bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of the 5‐HT receptor subtypes involved in the motor behaviours produced by intrathecal administration of 5‐HT agonists in rats
Authors: Fone K.C.F. , Robinson A.J. , Marsden C.A.
Published: July 2012

The motor behavioural effects of intrathecal injections of 5‐hydroxytryptamine (5‐HT) and a variety of 5‐HT receptor agonists were examined in adult Wistar rats to establish; (a) which 5‐HT receptor subtype/s elicit each behaviour and (b) whether these receptors are located within the spinal cord.

Intrathecal injection of 5‐methoxy‐N,N′‐dimethyltryptamine (5‐MeODMT), (+)‐1‐(2,5‐dimethoxy‐4‐iodophenyl)‐2‐aminopropane hydrochloride (DOI) or 2,5‐dimethoxy‐α,4‐dimethylbenzene ethamine hydrochloride (DOM) produced dose‐related back muscle contractions (BMC) and wet dog shakes (WDS) which were both markedly attenuated by intraperitoneal pretreatment with either ritanserin (1 mg kg−1), ketanserin (0.16 mg kg−1) or mianserin (0.6 mg kg−1) indicating the involvement of 5‐HT2 receptors in both these motor behaviours. Both fluoxetine (1–20 mg kg−1, i.p.) and high doses of 5‐HT (50 μg) following fluoxetine (5 mg kg−1, i.p.) also elicited BMC, further confirming the involvement of 5‐HT in this behaviour.

Intrathecal 5‐carboxamidotryptamine (5‐CT) evoked a marked wet‐dog shake response without producing any BMC. Intrathecal pretreatment with 8‐hydroxy‐2‐(di‐n‐propylamino)tetraline (8‐OH‐DPAT) enhanced, while in contrast 2‐methyl‐5‐HT pretreatment attenuated, 5‐HT agonist‐induced BMC without affecting WDS. These data suggest that the spinal 5‐HT2 receptors mediating BMC are positively modulated by 5‐HT1A but negatively influenced by 5‐HT3 receptor activation and may be of a different subtype to the supra‐spinal 5‐HT2 receptors which elicit WDS.

A contrast, reciprocal forepaw treading, lateral head weaving, flat body posture and Straub‐tail were evoked by 5‐MeODMT, 8‐OH‐DPAT or 5‐CT but not by DOI or DOM indicating that these behaviours were not produced by 5‐HT2 receptor activation alone. Ritanserin (1 mg kg−1, i.p.) or ketanserin (0.16 mg kg−1, i.p.) pretreatment reduced the reciprocal forepaw treading induced by high intrathecal doses of either 5‐MeODMT (25 μg) or 5‐CT (50 μg) suggesting that this behaviour may be facilitated by 5‐HT2 receptor activation.

Intrathecal injection of 5‐HT (0.05–50 μg, after systemic fluoxetine, 5 mg kg−1, i.p.), or 1‐(3‐chlorophenyl)piperazine (mCPP) produced dose‐related forepaw‐licking and grooming, neither of which were attenuated by ketanserin (0.16 mg kg−1, i.p.) pretreatment suggesting these behaviours may be mediated by 5‐HT1C receptors. In contrast, 2‐methyl‐5‐HT (50 and 100 μg) produced sideward tail‐flicks, not evoked by any other 5‐HT agonist and could therefore be mediated by spinal 5‐HT3 receptor activation.

These data provide behavioural evidence for the existence of spinal 5‐HT2 receptors which produce a novel motor behaviour, BMC. Ligand binding studies and dose‐response studies with a range of selective 5‐HT antagonists are required to establish whether BMC and WDS are mediated by different subtypes of 5‐HT2 receptors.
Rate and concentration‐dependent effects of UK‐68,798, a potent new class III antiarrhythmic, on canine Purkinje fibre action potential duration and Vmax
Authors: Knilans Timothy K. , Lathrop David A. , Nánási Péter P. , Schwartz Arnold , Varró András
Published: July 2012

The frequency‐dependent electrophysiological effects of UK‐68,798 in concentrations of 1, 3, 10 and 30 nm were examined in isolated cardiac Purkinje fibres of the dog at both a number of constant rates of stimulation and following abrupt changes in pacing cycle length.

In all concentrations evaluated, UK‐68,798 lengthened action potential duration in a concentration‐and rate‐dependent manner (e.g., at a cycle length = 500 ms, control APD90 = 234.0 ± 3.3 ms, while after 10 nm UK‐68,798, APD90 = 315.0 ± 5.9 ms).

The duration of action potentials evoked following abrupt changes in pacing rate were also increased in a concentration‐dependent manner at all diastolic intervals tested.

The fast and slow time constants for restitution of APD were not altered by UK‐68,798. However, the amplitude terms for this relation were increased.

In addition, the maximum upstroke velocity (V̇max) was not significantly affected by exposure to UK‐68,798 at any concentration or diastolic interval. The kinetics for recovery of V̇max were thus unaffected.

These findings are similar to those previously reported for recognized class III antiarrhythmic agents (e.g., bretylium, clofilium, and sotalol); however, UK‐68,798 was 1,000 to 10,000 times more potent.

The combined potency and selectivity of this agent seem to make it an ideal tool for the investigation of cardiac potassium channels believed responsible for controlling the duration of the action potential.

This potent and highly selective compound may prove extremely useful in the control of cardiac arrhythmias.
Inhibitory and excitatory effects of adenosine receptor agonists on evoked transmitter release from phrenic nerve endings of the rat
Authors: Correia‐de‐Sá P. , Sebastião A.M. , Ribeiro J.A.
Published: July 2012

The effects of the adenosine analogues, 5′‐N‐ethyl‐carboxamide adenosine (NECA), R‐N6‐phenylisopropyladenosine (R‐PIA), 2‐chloroadenosine (CADO), and CGS 21680C on electrically evoked tritium outflow from preparations loaded with [3H]‐choline and on evoked endplate potentials (e.p.ps), as well as the ability of the xanthines, 1,3‐dipropyl‐8‐cyclopentylxanthine (DPCPX) and PD 115,199 to antagonize the effects of the adenosine analogues, were investigated in phrenic nerve‐diaphragm preparations.

