bluuebunny/crossref_metadata_2025 huggingface dataset:
Methylflavonolamine hydrochloride inhibits contractions induced by noradrenaline, calcium and potassium in rabbit isolated aortic strips
Authors: Zhang Ming‐Sheng , Zhou Er‐Feng
Published: July 2012

The effects of methylflavonolamine hydrochloride (4′‐methyl‐7‐(2‐hydroxy‐3‐isopropylaminopropoxy)‐flavone hydrochloride, MFA) were investigated and compared with verapamil and papaverine on rabbit isolated aortic strips, which were contracted by noradrenaline, calcium and potassium.

Pre‐incubation for 25 min with either MFA (0.03 to 0.2 mm) or papaverine (0.03 to 0.2 mm) induced non‐parallel and concentration‐dependent rightward displacements of the curves to noradrenaline (0.00001 to 0.1 mm) with the maximal response depressed. The calculated pD′2 values (mean ± s.d.) were 3.89 ± 0.15 for MFA and 3.93 ± 0.05 for papaverine, respectively. Verapamil (0.03 to 0.2 mm) inhibited the contraction induced by noradrenaline in a competitive manner with a pA2 value of 5.91 ± 0.83.

In depolarized aortic strips of the rabbit, prior exposure to MFA (0.03 to 0.3 mm) and papaverine (0.03 to 0.2 mm) shifted the cumulative curves to Ca2+ (0.003 to 100 mm) parallel to the right with the maximal responses depressed, pD′2 values being 3.88 ± 0.05 and 3.89 ± 0.13, respectively. Verapamil produced comparable inhibition of the contraction at much lower concentrations (30 to 300 nm).

MFA (0.03 and 0.1 mm) inhibited the contraction elicited by graded depolarization at a constant Ca2+ concentration with a pD′2 value of 4.09 ± 0.07.

The present results show that MFA has some actions consistent with a calcium antagonist. It resembles papaverine more closely than verapamil.
The lack of involvement of cyclic nucleotides in the smooth muscle relaxant action of BRL 34915
Authors: Gillespie John S. , Sheng Hong
Published: July 2012

The relaxant effect of BRL 34915 has been examined on four isolated preparations, the bovine retractor penis (BRP), guinea‐pig taenia coli, guinea‐pig trachea and rabbit aortic strip contracted by either histamine, carbachol, noradrenaline or 10 mM KCl. Even though the probability of the involvement of external calcium entering through voltage‐operated channels in these tissues varied, there was little corresponding variation in sensitivity to BRL 34915.

The relaxant effect of BRL 34915 on the BRP and guinea‐pig taenia coli was unaffected by haemoglobin 3.3 μm or Apamin 0.5 μm, concentrations which blocked completely the relaxant effect of non‐adrenergic, non‐cholinergic (NANC) nerve stimulation in these tissues.

BRL 34915 in doses causing maximum relaxation did not increase the levels of either cyclic AMP or cyclic GMP in the BRP, although the appropriate enzymes were present and could be stimulated by forskolin or sodium nitroprusside.

In the BRP isoprenaline 30 μm acting through β‐receptors caused maximum relaxation but did not raise the levels of cyclic AMP, even though lower doses of 2 μm did raise the levels of this nucleotide in the rabbit uterus.

These results provide some indirect evidence that membrane hyperpolarization may not be the only cause of the smooth muscle relaxation induced by BRL 34915. However, neither a rise in cyclic AMP nor cyclic GMP are satisfactory alternative mechanisms.
Characterization of receptors for platelet‐activating factor on platelets, polymorphonuclear leukocytes and macrophages
Authors: Stewart A.G. , Dusting G.J.
Published: July 2012

We have compared the potency of the putative platelet‐activating factor (Paf) receptor antagonists (WEB 2086, L‐652,731 and BN 52021) against Paf‐induced aggregation of rabbit and guinea‐pig platelets, aggregation of rabbit polymorphonuclear leukocytes (PMNLs) and prostacyclin generation by guinea‐pig resident peritoneal macrophages.

On rabbit washed platelets and PMNLs WEB 2086, L‐652,731 and BN 52021 each antagonized competitively Paf‐induced aggregation. The rank order of potency was WEB 2086 ⋍ L‐652, 731 > BN 52021 and was the same for the two cell types.

The pA2values for each of the three antagonists were similar on rabbit washed platelets and PMNLs. Moreover, the pA2for WEB 2086 on rabbit platelets (7.58) did not differ significantly from that on guinea‐pig platelets (7.69).

On guinea‐pig resident peritoneal macrophages WEB 2086 was 10 fold less potent for receptors mediating increased generation of 6‐oxo‐prostaglandin F1α(6‐oxo‐PGF1α) than for those mediating platelet aggregation.

The potencies of L‐652,731 and BN 52021 were also markedly less (2 log units) for the macrophage receptors than for platelet or PMNL receptors and BN 52021 was more potent than L‐652, 731 in the macrophages.

WEB 2086 and L‐652,731 significantly reduced basal 6‐oxo‐PGF1αproduced by macrophages, but none of the antagonists affected 6‐oxo‐PGF1αproduction during stimulation by A23187.

These data raise the possibility that there may be a Paf receptor‐subtype mediating prostacyclin generation in macrophages that is different from that on the platelet and PMNL. Hence, the potency of Paf antagonists against platelet aggregation would not be a good predictor of antagonist potency in disorders involving macrophages.
Dicyclomine discriminates between M1‐ and M2‐muscarinic receptors in the guinea‐pig ileum
Authors: Kilbinger H. , Stein A.
Published: July 2012

The affinity of the antagonist dicyclomine for subtypes of muscarinic receptors has been assessed in the myenteric plexus‐longitudinal muscle preparation of the guinea‐pig.

Dicyclomine had a high affinity (pA2 9.13) for the neuronal M1‐receptor whose activation by pilocarpine causes an increase in acetylcholine release. Dicyclomine had a low affinity for both the prejunctional M2‐receptor (pA2 7.61) mediating inhibition of the electrically‐evoked acetylcholine release and the postjunctional M2‐receptor (pA2 7.21).

