bluuebunny/crossref_metadata_2025 huggingface dataset:
Pharmacological effects of isopolar phosphonate analogues of ATP on P2‐purinoceptors in guinea‐pig taenia coli and urinary bladder
Authors: Cusack Noel J. , Hourani Susanna M.O. , Loizou George D. , Welford Laurence A.
Published: July 2012

Isopolar methylene phosphonate analogues of adenosine triphosphate (ATP) were synthesized and tested on the guinea‐pig isolated taenia coli (where ATP causes relaxation) and urinary bladder (where ATP causes contraction), to see if restoration of the electronegativity of the methylene linkage would enhance pharmacological potency. The compounds used were the dichloromethylene and difluoromethylene analogues of adenosine 5′‐(β,γ‐methylene)triphosphonate (AMP‐PCP), l‐adenosine 5′‐(β,γ‐methylene)triphosphonate (l‐AMP‐PCP) and 2‐methylthioadenosine 5′‐(β,γ‐methylene)‐triphosphonate (2‐methylthio‐AMP‐PCP).

The order of potency of the analogues depended on the tissue, and was independent of the nature of the purine or ribose moieties. None of the analogues was degraded by ectonucleotidases on either tissue.

In the taenia coli the order of potency for relaxation was difluoromethylene > dichloromethylene > methylene, and this reflected the order of electronegativity of the analogues. The isopolar analogues of l‐AMP‐PCP were inactive in the taenia coli.

In the bladder the order of potency for contraction was difluoromethylene > methylene > dichloromethylene, suggesting that electronegativity is of lesser importance here. The isopolar analogues of l‐AMP‐PCP were active in this tissue.

The differences between the two tissues in the order of potency for these non‐degradable analogues supports suggestions that P2‐purinoceptors in the taenia coli (P2Y) are different from those in the bladder (P2X). The isopolar analogues of l‐AMP‐PCP, like l‐AMP‐PCP itself, were selective agonists at the P2X‐purinoceptor.
Increased intestinal formation of Paf in endotoxin‐induced damage in the rat
Authors: Whittle B.J.R. , Boughton‐Smith N.K. , Hutcheson I.R. , Esplugues J.V. , Wallace J.L.
Published: July 2012

Platelet‐activating factor (Paf) has been proposed as a mediator of the gastrointestinal damage in endotoxic shock. The formation of Paf in rat jejunal tissue, determined following extraction and bioassay on rabbit washed platelets has therefore been correlated with the induction of damage following endotoxin administration. Intravenous injection of E. coli endotoxin led to a time‐dependent increase in the jejunal formation of Paf, which after 20 min was twenty fold greater than the control level. There was a significant correlation between elevated Paf release and intestinal hyperaemia and haemorrhage, thus supporting a role for Paf as a mediator of such damage.
Is co‐transmission involved in the excitatory responses of the rat anococcygeus muscle?
Authors: Cunnane T.C. , Muir T.C. , Wardle Kay A.
Published: July 2012

Electrical and mechanical responses to field (transmural) and extrinsic nerve stimulation were recorded simultaneously in the rat anococcygeus muscle. Membrane potential changes recorded intracellularly following either method of stimulation were indistinguishable. Single stimuli usually produced a slow depolarization; trains of pulses produced a fast excitatory junction potential (e.j.p.) initially, followed by a slow depolarization similar to that produced by single pulses. The fast e.j.ps, the slow depolarizations and the accompanying contractions were abolished by the α‐adrenoceptor antagonists, phentolamine (1 × 10−6 m) or prazosin (1 × 10−7 m) and by tetrodotoxin (TTX, 1 × 10−6 m) but unaffected by α, β‐methylene adenosine triphosphate (α, β‐MeATP, 1–10 × 10−6 m), an agent known to desensitize purinoceptors.

Application of noradrenaline (NA, 1 × 10−8‐1 × 10−6 m), by pressure ejection from a micropipette, depolarized the membrane and produced a localized contraction, both of which were abolished by phentolamine (1 × 10−6 m) or prazosin (1 × 10−7 m).

Application of adenosine‐5′‐triphosphate (ATP, 1 × 10−4‐1 × 10−3 m), by pressure ejection from a micropipette, produced a small membrane depolarization and localized contraction which were unaffected by phentolamine (1 × 10−6 m) or prazosin (1 × 10−7 m) but abolished by α, β‐MeATP (1 × 10−6 m).

The results show that, in the rat annococcygeus muscle, (1) field or extrinsic nerve stimulation released only one excitatory transmitter, namely NA, although receptors for both NA and ATP were present on the muscle, (2) α, β‐MeATP was selective for purinoceptors and (3) there was no evidence for excitatory co‐transmission in this tissue.
The effects of external and internal application of disopyramide on the ionic currents of the squid giant axon
Authors: Elliott J.R. , Hendry B.M.
Published: July 2012

The actions of the class I anti‐arrythmic agent, disopyramide, on the ionic currents of the voltage‐clamped squid axon have been investigated, by use of both extra‐axonal and intra‐axonal routes of application.

Extra‐axonal application of 0.1 mm disopyramide produced no significant effects on the membrane currents. External disopyramide at 1.0 mm caused small, poorly reversible inhibition of both sodium and potassium currents. This block was use‐dependent and was enhanced by use of test stimuli to more positive membrane potentials.

Intra‐axonal application of 0.1 mm disopyramide caused a 40% reduction in the first‐pulse sodium current (tonic block) and an additional use‐dependent block. Analysis of first‐pulse currents in terms of the Hodgkin‐Huxley formalism indicated that the block resulted mainly from a reduction in the maximum available sodium conductance (gNa); there were no effects on the voltage dependence of the steady‐state activation and inactivation parameters, m∞ and h∞.

The use‐dependent actions of disopyramide were investigated with a double voltage‐clamp pulse protocol. The significant use‐dependent effects of the drug were a further reduction in gNa and an increase in the time constant of inactivation (∞h).

