The selective cyclooxygenase-2 inhibitor parecoxib markedly improves the ability of the duodenum to regulate luminal hypertonicity in anaesthetized rats

Hypotonicity-Induced Increase in Duodenal Mucosal Permeability Is Regulated by Cholinergic Receptors in Rats

BACKGROUND

The role of cholinergic receptors in the regulation of duodenal mucosal permeability in vivo is currently not fully described.

AIMS

To elucidate the impact of nicotinic and muscarinic acetylcholine receptor signaling in response to luminal hypotonicity (50 mM NaCl) in the proximal small intestine of rat.

METHODS

The effect on duodenal blood-to-lumen clearance of ⁵¹Cr-EDTA (i.e., mucosal permeability) and motility was studied in the absence and presence of nicotinic and muscarinic receptor agonists and antagonists, a sodium channel blocker (tetrodotoxin), and after bilateral cervical vagotomy.

RESULTS

Rats with duodenal contractions responded to luminal hypotonicity by substantial increase in intestinal permeability. This response was absent in animals given a non-selective nicotinic receptor antagonist (mecamylamine) or agonist (epibatidine). Pretreatment with tetrodotoxin reduced the increase in mucosal permeability in response to luminal hypotonicity. Further, the non-selective muscarinic receptor antagonist (atropine) and agonist (bethanechol) reduced the hypotonicity-induced increase in mucosal permeability, while vagotomy was without an effect, suggesting that local enteric reflexes dominate. Finally, neither stimulating nor blocking the α7-nicotinic receptor had any significant effects on duodenal permeability in response to luminal hypotonicity, suggesting that this receptor is not involved in regulation of duodenal permeability. The effect of the different drugs on mucosal permeability was similar to the effect observed for duodenal motility.

CONCLUSIONS

A complex enteric intramural excitatory neural reflex involving both nicotinic and muscarinic receptor subtypes mediates an increase in mucosal permeability induced by luminal hypotonicity.

Effects of α2-adrenoceptor stimulation on luminal alkalinisation and net fluid flux in rat duodenum

The sympathetic nervous system is highly involved in the regulation of gastrointestinal functions such as luminal alkalinisation and fluid absorption. However, the exact mechanisms are not clear. This study aimed to delineate how α₂-adrenergic receptor stimulation reduces duodenal luminal alkalinisation and induces net fluid absorption. This was tested by perfusing the duodenum of anesthetized rats with isotonic solutions devoid of Cl^- and/or Na⁺, in the absence and presence of the α₂-adrenoceptor agonist clonidine. The clonidine was also studied in rats treated with dimethylamiloride (a Na⁺/H⁺ exchange inhibitor), vasoactive intestinal peptide, and the nicotinic receptor antagonist hexamethonium. Clonidine reduced luminal alkalinisation and induced net fluid absorption. The Cl^--free solution decreased luminal alkalinisation and abolished net fluid absorption, but did not prevent clonidine from doing so. Both the Na⁺-free solution and luminal dimethylamiloride increased luminal alkalinisation and abolished net fluid absorption, effects counteracted by clonidine. The NaCl-free solution (D-mannitol) did not affect luminal alkalinisation, but reduced net fluid absorption. Clonidine reduced luminal alkalinisation and induced net fluid absorption in rats perfused luminally with mannitol. However, clonidine did not affect the vasoactive intestinal peptide-induced increase in luminal alkalinisation or fluid secretion. Pre-treatment with hexamethonium abolished the effects of clonidine on luminal alkalinisation and net fluid flux. In summary, our in vivo experiments showed that clonidine-induced reduction in luminal alkalinisation and induction of net fluid absorption was unrelated to luminal Na⁺ and Cl^-, or to apical Na⁺/H⁺ or Cl^-/HCO₃^- exchangers. Instead, clonidine seems to exert its effects via suppression of nicotinic receptor-activated acetylcholine secretomotor neurons.

