bluuebunny/crossref_metadata_2025 huggingface dataset:
Pharmacological evidence for the presence of a peripheral postjunctional D2‐like dopamine receptor in rabbit splenic artery
Authors: Zanzottera Daniele , Ferlenga Pierpaolo , Marchini Francesco , Semeraro Claudio
Published: January 2005

This study was designed to investigate the involvement of postjunctional D2‐like receptors in a rabbit vasculature model used to evaluate the D1‐like agonist activity. Dopamine, epinine and (−)‐DP‐5,6‐ADTN, three mixed D1/D2‐like agonists, fenoldopam and SKF 82958, two selective D1‐like agonists and SKF 89124, a selective D2‐like agonist, were administered cumulatively in precontracted and α/β‐blocked rabbit splenic artery rings in order to evaluate their D1‐like‐mediated vasorelaxant activity before and after pretreatment with the selective D2‐like antagonist YM 09151‐2 (1 nM).

Dopamine (pD2=6.35±0.09), epinine (pD2=6.73±0.13), (−)‐DP‐5,6‐ADTN (pD2=7.56±0.09) and SKF 82958 (pD2=8.55±0.10) reversed completely the U46619‐induced contracture whereas SKF 89124 was inactive up to 10 μM and fenoldopam acted like a partial agonist (pD2=8.31±0.09, α=0.62). The selective D2‐like dopamine receptor antagonist YM 09151‐2 (1 nM) significantly (P<0.05) potentiated the vasorelaxant activity of dopamine (pD2=7.01±0.07), epinine (pD2=7.14±0.08), (−)‐DP‐5,6‐ADTN (pD2=8.19±0.09) and SKF 89124 (40% relaxation at 10 μM), whereas it did not alter the effects of fenoldopam (pD2=8.40±0.09, α=0.68) and SKF 82958 (pD2=8.58±0.08).

The D2‐like antagonist YM 09151‐2 induced the same degree of effect with all the substances tested in both endothelium‐denuded and endothelium‐intact preparations.

The selective D2‐like dopamine receptor agonist SKF 89124 did not produce any intrinsic effect on the splenic artery, but was able to produce a rightward shift of the forskolin‐induced relaxation.

The results of these experiments support the existence of a non‐endothelial postjunctional D2‐like dopamine receptor counteracting the D1‐like‐mediated vasodilatation in rabbit splenic artery, probably by the inhibition of adenylate cyclase.

British Journal of Pharmacology (1998) 123, 730–736; doi:10.1038/sj.bjp.0701651
Salmeterol‐induced desensitization, internalization and phosphorylation of the human β2‐adrenoceptor
Authors: January Bridgette , Seibold Anita , Allal Chafika , Whaley Brenda S. , Knoll Brian J. , Moore Robert H. , Dickey Burton F. , Barber Roger , Clark Richard B.
Published: January 2005

Partial agonists of the β2‐adrenoceptor which activate adenylyl cyclase are widely used as bronchodilators for the relief of bronchoconstriction accompanying many disease conditions, including bronchial asthma. The bronchodilator salmeterol has both a prolonged duration of action in bronchial tissue and the ability to reassert this activity following the temporary blockade of human β2‐adrenoceptors with antagonist.

We have compared the activation and desensitization of human β2‐adrenoceptor stimulation of adenylyl cyclase induced by salmeterol, adrenaline and salbutamol in a human lung epithelial line, BEAS‐2B, expressing β2‐adrenoceptor levels of 40–70 fmol mg−1, and in human embryonic kidney (HEK) 293 cell lines expressing 2–10 pmol mg−1. The efficacy observed for the stimulation of adenylyl cyclase by salmeterol was only ≈percnt;10% of that observed for adrenaline in BEAS‐2B cells expressing low levels of β2‐adrenoceptor, but similar to adrenaline in HEK 293 cells expressing very high levels of receptors. Salmeterol pretreatment of these cells induced a rapid and stable activation of adenylyl cyclase activity which resisted extensive washing and β2‐adrenoceptor antagonist blockade, consistent with binding to a receptor exosite and/or to partitioning into membrane lipid.

The desensitization and internalization of β2‐adrenoceptors induced by the partial agonists salmeterol and salbutamol were considerably reduced relative to the action of adrenaline. Consistent with these observations, the initial rate of phosphorylation of the receptor induced by salmeterol and salbutamol was much reduced in comparison to adrenaline.

Our data suggest that the reduction in the rapid phase of desensitization of β2‐adrenoceptors after treatment with salmeterol or salbutamol is caused by a decrease in the rate of β2‐adrenoceptor kinase (βARK) phosphorylation and internalization. In contrast, the rate of cyclic AMP‐dependent protein kinase (PKA)‐mediated phosphorylation by these partial agonists appears to be similar to adrenaline.

British Journal of Pharmacology (1998) 123, 701–711; doi:10.1038/sj.bjp.0701658
Direct effects of diazoxide on mitochondria in pancreatic B‐cells and on isolated liver mitochondria
Authors: Grimmsmann T , Rustenbeck I
Published: January 2005

The direct effects of diazoxide on mitochondrial membrane potential, Ca2+ transport, oxygen consumption and ATP generation were investigated in mouse pancreatic B‐cells and rat liver mitochondria.

Diazoxide, at concentrations commonly used to open adenosine 5′‐triphosphate (ATP)‐dependent K+‐channels (KATP channels) in pancreatic B‐cells (100 to 1000 μM), decreased mitochondrial membrane potential in mouse intact perifused B‐cells, as evidenced by an increase of rhodamine 123 fluorescence. This reversible decrease of membrane potential occurred at non‐stimulating (5 mM) and stimulating (20 mM) glucose concentrations.

A decrease of mitochondrial membrane potential in perifused B‐cells was also caused by pinacidil, but no effect could be seen with levcromakalim (500 μM each).

Measurements by a tetraphenylphosphonium‐sensitive electrode of the membrane potential of rat isolated liver mitochondria confirmed that diazoxide decreased mitochondrial membrane potential by a direct action. Pretreatment with glibenclamide (2 μM) did not antagonize the effects of diazoxide.

In Fura 2‐loaded B‐cells perifused with the Ca2+ channel blocker, D 600, a moderate, reversible increase of intracellular Ca2+ concentration could be seen in response to 500 μM diazoxide. This intracellular Ca2+ mobilization may be due to mitochondrial Ca2+ release, since the reduction of membrane potential of isolated liver mitochondria by diazoxide was accompanied by an accelerated release of Ca2+ stored in the mitochondria.

