bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of pyrogallol, hydroquinone and duroquinone on responses to nitrergic nerve stimulation and NO in the rat anococcygeus muscle
Authors: La Mylinh , Rand Michael J
Published: January 2005

The hypothesis that endogenous superoxide dismutase (SOD) protects the nitrergic transmitter from inactivation by superoxide and that this explains the lack of sensitivity of the transmitter to superoxide generators was tested in the rat isolated anococcygeus muscle.

Responses to nitrergic nerve stimulation or to NO were not significantly affected by exogenous SOD or by the Cu/Zn SOD inhibitor diethyldithiocarbamic acid (DETCA).

Hydroquinone produced a concentration‐dependent reduction of responses to NO with an IC50 of 27 μM, and higher concentrations reduced relaxant responses to nitrergic nerve stimulation with an IC50 of 612 μM. The effects of hydroquinone were only slightly reversed by SOD, so it does not appear to be acting as a superoxide generator.

Pyrogallol produced a concentration‐dependent reduction in responses to NO with an IC50 value of 39 μM and this effect was reversed by SOD (100–1000 u ml−1). Pyrogallol did not affect responses to nitrergic nerve stimulation. Treatment with DETCA did not alter the differentiating action of pyrogallol.

Duroquinone produced a concentration‐dependent reduction of relaxations to NO with an IC50 value of 240 μM and 100 μM slightly decreased nitrergic relaxations. After treatment with DETCA, duroquinone produced greater reductions of relaxant responses to NO and to nitrergic stimulation, the IC50 values being 8.5 μM for NO and 40 μM for nitrergic nerve stimulation: these reductions were reversed by SOD.

The findings do not support the hypothesis that the presence of Cu/Zn SOD explains the greater susceptibility of NO than the nitrergic transmitter to the superoxide generator pyrogallol, but suggest that it may play a role in the effects of duroquinone.

British Journal of Pharmacology (1999) 126, 342–348; doi:10.1038/sj.bjp.0702277
Transcriptional down‐regulation of the rabbit pulmonary artery endothelin B receptor during phenotypic modulation
Authors: Owe‐Young R , Schyvens C G , Qasabian R A , Conigrave A D , Macdonald P S , Williamson D J
Published: January 2005

We confirmed that endothelium‐independent contraction of the rabbit pulmonary artery (RPA) is mediated through both an endothelin A (ETAR) and endothelin B (ETB2R) receptor.

The response of endothelium‐denuded RPA rings to endothelin‐1 (ET‐1, pD2=7.84±0.03) was only partially inhibited by BQ123 (10 μM), an ETAR antagonist.

Pretreatment with 1 nM sarafotoxin S6c (S6c), an ETBR agonist, desensitized the ETB2R and significantly attenuated the response to ET‐3 (pD2=7.40±0.02 before, <6.50 after S6c).

Pretreatment with S6c had little effect on the response to ET‐1, but BQ123 (10 μM) caused a parallel shift to the right of the residual ETAR‐mediated response to ET‐1 (pD2=7.84±0.03 before S6c, 7.93±0.03 after S6c, 6.81±0.05 after BQ123).

Binding of radiolabelled ET‐1 to early passage cultures of RPA vascular smooth muscle cells (VSMC) displayed two patterns of competitive displacement characteristic of the ETAR (BQ123 pIC50=8.73±0.05) or ETB2R (S6c pIC50=10.15).

Competitive displacement experiments using membranes from late passage VSMC confirmed only the presence of the ETAR (ET‐1 pIC50=9.3, BQ123 pIC50=8.0, S6c pIC50<6.0).

The ETAR was functionally active and coupled to rises in intracellular calcium which exhibited prolonged homologous desensitization.

Using a reverse transcriptase polymerase chain reaction for the rabbit ETB2R, we demonstrated the absence of mRNA expression in phenotypically modified VSMC.

We conclude that the ETB2R expressed by VSMC which mediates contraction of RPA is rapidly down‐regulated at the transcriptional level during phenotypic modulation in vitro.

British Journal of Pharmacology (1999) 126, 103–110; doi:10.1038/sj.bjp.0702280
Effects of phrixotoxins on the Kv4 family of potassium channels and implications for the role of Ito1 in cardiac electrogenesis
Authors: Diochot Sylvie , Drici Milou‐Daniel , Moinier Danielle , Fink Michel , Lazdunski Michel
Published: January 2005

In the present study, two new peptides, phrixotoxins PaTx1 and PaTx2 (29–31 amino acids), which potently block A‐type potassium currents, have been purified from the venom of the tarantula Phrixotrichus auratus.

Phrixotoxins specifically block Kv4.3 and Kv4.2 currents that underlie Ito1, with an 5<IC50<70 nM, by altering the gating properties of these channels.

Neither are the Shaker (Kv1), Shab (Kv2) and Shaw (Kv3) subfamilies of currents, nor HERG, KvLQT1/IsK, inhibited by phrixotoxins which appear specific of the Shal (Kv4) subfamily of currents and also block Ito1 in isolated murine cardiomyocytes.

In order to evaluate the physiological consequences of the Ito1 inhibition, mice were injected intravenously with PaTx1, which resulted in numerous transient cardiac adverse reactions including the occurrence of premature ventricular beats, ventricular tachycardia and different degrees of atrio‐ventricular block.

The analysis of the mouse electrocardiogram showed a dose‐dependent prolongation of the QT interval, chosen as a surrogate marker for their ventricular repolarization, from 249±11 to 265±8 ms (P<0.05).

It was concluded that phrixotoxins, are new and specific blockers of Kv4.3 and Kv4.2 potassium currents, and hence of Ito1 that will enable further studies of Kv4.2 and Kv4.3 channel and/or Ito1 expression.

British Journal of Pharmacology (1999) 126, 251–263; doi:10.1038/sj.bjp.0702283
The effects of specific antibody fragments on the ‘irreversible’ neurotoxicity induced by Brown snake (Pseudonaja) venom
Authors: Jones R G A , Lee L , Landon J
Published: January 2005

Brown snake (Pseudonaja) venom has been reported to produce ‘irreversible’ post synaptic neurotoxicity (Harris & Maltin, 1981; Barnett et al., 1980).

