bluuebunny/crossref_metadata_2025 huggingface dataset:
Clonidine and morphine increase [3H]‐noradrenaline overflow in mouse vas deferens
Authors: Forsyth Karyn M. , Pollock David
Published: July 2012

Field stimulation of mouse isolated vas deferens produced a biphasic contraction that consisted of an initial brief non‐adrenergic, non‐cholinergic (NANC) twitch, followed by a more prolonged noradrenergic component.

Field stimulation of vasa, previously loaded with [3H]‐noradrenaline ([3H]‐NA), increased the amount of radioactivity in the Krebs bathing solution; 77% of this radioactivity was derived from [3H]‐NA.

Tetrodotoxin (3 × 10−6 m) abolished the biphasic motor response to field stimulation and the accompanying increased overflow of [3H]‐NA.

Morphine (10−7‐10−5 m) inhibited the initial NANC component but potentiated the secondary noradrenergic component of the motor response to field stimulation. Morphine also increased the field stimulation‐induced overflow of radioactivity. Naloxone (10−6 m) antagonized the effects of morphine on the motor response and also on the overflow of radioactivity.

Clonidine (10−9‐10−7 m) inhibited the initial NANC component but potentiated the secondary noradrenergic component of the motor response to field stimulation. Clonidine also increased the field stimulation‐induced overflow of radioactivity.

The ability of morphine (10−7 m) and of clonidine (10−9 m) to potentiate the field stimulation‐induced overflow of radioactivity persisted in the presence of a combination of tranylcypromine (10−5 m), desmethylimipramine (10−5 m) and 17‐β‐oestradiol (10−5 m).

The inhibition of the initial NANC component of the motor response to field stimulation produced by morphine and clonidine may be related to the ability of these drugs to potentiate both the secondary noradrenergic component and the overflow of radioactivity, if the NANC transmitter is involved in regulating NA release.
Zolantidine (SK&F 95282) is a potent selective brain‐penetrating histamine H2‐receptor antagonist
Authors: Calcutt C.R. , Ganellin C.R. , Griffiths R. , Leigh B.K. , Maguire J.P. , Mitchell R.C. , Mylek M.E. , Parsons M.E. , Smith I.R. , Young R.C.
Published: July 2012

The novel benzthiazole derivative zolantidine (SK&F 95282) is a potent antagonist of histamine at H2‐receptors in guinea‐pig atrium and rat uterus. Only apparent pA2 values of 7.46 and 7.26 respectively could be calculated since the slopes of the Schild plots were significantly less than unity.

Zolantidine is equally potent as an antagonist at histamine H2‐receptors in guinea‐pig brain. The compound inhibited histamine stimulated adenylate cyclase (pKi 7.3) and dimaprit stimulated adenosine 3′:5′‐cyclic monophosphate (cyclic AMP) accumulation (approx pA2 7.63), and competed with [3H]‐tiotidine binding (pKi 7.17).

Zolantidine is at least 30 fold more potent at H2‐receptors than at other peripheral and central receptors investigated.

Infusion of zolantidine into rats produces a brain concentration greater than the plateau blood concentration (brain/blood ratio 1.45).

Zolantidine is thus characterized as a potent selective brain‐penetrating H2‐receptor antagonist, and will be a valuable pharmacological tool for investigating possible physiological and pathological roles for histamine in the central nervous system.
A possible role of airway epithelium in modulating hyperresponsiveness
Authors: Aizawa H. , Miyazaki N. , Shigematsu N. , Tomooka M.
Published: July 2012

In order to examine the role of airway epithelium in the responsiveness of smooth muscle in man, we measured the contractile responses to acetylcholine (ACh), histamine, and prostaglandin F2α (PGF2α) and the relaxation response to isoprenaline (Isop), in 48 bronchi obtained from 10 patients who received surgery. Responses were measured in the presence and absence of the epithelium.

Removal of epithelium (by rubbing the mucosa gently with forceps) significantly increased the contractile responses evoked by ACh, histamine and PGF2α.

In contrast, removal of epithelium did not alter the relaxation response to Isop.

To clarify the mechanism underlying this epithelial inhibitory effect on smooth muscle contraction, we measured the contractile responses of dog trachea with the epithelium removed to increasing concentrations of ACh. After measuring the control response, we added about 0.1 g of the chopped epithelium in the organ chamber, and measured the response again.

After adding airway epithelium and incubating with tracheal strips, the contractile response of tracheal strips decreased significantly as compared to the control response.

These results show that airway epithelium possesses the ability to decrease the smooth muscle contraction to ACh, histamine and PGF2α in man and dogs.

The mechanism of this inhibitory effect of the airway epithelium is not explained by a change in mechanical property of the airway nor the change in diffusion of these drugs to the smooth muscle across the epithelium. Thus, these results suggest that airway epithelium may have an important role in modulating smooth muscle tone, possibly by inactivation of these mediators, or by releasing an epithelium‐derived relaxing factor.
Interactions of the imidazodiazepine Ro 15–4513 with chemical convulsants
Authors: Lister Richard G. , Nutt David J.
Published: July 2012

The proconvulsant effects of the imidazodiazepine Ro 15–4513, were investigated in mice by use of intravenous infusion of a variety of convulsant drugs.

Dose‐response and time course studies of Ro 15–4513 against γ‐aminobutyric acid (GABA) antagonists were performed. On the basis of these studies a maximally effective dose of 5 mg kg−1 was administered 5 min before the determination of seizure thresholds in subsequent experiments.

Ro 15–4513 (5 mg kg−1) significantly lowered seizure thresholds to pentylenetetrazole, bicuculline and the convulsant benzodiazepine Ro 5–3663, but failed to alter seizure thresholds to picrotoxin, strychnine, caffeine and quipazine.

Ro 15–4513 significantly raised seizure threshold to the benzodiazepine receptor inverse agonist methyl 6,7‐dimethoxy‐4 ethyl‐β‐carboline‐3‐carboxylate (DMCM).