It is concluded that dicyclomine distinguishes between M1‐ and M2‐muscarinic receptors in functional experiments.
Antagonism of PGD2 vasodepressor responses in the rat in vivo by the novel, selective antagonist, BW A868C
Authors: Hamid‐Bloomfield S. , Whittle B.J.R.
Published: July 2012

Bolus intravenous injection of prostaglandin D2 (PGD2, 1–160μg kg−1), the hydantoin prostanoid BW245C (0.25–160 μg kg−1) or prostacyclin (PGI2, 0.05–0.5 μg kg−1) caused a dose‐dependent fall in systemic arterial blood pressure (BP) in the anaesthetized rat, lasting 2–4 min.

Intravenous infusion of the novel 3‐benzyl substituted hydantoin, BW A868C (1–10 μg kg−1 min−1), in doses that had no direct effect on BP, dose‐dependently reduced the vasodepressor action of PGD2.

Bolus injection of BW A868C (30 and 100 μg kg−1, i.v.) likewise dose‐dependently antagonized the vasodepressor responses to PGD2, causing a 3.4 and 13.2 fold rightward shift of the dose‐response curve.

The thromboxane‐receptor antagonist, BM 13.177 (2.5 mg kg−1 i.v.) had little effect on the PGD2 vasodepressor responses, suggesting minimal contribution of a PGD2 interaction at thromboxane receptor‐sites in the systemic vasculature of this species.

BW A868C (10 μg kg−1 min−1 i.v.) caused a rightward shift (59 fold) of the dose‐response relationship for BW245C, the putative PGD2‐receptor agonist. This antagonism lasted for at least 1h after termination of the BW A868C infusion. Higher doses of BW A868C (20–100 μg kg−1 min−1) caused no further antagonism of the vasodepressor responses to BW245C, suggesting that this prostanoid also acts at vascular receptors other than of the DP‐type.

BW A868C (10 μg kg−1 min−1, i.v.) failed to alter the vasodepressor actions of prostacyclin.

These findings in the rat in vivo support the characterization of BW A868C as a potent and selective antagonist of the cardiovascular actions of PGD2 at the DP‐receptor.
Structure‐activity relationships of new analogues of arecaidine propargyl ester at muscarinic M1 and M2 receptor subtypes
Authors: Moser U. , Lambrecht G. , Wagner M. , Wess J. , Mutschler E.
Published: July 2012

The potency of arecaidine propargyl ester (APE) and of several analogues containing a modified ester side chain has been assessed at M1 and M2 muscarinic receptor subtypes. APE was shown to act as a potent agonist at ganglionic M1 receptors in the pithed rat, at M2 receptors in guinea‐pig isolated atria (‐log EC50 = 8.22) and ileum (‐log EC50 = 7.77).

The arecaidine 2‐butynyl and 2‐pentynyl esters were approximately equipotent with APE at M1 and M2 receptors, whereas the 2‐hexynyl derivative was found to be less potent than APE in atria (‐log EC50 = 6.80) and ileum (‐log EC50 = 6.70) by about one order of magnitude. The 2‐heptynyl and 3‐phenyl propargyl esters exhibited no agonist actions in atria and ileum.

Shifting the triple bond from the 2 to the 3 position and introducing a bulky group at position 1 of the ester side chain of APE and analogues resulted in competitive antagonists (pA2 ranging from 4.9 to 7.3).

APE and its 2‐butynyl analogue showed some agonistic selectivity for cardiac M2 receptors (potency ratio, ileum/atria = 2.8 and 4.6 respectively). All antagonists in this series of compounds were not selective in terms of affinity since their pA2 values at cardiac and ileal M2 receptors were similar (potency ratios, ileum/atria = 0.4 to 1.2).
Effect of selective agonists and antagonists on atrial adenosine receptors and their interaction with Bay K 8644 and [3H]‐nitrendipine
Authors: Borea Pier Andrea , Caparrotta Laura , de Biasi Mariella , Fassina Giuliana , Froldi Guglielmina , Pandolfo Luisa , Ragazzi Eugenio
Published: July 2012

(−)‐N6‐phenylisopropyladenosine (R‐PIA) and N6‐cyclohexyladenosine (CHA), highly selective agonists at A1‐adenosine receptors, 5′‐N‐ethyl‐carboxamidoadenosine (NECA), a non‐selective agonist at A1 and A2 receptors, and 2‐phenylaminoadenosine (CV‐1808), a selective A2 agonist, were compared in spontaneously beating and electrically driven atria. R‐PIA, CHA and NECA inhibited contraction in both preparations. CV‐1808 was not effective up to 500 nM.

1,3‐Dipropyl‐8‐cyclopentylxanthine (DPCPX), a new selective A1 receptor antagonist, competitively inhibited the effects of the adenosine agonists, at low concentrations (IC50 < 1 nm).

CHA and NECA were able to inhibit the positive inotropic effect of Bay K 8644 both in spontaneously beating and in electrically driven atria.

R‐PIA, CHA and NECA (agonists), 8‐phenyltheophylline (PT) and DPCPX (antagonists), failed to influence [3H]‐nitrendipine binding on microsomal membranes from guinea‐pig atria and ventricles in a range of concentrations from 1 nM to 100 μm.

The data support the existence of A1 receptors in atrial tissue. No evidence for a direct interaction between adenosine analogues and Bay K 8644 was found at the level of slow calcium channels. Adenosine analogues appear to antagonize the effects of Bay K 8644 indirectly by activation of A1 receptors.
Inhibitory effect of a selective thromboxane A2receptor antagonist, EP 092, on platelet aggregation in whole bloodex vivoandin vivo
Authors: Booth R.F.G. , Honey A.C. , Lad N. , Tuffin D.P. , Wade P.J.
Published: July 2012

The inhibitory effect of a selective prostaglandin H2(PGH2)/thromboxane A2receptor antagonist, EP 092, on platelet aggregatory responses in whole bloodex vivo(guinea‐pig: Rhesus monkey) and intravascular aggregationin vivo(rabbit) has been investigated.

