bluuebunny/crossref_metadata_2025 huggingface dataset:
Palytoxin‐induced contraction and release of endogenous noradrenaline in rat tail artery
Authors: Karaki H. , Nagase H. , Ohizumi Y. , Satake N. , Shibata S.
Published: July 2012

The mechanism of the contractile effect of a potent marine toxin, palytoxin (PTX) on the rat isolated tail artery was examined.

PTX (10−7 M) induced a contraction in the tail artery which was dependent on external Ca2+. This contraction was inhibited (by 75% or more) by 10−6 M prazosin, 2.4 × 10−5 M bretylium and 10−4 M 6‐hydroxydopamine (6‐OHDA), and partially (by 40%) by 10−5 M indomethacin. However, this contraction was not affected by 10−6 m tetrodotoxin (TTX), 10−6 M nifedipine or reserpine treatment. The PTX‐induced contraction in reserpine‐treated artery was partially inhibited by nifedipine and indomethacin but not by prazosin.

Transmural electrical stimulation induced a transient contraction which was dependent on external Ca2+. The contraction induced by electrical stimulation was inhibited by TTX, prazosin, bretylium, reserpine treatment and 6‐OHDA but not by nifedipine or indomethacin.

PTX increased the release of noradrenaline from this artery. However PTX did not release noradrenaline from reserpine‐treated arteries. PTX‐induced noradrenaline release was only partially inhibited by TTX or by Ca2+‐free solution.

These results suggest that PTX has pre‐ and postsynaptic effects in the rat tail artery. PTX may stimulate adrenergic nerves and release noradrenaline mainly by a TTX‐insensitive and Ca2+‐independent mechanism and partially by a TTX‐sensitive and Ca2+‐dependent mechanism. Further, PTX may also release prostaglandins and depolarize smooth muscle cell membrane to induce a contraction.
Differential role of extra‐ and intracellular calcium in the release of EDRF and prostacyclin from cultured endothelial cells
Authors: Lückhoff Andreas , Pohl Ulrich , Mülsch Alexander , Busse Rudi
Published: July 2012

The effects of extracellular Ca2+ on the release of endothelium‐derived relaxing factor (EDRF) and prostacyclin (PGI2), and on the intracellular free calcium concentration ([Ca2+]i), were studied in cultured bovine aortic endothelial cells.

Receptor‐mediated stimulation of endothelial cells with bradykinin (10 nM) elicited a transient release of EDRF (assayed by its stimulant effect on purified soluble guanylate cyclase) and of PGI2 (measured by radioimmunoassay for 6‐keto prostaglandin F1α).

Bradykinin (10 nM) also increased [Ca2+]i (measured with the fluorescent probe indo‐1) from 125 ± 11 nM to 631 ±59 nM, with the same time course as for autacoid release.

In Ca2+‐free medium, [Ca2+]i was still increased by bradykinin but declined faster (within 1 min) to resting levels than in the presence of extracellular Ca2+.

PGI2 release was almost completely abolished in Ca2+‐free medium. The intracellular calcium antagonist TMB‐8 evoked a similar inhibition of PGI2 release.

In contrast, bradykinin‐induced EDRF release was not significantly affected by TMB‐8 but was completely abolished in Ca2+‐free medium.

When endothelial cells were stimulated with the receptor‐independent drug thimerosal (an inhibitor of the enzyme acyl‐CoA‐lysolecithin‐acyl‐transferase; 5 μM), a long‐lasting release of EDRF (>90 min) and PGI2 (>20 min) was observed.

In contrast to bradykinin stimulation, thimerosal‐induced autacoid release was associated with only a slight increase of [Ca2+]i to 201 ± 13 nM after 40min.

After removal of extracellular Ca2+ from thimerosal‐stimulated endothelial cells, [Ca2+]i was little affected during the observation time of 90 s. EDRF release was completely abolished within 90 s whereas PGI2 release was unchanged.

We conclude that EDRF production is directly controlled by extracellular Ca2+ during both receptor‐dependent and independent stimulation. This effect of extracellular Ca2+ is not mediated by changes in [Ca2+]i. In contrast, PGI2 release is closely correlated to [Ca2+]i in bradykinin‐stimulated endothelial cells. However, the results obtained during thimerosal stimulation indicate that there is not necessarily a tight coupling between the absolute level of [Ca2+]i and the amount of PGI2 released.
Evaluation of opioid‐induced antinociceptive effects in anaesthetized and conscious animals
Authors: Clark S.J. , Folienfant R.L. , Smith T.W.
Published: July 2012

The activity profiles of opioid agonists and non‐steroidal analgesic agents have been compared against different nociceptive stimuli in the mouse and rat.

Opioid agonists, but not non‐steroidal analgesic agents, inhibited reflex depressor responses evoked by visceral distension in anaesthetized rats. The ranked order of potency of opioids in the visceral distension reflex was identical to that observed in the mouse writhing assay.

Opioid‐induced inhibition of reflex depressor responses and writhing was observed with ligands acting on μ‐ and κ‐, but not λ‐receptors. Antinociceptive activity of opioids in the rat cold water tail‐flick assay was restricted to μ‐receptor agonists.

Morphine‐ and ethylketocyclazocine (EKC)‐induced inhibition of the visceral distension reflex was blocked by naloxone, but not by the quaternary opioid antagonist N‐methylnalorphine.

Direct cardiovascular effects were observed with ligands for the μ‐ and κ‐receptor. Blood pressure changes induced by morphine and Tyr. D‐Ala. Gly. MePhe. Gly‐ol (DAGOL), but not EKC, were blocked by N‐methylnalorphine. Pretreatment with 16‐methylcyprenorphine (M8008) antagonized morphine‐, DAGOL‐ and EKC‐induced cardiovascular effects, but not those of dynorphin‐(1–13) or U50488.