These results are discussed in relation to other studies investigating the proconvulsant and alcohol‐antagonizing effects of Ro 15–4513.
Gastric mucosal damage induced by local intra‐arterial administration of Paf in the rat
Authors: Esplugues J.V. , Whittle B.J.R.
Published: July 2012

A technique for the close‐arterial administration of substances to the rat stomach in vivo has been developed.

Intra‐arterial infusion of platelet‐activating factor (Paf, 10–50 ng kg−1 min−1 for 10 min) induced macroscopically assessed damage in the corpus mucosa, characterized as vasocongestion and necrosis.

The threshold intra‐arterial doses of Paf that induced histologically assessed damage in the antrum and corpus of the stomach (10 and 5 ng kg−1 min−1, respectively) produced minimal systemic hypotension (< 20 mmHg) suggesting a dissociation between these events.

Pretreatment with the Paf‐antagonist, L‐652,731 (2.5 mg kg−1 i.v.) prevented the gastric damage induced by local infusion of Paf.

Intravenous infusion of Paf (25 ng kg−1 min−1) did not significantly damage the gastric mucosa, in contrast to the same dose infused locally, yet Paf administered by either route produced a comparable degree of hypotension. Such findings suggest minimal metabolism of Paf during its passage through the gastric circulation.

Local intra‐arterial infusion of Paf in doses as low as 0.25 ng kg−1 min−1, which had no systemic hypotensive actions, significantly induced gastric damage in the presence of intragastric 20% ethanol.

These observations support a local role for Paf in the pathogenesis of gastric irritation and ulceration, such as that observed during endotoxin shock or bacterial infection. The present technique is thus useful for the study of locally administered substances on gastric function and integrity.
The effects of prenylamine on single ventricular myocytes of guinea‐pig
Authors: Shimoni Y. , Posner P. , Spindler A.J. , Noble D.
Published: July 2012

The action of prenylamine, an antianginal drug, was studied in single ventricular guinea‐pig myocytes. In concentrations of 10–50 μm, prenylamine significantly (P < 0.01) shortened action potentials, and significantly (P < 0.001) reduced the inward calcium current by 29% to 76% (n = 7). This effect was also present in the presence of adrenoceptor‐blockade (with phentolamine and propranolol), and was thus not due to indirect changes in endogenous catecholamine action.

Prenylamine did not affect the steady state level of current at the end of long pulses, and does therefore not act by changing time‐dependent outward currents. Since the resting potential in the unclamped mode is unchanged during gross changes in action potential duration, it is also unlikely that there are any changes in the background, time‐independent potassium conductance.

It is concluded that prenylamine has a direct effect on cardiac calcium channels, not mediated by adrenoceptor activation.
Cardiovascular effects of the novel arteriovenous dilator agent, flosequinan in conscious dogs and cats
Authors: Sim M.F. , Yates D.B. , Parkinson R. , Cooling M.J.
Published: July 2012

Flosequinan (BTS 49 465, 7‐fluoro‐l‐methyl‐3‐methylsulphinyl‐4‐quinolone) a novel arteriovenous dilator agent was orally effective in conscious renal hypertensive dogs and normotensive cats. The hypotensive potency of flosequinan was approximately ten times less than that of hydralazine in renal hypertensive dogs, 10 mg kg−1 and 20 mg kg−1 flosequinan causing similar falls in mean blood pressure to 1 mg kg−1 and 3 mg kg−1 hydralazine respectively. In normotensive cats, 5 mg kg−1 flosequinan caused similar falls to 0.5 and l.0 mg kg−1 hydralazine. The onset of hypotensive effect after flosequinan appeared to be slightly slower than after hydralazine in the dog and slightly faster than hydralazine in the cat.

The degree of tachycardia and increase in plasma renin activity (PRA) for equivalent falls in mean blood pressure in both species was significantly less for flosequinan than for hydralazine (P < 0.05).

In normotensive dogs, flosequinan, 10 and 20 mg kg−1 orally, caused a small but non‐significant increase in sodium and chloride excretion and had little effect on urine volume whereas hydralazine, 1 and 3 mg kg−1 orally, caused a marked retention of sodium and chloride ions and a reduction in urine volume (P < 0.01).

Neither flosequinan, 10 mg kg−1 orally, nor hydralazine 1 mg kg−1 orally, affected either glomerular filtration rate measured as creatinine clearance or effective renal plasma flow measured as p‐aminohippuric acid clearance in normotensive dogs.

The lesser degree of tachycardia and increase in plasma renin activity together with a lack of sodium retaining activity associated with flosequinan suggest that this agent may have potential advantages over existing therapy as an antihypertensive in man.
Effects of the calcium channel activator Bay K 8644 on general anaesthetic potency in mice
Authors: Dolin S.J. , Halsey M.J. , Little H.J.
Published: July 2012

The effects of the calcium channel activator, Bay K 8644, on the anaesthetic potencies of ethanol, argon and pentobarbitone were examined in mice.

Bay K 8644, at 1 mg kg−1 i.p., significantly antagonized the general anaesthetic potencies of ethanol and argon, but at 5 and 10 mg kg−1 this compound increased the general anaesthetic potency of these drugs.

At doses of 1, 5 and 10 mg kg−1 Bay K 8644 antagonized the anaesthetic effects of pentobarbitone.

Bay K 8644, at the highest dose used, did not alter the brain concentrations of pentobarbitone or the blood concentrations of ethanol.

The effects of the different doses of Bay K 8644 on the actions of ethanol and of argon are compatible with the known partial agonist properties of this compound on calcium channels in vitro.

The actions of Bay K 8644 on the anaesthetic effects of pentobarbitone suggests that specific interactions may be involved in the anaesthetic actions of this compound.
Effects of cadmium on the slow inward current of frog heart muscle in relation to a lowering of pH in external solution
Authors: Pater Christine , Sauviat Martin‐Pierre
Published: July 2012

The effect of cadmium (Cd) on the slow inward current (Isi) of frog atrial fibres was studied by the double sucrose gap technique.

