Resistance to apoptosis in complicated Crohn's disease: Relevance in ileal fibrosis

BACKGROUND AND AIMS

The stiffening of the extracellular matrix, and changes in its cellular and molecular composition, have been reported in the pathogenesis of fibrosis. We analyze the mechanisms that perpetuate ileal fibrosis in surgical resections of complicated Crohn's disease patients.

METHODS

Ileal resections were obtained from affected and non-affected tissue of stenotic or penetrating Crohn's disease behavior. Ilea from non-IBD patients were used as control tissue. All samples underwent RNA sequencing. Human small intestinal fibroblasts were treated for 48 h with IL-1β, TFGβ1, PDGFB or TNF-α. Resistance to apoptosis was analysed by RT-PCR, western blot and immunohistochemistry in ileal tissue and by RT-PCR and FACS in cultured cells.

RESULTS

Growth factor-driven signaling pathways and increased RAS GTPase activity were up-regulated in affected ilea in which we found expression of both the antiapoptotic molecule MCL1 and the transcription factor ETS1 in submucosal fibroblasts, and a senescence-associated secretory phenotype. In cultured intestinal fibroblasts, PDGFB induced an ETS1-mediated resistance to apoptosis that was associated with the induction of both of TGFB1 and IL1B, a cytokine that replicated the expression of SASP detected in ileal tissue. ETS1 drove fibroblast polarization between inflammatory and fibrogenic phenotypes in IL1β-treated cells.

CONCLUSIONS

Our data show resistance to apoptosis in complicated ileal CD, and demonstrate that PDGFB induce an ETS1-mediated resistance to apoptosis associated with an inflammatory and fibrogenic pattern of expression in intestinal fibroblasts. Results point to PDGFRB, IL1R1 or MCL1 as potential targets against ileal fibrosis.

Role of the epithelial barrier in intestinal fibrosis associated with inflammatory bowel disease: relevance of the epithelial-to mesenchymal transition

In inflammatory bowel disease (IBD), chronic inflammation in the gastrointestinal tract can lead to tissue damage and remodelling, which can ultimately result in fibrosis. Prolonged injury and inflammation can trigger the activation of fibroblasts and extracellular matrix (ECM) components. As fibrosis progresses, the tissue becomes increasingly stiff and less functional, which can lead to complications such as intestinal strictures, obstructive symptoms, and eventually, organ dysfunction. Epithelial cells play a key role in fibrosis, as they secrete cytokines and growth factors that promote fibroblast activation and ECM deposition. Additionally, epithelial cells can undergo a process called epithelial-mesenchymal transition, in which they acquire a more mesenchymal-like phenotype and contribute directly to fibroblast activation and ECM deposition. Overall, the interactions between epithelial cells, immune cells, and fibroblasts play a critical role in the development and progression of fibrosis in IBD. Understanding these complex interactions may provide new targets for therapeutic interventions to prevent or treat fibrosis in IBD. In this review, we have collected and discussed the recent literature highlighting the contribution of epithelial cells to the pathogenesis of the fibrotic complications of IBD, including evidence of EMT, the epigenetic control of the EMT, the potential influence of the intestinal microbiome in EMT, and the possible therapeutic strategies to target EMT. Finally we discuss the pro-fibrotic interactions epithelial-immune cells and epithelial-fibroblasts cells.

The activation of Wnt signaling by a STAT6-dependent macrophage phenotype promotes mucosal repair in murine IBD

The complete repair of the mucosa constitutes a key goal in inflammatory bowel disease (IBD) treatment. The Wnt signaling pathway mediates mucosal repair and M2 macrophages that coordinate efficient healing have been related to Wnt ligand expression. Signal transducer and activator of transcription 6 (STAT6) mediates M2 polarization in vitro and we hypothesize that a STAT6-dependent macrophage phenotype mediates mucosal repair in acute murine colitis by activating the Wnt signaling pathway. Our results reveal an impaired mucosal expression of M2 macrophage-associated genes and delayed wound healing in STAT6(-/-) mice treated with 2,4,6-trinitrobenzenesulfonic acid (TNBS). These mice also exhibited decreased mucosal expression of Wnt2b, Wnt7b, and Wnt10a, diminished protein levels of nuclear β-catenin that is mainly located in crypts adjacent to damage, and reduced mRNA expression of two Wnt/β-catenin target molecules Lgr5 and c-Myc when compared with wild-type (WT) mice. Murine peritoneal macrophages treated with interleukin-4 (IL-4) and polarized toward an M2a phenotype overexpressed Wnt2b, Wnt7b, and Wnt10a in a STAT6-dependent manner. Administration of a Wnt agonist as well as transfer of properly polarized M2a macrophages to STAT6(-/-) mice activated the Wnt signaling pathway in the damaged mucosa and accelerated wound healing. Our results demonstrate that a STAT6-dependent macrophage phenotype promotes mucosal repair in TNBS-treated mice through activation of the Wnt signaling pathway.

Hypoxic macrophages impair autophagy in epithelial cells through Wnt1: relevance in IBD

A defective induction of epithelial autophagy may have a role in the pathogenesis of inflammatory bowel diseases. This process is regulated mainly by extracellular factors such as nutrients and growth factors and is highly induced by diverse situations of stress. We hypothesized that epithelial autophagy is regulated by the immune response that in turn is modulated by local hypoxia and inflammatory signals present in the inflamed mucosa. Our results reveal that HIF-1α and Wnt1 were co-localized with CD68 in cells of the mucosa of IBD patients. We have observed increased protein levels of β-catenin, phosphorylated mTOR, and p62 and decreased expression of LC3II in colonic epithelial crypts from damaged mucosa in which β-catenin positively correlated with phosphorylated mTOR and negatively correlated with autophagic protein markers. In cultured macrophages, HIF-1 mediated the increase in Wnt1 expression induced by hypoxia, which enhanced protein levels of β-catenin, activated mTOR, and decreased autophagy in epithelial cells in co-culture. Our results demonstrate a HIF-1-dependent induction of Wnt1 in hypoxic macrophages that undermines autophagy in epithelial cells and suggest a role for Wnt signaling and mTOR pathways in the impaired epithelial autophagy observed in the mucosa of IBD patients.

Nitric oxide, derived from inducible nitric oxide synthase, decreases hypoxia inducible factor-1alpha in macrophages during aspirin-induced mesenteric inflammation

BACKGROUND AND PURPOSE

Nitric oxide (NO) modulates expression of hypoxia inducible factor-1 (HIF-1), a transcription factor regulating function of myeloid cells. Here, we have assessed the role played by NO, formed by inducible NOS (iNOS), in the inflammation induced by aspirin in the gut, by modulating HIF-1 activity.

