bluuebunny/crossref_metadata_2025 huggingface dataset:
Alterations of responsiveness to adrenoceptor agonists and calcium of non‐infarcted hypertrophied muscles from rats with chronic myocardial infarction
Authors: Itaya Takehiko , Hashimoto Hisakuni , Uematsu Toshihiko , Nakashima Mitsuyoshi
Published: July 2012

The responsiveness of hypertrophied right ventricular muscle from rats with chronic myocardial infarction (MI) was examined. Myocardial infarction was produced by ligating the left coronary artery. The positive inotropic effects of α‐ and β‐adrenoceptor agonists and calcium on the isolated non‐ischaemic muscles were determined at one and four weeks after ligation, and were compared with those in sham‐operated (SO) rats.

The contractile force of electrically‐driven right ventricular papillary muscles was measured isometrically. We also determined the change of beating rate of the right atrium in response to a β‐adrenoceptor agonist.

Basal contractile force increased at four weeks after ligation.

The pEC50 values of the α1‐adrenoceptor agonist, methoxamine, and calcium increased at four weeks after ligation, but the pEC50 values of the β‐adrenoceptor agonist, dobutamine did not change.

Maximal contractile force did not change with these agonists at either one and four weeks after ligation.

Tissues from rats four weeks after MI exhibited slight increases in the Bmax of α‐ but not β‐receptors, without any changes of affinity.

The increases in the sensitivity to an α1‐adrenoceptor agonist and calcium may be compensatory mechanisms of non‐infarcted ventricular tissue which has undergone hypertrophy in chronic MI.
Somatostatin decreases the calcium inward current in guinea‐pig atria
Authors: Ohmura Tsuyoshi , Nishio Matomo , Kigoshi Shigeru , Muramatsu Ikunobu
Published: July 2012

The effects of somatostatin on mechanical and electrophysiological responses were studied in guinea‐pig atrial muscle preparations and single cells.

Somatostatin (≥ 10−8 m) decreased the twitch contraction in a concentration‐dependent manner in electrically driven left atria and spontaneously beating right atria. However, the beating rate was not affected.

The negative inotropic effect of somatostatin was transient. Desensitization to this agent developed slowly during continuous exposure to the peptide.

In single atrial cells, somatostatin significantly shortened the action potential duration, but the resting potential and action potential amplitude were not affected.

Under whole cell voltage‐clamp conditions, somatostatin decreased the calcium inward current without affecting the sodium and potassium currents.

These results suggest that somatostatin selectively acts on the calcium channel of guinea‐pig atrial cells to reduce the calcium inward current, which in turn gives rise to the negative inotropic effect.
The β1 and β2‐adrenoceptor affinity and β1‐blocking potency of S‐ and R‐metoprolol
Authors: Wahlund Göran , Nerme Viveca , Abrahamsson Tommy , Sjöquist Per‐Ove
Published: July 2012

The β‐adrenoceptor affinity and blocking potency of the two enantiomers and the racemate of metoprolol were investigated in vitro, by use of a receptor‐binding technique, and in vivo in the anaesthetized cat.

The enantiomeric purity of the S‐ and R‐form was: >99.2% and >99.9%, respectively.

The β1‐ and β2‐adrenoceptor affinity (–log equilibrium dissociation constant) of the enantiomers was determined from competition binding experiments (radioligand: [125I]‐(S)‐pindolol) performed in membranes prepared from the guinea‐pig left ventricular free wall (predominantly β1) and soleus muscle (β2). The β1‐adrenoceptor affinity was (means ± s.d.): 7.73 ± 0.10 and 5.00 ± 0.06 for the S‐ and R‐form of metoprolol, respectively. The corresponding values for β2‐adrenoceptors were 6.28 ± 0.06 (S) and 4.52 ± 0.09 (R). Thus, the difference in affinity for the two enantiomers was greater on β1 (about 500) than on β2‐adrenoceptors (about 50). The β1‐adrenoceptor selectivity of the S‐form (about 30) was similar to that of the racemic metoprolol, while the R‐form was almost non‐selective (3 fold β1‐selective).

In the anaesthetized cat, the (–log) intravenous doses (μmol kg−1) of S‐ and R‐metoprolol causing a 50% reduction (ED50) in the heart rate response to sympathetic nerve stimulation were determined. The doses inducing a 25% depression (DD25) of the basal myocardial contractility were also estimated. For the two enantiomers, the β1‐blocking potency (‐log ED50) was 7.04 ± 0.16 (S) and 4.65 ± 0.16 (R). A significant cardiodepressive effect was observed at high doses (‐log DD25): 4.18 ± 0.20 (S) and 4.08 ± 0.10 (R).

It is concluded that the binding of metoprolol to β1‐adrenoceptors has a stricter steric requirement than that for the binding of this β‐blocker to β2‐adrenoceptors. Furthermore, the non‐specific cardiodepressive effect of metoprolol was observed at equally high doses for the two enantiomers.
Effects of chain‐length and unsaturation on affinity and selectivity at muscarinic receptors
Authors: Barlow R.B. , Holdup D.W. , Harris Georgina , Veale M.A. , Williams Alex
Published: July 2012

Lengthening the chain in diphenylacetylcholine decreases affinity for muscarinic cholinoceptors in guinea‐pig ileum. Diphenylacetoxypropyldimethylamine and its quaternary trimethylammonium salt are roughly equiactive: the dimethylamine and the piperidine have some selectivity for ileum compared with atria, but are not as active nor as selective as 4‐diphenylacetoxy‐N‐methylpiperidine (4‐DAMP) methobromide (MeBr). With the weaker diphenylacetoxybutyl compounds the base is more active than the quaternary salt.

The diphenylacetoxybutyl‐, cis‐butenyl and trans‐butenyl compounds have similar affinities. The quaternary salts are less active than the tertiary bases, but they are less selective than the butynyl analogues studied in earlier work.

