Responses Of Guinea-pig Ileum Research Articles

Effects of a New Histamine H2-Receptor Antagonist, Z-300, on Gastric Secretion and Gastro-Duodenal Lesions in Rats: Comparison with Roxatidine

We examined the effects of a new compound, N-[3-[3-(piperidinomethyl)phenoxy]-propyl]-2-(2-hydroxyethyl-1-thio)acetamido-2-(4-hydroxy benzoyl)benzoate (Z-300), on the histamine H2-receptor, gastric secretion in rats and dogs, and acute gastro-duodenal lesions or chronic gastric ulcers in rats. Roxatidine acetate hydrochloride (roxatidine), a known histamine H2-receptor antagonist, was used as a reference compound. The pA2 values for Z-300 and roxatidine for the isolated guinea pig atrium were 6.8 and 7.0, respectively. These agents at <10−5 M did not affect the contraction of guinea pig ileum in response to carbachol. Z-300, administered either orally or parenterally, significantly inhibited the basal and histamine-stimulated gastric acid secretion in rats. Gastric acid secretion stimulated by histamine, pentagastrin or carbachol in Heidenhain pouch dogs was also significantly inhibited by the compound. The effect persisted for >7 hr in the case of histamine-stimulation. Oral Z-300 significantly protected the gastric mucosa from water-immersion stress-, indomethacin-, aspirin- and HCl* ethanol-induced lesions and protected the duodenal mucosa against mepirizole- and cysteamine-induced ulcers. These effects on gastric secretion and lesion formation were, as a whole, stronger than those observed with roxatidine. Z-300, but not roxatidine, significantly accelerated the spontaneous healing of acetic acid ulcers induced in rats and prevented the delay in ulcer healing caused by indomethacin. The mechanism of action of Z-300 on acute lesions and chronic ulcers appears to be mostly related to its potent antisecretory and mucosal-protective activities.

Synthesis, molecular modeling studies, and muscarinic receptor activity of azaprophen analogs

Synthesis, radioligand binding, and pharmacologic activities of a series of muscarinic receptor ligands including and related to azaprophen (6-methyl-6-azabicyclo[3.2.1]octan-3 alpha-ol 2,2-diphenylpropionate, 1) have been measured to determine activity and selectivity for muscarinic receptor subtypes. Pharmacologic affinities of antagonists were determined as pA2 values for antagonism of methacholine-induced tension responses in guinea pig ileum. Binding affinities were measured by competition against [3H]QNB binding in guinea pig ileum, rat heart and brain, and m1- or m3-transfected Chinese hamster ovary (CHO) cells. The efficacies of muscarinic agonists in brain were determined by the ratio of binding affinities against [3H]QNB or [3H]NMS and [3H]oxotremorine-M ([3H]Oxo-M). Nine muscarinic antagonists, including azaprophen, did not discriminate significantly between the subtypes of muscarinic receptors. KI values for receptor binding for azaprophen (1) were between 8.81 x 10(-11) and 4.72 x 10(-10) M in ileum, heart, brain, and m1- or m3-transfected CHO cells. The alpha- and beta-benzilate esters 5 and 6 are as potent as azaprophen, and diphenylacetate esters 3 and 4 and N-(6)-benzyl alpha-isomer 7 are less potent than azaprophen. Significant stereoselectivity was exhibited with (+)-azaprophen being approximately 200 times more potent than the (-)-enantiomers and the 3 beta-ol isomer 2 being ca. 50 times less potent than azaprophen in all systems. A molecular modeling-molecular mechanics study was conducted to account for the difference. Putative muscarinic agonists (analogues and isomers of 6-methyl-6-azabicyclo[3.2.1]octan-3-ol acetate) did not discriminate muscarinic receptor subtypes with KI values between 2.77 x 10(-6) and 4.33 x 10(-5) M without significant stereoselectivity in the systems examined. The most active analogue was (1R,3R,5S)-6-[1(R)-phenylethyl]-6-azabicyclo[3.2.1]octan-3 alpha-ol acetate. However, efficacies of these putative agonists were in general very low.

