bluuebunny/crossref_metadata_2025 huggingface dataset:
An electrophysiological study of the actions of angiotensin II at the sympathetic neuroeffector junction in the guinea‐pig vas deferens
Authors: Ziogas James , Cunnane Thomas C.
Published: July 2012

The effects of angiotensin II on sympathetic neuroeffector transmission in the guinea‐pig vas deferens have been investigated by the use of intracellular and focal extracellular recording techniques to measure indirectly, the release of adenosine 5′‐triphosphate (ATP).

Angiotensin II (10–100 nm) did not alter the amplitude of the first excitatory junction potential (e.j.p.) in a train but increased the amplitude of subsequent e.j.ps. There was a corresponding increase in the probability of occurrence of extracellularly recorded evoked excitatory junction currents (e.j.cs). Spontaneous quantal transmitter release was unaffected by angiotensin II.

The enhancement of transmitter release produced by angiotensin II was prevented by the angiotensin receptor antagonist, saralasin.

The increase in transmitter release produced by angiotensin II was due to an increase in the probability of transmitter release from individual varicosities and not due to any detectable change in the configuration of the nerve terminal impulse or to the induction of repetitive firing.

There was no overall enhancement of e.j.ps or e.j.cs by angiotensin II in reserpinized tissues. Surprisingly, the predominant effect of angiotensin II in reserpinized vasa deferentia was to inhibit evoked transmitter release, an effect reversed by indomethacin (3 μm).

The results show that angiotensin II increases the release of sympathetic transmitter by activating prejunctional angiotensin II receptors. However, when the co‐transmitter noradrenaline was depleted, angiotensin II now inhibited transmitter release indirectly, presumably by stimulating prostaglandin formation in the smooth muscle cells which then inhibited release transjunctionally.
Nedocromil sodium inhibits airway hyperresponsiveness and eosinophilic infiltration induced by repeated antigen challenge in guinea‐pigs
Authors: Schellenberg R. Robert , Ishida Kiyoshi , Thomson Randall J.
Published: July 2012

Repeated exposure to ovalbumin aerosol produced significant increases in epithelial eosinophils of airways of all sizes and produced increased pulmonary resistance (RL) to inhaled acetylcholine (ACh) in guinea‐pigs.

Nedocromil sodium 10 mg ml−1, by nebulization prior to each ovalbumin (OA) challenge inhibited both the airway eosinophilia and hyperresponsiveness to ACh.

Nedocromil sodium pretreatment (10 mg ml−1 by nebulization) 10 min prior to OA completely inhibited the acute bronchoconstrictor response to OA.

Our findings suggest that nedocromil sodium inhibits airway hyperresponsiveness by inhibiting eosinophilic infiltration, or by simultaneously inhibiting mechanisms involved in both processes.
Direct evidence for an important species difference in the mechanism of 8‐OH‐DPAT‐induced hypothermia
Authors: Bill D.J. , Knight M. , Forster E.A. , Fletche A.
Published: July 2012

Parallel series of experiments were carried out in the rat and mouse in order to investigate the mechanism(s) underlying the hypothermia induced in rodents by the selective 5‐HT1A receptor agonist, 8‐hydroxy‐2‐(di‐n‐propylamino)tetralin (8‐OH‐DPAT).

In the mouse, lesioning of central 5‐hydroxytryptaminergic neurones (by use of the neurotoxin, 5,7‐dihydroxytryptamine; 5,7‐DHT) abolished the hypothermic response to 8‐OH‐DPAT, and depletion of brain 5‐hydroxytryptamine (5‐HT) levels (with the 5‐HT synthesis inhibitor, p‐chlorophenylalanine) markedly attenuated the response in this species. These pretreatments did not significantly attenuate 8‐OH‐DPAT‐induced hypothermia in the rat, except for a significant attenuation of the response in 5,7‐DHT‐lesioned rats at the top dose of 8‐OH‐DPAT (1.0 mg kg−1, s.c.).

Pharmacological pretreatments which facilitate 5‐HT release (selective 5‐HT uptake inhibitors, precursor (5‐hydroxytryptophan) loading, or fenfluramine), markedly attenuated or abolished 8‐OH‐DPAT‐induced hypothermia in the mouse. These pretreatments generally had no significant effect on 8‐OH‐DPAT‐induced hypothermia in the rat.

The selective noradrenaline uptake inhibitor, desipramine, had no effect on the hypothermic response to 8‐OH‐DPAT in either species. The selective dopamine uptake inhibitor, nomifensin, significantly increased the hypothermic response to 8‐OH‐DPAT in the mouse, but did not affect the response in the rat except at high, motor stimulant doses, when the response was attenuated.

These data are consistent with the hypothesis that 8‐OH‐DPAT‐induced hypothermia is mediated by presynaptic autoreceptors in the mouse and by postsynaptic 5‐HT1A receptors in the rat. Preliminary data also indicate an involvement of dopamine release in the mouse but not in the rat.
Haemodynamic changes and acetylcholine‐induced hypotensive responses after NG‐nitro‐l‐arginine methyl ester in rats and cats
Authors: van Gelderen E. Marcel , Heiligers Jan P.C. , Saxena Pramod R.
Published: July 2012

The haemodynamic effects of NG‐nitro‐l‐arginine methylester (l‐NAME; 1, 3,10 and 30 mg kg−1) and its potential ability to attenuate the hypotensive responses to acetylcholine (0.03, 0.1, 1.0 and 3.0 μg kg−1) have been investigated in anaesthetized rats and cats.

In the rat, l‐NAME elicited a dose‐dependent pressor effect increasing mean arterial blood pressure from the baseline value of 116 ± 4 mmHg to a maximum of 156 ± 6 mmHg with 30 mg kg−1. This increase in blood pressure could be only partly reversed by l‐arginine (300 mg kg−1). However, the increase in blood pressure by lower doses (up to 10 mg kg−1) of l‐NAME was effectively reversed by l‐arginine (1000 mg kg−1).

