bluuebunny/crossref_metadata_2025 huggingface dataset:
The influence of thyroid states upon responses of the rat aorta to catecholamines
Authors: Gunasekera Ranjan D. , Kuriyama Hirosi
Published: July 2012

Mechanical responses to various stimulants and the distribution of adrenoceptor subtypes were investigated in smooth muscle cells of the rat aorta in eu‐ (control), hyper‐ and hypo‐thyroid states.

Concentration‐response relationships for K showed that the KCl EC50 value was slightly higher (28.4 mm K) in hypothyroid than in euthyroid and hyperthyroid states (22.5 mm and 22.8 mm K, respectively). The order of maximum amplitudes of KCl contraction was control > hypothyroid > hyperthyroid.

The EC50 values for the noradrenaline (NA)‐induced contraction for eu‐, hypo‐ and hyper‐thyroid states were 7.4, 12.5 and 5.5 nm, respectively. The density of α1‐adrenoceptors was increased to 1.4 times the control in the hypothyroid state and reduced to 0.26 times the control in the hyperthyroid state.

The EC50 values for the phenylephrine‐induced contraction in eu‐, hypo‐ and hyper‐thyroid states were 43.4, 247 and 41.5 nm, respectively, and those for clonidine 104, 1360 and 56.5 nm, respectively. The IC50 values for prazosin against 0.1 μm NA‐induced contractions in eu‐, hypo‐ and hyper‐thyroid states were 5.8, 3.5 and 0.7 nm, respectively, and those for yohimbine 8.9, 5.4 and 4.1 μm, respectively.

The IC50 values for isoprenaline against phenylephrine‐induced contractions were 63 nm and 2.4 μm in hyper‐ and eu‐thyroid states, respectively, and the corresponding IC25 values for eu‐ and hypo‐thyroid states were 72 and 423 nm, respectively. The density of β‐adrenoceptors was increased to 3.91 times the control in the hyperthyroid and reduced to 0.68 times the control in the hypothyroid states. The amount of adenosine 3′: 5′‐cyclic monophosphate (cyclic AMP) synthesized by isoprenaline increased in parallel with the density of β‐adrenoceptors in the three thyroid states.

NA consistently increased the amount of inositol 1,4,5‐trisphosphate (IP3) within 30 s in the three thyroid states. In the hypothyroid state, the amount of IP3 was slightly increased and in the hyperthyroid condition, it occurred to a lesser extent than in the euthyroid state.

The results indicate that in hypothyroidism, the density of α1‐adrenoceptors is increased and that of β‐adrenoceptors reduced in vascular beds. The latter but not the former is accompanied by corresponding mechanical responses. In hyperthyroidism, the density of α1‐adrenoceptors is decreased and β‐adrenoceptors increased with parallel changes in mechanical responses.
The effect of diltiazem on the coronary haemodynamic and cardiac functional effects produced by intracoronary administration of endothelin‐1 in the anaesthetized dog
Authors: Nichols Andrew J. , Koster Paul F. , Ohlstein Eliot H.
Published: July 2012

We have studied the effect of the calcium channel antagonist, diltiazem, on the coronary haemodynamic and cardiac functional responses produced by intracoronary (i.c.) administration of endothelin‐1 (ET‐1) in anaesthetized dogs.

ET‐1, 1, 3 and 10 ng kg−1 i.c., produced dose‐delated increases in coronary blood flow with no cardiac functional or systemic haemodynamic changes. ET‐1, 30, 100 and 300 ng kg−1 i.c., produced dose‐related reductions in coronary artery blood flow. The reduction in coronary blood flow was accompanied by dose‐related falls in cardiac output, mean arterial pressure, +dP/dt and –dP/dt and increases in left ventricular end‐diastolic pressure. However, there was no reflex tachycardia in response to the fall in blood pressure and at 300 ngkg−1, ET‐1 produced a 22% reduction in heart rate.

Following a series of abnormal ECG changes, four out of five dogs died of ventricular fibrillation at 13 ± 2 min after 300 ng kg−1 ET‐1.

The administration of diltiazem (15 μg kg−1 min−1, i.v.) reduced mean arterial pressure by 10% and heart rate by 15%, and increased coronary blood flow by 39%. Diltiazem did not have any significant effect on the coronary dilator response to low doses of ET‐1. Although there was a general trend for diltiazem to inhibit the coronary vasoconstrictor responses to ET‐1, diltiazem significantly attenuated only the reduction in coronary blood flow produced by 100 ng kg−1 ET‐1 by 60% but not the response to 30 or 300 ng kg−1 ET‐1. Two out of five diltiazem‐treated dogs died of ventricular fibrillation with a mean time to death of 20 min following treatment with ET‐1 (300 kg−1).

ET‐1 is a very potent coronary vasodilator. At slightly higher doses ET‐1 is also a coronary vasoconstrictor. ET‐1 also appears to have direct cardiotoxicity independent of myocardial ischaemia. The vasoconstrictor activity and direct cardiotoxicity are only weakly inhibited by diltiazem.
Regulation of gastric mucosal integrity by endogenous nitric oxide: interactions with prostanoids and sensory neuropeptides in the rat
Authors: Whittle B.J.R. , Lopez‐Belmonte J. , Moncada S.
Published: July 2012

The interactions between nitric oxide (NO), prostacyclin and sensory neuropeptides in the maintenance of gastric mucosal integrity have been investigated in the anaesthetized rat.

Administration of either NG‐monomethyl‐l‐arginine (l‐NMMA) to inhibit endothelium‐derived NO formation, indomethacin to inhibit prostanoid biosynthesis or chronic capsaicin pretreatment to deplete sensory neuropeptides, did not induce acute mucosal injury.

In capsaicin‐pretreated rats, however, l‐NMMA (12.5–100 mg kg−1 i.v.) dose‐dependently induced acute mucosal damage, characterized as vasocongestion and haemorrhagic necrosis. The enatiomer d‐NMMA (100 mg kg−1 i.v.) did not induce any detectable mucosal damage.

