bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mediation of noradrenaline‐induced contractions of rat aorta by the (α1B‐adrenoceptor subtype
Authors: Testa R. , Guarneri L. , Poggesi E. , Simonazzi I. , Taddei C. , Leonardi A. 
Published: July 2012

The subtypes of α1‐adrenoceptor mediating contractions to exogenous noradrenaline (NA) in rat aorta have been examined in both biochemical and functional studies.
Incubation of rat aortic membranes with the irreversible α1B‐adrenoceptor antagonist, chloroethylclonidine (CEC: 10 μm) did not change the KD of [3H]‐prazosin binding in comparison to untreated membranes, but reduced by 88% the total number of binding sites (Bmax).
Contractions of rat aortic strips to NA after CEC (50 μm for 30 min) incubation followed by repetitive washing, showed a marked shift in the potency of NA and a partial reduction in the maximum response. The residual contractions to NA after CEC incubation were not affected by prazosin (10 nm).
The competitive antagonists prazosin, terazosin, (R)‐YM‐12617, phentolamine, 5‐methylurapidil and spiperone inhibited contractions to NA with estimated pA2 values of 9.85, 8.54, 9.34, 7.71, 7.64 and 8.41, respectively.
The affinity of the same antagonists for the α1A‐ and α1B‐adrenoceptors was evaluated by utilizing membranes from rat hippocampus pretreated with CEC, and rat liver, respectively. 5‐Methylurapidil and phentolamine were confirmed as selective for the α1A‐adrenoceptors, whereas spiperone was α1B‐selective.
A significant correlation was found between the pA2 values of the α1‐adrenoceptor antagonists tested and their affinity for the α1B‐adrenoceptor subtype, but not for the α1A‐subtype.
In conclusion, these findings indicate that in rat aorta most of the contraction is mediated by α1B‐adrenoceptors, and that the potency (pA2) of an antagonist in this tissue should be related to its antagonistic effect on this subtype of the α1‐adrenoceptor population.
Effects of the selective I1 imidazoline receptor agonist, moxonidine, on gastric secretion and gastric mucosal injury in rats
Authors: Glavin Gary B. , Smyth Donald D. 
Published: July 2012

Previous reports of the effects of α2‐adrenoceptor stimulation on gastric secretion are inconsistent because it was not clear whether the compounds were activating α2‐adrenoceptors and/or newly described imidazoline receptors. In the present experiments, the effects of moxonidine, an I1‐imidazoline receptor agonist and antihypertensive agent, on gastric secretion and on experimental gastric mucosal injury were examined.
Moxonidine (0.01, 0.1 and 1.0 mg kg−1, i.p.) potently inhibited basal (non‐stimulated) gastric acid secretion in conscious rats with an ED50 of 0.04 mg kg−1. Two hours following administration of the highest dose of moxonidine (1.0 mg kg−1), gastric acid output was completely suppressed. Moxonidine also significantly increased intragastric pH, at the two highest doses.
The α2‐adrenoceptor agonist, clonidine (0.01, 0.1 and 1.0 mg kg−1, i.p.) decreased basal acid secretion at the lowest dose (37%) and at the highest dose (46%), while the intermediate dose did not affect gastric acid output.
In an ethanol‐induced model of gastric mucosal injury, moxonidine decreased the length of lesions at the lowest and highest doses (0.01 and 1.0 mg kg−1) as well as the number of the lesions, at the highest dose (1.0 mg kg−1).
In pylorus‐ligated rats, moxonidine significantly decreased acid secretion (all doses), total secretory volume (1.0 mg kg−1) as well as pepsin output (1.0 mg kg−1).
In comparison to clonidine, moxonidine appears to be a more potent anti‐secretory and gastric‐protective compound. These data indicate a potential role for imidazoline receptor agonists in the management of gastroduodenal diseases associated with hypertension. The relative contribution of the central and peripheral effects of moxonidine to these gastrointestinal actions remains to be determined.
Pertussis toxin‐sensitive muscarinic relaxation in the rat iris dilator muscle
Authors: Yamahara Natsuki S. , Tanaka Masako , Imaizumi Yuji , Watanabe Minora 
Published: July 2012