Disopyramide appears to enter a blocking site in the sodium channel which is only readily accessible from the axoplasmic phase. Partition to the site depends on membrane voltage and on the state of the channel gates. Disopyramide binds at a significant rate to both open and inactivated forms of the sodium channel.
Postjunctional α2‐adrenoceptors mediate venoconstriction in the hindquarters circulation of anaesthetized cats
Authors: Bentley Geoffrey A. , Widdop Robert E.
Published: July 2012

A study was made of the subtypes of postjunctional α‐adrenoceptors which mediate arterial and venous constriction in the hindquarters circulation of anaesthetized cats, as measured by changes in perfusion pressure and vena cava blood flow, respectively.

It was found that, while noradrenaline caused constriction in both the arterial and venous compartments, methoxamine caused only arterial constriction. Clonidine and B‐HT 920 also caused arterial and venous constriction although autodesensitization to both drugs occurred.

The ability of either prazosin or yohimbine to antagonize the constrictor effects of noradrenaline was also examined. It was found that the combination of both antagonist drugs abolished both the arterial and venous constrictor effects of noradrenaline. However, there was a greater prazosin‐resistant response to noradrenaline in the venous compartment as compared with the arterial effects of noradrenaline. Yohimbine caused approximately equal reductions in the effect of noradrenaline in both arteries and veins, which was greater than that observed with prazosin.

These results suggest that, in the cat hindquarters, both α1‐ and α2‐adrenoceptors are present in the arterial circulation, whereas there are mainly α2‐adrenoceptors in the venous circulation.
Inhibitors of prostaglandin dehydrogenase (Ph CL 28A and Ph CK 61A) increase output of prostaglandins from rat isolated lung
Authors: Bakhle Y.S. , Pankhania J.J.
Published: July 2012

Two potent inhibitors of prostaglandin dehydrogenase (PGDH), Ph CL 28A and Ph CK 61A, have been investigated for their effects on prostaglandin catabolism and synthesis in rat isolated lung.

Both CL 28A (0.3 μm) and CK 61A (0.5 and 5 μm) markedly increased the survival of prostaglandin E2 (PGE2) and PGF2α on a single passage through the pulmonary circulation.

Both inhibitors delayed the efflux of 14C following injection of [14C]‐PGE2 through the pulmonary circulation.

Output of PGE2 and PGF2α but not that of 6‐oxo‐PGF1α from exogenous arachidonic acid (AA) was increased by CL 28A.

Output of all three prostaglandins from endogenous AA stimulated by calcium ionophore A23187 was increased by CL 28A.

With CK 61A, output of 6‐oxo‐PGF1α from exogenous AA was not increased but that from endogenous AA was increased by either concentration of this inhibitor.

We conclude that it is possible to increase output of biologically active prostaglandins from lung by preventing their inactivation in situ.

The apparent selectivity of PGI2 synthesis from endogenous AA to potentiation by the inhibitors may have therapeutic possibilities.
α2‐Adrenoceptor blockade prevents cardiac glycoside‐evoked neurotransmitter release from sympathetic nerves in dog saphenous vein
Authors: Powis D.A.
Published: July 2012

The effect of α‐adrenoceptor antagonists upon neurotransmitter release evoked by cardiac glycosides from sympathetic nerve terminals has been investigated in dog saphenous vein.

In rings of saphenous vein preloaded with [3H]‐noradrenaline, acetylstrophanthidin (ACS) caused a concentration‐dependent efflux of 3H (EC50 ca. 4.4 μm) that was attenuated by phentolamine and yohimbine but not by prazosin.

In helical strips of saphenous vein superfused with ACS at EC50 the efflux of 3H‐compounds in general, and of [3H]‐noradrenaline in particular, occurred after a short delay and increased with time to a maximum reached at 75 min. Phentolamine and phenoxybenzamine, but not prazosin reduced the efflux of [3H]‐noradrenaline and of total 3H‐compounds throughout the time‐course of the ACS‐evoked effect.

In helical strips of saphenous vein the glycoside ouabain also caused an increase in [3H]‐noradrenaline and in total 3H‐efflux that was attenuated by phentolamine.

By contrast with the above, in bovine adrenal medullary chromaffin cells, which appear to have no functional α‐adrenoceptors, ACS caused a small, but significant increase in 3H‐efflux which was not prevented by phentolamine.

Phentolamine, at concentrations that attenuate markedly the ouabain‐or ACS‐evoked increase in 3H‐efflux from dog saphenous vein, did not cause significant inhibition of cocaine‐sensitive [3H]‐noradrenaline uptake nor did it reduce the extent of the 3H‐efflux evoked either by tyramine or by reduced extracellular Na+. These findings imply that phentolamine does not affect ACS‐evoked neurotransmitter release by an action on the catecholamine uptake mechanism.

It is concluded that the cardiac glycoside‐evoked increase in neurotransmitter release from noradrenergic nerve terminals of dog saphenous vein is modulated by a mechanism that involves an α2‐adrenoceptor.
Selective inhibition by gossypol of endothelium‐dependent relaxations augments relaxations to glyceryl trinitrate in rabbit coeliac artery
Authors: Alheid Ute , Dudel Christian , Förstermann Ulrich
Published: July 2012

Acetylcholine, substance P, prostaglandin E, and the nitrovasodilator glyceryl trinitrate induced concentration‐dependent relaxations of endothelium‐intact strips of rabbit coeliac artery precontracted with noradrenaline.

Endothelium‐denuded strip preparations contracted to acetylcholine and showed no response to substance P. The relaxant response to prostaglandin E1 was unimpaired after removal of endothelium, whereas the response to glyceryl trinitrate was increased.

A 20 min exposure of endothelium‐intact strips to gossypol, an irreversible inhibitor of the production and/or release of endothelium‐derived relaxing factor, abolished vasodilatation in response to the endothelium‐dependent agents acetylcholine and substance P, did not change relaxations to prostaglandin E1, but significantly enhanced relaxations in response to glyceryl trinitrate.

