Protective action of endogenous opioid-like peptides of different origins in duodenal ulcer in rats

A study was made of the effects of some endogenous opioids (beta-endorphin, gamma-endorphin, met-enkephalin, leu-enkephalin and dinorphin) formed in the body from different high-molecular precursors (pro-opiomelanocortin, proenkephalins A and B) on the development in rats of the cysteamine-induced duodenal ulcers. All the peptides under study, gamma-endorphin, in particular, had an anti-ulcerous activity which was mediated by specific opiate receptors. The majority of the opioids was characterized by reduction of the anti-ulcerous effect as the dose was raised. It is assumed that protection of the duodenal mucosa under ulcerogenic exposures is an essential property of endogenous peptides. It is concluded that opioid peptides derived from different precursors are arranged in a complex synergic system responsible for cytoprotection of the duodenum.     

The effects of antagonists of receptors for gastrin, cholecystokinin and bombesin on growth of gastroduodenal mucosa and pancreas.

The effects of gastrin, cholecystokinin (CCK) and bombesin on the DNA synthesis, as a biochemical indicator of trophic action in the gastroduodenal mucosa and the pancreas have been examined in rats fasted for 48 h and in rats refed for 16 h with or without administration of specific receptor antagonists for bombesin, gastrin and CCK. Bombesin and gastrin administered three times daily for 48 h in fasted rats significantly increased the rate of DNA synthesis as measured by the incorporation of [3H] thymidine into DNA in each tissue tested. CCK significantly increased DNA synthesis in the duodenal mucosa and pancreatic tissue, but not in the gastric mucosa. The stimulation of DNA synthesis induced by bombesin in the gastroduodenal mucosa and pancreas was abolished by bombesin/GRP receptor antagonist, RC-3095. RC-3095 did not affect DNA synthesis stimulated by gastrin and CCK in these tissues. L-365,260, a receptor antagonist for gastrin suppressed the DNA synthesis induced by gastrin but not by CCK or bombesin in the gastrointestinal mucosa and pancreas. L-364,718 a specific antagonist for CCK receptors was effective only against CCK stimulated duodenal mucosa and pancreatic growth. Refeeding of 48 h fasting rats strongly enhanced the DNA synthesis in all tissues tested, and this effect was significantly reduced in the gastroduodenal mucosa by blocking only gastrin receptors (with L-365,260) and that in the duodenal mucosa and the pancreas by antagonizing of CCK receptors (with L-364,718). Antagonism of bombesin receptors (with RC-3095) did not significantly affect the stimulation of DNA synthesis induced by refeeding in all tissues tested. This study indicates that the stimulation of DNA synthesis can be achieved by exogenous gastrin, CCK and bombesin acting through separate receptor but that only gastrin and CCK play the major role in the postprandial stimulation of the growth of gastroduodenal mucosa and pancreatic tissue.     

Effects of solution of low pH and taurocholate on release of beta-endorphin-like immunoreactivity from human duodenal mucosa in vitro

The presence of beta-endorphin-like immunoreactivity (beta-EpLI) in human duodenum and its release were studied. beta-EpLI was detected in the duodenum (mucosa, 26.7 +/- 6.3 pmol/g wet weight, mean +/- SEM; remaining tissue 23.1 +/- 5.3 pmol/g wet weight) and the stomach (7.1 pmol/g wet weight). The two activities gave similar curves for inhibition of beta-Ep radioimmunoassay of synthetic beta-Ep. On gel-filtration chromatography of a duodenal extract, two components of beta-EpLI were separated. When human duodenal mucosa was perfused with a solution of pH2 or 1mM or 5mM taurocholate, the release of beta-EpLI from mucosa into the perfusate increased 2-4 fold. These results indicate that beta-EpLI present in human duodenal is released by the direct action of low pH or taurocholate on the duodenal mucosa and suggest that it may have a physiological role.     

The effect of antagonist of receptors for gastrin, cholecystokinin and bombesin on growth of gastroduodenal mucosa and pancreas.