1,1‐Diphenyl‐1‐hydroxy‐2,4‐hexadiynyl dimethylamine and its trimethylammonium salt are inactive in concentrations below 100 μm, as are the (+)‐camphor‐sulphonyl ester of 4‐hydroxy‐N‐methyl piperidine and its methiodide. The (±)‐phenylcyclopentylacetyl ester of 4‐hydroxy‐N‐methylpiperidine methobromide is more active than its cyclohexyl analogue and than 4‐DAMP MeBr but it is less selective than 4‐DAMP MeBr.

The high selectivity of p‐fluoro‐hexahydrosila‐diphenidol is confirmed but this compound has relatively low affinity (for ileum log K = 7.8).

The results indicate steric constraints to binding at muscarinic receptors which could be used to check molecular modelling of the receptor based on its known amino acid sequence. The group binding the charged nitrogen is probably at the mouth of a cavity which can accommodate two large rings (as in 4‐DAMP MeBr) but with a depth less than about 7 Å so that the rod‐like hexadiynes cannot fit. Differences between types of receptor may only involve small changes in geometry secondary to differences in amino acids not directly involved in binding and the production of selectivity depends upon finding substituents which interfere with binding more at one type of receptor than at another.
Subclassification of β‐adrenoceptors responsible for steroidogenesis in primary cultures of bovine adrenocortical zona fasciculata/reticularis cells
Authors: Lightly E.R.T. , Walker S.W. , Bird I.M. , Williams B.C.
Published: July 2012

Forty eight hour primary cultures of purified bovine adrenocortical zona fasciculata/reticularis cells secreted hydrocortisone in response to stimulation with β‐adrenoceptor agonists. The observed order of potency was isoprenaline > noradrenaline > dobutamine > salbutamol > BRL37344.

Salbutamol acted as a partial agonist on these cells hence suggesting the presence of a β1‐adrenoceptor.

Schild analysis of the hydrocortisone response to isoprenaline showed that the selective β1‐antagonist practolol and the selective β2‐antagonist ICI118,551 gave pA2 values of 6.85 and 7.17, respectively. These values were in close agreement with corresponding pA2 values previously obtained for the β1‐adrenoceptor.

We conclude that β1‐adrenoceptors are responsible for mediating catecholamine‐stimulated hydrocortisone secretion from primary cultures of bovine zona fasciculata/reticularis cells.
The effects of anticholinesterases on the latencies of action potentials in mouse skeletal muscles
Authors: Kelly S.S. , Ferry C.B. , Bamforth J.P.
Published: July 2012

The purpose of this investigation was to determine the long‐term effects of a single dose of persistent anticholinesterases on muscle action potentials evoked by nerve stimulation.

Action potentials (APs), elicited by stimulation of the phrenic nerve, were recorded intracellularly in muscle fibres of mouse diaphragm. The time between stimulus and AP was measured and the variability of this latency was calculated during trains of APs. At the beginning of trains of APs there was an increase in latency, and this delay was also measured.

Within 3 h of subcutaneous injection, a single dose (500 nmol kg−1) of the anticholinesterase, ecothiopate produced about 90% reduction in the acetylcholinesterase activity of homogenates of mouse diaphragm muscle, but five days after injection, this activity was not different from values in untreated animals. The initial delay of APs and the variability of latencies were increased four fold and two fold respectively, remained at these maxima from the 1st to the 5th day after ecothiopate, and returned to the values in untreated animals between 15 and 27 days after ecothiopate.

These effects of ecothiopate on AP latency were dose‐dependent and were also seen in extensor digitorum longus and soleus muscles.

Other anticholinesterases used were BOS (pinacolyl S‐(2‐trimethylaminoethyl)methylphosphonothioate), a quaternary compound, and diisopropyl fluorophosphate, a tertiary compound, which had effects similar to those of ecothiopate; the greater duration of the effects of this compound may be related to the greater duration of reduction in cholinesterase activity.

Ecothiopate had no effect on the delay or variability of latencies of endplate potentials which were recorded in cut‐fibre preparations 5 days later.

It is concluded that the effects of ecothiopate on the latencies of indirectly‐evoked muscle APs are postjunctional, may not be related to the degree of reduction in cholinesterase activity at the time of recording, and are not directly linked to necrosis.
Effects of neuropeptide Y and calcitonin gene‐related peptide on sheep coronary artery rings under oxygenated, hypoxic and simulated myocardial ischaemic conditions
Authors: Kwan Y.W. , Wadsworth R.M. , Kane K.A.
Published: July 2012

The effects of calcitonin gene‐related peptide (CGRP) and neuropeptide Y (NPY) were examined on sheep circumflex (2–2.5 mm o.d.) coronary artery rings, with and without endothelium, under oxygenated, hypoxic and simulated ischaemic conditions. The interaction between the vasoconstrictor effects of NPY and the thromboxane mimetic, U46619, was also studied.

Ischaemia was simulated by modification of the composition of the physiological salt solution by increasing potassium and H+, including lactate and reducing glucose and Po2.

Hypoxia alone and simulated ischaemia increased the maximum vasodilatation produced by CGRP. CGRP (30 nm) abolished and markedly reduced the contraction that was induced by hypoxia and simulated ischaemia respectively.

Hypoxia increased and simulated ischaemia reduced the contractile response to NPY in endothelium intact rings. When the endothelium was removed, NPY caused a contraction under ischaemic conditions only. The hypoxic and ischaemic‐induced contractions were augmented by NPY (30 nm).

In the rings containing endothelium, NPY enhanced the contraction caused by U46619 during hypoxia only. In endothelium‐denuded preparations, NPY increased or partially restored the contraction caused by U46619.

