bluuebunny/crossref_metadata_2025 huggingface dataset:
Evidence for co‐transmitter role of neuropeptide Y in the pig spleen
Authors: Lundberg Jan M. , Rudehill Anders , Sollevi Alf , Hamberger Bertil
Published: July 2012

The possible involvement of neuropeptide Y (NPY) in relation to noradrenaline (NA) and adenosine triphosphate (ATP) mechanisms in the sympathetic nervous control of the vascular tone and capsule contraction in the blood perfused pig spleen was investigated in vivo.

Local injections or infusions of NA, NPY and α‐, β‐methylene ATP (mATP) caused vasoconstriction (perfusion pressure increase) and capsule contraction (increased venous blood flow). ATP only evoked vasodilatation. NPY was about 50 fold more potent than NA as a vasoconstrictor, and the NPY response was more long‐lasting. Reserpine treatment did not change the effects of NPY.

Electrical stimulation of the splenic nerves in control animals caused a frequency‐dependent, guanethidine‐sensitive output of both NPY‐like immunoreactivity (‐LI) and NA, suggesting co‐release. The output of NPY‐LI relative to NA was enhanced at high frequency stimulation. Furthermore, α‐adrenoceptor blockade by phentolamine enhanced both the output of NPY‐LI and NA while inhibition of the neuronal uptake of NA with desipramine reduced the low frequency stimulation‐evoked overflow of NPY‐LI. Preganglionic denervation did not change the output of NPY‐LI or NA.

Reserpine treatment reduced both the splenic content of NA and NPY‐LI. Preganglionic denervation inhibited the reserpine‐induced depletion of the NPY content but not of NA in terminal areas. The stimulation‐evoked NPY overflow was markedly enhanced, especially at low‐frequency stimulation after resperpine, and the plasma levels of NPY‐LI in the venous effluent were then in the nmolar range (i.e. where exogenous NPY induced vasoconstriction). The perfusion‐pressure increase upon stimulation in reserpine‐treated, preganglionically‐denervated animals was highly correlated (r = 0.91) to the NPY overflow. The functional 0.5 Hz responses were reduced after reserpine, while at higher frequencies the functional effects were of similar magnitude to controls but longer‐lasting.

Tyramine induced a release of NA but not of NPY‐LI. Furthermore, the increase in perfusion pressure induced by tyramine was absent after reserpine.

After tachyphylaxis to the vasoconstrictor effects of mATP, the nerve stimulation‐evoked, functional response as well as the NA and NPY‐LI overflow were unchanged. After reserpine treatment, both the perfusion‐pressure increase and NPY‐LI overflow to nerve stimulation were reduced after mATP tachyphylaxis.

In conclusion, release of NPY rather than ATP may explain the long‐lasting, non‐adrenergic, splenic functional responses in reserpinized animals upon sympathetic stimulation. However, NA is most likely the main splenic transmitter when low‐frequency stimulation is used under control conditions.
Effect of palytoxin on the calcium current and the mechanical activity of frog heart muscle
Authors: Sauviat Martin‐Pierre
Published: July 2012

The effect of palytoxin (PTX) on the Ca current (ICa) and the mechanical activity of frog atrial fibres was studied by use of the double sucrose gap voltage clamp technique.

In normal Ringer solution, PTX transiently increased the electrically‐evoked peak tension which then decreased while a major contracture developed. PTX slowed the time course of the relaxation phase of the evoked tension.

Evidence is presented which suggests that the toxin also increased the entry of Ca and Sr via the Na‐Ca exchange mechanism. It also induced the development of a Ca‐dependent outward current which was inhibited by Sr.

In Na‐free solution, PTX increased ICa and shifted the reversal potential for Ca towards more negative membrane potentials, thus suggesting that the internal Ca concentration had increased. Current‐voltage, tension‐voltage, time to peak‐voltage and inactivation time constant‐membrane potential curves were all shifted towards more negative membrane potentials in the presence of PTX.

These effects of PTX are similar to those caused by the increase in internal Ca concentration induced by Na ionophores by way of voltage‐dependent Ca influx of the Na‐Ca exchange mechanism.
Thapsigargin, a new calcium‐dependent epithelial anion secretagogue
Authors: Brayden D.J. , Hanley M.R. , Thastrup O. , Cuthbert A.W.
Published: July 2012

Thapsigargin, a sesquiterpene lactone, was shown to cause electrogenic anion secretion in monolayers of human colonic epithelial cells, an effect which was crucially dependent upon calcium and did not involve eicosanoid formation.

To measure the secretory effect calcium needed to be present in the external bathing solution. By means of Fura‐2 fluorescence measurements thapsigargin was shown to raise Cai by around 250 nm when the bathing solution contained calcium. In the nominal absence of external calcium thapsigargin raised Cai by only 60 nm, but from a lower basal value. This was insufficient to cause secretion.

Effects of other calcium‐dependent secretagogues (e.g. lysylbradykinin) were inhibited in the presence of thapsigargin, whereas kinin responses were potentiated if the peptide was added following a stimulus which increases cyclic AMP.

From the data given here and the known behaviour of colonic epithelia it is concluded that thapsigargin increases Cai by a non‐ionophoric mechanism by release from internal stores. Calcium‐stimulated calcium influx then follows resulting in the opening of basolateral K channels, increasing the electrochemical gradient for chloride efflux, or alternatively by activating anion channels in the apical membrane. It is concluded that thapsigargin is a potentially important tool for examining epithelial mechanisms.
Effects of the putative antagonists phaclofen and δ‐aminovaleric acid on GABAB receptor biochemistry
Authors: Robinson T.N. , Cross A.J. , Green A.R. , Toczek J.M. , Boar B.R.
Published: July 2012

Phaclofen and δ‐aminovaleric acid (δ‐AVA) have been reported to be antagonists at γ‐aminobutyric acidB (GABAB) receptors. Phaclofen, δ‐AVA and related compounds were examined for potency and specificity at GABAB and GABAA receptors in rat cortical membranes labelled with [3H]‐(−)−baclofen and [3H]‐muscimol, respectively. Additionally phaclofen and δ‐AVA were examined in two functional tests of central GABAB activity in rat cortical slices, namely the inhibition of forskolin‐stimulated cyclic AMP accumulation, and the potentiation of isoprenaline‐stimulated cyclic AMP accumulation.

