bluuebunny/crossref_metadata_2025_split huggingface dataset:
Possible mechanisms underlying the midazolam‐induced relaxation of the noradrenaline‐contraction in rabbit mesenteric resistance artery
Authors: Shiraishi Yoshihisa , Ohashi Masuo , Kanmura Yuichi , Yamaguchi Shunichiro , Yoshimura Nozomu , Itoh Takeo 
Published: August 2006

The mechanisms underlying the midazolam‐induced relaxation of the noradrenaline (NA)‐contraction were studied by measuring membrane potential, isometric force and intracellular concentration of Ca2+([Ca2+]i) in endothelium‐denuded muscle strips from the rabbit mesenteric resistance artery. The actions of midazolam were compared with those of nicardipine, an L‐type Ca2+‐channel blocker.
Midazolam (30 and 100μm) did not modify either the resting membrane potential or the membrane depolarization induced by 10μm NA.
NA (10μm) produced a phasic, followed by a tonic increase in both [Ca2+]i and force. Midazolam (10–100μm) did not modify the resting [Ca2+]i, but attenuated the NA‐induced phasic and tonic increases in [Ca2+]i and force, in a concentration‐dependent manner. In contrast, nicardipine (0.3μm) attenuated the NA‐induced tonic, but not phasic, increases in [Ca2+]i and force.
In Ca2+‐free solution containing 2mm EGTA, NA (10μm) transiently increased [Ca2+]i and force. Midazolam (10–100μm), but not nicardipine (0.3μm), attenuated this NA‐induced increase in [Ca2+]i and force, in a concentration‐dependent manner. However, midazolam (10 and 30μm), had no effect on the increases in [Ca2+]i and force induced by 10mm caffeine.
In ryanodine‐treated strips, which have functionally lost the NA‐sensitive Ca2+‐ storage sites, NA slowly increased [Ca2+]i and force. Nicardipine (0.3μm) did not modify the resting [Ca2+]i but partly attenuated the NA‐induced increases in [Ca2+]i and force. In the presence of nicardipine, midazolam (100μm) lowered the resting [Ca2+]i and further attenuated the remaining NA‐induced increases in [Ca2+]i and force.
The [Ca2+]i‐force relationship was obtained in ryanodine‐treated strips by the application of ascending concentrations of Ca2+ (0.16–2.6mm) in Ca2+‐free solution containing 100mm K+. NA (10μm) shifted the [Ca2+]i‐force relationship to the left and enhanced the maximum Ca2+‐induced force. Under these conditions, whether in the presence or absence of 10μm NA, midazolam (10 and 30μm) attenuated the increases in [Ca2+]i and force induced by Ca2+ without changing the [Ca2+]i‐force relationship.
It was concluded that, in smooth muscle of the rabbit mesenteric resistance artery, midazolam inhibits the NA‐induced contraction through its inhibitory action on NA‐induced Ca2+ mobilization. Midazolam attenuates NA‐induced Ca2+ influx via its inhibition of both nicardipine‐sensitive and ‐insensitive pathways. Furthermore, midazolam attenuates the NA‐induced release of Ca2+ from the storage sites. This effect contributes to the midazolam‐induced inhibition of the NA‐induced phasic contraction.
Effect of a selective 5‐HT reuptake inhibitor in combination with 5‐HT1A and 5‐HT1B receptor antagonists on extracellular 5‐HT in rat frontal cortex in vivo
Authors: Sharp T , Umbers V , Gartside S E 
Published: August 2006

