Aleksandra Szlachcic

Nitric oxide in pancreatic secretion and hormone-induced pancreatitis in rats.

SummaryThe aim of the present study was to determine the role of endogenous nitric oxide (NO) in pancreatic secretion in vivo and amylase release from pancreatic acini in vitro and in caerulein-induced acute pancreatitis in rats. Blockade of NO synthase byNG-nitro-L-arginine (L-NNA) (2.5 mg/kg iv) significantly reduced basal pancreatic protein secretion and that induced by the infusion of CCK (0.5 μg/kg-h), feeding, and the diversion of pancreatic juice in rats with pancreatic fistula. This inhibitory effect was partially reversed when L-arginine (50 mg/kg-h iv) was added to L-NNA. L-Arginine alone (50 mg/kg iv) did not affect basal or caerulein-induced pancreatic secretion. L-NNA, L-arginine, or their combination added in various concentrations to the incubation medium of dispersed acini failed to affect basal or secretagogue (caerulein or urecholine) stimulated amylase release. Infusion of caerulein (5 μg/kg-h) for 5 h produced histological changes of acute edematous pancreatitis accompanied by a marked increase in pancreatic protein content and about 50% reduction in tissue blood flow. L-NNA alone also reduced the pancreatic blood flow and caused a significant increase in pancreatic weight and protein content. L-NNA significantly potentiated the inflammatory changes in the pancreas caused by caerulein. Addition of L-arginine enhanced the pancreatic blood flow and ameliorated the pancreatitis induced by caerulein alone or that combined with L-NNA. We conclude that NO is involved in the stimulation of pancreatic secretion in vivo and exhibits a beneficial effect on pancreatitis, probably by improving the pancreatic blood flow.

Nitric oxide in gastroprotection by aluminium-containing antacids

Pretreatment with aluminium-containing antacids at their original pH or after acidification is known to protect the gastric mucosa against the damaging action of strong irritants and this protection is accompanied by an increase in gastric blood flow (GBF) but the mechanisms underlying these effects have not been elucidated. We investigated the role of endogenous nitric oxide (NO) and prostaglandins (PS) in the prevention of ethanol-induced gastric damage and the alteration of GBF by Maalox and its active component Al(OH)3. Maalox and Al(OH)3 at their original and acidic pH induced dose-dependent gastroprotection accompanied by attenuation of the reduction in GBF caused by 100% ethanol; similar protective and hyperemic effects were recorded after treatment with nocloprost, a locally active PGE2 analog, and nitroglycerin, a donor of NO. Pretreatment with indomethacin that suppressed mucosal PGE2 by about 90%, failed to affect the protective influence of Maalox or Al(OH)3 at their original or acidic pH. On the contrary, pretreatment with NG-nitro-L-arginine (L-NNA), a potent selective inhibitor of NO synthase, reversed the gastroprotective and hyperemic effects of Maalox or Al(OH)3 at original and acidic pH and this reversal was significantly antagonized by L-arginine but not D-arginine. The gastroprotective and hyperemic effects of nocloprost were not influenced by the pretreatment with L-NNA. We conclude that aluminium-containing antacids activate the NO system, which may contribute to the gastroprotective activity of these drugs through an increase in mucosal microcirculation.

Involvement of Orexigenic Peptides in the Mechanism of Gastric Mucosal Integrity and Healing of Chronic Gastric Ulcers

Orexigenic peptides are group of endocrine hormones exerting a pleiotropic influence on many physiological functions including regulation of the feeding behaviour and energy expenditure, release of growth hormone (GH) and inotropic effects on the heart. Some of these peptides such as ghrelin, originally identified in the gastric mucosa, has been involved not only in control of food intake and growth hormone release but also exerts the immunomodulatory and anti-inflammatory properties. This review summarizes the recent attempts to prove the concept that orexigenic peptides such as ghrelin, orexin-A and obestatin besides playing an important role in the mechanism of food intake, exhibit a potent gastroprotective action against the formation of acute gastric mucosal injury induced by various ulcerogens. This protective effect depends upon vagal activity and hyperemia mediated by NOS/NO and COX/PG systems and CGRP released from sensory afferent nerves. In addition, the appetite peptides such as ghrelin and orexin-A are implicated in the mechanism of the healing of preexisting gastric ulcers due to an activation of specific GHS-R1a and OX-R1 receptors and PG/COX system.