EXPERIMENTAL APPROACH

The role of iNOS-derived NO on leucocyte-endothelial interactions induced by aspirin was evaluated by intravital microscopy in mesenteric venules of rats pretreated with selective iNOS inhibitors, 1400W or l-N6-(1-iminoethyl)-lysine. NO was localized by fluorescence microscopy, using DAF-FM. iNOS, HIF-1alpha and CD36 were localized by immunohistochemistry.

KEY RESULTS

Leucocyte-endothelial interactions increased at 6 h and returned to normal levels 24 h after aspirin administration. Numbers of migrated leucocytes were similar between 6 and 24 h after aspirin. iNOS expression and iNOS-derived NO synthesis were observed in leucocytes of the mesentery of aspirin-treated rats. Blockade of iNOS activity in aspirin-treated rats: (i) did not modify leucocyte infiltration at 6 h, but reduced the number of polymorphonuclear leucocyte and increased that of macrophages at 24 h; (ii) increased HIF-1alpha immunostaining in macrophages of the mesentery; and (iii) prevented the decrease in CD36 immunostaining induced by aspirin in these cells.

CONCLUSIONS AND IMPLICATIONS

NO, associated with acute gut inflammation induced by aspirin, diminished HIF-1alpha stabilization in macrophages. Early inhibition of iNOS-derived NO synthesis, by increasing the activity of HIF-1 in these cells, may accelerate the clearance of leucocytes.

Induction of trefoil factor (TFF)1, TFF2 and TFF3 by hypoxia is mediated by hypoxia inducible factor-1: implications for gastric mucosal healing

BACKGROUND AND PURPOSE

Mucosal microcirculation is compromised during gastric damage induced by non-steroidal anti-inflammatory drugs, such as aspirin. Consequently, oxygen supply to epithelial cells is decreased. The trefoil factor (TFF) peptides are involved in mechanisms of defence and repair in the gastrointestinal tract but their regulation at sites of gastric injury is unknown.

EXPERIMENTAL APPROACH

Hypoxia and expression of TFF genes and peptides were measured in the damaged stomach of aspirin-treated rats. In a human gastric cell line (AGS cells), the effects of hypoxia and of hypoxia inducible factor (HIF)-1 (through transient transfection of HIF-1alpha siRNA or over-expression of HIF-1alpha) on TFF gene expression were evaluated.

KEY RESULTS

Hypoxyprobe immunostaining, up-regulation of TFF2 (1.9-fold) and TFF3 (1.8-fold) and a non-significant increase of TFF1 (1.5-fold) mRNA were observed in the damaged stomach of aspirin-treated rats, compared with control animals. Hypoxia (3% O(2), 16 h) induced mRNA for TFF1 (5.8-fold), TTF2 (9.1-fold) and TFF3 (9.3-fold) in AGS cells, an effect mediated by HIF-1, as transient transfection of HIF-1alpha siRNA reduced the effects of hypoxia. Over-expression of HIF-1alpha by transfection in non-hypoxic epithelial cells produced a similar pattern of TFF induction to that observed with hypoxia and transactivated a TFF1 reporter construct.

CONCLUSIONS AND IMPLICATIONS

Hypoxia inducible factor-1 mediated the induction of TFF gene expression by hypoxia in gastric epithelial cells. Low oxygen levels and up-regulation of TFF gene expression in the damaged stomach of aspirin-treated rats suggest that hypoxia induced expression of TFF genes at sites of gastric injury.

Nitrergic modulation of gastrointestinal function during early endotoxemia

After bacterial infection, the host reacts by signalling to the central nervous system where a cascade of physiologic, neuroendocrine and behavioural processes is orchestrated, collectively termed the acute phase response. Endotoxemia following Gram-negative bacterial infection induces a wide array of effects, including fever, loss of appetite and changes in gastrointestinal function that attempt to eliminate the challenge and restore homeostasis. Systemic administration of low doses of endotoxin (5-40 microg/kg) to rats is associated with changes in gastrointestinal motor function, inhibition of gastric acid secretion and increase in the gastric mucosal resistance to damage. These changes are rapid in onset (observed within one hour), not related to vascular dysfunction, and appear to be mediated by mechanisms that involve the peripheral and the central nervous system. Nitric oxide (NO) plays a central role in the physiology of the gastrointestinal tract and its response to illness. Accumulated evidence supports an increase of NO synthesis in the brainstem, as well as in the gastric myenteric plexus thirty minutes after endotoxin administration. Such a synthesis is due to constitutive nitric oxide synthase (NOS) and occurs before the induction of NOS takes place. In this review we provide experimental evidence supporting the hypothesis that activation of a physiologic mechanism, mediated by the autonomic and the central nervous systems as well as constitutive NOS isoforms, is involved in acute changes of gastrointestinal function during early endotoxemia.

Low endotoxemia prevents the reduction of gastric blood flow induced by NSAIDs: role of nitric oxide

1 The role of nitric oxide (NO) in the effects of low endotoxemia on gastric damage and blood flow has been evaluated in indomethacin-treated rats. 2 Pretreatment (-1 h) with endotoxin (40 micro g kg(-1)) reduced gastric damage induced by indomethacin (20 mg kg(-1)) in conscious rats. 3 Endotoxin prevented the reduction in gastric blood flow (laser Doppler flowmetry) induced by indomethacin in pentobarbital-anaesthetised rats. 4 Pretreatment with an NO-synthase (NOS) inhibitor (L-NAME, 1 mg kg(-1)) reversed the protective effect of endotoxin on gastric blood perfusion. 5 Endotoxin did not modify the expression of mRNA for endothelial NOS or inducible NOS in the gastric corpus when evaluated 1 h postinjection. However, a 3.8-fold increase in inducible NOS mRNA and a 61% reduction in endothelial NOS mRNA were observed in the gastric corpus 4 h after endotoxin administration. 6 Evaluation of both total and Ca(2+)-dependent NOS activity by analysing the rate of conversion of L-arginine to L-citrulline in gastric corpus homogenates showed no differences between animals treated with endotoxin and those treated with saline 1 or 4 h beforehand. Ca(2+)-independent NOS activity was almost non-apparent in control as well as in endotoxin-treated rats at all the time points analysed. 7 Low endotoxemia preserves blood perfusion and protects the gastric mucosa against the deleterious effects of indomethacin through the endogenous NO release. NO synthesis in response to endotoxin does not involve the inducible NOS, but probably depends on the post-translational/biochemical regulation in vivo of a Ca(2+)-dependent NOS, most probably endothelial NOS.

