bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of chronic intra‐accumbens administration of the TRH analogue CG3509 on histamine‐induced behaviour in the rat
Authors: Bristow L.J. , Bennett G.W.
Published: July 2012

The present study has investigated the effect of chronic intra‐accumbens administration of the thyrotrophin‐releasing hormone (TRH) analogue, CG3509, on CG3509‐ and histamine‐induced spontaneous motor activity and brain TRH‐like immunoreactive (TRH‐LI) levels in the rat.

Chronic intra‐accumbens administration of CG3509 (5 × 5 μg over 3 days) induced: (a) a significant (P <0.05) reduction in intra‐accumbens CG3509 (0.5 μg)‐induced hyperactivity, (b) reduced levels of TRH‐LI in the nucleus accumbens but not other brain regions, (c) a marked increase (107%, P < 0.01) in histamine‐induced non‐locomotor hyperactivity.

The present results demonstrate that alteration of central TRH function following treatment with a TRH analogue enhances the effect of intra‐accumbens histamine on behavioural hyperactivity, possibly via changes in H1 receptors and suggest that the neuropeptide, TRH and histamine interact in behavioural arousal mechanisms in rat brain.
Postjunctional α2‐adrenoceptors mediate vasoconstriction in human subcutaneous resistance vessels
Authors: Nielsen H. , Thom S.McG. , Hughes A.D. , Martin G.N. , Mulvany M.J. , Sever P.S.
Published: July 2012

In vitro studies have been performed on human medium‐sized muscular arteries (internal diameter 1–4 mm) in a classical organ bath and with human subcutaneous resistance arteries (internal diameter 103–626 μm) in a microvascular myograph.

Although the medium‐sized muscular arteries showed no response to either of the α2‐agonists B‐HT 933 or UK 14304 in concentrations up to 10 μm, the subcutaneous resistance arteries from all regions examined showed well‐pronounced and concentration‐dependent responses to B‐HT 933, the pD2 (‐log EC50) being 5.11 ± 0.09.

In the resistance arteries the α2‐antagonist yohimbine caused a parallel shift to the right of the B‐HT 933 concentration‐response curve; the yohimbine pA2 for the B‐HT 933 receptor was 7.86 ± 0.12.

There was an inverse relationship between the maximum response to B‐HT 933 and the calibre of the resistance vessels.

These results indicate the presence of a postjunctional α2‐adrenoceptor in human subcutaneous resistance arteries and not in medium sized muscular arteries.
PC12 phaeochromocytoma cells contain an atypical muscarinic receptor binding site
Authors: Michel Anton D. , Stefanich Eric , Whiting Roger L.
Published: July 2012

Kinetic, saturation and competition binding studies were conducted on the muscarinic receptor binding site labelled by [3H]‐N‐methylscopolamine ([3H]‐NMS) in intact PC12 cells and cell membranes. Similar studies were conducted on M1 receptors of rat cortex labelled with [3H]‐pirenzepine and M2 and M3 receptors present in rat heart and submaxillary gland respectively, and labelled with [3H]‐NMS.

The dissociation of [3H]‐NMS from muscarinic receptors in PC12 cells was slower than dissociation from both M2 and M3 muscarinic receptors.

The Kd of [3H]‐NMS in the PC12 cells was significantly lower than that obtained at the M2 and M3 receptor.

In competition studies the affinity data for pirenzepine, hexahydroadiphenine and 4‐diphenylacetoxy‐N‐methylpiperidine methiodide were consistent with the presence of an M3 receptor in the PC12 cells. However, for AF‐DX 116, cyclohexylphenyl(2‐piperidinoethyl)silanol and methoctramine affinity estimates in PC12 cells were 3–6 fold lower than at the M3 receptor.

On the basis of these data we conclude that the muscarinic receptor present in the PC12 cells differs from the M1, M2 and M3 subtypes already described.
Use of geographutoxin II (u‐conotoxin) for the study of neuromuscular transmission in mouse
Authors: Hong S.J. , Chang C.C.
Published: July 2012

Endplate potentials (e.p.ps) were investigated in the presence of geographutoxin II (GTXII) in the mouse phrenic nerve diaphragm preparation. This toxin preferentially blocks muscle Na+ channels which allows the study of e.p.ps in the absence of nicotinic receptor antagonists or substances to depress acetylcholine release.

GTXII abolished muscle action potentials and antagonized the depolarization of the muscle membrane produced by the crotamine‐induced opening of Na+ channels.

E.p.ps as large as 19–25 mV were observed after 2–4 μg ml−1 GTXII. These concentrations of GTXII did not cause discernible changes of resting membrane potential and frequency and amplitude of miniature e.p.ps.

Lower concentrations (1–2 μg ml−1) of GTXII caused incomplete blockade of the muscle Na+ channel resulting in exaggerated ‘e.p.ps’, while higher concentrations of GTXII (8 μg ml−1) abolished e.p.ps by a prejunctional effect.

Trains of e.p.ps on repetitive stimulation after GTXII neither ran down, as in tubocurarine‐treated preparations, nor facilitated, as in low Ca2+ and/or high Mg2+‐treated preparations, and were indistinguishable from those of untreated cut muscle preparation.

In cut muscle preparations, GTXII did not affect the rise and decay times, amplitude or rundown of e.p.ps.

It is concluded that GTXII is a useful agent for studying neuromuscular transmission. This method provides e.p.ps which are neither attenuated nor modified because manipulations that alter transmitter release and postjunctional receptor responses are avoided.
Comparison of the sodium currents in normal Purkinje fibres and Purkinje fibres surviving infarction—a pharmacological study
Authors: Bril Antoine , Kinnaird Anne A.A. , Man Ricky Y.K.
Published: July 2012

Purkinje fibres surviving infarction showed a lower maximum upstroke velocity (Vmax) and a longer action potential duration when compared to normal Purkinje fibres. A reduction in the fast sodium current and an increase in the sodium ‘window’ current may be responsible for the observed alterations in (Vmax and action potential duration respectively.