In view of the assumed common mechanism of action of endothelium‐derived relaxing factor and nitrovasodilators, these results suggest an interference of the two active principles at the level of the vascular smooth muscle cell.
Lack of evidence for increased descending inhibition on the dorsal horn of the rat following periaqueductal grey morphine microinjections
Authors: Dickenson Anthony H. , Le Bars Daniel
Published: July 2012

Recordings were made from 18 neurones in the dorsal horn of the rat, anaesthetized with halothane. All cells received A‐and C‐fibre inputs and responded to innocuous and noxious stimuli applied to their excitatory receptive fields located on the extremity of the ipsilateral hindpaw. Transcutaneous application of suprathreshold (mean 3.2T) 2 ms square‐wave pulses to the centre of the receptive fields resulted in responses to A‐and C‐fibre activation being observed; a mean 32.4 ± 6.0 C‐fibre latency spikes were evoked per stimulus.

A high dose (20 μg) of morphine in 0.5 μl sterile saline, microinjected into the periaqueductal grey matter (PAG) had no effect on the C‐fibre‐evoked activity of thirteen cells (72%) and facilitated 5 neurones (28%). Microinjection sites covered most of the PAG particularly the caudal medioventral zone.

A relatively high dose (6 mg kg−1, i.v.) of systemic morphine chloride, sufficient to elicit the direct spinal action of the opiate, inhibited all 5 cells tested.

We conclude that there is little evidence that the supraspinal action of morphine includes increased descending controls and depression of dorsal horn neurones in the rat.
[Met5]enkephalin acts via δ‐opioid receptors to inhibit pelvic nerve‐evoked contractions of cat distal colon
Authors: Kennedy Charles , Krier Jacob
Published: July 2012

The effects of opioids on the sacral parasympathetic outflow to cat distal colon were studied in vitro using muscle strips orientated in the axis of the longitudinal muscle layer, with pelvic nerves attached. Electrical stimulation of the pelvic nerves evoked contractions that were blocked by atropine (1 × 10−6 m) and tetrodotoxin (3 × 10−7 m).

[d‐Pen2, d‐Pen5]enkephalin and [Met5]‐ and [Leu5]enkephalin caused concentration‐dependent, reversible inhibition of pelvic nerve‐evoked contractions, with IC50 values of 8.3 × 10−10 m, 2.2 × 10−9 m and 2.1 × 10−9 m respectively.

Morphine (1 × 10−7‐1 × 10−5 m) and [d‐Ala2, MePhe4, Gly‐ol5]enkephalin (1 × 10−8‐1 × 10−6 m) and U‐50,488H (1 × 10−8‐1 × 10−6 m) were much less potent as inhibitors than [Met5]‐ or [Leu5]enke‐phalin.

Naloxone (1 × 10−7 m), an antagonist at each of the three opioid receptor types, antagonized the effects of both [Met5]enkephalin and morphine. However, ICI 174,864, a specific δ‐opioid receptor antagonist, antagonised the effects of [Met5]enkephalin only.

The inhibitory actions of [Met5]enkephalin were inversely related to frequency of pelvic nerve stimulation. Also, [Met5]enkephalin at a concentration (3 × 10−9 m) which produced a large inhibition of neurogenic contractions, had no effect on contractions to exogenous acetylcholine. These results suggest a prejunctional site for inhibitory opioid receptors.

In summary, prejunctional inhibitory δ‐opioid receptors are present on the sacral parasympathetic outflow to cat distal colon; κ‐and/or μ‐opioid receptors may also be present, but appear to be of lesser importance.
Renal vascular effects of leukotriene C4 in the isolated perfused kidney of the rat
Authors: Frölich Jürgen C. , Yoshizawa Mamoru
Published: July 2012

The vascular effects of leukotriene C4 (LTC4) were investigated in the isolated perfused kidney of the rat.

LTC4 (6.4 × 10−10 to 3.2 × 10−8 mol kg−1 min−1 given over 5 min) resulted in a prompt, dose‐dependent increase in renal vascular resistance in a recirculating system, which lasted for more than 60 min.

LTC4 was 10 to 20 fold and 1000 to 2000 fold, respectively, less active on a molar basis than noradrenaline and angiotensin II in eliciting renal vasoconstriction.

The vascular response to LTC4 was blocked dose‐dependently by FPL 55712, an antagonist of slow reacting substance of anaphylaxis. OKY 1581, a specific thromboxane synthetase inhibitor, and indomethacin, a cyclo‐oxygenase inhibitor, did not influence the LTC4 response.

LTC4 given in a single‐pass perfusion system resulted in a short lasting response with baseline values for renal vascular resistance reached after 4 min.

These results show that LTC4 is a short acting renal vasoconstrictor with less potency than noradrenaline and angiotensin II. Its pressor effects seem to be mediated by specific leukotriene receptors and independent of cyclo‐oxygenase products. The long‐lasting effect in the recirculating arrangement, in contrast to the single pass system, is compatible with formation of active metabolite(s).
Evidence that 8‐hydroxy‐2‐(n‐dipropylamino)tetralin (8‐OH‐DPAT) is a selective α2‐adrenoceptor antagonist on guinea‐pig submucous neurones
Authors: Crist J. , Surprenant Annmarie
Published: July 2012

Intracellular recordings were made from neurones of the submucous plexus and from submucosal arteriolar smooth muscle of the guinea‐pig ileum for the purpose of examining the actions of 8‐hydroxy‐2‐(n‐dipropylamino)tetralin (8‐OH‐DPAT).

8‐OH‐DPAT (10 nm‐20 μm) had no direct presynaptic or postsynaptic actions on submucous plexus neurones.

Membrane hyperpolarizations induced in neurones by noradrenaline or UK 14304 were competitively antagonized by 8‐OH‐DPAT. For dose‐ratios up to 40, Schild plots were linear with slopes not significantly different from unity; pA2 values for the 8‐OH‐DPAT antagonism of postsynaptic α2‐adrenoceptors were 6.9‐7.2.

The inhibitory synaptic potential, which is due to activation of α2‐adrenoceptors located on submucous plexus neurones, was selectively inhibited by 8‐OH‐DPAT; the IC50 value for inhibition of the inhibitory synaptic potential was 250 nm.