NECA, R‐PIA and CADO decreased, in a concentration‐dependent manner, the evoked tritium outflow from preparations loaded with [3H]‐choline. NECA and R‐PIA were about equipotent and more potent than CADO.

DPCPX shifted to the right in a near parallel fashion the concentration‐response curve for the inhibitory effect of R‐PIA on evoked tritium outflow.

In the presence of DPCPX, NECA increased, rather than decreased, evoked tritium outflow. PD 115,199 antagonized, in a concentration‐dependent manner, this excitatory effect of NECA.

CGS 21680C, in low nanomolar concentrations, increased evoked tritium outflow, an effect also antagonized by PD 115,199.

CGS 21680C increased, and R‐PIA decreased, the amplitude of e.p.ps recorded from preparations paralysed with tubocurarine. Both effects could be observed in the same endplate.

It is concluded that both inhibitory (probably A1) and excitatory (probably A2) adenosine receptors coexist at the rat neuromuscular junction, modulating the evoked release of acetylcholine.
Role of 5‐HT1‐like receptors in the reduction of porcine cranial arteriovenous anastomotic shunting by sumatriptan
Authors: den Boer Marinus O. , Villalón Carlos M. , Heiligers Jan P.C. , Humphrey Patrick P.A. , Saxena Pramod R.
Published: July 2012

The new tryptamine derivative sumatriptan (GR43175) is effective in the treatment of migraine. Since several antimigraine agents reduce cranial arteriovenous anastomotic blood flow in the anaesthetized pig, we have investigated the carotid haemodynamic effects of sumatriptan.

Sumatriptan (10, 30, 100 and 300 μg kg−1, i.v.) reduced total common carotid blood flow, exclusively by affecting its arteriovenous anastomotic fraction; the capillary fraction even increased with the highest doses.

These reductions in the carotid arteriovenous anastomotic (‘shunt’) blood flow were mediated by a 5‐HT1‐like receptor, as methiothepin, but not ketanserin, antagonized the responses to sumatriptan.

Sumatriptan increased the difference in oxygen saturation between arterial and jugular venous blood, which is likely to be a consequence of the reduction of the carotid shunt blood flow.

The selective reduction in arteriovenous anastomotic blood flow produced by sumatriptan may reflect its antimigraine action, thought to involve vasoconstriction of those cranial vessels, be they ‘shunt’ vessels or not, which are distended and inflamed during a migraine attack.
Characterization and actions of human umbilical endothelium derived relaxing factor
Authors: Chaudhuri G. , Buga Georgette M. , Gold Michele E. , Wood Keith S. , Ignarro Louis J.
Published: July 2012

A bioassay cascade superfusion technique was utilized to study the properties of endothelium derived relaxing factor (EDRF) from human umbilical vein (HUV) and compare its actions on umbilical, chorionic plate and bovine pulmonary arterial strips.

Histamine (1 μm), bradykinin (1 μm) and A‐23187 (0.3 μm, 1 μm) but not acetylcholine (1 μm) released EDRF.

The non‐innervated human foetoplacental vessels, i.e., umbilical and chorionic plate arteries, do relax to EDRF by a guanosine 3′: 5′‐cyclic monophosphate (cyclic GMP)‐mediated mechanism.

The sensitivity of the human umbilical arterial strips to EDRF was less than that of the chorionic plate arterial strips. Bovine pulmonary arterial strips were the most sensitive to the relaxant actions of human umbilical EDRF.
Yohimbine increases submaxillary kallikrein release into the saliva in dogs: evidence for α2‐adrenoceptor‐mediated inhibition of cholinergic pathways
Authors: Girolami Jean‐Pierre , Bascands Jean‐Loup , Pécher Christiane , Berlan Michel , Montastruc Jean‐Louis , Montastruc Paul
Published: July 2012

The effects of the α2‐adrenoceptor antagonist, yohimbine (0.5 mg kg−1, i.v.) on basal, sympathetic and parasympathetic stimulation‐induced submaxillary kallikrein release were investigated in the anaesthetized dog. Kallikrein was measured by its kininogenase activity before and after trypsin activation which also allowed a study of the proportion of active to total enzyme.

Yohimbine induced a rapid, three fold increase in basal kallikrein release correlated with an increase in salivary flow rate which lasted for 60 min following injection.

Sectioning the chorda tympani did not affect basal kallikrein release but abolished yohimbine‐induced rise in salivary kallikrein secretion.

Parasympathetic stimulation alone induced a 3 to 4 fold increase in basal kallikrein release correlated with an increase in salivary flow rate. Yohimbine induced a significant additional increase in parasympathetic‐stimulated kallikrein release.

When the cervical sympathetic nerve was sectioned the basal kallikrein release decreased by 30 to 40%.

Sympathetic stimulation alone also induced a 3 to 4 fold increase in basal kallikrein. This was not correlated with the salivary flow and unaffected by yohimbine.

The results indicate that yohimbine increases submaxillary kallikrein release into the saliva by inhibition of presynaptic α2‐adrenoceptors located on the chorda tympani nerve endings.
5‐HT1‐like receptors mediate 5‐hydroxytryptamine‐induced contraction of guinea‐pig isolated iliac artery
Authors: Sahin‐Erdemli I. , Hoyer D. , Stoll A. , Seiler M.P. , Schoeffter P.
Published: July 2012

The effects of 5‐hydroxytryptamine (5‐HT) and of the 5‐HT1‐like receptor agonists, 5‐carboxamidotryptamine (5‐CT) and sumatriptan (GR43175) were investigated in isolated ring preparations of guinea‐pig common iliac artery.

The three agonists induced very weak, if any, contractions of unstimulated preparations, whereas they elicited concentration‐dependent contractions in preparations given a moderate tone by a threshold concentration of prostaglandin F2α (PGF2α).

Under the latter conditions, Emax values for 5‐HT and 5‐CT reached about 45% of PGF2α maximal effect, whereas the Emax value of sumatriptan was significantly lower (about 35%). The rank order of potency (mean EC50 value, nm) was 5‐CT (6.6) > 5‐HT (22.9) > sumatriptan (155). Pargyline, cocaine or deoxycorticosterone were without significant effect on the contractions induced by 5‐HT.