Collagen (0.1–10.0 μgml−1) caused a concentration‐dependent decrease in single platelet count in samples of both guinea‐pig and Rhesus monkey citrated whole blood incubatedex vivo. EP 092 administered to guinea‐pigs by intravenous (0.1–3.0 mg kg−1) or oral (1.0–10.0 mg kg−1) routes significantly inhibited the platelet responses to collagen (ED50values 1.3 ± 0.2 and 1.4 ± 0.2 mg kg−1respectively). Similar potency against collagen‐induced whole blood aggregation was observed in Rhesus monkey blood samples following EP 092 given orally (ED500.9 ± 0.3 mg kg−1).

The duration of action of EP 092 against collagen aggregatory responsesex vivoin both guinea‐pigs and Rhesus monkeys was between 3 and 6h following oral administration at 3.0 mg kg−1.

The inhibitory activity demonstrated by EP 092 against collagen‐induced aggregation of Rhesus monkey whole bloodex vivowas not accompanied by any significant reduction in thromboxane A2formation except at the highest dose tested (10 mg kg−1).

The intravascular aggregatory response induced by collagen or thrombin in the anaesthetized rabbit was significantly inhibited by an intravenous infusion of EP 092 (10 mg kg−1). EP 092 appeared less potent and its effect was of shorter duration in this preparation compared with its inhibitory effect onex vivoaggregation, being evident immediately after infusion of drug but not after a further 30 min.

It is concluded that collagen‐induced platelet aggregatory responses in guinea‐pig and Rhesus monkey whole bloodex vivoand rabbitin vivoexhibit a thromboxane‐dependent component which can be inhibited in a dose‐related fashion by pretreatment with the thromboxane antagonist EP 092. In the rabbit, moreover, the data support the possibility of a role for thromboxane in the intravascular aggregatory response to thrombin.
Affinity of muscarinic receptor antagonists for three putative muscarinic receptor binding sites
Authors: Delmendo Ronald E. , Michel Anton D. , Whiting Roger L.
Published: July 2012

A range of muscarinic receptor antagonists were examined for affinity at the M1 muscarinic binding site, present in rat cerebrocortical membranes and the M2 muscarinic binding sites of rat cardiac and submaxillary gland membranes.

The results obtained were consistent with the presence of three classes of muscarinic binding site.

Both the M1 binding site, labelled by [3H]‐pirenzepine ([3H]‐Pir) in rat cerebrocortical membranes, and the M2 gland binding site, labelled by [3H]‐N‐methyl scopolamine ([3H]‐NMS) in rat submaxillary gland membranes, displayed higher affinity for pirenzepine, dicyclomine, 4‐diphenylacetoxy‐N‐methylpiperidine methiodide (4‐DAMP) and cyclohexylphenyl (2‐piperidinoethyl) silanol (CPPS) than did the M2 binding sites of cardiac membranes labelled by [3H]‐NMS.

The M2 cardiac sites displayed higher affinity for methoctramine, himbacine and AF‐DX 116 than did either the M1 binding site of cerebrocortical membranes or the M2 gland binding site present in rat submaxillary gland membranes.

The M1 and M2 gland binding sites could only be distinguished by considering the absolute affinity of compounds for these two sites. Thus, all compounds, with the exception of 4‐DAMP, displayed between a 2 and 8 fold higher affinity for the M1 than for the M2 gland binding site. There were no antagonists with higher M2 gland than M1 affinity.
Characterization of the muscarinic receptor subtype mediating contractions of the guinea‐pig uterus
Authors: Eglen R.M. , Michel A.D. , Whiting R.L.
Published: July 2012

The muscarinic receptor present on the guinea‐pig uterus has been characterized by use of both functional and radioligand binding studies. The contractile responses to carbachol were antagonized by atropine, pirenzepine, methoctramine and hexamethonium with pA2 values consistent with the presence of an M2 receptor (i.e. 9.5, 7.0, 8.0 and 3.7 respectively). In binding studies, pKi values were also observed for pirenzepine, methoctramine and AF‐DX 116 which were consistent with the presence of a homogeneous M2 receptor population (i.e. 6.6, 7.9 and 7.1 respectively). The uterus therefore possesses M2 receptors through which a functional contractile response is mediated and in this respect it is clearly different from other smooth muscles. M2 receptors in the uterus mediate excitatory responses, an effect in contrast to their action in other tissues.
Pharmacological characterization of postjunctional α‐adrenoceptors in cerebral arteries from the sheep
Authors: Gaw A.J. , Wadsworth R.M.
Published: July 2012

The responsiveness to noradrenaline was characterized in cerebral arteries from the sheep, since this species was large enough to permit a comparison of arteries from different parts of the cerebral vasculature.

Noradrenaline caused contraction of the basilar artery, middle cerebral artery and small pial arteries by stimulation of α1‐adrenoceptors.

The maximum contraction to noradrenaline was small in the basilar artery (28% of the 5‐hydroxytryptamine (5‐HT) maximum) but larger in the middle cerebral artery (78% of the 5‐HT maximum) and pial artery (92% of the 5‐HT maximum) of the sheep.

Cocaine (10 μm) potentiated noradrenaline‐induced contractions in the sheep middle cerebral artery but not in the sheep basilar artery.

The noradrenaline contraction, relative to the 5‐HT contraction, was not affected by removal of the endothelium in either the sheep basilar or middle cerebral artery.

The results showed a variation within the sheep cerebral vasculature in the response to noradrenaline which cannot be explained by regional differences in α‐adrenoceptor subtypes, noradrenaline uptake mechanisms or endothelial function.
Effects of receptor‐selective neurokinin agonists and a neurokinin antagonist on the electrical activity of spinal cord neurones in culture
Authors: Wienrich M. , Reuss K. , Harting J.
Published: July 2012

Rat spinal cord neurones grown in tissue culture were used to examine the electrophysiological effects of the neurokin in (NK)‐selective agonists (pGlu6, Pro9) substance P(6–11) (septide; NK1, 10−6 m.) and (pGlu5, MePhe8, MeGly9)SP(1–7) (DiMe‐C7; NK3, 10−6 m.). In addition, the effect of the neurokinin antagonist (D‐Arg1, D‐Pro2, D‐Trp7,9, Leu11)SP (10−5 m.) on the neurokinin‐evoked responses was investigated.