The effects of gastrin, cholecystokinin (CCK) and bombesin on the DNA synthesis, as a biochemical indicator of trophic action in the gastroduodenal mucosa and the pancreas, have been examined in rats fasted for 48 h and in rats refed for 16 h with or without administration of specific receptor antagonists for bombesin, gastrin and CCK. Bombesin and gastrin administered three times daily for 48 h in fasted rats significantly increased the rate of DNA synthesis as measured by the incorporation of [3H] thymidine into DNA in each tissue tested. CCK significantly increased DNA synthesis in the duodenal mucosa and pancreatic tissue, but not in the gastric mucosa. The stimulation of DNA synthesis induced by bombesin in the gastroduodenal mucosa and pancreas was abolished by bombesin/GRP receptor antagonist, RC-3095. RC-3095 did not affect DNA synthesis stimulated by gastrin and CCK in these tissues. L-365,260, a receptor antagonist for gastrin suppressed the DNA synthesis induced by gastrin but not by CCK or bombesin in the gastrointestinal mucosa and pancreas. L-364,718, a specific antagonist for CCK receptors was effective only against CCK stimulated duodenal mucosa and pancreatic growth. Refeeding of 48 h fasting rats strongly enhanced the DNA synthesis in all tissues tested, and this effect was significantly reduced in the gastroduodenal mucosa by blocking only gastrin receptors (with L-365, 260) and that in the duodenal mucosa and the pancreas by antagonizing of CCK receptors (with L-364,718). Antagonism of bombesin receptors (with RC-3095) did not significantly affect the stimulation of DNA synthesis induced by refeeding in all tissues tested. This study indicates that the stimulation of DNA synthesis can be achieved by exogenous gastrin, CCK and bombesin acting through separate receptors, but that only gastrin and CCK play the major role in the postprandial stimulation of the growth of gastroduodenal mucosa and pancreatic tissue.     

Certain Mechanisms regulating cell renewal in the gastric mucosa in peptic ulcer

A study was made of the effect of an aqueous extract of human gastric mucosa on the mitotic activity of the surface epithelium of the mouse stomach. The extract was found to exert a statistically significant inhibitory action. An extract from the mucosa of the stomach resected for duodenal ulcer exerted a more pronounced inhibitory action as compared with an extract from the stomach resected for gastric ulcer. This fact may be accounted for by a greater content of mature differentiated cells in duodenal ulcer. Tissue-specific action of gastric chalone is indicated by the absence of mitotic inhibition in the small intestinal mucosa.     

Comparison of effects of verapamil, low calcium diet and betamethasone on duodenal calcium absorption efficiency in the chick

The results indicate that oral administration of verapamil for 2 weeks to the chick is followed by an increase in the efficiency of the duodenal absorption of calcium. In these chicks both a decrease in serum calcium level and an increase in the activity of renal 1 alpha-hydroxylase were observed. The increased calcium absorption following prolonged treatment with verapamil resembles that induced by a low calcium diet. The mechanism of both responses presumably involves an increased production of 1,25-dihydroxyvitamin D3. Both verapamil- and low calcium diet-induced adaptations are capable of overcoming the inhibitory action of betamethasone on intestinal calcium absorption. No effects on calcium absorption were noted if verapamil was administered intraperitoneally which suggests that verapamil exerts its action directly on the intestinal mucosa.     

Effect of the hexapeptide dalargin on ornithine decarboxylase activity in the duodenal mucosa of rats in experimental duodenal ulcer

The effect of an opioid antiulcerogenic hexapeptide dalargin on ornithine decarboxylase activity of duodenal mucosa has been studied in rats with experimental duodenal ulcers induced by cysteamine. The intraperitoneal injection of 12.5 micrograms/kg of dalargin inhibited ulcerogenesis and activated the enzyme. The effect of the peptide was antagonized by an opiate antagonist naloxone. 5000 micrograms/kg of dalargin failed to inhibit the ulcer formation or to activate ornithine decarboxylase. Since ornithine decarboxylase activation is a marker of intensified cell proliferation and tissue regeneration, our results suggest that the antiulcerogenic effect of dalargin is due to the enhancement of duodenal mucosa regeneration.     

A comparison of the effects of duodenal glucose infusion on carbohydrate and lipid metabolism in liver, adipose tissue and small intestinal mucosa in sheep

The effects of duodenal glucose infusion on the specific activities of some enzymes of carbohydrate and lipid metabolism in the liver, perinephric adipose tissue and small intestinal mucosa of sheep were examined. Lipogenic enzyme activity was generally greatest in adipose tissue and lowest in liver and the response of these enzymes to glucose infusion was similarly greatest in adipose tissue. Glycolytic enzyme activity was significantly increased in all three tissues following duodenal glucose infusion. The effects of increasing carbohydrate availability in the small intestine in relation to tissue metabolism in sheep are discussed.     

