Endogenous opiates and stress ulceration

Peptic ulcer characteristics in oral opium and non-opium user patients with upper gastrointestinal bleeding

BACKGROUND/AIMS

Upper gastrointestinal bleeding (UGIB) is a frequent medical issue. The primary risk factors for bleeding peptic ulcers are Helicobacter pylori infection and non-steroidal anti-inflammatory drugs. The association between acute gastric/duodenal ulcer and opium use has been previously proposed; however, there is no available data on endoscopic findings of patients with acute UGIB who use opium.

MATERIALS AND METHODS

In the present descriptive cross-sectional study, endoscopic data of 50 consecutive patients with oral opium use and 50 consecutive patients without any opium use who were admitted for UGIB were recorded. The size (5-10 mm, 11-20 mm, or more than 20 mm), number (single, double, or multiple), and location of the ulcers (esophagus, gastric corpus including the fundus and body, antrum, angulus, or duodenum) were examined by endoscopy in both groups.

RESULTS

Three or more ulcers were observed in 46% and 16% of patients with oral opium use and without opium use, respectively (P-value = 0.001). The rate of giant ulcers (> 20 mm) was significantly higher in patients who used oral opium (40% vs. 12%; P-value = 0.007). Esophageal ulcers were also more common in oral opium users (30%) than non-users (8%) with UGIB (P-value = 0.01). Nevertheless, the location of the ulcers between the two groups generally was not statistically different.

CONCLUSIONS

This study has demonstrated that multiple, large peptic ulcers in GIB are potential complications of oral opium use. This could aid the needed modifications in the treatment protocol for these patients.

Gastric mucosal protection by aegle marmelos against gastric mucosal damage: role of enterochromaffin cell and serotonin

BACKGROUND/AIMS

Serotonin (5-hydroxytryptamine; 5-HT) released from enterochromaffin (EC) cells in gastric mucosa inhibits gastric acidity by increasing the gastric mucus secretion. In the present study, we evaluated the effect of aqueous extract of Aegle marmelos (AM) ripe fruit pulp (250 mg/kg body weight) on mean ulcer index (MUI), EC cells, 5-HT content, and adherent mucosal thickness of ulcerated gastric tissue in adult albino rats.

MATERIAL AND METHODS

Ulceration was induced by using aspirin (500 mg/kg, p.o.), cerebellar nodular lesion and applying cold-restraint stress.

RESULTS

In all cases increased MUI in gastric tissue along with decreased EC cell count was observed with concomitant decrease of 5-HT content and adherent mucosal thickness (P < 0.05). Pretreatment with AM for 14 days decreased MUI, increased EC cell count, and 5-HT content as well as adherent mucosal thickness in all ulcerated group (P < 0.05).

CONCLUSION

AM produces gastric mucosal protection mediated by increased EC cell count and 5-HT levels.

Perforation of peptic ulcer following abrupt cessation of long-term opiate use

PURPOSE

Unaided and abrupt cessation of opiate use without drug substitution and step-down, referred to as "cold turkey," is a common and difficult process for substance users, and is associated with several withdrawal symptoms and complications. This report presents a preliminary series of patients treated at an urban public hospital with acute perforation of peptic ulcers following abrupt cessation of long-term opiate use, a phenomenon that has not been previously described in the literature.

METHODS

Thirty-five patients with acute gastroduodenal perforation and a history of opiate addiction with a recent and abrupt cessation of opiate use were admitted between February 2004 and October 2008. This study evaluated the demographics, antecedent drug use, substance use characteristics, previous medical or surgical treatment of peptic ulcer disease, and surgical findings.

RESULTS

The mean age was 32.3 years (range, 21-41 years) and the patients were overwhelmingly male (94%). The most frequent agent in single opiate users was opium (62.9%) followed by heroin (22.9%). The time interval between opiate cessation and perforation onset was 2-65 days (mean, 6.1 days). All patients underwent an immediate exploratory laparotomy, and the majority of perforations were found to be in the postpyloric area (94%) with mean size of 4.3 x 5.1 mm. Two patients (6%) had perforations in the lesser curvature of the stomach.

CONCLUSION

All of the perforations occurred following sudden self-cessation without step-down or classic maintenance therapy, and this may prove the importance of supervised medical detoxification with special attention to gastroprotective agents such as antacid drugs.

Gastric healing effect of melatonin against different gastroinvasive agents in cholestatic rats

BACKGROUND AND OBJECTIVE

The frequency of gastrointestinal ulceration is higher in jaundiced patients than in healthy population. The aim of this study was to assess the effect of pretreatment with melatonin, a potent scavenger of reactive oxygen species, on stress-induced gastric ulcers of cholestatic rats.

MATERIALS AND METHODS

Cholestasis was induced by surgical ligation of bile-duct and sham-operated rats served as sham animals. The animals received saline or melatonin (1, 3 or 10mg/kg) before stress induction. Three different types of gastroinvasive agents including ethanol, indomethacin or water immersion were used as stress agents to induce gastric ulceration.

