Effect of amylin in various experimental models of gastric ulcer

Research progress on the roles of dopamine and dopamine receptors in digestive system diseases

Dopamine (DA) is a neurotransmitter synthesized in the human body that acts on multiple organs throughout the body, reaching them through the blood circulation. Neurotransmitters are special molecules that act as messengers by binding to receptors at chemical synapses between neurons. As ligands, they mainly bind to corresponding receptors on central or peripheral tissue cells. Signalling through chemical synapses is involved in regulating the activities of various body systems. Lack of DA or a decrease in DA levels in the brain can lead to serious diseases such as Parkinson's disease, schizophrenia, addiction and attention deficit disorder. It is widely recognized that DA is closely related to neurological diseases. As research on the roles of brain-gut peptides in human physiology and pathology has deepened in recent years, the regulatory role of neurotransmitters in digestive system diseases has gradually attracted researchers' attention, and research on DA has expanded to the field of digestive system diseases. This review mainly elaborates on the research progress on the roles of DA and DRs related to digestive system diseases. Starting from the biochemical and pharmacological properties of DA and DRs, it discusses the therapeutic value of DA- and DR-related drugs for digestive system diseases.

Treatment Effects of Jinlingzi Powder and Its Extractive Components on Gastric Ulcer Induced by Acetic Acid in Rats

Jinlingzi powder comprises Melia toosendan Sieb. et Zucc. and Corydalis yanhusuo (Y.H. Chou & Chun C.Hsu) W.T. Wang ex Z.Y. Su & C.Y. Wu and is usually applied in clinic as traditional Chinese medicine for pain. The present study aims to investigate the therapeutic actions of Jinlingzi powder and its extracted components and theirs treatment mechanism on the acetic acid induced-gastric ulcer in rats. The gastric ulcer model was induced by the administration of acetic acid in rats (84 male). Jinlingzi powder water decoction, its polysaccharide, and nonalkaloid and alkaloid components were used to investigate the therapeutic actions on the acetic acid induced-gastric ulcer by measuring the related pharmacy and pharmacodynamic factors, including ulcer index, ulcer area, ulcer healing rate, interleukin-8 (IL-8), tumor necrosis factor-α (TNF-α), neurotensin (NT), platelet activating factor (PAF), thromboxane B2 (TXB2), and vascular endothelial growth factor (VEGF) in rat serum, acetylcholinesterase (AChE) in brain tissue, prostaglandin E2 (PGE2), and basic fibroblast growth factor (bFGF) in gastric tissue. Among the various groups, Jinlingzi powder and the nonalkaloid components caused significant changes in IL-8, TNF-α, NT, PAF TXB2, and VEGF values in the serum. The AChE content in the rats' brain tissue was also reduced after using Jinlingzi powder and the nonalkaloid components. Additionally, Jinlingzi powder and the nonalkaloid components considerably affect the amount of PGE2 and bFGF in a rat's stomach tissue. Therefore, Jinlingzi powder and the nonalkaloid components can effectively inhibit neutral neutrophil activation, prevent capillaries thrombosis, and protect gastric mucosa. Thus, the nonalkaloid components of the Jinlingzi powder play a key role in the treatment of gastric ulcer.

Amylin prevents TRAIL-mediated apoptotic effects of reserpine in the rat gastric mucosa

We have previously shown that amylin has a protective effect upon the damaged rat gastric mucosa via a cytokine-mediated mechanism. Here, the effects of amylin on the proapoptotic cytokine TNF-related-apoptosis-inducing-ligand (TRAIL) were tested in the rat gastric mucosa damaged by reserpine administration in vivo. Intraperitoneal administration of reserpine in adult male Sprague-Dawley rats resulted in increased TRAIL expression in the gastric mucosa. Immunohistochemistry showed that the TRAIL death-receptor 5 (DR5) was constitutively expressed by the mucosa cells. Western blot showed that pretreatment of reserpine-treated rats with amylin was associated with attenuated expression of TRAIL. In the same samples, we also investigated about TRAIL-related signaling and observed that activation of caspases-8 and -3 occurs in parallel to increased TRAIL expression in rats treated with reserpine. Similarly to the latter, activation of caspases was attenuated in rats pretreated with amylin. Treatment with reserpine was associated with increased expression of the proapoptotic protein Bax, whereas that of the antiapoptotic protein Bcl-2 was significantly decreased. Amylin prevented the effects of reserpine on these genes. Reserpine sets into motion mechanisms of apoptosis in the rat gastric mucosa, which appear mediated, at least in part, by TRAIL. In addition, TRAIL downstream signaling is activated along with subversion of gene expression related to apoptosis. Amylin was able to prevent detrimental effects of reserpine. Finally, amylin and related molecules may be envisioned as protective agent in gastric mucosa damage.

