bluuebunny/crossref_metadata_2025 huggingface dataset:
Pharmacological analysis of muscarinic receptors coupled to oxyntic cell secretion in the mouse stomach
Authors: Black J.W. , Shankley N.P.
Published: July 2012

In the light of recent attempts to subclassify muscarinic receptors, agonist‐antagonist interactions at muscarinic receptors have been re‐examined using improved techniques, on the mouse, isolated, lumen‐perfused stomach gastric acid assay.

Using 5‐methylfurmethide as the muscarinic agonist, the pKB estimated for atropine was significantly lower on the stomach assay (7.78) than on the guinea‐pig trachea (8.93). However pKB values for N‐methylatropine, the quaternary ammonium derivative of atropine, at concentrations producing dose‐ratios above 20 on the stomach assay (pKB = 9.67), and over the full concentration range studied on the trachea (pKB = 9.69) were not significantly different.

The deviation from simple competitive behaviour at low dose‐ratios with N‐methylatropine in the stomach assay is consistent with the effects of a saturable uptake mechanism for quaternary ammonium compounds.

The pKB values for pirenzepine on the stomach (6.67) and the trachea (6.87) were not significantly different suggesting that pirenzepine behaves more like N‐methylatropine in terms of expressed affinity.

We conclude that the oxyntic cell muscarinic receptors are homogeneous with those in the guinea‐pig trachea. An initial exploration suggests that there is a relationship between the lipophilicity (log P) of the antagonists and the degree of apparent underestimation of antagonist affinity in the stomach assay. This supports the hypothesis that the underestimation of antagonist affinity is due to the loss of antagonist into the gastric secretion from the receptor compartment. Apparently, relatively selective inhibition of acid secretion, compared to atropine, could be explained without the need to postulate heterogeneity of muscarinic receptor populations.
The effect of prednisolone and ketotifen on the antigen‐induced bronchoconstriction and mediator release in rat isolated lungs
Authors: Ottenhof Maria , Ufkes Jan G.R. , Van Rooij Hans H.
Published: July 2012

Using a new method for inducing IgE‐mediated, systemic anaphylaxis in the rat both prednisolone and ketotifen had been shown previously to be effective in suppressing the bronchial anaphylaxis in vivo. In order to study the mode of action underlying their bronchoprotective effect, both agents were also tested on the antigen‐induced bronchoconstriction in rat isolated lungs in relation to the mediator release in the lung‐effluent.

The presence of histamine, 5‐hydroxytryptamine (5‐HT) and SRS‐A could be detected biologically in the lung‐effluent during bronchoconstriction. Histamine and 5‐HT were determined quantitatively by means of h.p.l.c. with fluorimetric detection, whereas SRS‐A was determined using the guinea‐pig ileum in a cascade set‐up.

Although both prednisolone and ketotifen inhibited the antigen‐induced bronchoconstriction effectively, it appeared that only prednisolone suppressed the release of histamine, 5‐HT and SRS‐A in the lung‐effluent significantly, whereas ketotifen had no effect.

On account of these data it is suggested that the bronchoprotective effect of prednisolone is mainly based on inhibition of the release of the mediators involved, whereas the effect of ketotifen may be based on receptor antagonism.
The effect of airway epithelium on smooth muscle contractility in bovine trachea
Authors: Barnes Peter J. , Cuss Francis M. , Palmer James B.
Published: July 2012

In bovine tracheal smooth muscle the presence of airway epithelium significantly reduced the sensitivity and maximum contractile response to histamine, 5‐hydroxytryptamine (5‐HT) or acetylcholine.

Muscle contraction induced by K+ and electrical field stimulation was of similar magnitude both in the presence or absence of adherent epithelium.

The effect of epithelium on smooth muscle contractility was unaffected by pretreatment with indomethacin (10−6 M) or mepacrine (5 × 10−5 M).

The relaxant response to isoprenaline was enhanced in the presence of epithelium, although this was significant only in the case of precontraction with 5‐HT.

It is concluded that the bronchial epithelium may produce a relaxant factor which is not a cyclo‐oxygenase or lipoxygenase product. The production of this factor may be reduced or lost following epithelial damage and this may be important in the pathogenesis of bronchial hyperresponsiveness in asthma.
Neuronal muscarinic receptors attenuate vagally‐induced contraction of feline bronchial smooth muscle
Authors: Blaber L.C. , Fryer Allison D. , Maclagan Jennifer
Published: July 2012

In anaesthetized cats, stimulation of the vagus nerves produced bradycardia and a bronchoconstriction which was measured as an increase in lung resistance (RL) and a fall in dynamic lung compliance (Cdyn); these effects were abolished by atropine.

Gallamine potentiated vagally‐mediated changes in RL and Cdyn at doses that blocked muscarinic receptors in the heart and inhibited neuromuscular transmission. (+)‐Tubocurarine and suxamethonium did not affect the response of the lung or the heart to vagal stimulation.

Bronchoconstriction induced by intravenous acetylcholine was not potentiated by gallamine, indicating that postsynaptic muscarinic receptors in the lung and changes in muscle tone were not involved.

Potentiation of vagally‐induced bronchoconstriction appears to be due to blockade of inhibitory muscarinic receptors located in the pulmonary parasympathetic nerves innervating both central and peripheral airways.

Pilocarpine was an agonist for these neuronal receptors as it inhibited vagally‐induced bronchoconstriction at low doses (10 ng to 1 μg kg−1).

