Strain-dependent effects of the histamine H4 receptor antagonist JNJ7777120 in a murine model of acute skin inflammation.

The effects of the histamine H(4) receptor antagonist JNJ7777120 were evaluated in a model of acute skin inflammation induced by local application of croton oil. The influence of strain on the effect of JNJ7777120 was investigated in four different mouse strains (CD-1, NMRI, BALB/c and C57BL/6J). In CD-1 mice, JNJ777720 (30-100 mg/kg subcutaneously, s.c.) exerted a dose-dependent inhibition of croton oil-induced ear inflammation and polymorphonuclear leucocyte infiltration, as confirmed by histological evaluation of ear tissues. JNJ7777120 (30-100 mg/kg) did not reduce ear oedema in NMRI, BALB/c or C57BL/6J mice. The positive control, dexamethasone (2 mg/kg s.c.) induced significant anti-inflammatory effects only in CD-1 and NMRI mice. In these strains, also the histamine H(1) -receptor blocker pyrilamine (30 mg/kg s.c.) significantly reduced ear oedema at 2 h after croton oil challenge, being as effective as JNJ7777120 in CD-1 mice. Taken together, these data demonstrate that the H(4) receptor antagonist JNJ7777120 may reduce acute croton oil-induced skin inflammation as effectively as H(1) receptor blockade. However, present experiments evidenced for the first time marked strain-related differences in the JNJ7777120 pharmacological activity, which have to be carefully considered when using this ligand to characterize histamine H(4) receptor functions in murine models and translating preclinical data to clinical human settings.

Effects of histamine H4 receptor ligands in a mouse model of gastric ulceration.

AIM: In the present study we examined whether histamine H(4) receptors (H(4)Rs) have a role in gastric ulcerogenesis using a mouse model of gastric damage. METHODS: The H(4)R antagonist JNJ7777120 and the H(4)R agonists VUF8430 and VUF10460 were investigated in fasted CD-1 mice against the ulcerogenic effect induced by co-administration of indomethacin(IND, 30 mg/kg s.c.) and bethanechol (BET, 5 mg/kg i.p.). Both macroscopic and histologic lesions were examined. Strain-related differences were investigated by testing JNJ7777120 also in NMRI, BALB/c and C57BL/6J mice. RESULTS: Neither JNJ7777120 nor the H(4)R agonists displayed effects in the normal stomach at any dose tested (10 and 30 mg/kg s.c.). As expected, IND+BET provoked several lesions in the fundic mucosa, which were significantly reduced by JNJ7777120 (10 and 30 mg/kg s.c.). The gastroprotective effect of JNJ7777120 (10 and 30 mg/kg s.c.) was observed in CD-1, NMRI and BALB/c, but not in C57BL/6J, mice. In CD-1 mice, the H(4)R agonists VUF8430 and VUF10460 (both at 10 and 30 mg/kg s.c.) did not modify the damage induced by IND+BET, however VUF8430 (10 mg/kg s.c.) prevented the gastroprotection induced by JNJ7777120 (10 mg/kg s.c.). CONCLUSIONS: Data obtained with selective ligands suggest that the H(4)R may have a role in mouse gastric ulcerogenesis. If confirmed in humans, these data would emphasize the potential advantage of H(4)R blockers as gastrosparing anti-inflammatory drugs. The lack of effects of JNJ7777120 in C57BL/6J mice has to be carefully considered in the pharmacological characterization of H(4)R functions and/or new selective ligands.

Histamine H(3) receptors are involved in the protective effect of ghrelin against HCl-induced gastric damage in rats.

In the present study, the effects of ghrelin against the gastric damage induced by intragastric administration of 0.6 N HCl and the involvement of histamine H3 receptors (H3Rs) were investigated in conscious rats with selective H3R ligands. Intraperitoneal (i.p.) injection of ghrelin (40 µg/kg) significantly reduced (43%) the gastric lesions caused by concentrated acid. The effect of ghrelin was prevented by prior administration of the ghrelin receptor antagonist [D-Lys³]-GHRP-6 (100 µg/kg i.p.) and by subcutaneous (s.c.) injection of the nonimidazole H3R antagonist UCL2138 (30 mg/kg). The selective H3R agonist immethridine (30 mg/kg s.c.) significantly inhibited (64.60%) the gastric lesions induced by 0.6 N HCl. The effect of immethridine was prevented by prior administration of UCL2138 (30 mg/kg s.c.), but not by [D-Lys³]-GHRP-6 (100 µg/kg i.p.). Neither [D-Lys³]-GHRP-6 nor UCL2138 modified HCl-induced gastric damage per se. These data enlarge previous studies showing protective effects of ghrelin against ulcerogenic stimuli; in addition, they clearly indicate that ghrelin-induced gastroprotection involves the release of histamine, which enhances gastric mucosal defense through the activation of histamine H3Rs.