Neurokinin‐evoked responses consisted of an increase in neuronal activity with or without long‐lasting (mean: 50s) depolarizations of the membrane potential of up to 25mV. The latter also occurred in the presence of tetrodotoxin (10−7 m.) (direct response).

In a number of spinal cord neurones (n = 17) only septide induced a membrane depolarization while DiMe‐C7 elicited no response. On the other hand, in 2 neurones a response was exclusively evoked by DiMe‐C7.

The neurokinin antagonist (D‐Arg1, D‐Pro2, D‐Trp7,9, Leu11)SP had no effect of its own but blocked the septide‐ and DiMe‐C7‐induced depolarizations. It had no effect on the glutamate (10−5 m.)‐evoked depolarization.

It is concluded that by the use of neurokinin receptor‐selective agonists, subpopulations of spinal cord neurones in primary dissociated cell culture can be differentiated which express the NK1 or the NK3 receptor. Cells expressing only the NK1 receptor outnumber those expressing only the NK3 receptor subtype. Both receptors can be blocked by the neurokinin antagonist (D‐Arg1, D‐Pro2, D‐Trp7,9, Leu11)SP.
Effects of hypoxia, elevated K+ and acidosis on the potency of verapamil, diltiazem and nifedipine in the guinea‐pig isolated papillary muscle
Authors: Robertson M.J. , Lumley P.
Published: July 2012

The effects of the structurally diverse calcium channel blockers verapamil, nifedipine and diltiazem were investigated on the force of contraction of guinea‐pig, electrically stimulated papillary muscles in vitro.

Calcium channel blocking potency was assessed either as a direct negative inotropic effect or as the ability of the drugs to antagonise the positive inotropic effects of added calcium (Ca2+). By either method, the rank order of potency was found to be nifedipine > verapamil > diltiazem.

Various factors which mimic some of the consequences of acute ischaemia in vivo, namely low pH, hypoxia and elevated K+, in combination, but not singly, enhanced the negative inotropic potency of verapamil and to lesser extent that of diltiazem, but not that of nifedipine.

Whilst the various interventions, especially in combination, produced a profound negative inotropic effect themselves, this was not responsible per se for the potentiation of the negative inotropic effects of verapamil and diltiazem, since the negative inotropic effects of nifedipine and dinitrophenol were not potentiated under the ‘ischaemic’ conditions.

By use of antagonism of the positive inotropic action of exogenous Ca2+ as an alternative measure of potency, the differential influence of ‘ischaemia’ on calcium channel blocker potency was confirmed. The effect of verapamil was potentiated some 9 fold, that of diltiazem about 2 fold, and that of nifedipine was unchanged.

The differential effect of ‘ischaemia’ on the potencies of the calcium channel blockers was unexpected. Verapamil (but not nifedipine) is thought to bind to the calcium channel at a specific site not easily accessible from the extracellular space. ‘Ischaemic’ conditions may cause membranal perturbations which allow verapamil easier access to its binding site thus increasing its negative inotropic potency.
Ryanodine reveals multiple contractile and relaxant mechanisms in vascular smooth muscle: simultaneous measurements of mechanical activity and of cytoplasmic free Ca2+ level with fura‐2
Authors: Hisayama Tetsuhiro , Takayanagi Issei , Okamoto Yu
Published: July 2012

The effects of ryanodine on changes in cytoplasmic Ca2+ level ([Ca2+]i) and muscle tension induced by maximum concentrations of phenylephrine (Phe; 1μm), prostaglandin F2α (PGF2α, 10 μm), caffeine (Caf, 30 mm) and isoprenaline (Iso, 1 μm) were examined in rat aortic strips using fura‐2.

In normal media, Phe and PGF2α produced a phasic contraction, followed by a tonic one. Caf elicited only a transient contraction. When the preparation was treated with 10 μm ryanodine, an increase in [Ca2+]i was induced accompanied by a nicardipine (1 μm)‐resistant contraction which was [Ca2+]o‐dependent.

In Ca2+‐free solution, the three stimulants elicited transient increases in [Ca2+]i. Transient contractions to Phe and Caf were accompanied by changes in [Ca2+]i. The transient increase in [Ca2+]i induced by PGF2α was not accompanied by a corresponding contraction.

Sustained contractions were induced by Phe and PGF2α in the absence of external Ca2+, while the increase in [Ca2+]i was reduced. A larger maximum contraction was induced by PGF2α than by Phe.

Ryanodine abolished both the Caf‐ and Phe‐induced [Ca2+]i transient increases and the corresponding contractions, but had no substantial effect on the PGF2α‐induced [Ca2+]i transient increase. Ryanodine had no influence on the sustained contractions induced by Phe and PGF2α.

Iso relaxed both sustained contractions almost completely, without any detectable change in [Ca2+]i. Treatment of the preparation with ryanodine had no effect on the concentration‐response curves for Iso in relaxing the 0.1 μm Phe‐ or 40 mm K+‐induced precontraction.

It is suggested that Phe and Caf mobilize Ca2+ from a ryanodine‐sensitive Ca2+ store and that PGF2α releases Ca2+ from a ryanodine‐insensitive Ca2+ store. The former contributes to the transient contraction through a Ca2+‐dependent process, while the latter seems not to be directly associated with the contraction. The sustained contraction under Ca2+‐free conditions might involve a Ca2+‐independent process or a change in the sensitivity of the contractile filaments to Ca2+.

