples showed that SD induced the villi alteration, which was prevented by MLT. In vivo experiments showed that SD altered the mice stomach mucosa and induced tissue damage that was prevented by MLT. The evaluation by quantitative reverse transcription PCR (RT-qPCR) of two biochemical markers, COX-2 and iNOS, showed an increase of both molecules in less injured tissues, suggesting that MLT promotes tissue healing by improving redox state and by increasing iNOS/NO that under non-oxidative condition is responsible for the maintenance of GI-epithelium integrity, increasing blood flow and promoting angiogenesis and that in presence of MLT, COX-2 may be responsible for wound healing in enterocyte. Therefore, we found that MLT may be a preventive agent of GI damages induced by NSAIDs.

Pharmacogenetics of analgesic drugs

• Individual variability in pain perception and differences in the efficacy of analgesic drugs are complex phenomena and are partly genetically predetermined.

• Analgesics act in various ways on the peripheral and central pain pathways and are regarded as one of the most valuable but equally dangerous groups of medications.

• While pharmacokinetic properties of drugs, metabolism in particular, have been scrutinised by genotype–phenotype correlation studies, the clinical significance of inherited variants in genes governing pharmacodynamics of analgesics remains largely unexplored (apart from the µ-opioid receptor).

• Lack of replication of the findings from one study to another makes meaningful personalised analgesic regime still a distant future.

• This narrative review will focus on findings related to pharmacogenetics of commonly used analgesic medications and highlight authors’ views on future clinical implications of pharmacogenetics in the context of pharmacological treatment of chronic pain.

Effect of Astragalus, Panax notoginseng and their compatibility on serum levels of prostaglandin E2, gastrin, pepsinogen II, and epidermal growth factor in rats with atrophic gastritis

AIM: To evaluate the effect of Astragalus, Panax notoginseng and their compatibility on serum levels of prostaglandin E2 (PGE2), gastrin (GAS), pepsinogen II (PGII), and epidermal growth factor (EGF) in rats with atrophic gastritis.

METHODS: Forty healthy male Wistar rats were randomized into 7 groups: control group, sham operation group, model group, teprenone group, Astragalus group, Panax notoginseng group, and Astragalus plus Panax notoginseng group. Atrophic gastritis was induced by implanting a pylorus spring and intragastrically administering hot salty starch paste. In the one-month therapeutic phase, the control, sham operation and model groups were given normal saline 2 mL daily. The Astragalus group was given water decoction of Astragalus containing crude drug 3.5 g/(kg•d). The Panax notoginseng group was infused with Panax notoginseng powder containing crude drug 0.7 g/(kg•d). The Astragalus plus Panax notoginseng group was given both Panax notoginseng powder and Astragalus water decoction. The teprenone group was given teprenone water suspension containing teprenone 200 mg/(kg•d). All drugs were given by gavage for one month. Serum levels of PGE2, gastrin, EGF and PGII were measured by radioimmunoassay or ELISA. Pathological assessment of stomach mucosa was performed using hematoxylin and eosin staining method.

RESULTS: Serum levels of EGF had no significant differences among different groups. Serum levels of PGE2 in the Panax notoginseng group and Astragalus plus Panax notoginseng group were significantly higher than that in the model group (41.511 ng/L ± 5.666 ng/L, 42.033 ng/L ± 5.150 ng/L vs 30.896 ng/L ± 5.964 ng/L, P < 0.01 and 0.05). Serum level of GAS in the Astragalus group was significantly higher than that in the model group (99.732 ng/L ± 16.123 ng/L vs 68.207 ng/L ± 5.866 ng/L, P < 0.01). Serum levels of PGII in the Astragalus group and Panax notoginseng group were signifiantly higher than that in the model group (9.275 μg/L ± 0.506 μg/L, 9.268 μg/L ± 0.931 μg/L vs 7.026 μg/L ± 0.638 μg/L, both P < 0.01). Gastric mucosal volume constituent ratio (GMVR) increased in the Astragalus group, Panax notoginseng group and Astragalus plus Panax notoginseng group compared to the model group, but showed no statistical difference with that in the teprenone group (all P > 0.05).

CONCLUSION: Astragalus, Panax notoginseng and their compatibility improve mucosal atrophy possibly by increasing serum levels of PGE2, GAS and PGII in rats with atrophic gastritis.

Leukotriene inhibition in small animal medicine

Leukotrienes are important mediators of inflammatory and allergic conditions in people and are suspected to play an important role in tumorigenesis and tumor growth of several different tumor types. Based on this, researchers are making great progress in identifying novel pharmacologic targets for several human diseases. Leukotriene inhibition has resulted in therapeutic benefit in clinical trials involving people with osteoarthritis, allergic asthma, and atopic dermatitis. Despite this progress and the possibility that leukotriene inhibition may also play an important therapeutic role in veterinary patients, parallel advances have not yet been made in veterinary medicine. This article summarizes leukotriene function and synthesis. It also reviews the published literature regarding potential therapeutic applications of leukotriene inhibition in both human and veterinary medicine, focusing primarily on osteoarthritis, NSAID induced gastrointestinal mucosal damage, allergic asthma, atopic dermatitis, and cancer.

The Clinical Pharmacology of Cyclooxygenase-2–Selective and Dual Inhibitors

Over the past decade, there have been several nonsteroidal anti-inflammatory drugs (NSAIDS) introduced in veterinary medicine with an increased gastrointestinal safety profile consistent with a cyclooxygenase (COX)-1-sparing effect. More recently, an NSAID with additional 5-lipoxygenase (5-LOX) activity has also been approved for use. Although it is tempting to equate in vitro COX-2/COX-1 and 5-LOX inhibition to overall in vivo safety, the data do not support this approach. The true overall safety for any individual compound is based on its evaluation in laboratory margin-of-safety studies, reproductive safety studies, and blind multicenter field studies in client-owned animals. Therefore, when choosing a COX-2-selective or dual-inhibitor NSAID for clinical use, all in vivo data must be taken into account to understand comparative safety, and continued use must be based on the drug's performance in the individual being treated. Until head-to-head trials in multicenter blind studies are published, comments on comparative safety and effectiveness must be reserved.