The results demonstrate that gallamine is an antagonist and pilocarpine an agonist at neuronal muscarinic receptors which attenuate parasympathetic nerve activity in feline lung.
Response and sensitivity of guinea‐pig airway muscle preparations to 5‐hydroxytryptamine during ontogenesis
Authors: Bayol Anne , Benveniste Jacques , Brink Charles , Cerrina Jacques , Gateau Olivier , Labat Carlos , Raffestin Bernadette
Published: July 2012

Responsiveness (g mm−2) and sensitivity (pD2 value) to 5‐hydroxytryptamine (5‐HT) were markedly reduced in isolated tracheal and bronchial tissues from guinea‐pigs during ontogenesis. Responsiveness of the trachea to 5‐HT was depressed much more than that to histamine.

Airway preparations from young guinea‐pigs of either sex always contracted when exposed to 5‐HT, an effect that was blocked by methysergide.

Airway muscle preparations from old animals exhibited a wide range of responses to 5‐HT, namely, no effect, relaxation or contraction.

The contractile effect of 5‐HT in tracheal and bronchial preparations from old animals was always blocked by methysergide, whereas, the relaxant effect was not.

These results indicate that there are significant alterations in the response to 5‐HT receptor stimulation in airway muscle preparations from guinea‐pigs during ontogenesis.
Mechanism of the antinociceptive action of mesaconitine: participation of brain stem and lumbar enlargement
Authors: Hikino Hiroshi , Murayama Mitsuo
Published: July 2012

The antinociceptive action of mesaconitine (MA) microinjected into the nucleus reticularis gigantocellularis (NRGC), the nucleus reticularis paragigantocellularis (NRPG), the periaqueductal gray (PAG) or the lumbar enlargement was investigated in rats by use of the tail immersion test. In addition, the effects of β‐adrenoceptor antagonists and an α‐adrenoceptor antagonist administered intrathecally (i.t.) on the antinociceptive action of MA given into the NRPG were also examined by the tail immersion test.

MA (50, 100 ng per rat) microinjected into the NRGC, the NRPG, the PAG and the lumbar enlargement increased the response latency in rats in a dose‐dependent fashion. MA (50 ng per rat) microinjected into neighbouring sites, the nucleus reticularis parvocellularis, the nucleus originis nervi abducentis and the fasciculus longitudinalis medialis, elicited no significant effect.

Intrathecally administered propranolol (1 and 5 μg per rat), atenolol (1 and 5 μg per rat) and IPS‐339 (1 and 5 μg per rat) remarkably inhibited the increase of the response latency induced by MA (50 ng per rat) given into the NRPG.

Intrathecally administered phenoxybenzamine (1 and 5 μg per rat) inhibited the increase of the response latency induced by MA (50 ng per rat) injected into the NRPG but to a lesser extent than the β‐adrenoceptor antagonists.

It is concluded that the NRGC, the NRPG, the PAG and the lumbar enlargement are involved in the sites of the antinociceptive action of MA and that the antinociceptive effect of MA administered into NRPG is elicited by activation of the inhibitory noradrenergic neurones from the NRPG in particularly via β‐receptor‐mediated effects of noradrenaline.
Effects of chronic administration of amitriptyline or mianserin on rat cardiac and central adrenoceptors
Authors: Choudhury L. , O'Donnell J.M.
Published: July 2012

Rats were administered either amitriptyline (20 mg kg−1, i.p.) or mianserin (10 mg kg−1, i.p.) for 21 consecutive days and the α‐ and β‐adrenoceptor characteristics of cardiac ventricles, cerebral cortex and hippocampus examined by ligand‐binding procedure.

Chronic administration of amitriptyline significantly reduced the maximum density of β‐receptors in the cerebral cortex without significantly altering cardiac α‐ or β‐receptors; mianserin treatment had no significant effect on any of the receptors studied.
Conjugated catecholamines and pressor responses to angiotensin, luteinizing hormone‐releasing hormone and prazosin in conscious toads
Authors: Wilson J.X.
Published: July 2012

Synthetic angiotensin II (Ang II), mammalian luteinizing hormone‐releasing hormone (LHRH) and salmon LHRH (sLHRH) were injected intravenously into conscious, adult toads (Bufo marinus) to elucidate the cardiovascular actions of the hormones. The maximal increases in pulse pressure elicited by the three peptides did not differ from each other but only Ang II increased cardiac frequency. The maximal increases in mean arterial blood pressure (MAP) caused by LHRH and sLHRH were identical, while Ang II caused a 100% greater maximal effect. The median effective doses (ED50) for both Ang II and LHRH were approximately 0.1 nmol kg−1 whereas the potency of sLHRH was 10 fold less. Pressor responses to LHRH and sLHRH were blocked completely by (D‐pGlu1, D‐Phe2, D‐Trp3,6)‐LHRH but this antagonist did not inhibit Ang II.

Significant proportions of circulating, endogenous dopamine, noradrenaline (NA) and adrenaline (Ad) were found to be sulphoconjugated. Arterial plasma concentration of free NA increased simultaneously with the rise in blood pressure following Ang II injection. The magnitude of the free NA response increased with increasing Ang II dose but even a high dose failed to augment the plasma level of conjugated NA. Ang II did not alter concentrations of free or conjugated dopamine and Ad.

Intraarterial injection of an α‐adrenoceptor antagonist, prazosin, caused sustained elevation of arterial pressure and free Ad. Subsequently Ang II lowered plasma Ad concentration. Prazosin inhibited the NA response to Ang II yet the pressor effects of the α‐adrenoceptor antagonist and Ang II were additive. Administration of a β‐adrenoceptor antagonist, propranolol, largely reversed the cardiovascular sequelae of α‐adrenoceptor blockade.

