bluuebunny/crossref_metadata_2025_split huggingface dataset:
Loss of endothelium‐derived nitric oxide in rabbit aorta by oxidant stress: restoration by superoxide dismutase mimetics
Authors: MacKenzie Andrew , Martin William 
Published: January 2005

Structurally distinct superoxide dismutase (SOD) mimetics were examined for their ability to protect nitric oxide (NO) from destruction by oxidant stress in rabbit aorta.
These were the spin traps, PTIYO (4‐phenyl‐2,2,5,5‐tetramethyl imidazolin‐1‐yloxy‐5‐oxide), tempol (4‐hydroxy 2,2,6,6,‐tetramethylpiperidine‐1‐oxyl) and tiron (4,5‐dihydroxy‐1,3‐benzene‐disulphonic acid), the metal salts, CuSO4 and MnCl2, and the metal‐based agents CuDIPS (Cu (II)‐[diisopropylsalicylate]2) and MnTMPyP (Mn (III) tetrakis [1‐methyl‐4‐pyridyl]porphyrin).
Oxidant stress was generated in isolated aortic rings by inactivating endogenous Cu/Zn SOD with diethyldithiocarbamate (DETCA; 60 min) either alone at 3 mM or at 0.3 mM in combination with superoxide generation using xanthine oxidase (XO; 4.8 mu ml−1) and hypoxanthine (HX; 0.1 mM).
Acetylcholine (ACh)‐induced relaxation was inhibited by DETCA (3 mM, 60 min) and was not restored by exogenous SOD (250 u ml−1), suggesting the oxidant stress was intracellular. MnTMPyP (600 μM and 1 mM) and MnCl2 (100 μM) were the only agents to reverse the blockade of ACh‐induced relaxation.
Addition of XO/HX to DETCA (0.3 mM)‐treated tissues powerfully impaired ACh‐induced relaxation and exogneous SOD (250 u ml−1) fully reversed the blockade, suggesting the oxidant stress was extracellular. CuDIPS (0.1–3 μM), CuSO4 (0.3–3 μM), MnCl2 (1–100 μM) and MnTMPyP (100–600 μM) also reversed blockade powerfully, tempol (30 μM–1 mM) and tiron (0.3–10 mM) reversed blockade weakly and PTIYO (10–300 μM) enhanced the blockade.
Thus, MnTMPyP was the only SOD mimetic to restore NO‐dependent relaxation in conditions of both extracellular and intracellular oxidant stress. This agent may, therefore, provide a lead in the development of SOD mimetics for the treatment of pathologies associated with oxidant stress.
Effect of sodium rhein on electrically‐evoked and agonist‐induced contractions of the guinea‐pig isolated ileal circular muscle
Authors: Izzo Angelo A , Mascolo Nicola , Capasso Francesco 
Published: January 2005

