Galanin suppresses neurally evoked contractions of circular muscle in the guinea-pig ileum

The effect of galanin, a 29 amino-acid peptide, on intestinal smooth muscles was studied in guinea-pig ileum. Galanin did not affect the basal activity of longitudinal or circular muscles. Galanin decreased neurally evoked circular muscle contractions in a dose-dependent manner, but failed to affect neurally evoked longitudinal muscle contractions. Galanin also decreased neurally evoked circular muscle contractions in the presence of atropine. The neurally evoked phasic contractions were blocked by TTX. These findings indicate that galanin has an inhibitory role in circular muscle contractions via myenteric neurons in the guinea-pig ileum.     

Mechanism involved in the spasmolytic effect of a mixture of two triterpenes, cycloartenol and cycloeucalenol, isolated from Herissanthia tiubae in the guinea-pig ileum

The smooth muscle relaxant properties of a mixture of the two triterpenoids cycloeuclalenol and cycloartenol (CC) isolated from Herissanthia tiubae (Malvaceae) were studied in several smooth muscle preparations. CC inhibited contractions induced by carbachol, histamine and KCl in the guinea-pig ileum, but no spasmolytic activity was found in guinea-pig trachea or rat aorta. In guinea-pig ileum, concentration-response curves to carbachol and CaCl (2) in high K(+) were shifted to the right by CC in a concentration-dependent manner with slopes of the Schild plot differing from the unity. IC(50) values were 3.4 +/- 0.8 x 10 (-5) M and 8.44 +/- 1.87 x 10 (-5) M for carbachol and CaCl(2), respectively. The phorbol ester TPA, which activates protein kinase C (PKC), potentiated contractions induced by submaximal concentrations of carbachol. This potentiation was inhibited by CC. Desensitization of PKC by TPA completely abolished the inhibition produced by CC on carbachol-induced contractions. Together, our results indicate that inhibition of PKC is involved in the spasmolytic effect of CC in the guinea-pig ileum.     

蛇床子素对豚鼠离体回肠和结肠带的作用

以豚鼠离体回肠和结肠带为标本,观察蛇床子素(Ost)的作用与Ca²⁺)的关系。结果表明:Ost和钙拮抗剂Ver产生剂量依赖性抑制乙酰胆碱(ACh)、组胺及KCl所致回肠条或结肠带的收缩;非竞争性拮抗CaCl₂累积量—效曲线,pD₂分别为4.41±0.15,7.0±0.2。Ost 100μmol/L和Ver 1μmol/L均能对抗小剂量Ca²⁺所致结肠带收缩,但被加入较大量Ca²⁺所取消。Ost和Ver均能抑制ACh诱导的依内钙性收缩,不影响依外钙性收缩。结果提示Ost具有钙拮抗作用,其作用方式与Ver类似。     

Effects of genistein, an isoflavone isolated from Genista tridentata, on isolated guinea-pig ileum and guinea-pig ileal myenteric plexus.

The inhibitory action of the major constituent of Genista tridentata L. (Papilionaceae), 4',5,7-trihydroxyisoflavone (genistein), on contractions induced by agonists and electrical field stimulation of smooth muscle was analysed. Genistein inhibited twitches evoked by electrical-stimulation of strips of guinea-pig ileum with an IC50 value of 34 microM. Genistein (34 microM) inhibited contractions of the guinea-pig ileum by several agonists in a non-selective, antispasmodic action and had no effect on inhibition of 3H-ACh release from ileal myenteric plexus. Genistein (34 microM) produces an increase in cAMP levels of guinea-pig ileum which resulted in a smooth muscle relaxation which leads us to think that there must be a blockade of its phosphodiesterase.     

Modification of electrical field stimulation-induced contractions in the guinea-pig ileum by metoclopramide and ICS 205-930 depends on the integrity of the mucosa

Contractions induced by electrical field stimulation of guinea-pig ileum longitudinal muscle strips were enhanced by metoclopramide and ICS 205-930 at concentrations similar to those required to antagonize at 5-hydroxytryptamine 'M' receptors. The enhancement of contraction was observed in intact ileum strips but was not recorded in the longitudinal muscle myenteric plexus preparation or from the ileum with the mucosal layer removed. It is concluded that an intact mucosal layer is required for metoclopramide and ICS 205-930 to enhance electrical field stimulation-induced contractions of the guinea-pig ileum.     

