bluuebunny/crossref_metadata_2025_split huggingface dataset:
Selective inhibition by barbiturates of the synthesis of endothelium‐derived hyperpolarizing factor in the rabbit carotid artery
Authors: Lischke Volker , Busse Rudi , Hecker Markus 
Published: July 2012

Several lines of evidence suggest that both volatile and intravenous anaesthetics may interfere with the synthesis and release of endothelium‐derived vasoactive factors. We have investigated the effects of three different barbiturates on the release of nitric oxide (NO) and endothelium‐derived hyperpolarizing factor (EDHF) in phenylephrine (1 μm)‐preconstricted, endothelium‐intact ring segments of the rabbit carotid artery. The segments were pretreated with the cyclo‐oxygenase inhibitor, diclofenac (1 μm), to prevent the formation of vasoactive prostanoids, such as prostacyclin (PGI2).
Acetylcholine (ACh) elicited a concentration‐dependent relaxation (EC50 0.15 μm) in control segments which was not significantly different from the relaxant responses of segments pretreated with methohexitone (0.03‐0.3 mM), phenobarbitone (0.1–0.3 mM) or thiopentone (0.1‐0.3 mM).
Inhibition of NO synthesis with NG–nitro‐L‐arginine (0.1 mM) significantly reduced the maximum relaxant response to ACh from 96 to 40%. This NO/PGI2‐independent relaxation appeared to be mediated by the release of EDHF, since it was strongly diminished in the presence of the K+ca inhibitors, tetrabutylammonium (1–3 mM) and charybdotoxin (10 nM), following preconstriction with potassium calcium (40 mM) or removal of the endothelium. Thiopentone or methohexitone markedly attenuated the EDHF‐mediated relaxant response to ACh, while phenobarbitone had no effect. The endothelium‐independent relaxation elicited by sodium nitroprusside (0.01 −10 μm), on the other hand, was only marginally affected by these anaesthetics.
The cytochrome P450 inhibitor, clotrimazole (3–100 μm), mimicked the inhibitory effect of thiopentone and methohexitone on the NO/PGI2‐independent relaxant response to ACh. Moreover the cytochrome P450‐catalyzed O‐dealkylation of 7‐ethoxycoumarin by rabbit liver microsomes was inhibited in the presence of thiopentone or methohexitone (0.3‐1 mM), while phenobarbitone was without effect.
These findings suggest that thiopentone and methohexitone selectively attenuate the EDHF‐mediated relaxant response to ACh in the rabbit carotid artery, presumably by interfering with its synthesis from arachidonic acid via the cytochrome P450 epoxygenase pathway.
NANC neurotransmission in lamina propria of the rabbit urethra: regulation by different subsets of calcium channels
Authors: Zygmunt Pia K.E. , Zygmunt Peter M. , Högestätt Edward D. , Andersson Karl‐Erik 
Published: July 2012

Electrical field stimulation (EFS) of the rabbit urethral lamina propria elicited a frequency‐dependent non‐adrenergic, non‐cholinergic (NANC) relaxation, which was abolished by NΩ–nitro‐L‐arginine (l‐NOARG).
Ω‐Conotoxin GVIA, a selective blocker of N‐type voltage‐operated calcium channels (VOCCs), and Ω‐conotoxin MVIIC (blocker of N‐ and Q‐type VOCCs) inhibited the NANC relaxation, and the inhibition was inversely related to the frequency of stimulation. Combined, the two toxins were more effective than co‐conotoxin GVIA alone.
The relaxation induced by the nitric oxide (NO) donor, 3‐morpholino‐sydnonimine (SIN‐1) was not affected by Ω‐conotoxin MVIIC.
Ω‐Agatoxin IVA (blocker of P‐type VOCCs) did not attenuate the NANC relaxation.
Reduction of the calcium concentration from 1.5 to 0.5 mM reduced the NANC relaxation at low but not at high frequencies of stimulation; the relaxation induced by SIN‐1 was not affected.
EFS (20Hz, 30 s) increased the cyclic GMP level 3 fold in normal Krebs solutions, but was unable to enhance significantly the cyclic GMP level after calcium omission. L‐NOARG reduced the cyclic GMP content in ‘calcium‐free’ medium, indicating an ongoing NO synthesis that was independent of extracellular calcium.
Caffeine, ryanodine and thapsigargin (inhibitors of sarcoplasmic calcium release), and CGP 37157 (inhibitor of mitochondrial sodium/calcium exchange) had no effect on the NANC relaxation.
It is suggested that nitrergic nerve activation in the rabbit urethral lamina propria is mediated in part by N‐type (co‐conotoxin GVIA‐sensitive) and in part by Q‐type (co‐conotoxin MVIIC‐sensitive) VOCCs. With high frequences of stimulation, another mechanism, possibly calcium‐independent, appears to become operational.
Modulation of the isoprenaline‐induced membrane hyperpolarization of mouse skeletal muscle cells
Authors: van Mil H.G.J. , Kerkhof C.J.M. , van Heukelom J. Siegenbeek 
Published: July 2012

