bluuebunny/crossref_metadata_2025 huggingface dataset:
Differential susceptibility of cholinergic and noncholinergic neurogenic responses to calcium channel blockers and low Ca2+ medium in rat urinary bladder
Authors: Bhat M.B. , Mishra S.K. , Raviprakash V.
Published: July 2012

The influence of calcium channel blockers and low Ca2+ medium on the neurogenic responses to single pulse electric field stimulation in rat urinary bladder has been examined.

Single pulse stimulation evoked a biphasic contractile response consisting of a fast component with a time to peak of 0.72 ± 0.05 s and a slow component that reached a maximal tension at 2.8 ± 0.21 s, possibly mediated by two different neurotransmitters.

Atropine (3 × 10−6m) selectively inhibited the slow component without altering the fast component, suggesting the involvement of cholinergic and non‐cholinergic neurotransmitters, respectively.

Reducing Ca2+ in the medium to 1/4 of the normal, abolished the slow component of the neurogenic response while the fast contractile response was not altered which may indicate a relatively greater dependence of the cholinergic component on extracellular Ca2+ than the noncholinergic one.

The IC50 values for the fast component with respect to verapamil and diltiazem were 1.08 μm and 1.76 μm, respectively. The greater susceptibility of the slow component to calcium channel blockers (IC50 values of verapamil: 0.07 μm and of diltiazem: 0.25 μm) indicates the differential activation of slow calcium channels by the endogenously released substances.

Calcium channel blockers inhibited the ATP‐induced contraction which was comparable to that of the non‐cholinergic component of the neurogenic response suggesting the involvement of ATP as a possible neurotransmitter.

ACh‐induced contractions were relatively less susceptible to calcium channel blockers and low Ca2+ medium than was the atropine‐sensitive cholinergic component of the neurogenic response.
Effects of hypoxia on the pharmacological responsiveness of isolated coronary artery rings from the sheep
Authors: Kwan Y.W. , Wadsworth R.M. , Kane K.A.
Published: July 2012

The effects of low oxygen tension on tone and on the responsiveness to contractile and relaxant agents were examined on circumflex coronary artery rings isolated from sheep.

When artery rings (2–2.5 mm o.d.) were set at their optimal resting tension, introduction of hypoxia (0% O2) caused a sustained contraction which was reversible on washing with oxygenated Krebs solution. In precontracted (40 mm KCl) arteries, hypoxia caused a similar response except that it was preceded by a transient relaxation.

The hypoxia‐induced contraction was potentiated by the combination of phentolamine (1 μm) and propranolol (1 μm), markedly reduced by verapamil (10 μm) and either abolished or reduced by indomethacin (1 μm). Indomethacin itself caused a contraction.

Under hypoxic conditions, the contractile effects of U46619 (a stable thromboxane analogue) and 5‐hydroxytryptamine (5‐HT) and the vasodilator effects of noradrenaline, iloprost (a prostacyclin mimetic) and adenosine were markedly potentiated. In contrast, vasoconstriction to potassium or acetylcholine was depressed.

Changing the gases from 95% O2 to 12% O2 had no significant effect on the contractile effects of U46619. However, the maximum contractile effect of U46619 was significantly enhanced by changing the gases from 12% O2 to 0% O2.

Rings from a smaller branch (0.6–1.3 mm o.d.) of the circumflex coronary artery of the sheep, in the presence of hypoxia, exhibited qualitatively similar changes in the responsiveness to U46619, 5‐HT and adenosine to those observed in the large artery. However, the effect of potassium was potentiated rather than depressed.

It is concluded that hypoxia‐induced contraction may involve a modified release of cyclo‐oxygenase products and be partly dependent upon the availability of extracellular calcium.

The change in the responsiveness of coronary arteries, under hypoxia, to both constrictor and dilator mediators may have clinical relevance to myocardial ischaemia and angina pectoris.
Hypoxia‐ and endothelium‐mediated changes in the pharmacological responsiveness of circumflex coronary artery rings from the sheep
Authors: Kwan Y.W. , Wadsworth R.M. , Kane K.A.
Published: July 2012

The role(s) of the endothelium in modulating the responsiveness of isolated circumflex coronary artery rings (o.d. = 2.0–2.5 mm and o.d. = 0.6–1.3 mm) from sheep was investigated under oxygenated and hypoxic conditions.

