bluuebunny/crossref_metadata_2025 huggingface dataset:
The resistance of some rat cerebral arteries to the vasorelaxant effect of cromakalim and other K+ channel openers
Authors: McPherson Grant A. , Stork Andrew P.
Published: July 2012

Cromakalim (0.01–30 μm) and sodium nitroprusside (SNP, 0.01–100 μm) were tested for their ability to relax a number of pre‐contracted small arteries (approximate diameter 200–700 μm at 100 mmHg) from the rat, rabbit and guinea‐pig.

In the rat, SNP (0.01–100 μm) caused near maximal relaxation in all vessels studied including the middle cerebral, anterior cerebellar, basilar, mesenteric and renal arteries. Cromakalim (0.01–30 μm) relaxed pre‐contracted mesenteric and renal arteries but was only a weak relaxant of all the rat cerebral arteries with the exception of the basilar artery. Similar experiments using mesenteric and cerebral vessels from the rabbit and guinea‐pig showed cromakalim could relax pre‐contracted vessels in a concentration‐dependent manner.

Two other K+ channel openers, nicorandil and pinacidil, were also tested for their ability to relax rat cerebral arteries. Nicorandil (0.01–100 μm) was ineffective in the rat anterior cerebellar artery at concentrations up to 100 μm. Pinacidil (0.01–100 μm) caused significant vasorelaxation, although high concentrations were required (> 10 μm) and the response was insensitive to the effects of glibenclamide (3 μm).

Electrophysiological experiments with the rat anterior cerebellar artery showed that cromakalim (up to 30 μm) failed to influence the resting membrane potential of impaled single smooth muscle cells.

The results showed that some rat small cerebral arteries were resistant to the effects of K+ channel openers including cromakalim, pinacidil and nicorandil. This is peculiar to this vascular tree since the same vessels from other species do not exhibit the same behaviour. Such a phenomenon could result from a lack of K+ channels opened by cromakalim in rat cerebral arteries.
Platelet‐activating factor synthesis by peritoneal mast cells and its inhibition by two quinoline‐based compounds
Authors: Hogaboam Cory M. , Donigi‐Gale Donna , Shoupe T. Scott , Bissonnette Elyse Y. , Befus A. Dean , Wallace John L.
Published: July 2012

Peritoneal mast cells from rat were co‐incubated in vitro in a platelet aggregometer cuvette with washed rabbit platelets. In response to stimulation with calcium ionophore (A23187; 1–5 μm), the mast cells released a substance which stimulated the platelets to aggregate. These concentrations of ionophore did not stimulate platelet aggregation in the absence of mast cells, nor affect the responsiveness of the platelets to aggregation induced by thrombin or PAF. Release of a PAF‐like substance was also observed in response to stimulation of the mast cells with antigen.

This pro‐aggregatory activity is attributable to the release of PAF by the mast cells, since the activity could be abolished by preincubating the platelets with a specific PAF receptor antagonist (WEB 2086; 10 μm). Furthermore, the platelet‐aggregating factor co‐migrated with PAF on thin‐layer chromatographs and could be abolished by incubation with phospholipase A2 (20 μg ml−1) or a specific antibody directed against PAF.

The release of PAF by peritoneal mast cells could be inhibited, in a concentration‐dependent manner, by PF‐5901 (IC50 of 3.9μm) or Wy‐50,295 (IC50 of 1.2μm), two structurally similar compounds with inhibitory effects on leukotriene synthesis, as well as leukotriene D4 (LTD4) receptor antagonist properties.

Inhibition of PAF synthesis was not observed when the mast cells were incubated with a structurally unrelated 5‐lipoxygenase inhibitor (A‐64077), a structurally dissimilar inhibitor of 5‐lipoxygenase activating protein (MK‐886) or with a structurally related LTD4 receptor antagonist (MK‐571) which lacks inhibitory effects on leukotriene synthesis, each at concentrations of up to 100 μm.

Neither PF‐5901 nor Wy‐50,295 (1 or 10 μm) significantly affected histamine release or prostaglandin D2 synthesis by peritoneal mast cells in response to calcium ionophore stimulation.

These results demonstrate the ability of a class of quinoline‐based compounds to inhibit PAF synthesis by peritoneal mast cells. This activity does not appear to be related to effects of these compounds on leukotriene synthesis or LTD4 receptors. The ability of these compounds to inhibit PAF synthesis may contribute to their anti‐inflammatory properties.
Binding properties of nine 4‐diphenyl‐acetoxy‐N‐methyl‐piperidine (4‐DAMP) analogues to M1, M2, M3 and putative M4 muscarinic receptor subtypes
Authors: Waelbroeck M. , Camus J. , Tastenoy M. , Christophe J.
Published: July 2012

We compared the binding properties of 4‐diphenyl‐acetoxy‐N‐methyl‐piperidine methiodide (4‐DAMP) and nine analogues of this compound on muscarinic receptors of human neuroblastoma NB‐OK1 cells (M1 subtype), rat heart (M2 subtype), rat pancreas (M3 subtype) and to the putative M4 subtype in striatum.

The requirements for high affinity binding were somewhat different for the four receptor subtypes. In general, the requirements of M3 receptors were more stringent than for M1, M2 or putative M4 receptors.

The abilities of the compounds to discriminate muscarinic receptor subtypes were not correlated with their affinities at any subtype.

The temperature‐dependence of binding of 4‐DAMP analogues to M2 receptors varied with the drug structure. In particular, the increased affinity of the α‐methyl derivative of 4‐DAMP could be ascribed to van der Waals interactions.

The affinities of most 4‐DAMP analogues for M2 and M3 receptors were similar to their pharmacological potencies on atrial and ileum preparations, respectively.