It is concluded that reflex circulatory responses evoked by visceral distension in anaesthetized rats are a valid index for the evaluation of opioid‐induced antinociception. A simultaneous assessment of cardiovascular effects of opioids was achieved.
Selective inhibition of adrenaline‐induced human platelet aggregation by the structurally related Paf antagonist Ro 19–3704
Authors: Schattner Mirta , Parini Angelo , Fouque Françoise , Vargaftig B. Boris , Touqui Lhousseine
Published: July 2012

Two non‐lipid antagonists of platelet‐activating factor acether (Paf), BN 52021 and WEB 2086, at concentrations which completely blocked Paf‐induced platelet aggregation, failed to interfere with aggregation by adrenaline. In contrast, Ro 19–3704, a structurally related antagonist of Paf, inhibited concentration‐dependently aggregation induced by adrenaline or by the simultaneous addition of submaximal concentrations of adrenaline and Paf. Reversal of aggregation was obtained when Ro 19–3704 was added to the platelet suspension after adrenaline.

Ro 19–3704 was selective for Paf and adrenaline since it failed to interfere with platelet aggregation induced by arachidonic acid or ADP. CV‐3988, an antagonist of Paf structurally similar to Ro 19–3704, also inhibited adrenaline‐induced aggregation. However, a morpholine analogue (MA) of Paf, which has no anti‐Paf activity, failed to interfere with the aggregation induced by adrenaline. This suggests that the effect of Ro 19–3704 and CV‐3988 on adrenaline is not simply due to their lipid structure.

Experiments on plasma membrane preparations showed that Ro 19–3704 inhibited [3H]‐yohimbine binding with an inhibition constant (Ki) of 7 ± 3 μm. In contrast, BN 52021 and MA did not interfere with [3H]‐yohimbine binding. Equilibrium binding experiments showed that Ro 19–3704 increased the apparent KD of [3H]‐yohimbine binding from 2.02 ± 0.15 to 7.3 ± 0.4 nm. The Paf antagonist Ro 19–3704 interacts specifically with the α2‐adrenoceptor and may thus prevent the early steps involved in the mechanism of adrenaline‐induced platelet activation.
Concurrent determination of effects of p‐chloroamphetamine on central extracellular 5‐hydroxytryptamine concentration and behaviour
Authors: Hutson P.H. , Curzon G.
Published: July 2012

The effects of p‐chloroamphetamine (PCA) (5 mg kg−1, i.p.) on extracellular concentrations of 5‐hydroxytryptamine (5‐HT) and 5‐hydroxyindoleacetic acid (5‐HIAA) were monitored in the frontal cortex of conscious, freely moving rats by means of intracerebral dialysis. Concomitant behaviour comprising the 5‐HT behavioural syndrome (reciprocal forepaw treading, headweaving, wet dog shakes) and locomotion and grooming was also recorded.

PCA markedly and transiently increased extracellular 5‐HT but extracellular 5‐HIAA values decreased to a moderate extent.

The time‐course of 5‐HT changes correlated positively (P < 0.001) with those of the three components of the 5‐HT syndrome but did not correlate significantly with locomotion and correlated negatively (P < 0.01) with grooming.

As previous work using conventional methodology did not reveal clear relationships between the effects of PCA on 5‐HT metabolism and behaviour, the present results emphasise the value of in vivo dialysis in the study of the neurochemical mediation of the behavioural effects of drugs.
Caesium ions: a glycine‐activated channel agonist in rat spinal cord neurones grown in cell culture
Authors: Smith Stephen M. , McBurney Robert N.
Published: July 2012

The chloride (Cl−) currents activated by caesium ions (Cs+), glycine and γ‐aminobutyric acid (GABA) were compared following their application to rat neurones that had been grown in cell culture. Recordings were made using the whole‐cell patch clamp technique under voltage clamp conditions.

In spinal cord neurones, bicuculline methiodide antagonized GABA‐activated currents more effectively than Cs+‐ or glycine‐activated currents. However, strychnine was more effective at blocking the currents activated by Cs+ or glycine than those activated by GABA.

Of the 3 agonists, only GABA activated currents in cells from the intermediate lobe of the rat pituitary.

In spinal neurones the size of the currents activated by 70 mm Cs+ was correlated to the size of the currents activated by 15 μm glycine (P < 0.005; n = 10, Spearman's rank correlation), but there was no significant correlation between the size of the currents activated by these agents and 10 μm GABA.

The joint application of glycine and Cs+ activated currents that were approximately twice as big as the sums of the currents activated by separate applications of the same doses. This synergism was consistent with Cs+ acting at the same receptor as glycine (7 μm glycine being equivalent to 31 ± 7 mm Cs+).

It was concluded that Cs+ activates the same Cl− channel as the inhibitory neurotransmitter glycine.
Antagonism of calcium by zinc in guinea‐pig isolated taenia caeci and trachealis muscle
Authors: Sarriá B. , Cortijo J. , Martí‐Cabrera M. , Morcillo E. , Esplugues J.
Published: July 2012

In guinea‐pig isolated taenia caeci and trachealis bathed in a K+‐rich, Ca2+‐free medium, CaCl2 (0.01–10 mm) produced a concentration‐dependent contraction. Zn2+ (0.01–1 mm), Cd2+ (0.01–1 mm), verapamil (0.01–100 μm) and trifluoperazine (1–100 μm) were effective antagonists of CaCl2‐induced responses.

Zn2+ and Cd2+ in concentrations from 0.01 to 1 mm were without effect on the tone of taenia and trachea in normal Tris solution. Conversely, Zn2+ and Cd2+, in concentrations of 1 mm, caused contraction of these tissues in a K+‐rich, Ca2+‐free medium. Zn2+ (1 mm)‐induced contractions of taenia and trachea were completely inhibited by verapamil (10 μm).

In taenia and trachea skinned of their plasma membranes, tension development induced by Ca2+ (10 μm or 1 μm, respectively) was unaffected by verapamil (100 μm), whereas trifluoperazine (100 μm) depressed the maximal tension produced by Ca2+. Segments of skinned preparations contracted in response to low concentrations of Zn2+ (10 μm) or Cd2+ (10 μm).