Cyclooxygenase Isozymes: The Biology of Prostaglandin Synthesis and Inhibition

Nonsteroidal anti-inflammatory drugs (NSAIDs) represent one of the most highly utilized classes of pharmaceutical agents in medicine. All NSAIDs act through inhibiting prostaglandin synthesis, a catalytic activity possessed by two distinct cyclooxygenase (COX) isozymes encoded by separate genes. The discovery of COX-2 launched a new era in NSAID pharmacology, resulting in the synthesis, marketing, and widespread use of COX-2 selective drugs. These pharmaceutical agents have quickly become established as important therapeutic medications with potentially fewer side effects than traditional NSAIDs. Additionally, characterization of the two COX isozymes is allowing the discrimination of the roles each play in physiological processes such as homeostatic maintenance of the gastrointestinal tract, renal function, blood clotting, embryonic implantation, parturition, pain, and fever. Of particular importance has been the investigation of COX-1 and -2 isozymic functions in cancer, dysregulation of inflammation, and Alzheimer's disease. More recently, additional heterogeneity in COX-related proteins has been described, with the finding of variants of COX-1 and COX-2 enzymes. These variants may function in tissue-specific physiological and pathophysiological processes and may represent important new targets for drug therapy.

Gastric mucosal integrity: gastric mucosal blood flow and microcirculation. An overview

The stomach is in a state of continuous exposure to potentially hazardous agents. Hydrochloric acid together with pepsin constitutes a major and serious threat to the gastric mucosa. Reflux of alkaline duodenal contents containing bile and pancreatic enzymes are additional important injurious factors of endogenous origin. Alcohol, cigarette smoking, drugs and particularly aspirin and aspirin-like drugs, and steroids are among exogenous mucosal irritants that can inflict mucosal injury. The ability of the stomach to defend itself against these noxious agents has been ascribed to a number of factors constituting the gastric mucosal defense. These include mucus and bicarbonate secreted by surface epithelial cells, prostaglandins, sulfhydryl compounds and gastric mucosal blood flow. The latter is considered by several researchers to be of paramount importance in maintaining gastric mucosal integrity. The aim of this paper is to review the experimental and clinical data dealing with the role of mucosal blood flow and in particular the microcirculation in both damage and protection of the gastric mucosa.

Aspirin-like drugs cause gastrointestinal injuries by metallic cation chelation

Aspirin-like (nonsteroidal anti-inflammatory) drugs may cause injuries including ulcers to the gastrointestinal tract by chelation of the divalent and/or multivalent metallic cations in the gastrointestinal mucus and mucosa, as suggested by the chemical properties of these drugs and supported by experimental and clinical data.

Circadian reactivity rhythm of rat gastric mucosa to restraint-cold stress and indomethacin: temporal variation in the protective effect of iloprost

In this study, the time-dependent ulcerogenic effects of restraint-cold stress and indomethacin on the gastric mucosa and the temporal variation in the protective effect of iloprost, a synthetic stable analog of prostacyclin, were investigated in rats synchronized to 12h light and 12h darkness, lights on at 08:00. The severity of gastric ulceration produced by either stress or indomethacin showed marked circadian variation; it was greatest at 11 HALO (hours after lights on) for restraint-cold stress and at 23 HALO for indomethacin. The severity of the induced ulcerogenesis was least at 7 HALO for both stimuli. The protective effect of iloprost against restraint-cold stress was most prominent at 15 HALO and 19 HALO with an approximately 80% protection score. On the other hand, pretreatment with iloprost reduced the indomethacin-induced mucosal injury only at 23 HALO. The circadian variation in the effect of iloprost and in the rhythmic modalities of these two experimental ulcer models are indicative of differences in their underlying mechanisms. In experimental models of ulceration, the circadian time of application of the ulcerogenic stimulus must be considered as an important experimental factor. Moreover, the protective effectiveness of antiulcer drugs can express time-dependent differences and must also be taken into account in investigative research.

Effect of a prostaglandin I2 analogue, beraprost sodium, on burn-induced gastric mucosal injury in rats

Stress ulcers still have a high mortality in critically burned patients and the pathophysiology remains relatively unknown. Impaired gastric mucosal perfusion is one of the factors contributing to gastric mucosal ulceration. Burn injury causes thrombosis and vascular occlusion by increasing the blood viscosity, resulting in decreased organ perfusion. Reduced blood flow is one of the most important factors in gastric mucosal ulceration. Beraprost sodium is a chemically stable prostaglandin I2 (PGI2) analogue with antiplatelet, vasodilator and cytoprotective actions. In the present study, we examined the effects of a PGI2 analogue, beraprost sodium (Procylin, Kaken Pharmaceutical Company, Tokyo, Japan) on burn-induced gastric mucosal changes in rats. Twenty male Sprague-Dawley rats weighing an average of 400 g were burned with hot water (90 degree C) and then divided into two groups of 10 animals. One group received 0.015 mg of beraprost sodium intraperitoneally immediately after burn injury, while the control group received the same volume of saline. Gastric mucosal blood flow was measured with a laser Doppler flowmeter and the area of mucosal necrosis was also determined macroscopically and histologically. Gastric mucosal damage was significantly reduced in the beraprost sodium-treated rats and gastric mucosal blood flow was significantly improved (p < 0.05). These findings demonstrate that PGI2 plays a very important role in the pathophysiology of burn-induced Curling's ulcer and that beraprost sodium can improve gastric mucosal blood flow and reduce mucosal damage.

Experimental and clinical observations on the role of endogenous and on the effect of exogenous prostacyclin in gastric mucosa. A personal view

In the gastric mucosa the exogenously administered prostacyclin seems to have a polyphasic effect which contains the following consecutive steps: 1. Binding to the cell surface; 2. Effect on the intracellular "second messenger system", i.e. on the cyclic nucleotide (cAMP, cGMP) turnover; 3. Activation of the calmodulin-system; 4. cAMP-dependent protein kinase activation; Nucleic acid,--DNA,RNA,--changes; 6. Influence on protein synthesis and finally; 7. New cell formation. On the other hand, the endogenous (mucosal) prostacyclin exerts a natural protection against different damaging noxae.