At concentrations above 1 μm, all 4‐DAMP analogues as well as atropine, reduced the [3H]‐N‐methyl scopolamine ([3H]‐NMS) dissociation rate from cardiac muscarinic receptors, with no obvious structure‐activity relationship.
The effects of vesamicol on trains of endplate currents and on focally recorded nerve terminal currents at mammalian neuromuscular junctions
Authors: Pemberton Karen E. , Prior Chris , Marshall Ian G.
Published: July 2012

The effects of vesamicol, an inhibitor of vesicular acetylcholine (ACh) storage, were studied on trains of endplate currents (e.p.cs) in the cut rat hemidiaphragm nerve‐muscle preparation and on trains of focally recorded nerve terminal current waveforms in the mouse triangularis sterni nerve‐muscle preparation.

In the rat, 0.1 and 1 μm (−)‐vesamicol produced an enhancement of the rundown of e.p.c. amplitudes during trains of high frequency (50 Hz) nerve stimulation. However, 1 μm (+)‐vesamicol had no effect on the rundown of e.p.c. amplitudes.

In the mouse, high concentrations of (−)‐vesamicol (10–100 μm) produced a concentration‐ and stimulation‐dependent decrease in the amplitude of the second negative‐going deflection of focally recorded nerve terminal current waveforms.

At 1 mm, (−)‐vesamicol produced a stimulation‐independent decrease in the amplitude of the first negative‐going deflection of the nerve terminal current waveforms, an increase in signal delay and evidence of nerve conduction failure. These all indicate a local anaesthetic‐like block of nodal Na+‐channels.

In contrast to its effects on trains of e.p.cs, the effects of vesamicol on the nerve terminal current waveforms were not stereoselective, the (+)‐isomer being equipotent with the (−)‐isomer.

Low concentrations of the Na+‐channel blocking toxin, tetrodotoxin (15–60 nm), produced similar changes in the focally recorded nerve terminal current waveforms to those seen with vesamicol.

It is concluded that the stereoselective rundown of e.p.c. amplitudes produced by (−)‐vesamicol is due to an effect, either direct or indirect, on ACh mobilization within motor nerve terminals. Furthermore, in mammalian species, the inhibitory effects of vesamicol on nodal Na+‐channels which are seen at high concentrations do not contribute to the principal neuromuscular effects of the compound.
X‐irradiation attenuates relaxant responses in the rabbit ear artery
Authors: Maynard Kenneth I. , Stewart‐Lee Anne L. , Milner Pam , Burnstock Geoffrey
Published: July 2012

The relaxant actions of acetylcholine, substance P and calcitonin gene‐related peptide, and the levels of neuropeptide Y and calcitonin gene‐related peptide were assessed in the rabbit central ear artery 1, 4 and 6 weeks after a single dose of 45 Gy X‐irradiation, a dose similar to that used clinically in intraoperative radiotherapy.

Relaxant responses induced by acetylcholine and substance P (both endothelium‐dependent) and calcitonin gene‐related peptide (endothelium‐independent) were reduced, and endogenous neuropeptide Y and calcitonin gene‐related peptide levels were unaffected after X‐irradiation.

The mechanism(s) by which a single dose of 45 Gy X‐irradiation may selectively damage relaxant, but not direct, contractile responses of the smooth muscle (as we have shown previously) of the rabbit central ear artery are discussed.
Differences in intrinsic efficacy of benzodiazepines are reflected in their concentration‐EEG effect relationship
Authors: Mandema Jaap W. , Kuck Maarten T. , Danhof Meindert
Published: July 2012

The relevance of EEG effect parameters as a measure of the central nervous system effects of benzodiazepines was evaluated. The concentration‐EEG effect relationships of the benzodiazepine agonist midazolam, partial agonist bretazenil, antagonist flumazenil and inverse agonist Ro 19–4603 were quantified and compared with the intrinsic efficacy and affinity of these compounds at the γ‐aminobutyric acid (GABA)‐benzodiazepine receptor complex.

The pharmacokinetics and pharmacodynamics of the compounds were determined after a single intravenous bolus administration of 5 mg kg−1 midazolam, 2.5 mg kg−1 bretazenil, 10 mg kg−1 flumazenil or 2.5 mg kg−1 Ro 19–4603 to male Wistar derived rats. In a separate experiment the distribution between blood, cerebrospinal fluid and brain concentrations of these compounds was determined. A sensitive assay was developed to measure bretazenil and Ro 19–4603 concentrations in small samples of biological fluids.

The benzodiazepine‐induced changes in amplitudes in the 11.5–30 Hz frequency band, as determined by aperiodic analysis, was used as EEG effect measure. Concentration‐EEG effect relationships were derived by a pharmacokinetic‐pharmacodynamic modelling procedure and in the case of midazolam, bretazenil and Ro 19–4603 successfully quantified by the sigmoidal Emax model. Large differences in maximal effect of midazolam (Emax = 73 ± 2 μVs−1), bretazenil (Emax = 19 ± 1 μVs−1) and Ro 19–4603 (Emax = −6.5 ± 0.4 μVs−1) were observed, reflecting their differences in intrinsic efficacy. A close correlation was found between the EC50 values based on free drug concentration and receptor affinity as determined by displacement of [3H]‐flumazenil in a washed brain homogenate at 37°C. In the concentration range of receptor saturation flumazenil did not produce any changes in the EEG effect measure.

The study demonstrated that the change in amplitudes in the 11.5–30 Hz frequency band of the EEG is a relevant measure of the pharmacological effect intensity of benzodiazepines, because it seems to reflect their affinity and intrinsic efficacy at the central GABA‐benzodiazepine receptor complex.
Endogenous nitric oxide and sensory neuropeptides interact in the modulation of the rat gastric microcirculation
Authors: Tepperman B.L. , Whittle B.J.R.
Published: July 2012

The effects of depletion of sensory neuropeptides from primary afferent neurones by capsaicin pretreatment, on the changes in resting gastric mucosal blood flow following administration of inhibitors of nitric oxide biosynthesis have been investigated in the pentobarbitone‐anaesthetized rat.

