Biomedical subjects

K A Sharkey

Publications and source records attributed to K A Sharkey.

At least 37 records · Page 2Linked to original sources

PubMed2000

Progressive development of a Th1-type hepatic cytokine profile in rats with experimental cholangitis.

Primary biliary cirrhosis (PBC) and primary sclerosing cholangitis (PSC) are presumed autoimmune chronic cholestatic liver diseases characterized by cholangitis and progressive loss of bile ducts. Cytokines have been postulated to be involved in the progression of these diseases, but their role is poorly defined. Our objectives were to characterize a rat model of cholangitis and to determine Type 1/Type 2 (Th1/Th2) cytokine profile shifts in this model. Cholangitis was induced in Sprague-Dawley rats (200 to 225 g) by low-dose oral administration of the biliary toxin alpha-naphthylisothiocyanate (ANIT) (1 g/kg powdered rat chow ad libitum) for 4, 7, and 14 days. Cholestasis was observed in ANIT-treated animals. Liver histology of ANIT-treated rats showed hepatic inflammation centered on damaged bile ducts, significant bile duct proliferation, and progressive fibrosis. Immunohistochemistry showed enhanced staining of hepatic major histocompatibility complex (MHC) II, CD4, and CD8 in portal areas of ANIT-treated animals. In addition, the hepatic cytokine profile became increasingly Th1 in nature with progressive ANIT treatment. In summary, experimental cholangitis biochemically and histologically mimics human chronic cholangitis and furthermore, is associated with a progressive shift to a more Th1-dominant hepatic cytokine profile. Therefore, this model may be useful for examining the role of cytokines in the progression of chronic cholangitic diseases.

Animals↗

PubMed2000

A novel receptor for calcitonin gene-related peptide (CGRP) mediates secretion in the rat colon: implications for secretory function in colitis.

The receptor responsible for CGRP-induced ion transport and permeability was examined in tissues from animals treated 7 days previously with trinitrobenzenesulfonic acid to induce colitis or in controls. CGRP caused a concentration-dependent increase in short circuit current (I(sc), EC(50) 21 nM), which was abolished in chloride-free buffer but was not blocked by CGRP(8-37) or tetrodotoxin (TTX). Amylin and adrenomedullin caused only a modest increase in I(sc). The responses to the linear CGRP(2) receptor agonists [Cys(Et)(2,7)] hCGRPalpha and [Cys(Acm)(2,7)] hCGRPalpha were considerably smaller than the response to CGRP. These responses were abolished in chloride-free buffer and were TTX sensitive. Atropine, doxantrazole, and indomethacin did not block the effects of CGRP or the CGRP(2) agonists. The response to [Cys(Et)(2,7)] hCGRPalpha was not affected by prior desensitization of the CGRP receptor and vice versa. Inflamed rats had a similar secretory response to CGRP (I(sc), EC(50) 15 nM) and [Cys(Et)(2,7)] hCGRPalpha as control tissues, while being hyporesponsive to carbachol. CGRP application increased electrical conductance of inflamed preparations. Taken together, these data suggest that CGRP may play an important role in the maintenance of host defense in colitis through an apparently novel CGRP receptor located on the colonic enterocyte.

Animals↗

PubMed2000

Spontaneously developing chronic colitis in IL-10/iNOS double-deficient mice.

Mice deficient in both inducible nitric oxide synthase (iNOS) and interleukin (IL)-10 (iNOS(-/-)/IL-10(-/-)) were created to examine the role of iNOS in spontaneously developing intestinal inflammation. IL-10(-/-)/iNOS(-/-) mice were compared with IL-10(-/-) (iNOS(+/+)) littermates over 6 mo. RT-PCR, Western blot analysis, and immunohistochemistry were performed to measure iNOS message and protein levels. Plasma nitrate/nitrite (NO(x)) levels were assessed by HPLC. Damage scores (macroscopic and microscopic) and granulocyte infiltration were assessed. At 3-4 wk, IL-10(-/-) and IL-10(-/-)/iNOS(-/-) mice had no signs of colonic inflammation or granulocyte infiltration. Plasma NO(x) levels were not different from controls. By 3-4 mo, IL-10(-/-) mice had increased damage scores and granulocyte infiltration concurrent with increased mRNA and protein synthesis (restricted to the epithelium) for iNOS in intestinal tissues but not other tissues. Plasma NO(x) levels increased fivefold. Interestingly, in the absence of iNOS induction or increased plasma NO(x), iNOS(-/-)/IL-10(-/-) mice had damage and granulocyte infiltration equivalent to those observed in IL-10(-/-) littermates. These data suggest that iNOS does not impact on the development or severity of spontaneous chronic inflammation in IL-10-deficient mice.