Protective Effects of Melatonin and Misoprostol against Experimentally Induced Increases in Intestinal Permeability in Rats

Intestinal mucosal barrier dysfunction caused by disease and/or chemotherapy lacks an effective treatment, which highlights a strong medical need. Our group has previously demonstrated the potential of melatonin and misoprostol to treat increases in intestinal mucosal permeability induced by 15-min luminal exposure to a surfactant, sodium dodecyl sulfate (SDS). However, it is not known which luminal melatonin and misoprostol concentrations are effective, and whether they are effective for a longer SDS exposure time. The objective of this single-pass intestinal perfusion study in rats was to investigate the concentration-dependent effect of melatonin and misoprostol on an increase in intestinal permeability induced by 60-min luminal SDS exposure. The cytoprotective effect was investigated by evaluating the intestinal clearance of ⁵¹Cr-labeled EDTA in response to luminal SDS as well as a histological evaluation of the exposed tissue. Melatonin at both 10 and 100 µM reduced SDS-induced increase in permeability by 50%. Misoprostol at 1 and 10 µM reduced the permeability by 50 and 75%, respectively. Combination of the two drugs at their respective highest concentrations had no additive protective effect. These in vivo results support further investigations of melatonin and misoprostol for oral treatments of a dysfunctional intestinal barrier.

The Impact of α-Adrenoceptors in the Regulation of the Hypotonicity-Induced Increase in Duodenal Mucosal Permeability In Vivo

The duodenal mucosa is regularly exposed to a low osmolality, and recent experiments suggest that hypotonicity increases mucosal permeability in an osmolality-dependent manner. The aim was to examine whether the sympathetic nervous system, via action on α-adrenoceptors, affects the hypotonicity-induced increase in duodenal mucosal permeability. The duodenum of anaesthetised rats was perfused in vivo with a 50 mM NaCl solution in the presence of adrenergic α-adrenoceptor drugs. Studied were the effects on mucosal permeability (blood-to-lumen clearance of ⁵¹Cr-EDTA), arterial blood pressure, luminal alkalinisation, transepithelial fluid flux, and motility. Hypotonicity induced a six-fold increase in mucosal permeability, a response that was reversible and repeatable. The α₂-adrenoceptor agonist clonidine abolished the hypotonicity-induced increase in mucosal permeability, reduced arterial blood pressure, inhibited duodenal motility, and decreased luminal alkalinisation. The α₂-adrenoceptor antagonists, yohimbine and idazoxan, prevented the inhibitory effect of clonidine on the hypotonicity-induced increase in mucosal permeability. The α₁-agonist phenylephrine or the α₁-antagonist prazosin elicited their predicted effect on blood pressure but did not affect the hypotonicity-induced increase in mucosal permeability. None of the α₁- or α₂-adrenoceptor drugs changed the hypotonicity-induced net fluid absorption. In conclusion, stimulation of the adrenergic α₂-adrenoceptor prevents the hypotonicity-induced increase in mucosal permeability, suggesting that the sympathetic nervous system has the capability to regulate duodenal mucosal permeability.

Melatonin-Activated Receptor Signaling Pathways Mediate Protective Effects on Surfactant-Induced Increase in Jejunal Mucosal Permeability in Rats

A well-functional intestinal mucosal barrier can be compromised as a result of various diseases, chemotherapy, radiation, and chemical exposures including surfactants. Currently, there are no approved drugs targeting a dysfunctional intestinal barrier, which emphasizes a significant medical need. One candidate drug reported to regulate intestinal mucosal permeability is melatonin. However, it is still unclear if its effect is primarily receptor mediated or antioxidative, and if it is associated with enteric neural pathways. The aim of this rat intestinal perfusion study was to investigate the mechanisms of melatonin and nicotinic acetylcholine receptors on the increase in intestinal mucosal clearance of 51Cr-labeled ethylenediaminetetraacetate induced by 15 min luminal exposure to the anionic surfactant, sodium dodecyl sulfate. Our results show that melatonin abolished the surfactant-induced increase in intestinal permeability and that this effect was inhibited by luzindole, a melatonin receptor antagonist. In addition, mecamylamine, an antagonist of nicotinic acetylcholine receptors, reduced the surfactant-induced increase in mucosal permeability, using a signaling pathway not influenced by melatonin receptor activation. In conclusion, our results support melatonin as a potentially potent candidate for the oral treatment of a compromised intestinal mucosal barrier, and that its protective effect is primarily receptor-mediated.