It is concluded, firstly, that the cardiovascular actions of Ang II and LHRH are mediated through different receptors. Secondly, although it had been shown that α‐ and β‐adrenoceptor mechanisms mediate the pressor effect of LHRH, the present experiments showed that mobilization of catecholamines cannot account for the pressor response to Ang II. Thirdly, both free and conjugated catecholamines circulate in toads; however the extent of conjugation can be dissociated from the changes in free NA and Ad induced by Ang II and prazosin
Pre‐incubation of guinea‐pig myenteric plexus with β‐funaltrexamine: discrepancy between binding assays and bioassays
Authors: Corbett A.D. , Kosterlitz H.W. , McKnight A.T. , Paterson S.J. , Robson L.E.
Published: July 2012

The acute effects of β‐funaltrexamine and the effects of pre‐incubation with this compound were examined in five in vitro assay tissues and in selective binding assays in homogenates of guinea‐pig brain and myenteric plexus.

In competitive displacement assays with selective ligands, β‐funaltrexamine had highest affinity for the μ‐binding site in the myenteric plexus and brain of guinea‐pig. Its affinity for the k‐site was about 15% of that for the μ‐site.

Pre‐incubation of the assay tissues with β‐funaltrexamine caused an increase in the IC50 values of μ‐and δ‐receptor agonists but not of k‐agonists. Although in bioassays on the myenteric plexus‐longitudinal muscle preparation of the guinea‐pig, the IC50 value of the μ‐receptor ligand [D‐Ala2, MePhe4, Gly‐ol5] enkephalin was increased up to 124 fold, its binding at the μ‐site in homogenates of the preparation was not affected by this treatment.

These findings indicate that the effects of pre‐incubation with β‐funaltrexamine on agonist potency of the μ‐receptor ligand are due to an interference with the coupling mechanism between the μ‐binding site and the effector system.
Comparative effects of cotrimoxazole (trimethoprimsulphamethoxazole) and spiramycin in pregnant mice infected with Toxoplasma gondii (Beverley strain)
Authors: Nguyen B.T. , Stadtsbaeder S.
Published: July 2012

The effects of cotrimoxazole (CTX) and spiramycin (Spir) in mice infected in midpregnancy with the Beverley (Bev) strain of Toxoplasma gondii were compared.

Therapeutic effectiveness was determined according to the following parameters: rate of successful delivery, litter size, offspring weight and survival.

When compared with the uninfected untreated control group, CTX showed a more beneficial therapeutic effect than Spir, with a statistically significant increase in the rate of both successful delivery and offspring survival.

Results based on antitoxoplasma antibody determinations in the offspring indicated a better in utero control of congenital infection by CTX than by Spir.
Simultaneous measurement of contractile effects in the circular and longitudinal smooth muscle of the rat vas deferens by drugs perfused externally or via the lumen
Authors: Busatto Pedro A. , Jurkiewicz Aron
Published: July 2012

The effects of noradrenaline and barium chloride were studied in the rat isolated vas deferens by perfusion of drugs either externally or through the lumen of the organ. Two effects were recorded simultaneously in the same preparation: (a) isometric contractions, due to the tension elicited by drugs on the external (longitudinal) smooth muscle layer and (b) pressure of internal perfusion, due to contractions of the internal (circular) smooth muscle layer.

2 It was found with the longitudinal muscle that: (a) the potency, expressed as pD2 values, and the maximum response to noradrenaline were lower if the drug was perfused internally rather than externally; (b) the differences in maximum effects were pronounced on the prostatic half but were not observed on the epididymal half; (c) the maximum response obtained by internal perfusion could be increased by simultaneously adding the same dose of drug externally; (d) when barium chloride was used instead of noradrenaline no significant differences were observed on pD2 values, but differences on maximal responses were similar to that observed for noradrenaline; (e) it was possible to block completely the effect of internal or external noradrenaline on the longitudinal muscle, by perfusing external phenoxybenzamine. In these conditions the responses of the circular muscle to the agonist were only partly blocked.

With the circular muscle, the differences related to internal and external perfusion were less marked than in the longitudinal muscle. However, unlike the latter, the circular layer was slightly more sensitive to drugs applied internally, in relation to pD2 values.

It is suggested that the difference in pD2 values may be due to the removal of noradrenaline by the neuronal uptake process, whereas the difference in maximal effect is due to the inaccessibility of part of the receptor population when drugs are added through the lumen.
Effects of H1 receptor blocking drugs on the frog sartorius neuromuscular junction
Authors: Katayama Sohta , Tasaka Kenji
Published: July 2012

The effects of H1‐receptor blocking agents, pyrilamine, promethazine, and diphenhydramine, on the amplitude and time course of endplate potentials (e.p.ps) were studied in the sartorius muscles of frogs.

H1‐receptor blockers (10−5‐10−4M) reduced the amplitude of e.p.ps recorded intracellularly without affecting the resting membrane potential.

The acetylcholine potential was decreased by perfusion of H1‐preceptor blockers. However, when the muscle fibre was stimulated directly, threshold and magnitude of action potential were not affected by H1‐receptor blockers.

The time constant of decay of the e.p.ps recorded extracellularly was reduced by H1‐receptor blockers and the decay remained exponential with a single time constant.

The quantal content was not reduced by perfusion of H1‐receptor blockers at a concentration of 10−4 M.

It is assumed that the major site of action of these H1‐receptor blocking agents is at the postsynaptic membrane.
Prostaglandin release mediates drug‐induced stimulation of sodium transport in frog skin: the effects of quinacrine
Authors: Erlij David , Gersten Lewis
Published: July 2012

Quinacrine markedly increased the release of prostaglandin E2 (PGE2) into the basolateral solution of the bullfrog skin from a control value of 32.7 ± 21.7 pg per 20 min period to a stimulated value of 8593.1 ± 4112.3 pg per 20 min period.

