Mechanism of spasmolytic activity of a fraction of Sarcostemma brevistigma Wight

The effect of chloroform soluble fraction (F-A) of twigs of Sarcostemma brevistigma on contractions induced by KCl, histamine, and acetylcholine in the isolated guinea pig ileum and taenia coli smooth muscles has been evaluated. F-A (19.5 microg/ml) significantly inhibited the contraction induced by 40 mM KCl to the extent of 87.6% in the isolated guinea pig ileum. In the isolated guinea pig ileum, F-A (64.3 and 59.2 microg/ml) significantly inhibited the contractions induced by acetylcholine and histamine to the extent of 85 and 83% respectively. In the isolated guinea pig taenia coli, F-A (65.2 microg/ml) significantly inhibited the contraction induced by 40 mM KCl to the extent of 96.0%. The inhibitory effect of F-A (40 microg/ml) on the isolated guinea pig taenia coli was reduced by Bay K 8644 (10(-6) M) to the extent of 61.6 from 73.6%. These results suggest that the F-A may exhibit smooth muscle relaxant activity by blocking the Ca2+ channels.     

Inhibitory effects of hot water extract of the Stevia stem on the contractile response of the smooth muscle of the guinea pig ileum

The effects of a hot water extract of the stem of Stevia rebaudiana on the smooth muscle of isolated guinea pig ileum were investigated. The butyl alcohol layer of the extract antagonized the contractions of the isolated guinea pig ileum induced by histamine (1 x 10(-5) M) and acetylcholine (1 x 10(-5) M) in a concentration-dependent manner. The butyl alcohol layer of the extract also showed inhibition of CaCl(2) (1 x 10(-3)-3.8 x 10(-1) M)-induced contractions. The antagonism of the extract was considered to be non-specific, but this action might be related to an influx of extracellular Ca(2+).With column chromatography preparation, the active component was assumed to be as stevioside. The antagonistic effects exerted by the stem extract of Stevia rebaudiana contributed to the gastroprotective activity of the extract in animals fed dietary histamine.     

Pharmacology of L-660,711 (MK-571): a novel potent and selective leukotriene D4 receptor antagonist

L-660,711 (3-(3-(2-(7-chloro-2-quinolinyl)ethenyl)phenyl) ((3-dimethyl amino-3-oxo propyl)thio)methyl)thio)propanoic acid is a potent and selective competitive inhibitor of [3H]leukotriene D4 binding in guinea pig (Ki value, 0.22 nM) and human (Ki value, 2.1 nM) lung membranes but is essentially inactive versus [3H]leukotriene C4 binding (IC50 value in guinea pig lung, 23 microM). Functionally it competitively antagonized contractions of guinea pig trachea and ileum induced by leukotriene (LT) D4 (respective pA2 values, 9.4 and 10.5) and LTE4 (respective pA2 values, 9.1 and 10.4) and contractions of human trachea induced by LTD4 (pA2 value, 8.5). L-660,711 (5.8 x 10(-8)M) antagonized contractions of guinea pig trachea induced by LTC4 in the absence (dose ratio = 28) but not in the presence of 45 mM L-serine borate (dose ratio less than 2). L-660,711 (1.9 x 10(-5)M) did not block contractions of guinea pig trachea induced by histamine, acetylcholine, 5-hydroxytryptamine, PGF2 alpha, U-44069, or PGD2. In the presence of atropine, mepyramine, and indomethacin, L-660,711 (1.9 x 10(-5)M) inhibited a small component of the response to antigen on guinea pig trachea but completely blocked anti-IgE-induced contractions of human trachea. L-660,711 (i.v.) antagonized bronchoconstriction induced in anesthetized guinea pigs by i.v. LTC4, LTD4, and LTE4 but did not block bronchoconstriction to arachidonic acid, U-44069, 5-hydroxytryptamine, histamine, or acetylcholine. Intraduodenal L-660,711 antagonized LTD4 (0.2-12.8 micrograms/kg)-induced bronchoconstriction in guinea pigs, and p.o. L-660,711 blocked LTD4- and Ascaris-induced bronchoconstriction in conscious squirrel monkeys and ovalbumin-induced bronchoconstriction in conscious sensitized rats treated with methysergide (3 micrograms/kg). The pharmacological profile of L-660,711 indicates that it is a potent, selective, orally active leukotriene receptor antagonist which is well suited to determine the role played by LTD4 and LTE4 in asthma and other pathophysiologic conditions.     