In addition to lowering cytoplasmic Ca2+ concentration, it is suggested that Iso counteracts the apparently Ca2+‐independent process. The ryanodine‐sensitive Ca2+ store plays no substantial role in active relaxation by Iso, although it does play a major role in the maintenance of cytoplasmic Ca2+ in a quiescent muscle.
Pharmacological profile of a tachykinin antagonist, spantide, as examined on rat spinal motoneurones
Authors: Yanagisawa Mitsuhiko , Otsuka Masanori
Published: July 2012

The pharmacological profile of a tachykinin antagonist, [d‐Arg1, d‐Trp7,9, Leu11] substance P (spantide), was studied on motoneurones of the isolated spinal cord of the newborn rat. For this purpose, potentials were recorded from a lumbar ventral root extracellularly and drugs were bath‐applied in the presence of tetrodotoxin (TTX).

Neurokinin A (NKA), a NK2‐receptor selective agonist, induced concentration‐dependent depolarizations, which were antagonized by spantide. Analyses of concentration‐response curves suggested a competitive type antagonism with a pA2 of 6.5.

Depolarizations induced by acetyl‐Arg6‐septide, a NK1‐receptor selective agonist, were also antagonized by spantide with a pA2 of 6.5.

Spantide (0.5–16 μm) had no depolarizing action on the ventral root in the presence of TTX.

Spantide antagonized the depolarizing action of substance P (SP) when SP was applied at low concentrations (0.1–0.3 μm) or by short duration pulses in artificial cerebrospinal fluid containing TTX, but much higher concentrations of spantide (4–10 μm) were needed to exert an antagonistic action against SP than against acetyl‐Arg6‐septide or NKA.

Thyrotrophin‐releasing hormone, l‐glutamate, GABA, and noradrenaline, also induced depolarizations of the ventral root in the presence of TTX but the responses to these agonists were not depressed by spantide (16 μm).

These results suggest that there is a subtype of tachykinin receptors on neonatal rat spinal motoneurones to which NKA, acetyl‐Arg6‐septide and spantide bind competitively with high affinity. The present results also suggest the existence on rat motoneurones of another class or other classes of tachykinin receptors that are less sensitive to the antagonistic action of spantide.
Evidence that central 5‐HT1A‐receptors play a role in the von Bezold‐Jarisch reflex in the rat
Authors: Bogle Richard G. , Pires Jose G.P. , Ramage Andrew G.
Published: July 2012

The effects of intracisternal (i.c.) application of putative 5‐hydroxytryptamine (5‐HT)1Aantagonists on the reflex bradycardia evoked by injection of phenylbiguanide (i.v.) were investigated in anaesthetized, atenolol‐pretreated rats.

Intracisternal application of spiperone (100 μg kg−1) reversibly attenuated the reflex bradycardia whilst the same dose given i.v. had no effect. The bradycardia was also attenuated by i.e. methiothepin (200 μg kg−1), (±)‐pindolol (100 μg kg−1) and buspirone (200 μ kg−1) but was not attenuated by antagonists selective for α1‐adrenoceptors (alfuzosin; 100 μg kg−1), 5‐HT2‐receptors (BW 501C67; 100 μg kg−1) or dopamine D2‐receptors ((−)−sulpiride; 100 μg kg−1) given i.e.

It is concluded that the 5‐HT1A‐receptor antagonist action of intracisternally applied spiperone, methiothepin, (±)‐pindolol and buspirone is responsible for the ability of these drugs to attenuate reversibly the excitation of cardiac vagal motoneurones caused by activation of the von Bezold‐Jarisch reflex.
Relationship between endothelin‐1 binding site densities and constrictor activities in human and animal airway smooth muscle
Authors: Henry Peter J. , Rigby Paul J. , Self Glenn J. , Preuss Janet M. , Goldie Roy G.
Published: July 2012

Endothelin‐1 (ET‐1) binding site densities and constrictor activities were compared in airway smooth muscle preparations of human, guinea‐pig, rat and mouse.

The mean contractile response to 0.3 μm ET‐1 (measured as the % maximum response to 10 μm carbachol, % Cmax ± s.e.mean) and the mean concentration of ET‐1 producing 30% (95% confidence limits) were respectively; 85.9 ± 5.4% and 3.4nm (2.4–5.0) for mouse trachea (n = 11), 88.8 ± 4.7% and 18.2 nm (11.2–25.2) for rat trachea (n = 6), 71.0 ± 7.1% and 35.2 nm (5.4–231) for human bronchus (n = 3), and 32.3 ± 3.0% and 241 nm (125–460) for guinea‐pig trachea (n = 6).

Light microscopic autoradiography revealed specific [125I]‐ET‐1 binding sites localized to the smooth muscle band, with very low levels of binding associated with cartilage, submucosal and epithelial cells.

Quantitative autoradiographic analyses of the concentration‐dependence of specific [125I]‐ET‐1 binding (0.1–2nm) to smooth muscle revealed similar dissociation constants but markedly different specific binding site densities for the various animal species. The order of densities of specific [125I]‐ET‐1 binding sites was rat trachea (69.0 ± 11.2 amol mm−2) > human bronchus (42.7 ± 17.5 amol mm−2) > mouse trachea (28.7 ± 2.6 amol mm−2) > guinea‐pig trachea (8.3 ± 1.8 amol mm−2).

A positive relationship between [125I]‐ET‐l binding site density and ET‐1 constrictor activity was observed in airway smooth muscle preparations from rat, human and guinea‐pig. The greater sensitivity of mouse trachea to the constrictor actions of ET‐1 was not dependent on the release of cyclo‐oxygenaseor epithelium‐derived constrictor substances, but may have been due to an inter‐species difference in the receptor‐effector system for ET‐1.
In vitro inhibition of intestinal motility by phenylethanolaminotetralines: evidence of atypical β‐adrenoceptors in rat colon
Authors: Bianchetti Alberto , Manara Luciano
Published: July 2012

The new compounds phenylethanolaminotetralines (PEAT), unlike the reference β‐adrenoceptor agonists isoprenaline (Iso), ritodrine (Ri) and salbutamol (Sal), produced half‐maximal inhibition of spontaneous motility of rat isolated proximal colon at substantially lower concentrations (EC50 2.7–30 nm) than those inducing β2‐adrenoceptor‐mediated responses (relaxation of guinea‐pig isolated trachea and rat uterus) and had virtually no chronotropic action (EC50 > 3 × 10−5 m.) on the guinea‐pig isolated atrium (a β1‐adrenoceptor‐mediated response).