This mucosal injury induced by l‐NMMA was inhibited by concurrent administration of l‐arginine (300 mg kg‐1 i.v.).

In indomethacin (5 mg kg−1 i.v.)‐pretreated rats, l‐NMMA also induced mucosal damage. Furthermore, following indomethacin administration in capsaicin‐pretreated rats, l‐NMMA induced widespread, severe haemorrhagic necrotic damage.

These findings suggest a role for endogenous NO formed from l‐arginine, acting in concert with prostacyclin and sensory neuropeptides, in the modulation of gastric mucosal integrity.
Suramin antagonizes responses to P2‐purinoceptor agonists and purinergic nerve stimulation in the guinea‐pig urinary bladder and taenia coli
Authors: Hoyle Charles H.V. , Knight Gillian E. , Burnstock Geoffrey
Published: July 2012

Suramin, an inhibitor of several types of ATPase, was investigated for its ability to antagonize responses mediated via P2X‐purinoceptors in the guinea‐pig urinary bladder and P2Y‐purinoceptors in the guinea‐pig taenia coli.

In isolated strips of bladder detrusor muscle, suramin (100 μm‐1 mm) caused a non‐competitive antagonism of responses to α,β‐methylene ATP with an estimated pA2 of approximately 4.7, and inhibited responses to stimulation of the intramural purinergic nerves, with a similar pA2 value. At a concentration of 10 μm, suramin had little effect, but at a concentration of 1 μm, suramin potentiated responses to α,β‐methylene ATP, and potentiated responses to electrical stimulation of intramural purinergic nerves.

In isolated strips of taenia coli, in which a standard tone had been induced by carbachol (100 nm), suramin at 100 μm and 1 mm significantly antagonized relaxant responses to ATP (at an EC50 concentration) with an estimated pA2 of 5.0 ± 0.82 and relaxant responses to electrical stimulation of the intramural non‐adrenergic, non‐cholinergic inhibitory nerves, either single pulses or trains of 8 Hz for 10 s, with estimated pA2 values of 4.9 ± 0.93 and 4.6 ± 1.01, respectively. Suramin had no significant effect at 1 or 10 μm.

Suramin, at any of the concentrations tested, did not affect contractile responses to histamine (10 μm) or carbachol (10 μm) in the bladder detrusor preparations. In the taenia coli, suramin did not affect either the relaxant responses to noradrenaline (at an EC50 concentration) or the contractile responses to carbachol (100 nm).

Thus, suramin at concentrations above 10 μm blocked actions mediated via P2X‐ and P2Y‐purinoceptors in the guinea‐pig urinary bladder and taenia coli respectively. Potentiation of purinoceptor‐mediated activity was seen only at a low concentration of suramin (1 μm) and only in the urinary bladder (P2X‐purinoceptor). For its antagonistic activity suramin did not discriminate between P2X‐ and P2Y‐purinoceptors, but it was selective for P2‐purinoceptor‐mediated activity rather than that mediated via cholinoceptors, adrenoceptors or histamine receptors.
Antigen challenge induces pulmonary airway eosinophil accumulation and airway hyperreactivity in sensitized guinea‐pigs: the effect of anti‐asthma drugs
Authors: Sanjar S. , Aoki S. , Kristersson A. , Smith D. , Morley J.
Published: July 2012

Guinea‐pigs were sensitized with 3 injections of ovalbumin (OA) (1 or 10 μg per animal) using Al(OH)3and pertussis vaccine as adjuvants at two week intervals.

Sensitized guinea‐pigs were challenged with an aerosol of OA (0.1%) over a one hour period and both airway reactivity and cellular content of bronchoalveolar lavage (BAL) fluid were assessed at intervals for up to 7 days.

Guinea‐pigs sensitized with 1 μg of ovalbumin responded to an aerosol of OA with increased pulmonary airway eosinophilia, which was evident 1 day after challenge and was present for up to 7 days. Airway hyperreactivity was not detectable in these animals.

Guinea‐pigs sensitized with 10 μg of ovalbumin responded to an aerosol of OA with increased pulmonary airway neutrophilia and eosinophilia and with increased airway reactivity which was maximal between 8 and 24 h after exposure to OA.

Depletion of circulating platelets or neutrophils, by use of selective antisera, did not alter either the magnitude of eosinophilia or the intensity of airway reactivity in sensitized guinea‐pigs (10 μg) exposed to an aerosol of OA.

Pretreatment of sensitized guinea‐pigs (10 μg) for 6 days with AH 21–132, aminophylline, dexamethasone or ketotifen inhibited pulmonary airway eosinophilia, but did not diminish airway hyperreactivity. Neither eosinophil accumulation nor development of airway hyperreactivity was influenced by treatment with mepyramine or salbutamol over a 6 day period before OA inhalation.

Although eosinophilia may occur in association with increased airway reactivity in this animal model, there is no evidence of a causal relationship.
Potassium channel blockers and the effects of cromakalim on the smooth muscle of the guinea‐pig bladder
Authors: Fujii K. , Foster C.D. , Brading A.F. , Parekh A.B.
Published: July 2012

The K+ channel blocking drugs tetraethylammonium Cl (TEA), procaine, 4‐aminopyridine (4AP) and quinidine all produced concentration‐dependent contractions of strips of smooth muscle from the guinea‐pig urinary bladder. Apamin and glibenclamide caused little increase in the mechanical activity, and tolbutamide inhibited it.

TEA, procaine, 4AP, quinidine and apamin all increased the frequencies of spontaneous action potentials recorded with microelectrodes. TEA, quinidine and procaine all caused prolongation of the falling phase of the spike, and procaine and apamin completely abolished the after‐hyperpolarization.