Histaminergic effect of crude papaya latex on isolated guinea pig ileal strips.

In the present study, we investigated the effect of the crude latex of Carica papaya L. (CPX) on isolated guinea pig ileal strips. CPX (0.5-512 microg/ml) caused concentration-dependent contraction of ileal strips suspended in Tyrode solution. The concentration of atropine (0.69 microM) that significantly blocked the contractile effect of acetylcholine on the isolated guinea pig ileum showed no significant effect on CPX- and histamine-induced contractions of the ileal strips. Mepyramine (87.6 nM) significantly blocked the contractile effect of histamine and CPX on the ileum. The same concentration of mepyramine, however, had no significant effect on acetylcholine-induced contraction of the isolated ileal strips. Removal of Ca2+ from the bathing medium abolished ileal contractions induced by acetylcholine, histamine and CPX. All the test substances were able to provoke ileal contractions after replacement of the Ca(2+)-free solution with Tyrode solution. Furthermore, 10(-5) M of nifedipine, a Ca(2+)-entry antagonist, reversibly inhibited the contractile effect of all the test substances on the ileal strips. Results of this study together appear to show that CPX-induced contraction of the isolated guinea pig ileum is mediated via H1-receptors and dependent on extracellular Ca2+ influx.     

The effect of calcium antagonists on contractions of the sensitized and normal guinea pig ileum

The purpose of this study was to learn wether a number of Ca²⁺ antagonists were effective in reducing contractile response of the isolated ileum of the sensitized and normal guinea pig. Contractions of the normal ileum in response to LTD₄, acetylcholine, histamine, and potassium chloride were obtained before and after verapamil, diltiazen and papaverine. Ovalbumin-induced contractions of the ovalbumin-sensitized ileum were obtained in the presence of the three Ca²⁺ antagonists. In the normal ileum, all the Ca²⁺ antagonists were highly effective in diminishing the contractile responses to LTD₄, acetylcholine, histamine and potassium chloride. In the sensitized ileum, ovalbumin-evoked contractions, with subsequent release of a potent contractile mediator (presumably SRS-A), were Ca²⁺-dependent since verapamil, diltiazem and papaverine caused a concentration-related reduction of contractions. Thus, the influx of extracellular Ca²⁺ plays a key role in the contractile responses of the normal and sensitized guinea pig ileum when stimulated by various potent agonists acting on specific receptors or on the cell membrane.     

Mechanisms of the contractile effect of the alcoholic extract of Aegle marmelos Corr. on isolated guinea pig ileum and tracheal chain

In the present work, the effect of the alcoholic extract of the leaves of Aegle marmelos Corr. on guinea pig isolated ileum and tracheal chain was investigated, as this plant is used traditionally to treat asthma and related afflictions. These effects were investigated using the isolated organ bath method. 1 mg/ml and 2 mg/ml doses of the alcoholic extract of this plant produced a positive relaxant effect in isolated guinea pig ileum and tracheal chain, respectively. In addition, they antagonized the contractions, which are produced by histamine. Because the alcoholic extracts elicited the antagonistic effect against histamine and also relaxed the histamine-induced contractions, it can be concluded that relaxations induced by A. marmelos in both guinea pig ileum and tracheal chain were due to the depression of H₁-receptors. Since we observed a complete relaxation of the guinea pig ileum and tracheal chain produced by the extract, we investigated its antagonistic effect against histamine. These results were due to the presence of one or more anti-histaminic constituents present in the alcoholic extract of this plant, therefore supporting to the traditional use of A. marmelos in asthmatic complaints.     