Bolus administration of the NO‐synthase inhibitor, NG‐nitro‐l‐arginine methyl ester (l‐NAME; 0.8–12.5 mg kg−1 i.v.), induced a dose‐dependent increase in systemic arterial blood pressure (BP) and a reduction in resting mucosal blood flow, as determined by laser Doppler flowmetry.

Concurrent administration of l‐arginine (300 mg kg−1 i.v.) attenuated the effects of l‐NAME (6.25 mg kg−1) on resting mucosal blood flow and BP. The enantiomer, d‐NAME (50 mg kg−1 i.v.), which does not inhibit NO biosynthesis, had no effect on either parameter.

The fall in mucosal blood flow induced by submaximal doses of l‐NAME (0.8–3.2 mg kg−1) was substantially augmented in rats pretreated 2 weeks earlier with capsaicin.

The fall in resting mucosal blood flow induced by the less potent NO‐synthase inhibitor, NG‐monomethyl‐l‐arginine (l‐NMMA; 1.6–25 mg kg−1 i.v.) was likewise significantly augmented in capsaicin‐pretreated rats.

Pretreatment (15 min) with indomethacin (5 mg kg−1 i.v.) did not augment further the microvascular actions of l‐NAME or l‐NMMA in capsaicin‐pretreated rats, suggesting the lack of interaction of endogenous prostanoids with these other mediators in regulating local blood flow. The effects of l‐NAME on BP were not altered by capsaicin and indomethacin administration.

These findings indicate that endogenous sensory neuropeptides and NO can interact in the regulation of the gastric microcirculation.
Imidazoline antagonists of α2‐adrenoceptors increase insulin release in vitro by inhibiting ATP‐sensitive K+ channels in pancreatic β‐cells
Authors: Jonas J.C. , Plant T.D. , Henquin J.C.
Published: July 2012

Islets from normal mice were used to study the mechanisms by which imidazoline antagonists of α2‐adrenoceptors increase insulin release in vitro.

Alinidine, antazoline, phentolamine and tolazoline inhibited 86Rb efflux from islets perifused with a medium containing 3 mm glucose, i.e. under conditions where many adenosine 5′‐triphosphate (ATP)‐sensitive K+ channels are open in the β‐cell membrane. They also reduced the acceleration of 86Rb efflux caused by diazoxide, an opener of ATP‐sensitive K+ channels.

ATP‐sensitive and voltage‐sensitive K+ currents were measured in single β‐cells by the whole‐cell mode of the patch‐clamp technique. Antazoline more markedly inhibited the ATP‐sensitive than the voltage‐sensitive current, an effect previously observed with phentolamine. Alinidine and tolazoline partially decreased the ATP‐sensitive K+ current.

The four imidazolines reversed the inhibition of insulin release caused by diazoxide (through opening of ATP‐sensitive K+ channels) or by clonidine (through activation of α2‐adrenoceptors) in a concentration‐dependent manner. Only the former effect correlated with the ability of each drug to increase control insulin release stimulated by 15 mm glucose alone.

It is concluded that the ability of imidazoline antagonists of α2‐adrenoceptors to increase insulin release in vitro can be ascribed to their blockade of ATP‐sensitive K+ channels in β‐cells rather than to their interaction with the adrenoceptor.
Different patterns of protein kinase C redistribution mediated by α1‐adrenoceptor stimulation and phorbol ester in rat isolated left ventricular papillary muscle
Authors: Otani Hitomi , Hara Mitsuyoshi , Xun‐Ting Zeng , Omori Kyoko , Inagaki Chiyoko
Published: July 2012

In rat left ventricular papillary muscle, phenylephrine, an α1‐adrenoceptor agonist, had a staurosporine‐sensitive positive inotropic effect and increased the particulate‐associated protein kinase C (PKC) activity without significant changes in total PKC activity or in cytosolic Ca2+/phospholipid‐independent kinase (PKI) activity.

A PKC stimulant, phorbol 12,13‐dibutyrate (PDBu), decreased contractility and slightly increased PKC activity in the particulate fractions, with a marked decrease and increase in total PKC and PKI activities, respectively.

The PDBu‐induced negative inotropic response was attenuated by two protease inhibitors, leupeptine and a microbial peptide isolated from Aspergillus japonicus (E‐64), which are known to inhibit the conversion of particulate‐associated PKC to PKI.

Such differences in the patterns of PKC redistribution, i.e. marked increases in particulate PKC and cytosolic PKI activities caused by phenylephrine and PDBu, respectively, may account for the opposite inotropic effects of PKC stimulation by an α1‐agonist and a phorbol ester.
Nucleotide‐dependent activation of KATP channels by diazoxide in CRI‐G1 insulin‐secreting cells
Authors: Kozlowski R.Z. , Ashford M.L.J.
Published: July 2012

Patch‐clamp recording techniques were used, to examine the effects of diazoxide on KATP currents in CRI‐G1 insulin‐secreting cells in the presence of non‐hydrolysable nucleotides.

In the presence of non‐ or slowly‐hydrolyzed ATP analogues, bathing the intracellular aspect of cell‐free membrane patches diazoxide inhibited KATP channel activity.

Under whole‐cell recording conditions, with various non‐hydrolysable nucleotides present intracellularly (after dialysis), diazoxide induced KATP current activation. The largest activation occurred with Mg‐adenylyl‐(β,γ‐methylene) diphosphate (Mg‐AMP‐PCP) present in the dialysing solution. This activation was diazoxide‐ and nucleotide‐concentration‐dependent.

In the absence of Mg2+, or in the presence of manganese (Mn2+) ions intracellularly, diazoxide did not induce KATP current activation, regardless of the species of nucleotide present in the pipette.

Intracellularly applied trypsin prevented the activation of KATP currents by diazoxide in the presence of Mg‐AMP‐PCP, an effect reversed by co‐application of intracellular polymethylsulphonyl fluoride with the trypsin.