Cd (5μm) depressed Isi in a voltage‐dependent manner without alteration of the apparent reversal potential for Isi.

Dose‐response curves indicated an apparent dissociation constant for the Cd blocking effect of 4.5 μm at 0 mV, with a one to one relationship between Cd and the slow channel.

Increasing the external concentration of Ca ions ([Ca]0) in the tetrodotoxin (TTX)‐containing Ringer solution antagonized the block of Isi by Cd. Double reciprocal plots for Isi versus [Ca]0 drawn in the presence or in the absence of Cd intersected at the ordinate, indicating that Cd competes with Ca for a common binding site.

Lowering the external pH from 7.3 to 6.3 depressed Isi. The block caused by H was voltage‐dependent. Double reciprocal plots for Isi versus [Ca]o drawn at pH 7.3 and 6.3 intersected at the abscissa, and indicated that H and Ca did not compete for a common site.

Lowering the external pH did not change the ability of Cd to inhibit Isi.

The data suggested the existence of two different sites within the slow channel in frog atrial fibres, one of them being H‐sensitive and the other cadmium‐sensitive.
Effects of halothane on membrane currents associated with contraction in single myocytes isolated from Guinea‐pig ventricle
Authors: Terrar D.A. , Victory J.G.G.
Published: July 2012

The effects of halothane on electrical activity and contraction were investigated in single myocytes isolated from guinea‐pig ventricle.

Halothane depressed the plateau and shortened the duration of action potentials.

Halothane also reduced the amplitude of inward calcium currents and of additional inward current activated by cytosolic calcium under voltage‐clamp conditions.

Contractions (measured by an optical technique) accompanying either action potentials or calcium currents were reduced by halothane. However, the extent of attenuation of contraction was greater than when a similar level of calcium channel blockade was induced by application of verapamil.

Actions of halothane on calcium‐activated tail currents in double‐pulse experiments were consistent with reduction by halothane of the cytosolic calcium transient, perhaps as a consequence of reduced uptake of calcium into sarcoplasmic reticulum stores.

It is concluded that the actions of halothane on inward currents contribute to its effects on action potentials. The reduction in contraction caused by halothane may result partly from a reduced influx of calcium to trigger contraction, and partly by a reduced release of calcium from sarcoplasmic reticulum stores.
Selective inhibition of arachidonate 5‐lipoxygenase by novel acetohydroxamic acids: effects on bronchial anaphylaxis in anaesthetized guinea‐pigs
Authors: Payne A.N. , Garland L.G. , Lees I.W. , Salmon J.A.
Published: July 2012

The effect of a novel series of orally‐active acetohydroxamic acid inhibitors of arachidonate 5‐lipoxygenase on ‘leukotriene‐dependent’ anaphylactic bronchoconstriction has been investigated in anaesthetized, pump‐ventilated guinea‐pigs actively sensitized to ovalbumin (OA). In a complementary series of experiments, the pharmacokinetics of these compounds in the plasma compartment following oral administration to guinea‐pigs has also been investigated.

In animals pretreated with mepyramine (2 mg kg−1 i.v.) and indomethacin (l0 mg kg−1 i.v.) and challenged with antigen aerosol (OA 10 mg ml−1; 5s) compounds BW A4C, BW A137C and BW A797C (10–200 mg kg−1, p.o., 1 h pre‐challenge) markedly reduced that component of anaphylactic bronchoconstriction shown to be ‘leukotriene‐dependent’.

The maximum degree of inhibition (up to 75%) of ‘leukotriene‐dependent’ anaphylactic bronchoconstriction by these three compounds was equivalent to that seen with the leukotriene antagonist FPL 55712 (10 mg kg−1, i.v.).

The peak levels of unchanged acetohydroxamic adds in the plasma compartment occurred 0.5 h after their oral administration and were as follows: BW A4C: 11.3 ± 3.9; BW A137C: 7.6 ± 2.4; BW A797C: 3.9 ± 1.3 μg ml−1 plasma.

The inhibition by BW A4C and BW A137C (50 mg kg−1, p.o.) of ‘leukotriene‐dependent’ anaphylactic bronchospasm persisted for up to 3 and 4h respectively but did not extend to 6h. The decline in inhibitory activity paralleled the fall in the concentration of unchanged drug in the plasma compartment over this time period.

The results of the present study are consistent with BW A4C, BW A137C and BW A797C attenuating ‘leukotriene‐dependent’ bronchial anaphylaxis in anaesthetized guinea‐pigs by selective inhibition of arachidonate 5‐lipoxygenase.
The action of prostanoid receptor agonists and antagonists on smooth muscle and platelets
Authors: Eglen R.M. , Whiting R.L.
Published: July 2012

Prostanoid receptors have been characterized in a range of guinea‐pig and rat smooth muscle and platelets, according to the scheme of Coleman et al., (1985a), using agonists (prostaglandin D2 (PGD2), PGE1, PGE2, 16,16 dimethyl PGE2, PGF2α, PGI2 and U46619) and putative selective antagonists (AH 6809 and SQ 29,548).

The ileum possesses EP1‐ and IP‐receptors; the trachea, EP1‐EP2‐ and TP‐receptors; the oesophageal muscularis mucosa, EP1‐ and TP‐receptors; the aorta and the portal vein TP‐receptors. The rat colon possesses IP‐, FP‐ and TP‐receptors.

Guinea‐pig platelets possess both IP and DP receptors mediating an inhibition of aggregation and TP receptors mediating proaggregation responses. No evidence was found for the presence of EP1‐, EP2‐ or FP‐receptors.

Misoprostol and fenprostalene were characterized using the above preparations. Misoprostol acts as a selective EP1‐agonist, and has little or no DP, FP, IP and TP activity. In the trachea precontracted with carbachol no evidence of EP2‐receptor stimulation was observed. Fenprostalene possesses FP and TP activity but no EP1, EP2, DP or IP activity.
Comparison of the binding of radiolabelled neurokinin A and eledoisin in rat cortex synaptic membranes
Authors: Foster Alan C. , Tridgett Robert
Published: July 2012

The binding of the 125I‐Bolton Hunter (BH) conjugates of neurokinin A and eledoisin to synaptic plasma membranes prepared from rat cerebral cortex was investigated.