This study examined the effects of sodium rhein (0.03–30 μM) on the contractions of the isolated circular muscle of guinea‐pig ileum induced by acetylcholine (100 nM), substance P (3 nM) and electrical stimulation (10 Hz for 0.3 s, 100 mA, 0.5 ms pulse duration). The effect of sodium rhein was also evaluated on the ascending excitatory reflex using a partitioned bath (oral and anal compartments). Ascending excitatory enteric nerve pathways were activated by electrical field stimulation (10 Hz for 2 s, 20 mA, 0.5 pulse duration) in the anal compartment and the resulting contraction of the guinea‐pig intestinal circular muscle in the oral compartment was recorded.
Sodium rhein (0.3, 3 and 30 μM) significantly potentiated (52±11% at 30 μM) acetylcholine‐induced contractions. In the presence of tetrodotoxin (0.6 μM) or ω‐conotoxin GVIA (10 nM) sodium rhein (3 and 30 μM) did not enhance, but significantly reduced (49±10% and 44±8%, respectively, at 30 μM) acetylcholine‐induced contractions.
Sodium rhein (0.3, 3 and 30 μM) significantly increased (65±11% at 30 μM) substance P‐induced contractions. In the presence of tetrodotoxin (0.6 μM), ω‐conotoxin GVIA (10 nM) or atropine (0.1 μM), sodium rhein (3 and 30 μM) significantly reduced (50±10%, 55±8% and 46±10%, respectively, at 30 μM) substance P‐induced contractions.
NG‐nitro‐L‐arginine methyl ester (L‐NAME, 100 μM) abolished the potentiating effect of sodium rhein on acetylcholine and substance P‐induced contractions. At the highest concentration (30 μM), sodium rhein, in presence of L‐NAME, reduced the acetylcholine (30±6%)‐ or substance P (36±6%)‐induced contractions.
Sodium rhein (30 μM) significantly potentiated (29±9%) the electrically‐evoked contractions. L‐NAME (100 μM), but not phentolamine, enhanced the effect of sodium rhein. Sodium rhein (30 μM) significantly increased (32±9%) the ascending excitatory reflex when applied in the oral, but not in the anal compartment.
These results indicate that sodium rhein (i) activates excitatory cholinergic nerves on circular smooth muscle presumably through a facilitation of Ca2+ entry through the N‐type Ca2+ channel, (ii) has a direct inhibitory effect on circular smooth muscle and (iii) does not affect enteric ascending neuroneural transmission. Nitric oxide could have a modulatory excitatory role on sodium rhein‐induced changes of agonist‐induced contractions and an inhibitory modulator role on sodium rhein‐induced changes of electrically‐induced contractions.
The anticonvulsant actions of σ receptor ligands in the Mg2+‐free model of epileptiform activity in rat hippocampal slices
Authors: Thurgur Claire , Church John 
Published: January 2005

The anticonvulsant potency of a series of structurally‐dissimilar compounds which possess nanomolar affinities for high‐affinity σ binding sites was examined in the Mg2+‐free model of epileptiform activity in rat hippocampal slices. Extracellular field potential recordings in the CA1 region were employed to examine the effects of test compounds on spontaneous epileptiform activity and multiple population spikes evoked by stimulation of the Schaffer collateral‐commissural pathway.
Applied at σ site‐selective (i.e. nanomolar) concentrations, dextromethorphan, ditolylguanidine, caramiphen and opipramol failed to modify Mg2+‐free epileptiform activity; neither pro‐ nor anticonvulsant effects were observed. However, applied at micromolar concentrations, these and additional test compounds reversibly inhibited orthodromically‐evoked epileptiform field potentials with a rank order potency (IC50 values in μM): dextrorphan (1.5)>ifenprodil (6.3)>dextromethorphan (10)>ditolylguanidine (15)>loperamide (28)>carbetapentane (38)>caramiphen (46)>opipramol (52). Micromolar concentrations of the same compounds also inhibited spontaneous epileptiform bursts recorded during perfusion with Mg2+‐free medium.
Co‐application of ropizine (10 μM), an allosteric modulator of dextromethorphan binding to high‐affinity σ receptors, failed to endow dextromethorphan 10 nM with anticonvulsant properties and did not modify the anticonvulsant potency of 10 μM dextromethorphan.
The effects of dextrorphan (10 μM), ifenprodil (20 μM), loperamide (50 μM) and caramiphen (100 μM) were examined in the presence of external Mg2+ on field potential input/output (I/O) relationships and paired‐pulse facilitation (PPF) of field excitatory postsynaptic potentials. Only caramiphen elicited effects on these parameters, affecting synaptic transmission at the point of synaptic transfer and depressing PPF ratios to below baseline values. The effects of caramiphen on I/O relationships mimicked those of the established anticonvulsant adenosine; in contrast, adenosine evoked an increase in PPF ratios.
Because anticonvulsant activity was observed only at micromolar concentrations of the σ ligands tested, the results indicate that their anticonvulsant actions should not be ascribed to their occupancy, observed at nanomolar concentrations, of high‐affinity σ binding sites. Rather, anticonvulsant activity more likely reflects functional NMDA receptor antagonism and/or blockade of high voltage‐activated Ca2+ channels, effects which are associated with micromolar concentrations of the test compounds. Modulation of GABAergic inhibitory mechanisms may also contribute to the anticonvulsant properties of caramiphen.
Pharmacological characterization of muscarinic receptors in rabbit isolated iris sphincter muscle and urinary bladder smooth muscle
Authors: Choppin A , Eglen R M. , Hegde S S. 
Published: January 2005