It is concluded that Zn2+ may suppress Ca2+‐induced spasm by a direct action on the binding sites of the Ca2+ channel.
The activation gate of the sodium channel controls blockade and deblockade by disopyramide in rabbit Purkinje fibres
Authors: Gruber R. , Carmeliet E.
Published: July 2012

The effect of disopyramide on the maximum upstroke velocity () and the sodium current of rabbit cardiac Purkinje fibres was studied with the two‐microelectrode voltage‐clamp technique.

In the absence of stimulation the drug did not cause block at membrane potentials ranging from −100 to −65 mV. Use‐dependent block of was most pronounced at −75 mV. At hyperpolarized membrane potentials development of use‐dependent block was faster than at depolarized membrane potentials. The time course of development of use‐dependent block was not significantly influenced by the duration of the depolarizing pulse. These results strongly suggest that disopyramide predominantly blocks activated sodium channels.

The relative decrease of the sodium current at the beginning of a 2 s depolarizing clamp to −45 mV was almost the same as at the end, implying a rapid blockade of activated sodium channels. The Hill plots were linear with slopes ranging from 0.98 to 1.08 indicating a first order reaction; the dissociation constant for activated channels was 70 μm.

Recovery of from use‐dependent block during rest was strongly voltage‐dependent, the time constant of recovery increasing upon hyperpolarization. When the fraction of charged molecules was reduced by changing the pH of the external solution, the voltage‐dependence of recovery was decreased. In contrast, recovery of for a change in holding potential from −80 to −95 mV was very fast during repetitive stimulation.

It is concluded that disopyramide blocks the sodium channel during activation and is trapped in the channel when the activation gate closes.
Prejunctional modulation of acetylcholine release from the skeletal neuromuscular junction: link between positive (nicotinic)− and negative (muscarinic)‐feedback modulation
Authors: Vizi E.S. , Somogyi G.T.
Published: July 2012

Presynaptic receptor‐mediated modulation of stimulation‐evoked [3H]‐acetylcholine([3H]‐ACh) release from the neuromuscular junction was studied in the region of the mouse hemidiaphragm which contains the motor endplates, and which can easily be loaded with [3H]‐choline. This method made it possible to detect exclusively the [Ca2+]o‐dependent, quantal release of [3H]‐ACh in response to axonal stimulation.

Atropine enhanced, and non‐depolarizing muscle relaxants ((+)‐tubocurarine, pancuronium and pipecuronium) reduced, the release of [3H]‐ACh evoked by high frequency trains of stimulation (50 Hz, 40 shocks) of the phrenic nerve. The effect of (+)‐tubocurarine was frequency‐dependent as at 5 Hz (40 shocks) it was less effective than at 50 Hz. The resting release of [3H]‐ACh was not affected by these compounds. These findings indicate that ACh released into the synaptic gap by axonal firing reaches a concentration sufficient to influence its own release by a prejunctional effect.

The anticholinesterase, physostigmine sulphate, enhanced the release of [3H]‐ACh in a concentration‐dependent manner. This effect was mediated via prejunctional nicotinic receptor stimulation: (+)‐tubocurarine, pancuronium and pipecuronium completely prevented the effect of physostigmine.

When the prejunctional nicotinic and muscarinic receptors were stimulated by a high concentration of extracellular ACh which had accumulated in the junctional gap in the presence of physostigmine, atropine did not influence the evoked release of [3H]‐ACh. However, when the effect of endogenous ACh on nicotinic receptors was prevented by (+)‐tubocurarine, atropine enhanced the release.

It is concluded that quantally‐released ACh from motor endplates is subject to prejunctional automodulation: (a) ACh facilitates its own release via an effect on prejunctional nicotinic receptors (positive feedback), (b) ACh release is reduced by an action on muscarinic receptors. When the nicotinic receptor‐mediated facilitation is fully operative, the muscarinic receptor‐mediated negative feedback is much less effective. It is supposed that there is a link between the two feedback mechanisms possibly at the level of the second messenger system(s).
Sympathetic denervation caused by long‐term noradrenaline infusions; prevention by desipramine and superoxide dismutase
Authors: Teixeira A. Albino , Azevedo Isabel , Branco Domingas , Rodrigues‐Pereira E. , Osswald Walter
Published: July 2012

The effects of continuous intravenous infusion of noradrenaline (0.01 and 0.1 μg kg−1 h−1) were studied in both the infused lateral saphenous vein and the contralateral saphenous vein of normal dogs. Noradrenaline, saline, noradrenaline + desipramine or noradrenaline + superoxide dismutase were infused using Alzet osmotic minipumps.

After a 5 day infusion period, the noradrenaline content in plasma and in both saphenous veins was determined, and the venous tissues submitted to light microscope morphometry and ultrastructural study and used for the determination of their O‐methylation capacity (with [3H]‐isoprenaline as a substrate).

Noradrenaline caused dose‐dependent damage to the sympathetic nerve endings of the lateral saphenous veins. Concomitant changes in extraneuronal structure and function were observed (hypertrophy of smooth muscle cells, nuclear dismorphy, thickening of the vessel wall, impairment in O‐methylation capacity).

Desipramine and superoxide dismutase prevented or reduced the effects of noradrenaline on both the morphological and the biochemical parameters; the protection afforded by superoxide dismutase was more marked than that by desipramine.

It is concluded that moderately high doses of noradrenaline exert a 6‐hydroxydopamine‐like effect and that this chemical sympathectomy is partially or totally prevented by desipramine or superoxide dismutase. The data suggest that a substance derived from noradrenaline, in the formation of which free oxygen radicals are involved and which is subject to neuronal uptake, is the chemical entity responsible for the neurotoxic effect observed.
Reactive blue 2 selectively inhibits P2y‐purinoceptor‐stimulated surfactant phospholipid secretion from rat isolated alveolar Type II cells
Authors: Rice Ward R. , Singleton Fannie M.
Published: July 2012

The effect of reactive blue 2 on adenosine 5′‐triphosphate (ATP), 12‐O‐tetradecanoylphorbol 13‐acetate (TPA) and terbutaline‐induced surfactant phospholipid secretion from rat isolated alveolar Type II cells was studied.