Biological activity and anti-prostaglandin effects of prostaglandin analogue, ent-11-epi-15-epi PGE2 methyl ester

The biological activity and anti-prostaglandin property of the prostaglandin analogue, ent-11-epi-15-epi PGE2 methyl ester, were studied on isolated guinea pig ileum. Ent-11-epi-15-epi PGE2 methyl ester contracted guinea pig ileum and produced a concentration-response curve parallel to that of PGE2. However, the former exhibited a lower maximal effect than PGE2. At concentrations greater than 10(-6)M, ent-11-epi-15-epi PGE2 methyl ester selectively antagonized contractile actions of PGE2 and PGE2 alpha without affecting contractions induced by acetylcholine. These observations suggest that the PG analogue acted like a competitive antagonist to PGE2 and PGF2 alpha on guinea pig ileum in vitro.     

Histamine H3 receptors in the guinea pig ileum: evidence for a postjunctional location.

The effect of the selective histamine H3 receptor agonists (R)alpha-methylhistamine, (R)MHA and immepip (IMM) on intestinal smooth muscle contractility was investigated on isolated cells from the longitudinal muscle of the guinea pig ileum. (R)MHA (10(-13)-10(-8) M) and IMM (10(-13)-10(-8) M) did not significantly modify the basal length of intestinal cells; in contrast both agonists (10(-15)-10(-11) M) prevented the contraction produced by acetylcholine (10(-7) M). The (S)-isomer of alpha-methylhistamine, (S)MHA, was inactive both on basal contractility and on acetylcholine-induced contractions. The relaxant effect of (R)MHA was not modified by famotidine (10(-7) M), but totally prevented by the selective H3 receptor antagonist clobenpropit (10(-8) M), which per se did not modify either basal contractility or the contractile response to acetylcholine. These data indicate that inhibitory histamine H3 receptors are present on smooth muscle cells of the guinea pig ileum and can be activated by very low concentrations of selective agonists. It is not clear, however, whether they can have a functional importance in the regulation of intestinal contractility in an intact system.     

Ranitidine potentiates ileum contractions caused by GABA and electrical stimulation

GABA-evoked contractions of the guinea pig ileum were significantly potentiated by the histamine H2-receptor antagonist ranitidine in concentrations above 10 microM. To help define the mechanism of this interaction, the present study compared the effects of ranitidine on contractile responses of the guinea pig ileum to GABA, acetylcholine (A Ch) and electrical stimulation of intrinsic cholinergic neurons. Ranitidine, at concentrations that potentiated responses to GABA, also potentiated contractions induced by transmural electrical stimulation. The ability of ranitidine to amplify these latter responses was antagonized by atropine. Contractile responses to exogenous A Ch, however, were unaffected by ranitidine at any concentration. These results suggest that prejunctional, rather than postjunctional mechanisms, are of primary importance in the interaction between ranitidine and GABA.     

L-648,051, sodium 4-[3-(4-acetyl-3-hydroxy-2-propylphenoxy)- propylsulfonyl]-gamma-oxo-benzenebutanoate: a leukotriene D4 receptor antagonist