Neuronal hyperpolarizations mediated through activation of δ‐opioid receptors or somatostatin receptors were unaffected by 8‐OH‐DPAT (0.1–1 μm).

The ability of noradrenaline and UK 14304 to inhibit the release of acetylcholine at synapses in the submucous plexus, and to inhibit the release of the transmitter which mediates the excitatory junction potential in the submucosal arteriolar smooth muscle, was also blocked by 8‐OH‐DPAT.

These results suggest that some of the actions of 8‐OH‐DPAT previously ascribed to agonism at 5‐hydroxytryptamine (5‐HT)1 receptors may actually result from blockade of the actions of endogenously released noradrenaline acting on α2‐adrenoceptors.
Increased GABAB receptor function in mouse frontal cortex after repeated administration of antidepressant drugs or electroconvulsive shocks
Authors: Gray Julian A. , Green A. Richard
Published: July 2012

Addition of baclofen to a medium containing slices of mouse frontal cortex inhibited the potassium‐evoked release of 5‐hydroxytryptamine (5‐HT) in a concentration‐dependent manner. The degree of inhibition was increased in frontal cortex tissue taken from animals treated for 14 days with amitriptyline (10 mg kg−1, twice daily) at all concentrations of baclofen tested (10−6 m − 10−4 m).

Administration of either desipramine, mianserin or zimeldine (10 mg kg−1 daily) for 14 days also approximately doubled the degree of inhibition evoked by addition of baclofen (10−5 m) to the medium.

One day of treatment with the antidepressant drugs did not alter the inhibitory effect of baclofen on K+‐evoked 5‐HT release.

Addition of the antidepressant drugs to the medium had no effect on the K+‐evoked release of 5‐HT.

Repeated administration of electroconvulsive shock (5 seizures spread out over 10 days), like amitriptyline, produced a significant enhancement of the baclofen‐induced inhibition of 5‐HT release over the range of baclofen concentrations studied. A single electroconvulsive shock had no effect.

These data suggest that repeated administration of the antidepressant drugs or electroconvulsive shock increases the function of the γ‐aminobutyric acid (GABA)B receptor in the frontal cortex modulating 5‐HT release and are consistent with the finding of increased GABAB receptor number in this region following various antidepressant treatments.
δ‐Opioid receptors mediate inhibition of fast excitatory postsynaptic potentials in cat parasympathetic colonic ganglia
Authors: Kennedy Charles , Krier Jacob
Published: July 2012

The effects of opioids on synaptic transmission in cat sacral parasympathetic colonic ganglia were studied in vitro, using intracellular electrophysiological techniques. Electrical stimulation of the pelvic nerve evoked fast excitatory postsynaptic potentials (e.p.s.ps), which were blocked by hexamethonium and tetrodotoxin.

[d‐Pen2, d‐Pen5] enkephalin and [Met5]enkephalinamide, δ‐opioid receptor agonists, caused concentration‐dependent, reversible depression of fast e.p.s.ps, but had no effect on depolarizations evoked by pressure ejection of the nicotinic agonist 1,1‐dimethyl‐4‐phenyl‐piperazinium. Cell transmembrane potential and membrane input resistance were also unaffected.

U‐50,488H, a κ‐opioid receptor agonist, had a very small depressant action while [d‐Ala2, MePhe4, Gly‐ol5] enkephalin, a μ‐opioid receptor agonist, had no effect on fast e.p.s.p. amplitude. Neither compound affected cell transmembrane potential or membrane input resistance.

The inhibitory actions of [d‐Pen2, d‐Pen5] enkephalin were antagonized by both naloxone, an antagonist at each of the three opioid receptor types, and by ICI 174,864, an antagonist selective for δ‐opioid receptors.

Naloxone and ICI 174,864 both also potentiated fast e.p.s.p. amplitude per se in 50% of cells tested.

It is concluded that exogenous opioids act at presynaptic δ‐opioid receptors to inhibit sacral parasympathetic synaptic transmission in cat colonic ganglia in vitro. Furthermore, the effects of opioid anatagonists alone, suggest that endogenous opioids may also be released by preganglionic nerve stimulation and so regulate the release of acetylcholine in these ganglia.
Positive inotropic effects of histamine in anaesthetized dogs
Authors: Einstein Rosemarie , Mihailidou Anastasia S. , Richardson Desmond P.
Published: July 2012

The cardiovascular effects of histamine were examined in dogs anaesthetized with pentobarbitone

The effect of histamine on heart rate, blood pressure, left ventricular pressure, dP/dtmax and dP/dt: IIT (integrated isometric tension) was compared in the presence and absence of autonomic reflexes and blood pressure control.

In innervated animals with no attempt to control blood pressure, histamine produced dose‐dependent decreases in blood pressure and heart rate and either positive or negative inotropic actions.

When autonomic reflexes were abolished, this variability in inotropic response was reduced and histamine produced a slight positive inotropic response. There was a decrease in blood pressure and a positive chronotropic response to histamine.

When blood pressure was controlled and the cardiac nerves were intact, histamine produced a decrease in heart rate. However, in the denervated animals, there was a slight increase in heart rate.

Inotropic responses to histamine in the blood pressure controlled groups were less variable than when blood pressure was uncontrolled. In all of these animals there was an increase in contractility, the increase being more marked in the denervated group.

The H2‐receptor agonist impromidine produced a positive inotropic action in intact animals with uncontrolled blood pressure.
Capsaicin enhances the non‐adrenergic twitch response of rat vas deferens
Authors: Moritoki Hideki , Iwamoto Takeshi , Kanaya Jun , Ishida Yukio , Ando Kenshi , Kitagawa Kouki
Published: July 2012

Capsaicin (Cap) enhanced the twitch response of the epididymal and prostatic portions of rat vas deferens induced by field stimulation at 0.1 Hz. The effect of Cap was reproducible and showed no desensitization.

