bluuebunny/crossref_metadata_2025 huggingface dataset:
The effect of SK&F 95654, a novel phosphodiesterase inhibitor, on cardiovascular, respiratory and platelet function
Authors: Murray Kenneth J. , Eden Roger J. , Dolan John S. , Grimsditch David C. , Stutchbury Catherine A. , Patel Bella , Knowles Aileen , Worby Angela , Lynham James A. , Coates William J.
Published: July 2012

SK&F 95654 inhibited the guanosine 3′:5′‐cyclic monophosphate (cyclic GMP)‐inhibited phosphodiesterase (cGI‐PDE) with an IC50 value of 0.7 μm. The IC50 values were greater than 100 μm for the other four phosphodiesterase isoenzymes tested. The R‐enantiomer of SK&F 95654 (IC50 = 0.35 μm) was a more potent inhibitor of cGI‐PDE than was the S‐enantiomer (IC50 = 5.3 μm).

In the guinea‐pig working heart, SK&F 95654 produced a positive inotropic response without altering heart rate.

Oral administration of SK&F 95654 to conscious dogs caused dose‐dependent increases in left ventricular dp/dtmax in the range 10–50 μg kg−1. These positive inotropic responses were maintained for 3 h without simultaneous changes in heart rate or blood pressure. The peak effects on left ventricular dp/dtmax were similar for orally and intravenously administered compound, indicating good oral bioavailability.

SK&F 95654 caused a potent inhibition of U46619‐induced aggregation in both a human washed platelet suspension (WPS) (IC50 = 70 nm) and in human platelet‐rich plasma (PRP) (IC50 = 60 nm), indicating that the compound shows negligible plasma binding.

The R‐enantiomer of SK&F 95654 was twenty fold more potent as an inhibitor of platelet aggregation than was the S‐enantiomer. The similarity of this ratio to that obtained on the cGI‐PDE suggests that SK&F 95654 inhibits platelet aggregation via its effects on cGI‐PDE. This was also indicated by studies which showed that SK&F 95654 increased adenosine 3′:5′‐cyclic monophosphate (cyclic AMP) levels and activated cyclic AMP‐dependent protein kinase in human platelets.

6 Collagen‐induced aggregation of rat PRP was also inhibited by SK&F 95654 (IC50 = 65 nm). The effects of SK&F 95654, administered intravenously, on ex vivo platelet aggregation were studied in the conscious rat. At 1 mg kg−1, SK&F 95654 inhibited aggregation for at least 4 h post dose and was more potent than the two other cGI‐PDE inhibitors studied (siguazodan and SK&F 94120).

7 In contrast to its potent effects on heart and platelets, SK&F 95654 caused only a modest relaxation of histamine‐ or U46619‐induced bronchoconstriction in the anaesthetized, ventilated guinea‐pig.

8 Taken together, these results indicate that SK&F 95654 may be a suitable agent for the treatment of congestive heart failure.
Effects of noradrenaline on rat paratracheal neurones and localization of an endogenous source of noradrenaline
Authors: Reekie Fiona M. , Burnstock Geoffrey
Published: July 2012

Intracellular recording techniques were used to study the actions of exogenous noradrenaline (NA) on rat paratracheal neurones in situ. The receptor subtypes underlying these actions were investigated by application of selective adrenoceptor antagonists.

Application of NA (0.1–10 μm) by superfusion evoked a membrane depolarization in 85% (52 out of 61) of all paratracheal neurones studied. The response consisted of a slow depolarization which was sometimes accompanied by action potential discharge. In 26 out of 31 cells the response was associated with a change in input resistance of the cell membrane. In 22 out of 26 cells there was a 30% increase, whilst in a further 4 cells there was a 15% decrease in input resistance. The amplitude of the NA depolarization was concentration‐dependent.

The depolarization evoked by NA was reversibly antagonized by prazosin (1 μm) but unaffected by yohimbine (1 μm) or propranolol (1–10 μm).

High performance liquid chromatography with electrochemical detection (h.p.l.c.‐e.c.d.) was used to assay for NA and dopamine in samples containing mainly paratracheal ganglia and in samples of tracheal smooth muscle with mucosa. NA was present in all samples assayed at a level of 1.6 μg NA g−1 and 0.5 μg NA g−1 wet weight of the two sample types respectively. Dopamine was not detected in any samples of either ganglia or smooth muscle with mucosa.

It is concluded that NA‐evoked depolarizations of rat paratracheal neurones result from stimulation of α1‐adrenoceptors, and that local levels of NA may be sufficiently high to activate these receptors directly.
Cytosolic calcium increase in coronary endothelial cells after H2O2 exposure and the inhibitory effect of U78517F
Authors: Kimura Masaaki , Maeda Kaori , Hayashi Shigehiro
Published: July 2012

Cytosolic calcium concentrations ([Ca2+]i were determined with fura‐2 on both resting (unstimulated) and A23187‐stimulated coronary endothelial cells following injury by hydrogen peroxide (H2O2).

Treatment of cells with H2O2 (10−4 m) caused an increase in the resting [Ca2+]i, which reached a maximum of five fold after 3 h.

The increase in resting [Ca2+]i was significantly attenuated by treatment with U78517F, a potent inhibitor of lipid peroxidation, at a concentration of 10−6 m or greater. Catalase (50 u ml−1) also markedly inhibited the H2O2‐induced rise in [Ca2+]i. Pretreatment with verapamil (10−5 m), nifedipine (10−6 m) or diltiazem (10−5 m) had no effect on the increase in [Ca2+]i following addition of H2O2.

A23187 produced a transient increase in [Ca2+]i followed by a sustained plateau. The initial peak and plateau phase responses to A23187 were augmented by H2O2. This augmentation of [Ca2+]i was suppressed by U78517F or catalase but not by Ca‐entry blockers.