TEA and procaine increased K+ efflux from the tissue, an effect blocked by nifedipine. TEA and apamin increased, whereas quinidine, procaine and 4AP decreased K+ uptake.

Cromakalim caused a concentration‐dependent hyperpolarization of the membrane, abolished spike activity, increased K+ fluxes and relaxed the smooth muscle. The relaxant effect of cromakalim was unaffected by apamin, and in its presence the effects of cromakalim on membrane potential and K+ fluxes were unchanged. Procaine abolished all the effects of cromakalim, and TEA at high concentrations reduced but did not abolish these effects. Quinidine reduced the effects of cromakalim on tension and membrane potential, but its actions were surmounted by higher concentrations of cromakalim. The effects of 4AP on tension and membrane properties were transitory, but it had some effects on the actions of cromakalim. Glibenclamide and tolbutamide reversed the relaxant effects of submaximal cromakalim concentrations, tolbutamide only transiently.

It is concluded that the channels opened by cromakalim are not those involved in generating the spike after‐hyperpolarization. They have properties similar to the delayed rectifier K+ channels responsible for spike repolarization, and also are similar to the ATP‐dependent K channels in vascular smooth muscle.
CGP 37849 and CGP 39551: novel and potent competitive N‐methyl‐d‐aspartate receptor antagonists with oral activity
Authors: Fagg G.E. , Olpe H.‐R. , Pozza M.F. , Baud J. , Steinmann M. , Schmutz M. , Portet C. , Baumann P. , Thedinga K. , Bittiger H. , Allgeier H. , Heckendorn R. , Angst C. , Brundish D. , Dingwall J.G.
Published: July 2012

The pharmacological properties of CGP 37849 (dl‐(E)‐2‐amino‐4‐methyl‐5‐phosphono‐3‐pentenoic acid; 4‐methyl‐APPA) and its carboxyethylester, CGP 39551, novel unsaturated analogues of the N‐methyl‐d‐aspartate (NMDA) receptor antagonist, 2‐amino‐5‐phosphonopentanoate (AP5), were evaluated in rodent brain in vitro and in vivo.

Radioligand binding experiments demonstrated that CGP 37849 potently (Ki 220 nm) and competitively inhibited NMDA‐sensitive l‐[3H]‐glutamate binding to postsynaptic density (PSD) fractions from rat brain. It inhibited the binding of the selective NMDA receptor antagonist, [3H]‐(±)‐3‐(2‐carboxypiperazin‐4‐yl)propyl‐1‐phosphonate (CPP), with a Ki of 35 nm, and was 4, 5 and 7 fold more potent than the antagonists ((±)‐cis‐4‐phosphonomethylpiperidine‐2‐carboxylic acid) (CGS 19755), CPP and d‐AP5, respectively. Inhibitory activity was associated exclusively with the trans configuration of the APPA molecule and with the d‐stereoisomer. CGP 39551 showed weaker activity at NMDA receptor recognition sites and both compounds were weak or inactive at 18 other receptor binding sites.

CGP 37849 and CGP 39551 were inactive as inhibitors of l‐[3H]‐glutamate uptake into rat brain synaptosomes and had no effect on the release of endogenous glutamate from rat hippocampal slices evoked by electrical field stimulation.

In the hippocampal slice in vitro, CGP 37849 selectively and reversibly antagonized NMDA‐evoked increases in CA1 pyramidal cell firing rate. In slices bathed in medium containing low Mg2+ levels, concentrations of CGP 37849 up to 10 μm suppressed burst firing evoked in CA1 neurones by stimulation of Schaffer collateral‐commissural fibres without affecting the magnitude of the initial population spike; CGP 39551 exerted the same effect but was weaker. In vivo, oral administration to rats of either CGP 37849 or CGP 39551 selectively blocked firing in hippocampal neurones induced by ionophoretically‐applied NMDA, without affecting the responses to quisqualate or kainate.

CGP 37849 and CGP 39551 suppressed maximal electroshock‐induced seizures in mice with ED50s of 21 and 4 mg kg−1 p.o., respectively.

CGP 37849 and CGP 39551 are potent and competitive NMDA receptor antagonists which show significant central effects following oral administration to animals. As such, they may find value as tools to elucidate the roles of NMDA receptors in brain function, and potentially as therapeutic agents for the treatment of neurological disorders such as epilepsy and ischaemic brain damage in man.
Influence of phorbol esters, and diacylglycerol kinase and lipase inhibitors on noradrenaline release and phosphoinositide hydrolysis in chromaffin cells
Authors: Jones J. Alison , Owen P. Jane , Boarder Michael R.
Published: July 2012

We have investigated the modification of catecholamine efflux and inositol phosphate formation in cultured adrenal chromaffin cells by tetradecanoyl phorbol acetate (TPA) and inhibitors of diacylglycerol kinase (R 59 022) and diacylglycerol lipase (RG 80267), the two principal pathways of diacylglycerol metabolism.

TPA (1 nm to 1 μm) elicited a slow, calcium‐dependent, sustained release of noradrenaline, which was partially blocked by the dihydropyridine calcium channel blocker (−)‐202 791 and potentiated by the channel enhancer (+)‐202 791.

R 59 022 enhanced noradrenaline efflux at 30 and 50 μm, while the lipase inhibitor RG 80267 failed to elicit release.

Neither R 59 022 nor RG 80267 affected bradykinin‐ or histamine‐stimulated release, but both drugs substantially attenuated nicotine‐ and high K+‐stimulated release.

Pretreatment for 10 min with TPA (but not the relatively inactive 4‐methoxyTPA) or the non‐phorbol protein kinase C stimulator mezerein potently inhibited bradykinin‐ and histamine‐stimulated accumulation of total [3H]‐inositol phosphate; inhibition of [3H]‐inositol phosphate formation was also seen with 24 h TPA treatment.