Inhibition of nerve-mediated contractions in isolated guinea-pig ileum by 1-methylisoguanosine, a novel purine from a sponge

1-Methylisoguanosine, a novel purine isolated from the sponge Tedania digitata (Schmidt) selectively inhibited contractions produced by nerve stimulation in the guinea-pig ileum but was without effect on contractions produced by acetylcholine or histamine. The ED50 for inhibition of nicotine responses or responses to submaximal transmural stimulation was 1.1 mumoles/l. The inhibition of nerve-mediated contractions appeared to be due to inhibition of transmitter release from nerve endings in the ileum, as has been suggested for the action of adenosine. Theophylline antagonized the action of 1-methylisoguanosine and overall the results suggest that 1-methyl-isoguanosine acts at an adenosine receptor in the guinea-pig ileum, but is approximately ten times more potent than adenosine itself. A series of related purines which were resistant to the action of adenosine deaminase were also tested for their effect on the nerve-mediated contractions of guinea-pig ileum and the results compared with the in vivo effect on muscle relaxation in mice. All active purines tested produced results qualitatively similar to those of 1-methylisoguanosine itself.     

Effects of the Anemonia sulcata Toxin (ATX II) on Intracellular Sodium and Contractility in Rat and Guinea-Pig Myocardium

Abstract: The effects of the Anemonia sulcata toxin ATX II on action potentials and contractility of isolated papillary muscles and single myocytes from rat and guinea-pig hearts have been studied. ATX II prolonged the action potential in both rat and guinea-pig papillary muscle. Although it produced a positive inotropic effect in guinea-pig papillary muscle, it failed to do so in rat papillary muscle. However, in single rat and guinea-pig ventricular cells, it both prolonged the action potential and had a positive inotropic effect. We suggest that ATX II does not cause a positive inotropic effect in rat papillary muscle, because it induces Ca²⁺ overload. In single cells the positive inotropic effect was reduced by ?50% when the contractions were triggered by voltage clamp pulses of constant duration rather than by action potentials. This suggests that the inotropic effect of ATX II is in part the result of the prolongation of the action potential. The intracellular Na⁺ activity (aⁱ_Na) in single ventricular cells was measured with the Na⁺-sensitive fluorescent dye SBFI. After exposure of the cells to ATX II, aⁱ_Na was increased by a maximum of 1.9 ± 0.3 and 2.2 ± 0.3 mM in rat and guinea-pig cells, respectively. It is suggested that the positive inotropic effect of ATX II is also in part the result of the rise in aⁱ_Na.     

CP-96,345, a non-peptide antagonist of substance P: I. Effects on the actions mediated by substance P and related tachykinins on the guinea-pig ileum and rabbit jejunum

Summary The effects of a non-peptide antagonist of substance P, CP 96,345, were investigated, in vitro, on the guinea-pig ileum and the rabbit jejunum.Contractions of the guinea-pig ileum, induced by substance P and neurokinin A, were specifically inhibited by the racemate (±)CP-96,345 (pIC₅₀ 7.8 and 7.3, respectively). The inhibition by (±)CP-96,345 of contractions evoked by neurokinin B and by bradykinin (pIC₅₀ 6.1 and 4.9, respectively) was attributed to unspecific effects of the antagonist. The inhibition of substance P-induced contractions of the rabbit jejunum required a 10 times higher concentration of (±)CP-96,345 (pIC₅₀ = 6.8) than was required with the guinea-pig ileum. The plateau phase of contraction of the guinea-pig ileum induced by high concentrations of substance P, neurokinin A or neurokinin B, which is known to be mediated through tachykinin receptors on intrinsic cholinergic neurones, was inhibited by 200 nM (±)CP-96,345 but not by the inactive enantiomer, CP-96,344. This indicates a specific inhibition of these neuronal tachykinin receptors by (±)CP-96,345 Contractions known to be mediated by the release of substance P, such as those evoked by capsaicin and by mesenteric nerve or field stimulation, were partially inhibited by (±)CP-96,345 at concentrations of 200 to 600 nM. Unspecific inhibitory effects of CP-96,345, in concentrations of 1 µM or higher, were observed on histamine-induced contractions, and on the cholinergic twitch response to electrical stimulation, of the guinea-pig ileum. Therefore, an inhibition by CP-96,345 of substance P-related effects can only be regarded as specific if the concentration of the antagonist is below 1 µM. No effect of CP-96,345 (1 µM) was seen on peristalsis in vitro. The peristaltic reflex, in situ, was also not affected by CP-96,345 (1.6 µmolkg^–1, i.v.).The present results demonstrate that, although inhibitory actions of CP-96,345 can be observed on certain motor responses in the guinea-pig small intestine, peristalsis, a physiologically relevant function, remains intact. Send offprint requests to F. Lembeck at the above address     