In the cat, l‐NAME did not significantly modify systemic haemodynamic variables (heart rate, mean arterial blood pressure, cardiac output, stroke volume or total peripheral resistance), when compared to the changes in saline‐treated animals. Administration of l‐arginine did not cause any significant effect in cats treated with l‐NAME, but some decrease in heart rate and increases in cardiac output and stroke volume were observed in the saline‐treated group.

With the lowest dose (1 mg kg−1), l‐NAME did not affect tissue blood flows in the cat, but higher doses (3 and 30 mg kg−1) significantly reduced blood flows to the mesentery, stomach, spleen, intestines, lungs and the total liver. l‐Arginine (300 mg kg−1) injected into the control (saline‐treated) animals resulted in a significant increase in blood flow to the heart, mesentery, lungs as well as the total liver, particularly its portal fraction. l‐Arginine‐induced increases in tissue blood flows (mesentery, kidneys, spleen, lungs, total liver and portal blood flow) in saline‐treated animals were attenuated in animals treated with l‐NAME.

The acetylcholine‐induced peak hypotensive response was not reduced in rats or cats by l‐NAME. The duration of acetylcholine response was, however, attenuated in both species by l‐NAME. Treatment with l‐arginine (10–100 mg kg−1) did not change the acetylcholine‐induced hypotension.

The above results reveal a marked difference between the haemodynamic effects of l‐NAME in rats and cats and suggest that in cats, unlike rats, the role of the l‐arginine‐NO pathway in the regulation of blood pressure is rather limited, although such a pathway may exist in several tissues. Furthermore, the hypotensive response to acetylcholine in both species seems to be mediated largely by NO‐independent pathways.
Blockade of intracellular actions of calcium may protect against ischaemic damage to the gerbil brain
Authors: Asano T. , Ikegaki I. , Satoh S. , Mochizuki D. , Hidaka H. , Suzuki Y. , Shibuya M. , Sugita K.
Published: July 2012

The brain cytoprotective effects of a putative calcium‐associated protein kinase inhibitor, HA1077, as well as a calcium entry blocker nicardipine were evaluated in models of cerebral ischaemia in Mongolian gerbils. Morphological changes characterizing delayed neuronal death of selectively vulnerable CA1 pyramidal neurones in the hippocampus of the Mongolian gerbil brain occurred 7 days after transient bilateral occlusion of the common carotid arteries.

A single injection of HA1077 (1 and 3 mg kg−1, i.p.) 5 min after the occlusion led to a dose‐dependent protection of the CA1 neurones. Repeated administrations of HA1077 (1 and 3 mg kg−1, i.p., twice daily for 7 days post‐ischaemia) revealed an increase in the number of normal cells, compared to findings with a single administration.

In contrast to HA1077, nicardipine (0.3 and 1 mg kg−1, i.p.) did not reduce neuronal degeneration.

HA1077 did not interact with the ion channel within which MK‐801 binds, as determined by receptor binding.

The calcium ionophore, A23187, caused a tonic contraction in canine cerebral arterial strips. HA1077, but not nicardipine, relaxed the A23187‐induced contraction, concentration‐dependently.

These results suggest that blockade of the intracellular actions of calcium may provide protection against ischaemic damage in the brain.
Effects of zaprinast and rolipram on platelet aggregation and arrhythmias following myocardial ischaemia and reperfusion in anaesthetized rabbits
Authors: Holbrook Mark , Coker Susan J.
Published: July 2012

This study was designed to compare the effects of two selective inhibitors of certain phosphodiesterase (PDE) isoenzymes on arrhythmias induced by coronary artery occlusion and reperfusion. The drugs used were zaprinast which inhibits guanosine 3′: 5′‐cyclic monophosphate (cyclic GMP)‐specific PDE (PDE V) and rolipram which inhibits cyclic GMP‐insensitive, adenosine 3′: 5′‐cyclic monophosphate (cyclic AMP)‐specific PDE (PDE IV).

Pretreatment of anaesthetized rabbits with zaprinast (300 μg kg−1 plus 30 μg kg−1 min−1) had no significant effect on ischaemia‐ or reperfusion‐induced ST‐segment changes, or arrhythmias. In contrast, rolipram (30 μg kg−1 plus 3μg kg−1 min−1) and (100 μg kg−1 plus 10μg kg−1min−1) increased the severity of arrhythmias. With the higher dose of rolipram, ST‐segment changes were increased in magnitude and mortality due to ventricular fibrillation during ischaemia or reperfusion was increased to 80% compared with 30% in controls (n = 10 per group).

Zaprinast caused small but significant increases in heart rate and arterial blood pressure whereas rolipram decreased diastolic arterial pressure, increased left ventricular (LV) dP/dtmax and substantially increased heart rate.

At the end of each experiment platelet aggregation was measured ex vivo. Pretreatment of rabbits with either dose of rolipram had no significant effect on platelet aggregation induced by adenosine diphosphate (ADP), collagen, arachidonic acid or thrombin or on isoprenaline‐ or prostacyclin‐induced inhibition of aggregation. Aggregatory responses to ADP and collagen were increased in platelets obtained from rabbits which had received zaprinast.

These results indicate that in the dose used here, the PDE V inhibitor zaprinast had no significant effect on arrhythmias. The effects of the PDE IV inhibitor rolipram on haemodynamics, combined with its lack of antiplatelet activity, may have contributed to the exacerbation of arrhythmias observed during myocardial ischaemia and reperfusion.
Characterization of diadenosine tetraphosphate (Ap4A) binding sites in cultured chromaffin cells: evidence for a P2y site
Authors: Pintor Jesús , Torres Magdalena , Castro Enrique , Miras‐Portugal M. Teresa
Published: July 2012

Diadenosine tetraphosphate (Ap4A) a dinucleotide, which is stored in secretory granules, presents two types of high affinity binding sites in chromaffin cells. A Kd value of 8 ± 0.65 × 10−11 m and Bmax value of 5420 ± 450 sites per cell were obtained for the high affinity binding site. A Kd value of 5.6 ± 0.53 × 10−9 m and a Bmax value close to 70,000 sites per cell were obtained for the second binding site with high affinity.

