Duodenal ulcerogens cysteamine and propionitrile induce gastroduodenal motility alterations in the rat

Dopamine D₂-receptor antagonists ameliorate indomethacin-induced small intestinal ulceration in mice by activating α7 nicotinic acetylcholine receptors

We have reported that nicotine and the specific α7AChR agonist ameliorate indomethacin-induced intestinal lesions in mice by activating α7 nicotinic acetylcholine receptors (α7nAChR). Dopamine D₂-receptor antagonists, such as domperidone and metoclopramide, enhance the release of ACh from vagal efferent nerves. The present study examined the effects of domperidone and metoclopramide on indomethacin-induced small intestinal ulceration in mice, focusing on the α7AChR. Male C57BL/6 mice were administered indomethacin (10 mg/kg, s.c.) and sacrificed 24 h later. Domperidone (0.1-10 mg/kg) and metoclopramide (0.03-0.3 mg/kg) were administered i.p. twice, at 0.5 h before and 8 h after indomethacin treatment, while methyllycaconitine (a selective antagonist of α7nAChR, 30 mg/kg) was administered twice, at 0.5 h before each domperidone treatment. Indomethacin caused severe hemorrhagic lesions in the small intestine, mostly to the jejunum and ileum, with a concomitant increase in myeloperoxidase (MPO) activity. Domperidone suppressed the severity of lesions and the increase in MPO activity at low doses (0.1-3 mg/kg), but not at a high dose (10 mg/kg). Similar effects were also observed by metoclopramide. The protective effects of domperidone and metoclopramide were totally abolished by prior administration of methyllycaconitine. Indomethacin treatment markedly enhanced inducible nitric oxide synthase and chemokine mRNA expression in the small intestine, but these responses were all significantly attenuated by either domperidone or metoclopramide. These findings suggest that dopamine D₂-receptor antagonists ameliorate indomethacin-induced small intestinal ulceration through the activation of endogenous anti-inflammatory pathways mediated by α7nAChR.

Modulation of gastric motility by brain-gut peptides using a novel non-invasive miniaturized pressure transducer method in anesthetized rodents

Acute in vivo measurements are often the initial, most practicable approach used to investigate the effects of novel compounds or genetic manipulations on the regulation of gastric motility. Such acute methods typically involve either surgical implantation of devices or require intragastric perfusion of solutions, which can substantially alter gastric activity and may require extended periods of time to allow stabilization or recovery of the preparation. We validated a simple, non-invasive novel method to measure acutely gastric contractility, using a solid-state catheter pressure transducer inserted orally into the gastric corpus, in fasted, anesthetized rats or mice. The area under the curve of the phasic component (pAUC) of intragastric pressure (IGP) was obtained from continuous manometric recordings of basal activity and in responses to central or peripheral activation of cholinergic pathways, or to abdominal surgery. In rats, intravenous ghrelin or intracisternal injection of the thyrotropin-releasing hormone agonist, RX-77368, significantly increased pAUC while coeliotomy and cacal palpation induced a rapid onset inhibition of phasic activity lasting for the 1-h recording period. In mice, RX-77368 injected into the lateral brain ventricle induced high-amplitude contractions, and carbachol injected intraperitoneally increased pAUC significantly, while coeliotomy and cecal palpation inhibited baseline contractile activity. In wild-type mice, cold exposure (15 min) increased gastric phasic activity and tone, while there was no gastric response in corticotropin releasing factor (CRF)-overexpressing mice, a model of chronic stress. Thus, the novel solid-state manometric approach provides a simple, reliable means for acute pharmacological studies of gastric motility effects in rodents. Using this method we established in mice that the gastric motility response to central vagal activation is impaired under chronic expression of CRF.

Magnet Tracking: a new tool for in vivo studies of the rat gastrointestinal motility

Digestive motility was studied in the rat using a miniaturized version of the Magnet Tracking system which monitored the progression of a small magnetic pill through the entire digestive tract. The dynamics of movement was followed and three-dimensional (3-D) images of digestive tract were generated. After a retention period in the stomach and rapid passage through duodenum, the magnet progressed along the small intestine with gradually decreasing speed and longer stationary periods. It remained in the caecum for variable intervals. In the colon, periods of progress alternated with long quiescent periods. Gastric activity oscillated at 5-6 min(-1). In the small intestine, two frequency domains coexisted, showing independent modulations and proximo-distal gradients (40 to >32 and 28 to >20 min(-1)). Caecal oscillations were of 1.5 min(-1). The data allowed the magnet location and calculation of gastric and small intestinal transit times (58 +/- 36 and 83 +/- 14 min respectively), both significantly prolonged by oleate administration (243 +/- 130 and 170 +/- 45 min respectively). Magnet Tracking is a non-invasive tool to study the in vivo spatial and temporal organization of gastrointestinal motility in the rat.

