Rat Stomach Strip Research Articles

Esaprazole, a new antiulcer compound, potentiates PGI2 activity on rat stomach strip

Esaprazole, a new antiulcer compound, potentiates PGI2 activity on rat stomach strip

Potentiation by phenolphthalein of the responses of guinea-pig ileum and rat stomach strip to PGE 2 and other agonists

Phenolphthalein was examined for its effect on the activity of isolated muscle (guinea-pig ileum and colon, rat stomach), and on the tissue responses to PGE 2, histamine and 5-HT. The ileal circular muscle and both muscle layers of the colon were unaffected by phenolphthalein. In contrast, the laxative potentiated the responses of the longitudinal muscle of guinea-pig isolated ileum and the rat stomach strip to the agoniss, particularly PGE 2. This potentiation was reduced by indomethacin in vivo, but mepyramine or methysergide had little or no effect. Augmentation of muscle activity by phenolphthalein, particularly in the response to PGE 2, may contribute to the laxative effect.

Purification of glomerulopressin.

The present investigation was undertaken to attempt the purification of glomerulopressin. Isolated rat livers were perfused with Krebs-Ringer bicarbonate, and the perfusate was concentrated at reduced pressure, extracted with n-butanol, and subjected to thin-layer chromatography (TLC) with different solvent systems. For monodimensional TLC, (a) acetic acid or (b) chloroform/methanol/formic acid (65:30:5, v/v) was used. For bidimensional TLC solvent (b) was used as the first mobile phase and as the second mobile phase three different solvent systems were employed as follows: ethyl acetate/n-butanol/formic acid (40:57:3; v/v), pyridine/methanol/formic acid (50:49:1, v/v), and acetic acid/n-butanol/water (5:50:10, v/v). The activity of the spots viewed under uv light was studied in three different biological assays: increase of the glomerular pressure index (GPI) in the toad and of the glomerular filtration rate (GFR) in the rat and increase of the tonic tension contraction in the rat stomach strip (TTC). In monodimensional TLC developed with system (a), three spots were detected, and with system (b), seven spots were observed. The biological activity of these seven spots was studied. Only the substance showing Rf 0.47 was active. This Rf 0.47 spot subjected to bidimensional TLC with the three different solvent systems moved in the second direction as only one spot. To confirm whether the Rf 0.47 spot was composed by only one substance, reverse-phase HPLC was performed in a Waters radial compression unit using three different elution systems and in a Hewlett-Packard model equipped with an ultrasphere ODS column. With these different HPLC columns and elution systems, only one peak was observed. This is the first attempt to purify a substance showing a biological activity similar to that of glomerulopressin.

Antagonistic actions of prostaglandins E 2 and F 2 alpha on the isolated lungs of the frog, Rana esculenta L.

1. Isolated lungs of the frog, Rana esculenta L., when incubated in amphibian Ringer solution for 30 min, produced a prostaglandin E 2-like substance (27.1 + 3.8 ng/g w.w.), as determined by bioassay on the isolated rat stomach strip. 2. The release of PGE 2-like substance from skin, heart and bowel is also reported. 3. The activity of synthetic prostaglandins E 2 (PGE 2 and F 2alpha (PGF 2alpha) on the muscular contractility of frog isolated lungs was investigated: PGE 2 and PGF 2alpha relaxed and contracted respectively in a dose-dependent manner this preparation, a result similar to that obtained in mammals.

Comparative effects of total flavonoids extracted from [formula omitted] leaves,rutinand isoquercitrinon biosynthesis and release of prostaglandins in the [formula omitted] rabbit heart

Experiments were carried out on isolated rabbit hearts: PG biosynthesis was induced by administration into the coronary circulation of a single dose of arachidonic acid (100 ug) and the PGs synthesized and released in the heart effluent were detected by bioassays. Total flavonoids (TF) extracted from Ribes niarum leaves and their 2 major components, rutin and isoquercitrin had neither spasmodic nor relaxing activity on rat stomach strip. They were not capable of inducing any biosynthesis and release of PG-like substances and did not act on PGE 2 receptors. They inhibited both biosynthesis and release of PG-like substances: TF were more active than rutin and isoquercitrin: ID30 was 1.03 ± 0.24 mg/ml for TF versus 3.75 ± 0.24 mg/ml and 2.31 ± 1.4 mg/ml for rutin and isoquercitrin respectively.