The effects of pertussis toxin (PTX) on contraction and/or relaxation induced by agonists or transmural nerve stimulation (TNS) were examined in the rat iris dilator and sphincter muscles.
TNS in the presence of phentolamine induced an atropine‐sensitive biphasic response: initial contraction followed by relaxation in dilator muscles. Exogenously applied acetylcholine (ACh) elicited a large relaxation at low doses (3 μm or less) and a concentration at high doses.
Only the ACh‐induced relaxation was affected by injection of PTX (10 ng) into the anterior eye chamber. Relaxation was decreased 12 h after injection and had completely disappeared after 24 h. Relaxation recovered in part 3 weeks and almost completely 8 weeks after PTX treatment. A gradual decrease in muscarinic relaxation in a dilator muscle was also observed in vitro after addition of PTX to the bathing solution.
The pA2 values of muscarinic blockers, pirenzepine, AF‐DX 116, 4‐DAMP, and himbacine for competitive antagonism to ACh‐induced contraction were 7.14, 6.53, 9.03, and 6.80, respectively, in PTX‐pretreated dilator muscles. These values are comparable to those obtained in parasympathectomized dilator muscles and may indicate involvement of M3 or M3‐like receptors in muscle contraction.
Pretreatment with PTX did not significantly affect contraction induced by noradrenaline or 5‐hydroxytryptamine or the relaxation induced by isoprenaline in dilator muscles.
In conclusion, among several agonist‐induced responses in the rat iris dilator and sphincter muscles, only muscarinic relaxation in dilator muscle occurs via activation of PTX‐sensitive GTP binding proteins.
Multiple effects and stimulation of insulin secretion by the tyrosine kinase inhibitor genistein in normal mouse islets
Authors: Jonas J.C. , Plant T.D. , Gilon P. , Detimary P. , Nenquin M. , Henquin J.C. 
Published: July 2012

Islets from normal mice were used to test the acute effects of genistein, a potent tyrosine kinase inhibitor, on stimulus‐secretion coupling in pancreatic β‐cells.
Genistein produced a concentration‐dependent (10–100 μm), reversible, increase of insulin release. This effect was marginal on basal release or in the presence of non‐metabolized secretagogues, and much larger in the presence of glucose or other nutrients. The increase in insulin release caused by 100 μm genistein was abolished by adrenaline or omission of extracellular Ca2+. It was not accompanied by any rise of cyclic AMP, inositol phosphate or adenine nucleotide levels.
Although genistein slightly inhibited ATP‐sensitive K+ channels, as shown by 86Rb efflux and patch‐clamp experiments, this effect could not explain the action of the drug on insulin release because the latter persisted when ATP‐sensitive K+ channels were all blocked by maximally effective concentrations of glucose and tolbutamide. Genistein was also effective when ATP‐sensitive K+ channels were opened by diazoxide and the β‐cell membrane depolarized by 30 mm K, but ineffective in the presence of diazoxide and normal extracellular K.
Genistein paradoxically decreased Ca2+ influx in β‐cells, as shown by the inhibition of glucose‐induced electrical activity, by the inhibition of Ca2+ currents (perforated patches) and by the lowering of cytosolic [Ca2+]i (fura‐2 technique). Genistein thus increases insulin release in spite of a lowering of [Ca2+]i in β‐cells.
Daidzein, an analogue of genistein reported not to affect tyrosine kinases, was slightly less potent than genistein on K+ and Ca2+ channels, but increased insulin secretion in a similar way. Three other tyrosine kinase inhibitors, tyrphostin A47, herbimycin A and an analogue of erbstatin variably affected insulin secretion.
Genistein exerts a number of heretofore unrecognized effects. The unusual mechanisms, by which genistein increases insulin release in spite of a decrease in β‐cell [Ca2+]i and without activating known signalling pathways, do not seem to result from an inhibition of tyrosine kinases.
Acute pro‐inflammatory actions of endothelin‐1 in the guinea‐pig lung: involvement of ETA and ETB receptors
Authors: Filep János G. , Fournier Alain , Földes‐Filep Éva 
Published: July 2012