Removal of the endothelium abolished the contraction produced by lowering the Po2 from 620 to 8 mmHg (either under optimal resting tension or precontracted by 40 mm KCl). In denuded artery rings sudden hypoxia caused relaxation.

Under oxygenated conditions, removal of the endothelium augmented the vasoconstrictor effects of U46619, 5‐hydroxytryptamine (5‐HT) and K+. In the denuded artery rings, hypoxia abolished the contractile effects of U46619 and reduced the contractile effects of 5‐HT and K+.

Under oxygenated conditions, the vasorelaxant effect of adenosine was depressed by removal of the endothelium. In endothelium‐denuded preparations, the small relaxant effect of adenosine remaining was greatly potentiated.

Haemolysate (1 μl ml−1) caused an endothelium‐dependent contraction under oxygenated conditions. The hypoxic contraction observed in the artery ring under resting tension was significantly potentiated by haemolysate (1 μl ml−l). Haemolysate 1 μl ml−l had no effect on the denuded artery rings under hypoxic conditions.

Haemolysate (1 μl ml−l) potentiated the vasoconstrictor effects of U46619 (0.5 μm), 5‐HT (1 μm) and K+ (24 mm) under oxygenated conditions.

These results indicate that endothelium profoundly modifies the effect of hypoxia on the responsiveness of sheep isolated left circumflex coronary artery rings.
Involvement of a pertussis toxin‐sensitive G‐protein in the pharmacological properties of septo‐hippocampal neurones
Authors: Rascol Olivier , Dutar Patrick , Lamour Yvon
Published: July 2012

The physiological and pharmacological properties of identified septo‐hippocampal neurones (SHNs) have been studied in rats pretreated with the bacterial toxin, pertussis toxin (PTX).

In rats anaesthetized with urethane and pretreated with PTX, the axonal conduction velocity was unchanged while the mean spontaneous activity was significantly increased.

PTX pretreatment had no effect on responses of SHNs to the iontophoretic application of γ‐aminobutyric acid (GABA) and cholinoceptor agonists (acetylcholine or carbachol).

Baclofen and 5‐hydroxytryptamine (5‐HT), almost exclusively inhibitory in control rats, had little effect or an excitatory effect in PTX pretreated rats.

These results suggest the involvement of a pertussis toxin‐sensitive G‐protein in responses mediated by 5‐HT and GABAB‐receptors but not in responses mediated by cholinoceptors and GABAA‐receptors in medial septum neurones projecting into the hippocampus.
Pertussis toxin prevents the inhibitory effect of adenosine and unmasks adenosine‐induced excitation of mammalian motor nerve endings
Authors: Silinsky E.M. , Solsona C. , Hirsh J.K.
Published: July 2012

Pertussis toxin (PTX), which blocks certain classes of guanine nucleotide binding proteins (G proteins), consistently blocked the inhibitory effects of adenosine (100 μm‐250 μm) on quantal acetylcholine (ACh) secretion in rat phrenic nerve hemidiaphragm preparations. PTX pretreatment also highlighted long‐lasting increases in evoked ACh release elicited by adenosine. The results suggest that specific G proteins are involved in mediating the inhibitory effects of adenosine at motor nerve endings.
The properties of 5‐HT3 receptors in clonal cell lines studied by patch‐clamp techniques
Authors: Lambert Jeremy J. , Peters John A. , Hales Tim G. , Dempster John
Published: July 2012

The characteristics of transmembrane currents evoked by 5‐hydroxytryptamine (5‐HT) in the neuroblastoma x Chinese hamster brain cell line NCB‐20 and neuroblastoma clonal cell line N1E‐115 have been studied under voltage‐clamp conditions by the whole‐cell recording and outside‐out membrane patch modes of the patch‐clamp technique.

In 73% of NCB‐20 cells examined (n = 221), and all N1E‐115 cells studied (n = 80), 5‐HT (10 μm) elicited a transient inward current at negative holding potentials, this being associated with an increase in membrane conductance. In both cell lines responses to 5‐HT reversed in sign at a potential of approximately −2mV and demonstrated inward rectification.