The 5‐HT3 receptor antagonist, (1αH,3α,5αH‐tropan‐3‐yl) 1‐H‐indole‐3‐carboxylic acid ester (ICS 205–930; 1 μm), had no effect on 5‐HT‐, 5‐CT‐ and sumatriptan‐induced contractions.

The 5‐HT2 receptor antagonist, ketanserin (1 μm) caused only small rightward shifts (concentration‐ratios, about 2) in the concentration‐response curves to 5‐HT, 5‐CT and sumatriptan without significantly depressing the maximum effects.

In the presence of ketanserin (1 μm), the non‐selective 5‐HT receptor antagonist, methiothepin (0.1 μm), shifted the concentration‐response curves to 5‐HT and 5‐CT to the right in a parallel manner and to a similar extent for both agonists (respective mean pKB values, 8.07 and 8.27). The effect of sumatriptan was also antagonized by methiothepin, but solvent effects precluded quantitative analysis of this antagonism.

It is concluded that 5‐HT1‐like receptors mediate the contractions induced by 5‐HT, 5‐CT and sumatriptan in guinea‐pig isolated iliac artery. For reasons not yet understood, these receptors are detected only when the tissues are moderately pre‐contracted by PGF2α.
An amplifying effect of exogenous and neurally stored 5‐hydroxytryptamine on the neurogenic contraction in rat tail artery
Authors: Szabó Csaba , Hardebo Jan Erik , Owman Christer
Published: July 2012

The interactions between sympathetic neuroeffector transmission and 5‐hydroxytryptamine (5‐HT) were investigated in segments of rat isolated tail artery.

Contractile responses to field stimulation of the artery segments were abolished by tetrodotoxin (3 × 10−7 m). A subthreshold concentration of acutely applied exogenous 5‐HT (10−8 m) markedly enhanced the contractions induced by sympathetic nerve stimulation, through an action on postjunctional 5‐HT2‐receptors.

The amplifying effect of 5‐HT involved an enhanced influx of extracellular calcium into the smooth muscle cells. In contrast, the neurogenic contractions in vessels not exposed to 5‐HT were not dependent on extracellular calcium.

The adrenergic component of the amplified response involved postjunctional α1‐ but not α2‐ adrenoceptor activation.

Exposure of the vessels to 5‐HT (5 × 10−7 m) for 30 min resulted in uptake of the amine into the perivascular sympathetic nerves, as demonstrated by immunohistochemistry. After chemical sympathectomy with 6‐hydroxydopamine in vitro or in vivo, or surgical sympathectomy, there was little or no uptake.

Exposure to 5‐HT followed by repeated washing resulted in an enhancement of the neurogenic contraction, which was still fully tetrodotoxin‐sensitive. The enhanced response was blocked by ketanserin (10−8 m) and prevented by the presence of the 5‐HT uptake blocker, paroxetine (3 × 10−8 m), during the period of exposure to 5‐HT.
Effects of acute paroxetine administration on tryptophan metabolism and disposition in the rat
Authors: Badawy Abdulla A.‐B. , Morgan Christopher J.
Published: July 2012

The effects of acute oral administration of paroxetine on tryptophan metabolism and disposition were examined in the rat.

Basal liver tryptophan pyrrolase activity was inhibited by paroxetine in vitro and after oral administration. Maximum inhibition was caused by a 1 mg kg−1 dose.

Paroxetine administration also inhibited pyrrolase activity that had previously been enhanced by hormonal induction by cortisol or cofactor activation by haematin. The cortisol induction of the enzyme was, however, not inhibited by pretreatment of rats with paroxetine.

Paroxetine increased tryptophan availability to the brain, because of the above pyrrolase‐inhibitory mechanism. Cerebral 5‐hydroxytryptamine (5‐HT) synthesis was accordingly enhanced, though this was apparent only with doses of the drug of up to 1 mg kg−1. With larger doses, decreased 5‐HT turnover, probably as a result of 5‐HT uptake inhibition, was the more dominant feature.

Paroxetine lowered circulating corticosterone concentration, but did not influence those of albumin, non‐esterified fatty acids or glucose.

It is concluded that, in addition to inhibiting brain 5‐HT turnover, paroxetine also, in common with 20 other antidepressants, enhances 5‐HT synthesis by increasing brain tryptophan concentration secondarily to inhibition of liver tryptophan pyrrolase activity.
Evidence for nitric oxide as mediator of non‐adrenergic, non‐cholinergic relaxations induced by ATP and GABA in the canine gut
Authors: Boeckxstaens Guy E. , Pelckmans Paul A. , Bult Hidde , De Man Joris G. , Herman Arnold G. , Van Maercke Yvan M.
Published: July 2012

The effects of haemoglobin, and the nitric oxide (NO) biosynthesis‐inhibitors NG‐monomethyl‐l‐arginine (l‐NMMA), its enantiomer d‐NMMA, and NG‐nitro‐l‐arginine (l‐NNA) were investigated on non‐adrenergic non‐cholinergic (NANC)‐mediated relaxation of circular muscle strips of the canine terminal ileum and ileocolonic junction induced by electrical stimulation, adenosine 5′‐triphosphate (ATP), γ‐aminobutyric acid (GABA) and NO.

Tetrodotoxin, l‐NMMA and l‐NNA, but not d‐NMMA, inhibited the relaxations induced by electrical stimulation, ATP and GABA, but not those in response to NO.

The inhibitory effect of l‐NMMA and l‐NNA was prevented by l‐arginine, but not by d‐arginine. l‐Arginine did not potentiate any of the NANC relaxations.

Haemoglobin reduced the relaxation induced by electrical stimulation, ATP and GABA, and abolished those in response to NO.

