Compensatory gastroprotective role of glucocorticoid hormones

Prostaglandings (PGs), nitric oxide (NO) and capsaicin-sensitive afferent neurons play a pivotal role in the defensive mechanisms against gastric mucosal injury. Glucocorticoid hormones released in response to ulcerogenic stimuli are naturally occurring gastroprotective factors and exert many of the same actions in the stomach as PGs, NO and capsaicin-sensitive afferent neurons. The results reviewed suggest that glucocorticoids exert a pivotal compensatory role in the maintenance of gastric mucosal integrity in the case of impaired gastroprotective mechanisms provided by PGs, NO and capsaicin-sensitive afferent neurons. The compensatory protective action of glucocorticoids may be provided by their maintenance of glucose homeostasis and gastric microcirculation.     

Role of gastric microcirculation in the gastroprotection by glucocorticoids released during water-restraint stress in rats

Our previous investigations demonstrated that glucocorticoids released in response to stress protect gastric mucosa against stress-induced ulceration. This study was designed to determine whether gastric microcirculation is involved in the mechanism of gastroprotective glucocorticoid action. For this we evaluated the effects of deficiency of glucocorticoid production during 3 hr water-restraint stress and corticosterone replacement on the stress-induced gastric erosions, gastric microcirculation and arterial pressure in rats. The stress was produced in awake rats and gastric microcirculation and arterial pressure were evaluated in animals anesthetized in 3 hr after the onset of water-restraint stress. An in vivo microscopy technique for the direct visualization of gastric microcirculation was employed. The gastric submucosal and the superficial mucosal microvessels were monitored on television screen through a microscope and the pictures were stored by microfilming for the analysis of red blood cell velocity and vessel diameter. Gastric microcirculation was estimated on the base of both the volume blood flow velocity in submucosal microvessels and the diameter of superficial mucosal venous microvessels. Gastric erosions were quantitated by measuring the area of damage. Plasma corticosterone levels were also measured after 3 hr stress by fluorometry. Water-restraint stress induced an increase in corticosterone level, an appearance of gastric erosions, a decrease in volume blood flow velocity of submucosal microvessels, a dilatation of superficial mucosal microvessels, a decrease in arterial pressure. The deficiency of glucocorticoid production during water-restraint stress promoted the stress-induced gastric ulceration, a dilatation of mucosal microvessels, a decrease of blood flow velocity in submucosal microvessels and of arterial pressure. Corticosterone replacement eliminated the effects of deficiency of glucocorticoid production on all of the parameters under study. Thus, the stress-induced corticosterone rise decreased gastric ulceration, restricted both the reduction of blood flow velocity in submucosal microvessels and a dilatation of superficial mucosal venous microvessels during water-restraint stress. These data suggest that the gastroprotective action of glucocorticoids during stress may be provided by the maintenance of gastric blood flow.     

Deficit of glucocorticoid production in rats aggravates ulcerogenic effects of stimuli of various modality and intensity

Effects of glucocorticoid deficiency and corticosterone replacement on gastric mucosal injury induced by various ulcerogenic stimuli have been evaluated in rats. Gastric erosions were induced in male rats by stimuli of different modalities and intensities. Glucocorticoid deficiency was induced by adrenalectomy or delayed inhibitory action after a single pharmacological dose of cortisol (300 mg/kg, i.p.) injected one week before the onset of ulcerogenic stimulus. Ulcerogenic stimuli induced both a plasma corticosterone rise and a gastric mucosal injury. The area of mucosal damages induced various stimuli ranging from a small to extensive those. Glucocorticoid deficiency significantly potentiated an ulcerogenic action of each ulcerogenic stimulus. Replacement by corticosterone (4 mg/kg, s.c., 15 min before the onset of ulcerogenic stimulus) prevented or significantly decreased the erosion--potentiating effect of glucocorticoid deficiency. These results show that endogenous glucocorticoids released during ulcerogenic influences help gastric mucous membrane to resist against a harmful action of both weak and strong ulcerogenic stimuli.     