Age Factors↗

PubMed2000

Effect of splanchnectomy on jejunal motility and fos expression in brain stem after intestinal anaphylaxis in rat.

This study was to determine whether alterations in jejunal motility observed after antigen challenge of sensitized rats occurred after extirpation of the celiac-superior mesenteric ganglia. Hooded-Lister rats were prepared with an intact or extirpated celiac-superior mesenteric ganglion, an isolated Thiry-Vella loop of ileum for instillation of antigen, and jejunal electrodes for myoelectric recording. Animals were sensitized by injection of 10 microg egg albumin (EA, ip), and specific anti-EA IgE titers were determined to be >1:64. In both control and splanchnectomized rats, normal fasting migrating myoelectric complexes (MMC) were observed before challenge with EA. MMCs were disrupted, and diarrhea was observed immediately after EA challenge of control but not splanchnectomized animals. Brain stems were removed and processed for Fos immunoreactivity. The absence of perivascular neuropeptide Y immunoreactivity in the submucosa was used to confirm the success of splanchnectomy. The number of Fos-immunoreactive neuronal nuclei was significantly reduced in the brain stem after splanchnectomy. Thus the mesenteric sympathetic ganglia are an integral part of the extramural neuronal pathways required for altered motility in this model of intestinal anaphylaxis.

Anaphylaxis↗

PubMed2000

Role of cyclooxygenase-2 in modulating gastric acid secretion in the normal and inflamed rat stomach.

Nonsteroidal anti-inflammatory drugs elevate gastric acid secretion, possibly contributing to their ability to interfere with gastric ulcer healing. Inhibitors of cyclooxygenase-2 have been shown to delay experimental gastric ulcer healing. In the present study, we tested the hypothesis that cyclooxygenase-2-derived prostaglandins modulate gastric acid secretion. Studies were performed in normal rats and in rats with iodoacetamide-induced gastritis. Inflammation in the latter group was confirmed histologically and by a threefold increase in tissue levels of the granulocyte marker myeloperoxidase and was also associated with overexpression of cyclooxygenase-2 in the stomach. Basal acid secretion in both groups of rats was not affected by pretreatment with DuP-697, a selective inhibitor of cyclooxygenase-2. A nonselective cyclooxygenase inhibitor, indomethacin, had no effect on acid secretion in normal rats but caused a doubling of acid secretion in the rats with gastritis. DuP-697 had no effect on pentagastrin-induced secretion in either group of rats. Gastritis itself was associated with significantly increased pentagastrin-induced acid secretion, and this was further increased in rats pretreated with indomethacin. These results suggest that in a setting of gastric inflammation, prostaglandins derived from cyclooxygenase-1, not cyclooxygenase-2, exert inhibitory effects on acid secretion.

Animals↗

PubMed1999

Nitric oxide participates in the recovery of normal jejunal epithelial ion transport following exposure to the superantigen, Staphylococcus aureus enterotoxin B.