Prazosin, and pretreatment with reserpine or Cap did not affect the potentiating effect of Cap, whereas pretreatment with 6‐hydroxydopamine abolished the action of Cap.

Cap tended to attenuate the contractions induced by noradrenaline, tyramine and ATP.

Like Cap, substance K and substance P augmented the twitch response without causing desensitization, but their effects differed somewhat from that of Cap. Calcitonin gene‐related peptide inhibited the twitch response.

These results suggest that Cap enhances a stimulation‐induced, prazosin‐resistant non‐adrenergic twitch response of rat vas deferens through an as yet undefined prejunctional mechanism. This mechanism is possibly mediated by some peptide released in response to Cap from sensory neurones, which in turn acts on sympathetic nerves and increases stimulation‐induced release of a mediator or co‐transmitter responsible for the non‐adrenergic twitch response. However, the possibility that Cap has a direct action on sympathetic nerves cannot be ruled out.
Involvement of β2‐adrenoceptor‐mediated mechanisms in the cardiovascular responses to α1‐ and α2‐adrenoceptor antagonism in conscious, unrestrained, Long Evans and Brattleboro rats
Authors: Gardiner Sheila M. , Bennett Terence
Published: July 2012

Intra‐arterial blood pressures and heart rates were recorded in conscious, unrestrained, Long Evans and Brattleboro rats receiving sequential, continuous administrations of selective α1‐ (prazosin) and α2‐ (idazoxan) adrenoceptor antagonists. The same protocols were also run in the presence of ICI 118551 (a selective antagonist of β2‐adrenoceptors).

Prazosin and idazoxan caused large, but transient, hypotensions in Long Evans and Brattleboro rats. In the continued presence of both drugs there were marked, intermittent, depressor episodes and tachycardias in both strains of rat.

In the presence of low or high doses of ICI 118551 the hypotensive responses to prazosin and idazoxan were markedly reduced in both strains of rat and blood pressures showed little variability, although intermittent tachycardias still occurred.

In adrenal‐demedullated Long Evans rats, the hypotensive responses to prazosin and idazoxan were attenuated and in the presence of both drugs, blood pressure was relatively steady, although intermittent tachycardias still occurred.

In the presence of prazosin and idazoxan, when a depressor episode was not occurring, administration of captopril caused hypotension in Long Evans and Brattleboro rats. In the latter, the reduction in blood pressure was sustained, whereas there was a recovery in blood pressure in Long Evans rats. This recovery was punctuated by depressor episodes, and was abolished by a V1‐receptor antagonist (d(CH2)5DAVP).

Long Evans rats given two primed doses of the non‐selective α‐adrenoceptor antagonist, phentolamine, exhibited variation in blood pressure similar to that seen in the presence of prazosin and idazoxan. As in the latter case, blood pressure variability was inhibited by the β2‐adrenoceptor antagonist, ICI 118551.

Administration of idazoxan into a lateral ventricle in Long Evans rats receiving phenoxybenzamine intravenously did not cause blood pressure instability. However, intravenous administration of idazoxan in the same animals produced intermittent depressor episodes and tachycardias similar to those seen in the presence of prazosin and idazoxan.

The simplest explanation of the results is that β2‐adrenoceptor‐mediated depressor mechanisms contribute to the hypotensive responses to α1‐ and α2‐adrenoceptor antagonism. Furthermore, in the presence of adequate peripheral α1‐ and α2‐adrenoceptor antagonism, blood pressure may be maintained by the renin‐angiotensin system and vasopressin (although it is only when the former system has been antagonized that a clear‐cut pressor action of vasopressin is apparent). Under these conditions, blood pressure maintenance is interrupted by intermittent depressor episodes that are largely due to adrenal medullary activation.
Highly potent and stereoselective effects of the benzoic acid derivative AZ‐DF 265 on pancreatic β‐cells
Authors: Garrino M.G. , Henquin J.C.
Published: July 2012

Mouse islets were used to define the characteristics and study the mechanisms of the stimulation of insulin release by compound AZ‐DF 265, 4‐[[N‐(α‐phenyl‐2‐piperidino‐benzyl) carbamoyl]methyl] benzoic acid, a substituted benzoic acid with an asymmetric carbon atom.

At a non‐stimulatory concentration of glucose (3 mm), (‐)‐AZ‐DF 265 reversibly inhibited 86Rb efflux from islet cells, depolarized the β‐cell membrane, induced electrical activity, stimulated 45Ca efflux, and triggered insulin release. Maximum inhibition of 86Rb efflux occurred at 0.03 μm (‐)‐AZ‐DF 265, whereas the threshold concentration for stimulation of release was 0.1 μm. Omission of extracellular Ca2+ abolished all effects of the drug but the inhibition of 86Rb efflux.

At a stimulatory concentration of glucose (10 mm), (‐)‐AZ‐DF 265 reversibly increased 86Rb efflux, potentiated electrical activity, augmented 45Ca efflux, and increased insulin release. Maximum stimulation of 86Rb efflux and insulin release was obtained with 0.03 μm (‐)‐AZ‐DF 265. Omission of extracellular Ca2+ abolished all effects of the drug.

The potency of (‐)‐AZ‐DF 265 was similar to that of glibenclamide, whereas the (+)‐enantiomer was about 10 times less potent on 86Rb efflux and insulin release.

It is concluded that, like sulphonylureas, compound AZ‐DF 265 decreases K+ permeability of the β‐cell membrane and thereby causes depolarization. This activates voltage‐dependent Ca channels, permits Ca2+ influx and eventually stimulates insulin release. Its stereoselectivity may help to elucidate the mechanisms of K channel blockade and, hence, lead to the design of more potent and specific insulinotropic drugs.
Effects of codeine, morphine and a novel opioid pentapeptide BW443C, on cough, nociception and ventilation in the unanaesthetized guinea‐pig
Authors: Adcock J.J. , Schneider C. , Smith T.W.
Published: July 2012

Antitussive, antinociceptive and respiratory depressant effects of codeine, morphine and H.Tyr.d>‐Arg.Gly.Phe(4‐NO2) Pro.NH2 (compound BW443C) were investigated in unanaesthetized guinea‐pigs. Antagonism of the antitussive and antinociceptive effects was investigated by the use of nalorphine and N‐methylnalorphine. Naloxone was used to antagonize respiratory depression.