Muscle relaxing activity of Hyssopus officinalis essential oil on isolated intestinal preparations

The muscle relaxing activity of the essential oil of Hyssopus officinalis L. (Lamiaceae) and some of its main components (isopinocamphone, limonene and beta-pinene) was studied on isolated preparations of guinea-pig and rabbit intestine. The essential oil and isopinocamphone inhibited the acetylcholine- and BaCl2-induced contractions in guinea-pig ileum in a concentration-dependent manner (IC50 42.4 microg/ml and 61.9 microg/ml to acetylcholine; 48.3 microg/ml and 70.4 microg/ml to BaCl2) whereas limonene or beta-pinene left tissue contraction unchanged. In guinea-pig ileum H. officinalis essential oil also blocked the contractions induced by CaCl2. In isolated rabbit jejunum the essential oil reduced the amplitude of spontaneous movements and decreased the basal tone; neither haemoglobin, methylene blue, N(omega)-nitro-L-arginine methyl ester (L-NAME) or propranolol blocked the myorelaxant effect.     

Different contractile effects of substance P on the intestine of mammals

Summary The contractile effect of substance P was examined on the longitudinal muscle of isolated sections of the gut of cat, guinea-pig, pig, rabbit, and rat. Substance P caused contraction of all intestinal regions investigated, but there were marked qualitative and quantitative differences in the contractile responses to substance P. Low concentrations of substance P that did not cause tonic contraction (0.22–2.2 nM), increased the phasic longitudinal contractions observed in the ileum of cat, pig, and rabbit. Higher concentrations induced a tonic longitudinal contraction of the ileum, which in the cat, pig and rat was accompanied by facilitation and in the rabbit by inhibition of the phasic contractions. While in the ileum of guinea-pig and rabbit the maximal longitudinal contraction induced by substance P was equal to the maximal effect of acetylcholine, the maximal response to substance P was only about 50% of that to acetylcholine in the ileum of cat, pig, and rat. The jejunum, ilcum and colon of the rabbit responded to substance P and acetylcholine with similar maximal contractions, but the jejunum appeared to be most and the ileum least sensitive to substance P. The results suggest qualitatively and quantitatively different roles of substance P in the intestinal motility of different mammals.     

THE MARINE NATURAL PRODUCT 3,5-DIBROMO-2-(2,4-DIBROMO-PHENOXY)PHENOL, INHIBITS CONTRACTILE ACTIVITY IN THE GUINEA-PIG ILEUM