Acetylcholine output and foetal vascular resistance of human perfused placental cotyleda.

The foetal villous vessels of single cotyleda of human placentae have been perfused with a constant flow of Krebs solution, recording inflow pressure and passing the venous perfusate in cascade over guinea-pig ileum and rat stomach strip preparations in vitro. Each cotyledon released for at least 4 h a substance that was probably acetylcholine. The perfusate caused contractions of both preparations which were inhibited by atropine or hyoscine and potentiated by physostigmine. Contractile activity was destroyed after incubation at 37 degrees C of perfusate with acetylcholinesterase but not with acetylcholinesterase plus physostigmine. When the perfusion temperature was lowered to 34 degrees C or below, acetylcholine output was reduced, the extent depending on the fall in temperature. No change in resistance of the villous vessels occurred during the changes in temperature or in the presence at 37 degrees C of atropine, hyoscine, hexamethonium, (+)-tubocurarine, hemicholinium-3 or bretylium. Submaximal vasoconstrictor responses of the villous vessels to the thromboxane A2-mimetic U46619 were not affected by reduction of the perfusion temperature to 30 degrees C, which lowered acetylcholine-like output by approximately 70%. Responses to U46619, at 37 degrees C, were unchanged during the presence of atropine or hyoscine. Acetylcholine is released into the foetal circulation of the human placenta but no evidence could be obtained that it affects villous vascular smooth muscle tone or vasoconstrictor responses.

Pharmacological evaluation of 5-(Z,E)-13,14-didehydro-20-methyl-carboprostacyclin (FCE 22509)

FCE 22509, 5-(Z,E)-13,14-didehydro-20-methyl-carboprostacyclin, a chemically stable prostacyclin (PGI 2) derivative, was 3.5 times more potent than PGI 2 in relaxing bovine coronary artery in vitro ; unlike PGI 2, it did not contract bovine coronary vein and it antagonized PGI 2-induced contractions of the coronary vein. In vitro smooth muscle(guinea pig ileum and trachea and rat stomach strip) was contracted to a lesser extent than with PGI 2. FCE 22509 was about five times less potent than PGI2 in deaggregating platelet clumps formed on rabbit Achilles tendon bathed with heparinized cat blood (ED 50 = 7.6 and 1.6 mcg/kg i.v. respectively). In the conscious normotensive and spontaneously hypertensive rat FCE 22509 lowered mean systemic arterial pressure (MSAP) (ED 25 = 11.5 and 4.8 mcg/kg i.v.) to a lesser extent than PGI2 (ED 25 = 2.1 and 2.34 mcg/kg i.v.) and increased heart rate but not dose-dependently. Orally administered, FCE 22509 likewise reduced MSAP though at high dosages (ED 30 = 1.33 and 1.02 mg/kg in normotensive and hypertensive rats). Heart rate (HR) was raised after i.v. and oral treatment but not dose-dependently. In the open-chest anaesthetized dog, FCE 22509, compared with PGI 2 at the same three doses, 0.2, 0.4 and 0.8 mcg/kg i.v., lowered MSAP but its hypotensive effect was less pronounced than that of PGI 2. Like PGI 2, FCE 22509 did not modify HR (though PGI 2 showed a tendency to a decrease and FCE 22509 seemed to increase this cardiovascular function) and mean pulmonary arterial pressure (MPAP) and likewise significantly reduced myocardial contractile force. After infusion of PGI 2 and FCE 22509 0.2 mcg/kg i.v. for 15 min in the open chest anaesthetized cat, the ex-vivo ADP-induced inhibition of platelet aggregation was the same for both compounds. Unlike PGI 2, which reduced MSAP and MPAP, FCE 22509 had no significant lowering effect on MSAP and MPAP.