Effect of paracellular permeation enhancers on intestinal permeability of two peptide drugs, enalaprilat and hexarelin, in rats

Transcellular permeation enhancers are known to increase the intestinal permeability of enalaprilat, a 349 Da peptide, but not hexarelin (887 Da). The primary aim of this paper was to investigate if paracellular permeability enhancers affected the intestinal permeation of the two peptides. This was investigated using the rat single-pass intestinal perfusion model with concomitant blood sampling. These luminal compositions included two paracellular permeation enhancers, chitosan (5 mg/mL) and ethylenediaminetetraacetate (EDTA, 1 and 5 mg/mL), as well as low luminal tonicity (100 mOsm) with or without lidocaine. Effects were evaluated by the change in lumen-to-blood permeability of hexarelin and enalaprilat, and the blood-to-lumen clearance of 51chromium-labeled EDTA (CLCr-EDTA), a clinical marker for mucosal barrier integrity. The two paracellular permeation enhancers increased the mucosal permeability of both peptide drugs to a similar extent. The data in this study suggests that the potential for paracellular permeability enhancers to increase intestinal absorption of hydrophilic peptides with low molecular mass is greater than for those with transcellular mechanism-of-action. Further, the mucosal blood-to-lumen flux of 51Cr-EDTA was increased by the two paracellular permeation enhancers and by luminal hypotonicity. In contrast, luminal hypotonicity did not affect the lumen-to-blood transport of enalaprilat and hexarelin. This suggests that hypotonicity affects paracellular solute transport primarily in the mucosal crypt region, as this area is protected from luminal contents by a constant water flow from the crypts.

Prevention of Rat Intestinal Injury with a Drug Combination of Melatonin and Misoprostol

A healthy intestinal barrier prevents uptake of allergens and toxins, whereas intestinal permeability increases following chemotherapy and in many gastrointestinal and systemic diseases and disorders. Currently, there are no approved drugs that target and repair the intestinal epithelial barrier while there is a medical need for such treatment in gastrointestinal and related conditions. The objective of this single-pass intestinal perfusion study in rats was to investigate the preventive cytoprotective effect of three mucosal protective drugs—melatonin, misoprostol, and teduglutide—with different mechanisms of action on an acute jejunal injury induced by exposing the intestine for 15 min to the anionic surfactant, sodium dodecyl sulfate (SDS). The effect was evaluated by monitoring intestinal clearance of ⁵¹Cr-labeled ethylenediaminetetraacetate and intestinal histology before, during, and after luminal exposure to SDS. Our results showed that separate pharmacological pretreatments with luminal misoprostol and melatonin reduced acute SDS-induced intestinal injury by 47% and 58%, respectively, while their use in combination abolished this injury. This data supports further development of drug combinations for oral treatments of conditions and disorders related to a dysregulated or compromised mucosal epithelial barrier.

Intestinal Permeability and Drug Absorption: Predictive Experimental, Computational and In Vivo Approaches

The main objective of this review is to discuss recent advancements in the overall investigation and in vivo prediction of drug absorption. The intestinal permeability of an orally administered drug (given the value P_eff) has been widely used to determine the rate and extent of the drug’s intestinal absorption (F_abs) in humans. Preclinical gastrointestinal (GI) absorption models are currently in demand for the pharmaceutical development of novel dosage forms and new drug products. However, there is a strong need to improve our understanding of the interplay between pharmaceutical, biopharmaceutical, biochemical, and physiological factors when predicting F_abs and bioavailability. Currently, our knowledge of GI secretion, GI motility, and regional intestinal permeability, in both healthy subjects and patients with GI diseases, is limited by the relative inaccessibility of some intestinal segments of the human GI tract. In particular, our understanding of the complex and highly dynamic physiology of the region from the mid-jejunum to the sigmoid colon could be significantly improved. One approach to the assessment of intestinal permeability is to use animal models that allow these intestinal regions to be investigated in detail and then to compare the results with those from simple human permeability models such as cell cultures. Investigation of intestinal drug permeation processes is a crucial biopharmaceutical step in the development of oral pharmaceutical products. The determination of the intestinal P_eff for a specific drug is dependent on the technique, model, and conditions applied, and is influenced by multiple interactions between the drug molecule and the biological membranes.