Transformation of physiological gastroprotective effects of glucocorticoids into pathological ulcerogenic consequences

The study was designed to investigate how physiological gastroprotective action of glucocorticoids could be transformed to pathological proulcerogenic effect. Time-dependent effects of single injection of dexamethasone on stress-induced gastric erosions, corticosterone and blood glucose levels, somatic parameters were investigated in fasted rats. Dexamethasone injected at the same dose attenuated or aggravated the stress-induced gastric erosions depending on the time of the injection. In case of dexamethasone injection 1-12 hrs before stress, we observed its gastroprotective action. Further increase in the time interval caused transformation of the gastroprotective action of dexamethasone to proulcerogenic effect. Accordingly to the results obtained, dexamethasone-induced long-lasting maintenance of blood glucose levels accompanied with signs of catabolic effect as well as dexamethasone-induced corticosterone deficiency may be responsible, at least partly, for the transformation of gastroprotective effect of dexamethasone to the proulcerogenic one.     

The comparison of gastroprotective properties of Semax and its metabolites

Semax (MEHFPGP) was shown to increase gastric mucosal homeostasis to the action of such ulcerogenic factors as ethanol and stress. In the case of the stress model of ulcer formation, Semax and its two metabolites—HFPGP and FPGP—at the wide range of doses (0.06–3.7 μmol/kg) have demonstrated protective antiulcerogenic properties. In the case of ethanol model of ulcer formation, only Semax in two used doses (0.06 and 0.37 μmol/kg) reported reliable protective antiulcerogenic property. It was supposed that Semax’s gastroprotective activity directed to peripheral mechanisms of ulcerogenesis did not depend on its metabolites’ activities. On the contrary, Semax’s gastroprotective activity directed to the central mechanisms of ulcerogenesis might be also caused by gastroprotective activities of HFPGP and FPGP metabolites.     

Various ulcerogenic stimuli are potentiated by glucocorticoid deficiency in rats

The effects of glucocorticoid deficiency with or without corticosterone replacement on susceptibility to gastric mucosal injury by various ulcerogenic stimuli have been evaluated in rats. Gastric erosions were induced in male rats by stimuli of different modalities and intensities: 20% ethanol (po), aspirin (300 mg/kg, ip), acidified aspirin (40 mM, po) and 100% acetic acid (applied to gastric serosa). Glucocorticoid supply was decreased by adrenalectomy or by delayed inhibitory action after a single pharmacological dose of cortisol (300 mg/kg, ip) injected one week before the onset of ulcerogenic stimulus. Corticosterone for replacement (4 mg/kg, sc) was injected in rats with glucocorticoid deficiency 15 min before the onset of ulcerogenic stimulus. Plasma corticosterone levels were measured by fluorometry. Gastric erosions were quantitated by measuring the area of damage. Ulcerogenic stimuli induced both plasma corticosterone rise and gastric mucosal injury. The area of mucosal damages induced various stimuli ranged from small to extensive. Glucocorticoid deficiency significantly potentiated an ulcerogenic action of every ulcerogenic stimulus. Replacing corticosterone prevented or significantly decreased erosion-potentiating effect of glucocorticoid deficiency. These results show that endogenous glucocorticoids released during ulcerogenic influences help gastric mucosa to resist a harmful action of both weak and strong ulcerogenic stimuli.     

Compensatory gastroprotective action of glucocorticoid hormones in the rats with ablation of capsaicin-sensitive neurons

We tested the hypothesis that contribution of glucocorticoids in gastroprotection become especially important during ablation of capsaicin-sensitive neurons. For this, the effect of desensitization of capsaicin-sensitive neurons on the gastric mucosa was compared in groups of rats with different glucocorticoid supply: sham-operated and adrenalectomized without and with corticosterone replacement (4 mg/kg sc). Functional ablation of capsaicin-sensitive neurons was performed with neurotoxic doses of capsaicin (20 + 30 + 50 mg/kg sc). Indomethacin in the dose 35 mg/kg was given as an ulcerogenic stimulus. It was shown that combination of adrenalectomy with desensitization of capsaicin-sensitive neurons potentiated the effect of sensory desensitization alone on indomethacin-induced gastric erosions. Corticosterone replacement prevented this effect of adrenalectomy. The results suggest a pivotal compensatory role of glucocorticoids in maintenance of gastric mucosal integrity during ablation of caspsaicin-sensitive sensory neurons.     

