bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of cromakalim on the contraction and the membrane potential of the circular smooth muscle of guinea‐pig stomach
Authors: Ito Katsuaki , Kanno Tomohiro , Suzuki Keiko , Masuzawa‐Ito Kaoru , Takewaki Tadashi , Ohashi Hidenori , Asano Masahisa , Suzuki Hikaru
Published: July 2012

. The effects of cromakalim on mechanical and electrical activities of the circular smooth muscles of guinea‐pig stomach antrum were observed.

. Cromakalim (> 1 × 10−7 m) decreased the amplitude of spontaneous rhythmic contractions and also the acetylcholine‐enhanced spontaneous contractions. Cromakalim was less effective against the 25.9 mm and 35.9 mm K+‐induced tonic contractions.

. Glibenclamide (1 × 10−6 m) itself caused no detectable change in the spontaneous contractions, those potentiated by acetylcholine or tonic contractions induced by high K+ solutions, but attenuated the actions of cromakalim. On the other hand, charybdotoxin (3 × 10−8 m) increased the amplitude of spontaneous contractions but failed to affect the actions of cromakalim.

. Cromakalim (> 1 × 10−6 m) decreased the amplitude and duration of slow waves, and hyperpolarized the membrane. These actions of cromakalim were completely antagonized by 1 × 10−6 m glibenclamide, whereas part of the effects of cromakalim on mechanical activity was resistant to glibenclamide.

. The results suggest that the inhibition by cromakalim of the electrical activity and the hyperpolarization, which may be associated with the opening of glibenclamide‐sensitive K+ channel, are responsible for its inhibitory action on circular smooth muscle of guinea‐pig stomach. Further, some effects independent of glibenclamide‐sensitive K+ channel may also be responsible for the mechanical effect.
Contributions of α1‐adrenoceptors, α2‐adrenoceptors and P2x‐purinoceptors to neurotransmission in several rabbit isolated blood vessels: role of neuronal uptake and autofeedback
Authors: MacDonald A. , Daly C.J. , Bulloch J.M. , McGrath J.C.
Published: July 2012

. The roles of autofeedback and neuronal uptake in neurotransmission produced by electrical field stimulation in several rabbit isolated blood vessels were examined.

. Blocking drugs were used to separate the possible purinergic and noradrenergic contributions to the end organ response: prazosin, antagonist at postjunctional α1‐adrenoceptors; rauwolscine and yohimbine, antagonists at pre‐ and postjunctional α2‐adrenoceptors; α,β‐methylene ATP, desensitizing agent at postjunctional P2x‐purinoceptors. In addition to desensitizing postjunctional P2x‐purinoceptors, α,β‐methylene ATP potentiated the noradrenergic component of the nerve‐induced responses.

. In the presence of an intact neuronal uptake mechanism, the vessels showed different contributions of purinergic (via P2x‐purinoceptors) and noradrenergic (via α1‐adrenoceptors and α2‐adrenoceptors) components to the end organ response to nerve stimulation: saphenous artery (approximately equal contributions from P2x‐purinoceptors and α1‐adrenoceptors), ileocolic artery (mainly P2x‐purinoceptors with a smaller contribution from α1‐adrenoceptors), plantaris vein (mainly α1‐adrenoceptors with a small contribution from α2‐adrenoceptors and P2x‐purinoceptors) and saphenous vein (α1‐adrenoceptors).

. The presence of α2‐adrenoceptor‐mediated autofeedback could be demonstrated for both purinergic and noradrenergic components of the nerve‐induced responses in the artery preparations. In the veins, potentiation of nerve‐induced responses by α2‐adrenoceptor antagonists could not be studied due to blockade of postjunctional α2‐adrenoceptor‐mediated vasoconstriction.

. Blockade of neuronal uptake with cocaine potentiated the noradrenergic component of the nerve‐induced responses. Both α1‐adrenoceptor‐ and α2‐adrenoceptor‐mediated components were potentiated, with a relatively greater potentiation of the α2‐adrenoceptor‐mediated component. In the case of saphenous vein an α2‐adrenoceptor‐mediated component which was previously absent was uncovered.

. Blockade of neuronal uptake with cocaine had no effect or reduced the purinergic component of responses, the latter effect presumably due to enhanced α2‐adrenoceptor‐mediated autofeedback.

. In the presence of cocaine, nerve‐induced responses in the saphenous vein were biphasic. Rauwolscine potentiated the first phase and inhibited the second phase thus demonstrating effects of pre‐ and postjunctional α2‐adrenoceptor‐mediated activation in the same preparation.

. In conclusion, neuronal uptake and autofeedback processes play important and complex interacting parts in determining the relative contributions of α1 and α2‐adrenoceptors and P2x‐purinoceptors in the end organ response to neurotransmission in blood vessels.
Characterization of postsynaptic α‐adrenoceptors in the arteries supplying the oviduct
Authors: Costa Gonzalo , Isla Miguel , García‐Pascual Angeles , Jimenez Eugenio , Recio Paz , Labadia Alicia , García‐Sacristán Albino
Published: July 2012

In vitro experiments were designed to characterize postjunctional α‐adrenoceptor subtypes in ring segments (1 mm length; outer diameter 300–500 μm) from arteries supplying the oviduct of the heifer.

Noradrenaline, adrenaline and phenylephrine evoked concentration‐dependent contractile responses. The pD2 values were 5.67, 5.89 and 5.93, respectively. Medetomidine, clonidine and B‐HT 920 (2‐amino‐6‐allyl‐5,6,7,8‐tetra‐hydro‐4H‐(thiazo)‐4,5‐d‐azepine) were ineffective.

The α‐adrenoceptor selective antagonists, prazosin (1 nm−0.1 μm) and rauwolscine (0.1–10 μm) competitively antagonized the response to noradrenaline. The pA2 values were 9.38 and 6.83, respectively.

The dissociation constant (KD) for noradrenaline calculated by use of the irreversible antagonist, dibenamine, was 3.95 (2.09–5.81) μm. The occupancy‐response relationship was non‐linear. Half‐maximal response to noradrenaline was obtained with 22% receptor occupancy while maximal response required 100% occupancy.