A murine phrenic nerve/diaphragm preparation was used to study the neurotoxic effects of this venom and pre‐ and post‐synaptic components were distinguished by varying the temperature and frequency of nerve stimulation. There were no myotoxic effects and the neurotoxicity proved irreversible by washing alone.

The effects of a new Fab based ovine antivenom have been investigated and proved able to produce a complete, rapid (<1 h) reversal of the neurotoxicity induced by Brown snake venom. A reversal was also possible when the antivenom addition was delayed for a further 60 min.

We believe that this is the first time such a reversal has been shown.

British Journal of Pharmacology (1999) 126, 581–584; doi:10.1038/sj.bjp.0702286
Neuroregulation by vasoactive intestinal peptide (VIP) of mucus secretion in ferret trachea: activation of BKCa channels and inhibition of neurotransmitter release
Authors: Liu Yu‐Chih , Patel Hema J , Khawaja Aamir M , Belvisi Maria G , Rogers Duncan F
Published: January 2005

The aims of this study were to determine: (1) whether vasoactive intestinal peptide (VIP) regulates cholinergic and ‘sensory‐efferent’ (tachykininergic) 35SO4 labelled mucus output in ferret trachea in vitro, using a VIP antibody, (2) the class of potassium (K+) channel involved in VIP‐regulation of cholinergic neural secretion using glibenclamide (an ATP‐sensitive K+ (KATP) channel inhibitor), iberiotoxin (a large conductance calcium activated K+ (BKca) channel blocker), and apamin (a small conductance Kca (SKca) channel blocker), and (3) the effect of VIP on cholinergic neurotransmission using [3H]‐choline overflow as a marker for acetylcholine (ACh) release.

Exogenous VIP (1 and 10 μM) alone increased 35SO4 output by up to 53% above baseline, but suppressed (by up to 80% at 1 μM) cholinergic and tachykininergic neural secretion without altering secretion induced by ACh or substance P (1 μM each). Endogenous VIP accounted for the minor increase in non‐adrenergic, non‐cholinergic (NANC), non‐tachykininergic neural secretion, which was compatible with the secretory response of exogenous VIP.

Iberiotoxin (3 μM), but not apamin (1 μM) or glibenclamide (0.1 μM), reversed the inhibition by VIP (10 nM) of cholinergic neural secretion.

Both endogenous VIP (by use of the VIP antibody; 1 : 500 dilution) and exogenous VIP (0.1 μM), the latter by 34%, inhibited ACh release from cholinergic nerve terminals and this suppression was completely reversed by iberiotoxin (0.1 μM).

We conclude that, in ferret trachea in vitro, endogenous VIP has dual activity whereby its small direct stimulatory action on mucus secretion is secondary to its marked regulation of cholinergic and tachykininergic neurogenic mucus secretion. Regulation is via inhibition of neurotransmitter release, consequent upon opening of BKCa channels. In the context of neurogenic mucus secretion, we propose that VIP joins NO as a neurotransmitter of i‐NANC nerves in ferret trachea.

British Journal of Pharmacology (1999) 126, 147–158; doi:10.1038/sj.bjp.0702288
Effect of acute and long‐term treatment with 17‐β‐estradiol on the vasomotor responses in the rat aorta
Authors: Andersen Heidi L , Weis Jan U , Fjalland Bjarne , Korsgaard Niels
Published: January 2005

This study sought to evaluate whether the effects of acute and long‐term treatment with 17‐β‐estradiol on the vasomotor responses in rat aortic rings are mediated through the same mechanism.

Ovariectomized rats were treated daily with either 17‐β‐estradiol‐3‐benzoate (100 μg kg−1) or vehicle for 1 week.

The effect of long‐term 17‐β‐estradiol treatment on the responses to cumulative doses of phenylephrine, 5‐HT, calcium, potassium and 17‐β‐estradiol was determined in aortic rings. In the same rings, the effect of acute exposure to 17‐β‐estradiol (5 and 10 μM) on the dose response curves for phenylephrine, 5‐HT, calcium, potassium and acetylcholine were estimated. The measurements were made in rings with and without intact endothelium. The tone‐related basal release of nitric oxide (NO) was measured in rings with intact endothelium.

Long‐term 17‐β‐estradiol treatment reduced the maximum developed contraction to all contracting agents studied. This effect was abolished in endothelium denuded vessels. Acute 17‐β‐estradiol treatment also reduced maximal contraction. This effect, however, was independent of the endothelium.

Long‐term 17‐β‐estradiol treatment significantly increased the ability of the rings to dilate in response to acetylcholine whereas acute exposure to 17‐β‐estradiol had no effect. The tone‐related release of NO was significantly increased after long‐term exposure to 17‐β‐estradiol.

In conclusion, this study indicate that the acute and long‐term effects of 17‐β‐estradiol in the rat aorta are mediated through different mechanisms. The long‐term effect is mediated through the endothelium most likely by increasing NO release. In contrast, the acute effect of 17‐β‐estradiol seems to be through an effect on the vascular smooth muscle cells.

British Journal of Pharmacology (1999) 126, 159–168; doi:10.1038/sj.bjp.0702289
Differences in the actions of some blockers of the calcium‐activated potassium permeability in mammalian red cells
Authors: Benton D C H , Roxburgh C J , Ganellin C R , Shiner M A R , Jenkinson D H
Published: January 2005

The actions of some inhibitors of the Ca2+‐activated K+ permeability in mammalian red cells have been compared.

Block of the permeability was assessed from the reduction in the net loss of K+ that followed the application of the Ca2+ ionophore A23187 (2 μM) to rabbit red cells suspended at a haematocrit of 1% in a low potassium solution ([K]0 0.12–0.17 mM) at 37°C. Net movement of K+ was measured using a K+‐sensitive electrode placed in the suspension.

The concentrations (μM±s.d.) of the compounds tested causing 50% inhibition of K+ loss were: quinine, 37±3; cetiedil, 26±1; the cetiedil congeners UCL 1269, UCL 1274 and UCL 1495, ∼150, 8.2±0.1, 0.92±0.03 respectively; clotrimazole, 1.2±0.1; nitrendipine, 3.6±0.5 and charybdotoxin, 0.015±0.002.

The characteristics of the block suggested that compounds could be placed in two groups. For one set (quinine, cetiedil, and the UCL congeners), the concentration‐inhibition curves were steeper (Hill coefficient, nH, 2.7) than for the other (clotrimazole, nitrendipine, charybdotoxin) for which nH∼amp;1.