L-648,051, sodium 4-[3-(4-acetyl-3-hydroxy-2-propylphenoxy) propylsulfonyl]-gamma-oxo-benzenebutanoate is a selective and competitive inhibitor of [3H]leukotriene D4 (KB value of 4.0 microM) and to a lesser extent [3H]leukotriene C4 (Ki value of 36.7 microM) binding in guinea pig lung homogenates. Functionally, it selectively antagonized contractions of guinea pig trachea induced by leukotrienes C4, D4, E4, and F4 in concentrations that did not antagonize contractions induced by acetylcholine, histamine, serotonin, prostaglandin F2 alpha, or U-44069 (endoperoxide analogue). Schild plot analysis indicated that L-648,051 competitively antagonized contractions of guinea pig ileum induced by leukotriene D4 (pA2 7.7) and contractions of trachea induced by leukotrienes D4, E4, and F4 (pA2 7.3, 7.4, and 7.5, respectively). Contractions of guinea pig trachea induced by leukotriene C4 were inhibited in a noncompetitive fashion (Schild plot slope, 0.45). Developed contractions of trachea induced by the leukotrienes were rapidly reversed by L-648,051 greater than FPL-55712 greater than L-649,923. Intravenous L-648,051 selectively blocked bronchoconstriction induced in anaesthetized guinea pigs by intravenous leukotrienes C4, D4, and E4 but not that induced by arachidonic acid, serotonin, U-44069, or acetylcholine. The compound displayed poor activity following intraduodenal administration. The profile of activity for L-648,051 indicates that it may be a useful topical agent for studying the role of leukotrienes in diseases such as bronchial asthma.     

Functional role of M2 muscarinic receptors in the guinea pig ileum

Muscarinic agonists elicit contraction in the standard guinea pig ileum bioassay through activation of M3 muscarinic receptors that are also linked to phosphoinositide hydrolysis. Surprisingly, the most abundant muscarinic receptor in the ileum is the M2 which causes a specific inhibition of cyclic AMP accumulation elicited by the beta-adrenergic receptor. After most of the M3 receptors are inactivated, the ileum still retains high sensitivity to muscarinic agonists provided that the contractile responses are measured in the presence of histamine and forskolin, which together, have no effect on contraction. Under these conditions, the potencies of antagonists for blocking the contractile response are consistent with those expected for an M2 response. Moreover, the muscarinic contractile response measured in the presence of histamine and forskolin after inactivation of M3 receptors is pertussis toxin sensitive. In contrast, muscarinic contractions in the standard bioassay are pertussis toxin insensitive. These results demonstrate that the M2 muscarinic receptor can cause an indirect contraction of the guinea pig ileum by preventing the relaxing effect of agents that increase cAMP.     

Effect of L-prolyl-L-leucyl-glycinamide (MIF-I) on some neutrotransmitter-receptor interactions

Some neurotransmitter-receptor interactions have been studied in an attempt to determine how L-prolyl-L-leucyl-glycinamide (MIF-I) exerts its antiparkinson effect. MIF-I affected neither the contractile responses of isolated mouse vas deferens and guinea pig ileum to noradrenaline, acetylcholine, substance P and histamine, nor the inhibitory effects of dopamine and GABA on the rat vas deferens and guinea pig ileum. MIF-I, as well as L-leucine and Pro-Leu, antagonized the contractile response of the ileum to 5-hydroxytryptamine (5-HT). Behavioural tests were used to examine the action of MIF-I on CNS transmitter-receptor interactions. MIF-I did not modify the circling produced by either dopamine agonists in nigro-striatal lesioned rats of 5-HT agonists in rats with a lesion of the medial raphe nucleus. MIF-I affected neither 5-hydroxytryptophan-induced head twitches in mice, which is a measure of 5-HT receptor stimulation, nor striatally-evoked head turning in the rat, which is a model for brain GABA function. It is concluded that MIF-I, at the doses used, does not directly modify the function of any of the CNS transmitter examined. Other possibilities to explain its antiparkinson action are discussed.     