The nonselective β‐adrenoceptor antagonists alprenolol and propranolol prevented the inhibition of rat colon motility by the PEAT with low and different potencies (pA2 values around 7.5 and 6.5 respectively). Conversely alprenolol and propranolol had a higher and similar potency (pA2 values around 9.0) in preventing typical β1‐ or β2‐responses (increase in atrial frequency by Iso or tracheal relaxation by Ri or Sal).

The selective β‐adrenoceptor antagonists CGP 20712A (β1) and ICI 118,551 (β2) either alone or in combination, did not prevent rat colon motility inhibition by the representative PEAT SR 58611A, which was also fully resistant to α‐adrenoceptor, acetylcholine, dopamine, histamine, opioid and 5‐hydroxytryptamine antagonists.

These results indicate that the PEAT are a new class of β‐adrenoceptor agonists and suggest that their preferential intestinal action may be accounted for by selectivity for atypical β‐adrenoceptors, abundant in the rat colon and distinct from the currently recognized β1 and β2 subtypes.
γ‐Aminobutyric acid inhibition of histamine‐induced inositol phosphate formation in guinea‐pig cerebellum: comparison with guinea‐pig and rat cerebral cortex
Authors: Crawford Melissa L.A. , Carswell Heather , Young J.M.
Published: July 2012

γ‐Aminobutyric acid (GABA), 2mm, inhibited basal accumulation of [3H]‐inositol monophosphate ([3H]‐IP1) in lithium‐treated slices of guinea‐pig cerebellum preincubated with [3H]‐inositol. In contrast, 2mm GABA stimulated the accumulation of [3H]‐IP1 in rat cerebral cortical slices over a 60 min incubation period, but had no significant effect in slices of guinea‐pig cerebral cortex. The estimated IC50 for the inhibitory action of GABA in guinea‐pig cerebellar slices was 0.52 ± 0.12 mm.

GABA inhibited histamine‐induced [3H]‐IP1 accumulation in guinea‐pig cerebellar slices in a noncompetitive manner. The best‐fit value for the maximum level of inhibition was 74 ± 6%. The estimated IC50 for GABA was 0.77 ± 0.15 mm and was not significantly different from the IC50 for inhibition of the basal accumulation of [3H]‐IP1. The response to histamine in guinea‐pig and rat cerebral cortical slices was also inhibited by 2 mm GABA.

In guinea‐pig cerebellar slices 2mm GABA potentiated histamine‐induced [3H]‐inositol bisphosphate ([3H]‐IP2) accumulation, whereas in both guinea‐pig and rat cerebral cortex the effect was inhibition.

Isoguvacine and muscimol, GABAA‐selective agonists, and (−)−baclofen, GABAB‐selective, had no significant effect on basal or histamine‐stimulated accumulation of [3H]‐IPs in guinea‐pig cerebellar slices. (−)−Baclofen had only a weak inhibitory effect on [3H]‐IP1 accumulation in guinea‐pig‐cerebral cortex (16 + 6% inhibition with 10 μm (−)−baclofen), whereas in rat cerebral cortex (−)−baclofen mimicked the inhibitory effect of GABA.

Nipecotic acid (1 mm) had qualitatively similar effects to those of 2mm GABA in guinea‐pig cerebellar slices.

The competitive GABA uptake inhibitors SK&F 89976‐A, SK&F 100330‐A and SK&F 100561‐A were potent histamine H1‐receptor antagonists, as indicated by the inhibition of [3H]‐mepyramine binding to homogenates of guinea‐pig cerebellum and cerebral cortex.

GABA (2mm) caused a small inhibition (12 ± 3%) of [3H]‐inositol incorporation into total inositol phospholipids in guinea‐pig cerebellar slices, as in rat cerebral cortical slices, whereas 0.2 mm histamine caused a small stimulation (15 ± 4%). In the presence of both GABA and histamine, [3H]‐inositol incorporation was unchanged from basal (101 ± 5%).

GABA also inhibited [3H]‐IP1 formation induced by endothelin‐1 in guinea‐pig cerebellar slices and increased, but not significantly, the amount of [3H]‐IP2 accumulated. This, taken with the inhibitory effect on basal and histamine‐stimulated accumulation, suggests that the action of GABA in guinea‐pig cerebellar slices may be non‐selective and may not be exerted through a specific GABA receptor.
The ontogeny of purinoceptors in rat urinary bladder and duodenum
Authors: Nicholls J. , Hourani S.M.O. , Kitchen I.
Published: July 2012

The ontogeny of responses to purines and analogues of smooth muscle preparations was studied in rat duodenum and rat urinary bladder.

Responses to adenosine and to adenosine 5′‐triphosphate (ATP) mediated by P1‐ and P2‐purinoceptors respectively were present as early as postnatal day 2, the earliest day studied.

In rat bladder, adenosine was inhibitory and ATP and adenosine 5′‐(β,γ‐methylene) triphosphonate (AMP‐PCP) were excitatory, acting on the P2X subtype of P2‐purinoceptors. Adenosine was more potent in the neonate than in the adult, while the potency of the nucleotides initially increased with age but then declined, being highest between postnatal days 10 and 25.

In rat duodenum also, adenosine was inhibitory, its potency being less than the adult before day 15.

ATP at low concentrations was inhibitory in rat duodenum at every age studied and its potency increased with age, but higher concentrations of ATP (3 μm and above) were excitatory until day 15. Both relaxations and contractions were mediated by the P2Y subtype of P2‐purinoceptors. These ATP‐induced contractions were not inhibited by indomethacin (25 μm) or by tetrodotoxin (1 μm) and are therefore not due to prostaglandin synthesis or to ATP‐induced release of transmitter substances from nerves.