Bacterial superantigens (SAgs) are potent T cell activators. Mice treated 4 h previously with the SAg, Staphylococcus aureus enterotoxin B (SEB), display reduced ion transport (assessed by short circuit current) responses to prosecretory stimuli, which normalize 24 h posttreatment. Here, mice were treated with SEB alone or in combination with an inhibitor of the inducible form of NO synthase (iNOS), l -NIL. Subsequently, jejunal iNOS expression was detected by immunohistochemistry, ion transport was evaluated in Ussing chambers, and serum levels of TNF-alpha and IFN-gamma were measured by ELISA. SEB-treated mice had increased epithelial iNOS immunoreactivity, and numerous iNOS-positive CD3+ T cells occurred in their mucosa and submucosa. Concomitant treatment with l -NIL did not affect the reduced short circuit current responsiveness to electrical nerve stimulation or the prosecretory agents, carbachol and forskolin, that occurred 4 h post-SEB (5 microgram) treatment. However, Isc responses in l -NIL- plus SEB-treated mice were still significantly reduced 24 h posttreatment, indicating a role for NO in the restoration of normal ion transport following exposure to SAgs. The prolongation of epithelial ion transport abnormalities correlated with elevated serum levels of TNF-alpha and IFN-gamma in mice treated 24 h previously with l -NIL plus SEB compared with those in controls and SEB-only-treated mice. Additionally, mice treated with l -NIL plus SEB and TNF-alpha- or IFN-gamma-neutralizing Abs displayed normal jejunal ion transport characteristics 24 h posttreatment. We conclude that NO mobilization is important in the homeostatic recovery response following immune stimulation by SAgs and that the beneficial effect of NO in this model system is probably via regulation of TNF-alpha and IFN-gamma production.

Animals↗

PubMed1999

c-Fos expression in the myenteric plexus, spinal cord and brainstem following injection of formalin in the rat colonic wall.

Fos expression induced by injection of dilute formalin (50 microl, 5% in physiological saline) into the colonic wall was examined in the myenteric plexus, lumbosacral spinal cord and brainstem of the rat. The aims of this study were (i) to determine whether neurons in these regions express Fos in response to the injection of formalin into the colon and (ii) to examine whether administration of an alpha 2 adrenoceptor agonist modulates Fos expression. Tissues were removed 2 h after the injection of saline or formalin. Saline injected in the colon induced Fos in enteric glia in the myenteric plexus. The number of Fos immunoreactive nuclei significantly increased in both myenteric neurons and enteric glia after the injection of formalin. Similarly, Fos immunoreactive neuronal nuclei were significantly increased in the spinal cord, area postrema and nucleus of the solitary tract after the injection of formalin. Pretreatment of rats with the alpha 2 adrenoceptor agonist xylazine (2, 4 and 8 mg/kg) 15 min before the injection of formalin, dose-dependently reduced the number of Fos immunoreactive neuronal and glial nuclei in the myenteric plexus, and neuronal nuclei in the spinal cord and brainstem. Simultaneous administration of xylazine (8 mg/kg) and the alpha 2 adrenoceptor antagonist yohimbine (1 mg/kg) reversed the effects of xylazine in the spinal cord and brainstem, but not in the myenteric plexus. These data show that injection of formalin in the colonic wall results in Fos expression in myenteric neurons and enteric glia, and neurons in the spinal cord and brainstem. This may be due to the direct chemical stimulation of the innervation of the colon and/or the subsequent acute colitis. The observed neuronal Fos expression can be modulated by an alpha 2 adrenoceptor agonist through noradrenergic pathways and/or reduction of the excitability of the enteric neural circuitry.

Adrenergic alpha-Agonists↗

PubMed1999

Correlation of morphology, electrophysiology and chemistry of neurons in the myenteric plexus of the guinea-pig distal colon.