Inhibition of intestinal smooth muscle function by tamoxifen and clomiphene

The acute in vitro effects of the oestrogen antagonists clomiphene (a racemic mixture) and tamoxifen were examined upon spasmogen induced contractions of the guinea pig ileum. Both oestrogen antagonists inhibited the contractions produced by acetylcholine, the muscarinic agonist beta-methylcholine, histamine and bradykinin in a manner which suggests non competitive antagonism. Concentration effect curves to each of the spasmogens were unaffected using 0.1 mumoles/litre of either of the oestrogen antagonists. Clomiphene at 1 mumole/litre reduced the maximum response to the spasmogens by 20 to 50%. Tamoxifen at the same concentration also inhibited the contractions but to a much smaller extent. Clomiphene at the highest concentration tested 10 mumoles/litre completely suppressed contractions to all the spasmogens. Tamoxifen at 10 mumoles/litre completely suppressed contractions to beta-methylcholine and bradykinin. A residue of a response to acetylcholine and histamine remained and this was abolished by raising the concentration to 100 mumoles/litre. The data indicated that clomiphene was more potent than tamoxifen upon the inhibition of the contractions of the ileum. The results demonstrate a non specific effect of the oestrogen antagonists upon smooth muscle function and do not substantiate early reports of specific anticholinergic activity. The possibility of these effects contributing to both the side effects and the antitumor activity of the oestrogen antagonists is discussed.     

Studies on anti-ulcer properties of Cissampelos mucronata leaf extract

The methanolic extract of the leaves of C. mucronata was screened for anti-ulcer properties using animal models. On isolated guinea pig ileum the extract inhibited contractions evoked by acetylcholine, histamine and serotonin. The extract remarkably decreased the propulsive movement of gastrointestinal content. The extract exhibited significant anti-ulcer activity protecting rats from indomethacin, histamine and stress-induced ulcers. It inhibited the growth of both Gram-positive and Gram-negative microorganisms. The oral LD50 value of the extract in mice was estimated to be 8.5 +/- 0.35 g/kg. The results revealed that the plant C. mucronata has potential medicinal value as an anti-ulcer agent.     

Modulatory effect of diclofenac on antispasmodic effect of pitofenone in cholinergic spasm

Biliary, ureteric and intestinal colic are extremely common clinical conditions associated with smooth muscle spasm. In the present study, antispasmodic activity was carried out against acetylcholine (10-640 ng/ml)-induced contractions on guinea pig ileum. Acetylcholine (10-640 ng/ml) induced concentration-dependent contraction of smooth muscle. Diclofenac, in varying concentration (9.4 x 10(-5) mol/l and 14.1 x 10(-5) mol/l) shifted the concentration response curve of acetylcholine to the right without suppressing the maximal response. However, in higher concentration diclofenac (18.9 x 10(-5) mol/l) blocked the response in an unsurmountable fashion. Further, analgin (11.09 x 10(-5), 16.63 x 10(-5) and 22.18 x 10(-5) mol/l) in equimolar concentrations did not alter the concentration response curve of acetylcholine, but in higher concentration analgin (44.36 x 10(-5) mol/l) also blocked the response in an unsurmountable fashion. Pitofenone (2.5 x 10(-6) mol/l) also, shifted the concentration response curve of acetylcholine to right in a parallel fashion with no change in maximal response. The present study confirms the potent antispasmodic activity of diclofenac-pitofenone combination in comparison to analgin-pitofenone in molar equivalent concentration (in comparison to diclofenac) against acetylcholine-induced contractions of guinea pig ileum.     

Species differences in the negative inotropic effect of acetylcholine and soman in rat, guinea pig, and rabbit hearts.

1. Acetylcholine reduced atrial contractions by 82.5% in guinea pig, 50.8% in rat, and 41.5% in rabbit. 2. The EC50 values for the negative inotropic effect of acetylcholine were 3.3 x 10(-7) M in rat and guinea pig atria and 4.1 x 10(-6) M in rabbit atria. 3. There was no correlation between the species differences in the negative inotropic effect of acetylcholine in atria and the density or affinity of acetylcholinesterase or muscarinic receptors. 4. Inhibition of atrial acetylcholinesterase with soman reduced the EC50 of acetylcholine three-fold in all species, but did not change the maximal inotropic effect of acetylcholine. 5. Species differences in the negative inotropic effect of acetylcholine may be caused by differences in the coupling between myocardial muscarinic receptors and the ion channels that mediate negative inotropy.     