Functional and histologic assessment of rat gastric mucosa after chronic treatment with sulphurous thermal water.

The effect of a chronic (4 weeks) administration of sulphurous thermal water on gastric acid secretion and mucosal defense was investigated in rats. Animals were randomized to receive daily intake of tap water or of thermal water obtained from a local spa center (Tabiano, Parma, Italy). Rats were followed for one month as for water and food consumption, body weight and general conditions. At the end of the watering period, the following study protocols were carried out: (a) study of basal and stimulated gastric acid secretion under general anesthesia, and (b) study of the gastric mucosal resistance against the damage induced by ethanol and indomethacin in conscious rats. Basal acid secretion and the acid response to pentagastrin or to histamine were similar in rats assuming ordinary drinking water or thermal water. As for resistance to gastric damage, histological, but not macroscopic, evaluation revealed that rats which assumed thermal water were slightly more resistant to the gastrolesive effect of ethanol (either absolute or diluted). Again, when indomethacin was used as a noxious stimulus, no difference was noted between the two groups as for macroscopic damage; only a nonsignificant reduction of damage was observed histologically in stomachs of rats assuming thermal water. In conclusion, these results indicate that chronic treatment of rats with thermal water, rich in sulphur compounds, may have only minimal effects on the rat gastric mucosa and did not significantly affect mucosal defense mechanisms. The observed tendency to gastroprotection would possibly need further investigation with longer periods of administration.

Relaxing effects of clenbuterol, ritodrine, salbutamol and fenoterol on the contractions of horse isolated bronchi induced by different stimuli.

ß2-adrenoceptor agonists are considered the most effective drugs to counteract bronchoconstriction in horses with asthma, but only clenbuterol is commonly employed in clinical practice. We evaluated the effects of different selective ß2 agonists: clenbuterol, ritodrine, salbutamol, and fenoterol on the contractions of isolated bronchial muscle of horses induced by electrical field stimulation (EFS), carbachol, histamine, and KCl. All ß2 agonists reduced the amplitude of contraction induced by the different stimuli but with variable efficacy and potency. Fenoterol and salbutamol were more effective than clenbuterol in relaxing the bronchial contractions induced by EFS and histamine, and were able to completely abolish carbachol-induced contractions, unlike clenbuterol and ritodrine. The respective potency values (pEC50) of clenbuterol, ritodrine, salbutamol, and fenoterol were 7.74 ±â€¯0.20, 7.77 ±â€¯0.17, 7.30 ±â€¯0.23, 8.01 ±â€¯0.13, for EFS-induced contractions; 8.39 ±â€¯0.26, 5.49 ±â€¯0.28, 6.63 ±â€¯0.14, 7.68 ±â€¯0.11, for carbachol-induced contraction; 7.39 ±â€¯0.27, 7.04 ±â€¯0.28, 6.45 ±â€¯0.34, 7.34 ±â€¯0.22, for histamine-induced contraction; 7.15 ±â€¯0.06, 6.07 ±â€¯0.20, 6.48 ±â€¯0.14, 6.70 ±â€¯0.18, for KCl-induced contraction. Salbutamol and fenoterol showed a higher efficacy than clenbuterol in relaxing horse bronchial muscle pre-contracted by most stimuli. Clenbuterol displayed a good potency but a rather low efficacy, and this may be due to its partial agonist nature; ritodrine showed lower or not significantly different efficacy and potency compared to the other agonists. An evaluation of the clinical efficacy by fenoterol and salbutamol in horses with asthma could be of great interest to assess if they could represent more effective bronchodilators compared to clenbuterol.

Treatments for COVID-19: emerging drugs against the coronavirus.