These results show that the responsiveness of coronary artery rings isolated from sheep to either CGRP or NPY is modified by hypoxia or simulated myocardial ischaemia.
Effects of torbafylline, pentoxifylline and buflomedil on vascularisation and fibre type of rat skeletal muscles subjected to limited blood supply
Authors: Hudlická Olga , Price Susan
Published: July 2012

Blood flow (measured by radio‐labelled microspheres), fibre composition and capillary/fibre ratio were estimated in rat fast twitch skeletal muscles (tibialis anterior and extensor digitorum longus) five weeks after unilateral ligation of the common iliac artery in animals treated with either saline, torbafylline, pentoxifylline or buflomedil.

The resting blood flow was lower in muscles with limited blood supply than in their contralateral controls; this difference became statistically insignificant after treatment. Capillary/fibre ratio was similar in all muscles with either intact or limited blood supply and did not change after administration of any of the drugs.

The percentage of glycolytic fibres was not changed by ligation, but it decreased significantly in animals treated with torbafylline. This may improve performance in muscles with limited blood supply.
Investigation of the selectivity of α, β‐methylene ATP in inhibiting vascular responses of the rat in vivo and in vitro
Authors: Dalziel H.H. , Gray G.A. , Drummond R.M. , Furman B.L. , Sneddon P.
Published: July 2012

The proposal that α,β‐methylene adenosine 5′‐triphosphate (mATP) inhibits pressor responses in the pithed rat by selective desensitization of P2x‐purinoceptors was examined by comparing the selectivity of its inhibitory effect on vascular responses in vitro and in vivo.

In isolated ring preparations of rat femoral and tail artery, which had been denuded of endothelium, mATP markedly reduced the contractile response to exogenous ATP but had no effect on the response of the arteries to exogenous noradrenaline (NA).

In the pithed rat a substantial proportion of the pressor response to sympathetic nerve stimulation was resistant to α‐adrenoceptor blockade, suggesting a non‐adrenergic component to the sympathetic vasoconstriction.

In the pithed rat, repeated administration of desensitizing doses of mATP attenuated the pressor response to sympathetic nerve stimulation by approximately 80%, suggesting that a component of the sympathetic vasoconstriction is mediated by ATP acting on vascular P2x‐purinoceptors. However, the same mATP treatment also attenuated, to a similar degree, the pressor responses to intravenous NA, angiotensin II and vasopressin, indicating that the desensitization procedure was non‐selective.

These results demonstrate that while mATP can be used to desensitize selectively P2x‐purinoceptors in vitro, its attenuation of the sympathetic nerve‐mediated pressor response in vivo is non‐selective.
Rapid tolerance to the hypotensive effects of glyceryl trinitrate in the rat: prevention by N‐acetyl‐l‐ but not N‐acetyl‐d‐cysteine
Authors: Newman Christopher M. , Warren John B. , Taylor Graham W. , Boobis Alan R. , Davies Donald S.
Published: July 2012

A new model of tolerance to the hypotensive effect of organic nitrates has been developed in the rat.

The fall in mean arterial pressure (MAP) in response to bolus doses of sodium nitroprusside (NP) (4 μg kg−1) and glyceryl trinitrate (GTN) (10 μg kg−1) was recorded both before and after a 60 min infusion of either 0.9% saline, NP (20 μg kg−1 min−1) or GTN (40 μg kg−1 min−1).

The hypotensive effects of NP or GTN were unchanged following saline infusion, but were reduced in both cases by approximately 40% following the infusion of NP.

Infusion of GTN for 60 min virtually abolished the hypotensive effect of a GTN bolus (i.e. nitrate tolerance), whilst the effect of a NP bolus was reduced only to a similar extent (30%) as after an infusion of NP. This latter effect is attributed to a degree of non‐specific cross‐tolerance between GTN and NP.

Co‐treatment of a group of rats with N‐acetyl‐l‐cysteine (l‐NAC) prevented the development of nitrate tolerance, confirming the role of thiols in this phenomenon, whereas N‐acetyl‐d‐cysteine (d‐NAC) did not.

The stereospecificity in the effect of NAC in preventing this specific tolerance to GTN suggests that the interaction between GTN and NAC and/or cysteine involves an enzyme‐dependent step.

NAC was unable to prevent the non‐specific cross‐tolerance to NP which followed infusion of GTN, suggesting that the mechanism does not directly involve NAC and/or cysteine.
Evidence for noradrenergic‐purinergic cotransmission in the hepatic artery of the rabbit
Authors: Brizzolara Antonia L. , Burnstock Geoffrey
Published: July 2012

Transmural electrical field stimulation produced a transient contraction of the isolated hepatic artery of the rabbit that was frequency‐dependent up to 64 Hz. A contraction was rarely evoked at a stimulation frequency of less than 8 Hz and never at 4 Hz or less. All contractions were abolished in the presence of tetrodotoxin.

Neurogenic contractions were partially inhibited by prazosin. After desensitization of the P2X‐purinoceptor with α,β‐methylene ATP, contractions in response to electrical stimulation were significantly reduced at all frequencies tested (4–64 Hz). In most cases, contractions were abolished by a combination of both drugs.

In vessels treated with 6‐hydroxydopamine, no nerve‐mediated contractile responses were observed.

In arteries from reserpine‐treated rabbits, nerve stimulation evoked contractions that were resistant to prazosin. After desentization of the P2X‐purinoceptor with α,β‐methylene ATP, no neurogenic contractile response remained.

The tissue contracted to exogenously applied noradrenaline and α,β‐methylene ATP. There was an increase in sensitivity to noradrenaline in 6‐hydroxydopamine‐treated vessels compared with control vessels, but no difference in potency to α,β‐methylene ATP was detected. The potency of noradrenaline and α,β‐methylene ATP was not significantly affected by reserpine treatment.

In control tissues, fluorescence histochemistry demonstrated the presence of noradrenergic nerve fibres. Noradrenaline‐containing nerves were not observed in 6‐hydroxydopamine‐treated or reserpine‐treated vessels.