Since voltage clamp studies were not feasible, a pharmacological approach was used. The responses to tetrodotoxin (TTX) and lignocaine in normal Purkinje fibres and Purkinje fibres surviving infarction were used to examine the sodium currents in these fibres.

Vmax, an indirect measure of the fast sodium current, was more sensitive to lignocaine in Purkinje fibres surviving infarction than in normal Purkinje fibres. The reduction in Vmax by lignocaine was more prominent at the shorter stimulation cycle length. Significant reduction of Vmax was observed with the higher concentration of TTX and no differential effect on Vmax between normal Purkinje fibres and Purkinje fibres surviving infarction was detected.

Reduction of action potential duration in the presence of TTX or lignocaine was used as a measure of the sodium ‘window’ current. A greater reduction of action potential duration by TTX and lignocaine was observed in normal Purkinje fibres than in Purkinje fibres surviving infarction.

The results suggested that the fast sodium current in Purkinje fibres surviving infarction is more sensitive to pharmacological agents with local anaesthetic properties and the prolonged action potential duration in these Purkinje fibres cannot be due to an increase in the sodium ‘window’ current. The results are compatible with an enhanced effect of antiarrhythmic drugs on Vmax and conduction in the ischaemic heart.
The cardiovascular actions of clonidine and neuropeptide‐Y in the ventrolateral medulla of the rat
Authors: McAuley M.A. , Macrae I.M. , Reid J.L.
Published: July 2012

The cardiovascular responses to neuropeptide‐Y (NPY) (25 and 50 pmol) and clonidine (10 and 20 nmol) were examined following microinjection into the rostral ventrolateral medulla (RVLM) and the caudal ventrolateral medulla (CVLM). Mean arterial pressure (MAP) and heart rate (HR) were measured in anaesthetized rats, pre‐ and post‐injection.

The α2‐adrenoceptor agonist clonidine (10 and 20 nmol) reduced MAP and HR significantly when microinjected into the CVLM and RVLM.

NPY (25 and 50 pmol) microinjected into the CVLM decreased MAP and HR. However, in the RVLM neither dose had a significant cardiovascular effect.

The possibility of a functional interaction between the adrenergic system and NPY was examined by co‐administration of clonidine and NPY in doses that gave submaximal blood pressure responses. In the CVLM this produced hypotension and bradycardia which was similar in magnitude to the sum of their individual responses, indicating that in this area their actions appear to be independent.

In the RVLM, where NPY has no significant cardiovascular effects, co‐administration with clonidine, did not alter the response to clonidine.

It appears that in the areas investigated, there is no functional interaction between NPY and clonidine.
The effect of EU4093 (azumolene sodium) on the contraction of intrafusal muscle in the soleus muscle of the anaesthetized rat
Authors: Leslie G.C. , Part N.J.
Published: July 2012

EU4093 (azumolene sodium) is a direct acting, skeletal muscle relaxant with structural similarities to dantrolene sodium in that the para‐nitro phenyl group of dantrolene sodium is replaced by a para‐bromo phenyl group.

The effect of EU4093 on the twitch of the intact rat soleus preparation is nearly maximal at a dose of 20 mg kg−1. This dose of EU4093 reduces the amplitude of the twitch to 31.9% of the control value. By comparison, dantrolene sodium reduced the twitch amplitude to 31.3% of the control value at a dose of 5 mg kg−1.

The contraction of intrafusal muscle as measured by the response of spindle afferent discharge was also reduced by EU4093.

The most significant difference between the effect of EU4093 and dantrolene sodium on the contraction of intrafusal muscle was that EU4093 had an appreciable depressant action at high stimulation frequencies at which dantrolene sodium had only a minimal relaxant effect on the intrafusal muscle contraction.

The significance of this difference in the actions of EU4093 and dantrolene sodium is discussed in terms of the possible effect of the drug in the intact animal and human patient. It is concluded that, because the discharge frequency is not likely to move into the high frequency range at which dantrolene sodium and EU4093 have significantly different effects, the overall effect of these two drugs is likely to be similar.
Modulation of non‐adrenergic, non‐cholinergic neural bronchoconstriction in guinea‐pig airways via GABAB‐receptors
Authors: Belvisi M.G. , Ichinose M. , Barnes P.J.
Published: July 2012

Evidence suggests that γ‐aminobutyric acid (GABA) and its receptors are present in the peripheral nervous system. We have now investigated the effect of GABA and related substances on non‐adrenergic, non‐cholinergic (NANC) neurally‐evoked bronchoconstriction in the anaesthetised guinea‐pig.

Bilateral vagal stimulation (5 V, 5 ms, 3 or 5 Hz) for 30 s, after propranolol (1 mg kg−1 i.v.) and atropine (1 mg kg−1 i.v.) evoked a NANC bronchoconstrictor response manifest as a mean tracheal pressure rise of 21.9 ± 1.04 cmH2O (n = 70). The bronchoconstrictor response was reproducible for any given animal.

GABA (10 μg‐10 mg kg−1 i.v.) did not alter basal tracheal pressure but reduced the NANC bronchoconstrictor response to vagal stimulation in a dose‐dependent manner (ED50 = 186 μg kg−1 with a maximal inhibition of 74 ± 3.4% at 10 mg kg−1). Neither the opioid antagonist naloxone (1 mg kg−1 i.v.) nor the α‐adrenoceptor antagonist phentolamine (2.5 mg kg−1 i.v.) had any significant effect on the inhibitory response produced by GABA (500 μg kg−1).

GABA‐induced inhibition was not antagonised by the GABAA‐antagonist bicuculline (2 mg kg−1 i.v.).

The GABAB‐agonist baclofen (10 μg‐3 mg kg−1 i.v.) caused a dose‐dependent inhibition of the NANC response (ED50 = 100 μg kg−1 with a maximal inhibition of 35.5 ± 2.8% at 3 mg kg−1). The GABAA‐agonist, 4,5,6,7‐tetrahydroisoxazolo[5,4‐C] pyridin‐3‐ol (THIP), also inhibited the NANC bronchoconstrictor response. However, the dose of THIP required for this effect was high (3 mg kg−1) and the effect (< 10% inhibition) was small.