Selective 5‐hydroxytryptamine (5‐HT; serotonin) reuptake inhibitors (SSRIs) cause a greater increase in extracellular 5‐HT in the forebrain when the somatodendritic 5‐HT1A autoreceptor is blocked. Here, we investigated whether blockade of the terminal 5‐HT1B autoreceptor influences a selective 5‐HT reuptake inhibitor in the same way, and whether there is an additional effect of blocking both the 5‐HT1A and 5‐HT1B autoreceptors.
Extracellular 5‐HT was measured in frontal cortex of the anaesthetized rat by use of brain microdialysis. In vivo extracellular recordings of 5‐HT neuronal activity in the dorsal raphe nucleus (DRN) were also carried out.
The selective 5‐HT reuptake inhibitor, paroxetine (0.8 mg kg−1, i.v.), increased extracellular 5‐HT about 2 fold in rats pretreated with the 5‐HT1A receptor antagonist, WAY100635. When administered alone neither paroxetine (0.8 mg kg−1, i.v.) nor WAY100635 (0.1 mg kg−1, i.v.) altered extracellular 5‐HT levels.
Paroxetine (0.8 mg kg−1, i.v.) did not increase 5‐HT in rats pretreated with the 5‐HT1B/D receptor antagonist, GR127935 (1 mg kg−1, i.v.). GR127935 (1 and 5 mg kg−1, i.v.) had no effect on extracellular 5‐HT when administered alone.
Interestingly, paroxetine (0.8 mg kg−1, i.v.) caused the greatest increase in 5‐HT (up to 5 fold) when GR127935 (1 or 5 mg kg−1, i.v.) was administered in combination with WAY100635 (0.1 mg kg−1, i.v.). Administration of GR127935 (5 mg kg−1, i.v.) plus WAY100635 (0.1 mg kg−1, i.v.) without paroxetine, had no effect on extracellular 5‐HT in the frontal cortex.
Despite the lack of effect of GR127935 on 5‐HT under basal conditions, when 5‐HT output was elevated about 3 fold (by adding 1 μM paroxetine to the perfusion medium), the drug caused a dose‐related (1 and 5 mg kg−1, i.v.) increase in 5‐HT.
By itself, GR127935 slightly but significantly decreased 5‐HT cell firing in the DRN at higher doses (2.0–5.0 mg kg−1, i.v.), but did not prevent the inhibition of 5‐HT cell firing induced by paroxetine.
In summary, our results suggest that selective 5‐HT reuptake inhibitors may cause a large increase in 5‐HT in the frontal cortex when 5‐HT autoreceptors on both the somatodendrites (5‐HT1A) and nerve terminals (5‐HT1B) are blocked. This increase is greater than when either set of autoreceptors are blocked separately. The failure of a 5‐HT1B receptor antagonist alone to enhance the effect of the selective 5‐HT reuptake inhibitor in our experiments may be related to a lack of tone on the terminal 5‐HT1B autoreceptor due to a continued inhibition of 5‐HT cell firing. These results are discussed in relation to the use of 5‐HT autoreceptor antagonists to augment the antidepressant effect of selective 5‐HT reuptake inhibitors.
Inhibition of eotaxin‐mediated human eosinophil activation and migration by the selective cyclic nucleotide phosphodiesterase type 4 inhibitor rolipram
Authors: Santamaria Luis F , Maria Palacios Jose , Beleta Jorge 
Published: August 2006

The effect of the selective type 4 phosphodiesterase (PDE 4) inhibitor rolipram on human eosinophil activation and migration mediated by eotaxin was investigated.
Studies were performed with human freshly isolated eosinophils from peripheral blood of healthy donors by a magnetic cell separation (MACS) technique to a purity>99%. To test the effect of rolipram, eosinophils were stimulated with recombinant human eotaxin and the cell surface activation markers CD11b and L‐selectin were analysed by flow cytometry. Furthermore, eotaxin mediated eosinophil migration was measured in a transendothelial chemotaxis assay.
Our results indicate that rolipram inhibited eotaxin‐induced CD11b up‐regulation up to 60.6±7.6% at the highest tested dose (10μm), whereas transendothelial chemotaxis was partially inhibited reaching a plateau of approx. 30% at a rolipram concentration of 0.1μm.
We conclude that the selective PDE 4 inhibitor rolipram decreases eotaxin mediated eosinophil activation, an observation that may contribute to elucidate the mechanism by which PDE 4 inhibitors reduce antigen‐induced eosinophil infiltration in different animal models of allergic inflammation.
Selective depolarization of the muscle membrane in frog nerve‐muscle preparations by a chromatographically purified extract of the dinoflagellate Ostreopsis lenticularis
Authors: Meunier Frédéric A , Mercado José A , Molgó Jordi , Tosteson Thomas R , Escalona de Motta Gladys 
Published: August 2006