It is concluded that noradrenaline and ATP are cotransmitters in the sympathetic nerves supplying the hepatic artery of the rabbit. In contrast to other vessels, the hepatic artery requires a relatively high frequency of stimulation to evoke contractions and the purinergic component is not frequency‐dependent. The significance of this finding in terms of the physiological demands of blood flow to the liver are discussed.
Characterization of cholecystokinin octapeptide‐stimulated endogenous dopamine release from rat nucleus accumbens in vitro
Authors: Marshall F.H. , Barnes S. , Pinnock R.D. , Hughes J.
Published: July 2012

The effect of cholecystokinin sulphated octapeptide (CCK8S) on endogenous dopamine release was examined in rat striatal and nucleus accumbens slices, by high performance liquid chromatography (h.p.l.c.) with electrochemical detection.

CCK8S was shown to increase dopamine release from slices of nucleus accumbens but not striatum in a dose‐dependent manner between 0.1 and 10 μm.

Pentagastrin was without effect on dopamine release at doses up to 10 μm.

The dopamine release produced in the presence of CCK8S was abolished by preincubation of the slice with 1.0 or 10.0 nm L‐364,718 (the CCKA‐selective antagonist) while 1 μm L‐365,260 (the CCKB‐selective antagonist) had no action.

These results suggest that the CCK8S‐evoked release of dopamine from the nucleus accumbens is mediated by a CCKA‐receptor.
Tolbutamide excites rat glucoreceptive ventromedial hypothallamic neurones by indirect inhibition of ATP‐K+ channels
Authors: Ashford M.L.J. , Boden P.R. , Treherne J.M.
Published: July 2012

The sulphonylureas, tolbutamide (0.1–10 mm) and glibenclamide (0.1–100 μm) were shown not to inhibit ATP‐K+ channel currents when applied to inside‐out membrane patches excised from rat cultured cerebral cortex or freshly‐dispersed ventromedial hypothalmic nucleus (VMHN) neurones.

Saturable binding sites for [3H]‐glibenclamide, with similar affinity constants are present in rat cerebral cortex and hypothalamic membranes. The density of binding sites was lower in the hypothalamus than cortex.

Intracellular recordings from glucoreceptive VMHN neurones in hypothalamic slices were obtained. In the absence of glucose, tolbutamide (0.1 mm) depolarized these cells, increased membrane resistance and elicited action potentials.

Tolbutamide (0.1 mm) inhibited ATP‐K+ channel currents and induced action current activity in cell‐attached recordings from glucoreceptive VMHN neurones.

Glibenclamide (10–500 nm) had no effect per se on glucoreceptive VMHN neurones but did antagonize the actions of tolbutamide.

It is concluded that the hypothalamic (and perhaps cortical) sulphonylurea receptors are not directly coupled to ATP‐K+ channels.
Spinal effects of four injectable anaesthetics on nociceptive reflexes in rats: a comparison of electrophysiological and behavioural measurements
Authors: Hartell N.A. , Headley P.M.
Published: July 2012

To assess the direct spinal contributions to the depression of reflexes caused by general anaesthetics, the intravenous potency of four injectable anaesthetics has been compared in two preparations: in decerebrate, spinalised rats, using a novel preparation requiring little surgical intervention, and in intact rats with chronically implanted i.v. cannulae.

Methohexitone (1–8 mg kg−1 i.v.), alphaxalone/alphadolone (0.5–8 mg kg−1 i.v.), alpha‐chloralose (20–80 mg kg−1 i.v.) and ketamine (0.5–16 mg kg−1 i.v.) all produced a dose‐dependent depression of single motor unit activity evoked by controlled noxious mechanical stimuli in decerebrate, spinalised animals.

The sedative and motor effects brought about by equivalent doses to those used in the electrophysiological experiments were assessed in intact rats. Methohexitone, alphaxalone/alphadolone and alpha‐chloralose all caused similar levels of behavioural sedation at the doses that caused depression of spinal reflexes. Ketamine required relatively much higher doses to cause sedation.

To determine whether background anaesthesia modulated the potency with which these compounds affected spinal reflex activity, depressant effects in decerebrate, unanaesthetized rats were compared with those in animals maintained under anaesthesia with either alpha‐chloralose or the steroid mixture of alphaxalone/alphadolone. The presence of either of these two agents as maintenance anaesthetics did not influence the effectiveness with which other compounds depressed nociceptive responses. However, additional doses of the maintenance anaesthetics were less effective than the same doses tested in decerebrate animals.

All the anaesthetics tested produced a significant depression of spinal reflex responses to noxious stimuli at doses well below those required for anaesthesia. Whilst the presence of maintenance anaesthetics appears not to distort pharmacological tests of other agents, there may nonetheless be a biasing of the samples of cells recorded.
Characterization of histamine H3‐receptors in guinea‐pig ileum with H3‐selective ligands
Authors: Hew R.W.S. , Hodgkinson C.R. , Hill S.J.
Published: July 2012

The effect of the selective histamine H3‐receptor agonist R‐(α)‐methylhistamine has been investigated on the contractile responses of the longitudinal smooth muscle of guinea‐pig ileum elicited by electrical field stimulation of acetylcholine release from myenteric nerve endings.

R‐(α)‐methylhistamine produced a concentration‐dependent (EC50 = 1.4 ± 0.2 × 10−8 m) inhibition of the response to electrical field stimulation which was insensitive to inhibition by mepyramine (1 μm) and tiotidine(2.4 μm).

This response to R‐(α)‐methylhistamine could be inhibited in a competitive fashion by a range of H3‐receptor antagonists including thioperamide (KB = 1.1 nm), impromidine (KB = 65 nm), nor‐burimamide (KB = 380 nm) and SKF 91486 (KB = 34 nm). Burimamide was also a potent inhibitor of this response but the Schild slope obtained (1.3) was significantly greater than unity.

The estimated KB values were all within a factor of three of those values reported for the histamine H3‐receptor mediating inhibition of histamine release in rat cerebral cortex.

