bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparative study of the control of basal acid output from rodent isolated stomachs
Authors: Welsh Nicola J. , Shankley Nigel P. , Black James W.
Published: July 2012

Isolated, lumen‐perfused, whole stomach preparations from mouse and immature rat produced a stable basal acid output which, although not blocked by histamine H2‐, acetylcholine M‐ or CCKB/ gastrin receptor antagonists, was almostly completely blocked by the H+/K+‐ATPase inhibitor, omeprazole, and the metabolic inhibitor, sodium thiocyanate (NaSCN).

Fully‐defined concentration‐effect curves could be obtained on both assays with the phosphodiesterase inhibitor, isobutyl methylxanthine (IBMX) and with dibutyryl cyclic AMP.

On the rat stomach assay, histamine H2‐receptor blockade had no effect on the IBMX curve. In contrast, the IBMX response in the mouse was abolished by histamine H2‐receptor blockade. On both assays responses to dibutyryl cyclic AMP were resistant to H2‐receptor blockade.

In the absence of suprathreshold endogenous histamine, it is argued that H+/K+‐ATPase mediated basal acid secretion from the mouse stomach assay is regulated by something other than cyclic AMP.
Effect of extracellular ATP on contraction, cytosolic calcium activity, membrane voltage and ion currents of rat mesangial cells in primary culture
Authors: Pavenstädt Hermann , Gloy Joachim , Leipziger Jens , Klär Bettina , Pfeilschifter Josef , Schollmeyer Peter , Greger Rainer
Published: July 2012

The effects of extracellular ATP on contraction, membrane voltage (Vm), ion currents and intracellular calcium activity [Ca2+]i were studied in rat mesangial cells (MC) in primary culture.

Addition of extracellular ATP (10−5 and 10−4 m) to MC led to a cell contraction which was independent of extracellular calcium.

Membrane voltage (Vm) and ion currents were measured with the nystatin patch clamp technique. ATP induced a concentration‐dependent transient depolarization of Vm (ED50: 2 × 10−6 m). During the transient depolarization ion currents were monitored simultaneously and showed an increase of the inward‐ and outward current.

In a buffer with a reduced extracellular chloride concentration (from 145 to 30 mm) ATP induced a depolarization augmented to −4 ± 4 mV.

ATP‐γ‐S and 2‐methylthio‐ATP depolarized Vm to the same extent as ATP, whereas α,β‐methylene‐ATP (all 10−5 m) had no effect on Vm.

The Ca2+ ionophore, A23187, depolarized Vm transiently from −51 ± 2 to −28 ± 4 mV and caused an increase of the inward current.

The intracellular calcium activity [Ca2+]i was measured with the fura‐2 technique. ATP stimulated a concentration‐dependent increase of [Ca2+]i (ED50: 5 × 10−6 m). The increase of [Ca2+]i was biphasic with an initial peak followed by a sustained plateau.

The [Ca2+]i peak was still present in an extracellular Ca2+‐free buffer, whereas the plateau was abolished. Verapamil (10−4 m) did not inhibit the [Ca2+]i increase induced by ATP.

The data indicate that extracellular ATP contracts MC and is able to increase [Ca2+]i by the release of Ca2+ from intracellular stores and recruitment from the extracellular space. In addition ATP depolarizes Vm of MC by activating a Cl− conductance. The ATP‐induced depolarization is mediated by a P2y receptor.
Bacterial endotoxin rapidly stimulates prolonged endothelium‐dependent vasodilatation in the rat isolated perfused heart
Authors: Baydoun Anwar R. , Foale Robert D. , Mann Giovanni E.
Published: July 2012

The effects of bacterial lipopolysaccharide (Escherichia coli 0111‐B4; LPS) on coronary vascular tone were examined in the isolated perfused heart of the rat. The role of nitric oxide and/or prostaglandin products of the cyclo‐oxygenase pathway in mediating the actions of LPS were also investigated.

Coronary vascular tone was raised and maintained by a continuous perfusion of the thromboxane‐mimetic U46619 (5 nm). LPS perfusion (0.1–100 μg ml−1) caused a concentration‐dependent fall in coronary tone without any significant change in the force of cardiac contractility.

At 5 μg ml−1, LPS reduced perfusion pressure by 38 ± 9 mmHg. This effect was rapid in onset, maximal within the first 5 min and sustained for 90 ± 10 min (n = 6).

The vasodilatation induced by LPS was dependent on the presence of an intact endothelium and abolished following endothelial damage caused by air embolism.

NG‐nitro‐l‐arginine methylester (l‐NAME; 50 μm) or NG‐nitro‐l‐arginine (l‐NOARG; 50 μm) blocked the vasodilatation induced by LPS (5 μg ml−1). The inhibition caused by these arginine analogues was partially reversed by 1 mm l‐ but not d‐arginine.

The vasodilator action of LPS was also completely blocked by the glucocorticoid, dexamethasone (10 μm) but unaffected by indomethacin (10 μm).

These results suggest that LPS evokes rapid release of nitric oxide (NO) in the microvasculature of the rat isolated heart presumably via activation of the constitutive l‐arginine‐NO pathway in the endothelium. Furthermore, the lack of effect of indomethacin suggests that prostaglandins released via the cyclo‐oxygenase pathway are not involved in mediating this action of LPS.
Heterogeneity of muscarinic receptors in lamb isolated coronary resistance arteries
Authors: Simonsen Ulf , Prieto Dolores , Rivera Luis , Hernández Medardo , Mulvany Michael J. , García‐Sacristán Albino
Published: July 2012

In vitro experiments in a microvascular myograph were designed to characterize postjunctional muscarinic receptors producing contraction both in the presence and absence of the endothelium in coronary resistance arteries (normalized diameter of 150–450 μm), isolated from the left ventricle of hearts from 3–6 month old lambs. Preferential muscarinic receptor antagonists were used to determine the receptor subtype: pirenzepine (M1 receptor), AFDX 116 (M2 receptor), 4‐DAMP and pFHHSiD (M3 receptor).