6 The application, by dialysis, of a CRI‐G1 cell lysate, with negligible Mg‐ATP, resulted in a substantial activation of the KATP current by diazoxide.

7 It is concluded that diazoxide can activate KATP channel currents by two separate pathways, one requiring a phosphorylation process, the other the presence of an intracellular protein coupled with a Mg‐purine nucleotide.
The role of complement, platelet‐activating factor and leukotriene B4 in a reversed passive Arthus reaction
Authors: Rossi A.G. , Norman K.E. , Donigi‐Gale D. , Shoupe T.S. , Edwards R. , Williams T.J.
Published: July 2012

The mechanisms underlying oedema formation induced in a reversed passive Arthus (RPA) reaction and, for comparison, in response to zymosan in rabbit skin were investigated.

Oedema formation at skin sites was quantified by the accumulation of intravenously‐injected 125I‐labelled human serum albumin.

Recombinant soluble complement receptor type 1 (sCR1), administered locally in rabbit skin, suppressed oedema formation induced in the RPA reaction and by zymosan.

The platelet‐activating factor (PAF) antagonists, WEB 2086 and PF10040 administered locally, inhibited oedema formation induced in the RPA reaction and by PAF but not by zymosan.

A locally administered leukotriene B4 (LTB4) antagonist, LY‐255283, inhibited oedema formation induced by LTB4 but did not inhibit oedema responses to PAF, zymosan or the RPA reaction.

6 The results demonstrate a role for complement in oedema formation in both the RPA reaction and in response to zymosan. An important contribution by PAF is indicated in the RPA reaction but not in response to zymosan whereas no evidence was obtained to suggest a role for LTB4 in either inflammatory response.
Albumin inhibits platelet‐activating factor (PAF)‐induced responses in platelets and macrophages: implications for the biologically active form of PAF
Authors: Grigoriadis George , Stewart Alastair G.
Published: July 2012

Platelet‐activating factor (PAF) binds with high affinity to albumin leading Clay et al. (1990) to suggest that the active form of PAF is the albumin‐PAF complex.

In the present study the proposal that albumin‐bound, rather than monomeric PAF, is the active form of PAF at PAF receptors was critically evaluated by examining the effect of albumin on the potency of PAF in isolated platelets and macrophages.

Bovine serum albumin inhibited concentration‐dependently PAF‐induced responses in platelets and macrophages. The most probable explanation of this finding is that BSA reduced the concentration of free PAF.

Thus, we conclude that free PAF, rather than the albumin‐PAF complex is the active form. Consequently, local concentrations of albumin will influence profoundly the potency of endogenously released PAF. Moreover, estimates of the affinity of PAF for PAF receptors made in buffers containing BSA, underestimate the true affinity of PAF for its receptors by approximately 3 orders of magnitude.
Reversal by cysteine of the cadmium‐induced block of skeletal neuromuscular transmission in vitro
Authors: Braga M.F.M. , Rowan E.G.
Published: July 2012

Neuromuscular transmission in isolated nerve‐muscle preparations was blocked by exposure to Cd2+ for less than 30 min or more than 2 h. The abilities of cysteine, Ca2+ or 3,4‐diaminopyridine (3,4‐DAP) to reverse the blockade induced by Cd2+ were studied.

On the mouse hemidiaphragm preparation, exposure to Cd2+ (10 μm) for 10 to 20 min induced a blockade which was easily reversed by increasing the extracellular Ca2+ concentration (5–10 mm) or by 3,4‐DAP (100 μm). Exposure to Cd2+ (3–10 μm) for over 2 h led to a blockade which was not reversed by Ca2+ (5–15 mm) or 3,4‐DAP (100 μm). Cysteine (1 mm) was able to reverse completely the blockade induced by both brief and prolonged exposures to Cd2+.

In chick biventer cervicis preparations, Cd2+ (100 μm) decreased the twitch height of indirectly stimulated preparations without affecting responses to exogenously applied acetylcholine, carbachol or KCl. Cysteine (1–3 mm) had no appreciable effect on twitch responses to indirect stimulation or to exogenously applied agonists but fully reversed the blockade induced by Cd2+ (100 μm).

In mouse triangularis sterni preparations, Cd2+ (1–30 μm) depressed the evoked quantal release of acetylcholine. Concentrations of Cd2+ which completely blocked endplate potentials (e.p.ps) were without significant effect on miniature endplate potential (m.e.p.p.) amplitude and frequency or time constant of decay. Cysteine (1–10 mm) alone had no effect on e.p.ps or m.e.p.ps, but completely reversed the blockade induced by Cd2+.

Extracellular recording of perineural waveforms from triangularis sterni preparations revealed that Cd2+ was able to block the long‐lasting positive component that is sensitive to Ca2+ channel blockers and the delayed negative deflection that is related to the Ca2+‐activated K+ current (IK,Ca) seen in the presence of 3,4‐DAP. Cysteine by itself had no effect on any component of the perineural waveform, but promptly reversed the blockade induced by Cd2+.

6 In addition to the competitive blocking action of Cd2+ at the prejunctional Ca2+ channels, long exposure to Cd2+ leads to a blockade that is not competitive. This probably involves binding of Cd2+ at an extracellular thiol site on, or close to, voltage‐operated Ca2+ channels.
The effects of calcitonin gene‐related peptide on formation of intra‐articular oedema by inflammatory mediators
Authors: Cruwys S.C. , Kidd B.L. , Mapp P.I. , Walsh D.A. , Blake D.R.
Published: July 2012

The temporal and quantitative effects of inflammatory mediators on plasma extravasation in the rat knee were investigated by use of a perfusion technique.

Intra‐articular perfusion of substance P (SP), bradykinin or histamine over a 5 min test period produced rapid‐onset and prolonged plasma extravasation in a dose‐dependent fashion. The rank order of potency was bradykinin > SP > histamine.