The actions of a chromatographically identified extract of the marine dinoflagellate Ostreopsis lenticularis, named ostreotoxin‐3 (OTX‐3), were studied on frog isolated neuromuscular preparations.
OTX‐3 (1–10μg ml−1) applied to cutaneous pectoris nerve‐muscle preparations depolarized skeletal muscle fibres and caused spontaneous contractions. The depolarization was neither reversed by prolonged washing nor by (+)‐tubocurarine.
OTX‐3 decreased the amplitude of miniature end plate potentials (m.e.p.ps) but did not affect their frequency.
Extracellular recording of compound action potentials revealed that OTX‐3 affected neither excitability nor conduction along intramuscular nerve branches.
End‐plate potentials (e.p.ps) elicited by nerve stimulation were reduced in amplitude by OTX‐3 and even showed reversed polarity in junctions deeply depolarized by the toxin.
Membrane depolarization induced by OTX‐3 was decreased about 70% in muscles pretreated for 30min with 10μm tetrodotoxin. In contrast, muscles pretreated with 5μm μ‐conotoxin GIIIA were completely insensitive to OTX‐3‐induced depolarization.
OTX‐3 did not affect e.p.p. amplitude and the quantal content of e.p.ps in junctions in which muscle depolarization was abolished by μ‐conotoxin GIIIA.
OTX‐3 is a novel type of sodium‐channel activating toxin that discriminates between nerve and skeletal muscle membranes.
P2‐receptor modulation of noradrenergic neurotransmission in rat kidney
Authors: Bohmann Christine , von Kügelgen Ivar , Christian Rump L 
Published: August 2006

ATP has previously been shown to act as a sympathetic cotransmitter in the rat kidney. The present study analyses the question of whether postganglionic sympathetic nerve endings in the kidney possess P2‐receptors which modulate noradrenaline release. Rat kidneys were perfused with Krebs‐Henseleit solution containing the noradrenaline uptake blockers cocaine and corticosterone and the α2‐adrenoceptor antagonist rauwolscine. The renal nerves were electrically stimulated, in most experiments by 30 pulses applied at 1 Hz. The outflow of endogenous noradrenaline (or, in some experiments, of ATP and lactate dehydrogenase) as well as the perfusion pressure were measured simultaneously.
The P2‐receptor agonist adenosine‐5′‐O‐(3‐thiotriphosphate) (ATPγS, 3–30 μM) reduced the renal nerve stimulation (RNS)‐induced outflow of noradrenaline (estimated EC50=8 μM). The P2‐receptor antagonist cibacron blue 3GA (30 μM) shifted the concentration‐inhibition curve for ATPγS to the right (apparent pKB value 4.7).
Cibacron blue 3GA (3–30 μM) and its isomer reactive blue 2 (3–30 μM) significantly increased RNS‐induced outflow of noradrenaline in the presence of the P1‐receptor antagonist 8‐(p‐sulphophenyl)theophylline (8‐SPT, 100 μM) by about 70% and 90%, respectively. The P2‐receptor antagonist suramin (30–300 μM) only tended to enhance RNS‐induced outflow of noradrenaline. When the nerves were stimulated by short pulse trains consisting of 6 pulses applied at 100 Hz (conditions under which autoinhibition is inoperative), reactive blue 2 did not affect the RNS‐induced outflow of noradrenaline.
RNS (120 pulses applied at 4 Hz) induced the outflow of ATP but not of the cytoplasmatic enzyme lactate dehydrogenase.
ATPγS (3–30 μM) concentration‐dependently reduced pressor responses to RNS at 1 Hz. Cibacron blue 3GA, reactive blue 2 as well as suramin also reduced pressor responses to RNS (maximally by 50 to 70%).
This study in rat isolated kidney, in which the release of endogenous noradrenaline was measured, demonstrates that renal sympathetic nerves possess prejunctional P2‐receptors that mediate inhibition of transmitter release. These prejunctional P2‐receptors are activated by endogenous ligands, most likely ATP, released upon nerve activity. Both, P2‐receptor agonists and P2‐receptor antagonists reduced pressor responses to RNS either by inhibiting transmitter release or by blocking postjunctional vasoconstrictor P2‐receptors.
Effects of moexiprilat on oestrogen‐stimulated cardiac fibroblast growth
Authors: Grohé C , Kahlert S , Löbbert K , van Eickels M , Stimpel M , Vetter H , Neyses L 
Published: August 2006

