bluuebunny/crossref_metadata_2025 huggingface dataset:
Pinacidil inhibits neuromuscular transmission indirectly in the guinea‐pig and rabbit mesenteric arteries
Authors: Nakashima Mikio , Li Yajun , Seki Narihito , Kuriyama Hirosi
Published: July 2012

Effects of pinacidil were investigated on neuromuscular transmission in smooth muscle tissues of the rabbit and guinea‐pig mesenteric arteries by both electrophysiological procedures and a bioassay of noradrenaline (NA) outflows.

Pinacidil (over 1 μm) hyperpolarized smooth muscle cell membranes in both tissues, in a concentration dependent manner. Pinacidil hyperpolarized and increased the ionic conductance of smooth muscle membrane more markedly in the rabbit mesenteric artery than in the guinea‐pig. The hyperpolarization induced by pinacidil occurred in the presence or absence of endothelial cells and was blocked by glibenclamide.

Perivascular adrenergic nerve stimulation produced excitatory junction potentials (e.j.ps) and repetitive stimulation produced a facilitation of e.j.ps in both tissues. Pinacidil (over 1 μm) reduced the amplitude and the decay time of e.j.ps to a consistently greater extent in the rabbit mesenteric artery than in the guinea‐pig. However, the facilitation process of e.j.ps was not modified following application of pinacidil (1 μm). The pinacidil‐induced inhibition of e.j.ps was prevented by pretreatment with glibenclamide.

Pinacidil (30 μm) marginally increased the overflows of NA and its metabolite, 3,4‐dihydroxyphenylglycol (DOPEG) released following repetitive perivascular nerve stimulations.

Pinacidil (10 μm) partly inhibited the voltage‐dependent Ca channel, as estimated from the recovery process following removal of pinacidil, of action potentials evoked on e.j.ps.

It is concluded that pinacidil increases ionic conductance and hyperpolarizes smooth muscle cell membranes of the guinea‐pig and rabbit mesenteric arteries and as a consequence, inhibits the neuromuscular transmission process occurring on adrenergic nerve stimulation with no reduction in the amount of released transmitter.
Negative inotropic effects of disopyramide on guinea‐pig papillary muscles
Authors: Kondo Noriaki , Mizukami Masami , Shibata Shoji
Published: July 2012

The inhibitory effects of disopyramide on electromechanical responses were investigated in guinea‐pig papillary muscles driven by electrical stimuli. Disopyramide up to 10−5 m did not cause a negative inotropic effect, while the maximum upstroke velocity of the action potential (dV/dtmax) was significantly decreased.

At higher concentrations, this drug dose‐dependently inhibited the contraction, and dV/dtmax was further decreased. This inhibition of contraction was accompanied by a depression of the slow action potential in partially depolarized preparations by increasing [K+]o (26 mm).

In preparations pretreated with nifedipine (10−6 m) and ryanodine (10−6 m), the contraction was almost completely inhibited. In such preparations, ouabain (2 × 10−6 m) markedly increased the contraction, probably through the Na+‐Ca2+ exchange mechanism. This contraction was inhibited by disopyramide above 10−8 m, and an almost complete inhibition was caused at 3 × 10−5 m.

A similar inhibitory effect was observed on the contraction increased by the lowering of [Na+]o (36 mm).

These results suggest that disopyramide at high concentrations inhibits Ca influx through slow Ca2+ channels and at low concentrations, it reduces the contraction increased through the Na+‐Ca2+ exchange mechanism. Disopyramide had a greater effect on cardiac contractility mediated by the Na+‐Ca2+ exchange mechanism.
Facilitation by 3,4‐diaminopyridine of regenerative acetylcholine release from mouse motor nerve
Authors: Hong S.J. , Chang C.C.
Published: July 2012

Effects of 3,4‐diaminopyridine (DAP) on endplate potentials (e.p.ps) were studied in mouse phrenic nerve‐hemidiaphragms.

In cut muscle preparations, low concentrations of DAP (2–20 μm) increased the amplitude of e.p.ps and shifted the curve relating Ca2+ concentration to e.p.p. amplitude leftward.

High concentrations of DAP (40–4000 μm) prolonged the duration of e.p.ps dose‐dependently up to one hundred fold (ca. 200 ms), yielding, in addition to the normal phasic e.p.p., a prolonged plateau depolarization component which was often preceded by an upstroke depolarization. During the plateau depolarization, nerve stimulations did not evoke any e.p.p.

The plateau component of prolonged e.p.ps was suppressed by tubocurarine, verapamil, nifedipine, Mn2+ and Cd2+ (but not by atropine) at low concentrations that had negligible effect on the amplitude of miniature e.p.ps or the phasic component of e.p.ps. Abolition of the plateau component by these agents restored the capability of the nerve terminal to evoke e.p.ps on nerve stimulation.

Low concentrations of neostigmine (0.01–0.02 μm) markedly lengthened DAP‐prolonged e.p.ps. However, the regenerative endplate depolarization evoked in the presence of high concentrations of neostigmine (0.3–0.5 μm) was not prolonged by DAP.

Tetraethylammonium (1 mm) did not provoke prolonged e.p.ps but acted cooperatively with DAP to prolong the duration of plateau depolarization. At a high concentration (3 mm), tetraethylammonium depressed the amplitude of miniature e.p.ps and abolished DAP‐prolonged e.p.ps.

In uncut muscle preparations, DAP apparently did not modify the time course and amplitude of miniature e.p.ps. Upon direct stimulation by current injection at endplate, DAP increased the muscle action potentials by only about 30%, but induced no prolonged depolarization.

These results suggest that the prolonged e.p.ps induced in the presence of DAP are due to a regenerative release of acetylcholine from motor nerve and the induction probably involves a presynaptic Ca2+ channel different from that for normal e.p.ps. It may be inferred that the regenerative acetylcholine release is recruited by Ca2+ channels modulated by nicotinic receptors and K+ channels.
Receptors involved in mechanical responses to catecholamines in the circular muscle of guinea‐pig stomach treated with meclofenamate
Authors: Syed Mohsin Md. , Parekh Anant B. , Tomita Tadao
Published: July 2012

In circular muscle strips of the fundus and corpus of guinea‐pig stomach, mechanical responses to catecholamines were studied mainly in the presence of a prostaglandin biosynthesis inhibitor, meclofenamate.

