bluuebunny/crossref_metadata_2025_split huggingface dataset:
Biphasic inhibition of stimulated endogenous dopamine release by 7‐OH‐DPAT in slices of rat nucleus accumbens
Authors: Patel Jyoti , Trout Stephen J. , Palij Peter , Whelpton Robin , Kruk Zygmunt L. 
Published: July 2012

Fast cyclic voltammetry was used to investigate the effect of 7‐OH‐DPAT (7‐hydroxy‐N,N‐di‐n‐propyl‐2‐aminotetralin), a putative D3 receptor agonist, on electrically stimulated endogenous dopamine release in slices of rat nucleus accumbens.
7‐OH‐DPAT inhibited single pulse stimulated dopamine release in a concentration‐dependent manner with a maximum inhibition of 95.5%. Analysis of concentration‐response curves to 7‐OH‐DPAT showed that they were biphasic, with the high affinity component contributing 18.0% to the total inhibition and the low affinity component 77.5%. 7‐OH‐DPAT exhibited a 560 fold selectivity between the high and low affinity components (0.015 nm compared to 8.4 nM).
Concentration‐response curves to the nonselective D2/D3 agonist, apomorphine, were monophasic. The maximum inhibition was 93.1% and the EC50 value 82 nM.
The selective D2 antagonist, haloperidol (30 nM), antagonized the low affinity component of the concentration‐response cuve to 7‐OH‐DPAT whilst the high affinity component was essentially unaffected. The pKB values calculated for the high and low affinity components were 7.89 and 9.45 respectively.
In conclusion, these results demonstrate that 7‐OH‐DPAT inhibits stimulated dopamine release by acting at two different sites. Furthermore, the results are consistent with the hypothesis that the high and low affinity components of the concentration‐response curve to 7‐OH‐DPAT may reflect activation of functional D3 and D2 release‐regulating autoreceptors respectively. However, the possibility that the biphasic nature of the curve may reflect different subtypes of the D2 receptor cannot be excluded.
Effect of methylguanidine on rat blood pressure: role of endothelial nitric oxide synthase
Authors: Sorrentino Raffaella , Pinto Aldo 
Published: July 2012

The effect of acute i.v. administration of methylguanidine (MG) on mean arterial blood pressure (MABP) was investigated in anaesthetized male Wistar rats.
MG (1–30 mg kg−l i.v.) produced an increase in MABP in a dose‐dependent manner both in normal and in hexamethonium (5 mg kg−1, i.v)‐treated rats.
L‐Arginine (30 or 150 mg kg−1, i.v.), but not its enantiomer D‐arginine (30 or 150 mg kg−1, i.v.), reversed the effect of MG on MABP in both normal and hexamethonium‐treated rats.
L‐Arginine (150 mg kg−1, i.v.) administered 2min before MG (30 mg kg−1, i.v.) prevented the increase in MABP caused by MG in either normal or hexamethonium‐treated rats. This effect was not observed with D‐arginine (150 mg kg−1, i.v.).
Thus, the rise in MABP caused by MG in the anaesthetized rat is due to inhibition of endothelial NO‐synthase activity. We speculate that the rise in the plasma concentration of endogenous MG associated with uraemia may contribute to the hypertension seen in patients with chronic renal failure.
All‐or‐none augmentation of Ca2+ sensitivity in c‐toxin‐permeabilized single smooth muscle cells from guinea‐pig taenia caecum
Authors: Mita Mitsuo , Hashimoto Takao 
Published: July 2012