Thus, it is likely that lipid peroxidation plays a critical role in the sustained increase in [Ca2+]i that occurs following treatment with H2O2 and that this continues in the presence of agonists which stimulate the endothelium. Voltage‐gated Ca2+ channels do not seem to be involved in the genesis of cellular damage associated with sustained large increases in [Ca2+]i.
Effects of long‐term oral administration of amiodarone on the electromechanical performance of rabbit ventricular muscle
Authors: Kodama Itsuo , Suzuki Ryoko , Kamiya Kaichiro , Iwata Hirokazu , Toyama Junji
Published: July 2012

The effects of long‐term administration of oral amiodarone on transmembrane action potential and contraction of ventricular muscle were investigated in rabbits.

ECGs of rabbits that received oral amiodarone 50 mg or 100 mg kg−1 daily for 4 weeks, showed a significant prolongation of RR, QT and corrected QT (QTc) intervals, whereas PQ and QRS were unaffected. Serum and myocardial tissue amiodarone concentrations were 0.14–0.18 μg ml−1 and 1.47–3.63 μg g−1 wet wt. respectively.

Right ventricular papillary muscles isolated from treated rabbits were characterized by a moderate prolongation of action potential duration (APD) compared with controls. A slight decrease of the maximum upstroke velocity was also observed at the higher dose. The APD prolongation by chronic amiodarone, unlike acute effects of sotalol, E‐4031, Cs+ and 4‐aminopyridine, did not show marked reverse use‐dependence.

APD and restitution following slow basic stimuli (0.03 Hz) were unaffected by chronic treatment with amiodarone.

Acute application of amiodarone (10 μm) caused a significant decrease in APD and developed tension, as well as a marked use‐dependent inhibition with fast recovery kinetics.

6 These findings suggest that a major and consistent electro‐physiological effect of chronic amiodarone is repolarization delay (Class‐III action) showing minimal frequency‐dependence. However, when amiodarone above a certain concentration is present in the extracellular space, a fast kinetic Class‐I action would be added as an acute effect.
Changes in intrinsic inhibition in isolated hippocampal slices during ethanol withdrawal; lack of correlation with withdrawal hyperexcitability
Authors: Whittington M.A. , Little H.J. , Lambert J.D.C.
Published: July 2012

Intracellular recordings were made from pyramidal cells in area CA1 in mouse isolated hippocampal slices, after chronic ethanol treatment in vivo.

Fast i.p.s.ps were isolated by injection of the impaled neurones with QX314 (to block fast sodium currents and the slow i.p.s.p.) and stimulating the interneurones in the presence of the glutamatergic blockers, CNQX and APV.

The isolated fast‐inhibitory postsynaptic potential (f.‐i.p.s.p.) was measured at intervals during the 7 h withdrawal period. The reversal potential and sensitivity to bicuculline suggested that the isolated f.‐i.p.s.p. was mediated by activation of the GABAA receptor‐chloride ionophore complex.

Measurement of stimulus‐response relationships for the f.‐i.p.s.ps revealed an initial increase in the maximum size of the i.p.s.p., evoked from a membrane potential of −50 mV, seen at 2 h into ethanol withdrawal. This was attributed to a negative shift in the reversal potential, Ei.p.s.p., with no observed change in conductance, Gi.p.s.p..

No differences in f.‐i.p.s.ps evoked during ethanol withdrawal or in control slices were seen at 4 h or 6 h. At these times, epileptiform activity was seen in previous field potential recordings.

6 Paired pulse depression of the f.‐i.p.s.p. was significantly increased at 2 h into withdrawal, when a 150 ms pulse interval was used. No differences were seen at later times in the ethanol withdrawal period.

7 The results suggest that ethanol withdrawal hyperexcitability in isolated hippocampal slices is not caused by primary decreases in inhibition mediated by the GABAA receptor‐chloride ionophore complex. The increase in the f.‐i.p.s.p. during the initial stages of the withdrawal might prevent the overt expression of epileptiform activity at this time.
Effect of histamine and histamine analogues on human isolated myometrial strips
Authors: Martínez‐Mir María Inocencia , Estañ Luis , Morales‐Olivas Francisco J. , Rubio Elena
Published: July 2012

The effect of histamine and histamine H1 and H2‐receptor agonists on isolated myometrium strips of premenopausal women has been examined. The effect of acetylcholine was also determined.

Histamine, 2‐pyridylethylamine, 4‐methylhistamine and acetylcholine, but not dimaprit, produced a concentration‐related contractile response in human isolated myometrial strips. Histamine also produced a further contraction in human isolated myometrial strips precontracted with KCl (55 mm).

The contractile response to histamine was antagonized by the histamine H1‐receptor angatonist, clemizole (0.1 μm) but was potentiated by the histamine H2‐receptor antagonist, ranitidine (10 μm). Clemizole (0.1 nm to 10 nm) competitively antagonized the contractile effect of 2‐pyridylethylamine (– log KB = 10.5 ± 0.5). The concentration‐response curve for acetylcholine was displaced to the right by atropine 0.1 μm.

Atropine (0.1 μm), propranolol (0.1 μm), prazosin (0.1 μm) and indomethacin (1 μm) failed to modify the contractile response to histamine.

In human isolated myometrial strips precontracted with KCl (55 mm), clemizole at 1 μm completely abolished the contractile response to histamine and revealed a concentration‐dependent relaxation. Dimaprit alone and 4‐methylhistamine (in the presence of clemizole), produced concentration‐related relaxation with a magnitude similar to that in response to histamine. The relaxant response to dimaprit was antagonized by ranitidine.

6 It is concluded that human isolated uterine strips possess histamine H1‐ and H2‐receptors: the former mediating contraction and the latter relaxation. The predominant response to histamine in this tissue is contraction.
Millimolar amiloride concentrations block K conductance in proximal tubular cells
Authors: Discala Françoise , Hulin Philippe , Belachgar Fouzia , Planelles Gabrielle , Edelman Aleksander , Anagnostopoulos Takis
Published: July 2012

Amiloride, applied at millimolar concentrations, results in the blockade of K+ conductance in amphibian proximal convoluted cells (PCT), fused into giant cells.

Amiloride results directly in a blockade of K+ conductance that is not related to inhibition of the Na+‐H+ antiport, which would lower intracellular pH, adversely affecting K+ conductance. On the contrary, high amiloride concentrations promote entry of this lipophilic base in the cell, leading to higher cell pH.