Substance P (SP; 5 μg kg−1 or 25 μg kg−1), produced a bronchoconstrictor response equivalent to that produced by NANC vagal stimulation. This response was significantly increased by injection of GABA. Baclofen had no significant effect on responses evoked by exogenous SP.

We conclude that GABA inhibits the release of transmitter from NANC nerves via an action at GABAB receptors and that GABA might play a role in the regulation of neurogenic responses in the airways.
Comparison of the prejunctional β‐adrenoceptor stimulating actions of adrenaline and isoprenaline in the dog mesenteric vein
Authors: Seki Narihito , Suzuki Hikaru
Published: July 2012

The prejunctional β‐adrenoceptor stimulating actions of adrenaline and isoprenaline were compared by recording junction potentials from smooth muscle cells of the dog mesenteric vein.

The potency of adrenaline and isoprenaline on β‐adrenoceptors in the postjunctional membrane was estimated from hyperpolarization of the membrane in smooth muscle cells of the guinea‐pig facial vein. In the presence of yohimbine, both agents hyperpolarized the membrane to a similar extent.

In the dog mesenteric vein, amplitude of the excitatory junction potential (e.j.p.) and slow depolarization was inhibited by adrenaline and potentiated by isoprenaline; the former but not the latter was accompanied by depolarization of the smooth muscle membrane.

In the presence of yohimbine, adrenaline inhibited the e.j.p. without depolarization of the smooth muscle membrane; the action was weaker than in the absence of yohimbine. The isoprenaline‐induced potentiation of the e.j.p. was further enhanced by yohimbine.

It is concluded that adrenaline and isoprenaline have similar stimulating actions on postjunctional β‐adrenoceptors in the guinea‐pig facial vein, but have different actions on prejunctional β‐adrenoceptors in the dog mesenteric vein; isoprenaline but not adrenaline stimulates this β‐adrenoceptor to facilitate the release of transmitter substances from perivascular noradrenergic nerves.
Perinatal lead exposure impairs opioid but not non‐opioid stress‐induced antinociception in developing rats
Authors: Jackson Helen C. , Kitchen Ian
Published: July 2012

The development of opioid systems has been shown to be sensitive to perinatal exposure to lead. We have studied the effects of such exposure on opioid and non‐opioid mediated stress‐induced antinociception in developing rats.

Lead was administered in the maternal drinking water from conception to postnatal day 14 at 300 and 1000 p.p.m. Twenty and 25 day old rats were subjected to swimming stress and antinociception measured using the tail immersion test.

A 3 min swim‐stress induced an opioid‐mediated antinociceptive response in 20 day old rats which was attenuated by 300 p.p.m. lead and by 1000 p.p.m. lead treatment in a dose‐related manner. A 10 min swim‐stress induced a non‐opioid mediated antinociceptive response in 25 day old rats which was not antagonised by 300 or 1000 p.p.m. lead.

Naloxone antagonised the residual antinociception observed in 20 day old animals treated with 300 p.p.m. lead and had no effect on antinociception in control or lead‐treated 25 day old rats.

Using a lead exposure model considered to represent subclinical lead toxicity in man, it was shown that perinatal lead exposure disrupts opioid but not non‐opioid mediated stress antinociception.
The effect of M&B 22948 on methacholine‐ and histamine‐induced contraction and inositol 1,4,5‐trisphosphate levels in guinea‐pig tracheal tissue
Authors: Langlands John M. , Rodger Ian W. , Diamond Jack
Published: July 2012

The effect of a cyclic GMP phosphodiesterase inhibitor, M&B 22948, on methacholine‐ and histamine‐induced contraction and inositol 1,4,5‐trisphosphate (IP3) elevation was studied in guinea‐pig tracheal rings. After addition of methacholine or histamine the rise in IP3 content was rapid and transient reaching a maximum after 5–15 s, which coincided with the maximum rate of tension development. Cyclic GMP levels of the tissue were elevated by M&B 22948 before agonist stimulation and further elevated by addition of methacholine or histamine. Cyclic AMP levels were not altered by any of these agents. M&B 22948 abolished IP3 generation induced by methacholine or histamine, but did not alter the rate or magnitude of tension development. Thus, IP3 generation does not appear to be responsible for the contractions induced by methacholine or histamine in this tissue.
Pharmacological properties of a C‐fibre response evoked by saphenous nerve stimulation in an isolated spinal cord‐nerve preparation of the newborn rat
Authors: Nussbaumer Jean‐Claude , Yanagisawa Mitsuhiko , Otsuka Masanori
Published: July 2012

An isolated spinal cord‐peripheral nerve preparation of the newborn rat was developed. In this preparation it is possible to record spinal reflexes from a lumbar ventral root in response to stimulation of the ipsilateral saphenous or obturator nerve.

Single shock, weak intensity stimulation of the saphenous nerve induced a fast conducted compound action potential in the L3 dorsal root and a fast depolarizing response in the ipsilateral L3 ventral root. As a stronger stimulus was applied to the saphenous nerve, a slowly conducted compound action potential appeared in the dorsal root and a slow depolarizing ventral root potential (v.r.p.) in the L3 ventral root.

Single shock stimulation of the obturator nerve induced a rapidly conducted compound action potential in the L3 dorsal root and monosynaptic and polysynaptic reflexes, with a fast time course, in the ipsilateral L3 ventral root.

The slow v.r.p. evoked by saphenous nerve stimulation was depressed by the tachykinin antagonist, [D‐Arg1, D‐Trp7,9, Leu11] substance P (spantide), 4–16 μm. The response recovered its original shape and size 30–60 min after the removal of this antagonist.