Calcitonin gene‐related peptide (CGRP) did not induce plasma extravasation but enhanced substance P‐induced plasma extravasation in a dose‐dependent fashion. A 5 min co‐perfusion of the two agents produced short‐term enhancement lasting 10 min while continuous co‐perfusion produced enhancement for the duration of the perfusion.

A 5 min perfusion of CGRP enhanced plasma extravasation when co‐perfused with bradykinin but not histamine. However, when CGRP and histamine were continuously co‐perfused over a 20 min test period, an enhanced response was apparent.

The results indicate that intra‐articular perfusion of CGRP enhances synovial plasma extravasation induced by agents that increase vascular permeability, but suggest that the response is not uniform and is critically dependent on the duration of perfusion within the joint.
Pharmacological characterization of adenosine A1 and A2 receptors in the bladder: evidence for a modulatory adenosine tone regulating non‐adrenergic non‐cholinergic neurotransmission
Authors: Acevedo Carmen Gloria , Contreras Enrique , Escalona Juan , Lewin Jorge , Huidobro‐Toro J. Pablo
Published: July 2012

The nerve‐evoked contractions elicited by transmural electrical stimulation of mouse urinary bladders superfused in modified Krebs Ringer buffer containing 1 μm atropine plus 3.4 μm guanethidine were inhibited by adenosine (ADO) and related nucleoside analogues with the following rank order of potency: R‐phenylisopropyladenosine (R‐PIA) > cyclohexyladenosine (CHA) > 5′N‐ethylcarboxamido adenosine (NECA) > ADO > S‐phenylisopropyladenosine (S‐PIA). Tissue preincubation with 8‐phenyltheophylline (8‐PT) displaced to the right, in a parallel fashion, the NECA concentration‐response curve.

The contractions elicited by application of exogenous adenosine 5′‐triphosphate (ATP) were also inhibited by ADO and related structural analogues. The rank order of potency to reduce the motor response to ATP was: NECA > 2‐chloroadenosine (CADO) > R‐PIA > ADO > CHA > S‐PIA.

The ADO‐induced ATP antagonism was of a non‐competitive nature and was not specific. Tissue incubation with 10 μm NECA not only reduced the motor responses elicited by ATP, but also 5‐hydroxytryptamine, acetylcholine and prostaglandin F2α. The action of NECA was antagonized following tissue preincubation with 8‐PT. The inhibitory action of NECA was not mimicked by 10 μm CHA.

The maximal bladder ATP contractile response was significantly increased by tissue preincubation with 5–30 μm 8‐PT.

The 0.15 Hz evoked muscular twitch was significantly increased by 8‐PT while dipyridamole consistently reduced the magnitude of the twitch response. These results are consonant with the hypothesis that an endogenous ADO tone modulates the bladder neurotransmission.

6 A working model is proposed suggesting the presence of ADO‐A1 and A2 receptors in the mouse urinary bladder. The A1 receptor subpopulation is probably of presynaptic origin whereas the smooth muscle membranes contain a population of the A2 receptor subtype.
Effects of cromakalim on the membrane potassium permeability of frog skeletal muscle in vitro
Authors: Benton D.C. , Haylett D.G.
Published: July 2012

The effects of the potassium channel opener, cromakalim, and its active enantiomer, lemakalim, have been investigated in frog skeletal muscle.

Cromakalim (30–300 μm) increased 86Rb efflux from muscles loaded with the isotope, hyperpolarized the fibres and reduced membrane resistance.

These effects were inhibited by the sulphonylureas, glibenclamide and tolbutamide. The IC50 for glibenclamide inhibition of 86Rb efflux was ca. 8 nm.

Phentolamine (300 μm) (which blocks responses to cromakalim in smooth muscle and inhibits ATP‐sensitive K+ channels in pancreatic β‐cells) had no effect on the reduction in membrane resistance caused by 100 μm lemakalim.

Diazoxide (600 μm) had no effect on 86Rb efflux.

6 The similarities of the K+ channel activated by cromakalim in frog skeletal muscle to the channel acted on in smooth muscle and to the ATP‐sensitive K+ channel of β‐cells are discussed.
Pharmacokinetic‐EEG effect relationship of midazolam in aging BN/BiRij rats
Authors: Hovinga The late Suzanne , Stijnen Annemiek M. , Langemeijer Mariska W.E. , Mandema Jaap W. , van Bezooijen Cornelis F.A. , Danhof Meindert
Published: July 2012

The purpose of the present investigations was to determine the influence of increasing age on the pharmacokinetics and pharmacodynamics of midazolam in male BN/BiRij rats as an animal model of aging.

Midazolam was administered intravenously at a dose of 2.5 mg kg−1 and its pharmacokinetics were determined on the basis of plasma concentrations as measured by high performance liquid chromatography (h.p.l.c.). Pharmacodynamics were studied using the midazolam‐induced changes in the electroencephalogram (EEG) as a measure of the pharmacological effect. Results were evaluated on the basis of stimultaneous pharmacokinetic‐pharmacodynamic modelling. In an attempt to differentiate between the effects of aging and of concurrent disease, an extensive clinical biochemical/pathological examination was conducted in individual rats by an independent pathologist.

The pharmacokinetics of midazolam were best characterized on the basis of a two exponential model. In the 4‐month‐old rats the values of the clearance, volume of distribution and elimination half‐life were 104 ± 13 ml min−1 kg−1 (mean ± s.e.mean), 3.4 ± 0.71 kg−1 and 30 ± 3 min, respectively. With increasing age, no changes in the pharmacokinetics of midazolam were observed.

The pharmacodynamics of midazolam were determined on the basis of the sigmoidal Emax model. In the 4‐month‐old rats the values of the parameters relative maximum effect, midazolam concentration at half maximum effect and Hill factor were 106 ± 10%, 50 ± 6 μg l−1 and 1.6 ± 0.3, respectively. In the group as a whole no significant changes in the pharmacodynamic parameters of midazolam were observed. However, when diseased animals were excluded from the evaluation, a tendency towards a decrease in the midazolam concentration at half maximum effect to 25 ± 14 μg l−1 was observed in the 36‐month‐old rats.