Thirteenth Gaddum Memorial Lecture. Neuronal and endothelium-derived mediators in the modulation of the gastric microcirculation: integrity in the balance

Images

Effects of chronic superficial injury on the rat gastric mucosa

The effects of chronic superficial injury on the stomach were studied in rats dosed with a mild irritant (2 mol/L NaCl intragastrically) every 48 hours for 1 month followed by 1-month recovery. A single exposure to this mild irritant induced gross protection against 6 mol/L NaCl for 1 but not 2 days. Leukotriene C4 (LTC4) levels increased slightly. Prostaglandin E2 (PGE2) concentration was unchanged. After 2-week dosing, protection was concomitant with markedly elevated PGE2 concentration. LTC4 values remained unchanged. Superficial epithelial cells were more resistant to damage. After 4-week dosing, protection occurred at 1 but not 2 days after the dose with an inverse correlation of PGE2. LTC4 concentration increased significantly at both times. Chronic injury for 1 month did not alter rapid epithelial restitution or PGE2 and LTC4 released 15 minutes after challenge with 6 mol/L NaCl. The recovery period showed loss of protection. PGE2 values returned to control levels but LTC4 values remained slightly elevated. It is concluded that short- or long-term (4-week) "adaptive cytoprotection" is not mediated by endogenous PGE2. Only extremely high levels of LTC4 correlated with loss of protection. The role of the more resistant superficial epithelium remains unknown.

Stress-induced gastric lesions and the synthesis of prostaglandins and leukotrienes

Prostaglandin E2 renders the mucosa of the GI tract more resistant to acute injury by aspirin, acid, bile salts, and stress, whereas leukotrienes promote inflammation and retard healing of ulcers. The relationship of stress ulcer formation to changes in the activities of prostaglandin synthetase and lipoxygenase was evaluated in this study. After a 24 hr fast, 10 rats were stressed by the cold-restraint method for 4 hr and 10 rats were not stressed. Rats were terminated, stomachs were excised, the number of lesions were counted, and the nonulcerated mucosa was assayed for prostaglandin E2 and leukotriene synthesis. The mucosa was minced, washed in buffered saline, and then incubated for 10 min in a 1.3 mM sodium arachidonate solution containing a nonionic detergent (poloxamer 188), NaCl, KCl, KPO4, glutathione, hemin, MgSO4 and Hepes at pH 8.0. An ANOVA was used to compare the groups. Following stress the number of gastric lesions increased from 0.7 +/- 0.6 to 13.5 +/- 2.6, while leukotriene synthesis increased from 173 +/- 20 to 2170 +/- 187 pg/mg/min. A shift in synthesis from prostaglandins to leukotrienes in the mucosa appears to be detrimental to cytoprotection.

Endothelium-derived relaxing factor participates in the increased blood flow in response to pentagastrin in the rat stomach mucosa

The stimulation of gastric-acid secretion by pentagastrin, a synthetic analogue of the endogenous peptide gastrin, is associated with an increased blood flow to the stomach mucosa, commonly referred to as functional hyperaemia. There are at least two potent vasodilator substances, the local release of which from endothelial cells could contribute to this hyperaemia, endothelium-derived relaxing factor (EDRF) and prostacyclin. EDRF has been identified as nitric oxide, released enzymatically from the guanidino group of L-arginine. In the present studies, the involvement of prostacyclin in the pentagastrin-induced increase in stomach blood flow was eliminated by using the cyclo-oxygenase inhibitor indomethacin. Thus this work was designed to elucidate the participation of EDRF/NO in the pentagastrin-induced hyperaemia and not its relative importance to prostacyclin. The increase in blood flow to the gastric mucosa in response to pentagastrin was measured by laser Doppler flowmetry in situ. Inhibition of EDRF/NO biosynthesis with the L-arginine analogues NG-monomethyl-L-arginine (MeArg) or N omega-nitro-L-arginine (NO2Arg) significantly attenuated (by more than 80%) the increase in mucosal blood flow in response to pentagastrin. However, infusions of the natural substrate L-arginine reversed the inhibitor effect of MeArg on pentagastrin-induced increase in mucosal blood flow. Local intra-arterial injections of the endothelium-independent vasodilator glyceryl trinitrate produced a dose-related increase in blood flow to the rat stomach mucosa that was unaffected by infusion of MeArg. Thus, in the absence of prostacyclin, EDRF/NO participates in the pentagastrin-induced increase in blood flow to the rat stomach mucosa.

Effective use of rabbit gastric antral mucosal slices in prostaglandin synthesis and metabolism studies

Intact slice preparations of rabbit stomach (antral mucosa, corporal mucosa, antral muscle and corporal muscle) were incubated and the released prostaglandins (PGs) were measured by reverse-phase high-performance liquid chromatography using 9-anthryldiazomethane for derivatization. With respect to total PG production, the highest amounts were generated by antral mucosal slices. Antral mucosal slices produced PGE2, 6-keto PGF1 alpha, thromboxane B2, PGF2 alpha and PGD2 (in descending order of magnitude) and possessed a high capacity for producing 13,14-dihydro-15-keto derivatives of both PGE2 and PGF2 alpha. Studies utilizing aspirin, EGTA or Ca2+ revealed that PG release by antral mucosal slices in the present in vitro system reflects a composite of the activities of phospholipase A3, PG cyclooxygenase and PG-metabolizing enzymes. These results show that antral mucosal slices will be useful in physiological and pharmacological studies on PG synthesis and metabolism of the stomach.