Polyamines and epidermal growth factor in the recovery of gastric mucosa from stress-induced gastric lesions.

Polyamines such as spermine or putrescine, resulting from increased activity of ornithine decarboxylase (ODC), are known for gastroprotective and mucosal growth-promoting effects. EGF exhibits similar effects, but little is known about the involvement of polyamines in acceleration of the healing of stress-induced gastric lesions by epidermal growth factor (EGF). In this study, rats with intact or suppressed ODC activity by alpha-difluoromethy-ornithine (DFMO, 400 mg/kg i.p.) were subjected to 3.5 h of water immersion and restraint stress (WRS) without or with addition of spermine or EGF. At 0, 2, 6, 12, or 24 h after stress, rats were sacrificed. The number of gastric lesions was determined and gastric blood flow (GBF) was recorded by the H2 gas clearance technique. Stress produced gastric lesions (mean number 18+/-2 per stomach) and decreased GBF (by approximately 43%), but at 2, 6, 12, and 24 h after stress, these lesions and the decrease in GBF were gradually attenuated. Pretreatment with DFMO or removal of an endogenous source of EGF by salivectomy resulted in a marked decrease in mucosal DNA synthesis and significantly delayed the healing of stress lesions. EGF or spermine significantly accelerated ulcer healing and increased the GBF in rats with intact or removed salivary glands. DFMO significantly reduced the enhancement of healing and the increase in GBF induced by EGF, but failed to influence those induced by exogenous spermine. We conclude that polyamines play an important role in mucosal recovery from stress lesions due to acceleration of mucosal repair and increase in gastric microcirculation and that increased ODC activity and resulting excessive polyamine release appear to act as primary mediators of EGF-induced acceleration of the healing of stress lesions.

Lipoxins, The Novel Mediators of Gastroprotection and Gastric Adaptation to Ulcerogenic action of Aspirin

Previous studies revealed that prostaglandins contribute to the mechanism of maintenance of gastrointestinal integrity and mediate various physiological aspects of mucosal defense. The suppression of prostaglandin synthesis in the stomach is a critical event in terms of the development of mucosal injury after administration of various NSAID including aspirin (ASA). A worldwide use of ASA is now accepted due to its remarkable analgesic, antipyretic and anti-thrombotic prophylactics against myocardial infarct and coronary disorders despite the fact that the use of NSAIDs is associated with the risk of gastrointestinal bleedings, haemorrhagic lesions and ulcerations. It has become clear that other mediators besides prostaglandins can similarly act to protect the gastrointestinal mucosa of experimental animals and humans from injury induced by ASA. For instance, nitric oxide (NO) released from vascular epithelium, epithelial cells of gastrointestinal tract and sensory nerves can influence many of the same components of mucosal defense as do prostaglandins. This review was designed to provide an updated overview based on the experimental and clinical evidence on the involvement COX-2 derived products, lipoxins in the mechanism of gastric defense, gastroprotection and gastric adaptation to ASA. Lipoxins were recently considered as another group of lipid mediators that can protect the stomach similarly as NO-donors known to exert protective influence on the stomach from the injury under condition where the mucosal prostaglandin levels are suppressed. The new class of NO-releasing NSAIDs, including NO-aspirin or NO-naproxen, represent a very promising approach to reducing the toxicity of their parent NSAIDs. Aspirin-triggered lipoxin (ATL) synthesis, via COX-2, acts to reduce the severity of damage induced by this NSAID. Lipoxin analogues may prove to be useful for preventing mucosal injury and for modulating mucosal inflammation. Evidence presented in this review documents that ATL also play in important role in gastric adaptation during chronic ASA administration. Suppression of COX-2 activity by selective COX-2 inhibitors such as rofecoxib or celecoxib was shown to abolish the production of ATL and to diminish the gastric tolerability of ASA and gastric adaptation developed in response to repetitive administration of this NSAID. Synthetic analogues of lipoxins as well as newer class of NSAIDs releasing NO may be used in the future as the therapeutic approach to counteract adverse effects in the stomach associated with NSAIDs ingestion.