Intracellular recordings were made from myenteric neurons of the guinea-pig distal colon to determine their electrical behaviour in response to intracellular current injection and stimulation of synaptic inputs. The recording microelectrode contained the intracellular marker biocytin, which was injected into impaled neurons so that electrophysiology, shape and immunohistochemistry could be correlated. Myenteric neurons in the distal colon were divided into four morphological groups based on their shapes and projections. One group (29 of the 78 that were characterized electrophysiologically, morphologically and immunohistochemically) was the multiaxonal Dogiel type II neurons, the majority (25/29) of which were calbindin immunoreactive. Each of these neurons had an inflection on the falling phase of the action potential that, in 24/29 neurons, was followed by a late afterhyperpolarizing potential (AHP). Slow excitatory postsynaptic potentials were recorded in 20 of 29 Dogiel type II neurons in response to high frequency internodal strand stimulation and two neurons responded with slow inhibitory postsynaptic potentials. Low amplitude fast excitatory postsynaptic potentials occurred in 3 of 29 Dogiel type II neurons. Neurons of the other three groups were all uniaxonal: neurons with Dogiel type I morphology, filamentous ascending interneurons and small filamentous neurons with local projections to the longitudinal or circular muscle or to the tertiary plexus. Dogiel type I neurons were often immunoreactive for nitric oxide synthase or calretinin, as were some small filamentous neurons, while all filamentous ascending interneurons tested were calretinin immunoreactive. All uniaxonal neurons exhibited prominent fast excitatory postsynaptic potentials and did not have a late AHP following a single action potential, that is, all uniaxonal neurons displayed S type electrophysiological characteristics. However, in 6/19 Dogiel type I neurons and 2/8 filamentous ascending interneurons, a prolonged hyperpolarizing potential ensued when more than one action potential was evoked. Slow depolarizing postsynaptic potentials were observed in 20/29 Dogiel type I neurons, 6/8 filamentous ascending interneurons and 8/12 small filamentous neurons. Six of 29 Dogiel type I neurons displayed slow inhibitory postsynaptic potentials, as did 2/8 filamentous ascending interneurons and 4/12 small filamentous neurons. These results indicate that myenteric neurons in the distal colon of the guinea-pig are electrophysiologically similar to myenteric neurons in the ileum, duodenum and proximal colon. Also, the correlation of AH electrophysiological characteristics with Dogiel type II morphology and S electrophysiological characteristics with uniaxonal morphology is preserved in this region. However, filamentous ascending interneurons have not been encountered in other regions of the gastrointestinal tract and there are differences between the synaptic properties of neurons in this region compared to other regions studied, including the presence of slow depolarizing postsynaptic potentials that appear to involve conductance increases and frequent slow inhibitory postsynaptic potentials.

Afferent Pathways↗

PubMed1999

Immediate-early gene expression in the inferior mesenteric ganglion and colonic myenteric plexus of the guinea pig.

Activation of neurons in the inferior mesenteric ganglion (IMG) was assessed using c-fos, JunB, and c-Jun expression in the guinea pig IMG and colonic myenteric plexus during mechanosensory stimulation and acute colitis in normal and capsaicin-treated animals. Intracolonic saline or 2% acetic acid was administered, and mechanosensory stimulation was performed by passage of a small (0.5 cm) balloon either 4 or 24 hr later. Lower doses of capsaicin or vehicle were used to activate primary afferent fibers during balloon passage. c-Jun did not respond to any of the stimuli in the study. c-fos and JunB were absent from the IMG and myenteric plexus of untreated and saline-treated animals. Acetic acid induced acute colitis by 4 hr, which persisted for 24 hr, but c-fos was found only in enteric glia in the myenteric plexus and was absent from the IMG. Balloon passage induced c-fos and JunB in only a small subset of IMG neurons and no myenteric neurons. However, balloon passage induced c-fos and JunB in IMG neurons (notably those containing somatostatin) and the myenteric plexus of acetic acid-treated animals. After capsaicin treatment, c-fos and JunB induction by balloon passage was inhibited in the IMG, but there was enhanced c-fos expression in the myenteric plexus. c-fos and JunB induction by balloon stimulation was also mimicked by acute activation of capsaicin-sensitive nerves. These data suggest that colitis enhances reflex activity of the IMG by a mechanism that involves activation of both primary afferent fibers and the myenteric plexus.

Acetic Acid↗

PubMed1999

Characterization of the inflammatory response to proteinase-activated receptor-2 (PAR2)-activating peptides in the rat paw.