The saphenous nerve‐evoked slow v.r.p. was depressed by [Met5] enkephalin (0.1–1 μm), dynorphin (1–13)(0.2 μm) and morphine (1–2 μm), and these effects were reversed by naloxone (1 μm).

Two endogenous peptides, galanin (1–2 μm) and somatostatin (1–2.5 μm), inhibited the slow v.r.p. evoked by saphenous nerve stimulation, whereas another endogenous peptide, calcitonin gene‐related peptide (0.1‐0.5 μm), potentiated the slow v.r.p. The slow v.r.p. was also inhibited by γ‐aminobutyric acid (GABA, 20 μm) and muscimol (0.2 μm), and their effects were antagonized by bicuculline (1 μm).

The present results suggest that substance P and neurokinin A are involved in the saphenous nerve‐evoked C‐fibre response in the spinal cord of the newborn rat.
The X‐ray crystal structure of 4‐diphenylcarbamyl‐N‐methylpiperidine methobromide (the carbamate analogue of 4‐DAMP methiodide)
Authors: Barlow R.B. , Johnson O.
Published: July 2012

Crystals of 4‐diphenylcarbamyl‐N‐methylpiperidine methobromide contain 2 conformers, one with the ester group equatorial and the other with the ester group axial to the piperidine ring.

In both conformers and diphenylcarbamyl nitrogen is trigonally substituted and flat compared with the tetrahedral substitution of the corresponding carbon atom in 4‐diphenylacetoxy‐N‐methylpiperidine (4‐DAMP) methiodide.

The low activity and selectivity of the carbamate at muscarinic receptors is comparable with that of compounds containing only one phenyl ring, e.g. phenylacetyl‐N‐methyl piperidine methiodide or phenylacetylcholine. It is suggested that the high affinity of 4‐DAMP metho‐salts and their selectivity depend upon interactions with groups arranged in three dimensions and that the trigonal arrangement about the nitrogen atom in the carbamate makes it impossible for both benzene rings to interact at once.
An examination of the putative σ‐receptor in the mouse isolated vas deferens
Authors: Kennedy Charles , Henderson Graeme
Published: July 2012

The effects of several ligands which interact with the σ‐binding site were studied on the electrically‐evoked (0.1 Hz) neurogenic twitch contractions of the mouse isolated vas deferens.

(+)‐3‐(3‐Hydroxyphenyl)‐N‐(1‐propyl)piperidine ((+)‐3‐PPP) (10−8–10−5m), inhibited the neurogenic twitch contractions. This inhibitory action was unaffected by naloxone (10−6m), idazoxan (10−6m), cocaine (10−6m) or tyramine (10−4–3 × 10−4m), but was abolished by the dopamine D2‐antagonist, sulpiride (10−6m). Therefore, in order to study the potentiating actions of σ ligands, sulpiride (10−6m) was used to prevent any inhibitory actions mediated via dopamine D2‐receptors.

In the presence of sulpiride (10−6m), haloperidol (10−6–10−5m), (+)‐3‐PPP (10−6−3 × 10−4m) and (+)‐N‐allyl‐N‐normetazocine ((+)‐SKF 10,047) (10−5–10−4m) each reversibly potentiated the neurogenic twitch contractions in a concentration‐dependent manner. The rank order of potency was haloperidol > (+)‐3‐PPP > (+)‐SKF 10,047.

The stereoisomers of 3‐PPP displayed stereoselectivity with (+)‐3‐PPP being more potent than (−)‐3‐PPP.

At a concentration that did not potentiate the twitch contractions, (3 × 10−7m), haloperidol did not antagonize the potentiating action of (+)‐3‐PPP (3 × 10−5m).

1,3‐Di‐O‐tolyguanidine (DTG) (10−8–10−5m) had no effect on the amplitude of twitch contractions and did not affect the potentiating action of (+)‐3‐PPP (10−5−3 × 10−5m).

It is concluded that σ‐ligands potentiate neurogenic twitch contractions of the mouse isolated vas deferens via a site that is different from the central σ‐binding site.
Demonstration in Tupaia papillary muscle preparations of α‐adrenoceptors mediating positive inotropic effects: comparison with guinea‐pigs
Authors: Koga T. , Shiraki Y. , Sakai K.
Published: July 2012

Positive inotropic responses to α‐ and β‐adrenoceptor agonists of isolated papillary muscles from the tree shrew (Tupaia), were compared with those from guinea‐pigs.

In Tupaia, the concentration‐response curve for phenylephrine, unlike that for isoprenaline, was not affected by pindolol in a concentration (10−8m) sufficient to block β‐adrenoceptor‐mediated responses, but it was significantly shifted to the right by phentolamine (10−6m). In guinea‐pig papillary muscles, however, the concentration‐response curve for phenylephrine, like that for isoprenaline, was shifted to the right by pindolol (10−8m) but was unaltered by phentolamine (10−6m). Furthermore, when the mean concentrations of agonists inducing maximal positive inotropic responses were compared (relative to that of isoprenaline = 1.0), phenylephrine was found to be only slightly less potent (0.84 ± 0.04; n = 5) in Tupaia and much less potent (0.33 ± 0.06; n = 5) in the guinea‐pig.

Although in Tupaia papillary muscles the increase in developed tension induced by a combination of phenylephrine and isoprenaline did not significantly differ from that by phenylephrine alone, it was approximately 3 times larger than that produced by phenylephrine alone in guinea‐pigs.

These results indicate that in papillary muscles from Tupaia, unlike the guinea‐pig, the positive inotropic effects of phenylephrine can be mediated by α‐adrenoceptors.
Muscarinic suppression of the M‐current in the rat sympathetic ganglion is mediated by receptors of the M1‐subtype
Authors: Marrion N.V. , Smart T.G. , Marsh S.J. , Brown D.A.
Published: July 2012

Under voltage‐clamp dissociated adult and foetal rat superior cervical ganglion (s.c.g.) cells exhibited a non‐inactivating voltage‐ and time‐dependent component of K+ current termed the M‐current (IM). IM was detected and measured from the current decay during hyperpolarizing voltage steps applied from potentials where IM was pre‐activated.