Secretion of acetylcholinesterase and butyrylcholinesterase from the guinea-pig isolated ileum.

1. Strips of longitudinal muscle from guinea-pig ileum, retaining Auerbach's plexus, were superfused with oxygenated Krebs solution. Addition of 50 mM KCl led to a pronounced Ca2+-dependent increase in the activities of both acetylcholinesterase and non-specific cholinesterase (butyrylcholinesterase) in the perfusate but with no change in lactate dehydrogenase activity. 2. No release of acetylcholinesterase, either spontaneous or K+-evoked was observed in tissue freed of the nerve plexus, although release of butyrylcholinesterase still occurred. 3. Carbachol induced a marked Ca2+-dependent increase in the release of acetylcholinesterase but had no effect on the release of butyrylcholinesterase or lactate dehydrogenase. This carbachol-evoked increase in acetylcholinesterase release was blocked by hexamethonium but not by atropine. 4. Four readily soluble molecular forms of acetylcholinesterase and three soluble molecular forms of butyrylcholinesterase were present in innervated longitudinal muscle strips, but insignificant amounts of acetylcholinesterase were detected in denervated strips of muscle. Only one of the four molecular forms of acetylcholinesterase was recovered in the perfusates. 5. It is concluded that acetylcholinesterase is secreted from the nerves of Auerbach's plexus in response to depolarizing stimuli or to nicotinic cholinergic stimulation, while butyrylcholinesterase is secreted from non-neural elements, possibly the longitudinal muscle cells, of guinea-pig ileum in response to a depolarizing stimulus.

Acetylcholine activates single sodium channels in smooth muscle cells

Using the whole-cell clamp technique with a patch electrode, single channel activities were recorded in dispersed single smooth muscle cells of the guinea-pig ileum in response to application of greater than 1 microM acetylcholine (ACh) or carbachol (CCh). Under physiological conditions (bath:Krebs, pipette:High K), these channels have a single channel conductance of 20-25 pS at the membrane potentials ranging between -100 and -40 mV and are activated in the membrane potential dependent manner. The amplitude of the channel current showed a strong dependence on the extracellular Na concentration but the reversal potential obtained by the extrapolation of the I-V relationship was not consistent with the equilibrium potential of Na ion. An approximate estimation of permeability ratio based on the independent principle described by Hodgkin et al. gave a value of Na:K = 1.0:0.3-0.4 to this channel. From features of the macroscopic and single channel currents, it is concluded that these muscarinic ACh(CCh)-activated channels mainly pass Na ion and play a major part in the membrane depolarization produced by ACh or CCh in mammalian intestinal smooth muscles.

Dexamethasone on the contractile responses of guinea-pig ileum to some agonists

Dexamethasone on the contractile responses of guinea-pig ileum to some agonists

Effects of phenoxybenzamine on responses to some receptor agonists and calcium in vitro.

Noradrenaline-induced contractions of the rabbit and rat isolated aorta and guinea-pig spleen strips were inhibited by concentrations of phenoxybenzamine which did not affect responses to calcium. This may suggest a specific action on alpha-adrenoceptors. However, analysis of noradrenaline concentration-effect curves in guinea-pig spleen indicated that 1 mumol/l phenoxybenzamine should have reduced the available receptor population to 6% of control, but data from radioligand binding experiments on the same tissues using [3H]-prazosin indicated a reduction of the receptor population to only 82% of control. The reduced responsiveness observed in the organ bath study after phenoxybenzamine pretreatment, whilst not apparently related to effects on voltage-dependent calcium channels, could be due to the actions of phenoxybenzamine on other (non-receptor) processes such as receptor-operated calcium channels. Maximal contractile responses to histamine in rabbit isolated aorta but not those in guinea-pig isolated ileal preparations, were depressed by concentrations of phenoxybenzamine which depressed responses to calcium. Phenoxybenzamine produced parallel rightward shifts of curves to carbachol in guinea-pig ileal preparations but only depressed maximal responses to the agonist in higher concentrations which reduced responses to calcium. On the basis of the results obtained with calcium it is possible that the effects of phenoxybenzamine on receptor-mediated responses could be produced through the actions of this antagonist at less specific sites such as voltage-dependent calcium channels for histamine in rabbit aorta and carbachol in guinea-pig ileum. For alpha-receptor mediated responses in aortic and splenic strip preparations and for histamine-mediated responses in guinea-pig ileum, the actions of phenoxybenzamine may reflect an interaction of the antagonist with receptor-operated calcium channels.