RESULTS

Gastric mucosal damage induced by different gastroinvasive agents was significantly greater in bile-duct-ligated rats than in sham ones. Melatonin was protective against ethanol-, indomethacin- and water immersion-induced gastric damage in bile-duct-ligated and sham rats, dose-dependently, but the protective effect of melatonin was greater in cholestatic rats than sham rats in all three different series of experiments.

CONCLUSIONS

In conclusion, pretreatment of rats with melatonin protected gastric mucosa of cholestatic rats more effectively than the sham ones possibly by a mechanism involving the scavenging of free radicals.

Protective effect of melatonin against multistress condition induced lipid peroxidation via measurement of gastric mucosal lesion and plasma malondialdehyde levels in rats

AIM

To study the protective effect of a natural antioxidant, melatonin, against multistress condition induced lipid peroxidation via determination of gastric damage and plasma malondialdehyde (MDA) level by high performance liquid chromatography in rats.

METHODS

We compared indomethacin-induced gastric damage and MDA plasma level in three groups of rats: unoperated, bile duct ligated and sham-operated and evaluated the role of the melatonin on gastric damage and plasma MDA level. Indomethacin and melatonin were injected intraperitoneally in doses of 50 mg/kg and 20 mg/kg, respectively. Animals were killed 4 h after indomethacin injection.

RESULTS

Indomethacin induced more severe gastric damage and plasma MDA level in bile duct ligated animals was significantly higher (3.1 +/- 0.04 micromol/L) than sham (2.8 +/- 0.04 micromol/L) and unoperated animals (1.4 +/- 0.08 micromol/L). Pretreatment with melatonin reduced indomethacin-induced gastric damage and plasma MDA level.

CONCLUSION

Considering the results of this study, we suggest that in multistress conditions the intensity of gastric damage and the plasma MDA level are great and melatonin reduces the negative effect of lipid peroxidation and cell damage by oxidative stress in multistress conditions due to its antioxidizing activity.

The Analgesic Effect of Tribulus terrestris Extract and Comparison of Gastric Ulcerogenicity of the Extract with Indomethacine in Animal Experiments

Tribulus terrestris has been used in traditional medicine for relieving rheumatic pain and as an analgesic plant for a long time. In this investigation the analgesic effect of methanolic extract of this plant on male albino mice was evaluated by formalin and tail flick test. Extraction of the fruits of the plant was done by two different methods (suxheletion and percolation) with methanol 80%. The percolated extract was injected intraperitoneally in mice at 50, 100, 200, 400, and 800 mg/kg. The results showed that a dose of 100 mg/kg of percolated extract had the highest significant analgesic effect compared to the control group (P < 0.01) in formalin and tail flick test. There is no significant difference in the analgesic effect of suxheleted and percolated extract. The analgesic effect of the extract was lower than morphine, 2.5 mg/kg in both tests, and higher than ASA 300 mg/kg in chronic phase of pain in formalin test (P < 0.05). Pretreatment of animal with naloxone did not change the analgesia induced by the plant extract in both tests, therefore the involvement of opioid receptor in the analgesic effect of this plant was excluded. The results of ulcerogenic studies indicate that the gastric ulcerogenecity of plant extract is lower than the indomethacin in the rat's stomach. It can therefore be concluded that T. terrestris extract has a suitable analgesic effect and further studies are required to produce a more effective product of this plant to substitute for conventional analgesic drugs.

Role of nitric oxide in the gastro-protective effect of lithium

BACKGROUND AND AIM

Lithium is widely used for the management of neuropsychiatric symptoms in bipolar disorders. A few studies have shown that lithium has a protective effect against gastric damage with an unknown mechanism. Some of the actions of lithium are mediated through nitric oxide (NO), which has an important role in the regulation of gastric wall blood flow as well as gastric mucosal integrity. The aim of this study was to test the hypothesis if the gastro-protective effect of lithium is mediated through NO.

METHODS

Male Wistar rats were pre-treated with either a non-selective NO synthase inhibitor (N(G)-nitro-l-arginine, 10mg/kg), a selective inducible NO synthase inhibitor (aminoguanidine, 100mg/kg) or saline. Lithium carbonate (10, 20, 50 and 100mg/kg) was then administered intraperitoneally 1h before the induction of gastric mucosal damage. Gastric damage was induced by either water immersion stress or ethanol gavage in rats.

RESULTS

Lithium had a significant protective effect in both stress and ethanol-induced gastric damage, but it needed in ethanol-induced gastric damage a higher dose than in the stress induced lesion. Lithium carbonate doses 20 and 50mg/kg produced plasma concentrations that were in the range of human therapeutic Li levels (0.6-1.0muM). Pre-treatment of animals with N(G)-nitro-l-arginine (20 and 40mg/kg) reduced the protective effect of lithium against ethanol-induced gastric damage, but not in stress-induced damage. Aminoguanidine administration showed no effect on the damage reduction either in control or lithium treated rats.

CONCLUSIONS

The results indicate that NO might play a role in the gastro-protective effect of lithium against ethanol-induced gastric damage in rats.