The diadenosine polyphosphates, Ap3A, Ap4A, Ap5A and Ap6A, displaced [3H]‐Ap4A from the two binding sites, the Ki values being 1.0 nm, 0.013 nm, 0.013 nm and 0.013 nm for the very high affinity binding site and 0.5 μm, 0.13 μm, 0.062 μm and 0.75 μm for the second binding site.

The ATP analogues displaced [3H]‐Ap4A with the potency order of the P2y receptors, adenosine 5′‐O‐(2 thiodiphosphate) (ADP‐β‐S) > 5′‐adenylyl imidodiphosphate (AMP‐PNP) > α,β‐methylene ATP (α,β‐MeATP), in both binding sites. The Ki, values were respectively 0.075 nm, 0.2 nm and 0.75 nm for the very high affinity binding site and 0.125 μm, 0.5 μm and 0.9 μm for the second binding site.
The effects of phosphoramidon on the regional haemodynamic responses to human proendothelin [1–38] in conscious rats
Authors: Gardiner Sheila M. , Compton Alix M. , Kemp Philip A. , Bennett Terence
Published: July 2012

Cardiovascular responses to human proendothelin [1–38], in the absence and presence of phosphoramidon, were studied in conscious Long Evans rats, chronically instrumented for the continuous recording of heart rate, systemic arterial blood pressure and renal, mesenteric and hindquarters blood flows.

A dose of 0.1 nmol kg−1 human proendothelin [1–38] caused a slight pressor effect (maximum 5 ± 2mmHg), but a clear bradycardia (maximum −29 ± 7 beats min−1). Renal haemodynamics were unchanged but there was mesenteric vasoconstriction and a vasodilatation followed by a vasoconstriction in the hindquarters.

A dose of 1.0 nmol kg−1 human proendothelin [1–38] caused a gradual hypertension (maximum 42 ± 4 mmHg at 10 min) and a profound bradycardia (–149 ± 10 beats min−1 at 30 min). There were gradual but marked, renal and hindquarters vasoconstrictions, whereas there was a substantial mesenteric vasoconstriction that was relatively rapid in onset.

In 2 animals, administration of human proendothelin [1–38] at a dose of 10 nmol kg−1 caused an initial hypotension followed by a rapidly‐developing pressor effect; there were renal and mesenteric vasoconstrictions and vasodilatation followed by vasoconstriction in the hindquarters. These changes were very similar to those seen following injection of endothelin‐1 (0.1 nmol kg−1).

Phosphoramidon (2 μmol kg−1) had no cardiovascular effects itself and it did not affect significantly the pressor or mesenteric vasoconstrictor effects of human proendothelin [1–38], but it reduced the bradycardia and renal and hindquarters vasoconstrictor responses. A higher dose of phosphoramidon (10 μmol kg−1) caused significant attenuation of all the responses to human proendothelin [1–38], but a substantial mesenteric vasoconstrictor response still occurred under these conditions.

The results are consistent with the involvement of phosphoramidon‐sensitive enzyme systems in the conversion of human proendothelin [1–38] to endothelin‐1 in vivo. In addition, considering the different patterns of responses to human proendothelin [1–38] in the effector tissues studied (heart, and renal, mesenteric and hindquarters vascular beds), and the differential degrees of inhibition of them by phosphoramidon, it is likely that the effects of human proendothelin [1–38] were due to its local (rather than systemic) conversion to endothelin‐1 by processes with differing degrees of susceptibility to phosphoramidon.
Potencies of antagonists indicate that 5‐HT1C receptors mediate 1–3(chlorophenyl)piperazine‐induced hypophagia
Authors: Kennett G.A. , Curzon G.
Published: July 2012

1–3(Chlorophenyl)piperazine (mCPP) (5 mg kg−1, i.p.) inhibited 2 h food intake in rats previously deprived of food for one day. Ten 5‐hydroxytryptamine (5‐HT) antagonists given s.c. opposed this hypophagic response. Calculated ID50 values correlated significantly with reported affinities (r = 0.81, n = 10, P < 0.01) for 5‐HT1C but not for 5‐HT2, 5‐HT1A, 5‐HT1B or 5‐HT1D receptors.

ID50 values of the ten antagonists against 5‐hydroxytryptophan (5‐HTP) + carbidopa‐induced head shakes (a 5‐HT2‐mediated response) correlated significantly (r = 0.81, n = 10, P < 0.01) with their affinities for 5‐HT2, but not for 5‐HT1A, 5‐HT1B, 5‐HT1C or 5‐HT1D receptors.

ID50 values for inhibition of hypophagia and head shakes did not correlate significantly with each other.

Ratios of ID50 values against hypophagia and 5‐HT2‐mediated head shakes gave indices of relative in vivo potencies independent of differences in drug metabolism and disposition. These ratios correlated highly significantly (r = 0.91, n = 10, P < 0.001) with the ratios of the affinities of the drugs for 5‐HT1C (but not for 5‐HT1A, 5‐HT1B or 5‐HT1B or 5‐HT1D receptors) and with their affinities for 5‐HT2 receptors. These results strongly support the hypothesis that mediation of mCPP‐induced hypophagia is by stimulation of 5‐HT1C receptors and the mediation of 5‐HTP‐induced head twitches by 5‐HT2 receptors.
The neuroprotective action of dizocilpine (MK‐801) in the rat middle cerebral artery occlusion model of focal ischaemia
Authors: Gill R. , Brazell C. , Woodruff G.N. , Kemp J.A.
Published: July 2012

An acute model of focal ischaemia, which involves permanent occlusion of the middle cerebral artery of the rat with 4 h survival, was used to find the minimum effective plasma concentration of dizocilpine (MK‐801) and to determine its dose‐effect relationship.

MK‐801 was administered at the time of occlusion and was given as an i.v. bolus followed by an infusion for 4 h to maintain a steady state plasma concentration of the drug throughout the study. MK‐801 was given at 3 dose levels; 0.04 mg kg−1 i.v. bolus + 0.6 μg kg−1 min−1 infusion; 0.12 mg kg−1 i.v. bolus + 1.8 μg kg−1 min−1 infusion; 0.4 mg kg−1 i.v. bolus + 6 μg kg−1 min−1 infusion, which gave mean plasma levels over the 4h of 8.0 ng ml−1, 18.9 ng ml−1 and 113.2 ng ml−1 respectively.