Catecholamine release and potentiation of thromboxane A2 production by nicotine in the greyhound.

Thromboxane A2 was generated by infusing arachidonic acid (2.5 micrograms ml-1) into an extra-corporeal circuit of blood withdrawn from anaesthetized dogs, and assayed on a blood-bathed bioassay cascade of porcine and bovine coronary artery strips, chick rectum and rat stomach strip. All tissues except chick rectum were treated with phentolamine and propranolol to abolish direct effects of catecholamines. The arachidonate-induced contractions of artery strips were abolished by a thromboxane synthetase inhibitor UK-38485 (3 mg kg-1, i.v.), but were not altered by the 5-hydroxytryptamine antagonist ketanserin (10 microM) administered over the tissues. Intravenous infusion of adrenaline (0.2 and 0.4 micrograms kg-1 min-1) reversibly potentiated the coronary contractions produced by arachidonate, but did not alter contractions when applied directly over the bioassay tissues. Intra-aortic infusion of nicotine (5 or 10 micrograms kg-1 min-1) also increased the arachidonate-induced contractions of the bioassay tissues but only on those experiments where nicotine caused appreciable adrenaline release, as indicated by relaxation of chick rectum. Phenoxybenzamine (2 mg kg-1, i.v.) blocked the potentiation effect of adrenaline and nicotine on coronary contractions. The specific alpha 2-adrenoceptor antagonist, idazoxan (1 mg kg-1, i.v.), also blocked nicotine-induced potentiation of the contractions. These findings suggest that the ability of nicotine to potentiate thromboxane release from circulating platelets and blood cells is dependent upon the release of adrenaline, and probably involves an action on alpha-adrenoceptors of the circulating blood elements.

Hemolysate-induced release of prostaglandinlike substances from the canine cerebral arteries

The release of prostaglandinlike substances from canine pial arteries that was induced by exposure of the pial arteries to red blood cell hemolysate was estimated by using a superfusion technique for prostaglandin bioassay. The assay organs used were strips of rat stomach for prostaglandin E 2- or prostaglandin F 2α-like substances, strips of dog coronary artery for prostaglandin I 2-like substance, and strips of dog ileum for prostaglandin F 2α-like substance. The substances released from the canine pial arteries induced contractions in rat stomach strips and relaxations in canine coronary arterial strips, whereas they did not induce any response in canine ileal strips. The equivalent prostaglandin E 2 doses for the contractions of the rat stomach strips and the equivalent prostaglandin 1 2 doses for the relaxations of the canine coronary arterial strips were 125.2 ± 19.4 (n = 8) and 59.5 ± 16.4 (n = 6) pmol/g wet wt ± SEM, respectively.

Disappearance of enkephalins in the isolated perfused rat lung

Enkephalin disappearance during a single passage through the isolated, Krebs'-perfused rat lung was examined by superfusion bioassay. The rat colon was used to quantitate enkephalin disappearance since it proved to be sensitive to physiologic concentrations (10 −11M) of met 5-enkephalin or an analog D-ala 2-D-leu 5-enkephalin. The rat stomach strip was used to assess the release of prostaglandins from the pulmonary vasculature. The rat lung rapidly degraded the enkephalins but released no prostaglandins in the dose-range of 0.1 – 50 ng. Captopril at doses which blocked conversion of angiotensin I to II inhibited the degradation of enkephalins across the lung.