Interleukin 1 beta-induced inhibition of gastric acid secretion involves glutamate, NO and cGMP synthesis in the brain

This study examines the role of a central pathway involving glutamate receptors, nitric oxide (NO) and cGMP in the acute inhibitory effects of central interleukin 1beta on pentagastrin-stimulated acid production.The acid-inhibitory effect of central interleukin 1beta was prevented by intracisternal (i.c.) microinjections of interleukin 1beta together with the NMDA receptor antagonist, dizocilpine maleate (MK-801). Intracisternal co-administration of the nitric oxide synthase inhibitor, N(G)-nitro- L-arginine methyl esther ( L-NAME) or 1H-[1,2,4]oxazodiolo[4,3-a]quinoxalin-1-one (ODQ), a soluble guanylyl cyclase (sGC) blocker, both reversed the hyposecretory effect of central interleukin 1beta. Peripheral administration of endotoxin significantly reduced pentagastrin-stimulated gastric acid secretion. I.c. pre-treatment with the interleukin 1 receptor antagonist, IL-1ra, failed to restore acid secretory responses in these rats. In addition, endotoxin did not modify the levels of endogenous mRNA for IL-1beta in the brainstem. We conclude that central glutamate receptors are involved in the acid inhibitory effect of centrally administered interleukin 1beta. This central pathway involves synthesis of NO, which acts on the enzyme sGC. However, endogenous interleukin 1beta does not seem to be involved in the inhibition of gastric acid secretion elicited by peripheral endotoxin.

Endotoxin inhibits gastric emptying in rats via a capsaicin-sensitive afferent pathway

The effects of endotoxin on gastric emptying of a solid nutrient meal and the neural mechanisms involved in such a response were investigated in conscious rats. The intraperitoneal (i.p.) administration of E. coli endotoxin (40 microg/kg) significantly reduced the 4-h rate of gastric emptying of a standard solid nutrient meal. Ablation of primary afferent neurons by systemic administration of high doses of capsaicin (20+30+50 mg/kg s.c.) to adult rats did not modify the rate of gastric emptying in control animals but prevented the delay in gastric transit induced by endotoxin. Local application of capsaicin to the vagus nerve rather than application of capsaicin to the celiac ganglion significantly repressed endotoxin-induced delay in gastric emptying. Neither treatment modified the rate of gastric emptying in vehicle-treated animals. Blockade of CGRP receptors (CGRP 8-37, 100 microg/kg i.v.) did not alter gastric emptying in control animals but significantly prevented endotoxin-induced inhibition of gastric emptying. In contrast, a tachykinin receptor antagonist ([D-Pro2, D-Trp7.9]-substance P, 2 mg/kg i.p.) significantly reduced the rate of gastric emptying in control animals and did not modify the inhibitory effects of endotoxin. Adrenergic blockade with phentolamine (3 mg/kg i.p.) +/- propranolol (5 mg/kg i.p.) or muscarinic antagonism with atropine (0.1 mg/kg i.p.) failed to reverse the delay in gastric emptying induced by endotoxin. These observations indicate that endotoxin-induced delay in gastric emptying of a solid nutrient meal is mediated by capsaicin-sensitive afferent neurons.

Role of nitric oxide in gastrointestinal inflammatory and ulcerative diseases: perspective for drugs development

Nitric oxide is a ubiquitous molecule involved in a variety of biological processes. The specific action of NO depends on its enzymatic sources namely neuronal nitric oxide synthase (nNOS), endothelial NOS (eNOS) and inducible NOS (iNOS) and all three isoforms have been localized in the gastrointestinal tract. Constitutive synthesis of NO by nNOS or eNOS isoforms is involved in the maintaining of the gastrointestinal mucosal integrity through modulation of gastric mucosal blood flow, epithelial secretion and barrier function. However, large amounts of NO synthesized from the inducible isoform have been implicated in tissue injury in the gut during inflammatory reactions. In this review we provide an overview of the dual role of nitric oxide in modulating gastrointestinal mucosal defense and injury. In addition, we highlight the therapeutic potential of NO modulation.

Role of central glutamate receptors, nitric oxide and soluble guanylyl cyclase in the inhibition by endotoxin of rat gastric acid secretion

1. This study examines the role of a central pathway involving glutamate receptors, nitric oxide (NO) and cyclic GMP in the acute inhibitory effects of low doses of peripheral endotoxin on pentagastrin-stimulated acid production. 2. Vagotomy or intracisternal (i.c.) microinjections of the NO-inhibitor, N(G)-nitro-L-arginine methyl esther (L-NAME; 200 microg rat(-1)) restored acid secretory responses in endotoxin (10 microg kg(-1), i.v.)-treated rats. 3. The acid-inhibitory effect of i.v. endotoxin (10 microg kg(-1), i.v.) was prevented by prior i.c. administration of the NMDA receptor antagonists, dizocilpine maleate (MK-801; 10 nmol rat(-1)) and D-2-amino-5-phosphono-valeric acid (AP-5; 20 nmol rat(-1)), or the AMPA/kainate antagonist 6,7-dinitroquinoxaline-2,3-dione (DNQX; 10 nmol rat(-1)). However, the competitive metabotropic glutamate receptor antagonist (+)-alpha-methyl-4-carboxyphenylglycine (MCPG; 20 - 1000 nmol rat(-1)) did not antagonize the effects of endotoxin. 4. I.c. administration of L-glutamate (0.1 nmol rat(-1)) inhibited pentagastrin-stimulated gastric acid secretion. Coadministration with L-NAME (200 microg rat(-1)) prevented the inhibition of gastric acid secretion by the aminoacid. 5. I.c. administration of 1H-[1,2, 4]Oxazodiolo[4,3-a]quinoxalin-1-one (ODQ; 100 nmol rat(-1)), a soluble guanylyl cyclase (sGC) blocker, reversed the hyposecretory effect of endotoxin. 6. I.c. administration of the cyclic GMP analogue 8-Bromoguanosine-3,5-cyclic monophosphate (8-Br-cGMP; 100 - 300 nmol rat(-1)) reduced gastric acid production in a dose-dependent manner. 7. We conclude that central NMDA and AMPA/kainate receptors are involved in the acid inhibitory effect of peripherally administered endotoxin. This central pathway involves synthesis of NO, which acts on the enzyme sGC.