In the present study, we have observed the development of an inflammatory reaction in the rat hindpaw, following the injection of specific agonists of PAR2 (two PAR2 activating peptides). This inflammation was characterized by oedema and granulocyte infiltration. Two selective PAR2 activating peptides, SLGRL-NH2 and trans-cinnamoyl-LIGRLO-NH2 induced significant oedema in the rat hindpaw from 1-6 h following subplantar injection. Six hours after the PAR2-activating peptide injection, the paw tissues showed a complete disruption of tissue architecture along with an inflammatory cell infiltrate. In the inflamed paw, PAR2-immunoreactivity was expressed on endothelial cells as well as on the infiltrating inflammatory cells. The oedema induced by the injection of the two PAR2 activating peptides was slightly reduced in rats pre-treated with compound 48/80, but was not modified by pre-treatment of rats with cromolyn, a mast cell stabilizer. Pre-treatment of rats with a cyclo-oxygenase inhibitor (indomethacin) or a nitric oxide synthase inhibitor (L-N(omega)-nitro-L-arginine methyl ester) had no effect on the oedema induced by the PAR2-activating peptides. These results demonstrate that the administration of PAR2-activating peptides into the rat paw induced an acute inflammatory response characterized by a persistent oedema (at least 6 h) and granulocyte infiltration. The PAR2-induced inflammatory response occurred through a mechanism largely independent of mast cell activation, and of the production of prostanoids and nitric oxide.

Animals↗

PubMed1999

Temporal distribution of neuronal and inducible nitric oxide synthase and nitrotyrosine during colitis in rats.

Nitric oxide (NO) has been implicated in the pathogenesis of inflammatory bowel disease since increased NO production is observed in this disease. NO can react with superoxide to generate peroxynitrite which causes and/or exacerbates colitis. Peroxynitrite, in turn, nitrates tyrosine residues to form nitrotyrosine which can be identified immunohistochemically. We investigated the distribution of neuronal and inducible nitric oxide synthase (iNOS) and nitrotyrosine over time in experimental colitis. Colitis was induced by intracolonic administration of trinitrobenzene sulphonic acid (TNBS) in rats. Animals were killed 1, 2, 7 and 14 days after treatment. Myeloperoxidase activity was used as an index of inflammation, and tissues were examined using immunohistochemistry. Neuronal NOS immunoreactivity was present throughout the colon, and was only slightly reduced 1 day after the induction of colitis. Conversely, iNOS immunoreactivity almost absent in controls dramatically increased in the mucosa and submucosa at the early stages of inflammation. iNOS was present in monocytes and macrophages and also another unidentified cell type. Seven and 14 days after the induction of colitis, iNOS was also found in nerves in the circular muscle and in the myenteric plexus. Nitrotyrosine immunoreactivity present in a few cells in the normal mucosa also increased 1 day after the induction of colitis and decreased thereafter. The pattern of distribution of nitrotyrosine immunoreactivity was distinct from that of iNOS. The increase of iNOS expression at the early stage of inflammation may play a role in causing tissue injury via peroxynitrite formation. The expression of iNOS seen in the enteric nerves in the later stage of inflammation correlates temporally with the beginning of tissue repair and with the re-innervation and compensatory growth of nerves. NO may potentially play a physiological as well as pathological role in experimental colitis.

Animals↗

PubMed1999

Role of inducible nitric oxide synthase in trinitrobenzene sulphonic acid induced colitis in mice.

BACKGROUND: Studies using inhibitors of nitric oxide synthase (NOS) to date are inconclusive regarding the role of inducible NOS (iNOS) in intestinal inflammation. AIMS: (1) To examine the role of iNOS in the development of chronic intestinal inflammation; (2) to identify the cellular source(s) of iNOS. METHODS: Colitis was induced by an intrarectal instillation of trinitrobenzene sulphonic acid (TNBS, 60 mg/ml, 30% ethanol), in wild type (control) or iNOS deficient mice. Mice were studied over 14 days; the colons were scored for injury and granulocyte infiltration was quantified. Blood to lumen leakage of (51)Cr-EDTA was measured as a quantitative index of mucosal damage. RESULTS: At 24 and 72 hours, iNOS deficient mice had significantly increased macroscopic inflammation compared with wild type mice. Granulocyte infiltration increased significantly at 24 hours and remained elevated in iNOS deficient mice at 72 hours, but significantly decreased in controls. However, by seven days post-TNBS macroscopic damage, microscopic histology, granulocyte infiltration, and mucosal permeability did not differ between wild type and iNOS deficient mice. A four- to fivefold increase in iNOS mRNA was observed in wild type mice at 72 hours and seven days post-TNBS and was absent in iNOS deficient mice. Immunohistochemistry techniques showed that iNOS expression was predominantly localised in neutrophils, with some staining also in macrophages. CONCLUSIONS: These results suggest that leucocyte derived iNOS ameliorates the early phase, but does not impact on the chronic phase of TNBS induced colitis despite the presence of iNOS.