The effects of 2‐2‐(1‐(ethoxycarbonyl)‐3‐phenylpropyl)‐[amino‐oxopropyl]−6,7‐dimethoxy‐1,2,3,4‐tetrahydroisoquinoline‐3 carboxylic acid (moexiprilat), 17β‐oestradiol (E2), oestrone (ES) and angiotensin II (AII) on growth and activation of oestrogen receptors and the immediate‐early gene egr‐1 were investigated in neonatal rat cardiac fibroblasts of female and male origin.
In BrdU proliferation assays, oestrone (10−7–10−9 M) stimulated cardiac fibroblast growth in a concentration‐dependent fashion (maximum at 10−7 M, 4.0 fold±0.14 in female and 3.1 fold±0.06 in male cells, n=9, P<0.05), while E2 (10−7–10−9 M) had no effect. Moexiprilat (10−7 M) completely inhibited oestrone‐induced cardiac fibroblast growth.
Angiotensin II (10−7 M) induced cardiac fibroblast growth (female 4.1 fold±0.1/male 3.9 fold±0.2; n=9, P<0.05). Angiotensin II induced oestrogen receptor (maximum 21.8 fold at 60 min) and egr‐1 (maximum 47.5 fold at 60 min) expression in a time‐dependent fashion.
In immunoblot experiments, oestrogen activated oestrogen receptor (ES: 12.8 fold±2.0; E2: 14.7 fold±4.9; n=3, P<0.05) and egr‐1 (ES: 5.1 fold,±0.24; E2: 3.8 fold,±0.25; n=3, P<0.05) expression. The induction of oestrogen receptor and egr‐1 protein expression was time‐dependent and inhibited by moexiprilat.
Our results show that oestrone and 17β‐oestradiol reveal a significant difference in their potential to activate cardiac fibroblast growth in female and male cells and that oestrone‐stimulated growth is inhibited by moexiprilat. The inhibition of oestrone‐stimulated cardiac fibroblast growth by moexiprilat may contribute to the beneficial effects seen in postmenopausal women with hypertensive heart disease treated with ACE inhibitors.
Resuscitating effect of melanocortin peptides after prolonged respiratory arrest
Authors: Guarini Salvatore , Bazzani Carla , Bertolini Alfio 
Published: August 2006

The resuscitating activity of melanocortin peptides (MSH‐ACTH peptides) was tested in an experimental model of prolonged respiratory arrest.
Anaesthetized, endotracheally intubated rats subjected to a 5 min period of ventilation interruption, invariably died from cardiac arrest within 6–9 min of resumption of ventilation.
When resumption of ventilation was associated with the simultaneous intravenous (i.v.) injection of a melanocortin peptide (α‐MSH or ACTH‐(1–24)) (160 μg kg−1) there was an almost immediate (within 1 min), impressive increase in cardiac output, heart rate, mean arterial pressure (+560% of the before‐treatment value) and pulse pressure (+356% of the before‐treatment value), with full recovery of electroencephalogram after 30–45 min. Blood gases and pH were normalized within 15–60 min after treatment, and all treated animals eventually recovered completely and survived indefinitely (=more than 15 days).
The same response was observed in adrenalectomized animals, as well as in animals pretreated with a β1‐adrenoceptor blocking agent (atenolol, 3 mg kg−1, i.v.), or with an α1‐adrenoceptor blocking agent (prazosin, 0.1 mg kg−1, i.v.), or with an adrenergic neurone blocking agent (guanethidine, 10 mg kg−1, intraperitoneally).
An effect quite similar to that produced by melanocortins was obtained with ouabain (0.1 mg kg−1, i.v.); the antioxidant drug, glutathione (75 mg kg−1, i.v.) also produced 100% resuscitation, but the effect was slower in onset. On the other hand, adrenaline (0.005 mg kg−1, i.v.) was able to resuscitate only 1 out of 8 rats and dobutamine (0.02 mg kg−1, i.v.) resuscitated 4 out of 8 rats; moreover, the effect of both catecholamines was much slower in onset than that of melanocortins and the initial, impressive stimulation of cardiovascular function was absent.
These results show that melanocortin peptides have a resuscitating effect in a pre‐terminal condition produced in rats by prolonged asphyxia. This effect seems primarily due to the restoration of cardiac function, not mediated by catecholamines. These data also suggest that these peptides may have potential therapeutic value in conditions of transient cardiac hypoxia and re‐oxygenation such as occur in coronary artery disease.
Properties of the pore‐forming P2X7 purinoceptor in mouse NTW8 microglial cells
Authors: Chessell I P , Michel A D , Humphrey P P A 
Published: August 2006