Normal preparations developed considerable muscle tone, and adrenaline (10–100 μm) in the presence of 3–5 μm propranolol produced a multiphasic response, generally consisting of transient relaxation and contraction, followed by slow relaxation and then contraction. Responses to phenylephrine were similar to those of adrenaline.

Meclofenamate (0.3 μm) nearly abolished the muscle tone and under this condition, both adrenaline and phenylephrine produced a simple contraction. This response was strongly inhibited by prazosin, but only weakly by yohimbine.

When muscle tone was maintained by prostaglandin E2 (10 nm) in the presence of meclofenamate, phenylephrine (30 μm) produced transient relaxation followed by slow contraction in most preparations. These were strongly inhibited by prazosin. Adrenaline produced a similar response, but the relaxation was only partially reduced by prazosin. The remaining relaxation was more dominant in the middle fundic region and this was considered to be mediated through β‐adrenoceptors.

It is concluded that in the circular muscle of the fundic region of guinea‐pig stomach, endogenous prostaglandins are involved in maintaining muscle tone and in modifying the response to catecholamines and that both contraction and relaxation are mediated by α1‐adrenoceptors.
Electrophysiological characterization of potent agonists and antagonists at pre‐ and postsynaptic GABAB receptors on neurones in rat brain slices
Authors: Seabrook G.R. , Howson W. , Lacey M.G.
Published: July 2012

Intracellular recordings were made from neurones in striatum (caudate‐putamen) and substantia nigra pars compacta in rat brain slices. Three GABAB agonists, baclofen, 3‐aminopropylphosphinic acid (3‐APPA) and 3‐aminopropyl(methyl)phosphinic acid (SK&F 97541), depressed excitatory postsynaptic potentials (e.p.s.ps) mediated by glutamate in the striatum, and hyperpolarized neurones in the substantia nigra. The ability of 3‐aminopropyl(diethoxymethyl)phosphinic acid (CGP 35348), 3‐aminopropyl (hexyl)phosphinic acid (3‐APHPA) and phaclofen to antagonize these responses was assessed.

Striatal e.p.s.ps, studied in the presence of bicuculline (30 μm), were reduced in amplitude by 92% with 6,7‐dinitroquinoxaline‐2,3‐dione (DNQX; 30 μm). These e.p.s.ps were depressed by up to 95% by SK&F 97541 and baclofen with EC50s of 0.092 μm and 1.25 μm respectively. The maximal effect of 3‐APPA was 67% with an EC50 of 0.83 μm. Agonist concentration‐effect data fitted a single‐site logistic model. GABAB agonists were without effect on striatal neurone membrane potential, input resistance or depolarizations induced by applied glutamate.

The depression of striatal e.p.s.ps by SK&F 97541 was reversibly antagonized by CGP 35348, 3‐APHPA and phaclofen with estimated equilibrium dissociation constants (KB) of 11.2 ± 1.7 μm (n = 4), 13.3 ± 0.4 μm (n = 3), and 405 ± 43 μm (n = 3) respectively. CGP 35348 and 3‐APHPA appeared to act competitively (Schild plot slopes of 0.99 and 1.01 respectively).

Nigral neurones were hyperpolarized by up to 25 mV by SK&F 97541 and baclofen with EC50s of 0.15 μm and 3.6 μm respectively. The maximum hyperpolarization by 3‐APPA was only 84% that of the other agonists, with an EC50 of 9.0 μm. Agonist concentration‐effect data fitted a single‐site logistic model.

The SK&F 97541‐induced hyperpolarization was reversibly antagonized by CGP 35348, 3‐APHPA and phaclofen with estimated KBs of 17.6 ± 4.4 (n = 3), 14.0 ± 1.5 (n = 4), and >400 μm (n = 1) respectively. CGP 35348 appeared competitive (Schild plot slope of 0.99). Antagonists were also tested with baclofen as agonist, yielding similar KB estimates as for SK&F 97541.

It is concluded that at both the presynaptic and postsynaptic sites examined, SK&F 97541 was about 10 fold more potent than baclofen or 3‐APPA. The antagonists CGP 35348 and 3‐APHPA (KB 10–20 μm) were about 20 fold more potent than phaclofen. The similarities in relative agonist potency and estimated antagonist affinity between these two functionally distinct GABAB receptors renders them pharmacologically indistinguishable at present.
Effect of clonidine, nimodipine and diltiazem on the in vitro opioid withdrawal response in the guinea‐pig ileum
Authors: Alfaro M.J. , Colado M.I. , López F. , Martín M.I.
Published: July 2012

The effects of clonidine, nimodipine and diltiazem, on the in vitro withdrawal contracture induced by naloxone in the guinea‐pig ileum obtained from morphine‐dependent animals, were evaluated.

The in vitro incubation with clonidine (0.01, 0.1 and 1 μm), diltiazem (0.25, 0.5 and 1 μm) or nimodipine (0.05, 0.1 and 1 μm) reduced significantly the force of the contracture induced by naloxone in the morphine‐dependent guinea‐pig ileum.

The intraperitoneal administration of clonidine (0.3 mg kg−1), nimodipine (5 mg kg−1) or diltiazem (20 mg kg−1) reduced the contractile response induced by naloxone in the morphine‐dependent guinea‐pig ileum.

It is concluded that at least part of the effect of clonidine, nimodipine and diltiazem on withdrawal contractures is mediated via a peripheral, rather than a central site of action. Even though, the mechanism responsible for the effect of the calcium channel blockers differs from that of α2‐adrenoceptor agonists, all of the drugs tested prevented the contracture induced by naloxone in morphine‐dependent guinea‐pig ileum.
Receptors mediating the effects of 5‐hydroxytryptamine on the tracheal vasculature and smooth muscle of sheep
Authors: Webber S.E. , Salonen R.O. , Widdicombe J.G.
Published: July 2012

The effects of 5‐hydroxytryptamine (5‐HT) and the selective 5‐HT3 receptor agonist 2‐methyl‐5‐HT were examined on the tracheal vasculature in anaesthetised, paralysed and artificially ventilated sheep. The cranial tracheal arteries were perfused with blood at constant flow and perfusion pressure was measured. 5‐HT and 2‐methyl‐5‐HT were injected into the arterial perfusate. Changes in tracheal smooth muscle tone were also measured.