Our results demonstrate that the ATP‐ and GABA‐induced relaxations resulting from stimulaton of intramural NANC neurones, in addition to those induced by electrical impulses, are mediated by NO or a NO releasing substance and thus provide further evidence in support of the proposal that NO is the final inhibitory NANC neurotransmitter in the canine terminal ileum and ileocolonic junction.
Effect of phorbol ester on the release of atrial natriuretic peptide from the hypertrophied rat myocardium
Authors: Kinnunen Päivi , Taskinen Tarja , Järvinen Mikko , Ruskoaho Heikki
Published: July 2012

To determine the cellular mechanisms of atrial natriuretic peptide (ANP) release from ventricular cardiomyocytes, the secretory and the cardiac effects of a phorbol ester, 12‐O‐tetradecanoyl‐phorbol‐13‐acetate (TPA), known to stimulate protein kinase C activity in heart cells, were studied in isolated, perfused heart preparations from 2‐ and 21‐month‐old Wistar‐Kyoto (WKY) and spontaneously hypertensive (SHR) rats. TPA was added to the perfusion fluid for 30 min at a concentration of 46 nm after removal of atrial tissue. Additionally, atrial and ventricular levels of immunoreactive ANP (IR‐ANP) and ANP mRNA, the distribution of ANP within ventricles as well as the relative contribution of atria and ventricles in the release of ANP were studied.

Ventricular hypertrophy that gradually developed in hypertensive rats resulted in remarkable augmentation of ANP gene expression, as reflected by elevated levels of immunoreactive ANP and ANP mRNA. The total amount of IR‐ANP in the ventricles of the SHR rats increased 41 fold and ANP mRNA levels 12.9 fold from the age of 2 to 21 months. At the age of 21 months, levels of IR‐ANP and ANP mRNA in the ventricles of SHR rats were 5.4 fold and 3.7 fold higher, respectively, than in the normotensive WKY rats. Immunohistochemical studies demonstrated ANP granules within the hypertrophic ventricles of the old SHR rats, but not within normal ventricular tissue.

In isolated perfused heart preparations, the severely hypertrophied ventricular tissue of SHR rats after atrialectomy secreted more ANP into the perfusate than did the control hearts. The phorbol ester TPA caused a marked vasoconstriction in both the 2‐month and 21‐month old normal and hypertrophied hearts. Interestingly, the ANP release from the hypertrophied ventricles of the old SHR rats increased considerably (from 413 ± 30 to the maximum of 623 ± 75 pg ml−1, F = 10.8, P < 0.001, two‐way analysis of variance), whereas only a small increase was seen in old WKY rats and no effect was observed in young animals of either strain. When intact rat hearts (without atrialectomy) were used, infusion of phorbol ester also increased the ANP secretion into the perfusate in young animals.

Our present results indicate that the phorbol ester TPA increases the release of ANP from the hypertrophied, but not from normal rat myocardium. Thus, hypertrophied rat ventricular myocytes appear to possess the cellular mechanisms necessary to secrete ANP by a regulated pathway. The results further suggest that protein kinase C activity may be involved in the the regulation of ANP secretion from ventricular cells, as has been shown earlier for atrial myocytes.
Diabetes‐induced changes in cardiac β‐adrenoceptor responsiveness: effects of aldose reductase inhibition with ponalrestat
Authors: Austin Clare E. , Chess‐Williams Russell
Published: July 2012

The responses of isolated left atria and papillary muscles to isoprenaline, forskolin and calcium have been examined in 3 week streptozotocin‐diabetic rats and the effects of oral ponalrestat administration (25 mg kg−1 daily) on diabetes‐induced changes in cardiac responsiveness investigated.

Three weeks after animals were made diabetic, cardiac responses to isoprenaline were enhanced and this was accompanied by an increase in the density of ventricular [3H]‐dihydroalprenolol binding sites. Treatment of animals with ponalrestat prevented the increase in cardiac β‐adrenoceptor responsiveness and receptor number.

Diabetes also enhanced the sensitivity of cardiac tissues to forskolin, an effect that was not prevented by the treatment of animals with ponalrestat.

Ponalrestat treatment increased the resting and maximum tensions developed by cardiac tissues from diabetic animals and increased the maximum tensions developed by tissues from control animals. Diabetes alone had no effect on resting or maximum developed tensions.

Ponalrestat therefore prevents the changes in β‐adrenoceptor density and responsiveness induced by short‐term diabetes in the rat and also increases the tension developed by cardiac muscle, an effect observed in diabetic and normal animals.
Relaxation of sheep cerebral arteries by vasoactive intestinal polypeptide and neurogenic stimulation: inhibition by l‐NG‐monomethyl arginine in endothelium‐denuded vessels
Authors: Gaw A.J. , Aberdeen J. , Humphrey P.P.A. , Wadsworth R.M. , Burnstock G.
Published: July 2012

Perivascular nerves of the sheep middle cerebral artery show immunoreactivity for both vasoactive intestinal polypeptide (VIP) and calcitonin gene‐related peptide (CGRP).

Rings of endothelium‐denuded sheep middle cerebral artery precontracted with 5‐hydroxytryptamine were relaxed by CGRP (maximum relaxation = 87.8 ± 8.1%, pD2 = 7.81 ± 0.12, n = 12) and by VIP (maximum relaxation = 55.1 ± 4.1%, pD2 = 7.65 ± 0.04, n = 18). Rings of endothelium‐denuded cat middle cerebral artery precontracted with U46619 were also relaxed by vasoactive intestinal polypeptide (maximum relaxation = 53.1 ± 6.1%, pD2 = 7.82 ± 0.11, n = 6).

Haemolysate (1 μl ml−1) inhibited VIP‐induced relaxation in endothelium‐denuded sheep and cat middle cerebral artery (n = 6) but had no effect on the CGRP‐induced relaxation of the sheep middle cerebral artery (n = 6).

The relaxant response to VIP in endothelium‐denuded sheep middle cerebral artery was inhibited by methylene blue (10 μm) and augmented by either M&B 22948 (10 μm) or superoxide dismutase (150 units ml−1). Indomethacin (1 μm) had no effect.

The addition of l‐NG‐monomethyl arginine (100 μm) inhibited both neurogenic and VIP‐induced relaxation of endothelium‐denuded sheep MCA by 56 ± 6% and 60 ± 6% (n = 5) respectively. The CGRP‐induced relaxation was unaffected.