B‐HT 920 evoked a biphasic contractile concentration‐dependent response in preparations incubated in a physiological solution containing 20 mm K+, 0.1 μm prazosin and 1 μm propranolol. Rauwolscine 0.1 μm significantly (P < 0.01) blocked the first component of the B‐HT 920 concentration‐response curve with an apparent pA2 value of 8.52 (7.86–9.18).

These results strongly suggest that α‐adrenoceptors in oviductal arteries are mainly of the α1 subtype, although a possible role for α2‐adrenoceptors cannot be excluded.
Endothelium‐dependent contractile responses to 5‐hydroxytryptamine in the rabbit basilar artery
Authors: Seager Joanna M. , Clark Angela H. , Garland C.J.
Published: July 2012

5‐Hydroxytryptamine (5‐HT) and 5‐carboxamidotryptamine (5‐CT) stimulated additional, endothelium‐dependent contractions in rabbit isolated basilar arteries which had been submaximally contracted with either histamine or potassium chloride.

The additional contractions to 5‐HT were not altered by the 5‐HT2 antagonist, ketanserin (1 μm), but were abolished in the presence of the cyclo‐oxygenase inhibitor indomethacin (3 μm).

The additional smooth muscle contraction stimulated by 5‐HT was increased in the presence of the competitive substrate inhibitor for nitric oxide synthase, NG‐nitro‐l‐arginine methyl ester (l‐NAME, 100 μm).

Neither of the selective 5‐HT agonists, 8‐hydroxy‐dipropylaminotetralin (8‐OH DPAT) or α‐methyl 5‐HT stimulated endothelium‐dependent contraction, but these agonists did reduce the rate at which histamine‐induced tension spontaneously declined. This effect represented a direct action on the smooth muscle cells, as it was independent of the presence of endothelial cells.

Smooth muscle relaxation was not obtained in response to 5‐HT, whether or not indomethacin was present to block endothelium‐dependent contraction. None of the other selective 5‐HT agonists, 5‐CT, 8‐OH DPAT or α‐methyl 5‐HT produced endothelium‐dependent smooth muscle relaxation, when applied against a background of contraction.

These data show that endothelium‐dependent smooth muscle contraction can be produced by stimulating 5‐HT receptors in the partially contracted rabbit basilar artery. Similar contraction to 5‐CT indicates an involvement by 5‐HT1 receptors. The susceptibility of the contractions to indomethacin suggest they are mediated by a metabolite of arachidonic acid.
Capsaicin‐induced bronchoconstriction in the guinea‐pig: contribution of vagal cholinergic reflexes, local axon reflexes and their modulation by BW443C81
Authors: Buchan P. , Adcock J.J.
Published: July 2012

The objective of the study was to investigate the central vagal and local axon reflex components of bronchoconstrictor responses evoked by inhalation of capsaicin aerosol in anaesthetized guinea‐pigs. This was accomplished by comparing the effects of bilateral vagotomy, atropine and the peripherally‐acting polar enkephalin analogue, BW443C81, on bronchoconstrictor responses evoked by capsaicin. The effects of codeine were also determined.

Aerosols of capsaicin were generated from a 0.9 μg ml−1 solution. Inhalation of capsaicin aerosol in 5, 10 and 15 breaths evoked dose‐related bronchoconstrictor responses. The responses were immediate in onset and of extended duration.

Capsaicin‐induced bronchoconstrictor responses were significantly inhibited following bilateral vagotomy or atropine (0.3 mg kg−1, i.v.) pretreatment by 46% ± 14% (P < 0.05) and 59% ± 13% (P < 0.01), respectively.

Administration of BW443C81 by intravenous infusion (3, 30 and 100 μg kg−1 min−1) caused a significant inhibition of capsaicin‐induced bronchoconstrictor responses which achieved a greater maximum than either bilateral vagotomy or atropine. Codeine (100 μg kg−1 min−1, i.v.) did not significantly inhibit the bronchoconstrictor responses.

Inhibition of capsaicin‐induced bronchoconstrictor responses by BW443C81 (30 μg kg−1 min−1, i.v.) was significantly (P < 0.05) reduced by the peripherally‐acting opioid antagonist N‐methyl nalorphine (100 μg kg−1 min−1, i.v.).

These results show that capsaicin‐induced bronchoconstrictor responses are mediated by at least two mechanisms, a vagal and/or cholinergic reflex pathway and a non‐cholinergic pathway. BW443C81, but not codeine, significantly inhibited (P < 0.005) both mechanisms of capsaicin‐induced bronchoconstriction probably by an action on peripheral opioid receptors located on vagal sensory nerves.
Comparison of pyrrolidinyl and piperidinyl benzamides for their anticonvulsant activity and inhibitory action on sodium channel
Authors: Zhu Yu , Im Wha Bin , Lewis Richard A. , VonVoigtlander Philip F.
Published: July 2012

A pair of benzamide analogues containing a pyrrolidinyl or piperidinyl group was examined for their anticonvulsant activity against the electroshock‐induced seizures in mice and the ability to block the voltage‐gated Na channel in N1E‐115 cells, in comparison with the prototype compound, U‐54494A, (±)‐cis‐3,4‐dichloro‐N‐methyl‐N‐[2‐(1‐pyrrolidinyl)‐cyclohexyl]‐benzamide, a potent anticonvulsant and a Na channel blocker.

The pyrrolidinyl benzamide (U‐49524E) was found to be effective against the electroshock‐induced seizures (ED50 = 35 mg kg−1, i.p.) whereas the benzamide with a piperidinyl moiety (U‐49132E) was inactive (ED50> 100 mg kg−1).

Using whole‐cell patch clamp techniques we found that U‐49132E was several times less potent, with an IC50 of 396 μm as compared to 118 μm for U‐49524E at the holding potential of − 80 mV, and was much slower in blocking Na channels with a half‐time of 10.7 ± 1.1 min vs. 2.2±0.4 min for its counterpart.

Qualitatively, their general modes of interaction with Na channels were similar to each other and to that of U‐54494A in that they interacted with the resting and slowly‐inactivated states of the channels and exhibited a use‐dependent inhibition because of a slow recovery from the inactivated state in the presence of the drugs.

Comparison of their physicochemical properties, shows the less potent and slowly acting U‐49132E is more hydrophobic and bulkier than U‐49524E, but has the same pKa. This suggests that the drugs approach the Na channel through a narrow and hydrophilic pathway.