In the presence of 500 μM diazoxide, ATP content of pancreatic islets incubated in 20 mM glucose for 30 min was significantly decreased by 29%. However, insulin secretion from mouse perifused islets induced by 40 mM K+ in the presence of 10 mM glucose was not inhibited by 500 μM diazoxide, suggesting that the energy‐dependent processes of insulin secretion distal to Ca2+ influx were not affected by diazoxide at this concentration.

The effects of diazoxide on oxygen consumption and ATP production of liver mitochondria varied depending on the respiratory substrates (5 mM succinate, 10 mM α‐ketoisocaproic acid, 2 mM tetramethyl phenylenediamine plus 5 mM ascorbic acid), indicating an inhibition of respiratory chain complex II. Pinacidil, but not levcromakalim, inhibited α‐ketoisocaproic acid‐fuelled ATP production.

In conclusion, diazoxide directly affects mitochondrial energy metabolism, which may be of relevance for stimulus‐secretion coupling in pancreatic B‐cells.

British Journal of Pharmacology (1998) 123, 781–788; doi:10.1038/sj.bjp.0701663
Distribution of P2Y receptor subtypes on haematopoietic cells
Authors: Jin Jianguo , Rao Dasari V , Sistare Frank D. , Kunapuli Satya P.
Published: January 2005

RT–PCR‐southern hybridization analyses with radiolabelled P2Y receptor cDNAs as probes indicated that the peripheral blood leukocytes and the human umbilical vein endothelial cells express P2Y1, P2Y2, P2Y4 and P2Y6 receptors.

Of the haematopoietic cell lines tested, promonocytic U937 cells express P2Y2 and P2Y6, but not P2Y1 or P2Y4; promyelocytic HL‐60 cells express the P2Y1, P2Y2 and P2Y6 receptors but not the P2Y4 receptor; K562 cells express P2Y1 but not P2Y2, P2Y4 or P2Y6; and Dami cells express P2Y1, P2Y2, P2Y4 and P2Y6 receptors.

Of the peripheral blood leukocytes tested, polymorphonuclear cells express P2Y4 and P2Y6 but not P2Y1 or P2Y2 receptors; monocytes express P2Y1, P2Y2, P2Y4 and P2Y6 receptors and lymphocytes express P2Y1, P2Y2, P2Y4 and P2Y6 receptors.

These results suggest a physiological role for different P2Y receptor subtypes in the extracellular nucleotide‐mediated stimulation of monocytes, neutrophils, lymphocytes and endothelial cells.

British Journal of Pharmacology (1998) 123, 789–794; doi:10.1038/sj.bjp.0701665
Potentiation by DL‐α‐aminopimelate of the inhibitory action of a novel mGluR agonist (L‐F2CCG‐I) on monosynaptic excitation in the rat spinal cord
Authors: Saitoh T. , Ishida M. , Shinozaki H.
Published: January 2005

Neuropharmacological actions of all the possible stereoisomers of 3′,3′‐difluoro‐2‐(carboxycyclopropyl)glycine (3′,3′‐difluoro‐CCG) were compared with those of the corresponding 2‐(carboxycyclopropyl)glycine (CCG) isomers in the isolated spinal cord of newborn rats. (2S,1′S,2′S)‐ and (2S,1′R,2′S)‐2‐(2‐carboxy‐3,3‐difluorocyclopropyl)glycine (L‐F2CCG‐I and L‐F2CCG‐IV) were the most potent in causing depolarization, their threshold concentrations being approximately 1 μM.

The depolarization evoked by L‐F2CCG‐I (30 μM) was depressed by (+)‐α‐methyl‐4‐carboxyphenylglycine (MCPG, 1 mM (n=4)) to 17±3% of the control: this depolarizing action was not decreased by 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX, 100 μM), and only slightly decreased by high concentrations of D‐2‐amino‐5‐phosphonopentanoic acid (D‐AP5, 100 μM), suggesting that L‐F2CCG‐I activates mainly metabotropic glutamate receptors.

L‐F2CCG‐I preferentially depressed the monosynaptic component of the spinal reflex approximately 3 times more effectively than (2S,1′S,2′S)‐2‐(carboxycyclopropyl)glycine (L‐CCG‐I). The depressant action of L‐F2CCG‐I (0.2 μM–0.7 μM) on monosynaptic excitation was antagonized by (2S,1′S,2′S)‐2‐methyl‐2‐(carboxycyclopropyl)glycine (MCCG, 0.3 mM–1 mM) and (S)‐2‐amino‐2‐methyl‐4‐phosphonobutanoic acid (MAP4, 0.3 mM).

DL‐α‐Aminopimelate (10 and 100 μM) selectively potentiated the depression of monosynaptic excitation caused by L‐CCG‐I (0.2 μM) and L‐F2CCG‐I (0.1 μM). The actions of (2S,1′R,2′R,3≈prime;R)‐2‐(2,3‐dicarboxycyclopropyl)glycine (DCG‐IV) (50 nM–0.2 μM), L‐2‐amino‐4‐phosphonobutanoic acid (L‐AP4) (0.3–1 μM), (1S,3R)‐1‐aminocyclopentane‐1,3‐dicarboxylic acid ((1S,3R)‐ACPD) (1–7 μM) and baclofen (0.1–0.7 μM) were unaffected by DL‐α‐aminopimelate. The threshold concentration for the potentiating actions of DL‐α‐aminopimelate was 3 μM.

The depolarization induced by quisqualate (3 μM, 10 s application) was increased to 115±2% and 137±5% of the control values during combined application of quisqualate with either 30 μM or 100 μM DL‐α‐aminopimelate, respectively.

Following the application and subsequent washout of L‐F2CCG‐I, DL‐α‐aminopimelate (3–100 μM) decreased the amplitude of the monosynaptic component of spinal reflexes in a concentration‐dependent manner, indicating a ‘priming’ effect of L‐F2CCG‐I.

British Journal of Pharmacology (1998) 123, 771–779; doi:10.1038/sj.bjp.0701670
Effects of Ca2+ channel antagonists on striatal dopamine and DOPA release, studied by in vivo microdialysis
Authors: Okada Motohiro , Wada Kazumaru , Kiryu Kazuhiro , Kawata Yuko , Mizuno Kazuhisa , Kondo Tuyoshi , Tasaki Hiroichi , Kaneko Sunao
Published: January 2005

To elucidate the mechanisms regulating the release of striatal dopamine and its precursor, 3,4‐dihydroxyphenylalanine (DOPA), we determined the effects of various Ca2+ channel antagonists, an N‐type Ca2+ channel antagonist, ω‐conotoxin GVIA, a P‐type Ca2+ channel antagonist, ω‐agatoxin IVA, and a Q‐type Ca2+ channel antagonist, ω‐conotoxin MVIIC, on the basal and Ca2+‐ and K+‐evoked release of striatal dopamine and DOPA, by use of in vivo microdialysis.