The rank order of potency for muscarinic agonist‐induced increases in tension in endothelium‐intact preparations was oxotremorine‐M = methacholine = acetylcholine (ACh) > carbachol. Removal of the endothelium increased the potency of ACh, but this procedure did not change either the sensitivity or maximal response to carbachol.

The contractile response to ACh was reproducible. Incubation with 3 × 10−7–3 × 10−6 m pirenzepine induced non‐parallel rightward shifts and depressed the maximum of the concentration‐response curve to ACh in endothelium‐intact arteries. The slope by Schild analysis was 2.9 ± 0.8 (P < 0.05, n = 7). Atropine, AFDX 116, 4‐DAMP and pFHHSiD produced parallel rightward shifts of the curves to ACh and the slopes of the Schild plots were not significantly different from unity. The pKB values for the antagonists from plots constrained to unity in endothelium‐intact segments were: atropine (9.4), 4‐DAMP (9.0), pFHHSiD (7.9) and AFDX 116 (6.2).

In endothelium‐denuded arteries, pirenzepine, AFDX 116 and pFHHSiD caused concentration‐dependent, parallel rightward displacements of the concentration‐response curves to ACh and the slopes of the Schild plots were not significantly different from unity. The plots constrained to a slope of unity gave the following pKB values: pFHHSiD (8.7), pirenzepine (7.5) and AFDX 116 (6.2).

In the presence of the endothelium, low concentrations of pirenzepine (10−9–10−7m) produced leftward shifts of the ACh concentration‐response curves. This potentiating effect of pirenzepine was reversed by endothelial cell removal. In preparations precontracted with the thromboxane‐mimetic, U46619, the putative M1‐selective agonist, McN‐A‐343, induced a biphasic relaxation with log IC50 of 8.53 ± 0.14 and 5.02 ± 0.08 for the first and second phase of the relaxation, respectively, and maximal relaxations of 22.8 ± 4.3% and 41.1 ± 5.4% (n = 16). McN‐A‐343 relaxed the vessels in the presence of 10−7m pFHHSiD and 3 × 10−7 m AFDX 116, but not after incubation with 10−9m pirenzepine.

It is concluded from the pKB values for the antagonists used, that contraction induced by ACh in lamb coronary resistance arteries, in either the presence or the absence of the endothelium, is mediated via the M3 subtype of muscarinic receptors, while muscarinic receptors of another subtype at the endothelium seem to modulate the contractile response to ACh.
β1‐ and β2‐adrenoceptor‐mediated relaxation in human internal mammary artery and saphenous vein: unchanged β‐ and α‐adrenoceptor responsiveness after chronic β1‐adrenoceptor blockade
Authors: Ferro A. , Kaumann A.J. , Brown M.J.
Published: July 2012

We have recently reported that patients taking β1‐adrenoceptor‐selective antagonists exhibit marked sensitization of β2‐adrenoceptor responses but unaltered β1‐adrenoceptor responses in the heart, both in vitro and in vivo. We therefore investigated β1‐ and β2‐adrenoceptor‐mediated relaxant responses in rings of human internal mammary artery and saphenous vein without endothelium, taken from β1‐blocked and non‐β‐blocked patients undergoing coronary artery bypass graft surgery, for comparison. We also examined α1‐adrenoceptor‐mediated contraction in these vessels, to determine whether β1‐blockade had any cross‐regulatory effect.

Following α‐blockade with 10 μm phenoxybenzamine, both noradrenaline and adrenaline produced concentration‐dependent relaxations in both blood vessels, their effects being mediated predominantly through β2‐adrenoceptors; a lesser β1‐adrenoceptor component to relaxation was also found in internal mammary artery and a minor β1‐adrenoceptor component was present in saphenous vein. No differences were found in β1‐ or in β2‐adrenoceptor‐mediated vasorelaxation between β1‐blocked and non‐β‐blocked patients.

Methoxamine produced concentration‐dependent contractions in both blood vessels, and the potency and efficacy were not significantly different between vessels from β1‐blocked and from non‐β‐blocked patients.

These findings indicate that, in these tissues, which possess a relatively minor β1‐adrenoceptor component in contrast to myocardial tissue, chronic β1‐blocker treatment does not alter either β1‐ or β2‐adrenoceptor responses. Likewise, in such tissues, α1‐adrenoceptor responses are unaffected by prior β1‐blockade.
Influence of epithelium on the inhibition of melittin‐induced contraction of guinea‐pig isolated trachea by the potassium channel opener NIP‐121
Authors: Shikada Ken‐ichi , Tanaka Sakuya
Published: July 2012

We have investigated the effect of the potassium channel opener, NIP‐121, on contraction elicited by melittin (a phospholipase A2 activator) in epithelium‐intact and epithelium‐denuded trachea isolated from guinea‐pigs. The effects of NIP‐121 were compared with those of isoprenaline, aminophylline and hydrocortisone.

In the presence of the cyclo‐oxygenase inhibitor, indomethacin (5 μm), melittin (3 μg ml−1) caused time‐dependent contraction. The melittin‐induced contractile response was significantly augmented by removal of the epithelium and was concentration‐dependently and completely inhibited by the phospholipase A2 (PLA2) inhibitor, p‐bromophenacyl bromide (BPB 10–100 μm), and the lipoxygenase inhibitor, phenidone (10–300 μm). Similar inhibition of the melittin response by BPB (10 μm) and phenidone (10 μm) was observed in the epithelium‐denuded trachea.

Concentration‐dependent inhibition of the melittin response was induced by preincubation with NIP‐121 (0.03 and 0.1 μm), isoprenaline (0.001 and 0.01 μm), aminophylline (30 and 100 μm) and hydrocortisone (100 and 300 μm). The effect of NIP‐121 was abolished by glibenclamide (1 μm).

The inhibitory effect of NIP‐121 on the melittin response was greatly reduced by removing the epithelium while that of the isoprenaline, aminophylline or hydrocortisone was not changed.

The inhibition of the melittin response by these drugs was similar to their inhibition of the contraction elicited by a low concentration (3 nm) of leukotriene D4 (LTD4) in the epithelium‐intact trachea. Inhibition of the LTD4 response by NIP‐121 was not observed in the epithelium‐denuded trachea. However, higher concentrations of NIP‐121 (0.3 and 1 μm) did inhibit LTD4‐induced contractions of epithelium‐denuded trachea.