5‐HT contracted the tracheal smooth muscle. This contraction was not affected by the 5‐HT2 receptor antagonist ketanserin, but was blocked by the combined ‘5‐HT1‐like’ and 5‐HT2 receptor antagonist methysergide. 2‐methyl‐5‐HT had no effect on the tracheal smooth muscle.

5‐HT had a complex action on the tracheal vasculature producing either a biphasic change (vasoconstriction followed by dilatation) or just a constriction. 2‐methyl‐5‐HT had a weak vasoconstrictor effect.

The vasoconstrictions produced by 5‐HT and 2‐methyl‐5‐HT were blocked by ketanserin. The vasodilatation produced by 5‐HT was resistant to ketanserin but was antagonised by methysergide.

Thus 5‐HT contracts the tracheal smooth muscle of sheep by stimulating ‘5‐HT1‐like’ receptors. 5‐HT constricts the tracheal vascular bed by stimulating 5‐HT2 receptors or dilates the vascular bed by stimulating ‘5‐HT1‐like’ receptors. 5‐HT3 receptors appear not to be involved in the responses of the tracheal vasculature or smooth muscle to 5‐HT.
The antimigraine drug, sumatriptan (GR43175), selectively blocks neurogenic plasma extravasation from blood vessels in dura mater
Authors: Buzzi M. Gabriella , Moskowitz Midiael A.
Published: July 2012

We describe the actions of GR43175, a 5‐hydroxytryptamine1 (5‐HT1)‐like receptor agonist, on neurogenically‐mediated plasma protein extravasation within an important pain‐sensitive intracranial tissue, the dura mater.

GR43175 markedly attenuated extravasation of 125I‐albumin from blood vessels within ipsilateral dura mater when administered to rats (100 μg kg−1) fifteen minutes before unilateral electrical trigeminal stimulation (1.2 mA, 5 Hz, 5 ms, 5 min.); the ratio (stimulated/unstimulated sides) decreased from 1.81 to 1.23, P < 0.005).

GR43175 (100 μg kg−1, i.v., rats; 30 μg kg−1, i.v., guinea‐pigs) decreased the leakage of radiolabeled albumin from 163% to 119% (P < 0.005, guinea‐pig) or from 174 to 118% (P < 0.05, rat) above vehicle‐treated controls when injected ten minutes before systemic capsaicin treatment (0.5 or 1 μmol kg−1, i.v.).

GR43175 (30–300 μg kg−1) did not block plasma protein extravasation within extracranial tissues of rats and guinea‐pigs innervated by the trigeminal nerve (conjunctiva, eyelid and lip).

The protein leakage which followed the i.v. administration of 5‐HT (1 μmol kg−1) or neuropeptides which mediate neurogenic plasma extravasation, substance P (0.3 nmol kg−1 or 1 nmol kg−1) and neurokinin A (1 nmol kg−1), was not blocked by GR43175 (100, 300 μg kg−1) despite the presence of leakage in amounts equivalent to that following neurogenic stimulation.

GR43175 (100 μg kg−1) decreased bradykinin (10 μmol kg−1)‐induced extravasation from 142 to 115% above vehicle‐treated animals (P < 0.05).

These results demonstrate an important action of GR43175 on neurogenic mechanisms in dural blood vessels. Since the ergot alkaloids possess a similar profile of drug activity, it is suggested that drugs useful in the treatment of acute vascular headaches may share a similar mechanism of action.
Locomotor activity in rats after administration of nicotinic agonists intracerebrally
Authors: Reavill C. , Stolerman I.P.
Published: July 2012

Nicotine (0.13 and 0.4 mg kg−1, s.c.) increased the ambulatory component of locomotor activity in rats previously exposed to the drug. Nicotine did not increase repeated movements reliably.

An infusion of either nicotine (8 μg) or the potent nicotinic agonist cytisine (4 μg) into the ventral tegmental area of the forebrain increased ambulation but not repeated movements.

An infusion of nicotine or cytisine into the nucleus accumbens, striatum, dorsal hippocampal formation or motor thalamus did not increase ambulatory or repeated movements.

Mecamylamine (0.1–1.0 mg kg−1, s.c.) blocked increases in locomotor activity produced by an infusion of nicotine or cytisine into the ventral tegmental area.

The locomotor activity produced by systemically administered nicotine may be mediated, in part, through nicotinic receptors located in the ventral tegmental area of the mesolimbic dopamine system.
Characterization of the muscarinic receptor subtype involved in phosphoinositide metabolism in bovine tracheal smooth muscle
Authors: Roffel A.F. , Meurs H. , Elzinga C.R.S. , Zaagsma J.
Published: July 2012

The muscarinic receptor subtype involved in the methacholine‐induced enhancement of phosphoinositide metabolism in bovine tracheal smooth muscle was identified by using the M2‐selective antagonist AF‐DX 116 and the M3‐selective antagonist 4‐diphenylacetoxy‐N‐methylpiperidine (4‐DAMP) methobromide, in addition to the M1‐selective antagonist pirenzepine, in a classical Schild analysis.

All the antagonists shifted the methacholine dose‐response curve to the right in a parallel and concentration‐dependent fashion, yielding Schild plots with slopes not significantly different from unity. The pA2 values (6.94, 6.32 and 8.54 for pirenzepine, AF‐DX 116 and 4‐DAMP methobromide respectively) indicate that it is the M3 (smooth muscle/glandular), but not the M2 (cardiac) muscarinic receptor subtype, present in this tissue, that mediates phosphoinositide turnover, in accordance with our previous contractile studies.

