Stomach Fundus Strip Research Articles

Novel sequential stress model for functional dyspepsia: Efficacy of the herbal preparation STW5

BackgroundMany screening procedures for agents with potential usefulness in functional dyspepsia (FD) rely on animals exposed to stress early in life (neonatal maternal separation, NMS) or in adulthood (restraint stress, RS). PurposeSince many clinical cases of FD have been associated with stress in early life followed by stress in adulthood, a sequential model simulating the clinical situation is described. To explore the validity of the model, the efficacy of STW5, a multicomponent herbal preparation of proven usefulness in FD, was tested. Study design/methodsA sequential stress model established where rats are exposed to NMS after birth followed later by RS in adulthood. Stress hormones and ghrelin were measured in plasma, while responsiveness of stomach fundus strips to smooth muscle stimulants and relaxants was assessed ex-vivo. The effectiveness of treatment with STW5 a few days before and during exposure to RS in preventing changes induced by the stress model is reported and compared to its efficacy when used in animals subjected to RS alone. ResultsResponses to both stimulants and relaxants were reduced to various extents in the studied models, but treatment with STW5 tended to normalize gastric responsiveness. Plasma levels of ghrelin, corticosterone releasing factor, and corticosterone were raised by RS as well as the sequential model. Treatment with STW5 tended to prevent the deranged parameters. ConclusionThe sequential stress model has a place in drug screening for potential usefulness in FD as it simulates more the clinical setting. Furthermore, the findings shed more light on the mechanisms of action of STW5 in FD.

Comparative effects of Sorghum bicolor leaf base extract on tissues isolated from some body systems of experimental animals

The knowledge of the effect(s) of substances to be used as medicines on different body systems is very vital in drug development vis-`a-vis drug safety. The effects of aqueous methanolic extract of Sorghum bicolor leaf base were tested on cardiovascular system-related in vitro models (such as isolated rat atria and rat portal vein), gastrointestinal system-related in vitro models (such as isolated rabbit jejunum, guinea pig ileum, rat stomach fundus strip) and reproductive system-related in vitro models (such as isolated rat uterus and rat vas deferens). The results showed that the extract did not alter the intrinsic myogenic contraction of both isolated rat atria and rat portal vein. The extract caused relaxation of rabbit jejunum and guinea pig ileum but contraction of rat stomach fundus strip. The extract did not alter the rhythmic contractions of stilboestrol pre-treated rat uteri. It, however, caused minimal contractions on the isolated rat vas deferens. The results of the studies therefore suggest that the extract may not have detrimental effect on the cardiovascular system if use as drug. The results also showed that the extract has the potential of being developed into antispasmodic and/or anti-motility agent as a remedy for gastro-intestinal system related problems. Results also suggest that the extract may be non-uterogenic and may not be contraindicated in pregnancy. It may, however, have effect on the male reproductive secretary activity and ultimately, fertility. Key words: Sorghum bicolor, atria, portal vein, jejunum, ileum, stomach fundus, uterus, vas deferens.

Participation of extracellular calcium in α-hederin-induced contractions of rat isolated stomach strips

Ethnopharmacological relevanceThe dry extract of Hedera helix leaves, due to its secretolytic and antispasmodic effects, is commonly used to produce pharmaceuticals applied in case of cough and other respiratory symptoms. The results of some in vitro studies as well as the clinical signs of poisoning caused by Hedera helix suggest however strong contractile effect on smooth muscle. In order to clarify the impact of α-hederin (the main active agent of ivy extract) on smooth muscle, the origin of activated calcium involved in α-hederin-induced contraction of gastric smooth muscle preparations was studied. Materials and methodsThe study was carried out on rat isolated stomach corpus and fundus strips, under isotonic conditions. The effect of α-hederin (100μM) on smooth muscle preparations was measured before and after the treatment with verapamil during the incubation in modified Krebs–Henseleit solution (M K–HS). Besides, the effect of saponin was measured during the incubation of preparation in Ca2+-free modified Krebs–Henseleit solution or Ca2+-free EGTA-containing modified Krebs–Henseleit solution. ResultsThe obtained results revealed that the application of verapamil significantly inhibited the reaction evoked by α-hederin. The incubation of stomach strips in calcium-free modified Krebs–Henseleit solution did not change the force of the observed contraction in comparison to the reaction of the preparations incubated in regular incubation solution (M K–HS). In contrary, the replacement of M K–HS by calcium-free chelator-containing solution inhibited totally the reaction to α-hederin. ConclusionsThe results indicated that α-hederin-induced contraction results from the influx of calcium which is located in intercellular spaces or bound to the outside of the cell membrane. The Ca2+ influx occurs predominantly through voltage-dependent calcium channels of L-type.