The pharmacological characteristics of muscarinic receptors in the rabbit iris sphincter muscle were studied and compared to M3 receptors in rabbit urinary bladder smooth muscle.
(+)‐Cis‐dioxolane induced concentration‐dependent contractions of the iris sphincter muscle (pEC50=6.41±0.10, Emax=181±17 mg, n=38) and urinary bladder smooth muscle (pEC50=6.97±0.04, Emax=4.28±0.25 g, n=54). These contractions were competitively antagonized by a range of muscarinic receptor antagonists (pKB values are given for the iris sphincter muscle and the bladder smooth muscle, respectively): atropine (9.30±0.07 and 9.40±0.04), AQ‐RA 741 (6.35±0.04 and 6.88±0.03), darifenacin (9.56±0.05 and 9.12±0.05), methoctramine (5.75±0.07 and 5.81+0.06), oxybutynin (8.10±0.09 and 8.59±0.06), pirenzepine (6.79±0.05 and 6.89±0.04), secoverine (7.54±0.05 and 7.66±0.05), p‐F‐HHSiD (7.55±0.09 and 7.50±0.05) and zamifenacin (8.69±0.10 and 8.36±0.06). A significant correlation between the pKB values in the bladder and the pKB values in the iris was obtained.
In both tissues, the pKB values correlated most favorably with pKi values for these compounds at human recombinant muscarinic m3 receptors. A reasonable correlation was also noted at human recombinant muscarinic m5 receptors given the poor discriminative ability of ligands between m3 and m5 receptors.
Overall, the data from this study suggest that the muscarinic receptors mediating contraction of the rabbit iris sphincter muscle and urinary bladder smooth muscle are similar and equate most closely with the pharmacologically‐defined muscarinic M3 receptor.
Systemic and renal effects of an ETA receptor subtype‐specific antagonist in healthy subjects
Authors: Schmetterer Leopold , Dallinger Susanne , Bobr Barbara , Selenko Nicole , Eichler Hans‐Georg , Wolzt Michael 
Published: January 2005

Endothelins (ETs) might play a pathophysiological role in a variety of vascular diseases. The aim of the present study was to characterize the effects of BQ‐123, a specific ETA receptor antagonist on systemic and renal haemodynamics in healthy subjects. This was done at baseline and during infusion of exogenous ET‐1.
The study was performed in a balanced, randomized, placebo‐controlled, double blind 4 way cross‐over design in 10 healthy male subjects. Subjects received co‐infusions of ET‐1 (2.5 ng kg−1 min−1 for 120 min) or placebo and BQ‐123 (15 μg min−1 for 60 min and subsequently 60 μg min−1 for 60 min) or placebo. Renal plasma flow (RPF) and glomerular filtration rate (GFR) were assessed by the para‐aminohippurate (PAH) and the inulin plasma clearance method, respectively.
BQ‐123 alone had no renal or systemic haemodynamic effect. ET‐1 significantly reduced RPF (−24%, P<0.001) and GFR (−12%, P=0.034). These effects were abolished by co‐infusion of either dose of BQ‐123 (RPF: P=0.0012; GFR: P=0.020).
BQ‐123 reversed the renal haemodynamic effects induced by exogenous ET‐1 in vivo. This indicates that vasoconstriction in the kidney provoked by ET‐1 is predominantly mediated by the ETA receptor subtype.
Selective potentiation by ouabain of naloxone‐induced withdrawal contractions of isolated guinea‐pig ileum following acute exposure to morphine
Authors: Mundey M K. , Mason R , Wilson V G. 
Published: January 2005