Isolated smooth muscle cells from guinea‐pig taenia caecum were permeabilized by use of Staphylococcus aureus α‐toxin, and the sarcoplasmic reticulum Ca2+ store was depleted by exposure to 0.1 μM A23187.
Shortening of α‐toxin‐permeabilized single smooth muscle cells was induced by increasing free Ca2+ but was not induced by 0.2 μM free Ca2+.
Shortening of the permeabilized cells was caused by application of acetylcholine (ACh) with free Ca2+ concentration held at 0.2 μM. Permeabilized smooth muscle cells responded to 0.3 μM or 1 μM ACh with 0.2 μM Ca2+ with maximal shortening. The concentration‐response relationship to ACh had a very steep slope and the cell shortening appeared to be an all‐or‐none response rather than a graded response, as was the shortening of intact cells to ACh.
The shortening of permeabilized cells was also induced by application of guanosine 5′‐triphosphate (GTP) with 0.2 μM free Ca2+, showing an all‐or‐none response. The threshold concentration of GTP that induced an all‐or‐none response was between 10 μM and 30 μM.
These results suggest that Ca2+ sensitivity is augmented by stimulation of the muscarinic receptor or GTP‐binding protein(s) in an all‐or‐none manner. It seems probable that this contributes to the all‐or‐none response to ACh in intact smooth muscle cells.
Determination β‐adrenoceptor subtype on rat isolated ventricular myocytes by use of highly selective β‐antagonists
Authors: Kitagawa Yoshihiro , Adachi‐Akahane Satomi , Nagao Taku 
Published: July 2012

The relative proportions of β1 and β2‐adrenoceptors were determined by radioligand binding studies in three different rat myocardial preparations: membranes prepared from rat ventricle (ventricular membranes), membranes prepared from rat isolated ventricular myocytes (myocyte membranes), and myocytes isolated from rat ventricle (myocytes).
Competition experiments using CGP 20712A or ICI 118,551 with [125I]‐iodocyanopindolol ([1251]‐ ICYP) revealed high‐ and low‐affinity binding sites in ventricular membranes. The concentration at which each β‐antagonist occupied 100% of its high‐affinity binding sites was 300 nM for CGP 20712A (β1‐adrenoceptor) and 50 μM for ICI 118,551 (β2‐adrenoceptor).
The density of high‐affinity (β1‐adrenoceptor) and low‐affinity (β2‐adrenoceptor) binding sites for CGP 20712A was measured by a saturation experiment using [125I]‐ICYP in the presence and absence of 300 nM CGP 20712A. In ventricular membranes, the proportions of high‐affinity and low‐affinity binding sites for CGP 20712A were 73% and 27%, respectively, whereas in myocyte membranes, the corresponding figures were 90% and 10%, respectively. The density of low‐affinity binding sites for CGP 20712A in ventricular membranes, defined as [125I]‐ICYP‐specific binding in the presence of 300 nM CGP 20712A, was decreased by addition of 50 nM ICI 118,551, whereas that in myocyte membranes was not affected.
In myocytes, specific binding of [125I]‐ICYP and [3H]‐CGP 12177 was not detected by saturation experiments performed in the presence of 300 nM CGP 20712A.
In myocytes, the activation of adenylate cyclase caused by β2‐adrenoceptors was not detected in the presence of 10 nM, 100 nM or 1000 nM CGP 20712A, which selectively antagonized β1‐adrenoceptors. Furthermore, the concentration‐response curve for isoprenaline‐stimulated cyclic AMP accumulation was not shifted by 10 nM or 100 nM ICI 118,551, which selectively antagonized β2‐adrenoceptors, but was shifted to the right by 1000 nM ICI 118,551.
These results indicate that β2‐adrenoceptors are not present on rat ventricular myocytes and that β2‐adrenoceptor stimulation does not cause any detectable production of cyclic AMP. We conclude that only β1‐adrenoceptors exist on rat ventricular myocytes.
Accelerated desensitization of nicotinic receptor channels and its dependence on extracellular calcium in isolated skeletal muscles of streptozotocin‐diabetic mice
Authors: Nojima Hiroshi , Tsuneki Hiroshi , Kimura Ikuko , Kimura Masayasu 
Published: July 2012