ω‐Conotoxin GVIA strongly inhibited striatal basal dopamine release (IC50=0.48 nM), whereas this toxin only weakly modulated basal striatal DOPA release (IC50=9.55 nM). Neither ω‐agatoxin IVA nor ω‐conotoxin MVIIC affected the basal striatal release of dopamine and DOPA.

ω‐Conotoxin GVIA strongly inhibited Ca2+‐evoked striatal dopamine release (IC50=0.40 nM), whereas Ca2+‐evoked striatal DOPA release only was weakly modulated (IC50=10.51 nM). Neither ω‐agatoxin IVA nor ω‐conotoxin MVIIC affected the Ca2+‐evoked release of striatal dopamine and DOPA.

Both ω‐agatoxin IVA and ω‐conotoxin MVIIC inhibited the K+‐evoked release of striatal dopamine (IC50 of ω‐agatoxin IVA=2.65 nM; IC50 of ω‐conotoxin MVIIC=12.54 nM) and DOPA (IC50 of ω‐agatoxin IVA=0.15 nM; IC50 of ω‐conotoxin MVIIC=3.05 nM), whereas ω‐conotoxin GVIA had no effect on the K+‐evoked release of striatal dopamine and DOPA.

An increase in the extracellular Ca2+ and K+ concentrations (Ca2+‐ and K+‐evoked stimulation) did not affect tyrosine hydroxylase activity in vivo.

These findings suggest that striatal DOPA release is neurotransmitter‐like and that, unlike the mechanisms of striatal dopaminergic transmission, this striatal DOPA transmission is at least partly regulated by voltage‐sensitive Ca2+ channels.

British Journal of Pharmacology (1998) 123, 805–814; doi:10.1038/sj.bjp.0701675
Roles of calcium‐activated and voltage‐gated delayed rectifier potassium channels in endothelium‐dependent vasorelaxation of the rabbit middle cerebral artery
Authors: Dong Hui , Waldron Gareth J. , Cole William C. , Triggle Christopher R.
Published: January 2005

The cellular mechanism(s) of action of endothelium‐derived vasodilator substances in the rabbit middle cerebral artery (RMCA) were investigated. Specifically, the subtypes of potassium channels involved in the effects of endothelium‐derived relaxing factors (EDRFs) in acetylcholine (ACh)‐induced endothelium‐dependent vasorelaxation in this vessel were systematically compared.

In the endothelium‐intact RMCA precontracted with histamine (3 μM), ACh induced a concentration‐dependent vasorelaxation, which was sensitive to indomethacin (10 μM) or NG‐nitro‐L‐arginine (L‐NOARG; 100 μM); pD2 values 8.36 vs 7.40 and 6.38, P<0.01 for both, n=6 and abolished by a combination of both agents. ACh caused relaxation in the presence of high K+ PSS (40 mM KCl), which was not affected by indomethacin, but abolished by L‐NOARG and a combination of indomethacin and L‐NOARG.

In the presence of indomethacin, relaxation to ACh in the endothelium‐intact RMCA precontracted with histamine was unaffected by either glibenclamide (10 μM), an ATP‐sensitive K+ channel (KATP) blocker, 4‐aminopyridine (4‐AP, 1 mM) or dendrotoxin (DTX, 0.1 μM), delayed rectifier K+ channel (KV) blockers. However, relaxation responses to ACh were significantly inhibited by either LY83583 (10 μM) and 1H‐[1,2,4]oxadiazolo[4,3,‐a]quinoxalin‐1‐one (ODQ, 10 μM), guanylyl cyclase inhibitors, or charybdotoxin (CTX; 0.1 μM), iberiotoxin (ITX, 0.1 μM) and apamin (APA, 0.1 μM), large conductance Ca2+ ‐activated K+ channels (BKCa) blocker and small conductance Ca2+ ‐activated K+ channel (SKCa) blocker, respectively.

In the presence of L‐NOARG, relaxation to ACh was unaffected by glibenclamide or the cytochrome P450 mono‐oxygenase inhibitor, clotrimazole (1 μM), but was significantly inhibited by either 9‐(tetrahydro‐2‐furanyl)‐9H‐purin‐6‐amine (SQ  22,536, 10 μM) and 2′,3′‐dideoxyadenosine (2′,3′‐DDA, 30 μM), adenylyl cyclase inhibitors, or 4‐AP, DTX, CTX, ITX and APA.

In the endothelium‐denuded RMCA precontracted with histamine, authentic NO‐induced relaxation was unaffected by glibenclamide, 4‐AP and DTX, but significantly reduced by ODQ, ITX and APA. Authentic prostaglandin I2 (PGI2)‐induced relaxation was unaffected by glibenclamide, but significantly reduced by 2′,3′‐DDA, 4‐AP, DTX, ITX and APA. Forskolin‐induced relaxation was significantly inhibited by high K+, CTX and 4‐AP.

These results indicate that: (1) in the RMCA the EDRFs released by ACh are NO and a prostanoid (presumably PGI2), and there is no evidence for the release of a non‐NO/PGI2 endothelium‐derived hyperpolarizing factor (EDHF), (2) KCa channels are involved in NO‐mediated relaxation of the RMCA but both KCa and Kv channels are involved in PGI2‐mediated relaxation.

British Journal of Pharmacology (1998) 123, 821–832; doi:10.1038/sj.bjp.0701680
Role of nitric oxide in regulation of gastric acid secretion in rats: effects of NO donors and NO synthase inhibitor
Authors: Kato Shinichi , Kitamura Motohiro , Korolkiewicz Roman P. , Takeuchi Koji
Published: January 2005

The role of nitric oxide (NO) in the regulation of acid secretion was examined in the anaesthetized rat.

A rat stomach was mounted in an ex vivo chamber, instilled with 2 ml of saline every 15 min, and the recovered sample was titrated at pH 7.0 against 0.1 N NaOH by use of an automatic titrator for acid secretion. Gastric mucosal blood flow (GMBF) was measured simultaneously by laser Doppler flowmeter.