Under voltage clamp conditions, control vs. amiloride, current‐voltage curves from PCT fused giant cells intersect at −86.2 ± 3.4 mV, a value close to the equilibrium potential for potassium.

Hexamethylene amiloride, 10−5 m, irreversibly depolarizes the membrane potential.

Barium decreased by 50% the initial slope of realkalinization, following removal of a solution containing NH4Cl, as did amiloride. In addition, these blockers reduced membrane conductance by 40%, suggesting that a fraction of the amiloride‐suppressible NH4+ efflux may be conductive.

6 Amiloride does not directly inhibit the Na+‐K+, ATPase in our preparation, contrary to the prevalent belief.

7 In vivo studies show that amiloride interferes with an apical K+ conductance but it does not alter basolateral K+ conductance.
5‐Hydroxytryptamine (5‐HT) mediates potent relaxation in the sheep isolated pulmonary vein via activation of 5‐HT4 receptors
Authors: Cocks T.M. , Arnold P.J.
Published: July 2012

We investigated the potent 5‐hydroxytryptamine (5‐HT)‐mediated vasorelaxation of the sheep pulmonary vein. Here we present evidence that this response is due to activation of 5‐HT4 receptors.

5‐HT (1–1000 nm) caused concentration‐dependent, maintained relaxations (pEC50 = 8.4 ± 0.1) of isolated rings of sheep pulmonary vein pre‐contracted with endothelin‐1 (3 nm).

The relaxation response to 5‐HT was unaffected by either removal of the endothelium or by inhibition of NO‐synthase by NG‐nitro‐l‐arginine (100 μm).

Ketanserin, methiothepin, methysergide and MDL 72222 at concentrations that selectively block 5‐HT2, 5‐HT1‐like and 5‐HT3 receptors respectively, had no effect on the concentration‐relaxation curve to 5‐HT.

ICS 205–930 (1–10 μm) competitively antagonized the concentration‐relaxation curve to 5‐HT with a pA2 of approximately 6.7.

6 Increasing the concentration of ICS 205–930 from 10 to 30 μm did not cause a further rightward shift of the 5‐HT concentration‐relaxation curve. The pEC50 of 6.50 for 5‐HT in the presence of ICS 205–930 (30 μm) was taken as an estimate of the affinity of 5‐HT for 5‐HT1‐like receptors since methiothepin (10 nm) unmasked further competitive inhibition of 5‐HT in the presence of this concentration of ICS 205–930.

7 Other 5‐HT agonists including 5‐carboxamidotryptamine (5‐CT), α‐methyl‐5‐HT and BIMU 8 (but not 2‐methyl‐5‐HT) also relaxed the pulmonary vein. The response to 5‐CT was inhibited by methiothepin (10 nm) and methysergide (100 nm) but unaffected by ICS 205–930 (30 μm), whilst that to α‐methyl‐5‐HT and BIMU 8 was unaffected by methiothepin (10 nm) but blocked by ICS 205–930 (estimated pKB values of 6.4 and 6.9 respectively). Relaxation curves to both 5‐HT and BIMU 8 were unaffected by cocaine (6 μm).

8 In conclusion, these results indicate that the sheep pulmonary vein possesses 5‐HT4 receptors that mediate potent endothelium‐independent relaxation. 5‐HT1‐like relaxant receptors are also present in this tissue but 5‐HT has a lower affinity at these receptors. This preparation may thus provide a robust and sensitive bioassay for future development of selective 5‐HT4 receptor agonists and antagonists.
Differential potentiation of GABAA receptor function by two stereoisomers of diimidazoquinazoline analogues
Authors: Im Haesook K. , Im Wha Bin , Pregenzer Jeff F. , Petke James D. , Hamilton Beverly J. , Carter Donald B. , VonVoigtlander Philip F. , Hansen Holger C. , Kristiansen Marit
Published: July 2012

U‐84935, diimidazo[1,5‐a;1′,2′‐C]quinazoline,5‐(5‐cyclopropyl‐1,2,4‐oxidiazol‐3yl)‐2,3‐dihydro, is a ligand of high affinity for the benzodiazepine site of the GABAA receptor composed of α1β2γ2 subunits.

The efficacy of its analogues was measured with their ability to potentiate GABA‐mediated Cl− currents in the whole cell configuration of the patch clamp techniques in human kidney cells (A293 cells) expressing the subtype of the GABAA receptor.

The analogues displayed various levels of efficacy including agonists, partial agonists and antagonists without marked changes in their affinity for the receptors.

The major determinant of their efficacy was the spacial configuration of a methyl substituent of the C2 atom of the rigid and planar diimidazoquinazoline ring: U‐90167, containing the methyl substituent projected below the plane of the ring, markedly enhanced the GABA current with a maximal potentiation of 220 ± 25%, while its stereoisomer, U‐90168, marginally increased the GABA response with a maximal potentiation of 45 ± 10%, to which its methyl group appeared to contribute very little.

U‐90167 potentiated the GABA response with an EC50 of 8.1 nm and a Hill coefficient of 1.1 and did not alter the reversal potential for the Cl− current.

6 From computational modelling, the sensitive methyl group of U‐90167 could be assigned to the general region for the 5‐phenyl group of diazepam. The diimidazoquinazoline, because of its rigid and plantar ring structure, may be useful to define further the out‐of‐plane region responsible for agonistic activity and to pinpoint other areas pivotal to the functionality of benzodiazepine ligands.
Inhibition of neurogenic plasma exudation in guinea‐pig airways by CP‐96,345, a new non‐peptide NK1 receptor antagonist
Authors: Lei Yu‐Hong , Barnes Peter J. , Rogers Duncan F.
Published: July 2012

A new non‐peptide tachykinin antagonist, CP‐96,345, inhibited airway plasma exudation induced in guinea‐pigs by i.v. substance P in a dose‐dependent manner with dose‐ratios in the main bronchi of 5 at 1 nmol kg−1 and 19 at 100 nmol kg−1. At 100 nmol kg−1, CP‐96,345 completely inhibited plasma exudation induced by either electrical stimulation of the cervical vagus nerves or i.v. capsaicin, indicating inhibition of the effects of endogenous tachykinins, but did not inhibit the bronchoconstrictor response to neurokinin A, suggesting selectivity for NK1 receptors. CP‐96,345 may be useful in examining the role of endogenous tachykinins in vivo.
Increase in vascular permeability produced in rat airways by PAF: potentiation by adrenalectomy
Authors: Boschetto Piera , Musajo Francesco G. , Tognetto Laura , Boscaro Marco , Mapp Cristina E. , Barnes Peter J. , Fabbri Leonardo M.
Published: July 2012

The effect of bilateral adrenalectomy on the sensitivity of blood vessels in rat airways to mediators that increase vascular permeability was examined.