Role of central oxytocin in the inhibition by endotoxin of distension-stimulated gastric acid secretion

The gastric acid hyposecretory state associated with endotoxemia is mediated by a nervous reflex involving the central nervous system. The aim of the present study was to analyse the central effects of different peptides on distension-stimulated gastric acid secretion and the endogenous role of such peptides on the hyposecretory effects of endotoxin. The effect of an intracisternal (i.c.) administration of oxytocin, vasopressin, corticotropin releasing factor (CRF), bombesin, somatostatin and the opioid receptor agonist BW443C or an intravenous (i.v.) injection of a small dose of endotoxin on distension-stimulated gastric acid secretion was studied in the continuously perfused stomach of anaesthetised rats. In some animals, specific receptor antagonists for oxytocin (Compound VI [d(CH2)5, Tyr(Me)2, Thr4, Tyr-NH2(9)]-OVT, 0.01-1 microg/rat), vasopressin (des-Gly9-[beta-Mercapto-beta,beta-cyclopentamethylene-propiony l1, O-Et-Tyr2, Val4, Arg8]-VP, 20 microg/rat), CRF (alpha-helical CRF [9-41], 50 microg/rat) or bombesin (D-Phe12-Bombesin, 20 microg/rat) were administered i.c. before endotoxin. Distension-stimulated acid secretion was significantly inhibited by central oxytocin (0.2, 2 or 4 nmol/rat, 45+/-16%, 69+/-10% and 79+/-5% reduction, respectively), CRF (0.5, 1 or 2 nmol/rat, 52.2+/-15.6%, 74.3+/-9.1% and 93.2+/-1.6% reduction, respectively) and bombesin (2 nmol/rat, 79.1+/-5.8% reduction). The hyposecretory effect induced by endotoxin (5 microg/kg, 60.2+/-2.3% reduction) was reversed in a dose-dependent manner by pretreatment with the oxytocin receptor antagonist (0.01, 0.1 and 1 microg/rat, 65.2+/-14.4%, 88.0+/-22.5% and 112.4+/-25.2% of control response, respectively) while the vasopressin (20 microg/rat), CRF (50 microg/rat) or bombesin (20 microg/rat) receptor antagonists had no effect. The present results support a role for the endogenous release and action in the central nervous system of oxytocin in the inhibitory effect of endotoxin on gastric acid secretion.

Intracerebroventricular leptin inhibits gastric emptying of a solid nutrient meal in rats

The effects of leptin injected intracerebroventricularly (i.c.v.) or i.p. on food intake and gastric emptying of a solid nutrient meal were studied in fasted Long-Evan rats. Leptin (3 microg, i.c.v.) reduced the 5 h cumulative food intake by 39% and gastric transit by 50% while i.p. leptin (300 microg) resulted in a 35% decrease in food intake and no change in gastric transit after 5 h. Lower i.p. doses of leptin (30 or 3 microg) did not alter food intake. These results show that central, unlike peripheral, injection of leptin inhibits gastric transit of an ingested meal; such a central action of leptin may contribute to the greater potency of i.c.v. than i.p. leptin to suppress food intake.

Changes in gastric mucosal permeability induced by haemorrhagic shock in the anaesthetized rat: modulation by acid

Gastric mucosal damage induced by haemorrhagic shock in the anaesthetized rat has been evaluated by studying changes in capillary-to-lumen clearance of fluorescein isothiocyanate (FITC)-labelled dextran. Haemorrhagic shock (20 min ischaemia + 20 min reperfusion) induced a significant increase in blood-to-lumen permeability to FITC-dextran of different molecular weight (10,000, 40,000 and 70,000) without modifying the macroscopic integrity of the gastric mucosa. The increase in vascular permeability was dependent on the time of administration of the tracer and was correlated with an elevation of the protein content of the gastric lumen. Intravenous administration of the secretagogue pentagastrin (20 or 50 micrograms kg-1 h-1) did not significantly modify the vascular permeability to dextran in control animals or in animals subjected to haemorrhagic shock. When the intraluminal pH was reduced by intragastric administration of acidic saline solution, only pH 1, which itself induced the appearance of macroscopic mucosal lesions, significantly increased vascular permeability to dextran, both in control animals and in animals subjected to haemorrhagic shock. These findings suggest that stress induced by haemorrhagic shock increases vascular gastric permeability to dextran, by an acid-independent mechanism, without affecting the macroscopic integrity of the gastric mucosa.

Fos expression in the brain induced by peripheral injection of CCK or leptin plus CCK in fasted lean mice

We previously reported a synergistic interaction between leptin and cholecystokinin (CCK) to reduce food intake through CCK-A receptors in lean mice fasted for 24 h. To identify the activated neuronal pathways, we investigated changes in Fos expression in brain nuclei 2 h after single or combined intraperitoneal (i.p.) injections of leptin (120 microg/kg) and sulfated CCK-8 (3.5 microg/kg) in male lean mice (C57BL/6) fasted for 24 h using immunohistochemistry for Fos, the protein product of the early gene, c-fos. Leptin did not increase Fos expression in the brain compared with vehicle-treated mice. CCK increased the numbers of Fos-positive neurons in the nucleus of the solitary tract (NTS)/area postrema (AP), central nucleus of the amygdala (CeA) and, to a smaller extent, in the paraventricular nucleus of the hypothalamus (PVN) (5.2-, 2.3- and 0. 3-fold respectively). Injections of leptin-CCK further enhanced Fos expression by 40% in the PVN compared with that induced by CCK alone, but not in the other nuclei. Devazepide (a CCK-A receptor antagonist, 1 mg/kg, i.p.) prevented the increase in Fos expression induced by leptin-CCK in the PVN and by CCK alone in the PVN, CeA and NTS/AP. These results indicate that in fasted mice, i.p. injection of CCK increases Fos expression in specific brain nuclei through CCK-A receptors while leptin alone had no effect. Leptin in conjunction with CCK selectively enhanced Fos expression in the PVN. The PVN may be an important site mediating the synergistic effect of leptin-CCK to regulate food intake.