The hyperpolarization of the resting membrane potential, Vm, induced by isoprenaline in the lumbrical muscle fibres of the mouse, was investigated by use of intracellular microelectrodes.
In normal Krebs‐Henseleit solution (potassium concentration: K+o=5.7mM, ‘control’), Vm was −74.0 ± 0.2 mV; lowering K+o to 0.76 mM (′low K+o) resulted in either a hyperpolarization (Vm= −95.7 ±2.9 mV), or a depolarization (Vm= −52.0 ±0.3 mV).
Isoprenaline (≥200 nM) induced a hyperpolarization of Vm by ΔVm= − 5.6 ±0.4 mV in control solution.
When Vm hyperpolarized after switching to low K+o, the addition of isoprenaline resulted in increased hyperpolarization Vm: ΔVm=−16.3±3.2 mV to a final Vm=−110.1 ±3.4 mV. Adding iso‐prenaline when Vm depolarized in low K+o, leads to a hyperpolarization of either by − 11.6±0.5mV to −63.6 ±0.8 mV or by −51.7 ±2.7 mV to −106.9 ±3.9 mV.
Ouabain (0.1 to 1 mm) did not suppress the hyperpolarization by isoprenaline in 5.7 mM K+o (ΔVm=−6.7±0.4mV) or the hyperpolarization of the depolarized cells in low K+o (ΔVm=−9.7 Δ1.5mV).
The hyperpolarization is a logarithmically decreasing function of K+o in the range between 2 and 20 mM (12 mV/decade).
IBMX and 8Br‐cyclic AMP mimicked the response to isoprenaline whereas forskolin (FSK) induced in low K+o a hyperpolarization of −7.0 ±0.7 mV that could be augmented by addition of isoprenaline (ΔVm=−8.2±1.8mV).
In control and low K+o, Ba2+ (0.6 mm) inhibited the hyperpolarization induced by isoprenaline, IBMX or 8Br‐cyclic AMP. Other blockers of the potassium conductance such as TEA (5 mm) and apamin (0.4 μm) had no effect.
We conclude that in the lumbrical muscle of the mouse the isoprenaline‐induced hyperpolarization is primarily due to an increase in potassium permeability.
Behavioural interactions between 5‐hydroxytryptophan, neuroleptic agents and 5‐HT receptor antagonists in modifying rodent responding to aversive situations
Authors: Costall B. , Naylor R.J. 
Published: July 2012