Ouabain, an inhibitor of Na+/K+ ATPase induces the release of acetylcholine from central and myenteric cholinergic neurones principally due to partial depolarization of the cell membrane. The effect of ouabain has been examined on neurogenic contractions in the guinea‐pig ileum arising from either electrical field stimulation or from naloxone in morphine‐exposed preparations.
Guinea‐pig isolated ileum preparations were stimulated transmurally (0.1 Hz, 0.3 ms, 200 mA) to elicit contractions of the myenteric plexus‐longitudinal smooth muscle.
Incubation with morphine (0.3 μM, 60 min) was followed by naloxone (1 μM) which produced withdrawal contractions in 16/26 preparations (median of 10.7 [2.2–40.0]% of a maximal contracture to KCl (60 mM)).
In parallel experiments, ouabain (1 μM) was added to the tissue before exposure to morphine (0.3 μM, 60 min). Naloxone (1 μM) subsequently displayed a withdrawal contraction in all 26/26 tissues (57.9 [30.5–151.7]% of a maximal contracture to KCl (60 mM).
Ouabain neither affected the concentration‐dependent contractions of guinea‐pig ileum produced by carbachol nor the inhibition of electrically‐evoked contraction produced by morphine (0.3 μM).
The muscarinic antagonist atropine (0.1 μM) antagonized control naloxone withdrawal responses. The atropine resistant component, evident in ouabain‐treated tissues, was blocked by SR140333((S)1‐{2‐[3‐(3,4‐dichlorophenyl)‐1‐(3‐isopropoxyphenylacetyl)piperidin‐3‐yl]ethyl}‐4‐phenyl‐1‐azoniabicyclo[2.2.2]octane, chloride), a substance P antagonist.
Clonidine (α2‐adrenoceptor agonist) inhibited electrically‐evoked contractions. Exposure to the α2‐adrenoceptor antagonist RX811059 (2‐(2‐ethoxy‐1,4‐benzodioxan‐2‐yl)‐2‐imidazoline), resulted in a contracture which was not significantly enhanced by ouabain (1 μM).
Ouabain selectively potentiates the naloxone‐induced withdrawal contraction following acute exposure to morphine the major components of which are mediated by both acetylcholine and substance P.
SUR2 subtype (A and B)‐dependent differential activation of the cloned ATP‐sensitive K+ channels by pinacidil and nicorandil
Authors: Shindo Takashi , Yamada Mitsuhiko , Isomoto Shojiro , Horio Yoshiyuki , Kurachi Yoshihisa 
Published: January 2005

The classical ATP sensitive K+ (KATP) channels are composed of a sulphonylurea receptor (SUR) and an inward rectifying K+ channel subunit (BIR/Kir6.2). They are the targets of vasorelaxant agents called K+ channel openers, such as pinacidil and nicorandil.
In order to examine the tissue selectivity of pinacidil and nicorandil, in vitro, we compared the effects of these agents on cardiac type (SUR2A/Kir6.2) and vascular smooth muscle type (SUR2B/Kir6.2) of the KATP channels heterologously expressed in HEK293T cells, a human embryonic kidney cell line, by using the patch‐clamp method.
In the cell‐attached recordings (145 mM K+ in the pipette), pinacidil and nicorandil activated a weakly inwardly‐rectifying, glibenclamide‐sensitive 80 pS K+ channel in both the transfected cells.
In the whole‐cell configuration, pinacidil showed a similar potency in activating the SUR2B/Kir6.2 and SUR2A/Kir6.2 channels (EC50 of ∼2 and ∼10 μM, respectively). On the other hand, nicorandil activated the SUR2B/Kir6.2 channel >100 times more potently than the SUR2A/Kir6.2 (EC50 of ∼10 μM and >500 μM, respectively).
Thus, nicorandil, but not pinacidil, preferentially activates the KATP channels containing SUR2B. Because SUR2A and SUR2B are diverse only in 42 amino acids at their C‐terminal ends, it is strongly suggested that this short part of SUR2B may play a critical role in the action of nicorandil on the vascular type classical KATP channel.
Effects of inhibitors of the activity of poly (ADP‐ribose) synthetase on the liver injury caused by ischaemia‐reperfusion: a comparison with radical scavengers
Authors: Bowes Joanne , Thiemermann Christoph 
Published: January 2005