Participation of cholinergic pathways in α-hederin-induced contraction of rat isolated stomach strips

The dry extract of Hedra helix leaves and its main active compounds, predominantly α-hederin and hederacoside C, has been traditionally believed to act spasmolytic. However, it has been recently proved that both, the extract of ivy and triterpenoid saponins, exhibit strong contractile effect on rat isolated stomach smooth muscle strips. It turned out that the most potent contractile agent isolated from the extract of ivy leaves is α-hederin. Thus, it seems reasonable to estimate the mechanism of the contractile effect of this saponin.The presented study was aimed at verifying the participation of cholinergic pathways (muscarinic and nicotine receptors) in α-hederin-induced contraction. The experiments were carried out on rat isolated stomach corpus and fundus strips under isotonic conditions. The preparations were preincubated with either atropine or hexamethonium and then exposed to α-hederin. All results are expressed as the percentage of the response to acetylcholine – a reference contractile agent.The obtained results revealed that the pretreatment of isolated stomach strips (corpus and fundus) with atropine neither prevented nor remarkably reduced the reaction of the preparations to α-hederin. Similarly, if the application of saponin was preceded by the administration of hexamethonium, the strength of the contraction of stomach fundus strips induced by α-hederin was not modified.Concluding, it can be assumed that the cholinergic pathways do not participate in α-hederin-evoked contraction of rat isolated stomach preparations.

The putative somatostatin antagonist cyclo-somatostatin has opioid agonist effects in gastrointestinal preparations

AimsSpecificity of receptor antagonists used is crucial for clarifying physiological/pathophysiological roles of the respective endogenous agonist. We studied the effects (somatostatin antagonist and possibly other actions) of cyclo-somatostatin (CSST), a putative somatostatin receptor antagonist on the guinea-pig small intestine, a preparation where somatostatin causes inhibition of nerve-mediated contractions. Main methodsIn isolated organ experiments, half-maximal cholinergic “twitch” contractions of the guinea-pig small intestine were evoked or tonic contractions of the rat stomach fundus strip (in the presence of physostigmine) were elicited by electrical field stimulation. The effects of somatostatin (somatostatin-14), CSST, naloxone, as well as of direct smooth muscle stimulants were examined. Key findingsSomatostatin (10nM–1μM) caused transient inhibition of the twitch contraction, in a naloxone-insensitive manner. Surprisingly, CSST (0.3–1μM) also inhibited twitch contractions (more than 50% reduction at 1μM). This effect was prevented by the opioid receptor antagonist naloxone. Responses to acetylcholine or histamine were not or only minimally inhibited by CSST (up to 3μM). CSST (0.3μM in the absence or 1–10μM in the presence of naloxone) failed to inhibit the effect of somatostatin. The SST2 receptor antagonist CYN-154806 (3μM) attenuated the effect of somatostatin and failed to evoke naloxone-sensitive inhibition of the twitch response. The naloxone-sensitive inhibitory effect of CSST on cholinergic contractions was also confirmed in the rat stomach fundus preparation. SignificanceCyclo-somatostatin exerts opioid agonist activity in the two preparations tested, while it does not behave as a somatostatin-receptor antagonist in the guinea-pig intestine.

No correlation exists between antidepressant activity and the ability of 5-HT uptake inhibitors to interact with 5-HT receptors of the rat stomach fundus strip.

Several 5-HT uptake inhibitors, established and potential antidepressant drugs, were tested for their ability to counteract contractions of the rat isolated stomach fundus strip induced by 5-HT and BaCl2. Of 12 inhibitors tested, only doxepine, amitriptyline, clomipramine, imipramine, Ro 11-2465 (cyan-imipramine), citalopram and fluvoxamine antagonized the contraction induced by 10(-6) M 5-HT with IC50 values below 10(-4) M. Amitriptyline, doxepine and cyproheptadine, at concentrations inhibiting the effect of 5-HT, did not antagonize the strip contractions induced by 3 X 10(-3) M BaCl2, while the remaining compounds that antagonized 5-HT-induced contractions, also antagonized--with at least a similar potency--the contractions induced by BaCl2. From among antidepressant compounds investigated, only doxepine and amitriptyline may be regarded as antagonists of the 5-HT receptor in the rat stomach strip.