Dual effects of acupuncture on gastric motility in conscious rats

The effects of manual acupuncture on gastric motility were investigated in 35 conscious rats implanted with a strain gauge transducer. Twenty (57.1%) rats showed no cyclic groupings of strong contractions (type A), whereas 15 (42.9%) rats showed the phase III-like contractions of the migrating motor complex (type B) in the fasting gastric motility. Acupuncture at the stomach (ST)-36 (Zusanli), but not on the back [Weishu, bladder (BL)-21], increased the peak amplitude of contractions to 172.4 +/- 25.6% of basal in the type A rats (n = 20, P < 0.05). On the other hand, the motility index for 60 min after the acupuncture was not affected by the acupuncture in this group. On the contrary, acupuncture decreased the peak amplitude and motility index to 72.9 +/- 14.0% and 73.6 +/- 16.2% in the type B rats (n = 15, P < 0.05), respectively. The stimulatory and inhibitory effects of acupuncture observed in each type were reproducible on the separate days. In 70% of type A rats, acupuncture induced strong phase III-like contractions lasting for over 3 h that were abolished by atropine, hexamethonium, atropine methyl bromide, and vagotomy. Naloxone significantly shortened the duration of the stimulatory effects from 3.52 +/- 0.21 to 1.02 +/- 0.15 h (n = 3, P < 0.05). These results suggest that acupuncture at ST-36 induces dual effects, either stimulatory or inhibitory, on gastric motility. The stimulatory effects are mediated in part via vagal efferent and opioid pathways.

From peptic ulcer disease to NSAID gastropathy. An evolving nosology

Nonsteroidal anti-inflammatory drug (NSAID)-induced gastropathy is an important clinical entity, most commonly encountered in elderly female patients. The expanding use of NSAIDs in the elderly population has led to an increased incidence of NSAID-induced gastropathy. The risk of gastric bleeding in these patients is 7-fold higher than in the younger population. Long term NSAID therapy in the elderly is apparently associated with failure of normal gastric mucosal adaptation. Silent unidentified gastric lesions are likely to be common with long term NSAID therapy, as symptomatology does not parallel pathological progression. This gastropathy, in contrast to peptic ulcer disease, is responsive to prostaglandins and other cytoprotective agents. A new generation of prostaglandin-sparing NSAIDs (e.g. nabumetone), in addition to the older nonacetylated salicylates, may represent less gastrotoxic alternatives. Therefore, these agents may substantially reduce the risk of NSAID-induced gastropathy. The debate continues as to whether to use NSAIDs, and under which circumstances. More importantly, the cost-benefit implications and justification for concomitant therapy with gastroprotective agents cloud the picture. Currently, there is a definite consensus that NSAIDs should not be casually used on a chronic basis, especially in patients at risk for serious gastropathy complications. In all cases, where possible, gastric prostaglandin-sparing NSAIDs or nonacetylated salicylates should be used in lowest effective dosages. In special circumstances, gastroprotective co-therapy can be considered. NSAID therapy probably should not be used or continued in elderly patients with a history of bleeding ulcers or recent major gastric ulcer activity.

Gastric and duodenal anti-ulcer activity of sulpiride, a dopamine D2 receptor antagonist, in rats

The gastric and duodenal anti-ulcer activity of sulpiride, a dopamine D2 receptor antagonist, was studied on various types of experimentally induced ulcers in rats, viz., pylorus ligation and water immersion + restraint stress-induced gastric ulcers, gastric mucosal damage induced by nonsteroidal anti-inflammatory drugs and reserpine, and duodenal ulcers induced by cysteamine hydrochloride. It has been found to possess significant anti-ulcer activity against all these models. In 19 h pylorus ligated rats, it significantly reduced the gastric secretion, increased the fucose and sialic acid concentration of the gastric juice and reduced its protein content, thus increasing the total carbohydrate:protein (TC/PR) ratio. These results suggest that the antisecretory and gastric mucosal barrier strengthening effects of sulpiride may be responsible for its anti-ulcer activity. A central component also appears to be involved in its anti-ulcer action against water immersion + restraint stress model. The results of this study provide a rationale for its beneficial effect seen in the therapy of peptic ulcer disease.