Quinacrine increased the amiloride‐sensitive short circuit current from 20.7 ± 2.1 μA cm−2 to 45.4 ± 6.5 μA cm−2.

The stimulatory effects of quinacrine on both short circuit current and prostaglandin release were blocked in skins pretreated with indomethacin (10−6 M).

Quinacrine did not block either the stimulation of the short circuit current or the increase in PGE2 release caused by the calcium ionophore, ionomycin.

These results suggest: (a) the release of PGE2 and the stimulation of the short circuit current caused by quinacrine are linked since blocking PGE2 release inhibits the stimulation of the short circuit current; (b) given the complexity of its actions, quinacrine is a poor tool to examine whether the effects of a given agent are mediated through the activation of endogenous phosopholipases. In addition our results taken together with other findings in the literature suggest that there is a diverse group of compounds that stimulate transepithelial sodium transport by releasing PGE2.
Transmembrane sodium and potassium gradients modulate histamine secretion induced by ionophore A23187
Authors: Amellal M. , Bronner C. , Landry Y.
Published: July 2012

Histamine secretion was induced from rat peritoneal mast cells by calcium ionophore A23187 in the presence of various extracellular calcium concentrations. Transmembrane sodium and potassium gradients were altered by cold pretreatment of mast cells or through the inhibition of sodium‐potassium ATPase by the use of ouabain or potassium‐deprivation.

Such pretreatments led to a parallel shift to the left of the extracellular calcium concentration‐histamine secretion curve, i.e. to an apparent decrease of extracellular calcium requirement for the ionophore‐induced histamine release.

These effects were fully reversed by warming mast cells, by washing out ouabain or by adding potassium. Metabolic inhibition of mast cells prevented the ionophore‐induced secretion in all the experimental conditions described. Secretion observed in the absence of added calcium was inhibited by short term treatment of cells with 5 times 10−6 M EGTA or EDTA provided magnesium was absent from the assay medium.

Data show that ionophore A23187 was able to induce secretion in the presence of micromolar concentrations of extracellular calcium, when the efficiency of the ionophore was not decreased by extracellular magnesium and when transmembrane sodium and potassium gradients were altered.
Platelet desensitization induced by arachidonic acid is not due to cyclo‐oxygenase inactivation and involves the endoperoxide receptor
Authors: Carmo L.G. , Hatmi M. , Rotilio D. , Vargaftig B.B.
Published: July 2012

Human platelets pre‐exposed to arachidonic acid (AA) (0.1‐1 mM) or to the endoperoxide analogue U46619 (1–3 μM) and then washed and resuspended, failed to respond with aggregation or secretion to a second challenge by either agonist. The response to thrombin at low (0.04‐0.1 u ml−1) but not at high (2.5 u ml−1) concentrations was also inhibited by pre‐exposure to AA and U46619.

The ability of platelets to synthesize thromboxane (Tx) B2 from AA or upon challenge with thrombin persisted despite platelet desensitization.

In the presence of the reversible cyclo‐oxygenase (CO) inhibitors methyl salicylate (MS) or L8027, pre‐exposure to AA had no effect on subsequent challenge by the same agonist or by U46619, whereas platelet desensitization by pre‐exposure to U46619 persisted. However, platelet activation by, and desensitization to AA and U46619, was prevented by trimetoquinol and compound L636499, two thromboxane/endoperoxide receptor antagonists.

In contrast to the CO inhibitors, the thromboxane synthetase inhibitor dazoxiben, which in 3 ‘responders’ out of 5 subjects suppressed aggregation, secretion, and Tx formation induced by AA, failed to prevent AA‐induced desensitization.

Compared to quiescent cells the distances between platelets desensitized after re‐exposure to AA were reduced in electron microscopy, but the tight connections associated with aggregated cells were not observed. Degranulation was also not observed and cell morphology resembled that of normal quiescent platelets.

In conclusion, (a) AA and U46619 desensitize human platelets at a similar site sensitive to prostaglandin/thromboxane receptor antagonists, and show cross‐desensitization; (b) desensitization by AA appears to be mediated by a CO‐dependent metabolite, as CO inhibitors prevent desensitization by AA but not to U46619; (c) the failure of dazoxiben to prevent desensitization by AA suggests that a metabolite other than TxA2, possibly the endoperoxides, mediates the phenomenon; (d) desensitization does not involve inactivation of CO or thromboxane synthetase enzymes.
Characterization of histamine receptors mediating the stimulation of cyclic AMP accumulation in rabbit cerebral cortical slices
Authors: Al‐Gadi M. , Hill S.J.
Published: July 2012

The characteristics of histamine‐stimulated adenosine 3′:5′‐cyclic monophosphate (cyclic AMP) accumulation in slices of rabbit cerebral cortex have been investigated.

The selective H2‐receptor antagonists, cimetidine, tiotidine, metiamide and ranitidine appeared to antagonize the stimulation of cyclic AMP accumulation elicited by histamine in a competitive manner consistent with an interaction with histamine H2‐receptors.

The H1‐preceptor antagonist mepyramine (0.8 μM) produced only a weak inhibition of the response to histamine. The inhibition appeared to be non‐competitive producing a decrease in the maximal response with little effect on the EC50 value.

The specific H2‐receptor agonist, impromidine, produced a maximum response of only 31 ± 2% of that obtained with histamine. Studies with histamine and impromidine in combination indicated that impromidine was not acting as a partial agonist. 2‐Thiazolylethylamine, a selective H1‐agonist, produced only a weak response (EC50 ∼ lmM) yielding a relative potency with respect to histamine (= 100) of 2.5.