These findings suggest that melittin causes epithelium‐dependent contraction of the guinea‐pig isolated trachea which is mediated by products of lipoxygenase activity. NIP‐121 may inhibit the melittin response by activating glibenclamide‐sensitive potassium channels, which appear to be epithelium‐dependent (an indirect effect of NIP‐121 apart from its direct effect on the airway smooth muscle) while isoprenaline, aminophylline and hydrocortisone act directly to relax the trachealis smooth muscle.
Bicuculline‐resistant paired‐pulse inhibition in the rat hippocampal slice
Authors: Higgins M.J. , Stone T.W.
Published: July 2012

An initial observation that paired‐pulse inhibition in hippocampal slices was increased rather than decreased by bicuculline prompted the present study to explore the mechanism underlying bicuculline‐resistant inhibition.

In the presence of bicuculline, paired‐pulse interactions were dependent on the interpulse interval (i.p.i.) but a medium‐latency inhibition was consistently observed at an i.p.i. of 300 to 500 ms.

The medium‐latency (300 ms) bicuculline‐resistant inhibition produced by paired orthodromic stimuli was substantially reduced by 2‐hydroxysaclofen and was probably largely mediated by GABAB‐receptor activation. Paired‐pulse inhibition produced by an orthodromic/antidromic stimulation sequence was not affected by 2‐hydroxysaclofen suggesting the possibility that the GABAB‐receptors involved in orthodromic inhibition may be located presynaptically on the Schaffer collateral terminals rather than on the postsynaptic surface. The medium latency inhibition was also reduced by baclofen and under some conditions, by adenosine.

In addition to the GABAB‐component, a hydroxysaclofen‐resistant depression of postsynaptic excitability contributed to bicuculline‐resistant paired‐pulse inhibition at the 300 ms latency.
[3H]‐5‐carboxamidotryptamine labels 5‐HT1D binding sites in bovine substantia nigra
Authors: Nowak Henry P. , Mahle Cathy D. , Yocca Frank D.
Published: July 2012

[3H]‐5‐hydroxytryptamine (5‐HT) has been shown to radiolabel at least five types of 5‐HT binding sites in mammalian brain tissue, 5‐HT1A, 5‐HT1B, 5‐HT1C, 5‐HT1D and 5‐HT1E (Frazer et al., 1990). Selective masking of 5‐HT1A and 5‐HT1C receptors, has uncovered binding sites which display both high (5‐HT1D) and low (5‐HT1E) affinity for 5‐carboxamidotryptamine (5‐CT). By utilizing [3H]‐5‐CT we have eliminated a portion of the complex binding (5‐HT1E) seen when [3H]‐5‐HT is used as a radioligand.

[3H]‐5‐CT binding to 5‐HT1D sites in bovine substantia nigra was rapid, reversible and saturable, displaying high affinity (Kd = 0.38 ± 0.04 nm) and low non‐specific binding (> 90% specific binding).

In bovine substantia nigra, [3H]‐5‐CT labelled an equivalent number of binding sites to [3H]‐5‐CT (403 ± 18 and 362 ± 20 fmol mg−1 protein, respectively) and binding was sensitive to guanine nucleotides.

A linear correlation (r2 = 0.99) existed between the potency of compounds to displace [3H]‐5‐HT and [3H]‐5‐CT in bovine substantia nigra.

Therefore, [3H]‐5‐CT is a novel radioligand for the examination of 5‐HT1‐like binding sites, which under proper experimental conditions can be used to radiolabel selectively 5‐HT1D‐like binding sites.
Evaluation of ICI D7114, a putative stimulant of brown adipocytes, on histamine‐contracted guinea‐pig ileum
Authors: Growcott J.W. , Wilson Campbell , Holloway Brian , Mainwaring Sally
Published: July 2012

Experiments were performed to characterize the effects of the novel brown adipocyte stimulant, ICI D7114, in the guinea‐pig isolated ileum, right atrium and tracheal chain. In the ileum, agonist‐induced inhibition of the contractile response to either histamine or prostaglandin E2 (PGE2) was assessed, along with effects on resting rate in the atrium and resting tone in the tracheal chain. In the latter two preparations, antagonism of isoprenaline‐induced responses by ICI D7114 was also assessed.

Inhibitory responses were obtained in the ileum to ICI D7114, isoprenaline, BRL37344, and noradrenaline. The responses to ICI D7114, isoprenaline and BRL37344 were resistant to blockade with propranolol (5 μm), naloxone (1 μm), methysergide (0.1 μm), cimetidine, indomethacin and 8‐phenyltheophylline (all 10 μm). These responses to isoprenaline, in the presence of propranolol (5 μm), were competitively antagonized by alprenolol (1–100 μm) with a pA2 value of 6.44. The responses to ICI D7114 and BRL37344 were antagonised by single concentrations of alprenolol (1 μm) with apparent pKB values of 6.53 and 6.57 respectively. These data indicate an effect of ICI D7114 at the atypical β‐adrenoceptor in the guinea‐pig ileum.

The order and relative potency of agonists at the atypical β‐adrenoceptor was BRL37344 (4) > isoprenaline (1) = ICI D7114 (1.1) > noradrenaline (0.5).

ICI D7114 (1 nm–10 μm) caused no significant change in the rate of beating or the resting tone of the guinea‐pig right atrium or tracheal chain respectively. It did, however, cause selective blockade of the responses to isoprenaline in these tissues (apparent pKB values 7.63 and 5.85 in atrium and tracheal chain respectively). Responses to histamine (atrium) and aminophylline (tracheal chain) were not significantly affected by 10 μm ICI D7114.

These results demonstrate that ICI D7114 possesses selective agonist activity at atypical β‐adrenoceptors in the guinea‐pig ileum and its use as a tool may help to establish a role for the atypical β‐adrenoceptor in the control of gastrointestinal motility.
Inhibition of the ATP‐sensitive potassium channel by class I antiarrhythmic agent, cibenzoline, in rat pancreatic β‐cells
Authors: Kakei Masafumi , Nakazaki Mitsuhiro , Kamisaki Takeshi , Nagayama Issei , Fukamachi Yuzo , Tanaka Hiromitsu
Published: July 2012

Cibenzoline, a class I antiarrhythmic agent, was investigated for its effect on the ATP‐sensitive K+ channel of pancreatic β‐cells by the patch clamp technique.