Effects of compound U74500A in animal models of gastric and duodenal ulceration

Pretreatment with U74500A (up to 0.65 mg/100 g) failed to affect gastric lesions induced by 100% EtOH gavage in Sprague-Dawley rats. Topical application of U74500A did not reduce lesions induced by 40% EtOH in ex vivo gastric chamber preparations. However, pretreatment of rats with U74500A (0.65 g/100 g per os) reduced the incidence and severity of experimental duodenal ulcer induced by cysteamine HCl, and duodenal ulcer induced by cysteamine-HCl plus GABA. These results show U74500A to have powerful and specific antiduodenal ulcer actions. Pharmacologic analysis of organ-bath preparations of the small intestine show this compound to reduce intestinal contractility to applied cholinergic and serotonergic agonists. However, relaxations induced by electrical or nicotinic ganglionic stimulation were unaffected. U74500A itself caused concentration-dependent contractions.

Disturbed gastroduodenal motility in patients with active and healed duodenal ulceration

Disordered gastroduodenal motility may promote duodenal ulceration by allowing prolonged acid contact with the duodenal mucosa. Using a multilumen perfused catheter incorporating 3 pH microelectrodes, antral and duodenal pH and antropyloroduodenal pressure activity were recorded in 36 subjects (10 with healed duodenal ulceration, 11 with active duodenal ulceration, and 15 healthy volunteers) during fasting and after a radiolabeled solid test meal. Correct pH probe/catheter position was continuously verified by recording transmucosal potential difference across the pylorus. Patients with active and healed duodenal ulcer had similarly disordered gastroduodenal motility. The chief abnormalities consisted of an increase in postprandial duodenal retroperistalsis (healed duodenal ulceration, 12 +/- 1 events per hour; active duodenal ulceration, 12 +/- 1; control, 6 +/- 1; mean +/- SEM: healed and active duodenal ulceration vs. control, P = 0.004 and P = 0.03, respectively), a reduction in pressure waves sweeping aborally through the duodenum after the meal (healed duodenal ulceration, 22 +/- 4 events per hour; active duodenal ulceration, 23 +/- 3; control, 34 +/- 4: healed and active duodenal ulceration vs. control, P = 0.04 and P less than 0.05, respectively), and an increased incidence of atypical, complex forms of coordinated duodenal motor activity throughout the study (postprandial data; healed duodenal ulceration, 8 +/- 1 events per hour; active duodenal ulceration, 10 +/- 1; control, 4 +/- 1: healed and active duodenal ulceration vs. control, P = 0.02 and P less than 0.02, respectively). In addition, gastric emptying of the solid test meal was significantly delayed in healed, but not active, duodenal ulceration [half-emptying time, healed duodenal ulceration 185 minutes (117-235); active duodenal ulceration 102 minutes (80-200); control 107 minutes (78-130): healed duodenal ulceration vs. control, P less than 0.009]. Duodenal bulb pH was similar in controls and patients with active duodenal ulceration; however, bulb pH was less than 4 for a significantly greater period of time in healed duodenal ulceration compared with active ulcer patients, particularly after the meal. In conclusion, duodenal ulcer disease is associated with disturbed gastroduodenal motility, even when the ulcer is quiescent and when intraduodenal acidity is low. In healed duodenal ulceration, disturbed motility may promote ulcer relapse by impairing acid clearance from the bulb. However, in active ulceration other factors such as mucosal bicarbonate secretion may have a more influential role in determining intraduodenal pH.

Duodenal SP-like immunoreactivity is decreased in experimentally-induced duodenal ulcers

Substance P-like immunoreactivity (SP-li) is decreased in duodenal samples of animals treated with a single dose of an ulcerogen such as dulcerozine, mepirizole or cysteamine. Unlike dulcerozine- or mepirizole-induced ulcers the degree of cysteamine-induced duodenal lesions is inversely correlated with the levels of duodenal SP-li. A significant decrease in duodenal SP-li was observed at 24 h, but not at 6 h after a single oral dose of cysteamine. These findings show that endogenous SP may play an important local role in duodenal ulcerogenesis.