In the presence of a supramaximal concentration of impromidine, histamine and 2‐thiazolylethylamine further elevated the response to impromidine. In these conditions the relative potency of 2‐thiazolylethylamine was increased to 59 (histamine = 100), a value which was comparable with that reported for H1‐receptor‐mediated contractions of guinea‐pig ileum.

The H1‐receptor antagonists mepyramine, promethazine, triprolidine and chlorpheniramine competitively antagonized the potentiation of impromidine‐stimulated cyclic AMP accumulation elicited by histamine and 2‐thiazolylethylamine in rabbit cerebral cortex without affecting the response to impromidine alone. (+)‐Chlorpheniramine was some 150 fold more potent than the (—)‐isomer in this respect.

Histamine and adenosine in combination had a much greater than additive effect on the accumulation of cyclic AMP in rabbit cerebral cortical slices. The potentiation of the adenosine response could be partially but not completely antagonized by either cimetidine or mepyramine.

In the presence of H2‐receptor blockade with 0.02 mM tiotidine, histamine elicited a significant potentiation (EC50 44 μM) of the response to adenosine. This response was antagonized competitively by mepyramine yielding a KB value of 0.05 μM similar to that obtained from inhibition of the potentiation of impromidine‐stimulated accumulation of cyclic AMP (0.02 μM).

These results suggest that there are two components in the response to histamine in rabbit cerebral cortical slices. The first component appears to be mediated by histamine H2‐receptors while the second, mepyramine‐sensitive, component has some of the characteristics of an H1‐receptor mediated response and requires prior stimulation of adenosine‐ or H2‐receptors to produce its effect.
Enthalpy‐entropy relationship in drug‐cholinoceptor interaction: a new approach
Authors: Cohen Sasson , Haberman Frank
Published: July 2012

The partial molal volume at infinite dilution, , was determined in toluene, benzene and acetonitrile for fifteen different drug molecules comprising muscarinic agonists, partial agonists and antagonists.

The difference in between a given drug, X, and hyoscine, expressed as was then multiplied by the internal pressure of the holding phase (P1 ∼ cohesive energy density) in order to obtain an estimate of the excess enthalpy (ΔH) over hyoscine in the interaction of drug molecule X with a common cholinoceptor. As a working hypothesis, ΔH for hyoscine is taken as zero, hyoscine having the lowest /affinity ratio of any drug in the series investigated.

The corresponding change in entropy (ΔS) was then calculated from the relationship: RT ln Kx= Pi, where Kx is the affinity constant of drug molecule X to the common cholinoceptor, obtained independently.

Linear regression of P1 ⋍ ΔH from the data in acetonitrile over ΔS gave a satisfactory isoequilibrium plot, r2 = 0.954, slope (β) = 231°K.

The present approach offers a new course for the study of the enthalpy‐entropy relationship in the interaction of drug molecules in a given series with a common receptor. It could provide an alternative to the Van't Hoff procedure for the estimation of relative ΔH, and is independent of the free energy of binding (ΔG).
Pharmaco‐mechanical coupling in the response to acetylcholine and substance P in the smooth muscle of the rat iris sphincter
Authors: Banno Hitoshi , Imaizumi Yuji , Watanabe Minora
Published: July 2012

In the rat iris sphincter muscle contractile responses to transmural stimulation consisted of two components, a fast cholinergic followed by a slow non‐adrenergic, non‐cholinergic (NANC) one. The magnitude of the latter varied widely and was on average 5% of that of the cholinergic component.

Exogenous substance P (1 nM‐1 μM) produced a concentration‐dependent contraction, the maximum amplitude of which was as large as that produced by acetylcholine (ACh).

Capsaicin (10 μM) induced a transient contraction only once in each preparation. After the treatment with capsaicin the NANC component disappeared.

Neither nerve nor direct electrical stimulation with short pulses elicited any active change in the membrane potential under physiological conditions, but an action potential was triggered by direct stimulation when the extracellular Ca ion was totally replaced by Ba ion. Under the latter conditions spontaneous spike potentials occurred repetitively.

ACh and substance P produced a large contraction without modifying the membrane potential. This was also the case in the presence of 5 mM Ba.

These results suggest that substance P‐ergic innervation may have a far lesser physiological significance than that which has been described in rabbits and that pure pharmaco‐mechanical coupling is characteristic of the responses to acetylcholine, substance P, and nerve stimulation in the rat iris sphincter muscle.
Pharmacological investigation into the effects of histamine and histamine analogues on guinea‐pig and rat colon in vitro
Authors: Aguilar María‐José , Morales‐Olivas Francisco J. , Rubio Elena
Published: July 2012

The effects of histamine and specific histamine agonists has been examined on isolated longitudinal colon strips of guinea‐pig and rat.

Histamine and 2‐pyridyl‐ethylamine but not 4 methylhistamine produced a concentration‐related contractile response in the guinea‐pig colon.

The H1‐antagonist clemizole antagonized competitively the effect of histamine but the H2‐antagonist ranitidine did not modify the dose‐response curve to histamine in the guinea‐pig colon.

Atropine, hexamethonium, prazosin and propranolol failed to modify the contractile response to histamine.

Tone induced with KCl in guinea‐pig isolated colon was not modified by histamine agonists even in tissues pretreated with clemizole or ranitidine.

Histamine and histamine analogues were without effect on the isolated longitudinal strip of the rat colon.