Intragastric application of NO donors such as FK409 (3 and 6 mg ml−1) and sodium nitroprusside (SNP; 6 and 12 mg  ml−1) as well as i.p. administration of cimetidine (60 mg kg−1), a histamine H2‐receptor antagonist, significantly inhibited the increase in acid secretion in response to pentagastrin (60 μg kg−1 h−1, i.v.), in doses that increased gastric mucosal blood flow (GMBF).

Intragastric application of FK409 (6 mg ml−1) increased both basal and stimulated acid secretion induced by YM‐14673 (0.3 mg kg−1, i.v.), an analogue of thyrotropin‐releasing hormone (TRH), but had no effect on the acid secretory response induced by histamine (4 mg kg−1 h−1, i.v.).

Pretreatment with NG‐nitro‐L‐arginine methyl ester (L‐NAME; 10 mg kg−1, i.v.) did not affect basal acid secretion, but significantly potentiated the increase in acid secretion induced by YM‐14673 and slightly augmented the acid secretory response to pentagastrin.

Both pentagastrin and YM‐14673 increased the release of nitrite plus nitrate (NOx), stable NO metabolites, into the gastric lumen, and these changes were completely inhibited by prior administration of L‐NAME (10 mg kg−1, i.v.).

Pentagastrin caused an increase in luminal release of histamine and this response was significantly suppressed by intragastric application of FK409 (6 mg ml−1).

These results suggest that either exogenous or endogenous NO has an inhibitory action on gastric acid secretion through suppression of histamine release from enterochromaffin‐like (ECL) cells.

British Journal of Pharmacology (1998) 123, 839–846; doi:10.1038/sj.bjp.0701691
Regulation of H1‐receptor coupling and H1‐receptor mRNA by histamine in bovine tracheal smooth muscle
Authors: Pype J L. , Dupont L J. , Mak J C W. , Barnes P J. , Verleden G M.
Published: January 2005

Pretreatment of bovine tracheal smooth muscle (BTSM) with histamine (1–100 μM, 1 h) induced a concentration‐dependent desensitization of the contractile response to subsequently administered histamine, with a reduction of the maximum response of 72±8% (n=5) following pre‐exposure to 100 μM histamine. In contrast, concentration‐response curves to the muscarinic agonist, methacholine were not affected following histamine pretreatment, indicating a homologous desensitization. Furthermore, concentration‐response curves to NaF, a G‐protein activator, were not altered following histamine pre‐incubation.

The histamine H1‐receptor (H1R) desensitization could be antagonized by mepyramine (an H1‐receptor antagonist, 1 μM) but not by cimetidine (an H2‐receptor antagonist, 10 μM), indicating that the desensitization occurred via stimulation of histamine H1‐receptors, without evidence for the involvement of histamine H2‐receptors.

Indomethacin (10 μM) did not block the H1R desensitization, suggesting no involvement of prostaglandins. Furthermore, histamine pre‐incubation in calcium free medium still induced a functional uncoupling of H1R.

GF 109203X, a protein kinase C (PKC) inhibitor, and H‐7, a non‐selective kinase inhibitor, did not antagonize the homologous H1R desensitization.

The steady‐state level of H1R mRNA, assessed by Northern blot analysis, was not affected by prolonged histamine exposure (100 μM, 0.5, 1, 2, 4, 16 and 24 h).

These results suggest that histamine induces desensitization of the H1R at the level of the receptor protein, which involves a mechanism independent of PKC, PKA, PKG and calcium influx, suggesting the involvement of a receptor‐specific kinase.

British Journal of Pharmacology (1998) 123, 984–990; doi:10.1038/sj.bjp.0701697
Functional and biochemical evidence for diazepam as a cyclic nucleotide phosphodiesterase type 4 inhibitor
Authors: Carmen Collado M , Beleta Jorge , Martinez Ester , Miralpeix Montse , Domènech Teresa , Maria Palacios José , Hernández Jesús
Published: January 2005

The responses of the electrically‐driven right ventricle strip of the guinea‐pig heart to diazepam were recorded in the absence and in the presence of different selective cyclic nucleotide phosphodiesterase (PDE) inhibitors.

Diazepam, at concentrations ranging from 1 μM to 100 μM, was devoid of effect on the contractile force in this preparation.

Conversely, diazepam (5 μM–100 μM) produced a consistent positive inotropic response in the presence of a concentration (1 μM), that was without effect in the absence of diazepam, of either of the selective PDE 3 inhibitors milrinone or SK&F 94120, but not in the presence of the selective PDE 4 inhibitor rolipram.

This effect of diazepam was not γ‐aminobutyric acid (GABA)‐dependent, since it was neither mimicked nor potentiated by GABA, and was not affected by either a high concentration (5 μM) of the antagonists of the benzodiazepine/GABA/channel chloride receptor complex, picrotoxin, flumazenil and β‐carboline‐3‐carboxylic acid methyl ester (βCCMe), or by the inverse agonists, β‐carboline‐3‐carboxylic acid N‐methylamide (βCCMa) and methyl 6,7‐dimethoxy‐4‐ethyl‐β‐carboline‐3‐carboxylate (DMCM, 0.1 μM). Furthermore, a specific antagonist of the peripheral benzodiazepine receptors, PK 11195 (5 μM), did not influence the effect of diazepam.

Biochemical studies with isolated PDEs, confirmed that diazepam selectively inhibits type 4 PDE from guinea‐pig right ventricle rather than the other PDEs present in that tissue. The compound inhibited this enzyme in a non‐competitive manner. Diazepam was also able to inhibit PDE 5, the cyclic GMP specific PDE absent from cardiac muscle, with a potency close to that shown for PDE 4.

Diazepam displaced the selective type 4 PDE inhibitor, rolipram from its high affinity binding site in rat brain cortex membranes, and also potentiated the rise in cyclic AMP levels induced by isoprenaline in guinea‐pig eosinophils, where only type 4 PDE is present.

The PDE inhibitory properties of diazepam were shared, although with lower potency, by other structurally‐related benzodiazepines, that also displaced [3H]‐rolipram from its high affinity binding site. The order of potency found for these compounds in these assays was not related to their potencies as modulators of the GABA receptor through its benzodiazepine binding site.

The pharmacological and biochemical data presented in this study indicate that diazepam behaves as a selective type 4 PDE inhibitor in cardiac tissue and this effect seems neither to be mediated by the benzodiazepine/GABA/channel chloride receptor complex nor by peripheral type benzodiazepine receptors.