The Coronavirus disease 19 (COVID-19) outbreak has been recognized as a global threat to public health. It is caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and no effective therapies currently exist against this novel viral agent. Along with extensive public health measures, an unprecedented global effort in identifying effective drugs for the treatment is being implemented. Potential drug targets are emerging as the result of a fast-evolving understanding of SARS-CoV-2 virology, host response to the infection, and clinical course of the disease. This brief review focuses on the latest and most promising pharmacological treatments against COVID-19 currently under investigation and discuss their potential use based on either documented efficacy in similar viral infections, or their activity against inflammatory syndromes. Ongoing clinical trials are also emphasized.

Stereospecific effects of benzo[d]isothiazolyloxypropanolamine derivatives at beta-adrenoceptors: synthesis, chiral resolution, and biological activity in vitro.

We performed the asymmetric synthesis of four enantiopure benzo[d] isothiazo-3-or 5-yloxypropanolamine derivatives, previously described as competitive antagonists at beta-adrenoceptors. The chemical characterization of each enantiomer was accomplished by (1)H NMR and HPLC/DAD/CD. The direct chromatographic separation of the enantiomers via chiral HPLC was investigated. The best resolutions were achieved using cellulose tris (3,5-dimethylphenyl carbamate) (Chiralcel OD-H) and amylose tris (3,5-dimethylphenyl carbamate) (Chiralpak AD). The enantiomers obtained had enantiomeric purities suitable for biological assays. Tested in isolated rat cardiac and intestinal tissues to evaluate their effects at beta(1)- and beta(3)-adrenoceptors, the (S)-enantiomers revealed a higher degree of antagonism than (R)-enantiomers at both subtypes, even though their activity was greater at the cardiac beta(1)-subtype. The potent and cardiospecific antagonistic effect exerted by the compounds tested suggests that the benzisothiazole moiety could be an interesting scaffold for discovering new chiral beta-blocking drugs.

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 90 micromol/kg, 12 h and 30 min before and 6 h 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 90 micromol/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.

Role of muscarinic receptors in the contraction of jejunal smooth muscle in the horse: An in vitro study.

Nonselective antimuscarinic drugs are clinically useful in several pathologic conditions of horses, but, blocking all muscarinic receptor (MR) subtypes, may cause several side effects. The availability of selective antimuscarinic drugs could improve therapeutic efficacy and safety. We aimed to enlighten the role of different MR subtypes by evaluating the effects of nonselective, and selective M1, M2 and M3 MR antagonists on the contractions of horse jejunum. Segments of circular muscle of equine jejunum, were put into organ baths, connected to isotonic transducers, and the effects on ACh concentration-response curves, and on electrical field stimulation (EFS)-evoked contractions of intestinal preparations, induced by nonselective or selective MR antagonists, compared to pre-drug level, were studied. Atropine (nonselective MR antagonist), pirenzepine (selective M1 antagonist), and p-FHHSiD (selective M3 antagonist) competitively antagonized ACh (pA2=9.78±0.21; 7.14±0.25 and 7.56±0.17, respectively). Methoctramine (selective M2 antagonist) antagonized ACh in a concentration-unrelated fashion; however, it competitively antagonized carbachol, a nonselective muscarinic agonist (pA2=6.42±0.23). Atropine dose-dependently reduced EFS-evoked contractions, reaching a maximal effect of -45.64±6.54%; the simultaneous block of neurokinin receptors, almost completely abolished the atropine-insensitive contractions. p-FHHSiD dose-dependently reduced EFS-induced contractions, while pirenzepine caused a minor decrease. Methoctramine, ineffective up to 10-7M, enhanced the contractions at 10-6M; the block of neurokinin receptors abolished the increase of contraction. Cholinergic contractions of horse jejunum are mainly mediated by M3 receptors; M2 selective antagonists seem to scarcely affect cholinergic, and to enhance neurokininergic contractions of equine jejunum, thus their use entails a lower risk of causing intestinal hypomotility, compared to nonselective drugs.

Intestinal effects of nonselective and selective cyclooxygenase inhibitors in the rat.