Evaluation of drug permeability calculation based on luminal disappearance and plasma appearance in the rat single-pass intestinal perfusion model

The rat single-pass intestinal perfusion (SPIP) model is commonly used to investigate gastrointestinal physiology and membrane drug transport. The SPIP model can be used with the intestinal segment inside or outside the abdomen. The rats can also be treated with parecoxib, a selective cycloxygenase-2 inhibitor that has been shown to affect some intestinal functions following abdominal surgery, such as motility, epithelial permeability, fluid flux and ion transport. However, the impact of extra-abdominal placement of the intestinal segment in combination with parecoxib on intestinal drug transport has not been investigated. There is also uncertainty how well intestinal permeability determinations based on luminal drug disappearance and plasma appearance correlate in the rat SPIP model. The main objective of this rat in vivo study was to investigate the effect of intra- vs. extra-abdominal SPIP, with and without, pretreatment with parecoxib. The effect was evaluated by determining the difference in blood-to-lumen ⁵¹Cr-EDTA clearance, lumen-to-blood permeability of a cassette-dose of four model compounds (atenolol, enalaprilat, ketoprofen, and metoprolol), and water flux. The second objective was to compare the jejunal permeability values of the model drugs when determined based on luminal disappearance or plasma appearance. The study showed that the placement of the perfused jejunal segment, or the treatment with parecoxib, had minimal effects on membrane permeability and water flux. It was also shown that intestinal permeability of low permeability compounds should be determined on the basis of data from plasma appearance rather than luminal disappearance. If permeability is calculated on the basis of luminal disappearance, it should preferably include negative values to increase the accuracy in the determinations.

Time-dependent effects on small intestinal transport by absorption-modifying excipients

The relevance of the rat single-pass intestinal perfusion model for investigating in vivo time-dependent effects of absorption-modifying excipients (AMEs) is not fully established. Therefore, the dynamic effect and recovery of the intestinal mucosa was evaluated based on the lumen-to-blood flux (J_abs) of six model compounds, and the blood-to-lumen clearance of ⁵¹Cr-EDTA (CL_Cr), during and after 15- and 60-min mucosal exposure of the AMEs, sodium dodecyl sulfate (SDS) and chitosan, in separate experiments. The contribution of enteric neurons on the effect of SDS and chitosan was also evaluated by luminal coadministration of the nicotinic receptor antagonist, mecamylamine. The increases in J_abs and CL_Cr (maximum and total) during the perfusion experiments were dependent on exposure time (15 and 60 min), and the concentration of SDS, but not chitosan. The increases in J_abs and CL_Cr following the 15-min intestinal exposure of both SDS and chitosan were greater than those reported from an in vivo rat intraintestinal bolus model. However, the effect in the bolus model could be predicted from the increase of J_abs at the end of the 15-min exposure period, where a six-fold increase in J_abs was required for a corresponding effect in the in vivo bolus model. This illustrates that a rapid and robust effect of the AME is crucial to increase the in vivo intestinal absorption rate before the yet unabsorbed drug in lumen has been transported distally in the intestine. Further, the recovery of the intestinal mucosa was complete following 15-min exposures of SDS and chitosan, but it only recovered 50% after the 60-min intestinal exposures. Our study also showed that the luminal exposure of AMEs affected the absorptive model drug transport more than the excretion of ⁵¹Cr-EDTA, as J_abs for the drugs was more sensitive than CL_Cr at detecting dynamic mucosal AME effects, such as response rate and recovery. Finally, there appears to be no nicotinergic neural contribution to the absorption-enhancing effect of SDS and chitosan, as luminal administration of 0.1 mM mecamylamine had no effect.