Reactive blue 2 significantly inhibited ATP‐induced surfactant phospholipid secretion, but was without effect on C‐kinase agonist (TPA) or β‐adrenoceptor agonist (terbutaline)‐stimulated surfactant phospholipid secretion. The IC50 for inhibition of ATP‐induced surfactant secretion was 1.5 × 10−4 m.

These data are consistent with a P2y‐purinoceptor regulating surfactant phospholipid secretion from isolated Type II cells and support previous work suggesting reactive blue 2 is a specific inhibitor at P2y‐purinoceptors.
Calcium mobilization and response recovery following P2‐purinoceptor stimulation of rat isolated alveolar type II cells
Authors: Dorn Curtis C. , Rice Ward R. , Singleton Fannie M.
Published: July 2012

The effect of adenosine 5′‐triphosphate (ATP) on surfactant phospholipid secretion, calcium mobilization, and the time course for recovery of the response system was studied in isolated alveolar Type II cells of the rat.

ATP (10 μm) stimulated a biphasic intracellular Ca2+ transient monitored by changes in Fura‐2 fluorescence, from a basal level of 126 ± 9 nm, to a rapid peak of 391 ± 1 nm, followed by a prolonged plateau 26 ± 4 nm above baseline (mean ± s.e.mean, n = 26).

ATP‐stimulated surfactant phospholipid secretion and peak Ca2+ levels had similar EC50 s** (1 × 10−6 m), and were unaffected by chelation of extracellular Ca2+. However, the prolonged plateau phase was abolished by chelation of extracellular Ca2+.

There was a 15 min refractory period before full recovery of the Ca2+‐response to ATP. Recovery was dependent on extracellular Ca2+, was accelerated by removing extracellular agonist and was prolonged following stimulation with the poorly hydrolyzed ATP analogue, ATP‐γ‐S.

While the Type II cell was capable of multiple ATP‐induced Ca2+ transients following recovery, no additional surfactant phospholipid was released with sequential stimulation.

These findings suggest initial exposure of Type II cells to ATP mobilizes intracellular Ca2+, stimulates phospholipid secretion and rapidly desensitizes the cell to further stimulation by ATP. Recovery of the ATP‐induced Ca2+‐response depends on presence of extracellular Ca2+ and removal of agonist.
Antagonism of Paf‐induced oedema formation in rabbit skin: a comparison of different antagonists
Authors: Hellewell Paul G. , Williams Timothy J.
Published: July 2012

Eight platelet activating factor (Paf) antagonists were evaluated as inhibitors of oedema formation in rabbit skin induced by intradermal injection of Paf plus prostaglandin E2 (PGE2). Antagonists were tested by both intradermal (i.d.) and intravenous (i.v.) routes.

Intradermal injection of two antagonists structurally‐related to Paf (SRI 63–675 and CV‐3988) resulted in a partial inhibition of Paf‐induced oedema formation but at high doses of antagonist, marked agonist activities were detected. CV‐3988 administered i.v. inhibited Paf‐induced plasma leakage by 73–80%; however, oedema responses to a range of other inflammatory mediators were also reduced, albeit to a lesser extent (40–60%). SRI 63–675 administered i.v. did not significantly inhibit Paf‐induced oedema.

The antagonist 48740 RP administered either i.d. or i.v. showed partial, but selective, inhibition of Paf‐induced oedema formation, although the doses required were high when compared with other antagonists.

BN 52021 was a weak Paf antagonist when injected i.d., but following i.v. administration the responses to Paf were inhibited by 63–71%. Responses to all other mediators tested were unaffected.

Kadsurenone and its synthetic derivatives, L‐652,731 and L‐659,989 all blocked responses to Paf in the skin. L‐659,989 was the most potent, achieving almost total inhibition when injected i.d. and i.v.; moreover, it was selective for Paf. L‐652,731 was more potent than kadsurenone.

WEB 2086 given i.d. and i.v. showed similar activity to L‐659,989 and it was also selective for Paf‐induced oedema formation.

These results illustrate that in rabbit skin not all Paf antagonists are selective for Paf, some showing agonist‐like activity which can mask antagonist properties. It is suggested that before ascribing a role for endogenous Paf in an inflammatory reaction based on results with antagonists, the activity of the antagonists in the model under investigation should be rigorously established.
Potentiation by TRH of the effect of antidepressants in the forced‐swimming test, involvement of dopaminergic and opioid systems
Authors: Reny‐Palasse Véronique , Constans Martine , Rips Richard
Published: July 2012

It has been shown that thyrotropin releasing hormone (TRH) can potentiate the effects of the antidepressant, imipramine, as measured by the mouse forced‐swimming test. This potentiation is not associated with an increase of effective levels of noradrenaline in the synaptic clefts, but depends upon the integrity of opioid systems. The present study was designed to investigate: (a) the potentiation by TRH of the effects of other antidepressants, using the same test; (b) the possible involvement of other neuronal systems, such as the 5‐hydroxytryptaminergic and dopaminergic systems; (c) the contribution of the opioid and dopaminergic systems to the potentiation of the actions of other antidepressants by TRH.