It is now widely recognized that nonsteroidal anti-inflammatory drugs (NSAIDs) may cause extensive damage to the intestine. The pathogenesis of NSAID-induced intestinal injury, however, is still controversial and both local irritant actions and cyclooxygenase (COX) inhibition have been proposed as underlying mechanisms. In this study we investigated further on NSAID-induced intestinal damage by using nonselective (indomethacin and ibuprofen), COX-1 selective (SC-560) or COX-2 selective (celecoxib) inhibitors. NSAIDs were administered orally to conscious rats and small intestinal injury was evaluated 24 h afterwards in terms of macroscopic and microscopic alterations, myeloperoxidase activity, lipid peroxidation, number of enterobacteria in the mucosa and epithelial mucin content. Oral administration of indomethacin (20 mg/kg) induced macroscopic and microscopic damage to the small intestine, increased translocation of enterobacteria from lumen into the mucosa, myeloperoxidase activity and lipid peroxidation. Ibuprofen (120 mg/kg), SC-560 (20 mg/kg), celecoxib (60 mg/kg) or the combination of SC-560 plus celecoxib did not cause any intestinal injury nor modified the number of bacteria in mucosal homogenates. SC-560 significantly increased both myeloperoxidase activity and lipid peroxidation, whereas celecoxib significantly reduced myeloperoxidase levels, while leaving unaltered lipid peroxidation. Finally, all NSAIDs, mostly indomethacin, increased neutral mucins and decreased acidic mucins in the intestinal goblet cells. These results indicate that inhibition of cyclooxygenase, although variably influencing mucosal integrity homeostasis, is not sufficient to initiate acute intestinal damage in rats. Moreover, topical mucosal injury induced by the NSAID molecule seems to be a critical factor in the development of intestinal injury.

Benzisothiazoles and beta-adrenoceptors: synthesis and pharmacological investigation of novel propanolamine and oxypropanolamine derivatives in isolated rat tissues.

In an attempt to examine the ability of benzisothiazole-based drugs to interact with beta-adrenoceptors, a series of 1,2-benzisothiazole derivatives, which were substituted with various propanolamine or oxypropanolamine side chains in the 2 or 3 position, were synthesised and tested. The pharmacological activity of these compounds at the beta-adrenoceptors was examined using isolated rat atria and small intestinal segments, which preferentially express the beta1- and beta3-adrenoceptor-mediated responses, respectively. None of these products showed any beta-adrenoceptor agonistic activity. In contrast, the 2- and 3-substituted isopropyl, tert-butyl, benzyl, and piperonyl derivatives 2a-d and 3a-d elicited surmountable inhibition of the isoprenaline-induced chronotropic effects in the atria, suggesting competitive antagonism at the beta1-recognition site. The pA2 values revealed tert-butyl 3b and the isopropyl substituted piperonyl derivatives 3a to be the most effective. Remarkably, many of the 2-substituted propanolamines were less active than the corresponding 3-substituted oxypropanolamines. With the exception of compound 3b, none of these drugs antagonised the muscle relaxant activity of isoprenaline in the intestine, suggesting no effect on the beta3-adrenoceptors. These results confirm the ability of the benzisothiazole ring to interact with the beta-adrenoceptors, and demonstrate that 2-substitution with propanolamine or 3-substitution with oxypropanolamine groups yields compounds with preferential antagonistic activity at the cardiac beta1-adrenoceptors. The degree of antagonism depends strongly on both the nature of the substituent and its position on the benzisothiazole ring.

Synthesis of 1,2-benzisothiazolyloxypropanolamine derivatives and investigation of their activity at beta-adrenoceptors.

