S Bertini

Gastric antisecretory role and immunohistochemical localization of cannabinoid receptors in the rat stomach

The role of cannabinoid (CB) receptors in the regulation of gastric acid secretion was investigated in the rat by means of functional experiments and by immunohistochemistry. In anaesthetized rats with lumen‐perfused stomach, the non selective CB‐receptor agonist WIN 55,212‐2 (0.30u2003–u20034.00u2003μmolu2003kg−1, i.v.) and the selective CB1‐receptor agonist HU‐210 (0.03u2003–u20031.50u2003μmolu2003kg−1, i.v.), dose‐dependently decreased the acid secretion induced by both pentagastrin (30u2003nmolu2003kg−1u2003h−1) and 2‐deoxy‐D‐glucose (1.25u2003mmolu2003kg−1, i.v.). By contrast, neither WIN 55,212‐2 (1u2003–u20034u2003μmolu2003kg−1, i.v.) nor HU‐210 (0.03u2003–u20031.50u2003μmolu2003kg−1, i.v.) did modify histamine‐induced acid secretion (20u2003μmolu2003kg−1u2003h−1). The selective CB2‐receptor agonist JWH‐015 (3u2003–u200310u2003μmolu2003kg−1, i.v.) was ineffective. The gastric antisecretory effects of WIN 55,212‐2 and HU‐210 on pentagastrin‐induced acid secretion were prevented by the selective CB1‐receptor antagonist SR141716A (0.65u2003μmolu2003kg−1, i.v.) and unaffected by the selective CB2‐receptor antagonist SR144528 (0.65u2003–u20032u2003μmolu2003kg−1, i.v.). Bilateral cervical vagotomy and ganglionic blockade with hexamethonium (10u2003mgu2003kg−1, i.v., followed by continuous infusion of 10u2003mgu2003kg−1u2003h−1) significantly reduced, but not abolished, the maximal inhibitory effect of HU‐210 (0.3u2003μmolu2003kg−1, i.v.) on pentagastrin‐induced acid secretion; by contrast, pretreatment with atropine (1u2003mgu2003kg−1, i.v.) did not modify the antisecretory effect of HU‐210. Immunoreactivity to the CB1 receptor was co‐localized with that of the cholinergic marker choline acetyltransferase in neural elements innervating smooth muscle, mucosa and submucosal blood vessels of rat stomach fundus, corpus and antrum. In contrast, CB2 receptor‐like immunoreactivity was not observed. These results indicate that gastric antisecretory effects of cannabinoids in the rat are mediated by suppression of vagal drive to the stomach through activation of CB1 receptors, located on pre‐ and postganglionic cholinergic pathways. However, the ineffectiveness of atropine in reducing the effect of HU‐210 suggests that the release of non cholinergic excitatory neurotransmitters may be regulated by CB1 receptors.

Protective effects of proton pump inhibitors against indomethacin-induced lesions in the rat small intestine

Proton pump inhibitors (PPIs) have been shown to be effective in preventing gastric and duodenal ulcers in high-risk patients taking nonsteroidal anti-inflammatory drugs (NSAIDs); by contrast, scarce information is available concerning the effects of PPIs on intestinal damage induced by NSAIDs in humans or in experimental animals. We examined the effects of lansoprazole and omeprazole on the intestinal injury induced by indomethacin in the conscious rat. PPIs were administered by the intragastric route at 30, 60 and 90xa0μmol/kg, 12xa0h and 30xa0min before and 6xa0h after indomethacin treatment. The effects of omeprazole and lansoprazole were evaluated on: (1) macroscopic and histologic damage; (2) mucosal polymorphonuclear cell infiltration; (3) oxidative tissue damage and (4) bacterial translocation from lumen into the intestinal mucosa. Lansoprazole and omeprazole (at 90xa0μmol/kg) significantly decreased (P<0.01) the macroscopic and histologic damage induced by indomethacin in the rat small intestine. Furthermore, both drugs greatly reduced (P<0.01) the associated increases in myeloperoxidase levels and lipid peroxidation induced by indomethacin, whereas they only moderately affected (P<0.05) the translocation of enterobacteria from lumen into the intestinal mucosa. These data demonstrate that omeprazole and lansoprazole can protect the small intestine from the damage induced by indomethacin in the conscious rat. The intestinal protection, possibly related to antioxidant and anti-inflammatory properties of these drugs, may suggest new therapeutic uses of PPIs in intestinal inflammatory diseases.