The reversal potential of 5‐HT‐induced currents (E5‐HT) recorded from either NCB‐20 or N1E‐115 cells was unaffected by total replacement of internal K+ by Cs+. In N1E‐115 cells, reducing internal K+ concentration from 140 to 20 mm produced a positive shift in E5‐HT of approximately 28 mV, whereas reducing external Na+ from 143 to 20 mm was associated with a negative shift in E5‐HT of about 37 mV. A large reduction in internal Cl− concentration (from 144 to 6 mm) had little effect on E5‐HT.

5‐HT‐induced currents of NCB‐20 cells were unaffected by methysergide (1 μm) or ketanserin (1 μm), but were reversibly antagonized by GR38032F (0.1–1.0 nm) with an IC50 of 0.25 nm. GR 38032F (0.3 nm) reduced 5‐HT‐induced currents in N1E‐115 cells to approximately 26% of their control value.

On outside‐out membrane patches excised from both NCB‐20 and N1E‐115 cells, 5‐HT induced small inward currents which could not be clearly resolved into discrete single channel events. Such responses were: (i) reversibly antagonized by GR 38032F (1 nm) (ii) reversed in sign at 0 mV, and (iii) subject to desensitization.

Fluctuation analysis of inward currents evoked by 5‐HT (1 μm) in N1E‐115 cells suggests that 5‐HT gates a channel with a conductance of approximately 310fS. Such a relatively small conductance could readily explain why the response of outside‐out membrane patches to 5‐HT cannot at present be resolved into clear single channel events.
The effect of medetomidine, an α2‐adrenoceptor agonist, on plasma atrial natriuretic peptide levels, haemodynamics and renal excretory function in spontaneously hypertensive and Wistar‐Kyoto rats
Authors: Ruskoaho Heikki , Leppäluoto Juhani
Published: July 2012

The effects of the selective α2‐adrenoceptor agonist, medetomidine, were assessed on plasma levels of immunoreactive atrial natriuretic peptide (IR‐ANP), haemodynamics and on urine water and solute excretion in conscious, chronically cannulated, 7 month‐old spontaneously hypertensive (SHR) and age‐matched Wistar‐Kyoto (WKY) rats, in order to examine the role of α2‐adrenoceptors in the control of ANP secretion.

A 60 min i.v. infusion of medetomidine (0.2 or 0.6 μg kg−1 min−1) decreased heart rate dose‐dependently in both strains. Medetomidine infusion (0.6 μg kg−1 min−1) resulted in an increase in mean arterial pressure in WKY, whereas both doses decreased blood pressure in SHR. There was a slight increase in the right atrial pressure in both strains (WKY: + 1.18 ± 0.26 mmHg; SHR: + 1.64 ± 0.64 mmHg, NS) in response to infusion of 0.6 μg kg−1 min−1 of medetomidine.

No differences were found in resting plasma IR‐ANP levels between WKY (114 ± 8 pg ml−1, n = 19) and SHR (117 ± 10 pg ml−1, n = 21). Infusion of equibradycardic doses of medetomidine increased dose‐dependently plasma IR‐ANP levels in WKY, but did not affect the plasma IR‐ANP concentration in SHR rats.

Despite the different effect of medetomidine on ANP release in WKY and SHR rats, i.v. administration of medetomidine affected renal excretory functions similarly in both strains; urine flow and sodium excretion increased and urine osmolality decreased significantly, while there was no consistent change in urinary potassium excretion. Urine osmolality decreased to hypo‐osmotic levels during the infusion of 0.6 μg kg−1 min−1 of medetomidine, suggesting a possible interaction between α2‐adrenoceptor stimulation and the vasopressin system.

These results show that the α2‐adrenoceptor agonist medetomidine increased plasma levels of ANP in WKY rats, probably through an increase in mean arterial and right atrial pressures, whereas the SHR had attenuated ANP release to α2‐adrenoceptor stimulation. Our findings, that medetomidine caused marked natriuretic and diuretic effects in both strains and that these effects on the excretory functions of the kidneys were not related to changes in plasma levels of IR‐ANP, demonstrate that changes in plasma ANP levels alone do not account for the diuretic and natriuretic effect of α2‐agonists.
Evidence for a dihydropyridine‐sensitive and conotoxin‐insensitive release of noradrenaline and uptake of calcium in adrenal chromaffin cells
Authors: Owen P. Jane , Marriott Deborah B. , Boarder Michael R.
Published: July 2012

It has been suggested that neuronal voltage‐sensitive calcium channels (VSCC) may be divided into dihydropyridine (DHP)‐sensitive (L) and DHP‐insensitive (N and T), and that both the L and the N type channels are attenuated by the peptide blocker ω‐conotoxin. Here the effects of ω‐conotoxin on release of noradrenaline and uptake of calcium in bovine adrenal chromaffin cells were investigated.