MK‐801 at 8.0 ng ml−1 gave 10% reduction in the volume of ischaemic brain damage in the cerebral cortex which just reached significance. The middle dose of MK‐801 (18.9 ng ml−1) gave a highly significant reduction in the volume of ischaemic brain damage in the cerebral cortex and hemisphere, volumes of ischaemic tissue being reduced by 60% and 50% compared to saline‐treated animals, respectively. The highest plasma concentration of MK‐801 (113.2 ng ml−1) resulted in a 35% reduction in the volume of hemispheric damage and a 40% reduction in the volume of cortical damage, which were significant.

The reduction in the amount of protection afforded by the highest dose of MK‐801 may be due to the hypotensive effect of this dose. There was no protection against the volume of damage in the caudate nucleus for any of the doses of MK‐801 tested.

Therefore the minimum effective plasma concentration of MK‐801 was 8.0 ng ml−1, although the greatest protection was seen with a plasma level of 18.9 ng ml−1. This correlates well with the concentration of MK‐801 required to block N‐methyl‐d‐aspartate (NMDA) receptors and prevent NMDA receptor mediated neurotoxicity in vitro.
Coronary vasodilatation induced by endotoxin in the rabbit isolated perfused heart is nitric oxide‐dependent and inhibited by dexamethasone
Authors: Smith Russell E.A. , Palmer Richard M.J. , Moncada Salvador
Published: July 2012

The coronary vasoconstriction induced by the thromboxane mimetic U46619 (9, 11 dideoxy methanoepoxy 9α, 11α prostaglandin F2α, 3–30 nm) was significantly attenuated in hearts obtained from rabbits treated with endotoxin (lipopolysaccharide, LPS, 200 μg kg−1, i.v.) 4 h before isolation of the heart. Under these conditions the vasoconstriction induced by two inhibitors of nitric oxide (NO) synthase, NG‐monomethyl‐l‐arginine (l‐NMMA) and N‐iminoethyl‐l‐ornithine (l‐NIO) (1–100 μm for each) was significantly enhanced when compared to that induced in hearts from control animals. Both the decreased response to U46619 and the increased response to inhibitors of NO synthase were significantly attenuated by administration of dexamethasone (4 mg kg−1, i.v.) 90 min before treatment with LPS. These data are consistent with the induction, by LPS, of an NO synthase, and the inhibition of this induction by dexamethasone. The enhanced NO synthesis contributes to the haemodynamic changes known to occur in endotoxin shock.
Prostacyclin activates tachykinin release from capsaicin‐sensitive afferents in guinea‐pig bronchi through a ruthenium red‐sensitive pathway
Authors: Mapp Cristina Elisabetta , Fabbri Leonardo Michele , Boniotti Anna , Maggi Carlo Alberto
Published: July 2012

We have investigated the ability of prostacyclin (PGI2) to contract guinea‐pig isolated bronchi and the possible involvement of capsaicin‐sensitive primary afferents in the response to PGI2.

PGI2 (0.1–100 μm) produced concentration‐dependent contractions of the guinea‐pig isolated bronchi. In vitro capsaicin desensitization (10 μm for 30 min followed by washing) significantly reduced the PGI2‐induced contraction at all concentrations tested. A capsaicin‐resistant component of contraction (40–60% of the overall response) was also evident.

Ruthenium red (3 μm), an inorganic dye which acts as a selective functional antagonist of capsaicin, significantly decreased PGI2‐induced contractions, without affecting the response to substance P, neurokinin A or acetylcholine.

MEN 10, 207, (Tyr5, d‐Trp6,8,9, Arg10)‐neurokinin A (4–10) (3 μm), a selective antagonist of NK2‐tachykinin receptors, significantly decreased PGI2‐induced contractions and neurokinin A‐induced contractions, without affecting the response to acetylcholine.

The effect of ruthenium red and MEN 10,207 on the one hand, and that of ruthenium red and capsaicin on the other was non additive.

These results indicate that PGI2‐induced contraction of the guinea‐pig isolated bronchi involves two distinct mechanisms, one of which involves transmitter (tachykinins) release from peripheral endings of capsaicin‐sensitive primary afferents. In as much as PGI2‐activation of primary afferents is sensitive to ruthenium red, we suggest that PGI2 shares a common mechanism of tachykinin release with that activated by capsaicin.
Fenoverine inhibition of calcium channel currents in single smooth muscle cells from rat portal vein and myometrium
Authors: Mironneau J. , Arnaudeau S. , Mironneau C.
Published: July 2012

The effects of fenoverine, an antispasmodic drug, have been studied on the Ca2+channel currents of isolated cells from rat portal vein and pregnant myometrium by the patch‐clamp technique (whole‐cell configuration).

Fenoverine inhibited both fast and slow Ca2+channel currents in a concentration‐dependent manner. Half‐inhibition of fast Ca2+channel current (holding potential of −70 mV) and slow Ca2+channel current (holding potential of −40 mV) in portal vein smooth muscle were obtained at concentrations of 7.5 and 1.9 μm, respectively. In myometrium, the fenoverine concentration which blocked 50% of the slow Ca2+channel current (holding potential of −70 mV) was 2.3 μm.

Administration of fenoverine at rest reduced both Ca2+channel currents. Currents activated repetitively, at a rate between 0.05 and 0.1 Hz, were inhibited equally which indicates an absence of use‐dependent inhibition.

When cells held at depolarized membrane potentials at which fast or slow Ca2+channel currents were strongly inactivated, the inhibitory effects of fenoverine were enhanced on both Ca2+channel currents which indicates that the fenoverine‐induced inhibition was voltage‐dependent. The fenoverine concentrations which blocked the inactivated Ca2+channels were 5–7 times lower than those which blocked the resting Ca2+channels.

Our results show that fenoverine depresses inward currents through fast and slow Ca2+channels. This effect may be explained by the preferential binding of fenoverine to resting Ca2+channels. In addition, fenoverine has a higher afinity for inactivated Ca2+channels than for resting channels.
Antagonism of relaxin by glibenclamide in the uterus of the rat in vivo
Authors: Downing Sandra J. , Hollingsworth M.
Published: July 2012

The effects of glibenclamide (a blocker of adenosine triphosphate [ATP]‐dependent K+‐channels) on the inhibition of uterine contractions by relaxin, salbutamol and cromakalim were compared in vivo.