δ‐AVA (IC50 = 11.7 μm) was 20 fold more potent than phaclofen (IC50 = 229 μm) on GABAB receptor binding. All compounds possessing a phosphonic acid group, including phaclofen, which were active at GABAB receptors were inactive at GABAA receptors, while δ‐AVA was equally potent at both receptors. Several compounds exhibited Hill coefficients of less than unity in displacing [3H]‐(−)−baclofen binding.

(−)−Baclofen inhibited forskolin‐stimulated cyclic AMP accumulation (IC50 = 7.9 μm) but this effect was not stereospecific. Phaclofen (1 mm) was inactive against this inhibition but produced a potentiation of the forskolin effect. δ‐AVA (1 mm) failed to antagonize the effect of baclofen; rather it mimicked baclofen.

(−)−Baclofen (10 μm) potentiated isoprenaline‐stimulated cyclic AMP accumulation, an effect antagonized by phaclofen (1 mm). δ‐AVA (1 mm) may be a weak antagonist but also potentiated basal cyclic AMP accumulation.

We conclude that neither δ‐AVA nor phaclofen are potent specific GABAB receptor antagonists.
Pharmacological characterization of 8‐OH‐DPAT‐induced inhibition of rat hippocampal 5‐HT release in vivo as measured by microdialysis
Authors: Sharp Trevor , Bramwell Steven R. , Hjorth Stephan , Grahame‐Smith David G.
Published: July 2012

We have previously found that the putative 5‐HT1A agonist 8‐hydroxy‐2‐(di‐n‐propylamino) tetralin (8‐OH‐DPAT) decreases hippocampal 5‐hydroxytryptamine (5‐HT) release in the anaesthetized rat, as measured by brain microdialysis. The present study attempted to characterize the receptor involved in this response using a range of monoamine receptor antagonists.

The classical 5‐HT receptor antagonists, metergoline (5 mg kg−1 s.c.), methysergide (10 mg kg−1 s.c.) and methiothepin (10 mgkg−1 s.c.) each reduced dialysate levels of 5‐HT which complicated their use as antagonists in these experiments. Nevertheless, pretreatment with metergoline but not methiothepin and methysergide partially reduced the 5‐HT response to a maximally effective dose of 8‐OH‐DPAT (0.25 mg kg−1 s.c.).

The mixed 5‐HT1/β‐adrenoceptor antagonist pindolol (8 mg kg−1 s.c.) was without effect on spontaneous 5‐HT output but attenuated the effect of both maximally (0.25 mg kg−1 s.c.) and submaximally (0.05 mg kg−1 s.c.) effective dose of 8‐OH‐DPAT. In comparison, propranolol (10 mg kg−1 s.c.) did not affect 5‐HT output when injected alone and did not alter the response to 8‐OH‐DPAT (0.25 mg kg−1 s.c.).

The 5‐HT2 receptor antagonist ritanserin (0.2 mg kg−1 s.c.) and the 5‐HT3 receptor antagonist BRL 43694 (0.5 mg kg−1 s.c.) neither altered 5‐HT output alone nor significantly changed the response to 8‐OH‐DPAT (0.25 mg kg−1 s.c.).

The 8‐OH‐DPAT (0.25 mg kg−1 s.c.) response was not affected by pretreatment with either the dopamine D2‐receptor antagonist sulpiride (10 mg kg−1 s.c.) or the α1/α2‐adrenoceptor antagonist phentolamine (10 mg kg−1 s.c.).

We conclude from these data that the decrease of hippocampal 5‐HT output induced by 8‐OH‐DPAT does not involve 5‐HT2, 5‐HT3, adrenoceptors or dopamine D2‐receptors and that activation of a 5‐HT1 class of receptor seems probable. Full classification of the 8‐OH‐DPAT response awaits development of a suitably selective 5‐HT1 receptor antagonist with low intrinsic activity at the somatodendritic 5‐HT autoreceptor.
Evidence for two P2‐purinoceptor subtypes in human small pulmonary arteries
Authors: Liu S.F. , McCormack D.G. , Evans T.W. , Barnes P.J.
Published: July 2012

P2‐purinoceptors have not been characterized in human pulmonary vessels and we therefore examined the effects of adenosine 5′‐triphosphate (ATP) and its analogues on human isolated small pulmonary arteries (SPA) in vitro.

Contractile responses were induced by all of the analogues, with the rank order of potency α,β‐methylene‐ATP (α,β‐meATP) = β,γ‐methylene‐ATP (β,γ‐meATP) > ATP > 2‐methylthio‐ATP, indicating the presence of vasoconstrictor P2x receptors.

In precontracted SPA, vasodilator responses were produced by all of the analogues. The rank order of potency for the analogues causing vasodilator responses was: 2‐methylthio‐ATP ATP β,γ‐meATP = α,β‐meATP, indicating a vasodilator P2y receptor.

Removal of endothelial cells had no significant effect on either the contractile or relaxant responses to any of the analogues.

After pretreatment of the endothelium‐denuded vessels with α,β‐meATP (to desensitize P2x receptors), the contractile response to β,γ‐meATP (a potent P2x receptor agonist) was abolished.

We conclude that both P2x‐ and P2y‐purinoceptors are present in human SPA and that both receptors reside on the vascular smooth muscle.
The effects of reported Ca2+ sensitisers on the rates of Ca2+ release from cardiac troponin C and the troponin‐tropomyosin complex
Authors: Smith Susan J. , England Paul J.
Published: July 2012

The calcium sensitivity of force production of cardiac muscle fibres is altered by certain drugs. The sites of action of three such compounds (pimobendan, sulmazole, isomazole) within the myofibril have been investigated. Calmodulin antagonists, perhexilene and bepridil, which have been shown to alter the calcium dependence of myofibrillar ATPase activity and oxmetidine, an H2‐receptor antagonist which binds to calmodulin, were also studied.