Overall, this study underscores the importance of inhibiting the Na channel to the anticonvulsant activity of the benzamide compounds.
Stimulation of noradrenaline release in human cerebral cortex mediated by N‐methyl‐d‐aspartate (NMDA) and non‐NMDA receptors
Authors: Fink Klaus , Schultheiß Rolf , Göthert Manfred
Published: July 2012

Human brain cortical slices from patients undergoing neurosurgery for treatment of epilepsy resistant to antiepileptic drugs were used to identify and characterize N‐methyl‐d‐aspartate (NMDA) and non‐NMDA receptors mediating stimulation of noradrenaline release. The slices preincubated with [3H]‐noradrenaline were superfused with Krebs‐Henseleit solution with or without Mg2+ (1.2 mmol 1−1) and were stimulated by 2‐min exposure to NMDA, kainic acid or (RS)‐α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid (AMPA).

In slices superfused without Mg2+, NMDA induced a concentration‐dependent tritium overflow.

The NMDA‐evoked tritium overflow was almost abolished by tetrodotoxin (TTX), Mg2+ or by omission of Ca2+ from the superfusion fluid. 2‐Amino‐5‐phosphonopentanoic acid (AP5; a competitive NMDA receptor antagonist) or dizocilpine (formerly MK‐801; an antagonist at the phencyclidine receptor within the NMDA‐gated ion channel) inhibited the NMDA‐evoked tritium overflow. The stimulatory effect of NMDA was not significantly enhanced by glycine added to the superfusion fluid but was reduced by 7‐chlorokynurenic acid (an antagonist at the glycine site coupled to the NMDA receptor).

In slices superfused with solution containing Mg2+, kainic acid or AMPA induced a concentration‐dependent tritium overflow which was susceptible to blockade by TTX.

The kainic acid‐evoked tritium overflow was not affected by dl‐(E)‐2‐amino‐4‐methyl‐5‐phosphono‐3‐pentanoic acid (CGP37849; a competitive NMDA receptor antagonist), but was inhibited by 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX; an antagonist at glutamate receptors of the non‐NMDA type).

The AMPA‐evoked tritium overflow was also inhibited by CNQX.

It is concluded that NMDA receptors as well as kainate‐ and AMPA‐recognizing non‐NMDA receptors stimulate noradrenaline release in the human brain cortex.
Haemodynamic effects of a new dihydropyridine calcium entry blocker, S‐12968‐(−), in a rat model of cardiovascular calcium overload
Authors: Makki Touria , Lartaud Isabelle , Boscs Laure Bray‐Des , Capdeville‐Atkinson Christine , Chillon Jean‐Marc , Hoffman Maurice , Nicolas Jean‐Pierre , Atkinson Jeffrey
Published: July 2012

The haemodynamic effects of S‐12968‐(−), a new dihydropyridine calcium entry blocker (enantiomer of S‐11568), were compared with those of the stereoisomer, S‐12967‐(+), nifedipine, and sodium nitroprusside.

A first experiment was performed in conscious, young male rats chronically implanted with femoral artery and vein cannula and repeated in rats previously treated with vitamin D3 and nicotine. Such treatment produces marked vascular calcium overload, especially of the compliance arteries, with no overt sign of toxicity as far as can be judged from the plasma profile.

In conscious rats the hypotensive effects of S‐12968‐(−), nifedipine and sodium nitroprusside were of similar potency. The falls in blood pressure produced by nifedipine and sodium nitroprusside were accompanied by reflex tachycardia which was less marked in the vascular calcium overload model. S‐12968‐(−) did not induce reflex tachycardia. S‐12967‐(+) increased blood pressure in both models.

A second experiment was performed in open‐chest pentobarbitone‐anaesthetized rats with electromagnetic flowprobes on the ascending aorta. In controls the falls in blood pressure produced by low doses (0.1 and 0.3 mg kg−1, i.v.) of S‐12968‐(−) were accompanied by falls in total peripheral resistance. The higher dose (1 mg kg−1, i.v.) of S‐12968‐(−) produced no change in total peripheral resistance, and in rats pretreated with vitamin D3 and nicotine, cardiac output fell.

In conclusion, S‐12968‐(−) appears to have a dual action and to lower blood pressure at higher doses at least in part by a cardiac effect. This phenomenon is more pronounced in rats pretreated with vitamin D3 and nicotine.

S‐12967‐(+) resembles a calcium channel activator in this model.
Chloride channels and anion fluxes in a human colonic epithelium (HCA‐7)
Authors: Henderson R.M. , Ashford M.L.J. , MacVinish L.J. , Cuthbert A.W.
Published: July 2012

Colonic epithelial cells, derived from a human adenocarcinoma (HCA‐7), were examined by the patch clamp technique.

Outwardly rectifying anion (Cl−) channels were identified in the apical membrane. The conductance was gin ≅ 26 pS, gout ≅ 40 pS. The open state probability of the channels increased with depolarization and the selectivity for Cl− over K+ (PCl/PK) was ≅ 7.5.

The channels were sensitive to intracellular adenosine 3′:5′‐cyclic monophosphate (cyclic AMP, 0.1 mm), but not to Ca2+ (at concentrations up to 1 mm). At depolarized potentials the channels were blocked by pirentanide (1–5 μm) applied intracellularly.

HCA‐7 monolayers loaded with 125I− (as a marker for Cl−) were used to measure I− efflux and converted to instantaneous rate constants.

The rate constant for I− efflux was increased by forskolin and lysylbradykinin (LBK). The effects of forskolin were not effected by BAPTA (an intracellular calcium chelator). The effects of LBK were inhibited by BAPTA and by Ba2+, indicating that LBK raised intracellular Ca2+ (Cai) which activates Ca2+‐sensitive K‐channels, the latter being blocked by Ba2+.

Although it cannot be conclusively proved that the outwardly rectifying chloride channels described here are solely or partially responsible for the increased anion efflux or transepithelial chloride secretion, the channels are likely to be more relevant for cyclic AMP‐requiring rather than Ca2+‐requiring secretagogues.
Contractions induced by potassium‐free solution and potassium relaxation in vascular smooth muscle of hypertensive and normotensive rats
Authors: Arvola Pertti , Pörsti Ilkka , Vuorinen Pauli , Pekki Anu , Vapaatalo Heikki
Published: July 2012

Vascular contractions induced by K+‐free solution and relaxation responses following the return of K+ to the organ bath were studied in mesenteric arterial rings from spontaneously hypertensive rats (SHR) and normotensive Wistar‐Kyoto rats (WKY) with particular focus on the role of vascular adrenergic nerve‐endings and endothelium.