Morphine as a drug for stress ulcer prevention and healing in the stomach

Morphine pretreatment protects against stress-induced gastric ulceration, however, the exact mechanism is still undefined. Interestingly, the effect of morphine on ulcer healing has not been investigated. In this report, we would like to study these effects in a defined stress ulcer model and to delineate a new implication for morphine to promote stress ulcer healing in rats. Our study showed that cold-restraint stress for 3 h induced hemorrhagic lesions and increased myeloperoxidase activity in the gastric mucosa. Stress also reduced the dimension of layer of periodic acid-Schiff reagent-stained cells in the gastric mucosa by about 50%. Morphine pretreatment (2 or 8 mg/kg, given intraperitoneally) at the time of stress dose-dependently reversed stress-induced gastric ulceration, increase of myeloperoxidase activity and reduction of thickness of mucus-stained cells in the gastric mucosa. Morphine treatment after stress (given at the end of a 3-h stress and also at 3 h thereafter) increased ulcer healing by reducing the ulcer size measured 24 h later. Such action was blocked by naloxone (8 mg/kg) given intraperitoneally 15 min before morphine treatment. Morphine also increased the number of cell proliferation and dimension of layer of cells stained for mucus but not the number of microvessels in the gastric mucosa. Moreover, the number of apoptotic cells was less evidenced in the morphine-treated rats. This study reports for the first time that morphine not only prevents stress ulceration but also promotes healing of stress ulcer through a defined mechanism.

Anti-inflammatory and analgesic activity of Biebersteinia multifida DC. root extract

The root of Biebersteinia multifida DC (Geraniaceae), a native plant of Iran, has been used topically for the treatment of musculoskeletal disorders as a folk medicine. The anti-inflammatory and analgesic effects of the root extract were studied using carrageenan induced edema and formalin tests. A similar activity was seen between Biebersteinia multifida root extract (10 mg/kg; i.p.) and indomethacin (4 mg/kg; i.p.) in carrageenan test. The results of formalin test showed the analgesic activity of the root extract (50 mg/kg; i.p.) was comparable with morphine (10 mg/kg; i.p.) at the first phase of formalin test. Furthermore, the probable ulcerogenic activity of the root extract was also studied. The extract did not show any ulcerogenic effect at anti-inflammatory doses (10 mg/kg; p.o.).

Clonidine pretreatment inhibits stress-induced gastric ulcer in rats

We studied the effects of clonidine (0.5 mg/kg) on hormonal stress response and antioxidant enzymes cold restraint-induced gastric lesions in rats. Rats in the study group were given 0.5 mg/kg intraperitoneal clonidine (n = 12), whereas the control group received 0.5 mL/kg intraperitoneal isotonic sodium chloride solution (n = 9). Animals were then subjected to immobilization at 4 degrees C in restraining devices for 4 h after a starvation period of 24 h. Gastric lesion index, gastric tissue malondialdehyde activity, and plasma cortisol concentrations were assayed. Histopathologic examination demonstrated a stress ulcer index of 3.17+/-0.92 mm in the clonidine group and 14.0+/-3.22 mm in the control group (P<0.05). The tissue malondialdehyde concentrations were slightly higher in the control group than in the clonidine group, but the differences were not statistically significant (P>0.05). Plasma cortisol levels were lower in the clonidine group (P<0.05). We concluded that clonidine attenuated the tissue damage and stress response in stress-induced gastric ulceration.

IMPLICATIONS

Stressful circumstances can cause stomach ulcers, which can bleed, exposing patients to potentially life-threatening complications. In the present animal study, we showed that clonidine, a routinely available medication, may be useful in preventing stress-induced stomach ulcers.

Enhancement of aspirin-induced gastric damage by cholestasis in rats

In this study the severity of aspirin-induced gastric mucosal damage was investigated in rats with obstructive cholestasis. Cholestasis was induced by ligation and resection of the bile duct under general anesthesia. Two weeks after operation, the rats were fasted for 24 hours. Aspirin was administered orally in doses of 0, 128, 192, 266 and 335 mg/kg, and the animals were killed four hours after dosing. The dose of 266 mg/kg was chosen for a study of the time-dependency; other groups of animals were killed at time intervals of one, three, five, seven and nine hours after aspirin administration. The results showed that aspirin induces more severe gastric damage in bile duct resected rats compared with sham-operated and control animals. Salicylate levels of serums were also measured but there was no significant difference in serum salicylate levels between bile duct resected, sham-operated and control rats. It can be concluded that cholestasis can potentiate aspirin-induced gastric damage in rats.

The effects of captopril and naloxone on restraint-cold-stress- and ethanol-induced gastric lesions in rats

1. This study was undertaken to investigate the effect of captopril (1 microgram/kg or 1 mg/kg, i.p.) on the actions of naloxone (5 mg/kg, i.p. in gastric ulceration induced by ethanol and restraint-cold-stress. 2. Neither naloxone (5 mg/kg, i.p.) nor captopril (1 mg/kg, i.p.) alone induced any change in the indices of the ulcer in either group. 3. Captopril at a lower dose (1 microgram/kg, i.p.), when combined with naloxone (5 mg/kg, i.p.), significantly reduced cumulative ulcer length only in the ethanol-treated group (from 54.9 +/- 7.2 mm to 22.5 +/- 6.2 mm). 4. However, a high dose of captopril (1 mg/kg) plus naloxone pretreatment caused a significant reduction in both ethanol (from 54.9 +/- 7.2 mm to 24.9 +/- 6.5 mm) and restraint-cold-stress (from 19.0 +/- 3.0 mm to 5.3 +/- 1.0 mm)-induced ulcer formation. 5. Acetylsalycilic acid, when used together with captopril, increased the ulcer formation induced by stress. 6. Naloxone, by increasing the release of prostaglandins, has been shown to prevent ulcer formation induced by several noxious stimuli. 7. Therefore, the effect of the combination might be due to the synergistic interaction of both drugs on prostaglandin synthesis.