Saturation analyses indicated that both radioligands labelled a similar number of binding sites, but [125I]BH‐eledoisin had a 7 fold higher affinity than [125I]BH‐neurokinin A.

An identical pharmacological profile was apparent for both radioligands and tachykinin peptides inhibited the binding in the order: neurokinin B > BH‐eledoisin > kassinin > L‐363,851, eledoisin > substance P, neurokinin A > physalaemin > DiMeC7 > substance P methylester, indicating a profile consistent with the NK3‐subtype of tachykinin receptors.

The binding of [125I]BH‐neurokinin A and [125I]BH‐eledoisin was equally sensitive to inhibition by the guanosine triphosphate (GTP) analogue, guanyly‐5′‐β‐γ‐imido) diphosphate.

These results indicate that [125I]BH‐neurokinin A and [125I]BH‐eledoisin appear to label a common site in rat cerebral cortex synaptic plasma membranes with the characteristics of an NK3‐receptor, and thus [125I]BH‐neurokinin A is not a selective radioligand for the NK2‐receptor.
Interactions between molecules of a steroid anaesthetic (alphaxalone) and ionic channels of nodal membrane in voltage‐clamped myelinated nerve fibre
Authors: Benoit E. , Carratù M.R. , Mitolo‐Chieppa D.
Published: July 2012

The effects of the anaesthetic alphaxalone (0.05 to 1 mm) on the node of Ranvier of isolated myelinated nerve fibres of the frog were studied under voltage‐clamp conditions.

When added to the solution bathing voltage‐clamped nodes, alphaxalone modified neither linear leakage nor capacitative currents but rapidly and reversibly blocked K and Na currents. The blocking effects of the anaesthetic on both types of current were not dependent on the frequency of stimulation of the nerve fibres between 0.7 and 10 Hz.

The kinetics of the Na current were not modified by alphaxalone but, in the presence of the drug, the K current showed an apparent fast inactivation.

Alphaxalone rapidly and reversibly shifted towards negative voltages both the steady‐state K conductance‐voltage and the peak Na steady‐state inactivation‐voltage relationships, without noticeable modification of their shape. In contrast, the anaesthetic reversibly decreased the slope of the peak Na conductance‐voltage curve.

The reduction of the K current induced by alphaxalone was voltage‐dependent with an apparent dissociation constant first decreasing from about 0.25 to 0.08 mM between −20 mV and +20 mV and then remaining constant above +20 mV. In contrast, the apparent dissociation constant for the Na current was almost constant with increasing voltages and equalled about 0.30 mM. Hill coefficient values for both K and Na currents were noticeably less than one.

It is concluded that, at higher concentrations than those attainable in the brain or in the plasma during surgical anaesthesia in man, alphaxalone has a local anaesthetic‐like' action on the peripheral nervous system in that it specifically and differentially interacts with K and Na channel gating systems: it is suggested that the anaesthetic would preferentially modify open K and inactivated Na channels.
AH6809, a prostaglandin DP‐receptor blocking drug on human platelets
Authors: Keery R.J. , Lumley P.
Published: July 2012

The effect of AH6809 (6‐isopropoxy‐9‐oxoxanthene‐2‐carboxylic acid) has been studied upon the antiaggregatory and aggregatory actions of various agents on human platelets in whole blood.

Prostaglandin D2 (PGD2), BW245C, 9α,11β‐PGF2, PGI2 and 5′‐N‐ethylcarboxamide adenosine (NECA) all inhibited ADP‐induced platelet aggregation in whole blood. The anti‐aggregatory activity of PGD2, BW245C and 9α,11β‐PGF2 but not PGI2 or NECA was antagonized by AH6809. NECA was antagonized by AH6809.

The antagonism of the anti‐aggregatory activity of PGD2 by AH6809 was concentration‐related and could be overcome by increasing the concentration of PGD2. Analysis of the data yielded an apparent pA2 for AH6809 of 5.35.

At approximately 10 fold higher concentrations than those required to antagonize the action of PGD2, AH6809 also antagonized the aggregatory effect of U‐46619 in whole blood (pA2 = 4.45). However, concentrations of AH6809 up to 300 μm were without effect upon either ADP‐ or platelet activating factor (Paf)‐induced aggregation (pA2 < 3.5).

The potency of AH6809 against PGD2 and U‐46619 was increased in a resuspended platelet preparation suggesting that the drug is extensively bound to plasma proteins. However, in resuspended platelets the specificity of AH6809 relative to that seen in whole blood was reduced since aggregation by ADP and Paf was also slightly antagonized.

In conclusion, AH6809 appears to be a weak but specific DP‐receptor blocking drug on human platelets and should prove to be a useful drug tool for defining the involvement of endogenous PGD2 in platelet aggregation and classifying the mode of action of anti‐aggregatory prostanoids.
Muscarinic inhibition of [3H]‐noradrenaline release on rabbit iris in vitro: effects of stimulation conditions on intrinsic activity of methacholine and pilocarpine
Authors: Bognar Irene T. , Pallas Sylvia , Fuder Hermann , Muscholl Erich
Published: July 2012

Rabbit isolated irides were loaded with [3H]‐noradrenaline and superfused with Tyrode solution. The inhibition by the muscarinic agonists (±)‐methacholine and pilocarpine of the [3H]‐noradrenaline overflow into the superfusate evoked by field stimulation (pulses of 1 ms duration, 75 mA) was measured as an index of activation of presynaptic muscarinic receptors.

The fractional rate of release per pulse during the first stimulation period (S1) was low with 360 pulses at 3 Hz, intermediate with 360 pulses at 10 Hz and high with 1200 pulses at 10 Hz. Upon repetitive stimulation (7 periods at 20 min intervals), the fractional rates of release per pulse during S7 no longer differed, suggesting a ‘long‐term’ regulation of [3H]‐noradrenaline release depending on the stimulation conditions.