Effects of epoxidation on the actions of normorphine, norcodeine, N-allylnormorphine(nalorphine) and N-allylnorcodeine on the electrically stimulated guinea pig ileum.

The effects of epoxidation of normorphine, norcodeine, N-allylnormorphine (nalorphine) and N-allylnorcodeine on the twitch response of guinea pig ileum to electrical stimulation were studied. Normorphine, norcodeine and their epoxides are narcotic agonists, while nalorphine, N-allylnorcodeine and their epoxides are agonist-antagonists. The agonistic effects (via mu-receptor) of normorphine and norcodeine were not influenced by epoxidation of the 7, 8-double bond. Epoxidation also little influenced the competitive antagonistic action (via mu-receptor) of nalorphine and N-allylnorcodeine against morphine. On the other hand, the agonistic action (via kappa-receptor) of nalorphine and N-allylnorcodeine was considerably decreased by epoxidation.

The effects of cisapride on serotonin-evoked mucosal responses in guinea-pig ileum

The effects of cisapride on serotonin-evoked mucosal responses in guinea-pig ileum

Receptors for substance P.I. The pharmacological preparations

The undecapeptide substance P (SP) is both a potent stimulant of intestinal (guinea pig ileum), vascular venous (rabbit mesenteric vein) and tracheal (guinea pig trachea) smooth muscles, and a relaxant of large arteries (dog common carotid artery, rabbit aorta). SP also decreases the peripheral vascular resistance in the coronary vessels of rabbit isolated hearts. The contractions of the guinea pig ileum in response to SP are partially antagonised by atropine and significantly depressed by indomethacin, while the contractions of the guinea pig trachea are strongly potentiated by indomethacin. Large arteries, but not the veins, are insensitive to SP when the endothelium is removed, and slightly less responsive to the peptide when this is applied in the presence of mepacrine, eicosatetraynoid acid or BW 755C. These results indicate that all myotropic actions of SP, except that on venous smooth muscle, are partially or completely indirect and most of them are due to the release of endogenous agents: these are acetylcholine, prostaglandins and possibly histamine in the guinea pig ileum, prostaglandins and possibly a leukotriene in the guinea pig trachea and a still unidentified factor of endothelial origin in dog and rabbit large arteries. The effect of substance P on the rabbit isolated anterior mesenteric vein appears to be a direct one.

Sites of action of Ca 2+ channel inhibitors

Ca2+ channel inhibitors are viewed as a subgroup of Ca2+ antagonists. Most of the currently used Ca2+ channel inhibitors are thought to act by reducing Ca2+ entry into the cell through Ca2+ channels. There is substantial electrophysiological evidence that the major site of action of verapamil, nifedipine and diltiazem in cardiac cells is a sarcolemmal Ca2+ channel. Cytosolic sites of action may contribute to their effects but probably only at higher than therapeutic concentrations. The recent ligand binding studies also tend to support the view that the sarcolemma is the site of action of Ca2+ channel inhibitors in smooth muscle. High affinity binding sites for 1,4-dihydropyridines without any established function are found in fast skeletal muscle and some neuronal membranes. The binding of [3H]nitrendipine to membranes from cardiac, skeletal and smooth muscle, and from brain is saturable, reversible and of high affinity; it is sensitive to cations and other drugs that interact with Ca2+ channels. Inhibition of [3H]nitrendipine binding and blockade of K+ responses in guinea pig ileum by 1,4-dihydropyridines are well correlated, supporting the view that the observed binding is to Ca2+ channel. In contrast, blockade of Ca2+ channels in cardiac and skeletal muscle and in brain synaptosomes occurs only at higher concentrations than needed to saturate the high affinity binding sites. The therapeutic success of Ca2+ channel inhibitors in the treatment of angina pectoris, hypertension, peripheral vascular diseases, and many other disease entities is based on selective inhibition of Ca2+ entry into smooth muscle cells. The specificity of some of these drugs for Ca2+ channels in different cell types, organs, or vascular beds is probably determined by receptor modulation and the effect of reflex mechanisms, which in turn determine the indications for their therapeutic use.