The rates of dissociation of calcium from both the regulatory and high affinity sites on bovine isolated cardiac troponin C (cTnC) were measured in a stopped‐flow fluorimeter. The rates of dissociation were found to be 136.5 ± 16s−1 and 1.3 ± 0.20s−1 (mean ± s.e.mean, n = 11 determinations; conditions: 100 mm KCl, 10 mm MOPS, 3 mm MgCl2, 0.1 mm dithriothreitol, pH 7.0, 15°C). Sulmazole, isomazole and perhexiline (final concentration of 50 μm) had no effect on the rate of Ca2+ dissociation from the regulatory Ca2+ site, indicating that these compounds do not act on cTnC directly.

The rate of dissociation of Ca2+ from the regulatory site was slightly reduced (∼20%) by pimobendan (50 and 100 μm) and was somewhat increased by oxmetidine (28% at 100 μm).

Bepridil (25 μm) reduced the rate of dissociation by 50%, indicating a direct effect of bepridil on TnC.

Sulmazole, isomazole, perhexiline, pimobendan (50 μm) and bepridil (25 μ) were without effect on the rate of dissociation of Ca2+ from the high affinity Ca2+/Mg2+ sites. Oxmetidine caused 24% decrease in the rate of Ca2+ dissociation from these sites.

The rate of dissociation of Ca2+ from the regulatory site on the complex of troponin‐tropomyosin (TnTm) was measured. Sulmazole and pimobendan (50 μm) were without effect on the rate of dissociation of Ca2+ from the regulatory site in the protein complex, and isomazole (50 μm) caused only a slight reduction (23%). Perhexiline (50 μm) or bepridil (10 μm) reduced the rate of Ca2+ dissociation by about 50%. The rate of dissociation of Ca2+ from the high affinity Ca2+/Mg2+ sites was not altered by sulmazole, isomazole, or pimobendan (50 μm), but was decreased ∼35% by perhexiline (50 μm) or bepridil (10 μm).
Differential effects of petit mal anticonvulsants and convulsants on thalamic neurones: GABA current blockade
Authors: Coulter Douglas A. , Huguenard John R. , Prince David A.
Published: July 2012

Currents evoked by applications of γ‐aminobutyric acid (GABA) to acutely dissociated thalamic neurones were analysed by voltage‐clamp techniques, and the effects of the anticonvulsant succinimides ethosuximide (ES) and α‐methyl‐α‐phenylsuccinimide (MPS) and the convulsants tetramethylsuccinimide (TMS), picrotoxin, pentylenetetrazol (PTZ), and bicuculline methiodide were assessed.

TMS (1 μm‐10 mm) reduced responses to iontophoretically applied GABA, as did picrotoxin (0.1–100 μm), PTZ (1–100 mm) and bicuculline (1–100 μm).

ES, in high concentrations (1–10 mm), reduced GABA responses to a lesser extent, and also occluded the reductions in GABA‐evoked currents produced by TMS, picrotoxin, and PTZ. ES did not occlude the effects of bicuculline on GABA responses. Therefore, we propose that ES acts as a partial agonist at the picrotoxin GABA‐blocking receptor.

MPS had no effect on GABA responses (at a concentration of 1 mm), and, like ES, occluded the GABA‐blocking actions of TMS, apparently acting as a full antagonist.

The anticonvulsant actions of ES and MPS against TMS and PTZ‐induced seizures may thus involve two independent mechanisms: (1) the occlusion of TMS and PTZ GABA‐blocking effects; and (2) the previously described specific effect of ES and MPS on low‐threshold calcium current of thalamic neurones. The latter cellular mechanism may be more closely related to petit mal anticonvulsant activity.
The effects of drugs on Sephadex‐induced eosinophilia and lung hyper‐responsiveness in the rat
Authors: Spicer B.A. , Baker R.C. , Hatt P.A. , Laycock S.M. , Smith H.
Published: July 2012

Rats given an intravenous injection of Sephadex particles (0.5 mg of G200 in 1 ml of saline) on days 0, 2 and 5 had a blood eosinophilia which was maximal on day 7.

On day 7, broncho‐alveolar lavage (BAL) fluids taken from the rats contained an increased number of eosinophils and fewer mononuclear cells but there was no change in the small number of neutrophils. In addition the rats were hyper‐sensitive to the increase in resistance to artificial respiration produced by 5‐hydroxytryptamine (5‐HT), given intravenously, with a shift to the left of the log dose‐response curve. Lung parenchymal strips, taken from the rats on days 6, 7 and 8, were hyper‐reactive to 5‐HT with an increase in slope of the log dose‐response curve.

Compounds with a wide variety of activities were evaluated for their effects on the blood eosinophilia on day 7 when given before each injection of Sephadex. The eosinophilia was reduced by glucocorticosteroids, β‐adrenoceptor agonists, aminophylline, dapsone and phenidone.

Dexamethasone, isoprenaline, dapsone and phenidone at doses that reduced the blood eosinophilia also reduced the changes in number of leucocytes in the BAL fluids and the hyper‐responsiveness to 5‐HT in vivo and in vitro, except that the effects of dapsone on the hyper‐sensitivity to 5‐HT in vivo did not reach significance. Aminophylline was the least effective of the drugs at reducing the blood eosinophilia and its effects on the other changes did not reach significance. Sodium cromoglycate reduced the BAL eosinophilia but had no effect on the other changes produced by Sephadex.

The correlation coefficients between blood eosinophil numbers and reactivity to 5‐HT in vitro and sensitivity in vivo were r = 0.76, (n = 88; P > 0.001) and r = 0.53, (n = 61; P > 0.001) respectively.

Doses of dexamethasone, isoprenaline, dapsone and phenidone that reduced the blood eosinophilia when given before each injection of Sephadex were inactive when given up to 8 h after the Sephadex.