1. The tetrabrominated diphenyl ether 3,5-dibromo-2-(2,4-dibromophenoxy)phenol (BPE), a natural marine product isolated from a sponge, was tested for pharmacological activity in guinea-pig ileum. 2. BPE (2 μmol/ L) decreased basal force and the frequency of spontaneous contractions of the ileum. It also significantly decreased contractions of the ileum induced by 5 mmol/L barium and to electrical stimulation at parameters which stimulated intrinsic nerves. 3. The slopes of concentration-response curves to acetylcholine (ACh), histamine and 5-hydroxytryptamine (5-HT) were significantly reduced by BPE at concentrations of 2 μmol/L or greater. 4. BPE (2 μmol/L) did not affect calcium-induced contractions of longitudinal muscle fibres from guinea-pig ileum which were stripped of their cellular membrane. It (6 μmol/L) also had no effect on ATP levels in longitudinal muscle fibres. 5. BPE (2 μmol/L) reduced both phasic and tonic components of contractions induced by raising the extracellular concentration of K⁺ to 15, 30, 45 or 60 mmol/ L (in the presence of atropine, propranolol, phentolamine and desensitization to 5-HT to inhibit the effects of nerve transmitter release). 6. BPE (2 μmol/L) reduced carbachol-induced contractions of ileum pre-incubated in 1 μmol/L felodipine, a blocker of l-type voltage-operated calcium channels (VOCC). 7. BPE dose dependently (0.6–6 μmol/L) reduced contractions induced by Ca²⁺ in both K⁺ depolarized ileum and in tissue exposed to carbachol (10 μmol/L) in the presence of felodipine (0.1 μmol/L). 8. These results suggest that BPE affects intracellular messenger systems controlling cytosolic calcium and/or blocks entry of calcium into the cell through both VOCC and receptor-operated channels (ROC).     

Relaxant and antispasmodic actions of methyleugenol on guinea-pig isolated ileum

The effects of methyleugenol (ME) on guinea-pig isolated ileum were studied. ME reversibly relaxed basal tonus (EC50 of 52.2 +/- 18.3 microM), an action unaltered by 0.5 microM tetrodotoxin or 0.5 mM hexamethonium, and relaxed the ileum pre-contracted with 60 mM KCl. ME slightly hyperpolarized the ileum from -57.3 to -62.8 mV but had no effect in depolarised tissues. ME inhibited contractions induced by ACh, histamine and KCl with IC50 values of approximately 82, 124, and 65 microM, respectively. Our results suggest that ME induces relaxation of guinea-pig ileum by a direct action on smooth muscle via a mechanism largely independent of alterations of membrane potential (Em).     

Effects of hispidulin, a flavone isolated from Inula viscosa, on isolated guinea-pig smooth muscle

1. In small concentrations (10(-7)-3 X 10(-6) M), hispidulin caused concentration-dependent contraction of isolated guinea-pig ileum and only mild relaxation of guinea-pig tracheal rings. 2. Larger concentrations (up to 3 X 10(-4) M) caused concentration-dependent relaxation of the ileum and the trachea. All the effects on the ileum and the trachea are reversible upon removal of the compound. 3. In concentrations from 10(-7) to 3 X 10(-4) M, hispidulin had no effect on the tone of the epinephrine-contracted rings of the guinea-pig main pulmonary artery. 4. Hispidulin caused a shift to the right of the acetylcholine concentration-effect curves on ileum and trachea and significantly inhibited the maximum contractions induced by acetylcholine. 5. In Ca2+-free, depolarizing solution, hispidulin caused both a shift to the right, and an inhibition of the maximum contractions, of the CaCl2 concentration-effect curves on ileum, trachea and pulmonary artery. 6. In Ca2+-free, EGTA-containing solution, hispidulin caused concentration-dependent inhibition of the contractions induced in the pulmonary artery by epinephrine and in the ileum by histamine. 7. These observations suggest that hispidulin may interfere with Ca2+ binding to the Ca2+-receptor protein(s) in the smooth muscle cell and/or with the agonist-induced Ca2+-release from intracellular stores. Less likely, hispidulin may interfere with Ca2+ influx through smooth muscle cell membrane.     