Release of noradrenaline in response to 25 mm K+, 65 mm K+, 10 nm bradykinin or 10 μm prostaglandin E1 was not affected by ω‐conotoxin in the range 10 nm‐1 μm.

45Ca2+ uptake stimulated by high K+ and prostaglandin was attenuated by 1 μm nitrendipine and enhanced by 1 μm Bay K 8644; these calcium fluxes were not modified by 20 nm ω‐conotoxin.

With superfused rat brain striatal slices in the same medium as the above cell studies, release of dopamine in response to 25 mm K+ was attenuated by 20 nm ω‐conotoxin.

These results show that in these neurone‐like cells, release may be effected by calcium influx through DHP‐sensitive but ω‐conotoxin‐insensitive VSCC, a result inconsistent with the suggestion that ω‐conotoxin blocks both L‐type and N‐type neuronal calcium channels.
TRH‐Induced blood flow and mean arterial pressure changes in the rabbit are not dependent on the anaesthetic used
Authors: Hugoson‐Seligsohn Eva E. , Koskinen Lars‐Owe D.
Published: July 2012

The effects of thyrotropin releasing hormone (TRH) on regional cerebral blood flow were studied in rabbits anaesthetized with pentobarbitone or ketamine. The blood flow was determined with the labelled microsphere method before and after the i.v. administration of either 50 μg kg−1 or 2 mg kg−1 TRH.

In order to measure the cerebral O2 consumption the arteriovenous difference in oxygen saturation in the brain (CAVOD) was measured before and after the administration of 2 mg kg−1 TRH.

In animals under pentobarbitone anaesthesia 50 μg kg−1 TRH elicited an increase in mean arterial blood pressure (MAP) of about 1 kPa and 2 mg kg−1 TRH elevated the MAP by about 2 kPa. With ketamine as the anaesthetic the corresponding values were 0.5 kPa and 7 kPa, respectively. TRH induced significant vasoconstriction in several peripheral tissues.

The total cerebral blood flow (CBFtot) increased from 54 ± 4 to 78 ± 5 g min−1 100 g−1 after the administration of 50 μg kg−1 TRH in pentobarbitone‐anaesthetized animals. An even greater effect was elicited by 2 mg kg−1 TRH, from 48 ± 6 to 113 ± 19 g min−1 100 g−1. In ketamine‐anaesthetized rabbits, 50 μg kg−1 TRH tended to enhance the CBFtot and 2 mg kg−1 increased it from 71 ± 6 to 141 ± 19 g min−1 100g−1.

In animals anaesthetized with pentobarbitone, the CAVOD decreased from 47.3 ± 1.7% to 35.1 ± 2.2% at 3 min after TRH delivery, and then gradually increased to the control level. In animals under ketamine anaesthesia the CAVOD decreased from 63.3 ± 2.0% to 45.2 ± 7.4% after the administration of 2 mg kg−1 TRH.

It is concluded that TRH elicits cerebral vasodilatation in excess of that required by the change in cerebral metabolism which may have taken place. The pattern of responses was similar to that produced in rabbits under urethane anaesthesia.
Negative inotropic activity of antilaminin IgG: participation of cholinergic mechanisms
Authors: Bacman Sandra , Borda Enri , Denduchis Berta , Lustig Livia , Sterin‐Borda Leonor
Published: July 2012

Antilaminin IgG decreased the dF/dt of mouse isolated atria and inhibited the mechanical effect of acetylcholine in a non‐competitive fashion.

Inhibitors of nicotinic and muscarinic cholinoceptors impaired the negative inotropic action of antilaminin IgG in mouse isolated atria. Hemicholinium and tetrodotoxin also reduced the response while the antihistamine, pyrilamine was without effect.