Effect of absorption-modifying excipients, hypotonicity, and enteric neural activity in an in vivo model for small intestinal transport

The small intestine mucosal barrier is physiologically regulated by the luminal conditions, where intestinal factors, such as diet and luminal tonicity, can affect mucosal permeability. The intestinal barrier may also be affected by absorption-modifying excipients (AME) in oral drug delivery systems. Currently, there is a gap in the understanding of how AMEs interact with the physiological regulation of intestinal electrolyte transport and fluid flux, and epithelial permeability. Therefore, the objective of this single-pass perfusion study in rat was to investigate the effect of three AMEs on the intestinal mucosal permeability at different luminal tonicities (100, 170, and 290 mOsm). The effect was also evaluated following luminal administration of a nicotinic receptor antagonist, mecamylamine, and after intravenous administration of a COX-2 inhibitor, parecoxib, both of which affect the enteric neural activity involved in physiological regulation of intestinal functions. The effect was evaluated by changes in intestinal lumen-to-blood transport of six model compounds, and blood-to-lumen clearance of ⁵¹Cr-EDTA (a mucosal barrier marker). Luminal hypotonicity alone increased the intestinal epithelial transport of ⁵¹Cr-EDTA. This effect was potentiated by two AMEs (SDS and caprate) and by parecoxib, while it was reduced by mecamylamine. Consequently, the impact of enteric neural activity and luminal conditions may affect nonclinical determinations of intestinal permeability. In vivo predictions based on animal intestinal perfusion models can be improved by considering these effects. The in vivo relevance can be increased by treating rats with a COX-2 inhibitor prior to surgery. This decreases the risk of surgery-induced ileus, which may affect the physiological regulation of mucosal permeability.

Short-chain fatty acids augment rat duodenal mucosal barrier function

NEW FINDINGS

What is the central question of this study? Small intestinal epithelium is exposed to high concentrations of short-chain fatty acids (SCFAs), but their role in regulating intestinal mucosal barrier function and motility is not fully understood. What is the main finding and its importance? By perfusing the duodenal segment in anaesthetized rats, we show that acetate and propionate significantly decrease mucosal paracellular permeability and transepithelial net fluid flux and increase mucosal bicarbonate secretion. Likewise, SCFAs administered i.v. decrease mucosal permeability but decrease bicarbonate secretion. Altered luminal chemosensing or aberrant signalling in response to SCFAs might contribute to symptoms observed in patients with suppressed mucosal barrier function. Short-chain fatty acids (SCFAs) are produced by bacterial fermentation in the large intestine, particularly from diets containing fibres and carbohydrates. The small intestinal epithelium is exposed to SCFAs derived mainly from oral bacteria or food supplementation. Although luminal nutrients are important in regulation of intestinal functions, the role of SCFAs in regulation of small intestinal mucosal barrier function and motility has not been fully described. The aim of the present study was to elucidate the effects of acetate and propionate on duodenal mucosal barrier function and motility. Rats were anaesthetized with thiobarbiturate, and a 30 mm segment of proximal duodenum with an intact blood supply was perfused. The effects on duodenal bicarbonate secretion, blood-to-lumen clearance of ⁵¹ Cr-EDTA, motility and transepithelial net fluid flux were investigated. Perfusion of the duodenum with acetate or propionate significantly decreased mucosal paracellular permeability and transepithelial net fluid flux and significantly increased bicarbonate secretion. Acetate or propionate administered as an i.v. infusion decreased the mucosal paracellular permeability, but significantly decreased bicarbonate secretion. Luminal SCFAs changed the duodenal motility pattern from migrating motor complexes to fed patterns. Systemic administration of glucagon-like peptide-2 induced increases in both bicarbonate secretion and net fluid absorption, but did not change motility. Glucagon-like peptide-2 infusion during luminal perfusion of SCFAs significantly reduced the motility. In conclusion, SCFAs decreased duodenal paracellular permeability and net fluid flux. Short-chain fatty acids induced opposite effects on bicarbonate secretion after luminal and i.v. administration. Presence of SCFAs in the lumen induces fed motility patterns. Altered luminal chemosensing and aberrant signalling in response to SCFAs might contribute to symptoms observed in patients with suppressed barrier function.

Long-term oral melatonin administration reduces ethanol-induced increases in duodenal mucosal permeability and motility in rats

AIM

Increased intestinal epithelial permeability is associated with intestinal inflammation and dysfunction. The aim of the present study was to investigate the role of long-term oral melatonin administration on ethanol-induced increases in duodenal mucosal permeability and hypermotility.