Although recent observations suggest that endothelin‐1 (ET‐1) may play a role in the pathogenesis of asthma, to date little is known about the effects of ET‐1 on parameters other than bronchoconstriction. The objectives of the present experiments were to study whether intravenously administered ET‐1 could exert pro‐inflammatory actions in the guinea‐pig lung and to assess the involvement of endothelin ETA and ETB receptors in these events by using the ETA receptor‐selective antagonist, FR 139317, the novel ETA/ETB receptor antagonist, bosentan and the ETB receptor‐selective agonist, IRL 1620.
Bolus i.v. injection of ET‐1 (0.1‐1 nmol kg−1) to anaesthetized guinea‐pigs evoked dose‐dependent increases in mean arterial blood pressure which lasted for 6‐12min. This was accompanied by a dose‐dependent haemoconcentration (8–15% plasma volume losses) and increases (up to 546%) in albumin extravasation in the trachea, upper and lower bronchi, but not in the pulmonary parenchyma. Qualitatively similar changes were observed following i.v. injection of the ETB receptor agonist, IRL 1620 (0.3 and 1 nmol kg−1), although IRL 1620 appeared to be about 3 times less potent than ET‐1. The ETA receptor‐selective antagonist, FR 139317 (2.5mg kg−1) inhibited the ET‐1 (1 nmol kg−1)‐induced pressor response, haemoconcentration and albumin extravasation by 75, 77 and 60–70%, respectively, whereas it did not attenuate IRL 1620 (1 nmol kg−1)‐induced changes. The ETA/ETB receptor antagonist, bosentan (10 mg kg−1) almost completely inhibited the pressor, haemoconcentration and permeability effects of both ET‐1 and IRL 1620.
ET‐1, but not IRL 1620 (0.1‐1 nmol kg−1), produced a dose‐dependent neutropenia with relative lymphocytosis and monocytosis, but did not induce influx of neutrophil granulocytes into pulmonary tissues or the bronchoalveolar space. ET‐1 (1 nmol kg−1)‐induced neutropenia was prevented by pretreatment of the animals with FR 139317 (2.5 mg kg−1), bosentan (10 mg kg−1) or adrenaline (90 nmol kg−1), indicating that ET‐1 caused intravascular sequestration of neutrophil granulocytes.
ET‐1 or IRL 1620 (10−1‐10−6 m) alone did not activate alveolar macrophages in vitro, whereas at a concentration of 10−8m, ET‐1, but not IRL 1620, markedly potentiated superoxide production in response to f‐Met‐Leu‐Phe (10−9‐10−7 m) and platelet‐activating factor (PAF, 10−9‐10−7 m), but not to phorbol 12‐myristate 13‐acetate (10−9m). ET‐1 did not affect f‐Met‐Leu‐Phe‐ or PAF‐induced increases in intracellular free calcium concentration. This potentiating effect of ET‐1 was abolished by FR 139317 (1.5 × 10−7m).
We conclude that, in addition to evoking airway contractions, ET‐1 exerts pro‐inflammatory actions via activation of the ETA and to a lesser extent the ETB receptors, and therefore, might contribute to the airway inflammation present in asthma. These findings also suggest the therapeutic potential of ETA/ETB receptor and perhaps ETA receptor‐selective antagonists in this disease.
Mechanism of block of a human cardiac potassium channel by terfenadine racemate and enantiomers
Authors: Yang Tao , Prakash Chandra , Roden Dan M. , Snyders Dirk J. 
Published: July 2012

The cardiac toxicity of racemic terfenadine (marked QT prolongation and polymorphic ventricular arrhythmias) is probably due to potassium channel blockade. To test whether one of its enantiomers would be a less efficient potassium channel blocker, we compared the mechanism of action of the racemate with that of the individual enantiomers.
We synthesized the individual enantiomers of terfenadine and examined under whole cell voltage‐clamp conditions the mechanism of action of the racemate, both enantiomers and a major metabolite on a cloned human cardiac potassium channel, hKvl.5. This delayed rectifier is sensitive to quinidine, clofilium and other ‘class III’ antiarrhythmic drugs at clinically relevant concentrations.
Upon depolarization, racemic terfenadine and its enantiomers induced a fast decline of hKvl.5 current towards a reduced steady state current level. During subsequent repolarization the tail currents deactivated more slowly than the control, resulting in a ‘crossover’ phenomenon.
The voltage‐dependence of block was biphasic with a steep increase in block over the voltage range of channel opening (−30 to 0 mV), and a more shallow phase positive to O mV (where the channel is fully open). The latter was consistent with a binding reaction sensing 21% of the transmembrane electrical field (with reference to the cell interior).
The EC50 for hKvl.5 block by racemic terfenadine was 0.88 μm, while the values for R‐ and S‐terfenadine were 1.19 μm and 1.16 μm, respectively. In contrast, the acid metabolite reduced hKvl.5 current by only 5% at a concentration of 50 μm.
These findings suggest that terfenadine blocks the hKvl.5 channel after it opens by entering into the internal mouth of the channel. We have previously shown that quinidine blocks hKvl.5 in a similar manner but with an apparent affinity of ∼6 μm. Thus, terfenadine and its enantiomers are approximately equipotent open state blockers of this human K+ channel and about 6 times more potent than quinidine. The similar state‐, time‐, and voltage‐dependence of hKvl.5 block by both enantiomers also indicates that the chiral centre does not significantly constrain the orientation of critical binding determinants of terfenadine with respect to the receptor site.
Involvement of multiple protein kinase C isozymes in the ACTH secretory pathway of AtT‐20 cells
Authors: McFerran B.W. , MacEwan D.J. , Guild S.B. 
Published: July 2012