These results show that responses to adenosine and to adenine nucleotides are present from birth and vary with age, and that the changes seen indicate a differential development for P1, P2X‐ and P2Y‐purinoceptors.
Electrophysiological effects of AFD‐21 and AFD‐19, new antiarrythmic compounds on papillary muscles and single ventricular myocytes isolated from guinea‐pig hearts
Authors: Kodama Itsuo , Kamiya Kaichiro , Kawamura Takashi , Suzuki Ryoko , Toyama Junji
Published: July 2012

The effects of AFD‐21, a newly synthesized antiarrhythmic compound, and AFD‐19, its active metabolite, on transmembrane action potentials were examined in right ventricular papillary muscles and single ventricular myocytes isolated from guinea‐pig hearts.

In papillary muscles, AFD‐21 10−5 m caused a slight prolongation of action potential duration (APD), while AFD‐19 above 10−6 m shortened APD in a dose‐dependent manner.

Both AFD‐21 and AFD‐19 above 10−6 m caused a significant and dose‐dependent decrease in the maximum upstroke velocity () of the action potential without affecting the resting membrane potential.

In the presence of AFD‐21 or AFD‐19, trains of stimuli at rates ≥ 0.2 Hz led to an exponential decline in . This use‐dependent block was enhanced at higher stimulation frequencies. A time constant for the recovery of from the use‐dependent block was 2.9 s for AFD‐21 and 3.6 s for AFD‐19.

The curves relating membrane potential and were shifted by AFD‐21 (10−5 m) or AFD‐19 (10−5 m) to the direction of more negative potentials by 5.3 mV and 5.1 mV respectively.

In single ventricular myocytes treated with AFD‐21 (10−5 m) or AFD‐19 (10−5 m), of test action potentials preceded by conditioning clamp pulses to 0 mV was decreased progressively as the clamp pulse duration was prolonged.

These findings suggest that both AFD‐21 and AFD‐19 have use‐ and voltage‐dependent inhibitory action on the sodium channel by binding to the channel during its inactivated state, and that the unbinding rate is comparable to that of Class I antiarrhythmic drugs with intermediate kinetics.
Effects of cyclic AMP‐affecting agents on contractile reactivity of isolated mesenteric and renal resistance arteries of the rat
Authors: Heesen Bart‐Jeroen , DE Mey Jo G.R.
Published: July 2012

Effects of adenosine 3′:5′‐cyclic monophosphate (cyclic AMP)‐affecting agents were compared in mesenteric and renal resistance arteries that had been isolated from 20 week old Wistar‐Kyoto rats, chemically sympathectomized, stretched to their optimal diameter for mechanical performance and made to contract in response to 30 mm potassium.

In mesenteric resistance arteries, isoprenaline, dopamine, NaF, forskolin, isobutyl‐methylxanthine, milrinone and dibutyryl‐cyclic AMP induced relaxation. Clonidine induced further increases in tension that could be reduced by pertussis toxin and prazosin but not by yohimbine. Clonidine also reduced relaxant responses to isoprenaline.

In renal resistance arteries, isoprenaline and dopamine failed to induce relaxation. Compared to mesenteric resistance arteries, renal vessels were less sensitive to the relaxant effect of NaF, forskolin and isobutyl‐methylxanthine. Relaxant responses to dibutyryl‐cyclic AMP did not differ between the two resistance arteries.

Indirect evidence thus suggests that in mesenteric resistance arteries, adenylate cyclase is susceptible to pharmacological activation and inhibition and is functionally coupled to relaxation. The refractory nature of renal resistance arteries to the relaxant effects of isoprenaline and dopamine could be due primarily to absence of appropriate receptors and to a relatively low activity of adenylate cyclase.
The antinociceptive activity of paracetamol in zymosan‐induced peritonitis in mice: the role of prostacyclin and reactive oxygen species
Authors: Doherty N.S. , Beaver T.H. , Chan K.Y. , Dinerstein R.J. , Diekema K.A.
Published: July 2012

Oral administration of high doses of paracetamol (600 mg kg−1 or more) resulted in inhibition of the writhing and reduced the levels of prostacyclin (PGI2, measured as 6‐keto‐PGF1α) induced by intraperitoneal administration of zymosan in mice. The high oral doses of paracetamol required were accompanied by behavioural toxicity which may have contributed to the inhibition of writhing.

The number of writhes per mouse and the proportion of mice writhing at least once correlated significantly with the levels of 6‐keto‐PGF1α. However, inhibition of writhing by paracetamol occurred at higher levels of 6‐keto‐PGF1α than was previously observed with acidic non‐steroidal anti‐inflammatory agents.

When injected i.p., PGI2, carbacyclin and iloprost (agonists at the PGI2 receptor) induced writhing. Intraperitoneal injection of PGI2 reversed the inhibition of writhing induced by indomethacin (1 mg kg−1, p.o.) but not that induced by oral administration of paracetamol.

Paracetamol at 800 mg kg−1, p.o., inhibited carbacyclin‐induced writhing but indomethacin at 1 mg kg−1 p.o. did not. Paracetamol administered i.p. at 100 mg kg−1 reduced the peritoneal levels of 6‐keto‐PGF1α and inhibited zymosan‐induced but not carbacyclin‐induced writhing and did not produce behavioural toxicity.

The in vitro potency of paracetamol as a prostaglandin synthesis inhibitor is known to be reduced by the presence of lipid peroxides. However, no lipid peroxides, measured as thiobarbituric acid reactive material, were detected in the peritoneal lavage fluid of zymosan‐injected mice.

Intraperitoneal administration of a mixture of superoxide dismutase and catalase reduced detectable superoxide anion by 98% without inhibiting the writhing response to zymosan or the antinociceptive potency of paracetamol.

The data are consistent with the suggestion that inhibition of PGI2 synthesis in the peritoneal cavity by paracetamol is responsible for only a part of its antinociceptive activity in this test. However, extremely high oral doses of paracetamol were required which produced behavioural toxicity which clearly contributed to the inhibition of writhing. The low potency of paracetamol in this model cannot be attributed to the generation of lipid peroxides via the oxidative burst.
Non‐adrenergic, non‐cholinergic contractions in the electrically field stimulated guinea‐pig trachea
Authors: Ellis James L. , Undem Bradley J.
Published: July 2012

The effects of drugs and altering stimulus parameters on neurogenic responses to electrical field stimulation (EFS) have been investigated in distal and proximal portions of the guinea‐pig trachea.