The evidence of the release of prostaglandin-like material from rabbit kidney and guinea-pig lung by (–)-trans- Δ9-tetrahydrocannabinol

Injection of (minus)-trans-delta9-tetrahydrocannabinol (THC) through the renal artery caused a decrease in perfusion pressure and an increase in urine produced by the isolated perfused rabbit kidney. Both effects of THC are inhibited by the prior addition of aspirin to the perfusion medium. THC also induced a dose-dependent increase in perfusion pressure on the isolated perfused lung of guinea-pig and the effluent from the lung produced a contraction on the isolated continuously superfused rat stomach fundus strip. These effects are prevented by the pretreatment of the lung with aspirin which inhibits the production of prostaglandins (PG) and SC 19220 which inhibits the pharmacological effects of PG.

The effect of the whole extract of common ivy (Hedera helix) leaves and selected active substances on the motoric activity of rat isolated stomach strips

The long tradition of using the dry extract of Hedera helix (common ivy) leaves in traditional and contemporary alternative medicine caused that many biological and pharmacological studies have been aimed at evaluating the effects of ivy. Some of the results suggest that Hedera helix extract possesses bronchodilatatory and antispasmodic activity. On the other hand, the symptoms of ivy intoxication in human and animals, as well as adverse-reactions observed during the therapy with ivy-based pharmaceuticals, indicate rather stimulant effect of the plant on smooth muscle. Thus, the aim of this study was to evaluate the effect of two main active substances extracted from the plant (α-hederin and hederacoside C) and the whole dry extract of Hedera helix on the gut motility. The experiments were carried out on isolated stomach corpus and fundus strips. The tissues were isolated from rats. The experiments were performed in isotonic conditions. The results are expressed as the percent of the reaction caused by a reference contractile substance, acetylcholine. The obtained results revealed that α-hederin applied in the concentration ranged from 25 to 320μM significantly changed the spontaneous motoric activity of rat stomach smooth muscle. The observed reaction had always the same character, a contraction, and its force was concentration dependent. The second tested saponin, hederacoside C, did not alter the motility of rat isolated stomach corpus and fundus strips when administered in the concentration up to 100 μM, however, if applied in the concentration of 350 μM it induced a remarkable concentration of smooth muscle. Eventually, the whole extract of Hedera helix in a dose containing 60 μM of hederacoside C produced a strong contraction which strength was comparable with the reaction generated by acetylcholine. According to the results, it is very likely that α-hederin, but not hederacoside C contributes to the contractile response of isolated stomach corpus and fundus strips to the application of Hedera helix leaves' extract.

English

The leaf base of Sorghum bicolor (Family: Gramineae, Poaceae) was cold-macerated with 70% v/v methanol. The aqueous methanolic extract was further fractionated into non-polar, medium polar and very polar components using hexane, ethylacetate and water (aqueous), respectively. The gastrointestinal effects of these extracts were tested on intestinal motility (transit) in mice, castor oil-induced diarrhoeal model in rats, isolated rabbit jejunum, guinea pig ileum and rat stomach fundus strip. The oral and intraperitoneal LD50 values for the extracts were determined in mice and rats. The aqueous methanolic extract (100 – 400 mg/kg i.p) significantly (P < 0.05) and dose-dependently decreased the intestinal motility, inhibited castor oil-induced diarrhoea, produced concentration-dependent relaxation of rabbit jejunum with half maximal effective concentration (EC50) of 0.21 mg/ml. This extract also produced both non-myogenic and slight relaxation effects on guinea pig ileum and a contraction on rat stomach fundus strips. Both aqueous and ethylacetate fractions also reduced intestinal motility. However, ethylacetate fraction caused greater reduction than the aqueous fraction. The oral LD50 value for the aqueous methanolic extact in both rats and mice was found to be ≥ 2000 mg/kg while the intraperitoneal values are 1414.2 mg/kg in rats and 1341.6 mg/kg in mice. The intrapertoneal value for both aqueous and ethylacetate fractions is ≥ 2000 mg/kg in mice. The study provided scientific bases for the traditional use of S. bicolor for treatment of gastrointestinal related problems such as diarrhoea.   Key words: Sorghum bicolor, gastrointestinal, motility, diarrhoea, jejunum, ileum, fundus.