Comparison of the effects of endothelin-1 and endothelin-3 on the rat stomach

The effects of systemic administration of endothelin-1 and endothelin-3 on the susceptibility of the stomach to injury were compared in the anesthetized rat, as were their effects on gastric vascular tone, systemic blood pressure and hematocrit. When infused at concentrations in the 10(-7)-10(-6) M range, endothelin-1 was a far more potent hypertensive agent than endothelin-3. Endothelin-1 caused significant hemoconcentration, while endothelin-3 did not Endothelin-1 was approximately 5- to 10-times more potent as a vasoconstrictor in the stomach and a similar difference in potencies was observed when the ability of these peptides to increase the susceptibility of the stomach to ethanol-induced damage was compared. The two peptides were equipotent in producing gastric mucosal hemorrhage in the absence of any exogenous irritant. These results demonstrate that like endothelin-1, endothelin-3 has ulcerogenic and vasoconstriction actions in the stomach. While there are very large differences in the potencies of the two peptides in terms of producing systemic hypertension and hemoconcentration, the differences in the potency of the gastric ulcerogenic and vasoconstrictor effects are much less marked.

Aspirin-induced gastric mucosal injury: lessons learned from animal models

This review of the mechanisms by which aspirin causes gastric mucosal damage points to the involvement of two potential mechanisms. Aspirin, which inhibits cyclooxygenase, is rapidly deacetylated to salicylate. Salicylate is toxic to cells and affects mucosal barrier function, reduces cytosolic adenosine triphosphate, stimulates sodium transport, and increases proton dissipation from surface epithelial cells. Cyclooxygenase inhibition makes the gastric mucosa more susceptible to injury, inhibits mucus and bicarbonate secretion, alters the physicochemical nature of mucus, stimulates fundic but not antral [3H]thymidine incorporation, and reduces epithelial surface hydrophobicity. No single mechanism seems to be involved. It is likely, instead, that the toxic effects of salicylate and the effect of cyclooxygenase inhibition work in concert to render the mucosa more susceptible to injury, resulting in mucosal damage.

Effects of cimetidine on prostanoid production in the gastric corpus specimens from rats

In order to examine the effect of cimetidine on the production of prostanoids in the stomach mucosa, the amounts of prostaglandin (PG) E2, F1 alpha and thromboxane (TX) B2 were determined after the specimens from the rat stomach corpus were incubated in the presence of cimetidine. Cimetidine significantly stimulated the production of PGE2 in the specimens at a concentration of 10 microM, but did not significantly affect the production of PGF1 alpha and TXB2 at concentrations of 1 to 100 microM.

Gastric mucosal blood flow and acid secretion in portal hypertensive rats

The purpose of this study was to examine gastric mucosal blood flow, measured by hydrogen gas clearance, and acid secretion in portal hypertensive rats. Chronic portal hypertension was induced by a two-stage complete portal vein occlusion procedure. Basal gastric mucosal blood flow was significantly higher in portal hypertensive rats than in sham-operated rats, but there was no difference in basal acid output. In response to administration of pentagastrin, there was the expected rise in both acid secretion and blood flow in sham-operated rats, but in portal hypertensive rats there was a significantly lower increase in acid output and no change in blood flow. In portal hypertensive rats pretreated with indomethacin to inhibit endogenous prostaglandin generation, both basal blood flow and acid secretion--and their response to pentagastrin administration--were the same as in non-indomethacin-treated sham-operated rats. We conclude that in portal hypertensive rats there is an increased gastric mucosal blood flow and an impaired acid output response to pentagastrin stimulation, and these changes appear to be mediated by an increase in endogenous prostaglandin.

Sulphasalazine and PhCL28A inhibit the formation of ethanol- and phenylbutazone-induced rat gastric ulcers: lack of involvement of endogenous prostaglandins?

1. The effects of sulphasalazine (SZP) and PhCL28A on macroscopic lesion formation and ex vivo prostaglandin inactivation were studied in the ethanol (ETOH) and phenylbutazone (PBT) models of gastric ulcers in the rat. Prostaglandin 'synthesis' during homogenisation of the stomachs was also studied in the latter model. 2. Both PhCL28A and SZP when injected i.p. prevented the formation of ETOH- and PBT-induced gastric ulcers with ED50 values of 13 and 41 mgkg-1 (vs ETOH) and 3 and 32 mgkg-1 (vs PBT) for PhCL28A and SZP respectively. However, neither compound was active orally in the dose ranges used (up to 30 mg kg-1 for PhCL28A and 100 mg kg-1 for SZP). 3. Irrespective of the route of administration, SZP (100 mg kg-1) and PhCL28A (30 mg kg-1) produced slight but statistically significant decreases in ex vivo prostaglandin inactivation by 100,000 g cytosolic supernatants prepared from stomachs not receiving ulcerogen. When tested in vitro, PhCL28A (IC50 = 230 nM) was approximatively 480 times mor potent than SZP (IC50 = 110 microM) against rat stomach cytosolic prostaglandin inactivation. 4. Both ETOH (50%, 5 ml kg-1, orally) and PBT (200 mg kg-1, orally) significantly decreased ex vivo gastric cytosolic prostaglandin inactivation. PhCL28A (30 mg kg-1, orally or i.p.) decreased prostaglandin inactivation still further after ulcerogen treatment except when given i.p. before ETOH treatment. SZP (100 mg kg-1) had a similar effect when given orally before PBT treatment. 5. When the prostaglandin content of the stomach homogenates was used as a measure of ex vivo prostaglandin synthesis in the PBT experiments, PhCL28A 30 mg kg-' orally (but not i.p.) produced an 88% increase in prostaglandin E2 (PGE2) levels, but had no effect on 6-keto-PGF,, or thromboxane B2 formation during homogenization. SZP (100mg kg' i.p. or orally) was without effect. 6. We conclude from these results that the anti gastric ulcer activity of SZP and PhCL28A is independent of prostaglandin inactivation and endogenous prostaglandin formation is probably not involved.