To elucidate the influence of the diabetic state on desensitization of nicotinic acetylcholine (ACh) receptor channels, we investigated the time course of the decrease in amplitude of ACh potentials elicited by iontophoretic application to isolated diaphragm muscle of streptozotocin‐diabetic mice. We also investigated time‐ and extracellular Ca2+‐dependent changes in the channel opening frequency of ACh‐activated channel currents and the involvement of protein kinases by use of the cell‐attached patch clamp technique in single skeletal muscle cells.
When ACh potentials were evoked at 10 Hz, the decline in trains of ACh potentials was accelerated in the diabetic state.
The time‐dependent decrease in the channel opening frequency of diabetic muscle cells was greatly accelerated compared with normal cells in 2.5 mM Ca2+ medium.
This accelerated decrease in channel opening frequency was restored by pretreatment with a protein kinase C inhibitor, staurosporine (10 nM) but neither a protein kinase A inhibitor, H‐89 (3 μM) nor a calmodulin kinase II inhibitor, KN‐62 (5 μM) were able to restore the fall in opening frequency.
These results demonstrate that in the diabetic state the desensitization of nicotinic ACh receptor channels may be greatly accelerated by activating protein kinase C, which is caused by an increase in the amount of available intracellular Ca2+.
Characterization of the prostanoid receptors mediating constriction and relaxation of human isolated uterine artery
Authors: Baxter G.S. , Clayton J.K. , Coleman R.A. , Marshall K. , Sangha R. , Senior J. 
Published: July 2012

This study was undertaken to characterize pharmacologically the prostanoid receptor subtypes mediating constriction and relaxation of human isolated uterine artery.
U‐46619 was a potent constrictor agonist on human uterine artery (EC50 [95% CL] = 3.5 [1.8‐6.7] μM). Prostaglandin E2 (PGE2α), PGF2, PGD2 and PGI2 only weakly constricted the uterine artery, being at least 100 times less potent than U‐46619. The PGE2 and PGI2 constrictor effects may be modified by the potent dilator effects of these compounds. A number of agonists which show selectivity for FP‐, DP‐ and EP‐receptors including ICI 81008, BW 245C, sulprostone, rioprostil and butaprost, failed to cause any constriction at concentrations up to 30 μM.
Constrictor responses induced by all agonists tested were reduced or abolished by the TP‐receptor blocking drugs, GR 32191 and EP 092. pA2 estimates for both antagonists versus U‐46619 were 8.50, values which are consistent with their affinities at TP‐receptors.
In preparations pre‐constricted with phenylephrine (1 μM) both PGI2 and PGE2 were potent relaxant agonists. The selective IP‐receptor agonists, cicaprost and iloprost, also dilated human uterine artery and were approximately 10 fold more potent than PGI2. The EP2‐receptor agonists, butaprost and rioprostil and the selective DP‐agonist, BW 245C, were at least 100 fold weaker than PGI2 and PGE2 suggesting that neither DP‐ nor EP2 receptors were involved.
We conclude that TP‐receptors mediate constriction, whereas IP‐ and possibly EP4‐receptors mediate relaxation of human uterine artery.
Inhibition of carrageenin‐induced rat paw oedema by crotapotin, a polypeptide complexed with phospholipase A2
Authors: Landucci Elen C.T. , Antunes Edson , Donato Jose L. , Faro Renato , Hyslop Stephen , Marangoni Sérgio , Oliveira Benedito , Cirino Giuseppe , de Nucci Gilberto 
Published: July 2012