METHODS

Male Sprague-Dawley rats were administered melatonin in their tap water (0.1 mg mL(-1) or 0.5 mg mL(-1) ) for 2 or 4 weeks. After the treatment period, the rats were anaesthetized with Inactin(®) , and a 30-mm duodenal segment was perfused in situ. The effects on duodenal mucosal paracellular permeability, bicarbonate secretion, fluid flux and motor activity were studied. The expression levels of the tight junction components, zona occludens (ZO)-1, ZO-2, and ZO-3, claudin-2, claudin-3, claudin-4, occludin, and myosin light chain kinase and of the melatonin receptors MT1 and MT2 were assessed using qRT-PCR.

RESULTS

Melatonin administration for 2 weeks significantly reduced the basal paracellular permeability, an effect that was absent after 4 weeks. Perfusing the duodenal segment with 15% ethanol induced marked increases in duodenal paracellular permeability, bicarbonate secretion and motor activity. Melatonin for 2 weeks dose-dependently reduced ethanol-induced increases in permeability and motor activity. Four weeks of melatonin administration reduced the ethanol-induced increases in duodenal motility and bicarbonate secretion but had no effect on the increases in permeability. Two weeks of melatonin administration upregulated the expression of MT1 and MT2 , although both were downregulated after 4 weeks. Melatonin downregulated the expression of ZO-3 and upregulated the expression of claudin-2, even as all other mRNA-levels investigated were unaffected.

CONCLUSION

Although further studies are needed, our data demonstrate that melatonin administration markedly improves duodenal barrier functions, suggesting its utility in clinical applications when intestinal barrier functions are compromised.

Prevention of duodenal ileus reveals functional differences in the duodenal response to luminal hypertonicity in Sprague-Dawley and Dark Agouti rats

AIM

The mechanism by which the duodenum adjusts the luminal osmolality remains unclear. The aim was to compare the duodenal osmoregulation in response to different hyperosmolar solutions in Sprague-Dawley and Dark Agouti rats and to elucidate whether cyclooxygenase-2 inhibition affects these responses.

METHODS

The duodenum was perfused in situ with a 700-milliosmolar solution (NaCl alone, D-glucose ± NaCl, D-mannitol ± NaCl or orange juice), and the effects on the duodenal motility, mucosal permeability, luminal alkalinization, fluid flux and osmoregulation were assessed in anaesthetized rats.

RESULTS

The change in net fluid flux and luminal osmolality, in response to a given hyperosmolar solution, was almost identical in control rats of both strains. In control rats, hypertonic D-glucose-NaCl induced fluid secretion only in the presence of phlorizin, an inhibitor of SGLT1. Cyclooxygenase-2 inhibition potentiated the hypertonicity-induced fluid secretion and increased the osmolality-adjusting capability in both strains, but the responses were greater in Dark Agouti rats. While cyclooxygenase-2-inhibited Dark Agouti rats responded to the hyperosmolar solutions with depression of motility and increased mucosal permeability, these effects were absent or smaller in the Sprague-Dawley strain. In contrast, orange juice induced the same duodenal responses in cyclooxygenase-2-inhibited Dark Agouti and Sprague-Dawley rats.

CONCLUSION

The duodenum possesses the ability to absorb fluid despite a very high luminal osmolality. Inhibition of cyclooxygenase-2 markedly enhanced the capability of the duodenum to secrete fluid and to decrease luminal osmolality, irrespective of the hyperosmolar solution or the rat strain used, and revealed notable differences between the two strains with regard to their osmolality-adjusting capability.

Application of parecoxib in post-uvulopalatopharyngoplasty analgesia

Objective

To investigate the postoperative analgesic effects of parecoxib for uvulopalatopharyngoplasty (UPPP).

Methods

Patients with obstructive sleep apnoea syndrome who underwent UPPP were randomly divided into two groups. In group A, the incision-local block was performed with 5 ml of 0.5% ropivacaine injected subcutaneously before the end of surgery, then 20 ml of physiological saline was injected intravenously every 12 h for 2 days. In group B, in addition to the incision-local block, 40 mg parecoxib was injected intravenously 30 min before the end of UPPP and 40 mg parecoxib was injected intravenously every 12 h for 2 days. Postoperative pain was measured using a visual analogue scale (VAS). Adverse reactions were recorded.