Neither R 59 022 nor RG 80267, separately or together, affected bradykinin‐stimulated [3H]‐inositol phosphate formation.

Thus while the mechanism exists for inhibition of formation of inositol phosphates by stimulation of protein kinase C, these studies failed to show that this mechanism is activated by agonists acting on phospholipase C linked receptors.
Front‐surface fluorometry with fura‐2 and effects of nitroglycerin on cytosolic calcium concentrations and on tension in the coronary artery of the pig
Authors: Abe Shimako , Kanaide Hideo , Nakamura Motoomi
Published: July 2012

By use of front‐surface fluorometry and fura‐2‐loaded strips of the coronary artery of the pig, the effects of nitroglycerin (NG) on cytosolic Ca2+ concentrations ([Ca2+]i) and on tension development were measured simultaneously.

Both high K+ depolarization and histamine increased [Ca2+]i and tension in a concentration‐dependent manner. However, the tension development in relation to the [Ca2+]i increase ([Ca2+]i‐tension relation) observed with histamine was much greater than that observed with K+ depolarization.

NG reduced in a concentration‐dependent manner both [Ca2+]i and tension, irrespective of whether the vascular strips were in a resting state or during exposure to high K+ or to histamine stimulation. However, the extent of reduction in tension (relaxation) was greater than that expected from the reduction in [Ca2+]i based on the [Ca2+]i‐tension relationship observed with K+‐depolarization.

In the absence of extracellular Ca2+, NG depleted stored Ca2+ and also inhibited Ca2+ release from histamine‐sensitive stores, but had no effect on the caffeine‐sensitive stores. NG inhibited the caffeine‐induced tension development with no change in [Ca2+]i.

We suggest that NG relaxes the coronary artery of the pig by reducing [Ca2+]i and also by directly controlling contractile elements through second messengers not related to changes in [Ca2+]i.
Effect of intracerebroventricular administration of the GABAB‐receptor agonist baclofen on operant feeding in satiated pigs
Authors: Ebenezer I.S. , Baldwin B.A.
Published: July 2012

The present study investigated the effects of intracerebroventricular (i.c.v.) administration of the GABAB‐receptor agonist baclofen on food and water intake in satiated pigs previously trained to make operant responses for food and water, which were available ad libitum.

Baclofen (25–100 nmol) i.c.v. produced a dose‐related increase in food intake. Baclofen (50 nmol) increased feeding during the first 15 min after administration (P > 0.01), while the 100 nmol dose increased feeding during the first 30 min (P > 0.01). None of these doses of baclofen had any affect on the daily (24 h) food intake.

The effect of baclofen (50 nmol) on feeding was prevented by pretreating the animals with the GABAB antagonist phaclofen (500 nmol, i.c.v.).

Baclofen (25–100 nmol) i.c.v. had no significant effects on water intake.

Intravenous administration of baclofen (100 nmol) had no effect on food intake, thus eliminating the possibility that i.c.v. baclofen might have stimulated feeding by a peripheral mode of action.

These results show that baclofen increases food intake in satiated pigs, and that this effect is mediated by the drug acting at central GABAB‐receptors.
Haemodynamic profile of the potassium channel activator EMD 52692 in anaesthetized pigs
Authors: Sassen L.M.A. , Duncker D.J.G.M. , Gho B.C.G. , Diekmann H.W. , Verdouw P.D.
Published: July 2012

The systemic and regional haemodynamic effects of the potassium channel activator EMD 52692 or its solvent were investigated after intravenous and after intracoronary administration in anaesthetized pigs.

Consecutive intravenous 10 min infusions of EMD 52692 (0.15, 0.30, 0.60, 1.20 μg kg−1 min−1; n = 7) dose‐dependently decreased mean arterial blood pressure by up to 50%. This was entirely due to peripheral vasodilatation, since cardiac output did not change. Heart rate increased by up to 50%, while left ventricular end diastolic pressure decreased dose‐dependently from 6 ± 1 mmHg to 3 ± 1 mmHg (P > 0.05), and stroke volume decreased from 30 ± 2 ml to 21 ± 2 ml (P > 0.05). Left ventricular dP/dtmax was not affected.

Although cardiac output did not change, EMD 52692 caused a redistribution of blood flow from the arteriovenous anastomoses to the capillary channels. Blood flow to the adrenals, small intestine, stomach, bladder, spleen and brain increased, while renal blood flow decreased and blood flow to several muscle groups and skin were not altered. Vascular conductance was increased dose‐dependently in all organs, except for the kidneys, where after the initial increase, vascular conductance returned to baseline with the highest dose. Particularly striking were the effects on the vasculature of the brain. With the highest dose of EMD 52692 blood flow more than doubled, while vascular conductance increased four fold.

Transmural myocardial blood flow increased slightly, which was entirely due to an increase in subepicardial blood flow. Myocardial O2‐consumption and segment length shortening were not significantly affected.

After consecutive 10 min intracoronary infusions (0.0095, 0.019, 0.0375 and 0.075 μg kg−1 min−1; n = 7) into the left anterior descending coronary artery (LADCA), mean arterial blood pressure was maintained with the lowest two doses, but decreased by up to 15% with the higher doses, whereas heart rate increased by up to 24%. Blood flow to the LADCA‐perfused myocardium doubled with the highest dose, the subepicardium benefitting the most. Coronary venous O2‐saturation increased dose‐dependently from 23 ± 2% to 60 ± 4%, while myocardial O2‐consumption of the LADCA‐perfused myocardium was not affected by the drug.