It is concluded that histamine produced dose‐dependent contractions of the guinea‐pig colon due to direct activation of H1‐histamine receptors. There is no evidence in favour of the existence of H2‐histamine receptors in this preparation. The lack of effect of histamine agonists in rat colon strip argues against the existence of histamine receptors in this preparation.
The antinociceptive action of some β‐adrenoceptor agonists in mice
Authors: Bentley G.A. , Starr Jennifer
Published: July 2012

The antinociceptive actions of several β‐adrenoceptor agonist drugs have been studied in mice by use of a modified abdominal constriction test.

All the drugs studied had high antinociceptive activity, with ID50 values in the nmol kg−1 range. (−)‐Isoprenaline and (±)‐isoxsuprine were the most potent, being about ten times more active than salbutamol, the least potent drug studied. All these drugs produced their action very rapidly and appear to act within the peritoneum.

(−)‐Isoprenaline had about six times the potency of the (+)‐isomer.

(±)‐Propranolol caused rightward shifts, usually parallel, of the dose‐response curves for (−)‐isoprenaline. (+)‐Propranolol was more than ten times less potent than the racemic drug.

Practolol also caused parallel, rightward shifts of the dose‐response curves for (−)‐isoprenaline, and was about twice as potent as (±)‐propranolol, whether given by subcutaneous or intraperitoneal injection. Atenolol and ICI 118551 had intermediate potencies.

Propranolol, practolol and ICI 118551 were all considerably less potent in antagonizing the antinociceptive actions of fenoterol and RO363, than (−)‐isoprenaline. None of these antagonist drugs showed more than a slight ability to discriminate between the β1‐ and β2‐selective agonist drugs.

No evidence was found for the involvement of opioid, dopamine, or α‐adrenoceptors in the antinociceptive action of the β‐adrenoceptor agonist drugs. Evidence for and against the involvement of β‐adrenoceptors is discussed, and it is concluded that if these receptors do mediate the antinociceptive action they appear to be atypical.
The effects of long‐term infusion of salbutamol, diltiazem and nifedipine on uterine contractions in the ovariectomized, post‐partum rat
Authors: Abel Margaret H. , Hollingsworth M.
Published: July 2012

The sensitivity of the uterus to the inhibition of contractions by salbutamol, diltiazem or nifedipine was assessed in the ovariectomized, post‐partum rat by dose‐response curves following bolus intravenous (i.v.) administration. These tests were performed before (day 1), immediately after a 20 h i.v. infusion of salbutamol, diltiazem, nifedipine or appropriate control infusate (day 2) and after a further 20 h infusion of saline (day 3). In a further group of animals sensitivity to nifedipine was assessed before and after a 20 h infusion of salbutamol. Uterine contractions were monitored throughout infusions.

Infusion of salbutamol (2 μg kg−1 min−1) produced an initial marked inhibition of uterine contractions, an effect which was not maintained despite continued infusion. Contractions reappeared after 2 h of infusion and reached pre‐infusion levels by 5 h. The dose‐response curve to salbutamol on day 2 was shifted more than 100 fold to the right compared with that on day 1. Sensitivity of the uterus on day 3 did not differ from that on day 1.

Nifedipine (25 μg kg−1 min−1) produced sustained inhibition of uterine contractions throughout the 20 h of infusion. Sensitivity of the uterus to nifedipine could not, therefore, be tested on day 2; sensitivity on day 3 did not differ from that on day 1. In addition, there was no change in sensitivity of the uterus to nifedipine after a 20 h infusion of salbutamol.

Diltiazem (200 μg kg−1 min−1) produced a marked initial inhibition of uterine contractions, with a partial return of contractions during continued infusion in 7 out of 12 animals so that mean integral values reached 40% of those pre‐infusion. The dose‐response curve to diltiazem on day 2 showed a 25 fold shift to the right compared with that on day 1 in 4 out of 12 animals where the test could be performed. Sensitivity of the uterus on day 3 did not differ from that on day 1.

These findings suggest that marked but reversible tolerance to the inhibitory actions of salbutamol on uterine contractions occurs during long‐term infusion. There was no evidence of tolerance to the uterine actions of nifedipine, but there was evidence of tolerance to diltiazem in some animals.1
Coronary vasoconstriction in the rat, isolated perfused heart induced by platelet‐activating factor is mediated by leukotriene C4
Authors: Piper Priscilla J. , Stewart A.G.
Published: July 2012

Platelet‐activating factor (Paf, 0.04‐4.50 nmol) dose‐dependently induced coronary vasoconstriction and decreased cardiac contractility in rat, isolated perfused hearts and concomitantly released leukotriene‐like bioactivity into the cardiac effluent.

Platelet‐activating factor (0.9 nmol) induced an increase in 6‐keto‐prostaglandin F1α (6‐keto‐PGF1α), PGF2α, PGE2 and thromboxane B2 (TXB2) measured by radioimmunoassay (RIA) of cardiac effluents following partial purification using C18 Sep‐Paks.

The leukotriene‐like bioactivity released by Paf was identified as leukotriene C4 (LTC4) using a combination of isolation on reverse phase‐h.p.l.c. (r.p.h.p.l.c.) and quantitation by RIA. In addition, LTB4 was also identified by r.p.h.p.l.c. and the levels, determined by RIA, were within the range having biological activity.

The release of cyclo‐oxygenase products by Paf was prevented by indomethacin (2.8 μM), markedly attenuated by diethylcarbamazine (7.7 mM) but unaffected by FPL 55712 (1.9 μM)‐pretreatment. Furthermore, LTC4 (50 pmol) did not increase the release of the cyclo‐oxygenase products measured.

The release of LTB4 and LTC4 appeared to be unaffected by indomethacin pretreatment whereas diethylcarbamazine‐pretreatment markedly inhibited release.