The synthesis of 3-methoxy-1,2-benzisothiazole derivatives, substituted in position 5- (compounds 1-7) or 7- (compounds 8-14), with oxypropanolaminic side chains and the pharmacological investigation on their activity at beta-adrenoceptors are described. Compounds were prepared in an attempt to explore the ability of the benzisothiazole ring to interact with the beta-adrenoceptor site and to establish whether oxypropanolaminic derivatives recognise the beta3-adrenoceptor subtype. All the products were tested on rat atria, bladder and small intestine, which preferentially (but not exclusively) express beta1-, beta2- and beta3-adrenoceptors, respectively. When compared with the reference, non-specific, beta-adrenoceptor agonist isoprenaline, the products tested did not show any consistent beta-adrenoceptor agonistic activity in the different models. Most compounds relaxed smooth muscle preparations, but such effect was resistant to the blockade by propranolol (1 micromol/l), ICI 118,551 (1 micromol/l) or bupranolol (1-10 micromol/l), thus excluding that the spasmolytic effect involves any beta-adrenoceptors. When tested as antagonists, some of these products showed a concentration-dependent attenuation of the isoprenaline-induced effects in rat atria, without affecting beta-adrenoceptor-mediated relaxation in smooth muscle. These data confirm the ability of the benzisothiazole ring to interact with beta-adrenoceptors, but the substitution in 5- or 7-positions with oxypropanolaminic groups does not generate compounds endowed with specific activity at beta3-adrenoceptors. Conversely, most of these compounds behave as (specific) antagonists at beta1- (cardiac) adrenoceptors. At the maximum concentrations tested (1-100 micromol/l), these compounds also exert direct spasmolytic and negative chronotropic effects, which could be related to a blockade of Ca2+-dependent mechanisms at an intracellular level and/or an anaesthetic-like activity at plasma membranes.

Water-soluble nitric-oxide-releasing acetylsalicylic acid (ASA) prodrugs.

A series of water-soluble (benzoyloxy)methyl esters of acetylsalicylic acid (ASA), commonly known as aspirin, are described. The new derivatives each have alkyl chains containing a nitric oxide (NO)-releasing nitrooxy group and a solubilizing moiety bonded to the benzoyl ring. The compounds were synthesized and evaluated as ASA prodrugs. After conversion to the appropriate salt, most of the derivatives are solid at room temperature and all possess good water solubility. They are quite stable in acid solution (pH 1) and less stable at physiological pH. In human serum, these compounds are immediately metabolized by esterases, producing a mixture of ASA, salicylic acid (SA), and of the related NO-donor benzoic acids, along with other minor products. Due to ASA release, the prodrugs are capable of inhibiting collagen-induced platelet aggregation of human platelet-rich plasma. Simple NO-donor benzoic acids 3-hydroxy-4-(3-nitrooxypropoxy)benzoic acid (28) and 3-(morpholin-4-ylmethyl)-4-[3-(nitrooxy)propoxy]benzoic acid (48) were also studied as representative models of the whole class of benzoic acids formed following metabolism of the prodrugs in serum. These simplified derivatives did not trigger antiaggregatory activity when tested at 300 µM. Only 28 displays quite potent NO-dependent vasodilatatory action. Further in vivo evaluation of two selected prodrugs, {[2-(acetyloxy)benzoyl]oxy}methyl-3-[(3-[aminopropanoyl)oxy]-4-[3-(nitrooxy)propoxy]benzoate⋅HCl (38) and {[2-(acetyloxy)benzoyl]oxy}methyl 3-(morpholin-4-ylmethyl)-4-[3-(nitrooxy)propoxy]benzoate oxalate (49), revealed that their anti-inflammatory activities are similar to that of ASA when tested in the carrageenan-induced paw edema assay in rats. The gastrotoxicity of the two prodrugs was also determined to be lower than that of ASA in a lesion model in rats. Taken together, these results indicated that these NO-donor ASA prodrugs warrant further investigation for clinical application.

Assessment of intestinal peristalsis in vitro.

The protocol detailed in this unit is designed to assess intestinal peristaltic motility in the isolated small intestine in vitro and to measure the effects of drugs able to interfere with gut propulsive activity. The procedure is based on Trendelenburg's classic technique, described at the beginning of the 20th century in the isolated guinea pig ileum and, later on, extended to other intestinal preparations from the same animal and other animal species. This unit illustrates the basic procedures for setting up the intestinal preparation, recording peristalsis under near-physiologic conditions, and testing the pharmaco-toxicological effects of drugs and pollutants on the contractile behavior of the gut wall. The protocol allows evaluating the action of drugs affecting sensory and/or motor neurons of the enteric nervous system and how these neurons control the development of the motor program of the gut wall. This model can be exploited to investigate novel compounds undergoing preclinical development and both inhibitors and stimulants of gastrointestinal peristaltic activity, as well as environmental or alimentary pollutants, like xenobiotics and naturally-occurring toxins, endowed with noxious activity with regard to digestive functions.

Role of histamine H4 receptors in the gastrointestinal tract.