Neither the resting membrane current nor the amplitude of these current decay relaxations were reduced by omitting Ca from the bathing fluid, showing that the M‐current was not a ‘Ca‐activated’ K‐current dependent on a primary Ca‐influx. Concentrations of (+)‐tubocurarine sufficient to block the slow Ca‐activated K‐current IAHP did not inhibit IM or antagonize the effect of muscarinic agonists on IM, showing that IM was not contaminated by IAHP. Tetraethylammonium (1 mm), which blocks the fast Ca‐activated K‐current Ic, produced a small inhibition of IM. This was not due to contamination of IM by Ic since muscarinic agonists did not consistently block Ic.

The muscarinic agonists muscarine, oxotremorine, McN‐A‐343 and methacholine reversibly suppressed IM, resulting in an inward (depolarizing) current. The rank order of potency was: oxotremorine ≥ muscarine > McN‐A‐343 > methacholine.

The suppression of IM by muscarine was similar in cultured cells derived from adult and foetal tissue to that seen in the intact ganglia.

IM‐suppression by muscarine was inhibited by pirenzepine (Pz) and AF‐DX 116 with mean pKB values of 7.53 ± 0.13 (n = 3) and 6.02 ± 0.13 (n = 4) respectively.

The suppression of IM by muscarinic agonists was not affected by gallamine (10–30 μm). 4‐Diphenylacetoxy‐N‐methylpiperidine methiodide inhibited the response at 300 nM.

Pirenzepine inhibited the contractions of the guinea‐pig isolated ileum produced by muscarine with a mean pKB of 6.37 ± 0.03 (n = 8).

These results suggest that the receptors mediating suppression of the M‐current accord with those designated pharmacologically as M1 and that these receptors reach maturity at a very early stage in the development of the rat s.c.g.
Antagonism of platelet activating factor‐induced chemiluminescence in guinea‐pig peritoneal macrophages in differing states of activation
Authors: Parnham Michael J. , Bittner Christine , Lambrecht Günter
Published: July 2012

The effects of the platelet activating factor (Paf) antagonists alprazolam, BN 52021, kadsurenone, L 652,731 and SRI 63119 have been studied on Paf‐induced chemiluminescence (CL) of guinea‐pig, C. parvum‐activated peritoneal macrophages in vitro.

All antagonists produced a shift to the right in the dose‐response curve to Paf (0.001–10 μmol l−1). Schild plots for BN 52021, L 652,731, kadsurenone and SRI 63119 were linear, but only for BN 52021 and kadsurenone did the mean slope not differ significantly from unity. Mean pA2 values for BN 52021 and kadsurenone were 6.60 ± 0.05 and 6.41 ± 0.14 (mean + s.e.mean) respectively. Calculation of IC50 values for all antagonists (at 0.1 μmol l−1 Paf) gave an order of potency: L 652731 > kadsurenone ≥ BN 52021 > alprazolam > SRI 63119.

When individual pA2 values for BN 52021 and kadsurenone were plotted against the maximal CL response to Paf of cell suspensions in the absence of antagonist (reflecting the degree of activation of the macrophages by the C. parvum), it was found that the affinity of both antagonists for macrophage Paf receptors remained relatively constant irrespective of the activation state of the cells.

We conclude that activation of guinea‐pig peritoneal macrophages does not account for the increased affinity for macrophage Paf receptors previously observed for kadsurenone. Kadsurenone and BN 52021 presumably bind to a site on Paf receptors which is not affected by the activation process, while alprazolam and SRI 63119 are non‐specific antagonists. The reason for the difference between the competitive nature of kadsurenone and its structural analogue L 652,731 is unclear.
Probucol attenuates the development of aortic atherosclerosis in cholesterol‐fed rabbits
Authors: Daugherty Alan , Zweifel Ben S. , Schonfeld Gustav
Published: July 2012

Probucol was administered to rabbits fed a cholesterol‐enriched (2% wt/wt) diet to determine potential anti‐atherogenic effects in a preparation in which the disease process is due to elevated plasma concentrations of cholesterol ester‐rich very low density lipoproteins (CER‐VLDL).

Probucol was supplemented to the diet at 1% wt/wt which resulted in plasma concentrations rising steadily to 53 ± 8 μg ml−1 after 14 days, with no significant changes during continued administration. Dietary consumption and body weight gains were comparable in the drug‐treated and control groups during the observation period.

Probucol treatment did not significantly affect plasma concentrations of total cholesterol, unesterified cholesterol, triglycerides or phospholipids.

The concentration of CER‐VLDL in plasma and its physicochemical characteristics were not significantly changed during administration of probucol. CER‐VLDL from both control and probucol‐treated animals was a potent stimulant of the augmentation of the intracellular incorporation of [3H]‐oleate into cholesteryl‐[3H]‐oleate in cultured macrophages.

Despite the lack of effect of probucol on concentrations of plasma lipids and the cell interaction characteristics of CER‐VLDL, administration of the drug markedly decreased the extent of intimal aortic surface area covered by grossly discernible atherosclerotic lesions from 55.6 ± 11.8% to 11.6 ± 1.9% in thoracic sections, and from 49.1 ± 10.2% to 7.2 ± 0.4% in abdominal sections. Furthermore, probucol treatment significantly reduced the deposition of total cholesterol in vascular tissue.

Probucol reduced the extent of aortic atherosclerosis produced by diet‐induced hypercholesterolemia in rabbits. This reduction occurred in the absence of any significant change in the characteristics of plasma lipoproteins that were determined. These results indicate that either there is a role of oxidation in the disease process of this animal model of atherosclerosis or that probucol is acting via a presently undefined mechanism.
Interaction of the Paf antagonist WEB 2086 and its hetrazepine analogues with human platelets and endothelial cells
Authors: Korth R. , Hirafuji M. , Keraly C. Lalau , Delautier D. , Bidault J. , Benveniste J.
Published: July 2012

Intact platelets and confluent human umbilical vein endothelial cells bound [3H]‐Paf‐acether (platelet activating factor, [3H]‐Paf) at 20°C in the presence of 0.25% (w/v) bovine serum albumin (BSA).