In perforated patch clamp experiments, cibenzoline depolarized the membrane of single β‐cells and thereafter, caused firing of action potentials in the presence of 2.8 mm glucose.

Cibenzoline inhibited the activity of the ATP‐sensitive K+ channel in cell‐attached recordings in the presence of 2.8 mm glucose and evoked repetitive fluctuations of the baseline current, apparently reflecting the action potentials of the β‐cell.

In whole‐cell clamp experiments, time‐independent outward current was induced by depleting cytoplasmic ATP with 0.1 mm ATP and 0.1 mm ADP in the solution contained in the pipette. The outward current was inhibited by cibenzoline in a dose‐dependent manner in the concentration range of 1 μm to 100 μm and half maximum inhibition occurred at 1.5 μm.

Cibenzoline blocked substantially the ATP‐sensitive K+ channel current when applied at the inner side of the membrane in isolated inside‐out membrane patches.

It is concluded that cibenzoline blocks the ATP‐sensitive K+ channel of pancreatic β‐cells and, thereby, stimulates insulin secretion at sub‐stimulatory levels of glucose.
Differential inhibition of a transient K+ current by chlorpromazine and 4‐aminopyridine in neurones of the rat dorsal root ganglia
Authors: Ogata Nobukuni , Tatebayashi Hideharu
Published: July 2012

K+ currents were recorded from neurones of the newborn rat cultured dorsal root ganglia, by a whole cell variation of the patch‐clamp technique.

Chlorpromazine (CPZ), a neuroleptic, reversibly reduced the amplitude of the transient K+ current (referred to as ‘IT’ hereafter) with a dissociation constant (Kd) of 4.5 μm. The inhibition of the delayed rectifier K+ current (IDR) was much less potent (Kd, 120 μm). CPZ (100 μm) had no effect on the inward rectifier K+ current.

The blocking action of CPZ on IT was about seven times more potent than that of 4‐aminopyridine (4‐AP) which had a Kd of 31 μm. The inhibition of IT followed one‐to‐one binding stoichiometry with both drugs.

The decay time course of IT was not affected by CPZ, whereas 4‐AP markedly accelerated the decay phase of IT.

The steady‐state inactivation curve of IT was shifted in the negative direction (about 5 mV) by CPZ, whereas the curve was shifted in the positive direction (about 13 mV) by 4‐AP.

The recovery from inactivation as measured by a conventional double pulse protocol was described by two exponential components in the control solution. CPZ markedly reduced the first component and slowed down the recovery from inactivation. In contrast, in the presence of 4‐AP, the peak amplitude of IT was rather increased by a preceding IT possibly through voltage‐dependent unbinding of 4‐AP molecules.

These results indicate that CPZ has a preferential blocking action on IT and the mechanism underlying this block is markedly different from the mechanism underlying the blocking action of 4‐AP.
Protection by nicorandil against the dysfunction of the central vagal baroreflex system following transient global cerebral ischaemia in dogs
Authors: Kurihara Junichi , Ochiai Nobuhiko , Kato Hitoshi
Published: July 2012

A possible cerebroprotective effect of nicorandil was investigated in a canine model of 5 min global cerebral ischaemia, and compared with protective effects of nitroglycerin and nicardipine.

Cerebral ischaemia was produced by occlusion of the left subclavian and the brachiocephalic arteries with preceding ligation of the intercostal arteries. The decrease in baroreflex sensitivity (BRS), measured by phenylephrine‐induced reflex bradycardia, was used to assess the cerebroprotective effect.

Nicorandil (10 or 30 μg kg−1 min−1, i.v.), nitroglycerin (3 μg kg−1 min−1, i.v.) or nicardipine (0.3 μg kg−1 min−1, i.v.) were infused for 60 min just before ischaemia. Nitroglycerin and nicardipine decreased mean arterial blood pressure to an extent similar to that induced by the lower dose of nicorandil. Blood flow in the dorsal medulla oblongata was increased by nicorandil and nicardipine, but not by nitroglycerin.

Nicorandil at both doses and nitroglycerin prevented the post‐ischaemic decrease in BRS. In these cases, bilateral vagotomy during the reperfusion period decreased BRS, indicating that the vagal component of BRS was protected from ischaemia. On the other hand, nicardipine failed to exert a cerebroprotective effect.

The present study suggests that nicorandil may possess a direct cerebroprotective effect and that its property as a nitrate might, at least in part, be important for the observed cerebral protection.
Prevention by an inhibitor of the l‐arginine‐nitric oxide pathway of the antiarrhythmic effects of bradykinin in anaesthetized dogs
Authors: Vegh Agnes , Papp Julius Gy , Szekeres Laszlo , Parratt James R.
Published: July 2012

The intracoronary administration of bradykinin (25 ng kg−1 min−1) markedly reduces the severity of arrhythmias that occur during a 25 min occlusion of the left anterior descending coronary artery in chloralose, urethane anaesthetized dogs. This protection was abolished by the prior administration, by the same route, of NG‐nitro‐l‐arginine methyl ester (l‐NAME), an inhibitor of the l‐arginine‐nitric oxide pathway. The protective effect of bradykinin on reperfusion‐induced VF was not affected by l‐NAME. These results strongly suggest that the antiarrhythmic effect of bradykinin in this model is mediated by nitric oxide release. It also supports the concept that bradykinin might be a ‘primary mediator’ of the protective, antiarrhythmic effects of ischaemic preconditioning.
Electrophysiological effects of Org 7797 in the closed‐chest anaesthetized dog
Authors: Leboeuf J. , Basiez M. , Massingham R.
Published: July 2012

The intravenous electrophysiological effects of a new antifibrillatory agent, Org 7797, were studied in closed chest anaesthetized dogs. Effects of fast sodium and slow calcium‐mediated action potentials were also examined in guinea‐pig isolated papillary muscle.