We have used whole‐cell patch clamping methods to study and characterize the cytolytic P2X7 (P2Z) receptor in the NTW8 mouse microglial cell line.
At room temperature, in an extracellular solution containing 2 mM Ca2+ and 1 mM Mg2+, 2′‐ and 3′‐O‐(4‐benzoylbenzoyl)‐adenosine‐5′‐triphosphate (Bz‐ATP; 300 μM), or ATP (3 mM), evoked peak whole cell inward currents, at a holding potential of −90 mV, of 549±191 and 644±198 pA, respectively. Current‐voltage relationships generated with 3 mM ATP reversed at 4.6 mV and did not display strong rectification.
In an extracellular solution containing zero Mg2+ and 500 μM Ca2+ (low divalent solution), brief (0.5 s) application of these agonists elicited larger maximal currents (909±138 and 1818±218 pA, Bz‐ATP and ATP, respectively). Longer application of ATP (1 mM for 30 s) produced larger, slowly developing, currents which reached a plateau after approximately 15–20 s and were reversible on washing. Under these conditions, in the presence of ATP, ethidium bromide uptake could be demonstrated. Further applictions of 1 mM ATP produced rapid currents of the same magnitude as those observed during the 30 s application. Subsequent determination of concentration‐effect curves to Bz‐ATP, ATP and 2‐methylthio‐ATP yielded EC50 values of 58.3, 298 and 505 μM, respectively. These affects of ATP were antagonized by pyridoxal‐phosphate‐6‐azophenyl‐ 2′, 4′‐disulphonic acid (PPADS; 30 μM) but not suramin (100 μM).
In low divalent solution, repeated application of 1 mM ATP for 1 s produced successively larger currents which reached a plateau, after 8 applications, of 466% of the first application current. PPADS (30 μM) prevented this augmentation, while 5‐(N,N‐hexamethylene)‐amiloride (HMA) (100 μM) accelerated it such that maximal augmentation was observed after only one application of ATP in the presence of HMA. At a bath temperature of 32°C, current augmentation also occurred in normal divalent cation containing solution.
These data demonstrate that mouse microglial NTW8 cells possess a purinoceptor with pharmacological characteristics resembling the P2X7 receptor. We suggest that the current augmentation phenomenon observed reflects formation of the large cytolytic pore characteristic of this receptor. We have demonstrated that pore formation can occur under normal physiological conditions and can be modulated pharmacologically, both positively and negatively.
Stereospecific effects of ketamine enantiomers on canine tracheal smooth muscle
Authors: Pabelick Christina M , Rehder Kai , Jones Keith A , Shumway Robin , Lindahl Sten G E , Warner David O 
Published: August 2006