These data show an association between blood eosinophilia and hyper‐responsiveness of the lung. The blood eosinophilia in the rats was triggered within the first few hours of injecting the Sephadex and drugs have been identified which inhibit this trigger.
Benzodiazepine analogues inhibit arachidonate‐induced aggregation and thromboxane synthesis in human platelets
Authors: Fonlupt P. , Croset M. , Lagarde M.
Published: July 2012

Benzodiazepine analogues inhibit human platelet aggregation induced by arachidonate with an EC50 value of 0.68 μm for PK 11195, the most potent analogue used.

There was a highly significant correlation between the inhibition of arachidonate‐induced aggregation and the affinity for the peripheral‐type of benzodiazepine binding sites.

There was no significant correlation between the inhibition of the platelet activating factor (PAF)‐induced aggregation and the binding to the peripheral‐type of benzodiazepine binding sites.

The inhibition of platelet aggregation seems to result from the inhibition of arachidonic acid cyclooxygenation, since the synthesis of thromboxane and 12‐hydroxy‐heptadecatrienoic acid, both cyclooxygenase products, was reduced.

Our results suggest that peripheral‐type of benzodiazepine binding sites on human platelets could be linked to cyclo‐oxygenase.
Ruthenium red selectively inhibits oedema formation and increased blood flow induced by capsaicin in rabbit skin
Authors: Buckley T.L. , Brain S.D. , Williams T.J.
Published: July 2012

It has been suggested that ruthenium red has a selective inhibitory effect on capsaicin‐induced nociceptor stimulation. We have investigated the effect of ruthenium red on oedema formation and vasodilatation induced by intradermal (i.d.) injection of capsaicin in the rabbit in vivo. Responses induced by capsaicin were inhibited by ruthenium red, but responses induced by bradykinin, N‐formyl‐methionyl‐leucyl‐phenylalanine (FMLP), platelet activating factor (PAF), histamine and calcitonin gene‐related peptide (CGRP) were not affected. These results suggest that ruthenium red selectively inhibits capsaicin‐induced local plasma protein leakage and vasodilatation in the rabbit skin microvasculature.
Responses to noradrenaline in human subcutaneous resistance arteries are mediated by both α1‐ and α2‐adrenoceptors
Authors: Nielsen H. , Mortensen F.V. , Mulvany M.J.
Published: July 2012

In vitro experiments in a microvascular myograph were designed to characterize postjunctional α‐adrenoceptors of human subcutaneous resistance arteries (normalised internal diameter 143–313 μm).

Both the α1‐selective agonist phenylephrine in the presence of 0.3 μm yohimbine and the α2‐selective agonist B‐HT 933 in the presence of 0.3 μm prazosin elicited prominent and concentration‐dependent contractions. The maximum response to phenylephrine and B‐HT 933 was not different from the response to high K physiological salt solution (125 mm K+), and the pD2 values (−log EC50) were 5.90 and 6.11, respectively.

In the presence of the α2‐selective antagonist yohimbine (0.3 μm), the α1‐selective antagonist prazosin competitively antagonised the responses to phenylephrine; the pA2 of prazosin for the receptor which mediated the response to phenylephrine was 8.41.

Blockade of either α2‐adrenoceptors with 0.1 μm yohimbine or α1‐adrenoceptors with 0.1 μm prazosin caused shifts to the right of the noradrenaline concentration‐response curves and the shifts in pD2 were 0.69 and 0.61, respectively. The combination of the two antagonists at the above‐mentioned concentrations caused a marked, parallel shift to the right of the noradrenaline concentration‐response curve, the shift of the pD2 was 2.68.

These results suggest that activation of both α1‐ and α2‐adrenoceptors produces contractions in human subcutaneous resistance arteries, and that responses to noradrenaline in these vessels are mediated by both α‐adrenoceptor subtypes.
Action of calcitonin gene‐related peptide upon bovine vascular endothelial and smooth muscle cells grown in isolation and co‐culture
Authors: Crossman D.C. , Dashwood M.R. , Brain S.D. , McEwan J. , Pearson J.D.
Published: July 2012

Bovine aortic endothelial cells (BAE) and smooth muscle cells (BASM) were grown separately and in co‐culture.

Calcitonin gene‐related peptide (CGRP) caused dose‐dependent activation of adenylate cyclase in each cell type when grown in isolation. The concentration of CGRP causing half‐maximal activation in BAE and BASM was 200 nm and 310 nm, respectively.

In cells grown in co‐culture exposure to bradykinin produced dose‐dependent elevations in cyclic GMP content which were maximal 1 min after application of the agonist.

CGRP (1 nm−1 μm) did not stimulate a rise in cyclic GMP in co‐cultures.

Displaceable CGRP binding was identified throughout the wall of the bovine aorta.

We conclude that CGRP receptors coupled to adenylate cyclase are present on BAE and BASM, but there is no coupling of these receptors to the release of any agent (such as endothelium‐derived relaxing factor) that activates guanylate cyclase.
Protective effect of beraprost sodium, a new chemically stable prostacyclin analogue, against the deterioration of baroreceptor reflex following transient global cerebral ischaemia in dogs
Authors: Kurihara Junichi , Sahara Tatsuhiro , Kato Hitoshi
Published: July 2012

A possible cerebroprotective effect of a chemically stable prostacyclin analogue, beraprost sodium, was investigated in a canine model of cerebral ischaemia. Cerebral ischaemia was produced by the combined occlusions of the left subclavian and the brachiocephalic arteries with preceding ligations of the intercostal arteries.

The decrease in baroreceptor reflex sensitivity (BRS), measured by phenylephrine‐induced reflex bradycardia, following 5 min ischaemia was used to assess the cerebroprotective effect.

Beraprost (1 μg kg−1 min−1 i.v., infused for 15 min just before ischaemia) completely prevented the decrease in BRS. Although the lower dose of beraprost (0.1 μg kg−1 min−1 i.v.) failed to show such a protective effect, its inhibitory effect on ADP‐induced platelet aggregation was as potent as that of the higher dose.