The major effects of a known antifibrillatory dose of Org 7797 (0.5 mg kg−1) were a protracted slowing of AV nodal conduction (for at least 20 min) and prolongation of the AV nodal functional refractory period. Conduction in the atria and His‐Purkinje system (reflected by the St‐A and HV intervals) were not significantly modified whilst ventricular conduction (reflected by the QRS interval) and the ventricular functional refractory period were only transiently prolonged. No other electrophysiological changes were seen.

A higher dose of Org 7797 (1.5 mg kg−1) slowed conduction at all levels of the myocardium (as evidenced by increases in the St‐A, AH, HV and QRS intervals), slightly shortened cardiac repolarization (as assessed from JTc) and decreased Wenckebach rate. Atrial refractory periods were increased whereas effects on ventricular refractory periods were modest.

Neither heart rate nor sinus node recovery time were modified by either dose of Org 7797.

Org 7797, at a concentration (20 μm) which reduced Vmax of fast sodium‐mediated action potentials in isolated papillary muscle by 83%, did not modify Vmax of slow calcium‐mediated action potentials. It prolonged duration of the latter but did not modify that of the former. However, the plateau phase of both the ‘fast’ and especially the ‘slow’ action potentials was prolonged.

It is concluded that the main electrophysiological effects of a known antifibrillatory dose of Org 7797 in dogs with normal cardiac function are seen at the level of the AV node, actions which are unlikely to be explained by calcium channel block. Higher doses display a class Ic profile. This preferential action on the AV node may contribute to the control of ventricular rate during atrial fibrillation in the absence of infra‐nodal conduction disturbances.

These results contrast with those previously obtained in infarcted dogs and might further suggest that myocardial infarction enhances the Class I action of Org 7797.
Acceleration by chronic treatment with clorgyline of the turnover of brain α2‐adrenoceptors in normotensive but not in spontaneously hypertensive rats
Authors: Ribas Catalina , Miralles Antonio , García‐Sevilla Jesús A.
Published: July 2012

The aim of this study was to quantitate and compare the turnover of α2‐adrenoceptors in the cerebral cortex of normotensive Wistar‐Kyoto (WKY) and spontaneously hypertensive (SHR) rats, and its modulation during chronic treatment with the monoamine oxidase (MAO) inhibitor, clorgyline.

In SHR, the specific binding of the agonist [3H]‐UK 14304 and of the antagonist [3H]‐RX 821002 was significantly reduced in the brain (Bmax 15–19% lower) as compared to that in sex‐ and age‐matched WKY rats. In contrast, no significant changes in the Kd values for both radioligands were found between WKY and SHR rats. Therefore, SHR rats offer a genetic model with a lower density of α2‐adrenoceptors in the brain.

Chronic treatment (21–35 days) with clorgyline (1 mg kg−1, i.p.) markedly decreased the density of brain α2‐adrenoceptors ([3H]‐UK 14304 binding) in Sprague‐Dawley (Bmax reduced by 50%) and in WKY (Bmax reduced by 30%) rats without any apparent change in the affinity of the radioligand. In contrast, the density of brain α2‐adrenoceptors in SHR was not down‐regulated by chronic clorgyline treatment.

The recovery of [3H]‐UK 14304 binding after irreversible inactivation by N‐ethoxycarbonyl‐2‐ethoxy‐1,2‐dihydroquinoline (EEDQ; 1.6 mg kg−1) (an alkylating agent for the α2‐adrenoceptor) was assessed in control and clorgyline‐treated (1 mg kg−1; i.p. for 7–21 days) WKY and SHR rats to study the process of α2‐adrenoceptor repopulation and to calculate receptor turnover parameters.

The simultaneous analysis of receptor recovery curves revealed that the turnover of brain α2‐adrenoceptors in SHR rats was accelerated (k = 0.141 day−1; t1/2 = 4.9 days; r/k = 40 fmol mg−1 protein) compared to that in WKY rats (k = 0.085 day−1; t1/2 = 8.1 days; r/k = 54 fmol mg−1 protein) and that the reduced density of cortical α2‐adrenoceptors (Bmax or r/k values) in SHR was probably due to an abnormal higher receptor degradation (Δk = 66%) and not to a decreased receptor synthesis which in fact showed a slight increase (Δr = 24%).

Treatment with clorgyline (1 mg kg−1, i.p. for 21 days) accelerated the turnover of brain α2‐adrenoceptors in WKY rats (k = 0.328 days−1; t1/2 = 2.1 days; r/k = 29 fmol mg−1 protein) and the greater increase in receptor degradation (Δk = 286%) over receptor synthesis (Δr = 109%) led to down‐regulation of receptor density (r/k = 46% lower). In contrast, treatment with clorgyline did not modify significantly the turnover of brain α2‐adrenoceptors in SHR (k = 0.192 days−1; t1/2 = 3.6 days; r/k = 39 fmol mg−1 protein), indicating that in this genetic model of hypertension, the desensitized α2‐adrenoceptors cannot be further down‐regulated by clorgyline treatment and that they lack the expected adaptative increase in receptor synthesis.
Leukotriene D4‐ and prostaglandin F2α‐induced airflow obstruction and airway plasma exudation in guinea‐pig: role of thromboxane and its receptor
Authors: Arakawa Hirokazu , Lötvall Jan , Kawikova Ivana , Löfdahl Claes‐Göran , Skoogh Bengt‐Eric
Published: July 2012

We studied the effects of a thromboxane A2 receptor (TP receptor) antagonist, ICI‐192,605 (0.5 mg kg−1, i.v.) and a selective thromboxane (Tx) synthetase inhibitor, OKY‐046 (30 mg kg−1, i.v.), on airway responses induced by leukotriene D4 (LTD4; 0.2 nmol) or prostaglandin F2α (PGF2α; 20 nmol) instilled via the airways route to anaesthetized guinea‐pigs. For a comparison, airway responses to a TxA2‐mimetic, U‐46619 (0.02 nmol) were also studied. We measured both lung resistance (RL) to monitor airflow obstruction, and extravasation of Evans Blue dye to quantify airway plasma exudation.