The effects of nortriptyline, amineptine, maprotiline, nomifensine and mianserin, but not that of clomipramine, were potentiated by TRH (2 mg kg−1, i.p.). The inhibitor of 5‐hydroxytryptamine synthesis, p‐chlorophenylalanine (PCPA), did not prevent the effect induced by imipramine plus TRH. Blockade of dopaminergic systems by γ‐butyrolactone (GBL) (37.5 mg kg−1, i.p.), α‐methyl‐p‐tyrosine (AMPT) (125 mg kg−1, i.p.) and apomorphine (0.025 mg kg−1, i.p.) antagonized the effects induced by various antidepressants alone (at high, effective doses) or at lower ineffective doses in association with TRH. The effect induced by imipramine plus TRH was also blocked by sulpiride (16 mg kg−1, i.p.). Pretreatment with the opioid antagonist, naloxone, inhibited the effects induced by nomifensine plus TRH or mianserin plus TRH but not those induced by nortriptyline plus TRH, maprotiline plus TRH or amineptine plus TRH. When high active doses of the antidepressants were used alone, only the clomipramine effect was blocked by naloxone.

These data indicate that TRH is able to potentiate the effect not only of imipramine but of other antidepressants in the mouse forced‐swimming test, although these other antidepressants act in various ways on cerebral amines. The antagonism of the effects induced by the antidepressants alone or in association with TRH after blockade of dopaminergic systems may indicate a reversal of the effect of the antidepressants by blockade of dopaminergic systems. Hence, the same mechanisms would be involved in the effects induced by antidepressants alone or in association with TRH, with respect to dopaminergic systems. However, different mechanisms of action seem to be responsible for the potentiation of TRH of the effect of the various antidepressants, since the involvement of the opioid systems varies according to the antidepressant tested.
Effect of 5‐hydroxytryptamine on [3H]‐acetylcholine release from guinea‐pig striatal slices
Authors: Bianchi Clementina , Siniscalchi Anna , Beani Lorenzo
Published: July 2012

The effect of 5‐hydroxytryptamine (5‐HT) on spontaneous and electrically‐evoked tritium efflux was studied in guinea‐pig caudate nucleus slices preloaded with [3H]‐choline.

5‐HT, 10–300 μmol1−1, temporarily increased the spontaneous tritium efflux (as well as the endogenous acetylcholine (ACh) release) and, after 15 min perfusion, inhibited it. The facilitatory effect of 5‐HT on spontaneous efflux was increased while the inhibitory effect did not occur in slices taken from dopamine‐depleted guinea‐pigs.

The increase in spontaneous tritium efflux by 5‐HT was blocked by methiothepin, methysergide (pA2 8.7) and by the selective 5‐HT2 antagonist, ritanserin (pA2 6.7).

The inhibition of spontaneous tritium efflux by 5‐HT was prevented by methysergide and methiothepin but not by ritanserin and (−)‐propranolol.

5‐HT, 100 μmol1−1, inhibited the electrically‐evoked tritium efflux and this effect was unchanged in dopamine‐depleted slices.

The inhibition of electrically‐evoked tritium efflux by 5‐HT was blocked by methiothepin and methysergide but not by (−)‐propranolol or ritanserin.

These results suggest that 5‐HT may exert a rapid and transient (excitatory) and a more prolonged (inhibitory) control over striatal cholinergic neurones.
A comparison of bradykinin‐ and capsaicin‐induced myocardial and coronary effects in isolated perfused heart of guinea‐pig: involvement of substance P and calcitonin gene‐related peptide release
Authors: Manzini Stefano , Perretti Francesca , de Benedetti Laura , Pradelles Philippe , Maggi Carlo Alberto , Geppetti Pierangelo
Published: July 2012

Bradykinin and capsaicin were compared for their ability to elicit functional effects and to release sensory neuropeptides from guinea‐pig isolated perfused hearts.

Both bradykinin (10 μm) and capsaicin (1 μm) produced a marked increase in coronary flow, a large positive chronotropic effect and a significant reduction in contractile strength. These actions were associated with a marked release of substance P‐like immunoreactivity (SP‐LI) and calcitonin gene‐related‐like immunoreactivity (CGRP‐LI). The percentage of the tissue content of SP‐LI and CGRP‐LI released by each agent was similar, although bradykinin was less effective than capsaicin. The ratio of SP‐LI/CGRP‐LI released by both agents was similar to that present in cardiac tissue.

Neuropeptide release could be evoked only once with capsaicin but at least four times with bradykinin. Also, functional responses to capsaicin underwent desensitization. After either in vitro or systemic capsaicin pretreatment, the release of SP‐LI and CGRP‐LI by bradykinin was reduced and the positive chronotropic effect of bradykinin was significantly reduced, while the increase in coronary flow and negative inotropic responses remained unchanged.

Pretreatment with indomethacin (10 μm) strongly antagonized the release of SP‐LI and CGRP‐LI by bradykinin and reduced the increase in heart rate.

These findings suggest that activation by bradykinin (probably through indirect mechanisms) of capsaicin‐sensitive sensory nerves in the heart, leads to a local release of sensory neuropeptides. These neuropeptides, in turn, could participate in determining the complex functional effects of this kinin on cardiac performance.
What confers specificity on glycine for its receptor site?
Authors: Tokutomi Naofumi , Kaneda Makoto , Akaike Norio
Published: July 2012

The structural requirements for activation of the glycine receptor were studied in isolated ventromedial hypothalamic neurones of rats by use of a ‘concentration‐clamp’ technique under single‐electrode voltage‐clamp conditions.

α‐Amino acids (l‐α‐alanine, and d‐α‐alanine, and l‐serine), and glycine‐methylester, glycine‐ethylester and β‐amino acids (β‐alanine and taurine) produced a transient inward Cl− current, which was similar to that induced by glycine.

The responses to individual α‐ and β‐amino acids were selectively antagonized by strychnine, but were not affected by bicuculline, picrotoxin or the taurine antagonist, TAG (6‐aminomethyl‐3‐methyl‐4H,1,2,4‐benzothiadiazine‐1,1‐dioxide hydrochloride), suggesting that α‐ and β‐amino acids activate the same glycine receptor.

β‐Amino acids were slightly more potent than the α‐amino acids in causing cross‐desensitization of the glycine response.