Acute Disease↗

PubMed1999

Differential induction of nitric oxide synthase in rat gastric and vascular smooth muscle tissue: distinct tissue distribution and distinctive signaling pathways.

In rat aorta rings (RA) and in gastric circular muscle (CM) and gastric longitudinal muscle (LM) preparations maintained in vitro, inducible nitric oxide synthase (iNOS) induction was monitored functionally (1 mM L-arginine-induced relaxation), biochemically (appearance of iNOS mRNA), and immunohistochemically. Functional iNOS (L-arginine-mediated relaxation) was induced in RA and CM tissues (but NOT in the LM preparation) over 2 to 5 h. iNOS induction was detected by immunocytochemistry in RA smooth muscle elements and in macrophage-like cells in CM. Functional iNOS induction correlated with iNOS mRNA induction. In the RA and CM, functional iNOS induction was blocked by both actinomycin D and cycloheximide; actinomycin D also blocked the appearance of iNOS mRNA in both tissues. In contrast, cycloheximide blocked CM (but not RA) iNOS mRNA induction. In CM tissue, functional iNOS induction was not affected by genistein, tyrphostin 47/AG213, or vanadate. But, in the RA, both genistein and tyrphostin 47/AG213 blocked the appearance of functional iNOS; neither inhibitor prevented the appearance of RA iNOS mRNA. Vanadate, in the RA tissue, blocked both the appearance of iNOS mRNA and the induction of functional iNOS. In RA tissue, but not in the CM, inhibitors of NF-kappaB activation blocked the appearance of both functional iNOS and iNOS mRNA. We conclude that in different smooth muscle preparations (aorta versus gastric), there can be a differential induction of iNOS mRNA and "functional" iNOS not only in different cellular elements but also in terms of different signaling pathways.

Animals↗

PubMed1998

Lack of beneficial effect of a tachykinin receptor antagonist in experimental colitis.

Nerves within the wall of the intestine may contribute to inflammatory responses, such as those occurring in inflammatory bowel disease. Studies in an experimental model of colitis have demonstrated that neuromodulation, through chemical sympathectomy or administration of lidocaine, can markedly attenuate granulocyte infiltration and tissue injury. Given the many pro-inflammatory effects of substance P, we have evaluated the effects of a tachykinin receptor (NK-1) antagonist, RP 67580, in models of acute colitis in the rat and guinea pig. While administration of RP 67580 and a second NK-1 antagonist (CP-96,345-1) significantly reduced the infiltration of granulocytes into colonic tissue during the first 12 h after induction of colitis in the rat, repeated administration of RP 67580 over a three day period failed to significantly affect granulocyte recruitment or the severity of tissue injury. In contrast, lidocaine enemas were effective in reducing both indices of inflammation/injury. In the guinea pig, similar observations were made. These observations demonstrate that blockade of NK-1 receptors over a three day period failed to significantly modify the course of experimental colitis. It remains possible that the beneficial effects of lidocaine may be due, in part, to inhibition of substance P release, and that the contribution of substance P to inflammation in experimental colitis occurs through NK-1 receptor-independent mechanisms.

Analgesics↗

PubMed1998

Effects of neuropeptides on serotonin release and protein and peroxidase secretion in the isolated rat lacrimal gland.

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Animals↗

PubMed1998

Electrophysiology, shape, and chemistry of neurons that project from guinea pig colon to inferior mesenteric ganglia.