Results

A total of 40 patients were randomized ( n = 20 per group). Under resting conditions, the mean ± SD VAS pain scores were significantly higher in group A compared with group B at 24 h and 48 h after UPPP (24 h 4.0 ± 0.8 versus 2.6 ± 0.6; 48 h 3.8 ± 0.7 versus 2.4 ± 0.5; respectively). Under swallowing conditions, the mean ± SD VAS pain scores were significantly higher in group A compared with group B at 8 h, 24 h and 48 h after UPPP. Postoperative adverse reactions were similar in the two groups.

Conclusion

Intravenous parecoxib combined with incision-local ropivacaine provided effective postoperative analgesia for patients with obstructive sleep apnoea syndrome, undergoing UPPP.

Melatonin inhibits alcohol-induced increases in duodenal mucosal permeability in rats in vivo

Increased intestinal permeability is often associated with epithelial inflammation, leaky gut, or other pathological conditions in the gastrointestinal tract. We recently found that melatonin decreases basal duodenal mucosal permeability, suggesting a mucosal protective mode of action of this agent. The aim of the present study was to elucidate the effects of melatonin on ethanol-, wine-, and HCl-induced changes of duodenal mucosal paracellular permeability and motility. Rats were anesthetized with thiobarbiturate and a ~30-mm segment of the proximal duodenum was perfused in situ. Effects on duodenal mucosal paracellular permeability, assessed by measuring the blood-to-lumen clearance of ⁵¹Cr-EDTA, motility, and morphology, were investigated. Perfusing the duodenal segment with ethanol (10 or 15% alcohol by volume), red wine, or HCl (25-100 mM) induced concentration-dependent increases in paracellular permeability. Luminal ethanol and wine increased, whereas HCl transiently decreased duodenal motility. Administration of melatonin significantly reduced ethanol- and wine-induced increases in permeability by a mechanism abolished by the nicotinic receptor antagonists hexamethonium (iv) or mecamylamine (luminally). Signs of mucosal injury (edema and beginning of desquamation of the epithelium) in response to ethanol exposure were seen only in a few villi, an effect that was histologically not changed by melatonin. Melatonin did not affect HCl-induced increases in mucosal permeability or decreases in motility. Our results show that melatonin reduces ethanol- and wine-induced increases in duodenal paracellular permeability partly via an enteric inhibitory nicotinic-receptor dependent neural pathway. In addition, melatonin inhibits ethanol-induced increases in duodenal motor activity. These results suggest that melatonin may serve important gastrointestinal barrier functions.

Melatonin decreases duodenal epithelial paracellular permeability via a nicotinic receptor-dependent pathway in rats in vivo

Intestinal epithelial intercellular tight junctions (TJs) provide a rate-limiting barrier restricting passive transepithelial movement of solutes. TJs are highly dynamic areas, and their permeability is changed in response to various stimuli. Defects in the intestinal epithelial TJ barrier may contribute to intestinal inflammation or leaky gut. The gastrointestinal tract may be the largest extrapineal source of endogenous melatonin. Melatonin released from the duodenal mucosa is a potent stimulant of duodenal mucosal bicarbonate secretion (DBS). The aim of this study was to elucidate the role of melatonin in regulating duodenal mucosal barrier functions, including mucosal permeability, DBS, net fluid flux, and duodenal motor activity, in the living animal. Rats were anesthetized with thiobarbiturate, and a ~30-mm segment of the proximal duodenum with an intact blood supply was perfused in situ. Melatonin and the selective melatonin receptor antagonist luzindole were perfused luminally or given intravenously. Effects on permeability (blood-to-lumen clearance of (51)Cr-EDTA), DBS, mucosal net fluid flux, and duodenal motility were monitored. Luminal melatonin caused a rapid decrease in paracellular permeability and an increase in DBS, but had no effect on duodenal motor activity or net fluid flux. Luzindole did not influence any of the basal parameters studied, but significantly inhibited the effects of melatonin. The nonselective and noncompetitive nicotinic acetylcholine receptor antagonist mecamylamine abolished the effect of melatonin on duodenal permeability and reduced that on DBS. In conclusion, these findings provide evidence that melatonin significantly decreases duodenal mucosal paracellular permeability and increases DBS. The data support the important role of melatonin in the neurohumoral regulation of duodenal mucosal barrier.