It is concluded that EMD 52692 is a potent vasodilator, with particularly pronounced effects on vasculature of the brain. Its selectivity for vascular smooth muscle cells exceeds that for the myocytes, since with doses that are much higher than those of potential clinical interest no negative inotropic effects were observed. The compound primarily dilates arteries but some venodilatation may also occur.
Behavioural evidence for functional interactions between 5‐HT‐receptor subtypes in rats and mice
Authors: Berendsen Hemmie H.G. , Broekkamp Chris L.E.
Published: July 2012

Different 5‐hydroxytryptamine (5‐HT) receptor subtypes mediate different behavioural responses. Compounds acting at more than one 5‐HT receptor exert behavioural effects which may be the result of response competition or a specific interaction between pathways within the CNS. Therefore the mutual interaction between different 5‐HT receptor subtypes was studied.

Hypothermia and hypoactivity in mice induced by the 5‐HT1A‐agonist 8‐hydroxy‐dipropylaminotetralin (8‐OH‐DPAT) could be attenuated by the preferential 5‐HT1C‐agonists MK 212, 1‐(meta‐chlorophenyl)‐piperazine (mCPP) and m‐trifluoromethyl phenyl piperazine (TFMPP), and by the mixed 5‐HT2/1C‐agonist 1‐(2,5‐dimethoxy‐4‐iodophenyl)‐2‐aminopropane (DOI). The mixed 5‐HT1A/1B‐agonist CGS 12066B at 10 mg kg−1 potentiated hypothermia and had no effect on hypoactivity.

Forepaw treading in rats induced by the 5‐HT1A‐agonist 8‐OH‐DPAT was attenuated by the 5‐HT1C‐agonists MK 212 and mCPP. The 5‐HT1C‐agonist TFMPP had a bimodal effect: at low doses (> 1 mg kg−1) it potentiated, and at higher doses (> 2.2 mg kg−1) it attenuated forepaw treading. the mixed 5‐HT2/1C‐agonist DOI produced 5‐HT2‐related behaviours and potentiated 8‐OH‐DPAT‐induced forepaw treading. This indicates an attenuating effect of 5‐HT1C‐receptor activation and a potentiating effect of 5‐HT2‐receptor activation. CGS 12066B had no effect in this respect.

Head shakes in rats induced by DOI could be attenuated by 8‐OH‐DPAT, TFMPP, mCPP and MK 212. The ID50s were 0.03, 0.7, 0.1 and 2 mg kg−1, respectively. This suggests that a 5‐HT2‐receptor‐mediated effect may be attenuated by activation of 5‐HT1A‐ or 5‐HT1C‐receptors. CGS 12066B attenuated the head shake response but only at 10 mg kg−1.

The results suggest that interactions exist between the different 5‐HT receptor subtype‐mediated events. Therefore, care is needed in drawing conclusions from functional measurements when compounds have more or less equal affinities for more than one 5‐HT‐receptor subtype.
The effects of cocaine on intracellular Ca2+ handling and myofilament Ca2+ responsiveness of ferret ventricular myocardium
Authors: Perreault Cynthia L. , Hague Nancy L. , Ransil Bernard J. , Morgan James P.
Published: July 2012

When ferret right ventricular papillary muscles were stimulated with threshold punctate pulses (0.33 Hz; 30°C), cocaine, 10−5 m, increased peak tension development from 815 ± 120 to 1125 ± 180 mg (P > 0.05) and increased the rate of relaxation from peak tension (time to 80% decline from peak tension decreased from 155 ± 11 to 144 ± 11 ms; P > 0.05). These changes in the twitch were associated with comparable changes in the amplitude and time course of the calcium transient measured with aequorin (amplitude increased from 62 ± 4 to 90 ± 7% (P > 0.05) of maximal values; time to 80% decline from peak amplitude decreased from 84 ± 8 to 64 ± 3 ms; P > 0.05). These effects were markedly attenuated in the presence of the β‐adrenoceptor‐blocking agent, propranolol, 6 × 10−7 m, or by maximization of catecholamine release from the adrenergic nerve endings with field pulses of supratheshold strength, indicating that catecholamine release from the adrenergic nerve endings is responsible for the positive inotropic and lusitropic responses to low and moderate doses of cocaine (i.e., ≤ 10−5 m).

High doses of cocaine (i.e., > 10−5 m) produced negative inotropic and lusitropic effects that were associated with a decreased amplitude and prolonged duration of the calcium transient.

In aequorin‐loaded intact fibres, cocaine 10−5 m did not affect the force‐calcium relationship unless catecholamines were present. Cocaine, 10−5 m, significantly shifted the force‐calcium relationship of saponin‐skinned muscles (pCa50 = 6.14 ± 0.05 versus 5.92 ± 0.07; P > 0.05), indicating reduced responsiveness of the myofilaments to calcium. Fmax (maximal Ca2+‐activated force) was reduced to 58% of control in the presence of 10−5 m cocaine, while the slope of the calcium‐force curve remained unchanged. These data indicate that cocaine may also decrease myofilament calcium sensitivity and maximal calcium‐activated force, via mechanisms independent of catecholamines, when cellular diffusion barriers are eliminated.
Nitrendipine decreases benzodiazepine withdrawal seizures but not the development of benzodiazepine tolerance or withdrawal signs
Authors: Dolin S.J. , Patch T.L. , Rabbani M. , Siarey R.J. , Bowhay A.R. , Little H.J.
Published: July 2012

The effects of the calcium channel blocking agent, nitrendipine, were studied on seizures in mice produced during withdrawal from chronic benzodiazepine treatment and on the development of tolerance to benzodiazepines.

Nitrendipine produced a dose‐dependent decrease in seizure incidence, when seizures were produced by the partial inverse agonist FG7142 during withdrawal from seven days treatment with flurazepam.

Nitrendipine did not raise the seizure thresholds in naïve mice to the full inverse agonist methyl‐6,7‐dimethoxy‐4‐ethyl‐β‐carboline‐3‐carboxylate (DMCM), or to the γ‐aminobutyric acid (GABA) antagonist, bicuculline.

When given concurrently with flurazepam for seven days, nitrendipine did not affect the incidence of seizures during flurazepam withdrawal.