An increase in vascular permeability was induced by intravenous platelet activating factor (PAF, 50, 100, 500, 1000 ng kg−1) and measured by quantifying the extravasation of Evans blue dye.

PAF consistently increased the amount of Evans blue extravasation in the larynx, trachea, main bronchi and intrapulmonary airways in sham‐operated rats.

The magnitude of this extravasation was significantly greater in the larynx (P < 0.05), trachea (P < 0.05) and main bronchi (P < 0.05) of the adrenalectomized rats than it was in these tissues of the sham‐operated rats.

When adrenalectomized rats were given subcutaneous dexamethasone (0.2 mg kg−1 4 h before PAF) the amount of plasma extravasation produced by PAF was decreased to the level of the sham‐operated rats.

We conclude that adrenalectomy potentiates the increase in airway vascular permeability induced by PAF in rats and that this effect may be due to the depletion of endogenous corticosteroids.
Extracellular ATP and UTP exert similar effects on rat isolated hepatocytes
Authors: Keppens Stefaan , Vandekerckhove Ann , DE Wulf Henri
Published: July 2012

Extracellular UTP and ATP show obvious similarities in their control of several metabolic functions of rat isolated hepatocytes.

They have a similar time‐course and concentration‐dependency for the activation of glycogen phosphorylase, the generation of inositol trisphosphate (IP3), the inhibition of glycogen synthase and the lowering of adenosine 3′: 5′‐cyclic monophosphate (cyclic AMP) levels.

There is a similar synergism of the nucleotides with glucagon in activating phosphorylase.

They undergo a similar inhibition by phorbol myristic acid of their glycogenolytic effect.

The ATP and UTP effect on IP3 levels are not additive.

It is tentatively concluded that UTP and ATP use a common receptor.
The actions of endothelins−1 and −3 on the vascular and capsular smooth muscle of the isolated blood perfused spleen of the dog
Authors: Withrington P.G. , Ansari N. , Croxton R. , DE Nucci G. , Vane J.R.
Published: July 2012

Endothelin‐1 (ET‐1), endothelin‐3 (ET‐3) and noradrenaline (NA) were administered as intra‐arterial bolus injections into the isolated, blood‐perfused spleen of the dog to assess agonist properties and relative molar potencies on the vascular and capsular smooth muscle.

An initial small vasodilatation was observed occasionally at low doses (1.0–10 pmol) of ET‐1.

ET‐1, ET‐3 and NA all caused graded increases in splenic arterial vascular resistance. The molar ED50 for the splenic vasoconstrictor response to ET‐1 was significantly less (P < 0.001) than that to ET‐3; both peptides were significantly more potent as vasoconstrictor agents than NA. The maximum increase in splenic arterial vascular resistance was not significantly different for either ET‐1, ET‐3 or NA.

The time course of the splenic vasoconstrictor response to ET‐1 was significantly (P < 0.01) longer than that to equieffective doses of ET‐3 or NA.

The splenic vasoconstrictor responses to ET‐1 and ET‐3 were accompanied by reductions in spleen volume. The rank order of molar potency in causing splenic capsular contraction was ET‐1 > ET‐3 > NA. The maximum reduction in splenic volume was significantly greater for NA than for either ET‐1 or ET‐3. The two peptides (ET‐1, ET‐3) were equiefficacious in contracting splenic capsular smooth muscle.

The high molar potency of ET‐1 as a splenic arterial vasoconstrictor, over 1,700 times more potent than NA, suggests that it may play an important local role in the control of splenic haemodynamics.
Comparison of the actions of acetylcholine and BRL 38227 in the guinea‐pig coronary artery
Authors: Eckman D.M. , Frankovich J.D. , Keef K.D.
Published: July 2012

The contractile and electrical responses to acetylcholine (ACh) in isolated segments of guinea‐pig and rabbit coronary arteries were compared to those of the putative adenosine 5′‐triphosphate (ATP)‐dependent K+ channel opener, BRL 38227.

Both ACh and BRL 38227 produced concentration‐dependent relaxation of vessel segments contracted with the H1‐receptor agonist, 2‐(2‐aminoethyl)pyridine.

An IC90 of either vasodilator also produced 17–20 mV of hyperpolarization of the guinea‐pig coronary artery.

Glibenclamide (1–35 μm) depolarized the guinea‐pig coronary artery by 8–12 mV and antagonized BRL 38227‐ but not ACh‐induced relaxation and hyperpolarization.

In the guinea‐pig coronary artery, the K+ channel blockers phencyclidine (PCP, 100 μm), tetraethylammonium (TEA, 10 mm) and scorpion venom (8.7 μg ml−1) all significantly reduced ACh‐induced relaxation and hyperpolarization whereas only PCP was an effective antagonist of both relaxation and hyperpolarization with BRL 38227.

Similar effects of glibenclamide and scorpion venom on ACh‐ and BRL 38227‐induced relaxation were observed in the rabbit coronary artery.

Apamin (3.5 μm) was without effect on either the ACh‐ or BRL 38227‐induced relaxation in the guinea‐pig coronary artery.