The extent of decrease in BRS was inversely correlated with the extent of the residual blood flow in the medulla oblongata during ischaemia. Since beraprost did not affect the extent of the residual blood flow during ischaemia, its cerebroprotective effect could not be ascribed to the reduction of the degree of ischaemia by increasing collateral blood flow to the brain.

Post‐ischaemic reduction of the regional blood flow in the medulla and the cerebral cortex was completely prevented by the higher dose of beraprost.

The present study suggests that the cerebroprotective effect of beraprost may be independent of its anti‐aggregatory and vasodilator effects. It is possible that the protection may be due to a prostacyclin‐like cytoprotective effect through membrane stabilization.
The effect of two lipophilic γ‐aminobutyric acid uptake blockers in CA1 of the rat hippocampal slice
Authors: Rekling Jens C. , Jahnsen Henrik , Laursen Arne Mosfeldt
Published: July 2012

Drugs that increase inhibitory synaptic transmission in the central nervous system may be valuable tools in the treatment of seizures. Theoretically, substances that block the uptake of inhibitory transmitters such as γ‐aminobutyric acid (GABA) into intracellular compartments should also increase inhibition and therefore have potential value as antiepileptic drugs. However, most of these substances penetrate the blood‐brain barrier poorly and have therefore until now had limited value. NO‐05–0328 and NO‐05–0329 are two new lipophilic GABA uptake inhibitors that readily enter the CNS from the blood.

We have investigated the effect of these two uptake inhibitors on the responses to exogenous GABA and on GABA‐mediated inhibitory synaptic potentials in pyramidal neurones of the CA1 region in the rat hippocampal slice.

We found that both drugs increased the amplitude and duration of responses to exogenous GABA. Furthermore, the inhibitory synaptic potentials increased in amplitude. This increase was seen in both early and late phases of the synaptic potentials. We conclude that NO‐05–0328 and NO‐05–0329, at least in vitro, are more effective than older GABA uptake inhibitors such as nipecotic acid and they therefore deserve consideration for clinical use.
2‐Substituted indazolinones: orally active and selective 5‐lipoxygenase inhibitors with anti‐inflammatory activity
Authors: Foster S.J. , Bruneau P. , Walker E.R.H. , McMillan R.M.
Published: July 2012

This paper describes the pharmacological profile of ICI207968, a novel, orally‐active and selective inhibitor of 5‐lipoxygenase.

Inhibition of leukotriene B4 (LTB4) synthesis by 2‐substituted indazolinones was not directly related to redox potential but was critically dependent on the nature of the N2 substituent. 2‐(3‐Pyridylmethyl)‐indazolinone (ICI207968) combined selectivity and oral potency.

In several in vitro systems ICI207968 exhibited similar lipoxygenase inhibitory potency (IC50 values from 1.5 μm to 6.0 μm) and was approximately 300 times less potent against cyclo‐oxygenase, as measured by inhibition of prostaglandin E2 (PGE2) synthesis.

ICI207968 also produced selective lipoxygenase inhibition following oral administration in the rat. ED50 values of 2.5, 10 and 25 mg kg−1 p.o. for inhibition of LTB4 release from A23187‐stimulated blood were obtained 1, 3 and 5 h after dosing. The compound did not inhibit PGE2 synthesis at oral doses up to 300 mg kg−1.

Co‐administration of ICI207968 with arachidonic acid, into rabbit dermis, potently inhibited both plasma extravasation and polymorphonuclear leucocyte (PMNL) infiltration induced by this inflammatory fatty acid. The anti‐inflammatory potency of a number of intradermally administered indazolinones, with similar redox potentials, was related to their inhibitory potency against leukotriene generation in blood. Oral administration of ICI207968 (100 mg kg−1) in the rabbit inhibited ex vivo leukotriene generation in blood and arachidonic acid‐induced skin inflammation.

These data demonstrate that ICI207968 is an orally active and selective inhibitor of 5‐lipoxygenase which has anti‐inflammatory properties. ICI207968 will be a valuable agent for clarifying the biological roles of leukotrienes and the therapeutic potential of 5‐lipoxygenase inhibitors.
Action of an irreversible acetylcholine esterase inhibitor, soman, on muscarinic hyperpolarization in cat bladder parasympathetic ganglia
Authors: Kumamoto Eiichi , Shinnick‐Gallagher Patricia
Published: July 2012

Intracellular recording techniques were used to examine the action of an irreversible acetylcholine esterase (AChE) inhibitor, soman, on the hyperpolarizations mediated through muscarinic cholinoceptors in cat bladder parasympathetic neurones.

Soman (0.1–10 μm) depressed the amplitude and prolonged the duration of the muscarinic slow inhibitory postsynaptic potential (s‐i.p.s.p.) elicited by a preganglionic tetanus (40 Hz for 1 s) in the presence of mecamylamine (20 μm), phentolamine (1 μm) and caffeine (1 mm), in a dose‐dependent manner. The effect of soman on the amplitude of the s‐i.p.s.p. was partially reversible, while the effect on the duration was irreversible.

Soman hyperpolarized the membrane and decreased input resistance, but this effect could not account for soman‐induced inhibition of the s‐i.p.s.p.

Soman depressed the amplitude and prolonged the duration of a muscarinic hyperpolarization induced by pressure application of acetylcholine (ACh) in the presence of mecamylamine, phentolamine and caffeine. The time course of this effect paralleled that on the synaptically‐evoked muscarinic s‐i.p.s.p.

A reversible AChE inhibitor, pyridostigmine (10–100 μm), also depressed the amplitude and prolonged the duration of a muscarinic hyperpolarization induced by either preganglionic stimulation or ACh pressure application. These actions were reversible, and not accompanied by a significant change in membrane potential or input resistance.

The inhibitory action of soman (1 μm) on the muscarinic hyperpolarization was prevented by pyridostigmine (10 μm), but not by atropine (1 μm).