Inhibitory effect of NCO-650 on the contractile response of guinea pig ileum to some agonists

The effect of NCO-650 on the contractile response to acetylcholine (ACh), histamine and BaCl2 was investigated using isolated guinea pig ileum. NCO-650(3×10−6 M,1×10−5M and 3×10−5m) caused a parallel shift to the right of the dose-response curve of ACh. The regression between log(DR-l) and log(B) was found to be liner with a slope of 1.04 and the estimated apparent Kg was 2.74×10−6m which is equvalent to pA2 of 5.74.NCO-650 also acts like a competitive antagonist of histamine (H1-receptor) because NCO-650 caused a parallel shift to the right of the dose-response curve for histamine(KB=5.34×10−6m;pA2=5.40,Slope= 1.09). On the other hand, a high concentration of NCO-650(1×10-4M) depressed the maximum contractions to ACh and histamine. Dose-response curve for BaCl2 was non-competitively antagonized by NCO-650 at 3×10−6m(pD2=4.21). NCO-650 dose-dependently inhibited the twitch response of the ileum to electrical stimulation at 0.1Hz. In the K-depolarized preparation, NCO-650(3×10-5M-3×10−4M) depressed the maximum contraction of the dose-response curve for CaCl2 (pD2=4.00). These results suggest that low concentrations of NCO-650 act as a competitive antagonist of muscarinic receptor and H1-receptor in guinea pig ileum, while high concentrations of NCO-650 inhibit the contractile response to ACh and histamine by reducing the release from membrane-bound Ca ion.

A POSSIBLE MECHANISM OF A NEW ANTISPASMODIC DRUG, 2-(1,2-BENZISOXAZOL-3-YL)-3-[2-(2-PIPERIDINOETHOXY) PHENYL]ACRYLONITRILE (SX-284)

A newly synthesized drug, SX-284, depressed the twitch response of the ileum from guinea pig to electrical stimulation at 0.1 Hz. SX-284 proved to be almost as active as atropine on electrically stimulated ileum. The responses of guinea pig ileum to nicotine and serotonin were also inhibited by SX-284. However, SX-284 did not influence the release of transmitters from the motor, sympathetic, nonadrenergic inhibitory, noncholinergic excitatory nerves, and responses of various smooth muscles mediated through drug receptors, and at these doses, SX-284 inhibited the release of acetylcholine from the vagus nerve. These facts indicate that SX-284 specifically inhibits the acetylcholine release from the vagus nerve. Furthermore, spontaneous movement of the guinea pig ileum was dose-dependently depressed by SX-284. The potency ratio for SX-284 relative to atropine was 1.7.

A possible mechanism of a new antispasmodic drug,2-(1,2-benzisoxazol-3-yl)-3-(2-(2-piperidinoethoxy) phenyl)acrylonitrile (SX-284).