Pharmacological Evidence for a Functional Serotonin-2B Receptor in a Human Uterine Smooth Muscle Cell Line

The present study investigated the serotonin-induced increase in phosphoinositide hydrolysis and mobilization of intracellular Ca2+ ([Ca2+]i) in human uterine smooth muscle cells (HUSMCs) to identify the serotonergic receptor positively coupled to phospholipase C in these cells. In phosphoinositide (PI) assays, serotonin (5-HT) and alpha-methyl-5-HT were potent, full agonists (EC50 = 20 and 4.1 nM, respectively), whereas the phenylethylamine, R-(-)-1-(4-iodo-2,5-dimethoxyphenyl)-2-aminopropane hydrochloride, was less active (EC50 = 63 nM). Proposed 5-HT2B-selective agonists, BW-723C86 [alpha-methyl-5-(2-thienylmethoxy)-1H-indole-3-ethanamine hydrochloride] and (+)-norfenfluramine, exhibited strong agonist potency and efficacy comparable with 5-HT (EC50 = 18 and 33 nM, respectively) and approximately 15-fold more potency than (-)-norfenfluramine (EC50 = 500 nM). 5-HT2C receptor agonists m-chlorophenylpiperazine and MK-212 [6-chloro-2-(1-piperaxinyl)pyrazine] were weak agonists in these cells, with potencies of 110 and 880 nM, respectively. A similar rank order of potency was observed in [Ca2+]i mobilization assays (r = 0.9, p < 0.005) in the HUSMC and with contraction of rat stomach fundus strips that contain a 5-HT2B receptor (r = 0.9, p < 0.001). Antagonist studies revealed that a 5-HT2B-selective antagonist, RS-127445 [2-amino-4-(4-fluoronaphth-1-yl)-6-isopropylpyrimidine] (Ki = 0.13 nM), was significantly more effective at inhibiting 5-HT-induced activity than a 5-HT2A antagonist, M-100907 (R-(+)-alpha-(2,3-dimethoxyphenyl)-1-[2-(4-fluorophenyl)ethyl]-4-piperidinemethanol]) (Ki= 914 nM) and the 5-HT2C antagonists RS-102221 (8-[5-(2,4-dimethoxy-5-(4-trifluoromethylsulfo-amido)phenyl-5-oxopentyl]-1,3,8-triazaspiro[4.5]decane-2,4-dione hydrochloride) (Ki = 2.5 microM) and SB-242084 (6-chloro-5-methyl-1-[6-92-methylpyridin-3-yloxy) pyridine-3-ylcarbamoyl] indoline) (Ki = 42.4 nM) in the HUSMC PI turnover assays. Taken together, these studies strongly suggest the presence of a functionally active 5-HT2B receptor subtype in HUSMCs. The physiological role of this receptor in these cells remains to be defined.

Effect of phorbol 12,13-dibutyrate on smooth muscle tone in rat stomach fundus

We investigated the effects of phorbol 12,13-dibutyrate (PDBu), a typical protein kinase C (PKC) activator, on smooth muscle tone in the rat stomach fundus. In 5-hydroxytriptamine (5-HT)-precontracted stomach fundus strips, PDBu induced dose-dependent relaxation, but 4alpha-phorbol 12,13-didecanoate, a phorbol ester that does not activate PKC, did not induce relaxation. A PDBu-induced dose-dependent relaxation was also observed in strips precontracted with platelet-activating factor (PAF), carbachol, or 60 mM K+. In stomach fundus strips pretreated with PDBu, the contractile responses to 5-HT and PAF were completely blocked, but those induced by carbachol and endothelin-1 (ET-1) were only partially inhibited. In stomach fundus strips preincubated with carbachol in Ca2+-free medium, the Ca2+-induced contraction was decreased by preincubation with PDBu. In strips preincubated with 5-HT, PAF, or ET-1 in Ca2+-free medium, Ca2+-induced contractions were greatly inhibited by pretreatment with PDBu. These results suggest that in rat stomach fundus strips, PDBu-induced relaxation is mediated by activation of PKC. We speculate that a major factor mediating the relaxant action of PDBu in rat stomach fundus smooth muscle is represented by a reduction in Ca2+ influx via an inhibition of Ca2+ channels.