Antitussive ED50s (with 95% confidence limits) for inhibition of cough induced by citric acid vapour were for codeine, morphine and BW443C respectively, 9.1(5.8‐15), 1.3(0.7‐2.4) and 1.2(0.6‐2.6) mg kg−1 s.c. and 8.7(4.2‐12), 1.6(1.2‐1.9) and 0.67(0.002‐3.3) mg kg−1, i.v. The antitussive effects of subcutaneous codeine (25 mg kg−1) morphine (8.1 mg kg−1) and BW443C (2.5 mg kg−1) were significantly antagonized by subcutaneous nalorphine (3.0 mg kg−1) and N‐methylnalorphine (3.0 mg kg−1).

In the multiple toe‐pinch test, the antinociceptive ED50s (with 95% confidence limits) of codeine and morphine were 18(16–22) and 2.3(0.4‐4.3) mg kg−1, s.c., respectively. Compound BW443C was ineffective in doses of 2.5 and 10 mg kg−1 s.c., a result consistent with its lacking penetration into the CNS. Subcutaneous nalorphine (3.0 mg kg−1) antagonized the antinociceptive action of codeine (25 mg kg−1) and morphine (8.1 mg kg−1). In contrast, N‐methylnalorphine (3.0 mg kg−1) had no significant effect on the antinociceptive action of codeine and morphine, suggesting lack of penetration of the CNS by N‐methylnalorphine.

At doses near to the i.v. ED50 values for the antitussive activity, morphine (1.5 mg kg−1, i.v.) and codeine (10 mg kg−1, i.v.) caused small but significant depressions of ventilation (7.0 ±2.3% and 16.5 ± 8.4% respectively). Higher doses of morphine (10, 30 and 60 mg kg−1, i.v.) caused further dose‐related depression of ventilation (9.6 ± 5.3%, 22.4 ± 6.2% and 36.2 ± 9.6% respectively) whereas codeine (30 and 60 mg kg−1 i.v.) caused stimulation of ventilation which was marked (191.3 ± 43.9%) at 60 mg kg−1.

Compound BW443C in doses of 1 or 10 mg kg−1, i.v. (approximately equal to, and 10 times the ED50 for antitussive activity) did not cause significant depression of ventilation. Only at higher doses of 30 and 60 mg kg−1, i.v. was there a significant decrease in minute volume (13.1 ±6.8% and 15.9 ± 1.89% respectively). The depression of ventilation caused by either BW443C (60 mg kg−1, i.v.) or morphine (60 mg kg−1, i.v.) was prevented by pretreatment with naloxone (3 mg kg−1, i.v.) administered 15 min before morphine or BW443C.

These results in the guinea‐pig support the hypothesis that the antitussive action of the opiates codeine and morphine and the opioid pentapeptide BW443C do not require penetration of these drugs into the CNS.
A comparison of fast and slow depolarizations evoked by 5‐HT in guinea‐pig coeliac ganglion cells in vitro
Authors: Wallis D.I. , Dun N.J.
Published: July 2012

5‐Hydroxytryptamine (5‐HT) was applied by pressure ejection to coeliac ganglion cells of the guinea‐pig maintained in vitro and responses measured intracellularly.

Cells responded in one of three ways to 5‐HT: by (a) a fast, transient depolarization (43%), (b) a fast transient followed by a slow depolarization (biphasic response, 30%) or (c) a slow sustained depolarization (25%).

Fast depolarizations (response (a) above)) were graded according to the duration of the ejection pulse. Maximal responses had a mean amplitude of 12 ± 0.8 mV, a duration of 6.4 ± 1.0 s, a latency of 0.4 ± 0.1 s, were associated with a fall in membrane input resistance, increased in amplitude by hyperpolarization and probably mediated by an increased conductance to Na and K. The estimated reversal potential was −22.8 ± 2.4 mV (n = 14). The maximal fast response seen in biphasically‐responding cells (b) appeared similar to fast response (a).

Fast depolarizations (a) showed marked tachyphylaxis and were abolished by superfusion of the ganglion with 5‐HT (100 μm). They were reduced in amplitude by tubocurarine (10–100 μm, pIC50 4.4), MDL 72222 (1–5 μm, pIC50 5.8), quipazine (1 μm reduced responses by 65 ± 15%, n = 3), ICS 205–930 (1 μm reduced responses by 64 ± 14%, n = 7) and metoclopramide (10 μm reduced responses by about 45%), but were unaffected by methysergide (up to 1 μm) or hexamethonium (up to 1 mm).

Slow depolarizations (c) varied in amplitude with the duration of the ejection pulse. Maximal responses had a mean amplitude of 6.4 ± 0.7 mV, a duration of 62 ± 6 s, a latency of 3.5 ± 0.8 s and were reduced in amplitude by methysergide (0.1–1 μm, pIC50 6.5) but not by MDL 72222 (1 μm). The maximal slow component in biphasically‐responding cells (b) was similar in amplitude and duration to slow response (c), was partially blocked by methysergide (1–5 μm) in 4 of 6 cells and was enhanced by tubocurarine (50 μm) which reduced the fast component.

Slow depolarizations (b,c) were associated with either a small reduction or no change in membrane input resistance depending on the cell studied. Hyperpolarization had variable effects on slow depolarization amplitude.

It was concluded that the fast, phasic depolarization is mediated by an ionic mechanism and by receptors both of which are distinct from those involved in the slow depolarization. The receptor mediating the fast depolarization is a 5‐HT3 receptor while that mediating the slow depolarization has yet to be identified.
Catecholamines released from the adrenal medulla exert a compensatory, protective effect at β2‐adrenoceptors against Paf‐induced death in mice
Authors: Criscuoli Marco , Subissi Alessandro
Published: July 2012

The effects of a number of drugs and experimental conditions, which inhibit or stimulate adrenergic function, were evaluated on platelet‐activating factor (Paf)‐induced death in conscious mice.