Influence of luminal acidification on bicarbonate transport by gastric and duodenal isolated mucosae

Transport of HCO₃⁻ was measured by pH-stat titration in pairs of amphibian fundic or proximal duodenal mucosae using a modified Ussing chamber. Separate unbuffered solutions bathed the luminal sides of two tissue while their serosal surfaces were in contact with a common buffered solution. Lowering luminal pH bathing one fundic mucosa from 7.40 to 1.85 significantly increased HCO₃⁻ transport by another fundus. However, acidification of fundic mucosa did not affect duodenal HCO₃⁻ transport. In duodenal mucosal pairs, lowering pH from 7.40 to 5.46 caused an increase in HCO₃⁻ transport by the other tissue. Luminal H⁺ ion concentration may therefore regulate HCO₃⁻ transport via a humoral mechanism.     

Opioid action of the intestine: the importance of the intestinal mucosa

Drug effects on the intestine are traditionally explained in terms of action on the muscle layers and the nerves that control them. This is particularly true in the case of the opioids but research starting two decades ago has identified the intestinal mucosa as the site of action of the antidiarrhoeal opioids. Continued research using the intestinal mucosa offers a fresh approach to solving some old problems. For example it could lead to more confident predictions to be made about the wanted and unwanted effects of opioid drugs on the intestine and may help to find better drug treatments for alleviating withdrawal diarrhoea in addicts. Eventually it may help to explain how the general process of opioid dependence occurs at a cellular level.     

Bile secretion in the chicken: effects of secretin, cholecystokinin- pancreozymin and duodenal mucosal extract

The effects of i.v. administration of secretin, CCK-PZ, acid extracts from the duodenal mucosa and the duodenal acidification of the intestine on bile secretion were studied in anaesthetized chickens. Secretin and acid extracts from the duodenal mucosa, which increase bile flow, caused comparable modifications in bile composition; infusion of HCl to the duodenum only induced slight modifications. CCK-PZ caused a pronounced cholecystokinetic effect and, to a lesser degree, it also showed choleretic effects. The results suggest that in the hormonal regulation of bile secretion in the chicken CCK-PZ is more important than secretin and furthermore that the choleretic activity of the latter must be carried out by other secretin-like peptides.     

Regulation of somatostatin-14 and gastrin I binding sites in rat gastrointestinal mucosa by ulcerogenic dose of cysteamine

A single duodenal ulcerogenic dose of cysteamine administered into rats induced time-dependent depletion of immunoreactive somatostatin in the gastric corporeal, antral, and duodenal mucosa with a parallel increase (up-regulation) of somatostatin binding sites. The concentration of somatostatin binding sites returned to the control level in the corporeal mucosa when measured at 24 hrs; however, in the duodenal mucosa there was only a partial return to the control level. Somatostatin binding sites in the antral mucosa did not return to control level even after 24 hrs. Except for the duodenum mucosal immunoreactive gastrin level was unaffected by cysteamine administration, but corporeal mucosal gastrin I binding sites were diminished (down-regulation) after 24 hrs.     

Effect of recombinant human interleukin-11 on motilin and substance P release in normal and inflamed rabbits

Recombinant human interleukin-11 (rhIL-11) normalizes depressed smooth muscle tension generation towards motilin and substance P (SP) in rabbits with colitis. The aim of this paper was to evaluate the effect of rhIL-11 treatment on motilin and SP release which could have an effect on the contractility changes. Rabbits received 4, 40, 72 or 720 microg/kg rhIL-11 s.c. or saline, 1 h later a continuous s.c. administration of rhIL-11 was started with or without the induction of colitis (135 mg/kg TNBS) for 5 days. Motilin and SP levels were measured by RIA, motilin mRNA expression by RT-PCR. TNBS-colitis did not affect plasma motilin levels but increased the motilin content of the duodenal mucosa 1.7-fold. rhIL-11 treatment dose-dependently increased plasma motilin levels (720 microg/kg day: 3.5-fold) and the motilin content of the duodenal mucosa (720 microg/kg day: 3.0-fold). The effects of rhIL-11 were similar in normal rabbits and were accompanied by an increased motilin mRNA expression. TNBS-colitis decreased plasma SP levels 2.7-fold and the SP content in the colonic muscle layer 7.1-fold. The decrease in the muscle layer, but not in the plasma, was normalized by rhIL-11 treatment. In normal rabbits, rhIL-11 caused a decrease in plasma SP levels, but had no effect on the tissue content of SP. In conclusion, treatment of inflamed or normal rabbits with rhIL-11 increases plasma and tissue levels of motilin in the duodenal mucosa via an increased expression of motilin in the endocrine cells and induces the release of SP from extrinsic neurons. These changes do not explain the beneficial effect of rhIL-11 on the lowered contractility in inflamed rabbits although a change in balance of neuropeptides may influence gastro-intestinal inflammation.     