The coronary vasoconstriction induced by Paf (0.9 nmol) was attenuated by pretreatment with indomethacin or diethylcarbamazine, whereas FPL 55712 caused a marked inhibition of the response. In contrast, the decrease in cardiac contractility was prevented by indomethacin or diethylcarbamazine and unaffected by FPL 55712 pretreatment.

It is concluded that LTC4 may be largely responsible for the coronary vasoconstriction induced by Paf with cyclo‐oxygenase products having a possible modulatory role whereas the latter appear to be involved in the Paf‐induced decrease in cardiac contractility.
Comparison of potency of α2‐adrenoceptor antagonists in vitro: evidence for heterogeneity of α2‐adrenoceptors
Authors: Alabaster V.A. , Keir R.F. , Peters C.J.
Published: July 2012

A comparison has been made of affinity of α‐adrenoceptor antagonists for α2 binding sites in radioligand binding assays, and functional antagonist activity at pre‐ and postjunctional α2‐adrenoceptors in various in vitro preparations.

The antagonists displaced [3H]‐rauwolscine from rat brain and rabbit spleen membranes but there were substantial differences in rank order and absolute potency in the two tissues.

pA2 values for yohimbine, phentolamine and Wy26703 against the selective α2 agonist UK‐14,304 were determined in the rat left atrium, rat and rabbit vas deferens and rabbit saphenous vein preparations. The pA2 values varied substantially between the tissues, differing by two orders of magnitude in the case of Wy26703. Yohimbine was more potent in rabbit preparations while Wy26703 was markedly more potent in all the rat preparations.

Yohimbine and Wy26703 were compared in the dog saphenous vein preparation where pre‐ and postjunctional α2 antagonist activity can be compared in the same tissue. As in the rabbit preparations, yohimbine was more potent than Wy26703 at both sites but the absolute potencies were different.

It is concluded that α2‐adrenoceptors are a heterogeneous population, different subgroups being more apparent between species rather than between tissue types or location.
Quantification of the actions of agonists that simultaneously act on a particular type of receptor and have separate functional interactant properties
Authors: Goodall Jacqueline , Hughes I.E. , Mackay D.
Published: July 2012

Null equations have been derived which allow quantification of the agonist properties of a compound that is able to modify the state of a tissue simultaneously by interacting with a particular type of receptor and by other means.

Parameters can be estimated which separately characterize the agonist properties of the compound and its functional interactant effect.

The null equations have been tested in a model system by using a mixture of papaverine (5 μM) and hexyltrimethylammonium bromide (30 μM) to mimic an agonist which also has functional antagonist properties.

The values obtained for the various parameters measured directly and indirectly are in good general agreement, confirming the validity of the model.
Meptazinol has a similar agonist action on opioid receptors in field‐stimulated mouse vas deferens and guinea‐pig ileum
Authors: Goodall Jacqueline , Hughes I.E. , Mackay D.
Published: July 2012

The effects of the opioid receptor agonist RX783006 and of the opioid receptor partial agonist (+)‐meptazinol have been examined on electrically induced twitch responses of the guinea‐pig isolated ileum and of the mouse isolated vas deferens.

Log10 concentration‐tissue state curves were determined for (+)‐meptazinol and RX783006, alone, in combination and in the presence of naloxone (30 nM).

Analysis of these log10 concentration‐tissue state curves using the null equations derived and tested in the preceding paper indicates that the opioid agonist action of (+)‐meptazinol on mouse vas deferens is quantitatively similar to that on guinea‐pig ileum.

The results also suggest that (+)‐meptazinol acts as a functional antagonist on the guinea‐pig ileum as well as on the mouse vas deferens.

The potency of (+)‐meptazinol relative to RX783006 has been measured by an indirect method which should eliminate any functional antagonistic action of (+)‐meptazinol. This method gives a relative potency of (+)‐meptazinol in both tissues which is three to six times greater than that measured directly on guinea‐pig ileum. This discrepancy may be due to experimental error but it may also indicate that direct measurements on guinea‐pig ileum underestimate the agonist potency of this compound on opioid receptors.
α2‐Adrenoceptor‐mediated contractile response to catecholamines in smooth muscle strips isolated from rainbow trout stomach (Salmo gairdneri)
Authors: Kitazawa Takio , Kondo Hiroshi , Temma Kyosuke
Published: July 2012

The type of adrenoceptor involved in the contractile response to catecholamines in smooth muscle strips isolated from rainbow trout stomach was determined.

Noradrenaline (10 nM‐10 μM) and adrenaline (10 nM‐3 μM) caused non‐sustained contractions which were markedly decreased by phentolamine (5.4 μM) but not by carteolol (5 μM). Phenylephrine (1 μM‐1 mM) was less effective in causing muscle contraction and methoxamine produced no contraction. Clonidine (100 nM‐300 μM) caused no mechanical response but inhibited the contraction to noradrenaline or adrenaline but not acetylcholine or 5‐hydroxytryptamine.

Yohimbine (10 nM‐1 μM) decreased the contraction induced by noradrenaline or adrenaline but prazosin (1 μM) did not.

Tetrodotoxin (780 nM) partially reduced the contraction induced by noradrenaline or adrenaline but atropine (500 nM) did not.

In the presence of atropine (1 μM), electrical transmural stimulation caused frequency‐dependent, tetrodotoxin‐sensitive contractions.