In conclusion, the actions of BRL 38227 in coronary artery are compatible with its proposed effects on ATP‐dependent K+ channels. In contrast, the results with ACh suggest that some step between the initial binding of ACh to endothelial muscarinic receptors and the final relaxation of the smooth muscle depends upon the opening of Ca2+‐activated K+ channels.
The involvement of potassium channels in the action of ciclazindol in rat portal vein
Authors: Noack Th. , Edwards G. , Deitmer P. , Greengrass P. , Morita T. , Andersson P.‐O. , Criddle D. , Wyllie M. G. , Weston A.H.
Published: July 2012

In whole portal veins, ciclazindol (0.3–10 μm) increased the amplitude and duration, but decreased the frequency of spontaneous contractions. Glibenclamide (0.3–10 μm) produced a small increase in contraction amplitude and duration with a small reduction in contraction frequency.

In whole portal veins, ciclazindol (1–10 μm) antagonized the relaxant effects of BRL 38227 in a non‐competitive manner. Under identical conditions, the effects of glibenclamide (0.3–10 μm) appeared to be competitive.

In whole portal veins loaded with 42K, ciclazindol itself (up to 3 μm) had no detectable effect on basal 42K exchange. However, the increase in 42K efflux produced by BRL 38227 (5 μm) was antagonized by ciclazindol (3 μm). Similar effects were produced by glibenclamide (up to 3 μm).

In freshly‐isolated portal vein cells examined by the whole‐cell voltage‐clamp technique, ciclazindol (1–100 μm) inhibited the slowly‐activating and inactivating transient outward current (ITO) which could be generated at potentials more positive than −30 mV. In addition ciclazindol (1–10 μm) inhibited the non‐inactivating K‐current (IKCO) induced by BRL 38227 (10 μm).

In freshly‐isolated portal vein cells under current‐clamp conditions, the hyperpolarization produced by BRL 38227 (10 μm) was reversed by ciclazindol (1–10 μm).

In porcine brain membrane fragments, glibenclamide (0.65 nm) displaced 50% of the binding of [3H]‐glibenclamide whereas ciclazindol (up to 10 μm) had no effect.

It is concluded that ciclazindol is a K‐channel blocker. Its action is not selective for the channel(s) which carry IKCO but also extends to those which carry ITO. Its inability to displace [3H]‐glibenclamide from porcine brain fragments may indicate that antagonism of BRL 38227 by ciclazindol in smooth muscle is exerted at a site different from that of glibenclamide.
Manifestations of acute opiate withdrawal contracture in rabbit jejunum after μ‐, κ‐ and δ‐receptor agonist exposure
Authors: Valeri Pacifico , Morrone Luigi A. , Romanelli Luca
Published: July 2012

Following a 5 min in vitro exposure to morphine (1.3 × 10−7 m), U‐50,488H (2.5 × 10−8 m) and deltorphin (1.6 × 10−8 − 6.5 × 10−9 m), the rabbit isolated jejunum exhibited a precipitated contracture after the addition of naloxone (2.75 × 10−7 m).

The precipitated responses to U‐50,488H and deltorphin but not to morphine were reproducible in the same tissue.

The precipitated contractures were blocked completely by tetrodotoxin (3 × 10−7 m), partially by atropine (1.5 × 10−7 m) and not affected by hexamethonium (1.4 × 10−5 m).

Naloxone administration (2.75 × 10−7 m) before the agonist prevented the development of the adaptive response to morphine and U‐50,488H but not to deltorphin.

The selective antagonists norbinaltorphimine (2.7 × 10−8 − 2.7 × 10−9 m) and naltrindole (1.1 × 10−7 m) prevented the adaptive response development only to the respective agonists.

The opioid agonists partially inhibited the spontaneous activity of the tissue. This study has shown that independent activation of μ‐, κ‐ and δ‐opioid receptors can induce dependence in this isolated tissue. Rabbit jejunum is a suitable tissue for studying the acute effects of opioids on the adaptative processes determined by their administration.
Mechanism of the vasodilator action of calcitonin gene‐related peptide in conscious rats
Authors: Abdelrahman Aly , Wang Yong‐Xiang , Chang Sylvia Diana , Pang Catherine C.Y.
Published: July 2012

The aim of this study was to investigate whether the hypotensive effect of rat α‐calcitonin gene‐related peptide (αCGRP) in conscious rats is mediated by endothelium‐derived nitric oxide (NO) or the opening of adenosine 5′‐triphosphate (ATP)‐sensitive potassium (KATP) channels.

Dose‐mean arterial pressure (MAP)‐response curves of αCGRP were examined in the presence of vehicle, phenylephrine, KATP channel antagonist glibenclamide or NO synthase inhibitors, NG‐nitro‐l‐arginine methyl ester (l‐NAME) and NG‐nitro‐d‐arginine methyl ester (d‐NAME). Dose‐MAP‐response curves for sodium nitroprusside were also constructed in the presence and absence of l‐NAME and d‐NAME.

αCGRP and nitroprusside produced dose‐dependent reductions in MAP which were potentiated by phenylephrine. Both l‐NAME and d‐NAME attenuated the depressor response to αCGRP but not nitroprusside.

Dose‐MAP‐response curves for pinacidil, a KATP‐channel activator, were also examined in the presence of glibenclamide or vehicle. Glibenclamide attenuated pinacidil‐ but not αCGRP‐induced reductions in MAP.

It is concluded that the hypotensive effects of αCGRP are partially mediated via endothelium‐derived NO but not via the opening of KATP channels.
Studies on curare‐like action of 2,2′,2″‐tripyridine in the mouse phrenic nerve‐diaphragm
Authors: Lin‐Shiau S.Y. , Hsu K.S. , Fu W.M.
Published: July 2012

The curare‐like action of 2,2′,2″‐tripyridine (a synthetic by‐product of the herbicide, paraquat) was studied in mouse phrenic nerve‐diaphragm preparation. The inhibition by 2,2′,2″‐tripyridine of nerve‐evoked twitches was dependent on the concentration, ranging from 1 to 100 μm, which had no significant effect on the twitch amplitudes evoked by direct muscle stimulation.

The twitch inhibition by 2,2′,2″‐tripyridine was reversible and could be antagonized by anticholinesterase agents such as neostigmine, physostigmine as well as ecothiophate.

Pretreatment with either 0.7 μm (+)‐tubocurarine or 2.2 μm succinylcholine shifted the concentration‐inhibition curve of 2,2′,2″‐tripyridine to the left.