Vasoactive hormones and mediators in the mechanism of the development of an aphthous process in the oral mucosa

Experiments on dogs were made to simulate aphthous process on the oral mucosa by occlusion of the common bile duct. The content of adrenaline, noradrenaline, serotonin, histamine and ascorbic acid was measured during the development of pathological process in the areas of oral mucosa tissue characterized by most frequent appearance of aphthas and in the tissue of the duodenal, small and large intestine mucosa. The magnitude of the characteristics indicated was determined 2, 6 and 12 h and 1, 3, 7 and 10 days after operation. Aphthas appeared on the 3d day. Within the first hours of the experiment there was a considerable increase in the content of noradrenaline, adrenaline and serotonin in the oral mucosa accompanied by a reduction in the histamine and ascorbic acid content. In the intestinal mucosa, shifts in the correlations between the hormones and transmitters were less pronounced. During aphthas appearance, the histamine content rose whereas other parameters decreased. The period of the reverse development was characterized by the recovery of the correlations of the hormones under study and transmitters.     

Influence of the hormone analogue 13-NLE-molitin and of 1-methyl-3-isobutylxanthine on tone and cyclic 3',5'-AMP content of antral and duodenal muscles in the rabbit.

1. By the action of 1-methyl-3-isobutylxanthine (isobutyltheophylline, 2 - 3 × 10⁻⁴ M), the content of cyclic 3', 5'-AMP in the antral and duodenal muscles of the rabbit is increased by 72 % and 126 %, respectively; by 1.8 × 10⁻⁷ M 13-norleucine-motilin and 1.8 × 10⁻⁶ M acetylcholine it is not changed. 13-norleucine-motilin is an analogue of the recently discovered duodenal tissue hormone motilin and has identical effects. 1-methyl-3-isobutylxanthine has a more powerful inhibiting effect on phosphodiesterase than has theophylline.2. 3 × 10⁻⁴ M isobutyltheophylline reduces the tone of the duodenal muscle while simultaneously increasing the content of cyclic AMP and negates the tone-enhancing effect of nle-motilin on the duodenal muscle, while nle-motilin increases the muscle tone lowered by isobutyltheophylline.3. The basic tone of the antral muscle is not reduced by isobutyltheophylline. However, the contraction-promoting effect of nle-motilin after an increase in cyclic AMP due to isobutyltheophylline is significantly lower.4. It is assumed that the changes in the tone or in the response of the antral and duodenal muscles to nle-motilin observed after the administration of isobutyltheophylline, are due to the increase of cyclic AMP in the tissue.5. The antagonistic effects of cyclic AMP and motilin on the gastro-intestinal muscles might be of physiological importance for the regulation of the gastro-intestinal motor activity.     

In vivo lipid and amino acid synthesis from 3-hydroxybutyrate in 15-day-old chick.

The in vivo utilization of 3-hydroxybutyrate for lipid and amino acid synthesis in liver, kidney and duodenal mucosa of overnight-starved 15-day-old chicks has been investigated. Lipid synthesis was higher in liver and duodenal mucosa than in kidney. Triglycerides were the main lipids synthesized from 3-hydroxybutyrate in liver and kidney, while in duodenal mucosa a higher amount of phospholipids was observed. This tissue utilized a high percentage of 3-hydroxybutyrate for the synthesis of free cholesterol, in agreement with the major role of intestine in body cholesterogenesis. All of the assayed tissues synthesized amino acids from 3-hydroxybutyrate at a similar rate, glutamate being always the main amino acid formed.     