Diabetes-related changes in contractile responses of stomach fundus to endothelin-1 in streptozotocin-induced diabetic rats

The contractile response of the stomach fundus to endothelin-1 (ET-1) was examined in streptozotocin (STZ)-induced diabetic rats. In STZ-diabetic rats (versus age-matched control rats) (a) ET-1 caused a longer-lasting contraction of stomach fundus strips, and (b) in the dose-response curve, the ET-1-induced contraction was significantly greater for a given concentration (3 x 10(-7) to 10(-7) M). Although repeated application of ET-1 led to desensitization, the desensitization was less pronounced in STZ-diabetic rats than in the controls. The density of the binding sites for [(125)I]-ET-1 was increased in the diabetic stomach fundus (versus the controls), but Kd values were similar between the two groups. The ET(B) receptor mRNA expression level was significantly increased in the diabetic stomach fundus. These results suggest that the diabetes-related enhancement of the ET-1-induced contraction of the stomach fundus may be due to an increase in the ET(B) receptor population.

Effects of EGIS-7625, a selective and competitive 5-HT2B receptor antagonist.

Our aim was to specify the 5-HT(2) subtype selectivity of EGIS-7625 (1-benzyl-4-[(2-nitro-4-methyl-5-amino)-phenyl]-piperazine), a new 5-HT(2B) ligand, in receptor binding studies and characterize its pharmacology at 5-HT(2A), 5-HT(2B) and 5-HT(2C) receptors in in vivo experiments and in isolated organs, in vitro. EGIS-7625 had high affinity for recombinant human 5-HT(2B) receptors (pK(i) = 9.0) but much weaker affinity for 5-HT(2A) and 5-HT(2C) receptors (pK(i) = 6.2 and 7.7, respectively). In the classic 5-HT(2B) test, EGIS-7625 produced a concentration-related parallel rightward shift in the concentration-response relationship for the 5-HT-induced smooth muscle constriction in rat stomach fundus strips with a pA(2) of 9.4. On the other hand, EGIS-7625 was a weak competitive antagonist at 5-HT(2A) receptors as it shifted 5-HT-induced concentration-response curves to the right at high concentrations (pA(2) = 6.7) in rabbit pulmonary artery strips. The m-chlorophenylpiperazine-induced hypomotility and hypophagia was only partially attenuated by EGIS-7625 even at a dose of 30 mg/kg i.p. while mianserin, a non-selective 5-HT antagonist was almost fully effective in these tests at 3 mg/kg i.p., suggesting weak antagonistic effect of EGIS-7625 at neuronal 5-HT(2C) receptors, in vivo. In conclusion, EGIS-7625 is a potent, selective and competitive 5-HT(2B) antagonist that seems to be a good research tool for the separation of the functional roles of vascular 5-HT(2A) and 5-HT(2B) receptors.

Mechanism of antiulcerogenic activity of semi-synthetic crotonin obtained from Croton cajucara Benth.

The bark of Croton cajucara Benth. is used in Brazilian folk medicine to treat gastrointestinal disorders. Transdehydrocrotonin (DHC) isolated from the bark of Croton cajucara has antiulcerogenic activity25. The presence of similar activity in semi-synthetic crotonin obtained from dehydrocrotonin from Croton cajucara was observed in gastric ulcer-induced models (HCl/ethanol, ethanol, indomethacin, stress and pylorus ligature). The aim of the present study was to assess the mechanisms involved in the antiulcerogenic activity of semi-synthetic crotonin. We investigated the effects of semi-synthetic crotonin on the response to histamine of right atria isolated from guinea pigs and on the response to carbachol of stomach fundus strips from rats. Semi-synthetic crotonin (3, 10 or 30 mM) induced a shift to the right in the concentrationresponse curves to carbachol in the isolated rat stomach at the pD2 level (pD2: 5.42±0.05, 5.76±0.061, 5.77±0.076, 6.48±0.012, respectively), without any alteration in the maximum response. Semi-synthetic crotonin also induced a shift to the right in the concentration-response curves to histamine in guinea pig right atria, pD2 (5.54±0.06, 6.01±0.06, 5.89±0.06, 5.92±0.03) and (%) maximum response (80±6.18, 118±6.18, 114±6.18, 122±1.4), respectively. Thus, the protective effect of semi-synthetic crotonin on induced gastric lesions could be due to antagonism of histaminergic and cholinergic effects on gastric secretion.