Glibenclamide (20 mg kg−1) did not antagonize salbutamol. Glibenclamide produced a parallel rightward shift in the dose‐response curve to cromakalim with a 5.5 fold decrease in uterine sensitivity (post‐vehicle log ID50, −0.87 mg kg−1; post‐glibenclamide log ID50, −0.07 mg kg−1). Glibenclamide produced a non‐parallel rightward shift in the dose‐response curve to relaxin (post‐vehicle log ID50, 0.99 μg kg−1; post‐glibenclamide log ID50, 2.28 μg kg−1).

Glibenclamide reversed established inhibition of uterine contractions by cromakalim or relaxin but not that by salbutamol.

Insulin produced no antagonism of relaxin on isolated uterus of the rat, demonstrating that glibenclamide antagonism of relaxin in vivo is not by released insulin. Apamin did not antagonize relaxin in vivo, suggesting that small calcium‐activated K+‐channels are not involved in the action of relaxin.

Comparison of the lack of antagonism of salbutamol with the non‐competitive‐like antagonism of relaxin by glibenclamide suggests that relaxin does not relax uterine smooth muscle predominantly by increasing intracellular adenosine 3′, 5′‐cyclic monophosphate concentrations. Comparison of the non‐competitive‐like antagonism of relaxin and the competitive‐like antagonism of cromakalim by glibenclamide suggests that the two relaxants may share, in part, a common mechanism of action and that additional mechanism(s) may also be involved in the inhibitory action of relaxin.
Effects of 5‐HT uptake inhibitors, agonists and antagonists on the burying of harmless objects by mice; a putative test for anxiolytic agents
Authors: Njung'e K. , Handley S.L.
Published: July 2012

The effects of 5‐hydroxytryptamine (5‐HT) uptake inhibitors, agonists and antagonists have been evaluated on mouse marble‐burying behaviour, a putative test for anxiolytic agents. The high levels of locomotor activity occurring on first exposure to a circular runway (runway activity) were used as a separate test of non‐specific drug effects.

Fluvoxamine, zimeldine, indalpine and citalopram dose‐dependently inhibited burying without affecting runway activity. 5‐Hydroxytryptophan (5‐HTP, with carbidopa), 5‐methoxy‐N,N‐dimethyltryptamine, 8‐hydroxy‐2‐(di‐n‐propylamino) tetralin (8‐OHDPAT), buspirone, gepirone and ipsapirone reduced burying only at doses reducing runway activity. RU 24969 increased runway activity at all effective doses. 1‐(2,5‐Dimethoxy‐4‐iodophenyl)‐2 aminopropane (DOI), 1,‐(3‐trifluoromethylphenyl) piperazine (TFMPP) and l‐(3‐chlorophenyl)‐piperazine (mCPP) potently and differentially reduced burying at doses below those affecting runway activity.

5‐HT antagonists only reduced burying at high doses which also reduced runway activity. Burying inhibition by DOI was antagonized by ritanserin, ICI 169 369 and cyproheptadine but not by pindolol or a low (0.25 mg kg−1) dose of metergoline. Burying inhibition by mCPP was not altered by any of these agents except that it was potentiated by pindolol 5 mg kg−1.

Zimeldine burying inhibition was potentiated by ritanserin, ICI 169 369, ICS 205–930, cyproheptadine and pindolol. Runway activity was not affected by these drug combinations.

Zimeldine was administered in drinking water at a dose of 10 mg kg−1 daily for 21 days. Burying inhibition had disappeared by day 14 and did not recur 24 or 48 h after withdrawal at which times responses to DOI were at control levels.

Selective inhibition of marble burying was not found to be a property of 5‐HT‐related putative and actual anxiolytics such as buspirone, gepirone, ipsapirone, ritanserin and ondansetron. Nevertheless it was a general property of both 5‐HT uptake inhibitors and 5‐HT releasing agents; this generality suggests that elevated synaptic 5‐HT could be responsible for the effects of these latter agents. The action of DOI may be attributable to effects at the 5‐HT2 receptor but those of the 5‐HT agonist and releasing agent mCPP, and the uptake inhibitor zimeldine, could not be attributed to effects at any one 5‐HT receptor subtype. This, together with the potentiating effect of several 5‐HT antagonists on the response to zimeldine, raises the possibility of multiple interactions between 5‐HT receptor subtypes.
Effects of Ca2+antagonists on glutamate release and Ca2+influx in the hippocampus with in vivo intracerebral microdialysis
Authors: Lu Y. Ming , Zhang J. Tian , Zhao F. Qing , Qin Y. Fi
Published: July 2012

The extracellular glutamate content and Ca2+level in vivo in rat hippocampus were measured by brain microdialysis following administration of two depolarizing agents (veratridine, KCl) and quinolinic acid (Quin).

The two depolarizing agents increased the extracellular glutamate level (to between 280 and 320% basal) and decreased the extracellular Ca2+content (to 48% of basal). However, Quin did not change the glutamate level but decreased the Ca2+content.

The effects of Ca2+antagonists on the changes of glutamate and Ca2+level were evaluated in this experimental model. At a dose of 0.5 mg kg−1, i.v., nimodipine (L‐type channel blocker) did not produce significant changes in the stimulated‐glutamate release. A statistically significant inhibition of Ca2+influx was observed at a dose of 0.05 mg kg−1. In contrast, in those animals receiving the N‐type Ca2+antagonist, daurisoline (0.1, 1 or 5 mg kg−1, i.v.), a potent attenuation of both glutamate release and Ca2+influx was found.