In the presence of indomethacin (3 μm) and propranolol (1 μm) two contractile phases were evident in both the proximal and distal trachea. The first rapid phase was abolished by atropine (0.1 μm), whereas the prolonged, second phase was abolished by capsaicin (10 μm) pretreatment. Tetrodotoxin (3 μm) abolished the initial response and greatly inhibited the second phase. In proximal trachea this second phase was evident only in 9 of 22 preparations. The addition of the peptidase inhibitor thiorphan (10 μm) however, caused a second phase to be seen in all the proximal tissues examined.

The two phases of the contractions to EFS were differentially sensitive to the pulse duration applied. The initial, cholinergic contractions were evident at lower pulse durations than were the prolonged capsaicin‐sensitive contractions, with the first phase being approximately 10 fold more sensitive than the second phase.

The magnitude of the capsaicin‐sensitive contraction to EFS was significantly greater in the distal trachea than in the proximal trachea. This difference prevailed in the presence of thiorphan, an inhibitor of neutral endopeptidase. In contrast, concentration‐response curves to capsaicin were similar in segments of proximal and distal trachea.

The non‐adrenergic non‐cholinergic (NANC) relaxant responses were studied in tissues in which excitatory neurogenic responses were pharmacologically abolished by capsaicin and atropine treatment. The NANC relaxant responses in the proximal trachea were evident at lower pulse frequencies and were of greater magnitude compared with NANC relaxant responses in the distal trachea.

These results indicate that, by pharmacologically manipulating the trachea and by selecting optimum stimulation parameters, a NANC contractile response to EFS can be seen throughout the length of the guinea‐pig trachea. This NANC response is most likely to be due to the release of tachykinins from capsaicin‐sensitive sensory fibres. It is suggested that NANC relaxant responses mask NANC contractile responses especially in the proximal trachea where NANC relaxant responses predominate.
Prostanoid stimulation of anion secretion in guinea‐pig gastric and ileal muscosa is mediated by different receptors
Authors: Bunce K.T. , Spraggs C.F.
Published: July 2012

The receptors that mediate stimulation of anion secretion by prostanoids in isolated preparations of guinea‐pig gastric and ileal mucosa have been compared by use of selective prostanoid agonists and antagonists.

In gastric mucosa, the relative potency of agonists suggested that the control of anion secretion in this tissue was complex and may be mediated by EP2, EP3, and TP receptors. A role for TP receptors was confirmed with the TP‐selective antagonist AH23848 which inhibited short circuit current responses to the TP receptor agonist U‐46619 with a pA2 value of 8.44 but was without effect on responses to prostaglandin E2 (PGE2) or the EP selective agonist, sulprostone.

In ileal mucosa, the relative potency of agonists differed from that observed in gastric mucosa and was consistent with the view that anion secretion in this region of intestine was controlled by DP and EP2 receptors.

These studies suggest that anion secretion in gastric and ileal mucosa is controlled by different prostanoid receptor subtypes and so provide important informtion for the design of prostanoids which may protect gastric mucosa and that are free from side effects such as diarrhoea.
Effects of several potassium channel openers and glibenclamide on the uterus of the rat
Authors: Piper Ian , Minshall Eleanor , Downing Sandra J. , Hollingsworth Michael , Sadraei Hassan
Published: July 2012

The ability of several potassium (K+) channel openers to inhibit spasm of the uterus of the nonpregnant rat and their susceptibility to antagonism by glibenclamide was assessed in vitro and in vivo.

In the isolated uterus exposed to oxytocin (0.2 nm), cromakalim, RP 49356 and pinacidil were of similar potency (mean pD2 = 6.4, 6.0 and 6.2 respectively) while minoxidil sulphate was of lower potency (pD2 = 4.7). Glibenclamide antagonized cromakalim and RP 49356 with the interactions consistent with competitive antagonism (mean pA2 of 6.57 and 7.00 respectively). Glibenclamide also antagonized pinacidil (pA2 = 6.22) but the slope of the Schild plot was significantly greater than −1. Neither salbutamol nor minoxidil sulphate was antagonized by glibenclamide (10 μm).

Cromakalim (1 and 10 μm), RP 49356 (1 and 10 μm), pinacidil (1 μm) and minoxidil sulphate (100 μm) suppressed spasm evoked by low (< 40 mm) but not high (≥ 40 mm) KCl concentrations. Glibenclamide (10 μm) prevented cromakalim (10 μm)‐, RP 49356 (10 μm)‐ and pinacidil (10 μm)‐induced suppression of KCl (20 mm)‐evoked spasm. Pinacidil (10 and 100 μm), cromakalim (100 μm) and salbutamol (0.01–1 μm) inhibited spasm evoked by all concentrations of KCl (10–80 mm). Suppression of spasm evoked by KCl (10–80 mm) by cromakalim (100 μm) and pinacidil (100 μm) was insensitive to glibenclamide (10 μm).

Cromakalim (0.1 mg kg−1) and RP 49356 (0.1 mg kg−1), given by i.v. bolus injection, inhibited uterine contractions, produced a fall in blood pressure and a slight tachycardia in the conscious ovariectomized rat. Glibenclamide (20 mg kg−1), given by i.v. infusion, antagonized the vascular and uterine smooth muscle relaxant properties of cromakalim and RP 49356.

Several K+ channel openers are uterine relaxants. The antagonism of cromakalim, RP 49356 and pinacidil, at low concentrations, by glibenclamide suggests their actions may involve an ATP‐sensitive K+ channel. High concentrations of pinacidil (10 and 100 μm) and cromakalim (100 μm) may exert an additional action in the uterus. The low potency of minoxidil sulphate and its insensitivity to glibenclamide in the isolated uterus suggests that its mechanism of action may differ from that of the other K+ channel openers.