The contractile effect of bombesin, gastrin releasing peptide and various fragments in the rat stomach strip

The contractile activity of bombesin (BB) and related peptides including the gastrin releasing peptide (GRP) was evaluated in the rat stomach strip. BB and GRP were found to elicit concentration-dependent contractile effects in concentrations varying between 5.0 × 10 −10 and 5.0 × 10 −7 M. EC 50 values of BB and GRP were 6.5 × 10 −9 and 10 −8 M, respectively. The contractile effect of BB (1.5 × 10 −8 M) was not modified by a mixture of antagonists containing atropine (1.7 × 10 −6 M), mepyramine (1.2 × 10 −6 M), methysergide (1.4 × 10 −6 M), phentolamine (1.8 × 10 −6 M), propranolol (1.9 × 10 −6 M) and indomethacin (7.0 × 10 −6 M), nor by the nerve paralyzing drug tetrodotoxin (1.6 × 10 −6 M). These results suggest the existence of BB receptors in the rat stomach strip. The results also suggest that the contractile effects of BB in this tissue result from a direct effect on the smooth muscle cell. The data derived from our structure-activity study indicate that deletion of the N-terminal sequence pGlu 1-Gln 2-Arg 3-Leu 4-Gly 5- from the BB molecule causes practically no loss of affinity and intrinsic activity. Further shortening of BB gives rise to a gradual reduction of both parameters. Residual contractile activity could still be observed with the tetra- and pentapeptide BB-(11–14) and BB-(10–14) at 10 −5 M. On the other hand, deletion of only two (Leu 13-Met 14) or three (His 12-Leu 13-Met 14) amino acids from the C-terminus gave BB fragments with low affinities (BB-(1–12) and BB-(1–11)) and, in the case of BB-(1–11), a reduced intrinsic activity. GRP-(14–27) and acetyl-GRP-(20–27) were found to be either as potent (GRP-(14–27)), or slightly more potent (Ac-GRP-(20–27)) than BB itself. GRP and its two fragments exhibited the same intrinsic activity as BB. These results underline the essential contribution of the chemical groups scattered in the C-terminal region of BB and GRP for their myotropic effects in the rat stomach strip. The sequence His 12-Leu 13-Met 14 seems to be critical to provide full activation of BB receptors in the rat stomach strip since BB-(1–11) exhibited only 50% of the intrinsic activity of BB.

Continuous monitoring of prostacyclin production by the isolated, intact, rat aorta using a bioassay technique

Isolated rat aortae were perfused with Krebs buffer in vitro and the synthesis of prostacyclin-like material (PGI 2-L) was continuously monitored by measuring the contraction of a superperfused rat stomach strip exposed to the aortic perfusate. PGI 2-L release was high after initiation of the aorta perfusion but then gradually declined and stabilized at a basal rate of production that was maintained for at least 180 min. Levels of 6 keto prostaglandin F 1α(6ketoPGF 1α), the stable breakdown product of PGI 2, in the aortic perfusate reflected the changes in biological activity. The concentration of PGE 2 in the aortic perfusate remained constant throughout the experiment while the level of thromboxane (Tx)B 2 (the stable product of TxA 2) decreased with time to below the level of detection of the radioimmunoassay (RIA) used. All biological activity was abolished by heating the aortic perfusate for 30 min at 37°C, while perfusing with 30 μM indomethacin inhibited aorta PGI-L formation. Analysis (by linear regression) of the relationship between PGI 2-L formation and the body weight or age of the animals used revealed that PGI 2-L synthesis was better related to body weight ( r 2 = 0.90) than age ( r 2 = 0.75).

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.