The results provide additional evidence for the involvement of phosphoinositide turnover in the pharmacomechanical coupling between muscarinic receptor stimulation and contraction in (bovine tracheal) smooth muscle.
Characterization of MDL 73005EF as a 5‐HT1A selective ligand and its effects in animal models of anxiety: comparison with buspirone, 8‐OH‐DPAT and diazepam
Authors: Moser P.C. , Tricklebank M.D. , Middlemiss D.N. , Mir A.K. , Hibert M.F. , Fozard J.R.
Published: July 2012

With radioligand binding techniques, MDL 73005 EF (8‐[2‐(2,3‐dihydro‐1,4‐benzodioxin‐2‐yl‐methylamino)ethyl]‐8‐azaspiro[4,5]decane‐7,9‐dione methyl sulphonate) shows high affinity (pIC50 8.6) and selectivity (>100 fold compared to other monoamine and benzodiazepine receptor sites) for the 5‐hydroxytryptamine (5‐HT)1A recognition site; it was both more potent and more selective than buspirone in this respect.

In rats pretreated with reserpine, 8‐hydroxy‐2‐(di‐n‐propyl‐amino) tetralin (8‐OH‐DPAT) induced forepaw treading and flat body posture; in the same model, MDL 73005EF and buspirone showed minimal agonist activity and at high doses MDL 73005EF inhibited responses to 8‐OH‐DPAT.

In rats trained to discriminate 8‐OH‐DPAT from saline in a drug discrimination paradigm, both MDL 73005EF and buspirone generalized dose‐dependently and completely to the 8‐OH‐DPAT cue.

To define the anxiolytic potential of MDL 73005EF, it was examined in the elevated plus‐maze test and in the water‐lick conflict test in comparison with diazepam and buspirone. In both tests MDL 73005EF induced effects similar to those seen following diazepam. Buspirone had similar effects to both MDL 73005EF and diazepam in the water‐lick conflict test but opposite effects in the elevated plus‐maze. 8‐OH‐DPAT also had opposite effects in the elevated plus‐maze test to MDL 73005EF and diazepam.

The anti‐conflict effects of MDL 73005EF were reversed by low doses of the 5‐HT1A receptor agonist, 8‐OH‐DPAT; those of buspirone were neither antagonised nor mimicked by 8‐OH‐DPAT.

These results suggest that an interaction with 5‐HT1A receptors is the basis of the anxiolytic‐like activity of MDL 73005EF. However, its mechanism of action is clearly different from that of buspirone, possibly reflecting a greater selectivity for the 5‐HT1A receptors located presynaptically on central 5‐hydroxytryptaminergic neurones.
Nimodipine has no effect on the cerebral circulation in conscious pigs, despite an increase in cardiac output
Authors: van der Giessen W.J. , Duncker D.J. , Saxena P.R. , Verdouw P.D.
Published: July 2012

We studied the effects of four doses of nimodipine (0.5, 1, 2 and 4 μg kg−1 min−1) on systemic haemodynamics and on regional vascular beds, in particular the cerebral circulation, in conscious pigs.

Nimodipine caused dose‐dependent, probably reflex‐mediated, increases in heart rate (42% with the highest dose) and cardiac output (54%), while arterial blood pressure was only minimally affected. Left ventricular end‐diastolic pressure and systemic vascular resistance decreased dose‐dependently (35–40% at the highest dose) while stroke volume remained unchanged.

Total brain blood flow was not affected by the drug. Furthermore, we could not demonstrate any regional cerebral differences, as blood flows to both cerebral hemispheres as well as the diencephalon, cerebellum and brain stem remained unchanged.

Blood flow to the kidneys, liver, small intestine and skin also did not change. Nimodipine caused dose‐dependent increases in blood flow to the stomach (95%), myocardium (97%) and adrenal glands (102%), while blood flow to skeletal muscles (267%) increased most.

It is concluded that in the conscious pig, nimodipine is an arterial vasodilator which shows some selectivity for the skeletal muscle vasculature but does not increase total or regional cerebral blood flow.
Effects of calmodulin antagonists on calcium‐activated potassium channels in pregnant rat myometrium
Authors: Kihira M. , Matsuzawa K. , Tokuno H. , Tomita T.
Published: July 2012

The effects of W‐7, trifluoperazine, and W‐5 on Ca2+‐activated K+‐channels were investigated with the inside‐out patch‐clamp method in smooth muscle cells freshly dispersed from pregnant rat myometrium. These drugs are known to have different potencies as calmodulin antagonists.

In the presence of 1 μm Ca2+ on the cytoplasmic side ([Ca2+]i), the fraction of time the channel was open (open probability, Po) was about 0.9 and the calmodulin antagonists (1–30 μm) applied to the cytoplasmic face reduced Po to 0.65‐0.55 dose‐dependently. In the presence of 0.1‐0.16 μm Ca2+, when Po was very low (0.02), calmodulin antagonists increased Po. All antagonists used produced almost identical effects at the same concentration.

The probability density function of the open time distribution could be described by the sum of two exponentials. W‐7 decreased the time constant of the slow component of distribution and at 30 μm the slow component disappeared both at 1 and 0.25 μm [Ca2+]i, reflecting the appearance of flickering channel activity. The probability density function of the closed time distribution could be fitted with three exponentials. The time constants of these components were not significantly altered by W‐7.

Internally applied calmodulin (1–5 μm) did not produce any significant effect on channel activity.

The effects of calmodulin antagonists are considered to be due to a direct action of these compounds on the channel, and suggest that channel activation by Ca2+ is not mediated by calmodulin.
Effects of μ‐opioid receptor agonists on circulatory responses to simulated haemorrhage in conscious rabbits
Authors: Evans Roger G. , Ludbrook John
Published: July 2012

Cardiac output, arterial pressure, heart rate, systemic vascular conductance, respiratory rate and arterial blood Po2 and Pco2 were measured in unanaesthetized rabbits. Haemorrhage was simulated by inflating a cuff placed around the inferior vena cava so that cardiac output fell at a constant rate of about 8% of its resting value per min.