Action of 2-hydroxy-4,6-dimethoxyacetophenone isolated from Sebastiania schottiana

The inhibitory action of the major constituent of Sebastiania schottiana (Euphorbiaceae), 2-hydroxy-4,6-dimethoxyacetophenone (xanthoxyline) on contractions induced by agonists and electrical stimulation of smooth and cardiac muscle preparations was analysed. Xanthoxyline (30 to 300 microM) inhibited contractions of the rat uterus, guinea-pig ileum, and urinary bladder induced by several agonists in a non-competitive, non-selective, concentration-related manner, with the IC50's ranging between 47 and 190 microM. Twitches evoked by electrical-stimulation of strips of guinea-pig longitudinal ileum, urinary bladder, dog ureter, and rat left atrium were also inhibited dose-dependently by cumulative additions of xanthoxyline (IC50's between 50 and 480 microM). Xanthoxyline was found to be a potent inhibitor of spontaneous contractions of the circular smooth muscle layer of the dog ureter, yielding an IC50 of 54 microM. Repeated washing of all preparations completely reversed the inhibitory effects of xanthoxyline. Therefore, it appears that xanthoxyline induces a direct and non-selective inhibition of contractions triggered by agonists or electrical stimulation of smooth and cardiac muscle preparations. The elucidation of the mechanism(s) by which xanthoxyline induced muscle relaxation requires further investigations.     

Nitrergic modulation of acetylcholine release in the enteric nervous system: differences between guinea-pig and man

The effects of the NO donor, SNAP, and of the NO-synthase inhibitor, L-NNA, on release of acetylcholine and contractions were studied in isolated ileum preparations of man and guinea-pig. Strips were incubated with [³H]choline and superfused with a physiological salt solution. Release of [³H]acetylcholine was elicited by electrical stimulation. In the guinea-pig ileum, SNAP (100 M) increased basal [³H]acetylcholine release and muscle tone, and, in addition, inhibited the electrically-evoked release and contractions. In contrast, SNAP had no effect on basal or evoked [³H]acetylcholine release in the human ileum. L-NNA (300 M) facilitated the evoked release and contractions of the guinea-pig ileum, but had no effect in the human ileum. It is concluded that endogenous NO exerts a tonic inhibitory effect on cholinergic neurotransmission in the guinea-pig ileum which contributes to the relaxant effect of NO. The results do not indicate that NO has a similar function in the human ileum.     

Effect of prostaglandins E1 and E2 on intestinal motility in the guinea-pig and rat

1. Prostaglandins E(1) and E(2) affected intestinal activity both in vitro and in vivo.2. Serosal application of prostaglandin to guinea-pig isolated ileum stimulated the longitudinal muscle but reduced peristaltic contractions of the circular muscle and the propulsion of fluid through the gut. Intraluminal application had little effect.3. Injection of prostaglandin into the bloodstream of anaesthetized rats stimulated the longitudinal muscle of the ileum and increased the intraluminal pressure. A similar response sometimes occurred in the guinea-pig, but in general the effect was variable.4. Release of prostaglandin in the gut wall, but probably not into the blood or into the lumen of the gut, may play a part in controlling intestinal motility.     

Effect of prostaglandin E1 and indomethacin on responses of longitudinal muscle of guinea-pig ileum to cholecystokinin.

The effect of prostaglandin E1 (PGE1) and indomethacin (IND) cholecystokinin (CCK)-induced contractions of guinea-pig isolated ileum longitudinal muscle were studied. PGE1 (2.8--28 nM) consistently and dose dependently increased the contractions evoked by CCK (indirect muscle stimulation) or by ACh. IND (2.7 microM) decreased the contractions to both compounds and this was reversed with 2.8--7 nM PGE1. Pretreatment of the preparations with phentolamine (2.6 microM) or pretreatment of the animals with reserpine (2 mg/kg i.p. 24 h before killing) did not affect PGE1 potentiation or IND inhibition of CCK-induced contractions. The results indicated that PGE1 potentiated CCK-induced contractions of the longitudinal muscle of guinea-pig ileum by increasing the response to released ACh. Experiments with IND suggested that endogenous PGs may modulate the effect of CCK or related gastrointestinal hormones.     

Antagonism by fenamates of prostaglandin action in guinea-pig and human alimentary muscle.