Instilled LTD4 into the tracheal lumen induced an immediate peak and subsequently persistent increase in RL and produced a large amount of extravasation of Evans Blue dye at all airway levels. Both ICI‐192,605 and OKY‐046 significantly attenuated the persistent increase in RL following the immediate response and reduced LTD4‐induced extravasation of Evans Blue dye in the trachea and proximal intrapulmonary airway. Instilled LTD4 produced significant increases in immunoreactive TxB2 in bronchoalveolar lavage fluid obtained 1.5 min after instillation of LTD4.

Instilled PGF2α into the tracheal lumen induced an immediate increase in RL which peaked at approximately 15 s. We also observed a delayed sustained increase in RL, reaching a second peak at approximately 4 min. PGF2α produced small but significant increases in the amount of Evans Blue dye at all airway levels. As with PGF2α, instillation of U‐46619 produced a biphasic increase in RL and extravasation of Evans Blue dye. The potency of PGF2α in inducing these airway responses was about 1000 times less than U‐46619. ICI‐192,605 abolished both the immediate and the delayed increase in RL after PGF2α, and also blocked PGF2α‐induced extravasation of Evans Blue dye. However, OKY‐046 had no inhibitory effects on these responses.

We conclude that airflow obstruction and airway plasma exudation induced by instilled LTD4 is, in part, mediated via TxA2 generation and subsequent activation of TP‐receptors. On the other hand, instilled PGF2α, while inducing similar responses, does so primarily by direct activation of TP receptors, rather than via TxA2 generation.
Kinetics of rate‐dependent slowing of intraventricular conduction by the class Ib antiarrhythmic agent tocainide in vivo
Authors: Todt Hannes , Zojer Niklas , Raberger Gerhard
Published: July 2012

The effects of the class I antiarrhythmic agent, tocainide, on intraventricular conduction were assessed in guinea‐pigs, anaesthetized with pentobarbitone sodium 60 mg kg−1, i.p.

After electrical ablation of the sinus node, heart rate was controlled by atrial pacing. His bundle electrograms were recorded by means of an epicardial bipolar electrode.

During continuous stimulation, comparison of HV intervals measured at a cycle length of 475 ms, with HV intervals measured at a cycle length of 250 ms yielded the following results: 25.26 ± 0.64 ms versus 25.02 ± 0.70 ms (NS), at baseline, 26.65 ± 0.80 ms versus 29.881 1.13 ms (P < 0.001) after i.v. administration of 30 mg kg−1 tocainide, and 28.04 ± 0.64 ms versus 36.24 ± 1.31 ms (P < 0.001), after addition of 20 mg kg−1 tocainide. Thus, tocainide caused HV intervals to increase in a strictly rate‐dependent fashion.

In order to characterize the rate‐dependent class I activity of tocainide in terms of its binding kinetics to sodium channels, fractional sodium channel block was estimated from drug induced reductions of intraventricular conduction velocity (Δθ). On abruptly changing the drive cycle length from 500 ms to 250 ms, Δθ reached a new steady state with rate constants of 1.23 ± 0.09 beat−1 and 1.28 ± 0.09 beat−1, after administration of 30 mg kg−1 and addition of 20 mg kg−1 tocainide, respectively. At a basic drive cycle length of 250 ms Δθ recovered with time constants of 250.29 ± 23.32 ms and 183.04 ± 8.03 ms after administration of 30 mg kg−1 and addition of 20 mg kg−1 tocainide, respectively.

The experimentally determined kinetic parameters were implemented into a mathematical model that assumes drug binding to sodium channels in terms of a periodical two‐state process. Rate‐dependent reductions in conduction velocity during continuous stimulation after administration of tocainide were closely approximated by steady state reductions in sodium channel availability as calculated on the basis of the aforementioned model.

In agreement with previously published in vitro studies, our data, obtained in vivo, confirm the classification of tocainide as a class I antiarrhythmic agent with fast onset and offset kinetics. The kinetic parameters obtained in vivo can be used in order to predict steady state reductions in conduction velocity at a wide range of frequencies.
Evidence for participation of B1 and B2 kinin receptors in formalin‐induced nociceptive response in the mouse
Authors: Corrêa Clóvis R. , Calixto João B.
Published: July 2012

This study was designed to investigate the role of bradykinin (BK), as well as the subtype of BK receptors involved, in formalin‐induced hindpaw pain in the mouse by use of selective B1 and B2 receptor antagonists. In addition, we have analysed whether or not BK may be involved in formalin‐induced hindpaw oedema in the mouse.

The pretreatment of animals with captopril (2 and 5 mg kg−1, s.c.) significantly increase the first and the second phases of formalin‐induced pain.

Co‐injection of the selective B1 receptor antagonist des‐Arg9[Leu8]‐BK (0.2–0.4 nmol/paw), together with formalin, caused graded and similar inhibitions of both phases of formalin‐induced pain. Similar results were obtained with the B2 antagonists NPC 349 (d‐Arg[Hyp3,Thi5,8‐d‐Phe7]‐BK) and NPC 567 (d‐Arg[Hyp3, d‐Phe7]‐BK) (0.2 and 0.6 nmol/paw). Higher concentrations of these antagonists (1 nmol/paw) failed to antagonize formalin‐induced pain.

The new potent and selective B2 receptor antagonists, Hoe 140 (d‐Arg[Hyp3,Thi5,d‐Tic7,Oic8]‐BK), NPC 17731 (d‐Arg[Hyp3, trans‐4‐propoxy‐d‐proline (transpropyl)7, Oic8]‐BK), and NPC 17761 (d‐Arg[Hyp3, trans‐4‐propoxy‐d‐proline (trans thiophenyl)7, Oic8]‐BK) (0.02 to 1.0 nmol/paw), also caused significant inhibitions of both phases of formalin‐induced pain. When Hoe 140 was injected subcutaneously 30 min before formalin injection (9.9 and 99 nmol kg−1), it significantly attenuated both phases of formalin‐induced pain. The putative non‐peptide BK antagonist, MV 8612 (1.6 to 9.6 nmol/paw), but not MV 8608 (5.5 to 33 nmol/paw), caused a graded inhibition of both phases of formalin‐induced pain, being, however, more active against the first phase.