Nitric oxide modulates the acute increase of gastrointestinal transit induced by endotoxin in rats: a possible role for tachykinins

Because of the evidence that endogenous nitric oxide (NO) plays an essential role in the physiological regulation of gastrointestinal motility we have investigated, by use of the NO synthase inhibitor, NG-nitro-L-arginine methyl ester (L-NAME), the role of endogenous NO in the acute endotoxin-induced changes of gastrointestinal transit. Pre-treatment with E. coli endotoxin (100 micrograms kg-1, i.v.) induced a significant increase in the gastrointestinal transit of a charcoal suspension in anaesthetized rats. Previous administration of the NO synthase inhibitor, L-NAME (10 mg kg-1, i.v.) significantly prevented the effects of endotoxin. L-arginine (200 mg kg-1, i.v.) and the substance P antagonist [D-Pro2, D-Trp7,9]-substance P (SPA), significantly reversed the effects of L-NAME on gastrointestinal transit in rats treated with endotoxin. Pre-treatment with dexamethasone (5 mg kg-1, s.c., twice), an inhibitor of the expression of inducible NO synthase, did not affect the increase in the gastrointestinal transit through constitutive NO synthesis. The results suggest that constitutive nitric oxide is involved in the increase of gastrointestinal transit induced by endotoxin and that the reduction in transit induced by L-NAME in endotoxin-treated rats is mediated by endogenous tachykinins.

Synergistic interaction between leptin and cholecystokinin to reduce short-term food intake in lean mice

Leptin is a circulating protein involved in the long-term regulation of food intake and body weight. Cholecystokinin (CCK) is released postprandially and elicits satiety signals. We investigated the interaction between leptin and CCK-8 in the short-term regulation of food intake induced by 24-hr fasting in lean mice. Leptin, injected intraperitoneally (i.p.) at low doses (4-120 microg/kg), which did not influence feeding behavior for the first 3 hr postinjection, decreased food intake dose dependently by 47-83% during the first hour when coinjected with a subthreshold dose of CCK. Such an interaction was not observed between leptin and bombesin. The food-reducing effect of leptin injected with CCK was not associated with alterations in gastric emptying or locomotor behavior. Leptin-CCK action was blocked by systemic capsaicin at a dose inducing functional ablation of sensory afferent fibers and by devazepide, a CCK-A receptor antagonist but not by the CCK-B receptor antagonist, L-365,260. The decrease in food intake which occurs 5 hr after i.p. injection of leptin alone was also blunted by devazepide. Coinjection of leptin and CCK enhanced the number of Fos-positive cells in the hypothalamic paraventricular nucleus by 60%, whereas leptin or CCK alone did not modify Fos expression. These results indicate the existence of a functional synergistic interaction between leptin and CCK leading to early suppression of food intake which involves CCK-A receptors and capsaicin-sensitive afferent fibers.

Effects of Mn2+ on the responses induced by different spasmogens in the oestrogen-primed rat uterus

We investigated the effect of Mn2+ on the mechanical responses evoked by high K+ (60 mM) or low Na+ (25 mM) solutions, oxytocin and neurokinin A in the oestrogen-primed rat uterus. In a Ca2+-free, Mn2+ (0.54 mM)-containing solution, high K+ or low Na+ solutions produced contractions of smaller amplitude than those observed in a normal Ca2+ (0.54 mM) solution, which were abolished by nifedipine (1 microM). Oxytocin (1 microM) and neurokinin A (1 microM, in the presence of phosphoramidon 1 microM) evoked nifedipine-insensitive contractile responses similar to (oxytocin) or smaller (neurokinin A) in amplitude than those observed in Ca2+ (0.54 mM)-containing solution. In strips loaded with Ca2+ (2.16 mM) for 10 min and then exposed to a Ca2+- and Mn2+-free, EGTA (3 mM)-containing medium for 4 min, both oxytocin and neurokinin A induced transient contraction followed by a small sustained response. The transient component of the response was abolished by cyclopiazonic acid (10 microM). When preparations were loaded with Mn2+ (2.16 mM) for 10 min, only the small, tonic contraction was observed. In Ca2+-containing solution, Mn2+ (0.01-10 mM) inhibited in a concentration-dependent manner the rhythmic contractions developed either spontaneously or by electrical stimulation as well as high K+- and neurokinin A-induced contractions. Mn2+ also abolished the rhythmic, but not the tonic component of the response to oxytocin, and the preparation remained maximally contracted. These data suggest that in the oestrogen-primed rat uterus, Mn2+ acts as an antagonist of Ca2+ influx through L-type voltage-operated Ca2+ channels. In addition, Mn2+ enters the cell mainly through nifedipine-insensitive receptor-operated channels and, to a lesser degree, through L-type Ca2+ channels to produce contraction by directly activating the contractile machinery.

Leptin-induced decrease in food intake is not associated with changes in gastric emptying in lean mice

Chronic treatment with leptin regulates body weight and energy balance and reduces food intake in obese and lean mice. In 18- to 20-h fasted lean mice (C57BL/6, +/+), we examined the acute effect of a single intraperitoneal injection of recombinant mouse leptin (0.12 mg/kg) on food intake and gastric emptying. Leptin reduced food intake, with a peak inhibition at the 5th h postinjection (69 +/- 12%/h), although there was no change in food consumption at the 1st h. Leptin did not alter the 4-h rate of gastric emptying of a solid nutrient meal (free access to Purina chow for either 1-, 2-, or 4-h period). In normal Sprague-Dawley rats fasted for 18-20 h, a single intraperitoneal injection of recombinant mouse leptin (0.2 or 1.2 mg/kg) did not modify the 7-h cumulative or hourly food intake. These results show that a single intraperitoneal injection of recombinant mouse leptin reduces food intake within 5 h while not influencing gastric emptying of ingested food in lean mice. Sprague-Dawley rats are unresponsive to the food intake-reducing effect of a single intraperitoneal injection of mouse leptin at a dose 10-fold higher than that shown to be effective in mice within the first 4-7 h postinjection.

Inhibition of gastric acid secretion by stress: a protective reflex mediated by cerebral nitric oxide

Moderate somatic stress inhibits gastric acid secretion. We have investigated the role of endogenously released NO in this phenomenon. Elevation of body temperature by 3 degrees C or a reduction of 35 mmHg (1 mmHg = 133 Pa) in blood pressure for 10 min produced a rapid and long-lasting reduction of distension-stimulated acid secretion in the rat perfused stomach in vivo. A similar inhibitory effect on acid secretion was produced by the intracisternal (i.c.) administration of oxytocin, a peptide known to be released during stress. Intracisternal administration of the NO-synthase inhibitor, NG-nitro-L-arginine methyl ester (L-NAME) reversed the antisecretory effect induced by all these stimuli, an action prevented by intracisternal coadministration of the NO precursor, L-arginine. Furthermore, microinjection of L-NAME into the dorsal motor nucleus of the vagus nerve reversed the acid inhibitory effects of mild hyperthermia, i.v. endotoxin, or i.c. oxytocin, an action prevented by prior microinjection of L-arginine. By contrast, microinjection of L-NAME into the nucleus tractus solitarius failed to affect the inhibitory effects of hyperthermia, i.v. endotoxin, or i.c. oxytocin. Immunohistochemical techniques demonstrated that following hyperthermia there was a significant increase in immunoreactivity to neuronal NO synthase in different areas of the brain, including the dorsal motor nucleus of the vagus. Thus, our results suggest that the inhibition of gastric acid secretion, a defense mechanism during stress, is mediated by a nervous reflex involving a neuronal pathway that includes NO synthesis in the brain, specifically in the dorsal motor nucleus of the vagus.