The location and functional role of histamine H4 receptors (H4Rs) in the gastrointestinal tract (GI) is reviewed, with particular reference to their involvement in the regulation of gastric acid secretion, gastric mucosal defense, intestinal motility and secretion, visceral sensitivity, inflammation, immunity and carcinogenesis. H4Rs have been detected in different cell types of the gut, including immune cells, paracrine cells, endocrine cells and neurons; moreover, H4R expression was reported in human colorectal cancer specimens. Functional studies with selective H4R ligands demonstrated protective effects in several experimental models of gastric mucosal damage and intestinal inflammation, suggesting a potential therapeutic role of drugs targeting this new receptor subtype in GI disorders, such as allergic enteropathy, inflammatory bowel disease (IBD), irritable bowel syndrome (IBS) and cancer.

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.

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.

Selective histamine H3 and H4 receptor agonists exert opposite effects against the gastric lesions induced by HCl in the rat stomach.

The present study investigated the role of histamine H(3) and H(4) receptors in gastric mucosal defense, by the use of selective ligands. Firstly, the affinities of several histaminergic agonists for the rat histamine H(3) and H(4) receptors were checked in HEK 293T cells transfected with either receptor subtype. Next, functional activities were determined in conscious rat against the ulcerogenic effect of 0.6N HCl. Radioligand binding studies showed that immethridine and methimepip were the most selective agonists at rat H(3) receptors, whereas VUF10460 displayed approximately a 50-fold selectivity for the rat H(4) receptor over the H(3) receptor. In conscious rats, immethridine and methimepip significantly reduced (66% and 48% inhibition, respectively) the gastric lesions induced by HCl; the effect of immethridine was antagonized by the H(3) receptor antagonist A-331440, but not by the H(4) receptor antagonist JNJ7777120. The mixed H(3)/H(4) receptor agonist immepip induced a significant aggravation of HCl damage, which was prevented by JNJ7777120; HCl-induced lesions were also significantly enhanced by the H(4) receptor agonists VUF10460 and VUF8430; however, this effect was not modified by JNJ7777120. Overall, this study indicates that, whereas the histamine H(3) receptor is involved in the protection of rat stomach against concentrated HCl, the functional role of the H(4) receptor is still to be defined, although selective agonists induce proulcerogenic effects under HCl challenge. Finally, the species-dependent variations in affinity and receptor selectivity observed for most ligands need to be carefully addressed in the pharmacological characterization of histamine H(3) and H(4) receptor functions in vivo.

Assessment of gastrointestinal motility using three different assays in vitro.

The protocols detailed in this unit are designed to assess the motor activity of different gastric and intestinal muscle preparations in vitro and the effects of drugs that modulate gastrointestinal motility. The preparations described are characterized by different contractile behaviors, consisting of spontaneous (duodenum), neurogenic (ileum), and drug-stimulated (fundus, ileum) motility; these reproduce motility patterns occurring in the gut wall in vivo. These protocols document the variety of factors that can influence the responses of isolated tissues and describe how such tissues can be used for testing substances that affect gut movements. These preparations allow evaluation of direct interactions with the processes that control contractile machinery, as well as indirect effects resulting from the modification of neurotransmitter release from myenteric neurons. These models can be exploited to assay novel compounds undergoing preclinical development or to evaluate the functional toxicity exerted by environmental or alimentary pollutants, like xenobiotics and naturally occurring toxins, as well as the mechanisms underlying these effects.

Assessment of gastrointestinal propulsive activity using three different models of peristalsis in vivo in the mouse.

The protocols described in this unit are designed to assess the acute effects of drugs on the propulsive activity of the gastrointestinal muscles in the conscious mouse. These protocols are currently applied to investigate the pharmacological activity of novel compounds undergoing preclinical development and to obtain predictive data needed to advance drugs into clinical trials. Moreover, these methods could be useful in evaluating the functional toxicity by environmental or alimentary pollutants, like xenobiotics and naturally occurring toxins endowed with noxious activity in the control of physiologic peristalsis. The three models detailed-the measurement of gastric emptying, ileal transit, and colonic propulsion-are substantially non-invasive and do not require analgesic pretreatments or the induction of general anesthesia. In contrast to an in vitro approach, these in vivo studies provide a unified understanding of drug effects on gut functionality, in particular when the central nervous system, the extrinsic nerves, or the (neuro)endocrine system is targeted by the test drugs.