In endothelium‐denuded rings the omission of K+ from the incubation medium resulted in gradual contractions, the rate of which was slower in SHR than WKY. Nifedipine (1 μm) inhibited the contractions more effectively in SHR than WKY.

Adrenergic denervation in vitro with 6‐hydroxydopamine reduced the contractions induced by the K+‐free medium in endothelium‐denuded rings. The remaining contractions after denervation were markedly greater in SHR than WKY.

The presence of intact vascular endothelium attenuated the K+‐free contractions in both strains, the attenuation being smaller in SHR than WKY. NG‐nitro‐l‐arginine methyl ester (l‐NAME, 0.1 mm) and methylene blue (10 μm), but not indomethacin (10 μm), abolished the attenuating effect of endothelium on the K+‐free contractions. l‐Arginine (1 mm) reversed the effect of l‐NAME in WKY but not in SHR.

The re‐addition of K+ after full K+‐free contractions dose‐dependently relaxed the rings. The rate of this K+‐induced relaxation was significantly slower in SHR than WKY at all K+ concentrations (0.1–5.9 mm) studied, whether the endothelium or functioning adrenergic nerve‐endings were present or not. Ouabain (1 mm) totally inhibited the K+ relaxation in SHR but only partially in WKY.

Vascular smooth muscle contractions induced by high concentrations of potassium were comparable between the strains. The EC50 for noradrenaline‐induced contractions was lower in SHR than WKY, but the maximal forces did not differ significantly.

In conclusion, the contractile response in K+‐free solution more clearly differentiates vascular rings from SHR and WKY than the responses induced by the classical contractile agents noradrenaline and high concentrations of potassium. The depressant effect of the presence of intact endothelium on the K+‐free contractions, which was smaller in SHR than WKY, is mediated via the endothelium‐derived relaxing factor. Neurotransmitter release from vascular adrenergic nerve‐endings participates less in the K+‐free contractile response in SHR than WKY. Moreover, the contractile response is more dependent on calcium entry through nifedipine‐sensitive calcium channels in SHR than WKY. The greater K+‐free contractions of denervated endothelium‐denuded rings and the reduced K+ relaxation rate in SHR when compared to WKY suggest increased cell membrane permeability and decreased activity of vascular Na+, K+‐ATPase, respectively, in this type of genetic hypertension.
Influence of NG‐nitro‐L‐arginine on non‐adrenergic non‐cholinergic relaxation in the guinea‐pig gastric fundus
Authors: Lefebvre R.A. , Baert E. , Barbier A.J.
Published: July 2012

The influence of NG‐nitro‐l‐Arginine (l‐NNA) on non‐adrenergic non‐cholinergic (NANC) relaxations induced by electrical field stimulation was investigated in circular muscle strips of the guinea‐pig gastric fundus.

In the presence of 10−6 m. atropine and 4 × 10−6 m guanethidine, electrical field stimulation (40 V, 1 ms, 0.125–16 Hz) with 10 s trains at 5 min intervals induced short‐lasting, frequency‐dependent relaxations. Continuous stimulation, with cumulative increase of the stimulation frequency, induced sustained frequency‐dependent relaxations. Both types of response were abolished by 3 × 10−6 m tetrodotoxin.

l‐NNA (10−5 m and 10−4 m) concentration‐dependently reduced both types of NANC response. Pre‐incubation with 2 × 10−3 m l‐arginine prevented the inhibitory action of 10−5 m l‐NNA and partially antagonized that of 10−4 m l‐NNA. d‐arginine (2 × 10−3 m) did not protect against the inhibitory effect of l‐NNA.

l‐NNA did not consistently influence the basal tone of the tissues. l‐Arginine and d‐arginine likewise did not influence basal tone; they also had no influence on the electrically‐induced NANC relaxations.

NO (10−6−10−4 m) induced short‐lasting concentration‐dependent relaxations, while vasoactive intestinal polypeptide (VIP, (10−9−10−7 m) induced more sustained relaxations, that developed at a slower rate. The NO‐ and VIP‐induced relaxations were not influenced by 10−4 m l‐NNA.

These results suggest that NO is involved in NANC neurotransmission of the guinea‐pig gastric fundus; its contribution to sustained NANC relaxation in the guinea‐pig gastric fundus is much more important than in the rat.
Effects of cyclopiazonic acid, a novel Ca2+‐ATPase inhibitor, on contractile responses in skinned ileal smooth muscle
Authors: Uyama Yoshiaki , Imaizumi Yuji , Watanabe Minoru
Published: July 2012

Effects of cyclopiazonic acid (CPA), a specific inhibitor of the Ca2+‐ATPase in sarcoplasmic reticulum (SR) of skeletal and cardiac muscles, on contractile responses induced by Ca2+‐release from intracellular storage sites were examined in the longitudinal smooth muscle strip of the guinea‐pig ileum skinned with β‐escin.

Ca2+‐loading of storage sites (Ca2+‐uptake) was performed in pCa 6.3 solution. The amount of Ca2+ taken up was monitored by use of the amplitude of contraction following application of 25 mm caffeine or 25 μm inositol 1,4,5‐trisphosphate (IP3).

Contractile responses to caffeine or IP3 were reduced or abolished when the preceding Ca2+‐uptake was performed in the presence of 0.1–10 μm CPA. The dose of CPA required to inhibit the contraction induced by caffeine or IP3 by 50% was approximately 0.6 μm. The CPA‐sensitive Ca2+‐uptake completely depended upon the presence of ATP in the solution during Ca2+‐uptake.

When 1 μm CPA was added after Ca2+‐uptake, the subsequent caffeine‐ or IP3‐induced contraction was not significantly affected by the presence of CPA.

Acetylcholine‐induced contraction was also almost abolished when the preceding Ca2+‐uptake was performed in the presence of 10 μm CPA.

The relationship between pCa and contraction was not affected by the presence of 10 μm CPA in skinned fibres where Ca2+ storage sites had been destroyed by treatment with A23187. The enhancement of contraction in pCa 6.0 solution by calmodulin was not affected by 10 μm CPA.