2,2′2″‐Tripyridine inhibited not only acetylcholine‐induced contracture of the denervated mouse diaphragm but also that of the chick biventer cervicis muscle. Like (+)‐tubocurarine, 2,2′,2″‐tripyridine protected the twitches from the inhibition by α‐bungarotoxin and also specifically inhibited the binding of [125I]‐α‐bungarotoxin to the mouse diaphragm. All of these findings indicate that 2,2′,2″‐tripyridine possesses curare‐like action and inhibits the muscle contractions through binding to postsynaptic acetylcholine receptors.

The postsynaptic inhibition exhibited by 2,2′,2″‐tripyridine was also implicated in the tetanic fade, a decrease in the amplitude of miniature endplate potential (m.e.p.p.) and endplate potential (e.p.p.).

The clinical implication of these findings is that 2,2′,2″‐tripyridine may be involved in the cause of respiratory failure in paraquat‐intoxicated workers since 2,2′,2″‐tripyridine is a by‐product of paraquat synthesis.
The effect of pertussis toxin on β‐adrenoceptor responses in isolated cardiac myocytes from noradrenaline‐treated guinea‐pigs and patients with cardiac failure
Authors: Brown L.A. , Harding S.E.
Published: July 2012

A decreased responsiveness to the positive inotropic effects of β‐adrenoceptor agonists is a characteristic of human heart failure. We have investigated the involvement of inhibitory guanine nucleotide binding proteins (G‐proteins) in this process using pertussis toxin treatment of isolated cardiac myocytes.

Myocytes isolated from failing human myocardium had a reduced maximum contractile response to isoprenaline relative to that for maximally stimulating concentrations of calcium, giving an isoprenaline/calcium ratio of 0.71 ± 0.06 (n = 7 patients). This was significantly lower than in myocytes from non‐failing myocardium, where the isoprenaline/calcium ratio was 1.16 ± 0.07 (n = 6, P < 0.001). Responses to high calcium were unchanged.

Myocytes were treated with pertussis toxin for 3–5 h at 35°C. Successful inactivation of inhibitory G‐proteins by pertussis toxin treatment was indicated by a loss of responsiveness to 10 μm adenosine (in the presence of submaximal isoprenaline).

Following pertussis toxin treatment of the myocytes from failing human heart the isoprenaline/calcium ratio increased to 1.43 ± 0.27 (n = 7, P < 0.05). Pertussis toxin treatment had no effect upon the maximum calcium contraction. The isoprenaline/calcium ratio in myocytes from non‐failing human ventricle was not affected by the toxin treatment (n = 3). These observations support the hypothesis that increased inhibitory G‐protein levels or activities contribute to β‐adrenoceptor desensitization in human heart failure.

β‐Adrenoceptor desensitization in human heart failure is thought to be secondary to raised noradrenaline levels in these patients. Experiments were repeated on myocytes isolated from hearts of guinea‐pigs which had been chronically infused with noradrenaline. The isoprenaline/calcium ratio of these myocytes was reduced below that of myocytes from sham‐operated animals (0.65 ± 0.04, n = 6 compared with 0.88 ± 0.02, n = 7, P < 0.001).

Pertussis toxin treatment (2 h at 35°C) increased the isoprenaline/calcium ratio to 1.02 ± 0.02 (n ≅ 6, P < 0.01) in myocytes from noradrenaline‐treated guinea‐pigs. This effect of pertussis toxin treatment was not seen in myocytes from sham‐operated guinea‐pig hearts.

Incubation at 35°C for similar periods in the absence of pertussis toxin also restored the isoprenaline/calcium ratio towards normal in the myocytes from both failing human and noradrenaline‐treated guinea‐pig hearts, although the effect was significantly smaller than that produced by the toxin. Myocytes kept at room temperature (22°C) showed no such evidence of resensitization over periods up to 6 h.

These observations are consistent with the hypothesis that raised catecholamine levels result in increased inhibitory G‐protein levels and functional β‐adrenoceptor desensitization in heart failure.
FR 113680: a novel tripeptide substance P antagonist with NK1 receptor selectivity
Authors: Morimoto Hiroshi , Murai Masako , Maeda Yasue , Hagiwara Daijiro , Miyake Hiroshi , Matsuo Masaaki , Fujii Takashi
Published: July 2012

We have discovered a novel tripeptide substance P (SP) antagonist, FR 113680 [Nα‐[Nα‐(Nα‐acetyl‐l‐threonyl)‐N′‐formyl‐d‐tryptophyl]‐N‐methyl‐N‐phenylmethyl‐l‐phenylalaninamide]. In binding experiments, FR 113680 inhibited [3H]‐SP binding to guinea‐pig lung membranes (NK1) in a competitive manner but had not effect on [3H]‐SP binding to rat cerebral cortical membranes (NK1), [3H]‐neurokinin A ([3H]‐NKA) binding to rat duodenum smooth muscle membranes (NK2) and [3H]‐eledoisin (Ele) binding to rat cerebral cortical membranes (NK3).

In bioassay experiments, FR 113680 dose‐dependently inhibited SP‐induced guinea‐pig ileum contraction (NK1), but did not inhibit either NKA‐induced rat vas deferens contraction (NK2) or neurokinin B (NKB)‐induced contraction of rat portal vein (NK3). According to Schild plot analysis, the inhibitory effect of FR 113680 on SP‐induced guinea‐pig ileum contraction is competitive and the pA2 value is 7.53.

The inactivity of FR 113680 on NK1 receptors in rat compared to guinea‐pig may represent species‐specific forms of the NK1 receptor.

These findings suggest that FR 113680 interacts selectively with the NK1 neurokinin receptor.
Modulation of vascular tone by endothelin‐1: role of preload, endothelial integrity and concentration of endothelin‐1
Authors: Mehta J.L. , Lawson D.L. , Yang B.C. , Mehta P. , Nichols W.W.
Published: July 2012

Endothelin‐1 (ET‐1) has been shown to exert both arterial relaxant and constrictor effects. To examine the mechanisms of these divergent effects, rat aortic rings were suspended in an organ bath (baseline preload, 5 g) and exposed to ET‐1 (10−11 to 10−7 m). ET‐1 contracted these rings in a concentration‐dependent fashion.