Enzymatic inactivation of 6-keto-prostaglandin E 1 in vitro: Comparison with prostaglandin E 1

The inactivation of 6-keto PGE 1, a biologically active and stable metabolite of prostacyclin, was studied in 100,000 g cytosolic supernatants by bioassay on rat stomach strip (contraction) and human platelets (inhibition of ADP-induced aggregation). PGE 1 was used as a reference compound. Both PGs were inactivated in supernatants from colon, kidney and liver of rat, rabbit and guinea-pig. Inactivation was time- and NAD +-dependent and was generally greater for PGE 1 than 6-keto-PGE 1. The enzyme responsible for 6-keto-PGE 1 inactivation in cytosolic supernatants is distinct from prostaglandin 15-hydroxydehydrogenase and 9-keto reductase, is not inhibitable by sulphasalazine-like drugs and its activity is recoverable after precipitation by ammonium sulphate. We conclude that 6-keto-PGE 1 can be inactivated by enzymes with wide tissue distribution, but further studies are needed for identification of these novel enzymes and the products formed as well as to assess their significance in the intact animal.

The cyclo-oxygenase pathway in the avascular heart of the frog, Rana esculenta L.

1. A modification of Vane's cascade is reported, allowing the superfusion bioassay of prostaglandin-like substances (PLS) in the outflow of isolated and perfused heart of the frog Rana esculenta L. 2. Using both this technique and radioimmunoassay determination, the cyclo-oxygenase pathway in perfused frog heart has been investigated. 3. Arachidonate (AA) (2–20 μg) injected into the perfusing fluid, was transformed by the heart into PLS, as shown by the response of the bioassay tissues (rat stomach strip, chick rectum, rat colon). A compound capable of relaxing rabbit mesenteric artery and a rabbit aorta contracting substance were also generated. The release was inhibited by indomethacin (1.0 × 10 −5 M) 4. Radioimmunoassay determination of PGE 2, TXB 2 and 6-keto-PGF 1α in frog heart effluent, before and after AA injection (20 μg), gave the following yields (ng/ml of effluent). Basal: PGE 2 = 0.45 ± 0.15; TXB 2 = 0.46 ± 0.13; 6-keto-PGF 1 α - 2.21 ± 0.3. Following AA: PGE 2 = 1.55 ±0.35; 6-keto-PGF 1 α = 3.4 ± 0.4; TXB 2 = 1.00 ± 0.06. 5. Our results suggest that prostacyclin is a major product of the cyclo-oxygenase pathway in frog perfused heart. The biological significance of this finding is discussed in relation to both the absence of a coronary circulation in amphibians and to the spongy nature of frog myocardium.

Smooth muscle stimulation by an immunomodulatory compound muramyl dipeptide: does it involve serotoninergic system?

Contractions evoked by muramyl dipeptide (MDP), a synthetic compound possessing immunostimulatory properties, were studied in several isolated nerve-smooth muscle preparations. The contractions by micromolar concentrations of MDP were evoked either by direct interaction with smooth muscle (rat stomach strip) or at least partly indirectly via neurogenic stimulation (guinea pig ileum); the effect was stereospecific since the MDP-D was not active. The insensitivity of the preparations to serotonin (5-HT), either inherent (vas deferens) or after 5-HT antagonists or after desensitization to 5-HT, prevented or markedly reduced the contractile activity by MDP. On the other hand, a nanomolar concentration of MDP enhanced the sensitivity of the rat stomach strip to 5-HT.

Comparison of the actions of 11.9 epoxymethano PGH 2 and 9.11 AZO PGH 2 on rat aorta and stomach strip preparations

Two synthetic thromboxane A 2 agonists were compared on two isolated smooth muslce preparations, the rat aorta and stomach-strip using a superfusion cascade. 11.9 epoxymethano-PGH 2 contracted both preparations in a concentration dependent manner. Cumulative concentration-response curves showed that azo PGH 2 was twice as active as 11.9 epoxymethano PGH 2 on the aorta and nearly four times as active as 11.9 epoxymethano PGH 2 on the stomach-strip. Statistical analysis of the agonist concentration-response curves showed a significant differences when responses to azo PGH 2 were compared on the two preparations and when responses to azo PGH 2 and 11.9 epoxymethano PGH 2 were compared to the aorta preparation. When EP045, a thromboxane receptor antagonist was used the PA 2 values obtained were not significantly different using the two agonists on the two preparations. The pA 2 values indicate that both agonists act on the same receptor but the comparison of the concentration-response curves suggest that azo PGH 2 may be acting at another receptor as well as the thromboxane receptor in the stomach-strip.