Adrenalectomy markedly potentiated Paf toxicity, while guanethidine and reserpine did not. However, reserpine, which produced a virtually complete depletion of cathecolamines (CA) in cardiac tissue, was not able to reduce adrenal CA by more than 58%. Drugs which release noradrenaline from the adrenergic nerve terminals, such as tyramine and amphetamine, did not protect mice from Paf toxicity, while drugs or conditions which favour the release of CA from the adrenal medulla, such as urethane and cold‐induced stress, did.

β2‐ and β1 + β2‐adrenoceptor antagonists (ICI 118551, propranolol and nadolol), but not β1‐ antagonists (atenolol, practolol, metoprolol and CGP 20712 A), potentiated Paf toxicity at low doses; β2‐ and β1 + β2‐agonists (salbutamol, fenoterol and isoprenaline), but not β1‐agonists (prenalterol and tazolol) were potent inhibitors of Paf toxicity. α1‐ and α2‐adrenoceptor agonists and antagonists did not exert significant effects. Propranolol did not appear to enhance the hypotensive action of Paf in pentobarbitone‐anaesthetized mice.

It is concluded that manipulation of the release of CA from the adrenal medulla, but not from adrenergic nerves, has profound effects on Paf toxicity in mice. A number of considerations support the hypothesis that bronchoconstriction is a major determinant of Paf‐induced death in mice.
Release of tissue‐type plasminogen activator is induced in rats by leukotrienes C4 and D4, but not by prostaglandins E1, E2 and I2
Authors: Tranquille N. , Emeis J.J.
Published: July 2012

Acute release of plasminogen activator (PA) was studied in rat isolated hindleg system perfused with Tyrode solution.

Leukotriene C4 (LTC4) and LTD4 dose‐dependently induced the release of PA, which plateaued at 160 nmol l−1 and 200 nmol l−1, respectively. The amount of PA released was about 1 iu ml−1. The effects of LTC4 and LTD4 were not additive.

The PA released was identified as tissue‐type PA (t‐PA) by quenching experiments using anti‐human t‐PA IgG, by fibrin autography, and by the dependence of its activity on the presence of soluble fibrin.

LTE4 (300 and 450 nmol l−1) and 5‐hydroxy‐eicosatetraenoic acid (600 nmol l−1) did not induce any t‐PA release in the perfusion system used.

Release of t‐PA induced by LTC4 and LTD4 was inhibited by the leukotriene‐receptor antagonist FPL 55712 (10 μmol l−1), whereas FPL 55712 did not inhibit t‐PA release induced by platelet‐activating factor (Paf‐acether).

In vivo LTC4 and LTD4 (2 μg kg−1 i.v.) also induced an acute increase of t‐PA activity in rat blood as evidenced by decreased blood clot lysis times.

Prostaglandin E1 and E2, prostacyclin and the stable prostacyclin analogue ZK 36374 at concentrations of 0.1–3.0 μmol l−1 induced little or no t‐PA release.
Cardiovascular effects of two new calcium antagonists, PY 108‐068 and PN 200‐110, in conscious spontaneously hypertensive rats
Authors: Barrès Christian , Cerutti Catherine , Morin Benoît , Sassard Jean
Published: July 2012

The acute cardiovascular effects of PY 108‐068 and PN 200‐110 were studied by means of a computerized analysis of the intra‐aortic blood pressure (BP) recorded continuously for 26 h in conscious unrestrained spontaneously hypertensive rats. Both compounds were studied at three doses (50, 100 and 200 μg kg−1) and each dose was administered intravenously 5 times (09 h 00 min, 14 h 00 min, 19 h 00 min, 24 h 00 min and 09 h 00 min). Baroreflex sensitivity was measured 1 h following the last injection.

The two compounds were found to induce rapid (3 min) and dose‐dependent falls in BP. After the first administration, these decreases reached −20% and −35% for systolic BP (SBP) and diastolic BP (DBP) respectively with PY 108‐068 (200 μg kg−1) and −25% and −45% for SBP and DBP respectively with PN 200‐110 (200 μg kg−1).

The duration of the reduction in BP increased with the dose and was much longer for PN 200‐110 (180 min for SBP) than for PY 108‐068 (20 min for SBP).

A tachycardia was associated with the decrease in BP which did not differ at 200 μg kg−1 between PY 108‐068 (+ 108 beats min−1) and PN 200‐110 (+ 103 beats min−1). Baroreflex sensitivity was not significantly increased by either drug.

The 5 repeated injections of PY 108‐068 and PN 200‐110 evoked similar responses.

In conclusion, both compounds exhibited marked hypotensive properties. PN 200‐110 appeared to be more suitable for further development since its effects were found to be greater and much longer lasting than those of PY 108‐068.
Antihaemophilic effect of vasopressin, deamino‐(d‐arginine8)‐vasopressin and adrenaline in sheep: proposal for an in vivo assay system
Authors: Heiniger Jörg , Kissling‐Albrecht Luzia , Neuenschwander Stefan , Rösli Regula , Pliška Vladimir
Published: July 2012

Female sheep were used to assay antihaemophilic (factor VIII enhancing) activity of arginine vasopressin, deamino‐(d‐arginine8)‐vasopressin (DDAVP) and adrenaline. The time course of the response was biphasic, two surges of factor VIII being observed. DDAVP was found to be the most potent of the substances investigated. Its optimal dose was 1 μg kg−1 body wt (i.v.). It is suggested that a similar procedure can be employed to search for new peptides with antihaemophilic action.
Attenuation of arterial blood pressure fall in endotoxin shock in the rat using the competitive bradykinin antagonist Lys‐Lys‐[Hyp2, Thi5,8, DPhe7]‐Bk (B4148)
Authors: Weipert J. , Hoffmann H. , Siebeck M. , Whalley E.T.
Published: July 2012