Implications of nitric oxide in the action of cytoprotective drugs on gastric mucosa

Cytoprotective drugs, including sucralfate, colloidal bismuth (De-Nol), aluminium-containing antacids (Maalox), carbenoxolone-like agents (sofalcone), and stable PGE2 analogues (nocloprost), are known to prevent acute gastric mucosal damage induced by topical irritants. This effect is usually accompanied by an elevation in mucosal blood flow. Recently, nitric oxide (NO), a potent vasorelaxant, has been implicated in gastroprotection by carbenoxolone, the prototype of cytoprotective drugs. In this study we assessed the involvement of NO in acute gastric damage induced by ethanol and in the prevention of this damage by sucralfate, Maalox, De-Nol, sofalcone, and nocloprost. Each of these drugs dose-dependently reduced the formation of ethanol-induced gastric lesions. The optimal gastroprotective dose was used in further studies to check the possible contribution of NO in this protection. Pretreatment with NG-nitro-L-arginine (L-NNA) (12.5-50 mg/kg i.v.), an inhibitor of NO synthase, dose-dependently enhanced the mucosal damage by ethanol itself and reduced the protective effects of sucralfate and Maalox but not those of sofalcone, De-Nol or nocloprost against the ethanol injury. Reduction by L-NNA of the mucosa-protective action of sucralfate or Maalox was accompanied by a decrease in gastric blood flow, which was antagonized by L-arginine (a substrate of NO synthase) but not by D-arginine. This study suggest that gastroprotective agents such sucralfate and Maalox, but not sofalcone or De-Nol, activate the NO system that may contribute to mucosal integrity and preservation of mucosal microcirculation.

Plasma amino acid consumption and pancreatic secretion during and after cerulein-induced pancreatitis in rats

SummaryThe decrease in pancreatic exocrine secretion during the course of acute pancreatitis is a well-documented process. However, the mechanisms underlying this reduced pancreatic function are not fully understood. To analyze pancreatic protein synthesis and secretion during and after cerulein-induced pancreatitis, we performed the plasma amino acid consumption test on conscious rats. After stimulation with 1 μg cerulein/kg/h sc for 1 h, the control group with intact pancreas exhibited a decrease in plasma amino acid by about 15%, and this decrease could be abolished by the administration of the specific CCK-receptor antagonist, loxiglumide. Protein and amylase secretion were augmented by cerulein to about 400% of control values. Upon supramaximal stimulation of the pancreas with cerulein (20 μg/kg/h sc for 5 h), we observed a profound decrease of pancreatic secretion, which was accompanied by a more prolonged and more pronounced decrease of plasma amino acids (25%). Two hours after cessation of the supramaximal stimulation of pancreatic secretion (to induce pancreatitis), the administration of 1 μg/kg/h of cerulein for 1 h resulted in a further decrease of amino plasma acid level, whereas no stimulation of exocrine pancreatic secretion was observed. Eighteen hours later, repeated administration of 1 μg/kg/h of cerulein was still able to induce amino acid decrease by 20%, but again, no stimulation of exocrine pancreatic secretion was detectable. We conclude that, in the time course of acute cerulein-induced hyperstimulation, there might be an imbalance between synthesis of pancreatic enzymes (reflected by amino acid consumption) and the release of exocrine pancreatic secretion into the duodenum, which may be explained by leakage of proteolytic enzymes from damaged acinar cells into the extracellular space of the pancreas.