It is concluded that neurally mediated vasodilatation in the sheep middle cerebral artery is mediated largely by VIP through a direct action on smooth muscle through a cyclic‐GMP‐mediated mechanism that appears to involve synthesis of nitric oxide from l‐arginine. Vasodilatation by CGRP, which is also contained in perivascular nerves, does not utilize this pathway.
Local application of drugs to sympathetic nerve terminals: an electrophysiological analysis of the role of prejunctional α‐adrenoceptors in the guinea‐pig vas deferens
Authors: Brock J.A. , Cunnane T.C.
Published: July 2012

Focal extracellular recording techniques were used to study the effects of clonidine, yohimbine and tyramine on the intermittent transmitter release mechanism in the guinea‐pig vas deferens in vitro. Drugs were applied locally to the varicosities located within the recording electrode. Statistical methods were used to determine whether noradrenaline (NA) acts locally to inhibit secretion from the same or a closely related release site (local regulation) on an impulse‐to‐impulse basis.

The α‐adrenoceptor agonist, clonidine, inhibited transmitter release, an effect reversed by the α‐adrenoceptor antagonist, yohimbine. Yohimbine alone increased action potential‐evoked transmitter release, findings consistent with the idea that transmitter release is regulated through prejunctional α‐adrenoceptors.

The indirectly acting sympathomimetic, tyramine, powerfully inhibited evoked transmitter release, an effect reversed by both yohimbine and phentolamine. The inhibitory effects of tyramine were greatly reduced in tissues taken from animals pretreated with reserpine. Clonidine powerfully inhibited transmitter release in reserpinized tissues showing that prejunctional α‐adrenoceptors were functionally intact. The inhibitory effects of tyramine on transmitter release are therefore mediated indirectly through the release of endogenous NA.

Paradoxically, when transmitter release from a small population of variscosities on a single nerve fibre was studied in the absence of α‐adrenoceptor antagonists, no evidence was found for local regulation of transmitter release.

The intermittent character of the transmitter release process makes it difficult to envisage how impulse‐to‐impulse regulation could occur. Furthermore, it is unlikely that NA will accumulate to any appreciable extent in the vicinity of the secreting varicosity.

The pharmacological evidence clearly supports the view that NA released from sympathetic nerve terminals by nerve impulses modulates subsequent transmitter release. However, the evidence does not support the view that released NA acts locally to inhibit secretion from recently activated varicosities.
The pressor response to central administration of β‐endorphin results from a centrally mediated increase in noradrenaline release and adrenaline secretion
Authors: May Clive N. , Whitehead Catherine J. , Mathias Christopher J.
Published: July 2012

The effects of intracerebroventricular (i.c.v.) and intracisternal (i.c.) administration of β‐endorphin (0.01, 0.1 and 1.0 nmol kg−1) were examined in conscious rabbits.

After i.c.v. β‐endorphin, mean arterial pressure (MAP) increased, heart rate (HR) fell, plasma noradrenaline, adrenaline and glucose increased and there was a rise in Paco2 and fall in Pao2; these effects were reversed by intravenous (i.v.) naloxone (300 nmol kg−1).

A combination of prazosin (2 mg kg−1) and yohimbine (1 mg kg−1), given i.v., prevented the rise in MAP induced by i.c.v. β‐endorphin.

After i.c. β‐endorphin, MAP, HR and plasma catecholamines were not significantly altered but there was a similar degree of respiratory depression.

Clonidine (1.0 μg kg−1, i.c.) reduced MAP and HR; these effects were not blocked by i.v. naloxone (6 μmol kg−1).

These results demonstrate that β‐endorphin acts centrally, probably mainly on periventricular μ‐opioid receptors, to increase adrenaline secretion and sympathetic nerve activity leading to α‐adrenoceptor‐mediated vasoconstriction. The respiratory depression is probably mediated by brainstem μ‐receptors.

A role for β‐endorphin in the central hypotensive action of α2‐adrenoceptor agonists was opposed by finding that opioid receptor antagonism with naloxone did not block the effects of clonidine.
Pharmacokinetic‐pharmacodynamic modelling of the EEG effects of midazolam in individual rats: influence of rate and route of administration
Authors: Mandema Jaap W. , Tukker Erica , Danhof Meindert
Published: July 2012

The purpose of the present investigation was to quantify the concentration‐pharmacological effect relationship of midazolam in individual rats by use of effect parameters derived from aperiodic EEG analysis. By varying the rate and route of administration the role of (inter)active metabolites and development of acute tolerance was evaluated.

The pharmacokinetics and pharmacodynamics of midazolam were determined after intravenous administration of 10 mg kg−1 during 5, 30 and 60 min and oral administration of 15 mg kg−1. Following intravenous administration the pharmacokinetics were most adequately described by a bi‐exponential equation. The values (mean ± s.e.mean, n = 20) of clearance, volume of distribution at steady‐state and terminal half‐life were 67 ± 2 ml min−1 kg−1, 1.61 ± 0.071 kg−1 and 27 ± 1 min, respectively. Following oral administration midazolam was rapidly absorbed with a systemic availability of 45 ±9%.

The averaged amplitudes in the 11.5–30 Hz (beta) frequency band of the fronto‐central lead on the left‐hemisphere, as derived by aperiodic EEG analysis, was selected as a measure of the pharmacological effect of midazolam. By pharmacokinetic‐pharmacodynamic modelling the individual concentration‐EEG effect relationships of midazolam were derived, which were successfully quantified by the sigmoidal Emax model. No marked and systematic differences in pharmacodynamic parameters were found between the rates and routes of administration. The averaged pharmacodynamic parameters of midazolam obtained after combining the results of all rates and routes of administration were (mean ± s.e.mean, n = 27): Eo = 61 ± 3 μV s−1, Emax = 85 ± 3 μV s−1, EC50 = 40 ± 3ng ml−1 and N = 0.84 ± 0.04.