These data suggest that the histamine receptor mediating inhibition of cholinergic neurotransmission by R‐(α)‐methylhistamine in guinea‐pig ileum is the same as the H3‐receptor present in rat cerebral cortex.
Evidence that the agonist action of dynorphin A(1–8) in the guinea‐pig myenteric‐plexus may be mediated partly through conversion to [Leu5]enkephalin
Authors: Dixon Diane M. , Traynor J.R.
Published: July 2012

The agonist action of the opioid peptide dynorphin A(1–8) on the myenteric plexus‐longitudinal muscle of the guinea‐pig ileum has been characterized.

The endogenous opioid peptide dynorphin A(1–8) was rapidly degraded by slices of myenteric plexus‐longitudinal muscle of the guinea‐pig ileum.

A product of the degradation was the δ‐receptor preferring [Leu5]enkephalin. Levels of [Leu5]enkephalin were markedly increased in the presence of the peptidase inhibitors bestatin, thiorphan and captopril.

In the myenteric plexus dynorphin A(1–8) acted as a κ‐receptor agonist. In the presence of bestatin, thiorphan and captopril a μ‐receptor agonist effect was observed. This μ‐agonist action was lost in the presence of N‐[1‐(RS)‐carboxy‐2‐phenylethyl]Ala‐Ala‐Phe‐p‐aminobenzoate, an inhibitor of the endopeptidase enzyme EC 3.4.24.15.

The results suggest that formation of [Leu5]enkephalin from dynorphin A(1–8) may be an important conversion process. The enzyme responsible may be the Zn2+‐metalloendopeptidase, EC 3.4.24.15.
Actions of capsaicin on peripheral nociceptors of the neonatal rat spinal cord‐tail in vitro: dependence of extracellular ions and independence of second messengers
Authors: Dray A. , Bettaney J. , Forster P.
Published: July 2012

We have tested the hypothesis that capsaicin‐induced activation, desensitization and impairment of peripheral nociceptor function is mediated by separate mechanisms. This was investigated by use of an in vitro preparation of the neonatal rat spinal cord with the functionally attached tail in which the cord and tail were separately superfused with physiological solution. Activation of peripheral fibres by noxious (capsaicin, bradykinin, 5‐hydroxytryptamine, heat, pinch) and innocuous (light brush) stimuli was assessed by recording the depolarization of a spinal ventral root (L3‐L5).

Brief administration of capsaicin produced dose‐related depolarizing responses (EC50 = 280 nm). These responses could be reproduced for many hours following the repeated application of capsaicin at a submaximal concentration. Prolonged application of 0.5–2.0 μm capsaicin induced a selective desensitization to subsequent brief administrations of capsaicin. Prolonged administration at 20–50 μm produced an additional non‐selective reduction in responses to all noxious stimuli without changing innocuous brush responses.

Removal of extracellular calcium from the tail superfusate did not reduce the response to capsaicin or prevent capsaicin‐induced desensitization. However, high concentrations of capsaicin no longer induced a non‐specific reduction of responses to other noxious stimuli. The response to a brief administration of capsaicin was unaffected by calcium channel blocking drugs including nifedipine, cadmium or ω‐conotoxin. On the other hand high extracellular calcium increased the incidence of the non‐selective reduction of responses to all noxious stimuli produced by high concentrations of capsaicin.

Replacement of extracellular sodium with choline blocked peripheral nerve conduction but did not prevent the desensitization produced by capsaicin. In addition, high concentrations of capsaicin were less effective in reducing the responsiveness to other noxious stimuli.

Neither capsaicin‐evoked responses nor capsaicin‐induced desensitization were affected by the administration of forskolin, dibutyryl cyclic AMP, nitroprusside, dibutyryl cyclic GMP, β‐12,13 phorbol dibutyrate, trifluoperazine, indomethacin, staurosporine or mepacrine, in the tail superfusate.

These data suggest that capsaicin‐induced activation, desensitization and impairment of peripheral nociceptors may be separable phenomena. Extracellular calcium is not required for capsaicin‐induced activation or desensitization but calcium as well as sodium are important for capsaicin‐induced impairment of nociceptive responses. Desensitization may occur independently of peripheral fibre activation and cannot be attributed to a central mechanism. Finally neither capsaicin‐induced activation nor desensitization require the participation of a second messenger.
Selective antagonism of calcium channel activators by fluspirilene
Authors: Kenny Barry A. , Fraser Stuart , Kilpatrick Andrew T. , Spedding Michael
Published: July 2012

Fluspirilene has been claimed to bind to a high affinity site in the calcium channel in skeletal muscle. We have investigated its calcium‐antagonistic effects in smooth muscle and affinity for the channel in radioligand binding assays.

Fluspirilene was weakly active as an antagonist of Ca2+‐induced contractions in K+‐depolarized taenia preparations from the guinea‐pig caecum, with threshold antagonism starting from concentrations of 30 nm. Nitrendipine, nicardipine and nimodipine were very potent antagonists in this model (threshold antagonism, > 1 nm).

In contrast, fluspirilene (10–1000 nm) was a potent non‐competitive antagonist of the effects of Bay K 8644 (1–3000 nm) on Ca2+‐induced contractions and, at 10 nm, selectively antagonised the effects of Bay K 8644, abolished the Ca2+‐channel activator effects of CGP 28392, without changing the calcium antagonist effects of nitrendipine, or modifying the sensitivity of the tissues to Ca2+. In contrast, the dihydropyridines were more effective as antagonists of Ca2+ than of Bay K 8644. Fluspirilene therefore selectively antagonised the effects of dihydropyridine Ca2+ channel activators without affecting the antagonist potency.