A study of the actions of naloxone and morphine on gastric acid secretion and gastric mucosal damage in the rat

There exists a considerable controversy in the literature with regard to the effect of either opiate receptor blockade or that of morphine in different gastric and intestinal ulcer models in the rat. We performed experiments to evaluate the effects of naloxone and morphine on gastric acid secretion and gastric mucosal damage in different experimental models of gastric mucosal injury, namely in indomethacin-, HCl (0.6N)- and ethanol (96%)-models. We found that: 1) 10 mg/kg naloxone i.p. given twice, effectively protected gastric mucosa against indomethacin (30 mg/kg i.p.) and against the acid-dependent injury caused by 0.6 N HCl (1 mL i.g.), but not against the non acid-dependent injury caused by 96% ethanol (1 mL i.g.); 2) morphine (10 + 10 mg/kg i.p.) increased ulcers in the HCl-model, but had no effect in the two other models; 3) this ulcer-aggravating effect of morphine in the HCl-model was blocked by pretreatment of 2 mg/kg i.p. naloxone; and 4) both naloxone (5 + 5 and 10 + 10 mg/kg i.p.) and morphine (10 + 10 mg/kg i.p.) significantly decreased gastric acid secretion in 1-h pylorus ligated rats. We conclude that: 1) naloxone dose-dependently protects against the indomethacin- and HCl-, but not against the ethanol-induced gastric mucosal damage; 2) morphine aggravates the HCl-induced ulcerogenesis; and 3) both opioid receptor agonist and antagonist decrease gastric acid secretion.

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

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Naloxone-sensitive potentiation at granule cell synapses in the ventral dentate gyrus and stress ulcers

Continuous perfusion of the granule cells in the ventral dentate gyrus with naloxone blocked the long-term potentiation (LTP) induced by high-frequency electrical stimulation of the posterolateral amygdala in freely-moving rats. This treatment also aggravated the stomach ulceration produced by cold restraint. LTP, on the other hand, attenuated the gastric stress pathology. It was suggested that a naloxone-sensitive granule cell gate modulates the impact of environmental stressors.

Antisecretory and anti-ulcer effects of morphine in rats after gastric mucosal aggression

The effects of morphine on gastric secretion, barrier mucus and mucosal lesions were studied in pylorus-ligated rats treated with the ulcerogenic agents, indomethacin, aspirin or taurocholic acid. All three ulcerogenic agents induced significant mucosal lesions. Morphine decreased gastric acid secretion and suppressed the aspirin- and taurocholic acid-induced, but not the indomethacin-induced mucosal lesions. These results suggest that the ulcerogenic mechanisms of indomethacin and the other agents are not identical. Moreover the antiulcer effect of morphine appears to be mediated by an increased barrier mucus level: the amount of Alcian blue bound to the mucosa, an indirect estimate of the adherent mucus layer, was increased by morphine and correlated with its protective effect. All morphine effects were reversed by naloxone.

Effect of indomethacin on opioid-induced gastric protection in cold-restrained stress

Morphine and the synthetic opioid met-enkephalin analog [D-Ala2, MePhe4, Met(0)5ol] enkephalin (FK 33-824) injected intraperitoneally to rats at doses of 5-20 and 0.5-2 mg/kg respectively showed a protective effect on gastric lesion induced by cold-restraint stress. This protective effect was abolished by pretreatment with indomethacin. This suggests a role for prostaglandins in the protection, induced by opioids of the gastric mucosa against the development of stress-induced ulcers.

Modulation by opiates of small intestinal prostaglandin E2 and 3',5'cyclic adenosine monophosphate levels and of indomethacin-induced ulceration in the rat

We studied the effect of parenteral morphine and naloxone administration on intestinal mucosal Prostaglandin E2 (PGE2) and 3',5' cyclic adenosine monophosphate (cAMP) levels and on indomethacin-induced intestinal ulceration in the rat. Compared to the control group, morphine significantly decreased whereas naloxone markedly increased both PGE2 and cAMP mucosal levels, respectively. Morphine or naloxone alone did not cause mucosal injury. However, when given with indomethacin, morphine significantly potentiated the ulcerogenic effect of indomethacin while naloxone exerted a protective effect. These results suggest that opioid peptides may play a role in modulation of intestinal mucosal PGE2 and cAMP levels. In addition, enhancement of indomethacin-induced ulcer formation by morphine and amelioration by naloxone might be in part mediated through their effect on mucosal PGE2 and cAMP levels.