Biological activities of a chemically synthesized form of leukotriene E4

A chemically synthesized form of leukotriene E₄ (LTE₄) has been studied for its ability to induce contractions in isolated guinea pig ilea, to induce vascular permeability changes in rat skin when injected intradermally, and to induce bronchoconstriction in guinea pigs after intravenous injection. The synthetic compound induced a contraction in the guinea pig ileum which was slower in developing than that induced by histamine but faster in developing than that induced by a crude preparation of SRS-A isolated from guinea pig lung. The compound was 70-fold more active than histamine on the guinea pig ileum (EC₅₀ of 5 × 10^?9 and 3.5 × 10^?7 M, respectively). FPL 55712, a known SRS-A antagonist, exhibited the same potency in blocking the contractions elicited by the synthetic material as it did in blocking contractions produced by guinea pig SRS-A generated biologically (IC₅₀ of 3.5 × 10^?8 M). The synthetic LTE₄ induced a dose dependent increase in vascular permeability in the rat skin which was antagonized by the intravenous injection of FPL 55712 (ID₅₀ of 1.2 mg/kg). The synthetic material was also a potent bronchoconstrictor in the guinea pig when injected intravenously. The bronchoconstriction, too, was antagonized by FPL 55712 when injected intravenously (ID₅₀ of 0.2 mg/kg). In both the rat and guinea pig, FPL 55712 exhibited a short duration of action $\text{in vivo}$. The $\text{in vivo}$ model systems discussed in this study, utilizing the synthetic form of LTE₄ should be useful in the future evaluation of other SRS-A antagonists.     

Studies on the loss of sensitivity in smooth muscle.

Specificity of desensitization effect was investigated at guinea pig ileum using the desensitizing agonists acetylcholine, carbachol, histamine, and serotonine. The desensitization with acetylcholine markedly diminished the contraction effects to test doses of all tested agonists. Contrary to acetylcholine, the histamine desensitization is mainly specific, the serotonine desensitization is a complete specific effect. A different influence of the tested agonists on intracellular ions is discussed.     

Prejunctional alpha 2 adrenoceptors inhibit contraction of tracheal smooth muscle by inhibiting cholinergic neurotransmission

Ring preparations obtained from the guinea pig trachea contracted on short trains of electrical field stimulation. These contractions were mediated by activation of cholinergic nerves since they were abolished by atropine or tetrodotoxin. In the presence of beta blocking drugs noradrenaline and adrenaline dose-dependently inhibited contractions induced by field stimulation. By contrast, contractions on exogenous acetylcholine were left completely unaffected. It is concluded that the adrenergic agonists inhibited cholinergic neurotransmission by a prejunctional action. In order to characterize the noradrenaline receptor the effects of alpha₁ and alpha₂ blockers were evaluated using the Schild plot. For comparison experiments were also conducted on the guinea pig aorta and electrically stimulated guinea pig ileum. The results indicate that in guinea pig trachea and ileum noradrenaline inhibits cholinergic neurotransmission by acting on prejunctional alpha₂ receptors whereas in guinea pig aorta it induces contraction by stimulating alpha₁ receptors.     

Pharmacological actions of tentacle extract of the jellyfish, Acromitus rabanchatu, occurring in the Bay of Bengal

Tentacle extract of A.rabanchatu, produced a fall of blood pressure in cat, rat and guinea pig. Hypotension produced in cat remained unantagonized by blockers of acetylcholine, histamine and 5-HT. On isolated guinea pig heart, the extract significantly reduced the rate and amplitude of contraction leading to irreversible cardiac arrest. In cats and rats, the respiratory rate and amplitude was decreased significantly and resulted in temporary apnoea. The extract also produced vasoconstriction in perfused rat hindquarter preparation and increased cutaneous capillary permeability. The extract produced contraction in several isolated smooth muscle preparations. Contraction on guinea pig ileum was partly antagonized by atropine and cyproheptadine. On isolated rat phrenic nerve diaphragm and chick biventer cervicis, the extract produced irreversible blockade of the electrical stimulation-induced twitch responses. Haemolytic and myonecrotic activity was exhibited by the extract. LD50 was found to be 7.7 mg/kg (iv, mice).