Capsaicin and gastric ulcers

In recent years, infection of the stomach with the organism Helicobacter Pylori has been found to be the main cause of gastric ulcers, one of the common ailments afflicting humans. Excessive acid secretion in the stomach, reduction in gastric mucosal blood flow, constant intake of non-steroid anti-inflammatory drugs (NSAIDS), ethanol, smoking, stress etc. are also considered responsible for ulcer formation. The prevalent notion among sections of population in this country and perhaps in others is that "red pepper" popularly known as "Chilli," a common spice consumed in excessive amounts leads to "gastric ulcers" in view of its irritant and likely acid secreting nature. Persons with ulcers are advised either to limit or avoid its use. However, investigations carried out in recent years have revealed that chilli or its active principle "capsaicin" is not the cause for ulcer formation but a "benefactor." Capsaicin does not stimulate but inhibits acid secretion, stimulates alkali, mucus secretions and particularly gastric mucosal blood flow which help in prevention and healing of ulcers. Capsaicin acts by stimulating afferent neurons in the stomach and signals for protection against injury causing agents. Epidemiologic surveys in Singapore have shown that gastric ulcers are three times more common in the "Chinese" than among Malaysians and Indians who are in the habit of consuming more chillis. Ulcers are common among people who are in the habit of taking NSAIDS and are infected with the organism "Helicobacter Pylori," responsible for excessive acid secretion and erosion of the mucosal layer. Eradication of the bacteria by antibiotic treatment and avoiding the NSAIDS eliminates ulcers and restores normal acid secretion.

Effects on digestive secretions

Rat amylin subcutaneously injected into rats dose-dependently inhibits pentagastrin-stimulated gastric acid secretion and protects the stomach from ethanol-induced gastritis. The ED50s for these actions (0.050 and 0.036 microg, respectively) are the lowest for any dose-dependent effect of amylin thus far described, and their similar potencies are consistent with a mechanistic (causal) association. At higher amylin doses, inhibition of gastric acid secretion was almost complete (93.4%). Gastric injury (measured by a subjective analog scale) was inhibited by up to 67%. The observation that effective doses of amylin result in plasma concentrations of 7-10 pM (i.e., within the reported range; Pieber et al., 1994) supports the interpretation that inhibition of gastric acid secretion and maintenance of gastric mucosal integrity are physiological actions of endogenous amylin. The pharmacology of these responses fits with one mediated via amylin-like receptors. Rat amylin inhibited CCK-stimulated secretion of pancreatic enzymes,amylase, and lipase by up to approximately 60% without having significant effect in the absence of CCK. ED50s for the effect were in the 0.1-0.2 microg range, calculated to produce plasma amylin excursions within the physiological range. Effects of informative ligands are consistent with the concept of amylin receptor mediation. Amylin was effective in ameliorating the severity of pancreatitis in a rodent model. The amylin analog pramlintide inhibited gallbladder emptying in mice as measured by total weight of acutely excised gallbladders. Amylin inhibition of gastric acid secretion, pancreatic enzyme secretion, and bile secretion likely represents part of an orchestrated control of nutrient appearance. Modulation of digestive function fits with a general role of amylin in regulating nutrient uptake. Rate of ingestion, rate of release from the stomach, and rate of digestion of various food groups appear to be under coordinate control.