In radioligand binding experiments, fluspirilene was a potent displacer of [3H]‐PN‐200‐110 binding to rat cerebral cortical membranes (EC50 30 nm), albeit with a low Hill slope (0.66), and was more potent than other lipophilic diphenylalkylamines such as flunarizine and lidoflazine. Fluspirilene interacted non‐competitively with [3H]‐PN‐200‐110 and increased dissociation of the radioligand.
Co‐release of PHI and VIP in dog stomach by peripheral and central vagal stimulation
Authors: Ohta Toshio , Ito Shigeo , Ohga Akira
Published: July 2012

The purpose of this investigation was to examine the outputs of peptide histidine isoleucine (PHI) and vasoactive intestinal peptide (VIP) from the gastric corpus in response to stimulation of the peripheral (PVS) and central (CVS) ends of the vagus nerve and to compare the effects of PHI on gastric motility and blood flow with those of VIP in atropine‐treated dogs.

PVS and CVS caused parallel increases in gastric venous plasma concentrations of VIP and PHI. The molar ratios of the peptides (VIP/PHI) appearing in the gastric venous plasma were about 1.5 for PVS at 10 Hz, 0.65 for PVS at 40 Hz and about 0.7 for CVS at 10 Hz.

The molar ratio of peptide concentration extracted from the gastric corpus was about 1.5 in the muscle layer and 2.7 in the mucosal layer.

Intra‐arterially‐injected PHI was about 5 fold and 50 fold less effective in producing gastric relaxation and vasodilatation, respectively, than VIP.

These results indicate that PHI is co‐released with VIP by peripheral vagal stimulation and by initiation of the vago‐vagal reflex, and that PHI seems to have an important role in the regulation of gastric motility but not gastric blood flow in the dog.
Interactions of palmitoyl carnitine with the endothelium in rat aorta
Authors: Dainty I.A. , Bigaud M. , McGrath J.C. , Spedding M.
Published: July 2012

Palmitoyl carnitine (10–1000 μm) resembled Bay K 8644 (10–1000 nm) in that it directly contracted rat aortic rings which were partially depolarized with K+ (12 mm). However, the effects of Bay K 8644 were reduced in the presence of endothelium whereas the presence of the endothelium hardly affected the palmitoyl carnitine‐induced contractions, which occurred at high concentrations (< 10 μm).

Lower concentrations of palmitoyl carnitine (0.3–30 μm; EC50 1.1 μm), but not Bay K 8644, carnitine or palmitic acid, antagonized the relaxant effects of acetylcholine in rat aorta. The antagonism was specific for endothelium‐dependent relaxations, in that the relaxations to ATP and the calcium ionophore A23187 were also non‐competitively antagonized, albeit at slightly higher concentrations, whereas the direct relaxant effects of sodium nitroprusside were unaffected. Palmitoyl carnitine therefore antagonizes the effects or the release of endothelial‐derived relaxant factor (EDRF). The inhibitory effects were reversed on prolonged washout, indicating that the effects were not due to destruction of the endothelial cells.

In superfusion experiments, palmitoyl carnitine inhibited the release of EDRF from rat aorta but did not affect the responsiveness to exogenous EDRF, indicating a site of action at the endothelial cell. In superfusion experiments, palmitoyl carnitine, and lysophosphatidyl choline, caused direct relaxations of the aorta, indicating EDRF release, prior to inhibition of release evoked by receptor stimulation. These substances may modulate vascular responsiveness under certain conditions.
Responses of rat substantia nigra compacta neurones to L‐DOPA
Authors: Mercuri Nicola B. , Calabresi Paolo , Bernardi Giorgio
Published: July 2012

The electrophysiological actions of l‐DOPA were studied on substantia nigra dopamine‐containing neurones by use of intracellular recordings, current and voltage clamp, in vitro.

l‐DOPA (3–300 μm), applied by superfusion, decreased the spontaneous firing activity of the neurones, hyperpolarized the membrane potential and produced an outward current.

These effects of l‐DOPA were graded and were antagonized by sulpiride, a D2‐receptor antagonist.

The l‐DOPA activated membrane hyperpolarization persisted in slices exposed to tetrodotoxin while it was markedly reduced or abolished in solutions with no calcium plus cobalt (2 mm).

In slices treated with carbidopa, an inhibitor of the aromatic amino acid decarboxylase enzyme, the actions of l‐DOPA were greatly reduced.

We propose that l‐DOPA inhibits the firing of substantia nigra zona compacta neurones by being converted to dopamine which is then released by these cells.
The actions of adenosine 5′‐triphosphate on guinea‐pig intracardiac neurones in culture
Authors: Allen T.G.J. , Burnstock G.
Published: July 2012

The actions of adenosine 5′‐triphosphate (ATP) and related nucleotides and nucleosides on the membrane ion conductances of m and AH type intracardiac neurones cultured from ganglia within the atria and interatrial septum of newborn guinea‐pig heart were studied with intracellular current‐ and voltage‐clamp techniques.

Approximately 74% (120 out of 161) of AH type cells and 41% (5 out of 12) m cells responded to direct application of ATP (500 μm) onto their soma.

In 41% of m and 43% of AH type cells, focal application of ATP (500 μm) evoked rapid depolarization with an increase in conductance which frequently elicited action potential discharge. The underlying inward current had a null potential of −11.2 mV and was reduced in solutions containing low extracellular sodium and calcium but unaffected by reduced chloride‐containing solutions.

In a further 31% of AH type cells, ATP evoked a multi‐component response consisting of an initial depolarization followed by a hyperpolarization and a slow prolonged depolarization. The current underlying the initial depolarization resulted from an increase in conductance and had a null potential of −19.1 mV. The current was increased in low chloride‐containing solutions and was only slightly reduced in low sodium‐ and calcium‐containing solutions. The subsequent hyperpolarization and outward current resulted from an increase in membrane conductance and had a null potential of −88.5 mV, which was close to the potassium equilibrium potential in these cells. The slow depolarization and inward current was not associated with change in membrane conductance.