From the results of the structure‐activity analysis of the optical isomers of α‐alanine, serine and cysteine, a tentative structure of the glycine receptor is proposed.
Heterogeneity of nucleoside transport inhibitory sites in heart: a quantitative autoradiographical analysis
Authors: Parkinson Fiona E. , Clanachan Alexander S.
Published: July 2012

The distribution of nucleoside transport inhibitory sites in rat and guinea‐pig cardiac sections was investigated by use of [3H]‐nitrobenzylthioinosine ([3H]‐NBMPR) autoradiography. The distribution of these sites was heterogeneous in guinea‐pig sections and homogeneous in rat sections.

The areas of high density of nucleoside transport inhibitory sites found in guinea‐pig cardiac sections were compared to the distribution of an endothelial cell marker, von Willebrand Factor, determined by radioimmunocytochemistry. These two markers were co‐localized suggesting that coronary endothelial cells from guinea‐pig have a high density of NBMPR binding sites and thus may have a high nucleoside transport capacity.

Nucleoside transporter subtypes with differing affinity for NBMPR or dipyridamole were investigated by quantitative autoradiography. Sites in rat tissues had high affinity for NBMPR (KD = 0.6 nm) but were of low sensitivity to dipyridamole (Ki = 3.1 μm). In guinea‐pig sections, areas of high and low [3H]‐NBMPR binding site density were analyzed separately. In both areas, sites had high affinity for NBMPR (KD = 1.4 nm, 4.5 nm, respectively) and dipyridamole (Ki = 108 nm, 245 nm, respectively).

While differences in density of nucleoside transport inhibitory sites are detectable between distinct regions of the heart, subtypes differing in affinity for NBMPR or dipyridamole were not evident. Therefore, more detailed structure activity studies are required to determine if subtypes of these sites exist within a single heart.
Inotropic and chronotropic effects of N6‐substituted derivatives of cyclic AMP as assessed in guinea‐pig isolated right atria and papillary muscle
Authors: Kawada Tomie , Yoshida Yutaka , Imai Shoichi
Published: July 2012

The inotropic and chronotropic actions of N6‐substituted adenosine 3″:5″‐cyclic monophosphate (cyclic AMP) derivatives (N6‐R cyclic AMPs) were studied in guinea‐pig isolated right atrial preparations and in the papillary muscle preparations from guinea‐pig right ventricle.

All the N6‐R cyclic AMPs except N6‐C14H29 produced positive inotropic effects in papillary muscle. The C5H11, C6H13, C7H15, C8H17 and C9H19 compounds were the most potent as inotropic agents, the potency being lower with compounds having longer or shorter N6‐side chains than these.

In right atria N6‐C2H5‐C7H15 cyclic AMPs produced negative chronotropic effects. However, after treatment of the preparations with 8‐phenyltheophylline the negative chronotropic effects were either much attenuated or abolished, indicating the involvement of adenosine receptors.

All the N6‐R cyclic AMPs except N6‐C14H29 were more potent activators of bovine myocardial protein kinase than cyclic AMP. The partition coefficients between octanol and an aqueous phase of N6‐R cyclic AMPs became greater as the numbers of carbon atoms increased, and there appeared to be a relationship between partition coefficient and inotropic potency. It was concluded that membrane penetrativeness rather than potency as activators of protein kinase determined the potencies of N6‐R cyclic AMPs as positive inotropic agents.

Derivatives such as N6‐C7H15 cyclic AMP, which have positive inotropic activity without any marked negative chronotropic effect, may be useful as cardiotonic agents in heart failure.
The cardiovascular pharmacology of ICI 170777 ((6RS)−6‐methyl‐5‐(pyrid‐4‐yl)−3H,6H‐1,3,4‐thiadiazin‐2‐one) a novel compound with positive inotropic and vasodilator effects
Authors: Collis M.G. , Keddie J.R. , Rouse W.
Published: July 2012

This paper describes the cardiovascular effects of ICI 170777, a novel compound which enhances cardiac contractility and causes arterial and venous dilatation.

The positive inotropic effects of ICI 170777 on the heart were demonstrated by an increase in left ventricular dP/dtmax in the anaesthetized and conscious dog, and by an increase in tension development in isolated papillary muscles from the cat.

In the anaesthetized dog, the positive inotropic effects of ICI 170777 and of isoprenaline were attenuated by atenolol (5 mg kg−1, i.v.). Atenolol displaced the dose‐response curve to ICI 170777 to the right by 4 fold but displaced the isoprenaline dose‐response curve to the right by 247 fold. In vitro, however, atenolol (10 μm) had no significant effect on the positive inotropic response to ICI 170777. In the ganglion‐blocked anaesthetized dog, infusion of a low dose of ICI 170777 which had no effect on the basal left ventricular dP/dtmax, selectively potentiated the positive inotropic effects of isoprenaline. These results indicate that ICI 170777 has both a non‐adrenoceptor‐mediated positive inotropic effect on the heart and also facilitates the β‐adrenoceptor‐mediated control of contractility.

In the denervated and perfused hind‐limb of the dog, ICI 170777 reduced arterial perfusion pressure and increased limb circumference at a constant arterial flow and venous pressure. This indicates that ICI 170777 has direct dilator actions on both arterial and venous vessels. In this preparation, diazoxide exerted an arterial selective vasodilator effect and sodium nitroprusside was a relatively selective venous dilator. ICI 170777 exhibited a balanced arterial and venous dilator effect which was intermediate in profile between that of diazoxide and that of sodium nitroprusside.

In the conscious dog, low doses (2–5 mg kg−1, orally) of ICI 170777 evoked an increase in left ventricular dP/dtmax with no significant effect on heart rate or blood pressure. At a higher dose (10 mg kg−1, orally) it also reduced blood pressure and caused a significant increase in heart rate. The duration of the positive inotropic effect of 5 mg kg−1 (orally) of ICI 170777 was 10–12 hours. This response did not diminish following repeated administration of the compound.