Antiulcer effects of amylin: a review

Amylin belongs to the calcitonin peptide family. Amylin is a peptide synthesized not only in the beta cells of pancreatic islets, but in small quantities also in other organs like in the intestinal and gastric mucosa, lungs and central nervous system. It is located in the same secretory granules as insulin. Amylin participates in the maintenance of glucose and calcium homeostasis. It also inhibits food intake and decreases body weight. Furthermore, amylin inhibits gastric acid secretion. It protects the gastric mucosa in ulcer models like stress, vagal stimulation, ethanol, acetic acid, reserpine and serotonine administration and pylorus ligation. This protective antiulcer is seen not only at pharmacological but also at near-physiological doses-0.5mkg/kg. Moreover amylin also exerts curative properties in the acetic acid and indomethacin ulcer models. Amylin decreases the aggressive factors like acid-pepsin secretion, increases mast cell stability and increases protective mechanisms like bicarbonate gastric secretion, dilates blood vessels, and it increases lymphatic mesenteric activity. Amylin seems to be a powerful protector of gastric mucosa in animals by increasing the stability of gastric mucosa. Further research remains, however, to be done.

Pharmacological effects of fermented red pepper

The pharmacological effects were investigated of fermented red pepper (HF-S), which consisted of 14.7% carbohydrate, 1.5% lipid, 4.9% protein, 0.3% ash, 78.2% moisture content, with 0.15% capsaicin and 0.06% dihydrocapsaicin. Oral administration of 0.25 mL HF-S for 3 weeks produced significant changes of the perirenal fat pad weight compared with the HF-control group, suggesting a suppressive effect on lipid accumulation and a significant decrease in the risk of arteriosclerosis. The HF-S (0.25 mL) group also showed a lower plasma TG, TC level and atherogenic index than that of the HF-control. In addition, the HF-S (0.25 mL) group showed a marked increase in the production of glutathione, which is the major endogenous antioxidant, and a decrease in the production of lipid peroxide as the product of chemical damage by oxygen free radicals. It is assumed that the effect of HF-S might relate to high glutathione production on the suppression of lipid peroxidation. HF-S stimulated not only the proliferation of macrophages (as high as the positive control, LPS at 1000 microg/mL) but also mitogenic activity (1.2-fold of LPS at 100 microg/mL).

Regulation of amylin release from cultured rabbit gastric fundic mucosal cells

Background

Amylin (islet amyloid polypeptide) is a hormone with suggested roles in the regulation of glucose homeostasis, gastric motor and secretory function and gastroprotection. In the gastric mucosa amylin is found co-localised with somatostatin in D-cells. The factors regulating gastric amylin release are unknown. In this study we have investigated the regulation of amylin release from gastric mucosal cells in primary culture. Rabbit fundic mucosal cells enriched for D-cells by counterflow elutriation were cultured for 40 hours. Amylin and somatostatin release over 2 hours in response to agonists were assessed.

Results

Amylin release was significantly enhanced by activation of protein kinase C with phorbol-12-myristate-13-acetate, adenylate cyclase with forskolin and elevation of intracellular calcium with A23187. Cholecystokinin (CCK), epinephrine and glucagon-like peptide-1 (GLP-1) each stimulated amylin release in a dose-dependent manner. Maximal CCK-stimulated release was greater than either epinephrine or GLP-1, even when the effects of the latter two were enhanced by isobutylmethylxanthine. Stimulated amylin release was significantly inhibited by carbachol (by 51–59%) and octreotide (by 33–42%). Somatostatin release paralleled that of amylin.

Conclusions

The cultured D-cell model provides a means of studying amylin release. Amylin secretion is stimulated by receptor-dependent and -independent activation of Ca²⁺/protein kinase C and adenylate cyclase pathways. Inhibition involves activation of muscarinic receptors and auto-regulation by somatostatin.