Melatonin in Prevention of the Sequence from Reflux Esophagitis to Barrett’s Esophagus and Esophageal Adenocarcinoma: Experimental and Clinical Perspectives

Melatonin is a tryptophan-derived molecule with pleiotropic activities which is produced in all living organisms. This “sleep” hormone is a free radical scavenger, which activates several anti-oxidative enzymes and mechanisms. Melatonin, a highly lipophilic hormone, can reach body target cells rapidly, acting as the circadian signal to alter numerous physiological functions in the body. This indoleamine can protect the organs against a variety of damaging agents via multiple signaling. This review focused on the role played by melatonin in the mechanism of esophagoprotection, starting with its short-term protection against acute reflux esophagitis and then investigating the long-term prevention of chronic inflammation that leads to gastroesophageal reflux disease (GERD) and Barrett’s esophagus. Since both of these condition are also identified as major risk factors for esophageal carcinoma, we provide some experimental and clinical evidence that supplementation therapy with melatonin could be useful in esophageal injury by protecting various animal models and patients with GERD from erosions, Barrett’s esophagus and neoplasia. The physiological aspects of the synthesis and release of this indoleamine in the gut, including its release into portal circulation and liver uptake is examined. The beneficial influence of melatonin in preventing esophageal injury from acid-pepsin and acid-pepsin-bile exposure in animals as well as the usefulness of melatonin and its precursor, L-tryptophan in prophylactic and supplementary therapy against esophageal disorders in humans, are also discussed.

Involvement of Renin-Angiotensin System and Vasoactive Angiotensin-(1–7) Metabolite of Angiotensin II in Gastric Mucosal Injury and Gastroprotection

The renin-angiotensin system (RAS) plays an important role in the maintenance of blood pressure, cardiovascular functions, body fluids homeostasis and kidney reabsorption process but little is known w

Nesfatin-1: a new hormone in the control of food intake and the mechanism of damage and protection of gastric mucosa

Nesfatyna 1 jest 82-aminokwasowym peptydem powstałym w wyniku potranslacyjnej hydrolizy N-końcowego fragmentu innego białka nucleobindin2 (NUCB2), będącego prekursorem dla nesfatyny 1 o rozpoznanej i ustalonej sekwencji aminokwasów, występującej powszechnie wśród ssaków. Interesujący jest fakt, że genową ekspresję peptydowego układu NUCB2/nesfatyna 1 zaobserwowano w przewodzie pokarmowym gryzoni, zwłaszcza w błonie śluzowej szczurzego żołądka, szczególnie w bliskiej lokalizacji komórek neuroendokrynnych części trzonowej odpowiedzialnych m.in. za uwalnianie greliny. Pierwotnie wykryto, że NUCB2 i nesfatyna 1 podawane do komór bocznych mózgu hamują przyjmowanie pokarmu w fazie nocnej u szczurów i że efekt ten jest połączony ze zmniejszeniem masy ciała tych zwierząt, co sugeruje, że nesfatyna 1 jest peptydem anoreksygenicznym, hamującym apetyt. Dalsze badania nad fizjologicznym znaczeniem nesfatyny 1 dowodzą, że podobnie jak w przypadku innych hormonów pobudzających apetyt (np. grelina) czy hamujących apetyt (np. leptyna), peptyd ten odznacza się właściwościami gastroprotekcyjnymi i chroni błonę śluzową żołądka przed uszkodzeniami indukowanymi przez czynniki korozyjne oraz mikrokrwa wienia wywoływane przez stres. W ten gastroprotekcyjny mechanizm działania nesfatyny 1 zaangażowane są układy endogennych prostaglandyn (PG) uwalnianych na drodze aktywacji cyklooksygenaz (COX) – COX-1 i COX-2 – oraz tlenku azotu (NO) produkowanego przez enzymy syntaz NO, odpowiedzialne za wzrost żołądkowego przepływu krwi, któremu towarzyszy wzrost stężenia nesfatyny 1 w osoczu. Podsumowując – endogenne PG i NO są mediatorami gastroprotekcji i przekrwienia obserwowanego w błonie śluzowej żołądka Abstract