Poly (ADP‐ribose) synthetase (PARS) is a nuclear enzyme activated by strand breaks in DNA which are caused by reactive oxygen species (ROS) and peroxynitrite. Excessive activation of PARS may contribute to the hepatocyte injury caused by ROS in vitro and inhibitors of PARS activity reduce the degree of reperfusion injury of the heart, skeletal muscle and brain in vivo. Here we compared the effects of various inhibitors of the activity of PARS with those of deferoxamine (an iron chelator which prevents the generation of hydroxyl radicals) and tiron (an intracellular scavenger of superoxide anion) on the degree of hepatic injury caused by ischaemia and reperfusion of the liver in the anaesthetized rat or rabbit.
In the rat, ischaemia (30 or 60 min) and reperfusion (120 min) of the liver resulted in significant increases in the serum levels of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) indicating the development of liver injury. Intravenous administration of the PARS inhibitors 3‐aminobenzamide (3‐AB, 10 mg kg−1 or 30 mg kg−1), 1,5‐dihydroxyisoquinoline (ISO, 1 mg kg−1) or 4‐amino‐1,8‐naphthalimide (4‐AN, 3 mg kg−1) before reperfusion did not reduce the degree of liver injury caused by ischaemia‐reperfusion.
In contrast to the PARS inhibitors, deferoxamine (40 mg kg−1) or tiron (300 mg kg−1) significantly attenuated the rise in the serum levels of AST and ALT caused by ischaemia‐reperfusion of the liver of the rat.
In the rabbit, the degree of liver injury caused by ischaemia (60 min) and reperfusion (120 min) was also not affected by 3‐AB (10 mg kg−1) or ISO (1 mg kg−1).
These results support the view that the generation of oxygen‐derived free radicals mediates the liver injury associated with reperfusion of the ischaemic liver by mechanism(s) which are independent of the activation of PARS.

British Journal of Pharmacology (1998) 124, 1254–1260; doi:10.1038/sj.bjp.0701930
Mechanism of neuromuscular blockade induced by phenthonium, a quaternary derivative of (−)–hyoscyamine, in skeletal muscles
Authors: Souccar Caden , Lima‐Landman Maria Teresa R. , Ballejo Gustavo , Lapa Antonio José 
Published: January 2005

The mechanisms underlying the postjunctional blockade induced by phenthonium [N‐(4‐phenyl) phenacyl 1‐hyoscyamine] were investigated in mammalian and amphibian muscles. This muscarinic antagonist was previously shown to enhance specifically the spontaneous acetylcholine (ACh) release at concentrations that blocked neuromuscular transmission.
In both rat diaphragm and frog sartorius muscles, phenthonium (Phen, 1–100 μm) depressed the muscle twitches elicited by nerve stimulation (IC50: 23 μm and 5 μm, respectively), and blocked the nerve‐evoked muscle action potential. The neuromuscular blockade was not reversed after incubation with neostigmine.
Equal concentrations of Phen decreased the rate of rise and prolonged the falling phase of the directly elicited action potential in frog sartorius muscle fibres, indicating that the drug also affects the sodium and potassium conductance.
Phen (50 and 100 μm) protected the ACh receptor against α‐bungarotoxin (BUTX) blockade in the mouse diaphragm allowing recording of endplate potentials and action potentials after 5 h wash with physiological salt solution.
Phen (10–100 μm) produced a concentration‐ and voltage‐dependent decrease of the endplate current (e.p.c.), and induced nonlinearity of the current‐voltage relationship. At high concentrations Phen also shortened the decay time constant of e.p.c (τe.p.c.) and reduced its voltage sensitivity.
At the same range of concentrations, Phen also reduced the initial rate of [125I]‐BUTX binding to junctional ACh receptors of the rat diaphragm (apparent dissociation constant = 24 μm), the relationship between the degree of inhibition and antagonist concentration being that expected for a competitive mechanism.
It is concluded that Phen affects the electrical excitability of the muscle fibre membrane, and blocks neuromuscular transmission through a mechanism that affects the agonist binding to its recognition site and ionic channel conductance of the nicotinic ACh receptor.