BACKGROUND & AIMS: Prevertebral sympathetic ganglia receive inputs from intestinofugal neurons, with cell bodies located in the wall of the bowel. Intestinofugal neurons are part of the afferent limbs of intestino-intestinal reflexes. The aim of this study was to define the properties of intestinofugal neurons using intracellular recordings. METHODS: Intestinofugal neurons of the distal colon were retrogradely labeled from the inferior mesenteric ganglia. In whole mounts of the myenteric plexus/longitudinal muscle of the distal colon, labeled neurons were identified by their fluorescence and recordings were made using biocytin-filled electrodes. Labeled nerves were characterized immunohistochemically and morphologically. RESULTS: Intestinofugal neurons were uniaxonal neurons with multiple dendrites that had lamellar expansions. They were immunoreactive for choline acetyltransferase. Stimulation of nerve fiber tracts elicited large-amplitude excitatory postsynaptic potentials in all labeled neurons. Some received spontaneous fast excitatory postsynaptic potentials. Those cells that fired action potentials fired only one or two at the start of a depolarizing current pulse. No intestinofugal neurons had Dogiel type II morphology or a late afterhyperpolarizing potential. CONCLUSIONS: Intestinofugal neurons are likely to be activated by other neurons in the gut wall. They are not AH or Dogiel type II neurons. Thus they seem to be second order neurons in afferent pathways of intestino-intestinal reflexes.

Animals↗

PubMed1998

Cyclooxygenase 1 contributes to inflammatory responses in rats and mice: implications for gastrointestinal toxicity.

BACKGROUND & AIMS: Selective inhibitors of cyclooxygenase (COX)-2 are being developed as gastrointestinal-sparing anti-inflammatory drugs based on the premise that this isoform is solely responsible for prostaglandin synthesis at sites of inflammation, whereas COX-1 produces prostaglandins important for maintenance of mucosal integrity. We investigated the relationship between suppression of inflammation by COX-2 inhibitors (NS-398, nimesulide, DuP697, and etodolac) and their effects on gastric prostaglandin synthesis. METHODS: Effects of pretreatment of rats with drugs with a range of in vitro selectivity for COX-2 vs. COX-1 on carrageenan-induced paw inflammation were assessed, along with extent of suppression of COX-1 and COX-2. The role of COX-1 in inflammation was also assessed in COX-2-deficient mice. RESULTS: Significant anti-inflammatory effects were only observed at doses of the drugs that inhibited COX-1. At these doses, the drugs also significantly suppressed gastric prostaglandin synthesis and elicited gastric mucosal erosions. The degree of suppression of prostaglandin synthesis at the site of inflammation correlated significantly with inhibition of COX-1 but not COX-2. CONCLUSIONS: COX-1 makes an important contribution to inflammatory responses. To achieve desirable anti-inflammatory effects, COX-2 inhibitors needed to be given at doses in which selectivity was lost, leading to suppression of gastric prostaglandin synthesis and to mucosal injury.

Animals↗

PubMed1998

Effect of intracolonic benzalkonium chloride on trinitrobenzene sulphonic acid-induced colitis in the rat.

BACKGROUND: We investigated the effects of benzalkonium chloride (BAC) on trinitrobenzene sulphonic acid (TNBS)-induced colitis in rats. METHODS: TNBS was administered intrarectally before and/or after BAC treatment. In the first study, the effects of treatment with BAC 6, 12 or 24 h after TNBS were examined. In the second study, animals were treated with BAC before, after or before and after TNBS, and were examined 7 days later. The severity of colitis was assessed by macroscopic and histological scoring of the colonic damage and by determination of colonic myeloperoxidase (MPO) activity. Macrophages and CD4+ and CD8+ T cells were examined by immunohistochemistry. RESULTS: When BAC was instilled into the colon 6, 12 or 24 h after TNBS, weight loss and macroscopic and histological features of the colon were similar to that of controls (TNBS alone). In contrast, MPO activity was significantly reduced in all three groups post-treated with BAC. In the groups examined 7 days after TNBS treatment, rats post-treated with BAC exhibited increased weight gain and significantly reduced macroscopic damage and MPO activity compared to the TNBS control group. Rats pre-treated with BAC exhibited less macroscopic damage of the colon than rats receiving only TNBS, but histological damage, MPO and weight gain were unchanged from TNBS controls. Immunohistochemistry revealed that BAC pre-treatment increased the numbers of macrophages and T cells in the colon. After TNBS treatment, macrophage accumulation was evident in the colon, but T cells were scarce. However, these cells were preserved or enhanced in the colonic mucosa in TNBS-treated rats that had been pre-treated with BAC. CONCLUSIONS: Treatment with BAC, particularly after induction of colitis, produces a significant reduction in the severity of tissue injury and inflammation through mechanisms that are not fully understood.

Animals↗