These results demonstrate that soman prolongs not only the muscarinic hyperpolarization, but also inhibits its amplitude through a postsynaptic action, probably through AChE inhibition, in cat bladder parasympathetic neurones.
Presynaptic α2‐autoinhibition in a vascular neuroeffector junction where ATP and noradrenaline act as co‐transmitters
Authors: Bulloch J.M. , Starke K.
Published: July 2012

α2‐Autoinhibition of transmitter release was investigated in the largest rami caecales of the rabbit ileocolic artery. Vasoconstriction, elicited by electrical field stimulation or by exogenous agonists, was measured as an increase in perfusion pressure.

Short periods of electrical stimulation elicited monophasic vasoconstriction, whereas longer periods (>10s) produced biphasic vasoconstriction. Prazosin had no significant effect on the first component of the biphasic vasoconstriction elicited by electrical stimulation, but did reduce the second component at higher frequencies. α,β‐Methylene ATP significantly attenuated the first component whilst the second component was relatively resistant.

The α2‐adrenoceptor antagonist yohimbine did not change responses evoked by very short pulse trains (< 2 s) but enhanced responses to longer pulse trains. When vasoconstriction was biphasic, both phases were potentiated by yohimbine.

The results indicate that the vasoconstriction elicited by brief trains of sympathetic nerve impulses is mainly or exclusively mediated by ATP, whereas at longer pulse trains a noradrenergic component comes into play. The potentiation produced by yohimbine is due to interruption of presynaptic α2‐adrenoceptor‐mediated autoinhibition of transmitter release. The autoinhibition affects both purinergic and adrenergic components of sympathetic neurotransmission.
Modification of the ischaemic‐induced contraction in the sheep circumflex coronary artery by various pharmacological antagonists
Authors: Kwan Y.W. , Wadsworth R.M. , Kane K.A.
Published: July 2012

Sheep isolated circumflex coronary artery rings were exposed to simulated ischaemia (increased K+ reduced pH, hypoxia, reduced glucose and addition of lactate). Simulated ischaemia caused a transient relaxation lasting approximately 5 min followed by a sustained contraction that was reversible on washing with oxygenated Krebs solution.

Haemolysate caused a rise in baseline tension and augmented the ischaemic contraction.

The ischaemic contraction was abolished by BW 755C 5 μm and reduced by indomethacin 1 μm, quinacrine 50 μm or the thromboxane A2 antagonist BM 13177 10 μm. The leukotriene D4 antagonist, ICI 198615, had no effect.

The ischaemic‐induced contraction was enhanced by propranolol 1 μm, methiothepin 1 μm and reduced by ketanserin 1 μm.

The ischaemic contraction was markedly inhibited by trypsin (1 u ml−1) and by verapamil, cromakalim or sodium nitroprusside.

The following had no or little effect on the ischaemic contraction: Sar1‐Thr8‐angiotensin II, mepyramine, atropine, the spin trapping agent PBN or the free radical scavenger dimethylsulphoxide. Superoxide dismutase caused a slight enhancement.

The ischaemic‐induced contraction was abolished by the simultaneous administration, at subthreshold concentrations, either of two vasodilators (iloprost and adenosine) or of a vasodilator and a vasoconstrictor (iloprost and U46619).

The ischaemic relaxation phase was reduced by propranolol and indomethacin, abolished by haemolysate and enhanced by quinacrine or cromakalim.

It is concluded that the ischaemic‐induced contraction is caused by mediators released from the endothelium including a product of the lipoxygenase pathway. There is also evidence that simulated ischaemia causes the release of noradrenaline and 5‐hydroxytryptamine.
Endothelium‐dependent and BRL 34915‐induced vasodilatation in rat isolated perfused mesenteric arteries: role of G‐proteins, K+ and calcium channels
Authors: Adeagbo Ayotunde S.O. , Malik Kafait U.
Published: July 2012

In the isolated perfused, noradrenaline (NA)‐constricted mesenteric arteries of the rat, acetylcholine (0.003‐1 nmol), histamine (0.01–10 nmol) and the calcium ionophore A23187 (0.01‐1 nmol), caused endothelium‐dependent vasodilatation while the vasodilatation by the K+ channel activator BRL 34915 (0.1‐1 nmol) was independent of endothelium.

The guanylate cyclase inhibitor, methylene blue at 10 μm did not inhibit the action of any of the vasodilators but at 50 μm reduced the vasodilator effect of acetylcholine (ACh), histamine and A23187.

Infusion of ouabain or perfusion with K+‐free or excess K+ (50 mm) Krebs solution reduced the vasodilator effect of ACh, histamine and A23187, suggesting the action of these agents involves, at least in part, activation of Na+/K+‐ATPase. The vasodilator effect of BRL 34915 was not affected by ouabain, but abolished during perfusion with Krebs solution containing excess K+ or depleted of K+.

Five structurally distinct K+ channel blockers (apamin, crude scorpion venom, procaine, quinidine and tetraethylammonium) attenuated the vasodilator effect of ACh, histamine and A23187. The K+ channel blockers, except apamin and crude scorpion venom, also inhibited the vasodilatation produced by BRL 34915.

The vasodilator effect of ACh, histamine or A23187 was not altered in mesenteric vessels of pertussis toxin‐treated rats, suggesting that the K+ channels associated with the endothelium‐dependent vasodilator effect of these agents are either not coupled to G‐proteins or are coupled to G‐proteins that are insensitive to pertussis toxin.

The calcium channel blockers, diltiazem (0.1 or 1 μm), nifedipine (0.01 or 0.1 μm) or nitrendipine (1 nm) attenuated the vasodilatation produced by ACh, histamine, A23187 and also that by BRL 34915.

We conclude that endothelium‐dependent vasodilatation induced by ACh, histamine and A23187 is mediated via activation of membrane K+ channels and Na+/K+‐ATPase. The K+ channels involved in the vasodilator action of these agents are not coupled to pertussis toxin‐sensitive G‐proteins and appear to be regulated by Ca2+.
Angiotensin converting enzyme inhibitors potentiate the bronchoconstriction induced by substance P in the guinea‐pig
Authors: Subissi Alessandro , Guelfi Marco , Criscuoli Marco
Published: July 2012

The effects of intravenous captopril and enalaprilic acid on the increase in pulmonary inflation pressure induced by different bronchoconstrictor agents were evaluated in the anaesthetized guinea‐pig.