The effect of purified crotapotin, a non‐toxic non‐enzymatic chaperon protein normally complexed to a phospholipase A2 (PLA2) in South America rattlesnake venom, was studied in the acute inflammatory response induced by carrageenin (1 mg/paw), compound 48/80 (3 μg/paw) and 5‐hydroxytryptamine (5‐HT) (3 μg/paw) in the rat hind‐paw. The effects of crotapotin on platelet aggregation, mast cell degranulation and eicosanoid release from guinea‐pig isolated lung were also investigated.
Subplantar co‐injection of crotapotin (1 and 10 μg/paw) with carrageenin or injection of crotapotin (10 μg/paw) into the contralateral paw significantly inhibited the carrageenin‐induced oedema. This inhibition was also observed when crotapotin (10–30 μg/paw) was administered either intraperitoneally or orally. Subplantar injection of heated crotapotin (15 min at 60°C) failed to inhibit carrageenin‐induced oedema. Subplantar injection of crotapotin (10 μg/paw) also significantly inhibited the rat paw oedema induced by compound 48/80, but it did not affect 5‐HT‐induced oedema.
In adrenalectomized animals, subplantar injection of crotapotin markedly inhibited the oedema induced by carrageenin. The inhibitory effect of crotapotin was also observed in rats depleted of histamine and 5‐HT stores.
Crotapotin (30 μg/paw) had no effect on either the histamine release induced by compound 48/80 in vitro or on the platelet aggregation induced by both arachidonic acid (1 mm) and platelet activating factor (1 μm) in human platelet‐rich plasma. The platelet aggregation and thromboxane B2 (TXB2) release induced by thrombin (100 mu ml−1) in washed human platelets were also not affected by crotapotin. In addition, crotapotin (10 μg/paw) did not affect the release of 6‐oxo‐prostaglandin F1α and TXB2 induced by ovalbumin in sensitized guinea‐pig isolated lungs.
Our results indicate that the anti‐inflammatory activity of crotapotin is not due to endogenous corticosteroid release or inhibition of cyclo‐oxygenase activity. It is possible that crotapotin may interact with extracellular PLA2 generated during the inflammatory process thereby reducing its hydrolytic activity.
Regional haemodynamic effects of human and rat adrenomedullin in conscious rats
Authors: Gardiner S.M. , Kemp P.A. , March J.E. , Bennett T. 
Published: July 2012

Male, Long Evans rats were chronically instrumented with pulsed Doppler flow probes and intravascular catheters to permit assessment of the regional haemodynamic responses to human and rat adrenomedullin, to compare the responses to human adrenomedullin to those of human α‐CGRP in the absence and presence of the CGRP1‐receptor antagonist, human α‐CGRP [8–37], and to determine the involvement of nitric oxide (NO)‐mediated mechanisms in the responses to human adrenomedullin, relative to human α‐CGRP.
Human and rat adrenomedullin (0.3, 1, and 3 nmol kg−1, i.v.) caused dose‐dependent hypotension and tachycardia, accompanied by increases in renal, mesenteric and hindquarters flows and vascular conductances. At the lowest dose only, the hypotensive and mesenteric vasodilator effects of rat adrenomedullin were significantly greater than those of human adrenomedullin.
Human α‐CGRP at a dose of 1 nmol kg−1 caused hypotension, tachycardia and increases in hindquarters flow and vascular conductance, but reductions in renal and mesenteric flows, and only transient vasodilatations in these vascular beds. These effects were substantially inhibited by human α‐CGRP [8–37] (100 nmol kg−1 min−1), but those of human adrenomedullin (1 nmol kg−1) were not; indeed, the mesenteric haemodynamic effects of the latter peptide were enhanced by the CGRP1‐receptor antagonist.
In the presence of the NO synthase inhibitor, NG‐nitro‐1‐arginine methyl ester (1‐NAME, 183 nmol kg−1 min−1), there was only a slight, but significant, inhibition of the hindquarters hyperaemic vasodilator effect of human adrenomedullin, but not that of human α‐CGRP.
These results indicate that the marked regional vasodilator effects of human (and rat) adrenomedullin are largely independent of NO and, in vivo, do not involve CGRP1‐receptors.
Different pressor and bronchoconstrictor properties of human big‐endothelin‐1, 2 (1–38) and 3 in ketamine/xylazine‐anaesthetized guinea‐pigs
Authors: Gratton Jean‐Philippe , Rae Giles A. , Claing Audrey , Télémaque Sabine , D'Orléans‐Juste Pedro 
Published: July 2012