Modulation of Pentagastrin-Induced Histamine Release by Histamine H3 Receptors in the Dog

BACKGROUNDnThe histamine H3 receptor has been shown to inhibit pentagastrin-induced gastric acid secretion in dogs. Since pentagastrin releases histamine in dogs, we have now assessed whether the effects of H3-receptor ligands may be indirectly mediated by changes in gastric histamine release.nnnMETHODSnPentagastrin infusions (1 or 6 micrograms/kg/h), alone or together with the H3-receptor agonist (R) alpha-methylhistamine (1.2 mumol/kg/h) or the antagonist thioperamide (0.1 mumol/kg/h), were performed in dogs. One group (anaesthetized) was used for enzyme immunoassays of plasma histamine and, when required. (R) alpha-methylhistamine in the gastrosplenic vein, and another group (non-anaesthetized) for measurement of gastric acid secretion.nnnRESULTSnHistamine levels were increased five- and eight-fold after 1 and 6 micrograms/kg/h pentagastrin, respectively, whereas acid output was nearly maximal at the lower dosage. (R) alpha-methylhistamine, at a plasma concentration of 0.15 microM, inhibited histamine release by 78% (P < 0.007) and 37% (not significant) and the total acid output by 44% (P < 0.05) and 19% (not significant) after infusion of 1 and 6 micrograms/kg/h pentagastrin, respectively. Thioperamide, together with pentagastrin in low dose, significantly increased histamine release by 212% (P < 0.05), whereas acid output increased by 34% (not significant).nnnCONCLUSIONSnThe histamine H3 receptor mediates a negative feedback control of pentagastrin-induced release of gastric histamine. It is tonically activated by endogenous histamine after pentagastrin in low dosage. The control of acid secretion by the H3 receptor seems to involve modulation of endogenous histamine release, possibly by means of enterochromaffin-like cells.

Effects of Cannabinoid Receptor Agonists on Rat Gastric Acid Secretion: Discrepancy Between In Vitro and In Vivo Data

The effects of the cannabinoid (CB)-receptor agonists WIN55,212-2 and HU-210 and the selective CB1-receptor antagonist SR141716A were tested on in vitro and in vivo acid secretion assays from the rat. In the isolated gastric fundus from immature rats, WIN55,212-2 (0.001–30 μ M), HU-210 (0.001–10 μ M), or SR141716A (0.1–10 μ M) did not change the basal acid output or acid responses to histamine, pentagastrin, or electrical field stimulation. HU-210 (0.3 μ mol/kg, intravenously) inhibited the acid response to pentagastrin in anesthetized adult, young, or immature rats with lumen-perfused stomachs; moreover, HU-210 reduced vagally induced acid secretion in adult animals, its antisecretory effect being reversed by SR141716A (0.65 μ mol/kg, intravenously). In vitro and in vivo data indicate that CB1 receptors are not located on parietal cells but, rather, on vagal pathways (possibly at preganglionic sites) supplying the gastric mucosa. The lack of effect of CB-receptor ligands in vitro cannot be ascribed to the use of immature rats, since HU-210 inhibited stimulated acid secretion in vivo, irrespective of the animal age.

Effects of α2-adrenergic drugs on small intestinal motility in the horse: an in vitro study.