These findings suggest, that increasing age is associated with a tendency towards an increased brain sensitivity to midazolam, which is reflected in a parallel shift of the concentration vs. EEG effect relationship towards lower concentrations. However, it appears that factors other than age also contribute to interindividual variability in pharmacodynamics, considering the substantial interindividual variability within certain age groups.
Effects of inhibition of the l‐arginine/nitric oxide pathway in the rat lower urinary tract in vivo and in vitro
Authors: Persson K. , Igawa Y. , Mattiasson A. , Andersson K.‐E.
Published: July 2012

The present study was performed to investigate how blockade of the l‐arginine/nitric oxide (NO) pathway influences the function of the lower urinary tract in vivo, as studied by cystometry in conscious rats and in vitro, in isolated muscle preparations from the rat detrusor and urethra.

l‐NG‐nitro arginine methyl ester (l‐NAME), 10 and 20 mg kg−1, administered intra‐arterially, decreased micturition volume and bladder capacity, and increased spontaneous bladder contractions. d‐NAME (20 mg kg−1) had no effect. No changes in the urodynamic parameters were recorded if l‐NAME (20 mg kg−1) was administered in combination with l‐arginine (200 mg kg−1).

Cystometries performed after intra‐arterial administration of sodium nitroprusside (SNP) (3 mg kg−1) and 3‐morpholino‐sydnonimin hydrochloride (SIN‐1, 2 mg kg−1) showed a decrease in bladder capacity, micturition volume and threshold pressure. SIN‐1, but not SNP, induced spontaneous bladder contractions.

Isolated precontracted urethral preparations responded to electrical stimulation with a frequency‐dependent tetrodotoxin‐sensitive relaxation. l‐NAME (10−4 m), but not d‐NAME, reduced the maximal relaxation to 31 ± 8% (n = 8) of the response prior to drug administration. The inhibition induced by l‐NAME was completely reversed by l‐arginine (10−3 m). SNP (10−8−10−4 m), SIN‐1 (10−6−3 × 10−4 m) and NO (10−5−10−3 m; present in acidified solution of NaNO2), caused relaxation (93–100%) of urethral preparations. l‐NAME did not affect these relaxations.

Detrusor strips contracted by carbachol or K+ showed contractions in response to electrical stimulation, even when pretreated with α,β‐methylene ATP and/or atropine. Small relaxations (14–41%) of detrusor strips were evoked by SNP (10−6−10−4 m), SIN‐1 (10−5−3 × 10−4 m) and NO (10−5−10−3 m). Electrically (20 Hz) induced contractions of the detrusor muscle were unaffected by addition of l‐NAME (10−6−10−4 m) or l‐arginine (10−3 m).

6 The present results suggest that the l‐arginine/NO pathway is of functional importance for the bladder outlet region, but that its role in the detrusor is questionable. They also suggest that the site of action of l‐NAME for inducing bladder hyperactivity in the rat is the outlet region rather than the detrusor muscle.
Determination of α1‐adrenoceptor subtype selectivity by [3H]‐prazosin displacement studies in guinea‐pig cerebral cortex and rat spleen membranes
Authors: Veenstra D.M.J. , van Buuren K.J.H. , Nijkamp F.P.
Published: July 2012

[3H]‐prazosin homogeneously labels α1‐adrenoceptors in guinea‐pig cerebral cortex and rat spleen membranes with dissociation constants of 1.28 and 1.49 × 10−10 m respectively.

Phentolamine and WB 4101 displacement studies show that guinea‐pig cerebral cortex contains 30% α1A‐ and 70% α1B‐adrenoceptor subtypes, whereas rat spleen contains a virtually homogeneous α1B‐adrenoceptor subtype population. The α1‐adrenoceptor population of rat thoracic aorta is predominantly of the α1A‐adrenoceptor subtype, and in guinea‐pig thoracic aorta it is mainly of the α1B‐adrenoceptor subtype.

Half of the compounds displacing [3H]‐prazosin bound to guinea‐pig cerebral cortex membranes display α1A‐adrenoceptor selectivity. Among these compounds, WB 4101 and methoxamine are most selective, displaying selectivity ratios of ∼38 and ∼26 respectively.

The affinity constants of the non‐selective compounds for the α1‐adrenoceptors in guinea‐pig cerebral cortex membranes correlate well with the affinity constants obtained for α1B‐adrenoceptors in rat spleen membranes. The affinities of selective compounds for the α1B‐adrenoceptor subtype in guinea‐pig cerebral cortex correlate very well with their affinity for α1B‐adrenoceptor in the rat spleen homogenate. Both regression lines coincide with the line of identity. The affinity constants of selective compounds for the α1A‐adrenoceptors in guinea‐pig cerebral cortex only apparently correlate with the affinity for either the α1B‐adrenoceptors in guinea‐pig cerebral cortex or in the rat spleen. Regression analyses indicate a straight line relationship (r2 > 0.9) between pKα1A and pKα1B but the regression lines deviate from the line of identity.
Nitric oxide mediates the inhibition by interleukin‐1β of pentagastrin‐stimulated rat gastric acid secretion
Authors: Esplugues Juan V. , Barrachina M. Dolores , Calatayud Sara , Pique Josep M. , Whittle Brendan J.R.
Published: July 2012