These results suggest that CPA selectively inhibits ATP‐dependent Ca2+‐uptake into intracellular storage sites in skinned ileal smooth muscle strips. CPA appears to be a potent, reversible, and very specific inhibitor of the Ca2+‐pump in the storage sites of smooth muscle, and is an extremely valuable pharmacological tool.
A68930 is a potent, full agonist at dopamine1 (D1) receptors in renal epithelial LLC‐PK1 cells
Authors: Grenader Arcady , Healy Dennis P.
Published: July 2012

The selective dopamine1 (D1) receptor agonists SK&F 82526 (fenoldopam) and A68930 and the mixed D1/D2 agonist SK&F 85174 were tested for their ability to stimulate adenosine 3′:5′‐cyclic monophosphate (cyclic AMP) accumulation in the porcine renal epithelial cell line, LLC‐PK1. SK&F 82526 and SK&F 85174 were potent stimulators of cyclic AMP accumulation (EC50s 21.4 and 14.5 nm, respectively), but only partial agonists (intrinsic activities 31% and 46% of dopamine respectively). In contrast, A68930 was a potent, full agonist (EC50 12.7 nm, intrinsic activity 102% of dopamine). The stimulatory effects of A68930 and dopamine on cyclic AMP accumulation were not additive, and the stimulation of cyclic AMP accumulation by A68930 was blocked by the D1‐selective antagonist, SCH 23390. These properties of A68930 suggest that it may be a useful D1‐selective agonist to study renal D1 receptor mechanisms in vitro and in vivo.
Cannabinoid receptor agonists inhibit Ca current in NG108–15 neuroblastoma cells via a Pertussis toxin‐sensitive mechanism
Authors: Caulfield M.P. , Brown D.A.
Published: July 2012

Cannabinoid receptor ligands irreversibly inhibited peak voltage‐activated Ca currents (44%) in NG108–15 cells; this inhibition was Pertussis toxin‐sensitive. Inhibition was largely due to a reduction in the ω‐conotoxin sensitive portion of high‐voltage activated (HVA) current, although there was also a significant decrease in low‐voltage activated current (56%) and in the nifedipine‐sensitive portion of HVA current (41%).
Functional comparisons of gastrin/cholecystokinin receptors in isolated preparations of gastric mucosa and ileum
Authors: Patel Mina , Spraggs Colin F.
Published: July 2012

The gastrin cholecystokinin (CCK) receptors mediating stimulation of acid secretion in rat isolated gastric mucosa (RGM) and contraction in guinea‐pig isolated ileum longitudinal muscle‐myenteric plexus (GPI) have been characterized by use of peptide agonists and the non‐peptide antagonists, lorglumide, devazepide and L‐365,260.

In RGM, gastrin peptides (sulphated gastrin heptadecapeptide (G‐17), non‐sulphated (ns) G‐17 and pentagastrin) were potent agonists of acid secretion (EC50 values of 4.3, 16 and 27 nm respectively). Sulphated CCK octapeptide (CCK‐8) was also a potent agonist, (EC50 = 0.9 nm), but was less efficacious, producing a lower maximal response. In contrast, in GPI, CCK‐8 was a potent full agonist (EC50= 1.4 nm) and was more than 1000 times more potent than the gastrin peptides in producing a sustained contractile response.

In GPI, CCK‐8 (0.1 to 100 nm) produced sustained contractile responses, whilst CCK‐4 (3 to 1000 nm) produced transient responses. These responses had different sensitivities to atropine (1 μm), suggesting that more than one receptor may mediate contraction in this tissue.

In RGM, L‐365,260 was the most potent antagonist of pentagastrin‐stimulated acid secretion (pA2 = 7.6). This functional affinity estimate was similar to that for L‐365,260 as an antagonist of excitatory responses in rat ventromedial hypothalamic slices (Kemp et al., 1989) but differed from binding affinity estimates in guinea‐pig cortex and gastric glands (Freidinger, 1989).

In GPI, devazepide, L‐365,260 and lorglumide yielded different affinity estimates when compared against CCK‐8 and CCK‐4 or pentagastrin respectively. These studies were consistent with the view that the sustained response produced by CCK‐8 was mediated by CCKA receptors and the transient response produced by CCK‐4 and pentagastrin was mediated by CCKB receptors.

Affinity estimates for L‐365,260 and lorglumide against CCK‐4 or pentagastrin in GPI were significantly different from corresponding estimates against pentagastrin in RGM. These studies are consistent with the view that gastrin/CCKB receptors in GPI may differ from those in RGM.
Effect of MgATP on pinacidil‐induced displacement of glibenclamide from the sulphonylurea receptor in a pancreatic β‐cell line and rat cerebral cortex
Authors: Schwanstecher Mathias , Brandt Christian , Behrends Sönke , Schaupp Ursula , Panten Uwe
Published: July 2012

The effects of blockers and openers of K+ channels on binding of [3H]‐glibenclamide to microsomes obtained from a pancreatic β‐cell line (HIT‐T15) or rat cerebral cortex were examined.

The blockers quinine, chlorpromazine and thiopentone and the openers cromakalim [(±) 6‐cyano‐3,4‐dihydro‐2,2‐dimethyl‐trans‐4‐(2‐oxo‐1‐pyrrolidyl)‐2H‐benzo[b]pyran‐3‐ol] and minoxidil sulphate did not significantly interact with the sulphonylurea receptor of HIT‐cells both at phosphorylating (presence of MgATP) and dephosphorylating (absence of MgATP) conditions.

In the absence of MgATP, pinacidil (200‐ 500 μm) did not significantly displace [3H]‐glibenclamide binding to microsomes from HIT‐cells. The displacement of [3H]‐glibenclamide binding was strongly enhanced by MgATP and was due to a decrease in the number of high affinity binding sites for glibenclamide.

MgATP enhanced pinacidil‐induced inhibition of [3H]‐glibenclamide binding to microsomes from rat cerebral cortex.

The effect of MgATP on pinacidil‐induced inhibition of [3H]‐glibenclamide binding was maintained after solubilization of the membranes from HIT‐cells or rat cerebral cortex.