Gastroprotective action of glucocorticoids during the formation and the healing of indomethacin-induced gastric erosions in rats.

The aim of the present study consisted of the investigation of glucocorticoid role in the formation and the healing of indomethacin-induced (25 mg/kg, s.c.) gastric erosions in rats. The effect of deficiency of glucocorticoid production followed by corticosterone replacement on the formation and the healing of the gastric erosions was evaluated. Glucocorticoid production was decreased by adrenalectomy or by delayed inhibitory action after a single pharmacological dose of cortisol (300 mg/kg i.p.) injected 1 week before the onset of ulcerogenic stimulus. Indomethacin induced corticosterone rise and caused gastric erosions. The loss of indomethacin-induced plasma corticosterone rise potentiated the formation of indomethacin-induced erosions in both models. The area of gastric erosions in rats with glucocorticoid deficiency was considerably larger than that in control animals 4 h after indomethacin administration as well as during 48 h after the drug administration (period of erosion healing). Injecting corticosterone in rats with glucocorticoid deficiency significantly decreased the formation of indomethacin-induced gastric erosions and promoted their healing. Thus, the present data support the gastroprotective action of glucocorticoids in the formation and in the healing of indomethacin-induced mucosal injury.     

Deficiency of glucocorticoid production delays the healing of acute gastric mucosal erosion and chronic ulcers in rats

Effects of glucocorticoid deficiency followed by corticosterone replacement on the healing of gastric erosions and chronic gastric ulcers have been investigated in rats. Glucocorticoid deficiency was induced by adrenalectomy performed after the formation of gastric erosions or ulcers. Gastric erosions were produced by indomethacin (35 mg/kg, i.p.) or by 6 h immobilization at temperature 8 degrees C, chronic gastric ulcers were induced by 60% acetic acid. All ulcerogenic stimuli caused an increase in corticosterone production. Adrenalectomy created corticosterone deficiency and delayed the healing of gastric erosions and chronic gastric ulcers. The effect of adrenalectomy was more evident in the indomethacin ulcerogenic model. Replacement by corticosterone prompted the healing of gastric erosions and ulcers in adrenalectomized animals. These data suggest a participation of endogenous glucocorticoids in a restoration of gastric mucosal integrity.     

Leukotrienes in mucosal damage and protection.

Exposure of the rat gastric mucosa to ethanol stimulates the generation of leukotriene (LTC4) and 15-hydroxyeicosatetraenoic acid, but not of thromboxanes and prostaglandins. Lipoxygenase activation is not found with other topical irritants or nonsteroidal anti-inflammatory drugs. A number of gastroprotective drugs dose-dependently inhibit the stimulatory action of ethanol on mucosal LTC4 formation closely parallel to their protective activity suggesting that ethanol-induced damage and activation of lipoxygenases may involve common targets which are simultaneously counteracted by certain types of protective agents. Selective inhibition of 5-lipoxygenase, however, does not confer protection against gastric mucosal damage caused by topical irritants or non-steroidal anti-inflammatory drugs. Thus, although leukotrienes may mediate certain reactions elicited by gastric ulcerogens such as submucosal venular constriction and mucosal microvascular engorgement, they do not appear to be major mediators of ulcerogen-induced tissue necrosis. The contribution of other products of the various pathways of arachidonic acid metabolism to gastric mucosal injury and the mechanism underlying the close interrelationship between protection and inhibition of LTC4 formation observed with certain compounds remains to be investigated.     

Role of polyamines in gastroprotection induced by epidermal growth factor.