The role of the hypothalamus and dorsal vagal complex in gastrointestinal function and pathophysiology

A foregone conclusion is that central neural and endocrine control of gastrointestinal functions is based on a complex array of interconnecting brain structures, neurochemical systems, and hormonal modulators. As might be expected, a considerable degree of redundancy is seen not only in the manner in which certain brain structures appear to participate in the regulation of GI functions, but also in the extent to which certain neurotransmitters or brain-gut peptides, when injected centrally, alter these functions. Despite the seemingly ambiguous nature of brain-gut interactions, a picture is beginning to unfold that suggests that GI properties are based on certain reflexes (e.g., vago-vagal). These reflexes, in turn, appear to be influenced by brain structures in a hierarchical manner, not all that dissimilar to the system described by Papez and expanded on by MacLean several years ago. For example, the perceptual or cognitive aspects of both external and internal stimuli are monitored at various brain levels, but obviously higher cortical processes are intimately involved. Aversive events provide sensory information, which is integrated primarily by the limbic system (e.g., amygdala) and translated into the expression of emotional behavior and associated autonomic response patterns. Various hypothalamic structures, in turn, appear most strongly to influence physiological changes associated with aversive events by virtue of the direct connections to the autonomic and endocrine systems. Ultimately, the visceral outcome can be seen as being based on the integrated convergence of information from cortical, limbic, and hypothalamic structures onto medullary nerve nuclei as well as other efferent systems. With respect to animal models of neurogenic or stress ulcer, activity of the dorsal vagal complex and vagal efferents appears to be the final common pathway for pathologic changes in the gut.

Naloxone-insensitive modulation of gastric acid output by [D-Met2,Pro5]enkephalinamide in rats

Studies from our laboratory have previously shown that two opioid agonists (morphine and [D-Met2,Pro5]enkephalinamide) aggravate, whereas naloxone inhibits cold-restraint stress-induced ulceration in rats. In the present study the effects of these substances were examined using the Shay-model. Contrary to expectations, both naloxone and the opioid agonists decreased gastric acid output. Naloxone in combination with either opioid agonist failed to reverse their inhibitory action. Thus the secretory activity of the stomach may be modulated by opioids in both naloxone-reversible and irreversible ways.

Morphine potentiation of ethanol-induced gastric mucosal damage in the rat. Role of local sensory afferent neurons

Local capsaicin-sensitive sensory afferent neurons may regulate the ability of the gastric mucosa to withstand challenge. Since opioids can modulate the activity of afferent neurones by actions at peripheral sites, the effects of morphine on gastric mucosal damage has been investigated in the rat. Morphine (3-9 mg.kg-1 i.v.) dose-dependently augmented the damage induced by a 5-min intragastric challenge with ethanol (25%-100%), as assessed by macroscopic and histological evaluation. These effects of morphine were significantly inhibited by the opioid antagonists naloxone and the peripherally acting N-methylnalorphine. Pretreatment of rats with capsaicin 2 weeks before the study to induce functional ablation of primary afferent neurons likewise significantly augmented the damage induced by ethanol. Both morphine administration and capsaicin pretreatment substantially augmented histologically assessed damage to the glandular mucosa and enhanced deep hemorrhagic damage following challenge with the low ethanol concentrations, with the appearance of macroscopically distinct antral damage. The enhanced damage induced by 50% ethanol in capsaicin-pretreated rats was not further enhanced by morphine administration, suggesting actions on a common mechanism. These findings support a pathophysiological role for activation of local opioid-sensitive afferent neurons in the modulation of mucosal injury following challenge.

Enkephalin-dopamine interactions in the central amygdalar nucleus during gastric stress ulcer formation in rats

Intra-amygdalar (i/am) microinjections of the enkephalin analog, (D-Ala2)-Met-enkephalinamide (DAME, 3, 10 and 30 micrograms) into the central amygdalar nucleus (CEA) produced a dose-related, naltrexone-reversible attenuation of cold restraint (3 h at 4 degrees C)-induced gastric mucosal lesions in rats. Similarly, gastric stress ulcer formation was also inhibited by i/am dopamine (DA, 10 micrograms) - an effect which was reversed by the DA-antagonist, clozapine (5 mg/kg) pretreatment. Further, pretreatment of rats with clozapine or the DA-neurotoxin, 6-hydroxydopamine (6-OHDA, 10 micrograms, i/am) clearly reversed and/or antagonized the gastric cytoprotective effect of DAMEA (30 micrograms). The results indicate interactions between enkephalinergic and DAergic systems at the level of the CEA in the maintenance of gastric mucosal integrity during immobilization stress.