A newly synthesized drug, SX-284, depressed the twitch response of the ileum from guinea pig to electrical stimulation at 0.1 Hz. SX-284 proved to be almost as active as atropine on electrically stimulated ileum. The responses of guinea pig ileum to nicotine and serotonin were also inhibited by SX-284. However, SX-284 did not influence the release of transmitters from the motor, sympathetic, nonadrenergic inhibitory, noncholinergic excitatory nerves, and responses of various smooth muscles mediated through drug receptors, and at these doses, SX-284 inhibited the release of acetylcholine from the vagus nerve. These facts indicate that SX-284 specifically inhibits the acetylcholine release from the vagus nerve. Furthermore, spontaneous movement of the guinea pig ileum was dose-dependently depressed by SX-284. The potency ratio for SX-284 relative to atropine was 1.7.

Caerulein, substance P, serotonin and cholinomimetics induce rhythmic contractions of the intestinal circular muscle.

1. The mechanical activity of the circular muscle of the isolated guinea-pig ileum in response to various spasmogenic compounds was investigated. Contractions were recorded isotonically. 2. Caerulein (>0.1 nM), bombesin (>1 nM), substanceP (>2 nM), 5-hydroxytryptamine and bethanechol (>0.5 μM), and dimethylphenylpiperazinium (>3 μM) induced rhythmic contractions superimposed on an increased tone. 3. Tetrodotoxin (0.93 μM) abolished the actions of caerulein, bombesin, 5-hydroxytryptamine, and dimethylphenylpiperazinium, partially inhibited the effect of substance P, but did not influence the contractile response to bethanechol. 4. The met-enkephalin analogue FK 33-824 (0.17 μM) abolished the action of only those compounds whose action was suppressed by tetrodotoxin, whereas noradrenaline (1.78 μM) blocked the effect of all six spasmogenic compounds studied. 5. An indirect action of caerulein, bombesin, substance P, 5-hydroxytryptamine, or dimethylphenylpiperazinium on the circular muscle by excitation of cholinergic neurones could be excluded because of the ineffectivity of tropicamide (3.64 μM). 6. Experiments employing tachyphylaxis to either substance P or 5-hydroxytryptamine showed that the contractile response to caerulein may involve release of endogenous substance P and that the action of substance P may be mediated via an indoleaminergic pathway. 7. The results imply that excitatory neurotransmitter candidates of the intestine such as cholecystokinin-like peptides (an analogue of which is caerulein), bombesin-like peptides, substance P, 5-hydroxytryptamine, and acetylcholine are able to induce rhythmic, peristalsis-like contractions of the intestinal circular muscle in physiologically relevant concentrations.

The effect of several alpha-adrenoceptor antagonists on the response to histamine in various tissues.

The effect of various α-receptor antagonists on the histamine-induced response of guinea pig ileum, guinea pig heart, and rabbit portal vein have been studied. In guinea pig ileum, an H1 receptor system, phenoxybenzamine and dibozane are effective antagonists, phentolamine is a weak antagonist, azapetine is without antagonist effect, and tolazoline is a weak agonist. In the H2 system of guinea pig right ventricle, phentolamine and azapetine are antagonists, phenoxybenzamine and dibozane are inactive, and tolazoline is an agonist. All antagonists except tolazoline block the histamine response in portal vein which is believed to be mediated by a receptor of low selectivity. Tolazoline is an agonist in portal vein.