Polyamines have been shown to stimulate cellular growth and differentiation, though their role in the prevention of acute gastric lesion induced by various noxious agents has been little studied. Epidermal growth factor (EGF) exhibits gastroprotective and ulcer healing properties due to its potent mitogenic and growth promoting action. This study was designed to compare the gastroprotective effects of spermine and EGF against gastric damage induced by absolute ethanol, acidified aspirin and stress and to determine the role of endogenous polyamines in EGF-induced gastroprotection. Spermine and EGF significantly reduced the lesions induced by all three ulcerogens. Oral administration of spermine or subcutaneous infusion of EGF in 24 h fasted rats with chronic gastric fistula resulted in similar inhibition of gastric acid and pepsin secretion. Pretreatment with difluoromethylornithine (DFMO), an irreversible inhibitor of ornithine decarboxylase (ODC), a key enzyme in the biosynthesis of polyamines, did not affect ethanol lesions, but reversed the protective effect EGF but not spermine against ethanol. This finding indicates that polyamines mediate, at least in part, EGF-induced gastroprotection. In tests with oral administration of aminoguanidine that is known to suppress the activity of diamino-oxidase (DAO) and to inhibit the degradation of polyamines, EGF showed a markedly enhanced gastroprotective activity against ethanol damage. Since indomethacin failed to affect the gastroprotective effects of spermine and EGF and neither of these agents influenced the mucosal generation of PGE2 in intact or injured gastric mucosa, we conclude that prostaglandins are not the major factors in spermine- and EGF-induced gastroprotection. This study demonstrates that polyamines are highly effective against gastric lesions induced by various ulcerogens and that they act as primary mediators of EGF-induced gastroprotection.     

Effect of malotilate on ethanol-induced gastric mucosal damage in capsaicin-pretreated rats

We studied the role of afferent sensory neurons in malotilate-mediated gastric mucosal protection. Intact and capsaicin sensory-denervated rats were used in the experiments. Gross gastric mucosal injury was assessed and evaluated as a main criterion of the gastroprotective effect of the tested substances. Besides malotilate, methyl-prostaglandin E2 was applied alone or in combination with malotilate to compare the effects and the mechanism of action of both substances. The results revealed that both malotilate as well as methyl-prostaglandin E2 exerted a significant protective action on 96% ethanol-induced gastric mucosal damage. However, there were no significant differences between intact and capsaicin-denervated rats. Only the use of 50% ethanol as a milder mucosal irritating agent resulted in significant differences in both groups of animals. We propose that malotilate (like methyl-prostaglandin E2) has a gastroprotective effect on ethanol-induced gastric mucosal injury. This effect is partly dependent on the sensory nervous system and the combination of both above substances has an additive effect.     

Role of Pterocarpus santalinus against mitochondrial dysfunction and membrane lipid changes induced by ulcerogens in rat gastric mucosa

Free radicals produced by ulcerogenic agents affect the TCA cycle enzymes located in the outer membrane of the mitochondria. Upon induction with ulcerogens, peroxidation of membrane lipids bring about alterations in the mitochondrial enzyme activity. This indicates an increase in the permeability levels of the mitochondrial membrane. The ability of PSE to scavenge the reactive oxygen species results in restoration of activities of TCA cycle enzymes. NSAIDs interfere with the mitochondrial beta-oxidation of fatty acids in vitro and in vivo, resulting in uncoupling of mitochondrial oxidative phosphorylation process. This usually results in diminished cellular ATP production. The recovery of gastric mucosal barrier function through maintenance of energy metabolism results in maintenance of ATP levels, as observed in this study upon treatment with PSE. Membrane integrity altered by peroxidation is known to have a modified fatty acid composition, a disruption of permeability, a decrease in electrical resistance, and increase in flip-flopping between monolayers and inactivated cross-linked proteins. The severe depletion of arachidonic acid in ulcer induced groups was prevented upon treatment with PSE. The acid inhibitory property of the herbal extract enables the maintenance of GL activity upon treatment with PSE. The ability to prevent membrane peroxidation has been traced to the presence of active constituents in the PSE. In essence, PSE has been found to prevent mitochondrial dysfunction, provide mitochondrial cell integrity, through the maintenance of lipid bilayer by its ability to provide a hydrophobic character to the gastric mucosa, further indicating its ability to reverse the action of NSAIDs and mast cell degranulators in gastric mucosa.     