Compounds in the first set alone became less active on raising the concentration of K+ in the external solution to 5.4 mM.

The rate of K+ loss induced by A23187 slowed in the presence of high concentrations of cetiedil and its analogues, suggesting a use‐dependent component to the inhibitory action. This was not seen with clotrimazole.

The blocking action of the cetiedil analogue UCL 1274 could not be overcome by an increase in external Ca2+ and its potency was unaltered when K+ loss was induced by the application of Pb2+ (10 μM) rather than by A23187.

These results, taken with the findings of others, suggest that agents that block the red cell Ca2+‐activated K+ permeability can be placed in two groups with different mechanisms of action. The differences can be explained by supposing that clotrimazole and charybdotoxin act at the outer face of the channel whereas cetiedil and its congeners may block within it, either at or near the K+ binding site that determines the flow of K+.

British Journal of Pharmacology (1999) 126, 169–178; doi:10.1038/sj.bjp.0702292
Antagonist activity of α‐substituted 4‐carboxyphenylglycine analogues at group I metabotropic glutamate receptors expressed in CHO cells
Authors: Doherty A J , Collingridge G L , Jane D E
Published: January 2005

We have investigated the antagonist properties of 6 α‐substituted phenylglycine analogues based on the structure of 4‐carboxyphenylglycine (4‐CPG) for group I metabotropic glutamate receptors (mGlu1α and mGlu5a) permanently expressed in CHO cells.

(S)‐4‐CPG and (S)‐MCPG were the most selective mGlu1α receptor antagonists. Longer chain α‐carbon substitutions resulted in a progressive loss of antagonist affinity at mGlu1α receptors but not at mGlu5a receptors. Thus mGlu1α receptor antagonists require small aliphatic groups at the α‐position. α‐cyclopropyl‐4‐CPG showed a tendency towards mGlu5a selectivity, suggesting that bulky groups at this position may favour mGlu5a receptor antagonism.

We demonstrate that the mGlu5a receptor displays agonist‐dependent antagonism. L‐glutamate‐induced Ca2+ release in mGlu5a receptor expressing cells was more susceptible to antagonism by cyclic α‐carbon derivatives than (S)‐3,5‐dihydroxyphenylglycine (DHPG)‐induced Ca2+ release in the same cell line.

The data presented suggests that mGlu1α and mGlu5a receptors have different steric and/or conformational requirements for the binding of antagonists and different amino acids which could interact with agonists.

These phenylglycine analogues could provide leads for the development of subtype selective antagonists.

British Journal of Pharmacology (1999) 126, 205–210; doi:10.1038/sj.bjp.0702297
Acetylcholine‐induced relaxation in blood vessels from endothelial nitric oxide synthase knockout mice
Authors: Chataigneau Thierry , Félétou Michel , Huang Paul L , Fishman Mark C , Duhault Jacques , Vanhoutte Paul M
Published: January 2005

Isometric tension was recorded in isolated rings of aorta, carotid, coronary and mesenteric arteries taken from endothelial nitric oxide synthase knockout mice (eNOS(−/−) mice) and the corresponding wild‐type strain (eNOS(+/+) mice). The membrane potential of smooth muscle cells was measured in coronary arteries with intracellular microelectrodes.

In the isolated aorta, carotid and coronary arteries from the eNOS(+/+) mice, acetylcholine induced an endothelium‐dependent relaxation which was inhibited by Nω‐L‐nitro‐arginine. In contrast, in the mesenteric arteries, the inhibition of the cholinergic relaxation required the combination of Nω‐L‐nitro‐arginine and indomethacin.

The isolated aorta, carotid and coronary arteries from the eNOS(−/−) mice did not relax in response to acetylcholine. However, acetylcholine produced an indomethacin‐sensitive relaxation in the mesenteric artery from eNOS(−/−) mice.

The resting membrane potential of smooth muscle cells from isolated coronary arteries was significantly less negative in the eNOS(−/−) mice (−64.8±1.8 mV, n=20 and −58.4±1.9 mV, n=17, for eNOS(+/+) and eNOS(−/−) mice, respectively). In both strains, acetylcholine, bradykinin and substance P did not induce endothelium‐dependent hyperpolarizations whereas cromakalim consistently produced hyperpolarizations (−7.9±1.1 mV, n=8 and −13.8±2.6 mV, n=4, for eNOS(+/+) and eNOS(−/−) mice, respectively).

These findings demonstrate that in the blood vessels studied: (1) in the eNOS(+/+) mice, the endothelium‐dependent relaxations to acetylcholine involve either NO or the combination of NO plus a product of cyclo‐oxygenase but not EDHF; (2) in the eNOS(−/−) mice, NO‐dependent responses and EDHF‐like responses were not observed. In the mesenteric arteries acetylcholine releases a cyclo‐oxygenase derivative.

British Journal of Pharmacology (1999) 126, 219–226; doi:10.1038/sj.bjp.0702300
Roles of threonine 192 and asparagine 382 in agonist and antagonist interactions with M1 muscarinic receptors
Authors: Huang Xi‐Ping , Nagy Peter I , Williams Frederick E , Peseckis Steven M , Messer William S
Published: January 2005

Conserved amino acids, such as Thr in transmembrane domains (TM) V and Asn in TM VI of muscarinic receptors, may be important in agonist binding and/or receptor activation. In order to determine the functional roles of Thr192 and Asn382 in human M1 receptors in ligand binding and receptor activation processes, we created and characterized mutant receptors with Thr192 or Asn382 substituted by Ala.

HM1 wild‐type (WT) and mutant receptors [HM1(Thr192Ala) and HM1(Asn382Ala)] were stably expressed in A9 L cells. The Kd values for 3H‐(R)‐QNB and Ki values for other classical muscarinic antagonists were similar at HM1(WT) and HM1(Thr192Ala) mutant receptors, yet higher at HM1(Asn382Ala) mutant receptors. Carbachol exhibited lower potency and efficacy in stimulating PI hydrolysis via HM1(Thr192Ala) mutant receptors, and intermediate agonist activity at the HM1(Asn382Ala) mutant receptors.