When given concurrently with the benzodiazepines, nitrendipine did not prevent the development of tolerance to midazolam general anaesthesia or tolerance to the ataxic actions of flurazepam or midazolam.

Chronic treatment with flurazepam for seven days did not affect the Kd or Bmax of [3H]‐nimodipine binding in mouse whole brain or cerebral cortex.

These results with benzodiazepines are partially in contrast with those for ethanol, where nitrendipine not only decreased ethanol withdrawal seizures when given acutely, but also prevented the development of tolerance and withdrawal signs when given concurrently with ethanol. However, they do confrm the selectivity of nitrendipine for withdrawal‐induced seizures.
Inhibitory effect of 5‐hydroxytryptamine on penile erectile function in the rat
Authors: Finberg J.P.M. , Vardi Y.
Published: July 2012

An increase in corporal pressure was elicited in pithed rats by stimulation of the sacral part of the spinal cord. This response was inhibited by intravenous injection of 5‐hydroxytryptamine (5‐HT) (ED50 = 28.5 ± 2.2 μg kg−1).

The inhibitory effect of 5‐HT was blocked by methysergide and methiothepin (each 1 mg kg−1), but not by ketanserin (0.02 mg kg−1), MDL 72222 (1 mg kg−1) or prazosin (0.1 mg kg−1).

An inhibitory effect on the corporal pressure response to spinal stimulation was also produced by 5‐carboxyamidotryptamine (ED50 = 5.6 ± 2.8 μg kg−1), but not by m‐chlorophenylpiperazine (mCPP), RU 24969, 8‐hydroxy‐2‐[di‐n‐propyl‐amino]‐tetralin (8‐OH‐DPAT) or fenfluramine (doses up to 1–2 mg kg−1).

Neither methiothepin (1 mg kg−1) nor clomipramine (1 mg kg−1) had any effect on the frequency‐response curve for increase in corporal pressure by spinal stimulation.

The results indicate that 5‐HT exerts an inhibitory action on penile erection by a peripheral mechanism. This effect may be mediated by vasoconstriction in cavernosal vessels, or inhibition of release of a vasodilator neurotransmitter. From the spectrum of agonist and antagonist responses, the receptor involved may be of the 5‐HT1D subtype.
Characterization of responses to cromakalim and pinacidil in smooth and cardiac muscle by use of selective antagonists
Authors: McPherson Grant A. , Angus James A.
Published: July 2012

In dog isolated coronary artery (precontracted with endothelin, 10 nm) cromakalim (0.1–30μm) and pinacidil (1–30μm) produced concentration‐dependent vasorelaxant responses. The effects of these compounds could be blocked by glibenclamide (3μm), phentolamine (30 μm) or alinidine (30 μm) to a similar extent, indicating that both agents alter vascular tone through the same mechanism in this preparation.

The ability of the antagonists glibenclamide, phentolamine and alinidine to block the response to cromakalim in a number of smooth muscle types from the guinea‐pig was determined. Cromakalim (0.1–30 μm) produced concentration‐dependent relaxant responses in thoracic aorta (precontracted with endothelin, 30 nm), ileum (precontracted with K+, 25 mm) and trachea (spontaneously contracted). Responses to cromakalim in all tissues could be blocked by the three antagonists. However, significantly higher concentrations of the antagonists were required to block responses in the thoracic aorta than in the ileum or trachea. Given that the rank order of potency of the antagonists was similar in all tissues (i.e. glibenclamide > phentolamine = alinidine), this result may suggest vascular K+ channels opened by cromakalim are quantitatively but not qualitatively different in vascular compared with non‐vascular smooth muscle. Glibenclamide was approxmately 10 times more potent than phentolamine or alinidine.

Cromakalim had minimal functional effects on the rat spontaneously beating right atrial (rate) or electrically driven left ventricular strip (force) preparations. Similarly the three antagonists studied failed to alter force generation in the right ventricular strip. However alinidine and phentolamine did produce a dose‐related bradycardia in the spontaneously beating right atria. This effect appears to be unrelated to blockade of the K+ channel opened by cromakalim since glibenclamide, the most potent K+ channel antagonist studied, failed to produce the same response.

It would appear that the K+ channel opened by cromakalim is present in a number of vascular and non‐vascular smooth muscle. Based on the potency of the three antagonists studied, there appears to be little heterogeneity in the process activated by cromakalim in vascular and non‐vascular smooth muscle.
Renal vascular responsiveness to arachidonic acid in experimental diabetes
Authors: Quilley J. , McGiff J.C.
Published: July 2012

Isolated perfused kidneys from diabetic rats (duration 4–6 and 20–24 weeks) were more sensitive to the vasoconstrictor effects of arachidonic acid than kidneys from age‐matched control rats. Sensitivity diminised with age in both control and diabetic groups.

The enhanced vasoconstrictor effect of arachidonic acid in diabetic rat kidneys was associated with increased conversion to prostaglandins.

The renal vasoconstrictor response to arachidonic acid in both groups was reduced by thromboxane A2/prostaglandin H2 receptor antagonism but not by inhibition of thromboxane synthase.

Diabetic rat kidneys were also more sensitive to the vasoconstrictor effects of the endoperoxide analogue, U46619, while vasoconstrictor responses to phenylephrine were not markedly different from those of control rat kidneys.

In conclusion, prostaglandin endoperoxides appear to mediate arachidonic acid‐induced vasoconstriction in diabetic and control rat kidneys. The enhanced renal vasoconstrictor response to arachidonic acid in diabetic rats results from increased sensitivity to endoperoxides and increased formation of endoperoxides from arachidonic acid.
A calcium channel antagonist stereoselectively decreases ethanol withdrawal hyperexcitability but not that due to bicuculline, in hippocampal slices
Authors: Whittington M.A. , Little H.J.
Published: July 2012

Extracellular recordings were made from CA1 area of isolated hippocampal slices of the mouse after chronic ethanol administration in vivo, with orthodromic stimulation of the Schaffer collateral/commissural fibres.