When aortic rings were contracted with noradrenaline (NA) to 1 g of tension, ET‐1 caused further contraction of these rings. In rings precontracted to 2 to 4 g of tension, low concentrations of ET‐1 (10−11 to 10−9 m) caused a significant relaxation, but high concentrations (≥5× 10−9 m) caused a marked contraction, indicating both relaxant and contractile effects of ET‐1 depending on the preload and ET‐1 concentration.

To determine the mechanism of ET‐1‐induced relaxation, aortic rings were pretreated with the cyclo‐oxygenase inhibitor indomethacin, NG‐monomethyl‐l‐arginine (l‐NMMA) an inihibitor of synthesis of endothelium‐derived relaxing factor (EDRF), or oxyhaemoglobin (Hb) which decreases the activity of EDRF, prior to their exposure to ET‐1. Both indomethacin and l‐NMMA markedly (P < 0.01) attenuated ET‐1‐induced relaxation, whereas Hb totally abolished it. Removal of the endothelium from aortic rings also abolished ET‐1‐mediated relaxation.

The relaxant effect of ET‐1 in NA‐precontracted rings was associated with marked accumulation of guanosine 3′:5′‐cyclic monophosphate (cyclic GMP), whereas ET‐1‐induced contraction of quiescent rings was not.

In manually stretched rings (4 g of tension), ET‐1 caused only concentration‐dependent contraction, but no cyclic GMP accumulation.

Thus, ET‐1 contracts rat aortic rings with intact endothelium and those which are passively stretched. However, stimulation of rat aortic rings with NA to modest tension alters the contractile effect of ET‐1 to a potent relaxant effect. The ET‐1‐mediated relaxation in this setting appears to be endothelium‐dependent and is related to release of both cyclo‐oxygenase products and EDRF.
Opposing roles for 5‐HT1B and 5‐HT3 receptors in the control of 5‐HT release in rat hippocampus in vivo
Authors: Martin Keith F. , Hannon Serina , Phillips Ian , Heal David J.
Published: July 2012

Intracerebral microdialysis was used to determine whether 5‐hydroxytryptamine (5‐HT) release in the ventral hippocampus of rats anaesthetized with chloral hydrate was modulated by 5‐HT3 receptors.

It was confirmed that 5‐methoxy‐3‐(1,2,3,6‐tetrahydro‐4‐pyridinyl)‐1H‐indole (RU 24969), a selective 5‐HT1B receptor agonist, decreased 5‐HT release in a dose‐ and concentration‐related manner when administered i.p. (1 and 5 mg kg−1) or via the dialysis probe (0.1 and 1 μm) respectively. The effect of RU 24969 infusion (1 μm) was attenuated by concurrent infusion of metitepine (10 μm) into the hippocampus.

When infused into the hippocampus for 15 min, the selective 5‐HT3 receptor agonist, 2‐methyl‐5‐hydroxytryptamine (2‐methyl‐5‐HT; 0.1–10 μm) increased dialysate 5‐HT levels in a concentration‐related manner; an effect which was abolished by concurrent infusion of 3‐tropanyl‐3,5‐dichlorobenzoate (1 μm, MDL 72222), a selective 5‐HT3 antagonist.

MDL 72222 had no effects on hippocampal 5‐HT release when administered via the dialysis probe (1 or 10 μm).

The data show that 5‐HT3 and 5‐HT1B receptors have opposing roles in the control of 5‐HT release in the hippocampus, with 5‐HT3 receptors facilitating and 5‐HT1B receptors inhibiting 5‐HT efflux, respectively. They also indicate that the facilitatory 5‐HT3 receptors are not tonically activated.
Effects of a new pteridine derivative on urinary sodium, potassium and magnesium excretion in conscious saline‐loaded rats
Authors: Netzer T. , Ullrich F. , Priewer H. , Majewski M. , Mutschler E.
Published: July 2012

Two recently synthesized pteridine derivatives (RPH 3036; RPH 3038) were tested in conscious saline‐loaded rats and showed natriuretic and antimagnesiuretic properties but hardly reduced potassium excretion.

In the same model a dose‐response curve was performed for RPH 3036. ED50 and Emax values were calculated for the natriuretic (ED50 = 13.4 μmol kg−1; Emax = 1.08 mmol kg−1) and antimagnesiuretic (ED50 = 11.3 μmol kg−1; Emax = − 0.099 mmol kg−1) properties of RPH 3036. There were no significant changes of potassium and calcium excretion.

After a single dose of RPH 3036 (100 μmol kg−1) the time course of electrolyte excretion was analysed over 6 h. RPH 3036 did not show any significant effects on renal potassium and calcium excretion whereas a pronounced decrease (P < 0.01) in renal magnesium excretion was evident during the 6 h. A moderate increase of sodium excretion was observed only after 3, 5 and 6 h.

A selective reduction of magnesium secretion in the late distal tubule and collecting duct was proposed as a possible mechanism of action of RPH 3036. This would explain the fast onset of action as well as the lack of antikaliuretic and anticalciuretic effects. The high selectivity of RPH 3036 makes it potentially valuable for the future investigation of renal magnesium transport.
Evidence that the apparent complexity of receptor antagonism by angiotensin II analogues is due to a reversible and syntopic action
Authors: Liu Y.J. , Shankley N.P. , Welsh N.J. , Black J.W.
Published: July 2012

The interactions between angiotensin II (AII), two non‐peptide antagonists DuP 753 and IMI, and eight peptide analogues of AII were investigated on the rabbit isolated aorta assay. DuP 753 and IMI behaved as simple competitive antagonists (pKB values 8.4 and 6.8, respectively). To different degrees, all the AII‐peptide analogue interactions failed to meet the basic criteria for simple competition. In addition to rightward shift, the most significant feature was a concentration‐dependent saturable depression of the upper asymptote of the AII concentration‐effect curves.

‘Washout’ and combined dose‐ratio analysis experiments, in which DuP 753 was used as a reference antagonist, indicated that the profile of peptide antagonism was solely due to a reversible and syntopic action at the AII receptor.