We propose that the pharmacological properties of Ca2+influx and of neurotransmitter release differ and that nimodipine‐sensitive L‐type channels may not be very common in nerve terminals but are localized in cell soma. Daurisoline‐sensitive N‐type channels in nerve terminals have a much greater influence on excitatory amino acid release.
Muscarinic antagonists attenuate the increase in accumbens and striatum dopamine metabolism produced by clozapine but not by haloperidol
Authors: Rivest Robert , Marsden Charles A.
Published: July 2012

The effect of the muscarinic antagonists, scopolamine and atropine, were examined on the increase in extracellular 3,4‐dihydroxyphenylacetic acid (DOPAC) in the nucleus accumbens and the striatum induced by haloperidol and clozapine by use of in vivo differential pulse voltammetry with carbon fibre electrodes in anaesthetized rats.

Animals received saline (1 ml kg−1, s.c.), scopolamine (1 mg kg−1, o.p.) or atropine (20 μg, i.c.v.) followed 15 min later by saline (10 μ1, i.c.v.), haloperidol (1 mg kg−1, s.c.) or clozapine (30 mg kg−1, i.p.) and extracellular DOPAC was simultaneously recorded in the nucleus accumbens and the striatum every 5 min for 60 min after drug administration.

Scopolamine or atropine alone had no effect on the DOPAC peak height but attenuated the increase in extracellular DOPAC induced by clozapine in both brain regions. Neither scopolamine nor atropine altered the haloperidol‐induced increase in accumbens or striatal extracellular DOPAC.

The present results demonstrate that muscarinic antagonists attenuate the increase in accumbens and striatal dopamine metabolism in vivo produced by the atypical neuroleptic clozapine but not the haloperidol‐induced increase in dopamine metabolism. The results indicate that central muscarinic receptors are involved in the actions on dopaminergic function of clozapine but not haloperidol.
Sedation and histamine H1‐receptor antagonism: studies in man with the enantiomers of chlorpheniramine and dimethindene
Authors: Nicholson A.N. , Pascoe Peta A. , Turner Claire , Ganellin C.R. , Greengrass P.M. , Casy A.F. , Mercer Amanda D.
Published: July 2012

The effects of 10 mg (+)‐ and (−)‐chlorpheniramine and 5 mg (+)‐ and (−)‐dimethindene on daytime sleep latencies, digit symbol substitution and subjective assessments of mood and well‐being were studied in 6 healthy young adult humans. Each subject also took 5 mg triprolidine hydrochloride as an active control and two placebos.

Daytime sleep latencies were reduced with triprolidine, (+)‐chlorpheniramine and (−)‐dimethindene, and subjects also reported that they felt more sleepy after (+)‐chlorpheniramine and (−)‐dimethindene. Performance on digit symbol substitution was impaired with (+)‐chlorpheniramine.

Changes in measures with (−)‐chlorpheniramine and (+)‐dimethindene were not different from changes with placebo.

In the present study, changes in measures of drowsiness and performance were limited to the enantiomers with high affinity for the histamine H1‐receptor. These findings strongly suggest that sedation can arise from H1‐receptor antagonism alone, and provide further support for the belief that the histaminergic system is concerned with the regulation of alertness in man.
Differences in inositol phosphate production in blood vessels of normotensive and spontaneously hypertensive rats
Authors: Vila E. , Macrae I.M. , Reid J.L.
Published: July 2012

Total inositol phosphate formation was measured in labelled femoral and iliac arteries and veins of 14 week‐old spontaneously hypertensive rats (SHR) and age‐matched Wistar Kyoto (WKY) controls, either unstimulated or in the presence of noradrenaline.

Basal levels of [3H]‐inositol phosphates and [3H]‐phosphatidylinositol were significantly enhanced in SHR femoral artery, but not in the other 3 vessels, compared with WKY.

Noradrenaline stimulated phosphoinositide hydrolysis in all four vessels of SHR and WKY. Pretreatment with prazosin (10−7–10−6m) but not with yohimbine (10−7m), inhibited the noradrenaline‐induced inositol phosphate formation indicating an α1‐adrenoceptor‐mediated response.

In the femoral artery of SHR compared to WKY, [3H]‐inositol phosphate accumulation induced by noradrenaline (10−7–10−5m) was significantly reduced when expressed relative to basal values although the response to higher concentrations (10−4–10−3m) was not altered. In contrast, a significant reduction of inositol phosphates was seen only with 10−7m noradrenaline when absolute values were compared. In the other three vessels, no difference in noradrenaline‐induced [3H]‐inositol phosphate formation was observed between strains.

These data suggest that phosphoinositide hydrolysis‐mediated by α1‐adrenoceptors may be reduced in some but not all blood vessels of adult SHR.
Characterization of the biological effects of 2‐methylthio‐ATP on rat hepatocytes: clear‐cut differences with ATP
Authors: Keppens Stefaan , De Wulf Henri
Published: July 2012

In several tissues, 2‐methylthio adenosine triphosphate (2MeSATP) is a very potent P2Y‐purine agonist. In rat hepatocytes, 2MeSATP half‐maximally activated glycogen phosphorylase at 20 nm and was therefore about 25 times more effective than ATP (Ka 0.5–0.8 μm). This strong glycogenolytic potency of 2MeSATP suggests on its own the presence of P2Y‐purinoceptors in liver.

Displacement of the radioligand ATPα[35S] from its receptor however occurred at much higher concentrations of 2MeSATP than was anticipated on the basis of its glycogenolytic potency.

The interaction of 2MeSATP with the receptor, characterized with ATPα[35S] as radioligand, cannot be considered as a pure competitive interaction.

2MeSATP did not share the ability of ATP to counteract the effect of glucagon on the adenosine 3′:5′‐cyclic monophosphate levels.

2MeSATP barely increased the levels of inositol trisphosphate (IP3).

The glycogenolytic effect of 2MeSATP was completely abolished by pretreatment of the hepatocytes with phorbol myristic acetate.

It is tentatively concluded that 2MeSATP and ATP are interacting with different P2 purinoceptors.
Investigation of the effects of IVth ventricular administration of the 5‐HT2 agonist, 1‐(2,5‐dimethoxy‐4‐iodophenyl)‐2‐aminopropane (DOI), on autonomic outflow in the anaesthetized cat
Authors: Shepheard Sara L. , Jordan David , Ramage Andrew G.
Published: July 2012

The effects of IVth ventricular injections of 1‐(2,5‐dimethoxy‐4‐iodophenyl)‐2‐aminopropane (DOI) on renal, splanchnic and cardiac sympathetic nerve activities, phrenic nerve activity, arterial blood pressure, heart rate, femoral arterial conductance, tracheal and intragastric pressures were investigated in α‐chloralose anaesthetized, neuromuscular blocked and artificially ventilated cats.