These results suggest that antilaminin IgG modulates cholinergic function in mouse isolated atria. Possible mechanisms are discussed.
Reduction of cephalic arteriovenous shunting by ergotamine is not mediated by 5‐HT1‐like or 5‐HT2 receptors
Authors: Bom Anton H. , Heiligers Jan P.C. , Saxena Pramod R. , Verdouw Pieter D.
Published: July 2012

The potent, antimigraine drug ergotamine has affinity for both 5‐HT1 and 5‐HT2 binding sites and constricts arteriovenous anastomoses. Since 5‐HT also constricts arteriovenous anastomoses (mainly via 5‐HT1‐like receptors), this study investigates the involvement of 5‐HT receptors in the ergotamine‐induced reduction of arteriovenous shunting in the carotid circulation of the cat and pig.

In the cat, ergotamine (3, 10 and 30 μg kg−1, i.v.) reduced carotid blood flow, predominantly by a reduction in arteriovenous anastomotic blood flow. Pretreatment with ketanserin (0.5 mg kg−1, i.v.) or methiothepin (1 mg kg−1, i.v.) did not antagonize the effects of ergotamine.

In the pig, ergotamine (2.5, 5, 10 and 20 μg kg−1, i.v.) also reduced carotid blood flow and arteriovenous shunting, which was not affected by pretreatment with methiothepin (1 mg kg−1, i.v.).

These results suggest that the reduction by ergotamine in the shunting of carotid arterial blood via cephalic arteriovenous anastomoses is not mediated by 5‐HT1‐like or 5‐HT2 receptors.
Defibrotide reduces infarct size in a rabbit model of experimental myocardial ischaemia and reperfusion
Authors: Thiemermann Christoph , Thomas G. Roger , Vane John R.
Published: July 2012

Defibrotide, a single‐stranded polydeoxyribonuncleotide obtained from bovine lungs, has significant anti‐thrombotic, pro‐fibrinolytic and prostacyclin‐stimulating properties.

The present study was designed to evaluate the effects of defibrotide on infarct size and regional myocardial blood flow in a rabbit model of myocardial ischaemia and reperfusion.

Defibrotide (32 mg kg−1 bolus + 32 mg kg−1 h−1, i.v.) either with or without co‐administration of indomethacin (5 mg kg−1 × 2, i.v.) was administered 5 min after occlusion of the left anterior‐lateral coronary artery and continued during the 60 min occlusion and subsequent 3 h reperfusion periods.

Defibrotide significantly attenuated the ischaemia‐induced ST‐segment elevation and abolished the reperfusion‐related changes (R‐wave reduction and Q‐wave development) in the electrocardiogram. In addition, defibrotide significantly improved myocardial blood flow in normal and in ischaemic, but not in infarcted sections of the heart. The improvement in blood flow in normal perfused myocardium, but not in the ischaemic area was prevented by indomethacin.

Although the area at risk was similar in all animal groups studied, defibrotide treatment resulted in a 51% reduction of infarct size. Indomethacin treatment abolished the reduction of infarct size seen with defibrotide alone.

The data demonstrate a considerable cardioprotective effect of defibrotide in the reperfused ischaemic rabbit myocardium. This effect may be related, at least in part, to a stimulation of endogenous prostaglandin formation. Other possible mechanisms are discussed.
Mechanism of xanthine‐induced relaxation of guinea‐pig isolated trachealis muscle
Authors: Ogawa K. , Takagi K. , Satake T.
Published: July 2012

Four 3‐alkylxanthines (3‐methylxanthine, 3‐n‐propylxanthine (enprofylline), 3‐n‐butylxanthine and 3‐iso‐butylxanthine) and four 1‐methyl‐3‐alkylxanthines (1‐methyl‐3‐methylxanthine (theophylline), 1‐methyl‐3‐n‐propylxanthine, 1‐methyl‐3‐n‐butylxanthine and 1‐methyl‐3‐iso‐butylxanthine (IBMX)), were compared in terms of cyclic AMP phosphodiesterase (PDE) inhibition and trachealis muscle relaxation. The relationship between xanthine structure and cyclic AMP PDE inhibition was also studied.