The Asn382 residue in TM VI but not the Thr192 residue in TM V of the human M1 receptor appears to participate directly in antagonist binding. Both Thr192 and Asn382 residues are involved differentially in agonist binding and/or receptor activation processes, yet the Asn382 residue is less important than Thr192 in agonist activation of M1 receptors.

Molecular modelling studies indicate that substitution of Thr192 or Asn382 results in the loss of hydrogen‐bond interactions and changes in the agonist binding mode associated with an increase in hydrophobic interactions between ligand and receptor.

British Journal of Pharmacology (1999) 126, 735–745; doi:10.1038/sj.bjp.0702301
Trigeminal nerve ganglion stimulation‐induced neurovascular reflexes in the anaesthetized cat: Role of endothelinB receptors in carotid vasodilatation
Authors: Raval Pravin , Bingham Sharon , Aiyar Nambi , Elliott John D , Hunter A Jackie , Ohlstein Eliot H , Parsons Andrew A
Published: January 2005

The effects of intravenous administration of endothelin (ET) receptor antagonists SB‐209670 (0.001–10.0 mg kg−1), SB‐217242, SB‐234551 (0.01–10.0 mg kg−1) and BQ‐788 (0.001–1.0 mg kg−1) were investigated on trigeminal nerve ganglion stimulation‐induced neurovascular reflexes in the carotid vasculature of the anaesthetized cat. Comparisons were made with sumatriptan (0.003–3.0 mg kg−1) and α‐CGRP8–37 (0.001–0.1 mg kg−1).

Trigeminal nerve ganglion stimulation produced frequency related increases in carotid blood flow, reductions in carotid vascular resistance and non‐frequency related increases in blood pressure. Guanethidine (3 mg kg−1, i.v.) blocked trigeminal nerve ganglion‐induced increases in blood pressure but had no effect on changes in carotid flow or resistance. Maximal reductions in carotid vascular resistance was observed at 10 Hz, and this frequency was selected to investigate the effects of drugs on trigeminal nerve ganglion stimulation‐induced responses in guanethidine treated cats.

Saline, α‐CGRP8–37 SB‐209670 and BQ‐788 had little or no effect on resting haemodynamic parameters. SB‐217242 (10 mg kg−1, n=3) produced a 56% reduction in arterial blood pressure whereas SB‐233451 (10 mg kg−1, n=3) produced a 30% reduction in carotid vascular resistance. Sumatriptan produced dose‐related reductions in resting carotid flow and increases (max. 104% at 0.3 mg kg−1, n=5) in vascular resistance.

SB‐209670 (n=6–7), SB‐217242 (n=3) and BQ‐788 (n=3) produced inhibition of trigeminal nerve ganglion stimulation‐induced reductions in carotid vascular resistance. Saline, SB‐234551, α‐CGRP8–37 and sumatriptan had no effect.

These data demonstrate ETB receptor blockade attenuates the vasodilator effects of trigeminal nerve ganglion stimulation in the carotid vascular bed of guanethidine pretreated anaesthetized cats.

British Journal of Pharmacology (1999) 126, 485–493; doi:10.1038/sj.bjp.0702306
Effects of vanadium complexes with organic ligands on glucose metabolism: a comparison study in diabetic rats
Authors: Reul Bénédicte A , Amin Sean S , Buchet Jean‐Pierre , Ongemba Lumbe N , Crans Debbie C , Brichard Sonia M
Published: January 2005

Vanadium compounds can mimic actions of insulin through alternative signalling pathways. The effects of three organic vanadium compounds were studied in non‐ketotic, streptozotocin‐diabetic rats: vanadyl acetylacetonate (VAc), vanadyl 3‐ethylacetylacetonate (VEt), and bis(maltolato)oxovanadium (VM). A simple inorganic vanadium salt, vanadyl sulphate (VS) was also studied.

Oral administration of the three organic vanadium compounds (125 mg vanadium element l−1 in drinking fluids) for up to 3 months induced a faster and larger fall in glycemia (VAc being the most potent) than VS. Glucosuria and tolerance to a glucose load were improved accordingly.

Activities and mRNA levels of key glycolytic enzymes (glucokinase and L‐type pyruvate kinase) which are suppressed in the diabetic liver, were restored by vanadium treatment. The organic forms showed greater efficacy than VS, especially VAc.

VAc rats exhibited the highest levels of plasma or tissue vanadium, most likely due to a greater intestinal absorption. However, VAc retained its potency when given as a single i.p. injection to diabetic rats. Moreover, there was no relationship between plasma or tissue vanadium levels and any parameters of glucose homeostasis and hepatic glucose metabolism. Thus, these data suggest that differences in potency between compounds are due to differences in their insulin‐like properties.

There was no marked toxicity observed on hepatic or renal function. However, diarrhoea occurred in 50% of rats chronically treated with VS, but not in those receiving the organic compounds.

In conclusion, organic vanadium compounds, in particular VAc, correct the hyperglycemia and impaired hepatic glycolysis of diabetic rats more safely and potently than VS. This is not simply due to improved intestinal absorption, indicating more potent insulin‐like properties.

British Journal of Pharmacology (1999) 126, 467–477; doi:10.1038/sj.bjp.0702311
Modification of left ventricular hypertrophy by chronic etomoxir treatment
Authors: Turcani Marian , Rupp Heinz
Published: January 2005

Etomoxir (2[6(4‐chlorophenoxy)hexyl]oxirane‐2‐carboxylate), an irreversible carnitine palmitoyltransferase 1 inhibitor, reduces the expression of the myocardial foetal gene programme and the functional deterioration during heart adaption to a pressure‐overload. Etomoxir may, however, also improve the depressed myocardial function of hypertrophied ventricles after a prolonged pressure overload.

To test this hypothesis, we administered racemic etomoxir (15 mg kg−1 day−1 for 6 weeks) to rats with ascending aortic constriction beginning 6 weeks after imposing the pressure overload.

The right ventricular/body weight ratio increased (P<0.05) by 20% in etomoxir treated rats (n=10) versus untreated rats with ascending aortic constriction (n=10). Left ventricular weight was increased (P<0.05) by 8%. Etomoxir blunted the increase in left ventricular chamber volume. Etomoxir raised the proportion of V1 isomyosin (35±4% versus 24±2%; P<0.05) and decreased the percentage of V3 isomyosin (36±4% versus 48±3%; P<0.05).