1 Low concentrations of meclofenamate, flufenamate or mefenamate had little effect on contractions in response to acetylcholine in any tissue studied. 2 Sodium meclofenamate potently antagonized contractions of guinea-pig ileum longitudinal muscle to prostaglandin E2 (PGE2), PGF2 alpha or PGD2. 3 In guinea-pig colonic longitudinal muscle, contractions to PGE2 were reduced by sodium meclofenamate, but contractions of the longitudinal or circular muscle to PGF2 alpha or PGD2 were less effectively inhibited. 4 In human gastrointestinal longitudinal muscle, sodium meclofenamate or flufenamate potently inhibited contractions to PGF2 alpha, but not to PGE2. 5 Sodium mefenamate or mefenamic acid, even in high concentrations, had little effect on contractions to PGF2 alpha, but tended to inhibit PGE2-induced contractions of human gastrointestinal longitudinal muscle. 6 The therapeutic advantages of prostaglandin synthesis inhibitors which also antagonize responses to certain prostaglandins are discussed.     

Mechanism of the Hypotensive Effect of Scopoletin Isolated from the Fruit of Tetrapleura tetraptera

The plausible mechanisms of the hypotensive effect of scopoletin, a coumarin isolated from the fruits of TETRAPLEURA TETRAPTERA T AUB (Mimosaceae), have been investigated IN VIVO and IN VITRO. The results obtained show that scopoletin inhibits the indirect electrical stimulation-evoked contractions of the cat nictitating membrane ( IN VIVO); and also the contractions of isolated perfused central ear artery of rabbit, induced by electrical stimulation or intraluminal noradrenaline administration. This coumarin, like papaverine, reduces the amplitude and frequency of the spontaneous, myogenic, rhythmic contractions, and exogenous noradrenaline-evoked contractions of the rat isolated portal vein. Scopoletin also inhibits the spontaneous, myogenic, pendular, rhythmic contractions of the rabbit isolated duodenum and attenuates the indirect electrical stimulation-provoked or exogenous noradrenaline-induced relaxations of the muscle preparation. It also depresses the electrical stimulation-evoked contractions of the chick isolated oesophagus. Scopoletin, on its own accord, relaxes all the smooth muscles examined and inhibits the spasmogenic activities of a wide variety of agonists on guinea-pig isolated ileum to approximately the same extent. It is therefore speculated that scopoletin probably produces hypotension in laboratory animals through (a) its smooths muscle relaxant activity - by which means it presumably dilates blood vessels; and (b) by acting as a non-specific spasmolytic agent (like papaverine).     

Pharmacology of B-HT 920 in some Isolated Smooth Muscles of the Guinea-pig

Abstract: The effects of B-HT 920 were investigated on four isolated preparations from the guinea-pig, namely the aorta, trachea, ileum and vas deferens. The latter three preparations were studied during electrical field stimulation, which induced contractions by activating cholinergic neurones (trachea and ileum) or adrenergic neurones (vas deferens), respectively. Comparative studies were also made with clonidine and noradrenaline. In ileum and trachea B-HT 920 was almost equipotent with noradrenaline to inhibit the electrically induced contractions. In these tissues, B-HT 920 also displayed almost the same maximal effect as noradrenaline. Clonidine also inhibited the contractions in ileum and trachea; the drug was slightly more potent than noradrenaline. However, in contrast to the intrinsic activity of B-HT 920 that of clonidine was only submaximal. In vas deferens both B-HT 920 and clonidine induced inhibition of contractions on electrical field stimulation at low concentrations. In this organ, both drugs were capable of inducing complete inhibition of the contractile response. In aorta B-HT 920 as well as clonidine were only weak agonists in comparison to noradrenaline. The α₂-blocker, yohimbine, completely blocked the effect of B-HT 920 in ileum at low concentrations (1 × 10^?7 M). Remarkably, however, the inhibitory action of B-HT 920 in trachea was only marginally affected even by high concentrations of yohimbine (1 × 10^?6 M). It is suggested from the present results that B-HT 920 can induce inhibition of both cholinergic and adrenergic neurotransmission presumably by inducing selective stimulation of prejunctional α₂-receptors. In fact, the selectivity of B-HT 920 seems to be comparable to that of clonidine for the α₂-receptor. However, the mode of action of B-HT 920 in trachea may be somewhat uncertain since its effect was not inhibited by yohimbine.