The evoked [3H]‐noradrenaline overflow was depressed by (±)‐methacholine in a concentration‐dependent manner. The EC50 ranged from 0.29 to 0.42 μm. Methacholine nearly abolished the transmitter release evoked at 3 Hz but reduced that induced at 10 Hz by only 50%. Under the latter condition the methacholine concentration‐inhibition curve was bell‐shaped and no muscarinic inhibition was observed in the presence of methacholine 30 μm. After washout of methacholine the evoked [3H]‐noradrenaline release was temporarily enhanced.

Atropine 0.1 μm enhanced the [3H]‐noradrenaline overflow (evoked by stimulation with 360 or 1200 pulses at 10 Hz), probably antagonizing a presynaptic inhibition by endogenous acetylcholine. The inhibition by methacholine was competitively antagonized by atropine 0.1 μm (apparent ‐log KB = 8.5–9.0).

Depending on the concentration, pilocarpine reduced the [3H]‐noradrenaline overflow evoked by 360 pulses at 3 Hz up to 63%. However, at 10 Hz stimulation frequency the compound was inactive as an agonist but competitively antagonized the presynaptic inhibition induced by methacholine. The KB under the latter condition (0.95 μm) was very close to the EC50 value determined at 3 Hz (0.85 μm).

The results demonstrate a muscarinic inhibition of noradrenaline release from the rabbit isolated iris. The activation by pilocarpine of the presynaptic receptors provides an alternative explanation for the miosis induced in the rabbit in vivo, which might be the result of a decreased sympathetic tone in the iris dilator muscle.
Characterization of histamine receptors in isolated human cerebral arteries
Authors: Ottosson Anders , Jansen Inger , Edvinsson Lars
Published: July 2012

The subtypes of histamine‐receptors which mediate dilatation of small human cerebral arteries have been characterized in vitro using ‘selective’ agonists and antagonists.

Dilator responses were studied after preconstriction with prostaglandin F2α, since contraction was not seen with histamine concentrations up to 10−4 m. Histamine caused a concentration‐related relaxation of cerebral vessels with an IC50 value of 5.2 ± 1.6 × 10−8 m.

Mepyramine caused a parallel shift to the right of the histamine concentration‐response curve whereas cimetidine was without observable effect. This suggests the presence of histamine H1‐receptors only. However, combined treatment with mepyramine and cimetidine caused a more marked displacement of the concentration‐response curve to the right. Schild analysis indicated that in situations of near complete blockade of either of the histamine receptor subtypes, simple competitive antagonism both at H1‐ and H2‐receptors can be revealed with a pA2 value of 8.64 for mepyramine and a pA2 value of 6.52 for cimetidine.

The ‘selective’ H1‐receptor agonists pyridylethylamine, 2‐methylhistamine (2‐Me‐histamine) and thiazolylethylamine, and the H2‐receptor agonists dimaprit, impromidine and 4‐methylhistamine (4‐Me‐histamine) all mimicked the histamine response, but were less potent than histamine. The order of potency was thiazolylethylamine > dimaprit > impromidine > 2‐Me‐histamine > pyridylethylamine > 4‐Me‐histamine.

These results indicate that the histamine‐induced dilatation in small human cerebral arteries is mediated by both H1‐ and H2‐receptors and that the former subtype of histamine receptor predominates.
The effect of ozone on reactivity of upper and lower airways in guinea‐pigs
Authors: Holroyde Martin C. , Norris Alan A.
Published: July 2012

The effect of ozone inhalation on the responsiveness of upper and lower airways to histamine was examined in guinea‐pigs.

The exposure of conscious guinea‐pigs to 3.5 p.p.m. ozone for 30 min rendered their lower airways 2–3 fold more sensitive to the bronchoconstrictor action of i.v. histamine, as assessed subsequently under anaesthesia.

The development of lower airway hyperreactivity was not modified by bilateral cervical vagotomy or pretreatment with BW 755C, FPL 55712 or SC‐39070.

Under the conditions used, ozone exposure produced a mild inflammatory response as monitored by bronchoalveolar lavage, characterized by epithelial damage and prostaglandin E2 generation, but no cellular infiltration or oedema.

In contrast to the lower airways, upper airway resistance was reduced by i.v. histamine. This response was not affected by ozone exposure.

Isolated tracheal preparations taken from ozone‐exposed guinea‐pigs were not significantly more sensitive to histamine than control tissues.

The mechanism of hyperreactivity in this model is unknown but does not depend on leukotriene generation or a vagal reflex.
Neuropeptide Y and reserpine‐resistant vasoconstriction evoked by sympathetic nerve stimulation in the dog skeletal muscle
Authors: Pernow John , Kahan Thomas , Lundberg Jan M.
Published: July 2012

The effects of sympathetic nerve stimulation (evoked by recordings of authentic irregular vasoconstrictor nerve fibre discharge with average frequencies of 0.59, 2.0 and 6.9 Hz) on the perfusion pressure and the overflow of noradrenaline (NA) and neuropeptide Y‐like immunoreactivity (NPY‐LI) were investigated in the blood‐perfused gracilis muscle of the dog in situ.

Nerve stimulation in the untreated control group evoked a frequency‐dependent increase in perfusion pressure and overflow of NA. A significant overflow of NPY‐LI was found at the highest frequency only.

In a separate group of animals, the sympathetic supply was unilaterally interrupted by preganglionic decentralization before the administration of reserpine (1 mg kg−1 i.v.) 24 h before the experiment. Reserpine reduced the NA content of the intact and decentralized gracilis and gastrocnemius muscle by 98–99%. Reserpine also induced a marked (80%) reduction of the muscular content of NPY‐LI. The depletion of NPY‐LI was, in contrast to that of NA, prevented by the decentralization, suggesting that nerve impulse activity was of primary importance for the reserpine‐induced depletion of NPY‐LI.