The (+)‐isomer of the calcium channel antagonist PN 200–110 (isradipine) significantly decreased all the recorded signs of hyperexcitability in the slices during ethanol withdrawal. These included increased paired pulse potentiation and decreases in the thresholds for elicitation of single and multiple population spikes.

The (–)‐isomer of PN 200–100 did not affect ethanol withdrawal hyperexcitability in the slices.

Neither isomer of PN 200–110 affected the field potentials in slices from control animals.

The γ‐aminobutyric acid (GABA) antagonist, bicuculline, lowered thresholds for eliciting population spikes in hippocampal slices from untreated animals. The active, (+)‐isomer of PN 200–110 did not affect this action of bicuculline in hippocampal slices from untreated animals.

The stereoisomerism of the action of PN 200–110 on ethanol withdrawal hyperexcitability in the hippocampal slice was therefore the same as that seen in blockade of calcium channels. The results suggested that ethanol withdrawal hyperexcitability recorded in the isolated hippocampal slice involved increased activity of voltage‐sensitive calcium channels.
The effects of endothelin‐1 and NG‐nitro‐l‐arginine methyl ester on regional haemodynamics in conscious rats with streptozotocin‐induced diabetes mellitus
Authors: Kiff RJ. , Gardiner S.M. , Compton A.M. , Bennett T.
Published: July 2012

Resting haemodynamic status and responses to endothelin‐1 (0.004, 0.04, 0.4 nmol kg−1) and NG‐nitro‐l‐arginine methyl ester (l‐NAME, 10 mg kg−1) were assessed in conscious, Wistar rats treated with streptozotocin (STZ) to induce diabetes mellitus, and in control animals treated with saline.

In the resting state, STZ‐treated rats had a bradycardia relative to control animals (291 ± 13 and 337 ± 10 beats min−1, respectively), but mean arterial blood pressures were the same in the two groups (STZ‐treated 109 ± 3; control 114 ± 4 mmHg). However, the STZ‐treated rats had raised renal (105 ± 9 units) and mesenteric (114 ± 16 units) vascular conductances and reduced hindquarters vascular conductance (26 ± 4 units) relative to control rats (renal, 80 ± 6; mesenteric, 75 ± 7; hindquarters, 37 ± 3 units).

Increasing doses of endothelin‐1 caused similar, early falls and subsequent rises in mean arterial blood pressures in both groups of rats. Although there were initial hindquarters vasodilatations with endothelin‐1 that were not different in STZ‐treated and control rats, there were subsequent renal and mesenteric vasoconstrictions that were greater in the former. Hence, the similar rises in mean arterial blood pressures must have been accompanied by a greater reduction in cardiac output in the STZ‐treated rats.

l‐NAME caused similar renal and mesenteric vasoconstrictions in control and STZ‐treated rats, but there was a smaller pressor effect and an attenuated hindquarters vasoconstrictor response to l‐NAME in STZ‐treated rats.

Collectively, the results indicate that the resting renal and mesenteric vasodilatations in STZ‐treated rats relative to control were probably not due to diminished vascular sensitivity to endogenous endothelin‐1 or to enhanced sensitivity to, or production of, nitric oxide in these vascular beds. However, the relative hindquarters vasoconstriction in the resting state and the diminished hindquarters vasoconstrictor response to l‐NAME in STZ‐treated rats is consistent with diminished nitric oxide production in that vascular bed.
Characterization of catecholamine‐mediated relaxations in rat isolated gastric fundus: evidence for an atypical β‐adrenoceptor
Authors: McLaughlin Daniel P. , MacDonald Allan
Published: July 2012

Experiments were carried out in order to characterize the receptors mediating relaxant responses to catecholamines in the rat gastric fundus. The effects of noradrenaline, isoprenaline and the ‘atypical’ or β3‐adrenoceptor agonist, BRL 37344, on methacholine‐induced tone were measured. Prazosin, propranolol and cyanopindolol were used as antagonists.

Relaxant responses to noradrenaline, in the presence of propranolol (1 μm) were antagonized in a concentration‐dependent manner by prazosin (0.01 to 1 μm), although this antagonism was weak and non‐competitive in nature. Relaxant responses to isoprenaline, in the presence of prazosin (0.1 μm), were antagonized only by the highest concentration of propranolol (1 μm) giving a pKB of 6.3. BRL 37344 also relaxed the rat gastric fundus in the presence of prazosin (0.1 μm), and the responses to BRL 37344 were unaffected by propranolol (1 μm).

Tachyphylaxis to BRL 37344 was observed, a second concentration‐response curve being significantly shifted to the right. Exposure of tissues to BRL 37344 (1 μm) between concentration‐response curves also caused an 11 fold rightward shift in the response to isoprenaline.

In the presence of prazosin (0.1 μm) and propranolol (1 μm), the rank order of potency of the agonists was: (–)‐isoprenaline (1.0) > (–)‐noradrenaline (0.39) > BRL 37344 (0.10).

Responses to BRL 37344 in the presence of prazosin (0.1 μm) and propranolol (1 μm) were antagonized by (±)‐cyanopindolol (1 μm), with a pKB of 6.56. Responses to isoprenaline, under the same conditions, were antagonized in a competitive manner by (±)‐cyanopindolol (0.1–1 μm), with the slope of a Schild plot close to unity and a pA2 value of 7.44.

The resistance to blockade by prazosin and propranolol and the antagonism by cyanopindolol of the responses mediated by isoprenaline and BRL 37344 suggest that atypical β‐adrenoceptors similar to ‘atypical’ β‐adrenoceptors in rat adipocytes and other tissues are present in the rat gastric fundus.
Selective impairment of hindquarters vasodilator responses to bradykinin in conscious Wistar rats with streptozotocin‐induced diabetes mellitus
Authors: Kiff R.J. , Gardiner S.M. , Compton A.M. , Bennett T.
Published: July 2012

Male, Wistar rats were treated with streptozotocin (STZ, 70 mgkg−1, i.p.) or saline and chronically instrumented with pulsed Doppler probes and intravascular catheters (implanted under sodium methohexitone anaesthesia) to allow assessment of haemodynamics in the conscious state 28 days later.