It is concluded that the sulphonylurea receptor is regulated not only by sulphonylureas but also by the K+ channel openers, diazoxide and pinacidil, and by protein phosphorylation. The binding sites for sulphonylureas and these K+ channel openers are not identical, but appear to be located at a single protein or at tightly associated proteins.
Pharmacological characterization of non‐NMDA subtypes of glutamate receptor in the neonatal rat hemisected spinal cord in vitro
Authors: Zeman Sophie , Lodge David
Published: July 2012

A grease‐gap technique was used to record depolarizing responses to α‐amino‐3‐hydroxy‐5‐methyl‐isoxazole‐4‐propionate (AMPA), kainate and N‐methyl‐d‐aspartate (NMDA) in the hemisected spinal cord of the neonatal rat. The pharmacology of non‐NMDA subtypes of glutamate receptor was investigated with the novel quinoxalinedione, 2,3‐dihydroxy‐6‐nitro‐7‐sulphamoyl‐benzo (F)‐quinoxaline (NBQX) and with a series of barbiturates.

NBQX antagonized AMPA‐ and kainate‐, but not NMDA‐ induced depolarizations. The near parallel shifts of the major part of the dose‐response curves for AMPA and kainate by NBQX gave pA2 values (± s.e.) of 6.7 ± 0.2 and 6.8 ± 0.2 respectively, consistent with a common site of action for these two agonists.

Below the 50% level at which these pA2 values were calculated, however, an NBQX‐resistant plateau was seen within the kainate, but not the AMPA, dose‐response curve.

In decreasing order of potency, methohexitone, secobarbitone, thiopentone, pentobarbitone and phenobarbitone preferentially reduced kainate‐, rather than AMPA‐ and NMDA‐, induced depolarizations. Methohexitone was also the most selective with IC50s against kainate, AMPA and NMDA of 31 ± 7, 172 ± 47 and >200 μm respectively.

The NBQX‐resistant plateau seen within the kainate dose‐response curve was reduced by methohexitone. Kainate antagonism by methohexitone was not reduced by 50 μm picrotoxin.

We conclude that, while mixed agonist actions may hamper demonstration of antagonist selectivity, depolarizations induced by the non‐NMDA ionotropic agonists, AMPA and kainate, are mediated in part via distinct receptors.
The effects of idazoxan and other α2‐adrenoceptor antagonists on urine output in the rat
Authors: Jackson Helen C. , Griffin Ian J. , Birkett Sonia D. , Nutt David J.
Published: July 2012

In normally‐hydrated Wistar rats the α2‐adrenoceptor antagonist, idazoxan (1, 3, 10 mg kg−1 i.p.), increased urine output during the 6 h following injection.

The more selective and specific α2‐adrenoceptor antagonist, RX811059 (0.3, 1, 3 mg kg−1 i.p.), and the peripherally‐acting α2‐adrenoceptor antagonist, L‐659,066 (1, 3, 10 mg kg−1 i.p.), had no effect on urine output in normally‐hydrated animals.

In rats given a 25 ml kg−1 water‐load orally, idazoxan (10 mg kg−1, i.p.) produced an initial antidiuretic response which was followed by an increase in urine output which was apparent 4 and 6 h after drug administration.

RX811059 (1, 3 mg kg−1 i.p.) and L‐659,066 (3, 10 mg kg−1 i.p.) significantly decreased urine output in water‐loaded rats in the 2 h after injection.

The antidiuretic effects of L‐659,066 were attenuated in Brattleboro rats which are deficient in vasopressin; only the highest dose (10 mg kg−1 i.p.) decreased urine output, and this was only a small response in comparison with its virtual abolition of urine output in water‐loaded Wistar rats.

The results with the selective α2‐adrenoceptor antagonists in Wistar and Brattleboro rats suggest that α2‐adrenoceptors in the periphery may play a physiological role in the control of water balance through a mechanism which involves vasopressin.

The paradoxical diuretic effects of idazoxan contrast with the effects of the other α2‐adrenoceptor antagonists and therefore may be attributed to a property of this compound unrelated to α2‐adrenoceptor blockade.
Peripheral analgesic activities of peptides related to α‐melanocyte stimulating hormone and interleukin‐1β193–195
Authors: Poole S. , Bristow A.F. , Lorenzetti B.B. , Das R.E. Gaines , Smith T.W. , Ferreira S.H.
Published: July 2012

The hyperalgesic effects of interleukin‐1β (IL‐1β) and prostaglandin E2 (PGE2) were measured in rats.

Hyperalgesic responses to IL‐1β were inhibited in a dose‐dependent manner by α‐melanocyte stimulating hormone (α‐MSH)‐related peptides with the following order of potency: [N14,d‐Phe7]α‐MSH > α‐MSH > Lys‐d‐Pro‐Val > Lys‐Pro‐Val > Lys‐d‐Pro‐Thr > d‐Lys‐Pro‐Thr.

Hyperalgesic responses to PGE2 were not inhibited by Lys‐d‐Pro‐Thr and d‐Lys‐Pro‐Thr but were inhibited in a dose‐dependent manner by the other peptides with the same order of potency as against IL‐1β.

The potencies of [N14, d‐Phe7]α‐MSH and α‐MSH were greatly diminished by deletion of their C‐terminal tripeptide, Lys11‐Pro‐Val13.

Nor‐binaltorphimine (Nor‐BNI) largely reversed the analgesic effects of α‐MSH, [N14, d‐Phe7]α‐MSH, Lys‐Pro‐Val and Lys‐d‐Pro‐Val indicating that κ‐opioid receptors mediated the analgesic activity of these peptides.

Nor‐BNI did not antagonize the inhibition by Lys‐d‐Pro‐Thr and d‐Lys‐Pro‐Thr of IL‐1β evoked hyperalgesia indicating that these peptides were not acting via κ‐opioid receptors.
Pituitary adenylate cyclase activating polypeptides, PACAP‐27 and PACAP‐38: stimulators of electrogenic ion secretion in the rat small intestine
Authors: Cox Helen M.
Published: July 2012

The effects of pituitary adenylate cyclase activating polypeptide (PACAP)‐27 and PACAP‐38 were investigated and compared with vasoactive intestinal polypeptide (VIP) responses in voltage clamped preparations of rat jejunum. Under these conditions electrogenic ion secretion was continuously recorded.

PACAP‐27 is the most potent secretagogue described thus far, exhibiting a concentration‐dependent dual secretory action. At low concentrations it stimulated rapid, transient secretory responses (not seen with either PACAP‐38 or VIP) and these were inhibited by tetrodotoxin (TTX). At higher nm concentrations of PACAP‐27 more prolonged secretory responses predominated which were insensitive to TTX.