Maximum isovolumically developed pressure was higher in etomoxir treated rats than in untreated pressure overloaded rats (371±22 versus 315±23 mmHg; P<0.05). Maximum rates of ventricular pressure development (14,800±1310 versus 12,340±1030 mmHg s−1; P<0.05) and decline (6440±750 versus 5040±710 mmHg s−1; P<0.05) were increased as well. Transformation of pressure values to ventricular wall stress data revealed an improved myocardial function which could partially account for the enhanced function of the whole left ventricle.

The co‐ordinated action of etomoxir on ventricular mass, geometry and myocardial phenotype enhanced thus the pressure generating capacity of hypertrophied pressure‐overloaded left ventricles and delayed the deleterious dilative remodelling.

British Journal of Pharmacology (1999) 126, 501–507; doi:10.1038/sj.bjp.0702312
Characterization of α1‐adrenoceptor subtypes mediating vasoconstriction in human umbilical vein
Authors: Errasti Andrea Emilse , Velo María Pía Rogines , Torres Rodrigo Martín , Sardi Sergio Pablo , Rothlin Rodolfo Pedro
Published: January 2005

The present study attempted to characterize pharmacologically the subtypes of α‐adrenoceptors mediating contractions in human umbilical vein (HUV).

HUV rings were mounted in isolated organ baths and cumulative concentration‐response curves were constructed for the α‐adrenoceptor agonists phenylephrine and adrenaline. Adrenaline was more potent than phenylephrine (pD2=7.29 and 6.04 respectively).

Isoproterenol exhibited no agonism on KCl pre‐contracted HUV rings. Propranolol (1 μM) and rauwolscine (0.1 μM) did not affect the concentration‐response curves to adrenaline. These results demonstrate the lack of involvement of functional β‐ or α2‐adrenoceptors in adrenaline‐induced vasoconstriction.

The non subtype selective α1‐adrenoceptor antagonist prazosin was evaluated on phenylephrine and adrenaline concentration‐response curves. The effects of the competitive α1A and α1D‐adrenoceptor antagonists, 5‐methyl urapidil and BMY 7378 and the irreversible α1B selective compound chloroethylclonidine (CEC) were also evaluated on adrenaline concentration‐response curves.

The potencies of prazosin against responses mediated by adrenaline (pA2=10.87) and phenylephrine (pA2=10.70) indicate the involvement of prazosin‐sensitive functional α1‐adrenoceptor subtype in vasoconstriction of the HUV.

The potencies of 5‐methyl urapidil (pA2=6.70) and BMY 7378 (pA2=7.34) were not consistent with the activation of an α1A‐ or α1D‐adrenoceptor population.

Exposure to a relatively low CEC concentration (3 μM) abolished the maximum response to adrenaline suggesting that this response was mediated by an α1B‐adrenoceptor subtype.

We conclude that HUV express a prazosin‐sensitive functional α1‐adrenoceptor resembling the α1B‐subtype according with the low pA2 values for both 5‐methyl urapidil and BMY 7378 and the high sensitivity to CEC.

British Journal of Pharmacology (1999) 126, 437–442; doi:10.1038/sj.bjp.0702320
Canine external carotid vasoconstriction to methysergide, ergotamine and dihydroergotamine: role of 5‐HT1B/1D receptors and α2‐adrenoceptors
Authors: Villalón Carlos M , De Vries Peter , Rabelo Gonzalo , Centurión David , Sánchez‐López Araceli , Saxena Pramod
Published: January 2005

The antimigraine drugs methysergide, ergotamine and dihydroergotamine (DHE) produce selective vasoconstriction in the external carotid bed of vagosympathectomized dogs anaesthetized with pentobarbital and artificially respired, but the receptors involved have not yet been completely characterized. Since the above drugs display affinity for several binding sites, including α‐adrenoceptors and several 5‐HT1 and 5‐HT2 receptor subtypes, this study has analysed the mechanisms involved in the above responses.

Intracarotid (i.c.) infusions during 1 min of methysergide (31–310 μg min−1), ergotamine (0.56–5.6 μg min−1) or DHE (5.6–31 μg min−1) dose‐dependently reduced external carotid blood flow (ECBF) by up to 46±4, 37±4 and 49±5%, respectively. Blood pressure and heart rate remained unchanged.

The reductions in ECBF by methysergide were abolished and even reversed to increases in animals pre‐treated with GR127935 (10 μg kg−1, i.v.).

The reductions in ECBF by ergotamine and DHE remained unchanged in animals pre‐treated (i.v.) with prazosin (300 μg kg−1), but were partly antagonized in animals pre‐treated with either GR127935 (10 or 30 μg kg−1) or yohimbine (1000 μg kg−1). Pre‐treatment with a combination of GR127935 (30 μg kg−1) and yohimbine (1000 μg kg−1) abolished the responses to both ergotamine and DHE. The above doses of antagonists were shown to produce selective antagonism at their respective receptors.

These results suggest that the external carotid vasoconstrictor responses to methysergide primarily involve 5‐HT1B/1D receptors, whereas those to ergotamine and DHE are mediated by 5‐HT1B/1D receptors as well as α2‐adrenoceptors.

British Journal of Pharmacology (1999) 126, 585–594; doi:10.1038/sj.bjp.0702324
Cyclo‐oxygenase‐2 mediates P2Y receptor‐induced reactive astrogliosis
Authors: Brambilla Roberta , Burnstock Geoffrey , Bonazzi Albino , Ceruti Stefania , Cattabeni Flaminio , Abbracchio Maria P
Published: January 2005

Excessive cyclo‐oxygenase‐2 (COX‐2) induction may play a role in chronic neurological diseases characterized by inflammation and astrogliosis. We have previously identified an astroglial receptor for extracellular nucleotides, a P2Y receptor, whose stimulation leads to arachidonic acid (AA) release, followed, 3 days later, by morphological changes resembling reactive astrogliosis. Since COX‐2 may be upregulated by AA metabolites, we assessed a possible role for COX‐2 in P2Y receptor‐mediated astrogliosis. A brief challenge of rat astrocytes with the ATP analogue α,β‐methylene ATP (α,βmeATP) resulted, 24 h later, in significantly increased COX‐2 expression. The selective COX‐2 inhibitor NS‐398 completely abolished α,βmeATP‐induced astrocytic activation. Constitutive astroglial COX‐1 or COX‐2 did not play any role in purine‐induced reactive astrogliosis. PGE2, a main metabolite of COX‐2, also induced astrocytic activation. These data suggest that a P2Y receptor mediates reactive astrogliosis via induction of COX‐2. Antagonists selective for this receptor may counteract excessive COX‐2 activation in both acute and chronic neurological diseases.