The ability of 5‐hydroxytryptophan, 5‐HT2 receptor antagonists and typical and atypical neuroleptic agents to modify behavioural responding to aversive situations was investigated in the mouse light/dark test and rat social interaction.
The administration of 5‐hydroxytryptophan inhibited rat social interaction and the exploratory behaviour of mice in the light/dark test.
The 5‐HT2 receptor antagonists, ketanserin, ritanserin, MDL11939, methysergide and RP62203, the neuroleptic agents, spiperone, haloperidol and benperidol, and the atypical neuroleptic agent, clozapine, when administered alone failed to modify mouse or rat behaviour. In contrast, when administered alone, sulpiride in rats and mice and thioridazine in rats disinhibited behaviour.
Methysergide, RP62203, ketanserin, ritanserin and MDL 11939 antagonized the inhibitory effects of 5‐hydroxytryptophan or reversed the inhibitory effects to one of disinhibition.
Low doses of spiperone (but not haloperidol or benperidol) also antagonized the inhibitory effects of 5‐hydroxytryptophan in the rat but not the mouse. Higher doses of the three neuroleptic agents caused locomotor depression in both rats and mice which obscured any specific changes in behavioural responding to the aversive situations.
The disinhibitory profile of sulpiride in both mice and rats and thioridazine in rats was evident during their interaction with 5‐hydroxytryptophan. Thioridazine in the mouse and clozapine in rats and mice also reversed the inhibitory effects of 5‐hydroxytryptophan to one of disinhibition.
In summary, we present evidence that the atypical neuroleptic agents, thioridazine and clozapine, with their known affinity for the 5‐HT2 receptors, can mimic the actions of reference 5‐HT2 receptor antagonists to antagonize the inhibitory effects of 5‐hydroxytryptophan in rodent models of anxiety. The results are intepreted in terms of drug action on different 5‐HT2 and other 5‐HT receptor subtypes. In addition, thioridazine and sulpiride have disinhibitory effects in their own right which remain to be explained.
Discrimination by benextramine between the NPY‐Y1 receptor subtypes present in rabbit isolated vas deferens and saphenous vein
Authors: Palea S. , Corsi M. , Rimland J.M. , Trist D.G. 
Published: July 2012

In order to characterize the neuropeptide Y (NPY) Y1 receptors known to be present in rabbit isolated vas deferens and saphenous vein, the pharmacological activity of the selective NPY Y1 receptor agonists, [Leu31Pro34] NPY and various other peptide agonists, together with the putative NPY antagonist, benextramine, were compared in the two tissues.
In rabbit isolated saphenous vein, cumulative dose‐response curves to various NPY agonists were obtained. All the peptides tested caused contractions which developed quite slowly. The rank order of potency obtained was: PYY>NPY>[Leu31, Pro34] NPY = NPY2–36>hPP>>NPY13–36 = NPYl8‐36. Incubation with benextramine (BXT) at 100 μM for 30min irreversibly abolished the contractile response to [Leu31, Pro34] NPY but was ineffective against NPY18‐3‐induced contractions.
Cumulative dose‐response curves to [Leu31, Pro34] NPY were performed in the same preparation before and after incubation with 100 μM BXT for 20 min in order to inactivate NPY Y1 receptors. The pKA (‐logATA) estimation for [Leu31, Pro34] NPY was 7.60 ±0.30 using the operational model and 7.20 ± 0.33 using the null method; the difference between the two methods was not statistically significant (P = 0.36).
Prostatic segments of rabbit vas deferens were electrically stimulated with single pulses. Immediately after stabilization of the contractile response, a cumulative dose‐response curve to various NPY agonists was obtained in each tissue. The rank order of potency for twitch inhibition was: PYY>[Leu3l, Pro34] NPY ≥ NPY ≥ hPP>NPY2–36gGt;NPY13–36≫NPY18–36 which indicates the presence of a prejunctional NPY Y1 receptor. BXT at 100 μM incubated for 10 or 60 min did not antagonize the response to [Leu3l, Pro34] NPY.
We conclude that rabbit isolated saphenous vein contains a population of post‐junctional NPY Y1 receptors irreversibly blocked by BXT, as well as a population of post‐junctional NPY Y2 receptors, which are insensitive to BXT. In contrast, the rabbit isolated vas deferens express a prejunctional NPY Y1 receptor subtype which is not blocked by BXT. Tetramine disulphides such as BXT could be useful tools in classifying NPY receptors.
Hyperpolarization by GABAB receptor agonists in mid‐brain periaqueductal gray neurones in vitro
Authors: Chieng B. , Christie M.J. 
Published: July 2012