The effects of drug treatments on resting haemodynamic and respiratory variables, and on the haemodynamic response to simulated haemorrhage, were tested. The treatments were; 4th ventricular (−)−naloxone HCl (10–100 nmol), 4th ventricular H‐Tyr‐d‐Ala‐Gly‐MePhe‐NH(CH2)2OH (DAMGO; 30–300 pmol), and i.v. morphine sulphate (0.5‐5.0 μmol kg−1). The interactions of graded 4th ventricular doses of naloxone (3–100 nmol) with the actions of DAMGO (100–300 pmol) on these responses were also assessed.

After sham treatments, the circulatory response to simulated haemorrhage had two phases. During the first compensatory phase, systemic vascular conductance fell, heart rate rose, and mean arterial pressure fell by only about 7 mmHg. A second decompensatory phase supervened when cardiac output had fallen by about 50%. At this point systemic vascular conductance rose abruptly and arterial pressure fell to ≥ 40 mmHg.

Low 4th ventricular doses of naloxone (10–30 nmol) and DAMGO (30–100 pmol) had no discernible effect on the circulatory response to simulated haemorrhage. Higher doses of naloxone (30–100 nmol) and DAMGO (100–300 pmol) prevented the decompensatory phase. These high doses of naloxone and DAMGO lowered resting heart rate without affecting the other haemodynamic or respiratory variables.

Low doses of i.v. morphine (0.5‐1.5 μmol kg−1) also had no discernible effect on the circulatory response to simulated haemorrhage. Higher doses of morphine (1.5‐5.0 μmol kg−1) abolished the decompensatory phase. These high doses caused respiratory depression without affecting the resting haemodynamic variables.

The prevention of circulatory decompensation by high doses of DAMGO was reversed by 3–10 nmol of naloxone in 3 out of 4 rabbits and by 10–30 nmol of naloxone in all 4 rabbits. The decompensatory phase was, however, prevented by the combined high doses of DAMGO (100–300 pmol) and naloxone (30–100 nmol).

These findings provide strong evidence that activation of μ‐opioid receptors in the central nervous system abolishes circulatory decompensation during acute reduction of central blood volume in conscious rabbits. This effect does not appear to be due to activation of arterial chemoreceptors or to a non‐specific increase in sympathetic vasoconstrictor drive, since respiratory depression and hypertension were not observed after 4th ventricular doses of DAMGO which abolished circulatory decompensation. Our results also provide indirect confirmation of our previous finding that naloxone acts to prevent circulatory decompensation by an antagonist action at central δ‐receptors.
Systemic and regional haemodynamic interactions between K+ channel openers and the sympathetic nervous system in the pithed SHR
Authors: Richer Christine , Mulder Paul , Doussau Marie‐Pascale , Gautier Patrick , Giudicelli Jean‐François
Published: July 2012

The interactions between two K+ channel openers, cromakalim and SR 44866 (infused i.v. at equihypotensive doses), and the sympathetic nervous system at the systemic and regional (mesentery, kidney, hindlimb) vascular levels were investigated in the pithed spontaneously hypertensive rat (SHR) by use of the pulsed Doppler technique.

The two K+ channel openers did not affect postsynaptic α1‐ but slightly reduced postsynaptic α2‐adrenoceptor mediated systemic pressor and regional vasoconstrictor responses.

Both drugs significantly decreased the systemic pressor and regional vasoconstrictor responses elicited by spinal cord stimulation. These sympathoinhibitory effects were not homogeneously distributed among the different vascular beds, the decreasing rank order being: mesentery > kidney > hindlimb. Simultaneously, the spinal cord stimulation‐induced tachycardia remained unaffected.

After treatment with K+ channel openers, restoration of initial blood pressure and vascular tone values by infusion of prostaglandin F2α (PGF2α) and vasopressin respectively did not affect and abolished the sympathoinhibitory effects of cromakalim and SR 44866.

We conclude that in SHRs the two K+ channel openers that we investigated exert similar sympathohibitory effects which affect some vascular beds more than others. These effects are not dependent upon the arterial blood pressure level and are most likely prejunctionally located.
The effects of thromboxane receptor antagonists on oestrogen‐induced uterotrophic responses in the spontaneously hypertensive rat
Authors: Kerr M.B. , Marshall K. , Senior J.
Published: July 2012

The possible role of thromboxane in the uterotrophic response to oestrogen, in the spontaneously hypertensive rat was investigated by use of the thromboxane receptor antagonists EP092, AH23848 and BM 13.505.

The parameters studied were uterine blood flow (measured by the microsphere technique), uterine wet and dry weights and the concentrations of cytosolic and nuclear oestrogen receptors.

The antagonists attenuated oestradiol‐induced uterine blood flow and significantly reduced both wet and dry uterine weight. These changes were accompanied by decreases in nuclear oestrogen receptor levels.

The results suggest a supportive role for thromboxane in oestradiol‐induced uterine growth.
Naloxone‐induced cardiovascular depression in rats that had received chronic morphine‐treatment
Authors: Dai Soter , Wang Yu
Published: July 2012

Cardiovascular changes in response to intravenous injection of naloxone were studied in pentobarbitone‐anaesthetized rats which had been given morphine in their drinking water for 1–21 days. The mechanisms of the observed changes were investigated in intact animals and in isolated hearts and tail arteries.

In rats that had received chronic morphine‐treatment, intravenous administration of naloxone caused immediate decreases in blood pressure, heart rate, left ventricular pressure and dLVP/dtmax which were followed by the occurrence of atrial or ventricular extrasystoles and other signs of opiate withdrawal such as faecal passage and muscle twitching.

The intensities of the naloxone‐precipitated cardiovascular changes were directly related to the duration of chronic morphine pretreatment, reaching statistically significant levels on day 2 or 3 and maximal levels on day 7 or 14. This phenomenon disappeared on days 3 to 14 following opiate withdrawal in animals which had been treated previously with morphine for 21 days.

Either atropine or clonidine pretreatment significantly prevented the occurrence of faecal passage or muscle twitching during naloxone‐precipitated opiate withdrawal. However, clonidine, but not atropine or yohimbine, abolished the decreases in various haemodynamic parameters. The occurrence of cardiac extrasystoles was not affected.

In isolated heart or tail artery preparations from chronically morphine‐treated rats, naloxone administration did not elicit reactions which differed from those of the preparations from naive animals.