Damage and protection of the human gastric mucosa. A multiparameter assessment

Studies in animals and humans have indicated that endogenous prostaglandins as well as synthetic prostaglandin analogues can prevent gastric mucosal damage induced by various agents. Methods were developed to assess induced damage and the effects of potentially protective agents (synthetic prostaglandin analogues and the histamine [H2]-receptor antagonist cimetidine) on the human gastric mucosa by measuring ion fluxes and transmucosal potential difference, as well as by observations with gastrointestinal endoscopy. Commonly ingested agents, such as aspirin, 1,300 mg, and 20 percent ethanol increased hydrogen ion and sodium ion fluxes, decreased potential difference, and caused gross mucosal damage, as observed by endoscopy. Conversely, acetaminophen, 2,600 mg, and 10 percent ethanol did not have any significant effects. Hyperosmolar solutions (1,800 and 3,600 mOsm/kg) also produced acute damage. Sodium taurocholate (10 mmol/liter) when instilled into the stomach, either at pH 1.1 or 7.0, produced both functional and structural damage. When given as a single dose, neither 15(R)15-methyl PGE2 nor the synthetic PGE1 analogue, misoprostol, prevented mucosal damage induced by aspirin and taurocholate (pH 1.1), respectively. Cimetidine, 400 mg orally, however, did reduce aspirin-induced mucosal damage, and this effect was independent of gastric acid inhibition.

Mechanism of gastrointestinal toxicity of NSAIDs

Non-steroidal anti-inflammatory drugs (NSAIDs) can damage the gastrointestinal tract, mainly the stomach, by a local effect and by systemic interactions with prostaglandin synthesis. A local damaging effect was first suggested by Davenport, who demonstrated that aspirin, at an acid pH, enters the gastric mucosa by non-ionic diffusion, leading to a disruption of the gastric barrier and subsequent back-diffusion of hydrogen ions into the mucosa. Consequently, this leads to local haemorrhage and cell necrosis. Systemic damage is thought chiefly to occur by inhibition of prostaglandin synthesis, with consequent interaction of the defensive functions of the gastric mucosa. Inhibition of cyclo-oxygenase is the specific target of NSAIDs. However, the lipoxygenase pathway is also affected indirectly since cyclo-oxygenase inhibition results in a spill-over effect of leukotrienes, as both prostaglandins and leukotrienes are produced from arachidonic acid. Indeed, leukotriene B4, an extremely potent vasoconstrictor, may be responsible for some of the NSAID damage. In addition, cyclo-oxygenase inhibition blocks the integrity and synthesis of mucus, the secretion of bicarbonate and profoundly changes the life cycle of gastric mucosal cells. Following acute NSAID medication, the overall cell migration from the proliferative zone to the surface is accelerated and cell shedding is increased. However, during prolonged NSAID treatment, adaptation to the noxious effects of NSAIDs can occur with increased cell reproduction and subsequent compensation of the initially increased cell loss.

Effect of an anti-ulcer drug, plaunotol, and its metabolites on NAD+ dependent 15-hydroxyprostaglandin dehydrogenase from gastric mucosa

15-Hydroxyprostaglandin dehydrogenase was partially purified from hog gastric mucosa by about 1000-fold with a 13.5% yield. Its molecular weight was estimated to be 32,000 daltons by gel filtration. The enzyme was inhibited by some metabolites of plaunotol [(2E, 6Z, 10E)-7-hydroxymethyl-3,11,15-trimethyl-2,6,10,14-hexadecatetrae n-1- ol], a new anti-ulcer drug. The inhibition patterns for substrates, prostaglandin E1 and NAD+ were both uncompetitive with Ki values of 7.8 and 19.7 microM, respectively.

Protective effect of iloprost and UK 38 485 against gastric mucosal damage induced by various stimuli

This study was undertaken to evaluate the efficacy of iloprost and UK 38485 in the prevention of gastric lesions due to restraint-cold stress, ethanol or indomethacin. Prior injection of iloprost to the rats significantly prevented the increase in ulcer index by restraint- cold stress or indomethacin but nonsignificantly reduced the ulcer index induced by ethanol. UK 38 485 at lower doses caused a highly significant decrease in the ulcer index induced by all noxious stimuli used in this study. UK 38 485 also reduced the increased 3H back diffusion due to restraint-cold stress. Higher doses of the compound, however, failed to decrease the mucosal damage due to restraint-cold stress. Combination of iloprost and UK 38 485 produced a further significant decrease in the ulcer index induced by all noxious stimuli and increased 3H back diffusion induced by restraint-cold stress. In relation to these results the importance of PGI2/TXA2 ratio in the production of gastric mucosal lesions is discussed.

Gastric mucosal protection by OPC-12759, a novel antiulcer compound, in the rat

OPC-12759, 2-(4-chlorobenzoylamino)-3-[2(1H)-quinolinon-4-yl]-propionic acid, was studied for its efficacy to prevent the gastric mucosal damage induced by several necrotizing agents. Experiments were also performed to elucidate the mechanism of this mucosal protective activity. OPC-12759 dose dependently prevented the formation of mucosal necrosis induced by absolute ethanol, 0.2 N NaOH or 0.6 N HCl. PGE2 was also shown to prevent the gastric mucosal erosion induced by necrotizing agents. The mucosal protective effect of OPC-12759 was completely counteracted by pretreatment with indomethacin while that of PGE2 was not. In addition, OPC-12759 given alone increased the generation of gastric mucosal PGE2-like activity. OPC-12759 dose dependently reduced the volume, acid output and pepsin output of the gastric juice in pylorus-ligated rats. The inhibitory effect of OPC-12759 but not of cimetidine or atropine on gastric secretion was also abolished by concurrent administration of indomethacin. These findings suggest that the mucosal protective effect and antisecretory effect of OPC-12759 presumably result from enhancement of the generation of endogenous PGs.

Microsomal arachidonate bioconversion in rat small intestine during maturation

This study was designed to compare prostaglandin (PG)-synthesizing activity in rat small intestinal microsomes in the 1st, 3rd, and 6th weeks of life and at maturity (greater than 100 days). When an incubation system was used containing 2 mg microsomal protein, 0.5 mM (-)-epinephrine and 1 mM reduced glutathione, the highest PG-synthesizing activity was achieved by incubating 0.157 mM 1-(14)C-arachidonate (specific activity 2.6 X 10(6) dpm/mumol) at 37 degrees C for 5 min. The labeled metabolites were extracted and then separated with high performance liquid chromatography. The four PGs analyzed were 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha), thromboxane B2, prostaglandin F2 alpha and prostaglandin E2. Enzymatic activity for the synthesis of 6-keto-PGF1 alpha was much higher than that for the other PGs. A significant difference was observed for the bioconversion from arachidonate to 6-keto-PGF1 alpha and total PGs among the four age groups of rats. The postweanling groups (week 6 and adult) showed significantly higher enzymatic activities for the syntheses of 6-keto-PGF1 alpha and total PGs than did the preweanling groups (weeks 1 and 3).