By use of an operational model of agonism (Black & Leff, 1983) as a starting point, it was possible to account for the data with a new model which describes reversible receptor occupancy and occupied receptor‐determined, saturable reduction in the efficacy of AII. Model‐fitting gave estimates of pKB values for the peptide analogues and agonist affinity and efficacy parameters for AII.

The model was successfully tested by applying it to qualitatively similar results obtained in a cross‐tissue analysis on guinea‐pig aorta, ileum and stomach.

A ‘molecular’ interpretation of the efficacy changes, based on the concepts of receptor internalisation and expression, is offered.
Involvement of substance P present in primary afferent neurones in modulation of cutaneous blood flow in the instep of rat hind paw
Authors: Yonehara Norifumi , Chen Ji‐Qiang , Imai Yasuo , Inoki Reizo
Published: July 2012

The participation of small‐diameter afferent fibres in the microcirculatory haemodynamics of cutaneous tissue was examined by studies on the effects of antidromic stimulation of primary afferent neurones on cutaneous blood flow (CBF) and tachykinin release into the subcutaneous space in the instep of the hind paw of rats.

Antidromic stimulation of the sectioned sciatic nerve induced a biphasic flow response, an initial transient decrease followed by an increase, with no alteration in the blood pressure.

Neither phase was affected by pretreatment with phentolamine (0.1 mg kg−1, i.a.), propranolol (0.5 mg kg−1, i.a.), atropine (0.5 mg kg−1, i.a.), methysergide (0.5 mg kg−1, i.a.) or mepyramine (10 mg kg−1, i.a.) plus cimetidine (10 mg kg−1, i.a.), but both were significantly inhibited by pretreatment with capsaicin (50 mg kg−1, s.c).

Spantide (1–2 μmol kg−1, i.a.), a substance P (SP) antagonist, reduced the basal CBF, and also inhibited both phases of the biphasic flow response evoked by antidromic stimulation of the sectioned sciatic nerve.

Intra‐arterial infusion of SP (0.5 μmol kg−1, i.a.) induced a biphasic flow response similar to that elicited by antidromic stimulation of the sectioned sciatic nerve.

Antidromic stimulation of the sectioned sciatic nerve caused a marked increase in SP release into the subcutaneous perfusate of the instep of the rat hind paw, but no detectable increase in neurokinin A release.

We suggest that SP and its receptors are mainly responsible for the vascular response induced by stimulation of the sectioned sciatic nerve, and that small‐diameter afferent fibres containing SP tonically regulate vascular tone in cutaneous microvessels.
Platelet activating factor and systemic anaphylaxis in Nippostrongylus brasiliensis‐sensitized rats: differential effects of PAF antagonists
Authors: Mathison Ronald , Davison J.S. , Befus A. Dean
Published: July 2012

The effects of two platelet‐activating factor (PAF) antagonists, WEB 2086 and BN 52021, in reducing the changes in extravasation (Evans blue technique) and blood flow (radiolabelled microsphere method) to various organs and tissues following anaphylactic shock in the Nippostrongylus brasiliensis‐sensitized rat were investigated.

Both antagonists attenuated anaphylaxis‐induced increases in plasma protein leak in the trachea, stomach and small intestine, although they did not block extravasation in the colon and kidneys.

Anaphylaxis‐induced decreases in blood flow to the adrenals were effectively antagonized by WEB 2086, although this antagonist did not reverse blood flow decreases to any other tissues. BN 52021, on the other hand, did not alter anaphylaxis‐induced decreases in blood flow to the adrenals, but effectively prevented dramatic decreases in blood flow to the large and small bowel and spleen.

Anaphylactic shock produced marked reduction in blood pressure that was partly reversed by WEB 2086, whereas BN 52021 effectively blocked the decreases in cardiac output.

Thus, PAF is responsible for some of the haemodynamic and extravasation of protein changes associated with systemic anaphylaxis in the rat, although the differential inhibition observed with the two antagonists suggests that PAF alters vascular responsiveness through different mechanisms in selected tissues.
The role of CD 18 in IL‐8 induced dermal and synovial inflammation
Authors: Forrest M.J. , Eiermann G.J. , Meurer R. , Walakovits L.A. , MacIntyre D.E.
Published: July 2012

The intradermal administration of endothelial IL‐8 (IL‐81–77) or monocyte derived IL‐8 (IL‐81–72) to rabbits produced a concentration‐dependent increase in plasma extravasation and an accumulation of polymorphonuclear leukocytes (PMNs) when measured over a 3 h time period. When plasma extravasation and PMN accumulation were measured over a 30 min time period no significant increases in PMN accumulation or plasma extravasation were observed in response to IL‐8 alone. However, under these conditions, the addition of prostaglandin E2 (100 pmol) produced a significant potentiation of IL‐8‐induced plasma extravasation. There was no significant difference between the biological activities of IL‐8177 and IL‐81–72.

Plasma extravasation and PMN accumulation induced by IL‐8 were inhibited in rabbits pretreated with the monoclonal antibody designated IB4 (1 mg kg−1, i.v.) directed against the common β chain (CD 18) of the leukocyte integrins.

The intra‐articular administration to rabbits of IL‐81–77 (1 nmol) resulted 24 h later in the appearance of a mixed population of leukocytes (PMNs and mononuclear cells) in synovial lavage fluid. Biochemical analyses revealed the presence of an increased level of sulphated proteoglycans (sPG) and of the metalloproteinase stromelysin. Pretreatment of rabbits with IB4 (3 mg kg−1, i.v.) inhibited the accumulation of PMNs but had no effect on the mononuclear infiltrate nor on the levels of sPG or stromelysin.

The intradermal or intra‐articular injection of E. coli‐derived endotoxin induced similar inflammatory changes to those observed with IL‐8. The possibility that the biological activities of IL‐8 were attributable to minor contamination with endotoxin is unlikely for two reasons. Firstly, biological effects of endotoxin were observed at levels greater than that contained in the IL‐8 preparation. Secondly, reduction of the endotoxin content of the IL‐8 preparation by a factor of 10 did not produce a concomitant reduction in the observed biological activity of the IL‐8.