The effects of GABAB receptor stimulation on membrane properties of rat periaqueductal gray neurones were studied by use of intracellular recordings from single neurones in superfused brain shoes. Intracellular staining with biocytin was used to characterize the anatomical location of each impaled neurone.
The GABAB receptor agonist, baclofen, directly hyperpolarized or produced an outward current (single electrode voltage‐clamp) in all 66 neurones tested. Baclofen‐induced hyperpolarizations were concentration‐dependent with an EC50 of approximately 0.6 μM and maximum hyperpolarization with 10 μM baclofen. Hyperpolarizations persisted in the presence of tetrodotoxin (1 μM, n = 2).
2‐OH‐saclofen, a selective GABAB receptor antagonist, competitively antagonized baclofen‐induced hyperpolarizations (n = 4) with equihbrium dissociation constants estimated in two neurones to be 6 and 23 μM. Naloxone (1 μM) did not prevent hyperpolarizations induced by baclofen (n = 34).
Hyperpolarizations induced by baclofen were associated with an increased inwardly rectifying potassium conductance. Ba2+ superfusion (5 to 10 mM) blocked this conductance increase (n=4). Elevation of extracellular potassium concentration (from 2.5 to 6.5 mM) shifted the reversal potential in agreement with predictions of the Nerast equation.
Hyperpolarizations produced by baclofen (10 μM) desensitized (>5% inhibition of the maximum response) in 7/22 neurones during continuous superfusion for 5 min. Strong desensitization (>25% inhibition of the maximum response) was observed in only 2/22 neurones in the ventrolateral periaqueductal gray. In contrast 6/9 neurones in the laterodorsal tegmental nucleus displayed strong desensitization.
These studies demonstrate that baclofen acting on GABAB receptors increases potassium conductance in all lateral and ventrolateral periaqueductal gray neurones. The neurones hyperpolarized by baclofen are likely to be involved in the well‐established antinociceptive actions of baclofen in the ventrolateral periaqueductal gray, but might also be involved in other functions because many of them lie outside the main ‘antinociceptive’ zone of this region. The cellular mechanisms underlying baclofen‐induced antinociception presumably differ from the postulated antinociceptive action of opioids, thought to be mediated via disinhibition of periaqueductal gray neurones which project to the ventromedial medulla.
α1A‐Adrenoceptor‐mediated contractile responses of the human vas deferens
Authors: Furukawa K. , Rosario D.J. , Smith D.J. , Chappie C.R. , Uchiyama T. , Chess‐Williams R. 
Published: July 2012

The predominant α‐adrenoceptor mediating contractions of the human vas deferens has been characterised in vitro by use of subtype selective antagonists.
Responses of human epididymal vas deferens were obtained to phenylephrine in the presence of amine uptake inhibitors and propranolol. The effects of the α1‐adrenoceptor antagonists, 5‐methylurapidil, oxymetazoline, WB4101, prazosin and chloroethylclonidine were examined and also the L‐type calcium channel blocker, nifedipine.
5‐Methylurapidil, WB4101, oxymetazoli and prazosin acted as competitive antagonists of the responses to phenylephrine, yielding pA2 values of 8.8, 9.2, 7.7 and 8.8 respectively. All four antagonists produced Schild plots with slopes similar to unity and maximum responses to phenylephrine were not altered in the presence of any of the antagonists.
Tamsulosin (1 nM) caused rightward shifts of phenylephrine concentration‐response curves yielding an apparent pKB value of 10.0. However, maximum responses were also reduced by 51% with this concentration of antagonist.
Incubation of tissues with chloroethylclonidine (100 μM for 40 min) failed to alter responses significantly but the presence of nifedipine (1 μM) reduced maximum responses to phenylephrine by 32%.
The high affinity of 5‐methylurapidil, oxymetazoline and WB4101, together with the failure of chloroethylclonidine to antagonize responses, indicate that the predominant α‐adrenoceptor mediating contraction of the human vas deferens has the characteristics previously described for the pharmacologically‐defined α1A‐adrenoceptor. The data are also consistent with those described for the cloned α1C‐adrenoceptor subtype thereby supporting the hypothesis that the two receptors are identical. The human vas deferens therefore represents a readily accessible preparation for functional studies of the human α1A‐adrenoceptor.
Selectivity of the imidazoline α‐adrenoceptor agonists (oxymetazoline and cirazoline) for human cloned α1‐adrenoceptor subtypes
Authors: Hone Kuniko , Obika Kenji , Foglar Rudolf , Tsujimoto Gozoh 
Published: July 2012