Involvement of prostaglandins and 5-hydroxytryptamine in the contractile effect of platelet-activating factor in rat isolated gastric corpus

The present study characterizes the nature of the response to the platelet-activating factor (PAF) in isolated gastric corpus with and without mucosa. PAF (10(-8) M) induced contraction of rat isolated gastric corpus strips followed by desensitization of this tissue. Incubation of strips with the specific PAF-receptor antagonist WEB 2086 (5 x 10(-8) -5 x 10(-5) M) the prostaglandin blocker indomethacin (10(-6) M) and the 5-hydroxytryptamine antagonist methysergide (10(-5) M) reduced significantly the contraction induced by PAF. Neither of the histamine H1/H2 antagonists diphenhydramine (10(-6) M) or cimetidine (10(-5) M) affected the contraction induced by PAF. In contrast with the whole gastric corpus, in mucosa-free strips, the contractile effect of PAF was not modified by methysergide. The present study supports the view that the effect of PAF is mediated by activation of specific PAF receptors and the release of prostaglandins and 5-hydroxytryptamine in isolated gastric corpus. Furthermore, our results suggest a role of the gastric mucosa via the release of 5-hydroxytryptamine which contributes to the contractile effect of PAF in the gastric smooth muscle.

Protection by almagate of ethanol-induced gastric mucosal damage in rats

The study was designed to analyse the protective effects of almagate on a model of gastric injury, ethanol-induced mucosal damage, in which acid plays little, if any, role. Pretreatment with almagate dose-dependently reduced the level of gastric damage induced by oral administration of 1 mL 100% ethanol. Administration of 12 mumol kg-1 alamagate 30 min before ethanol significantly reduced the area of mucosal damage by 65 +/- 10%, and the maximum level of inhibition (74 +/- 11%) was obtained with 150 mumol kg-1 almagate. Administration of higher doses of almagate (200-250 mumol kg-1) did not result in any further increase in the level of protection against ethanol-induced gastric damage. Administration of 1 mL 100% ethanol induces substantial damage to the gastric mucosa, with nearly 40% of the length of the section evaluated exhibiting deep necrotic and haemorrhagic damage. Pretreatment with almagate caused a significant diminution in all parameters of histological damage, whereas damage to the epithelial cell layer was only significantly reduced by pretreatment with the highest doses evaluated (25, 50 and 150 mumol kg-1). Administration of aluminium hydroxide did not modify ethanol-induced mucosal damage, even at doses containing concentrations of aluminium higher than those present in gastroprotective doses of almagate. Pretreatment with sucralfate, another aluminium containing compound, at doses of 250 mumol kg-1 protected the mucosa, although lower doses did not. The present study has shown that almagate prevents ethanol-induced gastric mucosal damage.(ABSTRACT TRUNCATED AT 250 WORDS)

Endotoxin inhibition of distension-stimulated gastric acid secretion in rat: mediation by NO in the central nervous system

1. The involvement of nitric oxide in the acute inhibitory effects of low doses of endotoxin, following intracerebroventricular (i.c.v.) or intravenous (i.v.) administration, on gastric acid secretion stimulated by distension or i.v. infusion of pentagastrin has been investigated in the continuously perfused stomach of the anaesthetized rat. 2. The i.c.v. administration of E. coli endotoxin (800 ng kg-1) abolished the acid secretory response induced by gastric distension (20 cm water intragastric pressure) within 30 min of administration. 3. By contrast, submaximal rates of acid secretion induced by i.v. infusion of pentagastrin (8 micrograms kg-1 h-1) were not inhibited by i.c.v. administration of endotoxin (800 ng kg-1). 4. Prior i.c.v. administration of the NO synthase inhibitor, NG-nitro-L-arginine methyl ester (L-NAME, 800 micrograms kg-1) restored the acid secretory responses to distension in rats treated with endotoxin (i.c.v.). 5. Likewise, i.v. administration of endotoxin (5 micrograms kg-1) abolished the acid secretory response induced by gastric distension within 30 min of administration. Prior i.c.v. injection of L-NAME (800 micrograms kg-1) or its i.v. administration (10 mg kg-1) restored acid secretory responses in rats receiving i.v. endotoxin. 6. The reversal by L-NAME (i.v.) of the acid inhibitory effects of endotoxin (i.v.) was prevented by L-arginine (12 mg kg-1, i.c.v. or 100 mg kg-1, i.v.), but not by its enantiomer D-arginine. 7. The present results imply the existence of an acute response to endotoxin involving NO synthesis in the brain. NO may act as a neuromodulator or neurotransmitter in a nervous reflex leading to the inhibition of acid secretion stimulated by gastric distension.

Neonatal capsaicin treatment does not prevent splanchnic vasodilatation in portal-hypertensive rats

It has been suggested that the peripheral sensory neurons are involved in the splanchnic hemodynamic changes of portal hypertension. Therefore the influence of permanent ablation of sensory neurons by neonatal capsaicin pretreatment (50 mg/kg, subcutaneously) on the development of the hyperdynamic splanchnic circulation in portal-hypertensive rats was studied. In adulthood, portal hypertension was induced with partial portal vein ligation. In study 1, systemic and splanchnic hemodynamics were measured by means of a radiolabeled-microsphere technique in portal-hypertensive rats, under ketamine anesthesia, pretreated with capsaicin or vehicle. Mean arterial pressure, heart rate, cardiac index, systemic and splanchnic vascular resistance, portal pressure, portal venous inflow, portal-collateral resistance and portal-systemic shunting were not significantly different between capsaicin-pretreated and vehicle-pretreated rats. In study 2, gastric mucosal blood flow, measured by means of hydrogen gas clearance, and the hemoglobin and oxygen content of the gastric mucosa, as assessed with reflectance spectrophotometry, were not significantly different in the two groups of anesthetized portal-hypertensive rats pretreated with capsaicin or vehicle. In study 3, we confirmed the effectiveness of neonatal capsaicin pretreatment by measuring calcitonin gene-related peptide content of the gastric corpus wall. Capsaicin pretreatment caused a depletion of calcitonin gene-related peptide by at least 98% compared with that in vehicle-pretreated rats. These results do not support a role of capsaicin-sensitive sensory neurons that innervate the gastrointestinal tract in the development of the splanchnic vasodilatation characteristically observed in chronic portal hypertension.