The role of sensory neurons in the antiulcer effect of centrally injected amylin in rat

Central administration of amylin (2.2 microg/rat, i.c.v.) reduces (from a minimum of 67% to 83%) indomethacin (Indo, 20 mg Kg(-1), orally) induced ulcers in rats. The anti-ulcer effect of the peptide is not removed by the administration of prokinetic drugs like domperidone or neostigmine but it is reduced by 35% in rats treated with capsaicin or with the CGRP antagonist, CGRP(8-37). These data indicate that amylin gastroprotection involves capsaicin-sensitive nerve fiber leading to CGRP-dependent gastric vasodilatory effect. Additional mechanisms could involve noradrenergic alpha(2) receptors as the peptide gastroprotective activity is reduced from 67% to 20% by the alpha(2) antagonist yohimbine.

Gastroprotections of escins Ia, Ib, IIa, and IIb on ethanol-induced gastric mucosal lesions in rats

Effects of escins Ia, Ib, IIa, and IIb isolated from horse chestnuts on ethanol-induced gastric mucosal lesions and the roles of capsaicin-sensitive afferent neurons, endogenous nitric oxide (NO), sulfhydryls, prostaglandins, as well as gastric secretion and the sympathetic nervous system, were investigated in rats. Test samples were given orally to fasted rats 1 h before ethanol (1.5 ml/rat, p.o.) treatment or ligation of the pylorus. Escins Ia-IIb (10-50 mg/kg) potently inhibited ethanol-induced gastric mucosal lesions, whereas desacylescins I and II (50 mg/kg) showed no such effect. These active saponins (10 and 20 mg/kg) did not decrease the gastric secretion. The gastroprotections of escins Ia-IIb were attenuated by the pretreatment with capsaicin, N(G)-nitro-L-arginine methyl ester, and indomethacin, but not by N-ethylmaleimide. The effects of escins Ia-IIb were also attenuated in streptozotocin-induced diabetic rats, in which the activity of the sympathetic nervous system was abnormal. These results suggest that the gastroprotections of escins Ia-IIb on ethanol-induced gastric mucosal lesions are acid-independent, whereas endogenous prostaglandins, NO, capsaicin-sensitive afferent neurons, and the sympathetic nervous system participate.

Investigation on the mechanisms involved in the central protective effect of amylin on gastric ulcers in rats

1. The mechanisms involved in the protective effect of amylin (administered into the brain ventricle, i.c.v.) on gastric ulcers induced by the oral administration of ethanol 50% (EtOH, 2 ml/rat) or indomethacin (indomethacin, 20 mg kg(-1), at a dosing volume of 5 ml) were investigated in rats. 2. The possible involvement of endogenous nitric oxide (NO) in the beneficial effect of amylin against EtOH-induced ulcers was examined. The inhibitor of NO-synthesis, NG-nitro-L-arginine methyl ester (L-NAME, 70 mg kg(-1), s.c.) was injected 30 min before amylin (2.2 microg/rat, i.c.v.) followed by EtOH after a further 30 min. Rats were sacrificed 1 h after EtOH. L-NAME completely removed the protective effect of amylin. 3. The interaction between amylin and gastric nonprotein sulfhydryl groups was studied. The rats were treated with N-ethyl-maleimide (NEM, 25 mg kg(-1), s.c.) 30 min before amylin (2.2 microg/rat, i.c.v.) followed by EtOH 30 min after or by indomethacin 5 min after amylin. Rats were sacrificed 1 h or 6 h respectively after EtOH or indomethacin. NEM counteracted the protective effect of amylin against EtOH-induced ulcers but not against those provoked by indomethacin. 4. To determine whether amylin was able to promote ulcer healing, the peptide was injected 5 min after EtOH or 1 h after indomethacin. In the case of EtOH, the beneficial effect of amylin was lost whereas it was still effective on indomethacin-induced ulcers. 5. The results indicate that: the mechanisms involved in the antiulcer effects of amylin are different in these two types of gastric lesions probably because of the different etiopathology of various types of ulcers. Endogenous NO and nonprotein sulfhydryl groups are involved in the mucosal protective effects of amylin on EtOH and not on indomethacin-induced ulcers. Furthermore the effectiveness of amylin against indomethacin-induced lesions when administered after the ulcerogenic process has started suggests that amylin is involved not only in the protection but also in the healing mechanisms in this type of ulcer.