The pretreatment of animals with morphine (2.6 to 13μmol kg−1, s.c.) caused dose‐dependent and equipotent inhibitions of both phases of formalin‐induced pain. In contrast, indomethacin (2.7 to 27 μmol kg−1) antagonized only the second phase of formalin‐induced pain.

The B2 receptor antagonists, Hoe 140, NPC 17731, NPC 17761, NPC 349 and NPC 567, all caused a significant inhibition of formalin‐induced hindpaw oedema. A similar inhibition was also observed with indomethacin but not with captopril or morphine.

Our results provide strong evidence for the important role of endogenous BK, acting through both B1 and B2 receptors, in the genesis of both phases of formalin‐induced persistent pain in the mouse. In addition, the current results also demonstrate that the inflammatory oedema associated with the later phase of formalin‐induced pain seems to be mediated by endogenous BK, via activation of B2 receptors.
Interaction of nitric oxide and salivary gland epidermal growth factor in the modulation of rat gastric mucosal integrity
Authors: Tepperman B.L. , Soper B.D.
Published: July 2012

The interaction between endogenous nitric oxide (NO) and factors from the rat submandibular salivary gland such as epidermal growth factor (EGF) on gastric mucosal integrity in the rat has been investigated.

Bolus administration of the NO synthase inhibitor, NG nitro‐l‐arginine methyl ester (l‐NAME; 6.25–50 mg kg−1, i.v.) to animals treated intraluminally with 0.15 n HCl resulted in a significant increase in the area of mucosal haemorrhagic damage at doses 12.5 and 50 mg kg−1. Concurrent administration of indomethacin (5 mg kg−1, i.v.) resulted in a significant haemorrhagic mucosal damage in response to l‐NAME (12.5–50 mg kg−1). Administration of the highest dose of l‐NAME resulted in an increase in histological damage to the rat gastric mucosa.

When compared to control animals, the extent of damage produced by l‐NAME or l‐NAME in combination with indomethacin was significantly exacerbated in rats which had been sialoadenectomized (SALX) by removal of the submandibular salivary glands. The mucosal damage in SALX rats was ameliorated by treatment with EGF (5 and 10 μg kg−1, i.v.).

l‐NAME administration resulted in a small reduction of gastric mucosal blood flow as assessed by laser Doppler flowmetry (LDF). The reduction in LDF by 25 and 50 mg kg−1 l‐NAME was significantly greater in SALX rats than in rats with intact salivary glands. Pretreatment of SALX rats with indomethacin did not augment this large decrease in LDF suggesting that endogenous prostanoids do not interact with NO and salivary factors in regulating mucosal microcirculation.

Mucosal NO biosynthesis as assessed by [14C]‐citrulline formation was reduced in SALX rats when compared to control animals. Pretreatment of SALX animals with parenterally‐administered EGF (10 μg kg−1) was associated with an increase in [14C]‐citrulline formation in the gastric mucosa to levels observed in control SALX rats.

These data suggest that factors which originate from the salivary gland such as EGF interact with NO in the maintenance of mucosal integrity. The effects may be mediated at least in part by changes in gastric mucosal blood flow. Salivary glands and EGF may mediate these effects to some extent via changes in mucosal NO biosynthesis.
Eicosanoid‐dependence of responses of pre‐ but not postglomerular vessels to noradrenaline in rat isolated kidneys
Authors: Zhang Bei‐Li , Sassard Jean
Published: July 2012

We investigated the role of nitric oxide (NO) and of vasoactive eicosanoids in the control of renal vascular resistance (RVR) and glomerular filtration rate (GFR) and of their responses to noradrenaline (NA). This study was conducted in single‐pass perfused, isolated kidney preparations of the rat.

NA (63, 110 and 160 nm) dose‐dependently increased RVR and to a lesser degree GFR.

In baseline conditions, Nω‐nitro‐l‐arginine methylester (l‐NAME, 100 μm) increased GFR more than RVR, thus demonstrating a basal release of NO which predominates in postglomerular vessels.

In kidneys stimulated with NA, l‐NAME potentiated the increases in RVR but not in GFR. Indomethacin (1.5, 150 nm and 15 μm) did not alter GFR but markedly and dose‐dependently reduced the NA‐induced increase in RVR. Similar results were obtained with GR 32191B (10 and 100 μm), a prostaglandin H2/thromboxane A2 (PGH2/TxA2) receptor antagonist.

Indomethacin (15 μm) suppressed the enhancing effects of l‐NAME on RVR responses to NA but did not affect those on GFR.

It is concluded that the mechanisms of the response to NA differ among pre‐ and postglomerular vessels. In preglomerular vessels the vasoconstrictor action and the NO release depend upon the activation of PGH2/TxA2 receptors, while both are eicosanoid‐independent in the postglomerular vessels.
Mechanical and electrophysiological studies on the positive inotropic effect of 2‐phenyl‐4‐oxo‐hydroquinoline in rat cardiac tissues
Authors: Su Ming Jai , Chang Gwo Jyh , Kuo Sheng Chu
Published: July 2012

The pharmacological and electrophysiological effect of 2‐phenyl‐4‐oxo‐hydroquinoline (YT‐1), a new synthetic agent, were determined in rat isolated cardiac tissues and ventricular myocytes.

YT‐1 was found to have a positive inotropic effect in both atria and ventricular muscles but did not cause significant increases in the spontaneously beating rate of right atria.

The positive inotropic effect of YT‐1 was antagonized neither by β‐nor by α‐adrenoceptor antagonists but was partially antagonized by a Ca2+ channel blocker (verapamil) and a K+ channel blocker (4‐AP).

The action potential duration and amplitude of ventricular cells were progressively increased as the concentration of YT‐1 was increased from 3 to 30 μm.

A voltage clamp study revealed that the prolongation of action potential duration by YT‐1 was associated with a prominent inhibition of 4‐AP‐sensitive transient outward current (Ito). At potentials negative to the reversal potential of K1‐channels, the inward current through these channels was partially reduced by YT‐1. At potentials positive to the reversal potential, the outward current through these channels was affected very little.