A slowly developing and long‐lasting perfusion pressure increase was evoked by nerve stimulation, at 2.0 and 6.9 Hz after reserpine treatment. These responses were larger in the decentralized, as compared to the intact gracilis muscle and correlated with the nerve stimulation evoked overflow of NPY‐LI (r = 0.79, P < 0.001). Stimulation at 0.59 Hz caused vasoconstriction in the decentralized but not in the intact gracilis.

Administration of α,β‐methylene adenosine triphosphate did not evoke an increase in perfusion pressure in the gracilis muscle of reserpine‐treated animals.

In conclusion, a large perfusion pressure increase to sympathetic nerve stimulation occurs in the reserpine‐pretreated skeletal muscle vasculature of the dog in vivo, providing that preganglionic decentralization has been performed. It is suggested that the released NPY‐LI may mediate this vasoconstrictor response.
Behavioural responses to the selective D1‐dopamine receptor agonist R‐SK&F 38393 and the selective D2‐agonist RU 24213 in young compared with aged rats
Authors: Molloy Anthony G. , Waddington John L.
Published: July 2012

In aged male Sprague‐Dawley rats (22 months) with a selective loss of D2‐ but not of D1‐dopamine receptors, stereotyped behaviour induced by 0.5 mg kg−1 apomorphine was increased and prolonged in comparison with young (4 month) counterparts. This suggested a pharmacokinetic effect rather than a pharmacodynamic change.

The syndrome of non‐stereotyped behavioural responses to the selective D1‐agonist R‐SK&F 38393, 1.25–20.0 mg kg−1, was unchanged in aged vs young animals, but the topography of individual behaviours constituting this overall syndrome was altered with aging.

Neither the overall syndrome of low intensity stereotyped behaviour nor the topography of individual behaviours induced by the selective D2‐agonist RU 24213, 1.25–20.0 mg kg−1, were altered in aged vs young animals.

Loss of D2‐ but not D1‐receptors with aging was therefore found to be associated with no change in responsivity to a D2‐receptor agonist. The decreased intense grooming and increased vacuous chewing responses to the D1‐agonist with aging parallel the previously demonstrated effects of selective D2‐antagonists on these D1‐stimulated behaviours.

It is suggested that age‐related decline in D2‐receptor activity may have greater functional consequences in relation to D1‐:D2‐interactions than in simply influencing responsivity to a D2‐agonist. Such interactive effects should be taken into account when considering the pathophysiology and treatment of age‐related extrapyramidal movement disorders.
Adenosine receptor‐mediated contraction and relaxation of guinea‐pig isolated tracheal smooth muscle: effects of adenosine antagonists
Authors: Farmer Stephen G. , Canning Brendan J. , Wilkins Deidre E.
Published: July 2012

The effects of several adenosine analogues and antagonists on guinea‐pig isolated trachea have been examined.

5′‐N‐ethylcarboxamidoadenosine (NECA), 5′‐N‐methylcarboxamidoadenosine (MECA) and adenosine (in the presence and absence of dipyridamole) elicited concentration‐dependent tracheal relaxation.

The R(−)− and S(+)‐enantiomers of N6‐(2‐phenylisopropyl)adenosine (R‐PIA and S‐PIA respectively), N6‐cyclohexyladenosine (CHA) and 2‐chloroadenosine (CADO) caused contractions at low concentrations (0.05–2.0 μm), whereas at higher concentrations, relaxation resulted.

For tracheal relaxation, the adenosine analogues exhibited the following rank order of potency: NECA > CADO > R‐PIA = MECA > S‐PIA > adenosine. The rank order of potency for inducing contractions was R‐PIA > CHA > CADO > S‐PIA. These data suggest that relaxation is mediated by adenosine A2‐receptors, whereas contraction is the result of activation of A1‐receptors.

8‐Phenyltheophylline (8‐PT), aminophylline, the triazoloquinazoline CGS 15943A and NPC205 (1,3‐di‐n‐propyl‐8‐(4‐hydroxyphenyl)xanthine) each inhibited the R‐PIA‐induced contractile response, whereas enprofylline was without effect. NPC205, aminophylline and 8‐PT were competitive antagonists, but CGS15943A was non‐competitive.

That the most potent antagonist was the A1‐selective agent, NPC205 (pA2 = 7.80), further suggests that the contraction is mediated by A1‐receptors. Moreover, NPC205 was 13 times more potent as an antagonist of R‐PIA‐induced contractions (A1) than of NECA‐induced relaxations (A2).

The antagonists were also found to relax the trachea by an unknown mechanism. That enprofylline did not antagonize the R‐PIA‐induced contractions, but was 3–4 times more potent a tracheal relaxant than aminophylline, further suggests that a direct effect on airway smooth muscle, rather than antagonism of endogenous adenosine, is more relevant to the bronchodilator effect of alkylxanthines in the treatment of asthma.
Potentiation by neuropeptide Y of vasoconstriction in rat resistance arteries
Authors: Andriantsitohaina Ramaroson , Stoclet Jean Claude
Published: July 2012

The effects of neuropeptide Y (NPY) on resistance arteries were investigated on 3rd generation mesenteric arterioles of the rat.

Contractions were elicited by noradrenaline (NA), 5‐hydroxytryptamine (5‐HT), prostaglandin F2α (PGF2α), depolarization (KCl substituted for NaCl) and by the calcium agonist Bay K 8644, in the absence and in the presence of NPY (100 nm), a concentration which by itself did not induce vasoconstriction.

NPY produced a leftward shift of the concentration‐response curves to the agonists and to KCl, without any alteration of maximal contractions.

NPY also potentiated contractions elicited by addition of CaCl2 to KCl‐depolarized vessels, but its effect on calcium‐induced contractions decreased with increasing KCl concentrations (from 20 to 100 mm).

Calcium‐induced contractions were inhibited by the calcium channel blocker nitrendipine, both in the presence and absence of NPY (100 nm). NPY increased slightly (but significantly) the sensitivity to nitrendipine (the apparent KB increased from 2.9 × 10−10 m to 1.6 × 10−10 m).