Intracellular calcium mobilization by muscarinic receptors is regulated by micromolar concentrations of external Ca2+

Carbachol-induced contractions of rat stomach fundus strips, obtained in a nutrient solution containing 1.8 mM Ca2+, were resistant to Ca2+ withdrawal, even after 1 h of bathing the tissues in a nominal 0 Ca2+ solution. This was not observed when K+ was used to evoke contractions, which were rapidly inhibited after Ca2+ removal (t1/2=2 min). The effect of carbachol in 0 Ca2+ solution was reduced by using drugs that reduce intracellular pools of Ca2+, such as caffeine (1-3 mM), ryanodine (30 microM) or thapsigargin (1 microM), corroborating the involvement of intracellular Ca2+ stores. On the other hand, when the 0 Ca2+ solution contained EGTA, a complete decline of carbachol effects was observed within about 8 min, indicating the involvement of extracellular Ca2+. Atomic absorption spectrometry showed that our 0 Ca2+ solution still contained 45 microM Ca2+, which was drastically reduced to 5.9 nM in the presence of EGTA. Taken together, our results indicate that the effects of carbachol are due to the mobilization of caffeine-, ryanodine- and thapsigargin-sensitive intracellular Ca2+ stores, and that these stores are not inactivated or depleted if micromolar concentrations (45 microM), but not nanomolar concentrations (5.9 nM) of Ca2+ are maintained in the extracellular milieu.

Antiulcerogenic mechanisms of dehydrocrotonin, a diterpene lactone obtained from Croton cajucara.

The bark of Croton cajucara Benth, is used in Brazilian folk medicine as an infusion to treat gastrointestinal disorders. The aim of the present study was to assess the mechanisms involved in the antiulcerogenic activity of dehydrocrotonin (DHC), a diterpene isolated from C. cajucara bark. We studied the effects of DHC on pylorus ligature (Shay) in mice treated with the drug (100 mg/kg) by the intraduodenal route. DHC did not induce any alteration in gastric volume in Shay mice but modified the pH and total acid concentration of gastric juice. Incubation of gastric juice with DHC did not reduce gastric acidity compared to control. We also investigated the effects of DHC on the response to histamine of right atria isolated from guinea pigs and on the response to carbachol of stomach fundus strips from rats. The concentration-response curves for the chronotropic effect of histamine in guinea pig right atria were shifted to the right, with a significant decrease in the maximum response, in the presence of DHC. Similar results were obtained with DHC (30 microM) for the concentration-response curves to carbachol in the isolated rat stomach. The ability of DHC to increase PGE2 release from rat stomach mucous cells was also studied. We observed that DHC induced a significant increase in PGE2 production (60% compared to control). In addition, the effects of DHC on the healing of acetic acid-induced gastric ulcer in rats were evaluated 14 days after acid injection. Oral administration of DHC (100 mg/kg per day) for 14 consecutive days had no effect on gastric ulcer healing in rats. Thus, the protective effect of DHC on induced gastric lesions could be due to synergistic effects, e.g., an increase in PGE2 release and non-competitive antagonism of H2-receptors and of muscarinic receptors. Whereas the former result represents an increase in the protective factors, the latter one shows a decrease in the aggressive factors against the gastric mucosa.

Effects of ondansetron on electrically evoked contraction in rat stomach fundus: Possible involvement of 5-HT 2B receptors

This study examined the effects of ondansetron, an antagonist of the 5-hydroxytryptamine (5-HT 3) receptor without 5-HT 4 receptor agonistic activity, on electrically evoked contractions and acetylcholine release in rat stomach fundus strips. Ondansetron (10 −8–10 −4 M) produced a concentration-dependent increase in the magnitude of the electrically evoked contraction, while it inhibited the release of acetylcholine induced by electrical field stimulation. The stimulatory effect of ondansetron (10 −6 M) on electrically evoked contractions was antagonized by yohimbine, a 5-HT 2B receptor antagonist, but not by SDZ 205-557 (2-methoxy-4-amino-5-chloro-benzoic acid 2-[diethylamino] ethyl ester), a 5-HT 4 receptor antagonist. In the presence of tetrodotoxin, ondansetron (10 −7–10 −5 M) enhanced the contractions induced by acetylcholine. This stimulatory effect of ondansetron on acetylcholine-induced contractions was antagonized by yohimbine. These data suggest that ondansetron potentiates the contractile response to acetylcholine in the rat stomach fundus through the activation of 5-HT 2B receptors.