Although YT‐1 blocked the amplitude of Ito, the voltage‐dependence of the steady‐state inactivation of Ito, was unaffected.

Apart from the inhibition of K+ currents, YT‐1 also inhibited the sodium inward current.

The evidence suggests that YT‐1 increases the slow inward Ca2+ current (ICa) significantly.

It is concluded that the positive inotropic effect of YT‐1 is due predominantly to the increase of ICa and inhibition of Ito.
Effect of endopeptidase‐24.11 inhibition and of atrial natriuretic peptide clearance receptor ligand on the response to rat brain natriuretic peptide in the conscious rat
Authors: Kirk Jane E. , Wilkins M.R.
Published: July 2012

The present studies examined the effect of (a) a specific endopeptidase‐24.11 (E‐24.11) inhibitor (candoxatrilat) and (b) a ligand for the atrial natriuretic peptide (ANP) clearance receptor (SC 46542) on the renal and blood pressure response to brain natriuretic peptide (BNP) in conscious rats.

Infusion of BNP 200 ng kg−1 min−1 for 60 min produced a small rise in urinary sodium and guanosine 3′:5′‐cyclic monophosphate (cyclic GMP) excretion with a non‐significant fall in mean arterial blood pressure.

Candoxatrilat (3 mg kg−1) alone had no significant effect on sodium excretion or blood pressure but markedly potentiated the natriuretic response to BNP.

Similarly SC 46542 (68 μg kg−1; 6.8 μg kg−1 min−1) which produced no significant effect on its own, potentiated the natriuresis‐induced by BNP, although the effect was of shorter duration compared to that of candoxatrilat.

The data indicate two approaches to the potentiation of the renal activity of BNP and suggest that BNP may mediate some of the activity of E‐24.11 inhibitors reported in cardiac failure.
The interaction of the NK1 receptor antagonist CP‐96,345 with L‐type calcium channels and its functional consequences
Authors: Guard S. , Boyle S.J. , Tang K.‐W. , Watling K.J. , McKnight A.T. , Woodruff G.N.
Published: July 2012

We investigated the effects of the non‐peptide NK1 receptor antagonist, CP‐96,345, its inactive enantiomer CP‐96,344, and the racemic mixture (±)‐CP‐96,345, on the binding of [3H]‐nimodipine and [3H]‐diltiazem to L‐type calcium channels in rat cerebral cortex membranes. In isolated peripheral tissues containing tachykinin receptors, the effects of (±)‐CP‐96,345 have been compared with those of diltiazem.

In guinea‐pig trachea, (±)‐CP‐96,345 produced antagonism of responses to the selective NK1 agonists [Sar9, Met(O2)11]SP and substance P‐methyl ester that was apparently competitive in nature (pKB 7.0–7.5), while in guinea‐pig ileum the antagonism was not surmountable.

The reduction of maximum responses by (±)‐CP‐96,345 in the guinea‐pig ileum was not selective; it was obtained with muscarinic agonists and other agents, and was also observed in the portal vein of the rat where NK1 receptors are not present.

The tissue‐specific reduction of maximum responses by (±)‐CP‐96,345 in ileum was reproduced by diltiazem.

(±)‐CP‐96,345 produced a concentration‐dependent enhancement of [3H]‐nimodipine binding to rat cerebral cortex membranes with a maximal stimulation of 186 ± 29% above control (EC50 83.2 nm). Scatchard analysis revealed that (±)‐CP‐96,345 increased the affinity of [3H]‐nimodipine for its binding sites without affecting Bmax (control: KD = 0.32 nm; with 100 nm (±)‐CP‐96,345: KD = 0.074 nm).

CP‐96,345, CP‐96,344, and the racemate all inhibited [3H]‐diltiazem binding in rat cerebral cortex membranes with Ki values of 22.5 nm, 34.5 nm and 29.9 nm respectively; a similar value was obtained for diltiazem itself (33.6 nm). In comparison, CP‐96,345 and (±)‐CP‐96,345 inhibited the binding of [125I]‐Bolton‐Hunter‐conjugated substance P in this tissue with Ki values of 59.6 nm and 82.0 nm respectively, while CP‐96,344 had no measurable affinity (IC50 > 10 μm).

Substance P and a range of ligands selective for NK1, NK2, or NK3 receptors had no significant effect at 10 μm on either [3H]‐diltiazem or [3H]‐nimodipine binding.

The results indicate that in addition to possessing affinity for the NK1 receptor, the non‐peptide antagonist, CP‐96,345, displays high affinity for [3H]‐diltiazem binding sites on L‐type calcium channels. The functional effect that may be observed in integrated models will be a consequence of either property, or be a composite effect of NK1 receptor antagonism and L‐channel blockade.
Effect of trimebutine on voltage‐activated calcium current in rabbit ileal smooth muscle cells
Authors: Nagasaki Masaaki , Komori Seiichi , Ohashi Hidenori
Published: July 2012

The effect of trimebutine on the voltage‐dependent inward Ca2+ current was investigated by the whole‐cell voltage‐clamp technique in single smooth muscle cells from rabbit ileum.

Trimebutine (3–100 μm) reduced the Ca2+ current in a concentration‐dependent manner. The inhibitory effect on the Ca2+ current was also dependent on the holding potential. The Ca2+ current after a low holding potential was inhibited to a greater extent than that after a high membrane potential: the IC50 values were 7 μm and 36 μm at holding potentials of −40 mV and −60 mV, respectively. The Ca2+ current elicited from a holding potential of −80 mV could not be reduced by as much as 50% of the control by trimebutine at concentrations as high as 100 μm.

Trimebutine (30 μm) shifted the voltage‐dependent inactivation curve for the Ca2+ current by 18 mV in the negative direction. The affinity of the drug for Ca2+ channels was calculated to be 36 times higher in the inactivated state than in the closed‐available state.

Blockade of the Ca2+ current by trimebutine, unlike verapamil, was not use‐dependent.

The results suggest that trimebutine inhibits the voltage‐dependent inward Ca2+ current through a preferential binding to Ca2+ channels in the inactivated state in the smooth muscle cell from rabbit ileum. The inhibitory effect of trimebutine on gastrointestinal motility is discussed in the light of the present findings.