The KCl concentration necessary for the maximal effect of Bay K 8644 was decreased in the presence of NPY, and the sensitivity to the calcium channel agonist was increased.

Elevating the KCl concentration in the bath from 5 to 20 mm (which gives the same displacement to the left of the KCl concentration‐effect curve seen in the presence of NPY) induced a parallel leftward shift of NA and 5‐HT concentration‐response curves. This shift was identical to the one induced by NPY on 5‐HT‐evoked contractions, but it was significantly smaller (P < 0.001) than the shift of the NA concentration‐response curve observed in the presence of NPY. In the latter case, NPY enhanced more markedly the contractions induced by low NA concentrations (between 10−9 and 3 × 10−8 m) than those induced by high concentrations (up to 3 × 10−7 m), thus giving a shallow concentration‐response curve.

The results strongly suggest that NPY partially depolarizes the arterioles and induces an increase in calcium entry through voltage‐dependent channels, thus enhancing contractions elicited by agonists or by KCl‐depolarization. In addition, they support the view that another mechanism also plays a part in the potentiation by NPY of the effects of low concentrations of NA.
Mechanism of action of nicotine in isolated urinary bladder of guinea‐pig
Authors: Hisayama Tetsuhiro , Shinkai Michiko , Takayanagi Issei , Toyoda Toshie
Published: July 2012

Nicotine produced a transient contraction of isolated strips of guinea‐pig urinary bladder. The response to nicotine was antagonized by the nicotinic receptor antagonist, hexamethonium but was insensitive to tetrodotoxin.

The nicotine‐induced contraction was potentiated by the cholinesterase inhibitor, physostigmine, and was reduced to 50% and 70% by the muscarinic cholinoceptor antagonist, atropine and the sympathetic neurone blocking drug, guanethidine, respectively. Chemical denervation with 6‐hydroxydopamine abolished the inhibitory effect of guanethidine. Simultaneous treatment with atropine and guanethidine did not abolish the response to nicotine, but the degree of inhibition was comparable to that obtained with atropine alone.

The nicotine‐induced contraction was insensitive to bunazosin and yohimbine (α1‐ and α2‐adrenoceptor antagonists, respectively), and exogenously applied noradrenaline did not cause a contraction even in the presence of blockade of noradrenaline uptake mechanisms with desipramine and normetanephrine and of β‐adrenoceptors with propranolol, suggesting a non‐adrenergic nature of the sympathomimetic effect of nicotine in this tissue.

The nicotine‐induced contraction in the presence of atropine was abolished after desensitization of P2‐purinoceptors with α, β‐methylene adenosine 5′‐triphosphate, a slowly degradable ATP analogue selective for P2‐purinoceptors. By this desensitization, the response to ATP, but not to histamine, was also abolished.

A cyclo‐oxygenase inhibitor flurbiprofen partially inhibited the nicotine‐induced contraction. The degree of the inhibition was more pronounced in the presence of atropine than in its absence. Flurbiprofen antagonized the response to exogenously applied ATP in an unsurmountable manner, but not that to carbachol.

The present results suggest that nicotine might induce a contraction through an interaction with nicotinic receptors located on the terminals of, possibly, (i) parasympathetic cholinergic, (ii) sympathetic non‐adrenergic and (iii) non‐sympathetic purinergic nerves in guinea‐pig detrusor preparations, and that a portion of the contraction due to the purine nucleotide released is possibly potentiated by intramural prostaglandin(s). Parasympathetic cholinergic output might be modulated by an unknown excitatory substance released by nicotine from sympathetic nerve.

Nicotine reveals a latent excitatory effect of the sympathetic hypogastric nerve which innervates guinea‐pig detrusor.
Pharmacological analysis of postjunctional α‐adrenoceptors mediating contractions to (−)‐noradrenaline in the rabbit isolated lateral saphenous vein can be explained by interacting responses to simultaneous activation of α1‐and α2‐adrenoceptors
Authors: Daly C.J. , McGrath J.C. , Wilson V.G.
Published: July 2012

The pharmacological characteristics of the α‐adrenoceptor population in the rabbit isolated saphenous vein has been examined with (–)‐noradrenaline (NA), as principal agonist, and a number of antagonists with selectivity for either α1‐ or α2‐adrenoceptors.

The rank order of potency of various agonists is consistent with a population of α2‐adrenoceptors; UK‐14304 > (—)‐noradrenaline = (—)‐adrenaline > B‐HT 920 = cirazoline > phenylephrine > amidephrine, but the rank order of pA2 values for the antagonists against (—)− noradrenaline: BDF‐6143 > rauwolscine = prazosin > CH‐38083 = YM‐12617 > Wy‐26703 = phentolamine > corynanthine, is indicative of a mixed population of α1‐ and α2‐adrenoceptors or, alternatively, a new subtype with characteristics of both the α1‐ and α2‐subtypes.

Further evidence for two discrete populations of α‐adrenoceptors is provided by, (a) the potent but non‐competitive effect of prazosin against (—)‐noradrenaline, (b) the presence of a component of the contractions elicited by NA and phenylephrine which is resistant to the selective α2‐adrenoceptor antagonists rauwolscine and CH‐38083: these responses were inhibited by the selective α1‐adrenoceptor antagonists prazosin and YM‐12617, but not by the selective α2‐adrenoceptor antagonist BDF‐6143 and, (c) the relative potency of the yohimbine diastereoisomers rauwolscine and corynanthine against NA, phenylephrine and UK‐14304.

In spite of the overwhelming evidence for a population of postjunctional α2‐adrenoceptors, prazosin was similarly effective against all agonists and failed to discriminate between those with putative selectivity for α1‐ and α2‐adrenoceptors. This suggests an interaction of the effects of agonists at the two α‐adrenoceptor subtypes.