British Journal of Pharmacology (1998) 123, 1047–1054; doi:10.1038/sj.bjp.0701698
Receptor mechanisms involved in the 5‐HT‐induced inotropic action in the rat isolated atrium
Authors: Läer Stephanie , Remmers Freerk , Scholz Hasso , Stein Birgitt , Ulrich Müller Frank , Neumann Joachim
Published: January 2005

The effects of 5‐hydroxytryptamine (5‐HT) in rat cardiac preparations were studied. 5‐HT up to 10 μM failed to affect contractility in papillary muscles. However, in electrically driven (1 Hz) left atria 5‐HT exerted a positive inotropic effect that started at 1 μM and attained its maximum at 10 μM (312±50% of predrug value, n=8).

5‐HT 10 μM stimulated the content of inositol‐1,4,5‐trisphosphate but not of cyclic AMP in rat left atria.

Plasma and serum levels of 5‐HT amounted to about 0.3 μM and 15 μM, respectively.

The selective 5‐HT4 receptor antagonists GR 125487 (10 nM and 1 μM) and SB 203186 (1 μM) did not attenuate the positive inotropic effect of 5‐HT in rat left atria. In contrast, the 5‐HT2 receptor antagonist ketanserin (5 nM, 50 nM, 1 μM) resulted in a concentration‐dependent diminution of the positive inotropic effect of 5‐HT in rat left atria.

Reverse transcriptase polymerase chain reaction with specific primers detected mRNA of the 5‐HT2A receptor in rat atria and ventricles, while expression of the 5‐HT4 receptor was confined to atria.

It is suggested that the positive inotropic effect of 5‐HT in electrically driven rat left atria is mediated by ketanserin‐sensitive 5‐HT2A receptors and not through 5‐HT4 receptors.

British Journal of Pharmacology (1998) 123, 1182–1188; doi:10.1038/sj.bjp.0701702
Salmeterol inhibition of mediator release from human lung mast cells by β‐adrenoceptor‐dependent and independent mechanisms
Authors: Chong Lee K. , Cooper Elizabeth , Vardey Christopher J. , Peachell Peter T.
Published: January 2005

The long‐acting β2‐adrenoceptor agonist, salmeterol (10−9–10−5 M), inhibited the IgE‐mediated release of histamine from human lung mast cells (HLMC) in a dose‐dependent fashion. Additional β‐adrenoceptor agonists were studied and the rank order of potency for the inhibition of histamine release from HLMC was isoprenaline>salmeterol>salbutamol. Approximate EC50 values for the inhibition of histamine release were 10 nM for isoprenaline and 100 nM for salbutamol. An EC50 value for salmeterol could not be calculated because maximal responses to salmeterol were not observed over the concentration range employed.

Both salmeterol and isoprenaline inhibited the generation of sulphopeptidoleukotrienes (sLT) more potently and more efficaciously than the release of histamine from immunologically‐activated HLMC. Salmeterol (EC50<0.1 nM) was more potent than isoprenaline (EC50 0.4 nM) at attenuating sLT generation.

The β‐adrenoceptor antagonist, propranolol (1 μM), and the selective β2‐adrenoceptor antagonist, ICI 118,551 (0.1 μM), both caused rightward shifts in the dose‐response curve for the inhibition of histamine release by isoprenaline. The antagonism of salmeterol effects by propranolol and ICI 118,551 was more complex. At lower concentrations (<1 μM) of salmeterol, both antagonists shifted the dose‐reponse curve to salmeterol rightward. At a higher concentration (10 μM) of salmeterol, neither ICI 118,551 nor propranolol was an effective antagonist of the salmeterol‐mediated inhibition of histamine release.

Prolonged exposure (4 h) of HLMC to isoprenaline (1 μM) caused an approximately 50% reduction in the effectiveness of a second exposure to isoprenaline (10 μM) at inhibiting the release of histamine, whereas this pretreatment did not affect the salmeterol (10 μM) inhibition of histamine release.

Isoprenaline (10−9–10−5 M) caused a dose‐dependent increase in total cell cyclicAMP levels in purified HLMC which paralleled the inhibition of histamine release. Salmeterol (10−9–10−5 M) was considerably less potent than isoprenaline at increasing HLMC cyclicAMP levels.

In summary, these data indicate that salmeterol is an effective inhibitor of the stimulated release of mediators from HLMC. The present data also suggest that salmeterol may act to inhibit mediator release from HLMC by β‐adrenoceptor‐dependent and independent mechanisms.

British Journal of Pharmacology (1998) 123, 1009–1015; doi:10.1038/sj.bjp.0701703
Resistance to myocardial infarction induced by heat stress and the effect of ATP‐sensitive potassium channel blockade in the rat isolated heart
Authors: Joyeux Marie , Godin‐Ribuot Diane , Ribuot Christophe
Published: January 2005

Heat stress (HS) is known to protect against myocardial ischaemia‐reperfusion injury by improving mechanical dysfunction and decreasing necrosis. However, the mechanisms responsible for this form of cardioprotection remain to be elucidated. ATP‐sensitive potassium (KATP) channels have been shown to be involved in the delayed phase of protection following ischaemic preconditioning, a phenomenon closely resembling the HS‐induced cardioprotection. The aim of this study was thus to investigate the role of KATP channels in HS‐induced protection of the isolated rat heart.

Twenty four hours after whole body heat stress (at 42°C for 15 min) or sham anaesthesia, isolated perfused hearts were subjected to a 15 min stabilization period followed by a 15 min infusion of either 10 μM glibenclamide (Glib), 100 μM sodium 5‐hydroxydecanoate (5HD) or vehicle (0.04% DMSO). Regional ischaemia (35 min) and reperfusion (120 min) were then performed.

Prior heat stress significantly reduced infarct‐to‐risk ratio (from 42.4±2.4% to 19.4±2.9, P<0.001). This resistance to myocardial infarction was abolished in both Glib‐treated (40.1±1.8% vs 42.3±1.8%) and 5HD‐treated (41.2±1.8% vs 41.8±1.2%) groups.

The results of this study suggest that KATP channel activation contributes to the cytoprotective response induced by heat stress.