Experimental evidence and dynamic aspects of spare receptor

Data obtained in radioligand - binding studies on guinea pig and mouse ileum were compared with those on the contractile responses to the muscarinic agonists methacholine (MCh), oxotremorine, bethanechol (BCh) and pilocarpine. Guinea pig ileum has a large amount of binding sites for 3H-quinuclidinyl benzilate (QNB), a muscarinic antagonist, (102 fmoles/mg tissue), whereas mouse ileum has a small amount of these binding sites (19 fmoles/mg tissue). MCh, oxotremorine and BCh were full agonists in the contractile responses ofboth ilea, but pilocarpine was full agonist only in guinea pig ileum. After treatment with dibenamine (0.15 mM) (for 15 min at 30°C) guinea pig ileum exhibited maximal responses to MCh, oxotremorine and BCh, but not to pilocarpine, although the ED 50 values for the agonists in the muscle were increased by this treatment. The amount of binding sites of 3H-QNB in dibenamine-treated guinea pig ileum was 55% of that in untreated ileum. When the amount of 3H-QNB-binding sites in mouse ileum was decreased to 54% by dibenamine-treatment for 15 min, the maximal contractions induced by MCh, oxotremorine and BCh were also decreased to some degree. In low Ca 2+ medium, pilocarpine became a partial agonist in the contractile responses of guinea pig ileum. The following conclusions were drawn from these findings: 1. 1. The spare receptors proposed by Stephenson actually exist, and change in the amount of spare receptors, which can be brought about by dibenamine-treatment, or in low Ca 2+ medium, can change the ED 50 value of agonists. 2. 2. In a single tissue, the amount of spare receptors for different agonists differ, probably depending on the efficacy of the agonists. 3. 3. For a single agonist, the amount of spare receptors in a tissue differs from species to species, presumably depending on the total amounts of receptors.

ANTIFOAMING AND CARMINATIVE ACTIONS OF VOLATILE OILS

Summary An apparatus is described for generating and assessing foams in digestive fluids in vitro. The effects of caraway, cinnamon, dill, orange and peppermint oils on gastric and intestinal foams were examined. Reductions in foam volume were observed in every case, although the effects were not as great as those produced by a combination of dimethicone and silica. m-Cresol, p-hydroxybenzaldehyde, isobutanol, menthol and phenoxyethanol also reduced foam volume, but anti-foaming activity could not be related to published data on the ability to produce a 50% inhibition of a standard response in guinea pig ileum to carbachol. It is suggested that carminative action is a combination of effects, one of which is a reduction of gastrointestinal foam.

231) - Response of guinea pig ileum and atria to cholinergic agents following administration of an organophophorus compound

231) - Response of guinea pig ileum and atria to cholinergic agents following administration of an organophophorus compound

Influence of substance P on the response of guinea pig ileum to transmural nerve stimulation.

Influence of substance P on the response of guinea pig ileum to transmural nerve stimulation.

Comparison of effect of morphine-like analgesics on transmurally stimulated guinea-pig ileum.

1. Morphine-like analgesic drugs caused depression of twitches of the isolated guinea-pig ileum in response to transmural electrical stimulation. The drugs tested were the narcotic analgesics codeine, diamorphine, fentanyl, morphine, morphine-N-oxide, normorphine, oxymorphone, pethidine, phenazocine and phenoperidine and the analgesic narcotic antagonists nalorphine and pentazocine.2. With the first application of one of these drugs the extent of depression of twitches was proportional to concentration. Except in the case of pethidine, there was no further depression when additional drug was added to the organ bath. With the second application of a drug after washing out the first dose, the depressant effect was less; that is, tolerance developed. With pethidine, the depression of twitches was proportional to concentration and tolerance could not be observed.3. When tolerance had been produced by cumulative addition of these drugs, a concentration was reached at which further addition resulted in increased activity of the ileum.4. With codeine, morphine and normorphine, the twitches were increased in height and regular.5. With diamorphine, fentanyl, oxymorphone, pentazocine, phenazocine and phenoperidine there were increased but irregular responses to transmural stimulation.6. Having reached the concentration at which these effects were observed, washout of the drug resulted in reduction of activity; the twitches became smaller or the irregular responses ceased.7. Readministration of a drug after activity of the ileum had been depressed by withdrawal of that drug resulted in restoration of activity, the ileum being dependent on the presence of the drug for its activity.8. Codeine and nalorphine did not produce as great an increase in activity on readministration to a dependent ileum as did morphine: they seem to act as partial agonists in producing this effect.9. In similar experiments with the isolated urinary bladder of the rat and guinea-pig, morphine was less active in depressing responses to stimulation than it was on the ileum, and tolerance to the drug and dependence on it did not occur.10. These observations have been discussed in relation to analgesic activity, tolerance and dependence in man.