Captopril and enalaprilic acid (1.6–200 μg kg−1) enhanced dose‐dependently the bronchoconstriction (BC) induced by substance P. The threshold effective dose was 1.6 μg kg−1 and maximal potentiation over the control response was more than 400% for both agents. Enalaprilic acid was also assayed for serum and lung angiotensin converting enzyme (ACE) inhibition in anaesthetized guinea‐pigs. This drug produced a dose‐dependent inhibition of ACE in both tissues, with ED50 s of 7.6 and 9.4 μg kg−1, respectively: this inhibitory activity was positively correlated to substance P potentiation.

Captopril (8–1000 μg kg−1) enhanced dose‐dependently the BC induced by capsaicin. The threshold effective dose was 40 μg kg−1 and maximal potentiation about 90%.

Captopril (200–1000 μg kg−1) did not affect BC induced by bradykinin. However, this response was markedly enhanced (about 200%) by captopril 200 μg kg−1 in propranolol‐pretreated animals.

Captopril and enalaprilic acid (200–1000 μg kg−1) slightly (20–40%) but significantly enhanced the BC induced by 5‐hydroxytryptamine. However, this response was potentiated to the same extent by a dose of prazosin, which produced a degree of hypotension similar to that observed after administration of the ACE inhibitors.

In conclusion, ACE inhibitors potentiate the BC induced by substance P and, to a minor extent, that induced by capsaicin in the anaesthetized guinea‐pig. Potentiation of substance P is well correlated with ACE inhibition in guinea‐pig serum and lungs. These experimental results may offer a mechanistic interpretation of cough and bronchial hyperreactivity observed in patients receiving treatment with ACE inhibitors.
Sympathetic neurotransmission in the rabbit isolated central ear artery is affected as early as one week following a single dose of X‐irradiation
Authors: Stewart‐Lee A.L. , Maynard K.I. , Lincoln J. , Burnstock G.
Published: July 2012

The short‐term effect of a single dose of 4500 rad X‐irradiation on sympathetic neurotransmission (involving both noradrenergic and purinergic components) was assessed in the rabbit central ear artery, 1, 4 and 6 weeks post‐irradiation.

Neurally mediated contractions were reduced as early as 1 week post‐irradiation, with responses to lower frequency stimulation being initially most affected. This suggests that the purinergic component of the contractile response is affected earlier than the adrenergic component.

There was no change in the amplitude or sensitivity of treated preparations to the cumulative application of noradrenaline when compared with untreated preparations. In contrast, contractions to α,β‐methylene ATP (1 μm), a P2‐purinoceptor agonist, were significantly increased at 4 and 6 weeks post‐irradiation, although not at 1 week post‐irradiation.

There were no apparent changes in the pattern of catecholamine fluorescence as a result of irradiation. However, the tissue content of noradrenaline was significantly reduced 6 weeks post‐irradiation when compared with control preparations.

It is concluded that damage to sympathetic cotransmission is one of the early effects of irradiation, with initial impairment predominantly of the purinergic component.
Modes of hexamethonium action on acetylcholine receptor channels in frog skeletal muscle
Authors: Adams D.J. , Bevan S. , Terrar D.A.
Published: July 2012

The antagonism between hexamethonium and cholinoceptor agonists was investigated in frog skeletal muscle fibres with voltage‐clamp techniques. Hexamethonium caused a voltage‐dependent reduction in the amplitude of endplate currents. For neurally evoked endplate currents, the reduction increased e‐fold with a 38 mV membrane hyperpolarization.

The effect of hexamethonium on the time course of endplate currents was small, and was most apparent as a slight prolongation of the decay phase at hyperpolarized potentials (more negative than—100 mV). A similar small prolongation of single channel lifetime was detected with fluctuation analysis techniques. Hexamethonium produced a voltage‐dependent reduction in apparent single channel conductance as the membrane was hyperpolarized.

Log (concentration‐response) curves for acetylcholine (ACh)‐induced currents, determined either from currents accompanying ramp changes in membrane potential or from steady state currents in voltage‐jump experiments, were less steep for responses in the presence of hexamethonium. This reduction in slope became more pronounced at more negative membrane potentials. Observations at +50 mV suggested that the equilibrium constant for competitive antagonism was approximately 200 μm.

In voltage‐jump experiments with a two‐microelectrode voltage clamp, the current evoked by ACh in the presence of hexamethonium differed from that recorded with ACh alone. In the presence of hexamethonium, the expected ‘instantaneous' ohmic increase in membrane current in response to a hyperpolarizing step was not detected; instead a decrease in current was observed. This problem was further investigated with a vaseline‐gap voltage‐clamp technique which provides improved temporal resolution. With this method a rapid decrease in the ACh‐induced inward current was observed with step hyperpolarizations in the presence of hexamethonium.

When the membrane potential was stepped back to its resting level from a more hyperpolarized potential in the presence of hexamethonium, there was a surge of ACh‐induced inward current that decayed with a time constant of less than 100 μs.

The slow relaxation in the ACh‐induced current that followed a voltage step recorded in the presence of hexamethonium was slower than that recorded with ACh alone. In the presence of hexamethonium the time constant of this relaxation increased e‐fold for a 67 mV hyperpolarization.

The results are consistent with a rapid voltage‐dependent block of ACh‐activated channels by hexamethonium with hyperpolarization, and voltage‐dependent unblock with depolarization. The voltage‐dependent block is combined with competitive antagonism at the ACh receptors. However, not all observations appear to be compatible with a simple sequential block of open ion channels, but rather suggest that occupation of the channel by hexamethonium may not prevent channel closure.
Inhibition of inositol 1,4,5‐trisphosphate formation by cyclic GMP in cultured aortic endothelial cells of the pig
Authors: Lang Derek , Lewis Malcolm J.
Published: July 2012

In cultured endothelial cells of the pig the endothelium‐derived relaxing factor (EDRF) releasing agent thrombin (2 u ml−1) caused a significant increase in basal levels of both guanosine 3′:5′‐cyclic monophosphate (cyclic GMP) and inositol 1,4,5‐trisphosphate (IP3). This increase was time dependent, with peak levels occurring at 2 min and returning towards basal values after 5 min.