British Journal of Pharmacology (1999) 126, 563–567; doi:10.1038/sj.bjp.0702333
Effect of the cannabinoid receptor agonist WIN55212‐2 on sympathetic cardiovascular regulation
Authors: Niederhoffer Nathalie , Szabo Bela
Published: January 2005

The aim of the present study was to analyse the cardiovascular actions of the synthetic CB1/CB2 cannabinoid receptor agonist WIN55212‐2, and specifically to determine its sites of action on sympathetic cardiovascular regulation.

Pithed rabbits in which the sympathetic outflow was continuously stimulated electrically or which received a pressor infusion of noradrenaline were used to study peripheral prejunctional and direct vascular effects, respectively. For studying effects on brain stem cardiovascular regulatory centres, drugs were administered into the cisterna cerebellomedullaris in conscious rabbits. Overall cardiovascular effects of the cannabinoid were studied in conscious rabbits with intravenous drug administration.

In pithed rabbits in which the sympathetic outflow was continuously electrically stimulated, intravenous injection of WIN55212‐2 (5, 50 and 500 μg kg−1) markedly reduced blood pressure, the spillover of noradrenaline into plasma and the plasma noradrenaline concentration, and these effects were antagonized by the CB1 cannabinoid receptor‐selective antagonist SR141716A. The hypotensive and the sympathoinhibitory effect of WIN55212‐2 was shared by CP55940, another mixed CB1/CB2 cannabinoid receptor agonist, but not by WIN55212‐3, the enantiomer of WIN55212‐2, which lacks affinity for cannabinoid binding sites. WIN55212‐2 had no effect on vascular tone established by infusion of noradrenaline in pithed rabbits.

Intracisternal application of WIN55212‐2 (0.1, 1 and 10 μg kg−1) in conscious rabbits increased blood pressure and the plasma noradrenaline concentration and elicited bradycardia; this latter effect was antagonized by atropine.

In conscious animals, intravenous injection of WIN55212‐2 (5 and 50 μg kg−1) caused bradycardia, slight hypotension, no change in the plasma noradrenaline concentration, and an increase in renal sympathetic nerve firing. The highest dose of WIN55212‐2 (500 μg kg−1) elicited hypotension and tachycardia, and sympathetic nerve activity and the plasma noradrenaline concentration declined.

The results obtained in pithed rabbits indicate that activation of CB1 cannabinoid receptors leads to marked peripheral prejunctional inhibition of noradrenaline release from postganglionic sympathetic axons. Intracisternal application of WIN55212‐2 uncovered two effects on brain stem cardiovascular centres: sympathoexcitation and activation of cardiac vagal fibres. The highest dose of systemically administered WIN55212‐2 produced central sympathoinhibition; the primary site of this action is not known.

British Journal of Pharmacology (1999) 126, 457–466; doi:10.1038/sj.bjp.0702337
Bradykinin B1 and B2 receptors, tumour necrosis factor α and inflammatory hyperalgesia
Authors: Poole S , Lorenzetti B B , Cunha J M , Cunha F Q , Ferreira S H
Published: January 2005

The effects of BK agonists and antagonists, and other hyperalgesic/antihyperalgesic drugs were measured (3 h after injection of hyperalgesic drugs) in a model of mechanical hyperalgesia (the end‐point of which was indicated by a brief apnoea, the retraction of the head and forepaws, and muscular tremor).

DALBK inhibited responses to carrageenin, bradykinin, DABK, and kallidin.

Responses to kallidin and DABK were inhibited by indomethacin or atenolol and abolished by the combination of indomethacin+atenolol.

DALBK or HOE 140, given 30 min before, but not 2 h after, carrageenin, BK, DABK and kallidin reduced hyperalgesic responses to these agents.

A small dose of DABK+a small dose of BK evoked a response similar to the response to a much larger dose of DABK or BK, given alone.

Responses to BK were antagonized by HOE 140 whereas DALBK antagonized only responses to larger doses of BK. The combination of a small dose of DALBK with a small dose of HOE 140 abolished the response to BK.

The hyperalgesic response to LPS (1 μg) was inhibited by DALBK or HOE 140 and abolished by DALBK+HOE 140. The hyperalgesic response to LPS (5 μg) was not antagonized by DALBK+HOE 140.

These data suggest: (a) a predominant role for B2 receptors in mediating hyperalgesic responses to BK and to drugs that stimulate BK release, and (b) activation of the hyperalgesic cytokine cascade independently of both B1 and B2 receptors if the hyperalgesic stimulus is of sufficient magnitude.

British Journal of Pharmacology (1999) 126, 649–656; doi:10.1038/sj.bjp.0702347
GABAB receptor‐mediated stimulation of adenylyl cyclase activity in membranes of rat olfactory bulb
Authors: Olianas Maria C , Onali Pierluigi
Published: January 2005

Previous studies have shown that GABAB receptors facilitate cyclic AMP formation in brain slices likely through an indirect mechanism involving intracellular second messengers. In the present study, we have investigated whether a positive coupling of GABAB receptors to adenylyl cyclase could be detected in a cell‐free preparation of rat olfactory bulb, a brain region where other Gi/Go‐coupled neurotransmitter receptors have been found to stimulate the cyclase activity.

The GABAB receptor agonist (−)‐baclofen significantly increased basal adenylyl cyclase activity in membranes of the granule cell and external plexiform layers, but not in the olfactory nerve‐glomerular layer. The adenylyl cyclase stimulation was therefore examined in granule cell layer membranes.

The (−)‐baclofen stimulation (pD2=4.53) was mimicked by 3‐aminopropylphosphinic acid (pD2=4.60) and GABA (pD2=3.56), but not by (+)‐baclofen, 3‐aminopropylphosphonic acid, muscimol and isoguvacine. The stimulatory effect was counteracted by the GABAB receptor antagonists CGP 35348 (pA2=4.31), CGP 55845 A (pA2=7.0) and 2‐hydroxysaclofen (pKi=4.22). Phaclofen (1 mM) was inactive.