The effects of selective α(2)-agonists (xylazine, detomidine and medetomidine) and antagonists (yohimbine and atipamezole) on in vitro small intestine motility in the horse were evaluated. Samples of equine jejunum were placed in isolated organ baths and drug-induced modifications of motility were measured by means of an isotonic transducer. All tested α(2)-agonists dose-dependently reduced both spontaneous and electrically-evoked phasic contractions. Conversely, α(2)-antagonists were ineffective when tested alone, and showed a heterogeneous and dose-independent ability to inhibit agonist activity. In particular, the antagonism exerted by higher concentrations of both yohimbine and atipamezole against α(2)-agonists was weaker than when lower concentrations were used. The data are indicative of the presence of both pre- and post-synaptic α(2)-adrenoceptors with inhibitory activity on equine jejunum motility, and support a possible therapeutic utility of these drugs in horse intestinal disorders associated with hypermotility.

Effects of nonselective and selective cyclooxygenase inhibitors on small intestinal motility in the horse.

We investigated the effects of nonselective cyclooxygenase (COX) inhibitors (indomethacin and flunixin meglumine) and selective COX-1 (SC-560) or COX-2 (celecoxib, DUP-398 and NS-697) inhibitors on horse small bowel motility in vitro. At this purpose, samples of equine ileum were put in isolated organ baths for the motility experiments. Nonselective COX inhibitors were devoid of major effects on motility, except for an inhibition of tonic contraction shown by flunixin meglumine. SC-560, selective COX-1 inhibitor, was devoid of significant effects on ileal motility. Selective COX-2 inhibitors reduced both tonic contraction and spontaneous phasic contractions, while prostaglandin (PG) receptor antagonists were uneffective. Some of the intestinal samples were submitted to histological investigation or reverse transcription-polymerase chain reaction (RT-PCR), which revealed the presence of an inflammation reaction and the presence of both COX isoforms mRNAs. Present data support the hypothesis that the effects of COX inhibitors on horse small intestinal motility are not linked to PG depletion.

Diazoxide attenuates indomethacin-induced small intestinal damage in the rat.

ATP-sensitive potassium (K(ATP)) channel openers have been shown to protect against cellular damage in neurons, cardiac muscle, and kidney and to effectively reduce nonsteroidal anti-inflammatory drug (NSAID)-induced gastric damage in rats. We investigated the effects of K(ATP) channel opener diazoxide on small intestinal injury induced in rats by indomethacin administration. The effect of glibenclamide, a K(ATP) channel blocker, was also evaluated. Diazoxide (15, 45 and 135mg/kg) or glibenclamide (18mg/kg), were given by oral gavage 1h before and 6h after indomethacin treatment (20mg/kg p.o.). After 24h, macroscopic and histologic lesions, myeloperoxidase (MPO) activity and lipid peroxidation levels were evaluated. Diazoxide at 15mg/kg was ineffective, while at doses of 45mg/kg and 135mg/kg was able to significantly improve all damage parameters. Glibenclamide administration enhanced intestinal injury. These results show for the first time a beneficial effect of diazoxide in indomethacin-induced enteritis in the rat. Several mechanisms, such as oxidative phosphorylation uncoupling and hypermotility seem particularly important in NSAID-induced intestinal injury. Such events lead to increased mucosal permeability and to penetration of noxious lumen components, which ignite the inflammatory response. Since K(ATP) channel openers were shown to protect against mitochondrial damage, to reduce intercellular permeability and to relax smooth muscle, we suggest that diazoxide could exert its beneficial effects by one or more of these actions.

Rifaximin is an effective alternative to metronidazole for the treatment of chronic enteropathy in dogs: a randomised trial.