In the present study, the precursors of endothelin‐1, endothelin‐2 and endothelin‐3 were tested for their pressor and bronchoconstrictor properties in the anaesthetized guinea‐pig. In addition, the effects of big‐endothelin‐1 and endothelin‐1 were assessed under urethane or ketamine/xylazine anaesthesia.
When compared to ketamine/xylazine, urethane markedly depressed the pressor and bronchoconstrictor properties of endothelin‐1 and big‐endothelin‐1.
Under ketamine/xylazine anaesthesia, the three endothelins induced a biphasic increase of mean arterial blood pressure. In contrast, big‐endothelin‐1, as well as big‐endothelin‐2 (1–38), induced only sustained increase in blood pressure whereas big‐endothelin‐3 was inactive at doses up to 25 nmol kg−1.
Big‐endothelin‐1, but not big‐endothelin‐2, induced a significant increase in airway resistance. Yet, endothelin‐1, endothelin‐2 and endothelin‐3 were equipotent as bronchoconstrictor agents.
Big‐endothelin‐1, endothelin‐1 and endothelin‐2, but not big‐endothelin‐2, triggered a marked release of prostacyclin and thromboxane A2 from the guinea‐pig perfused lung.
Our results suggest the presence of a phosphoramidon‐sensitive endothelin‐converting enzyme (ECE) which is responsible for the conversion of big‐endothelin‐1 and big‐endothelin‐2 to their active moieties, endothelin‐1 and 2. However, the lack of bronchoconstrictor and eicosanoid‐releasing properties of big‐endothelin‐2, as opposed to endothelin‐2 or big‐endothelin‐1, suggests the presence of two distinct phosphoramidon‐sensitive ECEs in the guinea‐pig. The ECE responsible for the systemic conversion of big‐endothelins possesses the same affinity for big‐endothelin‐1 and 2 but not big‐endothelin‐3. In contrast, in the pulmonary vasculature is localized in the vicinity of the sites responsible for eicosanoid release, an ECE which converts more readily big‐endothelin‐1 than big‐endothelin‐2.
Involvement of NK2 receptors rather than NK1 receptors in bronchial hyperresponsiveness induced by allergic reaction in guinea‐pigs
Authors: Mizuguchi Masayuki , Fujimura Masaki , Amemiya Tokunao , Nishi Kouichi , Ohka Takio , Matsuda Tamotsu 
Published: July 2012

In this study, the role of neuropeptides in antigen‐induced bronchoconstriction and bronchial responsiveness in guinea‐pigs was evaluated by use of phosphoramidon, the inhibitor of neutral endopeptidases (NEP), the NK1 receptor antagonist, FK888, and the dual NK1/NK2 receptor antagonist, FK224. The role of endogenous tachykinins in bronchial hyperresponsiveness induced by inhaled capsaicin was also observed with FK888 and FK224.
Allergic bronchoconstriction and bronchial responsiveness was evoked by inhalation of ovalbumin (OA), and increasing doses of methacholine were inhaled at 5‐min intervals for 30 min after OA challenge in passively sensitized and artificially ventilated guinea‐pigs. Animals were treated with a 30 s inhalation of phosphoramidon (10−3m) or saline 10 min before the OA challenge. FK888 (1.0 or 10 mg kg−1) or FK224 (1.0 or 10 mg kg−1) was administered intravenously 5 min before the OA challenge.
Treatment with phosphoramidon did not alter the increase in the lateral pressure at the tracheal tube (Pao) caused by OA inhalation or the increase in bronchial response to methacholine following the allergic reaction. Pretreatment with FK224 did not inhibit the increase in Pao after antigen provocation but did significantly inhibit antigen‐induced bronchial hyperresponsiveness in a dose‐dependent manner, while FK888 did not affect either allergic bronchoconstriction or post‐allergic bronchial hyperresponsiveness.
Histamine, 25, 50, 100 or 200 μ ml−1 was inhaled for 20 s at 5‐min intervals in non‐sensitized guinea‐pigs which were pretreated with inhalation of subthreshold dose of capsaicin (10−7 m). FK888 or FK224, each at a dose of 0.1 or 1.0 mg kg−1, or vehicle was given to guinea‐pigs intravenously 3 min before inhalation of capsaicin. The capsaicin inhalation significantly potentiated bronchial responsiveness to histamine, compared with control. The capsaicin‐induced bronchial hyperresponsiveness was completely blocked by FK224 in a dose‐dependent manner but not by FK888.
These results suggest that NK2 receptors rather than NK1 receptors may play an important role in bronchial hyperresponsiveness induced by antigen challenge as well as capsaicin while tachykinins do not play a primary role in the acute bronchospasm elicited by antigen challenge in passively sensitized guinea‐pigs.
Characterization of the endothelin receptor selective agonist, BQ3020 and antagonists BQ123, FR139317, BQ788, 50235, Ro462005 and bosentan in the heart
Authors: Peter Markus G. , Davenport Anthony P. 
Published: July 2012