The (−)‐baclofen stimulation was not affected by quinacrine, indomethacin, nordihydroguaiaretic acid and staurosporine, but was completely prevented by pertussis toxin and significantly reduced by the α subunit of transducin, a βγ scavenger. The βγ subunits of transducin stimulated the cyclase activity and this effect was not additive with that produced by (−)‐baclofen.

In the external plexiform and granule cell layers, but not in the olfactory nerve‐glomerular layer, (−)‐baclofen enhanced the adenylyl cyclase stimulation elicited by the neuropeptide pituitary adenylate cyclase activating polypeptide (PACAP) 38.

Conversely, the adenylyl cyclase activity stimulated by either forskolin or Ca2+/calmodulin‐(Ca2+/CaM) was inhibited by (−)‐baclofen in all the olfactory bulb layers examined.

These data demonstrate that in specific layers of rat olfactory bulb activation of GABAB receptors enhances basal and neurotransmitter‐stimulated adenylyl cyclase activities by a mechanism involving βγ subunits of Gi/Go. This positive coupling is associated with a widespread inhibitory effect on forskolin‐ and Ca2+/CaM‐stimulated cyclic AMP formation.

British Journal of Pharmacology (1999) 126, 657–664; doi:10.1038/sj.bjp.0702349
Agonist‐inverse agonist characterization at CB1 and CB2 cannabinoid receptors of L759633, L759656 and AM630
Authors: Ross Ruth A , Brockie Heather C , Stevenson Lesley A , Murphy Vicki L , Templeton Fiona , Makriyannis Alexandros , Pertwee Roger G
Published: January 2005

We have tested our prediction that AM630 is a CB2 cannabinoid receptor ligand and also investigated whether L759633 and L759656, are CB2 receptor agonists.

Binding assays with membranes from CHO cells stably transfected with human CB1 or CB2 receptors using [3H]‐CP55940, confirmed the CB2‐selectivity of L759633 and L759656 (CB2/CB1 affinity ratios=163 and 414 respectively) and showed AM630 to have a Ki at CB2 receptors of 31.2 nM and a CB2/CB1 affinity ratio of 165.

In CB2‐transfected cells, L759633 and L759656 were potent inhibitors of forskolin‐stimulated cyclic AMP production, with EC50 values of 8.1 and 3.1 nM respectively and CB1/CB2 EC50 ratios of >1000 and >3000 respectively.

AM630 inhibited [35S]‐GTPγS binding to CB2 receptor membranes (EC50=76.6 nM), enhanced forskolin‐stimulated cyclic AMP production in CB2‐transfected cells (5.2 fold by 1 μM), and antagonized the inhibition of forskolin‐stimulated cyclic AMP production in this cell line induced by CP55940.

In CB1‐transfected cells, forskolin‐stimulated cyclic AMP production was significantly inhibited by AM630 (22.6% at 1 μM and 45.9% at 10 μM) and by L759633 at 10 μM (48%) but not 1 μM. L759656 (10 μM) was not inhibitory. AM630 also produced a slight decrease in the mean inhibitory effect of CP55940 on cyclic AMP production which was not statistically significant.

We conclude that AM630 is a CB2‐selective ligand that behaves as an inverse agonist at CB2 receptors and as a weak partial agonist at CB1 receptors. L759633 and L759656 are both potent CB2‐selective agonists.

British Journal of Pharmacology (1999) 126, 665–672; doi:10.1038/sj.bjp.0702351
Endothelium‐derived relaxing, contracting and hyperpolarizing factors of mesenteric arteries of hypertensive and normotensive rats
Authors: Sunano S , Watanabe H , Tanaka S , Sekiguchi F , Shimamura K
Published: January 2005

Differences in the acetylcholine (ACh)‐induced endothelium‐dependent relaxation and hyperpolarization of the mesenteric arteries of Wistar Kyoto rats (WKY) and stroke‐prone spontaneously hypertensive rats (SHRSP) were studied.

Relaxation was impaired in preparations from SHRSP and tendency to reverse the relaxation was observed at high concentrations of ACh in these preparations.

Relaxation was partly blocked by NG‐nitro‐L‐arginine (L‐NOARG, 100 μM) and, in the presence of L‐NOARG, tendency to reverse the relaxation was observed in response to higher concentrations of ACh, even in preparations from WKY. The relaxation remaining in the presence of L‐NOARG was also smaller in preparations from SHRSP.

The tendency to reverse the relaxation observed at higher concentrations of ACh in preparations from SHRSP or WKY in the presence of L‐NOARG were abolished by indomethacin (10 μM).

Elevating the K+ concentration of the incubation medium decreased relaxation in the presence of both indomethacin and L‐NOARG.

Relaxation in the presence of L‐NOARG and indomethacin was reduced by the application of both apamin (5 μM) and charybdotoxin (0.1 μM). This suggests that the relaxation induced by ACh is brought about by both endothelium‐derived relaxing factor (EDRF, nitric oxide (NO)) and hyperpolarizing factor (EDHF), which activates Ca2+‐sensitive K+ channels.

Electrophysiological measurement revealed that ACh induced endothelium‐dependent hyperpolarization of the smooth muscle of both preparations in the presence of L‐NOARG and indomethacin; the hyperpolarization being smaller in the preparation from SHRSP than that from WKY.

These results suggest that the release of both NO and EDHF is reduced in preparations from SHRSP. In addition, indomethacin‐sensitive endothelium‐derived contracting factor (EDCF) is released from both preparations; the release being increased in preparations from SHRSP.

British Journal of Pharmacology (1999) 126, 709–716; doi:10.1038/sj.bjp.0702355
Functional and molecular biological evidence for a possible β3‐adrenoceptor in the human detrusor muscle
Authors: Igawa Yasuhiko , Yamazaki Yoshinobu , Takeda Hiroo , Hayakawa Kohichi , Akahane Masuo , Ajisawa Yukiyoshi , Yoneyama Takehisa , Nishizawa Osamu , Andersson Karl‐Erik
Published: January 2005

The possible existence of a β3‐adrenergic receptor (β3‐AR) in the human detrusor muscle was investigated by in vitro functional studies and analysis of mRNA expression.