The positive inotropic action and balanced arterial and venous dilator effect of ICI 170777 indicate that the compound may be useful in the treatment of congestive heart failure, a disorder that is characterized by decreased cardiac contractility and enhanced arterial and venous constrictor tone.
Prevention of physostigmine‐, DFP‐, and diazinon‐induced acute toxicity by monoethylcholine and N‐aminodeanol
Authors: Patterson T.A. , Terry A.V. , Kosh J. W.
Published: July 2012

Choline, and the choline analogues monoethylcholine (MEC) and N‐aminodeanol (NAD) were examined for prophylactic activity in acute acetylcholinesterase inhibitor toxicity in mice. The rank order of potency of the compounds was MEC > NAD > choline.

Simultaneous administration of MEC (60 mg kg−1) or NAD (200 mg kg−1) with physostigmine reduced lethality to 17 and 13% respectively. MEC (60 mg kg−1) completely protected against di‐isopropylfluorophosphate (DFP) and diazinon toxicity, and NAD reduced lethality to 17% for both agents. Choline (200 mg kg−1) exhibited only negligible antidotal activity against the inhibitors.

In vitro concentrations of choline, MEC, and NAD, similar to the estimated concentration obtained in vivo in the acute toxicity study, produced mixed inhibition of mouse brain acetylcholinesterase. The inhibition was dose‐related and was additive to the inhibition produced by the cholinesterase inhibitors.

All three analogues reduced ligand binding at the nicotinic, M1, and M2 receptors. The rank order of potencies for the analogues at each receptor was nicotinic: (choline > MEC > NAD), M1: (MEC > choline > NAD), and M2: (MEC > choline > NAD).

It is proposed that the analogues prevent acetylcholinesterase inhibitor toxicity peripherally by interacting with acetylcholinesterase, and/or by competing with acetylcholine for binding to cholinoceptors.
Divalent cation dependence of the inhibition by phenothiazines of mediator release from mast cells
Authors: Peachell Peter T. , Pearce Frederick L.
Published: July 2012

The divalent cations calcium, strontium and barium — and in that order of decreasing effectiveness — were capable of supporting the stimulated release of histamine from rat peritoneal mast cells (RPMC).

The responsiveness of mast cells to stimulation in the presence of divalent cations was, in general, markedly enhanced when the cells were first depleted of their intracellular calcium stores.

The putative calmodulin antagonists, chlorpromazine, promethazine, thioridazine (phenothiazines) and W‐7 (a naphthalene sulphonamide) all inhibited histamine release in the presence of divalent cations in both untreated cells and in RPMC depleted of their intracellular calcium.

Histamine release induced by antigen, compound 48/80 and ionophore A23187 was inhibited by this class of compounds most effectively in the presence of extracellular barium, less so in the presence of strontium and least so in calcium‐containing media.

In the experimental situation where the extracellular calcium concentration was reduced (< 1 mm), the phenothiazines inhibited the stimulated release of histamine more effectively.

In toto, these results suggest that strontium and barium, as well as calcium, can support histamine release from RPMC by directly interacting with an intracellular divalent cation‐binding site that may be calmodulin. As a consequence, one mechanism by which the phenothiazines and W‐7 may modulate the secretory response could reflect an antagonism of a divalent cation interaction at that same site, although other additional potential sites of inhibitory action are indicated, dependent on the stimulus employed for secretion.
Depression of maximum rate of depolarization of guinea‐pig ventricular action potentials by metabolites of encainide
Authors: Hemsworth Paul D. , Campbell Terence J.
Published: July 2012

Standard microelectrode methods have been used to record action potentials from guinea‐pig ventricular myocardium and dog Purkinje fibres, and to study the effects of the two major metabolites of encainide, O‐desmethyl encainide (ODE) and 3‐methoxy‐O‐desmethyl encainide (MODE).

In concentrations similar to those found in patients during chronic encainide therapy, neither ODE nor MODE produced significant depression of maximum rate of depolarization () of action potentials in unstimulated tissue. Repetitive stimulation, however, was associated with depression of which increased with increasing driving rates (rate‐dependent block, RDB). At the fastest rate studied (interstimulus interval = 300 ms) ODE 1 μm depressed by 47.5 ± 5.7% and MODE 1 μm, reduced by 52.2 ± 12%.

The onset and offset kinetics of this rate‐dependent block were very slow. Full development of RDB during a train required over 100 action potentials and the time constants of recovery of from RDB were 86.4 ± 37 s for ODE and 100.4 ± 18 s for MODE. The amount of RDB and its rate of onset increased with drug concentration. The recovery time constants were independent of interstimulus interval or drug concentration. Both metabolites also produced rate‐dependent depression of conduction velocity in canine Purkinje fibres, but no evidence of selective depression of conduction of interpolated premature potentials was seen.

Early afterdepolarizations occurred spontaneously in three preparations in the presence of MODE, 1 μm and one preparation in ODE, 1 μm.

It is concluded that these metabolites of encainide may play a role in producing both its antiarrhythmic and its proarrhythmic effects.
Investigation of the vasoconstrictor action of subarachnoid haemoglobin in the pig cerebral circulation in vivo
Authors: Byrne J.V. , Griffith T.M. , Edwards D.H. , Harrison T.J. , Johnston K.R.
Published: July 2012

Angiographic techniques have been used to study the influence of intracisternally injected haemoglobin on the diameters of the main intrathecal and representative extrathecal (ascending pharyngeal and facial) cranial arteries of the anaesthetized pig.

Intracisternal injection of haemoglobin caused concentration‐dependent decreases in the diameters of intra‐ but not extrathecal arteries suggesting that haemoglobin possesses local vasoconstrictor activity.

When infused into one ascending pharyngeal artery, acetylcholine (ACh) caused slight dilatation of the intrathecal arteries but no change in the diameters of the ascending pharyngeal and facial arteries. The dilator response induced by ACh in the intrathecal arteries was converted into frank constriction after intracisternal injection of haemoglobin (cerebrospinal fluid concentration approximately 2 × 10−5 m).