These results suggest that the contractile response induced by noradrenaline or adrenaline is mediated by α2‐adrenoceptors. It is also suggested that noradrenaline and adrenaline contract the smooth muscle by direct action and by indirect action through the non‐cholinergic excitatory nerve.
5‐Methoxy‐N,N‐dimethyltryptamine‐induced analgesia is blocked by α‐adrenoceptor antagonists in rats
Authors: Archer Trevor , Danysz Wojciech , Jonsson Gösta , Minor Bruce G. , Post Claes
Published: July 2012

The effects of the α‐adrenoceptor antagonists prazosin, phentolamine and yohimbine upon 5‐methoxy‐N,N‐dimethyltryptamine (5‐MeODMT)‐induced analgesia were tested in the hot‐plate, tail‐flick and shock‐titration tests of nociception with rats.

Intrathecally injected yohimbine and phentolamine blocked or attenuated the analgesia produced by systemic administration of 5‐MeODMT in all three nociceptive tests. Intrathecally administered prazosin attenuated the analgesic effects of 5‐MeODMT in the hot‐plate and tail‐flick tests, but not in the shock titration test.

Intrathecal yohimbine showed a dose‐related lowering of pain thresholds in saline and 5‐MeODMT‐treated animals. Phentolamine and prazosin produced normal dose‐related curves in the hot‐plate test and biphasic effects in the shock titration and tail‐flick tests.

These results demonstrate a functional interaction between α2‐adrenoceptors and 5‐HT agonist‐induced analgesia at a spinal level in rats.
Effects of opioid peptides and morphine on histamine‐induced catecholamine secretion from cultured, bovine adrenal chromaffin cells
Authors: Livett Bruce G. , Marley Philip D.
Published: July 2012

The effect of opioid peptides and morphine on histamine‐induced catecholamine secretion has been studied in monolayer cultures of dispersed, bovine adrenal chromaffin cells.

Histamine‐induced a dose‐dependent secretion of both adrenaline and noradrenaline with a threshold dose of approximately 5 nM, an EC50 of 150 nM and maximal secretion at 10 μM.

Catecholamine secretion induced by 1 μM histamine was completely dependent on extracellular calcium, was inhibited in a dose‐dependent manner by mepyramine (1 nM‐1 μM), and was unaffected by cimetidine (10 μM) and hexamethonium (0.1 mM).

Dynorphin‐1–13 (1 nM‐20μM), metorphamide (0.1 nM‐10μM), morphine (1 nM − 0.1 mM) and diprenorphine (1 nM − 0.1 mM) each had no effect on adrenaline or noradrenaline secretion induced by 1 μM histamine.

The characteristics of histamine‐induced catecholamine secretion from bovine adrenal chromaffin cells were similar to those reported previously for cat and rat adrenal medulla being calcium‐dependent and mediated by H1 histamine‐receptors. The results with opioid peptides and morphine suggest that endogenous adrenal opioid peptides do not act on the opioid binding sites found on adrenal medullary chromaffin cells to modify their secretory response to histamine.
Pharmacological modulation of the effects of N‐formyl‐L‐methionyl‐L‐leucyl‐L‐phenylalanine in guinea‐pigs: involvement of the arachidonic acid cascade
Authors: Boukili M. Abdelhakim , Bureau Michel , Lagente Vincent , Lefort Jean , Lellouch‐Tubiana Arielle , Malanchère Evelyne , Vargaftig B. Boris
Published: July 2012

The intravenous administration of the chemotactic and secretagogue peptide N‐formyl‐L‐methionyl‐L‐leucyl‐L‐phenylalanine (FMLP; 0.3–30 μg kg−1) to the guinea‐pig induces bronchoconstriction and dose‐dependent leukopenia accompanied by mild thrombocytopenia. No electron microscopic evidence of platelet aggregation in lungs or significant accumulation of 111In‐labelled platelets in the thoracic region at the height of bronchoconstriction was noted.

Bronchoconstriction and leukopenia induced by FMLP were not affected by prostacyclin, by platelet depletion, by the platelet‐activating factor (Paf‐acether) antagonist BN 52021 or by the histamine H1‐antagonist mepyramine. Bronchoconstriction, but not leukopenia, was inhibited by aspirin, whereas the peptido‐leukotriene antagonist compound FPL 55712 and the cyclo‐oxygenase lipoxygenase inhibitor indomethacin reduced bronchoconstriction to a limited extent only. The mixed cyclo‐oxygenase/lipoxygenase inhibitor compound BW 755C was very effective in blocking bronchoconstriction by the highest dose of FMLP used, but failed to interfere with leukopenia.

FMLP‐induced dose‐dependent contraction of parenchymal lung strips was accompanied by the formation of immuno‐reactive thromboxane B2 in amounts markedly less than those formed from exogenous arachidonic acid at concentrations equieffective in inducing contractions.

FMLP‐induced contractions of the guinea‐pig lung strip were not modified by mepyramine nor by FPL 55712. They were reduced by indomethacin and aspirin and an even greater reduction was obtained with aspirin used in combination with FPL 55712. BW 755C suppressed the effects of all the concentrations of FMLP tested, whereas tert‐butyloxy‐carbonyl‐L‐methionyl‐L‐leucyl‐L‐phenylalanine, a chemical analogue of FMLP, displaced the concentration‐response curve to the right, without reducing the maximal contraction obtained.

The present results indicate that: (a) bronchoconstriction by FMLP is not due to platelet activation, to cyclo‐oxygenase‐dependent mechanisms or to peptido‐leukotriene formation. The inhibitory effect of aspirin and BW 755C involves a property other than cyclo‐oxygenase inhibition, which is not shared by indomethacin. (b) The contractile effects of FMLP on parenchymal lung strips follow an interaction with specific receptor sites, as shown by the effectiveness of tert‐butyloxy‐carbonyl‐L‐methionyl‐L‐leucyl‐L‐phenylalanine, and involves the combined effects of cyclo‐oxygenase and lipoxygenase metabolites.