Xanthine induced relaxation of guinea‐pig isolated trachealis muscle was measured against spontaneous tone.

The four 1‐methyl‐3‐alkylxanthines were each significantly more potent than the corresponding 3‐alkylxanthines in relaxing the isolated trachealis muscle. The 1‐methyl‐3‐alkylxanthines were similarly more potent than the corresponding 3‐alkyl derivatives in inhibiting low Km cyclic AMP PDE. There was a strong positive correlation between low Km cyclic AMP PDE inhibition and the tracheal smooth muscle relaxation evoked by the xanthine derivatives.

Since methylation of the 1‐position of each 3‐alkylxanthine increased the potency of the derivative in inhibiting low Km cyclic AMP PDE and in relaxing trachealis muscle and since a strong positive correlation was observed between the relaxant EC50 and the Ki value of each xanthine derivative, it is suggested that low Km cyclic AMP PDE inhibition by xanthines plays an important role in their tracheal relaxant effect.
Subclassification of atrial and intestinal muscarinic receptors of the rat—direct binding studies with agonists and antagonists
Authors: Brunner F.
Published: July 2012

Although extensively investigated, the extent of differences between receptors mediating negative inotropic and chronotropic responses is still unclear. In the present study atrial and intestinal muscarinic receptors were identified by [3H]‐N‐methyl‐scopolamine ([3H]‐NMS) binding and the affinities of some presumably inotropy‐ or chronotropy‐selective agonists and several antagonists determined.

All the agonists tested showed similar affinity for right and left atrial receptors. Accepting an affinity difference of 0.4 log units as experimental error, none of the agonists tested was selective for either atrium.

Affinity differences of the cardioselective antagonists himbacine, AF‐DX 116 and methoctramine and the M1‐selective antagonist dicyclomine for right and left atrial muscarinic receptors were also minimal (less than 2 fold selective). When compared to intestinal receptors, AF‐DX 116 was 3 to 4 fold, methoctramine 10 to 13 fold selective and himbacine and dicyclomine non‐selective.

These data provide evidence for differences between atrial and intestinal but not between right and left atrial muscarinic receptors.
Presynaptic muscarinic receptors inhibiting endogenous noradrenaline release in the portal vein of the freely moving rat
Authors: Remie R. , Coppes R.P. , Zaagsma J.
Published: July 2012

In the portal vein of the freely moving unanaesthetized rat, the existence of presynaptically located inhibitory muscarinic receptors was investigated by use of the muscarinic agonist methacholine (MCh)

Infusion of MCh (0.3 μg min−1) did not significantly inhibit the endogenous noradrenaline (NA) overflow in portal plasma. However, after inducing high intra‐synaptic concentrations of NA by blocking the presynaptic α2‐adrenoceptors with yohimbine (1 mg kg−1), MCh (0.3 μg min−1) was able to reduce the yohimbine‐induced enhanced NA overflow by 38%.

The MCh‐induced inhibition was almost completely abolished after blockade of the presynaptic muscarinic receptors with atropine (0.6 mg kg−1).

During electrical stimulation of the portal vein nervous plexus the evoked NA overflow was strongly inhibited (95%) during MCh‐infusion (0.3 μg min−1). Again atropine (0.6 mg kg−1) was able to reverse this inhibition.

These results show the existence of presynaptic muscarinic receptors inhibiting endogenous NA overflow from the portal vein nervous plexus under conditions of enhanced sympathetic activity in the freely moving rat.
Ketamine‐induced relaxation in intact and skinned smooth muscles of the rabbit ear artery
Authors: Kanmura Y. , Yoshitake J. , Casteels R.
Published: July 2012

The effects of ketamine, an intravenous anaesthetic, on the rabbit ear artery were investigated by measuring the tension in intact and saponin‐treated skinned smooth‐muscle fibres.

Ketamine dose‐dependently inhibited contractions of intact smooth‐muscle fibres induced by high K+ solution and by noradrenaline (NA) or histamine in Krebs solution. This drug similarly attenuated both phasic and tonic contractions induced by high K+ solution.

Ketamine also inhibited NA‐ or histamine‐induced contractions in Ca2+‐free solution containing 2 mm EGTA, but it did not affect the caffeine‐induced contraction in this solution.