The results of the present study show that the concentration‐EEG effect relationship of midazolam can be characterized in individual animals using the amplitudes in the 11.5–30 (beta) frequency band as a measure of pharmacological response. Acute tolerance did not develop and (inter)active metabolites did not contribute to this effect parameter within the time span of the experiments.
Selectivity of Ca2+channel blockers in inhibiting muscular and nerve activities in isolated colon
Authors: Lecchini S. , Marcoli M. , De Ponti F. , Castelletti C.A. , Frigo G.M.
Published: July 2012

Potency and efficacy of nifedipine, verapamil and diltiazem and of Bay K 8644 in modifying propulsion and nerve or smooth muscle activities have been compared in the guinea‐pig isolated distal colon. Both the neuronal and muscular effects of Ca2+channel blockers seem to develop at concentrations that are devoid of any significant effect apart from that on Ca2+channels.

Nifedipine, verapamil and diltiazem were all able to impair propulsion, resting and stimulated acetylcholine (ACh) release and smooth muscle contractility in a concentration‐dependent way. However, some degree of selectivity for neuronal and muscular effects could be observed. Nifedipine was more than 500 fold more potent than verapamil in relaxing musculature but less than twice as potent in reducing ACh release. On the other hand, verapamil was the most efficacious Ca2+channel blocker tested in inhibiting ACh release, its effects being inversely correlated to the external Ca2+concentration, and completely abolished by Bay K 8644.

By comparing the potencies exhibited by each drug against peristaltic reflex, smooth muscle contractility and ACh release, verapamil proved to be almost as potent in slowing the peristaltic reflex as in reducing ACh release, while nifedipine was about 100 fold more potent against the peristaltic reflex than against ACh release, but nearly equal against the peristaltic reflex and smooth muscle tone. Therefore, interference with cholinergic neurotransmission is likely to play a major role in the antipropulsive effect of verapamil, while peristaltic reflex impairment by nifedipine is likely to be dependent on inhibition of smooth muscle.

A facilitatory effect of Bay K 8644 on both the efficiency of the peristaltic reflex and the non‐adrenergic, non‐cholinergic (NANC) nerve‐mediated relaxation could be observed at concentrations at least 10 fold lower than those required to affect ACh release or smooth muscle.

It is concluded that the effects of Ca2+channel blockers on neurotransmitter release may be relevant to their effects on the gastrointestinal motor function.
4‐Aminopyridine‐induced increase in basal and stimulation‐evoked [3H]‐NA release in slices from rat hippocampus: Ca2+ sensitivity and presynaptic control
Authors: Hu Ping‐Sheng , Fredholm Bertil B.
Published: July 2012

We have examined the mechanisms by which the K+‐channel blocker 4‐aminopyridine (4‐AP) can dose‐dependently increase both basal [3H]‐noradrenaline ([3H]‐NA) release and the [3H]‐NA release evoked by electrical stimulation, but not the release of [3H]‐acetylcholine ([3H]‐ACh), from slices of rat hippocampus.

Both the electrically evoked and the 4‐AP‐induced release were blocked by tetrodotoxin (TTX) (3 μm). The Ca2+‐dependence of the 4‐AP‐induced release (EC50 0.15 mm) was, however, different from that of the electrically evoked [3H]‐NA release (EC50 0.76 mm).

The 4‐AP‐induced release could be inhibited by CdCl2(10 μm) and ω‐conotoxin (30 nm), but not by nifedipine (1 μm).

Transmitter release evoked by 100 μm 4‐AP could be blocked by the α2‐adrenoceptor agonist, UK 14,304 (0.1 μm) and by the A1‐receptor agonist R‐N6‐phenylisopropyl adenosine (R‐PIA, 1 μm) and increased by the α2‐adrenoceptor antagonist, yohimbine (1 μm), both in 0.25 and 1.3 mm Ca2+‐containing medium. By contrast, the effect of α2‐adrenoceptor agonists and antagonists on transmitter release evoked by electrical stimulation was markedly reduced in the presence of 4‐AP (100 μm).

The results suggest that 4‐AP can depolarize some nerve endings in the central nervous system, leading to transmitter release that is dependent on nerve impulses and Ca2+. Furthermore, the fact that α2‐receptors and adenosine A1 receptor agonists can influence the release of NA evoked by 4‐AP suggests that these drugs may have actions that are independent of blockade of aminopyridine‐sensitive K+‐channels.
Hoe 140 a new potent and long acting bradykinin‐antagonist: in vivo studies
Authors: Wirth K. , Hock F.J. , Albus U. , Linz W. , Alpermann H.G. , Anagnostopoulos H. , Henke St. , Breipohl G. , König W. , Knolle J. , Schölkens B.A.
Published: July 2012

The potency, duration of action and tolerability of Hoe 140, a novel and highly potent bradykinin (BK) antagonist in vitro, has been tested in different in vivo models and compared with the well‐known BK antagonist d‐Arg‐[Hyp2, Thi5,8, d‐Phe7]BK.

Hoe 140 is highly potent and long acting in inhibiting BK‐induced hypotensive responses in the rat. Four hours after s.c. administration of 20 nmol kg−1, inhibition still amounted to 60% whereas the effect of 200 nmol kg−1 of d‐Arg‐[Hyp2, Thi5,8, d‐Phe7]BK was not significant.

BK‐induced bronchoconstriction in guinea‐pigs was strongly inhibited by Hoe 140. The magnitude and duration of inhibition confirmed the findings obtained in the blood pressure experiments in the rat.

Carrageenin‐induced inflammatory oedema of the rat paw was considerably inhibited at i.v. doses between 0.1 and 1 mg kg−1.

In conscious dogs, intravenous doses of 0.01 and 0.1 mg kg−1 of Hoe 140 and d‐Arg‐[Hyp2, Thi5,8, d‐Phe7]BK were well tolerated. At doses of 1 mg kg−1 adverse effects occurred that were attributed to the residual BK agonistic activity of both compounds.

Hoe 140 has been shown to be a highly potent and long acting BK antagonist in vivo in different animal species and models. This makes it appropriate to investigate further the physiological and pathophysiological role of BK.
Effect of p‐chlorophenylalanine on release of 5‐hydroxytryptamine from the rat frontal cortex in vivo
Authors: O'Connell M.T. , Portas C.M. , Sarna G.S. , Curzon G.
Published: July 2012

Rats were given p‐chlorophenylalanine (PCPA, 150 mg kg−1, i.p.) to inhibit partially 5‐hydroxytryptamine (5‐HT) synthesis so that its concentration in the frontal cortex fell by about half. The effects of this treatment on frontal cortex dialysate 5‐HT and 5‐hydroxyindoleacetic acid (5‐HIAA) concentrations were determined before and after stimulation by increasing K+ concentration in the perfusion fluid by 100 mm for 20 min. Rates of 5‐HT synthesis as indicated by the effects of 3‐hydroxybenzylhydrazine (NSD 1015, 150 mg kg−1, i.p.) on frontal cortex tissue and dialysate 5‐hydroxytryptophan (5‐HTP) and dialysate 5‐HIAA were also measured in rats that had not been stimulated with K+.