Ketamine is a potent bronchodilator which relaxes airway smooth muscle (ASM). Clinically, ketamine is used as a 1:1 racemic mixture of enantiomers that differ in their analgesic and anaesthetic effects. The aim of this study was to determine whether there was a difference between the enantiomers in their ability to relax isolated ASM and to explore mechanisms responsible for any observed differences.
Canine tracheal smooth muscle strips were loaded with fura‐2 and mounted in a photometric system to measure simultaneously force and [Ca2+]i. Calcium influx was estimated by use of a manganese quenching technique.
In strips stimulated with 0.1 μM ACh (EC50) R(−)‐ketamine (1–100 μM) caused a significantly greater concentration‐dependent decrease in force (P<0.0001) and [Ca2+]i than S(+)‐ketamine (1–100 μM) (P<0.0005). In contrast, there was no significant difference between the enantiomers in their ability to inhibit calcium influx (45% decrease in influx rate for R(−)‐ketamine and 44% for S(+)‐ketamine, P=0.782). In strips contracted with 24 mM isotonic KCl (which activates voltage‐operated calcium channels), the enantiomers modestly decreased force and [Ca2+]i; there was no significant difference between the enantiomers in their effects on force (P=0.425) or [Ca2+]i (P=0.604).
The R(−)‐enantiomer of ketamine is a more potent relaxant of ACh‐induced ASM contraction than the S(+)‐enantiomer. This difference appears to be caused by differential actions on receptor‐operated calcium channels.
NANC transmitters in the female pig urethra–localization and modulation of release via α2‐adrenoceptors and potassium channels
Authors: Werkström Viktoria , Persson Katarina , Andersson Karl‐Erik 
Published: August 2006

To investigate further the release, localization and identity of a non‐nitrergic mediator of smooth muscle relaxation in the female pig urethra, we studied the effects of drugs acting at α2‐adrenoceptors or K+ channels, the effects of capsaicin and chemical sympathectomy, and the actions of several transmitter candidates.
Electrical field stimulation (EFS; frequencies above 12 Hz) of spontaneously contracted smooth muscle strips from the female pig urethra evoked long‐lasting, frequency‐dependent relaxations in the presence of prazosin, scopolamine, and NG‐nitro‐L‐arginine. Treatment with the selective α2‐adrenoceptor agonist UK‐14 304 markedly reduced the relaxations evoked by EFS at all frequencies tested (16–30 Hz). The inhibitory effect of UK‐14 304 was completely antagonized by the α2‐adrenoceptor antagonist rauwolscine. The muscarinic M1 receptor antagonist, pirenzepine, or exogenously administered carbachol, did not have any effects on the electrically evoked relaxations.
Inhibition of high conductance Ca2+ activated K+ channels by iberiotoxin or charybdotoxin significantly enhanced the relaxations evoked by EFS at all frequencies. However, inhibition of voltage‐sensitive K+ channels with 4‐aminopyridine or dendrotoxin‐1, treatment with the ATP‐sensitive K+ channel blocker, glibenclamide, or treatment with the high and low conductance Ca2+ activated K+ channel blockers, tetraethylammonium chloride and apamin, had no effect on the relaxations evoked by EFS.
Electrically evoked relaxations were not affected by adrenergic denervation with 6‐hydroxydopamine (6‐OHDA) at any frequency. However, treatment with 6‐OHDA abolished prazosin‐sensitive electrically induced contractions, and a long‐lasting relaxation was revealed. Treatment with capsaicin, believed to damage selectively a subpopulation of primary afferent fibres, did not affect basal tone or relaxations evoked by EFS.
Exogenously applied vasoactive intestinal polypeptide (VIP), pituitary adenylate cyclase‐activating peptide (PACAP)‐27, PACAP‐38, adenosine, ATP and 5‐hydroxy‐tryptamine caused relaxations of the urethral preparations, whereas prostaglandin E2 and calcitonin gene‐related peptide had no effects. VIP 10‐28, α, β‐methylene‐ATP, reactive blue‐2, suramin or indomethacin did not reduce the electrically‐evoked relaxations at any frequency. However, the relaxations were slightly reduced by trypsin or α‐chymotrypsin.
The present results suggest that the release of the unknown mediator in the female pig urethra can be modulated via α2‐adrenoceptors and high conductance Ca2+ activated K+ channels. Furthermore, the mediator does not appear to be localized to or released from adrenergic or capsaicin‐sensitive sensory nerve‐endings. The identity of the transmitter remains to be established.

British Journal of Pharmacology (1997) 121, 1605–1612; doi:10.1038/sj.bjp.0701308