Because the pCa‐tension relationship of saponin‐treated skinned smooth‐muscle fibres was not affected, it can be proposed that ketamine does not have an effect on the contractile proteins.

In the presence of 5 mm NaN3, 20 μm inositol 1,4,5‐trisphosphate (InsP3) or 25 mm caffeine produced a contraction in skinned smooth‐muscle fibres after accumulation of Ca2+ by intracellular stores. Analysis of the InsP3‐ or caffeine‐induced contractions indicates that ketamine does not have an effect on the Ca2+ accumulation into and Ca2+ release from the intracellular stores.

These results indicate that the relaxant effects produced by ketamine in the rabbit ear artery are not likely to be due to an intracellular action. The inhibitory effects of ketamine could be caused by a decrease of the Ca2+ influx through the plasma membrane or interference with the process of signal transduction between receptors on the plasma membrane and intracellular stores.
The effect of relaxants working through different transduction mechanisms on the tonic contraction produced in rat aorta by 4β‐phorbol dibutyrate
Authors: Obianime A.W. , Dale M. Maureen
Published: July 2012

We have examined the effects of a range of smooth muscle relaxants on the maintained contractions produced in rat aortic rings by the protein kinase C activator, 4β‐phorbol dibutyrate; these effects were compared with those on the contraction induced by the selective α1‐adrenoceptor agonist, methoxamine. The phorbol ester, at 0.3 μm, gave a sustained contraction which was, on average, of approximately the same magnitude as the maximum contraction produced by methoxamine, 10 μm.

The β‐adrenoceptor agonist, isoprenaline (0.01–1 μm) caused a dose‐related relaxation of the methoxamine‐induced contraction but had no effect on the contraction induced by the phorbol ester.

An activator of adenylate cyclase, forskolin (0.01–1 μm) produced a dose‐related relaxation of the methoxamine‐induced contraction and at 0.01–10 μm caused relaxation of the contraction induced by the phorbol ester. Similar results were obtained with the potassium channel activator, cromakalim (0.001–10 μm).

An activator of guanylate cyclase, sodium nitroprusside (0.001–100 μm) caused a dose‐related relaxation of both the methoxamine‐induced and the phorbol ester‐induced contraction, being more effective on the former than on the latter. Similar results were obtained with enprofylline (11000 μm).

Methoxamine (10 nM‐100 μm), given cumulatively, caused a dose‐related contractile response. Pretreatment with isoprenaline (1 μm), enprofylline (10 μm) and nicorandil (1 μm) resulted in partial decrease of the subsequent response to methoxamine, while nicorandil (10 μm), forskolin (1 μm), sodium nitroprusside (10 μm) and cromakalim (1 μm) totally abolished it.

The phorbol ester, given cumulatively, caused increasing contraction in the concentration range 30 nM‐10 μm. Pretreatment with forskolin (1 μm), sodium nitroprusside (10 μm), isoprenaline (1 μm), enprofylline (10 μm), nicorandil (1 μm or 10 μm), or cromakalim (1 μm or 10 μm), resulted in partial decrease of the subsequent response to 4β‐phorbol dibutyrate.

These results are discussed in the light of the suggestion that protein kinase C may have a role in the ‘latch‐bridge’ phase of smooth muscle contraction, and that inappropriate activation of protein kinase C may contribute to the pathogenesis of hypertension and other conditions involving vasospasm.
Central nervous system kinin receptors and the hypertensive response mediated by bradykinin
Authors: Lindsey C.J. , Nakaie C.R. , Martins D.T.O.
Published: July 2012

Bradykinin (Bk) administered intracerebroventricularly to the rat causes an increase in arterial pressure.

Analogues of Bk with agonist and antagonist activity were injected, over a wide dose‐range, into the posterior region of the fourth ventricle of unanaesthetized rats implanted with permanent ventricular canullae, and blood pressure was measured directly from the abdominal aorta.

The analogues Ile‐Ser‐Bk (T‐kinin) and Lys‐Lys‐Bk, which interact with both B1 and B2 Bk receptors, produced pressor effects similar to those of Bk, although of greater duration, whereas des‐Arg9‐Bk, a B1 ‐receptor agonist, had no effect.