[3H]‐Paf binding to platelets was inhibited in a concentration‐dependent manner by WEB 2086. An excess of WEB 2086 indicated the presence of specific, saturable Paf binding which reached a maximum of 28.3 ± 3.7 fmol [3H]‐Paf per 5 × 107 platelets. In platelets, different hetrazepines (WEB 2098, 2105, but not 2118) also inhibited [3H]‐Paf binding in a concentration‐dependent manner.

WEB 2086 partially displaced platelet‐bound [3H]‐Paf in a concentration‐dependent manner reaching a plateau at 400 nM WEB 2086. No further displacement was observed when WEB 2086 and an excess of unlabelled Paf were added together.

The hetrazepines inhibited platelet aggregation. Platelet aggregation IC50 values correlated well with the IC50 values of the hetrazepines against [3H]‐Paf binding (r2 = 0.99). WEB 2086 shifted the Paf dose‐response curve rightwards in a parallel manner. Tested against platelet aggregation the pA2 obtained for WEB 2086 was 7.9.

WEB 2086 inhibited [3H]‐Paf binding to endothelial cells in a concentration‐dependent manner. WEB 2086 also inhibited the Paf‐mediated cytosolic calcium increase in endothelial cells with an IC50 value of 23.1 ± 10.4 nM as compared with an IC50 of 21.6 ± 10.4 nM WEB 2086 for platelet aggregation.

These results demonstrate an inhibition of [3H]‐Paf binding to platelets and endothelial cells by different hetrazepines, most probably at the Paf receptor level.
Effects of iloprost (ZK 36374) on glutathione status during ischaemia and reperfusion of rabbit isolated hearts
Authors: Ferrari Roberto , Cargnoni Anna , Curello Salvatore , Boffa Giovanni M. , Ceconi Claudio
Published: July 2012

Reperfusion of rabbit isolated hearts after 60 min of ischaemia resulted in poor recovery of mechanical function, release of creatine Phosphokinase (CPK) and of reduced (GSH) and oxidized (GSSG) glutathione, reduction of mitochondrial superoxide dismutase (Mn SOD) activity and of tissue GSH/GSSG ratio with a shift of cellular thiol redox state toward oxidation, suggesting the occurrence of oxidative stress.

Pretreatment of the isolated heart with the stable prostacyclin analogue (iloprost) at 27 or 270 nM, but not at 2.7 nM, improved the functional recovery of the myocardium, reduced CPK, GSH and GSSG release, maintained Mn SOD activity and attenuated the occurrence of oxidative stress.

This effect of iloprost cannot be explained by a decreased demand or an enhanced delivery of oxygen during ischaemia or by a direct effect on glutathione peroxidase and reductase activity.
Voltage‐dependence of ryanodine‐sensitive component of contraction in A23187‐ and isoprenaline‐treated cardiac muscles
Authors: Kondo Noriaki
Published: July 2012

The ryanodine‐sensitive component (RSC) of contraction electrically induced in the presence of A23187 (10−6 M) and isoprenaline (5 × 10−8 M) was investigated in guinea‐pig papillary muscles that had been partially depolarized to various membrane potentials by increasing [K+]o, and current and voltage clamp techniques.

Two components of contraction were produced by A23187 and isoprenaline at a stimulation frequency of 0.2 Hz. The early component was sensitive to ryanodine (10−6 M) (corresponding to RSC), while the late component was sensitive to nifedipine (10−6 M).

In the presence of nifedipine, RSCs produced by these drugs were selectively observed. Under these conditions, RSCs were voltage‐dependently inhibited by a reduction in resting potential that was brought about by increasing [K+]o (10–26 mM). The onset of inhibition of RSCs appeared at a resting potential between −75 and −70 mV, and almost complete inhibition was observed at a potential between −55 and −50 mV, indicating that RSCs produced by these drugs have the same voltage‐dependence.

In the absence of nifedipine, this voltage‐dependent inhibition was also observed on the early component of contraction produced by A23187 without affecting the late component.

RSC produced by A23187 was not affected by blocking Na channel activation with tetrodotoxin (6 × 10−6 M).

In current and voltage clamp experiments, this RSC was inhibited by reducing the resting and the holding potentials in much the same way as observed on the preparations depolarized by increasing [K+]o. Such dependence on voltage was not observed with either the slow action potential or the slow Ca inward current.

These results suggest that the dependence of RSC on resting potentials is not due to the changes in the fast Na and the slow Ca inward currents. The present RSC via ryanodine‐sensitive internal Ca release may be mainly triggered by a mechanism different from Ca influx through slow channels.
Baclofen and phaclofen modulate GABA release from slices of rat cerebral cortex and spinal cord but not from retina
Authors: Neal M.J. , Shah M.A.
Published: July 2012

The effects of (−)‐baclofen, muscimol and phaclofen on endogeneous γ‐aminobutyric acid (GABA) release from rat cortical slices, spinal cord slices and entire retinas were studied.

The spontaneous resting release of GABA from the three tissues was 3 to 6 pmol mg−1 wet wt 10 min−1 Depolarization of cortical slices with KCl (50 mM) (high‐K) produced an 8 fold increase in GABA release but high‐K did not evoke an increased release of GABA from spinal slices or retinas.

When rats were injected with γ‐vinyl‐GABA (250 mg kg−1 i.p.) (GVG) 18 h before death, the tissue GABA stores were increased 3 to 6 fold and high‐K then evoked striking Ca‐dependent releases of GABA from all three tissues. Thus, in subsequent experiments, unless otherwise stated, the nervous tissues were taken from GVG‐treated rats.