In less than 2% of AH cells, ATP evoked a second type of slow depolarization. This was associated with a fall in conductance and had a null potential of −90.7 mV.

In 40% of AH cells, adenosine (10–100 μ m) inhibited the calcium‐sensitive potassium current responsible for the after‐hyperpolarization. The action of adenosine was antagonized by the P1‐purinoceptor antagonist 8‐phenyltheophylline (1–10 μm).

The potency order of agonists for all of the ATP‐evoked responses, except the slow depolarization associated with a fall in conductance was ATP > ADP with AMP and adenosine being ineffective.

Responses to ATP were only weakly desensitized by α,β‐methylene ATP (3 × 10−6 m) and the potency order of analogues was 2‐methylthio ATP ≤ ATP > α,β‐methylene ATP, indicating the involvement of receptors similar to P2Y purinoceptors.
Refractoriness of the gravid rat uterus to tocolytic and biochemical effects of atrial natriuretic peptide
Authors: Potvin W. , Varma D.R.
Published: July 2012

Effects of atrial natriuretic peptide (ANP) on tension development, particulate guanylate cyclase activity and guanosine 3′:5′‐cyclic monophosphate (cyclic GMP) concentrations of uteri from oestrogen‐treated, progesterone‐treated, ovariectomized and pregnant rats were determined in vitro.

ANP inhibited the tension development by myometrial tissues from oestrogen‐treated virgin rats and the sterile horn of 10 to 14 day pregnant rats but not of the uterus from pregnant and progesterone‐treated rats.

Inhibition of cyclo‐oxygenase and lipoxygenase activities did not restore the tocolytic activity of ANP on gravid uterus. ANP exerted a tocolytic effect on nongravid uterus submaximally stimulated by prostaglandin F2α (PGF2α), oxytocin, vasopressin, angiotensin II or 5‐hydryoxtryptamine (5‐HT).

Ovariectomy decreased the tocolytic effects of ANP, which could be restored by oestrogen treatment.

The refractoriness to the tocolytic effect of ANP in pregnant rats was not accompanied by a decrease in its relaxant effects on isolated aortic strips.

Tocolytic effects of isoprenaline, isobutylmethyl xanthine and hydroxylamine were not influenced by pregnancy or progesterone treatment. Up to a concentration of 3 mm, sodium nitroprusside did not affect myometrial tension development.

Pregnancy and progesterone treatment markedly inhibited ANP‐induced increases in myometrial particulate guanylate cyclase activity and cyclic GMP concentrations but did not influence the effects of ANP on aortic cyclic GMP concentrations.

It is concluded that exposure of the myometrium to circulating and placentally‐produced progesterone is responsible for the pregnancy‐induced decrease in the effects of ANP on myometrial particulate guanylate cyclase activity and cyclic GMP concentrations and in turn on myometrial tension development.
Cyclic AMP counteracts mitogen‐induced inositol phosphate generation and increases in intracellular Ca2+ concentrations in human lymphocytes
Authors: van Tits Lambertus J.H. , Michel Martin C. , Motulsky Harvey J. , Maisel Alan S. , Brodde Otto‐Erich
Published: July 2012

The effects of increases in intracellular adenosine 3′:5′‐cyclic monophosphate (cyclic AMP) on mitogen‐induced generation of inositol phosphates and increases in intracellular Ca2+ concentration were investigated in human peripheral blood mononuclear leukocytes (MNL).

The mitogens concanavalin A (Con A), pokeweed mitogen (PWM) and phytohaemagglutinin (PHA) concentration‐dependently stimulated generation of inositol phosphates. Catecholamines inhibited this process with an order of potency: isoprenaline > adrenaline > noradrenaline indicating involvement of β2‐adrenoceptors. This order of potency was also consistent with the catecholamine potencies for stimulating the generation of cyclic AMP.

In addition to catecholamines, the cyclic AMP formation‐stimulating agents prostaglandin E1 (PGE1) and forskolin concentration‐dependently inhibited mitogen‐induced inositol phosphate generation, too. Moreover, the inhibitory effect of isoprenaline was potentiated by co‐incubation with the phosphodiesterase inhibitor isobutylmethylxanthine demonstrating that these inhibitory effects were mediated by cyclic AMP.

Con A and PHA concentration‐dependently increased the intracellular Ca2+ concentration in human MNL (assessed by the fluorescent indicator dye Fura‐2). This increase was almost completely blocked by chelation of extracellular Ca2+, demonstrating influx rather than mobilization from intracellular stores.

The elevation of intracellular Ca2+ was not blocked by pretreatment with pertussis toxin, 100 ng ml−1, for 16 h.

Isoprenaline, PGE1, and forskolin, however, inhibited the mitogen‐stimulated elevation of intracellular Ca2+. This inhibition was enhanced by the phosphodiesterase inhibitors isobutylmethylxanthine and Ro 20–1724, demonstrating mediation by cyclic AMP.

We conclude that catecholamines and other cyclic AMP increasing agents can inhibit mitogen‐stimulated generation of inositol phosphates and elevation of intracellular Ca2+ in resting human MNL. Since generation of inositol phosphates and increases in intracellular Ca2+ are very early events in activation of MNL, attenuation of these events might well contribute to the inhibitory effect of cyclic AMP on MNL function.
Alkaline buffers release EDRF from bovine cultured aortic endothelial cells
Authors: Mitchell Jane A. , de Nucci Gilberto , Warner Timothy D. , Vane John R.
Published: July 2012

Release of endothelium‐derived relaxing factor (EDRF) and prostacyclin (PGI2) from bovine cultured aortic endothelial cells (EC) was measured by bioassay and radioimmunoassay, respectively.