BackgroundA clinical trial was conducted in order to assess the efficacy of rifaximin, a broad-spectrum antibiotic with negligible gastrointestinal absorption, in comparison with metronidazole, a commonly employed antimicrobial drug, in dogs with chronic enteropathy. Twenty-four pet dogs were randomly enrolled into two different groups: MET group (10 dogs) and RIF group (14 dogs). Dogs of MET group received metronidazole 15xa0mg/kg q12h for 21xa0days by oral route, whereas dogs of RIF group, were given rifaximin 25xa0mg/kg q12h for 21xa0days by oral route. Clinical signs of disease were evaluated the day before the beginning of drug administration (D0), and at the end of treatment (D21), by means of Canine IBD Activity Index (CIBDAI). Blood levels of C-reactive protein (CRP) at D0 and D21 were also measured, as another parameter of treatment efficacy. The primary outcome measure of efficacy was the complete remission at D21, defined as a 75xa0% or greater decrease of CIBDAI; secondary outcome measures were the variation of mean CIBDAI scores, of mean CRP serum levels, and any observed adverse effect from D0 to D21.ResultsTreatment with metronidazole or rifaximin greatly improved the clinical signs of disease in each group: in MET group the complete remission was achieved in 8 of 10 dogs (80.0xa0%), and partial remission in 2 subjects (20.0xa0%). In RIF group, 12 of 14 dogs showed complete remission (85.7xa0%), and the remaining 2 dogs were in partial remission (14.3xa0%). There were also significant decreases of CIBDAI scores (Pu2009=u20090.002 and Pu2009=u20090.0002 for MET and RIF, respectively), and CRP levels (Pu2009=u20090.002 and Pu2009=u20090.0001 for MET and RIF, respectively) compared to pre-treatment values in both groups. No significant difference, however, was found when comparing MET and RIF groups. No relevant side-effect was reported during the trial with either drugs.ConclusionsThe present study showed, for the first time, that oral rifaximin could represent an effective alternative to metronidazole for the induction of clinical remission in dogs with chronic enteropathy.

Pharmacological characterization of muscarinic receptors in the contractions of isolated bronchi in the horse

We investigated the effects of nonselective muscarinic antagonist (atropine) and of selective muscarinic subtype 1 (M1), 2 (M2), 3 (M3) antagonists (VU0255035, methoctramine, pFHHSiD, respectively) on the contractions evoked by electrical field stimulation (EFS) or by exogenous ACh in isolated horse bronchial muscle. Atropine completely inhibited neurogenic contractions in a concentration-dependent fashion, whereas selective muscarinic antagonists induced relevant modifications only at the highest concentration tested. Experiments with selective muscarinic antagonists in combination showed that only the simultaneous blockade of M1 /M3 or M2 /M3 receptors was able to induce a nearly complete suppression of contractions. The contractions induced by exogenous ACh were competitively antagonized only by atropine (pA2 = 9.01 ± 0.05). M3 selective antagonist, up to 10(-6) m, caused a moderate concentration-dependent rightward shift of ACh curve (pA2 = 7.96 ± 0.10). These data show that M3 muscarinic receptors possess a central role in mediating cholinergic contraction of horse bronchi, while M1 and M2 receptors seem to have a cooperative role. Selective muscarinic antagonists seem unlikely to be useful against bronchoconstriction associated with airway diseases in horses. Conversely, compounds with selectivity for both M1 and M3 receptors could be as effective as traditional anticholinergics and induce fewer cardiac side effects.

Pharmacological evidence for β3 adrenoceptors in the control of rat gastric acid secretion

The effect of the β3-adrenoceptor agonist BRL37344 on gastric acid secretion evoked by different secretory stimuli was investigated in anaesthetized rats with lumen-perfused stomachs in comparison with the β2-adrenoceptor agonist clenbuterol. Intravenous injections of BRL37344 (1–10 μmol/kg) and clenbuterol (0.01–1 μmol/kg) dose-dependently reduced 2-deoxy-D-glucose-induced acid secretion, with BRL37344 about forty times less potent than clenbuterol. BRL37344 (0.1–3 μmol/kg) inhibited pentagastrin-induced acid output, whereas clenbuterol was effective only at high doses (10–100 μmol/kg). The inhibitory effect of BRL37344 on pentagastrin-induced acid secretion was not modified by the nonselective β–adrenoceptor antagonist propranolol, but it was prevented by bupranolol, a β3-adrenoceptor antagonist. Furthermore, neither BRL37344 (10 μmol/kg) nor clenbuterol (100 μmol/kg) modified the acid secretion induced by histamine. These data suggest that β3 adrenoceptors have an inhibitory role in the control of rat gastric acid secretion induced by indirect stimuli.