These findings are consistent with the hypothesis that subarachnoid haemoglobin can induce cerebral artery constriction by acting as an extraluminal ‘sink’ for intimally released endothelium‐derived relaxing factor (EDRF) and may be relevant to the pathogenesis of vasospasm after subarachnoid haemorrhage in man.
Cholecystokinin‐octapeptide constricts guinea‐pig and human airways
Authors: Stretton C.D. , Barnes P.J.
Published: July 2012

Cholecystokinin‐octapeptide (CCK‐OP, 10−10‐3 × 10−6 m) produced a concentration‐dependent contractile response in guinea‐pig trachea which was enhanced by both the mechanical removal of the epithelium and by indomethacin (10−5 m), with an EC50 of 6.18 ± 0.10 × 10−8 m.

Sub‐threshold concentrations of CCK‐OP, which did not alter the resting tone of the smooth muscle, did not alter responses produced to electrical field stimulation (EFS) or to vagal nerve stimulation in an intact tracheal tube preparation. Atropine (2 × 10−6 m) did not alter the concentration‐response curve to CCK‐OP, indicating that CCK‐OP contraction is not mediated by cholinergic mechanisms.

The inhibition of neutral endopeptidase (endopeptidase‐24.11).by phosphoramidon (10−5 m) gave a leftward shift in the CCK‐OP concentration‐response curve in tissues with intact epithelium obtained from normal animals, but had no effect in tissues denuded of epithelium or in tissues obtained from animals which had been actively sensitized and challenged with ovalbumin (OA).

CCK‐OP‐induced contractile responses were antagonized by the CCK‐receptor antagonists dibutyryl cyclic guanosine monophosphate (pA2 = 4.3) and L‐364,718 (pA2 = 9.6).

CCK‐OP induced bronchoconstriction in large, but not small, human airways and was antagonized by the CCK‐receptor antagonist L‐364,718. CCK‐OP had no effect on cholinergic neural responses elicited by EFS in human airways.
β‐Adrenoceptor blocking effects of a selective β2‐agonist, mabuterol, on the isolated, blood‐perfused right atrium of the dog
Authors: Akahane Kunio , Furukawa Yasuyuki , Ogiwara Yasuhiro , Haniuda Masayuki , Chiba Shigetoshi
Published: July 2012

Effects of (±)−1‐(4‐amino‐3‐chloro‐5‐trifluoromethyl‐phenyl)−2‐tert.‐butylamino‐ethanol hydrochloride (mabuterol) on pacemaker activity and atrial contractility were investigated in the isolated and blood‐perfused right atrium of the dog.

Mabuterol, injected into the sinus node artery of the isolated atrium, dose‐dependently increased atrial rate and contractile force at doses of 0.01–10 nmol but the responses to over 10 nmol of mabuterol gradually decreased and mabuterol at higher doses induced biphasic cardiac responses, i.e., negative followed by positive cardiac responses.

The maximal increases in atrial rate and contractile force induced by mabuterol were 41.4% and 12.9%, respectively, of the maximal chronotropic and inotropic effects of isoprenaline.

Positive chronotropic and inotropic responses to mabuterol were dose‐dependently inhibited by a selective β2‐adrenoceptor antagonist, ICI 118,551. These responses were only slightly attenuated by atenolol.

Mabuterol (1–300 nmol) dose‐dependently inhibited both dobutamine‐ and procaterol‐induced positive chronotropic and inotropic responses.

These results indicate that mabuterol causes weak positive chronotropic and inotropic effects on the perfused canine right atrium by activating β2‐adrenoceptors, and that higher concentrations non‐selectively block both β1‐ and β2‐adrenoceptors.
Developmental disappearance of excitatory α1 adrenoceptor function in the oesophagus of chick embryo
Authors: Miyazaki Hideto , Taneike Tetsuro , Ohga Akira
Published: July 2012

Developmental change in the response to noradrenaline (NA) and 5‐hydroxytryptamine (5‐HT) was investigated in the chick oesophagus between 9 and 21 days of incubation and 4 days after hatching.

NA (5 μm) produced a significant contraction in the oesophagus at 9 days of incubation. The NA‐induced contraction progressively decreased with development and changed to an inhibition of spontaneous contraction or a small relaxation by 17 days of incubation.

The NA‐induced contractile response was inhibited by phentolamine (2.7 μm) and prazosin (0.55 μm). Phenylephrine (5 μm) but not clonidine (5–50 μm), also induced a contraction at early stages. The relaxation response to NA was sensitive to the β‐receptor blocker, carteolol (3.4 μm).

Pretreatment with carteolol unmasked the contractile responses to NA in preparations at 17–19 days of incubation. However, even in the presence of carteolol, the contraction produced by NA decreased and disappeared by the time of hatching. This change in response to NA is accompanied by a decline in the pD2 value. The response to phenylephrine (5 μm) followed the same pattern as that to NA.

The maximum binding sites of [3H]‐dihydroergocryptine to the crude membrane preparation from oesophagus changed little at 13, 17 and 21 days of incubation.

Isoprenaline (Iso, 0.01–20 μm) caused a carteolol‐sensitive relaxation in the carbachol‐contracted oesophagus after 13 days of incubation. The sensitivity (pD2 value) to Iso decreased slightly up to 17 days of incubation.

5‐HT (10 μm) caused a contraction in the oesophagus after 13 days of incubation and the amplitude of the response increased up to 17 days of incubation. The response to 5‐HT was abolished by methysergide (1 μm) but not by tetrodotoxin (0.78 μm) or atropine (1 μm) at every stage tested.

These results suggest that the response to NA changed from an α1‐adrenoceptor‐mediated contraction to a β‐receptor‐mediated relaxation during the embryonic period, resulting partly from the decline and disappearance of excitatory α1 ‐receptor function in the chick oesophagus.