In the presence of TTX, the concentration‐response curve to PACAP‐27 gave an EC50 value of 29.4 ± 5.4 nm (n = 4) compared with 0.8 ± 0.1 nm (n = 9) for PACAP‐27 alone and 30.6 ± 5.6 nm (n = 5) for PACAP‐38. C‐terminal fragments of PACAP‐38 were not significantly effective.

Blockade of muscarinic and nicotinic receptors partially inhibited the low concentration effects of PACAP‐27. Substance P densensitization and capsaicin pretreatment were effective at inhibiting the transient secretory PACAP‐27 responses. Evidence is presented for selective, high affinity PACAP‐27 receptors on submucous neurones innervating the mucosal region of the rat jejunum.
Ca2+ release from isolated sarcoplasmic reticulum of guinea‐pig psoas muscle induced by K+‐channel blockers
Authors: Ishida Yukisato , Honda Hiromi , Watanabe Takushi X.
Published: July 2012

A Ca2+‐sensitive electrode was used to measure the Ca2+ concentration of the medium containing the heavy fraction of the fragmented sarcoplasmic reticulum (SR) prepared from guinea‐pig psoas muscle. Among K+‐channel blockers tested, 4‐aminopyridine (4‐AP), tetraethylammonium (TEA) and charybdotoxin elicited Ca2+ release from the SR, but apamin and glibenclamide did not. These results suggest that a reduction of SR K+ conductance leads to Ca2+ release from the SR.
7‐Nitro indazole, an inhibitor of nitric oxide synthase, exhibits anti‐nociceptive activity in the mouse without increasing blood pressure
Authors: Moore P.K. , Babbedge R.C. , Wallace P. , Gaffen Z.A. , Hart S.L.
Published: July 2012

7‐Nitro indazole (7‐NI) inhibits mouse cerebellar nitric oxide synthase (NOS) in vitro with an IC50 of 0.47 μm. Following i.p. administration in mice, 7‐NI (10–50 mg kg−1) produces dose‐related anti‐nociception as evidenced by an inhibition of late phase (15–30 min) but not early phase (0–5 min) hindpaw licking time following subplantar injection of formalin (10 μl, 5% v/v). The ED50 for this effect was 26 mg kg−1 (equivalent to 159.5 μmol kg−1). Similar i.p. administration of 7‐NI (20 and 80 mg kg−1) in urethane‐anaesthetized mice failed to increase MAP. Thus, 7‐NI is a novel inhibitor of NOS which exhibits selectivity for the brain enzyme. Accordingly, 7‐NI may be a useful starting point for the development of selective, centrally acting NOS inhibitors devoid of cardiovascular side effects and as a tool to study the central pharmacological effects of nitric oxide (NO).
Enteral absorption of octreotide: absorption enhancement by polyoxyethylene‐24‐cholesterol ether
Authors: Drewe Jürgen , Fricker Gert , Vonderscher Jacky , Beglinger Christoph
Published: July 2012

The somatostatin octapeptide‐analogue octreotide was absorbed as an intact peptide from the gastro‐intestinal tract with an absolute bioavailability of about 0.3% in rats. Administration of octreotide in the presence of polyoxyethylene (24)‐cholesterol‐ether (POECE) resulted in an about 23 fold increase of bioavailability.

In vitro studies with Caco‐2 cells showed a dose‐dependent increase in octreotide permeation with increasing doses of coadministered POECE. The use of [3H]‐polyethyleneglycol (PEG) 4000 as an extracellular marker also indicated that higher doses of POECE may partly enhance paracellular transport of macromolecules.

By means of fluorescence microscopy it was shown that transepithelial transport of the fluorescent octreotide analogue (4‐nitrobenzo‐2‐oxa‐1,3‐diazol [NBD] labelled octreotide) was enhanced by the addition of POECE. Besides an increased enterocyte uptake, there was evidence of enhanced partition of NBD‐octreotide into the intercellular space between enterocytes after co‐administration of POECE. In addition, there appeared to be changes in the hepatic topographic disposition of NBD‐octreotide when it was given together with POECE compared with its administration alone.

In a study in healthy volunteers, 16 mg POECE significantly enhanced by 8 fold the absorption of octreotide after oral administration.
Protective effects of bradykinin on the ischaemic heart: implication of the B1 receptor
Authors: Chahine R. , Adam A. , Yamaguchi N. , Gaspo R. , Regoli D. , Nadeau R.
Published: July 2012

We studied the role of bradykinin (BK) and its active metabolite Des‐Arg9‐BK on noradrenaline release in association with the incidence of ventricular arrhythmias at reperfusion of the ischaemic myocardium.

Experiments were performed in Langendorff perfused isolated hearts of rats subjected to 30 min no flow followed by 5 min reperfusion. The electrocardiogram was monitored continuously and noradrenaline was measured in the effluent as well as in the myocardial tissue.

In untreated hearts, cumulative noradrenaline overflow following global ischaemia reached 226 ± 35 pmol g−1 of heart (n = 8, P < 0.05) during the 5 min of reperfusion along with ventricular tachycardia and/or fibrillation. A decrease in myocardial noradrenaline (–31%) was also observed.

Bradykinin perfused at concentrations between 0.01 and 1 μm, 10 min before flow was stopped and at reperfusion, inhibited noradrenaline overflow in a concentration‐dependent manner. At a concentration of 1 μm, bradykinin completely abolished noradrenaline overflow. For the same concentration of bradykinin, myocardial noradrenaline contents were significantly higher (n = 5–8, P < 0.05). Ventricular fibrillation but not ventricular tachycardia was also prevented.

Des‐Arg9‐BK (0.1 μm) in the same experimental conditions had similar effects. While Hoe 140, a selective antagonist at B2 receptors, did not abolish the effects of bradykinin, Lys [Leu8] Des‐Arg9‐BK, an antagonist at B1 receptors, abolished the effects of both Des‐Arg9‐BK and bradykinin.