Pretreatment of the cells with the EDRF inhibitors haemoglobin (1 μm) or l‐NG‐nitro arginine (50 μm) significantly reduced the cyclic GMP response to thrombin. Both agents also resulted in significant elevations in basal levels of IP3. The IP3 response to thrombin was significantly enhanced at all time points by haemoglobin and at 5 min for l‐NG‐nitro arginine, when compared with the response to thrombin alone.

Pretreatment of the cells with either sodium nitroprusside (10 μm) or atrial natriuretic peptide (1 μm) caused a significant elevation of basal cyclic GMP levels. Although subsequent exposure to thrombin caused a further increase in cyclic GMP, which together with the rise induced by the previous two agents was significantly greater than the increase caused by thrombin alone, the incremental increase induced by thrombin was markedly less in the presence of nitroprusside or atrial natriuretic peptide. Both these agents, as well as 8‐bromo cyclic GMP, resulted in a significant suppression of the IP3 response to thrombin.

These findings show that one mechanism for the inhibitory effect of cyclic GMP on EDRF release from endothelium may be through the inhibition of IP3 formation in response to EDRF releasing agents.
Muscarinic receptor subtypes coupled to generation of different second messengers in isolated tracheal smooth muscle cells
Authors: Yang Chuen Mao , Chou Sheng‐Ping , Sung Tsung‐Chang
Published: July 2012

Activation of muscarinic receptor subtypes leads to contraction, an increase in the accumulation of inositol phosphates (IPs) and a decrease in adenosine 3′: 5′‐cyclic monophosphate (cyclic AMP) synthesis in tracheal smooth muscle. The concentrations of carbachol that produced a half‐maximal effect (EC50) in inhibition of cyclic AMP generation, stimulation of IPs formation and contraction were 15 nm, 2.0 μm and 0.17 μm, respectively.

Pirenzepine, a selective M1 antagonist, displayed a low affinity for antagonizing cyclic AMP inhibition, IPs formation and contraction induced by carbachol (pKB = 6.8, 7.0, and 7.1, respectively).

Methoctramine, a cardioselective M2 antagonist, blocked cyclic AMP inhibition with a high affinity (pKB = 7.5), while it antagonized IPs formation and contraction with a low affinity (pKB = 6.2 and 6.1, respectively).

4‐Diphenylacetoxy‐n‐methylpiperidine (4‐DAMP), a selective smooth muscle M3 antagonist, possessed a high affinity in blocking IPs formation (pKB = 8.8) and contraction (pKB = 9.2) as well as a low affinity for antagonism of cyclic AMP inhibition (pKB = 8.1).

In conclusion, we have demonstrated that M2 and M3 receptor subtypes are coupled to different effector systems in tracheal smooth muscle. An M1 receptor subtype is not involved in the generation of the second messengers examined. Inhibition of cyclic AMP formation may be coupled to the M2 receptor subtype. The accumulation of IPs and presumably IP‐induced Ca2+ release may function as the transducing mechanism for cholinergic contraction of tracheal smooth muscle through the activation of M3 receptors.
Action of heptaminol hydrochloride on contractile properties in frog isolated twitch muscle fibre
Authors: Allard Bruno , Jacquemond Vincent , Lemtiri‐Chlieh Fouad , Pourrias Bernard , Rougier Oger
Published: July 2012

Heptaminol stopped or delayed the progressive decline in tension which characterizes the phenomenon of fatigue in frog isolated twitch muscle fibre.

Heptaminol had no action on the sodium, potassium and calcium voltage‐dependent ionic conductances.

The hypothesis of an action via an internal alkalinization was tested by comparison with the action of NH4Cl. Both substances increased the tension.

The action of heptaminol was suppressed in sodium‐free (TRIS) solution or in the presence of amiloride while the action of NH4Cl was always observed.

These results could be explained by a stimulation of the Na/H antiport by heptaminol.
Differential effects of phosphoramidon on neurokinin A‐ and substance P‐induced airflow obstruction and airway microvascular leakage in guinea‐pig
Authors: Lötvall Jan O. , Elwood Wayne , Tokuyama Kenichi , Barnes Peter J. , Chung K. Fan
Published: July 2012

The effects of the inhaled neuropeptides, neurokinin A (NKA) and substance P (SP) on lung resistance (RL) and airway microvascular permeability were studied in anaesthetized guinea‐pigs.

Single doses of inhaled NKA (3 × 10−5, 1 × 10−4, 3 × 10−4 m; 45 breaths) and SP (1 × 10−4, 3 × 10−4, 1 × 10−3; 45 breaths) caused a dose‐dependent increase in both RL and airway microvascular leakage, assessed as extravasation of the albumin marker, Evans blue dye.

NKA at 1 × 10−4 and 3 × 10−4 m resulted in a significantly higher increase in RL than SP at the same doses.

Inhaled SP (3 × 10−4 m; 45 breaths) caused significantly higher Evans blue dye extravasation in main bronchi and proximal intrapulmonary airways compared to the same dose of NKA.

Pretreatment with the specific inhibitor of neural endopeptidase (NEP24.11), phosphoramidon, caused an approximately 100 fold leftward shift of the RL responses to inhaled NKA and SP.

Phosphoramidon significantly potentiated both NKA‐ and SP‐induced airway microvascular leakage at proximal intrapulmonary airways, but not at any other airway level.

Inhibition of NEP24.11 potentiate both the SP‐ or NKA‐induced airflow obstruction to a larger extent than the induced airway microvascular leakage, suggesting that NEP24.11 is more important in the modulation of the airflow obstruction observed after these mediators.