These findings suggest that, under pentobarbitone anaesthesia, the cardiovascular systems of rats that had received chronic morphine treatment exhibit inhibitory, instead of excitatory, reactions to naloxone‐precipitated opiate withdrawal. The mechanisms remain unclear, but are unlikely to be due to cholinergic or noradrenergic hyperactivity, nor due to the direct withdrawal reactions of the cardiac or vascular tissues.
Response of the rat myometrium to phenylephrine in early pregnancy and the effects of 6‐hydroxydopamine
Authors: Kaulenas Andrew , Parkington Helena C. , Coleman Harold A.
Published: July 2012

The contractile responses of the longitudinal and circular muscle layers of the rat uterus to the α1‐adrenoceptor agonist phenylephrine were measured on days 3–6 of gestation. There was a progressive increase in sensitivity to phenylephrine in both muscle layers between days 3 and 6 of gestation. Overall, this amounted to a 13 and 9 fold increase in sensitivity in longitudinal and circular muscles, respectively. In longitudinal muscle the slope of the Hill plot was 2 on day 3 of pregnancy and was decreased to 1 thereafter.

The sympathetic nerve terminals innervating the smooth muscle of the uterus were destroyed by administration of 6‐hydroxydopamine (2 × 50 mg kg−1) 4–7 days before testing with phenylephrine. Following this treatment there was a significant increase in sensitivity to phenylephrine on day 3 in both muscle layers. After day 4, the longitudinal muscle was less sensitive to phenylephrine.

In the longitudinal muscle there was a progressive increase in the contractile response to maximal concentrations of phenylephrine and to high potassium (100 mm) between days 3 and 6 of pregnancy. In the circular muscle the responsiveness to both phenylephrine and potassium remained unchanged between days 3 and 6 of gestation. 6‐Hydroxydopamine had no effect on the maximal responses to phenylephrine or high potassium in either muscle layer.

In conclusion, denervation supersensitivity of uterine smooth muscle following injection of 6‐hydroxydopamine is observed only on day 3 of pregnancy and appears to be replaced by subsensitivity by day 6. The decrease in the slope of the Hill plot in longitudinal muscle after day 3 may be explained by changes in events between activation of α1‐adrenoceptors and contraction.
Lack of correlation between the antiarrhythmic effect of l‐propionylcarnitine on reoxygenation‐induced arrhythmias and its electrophysiological properties
Authors: Barbieri M. , Carbonin P.U. , Cerbai E. , Gambassi G. , Giudice P. Lo , Masini I. , Mugelli A. , Pahor M.
Published: July 2012

The antiarrhythmic effect of l‐propionylcarnitine (l‐PC) was evaluated in the guinea‐pig isolated heart; arrhythmias were induced with hypoxia followed by reoxygenation and by digitalis intoxication.

l‐PC 1 μm, was found to be the minimal but effective antiarrhythmic concentration against reoxygenation‐induced ventricular fibrillation. No antiarrhythmic effect was observed against digitalis‐induced arrhythmias. d‐Propionylcarnitine, l‐carnitine and propionic acid did not exert antiarrhythmic effects.

During hypoxia and reoxygenation l‐PC consistently prevented the rise of the diastolic left ventricular pressure, and significantly reduced the release of the cardiac enzymes creatine kinase (CK) and lactic dehydrogenase (LDH).

The electrophysiological effects of l‐PC were then studied on either normal sheep cardiac Purkinje fibres or those manifesting oscillatory afterpotentials induced by barium or strophanthidin.

l‐PC (1 and 10 μm) did not significantly modify action potential characteristics and contractility of normal Purkinje fibres, or the amplitude of OAP induced by strophanthidin or barium.

It is concluded that the antiarrhythmic action of l‐PC on reoxygenation‐induced arrhythmias is not correlated with its direct electrophysiological effects studied on normoxic preparations.
Mechanisms contributing to the differential haemodynamic effects of bombesin and cholecystokinin in conscious, Long Evans rats
Authors: Janssen Paul J.J.M. , Gardiner Sheila M. , Compton Alix M. , Bennett Terence
Published: July 2012

Long Evans rats were chronically instrumented with intravascular catheters and pulsed Doppler probes to assess changes in renal, mesenteric and hindquarters blood flows and vascular conductances in response to bombesin (2.5 μg kg−1, i.v.) and cholecystokinin (CCK) (0.5 and 5.0 μg kg−1, i.v.).

Bombesin caused an increase in heart rate and blood pressure, together with a transient renal vasoconstriction and prolonged mesenteric vasodilatation; there was an early hindquarters vasodilatation followed by vasoconstriction.

In the presence of phentolamine, bombesin caused a fall in blood pressure due to enhanced hindquarters vasodilatation; these effects were reversed by propranolol and hence were possibly due to circulating adrenaline acting on vasodilator β2‐adrenoceptors.

During concurrent administration of phentolamine, propranolol and atropine, bombesin caused prolonged tachycardia and a rise in blood pressure. The renal vasoconstrictor and mesenteric vasodilator effects of bombesin were not reduced under these conditions and thus probably were direct and/or indirect non‐adrenergic, non‐cholinergic (NANC) effects.

CCK caused dose‐dependent increases in blood pressure accompanied by renal, mesenteric and hindquarters vasoconstrictions followed, after the higher dose, by vasodilatations. The lower dose of CCK increased heart rate but there was a bradycardia followed by a tachycardia after the higher dose.

Experiments with antagonists as described above indicated the pressor effect of CCK was mediated largely through α‐adrenoceptors, as were the mesenteric and hindquarters vasoconstrictor effects; CCK exerted NANC negative chronotropic effects.