Local opioid-sensitive afferent sensory neurones in the modulation of gastric damage induced by Paf

1. The role of local sensory neurones in modulating the extent of gastric mucosal damage induced by close-arterial infusion of platelet-activating factor (Paf 50 ng kg-1 min-1 for 10 min) has been investigated in the anaesthetized rat. 2. Local intra-arterial infusion of the neurotoxin, tetrodotoxin (TTX), substantially augmented the mucosal damage induced by Paf, as assessed by both macroscopic and histological techniques. 3. In rats pretreated with capsaicin 2 weeks prior to study, to induce a functional ablation of primary afferent neurones, gastric damage induced by Paf was significantly augmented. 4. Administration of morphine (0.75-3 mg kg-1 i.v.) or its peripherally acting quaternary analogue, N-methyl morphine (15 mg kg-1 i.v.), also significantly enhanced the gastric damage induced by Paf. 5. The potentiation by morphine of Paf-induced gastric damage was inhibited by administration of the opioid antagonists, naloxone (1 mg kg-1 i.v.) or the peripherally acting N-methyl nalorphine (3 mg kg-1 i.v.). 6. Administration of TTX or morphine alone, or pretreatment with capsaicin did not induce any detectable mucosal damage, suggesting that interference with local sensory neuronal activity itself does not directly induce mucosal disruption. 7. These results indicate that peripheral opiate-sensitive afferent sensory neurones play a physiological defensive role in the mucosa, attenuating the extent of gastric damage induced by Paf.

Stress- and morphine-induced elevations of plasma and tissue cholesterol in mice: reversal by naltrexone

Our earlier studies indicated that stress-induced facilitation of gallstone formation could be prevented by the opiate antagonist naltrexone. In view of the possible link between gallstone formation and atherosclerosis, the present study examined the possibility that endogenous opioids might also mediate stress-induced hypercholesterolemia. A 28-day immobilization stress schedule was used to induce increases in plasma, aortic and liver cholesterol of mice maintained on a high cholesterol diet. These stress-induced increases in plasma, hepatic and aortic cholesterol were reversed by pretreatment with the opiate antagonist, naltrexone (1 mg/kg). Exposure of mice to morphine (0.1% in the drinking water for 28 days) resulted in elevations of plasma, liver, and aortic cholesterol levels, similar to those observed following immobilization. In contrast, chronic exposure to the peripherally restricted opiate agonist, loperamide (0.1% in the drinking water for 28 days), was ineffective. The antagonism by naltrexone and duplication by morphine but not loperamide suggest that stress-induced hypercholesterolemia may require the activation of central endogenous opioid systems.

Effect of [D-Met2,Pro5]enkephalinamide on gastric ulceration and transmucosal potential difference

The effects of [D-Met2,Pro5]enkephalinamide, morphine and naloxone have been examined in two different models of experimentally elicited gastric mucosal lesions. One of them was the classic cold-restraint stress-induced ulceration. The other was a less frequently applied procedure, involving the measurement of decreases in the transmucosal potential difference, which is also a sensitive indicator of mucosal damage. The opioid agonists studied, [D-Met2,Pro5]enkephalinamide and morphine, aggravated, whereas naloxone, the pure opiate antagonist, mitigated the lesions in both models. The protective action of naloxone points to an eventual role of endogenous opioids in the generation of these types of mucosal lesions. Morphine is selective ligand of mu-opiate receptors. The enkephalin analogue, however, binds to both mu- and delta-receptors. Therefore, the potent pro-ulcerogenic action of the enkephalin analogue indicates that both the mu- and delta-receptors were involved in these models of experimental gastric lesions. The clarification of the eventual role of kappa-receptors requires further experimental work with a selective ligand of this subtype of opiate receptors.

Opiate mechanisms in the central amygdala and gastric stress pathology in rats

Bilateral microinjections of the opiate antagonist naloxone (0.1, 1.0 and 10.0 micrograms) into the central nucleus of the amygdala (CEA) produced a significant potentiation of cold restraint-induced gastric pathology in rats. The opiate agonist, beta-endorphin (0.1, 1.0 and 10.0 micrograms), on the other hand, inhibited stress ulcer formation in a dose-related manner. Stress ulcer-attenuating effects were also seen with intra-CEA injections of the enkephalin analogs [D-Ala2,D-Leu5]enkephalin (10.0 micrograms) and [D-Ala2]Met-enkephalinamide (10.0 micrograms). Pretreatment of rats with naloxone (1.0 microgram) completely antagonized and even reversed the gastric cytoprotective effects of beta-endorphin (1.0 and 10.0 micrograms). The results indicate that the CEA is important in the gastric cytomodulatory effects of endogenous opiates during stressful experiences.

Central nervous system action of calcitonin to alter experimental gastric ulcers in rats

The central nervous system action of calcitonin to influence various experimental models of gastric ulcers and gastric function was studied in rats fasted for 24 h. Intracisternal injection of salmon calcitonin (5 micrograms) completely suppressed gastric ulcerations induced by exposure to cold restraint stress, intracisternal injection of a stable thyrotropin-releasing hormone analogue, or peroral administration of aspirin. By contrast, intracisternal calcitonin enhanced gastric lesions elicited by peroral administration of 40% ethanol or 0.6 N HCl. Calcitonin action was dose-dependent (0.01-1 microgram) and central nervous system mediated inasmuch as intravenous calcitonin, given at a dose 50-fold higher than that effective intracisternally, did not significantly modify gastric mucosal injuries elicited by aspirin or ethanol. Intracisternal injection of calcitonin at 0.01 microgram inhibited gastric acid output by 90% in pylorus-ligated rats and suppressed gastric emptying of a liquid meal by 63%-94% in doses ranging from 0.01 to 5 micrograms. Prostaglandin generation in the gastric mucosa was not modified by intracisternal injection of calcitonin. These results demonstrate that intracisternal calcitonin acts within the brain to potently prevent ulcer formation elicited by stress, thyrotropin-releasing hormone analogue, or aspirin, but is not cytoprotective against necrotizing agents. Calcitonin action is not related to modification of gastric prostaglandin generation but it may involve the inhibition of gastric secretory and motor function.