Prostaglandin synthesis along the gastrointestinal tract of the rabbit: differences in total synthesis and profile

In the present study we systematically investigated the synthesis of prostaglandins in the mucosa and the muscle layer along the length of the rabbit gut. Homogenates of mucosa and muscle layer were incubated with (14C)-labelled arachidonic acid, and prostaglandin formation was determined using thin-layer chromatography. With respect to total prostaglandin synthesis the highest values in the mucosa were measured in fundus, antrum and colon, whereas the prostaglandin synthesis in the muscle layer was maximal in the small bowel, particularly the ileum. In the mucosa, the prostaglandins E2 and F2a predominated, and there were minor differences along the gastrointestinal tract. In the muscle layer of the stomach, high amounts of 6-keto prostaglandin F1a, the stable degradation product of prostacyclin were produced, while small and large bowel homogenates synthesized mostly F2a. Consistently the prostaglandins A2/B2 were a major product in most locations. In addition, PG E2 catabolism to 15-keto PG E2 and 13,14-dihydro-15-keto PG E2 in the absence of NAD was slow. No significant changes in total prostaglandin synthesis and prostaglandin profile were detected between 24 hrs fasted and normally fed rabbits at any part of the gastrointestinal tract.

Stimulation of prostaglandin production by (2E,6Z,10E)-7-hydroxymethyl-3,11,15-trimethyl-2,6,10,14-++ +hexadecatetrae n-1-ol (plaunotol), a new anti-ulcer drug, in vitro and in vivo

Plaunotol [(2E,6Z,10E)-7-hydroxymethyl-3,11,15-trimethyl-2,6,10,14- hexadecatetraen-1-ol], a new anti-ulcer drug, was investigated for its effect on prostaglandin (PG) production. In cultured cells of 3T6 fibroblasts, plaunotol and its main metabolite (1-carboxylic plaunotol) at concentrations of 10-100 microM increased PGE2 and PGI2 production 2- to 4-fold. These compounds increased the release of radioactive arachidonic acid from [14C]arachidonic acid prelabeled 3T6 fibroblast cells 2-fold at 30 microM, and this increase was inhibited by addition of mepacrine, a phospholipase inhibitor. Plaunotol and its main metabolite had no effect on PG cyclooxygenase activity. These results indicate that plaunotol and its main metabolite stimulate PG production by activating cellular phospholipase. In gastric-mucosa slices, PGE2 and PGI2 production was increased significantly either by oral administration of plaunotol to rats at a dose of 300 mg/kg or by addition of the main metabolite to the incubation medium. All these results suggest that plaunotol increases the PG levels in gastric mucosa by stimulating the PG biosynthesis, particularly the cellular phospholipase activity. The increased levels of PG may participate in the anti-ulcer activity of plaunotol.

The effect of cigarette smoke on gastroduodenal mucosal endogenous prostacyclin level (experimental and clinical observations)

In our opinion the endogenous prostacyclin (PGI2) is one of the most important natural protective substances in the gastric mucosa. We have, therefore checked in experimental circumstances in rats, as well as in clinical observations in humans, the possible effect of smoking on endogenous gastroduodenal mucosal PGI2 level. The animal experiments seem to verify that cigarette smoke really has an unwanted effect on the gastric mucosa. The target of this action is the endogenous PGI2 content of the mucosa. According to our observations in humans there is a definite tendency toward decreased endogenous PGI2 production in the gastroduodenal mucosa of smokers too.

Phospholipase inhibition and prostacyclin generation by gastric muscularis and mucosa layers

The effects of drugs which interfere with arachidonate metabolism as well as glucocorticoid-induced anti-phospholipase proteins (APP) have been studied on PGI2 generation by rat stomach tissue. Indomethacin inhibited PGI2 generation both in vitro and ex vivo while dexamethasone was ineffective in both instances. APP inhibited PGI2 generation in vitro. The results are discussed in the light of the possible mode of action of glucocorticoids. Prostacyclin (PGI2) is the major cyclo oxygenase metabolite in the rat gastric mucosa and exerts gastroprotective actions. Therefore a correlation between the inhibition of PGI2 synthesis and the induction of gastric damage has been suggested for the non-steroidal anti-inflammatory drugs. Glucocorticoids inhibit phospholipase A2 (PLA2) by inducing in the target cells the synthesis of inhibitory proteins, the lipocortins, and consequently reduce the release of eicosanoids in a number of cells and tissues. However, there is a surprising paucity of information on the effect of glucocorticoids on arachidonic acid (AA) metabolism in the gastro-intestinal tract. Moreover, the relationship between steroid administration and gastric damage is still controversial. The present work was undertaken to investigate the effect of drugs which interfere with AA metabolism on the synthesis of PGI2 by rat stomach mucosa and by the underlying muscularis layer both in vitro and ex vivo.

Prostaglandins and the gastrointestinal mucosa: are they important in its function, disease, or treatment?

In 1971 interest in the role of prostaglandins in the gastrointestinal tract was stimulated by the publication of two hypotheses--that aspirin damaged the gastric mucosa by inhibiting prostaglandin synthesis (1) and that cholera toxin caused diarrhea by stimulating it (2). Subsequent research into the gastrointestinal actions of prostaglandins has been considerable and now impinges on clinical practice. This paper reviews the involvement of prostaglandins and related compounds in mucosal protection, in ulcer healing, in diarrhea, and in gastrointestinal inflammation, with particular reference to the growing body of human data.