British Journal of Pharmacology (1998) 123, 1085–1088; doi:10.1038/sj.bjp.0701710
Characterization of prejunctional 5‐HT1 receptors that mediate the inhibition of pressor effects elicited by sympathetic stimulation in the pithed rat
Authors: Morán A , Fernández M M. , Velasco C , Martín M L. , San Román L
Published: January 2005

A study was made of the effects of 5‐carboxamidotryptamine (5‐CT) on pressor responses induced in vivo by electrical stimulation of the sympathetic outflow from the spinal cord of pithed rats. All animals had been pretreated with atropine. Sympathetic stimulation (0.1, 0.5, 1 and 5 Hz) resulted in frequency‐dependent increases in blood pressure. Intravenous infusion of 5‐CT at doses of 0.01, 0.1 and 1 μg kg−1 min−1 reduced the pressor effects obtained by electrical stimulation. The inhibitory effect of 5‐CT was significantly more pronounced at lower frequencies of stimulation. In the present study we characterized the pharmacological profile of the receptors mediating the above inhibitory effect of 5‐CT.

The inhibition induced by 0.01 μg kg−1 min−1 of 5‐CT on sympathetically‐induced pressor responses was partially blocked after i.v. treatment with methiothepin (10  μg kg−1), WAY‐100,635 (100 μg kg−1) or GR127935T (250 μg kg−1), but was not affected by cyanopindolol (100 μg kg−1).

The selective 5‐HT1A receptor agonist 8‐OH‐DPAT and the selective 5‐HT1B/1D receptor agonists sumatriptan and L‐694,247 inhibited the pressor response, whereas the 5‐HT1B receptor agonists CGS‐12066B and CP‐93,129 and the 5‐HT2C receptor agonist m‐CPP did not modify the pressor symapthetic responses.

The selective 5‐HT1A receptor antagonist WAY‐100,635 (100 μg kg−1) blocked the inhibition induced by 8‐OH‐DPAT and the selective 5‐HT1B/1D receptor antagonist GR127935T (250 μg kg−1) abolished the inhibition induced either by L‐694,247 or sumatriptan.

None of the 5‐HT receptor agonists used in our experiments modified the pressor responses induced by exogenous noradrenaline (NA).

These results suggest that the presynaptic inhibitory action of 5‐CT on the electrically‐induced pressor response is mediated by both r‐5‐HT1D and 5‐HT1A receptors.

British Journal of Pharmacology (1998) 123, 1205–1213; doi:10.1038/sj.bjp.0701714
Reduced sympathetic noradrenergic neurotransmission in the tail artery of Donryu rats fed with high cholesterol‐supplemented diet
Authors: Karoon Parastoo , Burnstock Geoffrey
Published: January 2005

Sympathetic neurotransmission and noradrenaline content of the tail artery of Donryu rats fed for 2 months with a cholesterol‐supplemented diet enriched with 4% cholesterol, 1% cholic acid, 0.5% thiouracil (CCT), were examined.

Total serum cholesterol level of CCT fed rats (7.05±1.77 mg ml−1, n=8) was significantly greater than lab‐chow fed controls (2.58±0.32 mg ml−1, n=8). Low density lipoprotein level was also significantly increased in CCT‐fed (1.79±0.26 mg ml−1, n=8) compared with control fed rats (1.35±0.25 mg ml−1, n=8) but plasma levels of triglyceride and high density lipoproteins did not differ significantly between the two groups.

Contractile responses of the arterial rings to transmural nerve stimulation (65 V, 0.1 ms, 4–64 Hz, 1 s), were markedly attenuated in the CCT fed animals compared with the controls. This reduction involved the noradrenergic rather than purinergic component of sympathetic transmission.

Vasoconstrictor responses to exogenous noradrenaline (0.01–300 μM) and adenosine 5′‐triphosphate (0.3–1000 μM) were unaffected by CCT diet, indicating prejunctional alteration of sympathetic neurotransmission during CCT‐induced hyperlipidaemia.

The noradrenaline content of the tail arteries of CCT fed animals (2.64±0.36 ng mg−1, n=6) was significantly lower than that of controls (3.82±0.32 ng mg−1, n=6).

These findings show that chronic treatment of Donryu rats with a cholesterol‐supplemented diet led to altered levels of circulating lipid fractions accompanied by attenuated sympathetic noradrenergic neurotransmission and reduced noradrenaline content of the rat tail artery.

British Journal of Pharmacology (1998) 123, 1016–1021; doi:10.1038/sj.bjp.0701719
Effect of PDE4 inhibitors on zymosan‐induced IL‐8 release from human neutrophils: synergism with prostanoids and salbutamol
Authors: Au B‐ T. , Teixeira M M. , Collins P D. , Williams T J.
Published: January 2005

The activation of neutrophils with particulate stimuli such as zymosan induces the generation of the C‐X‐C chemokine interleukin (IL)‐8. There is evidence that neutrophil derived IL‐8 plays an important role in human diseases such as the adult respiratory distress syndrome. In the present study, we examined the effects of cyclic AMP elevating agents on the ability of human neutrophils to generate IL‐8 in response to zymosan particles.

The PDE4 inhibitor rolipram had limited effect on zymosan‐induced IL‐8 generation. In contrast, the PDE4 inhibitors RP 73401 and SB 207499 concentration‐dependently suppressed IL‐8 generation. The potency of these inhibitors was RP 73401 > SB 207499 > rolipram which is correlated with their rank order of potency at inhibiting the catalytic site of purified neutrophil PDE4. Pretreatment of neutrophils with the PDE3 inhibitor ORG 9935 or the PDE5 inhibitor zaprinast had no effect on IL‐8 generation.

The prostanoids prostaglandin E1 (PGE1) and PGE2 inhibited zymosan‐induced IL‐8 release from neutrophils in a dose‐dependent manner, in response to 10−5M PGE1 and PGE2 inhibiting IL‐8 generation by 89% and 75%, respectively. Similarly, the β2‐adrenoceptor agonist salbutamol also inhibited IL‐8 generation, but it was less effective than the prostanoids.

Significant synergism between prostanoids or salbutamol and the PDE4 inhibitors to inhibit IL‐8 generation was observed. In contrast, there was no significant synergism between PGE2 and the PDE3 inhibitor ORG 9935 or the PDE5 inhibitor zaprinast.

In order to evaluate the potential role of protein kinase A in mediating the inhibitory effects of cyclic AMP‐elevating agents, we used the protein kinase A inhibitors, H 89 and KT 5720. Pretreatment of neutrophils with these drugs completely reversed the inhibitory effects of a combination treatment with rolipram and PGE2 on zymosan‐induced IL‐8 release.

Microscopic examination revealed that most neutrophils contained one or more zymosan particles and that combination treatment with rolipram and PGE2 noticeably reduced the number of ingested particles. Moreover, there was a significant reduction in the percentage of neutrophils which ingested three or more zymosan particles.