(−)‐Baclofen (10 μm) significantly reduced the K‐evoked release of GABA from cortical and spinal slices but retinal release was not affected, even at a concentration of (±)‐baclofen of 1 mM. For cortical slices, the IC50 for baclofen was approximately 5.2 μm The inhibitory effect of baclofen on GABA release from cortical slices also occurred in slices prepared from saline‐injected rats, indicating that GVG treatment did not qualitatively affect the results.

The inhibitory effect of (−)‐baclofen on the K‐evoked release of GABA from cortical and spinal slices was antagonised by phaclofen (500 μm), confirming that baclofen was producing its effects by acting at the GABAB‐receptor.

Phaclofen (500 μm) increased the spontaneous resting release of GABA from cortical slices taken from GVG‐treated rats but not from saline‐injected rats. Phaclofen did not increase GABA release from spinal slices or retinas taken from GVG‐treated rats.

Baclofen (10 μm) significantly reduced the K‐evoked release from cortical slices of glutamate, aspartate, glycine and taurine.

Muscimol (10 μm) and δ‐aminolaevulinic acid (10 μm) had no effect on either the resting or K‐evoked release of GABA from cortical slices prepared from saline‐injected or GVG‐treated rats.

The results obtained with cortical and spinal slices are consistent with the presence of inhibitory GABAB‐autoreceptors. The phaclofen‐induced increase in GABA release from cortical slices taken from GVG‐treated rats, but not from saline‐injected rats, implies that under conditions of high GABA release, considerable feedback inhibition is occurring via activation of the GABAB inhibitory autoreceptors. No evidence was found for GABAB‐autoreceptors on retinal GABAergic amacrine cells or for GABAA‐autoreceptors in cortical slices or spinal cord slices.
Comparative effects of bepridil, its quaternary derivative CERM 11888 and verapamil on caffeine‐induced contracture in ferret hearts
Authors: Leboeuf J. , Leoty C. , Lamar J‐C. , Massingham R.
Published: July 2012

The effects of bepridil, its quaternary derivative: CERM 11888 (methyl‐pyrrolidinium bromide) (10−7‐10−5 M), and verapamil (10−7‐10−6 M) were compared on caffeine‐induced contracture of isolated ventricular trabeculae of the ferret.

Bepridil diminished the amplitude of contracture in a concentration‐dependent fashion, and this effect was significantly different from that of CERM 11888 which, like verapamil, only reduced the amplitude at the highest concentration used.

Bepridil (10−6 M) significantly shortened the time to peak tension and accelerated the relaxation phase of contracture. This latter effect was different from that of CERM 11888. Verapamil (10−6 M) also tended to accelerate the relaxation phase. At 10−5 m these actions of bepridil on the time to peak and relaxation tended to reverse.

At all concentrations bepridil and verapamil reduced the rate of repriming of contracture and this effect of bedpridil was significantly different from that of its quaternary derivative which only showed a significant effect at 10−5 M.

These results demonstrate a clear intracellular effect of bepridil in the ferret heart. Verapamil and CERM 11888 had only weak intracellular effects even at high concentrations.

Analysis of the results suggests that the main sites of action of bepridil in this model are the sarcoplasmic reticulum and one or two calcium compartments in the sarcolemma.
Effects of verapamil on ischaemia‐induced impairment of ATP‐dependent calcium extrusion in rat heart sarcolemma
Authors: van Amsterdam F. Th. M. , Goddijn M.M. , Haas M. , Punt N.C. , Zaagsma J.
Published: July 2012

The effects of ischaemia and reperfusion were studied on adenosine 5′‐triphosphate (ATP)‐dependent 45Ca2+‐transport in rat heart sarcolemma vesicles.

The effect of verapamil, 1 μmoll−1, was studied by pretreatment of the hearts during Langendorff‐perfusion and in vitro by adding the drug after isolation of the vesicles.

Without drug pretreatment the Ca2+‐uptake appeared to be strongly reduced after 30 and after 60 min of global ischaemia, whereas after 30 min of reperfusion it was restored to slightly above the control level.

Verapamil pretreatment during the Langendorff perfusion significantly increased Ca2+‐uptake in sarcolemma vesicles both before the onset of ischaemia and after 30 min of reperfusion, whereas no beneficial effect was found on the impaired uptake activity during the ischaemic period.

When tested in vitro after the isolation of the sarcolemma vesicles, verapamil only inhibited the Ca2+‐uptake activity with an IC50 of 112 μmol l−1, which was increased to 250μmol l−1 after ischaemia and reperfusion.

The present study indicates that pretreatment with verapamil, 1 μmol l−1, of the intact rat heart activates an ATP‐dependent Ca2+ extrusion process that may contribute to decrease cellular calcium levels in control and, more importantly, in a reperfusion situation. In contrast, in vitro only a less potent inhibition of the extrusion process was found, indicating that physiological regulatory mechanisms may be altered in the vesicles.
Binding and functional properties of antimuscarinics of the hexocyclium/sila‐hexocyclium and hexahydro‐diphenidol/hexahydro‐sila‐diphenidol type to muscarinic receptor subtypes
Authors: Waelbroeck M. , Tastenoy M. , Camus J. , Christophe J. , Strohmann C. , Linoh H. , Zilch H. , Tacke R. , Mutschier E. , Lambrecht G.
Published: July 2012

In an attempt to assess the structural requirements for the muscarinic receptor selectivity of hexahydro‐diphenidol (hexahydro‐difenidol) and hexahydro‐sila‐diphenidol (hexahydro‐sila‐difenidol), a series of structurally related C/Si pairs were investigated, along with atropine, pirenzepine and methoctramine, for their binding affinities in NB‐OK 1 cells as well as in rat heart and pancreas.

The action of these antagonists at muscarinic receptors mediating negative inotropic responses in guinea‐pig atria and ileal contractions has also been assessed.

Antagonist binding data indicated that NB‐OK 1 cells (M1 type) as well as rat heart (cardiac type) and pancreas (glandular/smooth muscle type) possess different muscarinic receptor subtypes.