Central basic fibroblast growth factor inhibits gastric ulcer formation in rats

We have recently reported that basic fibroblast growth factor (bFGF) acts in the brain to inhibit the secretion of gastric acid and pepsin, two major aggressive factors in the pathogenesis of gastric ulcer formation. In the present study, we determined whether or not bFGF has an anti-ulcer action via the central nervous system, using male Wistar rats. The intracisternal injection of bFGF dose-dependently (0.1-1.0 microgram(s)/rat) inhibited the severity of gastric ulcers induced by water-immersion restraint stress or central thyrotropin-releasing hormone. The same doses of peripherally injected bFGF failed to protect the gastric mucosa from these ulcerogenic procedures. These results suggest for the first time that bFGF has a mucosal protective effect through a mechanism involving the central nervous system. It is speculated that this anti-ulcer action of bFGF is, at least in part, dependent upon its gastric antisecretory effect.     

Annexin-1 is an endogenous gastroprotective factor against indomethacin-induced damage

Adherence of neutrophils to the vascular endothelium is an early and critical event in the pathogenesis of gastric injury induced by NSAIDs. Pretreatment with glucocorticoids has been shown to prevent NSAID-induced neutrophil adherence and, in turn, to protect the stomach from injury. Some of the anti-inflammatory effects of glucocorticoids, including inhibition of neutrophil adherence, are mediated via the release of annexin-1. In this study, we assessed the contribution of annexin-1 to the protective actions of a glucocorticoid (dexamethasone) against indomethacin-induced gastric damage. Dexamethasone pretreatment markedly reduced the extent of indomethacin-induced gastric damage in rats. Immunoneutralization of annexin-1 resulted in a reversal of the gastroprotective actions of dexamethasone. Similarly, pretreatment with either of two antagonists of the formyl peptide receptor family, to which annexin-1 binds, reversed the gastroprotective effects of dexamethasone. The inhibitory effects of dexamethasone on indomethacin-induced leukocyte adherence in the mesenteric microcirculation were abolished by pretreatment with an antibody directed against annexin-1 or with an antagonist of the formyl peptide receptors. These results demonstrate that annexin-1 mediates the gastroprotective effects of a glucocorticoid against NSAID-induced damage. We propose that in some circumstances, annexin-1 plays an important role as an endogenous mediator of mucosal defense.     

Analysis of the role of central and peripheral alpha2-adrenoceptor subtypes in gastric mucosal defense in the rat

The present study confirmed our previous assumption on the crucial role of central alpha2B-like adrenoceptor subtype in gastric mucosal defense. It was found that beside clonidine, rilmenidine, an alpha2/imidazoline receptor agonist and ST-91, an alpha2B-adrenoceptor preferring agonist inhibited the mucosal lesions induced by ethanol given intracerebroventricularly (i.c.v.). The ED50 values for clonidine, rilmenidine and ST-91 are 0.2, 0.01 and 16 nmol/rat i.c.v., respectively. The effect was reversed by the intracerebroventricularly injected alpha2B/2C-adrenoceptor antagonists prazosin and ARC-239, indicating the potential involvement of central alpha2B/2C-adrenoceptor subtype in the protective action. The gastroprotective effect of adrenoceptor stimulants was reversed by bilateral cervical vagotomy, suggesting that vagal nerve is likely to convey the central action to the periphery. In gastric mucosa both nitric oxide and prostaglandins may mediate the centrally-induced effect, since both indomethacin and N(G)-nitro-L-arginine reversed the protective effect of alpha2-adrenergic stimulants. Though expression of mRNA of alpha2B-, as well as alpha2A- and alpha2C-adrenoceptor subtypes was demonstrated in gastric mucosa of the rat, the hydrophilic ST-91, given peripherally (orally, subcutaneously), failed to exert mucosal protection, in contrast with clonidine and rilmenidine which were also effective. Consequently, while peripheral alpha2B-adrenoceptors are not likely to be involved in gastric mucosal protection, activation of central alpha2B-like adrenoceptor subtype may initiate a chain of events, which result in a vagal dependent gastroprotective action.     