The mouse AtT‐20/D16‐16 anterior pituitary tumour cell line was used as a model system for the study of protein kinase C (PKC)‐mediated enhancement of calcium‐ and guanine nucleotide‐evoked adrenocorticotrophin (ACTH) secretion.
A profile of the PKC isozymes present in AtT‐20 cells was obtained by Western blotting analysis and it was found that AtT‐20 cells express the α, β, ∍ and ζ isoforms of PKC.
PKC isozymes were activated by the use of substances reported to activate particular isoforms of the enzyme. The effects of these substances were investigated in both intact and electrically‐permeabilized cells. Phorbol 12‐myristate 13‐acetate (PMA, EC50 = 1 ± 0.05 nM, which activates all isozymes of PKC, except the ζ isozyme), thymeleatoxin (TMX, EC50 = 10 ± 0.5 nM, which activates the α, β and γ isozymes) and 12‐deoxyphorbol 13‐phenylacetate 20‐acetate (dPPA, EC50 = 3 ± 0.5 nm, α β1 selective isozyme activator) all stimulated ACTH secretion from intact cells in a concentration‐dependent manner. Maximal TMX stimulated ACTH secretion was of a similar degree to that obtained in response to PMA but maximal dPPA‐stimulated ACTH secretion was only 60–70% of that obtained in response to PMA or TMX.
Calcium stimulated ACTH secretion from electrically‐permeabilized cells over the concentration‐range of 100 nM to 10 μm. PMA (100 nM), TMX (100 nM) but not dPPA (100 nM) enhanced the amount of ACTH secreted at every concentration of calcium investigated. PMA (100 nM) and TMX (100 nM) significantly enhanced ACTH secretion in the effective absence of calcium (i.e. where the free calcium concentration is 1 nM).
GTP‐γ‐S stimulated ACTH secretion from permeabilized cells in a concentration‐dependent manner with a threshold of 1 μm. PMA (100 nM), TMX (100 nM) but not dPPA (100 nM) increased the amount of ACTH secretion evoked by every concentration of GTP‐γ‐S investigated.
The PKC inhibitor, chelerythrine chloride (10 μm), blocked the PMA (100nM)‐evoked enhancement of calcium‐ and GTP‐γ‐S‐stimulated ACTH secretion but did not significantly alter calcium‐ or GTP‐γ‐S‐evoked secretion itself.
The present paper indicates that AtT‐20 cells express multiple isoforms of PKC and that these act at different sites in the secretory pathway for ACTH secretion. The α and ∍ isozymes of PKC can act distal to calcium entry to modulate the ability of increased cytosolic calcium concentrations to stimulate ACTH secretion. This site of action is either at the level of, or at some stage distal to, a GTP‐binding protein which mediates the effects of calcium upon ACTH secretion. The β isozyme of PKC may act at a stage early in the secretory pathway to regulate the cytosolic calcium concentration.
Actions of the insecticide fipronil, on dieldrin‐sensitive and ‐resistant GABA receptors of Drosophila melanogaster
Authors: Hosie Alastair M. , Baylis Howard A. , Buckingham Steven D. , Sattelle David B. 
Published: July 2012

Blocking actions of the novel insecticide, fipronil, were examined on GABA responses recorded from Xenopus oocytes expressing either wild type (dieldrin‐sensitive) or mutant (dieldrin‐resistant) forms of the Drosphila melanogaster GABA‐gated chloride channel homo‐oligomer, RDL (the product of the resistance to dieldrin locus: Rdl).
In the case of the wild type receptor, fipronil blocked GABA‐induced currents inducing both a shift to the right in the GABA dose‐response curve and depressing the maximum amplitude of responses to GABA. The potency of fipronil was dependent on the GABA concentration but was unaffected by membrane potential.
Mutant RDL GABA‐receptors, which have a naturally occurring amino acid substitution (A302→SS) in the putative ion‐channel lining region, conferring resistance to dieldrin and picrotoxinin, were markedly less sensitive to fipronil than the wild‐type receptors.
Fipronil antagonism is qualitatively similar to that produced by the structurally distinct compound, picrotoxinin. As the mutation A302→S reduces the potency of both fipronil and picrotoxinin, homo‐oligomeric RDL receptors should facilitate detailed studies of the molecular basis of convulsant/ insecticide antagonist actions on GABA receptors.
Phosphorus‐containing peptides as mixed inhibitors of endopeptidase 3.4.24.15 and 3.4.24.16: effect on neurotensin degradation in vitro and in vivo
Authors: Vincent Bruno , Dive Vincent , Yiotakis Athanasios , Smadja Claire , Maldonado Raphaël , Vincent Jean‐Pierre , Checler * Frederic 
Published: July 2012