An attempt has been made to reconcile a number of paradoxical observations with regard to the identification of postjunctional α2‐adrenoceptors in vitro, and it is suggested that in many of the isolated blood vessels presently available for examination both subtypes reside on the same smooth muscle cell. The pharmacological consequences of multiple subtypes of receptors mediating the same response is considered.
Purine receptors and guinea‐pig trachea: evidence for a direct action of ATP
Authors: Welford Laurence A. , Anderson Wayne H.
Published: July 2012

Adenosine (3–300 μm) and ATP (1–300 μm) each induced concentration‐dependent relaxation of guinea‐pig isolated tracheal preparations that had been precontracted with methacholine.

Ectonucleotidase enzymes on the trachea dephosphorylated ATP to form adenosine which was then further metabolised to inosine and hypoxanthine.

Dipyridamole (2 μm) inhibited the metabolism of adenosine but did not inhibit the dephosphorylation of ATP. Nevertheless dipyridamole potentiated the effects of both adenosine and ATP in relaxing tracheal smooth muscle.

Although adenosine 5′‐[β,γ‐imido] triphosphate (AMP‐PNP), an analogue of ATP, was resistant to catabolism by ectonucleotidases, it was more potent at inducing relaxation than either ATP or adenosine, and was also potentiated by dipyridamole (2 μm).

Relaxations induced by ATP and by AMP‐PNP were more rapid than those induced by adenosine.

We therefore conclude that the intact ATP molecule can itself induce relaxation of the guinea‐pig trachea, without first having to be metabolised to adenosine, and furthermore that dipyridamole does not act simply by inhibiting the degradation (or uptake) of adenosine.
Acetylcholine induces vasodilatation in the rabbit isolated heart through the release of nitric oxide, the endogenous nitrovasodilator
Authors: Amezcua J.L. , Dusting G.J. , Palmer R.M.J. , Moncada S.
Published: July 2012

Acetylcholine (ACh, 0.03–3.0 μm) induced a dose‐dependent vasodilatation in the isolated Langendorff‐perfused heart of the rabbit. The vasodilatation was mimicked by exogenous nitric oxide (NO, 0.045–4.5 nmol).

There was no detectable vascular relaxing activity in the cardiac effluent when these concentrations of ACh or NO were injected through the heart, even in the presence of an infusion of superoxide dismutase (SOD).

Acetylcholine (0.03–3.0 μm), however, induced the release into the cardiac effluent of a material which produced a chemiluminescent signal when reacted with ozone, a response which could be mimicked with exogenous NO (0.045–4.5 nmol) injected through the heart.

The effects of ACh, but not those of NO, were antagonized by atropine (2 μm). Prostacyclin (1 μm) injected through the heart induced vasodilatation without the release of a biologically active or chemiluminescent material.

During passage through the heart, >99% of the biological activity of exogenous NO disappeared, whereas there was approximately 50% reduction of its chemiluminescent response. This indicates complete transformation into a mixture containing approximately 50% NO2− and 50% of other non‐chemiluminescent material(s), presumably NO3−.

This study suggests that ACh induces endothelium‐dependent vasodilatation in the coronary circulation through the release of the endogenous nitrovasodilator, NO, which is rapidly converted to NO2− and NO3−.
A comparison between the in vivo and in vitro activity of five potent and competitive NMDA antagonists
Authors: Lodge D. , Davies S.N. , Jones M.G. , Millar J. , Manallack D.T. , Ornstein P.L. , Verberne A.J.M. , Young N. , Beart P.M.
Published: July 2012

Phosphonate analogues of glutamate have been tested and compared as N‐methyl‐d‐aspartate (NMDA) antagonists in electrophysiological and binding experiments. The compounds tested were three established NMDA antagonists: d‐2‐amino‐5‐phosphonopentanoate (d‐AP5), dl‐2‐amino‐7‐phosphonoheptanoate (dl‐AP7), 3‐(2‐carboxypiperazin‐4‐yl)propyl‐l‐phospnonate (CPP), and two novel putative NMDA antagonists: 3‐(2‐carboxypiperidin‐4‐yl)propyl‐l‐phosphonate (CPPP) and 3‐(2‐carboxy‐piperidin‐4‐yl)methyl‐1‐phosphonate (CPMP).

When administered electrophoretically to rat spinal neurones in vivo, these compounds were found to be selective NMDA antagonists with little effect on excitations evoked by quisqualate and kainate. CPMP and CPPP were approximately equipotent with CPP and about 5 times more potent than d‐AP5.

Following systemic administration, 2–5 mg kg−1 i.v. of CPP, CPMP and CPPP reduced NMDA‐evoked excitations by 70–100% whereas 50–100 mg kg−1 of d‐AP5 and dl‐AP7 produced a similar effect. The onset of the effects required 20–30 min and lasted more than six hours.

On bath application to cortical wedges, the IC50 values (μm) for antagonism of 40 μm NMDA were: CPP, 0.64 ± 0.06 (mean ± s.e.mean; n > 4); CPMP, 1.65 ± 0.13; CPPP 0.89 ± 0.09; d‐AP5, 3.7 ± 0.32; dl‐AP7, 11.1 ± 2.1; and dl‐AP4 and dl‐AP6 were inactive at 100 μm.

In binding studies with [3H]‐CPP, the Ki values (nm) were: CPP, 446 ± 150 (mean ± s.e.mean; n ≥ 3); CPMP, 183 ± 74 and CPPP, 179 ± 13 whereas against NMDA (10 μm)‐stimulated [3H]‐TCP (thienylcyclohexylpiperidine) binding the IC50 values (μm) for CPMP and CPPP respectively were 5.6 ± 2.7 and 4.5 ± 2.2.

Systemic administration of CPPP and CPMP, at doses sufficient to antagonize NMDA, also reduced cardiovascular responses to 5‐hydroxytryptamine (Bezold‐Jarisch reflex). This illustrates a role for NMDA receptors in central cardiovascular control.

The results indicate the systemic doses of piperidine and piperazine analogues of d‐AP5 which may be used for assessing the role of NMDA receptors in central synaptic function.