The selective competitive bradykinin (Bk) antagonist, B4148 (Lys‐Lys‐[Hyp2, Thi5,8, DPhe7]‐Bk) infused at 100 μg kg−1 min−1 into rats produced a significant inhibition of the hypotensive effect of Bk and had no effect against acetylcholine‐induced responses. In a rat model of endotoxin shock, the fall in mean arterial blood pressure in response to an intravenous injection of lipopolysaccharide from E. coli was significantly attenuated by the same infusion of B4148 compared to controls. These findings suggest that kinins are involved in the hypotensive response to endotoxin shock in rats. The development of potent Bk antagonists offers a new experimental approach for evaluating the role of kinins in this and other disease states and potential therapy in such disorders.
Importance of magnesium and potassium concentration on basal tone and 5‐HT‐induced contractions in canine isolated coronary artery
Authors: Murakawa Toshisuke , Altura Bella T. , Carella Anthony , Altura Burton M.
Published: July 2012

In vitro studies were undertaken to investigate the effects of external potassium ([K+]o) and magnesium ([Mg2+]o) concentration on canine coronary arterial basal tone and on 5‐hydroxytryptamine (5‐HT)‐induced contractions.

Acute withdrawal of, or reduction in, [K+]o produced relaxation of basal tone in isolated coronary arteries, whereas acute withdrawal (but not reduction) of [Mg2+]o produced contraction of these blood vessels.

The magnitude of coronary contraction obtained on withdrawal of [Mg2+]o was dependent upon the [K+]o; the higher the [K+]o, the greater the contraction.

The precise ratio of [K+]o/[Mg2+]o appeared to be important in dictating the degree of contraction (maximum response) and sensitivity (EC50) of canine coronary vascular smooth muscle cells to 5‐HT. The EC50 to 5‐HT was enhanced by increases in the [K+]o/[Mg2+]o ratio, whereas the ability of 5‐HT to induce a maximal contraction was attenuated by decreases in the [K+]o; the latter being modulated by [Mg2+]o. Small changes in [Mg2+]o could effect large changes in the EC50 as [K+]o was lowered.

These actions took place over patho‐physiological ranges of [K+]o and [Mg2+]o.

Maintenance of a constant [K+]o/[Mg2+]o ratio, irrespective of the exact [K+]o and [Mg2+]o, produced similar degrees of maximum tension.

Use of intact vascular ring preparations and helically‐cut vascular strips produced similar results with varying [K+]o/[Mg2+]o.

A variety of pharmacological receptor antagonists (phentolamine, propranolol, atropine, diphenhydramine, cimetidine), as well as a prostaglandin cyclo‐oxygenase inhibitor, did not modify the altered contractile responses or basal tone evoked by varying [K+]o/[Mg2+]o ratios.

These results suggest: (1) that basal tone and contractility of canine coronary vascular smooth muscle cells appear to be exquisitely sensitive to alterations in extracellular K+ and Mg2+; and (2) 5‐HT receptor‐operated Ca2+ channels, as well as those Ca2+ channels involved in generation of coronary arterial basal tone are modulated and controlled by the precise concentrations of [K+]o and [Mg2+]o.
Positive inotropic effects induced by carbachol in rat atria treated with islet‐activating protein (IAP) — association with phosphatidylinositol breakdown
Authors: Imai Shoichi , Ohta Hideo
Published: July 2012

To elucidate the functional consequences of phosphatidyl inositol (PI) breakdown produced by activation of the muscarinic receptor of the atrial muscle, and to clarify the subtypes of the muscarinic receptor involved, the effects of muscarinic agonists and antagonists on mechanical function were studied in atria isolated from rats given intravenous islet‐activating protein (IAP; 50 μg kg−1 body weight) 48–72 h before the experiments.

The negative chronotropic and inotropic actions of carbachol (CCh) were attenuated and positive inotropic effects (62.5 ± 5.8% above basal level) were observed with 10−5‐10−3 m CCh. Oxotremorine did not produce positive inotropic effects even in doses as high as 3 × 10−4 m. High doses of carbachol produced positive chronotropic effects, although the effects were weak.

Propranolol (10−7 m) did not modify the positive inotropic effect of carbachol observed in IAP‐treated atria, nor was there any change in the tissue cyclic AMP levels after carbachol.

High doses (10−5‐10−3m) of carbachol produced PI breakdown in the absence and presence of IAP. Oxotremorine (3 × 10−4 m) did not produce PI breakdown. In the presence of oxotremorine, the positive inotropic effects and PI breakdown by carbachol were abolished.

The positive inotropic effect of carbachol was readily antagonized by atropine but pirenzepine and gallamine exhibited only weak antagonist effects.

These results suggest that a muscarinic agonist such as carbachol can produce a positive inotropic effect in IAP‐treated atria, in association with PI breakdown, through activation of a muscarinic receptor which shows some similarity to that previously identified in smooth muscles.
Effects of calcium channel blockade in canine saphenous veins after storage at −190°C
Authors: Ebeigbe Anthony B. , Müller‐Schweinitzer Else , Vogel Arnold
Published: July 2012

Canine saphenous veins were investigated in vitro either within 24 h after removal or after storage at −190°C for 4–5 weeks in foetal calf serum containing 1.8 m dimethyl sulphoxide.

Contractions and 45Ca2+ uptake in response to both depolarization and guanfacine were studied in the absence and presence of the calcium channel antagonists diltiazem, verapamil, nifedipine and the two stereoisomers of a 1,4‐dihydropyridine derivative, namely the (+)−(S) enantiomer and the (−)−(R) enantiomer of 202–791 (isopropyl 4‐(2,1,3‐benzoxadiazol‐4‐yl)‐l,4‐dihydro‐2, 6‐dimethyl‐5‐nitro‐3‐pyridinecarboxylate).

Comparison of the data obtained on unfrozen and frozen/thawed veins revealed a good preservation of both contractile responsiveness and 45Ca2+ uptake mechanisms after storage at −190°C.

It is suggested that cryopreservation is a useful technique for storing venous smooth muscle for pharmacological studies.