Acute normovolaemic anaemia prevents ethanol-induced gastric damage in rats through a blood flow related mechanism

The aim of the study was to assess whether changes in gastric mucosal blood flow induced by acute normovolaemic anaemia influence the susceptibility of the gastric mucosa to ethanol-induced damage, and the relationship of these changes with nitric oxide biosynthesis. Acute normovolaemic anaemia, promoted by exchanging 3 ml of blood by a plasma expander, induced a significant increase in gastric mucosal blood flow measured by hydrogen gas clearance, without changes in arterial blood pressure. After intragastric 60% ethanol administration, gastric blood flow was still significantly higher in anaemic than in control rats, and this was associated with a lower macroscopic and microscopic gastric damage. Following ethanol administration, anaemic rats pretreated with an inhibitor of nitric oxide biosynthesis (L-NMMA, 50 mg/kg, i.v.) had a lower gastric blood flow and a higher macroscopic gastric damage than anaemic rats without pretreatment. Anaemic rats pretreated with vasopressin also had after ethanol administration a lower gastric blood flow and a higher macroscopic gastric damage. It is concluded that acute normovolaemic anaemia protects the gastric mucosa against damage induced by intragastric ethanol. The inhibition of nitric oxide biosynthesis reverts in part this protective effect, and this seems to be related with the capability of nitric oxide to increase gastric mucosal blood flow, since vasoconstriction by a nitric oxide-independent mechanism causes a similar effect.

Involvement of neuronal processes and nitric oxide in the inhibition by endotoxin of pentagastrin-stimulated gastric acid secretion

Administration of E. coli endotoxin (1 mg kg-1, i.v.) abolished the acid response induced by the i.v. infusion of pentagastrin (8 micrograms kg-1 h-1) in the continuously perfused stomach of the anaesthetized rat. Local serosal application of tetrodotoxin (36 ng per rat) completely restored acid responses to pentagastrin in endotoxin-treated rats. However, pretreatment with atropine (0.5 mg kg-1, s.c.), capsaicin (20, 30, and 50 mg kg-1, s.c. 2 weeks before the study) or guanethidine (16 mg kg-1, s.c. 3 and 16h before) did not influence the inhibitory effects of endotoxin. Continuous i.v. infusion with NG-nitro arginine methyl ester (L-NAME, 10 mg kg-1 h-1) restored the secretory responses to pentagastrin in endotoxin treated rats. The effects of L-NAME were reversed by L-arginine (100 mg kg-1 h-1, i.v.), but not by its enantiomer D-arginine (100 mg kg-1 h-1, i.v.). The secretory responses elicited by pentagastrin (10(-10)-10(-6) M) in the isolated lumen perfused stomach of the rat were not influenced by incubation (100 min) with endotoxin (10 micrograms ml-1). These observations with tetrodotoxin indicate that inhibition of acid secretion by endotoxin in vivo involves neuronal activity, while inhibition of NO synthesis had a comparable inhibitory action. Activation of a systemic non-adrenergic non-cholinergic neuronal pathway involving NO could thus mediate the acute acid inhibitory effects of endotoxin.

Involvement of endogenous nitric oxide in the inhibition by endotoxin and interleukin-1 beta of gastric acid secretion

Administration of Escherichia coli endotoxin abolished the acid secretory response induced by a bolus injection of pentagastrin in the continuously perfused stomach of the anaesthetized rat. Likewise, acid secretion stimulated by the continuous intravenous perfusion of pentagastrin was inhibited by administration of interleukin-1 beta (IL-1 beta). In both cases pretreatment with NG-nitro-L-arginine methyl ester (L-NAME) but not dexamethasone or indomethacin substantially restored the secretory responses to pentagastrin. The actions of L-NAME were reversed by the prior administration of L-arginine but not by its enantiomer D-arginine. Even though L-NAME increased blood pressure, this does not seem to be the mechanism by which endotoxin-induced acid inhibition was prevented, since similar systemic pressor responses induced by phenylephrine had no such effect. The secretory response elicited by pentagastrin in the isolated lumen perfused stomach of the rat was not influenced by incubation (100 min) with IL-1 beta. These observations suggest that the acute inhibition of acid responses to pentagastrin by endotoxin and IL-1 beta involves nitric oxide (NO) synthesis from L-arginine.

Nitric oxide mediates the inhibition by interleukin-1 beta of pentagastrin-stimulated rat gastric acid secretion

Bolus injection of interleukin-1 beta (2 micrograms kg-1, i.v.) inhibited acid secretion induced by intravenous infusion of pentagastrin (8 micrograms kg-1 h-1) in the continuously perfused stomach of the anaesthetized rat. Administration of interleukin-1 beta did not modify mean systemic arterial blood pressure. Pretreatment with NG-nitro-L-arginine methyl ester (L-NAME, 2-10 mg kg-1, i.v.), but not dexamethasone (5 mg kg-1, s.c. twice over 16 h), restored the acid secretory responses to pentagastrin. The actions of L-NAME were reversed by the prior administration of L-arginine (100 mg kg-1, i.v.), but not by its enantiomer D-arginine (100 mg kg-1, i.v.). L-NAME (5 mg kg-1, i.v.) increased blood pressure but this was not the mechanism by which interleukin-induced acid inhibition was prevented, since similar systemic pressor responses induced by phenylephrine (10 micrograms kg-1 min-1, i.v.), had no such effect. These findings suggest that interleukin-induced inhibition of acid responses to pentagastrin involves synthesis of NO from L-arginine.