Pantethine, a somatostatin depleting agent, increases food intake in rats

During the course of studies of the effects of pantethine, a cysteamine precursor known to deplete tissue concentration of immunoreactive somatostatin, we observed that the subject rats continued to eat despite marked distension of the stomach. To determine whether this effect was caused by drug-altered food intake, we have measured food and water intake in pantethine-injected rats in the fed and fasting state. In three separate experiments, rats allowed free access to food until the morning of study showed significant increased food intake accompanied by an increased stomach content (at 4 hr) of both food and water following the IP injection of pantethine. In one experiment, intake at 3 hours was 0.60 g/100 g b.wt. (pantethine dose 0.74 g/kg b.wt.) and 0.64 g/100 g b.wt. (pantethine dose 1.47 g/kg b.wt.) compared with 0.24 g/100 g b.wt. in saline-treated animals (p less than 0.05). In contrast, pantethine, 1.47 g/kg b.wt., when administered to overnight-fasted rats, significantly inhibited food intake (3-hr intake 1.54 +/- 0.16 g/100 g b.wt. in rats injected with pantethine 1.47 g/kg b.wt. as compared with 3.3 +/- 0.21 g/100 g b.wt. in saline-injected controls). The intake-stimulating effect of pantethine in ad lib-fed rats was not demonstrable when the drug was administered shortly before the "lights out"-induced feeding at night. These findings indicate that pantethine, a cysteamine precursor, stimulates food intake in satiated rats, depending upon the stage of circadian rhythm, but is inhibitory to intake in fasted animals. We postulate that the effects are mediated directly or indirectly through the disinhibition of central appetite-regulating somatostatinergic pathways but, since cysteamine also inhibits dopamine-beta-hydroxylase, an effect on depletion of appetite-regulating central catecholamines cannot be excluded.

Interactions of the ulcerogen cysteamine with enteric inhibitory nerves and putative transmitters in the rat small intestine

1. The effects of the ulcerogen cysteamine (2-aminoethanethiol HCL) on spontaneous activity and evoked responses of rat isolated small intestine preparations were investigated in vitro. 2. Cysteamine induced concentration-dependent relaxations of isolated segments of the rat duodenum, jejunum and ileum. These actions were manifest simultaneously in both the circular and longitudinal muscle layers, where the responses displayed a similar profile. 3. Treatment with tetrodotoxin (0.1 microM) or cold storage of individual preparations to prevent nerve-mediated responses abolished the effects of cysteamine. The presence of atropine (0.1 microM), propranolol (3.0 microM) and phentolamine (3.0 microM) in the bathing solution did not affect the cysteamine-evoked relaxations, suggesting cysteamine was stimulating non-adrenergic, non-cholinergic (NANC) intrinsic inhibitory nerves. 4. Applied cysteamine reversibly reduced GABA- and DMPP-evoked NANC nerve-mediated relaxations via actions unrelated to the receptors for these agents. 5. Methysergide-sensitive (direct) actions of 5-HT on the muscularis but not 5-HT neurally evoked responses were blocked by cysteamine. 6. It would appear that cysteamine has excitatory and inhibitory actions on enteric inhibitory nerves as well as specifically interfering with myogenic but not neural actions of 5-HT.

Duodenal ulcers are associated with a depletion of duodenal calcitonin gene-related peptide-like immunoreactivity in rats

Calcitonin gene-related peptide-like immunoreactivity (CGRP-li) was decreased in duodenal samples from animals treated with ulcerogens such as dulcerozine, cysteamine or mepirizole. The degree of these experimental ulcers was inversely correlated with the levels of duodenal CGRP-li. These findings show that endogenous CGRP may play an important role in duodenal ulcerogenesis.

Effect of duodenal ulcerogens cysteamine, mepirizole, and MPTP on duodenal myoelectric activity in rats

Increased gastric acid secretion, enhanced acid delivery to the duodenum, and reduced alkaline secretion in the proximal duodenum are relatively well-established pathophysiologic abnormalities in duodenal ulcer. Impaired duodenal motility, however, may also contribute to duodenal ulceration by altering the distribution of acid and alkaline secretions along the upper digestive tract. We tested the hypothesis that the duodenal ulcerogens cysteamine, MPTP, and mepirizole modify duodenal motility in the rat and that motility changes might be a common and early alteration in experimental duodenal ulceration. All three duodenal ulcerogens rapidly produced extensive changes in duodenal myoelectric activity and reduced the frequency of myoelectric slow waves. Cysteamine induced marked hypermotility for at least 6 hr; MPTP rapidly decreased motility and fragmented the myoelectric migrating pattern. Mepirizole induced biphasic changes: an early hypermotility phase of about 30 min was followed by profound hypomotility. These results indicate that marked alterations of duodenal motility are common during experimental duodenal ulceration. In light of the differential effect of the ulcerogens on duodenal motility, it remains to be determined how these changes influence acid neutralization in the proximal duodenum. Nevertheless, our results suggest that all three duodenal ulcerogens, which are different in structure, alter duodenal motility.