Cumulative doses of DOI (80, 160 and 320 nmol kg−1) injected into the IVth ventricle caused an increase in mean arterial blood pressure, a fall in femoral arterial conductance, an increase in tracheal pressure and a decrease in the rate of phrenic nerve bursts but did not affect any of the other variables recorded.

Even after i.v. administration of the peripheral 5‐HT2 antagonist BW501C67 (2 mg kg−1) following the highest dose of DOI there was still a significant pressor response, a fall in femoral arterial conductance and small increase in tracheal pressure.

In control experiments, intravenous infusion of noradrenaline to raise blood pressure to the levels obtained during the cumulative doses of DOI caused large falls in renal, splanchnic and cardiac nerve activities which were all significantly lower than those recorded during the cumulative doses of DOI.

The results of this study provide evidence for a brainstem site of action of DOI in producing hypertension and further support the hypothesis that central 5‐HT2 receptors are involved in the control of skeletal muscle and skin vascular beds.
Adenosine modulation of potassium currents in postganglionic neurones of cultured avian ciliary ganglia
Authors: Bennett Max R. , Kerr Rod , Nichol Kerry
Published: July 2012

Potassium currents in cultured postganglionic neurones of avian ciliary ganglia were analysed under whole‐cell voltage clamp and their modulation by adenosine determined.

In the presence of tetrodotoxin (200 nm), and with moderate holding potentials (Vh = −40 mV), the steady‐state current‐voltage (I/V) curve was N‐shaped over the range from −70 mV to +155 mV. CsCl (1 m) blocked the current, indicating that it was carried by K+. If Ca2+influx was blocked by CdCl2 (500 μm) then the outward current was reduced and the N‐shaped I–V curve lost, indicating the presence of a calcium‐activated potassium current (IK(Ca)); the remaining current, due to the delayed rectifier (IK), increased with depolarization up to about a conductance of 10 nS near +50 mV. This IK was 50% activated at about +20 mV and 50% inactivated at about −50 mV. Adenosine (10 μm) had similar affects on the N‐shaped I/V curve as did CdCl2, indicating that it blocked IK(Ca). However, adenosine had little affect on the steady‐state current in the presence of CdCl2, indicating that it did not much affect IK.

In the presence of tetrodotoxin (200 nm), a large inward current occurred for large hyperpolarizations from a Vh = −50 mV. This inward rectifying current (IIR) had a reversal potential near EK and showed 50% activation at about −130 mV. Adenosine (10 μm) reduced IIR, by as much as 50% at large hyperpolarizations beyond −80 mV.

Relaxations of the outward current on hyperpolarization from Vh = −30 mV were blocked by carbachol (10 μm), had a reversal potential near EK, and an I/V curve typical of IM currents. These currents were little affected by adenosine (10 μm).

A fast transient outward current, due to depolarizing pulses from a large Vh = −110 mV was observed in the presence of tetrodotoxin (200 nm). This had the characteristics of an IA current as it could be blocked with 4‐aminopyridine (5 mm) and was 50% activated at about −20 mV and 50% inactivated at about −94 mV. The IA current was reduced by 42% at a depolarization of −20 mV by adenosine (10 μm).

Many neurones possessed a fast transient outward current that was blocked by tetrodotoxin (200 nm). This current could be blocked with 4‐aminopyridine (5 mm); it therefore has the characteristics of a sodium‐activated potassium current (IK(Na)). This IK(Na) was unaffected by adenosine (10 μm).

These results are discussed in relation to the role of adenosine in blocking Ca2+channels and thereby modifying calcium‐dependent components of K+currents.
Microinjections of 5‐HT1A agonists into the dorsal motor vagal nucleus produce a bradycardia in the atenolol‐pretreated anaesthetized rat
Authors: Sporton Simon C.E. , Shepheard Sara L. , Jordan David , Ramage Andrew G.
Published: July 2012

The effects of microinjections (100 nl) into the dorsal motor vagal nucleus of the 5‐HT1A receptor agonists 8‐hydroxy‐2‐(di‐n‐propylamino)tetralin (8‐OH‐DPAT) and flesinoxan, the 5‐HT2 receptor agonist (±)‐1‐(2,5‐dimethoxy‐4‐iodophenyl)‐2‐aminopropane hydrochloride (DOI), the 5‐HT3 receptor agonist phenylbiguanide (PBG), the α2‐adrenoceptor agonist clonidine and the excitatory amino acid glutamate on heart rate, blood pressure, tracheal pressure and phrenic nerve activity were investigated in atenolol‐pretreated rats anaesthetized with sodium pentobarbitone.

Microinjections of glutamate (2.5 nmol) caused decreases in blood pressure, heart rate and phrenic nerve activity. In contrast, microinjections of 5‐HT (1.2 nmol), 8‐OH‐DPAT (1.2 nmol) and flesinoxan (1.3 nmol) all caused a bradycardia but had no effect on blood pressure. In addition, 8‐OH‐DPAT and flesinoxan caused an increase in phrenic nerve activity.

Microinjections of DOI, PBG and clonidine had no significant effect on any of the variables recorded. None of the drugs used had any significant effect on tracheal pressure.

These results support the hypothesis that activation of 5‐HT1A receptors causes excitation of cardiac vagal motoneurones and suggest that these receptors are also important in the control of central respiratory drive.
The guinea‐pig ileum preparation as a model for 5‐HT1A receptors: anomalous effects with RS‐30199–193
Authors: Small Catherine , Brown Christine M. , Redfern William S. , Spedding Michael
Published: July 2012

Agents that have high and selective affinity for the 5‐HT1A site such as 8‐hydroxy‐2‐(di‐n‐propylamino)tetralin (8‐OH‐DPAT) and N,N‐dipropyl‐5‐carboxamidotryptamine (DP5CT) inhibited the responses to field stimulation in guinea‐pig ileum preparations; the inhibitory effects were antagonized by methiothepin and spiperone, consistent with effects at the 5‐HT1A site.