British Journal of Pharmacology (1998) 124, 1270–1276; doi:10.1038/sj.bjp.0701932
Opposite effects of CCKB agonists in grooming behaviour in rats: further evidence for two CCKB subsites
Authors: Ladurelle Nathalie , Sebret Angélique , Garbay Christiane , Roques Bernard P. , Daugé Valérie 
Published: January 2005

The hypothesis of the existence of two CCKB receptor subsites, CCKB1 and CCKB2 corresponding probably to different coupling states of CCKB receptors, was studied by measuring grooming behaviour in rats.
The B1 receptor agonist, BC197 (300 μg kg−1, i.p.) produced a 45–50% decrease in grooming activity, which was prevented by both the CCKB receptor antagonists CI‐988 (20 μg kg−1 i.p.) and L‐365,260 (200 μg kg−1, i.p.).
In contrast, 3, 10 and 30 μg kg−1, i.p., of the potent B2 receptor agonist, BC264, enhanced grooming (150–190%). This effect was prevented by previous injection of 75 μg kg−1 of L‐365,260 while higher doses (200 μg kg−1, i.p.) produced only a partial antagonism. Moreover, CI‐988 (20 μg kg−1, i.p.), showed an opposite effect in potentiating the responses induced by BC264. However, 200 μg kg−1 of CI‐988 tended to suppress the increase of grooming induced by BC264.
The effects of BC264 were prevented by the D1 receptor (SCH 23390) and D2 receptor (sulpiride) antagonists, while those of BC197 were only antagonized by sulpiride, emphasizing the existence of a link between peptidergic (CCK) and dopaminergic systems.
This study brings additional evidence for the existence of the two CCKB receptor subsites and suggests that particular attention should be focused on the selectivity of CCKB receptor agonists, notably to explain the fact that some compounds such as Boc‐CCK4 induce anxiogenic‐like effects while others, including BC264, are devoid of these effects.

British Journal of Pharmacology (1998) 124, 1091–1098; doi:10.1038/sj.bjp.0701933
Inhibition of gastric emptying and intestinal transit by amphetamine through a mechanism involving an increased secretion of CCK in male rats
Authors: Doong Ming‐Luen , Lu Chien‐Chen , Kau Mei‐Mei , Tsai Shiow‐Chwen , Chiao Yu‐Chung , Chen Jiann‐Jong , Yeh Jiun‐Yih , Lin Ho , Huang Seng‐Wong , Chen Tseng‐Shing , Chang Full‐Young , Wang Paulus S. 
Published: January 2005

The effect of amphetamine on gastrointestinal (GI) transit and the plasma levels of cholecystokinin (CCK) were studied in male rats.
Gastric emptying was inhibited both acutely and chronically by the administration of amphetamine. GI transit was decreased by the acute administration of amphetamine but not affected by the chronic administration of amphetamine.
Plasma CCK levels were increased dose‐dependently by amphetamine.
Proglumide, a CCK receptor antagonist, prevented amphetamine‐induced inhibition of gastric emptying and the decrease in GI transit in male rats.
The selective CCKA receptor antagonist, lorglumide, dose‐dependently attenuated the amphetamine‐induced inhibition of gastric emptying in male rats. In contrast, the selective CCKB receptor antagonist, PD 135,158, did not reverse the effect of amphetamine on gastric emptying.
Both lorglumide and PD 135,158 reversed the inhibitory effect of amphetamine on GI transit in male rats.
These results suggest that amphetamine‐induced inhibition of gastric emptying and intestinal transit is due in part to a mechanism associated with the hypersecretion of endogenous CCK.

British Journal of Pharmacology (1998) 124, 1123–1130; doi:10.1038/sj.bjp.0701937