We have examined several phosphorus‐containing peptides as potential mixed inhibitors of two neurotensin‐degrading zinc metallopeptidases, endopeptidase 3.4.24.15 and endopeptidase 3.4.24.16.
Among a series of 13 phosphonamide peptides, N‐(2‐(2‐naphtyl)ethylphosphonyl‐glycyl‐prolyl‐norleucine (phosphodiepryl 08) was found to inhibit potently the hydrolysis of neurotensin by purified endopeptidase 3.4.24.15 and 3.4.24.16 with an identical Ki value of 0.4 nM.
Phosphodiepryl 08 displayed a strong selectivity towards the two peptidases since it failed to inhibit several other zinc‐containing peptidases such as endopeptidase 3.4.24.11, angiotensin‐converting enzyme, aminopeptidase M, leucine aminopeptidase and carboxypeptidases A and B.
The protective effect of phosphodiepryl 08 on neurotensin degradation was examined in vitro and in vivo in central and peripheral bioassays.
Phosphodiepryl 08 virtually abolished neurotensin degradation by 4‐day‐old plated pure cultured neurones from mouse embryos and greatly potentiated neurotensin‐induced antinociception in the mouse hot plate test.
In the periphery, phosphodiepryl 08 inhibited neurotensin degradation by membranes prepared from isolated longitudinal smooth muscle of guinea‐pig ileum and greatly potentiated the neurotensin‐induced contraction of the same longitudinal smooth muscle preparation.
Our study indicates that phosphodiepryl 08 behaves as a potent and selective mixed inhibitor of endopeptidase 3.4.24.15 and 3.4.24.16 and can be used as a powerful agent to prevent neurotensin degradation, in vitro and in vivo, in central and peripheral assays.
Interaction between a selective 5‐HT1Areceptor antagonist and an SSRI in vivo: effects on 5‐HT cell firing and extracellular 5‐HT
Authors: Gartside S.E. , Umbers V. , Hajós M. , Sharp T. 
Published: July 2012

The acute inhibitory effect of selective 5‐hydroxytryptamine (serotonin) reuptake inhibitors (SSRIs) on 5‐HT neuronal activity may offset their ability to increase synaptic 5‐HT in the forebrain. 2Here, we determined the effects of the SSRI, paroxetine, and a novel selective 5‐HT1Areceptor antagonist, WAY 100635, on 5‐HT cell firing in the dorsal raphe nucleus (DRN), and on extracellular 5‐HT in both the DRN and the frontal cortex (FCx). Extracellular electrophysiological recording and brain microdialysis were used in parallel experiments, in anaesthetized rats.Paroxetine dose‐dependently inhibited the firing of 5‐HT neurones in the DRN, with a maximally effective dose of approximately 0.8 mg kg−1, i.v. WAY 100635 (0.1 mg kg−1, i.v.) both reversed the inhibitory effect of paroxetine and, when used as a pretreatment, caused a pronounced shift to the right of the paroxetine dose‐response curve.Paroxetine (0.8 mg kg−1, i.v.), doubled extracellular 5‐HT in the DRN, but did not alter extracellular 5‐HT in the FCx. A higher dose of paroxetine (2.4 mg kg−1, i.v.) did increase extracellular 5‐HT in the FCx, but to a lesser extent than in the DRN. Whereas 0.8 mg kg−1, i.v. paroxetine alone had no effect on extracellular 5‐HT in the FCx, in rats pretreated with WAY 100635 (0.1 mg kg−1), paroxetine (0.8 mg kg−1, i.v.) markedly increased extracellular 5‐HT in the FCx.In conclusion, pretreatment with the selective 5‐HT1Areceptor antagonist, WAY 100635, blocked the inhibitory effect of paroxetine on 5‐HT neuronal activity in the DRN and, at the same time, markedly enhanced the effect of paroxetine on extracellular 5‐HT in the FCx. These results may be relevant to recent clinical observations that 5‐HT1Areceptor antagonists in combination with SSRIs have a rapid onset of antidepressant effect.