An in vitro pharmacological examination of venom from the soldierfish gymnapistes marmoratus

The aim of the present study was to commence a characterisation of some of the basic pharmacological properties of venom from the soldierfish ( Gymnapistes marmoratus). Soldierfish venom was prepared by extraction into 10% glycerol and centrifugation to remove insoluble material. Protein content was determined and venom concentrations were expressed as μg venom protein. Soldierfish venom (0.5–15 μg/ml) produced concentration-dependent contractile responses in guinea-pig isolated ileum (GPI) and longitudinal smooth muscle (LSM) preparations. The muscarinic receptor antagonist atropine (10 nM) significantly inhibited responses of LSM to soldierfish venom (2.5 μg/ml). Responses to soldierfish venom (4–5 μg/ml) in GPI were not significantly affected by the ganglion-blocking drug mecamylamine (10 μM) or by incubation with blood cholinesterase. The cyclooxygenase inhibitor indomethacin (2 μM) significantly inhibited responses to soldierfish venom (2.5 μg/ml) in LSM. Neither the thromboxane A 2/prostaglandin H 2 receptor antagonist GR32191B (1 μM) nor the leukotriene receptor antagonist SB205312 (10 nM) significantly affected responses to soldierfish venom (5 μg/ml) in GPI. Responses to soldierfish venom (2.5-5 μg/ml) were not significantly inhibited by the histamine receptor antagonist mepyramine (0.5 μM), the angiotensin-converting enzyme inhibitor captopril (2 μM) or the neurokinin-1 receptor antagonist CP-99,994 (0.1 μM) in LSM. The angiotensin AT 1 receptor antagonist EXP3174 (0.1 μM) also failed to inhibit significantly the responses to soldierfish venom (5 μg/ml) in GPI. A fluorometric assay for the detection of 5-hydroxytryptamine (5-HT) and related compounds indicated a level in soldierfish venom of 1.60 ± 0.01 ng of 5-HT-like substance per μg venom protein. Soldierfish venom (0.5–10 μg/ml) produced concentration-dependent contractile responses in rat isolated stomach fundus strips, and these responses (2.5 μg/ml) were significantly inhibited by the 5-HT 1 5-HT 2 receptor antagonist methysergide (0.1 μM). These results suggest that soldierfish venom may stimulate the release of acetylcholine to act at muscarinic receptors on guinea-pig gastrointestinal smooth muscle. The venom also appears to be causing the release of cyclooxygenase products, such as prostaglandins, and contains 5-HT, or a 5-HT-like substance, that acts directly at 5-HT receptors.

O-37 - Stimulatory effect of ondansetron on electrically evoked contraction in rat stomach fundus strips: Possible involvement of 5-HT2B receptors

O-37 - Stimulatory effect of ondansetron on electrically evoked contraction in rat stomach fundus strips: Possible involvement of 5-HT2B receptors

Characterization of the contractile response induced by 5-methoxytryptamine in rat stomach fundus strips

This study examined effects of 5-methoxytryptamine (5-MOT), an agonist at 5-HT 4 and 5-HT 2B receptors, on the contractile response and acetylcholine release in rat stomach fundus strips. 5-MOT (10 −9 − 10 −5 M) produced a concentration-dependent increase in the contraction, while it evoked acetylcholine release in a ‘bell-shaped’ concentration-dependent manner. Atropine reduced 5-MOT (10 −8 − 10 −6 M)-induced contractions, but it had little effect on the contractions evoked by higher concentrations. 5-MOT-induced contraction and acetylcholine release were inhibited by SDZ 205–557 (2-methoxy-4-amino-5-chloro-benzoic acid 2-[diethylamino] ethyl ester), a 5-HT 4 receptor antagonist. In the presence of atropine, both SDZ 205–557 and yohimbine, a 5-HT 2B receptor antagonist, inhibited the contraction. In the presence of tetrodotoxin, the contraction was inhibited by yohimbine, but not by SDZ –557. These results suggest that the contractile action of 5-MOT in rat stomach fundus involves atropine-sensitive and atropine-resistant components. The sensitive contraction appears to be mediated through 5-HT 4 receptors located on cholinergic neurons, whereas the resistant contraction is mediated through 5-HT 4 receptors located on non-cholinergic neurons and through 5-HT 2B receptors.