Effects of dopamine on gastric mucosal lesions induced by ethanol in rats. Possible involvement of antigastric motor activity mediated with alpha 2-adrenoceptors

Acidified ethanol (60% ethanol in 150 mM HCl, per os) induced elongated bands of hemorrhagic lesions along the long axis of the stomach within 1 hr in rats. Pretreatment with dopamine hydrochloride (DA: 1-10 mg/kg, subcutaneously) dose-dependently reduced the severity of these lesions. In parallel study, DA had no effect on acid secretion but inhibited gastric motor activity in a dose-related manner. The inhibitory effects of DA on both acidified ethanol-induced lesions and gastric motor activity were significantly reversed by pretreatment with yohimbine, an inhibitor of alpha 2-adrenoceptors (5 mg/kg, subcutaneously), but not by prazosin, haloperidol, or indomethacin. Similar to DA, both norepinephrine (NE: 1 mg/kg, subcutaneously) and epinephrine (EPI: 1 mg/kg, subcutaneously) showed inhibition of the motor activity and gastroprotection against acidified ethanol, but these effects were also significantly attenuated by yohimbine. A highly significant relationship was found between the inhibitory effects of DA, NE, and EPI on the motor activity and the mucosal lesions (r = 0.8577, P less than 0.05). In addition, administration of gentian violet (0.5% w/v, per os) stained the mucosa deep blue as elongated wide bands in the corpus region, and such localized staining was significantly prevented by DA, suggesting a flattening of the mucosal foldings in the presence of DA. These results suggest that DA (and other catecholamines) protects the rat gastric mucosa against injury caused by acidified ethanol, probably through inhibition of gastric motor activity mediated with stimulation of alpha 2-adrenoceptors.

Biphasic effect of duodenal ulcerogens on gastric emptying in the rat

The effect of the duodenal ulcerogen cysteamine on gastric emptying of a liquid meal was compared to that of two newly identified duodenal ulcerogens, MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) and mepirizole. Emptying rates after acute and chronic treatment with duodenal ulcerogens were obtained. Acute administration of cysteamine, MPTP, or mepirizole significantly delayed gastric emptying of the meal. Chronically treated rats, however, showed either no change or accelerated gastric emptying after cysteamine, MPTP, or mepirizole. Gastric emptying in chronically treated animals was faster in rats that developed the most severe duodenal ulcers. These results indicate that delayed gastric emptying instead of accelerated emptying is a more common abnormality during duodenal ulceration. After the ulcer develops, however, unaltered or accelerated gastric emptying is observed experimentally, thus suggesting that accelerated gastric emptying in duodenal ulcers is an acquired alteration. The implications that these experimental findings may have in the pathogenesis of duodenal ulcer, in light of the clinical data available, are discussed.

Cysteamine-induced inhibition of mucosal and pancreatic alkaline secretion in rat duodenum

To determine the effect of cysteamine on the alkaline secretion by the duodenal epithelium, pancreas, and Brunner's glands in relation to the pathogenesis of duodenal ulceration, the alkaline secretion by various types of duodenal loops was comparatively studied. The results obtained were as follows: (1) Cysteamine significantly reduced both mucosal and pancreatobiliary alkaline secretion in the proximal duodenum of rats. (2) The ratio of contribution of pancreatobiliary alkaline secretion to total neutralization of acid in the proximal duodenum was 55.9% under continuous perfusion. (3) There was no significant difference between the amounts of alkali per unit volume of the proximal and distal duodenal loops. (4) The alkaline substance secreted by the proximal duodenal mucosa was confirmed to be the bicarbonate. From these findings, it has been concluded that the impairment of bicarbonate secretion by the mucosal epithelium of proximal duodenum, not by Brunner's glands, plays a causative role in cysteamine-induced duodenal ulceration.