Bradykinin (BK, 3–30 pmol), adenosine diphosphate (ADP, 2–6 nmol) or the sodium ionophore monensin (40–100 nmol) injected through a column of EC released EDRF. l‐Arginine free base (FB; 10–20 μmol) or d‐arginine FB (10–20 μmol) injected through the column of EC released similar amounts of EDRF and also caused an increase in pH of the Krebs solution perfusing the EC from 7.5–8.0 to 8.6–9.5. Sodium carbonate (Na2CO3) an alkaline buffer which caused the same changes in the pH of the Krebs solution also induced the same release of EDRF. The hydrochloride salts of l‐ or d‐arginine did not cause either release of EDRF when injected through the column of EC or increases in the pH of the Krebs solution.

Inhibitors of either diacylglycerol lipase (RHC 80267) or kinase (R59022) inhibited the release of EDRF induced by BK or ADP but potentiated the release induced by l‐arginine FB, monensin (40–100 nmol) or alkaline buffer (Na2CO3). R59022 and RHC 80267 infused through the EC increased the basal release of EDRF.

When calcium chloride was omitted from the Krebs solution the release of EDRF induced by alkaline buffer (Na2CO3; pH 8.6–9.5) or l‐arginine FB (10–20 μmol) was selectively inhibited when compared to that induced by BK (3–30 pmol) or ADP (2–6 nmol). This inhibition was reversed when calcium (2.5 mm) was restored.

NG‐monomethyl‐l‐arginine (NMMA; 30 μm) inhibited release of EDRF induced by BK (10–30 pmol) or alkaline buffers (Na2CO3 or d‐arginine FB; pH 8.6–9.5). This inhibition was partially reversed by l‐but not d‐arginine FB or HCl (30–100 μm).

Prostacyclin was released when BK (10 pmol), ADP (2 nmol) or arachidonic acid (30 nmol) were injected through the column of EC. However, monensin (40 nmol) or alkaline buffers (pH 8.6–9.5) did not release detectable amounts of PGI2 as measured by radioimmunoassay for 6‐oxo‐prostaglandin F1α.

Thus alkalinisation of the external bathing solution can release EDRF from cultured EC by a mechanism which does not involve receptor activation and which depends on the presence of extracellular calcium.
A novel anti‐inflammatory peptide from human lipocortin 5
Authors: Perretti Mauro , Becherucci Cristina , Mugridge Kenneth G. , Solito Egle , Silvestri Sergio , Parente Luca
Published: July 2012

A novel anti‐inflammatory peptide (residues 204–212) of human recombinant lipocortin 5 (hrLC5) found on the high similarity region with uteroglobin is described.

Peptide 204–212 dose‐dependently inhibited the contractions of rat isolated stomach strips elicited by porcine pancreatic phospholipase A2 (PLA2). Contractions caused by arachidonic acid (AA), prostaglandin E2 (PGE2) and 5‐hydroxytryptamine were not affected. No direct enzyme inhibition was observed in a radiochemical assay.

PGE2 release by both human fibroblasts and rat macrophages was reduced by peptide 204–212 in a dose‐dependent manner.

The development of carrageenin‐induced oedema in rats was significantly inhibited by the local administration of peptide 204–212.

The pattern and potency of the biological effects of peptide 204–212 are similar to those of antiflammin 2, a lipocortin 1‐derived peptide.

It is suggested that peptide 204–212 may represent the active site responsible for the anti‐inflammatory properties of lipocortin 5.
Blockade by the local anaesthetic, tetracaine, of desensitization of Ca‐induced Ca release after muscarinic stimulation in smooth muscle
Authors: Hishinuma Shigeru , Uchida Masaatsu K.
Published: July 2012

Desensitization of contractile responses dependent on release of intracellularly stored Ca elicited by carbachol, histamine or caffeine was measured after desensitizing treatment with carbachol or histamine in the presence or absence of local anaesthetics in Ca‐free solution containing 2 mm EGTA in the smooth muscle of guinea‐pig taenia caecum.

Histamine‐induced homologous desensitization was inhibited by tetracaine and procainamide. Dibucaine did not exert an inhibitory effect on the desensitization. This is consistent with our previous findings concerning the effects of local anaesthetics on the densitization of histamine H1‐receptors measured under normal physiological conditions.

Carbachol induced a functional change of intracellular Ca stores which resulted in heterologous desensitization. Tetracaine completely blocked carbachol‐induced desensitization of the caffeine‐elicited contraction, but in the case of carbachol‐induced desensitization of carbachol‐ and histamine‐elicited contractions, this blocking effect of tetracaine was very weak and absent, respectively. The other local anaesthetics used did not affect the desensitization. These results suggest that the Ca‐induced and inositol trisphosphate‐induced Ca release mechanisms were both desensitized by carbachol and that the desensitization of the Ca‐induced Ca release mechanism was selectively blocked by tetracaine.
Negative chronotropic effect of a novel class III antiarrhythmic drug, UK‐68,798, devoid of β‐blocking action on isolated guinea‐pig atria
Authors: Yang Tao , Tande Pål M. , Refsum Helge
Published: July 2012

The chronotropic effects of a novel class III antiarrhythmic drug, UK‐68,798, and the β‐adrenoceptor blocker, propranolol, for comparison, were studied on spontaneously beating right atria isolated from guinea‐pigs in the absence and presence of increasing concentrations of isoprenaline (10−10–10−4 m).

UK‐68,798 (10−9–10−5 m) decreased spontaneous atrial rate by 6–21%. Propranolol (10−8–10−6 m) also had a negative but significantly smaller chronotropic effect.

UK‐68,798 dose‐dependently reduced the maximal positive chronotropic effect induced by isoprenaline, but without significantly shifting the concentration‐response curve for isoprenaline in a parallel fashion. A pD'2 value of 5.88 was obtained. As expected, propranolol displayed a competitive inhibition with a pA2 value of 8.21.

The results demonstrate a negative chronotropic effect of UK‐68,798, which is not associated with a β‐adrenoceptor blocking action. We suggest that the negative chronotropic effect is linked with potassium channel blockade and thereby the class III antiarrhythmic action of UK‐68,798.