Role of intrinsic arachidonate metabolites in the vascular action of erythrocyte breakdown products.

In helically-cut strips of dog basilar and mesenteric arteries, the isometric tension developed by application of ghost-free hemolysate from dog erythrocytes was recorded. The hemolysate contracted basilar arteries in a concentration-dependent fashion, the response being attenuated by treatment with either aspirin or polyphloretin phosphate, a prostaglandin antagonist. Mesenteric arteries were contracted only slightly by high concentrations of hemolysate. When the mesenteric arteries had partially been contracted with prostaglandin F2 alpha or norepinephrine, the hemolysate induced relaxations, which were abolished by aspirin in approximately half the preparations used. Studies on rat stomach strips exposed to superfusate of dog cerebral arteries showed a release of prostaglandin-like substance by the hemolysate application. It may be concluded that the hemolysate contracts basilar arteries and relaxes mesenteric arteries, mainly through prostaglandins synthesized in and released from the vascular wall. Such a mechanism may be involved in the pathogenesis of cerebral vasospasm following a subarachnoid hemorrhage.

Extremely decreased release of prostaglandin E2-like activity from chopped lung of ethyl linolenate-supplemented rats.

Three groups of weanling male rats were reared on a fat-free diet for 13 weeks. One group received only the fat-free diet (FF rats), the other 2 groups received the fat-free diet and a daily supplement of 2 energy% ethyl linoleate ([n-6] rats), or 2 energy% ethyl linolenate ([n-3] rats). The chopped lung preparation was used to illustrate an in vitro prostaglandin formation. PGE2-like activity was quantified on rat stomach strip. The release of PGE2-like activity expressed as ng PGE2-equivalent per g lung tissue (mean +/- SD) was 23 +/- 7, less than 6, and 65 +/- 20 for the FF rats, the (n-3) rats, and the (n-6) rats, respectively. PGE2 quantification by radioimmunoassay of the chopped lung effluent collected after passing over the rat stomach strip revealed the same release pattern as the bioassay. Fractionation of chopped lung effluent on HPLC with radioimmunoassay detection indicated that the lung tissue from (n-3) rats released very little PGE3, if any, in spite of a 20:5(n-3)/20:4(n-6) ratio of 5.2 in the lipids of the lung. It is suggested that the pool of arachidonic acid for prostaglandin production in vitro is different from the one which functions in vivo, and the these pools are differently affected by dietary EFA.

The effect of some flavone drugs on the conversion of prostacyclin to 6-oxoprostaglandin E 1

Flavonoid drugs (rutin, naringenin and quercetin) were compared with indomethacin and sulphasalazine as inhibitors of rat and rabbit renal 9-hydroxyprostaglandin dehydrogenase, prostaglandin synthesis (bovine seminal vesicle microsomes) and inactivation (rabbit colon 100,000 g supernatant), vascular PGI 2 formation (rat aortic rings) and for effects on platelet aggregation and on the isolated rat stomach strip. Rutin and naringenin potently inhibited rabbit renal conversion of PGI 2 and PGF 2α to 6-oxoPGE 1 and PGE 2, respectively, but had no effect on rat renal 9-hydroxyprostaglandin dehydrogenase activity, prostaglandin breakdown, vascular PGI 2 synthesis, platelet aggregation or the antiaggregatory effect of PGI 2 and 6-oxoPGE 1. High concentrations (100 μM) of both drugs inhibited the spasmogenic effect of PGI 2on the rat stomach strip. Naringenin and quercetin (1 mM) inhibited whilst rutin (1 mM) stimulated microsomal prostaglandin synthesis. These results suggest that rutin and naringenin may be useful experimental tools to study the biological roles of 6-oxoPGE 1.