Thus, our results demonstrate that cyclic AMP‐elevating agents modulate the ability of neutrophils to generate IL‐8 in response to a particulate stimulus. However, these agents also modulate the ability of neutrophils to phagocytose zymosan particles. Whether this effect will translate into inhibition of the ability of neutrophils to deal with infectious agents needs to be investigated further.

British Journal of Pharmacology (1998) 123, 1260–1266; doi:10.1038/sj.bjp.0701723
A comparison of the effects of L‐NAME, 7‐NI and L‐NIL on carrageenan‐induced hindpaw oedema and NOS activity
Authors: Handy Rachel L C. , Moore Philip K.
Published: January 2005

Intraplantar injection of carrageenan (150 μl, 1–3% w/v) in the rat resulted in a dose‐related increase in hindpaw weight (oedema) characterized by a rapid ‘early’ phase (up to 2.5 h) response followed by a more sustained ‘late’ phase (2–6 h) response. No change in weight of either the contralateral (i.e. noninjected) hindpaw or hindpaws injected with saline was observed.

Six hours after intraplantar injection of carrageenan (1–3% w/v) hindpaw constitutive (i.e. calcium‐dependent) nitric oxide synthase (cNOS) activity (determined ex vivo as the conversion of radiolabelled L‐arginine to radiolabelled citrulline) was increased (e.g. 2% w/v; 0.64±0.08 pmol citrulline mg−1 protein 15 min−1 c.f. 0.08±0.04 pmol citrulline mg−1 protein 15 min−1 in saline‐injected, control animals, n=4, P<0.05). Carrageenan injection also resulted in the appearance in hindpaw homogenates of inducible (i.e. calcium‐independent) nitric oxide synthase (iNOS, e.g. 2% w/v; 0.67±0.14 pmol citrulline mg−1 protein 15 min−1, n=4). Hindpaw cyclic GMP concentration was also significantly increased 6 h after intraplantar injection of carrageenan (e.g. 2% w/v; 379.6±26.8 fmol mg−1 protein c.f. 261.8±42.2 fmol mg−1 protein, in saline‐injected, control animals, n=4, P<0.05).

Pretreatment (5–25 mg kg−1, i.p., 30 min before carrageenan, 2% w/v) of animals with L‐NG nitro arginine methyl ester (L‐NAME; isoform nonselective inhibitor of NOS) or 7‐nitro indazole (7‐NI; inhibitor of neuronal NOS, nNOS) caused dose‐related inhibition of both the early (2 h) and late (6 h) phase hindpaw oedema, associated with reduced hindpaw iNOS and cNOS activity and cyclic GMP concentration in animals killed at 6 h. Administration of 7‐NI (5–25 mg kg−1, i.p.) to animals 2.5 h after intraplantar carrageenan (2% w/v) injection (i.e. at the end of the early phase oedema response) produced dose‐related inhibition of the late phase response.

Pretreatment (5–25 mg kg−1, i.p., 30 min before carrageenan, 2% w/v) of animals with L‐N6‐iminoethyllysine (L‐NIL, selective inhibitor of iNOS) (5–25 mg kg−1) failed to affect the early phase hindpaw oedema response but did produce a dose‐related inhibition of the late phase oedema. L‐NIL pretreatment also inhibited the carrageenan‐induced increase in both hindpaw iNOS and cNOS activity as well as the rise in hindpaw cyclic GMP concentration.

The present experiments demonstrate an anti‐inflammatory effect of 7‐NI as evidenced by inhibition of carrageenan‐induced hindpaw oedema in the rat. Inhibition of nNOS (early phase) and iNOS (late phase) at the site of inflammation most probably accounts for the anti‐inflammatory activity observed. These data suggest a role for nitric oxide synthesized by the nNOS isoform (most probably within sensory nerves) in this model of inflammation.

British Journal of Pharmacology (1998) 123, 1119–1126; doi:10.1038/sj.bjp.0701735
The protective effects of CP‐060S on ischaemia‐ and reperfusion‐induced arrhythmias in anaesthetized rats
Authors: Koga Takaki , Fukazawa Masanori , Suzuki Yoshiyuki , Akima Michitaka , Adachi Yuichiro , Tamura Kazuhiko , Kato Tatsuya , Kuromaru Osamu
Published: January 2005

CP‐060S is a novel sodium and calcium overload inhibitor, and is also characterized as a calcium channel blocker. As these activities have each been shown independently to ameliorate ischaemia damage in the myocardium, the combination may synergistically exert cardioprotection. In this study, therefore, the protective effect of CP‐060S against ischaemia‐ and reperfusion‐induced arrhythmia was evaluated in anesthetized rats.

Rats were anaesthetized with pentobarbitone, and the left anterior descending coronary artery was occluded for either 5 min with subsequent reperfusion (a reperfusion‐induced arrhythmia model) or 30 min without (an ischaemia‐induced arrhythmia model). All drugs were intravenously administered 1 min before the onset of occlusion.

In the reperfusion‐induced arrhythmia model, the animals in the vehicle‐treated group exhibited ventricular tachycardia (VT) in 100%, ventricular fibrillation (VF) in 89%, and death caused by sustained VF in 56%. CP‐060S (30–300 μg kg−1) dose‐dependently suppressed the incidences of arrhythmias. Significant decreases occurred at 100 μg kg−1 in VF (incidence: 42%) and mortality (8%), and at 300 μg kg−1 in VT (50%), VF (33%) and mortality (8%). This protective effect of CP‐060S was 10 times more potent than that of a pure calcium channel blocker, diltiazem (30–1000 μg kg−1) we tested, in terms of effective dose ranges. As both drugs decreased myocardial oxygen consumption estimated by rate‐pressure product to a similar extent, the calcium channel blocking activity of CP‐060S would not seem to be sufficient to explain its potency.

In the same model, co‐administration of ineffective doses of diltiazem (300 μg kg−1) and a sodium and calcium overload inhibitor, R56865 (100 μg kg−1), produced significant suppression of VT (incidence: 62%), VF (46%) and mortality (8%). By contrast, co‐administration of R56865 at the same dose with CP‐060S (300 μg kg−1) did not add to the effect of a single treatment of CP‐060S.

In the ischaemia‐induced arrhythmia model, CP‐060S (300 μg kg−1) significantly decreased the incidence of VF from 75% to 29%, whereas diltiazem (1 mg kg−1) was ineffective.