Effect of a low-dose endotoxin pretreatment on the gastric mucosal damage induced by aspirin, phenylbutazone and reserpine in rats

The effect of endotoxin pretreatment (1 mg/kg body weight, i.p., once daily for 2 days) on the gastric mucosal damage induced by aspirin, phenylbutazone and reserpine has been studied in albino rats. When given alone, endotoxin did not produce any visibly discernible gastric lesions. It produced a significant augmentation of the gastric lesions produced by phenylbutazone and reserpine but did not significantly alter the ulcerogenicity of aspirin. The involvement of endogenous histamine formation and its release following phenylbutazone and reserpine administration and also in response to endotoxin pretreatment may be responsible for the exacerbation of gastric lesions induced by these drugs. Recent reports indicate the involvement of endorphins and platelet activating factor (PAF) in the ulcerogenic activity of endotoxin when used in high doses and their role in the potentiation of phenylbutazone- and reserpine-induced gastric lesions has to be worked out.

Effect of hypophysectomy, adrenalectomy, pituitary hormone secretion and gastric acid secretion on neurotensin induced gastric protection against stress gastric lesions

In previous studies we have established that intracisternal (i.c.) but not peripheral (intravenous) administration of neurotensin (NT), a brain and gastrointestinal tridecapeptide, totally prevents the development of gastric lesions produced by cold-restraint stress (CRS) with food-deprived rats. In this investigation, removal of the pituitary and adrenal gland, anterior pituitary hormone secretion and gastric acid secretion were evaluated independently as potential intermediates for NT's protective effect. NT (30 micrograms) produced a significant reduction of gastric lesions incidence and severity in intact and sham-operated controls. Adrenalectomy, but not hypophysectomy totally blocked the protective effect of i.c. NT. In addition, replacement therapy with s.c. prednisone (1 mg/kg) for 5 days following adrenalectomy did not restore the protective activity of central (i.c.) NT in adrenalectomized rats. A significant reduction of serum levels of TSH, PRL and GH following i.c. NT (30 micrograms) was observed after 2h of CRS. The gastrosecretory studies revealed that i.c. NT (30 micrograms) did not affect gastric acid secretion in pylorus ligated rats. However, blockade of peripheral (gut) cholinergic (muscarinic) receptors with i.p. atropine methylbromide (1 mg/kg) significantly raised gastric pH and reduced gastric acid concentration and output. In conclusion, the results of this study indicate that the acute protective effect of brain NT appears to be mediated, at least in part, by the sympathoadrenomedullary axis, and not by the pituitary gland or substances derived from the pituitary or by inhibition of gastric acid secretion.

The peptidergic brain-gut axis: influence on gastric ulcer formation

The existence of a relationship between the brain and the formation of gastric ulcers has been suspected since the last century. The advancement of stereotaxic procedures and the use of electrical lesion or stimulation have allowed localization within the limbic system, hypothalamus and brain stem, of discrete nuclei that influence the formation of gastric ulceration in experimental animals. Recently, further progress in the understanding of how the brain may influence gastric pathogenesis has been made by the demonstration that specific peptides act in the central nervous system to induce or prevent the formation of gastric ulcers and to markedly alter gastric secretory and motor function. Peptides established to have a centrally mediated protective effect are bombesin, calcitonin, corticotropin-releasing factor, neurotensin and opioid peptides. Growing evidence suggests a possible role for endogenous thyroptropin-releasing hormone in mediating cold-restraint stress induced gastric lesions. Circadian variations of the content and release of these peptides have been demonstrated in specific brain structures. To what extent such rhythms of peptide secretion are potentially linked to the circadian changes in the susceptibility to ulcer formation is worth investigating.

Neuroendocrine mechanisms of stress ulceration: focus on thyrotropin-releasing hormone (TRH)

It is generally accepted that stress ulceration, a multifactorial or pluricausal gastrointestinal disorder, may be the result of mechanistic interrelationships between mucosal, vascular, hormonal and neurogenic factors. The relative importance of each of these independent mechanisms remains unclear. This minireview represents an attempt to interpret many recent studies on certain neurogenic mechanisms and to integrate these observations into the existing body of knowledge. A variety of in vitro techniques and animal models to manipulate actual structures, organ systems, and certain well-defined hormonal influences have been utilized. The peripheral studies have followed, for the most part, the established observation that the stomach is under reciprocal control by sympathetic inhibitory and parasympathetic excitatory autonomic fibers. As a result, several autonomic adrenergic neurotransmitter substances have been found to promote mucosal resistance. Some of these include dopamine, epinephrine, and norepinephrine. Others in contrast, appear to promote vulnerability of the mucosa, and of these, the most well-studied include acetylcholine and histamine.