To investigate the structure‐activity relationships of α‐adrenoceptor agonists for the α1‐adrenoceptor subtypes*, we have compared the imidazoline class of compounds, oxymetazoline and cirazoline, with the phenethylamine, noradrenaline, in their affinities and also in their intrinsic activities in Chinese hamster ovary (CHO) cells stably expressing the cloned human α1‐adrenoceptor subtypes (α1a‐, α1b‐, and α1d‐subtypes)
Radioligand binding studies with [125I]‐HEAT showed that cirazoline and oxymetazoline had higher affinities at α1a‐subtype than at α1b‐ and (α1d‐subtypes, while noradrenaline had higher affinity at the α1d‐subtype than at α1a‐ and α1b‐subtypes.
In functional studies, cirazoline caused transients of cytosolic Ca2+ concentrations ([Ca2+] response) in a concentration‐dependent manner and developed a maximal response similar to that to noradrenaline in CHO cells expressing the α1a‐subtype, while it acted as a partial agonist at α1b‐ and α1d‐adrenoceptors. Oxymetazoline, on the other hand, was a weak agonist at α1a‐adrenoceptors, and has no intrinsic activity at the other subtypes.
Using the phenoxybenzamine inactivation method, the relationships between receptor occupancy and noradrenaline‐induced [Ca2+]i response for α1a‐ and α1d‐subtypes were found to be linear, whereas it was moderately hyperbolic for the α1b‐subtype, indicating the absence of receptor reserves in CHO cells expressing α1a‐ and α1d‐subtypes while there exists a small receptor reserve for CHO cells expressing the α1b‐subtype.
In summary, our data obtained in cells exclusively expressing a single receptor subtype support the idea that the relative role of agonist affinity and intrinsic activity may vary depending on the subtype of α1‐adrenoceptor.
Actions of ADP, but not ATP, on cytosolic free Ca2+ in single rat hepatocytes mimicked by 2‐methylthioATP
Authors: Dixon C. Jane , Cobbold Peter H. , Green Anne K. 
Published: July 2012

Aequorin‐injected, single rat hepatocytes generate series of repetitive transients in cytosolic free calcium concentration ([Ca2+]i) when stimulated with agonists acting through the phosphoinositide signalling pathway, including ADP and ATP. We have previously described differences in the [Ca2+]i responses of aequorin‐injected hepatocytes to ADP and ATP.
The effects of the phosphorothioate analogue of ATP, 2‐methylthioATP (2‐meSATP), have been examined on single rat hepatocytes. This analogue is believed to be the most potent agonist at the P2Y1 subclass of purinoceptor.
The [Ca2+]i transients induced by 2‐meSATP were indistinguishable from those induced by ADP, and in contrast to those induced by ATP.
At high concentrations, 2‐meSATP and ADP both induced transients at high frequency. In contrast, hepatocytes responded to high concentrations of ATP with an initial rapid rise in [Ca2+]i, followed by a slowly decaying fall.
The modulatory effects of elevated intracellular cyclic AMP concentration were the same on both 2‐meSATP‐ and ADP‐induced [Ca2+]i transients; the peak height and frequency of transients were enhanced. ATP‐induced transients, however, underwent either an increase in duration or conversion into a sustained rise in [Ca2+]i.
ATP‐induced transients were specifically potentiated by the co‐addition of α,β‐methyleneATP, whereas 2‐meSATP‐ and ADP‐induced transients were unaffected by this treatment.
We conclude that 2‐meSATP acts at the same receptor as ADP on rat hepatocytes, and that this is distinct from the receptor(s) mediating the effects of ATP.
Study of NO and VIP as non‐adrenergic non‐cholinergic neurotransmitters in the pig gastric fundus
Authors: Lefebvre R.A. , Smits G.J.M. , Timmermans J.‐P. 
Published: July 2012