Dialysate 5‐HT and 5‐HIAA concentrations of both vehicle‐ and PCPA‐treated rats fell into major (group 1) and minor (group 2) populations statistically distinguishable from each other by the high 5‐HT and low 5‐HIAA values of the latter group.

In group 1 animals, PCPA decreased both the dialysate 5‐HT concentration and its rise following stimulation by K+ in proportion with the decrease of 5‐HT in frontal cortex tissue. 5‐HIAA fell more markedly than 5‐HT and in similar proportion in both tissue and dialysate. The fall of dialysate 5‐HIAA on stimulation by K+ was also attenuated to the same degree. The elevated 5‐HT/5‐HIAA ratios after PCPA treatment imply increased conservation of the depleted 5‐HT stores.

PCPA decreased the above 5‐HIAA values and the effects of NSD 1015 on tissue 5‐HTP or dialysate 5‐HIAA concentrations in similar proportion. However, PCPA had little effect on corresponding dialysate 5‐HTP values.

The results are discussed with respect to relationships between synthesis, storage and release of 5‐HT. They indicate that (under the conditions of the present study) the availability of 5‐HT to receptors is directly proportional to total vesicular stores under both basal conditions and during neuronal firing.
Flosequinan, a vasodilator with a novel mechanism of action
Authors: Resnick Moira S. , Maitland L.A. , Morgan Kathleen G.
Published: July 2012

The mechanism of action of flosequinan was investigated in ferret aortic smooth muscle by the simultaneous measurement of aequorin luminescence and isometric force.

The control calcium‐force curve was obtained by plotting the calibrated aequorin luminescence against the force from potassium‐depolarized muscles. Flosequinan relaxed potassium‐depolarized muscles by causing parallel changes in [Ca2+]i and force with no shift in the control [Ca2+]i‐force relationship.

The [Ca2+]i‐force relationship in the presence of a maximally effective concentration of phenylephrine was significantly shifted to the left of that for the control, potassium‐depolarized muscle. Flosequinan relaxed the phenylephrine‐contracted muscle by causing a large decrease in force with only a minimal decrease in [Ca2+]i, resulting in an apparent rightward shift of the [Ca2+]i‐force relationship, toward the control curve.

In comparison, sodium nitroprusside caused relaxation of either the potassium‐ or phenylephrine‐induced contraction solely by a decrease in [Ca2+]i with no shift in either calcium‐force relationship.

Milrinone caused no significant rightward shift of the calcium‐force relationship during phenylephrine‐ or potassium‐induced contractions, but when milrinone was added in the absence of vasoconstrictors, relaxation was obtained with no significant decrease in [Ca2+]i.

Flosequinan appears to differ in mechanism of action from both nitroprusside and milrinone. It relaxes depolarization‐mediated contractions solely by decreasing [Ca2+]i but also appears to be capable of reversing the apparent calcium sensitizing action of phenylephrine.
P2 purinoceptor regulation of mucin release by airway goblet cells in primary culture
Authors: Kim K. Chul , Lee Bong C.
Published: July 2012

The effects of adenine analogues on mucin release by airway goblet cells have been examined in a hamster primary tracheal epithelial cell culture.

Adenosine, a P1 receptor agonist, had no effect on mucin release even at 2 mm, while ATP, a P2 receptor agonist, stimulated mucin release in a dose‐dependent fashion with an apparent EC50 of 20μm. The relative potency order among adenine nucleotides was ATP > ADP > AMP = adenosine.

ATPγS, a non‐hydrolyzable analogue of ATP, was equipotent with ATP in stimulating mucin release. The potency order among some ATP analogues was ATP > 2‐methylthio ATP > α,β‐methylene ATP > β,γ‐methylene ATP. Reactive blue 2, a putative P2y‐purinoceptor antagonist, did not block the ATP‐induced mucin release.

The present results indicate that mucin release by airway goblet cells is stimulated by extracellular ATP via P2 receptor‐mediated mechanism. We suggest that this mechanism may be important in the physiological regulation of airway goblet cell mucin release in vivo.
Pulse exposure to protein synthesis inhibitors enhances vascular responses to des‐Arg9‐bradykinin: possible role of interleukin‐1
Authors: deBlois Denis , Bouthillier Johanne , Marceau François
Published: July 2012

The modulation of the spontaneous increase in contractile responses to des‐Arg9‐bradykinin (des‐Arg9‐BK) of rabbit aortic strips incubated in vitro was studied. Rapid hypotensive responses to exogenous kinins were also measured in rabbits anaesthetized 5 h following pretreatment.

Continuous exposure to the protein synthesis inhibitors cycloheximide (71 μm) or anisomycin (3.8 μm) profoundly inhibited the sensitization to des‐Arg9‐BK in incubated aortic strips. However, temporary (3 h) inhibition of protein synthesis in vitro followed by further incubation (3 h) of tissues without inhibitor, paradoxically enhanced both the maximal contractile responses to des‐Arg9‐BK (1.7 μm) and the apparent affinity of the kinin without affecting contractions to noradrenaline (NA, 100 nm) at 6.5 h.

The stimulatory activity of the short treatment (pulse) with cycloheximide was abolished in the presence of dexamethasone sodium phosphate (100 μm throughout the incubation). The function of receptors for kinins did not appear to be altered directly by the steroid treatment.

Interleukin‐1β (IL‐1β), applied at low concentrations (100–250 pg ml−1) on aortic strips between 3 h and 6.5 h of incubation time, mimicked the selective stimulatory effect of the cycloheximide pulse on responses to des‐Arg9‐BK. Higher concentrations of IL‐1β (0.5–5 ng ml−1) did not further amplify the responses to des‐Arg9‐BK but decreased the contractile responses to NA.