Bolus injection of interleukin‐1β (2 μg kg−1, i.v.) inhibited acid secretion induced by intravenous infusion of pentagastrin (8 μg kg−1 h−1) in the continuously perfused stomach of the anaesthetized rat. Administration of interleukin‐1β did not modify mean systemic arterial blood pressure. Pretreatment with NG‐nitro‐l‐arginine methyl ester (l‐NAME, 2 −10 mg kg−1, i.v.), but not dexamethasone (5 mg kg−1, s.c. twice over 16 h), restored the acid secretory responses to pentagastrin. The actions of l‐NAME were reversed by the prior administration of l‐arginine (100 mg kg−1, i.v.), but not by its enantiomer d‐arginine (100 mg kg−1, i.v.). l‐NAME (5 mg kg−1, i.v.) increased blood pressure but this was not the mechanism by which interleukin‐induced acid inhibition was prevented, since similar systemic pressor responses induced by phenylephrine (10 μg kg−1 min−1, i.v.), had no such effect. These findings suggest that interleukin‐induced inhibition of acid responses to pentagastrin involves synthesis of NO from l‐arginine.
Functional characterization of a 5‐HT3 receptor which modulates the release of 5‐HT in the guinea‐pig brain
Authors: Blier Pierre , Bouchard Claude
Published: July 2012

The aims of the present study were to confirm the modulation by 5‐HT3 receptors of the electrically evoked release of tritium from slices preloaded with [3H]‐5‐HT of guinea‐pig frontal cortex, hippocampus and hypothalamus, and to assess their functional role in 5‐HT release.

The selective 5‐HT3 agonist, 2‐methyl‐5‐HT, introduced 8 min before the electrical stimulation, enhanced in a concentration‐dependent manner the evoked release of [3H]‐5‐HT in the three brain regions studied. The 5‐HT3 agonists, phenylbiguanide and m‐chlorophenyl‐biguanide, did not enhance the release of tritium in frontal cortex and hypothalamus slices.

In hypothalamus slices, this response was lost when 2‐methyl‐5‐HT was introduced 20 min before the stimulation, thus indicating that these 5‐HT3 receptors desensitize rapidly. When 2‐methyl‐5‐HT was added 20‐min before the first stimulation period to desensitize the 5‐HT3 receptors, removed for 24 min, and then re‐introduced 8 min before the second stimulation period, the enhancing effect of 2‐methyl‐5‐HT was restored, thus indicating that these 5‐HT3 receptors can rapidly regain normal sensitivity.

The enhancing effect of 2‐methyl‐5‐HT was attenuated by the 5‐HT3 receptor antagonists m‐chloro‐phenylpiperazine = quipazine = ondansetron ≥ ICS 205–930 = BRL 24924 > MDL 72222 = zacopride.

The 5‐HT reuptake blocker, paroxetine, enhanced the electrically evoked release of tritium when introduced 8 min before stimulation; this effect of paroxetine was blocked by ICS 205–930, thus indicating that these 5‐HT3 receptors can be activated by endogenous 5‐HT.

In the absence of electrical stimulation, 2‐methyl‐5‐HT (10 μm) produced a marked enhancement of the basal release of [3H]‐5‐HT which was calcium‐dependent and blocked by S‐zacopride but not by paroxetine.

The enhancing effect of 2‐methyl‐5‐HT was dependent both on the frequency of stimulation, as indicated by the attenuated effect of 120 stimulations delivered at 1 Hz instead of 5 Hz, and on the duration of the stimulation, as indicated by the more pronounced effect of pulses delivered at 5 Hz for 24 s instead of 72 s or 120 s.
Glucocorticoid — and non‐glucocorticoid induction of lipocortins (annexins) 1 and 2 in rat peritoneal leucocytes in vivo
Authors: Peers Susan H. , Smillie Frazer , Elderfield Amber J. , Flower Roderick J.
Published: July 2012

We have studied the occurrence, distribution and disposition of lipocortins (annexins) 1, 2 and 5 in mixed peritoneal leucocytes obtained from rats in which glucocorticoid levels were altered by adrenalectomy, administration of the glucocorticoid antagonist, RU486, or by injection of dexamethasone or hydrocortisone, as well as from rats in which the peritoneal cells were elicited by inflammatory stimuli.

In cells obtained from untreated rats with an intact adrenal cortex, lipocortins 1, 2 and 5 were readily detectable: the majority of each of the proteins was apparently located intracellularly with much smaller amounts in the membrane. Lipocortin 1 and to a lesser extent lipocortin 5 were also seen in a Ca2+‐dependent association with the external plasma membrane. Following administration of RU486 (2 × 20 mg kg−1) the amounts of lipocortin 1 and 2 in cells were greatly reduced. Conversely, injection of hydrocortisone (1 mg kg−1) or dexamethasone (0.08 mg kg−1) caused an increase in the amount of lipocortin 1 and 2 in peritoneal cells within 30 min. Lipocortin 5 was unchanged by any manipulation of glucocorticoid levels.

Lipocortins 1 and 2 were elevated in both intracellular and membrane‐associated fractions of macrophages elicited by intraperitoneal injection in inflammogens. This phenomenon also occurred in adrenalectomized animals.

Our data indicate that glucocorticoids control the synthesis of some members of the lipocortin family in rat mixed peritoneal cells but also suggest the existence of a separate system for controlling the generation of this protein. The significance of these observations is considered in relation to the mechanism of glucocorticoid hormone action on eicosanoid production.
Activation of the Na+/K+‐pump in rat peritoneal mast cells following histamine release: a possible role in cell recovery
Authors: Knudsen T. , Ferjan I. , Johansen T.
Published: July 2012

The activity of the Na+/K+‐pump in rat peritoneal mast cells was measured at various time intervals after induction of cellular histamine release by compound 48/80 or by the antigen‐antibody reaction. The Na+/K+‐pump activity was assessed as the ouabain‐sensitive potassium uptake of the cells using 86Rb+ as a tracer for potassium (K+(86Rb+)‐uptake).

Stimulation of the cells with compound 48/80 induced a time and concentration dependent increase of the Na+/K+‐pump activity. The pump activity was maximal 2 min after stimulation of the cells. Then, the activity gradually decreased and reached a level not significantly different from the controls after 2 h of incubation.

When the cells were stimulated by the antigen‐antibody reaction, there was also a rapid (within 5 min) stimulation of the Na+/K+‐pump. In contrast to the stimulation with compound 48/80, the pump activity returned to the control level after 60 min of incubation with antigen.