Differential effects of locally-applied capsaicin on distension-stimulated gastric acid secretion in the anesthetized rat

The effects induced by the local administration of capsaicin on acid production have been investigated in the continuously perfused stomach of the anesthetized rat. Basal acid secretion was not influenced by 10 min intragastric perfusion with capsaicin (300 micrograms min-1). Acid responses elicited by distension of the stomach with increases in intragastric pressure of 5 and 10 cm H2O were not modified after a 10 min intraluminal infusion with 80 or 300 micrograms min-1 of capsaicin. H+ output stimulated by higher intraluminal pressure (20 cm H2O) were significantly decreased by intraluminal infusion of capsaicin (20, 80, 300 and 600 micrograms min-1). Acid responses to carbachol (4 micrograms kg-1, i.p.) were not influenced by intragastric (300 micrograms min-1), or systemic neonatal, treatment with capsaicin. Intraluminal infusion of the neurotoxin tetrodotoxin (0.12 micrograms min-1, 10 min) decreased acid responses to an increase in intragastric pressure of 20 cm H2O but not those elicited by distention with a pressure of 10 cm H2O. Neonatal systemic treatment (s.c.) with capsaicin or local gastric serosal application of either capsaicin or tetrodotoxin abolished acid responses to gastric distension (+20 cm H2O). Capsaicin (80 micrograms min-1) and tetrodotoxin (0.12 micrograms min-1) infused concurrently into the lumen did not inhibit gastric acid secretion stimulated by an increase of 20 cm H2O in intragastric pressure to any greater extent than did either drug given alone.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of nitric oxide and platelet-activating factor in the inhibition by endotoxin of pentagastrin-stimulated gastric acid secretion

Administration of E. coli endotoxin (1 mg/kg i.v.) abolished the acid secretory response induced by a bolus injection of pentagastrin (100 micrograms/kg i.v.) in the continuously perfused stomach of the anaesthetized rat. Endotoxin administration did not modify mean systemic arterial blood pressure. Pretreatment with NG-nitro-L-arginine methyl ester (L-NAME; 5-20 mg/kg i.v.), but not dexamethasone (5 mg/kg s.c. twice) or indomethacin (5 mg/kg i.m.), substantially restored the secretory responses to pentagastrin. The actions of L-NAME were reversed by the prior administration of L-arginine (100 mg/kg i.v.), but not by its enantiomer D-arginine (100 mg/kg i.v.). L-NAME (10 mg/kg i.v.) increased blood pressure but this does not seem to be the mechanism by which endotoxin-induced acid inhibition was prevented, since similar systemic pressor responses induced by noradrenaline (15 micrograms/kg per min i.v.) had no such effect. The platelet-activating factor (PAF) receptor antagonist, WEB 2086 (2 mg/kg), induced a partial reversal of the inhibition by endotoxin of acid responses to pentagastrin. In endotoxin-treated rats, the combined administration of L-NAME (10 mg/kg) and WEB 2086 (2 mg/kg) completely restored the degree of H+ output induced by pentagastrin to levels similar to those of control, vehicle-treated animals. These findings suggest that endotoxin-induced acute inhibition of acid responses to pentagastrin involves NO synthesis and the release of PAF.

Modulation by peripheral opioids of basal and distension-stimulated gastric acid secretion in the rat

1. The influence of opioids in modulating gastric acid secretory responses has been investigated in the continuously perfused stomach of the anaesthetized rat. 2. Intravenous administration of morphine (0.75-3 mg kg-1) or the peripherally acting enkephalin analogue, BW443C (0.75-3 mg kg-1), substantially augmented acid secretion in basal conditions. These effects were significantly inhibited by the opioid antagonists naloxone (1 mg kg-1) and the peripherally acting N-methylnalorphine (2 mg kg-1). When administered alone, neither opioid antagonist influenced basal acid output. 3. Acid secretory responses to different levels of gastric distension (5-20 cmH2O) were significantly and dose-dependently reduced in rats pretreated with morphine (3 mg kg-1) or BW443C (1.5 mg kg-1). Previous administration of either naloxone or N-methyl nalorphine reversed the inhibitory effects of opioids on gastric acid secretion stimulated by distension. Likewise, blockade of opioid receptors with naloxone or N-methylnalorphine significantly increased acid output induced by distension. 4. Levels of serum gastrin in control animals were not increased after intragastric distension (20 cmH2O). Pretreatment with BW443C (1.5 mg kg-1) did not modify the levels of gastrin present during basal or distension stimulated conditions. 5. Pretreatment with morphine or BW443C did not influence the acid responses to i.v. injection of pentagastrin (100 micrograms kg-1), histamine (5 mg kg-1) or carbachol (4 micrograms kg-1). Acid secretion induced by i.v. administration of 2-deoxy-D-glucose (150 mg kg-1) was reduced in rats pretreated with morphine but not with BW443C. Gastric secretory responses to insulin (0.3 i.u. kg-1) were not modified by i.v. morphine.6. These observations support a role for peripherally acting opioids in the regulation of gastric acid secretion during basal and distension-stimulated conditions.

Response to noradrenaline and histamine in normal and sensitized guinea pig aorta and its relation to endothelium

Pharmacological reactivity of sensitized blood vessels has been less studied than that of airways. Aorta rings were obtained from normal and actively sensitized guinea pigs and prepared for isometric recording of tension changes. Noradrenaline (10 nM-10 microM), histamine (0.1 microM-0.1 mM) and KCl (10-100 mM) produced concentration-related contractions of normal tissues. Removal of endothelium resulted in a marked left upward shift of the concentration-response curve to noradrenaline but it did not alter histamine- or KCl-induced responses. Pretreatment with ibuprofen (10 microM) or L-NG-nitroarginine (L-NOARG, 3.3 microM) enhanced noradrenaline-induced responses without affecting those to histamine or KCl. Removal of endothelium or pretreatment with ibuprofen or L-NOARG did not alter agonist-induced responses in sensitized tissues. Neuronal uptake and release of [3H]-noradrenaline did not differ in normal and sensitized tissues. Loss of the modulatory role of endothelium and other mechanisms may be involved in the hyperreactivity of sensitized guinea pig aorta.

Differential effects of cyclooxygenase inhibitors on the cardiovascular response to hyperosmotic mannitol

The intravenous infusion of mannitol (1.37 mosm kg-1 min-1 during 4 min) to anesthetized, open-chest, intact dogs produced a hemodynamic response characterized by a positive inotropic effect and a decrease in total peripheral resistance. This response is attributable to a direct effect of hypertonicity (plasma osmolality raised from 309 +/- 4 to 332 +/- 5 mosm kg-1 H2O). Pretreatment with indomethacin (5 mg kg-1 i.v.) or meclofenamic acid (2 mg kg-1 i.v.) attenuated the mannitol-induced response but acetylsalycilic acid (10 mg kg-1 i.v.) was without effect. Indomethacin (5 mg kg-1 i.v.) did not change the decrease in canine hindlimb perfusion pressure produced by intra-arterial mannitol 5 mosm kg-1. Indomethacin (3 microM) did not alter the chronotropic and inotropic responses to mannitol (150 mosm above normal) in isolated rabbit atria. These results suggest that the cardiovascular response to hyperosmotic mannitol may be partly mediated in intact animals by prostaglandin release.