From cysteamine to MPTP: structure-activity studies with duodenal ulcerogens

Cysteamine is the first chemical identified that induces acute and chronic duodenal ulcers in rodents. Structure-activity studies with cysteamine, propionitrile and their derivatives, as well as with analogues of toluene, revealed numerous alkyl and aryl duodenal ulcerogens. Among these, one of the most interesting from an etiologic and pathogenetic point of view is the dopaminergic neurotoxin MPTP, which shows structural similarities with toluene. The chemically-induced duodenal ulcers are similar and localized on the anterior and posterior wall of the duodenal bulb. Both cysteamine and MPTP affect endogenous dopamine; MPTP is especially potent in depleting central dopamine and inducing lesions in the substantia nigra. MPTP given in high doses induces Parkinson's disease-like syndrome and gastric ulcers. Cysteamine and propionitrile also cause dyskinesia in large and multiple doses. The motility disorders and duodenal ulcers are abolished by dopamine agonists. Cysteamine and MPTP have been known to increase and decrease gastric acid secretion, respectively. However, both compounds induced duodenal dysmotility, decreased bicarbonate production, and reduced its delivery from distal to proximal duodenum. These factors decrease acid neutralization in the duodenal bulb and contribute to duodenal ulceration. Thus, studies with animal models may reveal endogenous mediators and specific receptors which might be involved in the pathogenesis of duodenal ulceration. Specific structure-activity studies in toxicology may lead to new insights in the pathogenesis and pharmacology of a poorly understood human disorder such as duodenal ulceration.

Alternatives to the acid-oriented approach to ulcer disease: does 'cytoprotection' exist in man? A new classification of antiulcer agents

This review summarizes the historical contradictions and inconsistencies that form the labile arguments advocating neutralization or inhibition of secretion of gastric acid for the prevention or treatment of gastroduodenal ulcers. Re-evaluation of old concepts is needed in the wake of recognition that even the most potent antisecretory agents do not change the natural history of ulcer disease; that is, the recurrence is high after termination of treatment. New biochemical, functional, and structural targets are listed for pharmacologic intervention in ulcer disease. As a supplement or alternative to the antisecretory agents, we should now consider prosecretory agents (for example, for bicarbonate and mucus secretion) and antioxidants (for example, free radical scavengers). Gastroduodenal motility, smooth muscle, the vascular endothelial cell, and the basement membrane seem to represent additional pharmacologic targets toward which new gastroprotective drugs can be directed even though the biochemical mechanism of action of these new agents may not be fully understood. New results suggest that these elements have a role in the pathogenesis of ulcer disease, and their modulations seem to exert a beneficial effect without inhibiting gastric secretion in rodents. In man, the acid antisecretory and cytoprotective doses seem to overlap, but arguments are presented to shift defining gastric 'cytoprotection' by the dose of drugs to the characterization of the phenomenon (for example, events such as the ethanol-induced hemorrhagic erosions which cannot be decreased by antisecretory agents). Furthermore, non-prostaglandin and non-H2-receptor antagonist drugs are available that exert acid-independent gastroprotection both in animals and humans. The future is thus bright for the development of new antiulcer agents.

The effects of cysteamine on neurogenic responses in the stomach and small intestine of the rat

The actions of the duodenal ulcerogen cysteamine in different regions of the rat stomach and small intestine were investigated utilizing isolated gut-bath preparations. Applied cysteamine caused concentration-dependent contractions of forestomach strips, primarily by direct actions at cholinergic muscarinic sites on the longitudinal muscle, and to a lesser extent indirectly via stimulation of intrinsic cholinergic motor nerves. In contrast to its gastric actions, applied cysteamine evoked nerve-mediated relaxations of segments of whole duodenum, jejunum and ileum. These actions were concentration-dependent and due to stimulation of the non-adrenergic, non-cholinergic (NANC) inhibitory nerves. In addition, cysteamine selectively inhibited nicotinic and GABA-ergic stimulation of the NANC inhibitory nerves, as well as electrically evoked cholinergic contractions. The interactions of cysteamine with the NANC inhibitory nerves appears to be via sites distinct from nicotinic or GABA receptors, and may have involved toxic effects.

The effect of muscarinic and beta-adrenergic blockade on cysteamine-induced gastrin secretion by the isolated perfused rat stomach

Cysteamine-induced duodenal ulceration in rats is accompanied by increased circulating gastrin. Although cysteamine appears to exert a direct action on the gastrin cell some groups have provided evidence for an involvement of the autonomic nervous system. The current experiments were performed to determine whether beta-adrenergic or cholinergic (muscarinic) pathways are involved in the acute effect of cysteamine on gastrin secretion in the isolated perfused rat stomach. Cysteamine (1 mM) increased gastrin (IRG) secretion to a maximum ranging between 100% and 192% above basal. A cysteamine concentration of 5mM resulted in peak levels ranging between 150% and 1050% above basal. Addition of atropine or propranalol did not influence the responses obtained. The present results, therefore, do not support a role for either cholinergic or beta-adrenergic pathways in cysteamine-induced gastrin release at the level of the stomach and suggest that in vivo such autonomic effects are mediated extrinsically.