The contribution of nitric oxide (NO) and vasoactive intestinal polypeptide (VIP) to non‐adrenergic non‐cholinergic (NANC) relaxations in the pig gastric fundus was investigated.
Circular and longitudinal muscle strips were mounted for isotonic registration in the presence of atropine and guanethidine; tone was raised with 5‐hydroxytryptamine. Electrical field stimulation with 10 s trains at 5 min intervals induced short‐lasting, frequency‐dependent relaxations while continuous stimulation with cumulative increase of the stimulation frequency induced sustained frequency‐dependent relaxations in both types of strips; the electrically induced responses were abolished by tetrodotoxin.
The short‐lasting as well as the sustained electrically induced NANC relaxations were significantly reduced by NG‐nitro‐L‐arginme methyl ester (l‐NAME). Pretreatment with L‐arginine but not D‐arginine, prevented the inhibitory effect of L‐NAME except for sustained relaxations in the longitudinal muscle strips.
Sodium nitroprusside, forskolin, zaprinast and 3‐isobutyl‐l‐methylxanthine induced concentration‐dependent relaxations. Exogenous NO mimicked the short‐lasting electrically induced relaxations, while endogenous VIP evoked sustained relaxations. The responses to exogenous NO and VIP were not influenced by tetrodotoxin and L‐NAME.
α‐Chymotrypsin abolished the responses to exogenous VIP but only moderately reduced NANC relaxations induced by continuous electrical stimulation. Zaprinast potentiated the relaxant responses to sodium nitroprusside and increased the duration of the NANC relaxations induced by electrical stimulation with 10 s trains in circular muscle strips but not in longitudinal muscle strips.
The cyclic GMP and cyclic AMP response to electrical stimulation, NO and VIP was measured in circular muscle strips. Short‐lasting as well as sustained electrical field stimulation induced an approximately 1.5 fold increase in cyclic GMP content, while NO induced nearly a 40 fold increase. An increase in cyclic AMP content was obtained only with sustained electrical field stimulation.
Immunocytochemistry for NO synthase (NOS) revealed immunoreactive neuronal cell bodies in the submucous and myenteric plexuses and nerve fibres in both the circular and longitudinal muscle layer; double‐labelling for NOS and VIP showed that VIP coexists in a major part of the intrinsic neurones. NADPH diaphorase‐histochemistry showed the same pattern of nitrergic neurones and nerves as NOS‐immunocytochemistry.
It is concluded that a cyclic GMP‐ and a cyclic AMP‐dependent pathway for relaxation is present in both the circular and longitudinal muscle layer of the pig gastric fundus. NO appears to contribute to short‐lasting as well as sustained NANC relaxations. A peptide, possibly VIP, may be involved during sustained stimulation at lower frequencies of stimulation.
Reflex circulatory collapse following intrapulmonary entrapment of activated platelets: mediation via 5‐HT3 receptor stimulation
Authors: Leañios O.L. , Hong E. , Amezcua J.L. 
Published: July 2012

The role of 5‐HT2 and 5‐HT3 receptors in the mediation of direct and reflex vascular responses to intrapulmonary platelet activation was investigated.
Anaesthetized rabbits were challenged intravenously with an emulsion of autologous bone marrow that produced a sharp increase in pulmonary blood pressure, a fall in systemic blood pressure, platelet consumption and death.
Platelet depletion before the challenge nearly abolished all the cardiovascular effects and prevented death. Bilateral vagotomy prevented the fall in systemic blood pressure and death but did not prevent the increase in pulmonary pressure. The intravenous administration of the 5‐HT3 antagonist, MDL‐72222, resembled the protection afforded by vagotomy whereas the 5‐HT2 antagonist, ketanserin, only reduced the increase in pulmonary pressure without affecting the systemic response or mortality.
The effects of intravenous 5‐HT and of electrical stimulation of the cephalic ends of the cut vagi nerves were also explored. 5‐HT injection increased the pulmonary vascular pressure but its effects on systemic blood pressure were variable. These responses were modified by the 5‐HT antagonists in a manner that resembles their effects on bone marrow embolism. Afferent vagal stimulation produced a fall in systemic blood pressure that was not prevented by MDL‐72222.
This study indicates that a centrally mediated reduction of peripheral vascular tone is the cause of the potentially lethal circulatory collapse that follows the intrapulmonary entrapment of activated platelets. This reflex is initiated by the action of 5‐HT on 5‐HT3 receptors in the lung.