Interrelation between the analgesic and ulcerogenic action of cysteamine

Interrelationship was studied between the influence of cysteamine on pain threshold and ulcerogenic effect on the duodenum. Cysteamine (350 mg/kg) induced analgesia in mice which was prevented by naloxone (1.5 mg/kg). In rats, cysteamine produced duodenal ulcers with concomitant analgesia. The intensity of ulceration was higher in animals with lower basal pain threshold. The correlation between central and peripheral effects of endogenous opioids in the development of experimental duodenal ulcers is discussed.     

Characterization of enzymes involved in formation of ethyl esters of long-chain fatty acids in humans.

Elevated fatty acid ethyl ester (FAEE) concentrations have been detected in postmortem organs from alcoholics and patients acutely intoxicated by alcohol, and FAEE have been implicated as mediators of ethanol-induced organ damage. The formation of FAEE is catalyzed by acyl-coenzyme A:ethanol O-acyltransferase (AEAT) and by FAEE synthase, which utilize acyl-CoA and free fatty acids, respectively, as substrates. Because little is known about the capacity of various human tissues to synthesize and hydrolyze FAEE, we investigated formation of FAEE by AEAT and FAEE synthase in tissue homogenates from human gastric ventricular and duodenal mucosa, pancreas, liver, heart, lung, and adipose tissue, gallbladder mucosa, and in serum. Liver, duodenal mucosa, and pancreas were found to have the highest capacities to synthesize FAEE, mainly due to AEAT. FAEE hydrolyzing activity was highest in liver and pancreas, but hardly detectable in adipose tissue or heart. Because fatty acids and alcohol are absorbed by the intestinal mucosa, intestine may be a major site of FAEE synthesis, and FAEE may be delivered via the circulation to other organs and taken up by lipoprotein receptor-mediated uptake. A very low rate of FAEE hydrolysis was detected in heart and adipose tissue, which probably accounts for the previously observed accumulation of FAEE in these organs.     

Effects of force-feeding on immunology,digestive function and oxidative stress in the duodenal and jejunal mucosa of Pekin ducks

Force-feeding was considered as a traditional high-efficiency approach to improve growth performance and accelerate fat deposition of Pekin ducks. However, force-feeding is a serious violation of international advocacy on animal welfare, because it can induce serious injuries to animals, such as damages to the digestive tract, effects on immunity and even severe oxidative stress. Therefore, it is urgent to stop force-feeding. The aim of this study was to determine the effects of force feeding on immune function, digestive function and oxidative stress in the mucosa of duodenum and jejunum of Pekin ducks. A total of 500 ducks were randomly divided into two groups. The control group was allowed to feed freely on a basal diet. The experimental group was force-fed by inserting a plastic feeding tube 8 to 10 inches long down the esophagus for 6 days. Compared with the control group, there was a significant (P<0.05) increase in serum diamine oxidase, d-lactic acid, endotoxin and corticosterone levels in the force-feeding group. The crypt depth in duodenum and jejunum showed significant differences (P<0.05) between the two groups and the intestinal villus epithelium cell was severely damaged in force-feeding group. Similarly, the activities of digestive enzymes as well as the levels of immune function in the duodenal and jejunal mucosa in the force-feeding group were significantly higher than the control group (P<0.05). However, there was a significant decrease in the superoxide dismutase, glutathione peroxidase and catalase levels with a marked increase in malondialdehyde level in duodenal and jejunal mucosa (P<0.05). In summary, at the end of the fattening period with force-feeding for 6 days, Pekin ducks experienced an adverse effect on the integrity of their duodenal and jejunal mucosa epithelium cell as well as their immune function and antioxidant capacity of Pekin ducks but also had improvement in digestive enzyme activities.     

Effect of ligation of common bile duct on somatostatin levels and binding in cytosol of rabbit duodenal mucosa

Rabbits with ligation of the common bile duct, of one and three weeks duration, showed a significant increase of somatostatin content in duodenal mucosa and plasma as compared with control animals. The increase of mucosal somatostatin was associated with a decrease in the binding capacity of both high- and low-affinity binding sites without changes in the affinity values in cytosol of duodenal mucosa. These findings suggest that the number of somatostatin binding sites is inversely related to local levels of the peptide and support the hypothesis of somatostatin regulating its own binding sites.To whom correspondence should be addressed.