Potent CNS action of calcitonin to inhibit cysteamine-induced duodenal ulcers in rat

Intracisternal injection of calcitonin (0.01-5 micrograms) dose dependently prevented the development of duodenal ulcers induced by cysteamine in female rats. By contrast, intravenous infusion of the peptide at a dose 50 times higher than an effective intracisternal dose, had no effect. Intracisternal injection of calcitonin increased by three fold the generation of 6-keto-PGF1 alpha, the stable hydrolysis product of PGI2, in the duodenal mucosa. These studies demonstrated that calcitonin acts within the brain to potently suppress duodenal ulcers induced by cysteamine. The mechanisms of the antiulcer effect may involve changes in prostaglandin generation along with alterations of gastrointestinal secretion and motility associated the central injection of calcitonin. Growing evidence suggests that salmon calcitonin may act as a neuromodulator or neurotransmitter in the central nervous system. Specific binding sites have been demonstrated for calcitonin in the hypothalamus, brain stem and dorsal horn of the spinal cord using homogenate and membrane preparations or in vitro autoradiography methods. The peptide injected into the cerebrospinal fluid (CSF) produces a wide spectrum of biological effects including analgesia, hyperthermia, changes in pituitary hormone release, decrease in food and water intake, locomotor activity, and blood pressure. Numerous studies also demonstrated that calcitonin acts within the brain to markedly influence gastrointestinal secretory and motor function in rats and dogs and gastric ulceration in rats. In particular, intracisternal injection of salmon calcitonin was found very potent to selectively inhibit gastric ulcers elicited by stress, aspirin and central thyrotropin-releasing factor but not by necrotizing agents. In the present study, we further investigated the antiulcer effect of salmon calcitonin using the well established cysteamine experimental model to induce duodenal ulcers in rats. Part of this work has been reported in abstract form.

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 cysteamine on cytosolic somatostatin binding sites in rabbit duodenal mucosa

Administration of cysteamine in rabbits elicited a rapid depletion of both duodenal mucosa and plasma somatostatin. A significant reduction was observed within 5 min, returning toward control values by 150 min. The depletion of somatostatin was associated with an increase in the binding capacity and a decrease in the affinity of both high- and low-affinity binding sites present in cytosol of duodenal mucosa. Incubation of cytosolic fraction from control rabbits with 1 mM cysteamine did not modify somatostatin binding. Furthermore, addition of cysteamine at the time of binding assay did not affect the integrity of 125I-Tyr11-somatostatin. It is concluded that in vivo administration of cysteamine to rabbits depletes both duodenal mucosa and plasma somatostatin and leads to up-regulation of duodenal somatostatin binding sites.

Role of local motility changes in the pathogenesis of duodenal ulcers induced by cysteamine in rats

The possible role of local motility in the pathogenesis of duodenal ulcers was investigated in rats using cysteamine. Duodenal motor activity was measured as intraluminal pressure recordings by means of a balloon positioned in the proximal duodenum. Subcutaneous administration of cysteamine (100 mg/kg) produced two linear bandlike lesions in the proximal duodenum within 6 hr. This dose of cysteamine significantly increased gastric acid secretion in acute fistula rats, and decreased duodenal HCO3- secretion caused by acid. During this period, this agent inhibited gastric motility but did produce markedly enhanced contractions in the duodenum. The changes in duodenal motility appeared within 5-10 min and were dose-dependent for cysteamine (10-100 mg/kg). Pretreatment with subcutaneously administered atropine (10 mg/kg), 16,16-dmPGE2 (30 micrograms/kg) or dopamine (10 or 30 mg/kg) significantly reduced the development of duodenal lesions caused by cysteamine, the inhibition being 86.8%, 49.7%, 54.5% or 67.8%, respectively. In the presence of cysteamine, dopamine had minimal effect on both acid and HCO3- secretion, while atropine or 16,16-dmPGE2 markedly inhibited acid secretion or increased HCO3- secretion, respectively. The enhanced duodenal motility induced by cysteamine was blocked partially by atropine and only slightly by 16,16-dmPGE2. Dopamine showed a dose-dependent inhibition on the duodenal hypermotility following cysteamine, and at 30 mg/kg almost completely abolished the development of contractions. These results suggest that abnormal hypermotility in the duodenum may be partly involved in the pathogenesis of cysteamine-induced duodenal ulcers.