A highly significant correlation was found between the binding affinities of the antagonists to muscarinic receptors in rat heart and pancreas, respectively, and the affinities to muscarinic receptors in guinea‐pig atria and ileum. This implies that the muscarinic binding sites in rat heart and the receptors in guinea‐pig atria are essentially similar, but different from those in pancreas and ileum.

The antimuscarinic potency of hexahydro‐diphenidol and hexahydro‐sila‐diphenidol at the three subtypes was influenced differently by structural modifications (e.g. quaternization). Different selectivity profiles for the antagonists were obtained, which makes these compounds useful tools to investigate further muscarinic receptor heterogeneity. Indeed, the tertiary analogues hexahydrodiphenidol (HHD) and hexahydro‐sila‐diphenidol (HHSiD) had an M1 = glandular/smooth muscle > cardiac selectivity profile, whereas the quaternary analogues HHD methiodide and HHSiD methiodide were M1 preferring (M1 > glandular/smooth muscle, cardiac).
Selectivity of bradykinin analogues for receptors mediating contraction and relaxation of the rat duodenum
Authors: Paiva Antonio C.M. , Paiva Therezinha B. , Pereira Claudia C. , Shimuta Suma I.
Published: July 2012

Bradykinin produces a biphasic response in the rat duodenum that consists of a relaxation (pD2 = 8.44) followed by a contraction (pD2 = 6.91).

The B1 agonist des‐Arg9‐bradykinin produced a contraction (pD2 = 7.16) but no relaxation. Des‐Arg9‐[Leu8]‐bradykinin, which is a B1 antagonist in other systems produced contraction (pD2 = 7.65) in the rat duodenum.

Four bradykinin analogues that are preferential B2 agonists in other tissues had a biphasic effect with pD2 values in the range 7.22‐8.68 for relaxation and 6.26‐6.91 for contraction.

[Thi5,8,D‐Phe7]‐bradykinin, which is a B2 antagonist in most other systems produced relaxation in the rat duodenum, with a pD2 of 7.49.

It is concluded that the contractile component of the response to bradykinin in rat duodenum may be mediated by a subtype of the B1 receptor and the relaxant component by a receptor of the B2 subtype.
Presynaptic β‐adrenoceptors in rat atria: evidence for the presence of stereoselective β1‐adrenoceptors
Authors: Heimburger M. , Montero M.J. , Fougeres V. , Beslot F. , Davy M. , Midol‐monnet M. , Cohen Y.
Published: July 2012

Presynaptic β‐adrenoceptor activity was studied in rat isolated atria, previously loaded with [3H]‐noradrenaline. The stimulation‐induced release of 3H transmitter was measured in the presence of cocaine, and adrenaline was used as a facilitatory β‐adrenoceptor agonist.

Adrenaline (0.1 and 2 nM) increased, by about 50%, the evoked efflux of tritium. With phenoxybenzamine present, the same activity was shown with 10 nM adrenaline.

The β2‐selective adrenoceptor blocking drugs: IPS 339 and ICI 118 551 caused a concentration‐dependent decrease in the activity of adrenaline. Cardioselective β‐blocking drugs: acebutolol, betaxolol, nebivolol and its isomers (R 67 138 and R 67 145) also reduced dose‐dependently the agonistic action of adrenaline. The order of potency for nebivolol and its isomers was R 67 138 > nebivolol > R 67 145. The activity of pindolol was not concentration‐dependent. The inhibitory effect of acebutolol was also observed in the presence of blockade of α‐adrenoceptors.

The postsynaptic β‐adrenoceptor blocking activity of nebivolol and its isomers was studied in pithed rats. They reduced isoprenaline‐induced tachycardia without altering hypotensive responses. The order of potency was: R 67 138 > nebivolol > R 67 145.

It is concluded that in rat isolated atria, presynaptic β2‐ and β1‐adrenoceptors coexist and that facilitatory β1 ‐adrenoceptors are stereospecific.
Opposite central and peripheral control by endogenous opioids of intestinal motility in fed rats
Authors: Rivière Pierre J.‐M. , Liberge Martine , Murillo‐Lopez Divina , Bueno Lionel
Published: July 2012

The effects of the inhibitors of endopeptidase EC 24.11, thiorphan and phosphoramidon administered i.c.v. (40 μg kg−1) i.p. (400 μgkg−1), or orally (400ugkg−1), on intestinal motor activity in fed rats was compared to the effects of similar doses of the angiotensin converting enzyme inhibitor, captopril and the synthetic enkephalin analogue [D‐Ala2 Met5] enkephalinamide (Dalamide). Drugs were administered alone or after pretreatment with naloxone or N‐methyl levallorphan (300 μg kg−1, i.p.) given 10 min prior to gavage with a standard meal.

In control conditions, in the duodenum, the disruption of the migrating myoelectric complex (MMC) by gavage with a standard meal lasted between 105.6 and 119.1 min. This duration was significantly decreased by thiorphan (60.3 ± 15.0 min), phosphoramidon (67.9 ± 7.3 min), captopril (26.3 ± 10.2 min) and Dalamide (42.4 ± 9.6 min), administered i.c.v.

In contrast, after the i.p. administration of thiorphan, phosphoramidon and Dalamide the delay in the return of the MMC pattern was increased. Such an effect was also seen after the oral administration of phosphoramidon or Dalamide. Neither i.p. nor oral captopril administration altered the duration of postprandial pattern.

A prior treatment with naloxone i.p. (300 μg kg−1) that had no effect per se, antagonized the effect produced by i.c.v. administration of thiorphan, phosphoramidon or Dalamide, but failed to reverse the effect of captopril. In contrast, i.p. administration of N‐methyl levallorphan (300 μg kg−1) did not affect the response induced by central administration of thiorphan, phosphoramidon, captopril or Dalamide, but was able to prevent that of thiorphan, phosphoramidon or Dalamide when they were administered i.p. or orally.

These data strongly support the hypothesis of a dual control by endogenous opioids of intestinal motility in the rat: a central component that favours, and a peripheral control that delays the occurrence of the MMC profile in fed rats.