Isoprenaline, noradrenaline and adrenaline each produced a concentration‐dependent relaxation of the human detrusor. The rank order for their relaxing potencies was isoprenaline (pD2 6.37±0.07) noradrenaline (pD2 6.07±0.12) adrenaline (pD2 5.88±0.11).

Neither dobutamine (β1‐ and β2‐AR agonist) nor procaterol (β2‐AR agonist) produced any significant relaxation at concentrations up to 10−5 M. BRL37344A, CL316243 and CGP‐12177A (β3‐AR agonists), relaxed the preparations significantly at concentrations higher than 10−6 M. The pD2 values for BRL37344A, CL316243 and CGP‐12177A were 6.42±0.25, 5.53±0.09 and 5.74±0.14, respectively.

CGP‐20712A (10−7–10−5 M), a β1‐AR antagonist, did not affect the isoprenaline‐induced relaxation. On the other hand, ICI‐118,551, a β2‐AR antagonist, produced a rightward parallel shift of the concentration‐relaxation curve for isoprenaline only at the highest concentration used (10−5 M) and its pKB value was 5.71±0.19. Moreover, SR58894A (10−7–10−5 M), a β3‐AR antagonist, caused a rightward shift of the concentration‐relaxation curve for isoprenaline in a concentration‐dependent manner. The pA2 value and slope obtained from Schild plots were 6.24±0.20 and 0.68±0.31.

The β1‐, β2‐ and β3‐AR mRNAs were all positively expressed in detrusor smooth muscle preparations in a reverse transcription polymerase chain reaction assay.

In conclusion, the present results provide the first evidence for the existence of the β3‐AR subtype in the human detrusor. They also suggest that the relaxation induced by adrenergic stimulation of the human detrusor is mediated mainly through β3‐AR activation.

British Journal of Pharmacology (1999) 126, 819–825; doi:10.1038/sj.bjp.0702358
Effects of varying the expression level of recombinant human mGlu1α receptors on the pharmacological properties of agonists and antagonists
Authors: Hermans Emmanuel , Challiss R A John , Nahorski Stefan R
Published: January 2005

Different expression levels of the human type 1α metabotropic glutamate (mGlu1α) receptor were obtained in transfected Chinese hamster ovary cells using an isopropyl β‐D‐thiogalactopyranoside (IPTG) inducible system. Expression of mGlu1α receptors could not be detected using immunoblotting or immunocytochemical approaches in non‐induced cells, however, controlled expression could be induced following IPTG addition in a time‐ and concentration‐dependent manner.

In induced cells (100 μM IPTG, 20 h) the agonists L‐quisqualate or 1‐aminocyclopentane‐1S,3R‐dicarboxylic acid stimulated large increases in [3H]‐inositol (poly)phosphate (in the presence of Li+) and inositol, 1,4,5‐trisphosphate levels.

Induction with 1–100 μM IPTG allowed the receptor density to be increased incrementally and this not only resulted in an increase in the maximum response to L‐quisqualate, 1‐aminocyclopentane‐1S,3R‐dicarboxylic acid and (S)‐3,5‐dihydroxy‐phenylglycine, but also in an increase in the respective potencies of each agent to activate phosphoinositide hydrolysis.

The intrinsic activity of the partial agonist 1‐aminocyclopentane‐1S,3R‐dicarboxylic acid dramatically increased with increasing receptor expression.

The activities of the competitive mGlu1α receptor antagonists (S)‐α‐methyl‐4‐carboxyphenylglycine and (S)‐4‐carboxy‐3‐hydroxyphenylglycine for inhibition of the effects of L‐quisqualate or (S)‐3,5‐dihydroxyphenylglycine were found to be independent of the receptor expression level.

When the mGlu1α receptor was expressed at very high levels, no evidence for receptor constitutive activity could be detected, and none of the antagonists tested revealed either any intrinsic activity or negative efficacy.

These data demonstrate that both the potency and efficacy of mGlu1α receptor agonists are influenced by expression level, whilst mGlu1α receptor antagonist activities are independent of expression level.

British Journal of Pharmacology (1999) 126, 873–882; doi:10.1038/sj.bjp.0702359
The subtype 2 of angiotensin II receptors and pressure‐natriuresis in adult rat kidneys
Authors: Liu K L , Lo M , Grouzmann E , Mutter M , Sassard J
Published: January 2005

The present work examined the effects of the subtype 2 of angiotensin II (AT2) receptors on the pressure‐natriuresis using a new peptide agonist, and the possible involvement of cyclic guanosine 3′, 5′ monophosphate (cyclic GMP) in these effects.

In adult anaesthetized rats (Inactin, 100 mg kg−1, i.p.) deprived of endogenous angiotensin II by angiotensin converting enzyme inhibition (quinapril, 10 mg kg−1, i.v.), T2‐(Ang II 4–8)2 (TA), a highly specific AT2 receptor agonist (5, 10 and 30 μg kg−1 min−1, i.v.) or its solvent was infused in four groups. Renal functions were studied at renal perfusion pressures (RPP) of 90, 110 and 130 mmHg and urinary cyclic GMP excretion when RPP was at 130 mmHg. The effects of TA (10 μg kg−1 min−1) were reassessed in animals pretreated with PD 123319 (PD, 50 μg kg−1 min−1, i.v.), an AT2 receptor antagonist and the action of the same dose of PD alone was also determined.

Increases in RPP from 90 to 130 mmHg did not change renal blood flow (RBF) but induced 8 and 15 fold increases in urinary flow and sodium excretion respectively. The 5 μg kg−1 min−1 dose of TA was devoid of action. The 10 and 30 μg kg−1 min−1 doses did not alter total RBF and glomerular filtration rate, but blunted pressure‐diuresis and natriuresis relationships. These effects were abolished by PD.

TA decreased urinary cyclic GMP excretion. After pretreatment with PD, this decrease was reversed to an increase which was also observed in animals receiving PD alone.

In conclusion, renal AT2 receptors oppose the sodium and water excretion induced by acute increases in blood pressure and this action cannot be directly explained by changes in cyclic GMP.

British Journal of Pharmacology (1999) 126, 826–832; doi:10.1038/sj.bjp.0702362