Control and STZ‐treated rats received bolus doses of glyceryl trinitrate (10–80 nmol kg−1), acetylcholine (0.1–5 nmol kg−1) and bradykinin (0.3–30 nmol kg−1).

Although, as reported previously, STZ‐treated rats had normal mean arterial blood pressure together with renal and mesenteric vasodilatations and hindquarters vasoconstriction relative to control rats, both groups showed similar hypotensive and regional haemodynamic responses to glyceryl trinitrate and acetylcholine. However, while the depressor effects of bradykinin were similar in control and STZ‐treated rats, the former showed a hindquarters vasodilator response to bradykinin that was absent in the STZ‐treated rats.

A loss of bradykinin‐mediated vasodilatation in the hindquarters vascular bed in STZ‐treated rats in the presence of normal, hindquarters vasodilator responses to other agents and normal bradykinin‐mediated vasodilator responses in other vascular beds is consistent with existing evidence that the vasodilatation elicited by bradykinin in the hindquarters vascular bed is particularly dependent on nitric oxide synthesis and that this is impaired selectively in STZ‐treated rats.
Interference of anti‐inflammatory and anti‐asthmatic drugs with neutrophil‐mediated platelet activation: singularity of azelastine
Authors: Renesto Patricia , Balloy Viviane , Vargaftig B. Boris , Chignard Michel
Published: July 2012

The capacity of various drugs (acetylsalicylic acid (ASA), ketoprofen, diclofenac, piroxicam, BW 755C, BW A4C, nedocromil sodium and azelastine) to inhibit human polymorphonuclear neutrophil (PMN)‐mediated platelet activation was investigated. In this model, stimulated PMN release cathepsin G (Cat G), a serine proteinase which, in turn, induces platelet activation.

Among the different tested drugs, azelastine (100 μm for 1 min) was the only one able to prevent platelet aggregation. The cyclo‐oxygenase inhibitors were all inactive, although used at effective concentrations as judged by inhibition of thromboxane B2 (TxB2) formation. Inhibition of platelet aggregation by azelastine was concentration‐dependent, the range of active concentrations being of 20–70 μm. Release from platelets of 5‐hydroxytryptamine was also inhibited at 30 μm and above, but never reached 100%.

The inhibition by azelastine is due to an effect on both cells. Indeed, β‐glucuronidase release from activated PMN and platelet activation by purified Cat G were both affected.

However, used at high concentrations (>100 μm) azelastine was toxic since it released significant amounts of lactate dehydrogenase (LDH) from PMN and platelets.

These results show the capacity of azelastine, an anti‐allergic and anti‐asthmatic compound, to inhibit the cell‐to‐cell communication between PMN and platelets, an effect which may be relevant for its therapeutic efficacy or for a new application in diseases in which PMN and platelets are involved.
Tachykinin antagonists and capsaicin‐induced contraction of the rat isolated urinary bladder: evidence for tachykinin‐mediated cotransmission
Authors: Maggi Carlo Alberto , Patacchini Riccardo , Santicioli Paolo , Giuliani Sandro
Published: July 2012

The possible involvement of tachykinins (TKs) in the contraction produced by capsaicin in the rat isolated urinary bladder was addressed on the hypothesis that co‐release of substance P (SP) and neurokinin A (NKA) occurs from sensory nerve terminals.

A low concentration of SP (30 nm) produced a rapid contraction which faded to baseline within 10 min. A low concentration of NKA (10 nm) produced a slowly developing contraction which was still evident at 10 min. Capsaicin (1 μm) produced a rapid phasic response and a tonic response (late response to capsaicin). Co‐administration of SP and NKA mimicked the response to capsaicin more than each TK alone.

Fading of the response to SP was not caused by receptor desensitization and was partially prevented by peptidase inhibitors.

Spantide (3 μm) selectively antagonized the SP‐induced contraction while L‐659,877 (3–10 μm) or MEN 10,376 (10–30 μm) which are NK2 receptor selective antagonists selectively blocked the response to NKA. Co‐administration of spantide and L‐659,877 inhibited the response to both SP and NKA by an amount not greater than that produced by each antagonist alone.

Spantide selectively reduced the peak response to capsaicin, while leaving the late response unaffected. L‐659,877 (3 μm) and MEN 10,376 (10 μm) selectively inhibited the late response to capsaicin while, at higher concentrations, also reduced the peak response to capsaicin. Co‐administration of spantide and L‐659,877 reduced the peak response to capsaicin more than that produced by each antagonist alone.

Bombesin (10 nm) produced a tonic contraction similar to that induced by NKA. The response to bombesin was not affected by spantide, L‐659,877 or MEN 10,376.

P2x purinoceptor desensitization by repeated administration of α,β‐methylene ATP depressed the twitch response to electrical stimulation of postganglionic nerves but did not affect the peak or the late response to capsaicin.

We conclude that multiple TKs are coreleased by capsaicin in the rat bladder and mediate the capsaicin‐induced contraction by activating both NK1 and NK2 receptors. Endogenous TK with preferential affinity for the NK1 receptor (putatively SP) are selectively involved in the peak response to capsaicin while endogenous TK with preferential affinity for the NK2 receptor (putatively NKA) are selectively involved in the late response to capsaicin and partly contribute to the peak response. These findings provide pharmacological evidence for tachykinin‐mediated cotransmission in the rat urinary bladder. ATP is unlikely to be involved in the efferent function of capsaicin‐sensitive sensory nerves in the rat bladder.