All the effects of CCK were markedly inhibited by L364,718. This observation, and the finding that L364,718 had no effect on the responses to bombesin, together with the dissimilarities in the regional haemodynamic effects of exogenous CCK and bombesin, indicate that the cardiovascular actions of the latter were not dependent on the release of endogenous CCK.
New, long‐acting, potent bradykinin antagonists
Authors: Lembeck F. , Griesbacher T. , Eckhardt M. , Henke S. , Breipohl G. , Knolle J.
Published: July 2012

Three new bradykinin (BK) antagonists, d‐Arg0‐Hyp3‐Thi5‐d‐Tic7‐Oic8‐BK (compound I), d‐Arg0‐Hyp3‐d‐Tic7‐Oic8‐BK (compound II), and Arg(Tos)1‐Hyp3‐Thi5‐d‐Tic7‐Oic8‐BK (compound III), were tested against the effects of BK in 9 bioassay preparations including visceral smooth muscles, vasoconstriction, plasma protein extravasation, release of prostaglandin E2, bronchoconstriction, and stimulation of afferent C‐fibre nociceptors. In some of these tests the effects of the new compounds were compared with those of the antagonist d‐Arg0‐Hyp2‐Thi5,8‐d‐Phe7‐BK (compound IV), described by Stewart & Vavrek (1987).

For all bioassays the general rank order of potency of the compounds was found to be I > II > III ≫ IV. The new antagonists were long‐acting; in some bioassays their effects outlasted the duration of the experiment.

The inhibitory effects of the new BK antagonists were specific for BK; actions of noradrenaline, angiotensin II, acetylcholine or histamine were unaffected by the antagonists. They did not stimulate the release of histamine or prostaglandins. An agonistic effect was observed only with very high concentrations of compounds I and II in the plasma protein extravasation test.

The long duration of action of the new BK antagonists is probably due to a high and long‐lasting affinity to the BK receptors. A high resistance of the antagonists to enzymatic destruction may be another reason.

The new BK antagonists will be valuable tools for the investigation of the pathophysiological role of BK. In addition they may offer a potential for therapeutic applications.
5‐Hydroxytryptamine‐stimulated accumulation of 1,2‐diacylglycerol in the rabbit basilar artery: a role for protein kinase C in smooth muscle contraction
Authors: Clark Angela H. , Garland C.J.
Published: July 2012

5‐Hydroxytryptamine (5‐HT) produced a concentration‐dependent increase in the membrane concentration of 1,2‐diacylglycerol (DG) in the rabbit isolated basilar artery, but did not stimulate the hydrolysis of membrane phosphoinositide.

The 5‐HT‐induced accumulation of DG could be blocked with the putative phospholipase C inhibitor 2‐nitro‐4‐carboxyphenyl‐N,N‐diphenylcarbamate (NCDC; 70 μm), but not with the protein kinase C inhibitor, 1‐(5‐isoquinolinesulphonyl)‐2‐methyl piperazine (H7; 50 μm).

Direct stimulation of protein kinase C with phorbol 12,13‐dibutyrate (PDBu) produced sustained smooth muscle contraction which was fairly rapid in onset and could be reversed by H7 but not by NCDC. The inactive phorbol, 4α phorbol 12,13‐didecenoate, did not produce contraction in the basilar artery.

5‐HT‐induced contractions (1 nm–100 μm) were blocked or greatly reduced in the presence of the protein kinase inhibitor H7 or polymyxin B, and with the phospholipase C inhibitor, NCDC. The concentrations of these inhibitors which abolished contraction to 5‐HT, did not alter smooth muscle contraction produced in response to 30 mm K+‐physiological salt solution (PSS).

These data suggest that DG production and the subsequent activation of PKC forms an important component of the cerebrovascular contractile response to 5‐HT. As the DG does not appear to arise from membrane phosphatidylinositol, it appears that 5‐HT can stimulate the production of this second messenger in cerebral arteries by a mechanism which is different from peripheral arteries.
Characterization in rat aorta of the binding sites responsible for blockade of noradrenaline‐evoked calcium entry by nisoldipine
Authors: Morel Nicole , Godfraind Théophile
Published: July 2012

The effectiveness of the calcium antagonist, 1,4‐dihydropyridine nisoldipine, as an inhibitor of contraction and 45Ca entry evoked by noradrenaline in rat aorta has been investigated and correlated with binding characteristics in intact artery.

Contractions evoked by noradrenaline were concentration‐dependently depressed by nisoldipine (0.3–300 nm). About 60% of the response was resistant to inhibition, while KCl‐induced contractions could be completely blocked. Noradrenaline‐induced contractions were also less sensitive to nisoldipine inhibition than were KCl‐induced contractions.

Preincubation of the aorta with nisoldipine in high KCl depolarizing solution increased the inhibition of the contraction evoked by a short application of noradrenaline or KCl to a similar extent.

The inhibition by nisoldipine of 45Ca influx evoked either by KCl depolarizing solution or by noradrenaline correlated well with the inhibition of the contractile responses. However, while KCl‐stimulated 45Ca influx was totally abolished by nisoldipine (300 nm), 38% of the noradrenaline‐stimulated 45Ca influx was resistant to inhibition by nisoldipine (300 nm).

The study of [3H]‐(+)‐PN 200‐100 ([3H]‐(+)‐isradipine) binding in intact aorta showed the presence of a homogeneous population of specific binding sites. KD values were dependent on the KCl concentration in the bath while Bmax was unaffected. Binding of [3H]‐(+)‐isradipine was also increased in tissue exposed to noradrenaline; in the presence of 10−5 m noradrenaline, binding parameters of [3H]‐(+)‐isradipine were close to the values obtained in aorta bathed in 20 mm KCl solution.

Displacement of [3H]‐(+)‐isradipine specific binding by nisoldipine was determined in segments of mesenteric artery and of aorta. The potency of nisoldipine was dependent on the incubation conditions applied to the vessel, as follows: KCl (100 mm) depolarizing solution > noradrenaline (10−5 m) = KCl (25 mm) solution > physiological solution. The Ki value measured in aorta exposed to noradrenaline (10−5 m) was close to the IC50 value of nisoldipine on the noradrenaline‐evoked contraction.

The membrane potential value of rat aorta was estimated by the distribution of [3H]‐tetraphenylphosphonium bromide ([3H]‐TPP+). [3H]‐TPP+ uptake concentration‐dependently decreased when the KCl concentration in the bath was increased from 5.9 to 130 mm. Noradrenaline also concentration‐dependently decreased [3H]‐TPP+ uptake; the maximum effect (1–10 μm noradrenaline) was comparable in amplitude to the effect of 25 mm KCl solution.