In this study we used ligand binding techniques to determine the affinity and selectivity of endothelin receptor agonists and antagonists in human left ventricle which expresses both ETA and ETB receptors, and compared these results with cardiovascular tissues from rat and porcine hearts.
The linear tripeptide antagonist, FR139317 competed for [125I]‐ET‐1 binding to human left ventricle with over 200,000 fold selectivity for the ETA receptor (KD ETA=1.20±0.28 nM, KDETB = 287±93 μm). The ETA‐selective non‐peptide antagonist, 50235, competed with lower affinity and selectivity (KDETA = 162±61 nM, KDETB= 171±42 μm) in this tissue. BQ123 and FR139317 also showed high selectivity (greater than 20,000 fold) and affinity in rat (BQ123: KDETA = 1.18±0.16 nM, KDETB = 1370±1150 μm; FR139317: KDETA = 2.28±0.30 nM, KDETB = 292±114 μm) and pig heart (BQ123: KDETA = 0.52±0.05 nM, KDETB = 70.4±4.0 μm; FR139317: KDETA = 2.17±0.51 nM, KDETB = 47.1±5.7 μm) (n≥3 individuals±s.e.mean).
Although BQ3020 competed with over 1000 fold selectivity for the ETB subtype in human heart KDETB = 1.38±0.72 nM, KDETA = 2.04±0.21 μm) the peptide inhibited only the binding of [125I]‐ET‐1 at concentrations greater than 100 nM in rat and porcine heart. This is in contrast to the data from the ETA‐selective antagonists which indicated the presence of ETB sites in these tissues from animal hearts.
The peptide antagonist, BQ788, had a low, micromolar affinity (KD = 1.98±0.13 μm) using human left ventricle and no significant selectivity for the human ETB‐subtype in this tissue.
The non‐peptide ET antagonists, Ro462005 (KD = 50.3±9.5 μm) and bosentan (Ro470203; KD = 77.9±7.9 nM) competed monophasically for [125I]‐ET‐1 binding sites in human left ventricle.
The results show that the ETA antagonists, BQ123 and FR139317, are highly selective for ETA receptors in all cardiac tissues tested, whereas BQ788 has a low affinity and no selectivity in this human tissue. Further we showed that there are species differences in the binding of BQ3020 to the ETB receptors in the hearts derived from human, rat and pig.
Electrophysiological effects of monoamine oxidase inhibition on rat midbrain dopaminergic neurones: an in vitro study
Authors: Mercuri Nicola B. , Bonci Antonello , Siniscalchi Antonio , Stefani Alessandro , Calabresi Paolo , Bernardi Giorgio 
Published: July 2012

The effects of the inhibition of monoamine oxidase (MAO) type A and B have been evaluated on the spontaneous firing activity of the dopaminergic (principal) neurones of the rat midbrain intracellularly recorded from a slice preparation.
The non‐specific MAO inhibitor, pargyline, superfused at a concentration of 10–100 μm, decreased or abolished the spontaneous firing discharge of the principal neurones in the subtantia nigra pars compacta and ventral tegmental area. This effect had a slow onset and appeared to be sustained.
The administration of the dopamine D2/3 receptor antagonist, sulpiride (100–300 μm), antagonized the pargyline‐induced effect, while the superfusion of the dopamine D1 receptor antagonist, SCH 23390 (1–3 μm) did not counteract the induced inhibition of the firing rate.
The inhibitor for the MAO A, clorgyline (30–100 μm), reduced the firing rate of the dopaminergic neurones. A similar depressant effect was also observed when a MAO B inhibitor, deprenyl (30–100 μm), was applied. Lower concentrations of both drugs (300 nM‐10 μm) did not produce consistent effects on neuronal discharge.
Our data suggest that only the blockade of both types of MAO enzymes favours the inhibitory action of endogenous dopamine on somato‐dendritic D2/3 autoreceptors.