These results suggest that the cardioprotective action of bradykinin in the preparation may be mediated partially by an inhibitory effect on noradrenaline liberation which could be mediated by the activation of B1 receptors.
Allopurinol and amlodipine improve coronary vasodilatation after myocardial ischaemia and reperfusion in anaesthetized dogs
Authors: Sobey Christopher G. , Dalipram Romina A. , Woodman Owen L.
Published: July 2012

We have assessed the effect of allopurinol, amlodipine and propranolol pretreatment on both endothelium‐dependent and endothelium‐independent coronary vasodilatation in vivo, by comparing pre‐ischaemic responses with those measured after 60 min of coronary artery occlusion and 30 min of reperfusion in anaesthetized dogs.

In 15 untreated dogs ischaemia and reperfusion attenuated the increases in coronary blood flow produced by either acetylcholine (0.01–0.05 μg kg−1, i.a.) or glyceryl trinitrate (0.05–0.2 μg kg−1, i.a.), to an average of 39 ± 4% and 42 ± 5% of the pre‐ischaemic control response, respectively (both P < 0.05).

In 5 dogs treated with allopurinol (25 mg kg−1, orally, 24 h previously, plus 50 mg kg−1, i.v., 5 min before occlusion), the increases in coronary blood flow after ischaemia and reperfusion (acetylcholine: 78 ± 12%, glyceryl trinitrate: 60 ± 3% of pre‐ischaemic response) were significantly larger than post‐ischaemic responses in untreated dogs (both P < 0.05).

Similarly, amlodipine treatment (3 μg kg−1 min−1, i.v., starting 90 min before occlusion) in 5 dogs improved post‐ischaemic increases in blood flow (acetylcholine: 58.5%, glyceryl trinitrate: 66 ± 6% of pre‐ischaemic response, significantly greater than post‐ischaemic responses in untreated dogs, P < 0.05).

In contrast, in a further 6 dogs pretreated with propranolol (1 mg kg−1, i.v., 30 min before occlusion, plus 0.5 mg kg−1 h−1, i.v.), blood flow responses after ischaemia and reperfusion were not different from post‐ischaemic responses in untreated dogs (acetylcholine: 46 ± 6%, glyceryl trinitrate: 46 ± 6% of pre‐ischaemic response).

These results suggest that allopurinol and amlodipine protect against the post‐ischaemic impairment of endothelium‐dependent and endothelium‐independent coronary vasodilatation in vivo by mechanisms additional to endothelial protection.
Mediators of nonadrenergic, noncholinergic inhibition in the proximal, middle and distal regions of rat colon
Authors: Suthamnatpong Naowarat , Hata Fumiaki , Kanada Atsunori , Takeuchi Tadayoshi , Yagasaki Osamu
Published: July 2012

The mediators of non‐adrenergic non‐cholinergic (NANC) relaxation of the longitudinal muscle of rat proximal, middle and distal colon were examined in vitro.

Electrical transmural stimulation (TMS) of proximal, middle and distal segments of rat colon induced NANC relaxations which were inhibited by tetrodotoxin (1 μm), but not by atropine (1 μm) or guanethidine (4 μm).

In the proximal colon, l‐nitro‐arginine (N5‐nitroamidino‐l‐2,5‐diaminopentanoic acid) inhibited the TMS‐induced NANC relaxation and l‐arginine (1 mm) reversed this inhibition. Nitric oxide (0.3–10 μm) induced relaxation of the proximal segment.

NANC relaxation of the proximal segments was still evident after desensitization to vasoactive intestinal peptide (VIP). A VIP antagonist (VIP 10–28, 10 μm) had no effect on the TMS‐induced NANC relaxation, which was also resistant to α‐chymotrypsin (2 units ml−1) and a substance P antagonist ([d‐Pro2, d‐Trp7,9]substance P, 1 μm).

In the middle colon, l‐nitro‐arginine did not inhibit the TMS‐induced NANC relaxation in 6 of 9 preparations tested and partially inhibited the relaxation in the other 3 preparations. l‐Arginine did not reverse the partial inhibition.

Complete desensitization to VIP was not achieved in the middle colon. The VIP antagonist had no effect on the TMS‐induced NANC relaxation. After α‐chymotrypsin treatment of the segment, desensitization of the segments to substance P, or in the presence of the substance P antagonist, the TMS‐induced NANC relaxation was augmented.

In the distal colon, l‐nitro‐arginine did not have any significant effect on the TMS‐induced relaxation and nitric oxide did not induce relaxation. The VIP antagonist significantly inhibited TMS‐induced NANC relaxation. α‐Chymotrypsin‐treatment of the distal segments resulted in significant inhibition of NANC relaxation. No desensitization to substance P was achieved. Treatment with the substance P antagonist had no effect.

These results suggest that nitric oxide is the mediator of the NANC inhibitory response in the proximal region of rat colon; in the middle colon, substance P acts as an excitatory neurotransmitter, antagonizing the NANC relaxation caused by the mediator of the response, which is still uncertain. Our results also suggest that VIP is the most likely candidate as a NANC transmitter in the distal colon.
Central α2‐autoreceptors: agonist dissociation constants and recovery after irreversible inactivation
Authors: Agneter E. , Drobny H. , Singer E.A.
Published: July 2012

Rats received an intraperitoneal injection of 1.6 mg kg−1 N‐ethoxycarbonyl‐2‐ethoxy‐1,2‐dihydroquinoline (EEDQ) to achieve an irreversible inactivation of presynaptic release‐modulating α2‐autoreceptors. Cerebral cortex slices were prepared at different times after the injection (24, 48, 96, 192, 336, 774 h), incubated with [3H]‐noradrenaline ([3H]‐NA), superfused and stimulated electrically with 4 pulses at 100 Hz (= autoinhibition‐free condition). Overflow of radioactivity was used to measure release. Furchgott analysis was used to estimate agonist dissociation constants (KA) and pool size of resynthesized receptors (q).

The KA values of the three α2‐autoreceptor agonists, bromoxidine (UK‐14304), clonidine and noradrenaline (NA) were 187 nm, 72 nm, and 1202 nm, respectively.

The release‐inhibiting effects of the agonists returned considerably faster than the receptor pool. The calculated half‐lives for the recovery of the maximal release‐inhibiting effects of bromoxidine, clonidine and NA were 30.7, 63.6 and 20.8 h, respectively, whereas the half‐life for the recovery of the receptor pool was 445 h.

The data indicate a large receptor reserve at presynaptic α2‐autoreceptors for the agonists used and validate the use of EEDQ as a tool for the determination of agonist dissociation constants.