The inhibitory effects of DP5CT were pronounced in Tyrode solution containing low Ca2+(0.9 mm), but were much less apparent in Tyrode solution containing 1.8 or 5.4 mm Ca2+.

Responses to DP5CT were abolished by pretreatment with phorbol dibutyrate (3 μm), whereas the responses to UK14304 were only slightly inhibited.

Buspirone and ipsapirone (1 μm) inhibited the responses to field stimulation, and the effects were resistant to idazoxan, but inhibited by 8‐OH‐DPAT or spiperone.

RS‐30199–193 (5‐chloro‐2‐methyl‐1,2,3,4,8,9,10,10a‐octahydronaphth‐[1,8‐cd]‐azepine hydrochloride) an azepine with high affinity for the 5‐HT1A site in rat cerebral cortex in binding experiments, augmented contractions, but did not antagonize the responses to DP5CT or to 8‐OH‐DPAT.

The hybrid compound of RS‐30199–193 with buspirone, RS‐64459–193 (5‐chloro‐2‐[4‐(8‐azaspiro[4,5] decane‐7,9‐dione)‐but‐1‐yl]‐1,2,3,4,8,9,10,10a‐octahydronaphth[1,8‐cd]‐3‐azepine hydrochloride) maintained high affinity for the 5‐HT1A binding site in rat brain and both inhibited the response to field stimulation and antagonized the responses to 8‐OH‐DPAT and DP5CT. Thus the buspirone side chain when added to RS‐30199–193 appears either to induce affinity for a distinct subset of receptors in the guinea‐pig ileum or is required for functional effectiveness at the 5‐HT1A receptor.
Effects of histamine and activators of the cyclic AMP system on protein synthesis in and release of high molecular weight glycoproteins from isolated gastric non‐parietal cells
Authors: Heim H.‐K. , Oestmann A. , Sewing K.‐Fr.
Published: July 2012

Glycoprotein and protein synthesis in and release from pig isolated, enriched gastric mucous cells were measured by the incorporation of N‐acetyl‐[14C]‐d‐glucosamine and [3H]‐l‐leucine, respectively, into cellular and released acid precipitable material.

Histamine and activators of the adenosine 3′:5′‐cyclic monophosphate (cyclic AMP) system maximally stimulated total protein and glycoprotein synthesis in and release from the cells at concentrations of histamine (10 μm), forskolin (10–100 μm), 3‐isobutyl‐1‐methylxanthine (100 μm), and dibutyryl cyclic AMP (1–3 mm), respectively. In the presence of 3‐isobutyl‐1‐methylxanthine (30 μm) histamine stimulation was enhanced.

As shown by gel chromatography, stimulation by histamine (100 μm), forskolin (10 μm), 3‐isobutyl‐1‐methylxanthine (100 μm) and dibutyryl cyclic AMP (1 mm) resulted in a release of high molecular weight (≅2 × 106daltons) glycoproteins from the cells. The histamine H2‐receptor antagonist, ranitidine (100 μm), blocked the effect of histamine.

We conclude that cyclic AMP‐dependent processes are involved in the regulation of protein and glycoprotein synthesis in and the release of high molecular weight (mucous) glycoproteins from pig gastric non‐parietal cells and that histamine may be a physiological activator of this system.
Endogenous nitric oxide modulates adrenergic neural vasoconstriction in guinea‐pig pulmonary artery
Authors: Liu S.F. , Crawley D.E. , Evans T.W. , Barnes P.J.
Published: July 2012

Electrical field stimulation (EFS) of guinea‐pig isolated pulmonary artery induced a frequency‐dependent contraction. This was abolished by tetrodotoxin (1 μm) and prevented by phentolamine and prazosin (both 1 μm), indicating a role for α1‐adrenoceptors activated by noradrenaline (NA) released from perivascular adrenergic nerves.

l‐NG‐monomethyl arginine (l‐NMMA, 0.3–100 μm) caused a concentration‐dependent enhancement of the EFS‐induced contraction with a 3.4 ± 0.5 fold increase at 100 μm (n = 6). The augmenting effect of 30 μm l‐NMMA on the contraction to EFS was completely reversed by 100–300 μm l‐arginine, but not by an identical concentration of d‐arginine.

The contractile response to exogenous NA was similarly enhanced by 30 μm l‐NMMA (2.9 ± 0.6 fold increase, n = 5).

The contractile responses to exogenous phenylephrine and prostaglandin F2α which matched the contraction to EFS (4 Hz) were equally augmented by 30 μm l‐NMMA.

In vessel rings submaximally contracted with the thromboxane analogue U44069 (2 μm), the selective α2‐adrenoceptor agonist UK14304 induced concentration‐dependent relaxation, which was abolished by removal of endothelium. NA had little relaxant effect on these precontracted vessel rings unless in the presence of prazosin (1 μm).

Indomethacin had no significant effect on the contractile response to EFS or NA, indicating that vasodilator cyclo‐oxygenase products such as prostacyclin are not involved in modulating these responses.

Our results suggest that endogenous nitric oxide inhibits the contractile response to adrenergic nerve stimulation in the guinea‐pig pulmonary artery by a postjunctional mechanism, but release of prostacyclin does not modulate these responses. Basal release of nitric oxide from endothelial cells may account for this inhibition.
The non‐peptide NK1 receptor antagonist, (±)‐CP‐96,345, produces antinociceptive and anti‐oedema effects in the rat
Authors: Birch P.J. , Harrison S.M. , Hayes A.G. , Rogers H. , Tyers M.B.
Published: July 2012

The non‐peptide NK1 receptor antagonist, (±)‐CP‐96,345, has been evaluated for antinociceptive activity in two well‐characterized inflammatory pain models in the rat. (±)‐CP‐96,345 abolished carrageenin‐induced mechanical hyperalgesia, significantly reduced carrageenin‐induced paw oedema and attenuated the second phase of the formalin response. The results suggest that NK1 receptor activation occurs during the induction of inflammatory pain states in the rat.