Effects of indomethacin, piroxicam and selected prostanoids on gastric acid secretion by the rat isolated gastric mucosa

The effects of the cyclo-oxygenase inhibitors indomethacin and piroxicam have been investigated on histamine- and dibutyryl cyclic AMP-induced acid secretion in the rat isolated gastric mucosa. The relative potencies of a number of prostanoids as inhibitors of histamine-induced acid secretion were determined in an attempt to classify the prostaglandin receptor mediating this response. Indomethacin (8 X 10(-9) - 2.7 X 10(-6) M) and piroxicam (3 X 10(-6) M) potentiated the secretory responses elicited by histamine. This effect might be due to inhibition of the biosynthesis of antisecretory prostanoids. Indomethacin (2.7 X 10(-6) M) and piroxicam (3 X 10(-6) M) also potentiated the secretory response to dibutyryl cyclic AMP, but since prostaglandin E2 (PGE2, 10(-5) M) did not inhibit this secretory response, the mechanism of the potentiation may differ from that of histamine. The potency of the thromboxane mimetic U-46619 as an inhibitor of histamine-induced acid secretion was markedly reduced in the presence of indomethacin, suggesting that U-46619 may release endogenous antisecretory prostanoids. In the presence of indomethacin (2.7 X 10(-6) M) all the prostanoids tested produced concentration-related inhibitions of histamine-induced gastric acid secretion. PGE-analogues were the most potent compounds, the rank order of potency being 16, 16 dimethyl PGE2 greater than PGE2 greater than PGF2 alpha greater than U-46619 greater than PGD2 greater than PGI2. This order of potency is very similar to that obtained in smooth muscle preparations containing 'EP' receptors, suggesting that this receptor type also mediates inhibition of histamine-induced acid secretion in the rat.

Role of prostanoids in the protective actions of BW755C on the gastric mucosa

The ability of BW755C to reduce ethanol- or indomethacin-induced gastric damage and the role of prostanoids in the mechanism of this action were examined in the rat. BW755C (1-100 mg/kg) caused a dose-related reduction in the amount of damage produced by oral administration of 40% ethanol in 100 mM HCl. At the doses tested, BW755C had no significant effect on mucosal 6-keto-prostaglandin F1 alpha synthesis, but did cause a dose-dependent reduction in thromboxane B2 synthesis. The effect on thromboxane synthesis may be due to a selective inhibition of platelet cyclo-oxygenase by BW755C. The higher doses of BW755C (50 and 100 mg/kg) caused a significant increase in the volume of fluid present in the gastric lumen, which may contribute to the protective action of the drug against ethanol-induced damage. Oral administration of BW755C (50 mg/kg) significantly reduced the extent of gastric damage caused by subcutaneous injection of indomethacin (20 mg/kg) indicating that it is unlikely that the protective action of BW755C is mediated by endogenous prostanoids. The mechanism of the protective actions of BW755C may be related to its reported ability to inhibit lipoxygenase or to its actions as a free-radical scavenger.

The role of endogenous prostaglandins in the regulation of gastric secretion in rhesus monkeys

Prostaglandins (PG) are known to alter a variety of gastrointestinal functions, but the physiological role of endogenous PG remains unclear. This experiment was designed to evaluate changes in gastric secretion following both acute and chronic inhibition of PG synthesis with indomethacin (5 mg/kg s.c.). Gastric juice was collected by continuous aspiration in 8 conscious chair-adapted male rhesus monkeys following treatment with saline or indomethacin for one or four days. The gastric juice was analyzed for H+, Na+, K+, and Cl- concentrations. The amount of soluble mucus in the gastric juice was estimated using Alcian Blue dye binding of acidic glycoproteins and Periodic Acid Schiff reaction with neutral glycoproteins. PG levels were measured in the plasma and in biopsy samples of fundus, antrum and duodenum. Both one and four days of indomethacin significantly (p less than 0.05) decreased tissue PG levels in the fundus, antrum and duodenum. Plasma levels of PGF2 alpha were significantly (p less than 0.05) decreased after both one and four days of indomethacin, while PGE2 and 6-keto PGF1 alpha were significantly inhibited only after four days of indomethacin. Both acute and chronic inhibition of PG synthesis was accompanied by a decrease in the concentration of sodium and mucus in the gastric juice but by an increase in the output and concentration of hydrogen ion. These changes suggest a possible mechanism by which endogenous PG play a role in the regulation of gastric secretion and in the protection against gastrointestinal damage.

Reduction of aspirin-induced fecal blood loss with low-dose misoprostol tablets in man

Misoprostol (SC-29333), a synthetic prostaglandin E1 methyl ester analog, was given simultaneously with acetylsalicylic acid in a double-blind, placebo-controlled randomized prospective study of 32 healthy human male subjects. Fecal blood loss was measured for eight days using the 51Cr-labeled red blood cell technique. Aspirin (650 mg qid) and misoprostol (25 micrograms qid) or placebo were given during days 3, 4, and 5. There was a significant (P less than 0.05) increase in median blood loss (modified Friedman test) from 0.81 to 6.05 ml/day in the aspirin with placebo group (N = 16). Median blood loss was increased (from 0.75 to 3.75 ml/day) in the aspirin with misoprostol group (N = 16), but this was significantly less (Mann-Whitney U test, P less than 0.01) than the placebo group. Mean serum salicylate concentrations in the placebo and misoprostol groups were similar (7.8 and 6.8 micrograms/ml, respectively). There were no significant changes in laboratory values in any of the subjects studied, nor were any major side-effects encountered. This study demonstrates that oral misoprostol reduces aspirin-induced gastrointestinal bleeding even when administered simultaneously and at a dose level below its threshold for significant acid inhibition. This indicates a potential role for misoprostol in the prevention of gastric mucosal damage in selected patients.