Development and significance of cysteamine and propionitrile models of duodenal ulcer

Cysteamine is widely used in rodents to induce duodenal ulcer. Herein, the pathogenesis of duodenal ulceration in its earliest stages was reviewed using findings from cysteamine- and propionitrile-induced duodenal ulcer in rodent models, especially taking into account changes in the secretion of gastric acid, duodenal and pancreatic bicarbonate as well as gastroduodenal motility. The effect of cysteamine-HCl in inducing ulcers in rats is circadian rhythm-dependent. The effect is greatest from just before the end of diurnal rest to just after the start of nocturnal activity. The chronobiologic effect may be in part due to the circadian rhythm-dependent increased gastric acid production from cysteamine. Titratable acidity was found to be twice as great in the gastric juice of rodents when cysteamine was given by injection at 2000 (just after the start of nocturnal activity) in comparison to when given at 0800 or 1200 (at the beginning or middle span of daily rest). Further studies have shown that adrenalectomy of rats 7 days before cysteamine administration obliterated the observed circadian susceptibility to ulcer formation. Duodenal ulceration, at least in the cysteamine model, appears to be under chronobiologic neuroendocrine control or influence, seemingly mediated by the adrenal glands.

Mechanisms of mucosal injury in the stomach and duodenum: time-sequence analysis of morphologic, functional, biochemical and histochemical studies

This review is based on results from our laboratory and those published by others, and is focused on the early stages of pathogenesis that can be studied mostly in animals. Gastric mucosal injury is analysed on the examples of ethanol- and aspirin-induced lesions. Ethanol (50-100%) rapidly penetrates the mucosa, causes directly and/or indirectly (e.g., release of vasoactive products) endothelial damage in superficial and deep capillaries and venules. The vascular damage results in increased vascular permeability and decrease in blood flow leading to complete circulatory standstill in superficial capillaries 1-2 min after intragastric administration of concentrated ethanol. The direct chemical damage to surface mucosal epithelium is then followed by hypoxia and deep hemorrhagic necrosis in 1-5 min (erosion or ulcer). Unionized aspirin initiates a similar and complex yet slower progressing and less extensive erosion than alcohol. Duodenal erosion and ulcer produced by cysteamine, mepirizole or MPTP are preceded by excess acid in the proximal duodenum. This could be due to increased gastric acid output (1-4 hr), decreased bicarbonate secretion or duodenal dysmotility (0.5-8 hr) preventing the proper mix of acid and base in duodenal bulb. Necrosis and desquamation of absorptive cells in duodenal villi are evident 2-4 hr, followed by villus amputation (4-8 hr), erosion and ulcer (8-24 hr). The pathogenesis of gastroduodenal mucosal injury can thus be reconstructed from results obtained with animal models and from human studies. The results should serve as a basis to design protective drugs that are active on the basis of pathogenetic events.

A new model of duodenal ulcers induced in rats by indomethacin plus histamine

We standardized a new method for producing duodenal ulcers in rats by administering indomethacin plus histamine, and investigated the pathogenesis. Indomethacin (5 mg/kg) was first given subcutaneously to rats fasted for 24 h, and subsequently histamine dihydrochloride (40 mg/kg) was given subcutaneously three times, at 2.5-h intervals, beginning 30 min after injection of indomethacin. This combined treatment induced one or two round lesions (9.8 +/- 1.4 mm2) in the proximal duodenum at an incidence of 100%, and a few lesions in the corpus and antrum of the stomach as well. Indomethacin or histamine alone had no effect on either the duodenum or the stomach. The lesions in the duodenum and antrum were inhibited by oral cimetidine (3-100 mg/kg) and 16,16-dimethyl prostaglandin E2 (dmPGE2) (3-30 micrograms/kg) in a dose-related manner, whereas those in the corpus were inhibited only by cimetidine. Indomethacin alone had no effect on gastric acid secretion, but did potentiate the increase of acid secretion caused by histamine. Histamine did not affect duodenal HCO3-secretion, whereas indomethacin slightly inhibited the basal HCO3-secretion and completely blocked the acid-stimulated HCO3-secretion. Intraduodenally administered cimetidine (30 mg/kg) or dmPGE2 (30 micrograms/kg) significantly inhibited acid secretion or increased HCO3-secretion, respectively, and both reduced the amount of acid emptied into the duodenum after treatment with indomethacin plus histamine. These results indicate that the development of duodenal lesions induced by indomethacin plus histamine in rats is due to both an increase in gastric acid secretion and an impairment of acid-induced duodenal HCO3-secretion. This newly established model will be useful for studying the pathogenesis of duodenal ulcers and for screening antiulcer agents.