These results suggest that CP‐060S inhibits both ischaemia‐ and reperfusion‐induced arrhythmia. The combination of the calcium channel blocking effect and the calcium overload inhibition was hypothesized to contribute to these potently protective effects.

British Journal of Pharmacology (1998) 123, 1409–1417; doi:10.1038/sj.bjp.0701742
Early effects of acute γ‐radiation on vascular arterial tone
Authors: Bourlier Virginie , Diserbo Michel , Joyeux Marie , Ribuot Christophe , Multon Eric , Gourmelon Patrick , Verdetti Jean
Published: January 2005

To determine the acute effects of irradiation on the functionality of vessel, rat aortic rings were mounted in an organ bath for isometric tension measurements and irradiated (60Co, 1 Gy min−1, 15 min).

Irradiation, which is without effect on non‐contracted or endothelium‐denuded vessels, led to an immediate and reversible increase in vascular tone on (−)‐phenylephrine (1 μM)‐precontracted aortic rings. The tension reached a plateau about 5 min after the beginning of irradiation.

The maximal radiation‐induced contraction occurred on aortic rings relaxed by acetylcholine (ACh) (1 μM). In this condition, the addition of catalase (1000 u ml−1), which reduces hydrogen peroxide, and DMSO (0.1% v/v), which scavenges hydroxyl radical, had no influence on tension level while superoxide dismutase (SOD) (100 u ml−1), a superoxide anion scavenger, reduced the observed contraction. A similar result was obtained in the presence of indomethacin (10 μM), a cyclo‐oxygenase blocker.

Pretreatment of rings with the nitric oxide synthase inhibitor, Nω‐nitro‐L‐arginine methyl ester (L‐NAME) (10–100 μM) inhibited the radiation‐induced contraction.

This effect was dose rate‐dependent and even occurred for a very low dose rate (0.06 Gy min−1).

The present results indicate that γ‐radiation induces an instantaneous vascular tone increase that is endothelium and dose rate‐dependent. This effect is (i) maximal when nitric oxide (NO) is produced, (ii) greatly reduced by SOD and (iii) inhibited by L‐NAME, suggesting a major involvement of complexes between NO and superoxide anion.

British Journal of Pharmacology (1998) 123, 1168–1172; doi:10.1038/sj.bjp.0701744
Effect of some cyclooxygenase inhibitors on the increase in guanosine 3′:5′‐cyclic monophosphate induced by NO‐donors in human whole platelets
Authors: Failli Paola , Cecchi Enrica , Tosti‐Guerra Cristina , Mugelli Alessandro , Laffi Giacomo , Zilletti Lucilla , Giotti Alberto
Published: January 2005

The effect of the NSAIDs indomethacin, indoprofen, diclofenac and acetylsalicylic acid on the increase in guanosine 3′:5′‐cyclic monophosphate (cyclic GMP) induced by nitric oxide‐donor agents was tested in human whole platelets and in platelet crude homogenate.

In whole platelets, indomethacin reduced the increase in cyclic GMP induced by the nitric oxide‐donors (NO‐donors) sodium nitroprusside (NaNP) and S‐nitroso‐N‐acetylpenicillamine (SNAP) in a dose‐dependent way, its IC50 being 13.7 μm and 15.8 μm, respectively.

Of the other cyclooxygenase inhibitors tested, only indoprofen reduced the increase in cyclic GMP induced by both NO‐donors in a dose‐dependent way (IC50=32.7 μm, NaNP and 25.0 μm, SNAP), while acetylsalicylic acid (up to 1000 μm) and diclofenac (up to 100 μm) were ineffective.

However, in platelet crude homogenate neither indomethacin nor indoprofen reduced the cyclic GMP production.

Indomethacin (10 μm), indoprofen (30 μm), diclofenac (100 μm) and acetylsalicylic acid (1000 μm) showed a comparable efficacy in inhibiting platelet thromboxane B2 (TXB2) production, suggesting that the inhibitory effect of indomethacin and indoprofen on the increase in cyclic GMP induced by both NO‐donors was not mediated by inhibition of cyclooxygenase.

In vitro, the NSAIDs analysed did not interfere with nitrite production of SNAP.

The unhomogeneous behaviour of NSAIDs on the increase in cyclic GMP induced by NO‐donors in whole platelets may contribute to the different pharmacological and toxicological characteristics of the drugs, providing new knowledge on the effect of indomethacin and indoprofen.

British Journal of Pharmacology (1998) 123, 1457–1463; doi:10.1038/sj.bjp.0701745
α1L‐Adrenoceptor mediation of smooth muscle contraction in rabbit bladder neck: a model for lower urinary tract tissues of man
Authors: Shannon Kava M. , Blue David R. , Vimont Rachel L. , Clarke David E. , Ford Anthony P. D. W.
Published: January 2005

The α1‐adrenoceptor population mediating contractile responses to noradrenaline (NA) in smooth muscles of the bladder neck from rabbit (RBN) has been characterized by use of quantitative receptor pharmacology.

Experiments with several ‘key’ α1‐adrenoceptor antagonists of varying subtype selectivities (RS‐17053, BMY 7378, indoramin, 5‐methylurapidil, prazosin, REC 15/2739, SNAP 5089, terazosin, WB 4101, tamsulosin, (+)‐cyclazosin and RS‐100329) were conducted. Schild regression analyses yielded affinity (mean pKb) estimates of 7.1, 6.2, 8.6, 8.6, 8.4, 9.3, 7.0, 7.4, 8.9, 10.0, 7.1 and 9.3, respectively, although deviations from unit Schild regression slope question the robustness of data for RS‐17053 and SNAP 5089.

The nature of antagonism by these agents and the profile of affinity determinations generated together suggest that a single α1‐adrenoceptor subtype mediates contractile responses of RBN to NA. Additional studies with phenylephrine indicated also an agonist‐independence of this profile. Pharmacologically, this profile was reminiscent of that described as ‘α1L’ ‐adrenoceptor, which has been shown to mediate contractions of several tissues including lower urinary tract (LUT) tissues of man. Furthermore, a similarity was noticed between the ‘α1L’ ‐adrenoceptor described here in RBN and the rabbit and human cloned α1a‐adrenoceptor (based on data from both whole cell radioligand binding at 37°C and [3H]‐inositol phosphates accumulation assays), characterizations of which have been published elsewhere.

In conclusion, the RBN appears to provide a predictive pharmacological assay for the study of NA‐induced smooth muscle contraction in LUT tissues of man.

British Journal of Pharmacology (1998) 123, 1359–1366; doi:10.1038/sj.bjp.0701748