Etodolac: effect on prostaglandin concentrations in gastric mucosa of rats

Etodolac is a structurally novel compound exhibiting potent analgesic and anti-inflammatory activity in laboratory animals and man, with excellent G. I. tolerance. Like other nonsteroidal anti-inflammatory drugs (NSAIDs) etodolac inhibits prostaglandin (PG) biosynthesis. In view of the cytoprotective role of PGE2, we have investigated in normal rats the effect of etodolac on the gastric mucosal concentration of PGE2 as well as of 6-keto-PGF1 alpha, the stable metabolite of prostacyclin; naproxen and piroxicam served as reference NSAIDs. The orally effective anti-inflammatory doses in the chronic arthritic rat model (3 mg/kg for etodolac and naproxen; 0.5 mg/kg for piroxicam), and their arbitrarily selected multiples of 10 were used. Rats were killed at 1, 2, 6 and 24 hr after single doses and the PG concentrations were measured by RIA. With the low dose, 2 and 6 hr after dosing, etodolac diminished the PGE2 concentration by 20-25% (vs control) while naproxen and piroxicam caused a fall of 53-65%; the difference between etodolac and the untreated control group is not statistically significant but the difference between etodolac and both piroxicam and naproxen is significant (p less than 0.001). At the high doses, the lowering in PGE2 was similar after all three drugs, i.e. about 70% at 1 and 2 hr; 50% at 6 hr, and 20-50% at 24 hr after dosing. Except for the consistently smaller reduction of concentrations after etodolac, the effects on 6-keto-PGF1 alpha concentration followed a similar pattern but the differences are not significant. The lack of the G.I. irritation of etodolac in rats and man at therapeutically effective doses may be attributed to the benefits of the relatively short-lived and slight decrease in gastric mucosal PGE2 concentrations found in this study.

The biology, pathophysiology and control of eicosanoids in inflammation

The involvement in inflammatory conditions of those cyclo-oxygenase and lipoxygenase derivatives of arachidonic acid (5,8,11,14-eicosatetraenoic acid), which are known as the eicosanoids, is reviewed in the light of recent studies. Although it is now generally recognized that cyclo-oxygenase products are fundamental to the inflammatory process as chemical mediators, and that inhibition of the cyclo-oxygenase enzyme pathway explains the mode of action of most non-steroidal anti-inflammatory drugs (NSAIDs) commonly prescribed in veterinary practice, evidence for the involvement of lipoxygenase products of arachidonate metabolism in inflammation is increasing. The leukotrienes (LTs) are 5-lipoxygenase-derived eicosanoids which have been shown to be leucotactic and involved in anaphylactic and hypersensitivity reactions. Leucocytes, drawn to sites of injury by chemotaxis, themselves liberate pro-inflammatory eicosanoids which perpetuate the response and may aggravate the clinical condition. At therapeutic dose rates, most NSAIDs have no effect on the biosynthesis of LTs, whereas corticosteroids, by inhibiting the release of arachidonic acid, may prevent the formation of both cyclo-oxygenase and lipoxygenase products. However, because of the undesirable side-effects of steroids, the clinical use of these agents in treating inflammatory conditions is sometimes limited. Novel non-steroid inhibitors of cyclo-oxygenase and lipoxygenase enzyme pathways could offer more effective and safer control of inflammation in animals.

Gastroduodenal ulceration in rabbits producing antibodies to prostaglandins

The consistent occurrence of gastric and duodenal ulcers was observed in laboratory rabbits used for production of high-titer plasma antibody to 6-keto PGF1 alpha and PGE2. Perforations developed in 7 of 10 animals, usually just distal to the pyloroduodenal junction. The remaining rabbits showed gross and/or microscopic evidence of imperforate ulcers and erosions. These lesions appeared to be direct pathologic complications of an immune response directed against prostaglandins since animals immunized against met-enkephalin with similar methods had no ulcers.

Protection of the gastroduodenal mucosa by prostaglandins

Like other nucleated cell populations in the body, the cells of the gastroduodenal mucosa are capable to metabolise arachidonic acid into prostaglandins, with prostaglandin E2 as the probable major metabolite. The production increases on demand and can be followed in the gastric lumen, where the output of prostaglandin E2 increases two to fourfold after exposure of the mucosa to hydrochloric acid. Exogenous prostaglandins, in particular of the E series, stimulate several identified mucosal defense factors in the upper gastrointestinal tract. Prostaglandins of the E series stimulate the transport of bicarbonate and the production and release of mucus glycoproteins from the gastroduodenal mucosa. They have trophic effects on gastrointestinal epithelia by increasing the survival time of mucosal cells and have cytoprotective properties. In addition, E2 prostaglandins suppress the gastric acid secretion and accelerate peptic ulcer healing. Non steroidal antiinflammatory drugs, which block the biosynthesis of prostaglandins, suppress the bicarbonate secretion, the production of mucus glycoproteins and cytoprotective properties. They interfere with the inhibitory feedback regulation of the gastric acid secretion and are ulcerogenic in experimental and clinical situations. These actions of PG biosynthesis blockers provide indirect information on the importance of local prostaglandin formation for maintenance of gastrointestinal mucosal integrity. It is hypothesised that biosynthesis of prostaglandins in the gastroduodenal mucosa is of importance and may be a key event in triggering the different components of the mucosal defense.

Prophylaxis and management of stress ulcers

Stress ulcers are located in the body and fundic part of the stomach. They occur in the majority of severely ill or injured patients, but only about 10% will bleed. The most effective prophylaxis are measures against the condition giving rise to risk factors as septicaemia, shock and malnutrition. The medical prophylaxis consists of antacids and/or histamine2-blockers. Most bleedings will stop after intensive care and medication with vasopressin particularly if risk factors can be eliminated. Gastric surgery should be the last step in the treatment of bleeding stress ulcers and then we recommend non-resectional surgery as gastric devascularisation or suture ligation of bleeding vessels.

Oxidation of prostacyclin and its analogs by three 15-hydroxyprostaglandin dehydrogenases

A study of the oxidation of prostacyclin and some of its analogs by three 15-hydroxyprostaglandin dehydrogenases was undertaken to determine the structural features of these compounds which might influence their rate of enzymatic inactivation. The effect of some structural changes seemed to be determined by the substrate specificity of individual enzymes. Other changes influenced the rate of oxidation by all three enzymes similarily. Among this latter group it was noted that a 15S hydroxyl group is necessary for oxidation to occur and that steric changes in the carboxy side chain and structural changes in the epoxy ring have a greater effect on the affinity of the substrate for the enzyme than on its maximum rate of oxidation. Certain analogs of prostacyclin are not substrates for one or more of the enzymes tested. Of these, (5S)-9-deoxy-5,9 alpha-epoxy-PGF1 and its methyl ester are potent inhibitors of only the placental enzyme---an interesting case of apparent selective metabolic regulation.