Effects of morphine and naloxone on stress ulcer formation and gastric acid secretion

The effect of both acute and chronic morphine and naloxone on restraint-stress gastric ulcer formation and on basal gastric acid secretion were examined in the conscious rat. Acute morphine administration produced a dose-related decrease in stress ulceration and basal gastric acid secretion. Acute naloxone treatment resulted in a dose-related increase in stress ulcer formation and markedly augmented gastric acid secretion. Naloxone (4.0 mg/kg) antagonized the ulcer-reducing effects at all doses of morphine tested (4.0-32.0 mg/kg). Morphine-dependent rats, restrained during spontaneous or naloxone-precipitated withdrawal, exhibited the most severe ulceration. However, only those subjected to naloxone-precipitated withdrawal produced a significant increase in gastric acid output. Chronic treatment with naloxone or with chronic naloxone followed by morphine (16.0 mg/kg) resulted in augmented stress ulcer formation relative to all acutely treated groups. Both chronic naloxone-treated groups exhibited markedly enhanced gastric secretion. These data suggest that central and/or peripheral opiate receptors can modulate both basal and stress-perturbed gastric function.

beta-Endorphin and enkephalins stimulate duodenal mucosal alkaline secretion in the rat in vivo

Secretion of HCO3- by duodenum just distal to the Brunner's glands area and devoid of pancreatic HCO3- was titrated in situ in anesthetized rats. Secretion increased significantly after intravenous injection of small amounts (10-20 ng/kg) of the opioid peptides beta-endorphin, methionine-enkephalin, and leucine-enkephalin. Maximum (approximately twofold) stimulation by beta-endorphin and leucine-enkephalin occurred at 20 ng/kg. Morphine (50 micrograms/kg) caused a similar stimulation and the mu-selective opiate antagonist naloxone prevented the stimulation by beta-endorphin and morphine. The synthetic analogue [D-Ala2,D-Leu5]-enkephalin (500 ng/kg), which is an agonist primarily at delta-opiate receptors, had no effect, further suggesting that the stimulation of duodenal HCO3- secretion is mediated by mu-receptors. Naloxone alone did not affect basal HCO3- secretion but reduced the duration of the rise in secretion in response to a 5-min exposure to luminal acid (pH 2.00). Endogenous opioid peptides may thus have a role in the humoral or neural control, or both, of duodenal surface epithelial HCO3- secretion and mucosal protection.

Naloxone is protective against indomethacin-induced intestinal ulceration in the rat

Naloxone, an opiate antagonist, was reported to protect against stress ulcers in dogs and rats. We studied its possible protective effect against indomethacin-induced intestinal ulceration in the rat. Naloxone was indeed found to possess a marked protective effect on the intestinal mucosa (ulcer index 73.3 +/- 13.6 vs. 273.8 +/- 21.8, p less than 0.001). Naloxone was found to elevate basal intestinal mucosal prostaglandin E2 (p less than 0.001) and cyclic adenosine monophosphate levels (p less than 0.005) but was unable to overcome the inhibition of prostaglandin E2 caused by indomethacin. An increase of cyclic adenosine monophosphate levels was seen, however, even in the presence of indomethacin, suggesting that cyclic adenosine monophosphate, but not prostaglandins, may play a role in the protective effect of naloxone.

Role of brain neurotransmitters on neurotensin-induced gastric cytoprotection

We have reported previously that intracisternal (IC) administration of neurotensin (NT) prevents stress-induced gastric ulcers in rats. This effect of NT appears to be mediated by the central nervous system because peripheral (IV) NT is totally ineffective. The present study sought to clarify the central mechanism of the cytoprotective effect of NT by utilizing pharmacological treatments which alter the function of brain neurotransmitter systems. Pretreatment with intracerebroventricular (ICV) administration of agonists and antagonists of acetylcholine (ACh), gamma-aminobutyric acid (GABA), and serotonin (5-HT) receptors or with an anti-opiate (naloxone) agent did not significantly alter NT-induced cytoprotection. However, pretreatment with ICV haloperidol, a dopamine (DA) receptor antagonist, totally blocked NT's cytoprotective effect. In addition, pretreatment with methylphenidate, a DA receptor agonist, produced cytoprotection similar to IC NT. These data indicate that NT-induced cytoprotection is not mediated by 5-HT, GABA, ACh (muscarinic) receptors, or endogenous opiate systems, but suggest interactions between brain DA systems and NT.

Endogenous opiates: 1982

This article is the fifth installment in an annual series of reviews of successive year's research dealing with the endogenous opiate peptides. Due to the continuing massive increase in the number of studies in this field, it has become impossible to continue comprehensive reviews of all aspects of this work. As a result we have decided that beginning this year the coverage will be abbreviated to emphasize non-analgesic and behavioral work. The specific areas discussed include stress, tolerance and dependence, consummatory responses, alcohol consumption, schizophrenia and emotional disorders, learning and memory, cardiovascular responses, respiratory effects, thermoregulatory effects, neurological deficits and other disorders, activity, and other, miscellaneous behaviors. As in previous years, we have attempted a relatively comprehensive review of the subjects covered only for the previous year and have not made an attempt to evaluate their contributions relative to those of past years.