The modulation by IL‐1β of vascular sensitivity to des‐Arg9‐BK and to NA was prevented by blockade of protein synthesis.

The induction in vivo by IL‐1β (5 μg kg−1) or by cycloheximide (10 mg kg−1) of cardiovascular responsiveness to des‐Arg9‐BK was demonstrated with a blood pressure assay of exogenous kinins or with tissues isolated ex vivo 5 h after pretreatment of animals. Evidence of active disposition of cycloheximide in vivo was also obtained.

We propose the production of endogenous IL‐1 as a possible mechanism for the enhancement of responsiveness to des‐Arg9‐BK observed in tissues pulsed with a protein synthesis inhibitor and for the inducing effect of cycloheximide or E. coli lipopolysaccharide in vivo. These results suggest that effects mediated by the BK1 receptor for kinins are potentially present in pathological conditions associated with IL‐1 production.
Comparison of the effects of the K+‐channel openers cromakalim and minoxidil sulphate on vascular smooth muscle
Authors: Wickenden A.D. , Grimwood S. , Grant T.L. , Todd M.H.
Published: July 2012

The actions of the potassium channel openers, cromakalim and minoxidil sulphate, were compared in a range of isolated blood vessel preparations.

Cromakalim and minoxidil sulphate inhibited spontaneous mechanical activity of the guinea‐pig portal vein and relaxed the noradrenaline precontracted rat aorta with similar potency. In contrast, minoxidil sulphate was less potent than cromakalim in inhibiting spontaneous activity in the rat portal vein and was essentially inactive in the noradrenaline precontracted rat mesenteric artery and rabbit aorta.

Minoxidil sulphate did not antagonize the effects of cromakalim in the rabbit aorta indicating it was not acting as a partial ‘agonist’.

Charybdotoxin, noxiustoxin and rubidium failed to discriminate between cromakalim and minoxidil sulphate indicating that the apparently selective effects of minoxidil sulphate were not mediated by either Ca2+‐activated potassium channels, delayed rectifiers or rubidium impermeable potassium channels.

Glibenclamide antagonized the effects of cromakalim in an apparently competitive manner whereas the effects of minoxidil sulphate were antagonized in a non‐competitive manner. The involvement of subtypes of ATP‐sensitive potassium channels is discussed.
Cardioprotective and endothelial protective effects of [Ala‐IL8]77 in a rabbit model of myocardial ischaemia and reperfusion
Authors: Lefer Allan M. , III Gerald Johnson , Ma Xin‐liang , Tsao Phillip S. , Thomas G. Roger
Published: July 2012

We studied the effects of a form of interleukin‐8 (i.e., [Ala‐IL8]77) on endothelial dysfunction and myocardial injury in rabbits. Pentobarbitone‐anaesthetized rabbits were subjected to 1.5 h occlusion of the marginal coronary artery and 3.5 h reperfusion. [Ala‐IL8]77 (50 μg or its vehicle) was given i.v. as a bolus 10 min prior to reperfusion. [Ala‐IL8]77 was also studied in isolated perfused hearts of rabbits.

Myocardial ischaemia plus reperfusion in untreated rabbits produced severe endothelial dysfunction and myocardial injury, including marked myocardial necrosis, elevated cardiac myeloperoxidase (MPO) activity in ischaemic cardiac tissue, and loss of response of marginal coronary rings to the endothelium‐dependent vasodilators, acetylchloline (ACh) and A23187.

Administration of [Ala‐IL8]77 10 min prior to reperfusion resulted in significant protective effects in post‐ischaemic reperfusion. Compared with untreated rabbits, [Ala‐IL8]77 caused a reduced necrotic zone (P < 0.01), lower MPO activity in the necrotic zone (P < 0.05), and significantly preserved vasorelaxant responses of marginal coronary artery rings to endothelium‐dependent vasodilators, ACh (P < 0.001) and A23187(P < 0.001).

These results indicate that myocardial ischaemia and reperfusion result in a severe endothelial dysfunction and myocardial injury which involved the interaction of neutrophils and endothelial cells. However, [Ala‐IL8]77 did not appear to exert a direct endothelial protective effect in the absence of neutrophils in rabbit isolated perfused hearts.

Inhibition of neutrophil accumulation in the myocardium, perhaps by prevention of endothelial dysfunction resulting from [Ala‐IL8]77, leads to significant protective effects in ischaemia and reperfusion in rabbits.
Short‐term effects of administration of anticonvulsant drugs on free carnitine and acylcarnitine in mouse serum and tissues
Authors: Camiña M.F. , Rozas I. , Gómez M. , Paz J.M. , Alonso C. , Rodriguez‐Segade S.
Published: July 2012

The short‐term evolution of concentrations of free carnitine and acylcarnitine was studied in the serum, liver, kidney, heart and skeletal muscle of mice after administration of single therapeutic doses of the anticonvulsant drugs, valproic acid (VPA), carbamazepine (CBZ), phenytoin (PHT) and phenobarbitone (PHB).

The effects of the drugs were immediate but transitory, control levels of free carnitine and acylcarnitine having been recovered or almost recovered in serum and in all tissues 8 h post administration (p.a.).

VPA was the only drug that significantly reduced free carnitine concentration in serum, which recovered control levels by 4 h p.a.

All the drugs studied brought about marked deficits of serum acylcarnitine, which had disappeared 2 h p.a. in the case of VPA and not until 8 h p.a. for CBZ, PHT or PHB.

The minimum concentrations of free carnitine and acylcarnitine in serum were invariably associated with the maximum concentration of drug in serum.

Free carnitine concentration was not affected by VPA in any tissue, PHT and PHB brought about significant deficits in heart and kidney, and CBZ a significant deficit in muscle.

Acylcarnitine concentration was significantly reduced in heart, kidney and muscle by CBZ, PHT and PHB, but in liver the effects of all drugs were very small.

These results are compatible with the hypothesis that the primary cause of anticonvulsant‐induced alteration of carnitine metabolism is interference with renal reabsorption of carnitine.