The role of gastric and duodenal pH in the cysteamine-induced duodenal ulcer in the rat

Many secretory studies reported an increase in gastric acid secretion by the duodenal ulcerogen cysteamine. A detailed analysis of these experiments, especially the results from rats with chronic gastric fistula suggest that direct stimulation of gastric acid secretion may not be the primary mechanism of the duodenal ulcerogenic action of cysteamine. We used a different approach and measured the pH at the site of ulceration in the proximal duodenum. A duodenal ulcerogenic dose of cysteamine did not change the pH at the anterior or posterior wall of the duodenum during 4 hr. In the same dose and by the same route of administration, cysteamine nevertheless induced duodenal ulcers in 24 hr. These experiments demonstrate that in addition to the effect on gastric acid secretion, other factors are needed to the effect on gastric acid secretion, other factors are needed to explain the early duodenal ulcerogenic action of cysteamine.     

Stress in physiological studies

The review focuses on the concept of biological stress pioneered by Hans Selye, who demonstrated a key involvement of the pituitary-adrenocortical axis in the response to stress. It discusses the historic background of development of the stress concept and some aspects of modern physiological researches related to stress-induced activation of the hypothalamic-pituitary-adrenocortical axis. We focus mainly on the results demonstrating that stress-induced activation of the hypothalamic-pituitary-adrenocortical axis is a gastroprotective component of stress response.     

The pharmacological differences and similarities between stress- and ethanol-induced gastric mucosal damage.

Stress- and ethanol-induced gastric mucosal damage are the two commonly used ulcer models in animals. They share some of the similarities but also have differences in the etiology of gastric ulceration. This article reviews the influences of various protective drugs on these two types of gastric damage in rats. Verapamil (a calcium antagonist) or N-ethylmaleimide (a sulfhydryl depletor) prevents cold restraint-, but potentiates ethanol-provoked gastric lesion formation. N-Acetylcysteine (a mucolytic agent) and acetaminophen (an antipyretic analgesic) have the opposite actions. Prostaglandins provide a much better antiulcer effect on ethanol-induced lesions. Cimetidine (a histamine H2-receptor antagonist) prevents only stress-induced mucosal damage. These differences in drug actions indicate that stress and ethanol may have dissimilar ulcerogenic mechanisms in rats. On the other hand, carbenoxolone (a mucus inducer), histamine H1-receptor antagonists, leukotriene inhibitors (FPL 55712 and nordihydroguaiaretic acid) and mast cell stabilizers (like zinc compounds, sodium cromoglycate, FPL 52694 and ketotifen), all protect against gastric mucosal damage by stress or ethanol in rats. However, the role of gastric sulfhydryls in both types of gastric lesions is still controversial. These findings imply that the two types of lesion formation share some of the ulcerogenic mechanisms. This communication attempts to analyze the various findings and to relate them to the etiology of stress and ethanol-induced gastric lesions. It also summarizes the uses, and the antiulcer mechanisms, of the drugs that have been studied utilizing these two animal ulcer models, and suggests their possible implications in man.     

Gastrotoxic activity and inhibitory effects on gastric mucosal PGE2 production with different non-steroidal anti-inflammatory drugs: Modifications induced by pretreatment with zinc acexamate

Gastrotoxic activities of different non-steroidal anti-inflammatory drugs (NSAIDs) (diclofenac, indomethacin, ketoprofen, naproxen and piroxicam) administered per os were compared with their ability to inhibit gastric prostaglandin E₂ (PGE₂) synthesis in the rat. In a parallel study, effects of pretreatment with zinc acexamate (ZAC) were also assessed. NSAIDs invariably caused gastric mucosal damage and a decrease of PGE₂ levels. A good correlation between the decrease of PGE₂ levels and the index of gastric lesion (r = 0.41; p < 0.021) was observed when results obtained with the different NSAIDs were pooled. ZAC pretreatment significantly decreased the overall severity of lesions induced by NSAIDs. However, no correlation between gastric lesion index and depletion of PGE₂ gastric levels was observed after treatment with ZAC (r = 0.012; p < 0.948). These data corroborate the hypothesis that preservation of the capability to synthesize endogenous PGs is of critical importance in the maintenance of gastric mucosal integrity. The gastroprotective action observed with ZAC involves alternative mechanisms other than modification of PGE₂ levels.