It is concluded that in rat aorta, noradrenaline activates voltage‐operated calcium channels that contain the specific, voltage‐sensitive binding sites for calcium antagonistic dihydropyridines. The existence of a fraction of noradrenaline‐stimulated 45Ca entry that is resistant to nisoldipine blockade suggests that another Ca2+ entry pathway is also opened by the agonist.
Novel selective agonists and antagonists confirm neurokinin NK1 receptors in guinea‐pig vas deferens
Authors: Hall Judith M. , Morton Ian K.M.
Published: July 2012

This study investigated the recognition characteristics of neurokinin receptors mediating potentiation of the contractile response to field stimulation in the guinea‐pig vas deferens.

A predominant NK1 receptor population is strongly suggested by the relative activities of the common naturally‐occurring tachykinin agonists, which fall within less than one order of magnitude. This conclusion is supported by the relative activities of the synthetic NK1 selective agonists substance P methyl ester, [Glp6,l‐Pro9]‐SP(6–11) and δ‐aminovaleryl‐[l‐Pro9,N‐MeLeu10]‐SP(7–11) (GR73632) which were 0.78, 9.3 and 120 as active as substance P, respectively. Furthermore, the NK2 selective agonist [Lys3, Gly8,‐R‐γ‐lactam‐Leu9]‐NKA(3–10) (GR64349) was active only at the highest concentrations tested (> 10 μm), and the NK3 selective agonist, succ‐[Asp6,N‐MePhe8]‐SP(6–11) (senktide) was essentially inactive (10 nm‐32 μm).

[d‐Arg1,d‐Pro2,d‐Trp7,9, Leu11]‐SP(1–11) antagonized responses to neurokinin A, neurokinin B, physalaemin, eledoisin, [Glp6,d‐Pro9]‐SP(6–11), GR73632 and GR64349 (apparent pKBs 5.6–6.2), but was less potent in antagonizing responses to substance P, substance P methyl ester and [Glp6,l‐Pro9]‐SP(6–11) (apparent pKBs ≤ 5.0–5.0).

In contrast, the recently developed NK1‐selective receptor antagonist [d‐Pro9[Spiro‐γ‐ lactam]Leu10, Trp11]‐SP(1–11) (GR71251) did not produce agonist‐dependent pKB estimates. Schild plot analysis indicated a competitive interaction with a single receptor population where the antagonist had an estimated overall pKB of 7.58 ± 0.13 for the four agonists of differing subtype selectivity tested (GR73632, GR64349, substance P methyl ester and neurokinin B). This estimate is similar to that we obtained for NK1‐mediated (substance P methyl ester) contraction in the guinea‐pig ileum preparation (pKB = 7.86 ± 0.05).

Tachykinin action appears not to depend on release of a number of intermediary mediators including acetylcholine, histamine or cyclo‐oxygenase products, nor to involve interaction with neuronal mechanisms including α2‐adrenoceptor feedback, noradrenergic Uptake‐1 or opioid‐release, since antagonism or inhibition of these mechanisms did not modify responses to tachykinins.

We conclude that tachykinin action in the field‐stimulated guinea‐pig vas deferens preparation is mediated through interaction with a predominant neurokinin NK1 receptor population and this preparation can therefore be used to study NK1 modulation of sympathetic neurotransmission.
Prejunctional prostanoid receptors on cardiac adrenergic terminals belong to the EP3 subtype
Authors: Mantelli Laura , Amerini Sandra , Rubino Annalisa , Ledda Fabrizio
Published: July 2012

The effects of prostaglandin E2 (PGE2) and of several synthetic prostanoids on the cardiac response to sympathetic nerve stimulation in guinea‐pig atria have been evaluated.

PGE2 (0.01–100 nm), sulprostone (0.01–100 nm) and misoprostol (0.1–100 nm), but not butaprost (0.1–100 nm), dose‐dependently reduced the increase in cardiac contractility induced by electrical field stimulation of sympathetic terminals.

The EP1 antagonist AH6809 (1 μm) did not modify the inhibition of cardiac response induced by PGE2, sulprostone and misoprostol.

In preparations preloaded with [3H]‐noradrenaline, tritium overflow induced by electrical field stimulation was greatly and significantly reduced by 100 nm PGE2 and by 100 nm sulprostone.

These results indicate that PGE2 and other synthetic prostanoids reduce noradrenaline release from cardiac adrenergic nerve terminals acting on prejunctional inhibitory receptors belonging to the EP3 subtype.
The effects of adenosine triphosphate (ATP) and related purines on human isolated subcutaneous and omental resistance arteries
Authors: Martin G.N. , Thorn S.A.McG. , Sever P.S.
Published: July 2012

Human resistance arteries were obtained from specimens of omentum and subcutaneous fat removed at surgery. They were studied in vitro by use of a myograph technique to determine the effects of purines on the arteries.

In preparations where tone had been raised with noradrenaline, low concentrations (1 nm–1 μm) of adenosine triphosphate (ATP) and 2‐methylthioATP, but not α,β‐methyleneATP, produced concentration‐dependent relaxation. There was a lack of relationship between the relaxation response to acetylcholine and that to ATP.

In preparations under basal tone, high concentrations (1 μm–1 mm) of ATP, 2‐methylthioATP and α,β‐methyleneATP produced concentration‐dependent contractions.

The rank order of potency of the purine nucleotide analogues for the relaxation response was 2‐methylthioATP > ATP > α,β‐methyleneATP and for the contractile response it was α,β‐methyleneATP > ATP = 2‐methylthioATP.

Adenosine produced concentration‐dependent relaxation in preparations under raised tone and was less potent than ATP but did not produce contraction in preparations at basal tone. Relaxation responses to adenosine, but not to ATP, were antagonized by 8‐phenyltheophylline.

These results indicate the presence of vasodilator P2y‐ and P1‐purinoceptors and vasoconstrictor P2x‐purinoceptors on human resistance arteries isolated from omental and subcutaneous sites.