The ouabain‐resistant potassium uptake of the cells was increased after stimulation of the cells, regardless of the secretagogue used. This probably reflects the increased surface area of the cells present after the histamine release.

On the basis of the present results, we suggest a role for the Na+/K+‐pump in the recovery process of the mast cell following histamine release.
Influences of the endothelium and hypoxia on α1‐ and α2‐adrenoceptor‐mediated responses in the rabbit isolated pulmonary artery
Authors: MacLean Margaret R. , McCulloch K.M. , McGrath J.C.
Published: July 2012

The effects of the inhibitor of nitric oxide synthase, Nω‐nitro‐l‐arginine methylester (l‐NAME, 10−4 m), mechanical disruption of the endothelium and hypoxia on contraction to noradrenaline (α1‐ and α2‐adrenoceptor agonist), phenylephrine (α1‐adrenoceptor agonist) and UK 14304 (α2‐adrenoceptor agonist) were compared in the rabbit isolated pulmonary artery. The effects of the selective antagonists rauwolscine (10−6 m, α2‐adrenoceptors) and prazosin (10−7 m, α1‐adrenoceptors) on the contractions to noradrenaline before and after exposure to l‐NAME were also assessed.

Noradrenaline, phenylephrine and UK 14304 all produced concentration‐dependent increases in vascular tone. The responses to noradrenaline were sensitive to both rauwolscine and prazosin (effect of prazosin >> rauwolscine). l‐NAME increased the potency of both noradrenaline and UK 14304, and also the maximum tension achieved. It had no effect on the responses to phenylephrine. After l‐NAME, contractions to noradrenaline, although still sensitivie to both rauwolscine and prazosin, were now more sensitive to inhibition by rauwolscine.

Endothelium removal augmented the potency and maximum contractions to noradrenaline, phenylephrine and UK 14304.

Hypoxia decreased both the potency of phenylephrine and its maximum contractile response, but increased the maximum response to noradrenaline without effecting responses to UK 14304.

In conclusion, in the rabbit pulmonary artery, augmentation of contractile responses to noradrenaline by l‐NAME involves a potentiation of α2‐adrenoceptor‐mediated contraction probably through an effect on the synthesis of endothelium‐derived nitric oxide. Experimental hypoxia had differential effects on all three agonists and did not mimic the effect of nitric oxide synthase inhibition.
Lack of effect of sumatriptan and UK‐14,304 on capsaicin‐induced relaxation of guinea‐pig isolated basilar artery
Authors: O'Shaughnessy C.T. , Waldron G.J. , Connor H.E.
Published: July 2012

The objectives of this study were to assess the effects of sensory neuropeptide antagonists and presynaptically acting receptor agonists on capsaicin‐induced relaxations of guinea‐pig isolated basilar artery (GPBA).

Capsaicin, human α‐calcitonin gene‐related peptide (CGRP) and substance P (SP) caused concentration‐related relaxations of GPBA which had been pre‐contracted with prostaglandin F2α (PGF2α). Responses to capsaicin were not modified by the peptidase inhibitors, phosphoramidon (1 μm) and bestatin (100 μm).

The relaxant responses to capsaicin were blocked in a selective manner by ruthenium red (3 μm) and by the CGRP antagonist, CGRP8_37 (1 μm). CGRP8_37 also selectively inhibited the relaxant effects of CGRP.

The selective NK1 receptor antagonist, GR82334 (10 μm), inhibited SP‐induced relaxations but had little effect on capsaicin‐induced relaxations.

The 5‐HT1 receptor agonist, sumatriptan, produced small contractions of GPBA under conditions of resting tone. In the presence of PGF2α, sumatriptan had no further contractile effect. Sumatriptan (0.3 and 3 μm) did not modify capsaicin‐induced relaxations of GPBA.

The α2‐adrenoceptor agonist, UK‐14,304 (0.1 μm), had no effect on basal or PGF2α‐induced tone. UK‐14,304 did not modify capsaicin‐induced relaxations.

These results suggest that capsaicin causes relaxation of GPBA via a release of CGRP. This process is amenable to blockade by CGRP8–37 and ruthenium red, but not to modulation by either sumatriptan or UK‐14,304.
Effects of hyperkalaemia on the depression of maximum rate of depolarization by class I antiarrhythmic agents in guinea‐pig myocardium
Authors: Wyse Kenneth R. , Ye Victor , Campbell Terence J.
Published: July 2012

Standard microeletrode methods were used to record intracellular action potentials from strips of guinea‐pig right ventricular myocardium superfused with either standard physiological saline ([K+] = 5.6 mm) or the same solution modified to contain [K+] = 11.2 mm.

The effects on action potential parameters of three therapeutic concentrations of mexiletine, quinidine and disopyramide were studied under both conditions at four different drive rates (interstimulus intervals = 2400, 1200, 600 and 300 ms).

Hyperkalaemia in the absence of drugs produced reductions in resting potential (−86.7 ± 2.5 mV to −71.8 ± 3.7 mV; n = 30; P < 0.001), maximum rate of depolarization (300 ± 46.5 Vs−1 to 205.6 ± 37.6 Vs−1; P < 0.0001), and action potential duration (205 ± 26 ms to 188 ± 32 ms; P < 0.05).

All three drugs produced increased depression of maximum rate of depolarization in hyperkalaemia compared to control conditions, but at all three concentrations this enhancement of effect was greater for mexiletine than for quinidine, with disopyramide exhibiting intermediate behaviour.

Mexiletine behaved very similarly to therapeutic concentrations of lignocaine as described in previous reports from this laboratory.

Quinidine behaved very similarly to Class Ic agents.

It is concluded that mexiletine demonstrated significantly greater selectivity for depolarized myocardium than quinidine and that this may have implications in terms of proarrhythmic potential.

Disopyramide exhibited intermediate selectivity for depolarized myocardium between mexiletine and quinidine.