The B1‐antagonist des‐Arg9‐[Leu8]‐Bk did not alter the Bk pressor response, but D‐Arg‐[Hyp3, Thi5,8,D‐Phe7]‐Bk, which interacts both with B1‐ and B2‐receptors blocked the responses to Bk, T‐kinin and Lys‐Lys‐Bk and caused parallel shifts to the right of the Bk dose‐response curves. Neither antagonist, by itself, had any effect on blood pressure.

It is concluded that the central pressor response to Bk is mediated by receptors of the B2 subtype.
The involvement of lactate and calcium as mediators of the electrical and mechanical responses of the myocardium to conditions of simulated ischaemia
Authors: Northover B.J.
Published: July 2012

Rat isolated and superfused atria were exposed to a lactate‐containing solution simulating the composition of extracellular fluid during myocardial ischaemia (SI).

Atria subjected to SI showed a decreased adenosine 5′‐triphosphate (ATP) content, a rise in diastolic tension, a diminished conduction velocity of action potentials and shortened refractory periods. All these changes were less pronounced during lactate‐free SI.

Atria preloaded with calcium displayed exaggerated responses measured electrically and mechanically during exposure to SI, whereas atria previously depleted of calcium displayed diminished electrical and mechanical responses to SI. Neither calcium loading nor calcium depletion modified the SI‐induced depletion of the atrial stores of ATP.

Sulphinpyrazone protected atria against all aspects of the response to SI, but failed to protect the muscle under conditions of lactate‐free SI. It is concluded that during SI, sulphinpyrazone protects against a lactate‐mediated inhibition of the glycolytic synthesis of ATP.

Flufenamate exaggerated all responses of the atria to SI. These deleterious actions were still observed during lactate‐free SI. It is concluded that flufenamate inhibits the synthesis of ATP in the mitochondria.
Physical dependence on diazepam in the dog: precipitation of different abstinence syndromes by the benzodiazepine receptor antagonists Ro 15–1788 and ZK 93426
Authors: Löscher Wolfgang , Hönack Dagmar , Faßbender Christian P.
Published: July 2012

The effects of the benzodiazepine receptor antagonists Ro 15–1788 (flumazenil) and the β‐carboline ZK 93426 were compared in dogs before and after chronic treatment with diazepam.

In diazepam‐naive dogs, the most prominent behavioural alterations occurring during or after i.v. infusion of Ro 15–1788 up to a dose of 20 mg kg−1 were transient sedation, ataxia, and ‘hot foot’ behaviour, whereas behavioural alterations observed after ZK 93426 were not different from those observed after i.v. infusion of vehicle alone. This indicates that, in contrast to Ro 15–1788, ZK 93426 did not exert partial agonistic activity at benzodiazepine receptors.

In dogs treated 3 times daily with diazepam, 1 mg kg−1 orally, for 1 week, both benzodiazepine antagonists precipitated abstinence symptoms but the number and severity of withdrawal signs induced by Ro 15–1788 were greater than with ZK 93426.

In dogs treated 3 times daily with diazepam, 2 mg kg−1 orally, for 2 weeks, severe abstinence symptoms were precipitated in all animals by infusion of either antagonist but differences were found in the type of the symptoms: Ro 15–1788 induced rigid postures or rigid walking with increased muscle tone, tremor, twitches and jerks, whereas ZK 93426 did not alter motility but induced generalized myoclonic jerks and tonic‐clonic seizures. A generalized tonic‐clonic seizure was also observed in one dog of the trial with infusion of Ro 15–1788.

Plasma level determinations during chronic treatment with diazepam showed marked accumulation of the major active metabolite desmethyldiazepam, whereas diazepam levels were at least 15 times lower, which might suggest that desmethyldiazepam was responsible for the development of physical dependence on diazepam.
Potassium channel blockers differentially affect carbachol and (−)‐N6‐phenylisopropyladenosine on guinea‐pig atria
Authors: de Biasi Mariella , Froldi Guglielmina , Ragazzi Eugenio , Pandolfo Luisa , Caparrotta Laura , Fassina Guliana
Published: July 2012

The effect of three different potassium channel blockers (tetraethylammonium, TEA; 4‐aminopyridine, 4‐AP; and apamin) and of variations in the concentration of K+ and Ca2+ in the medium, have been studied on the responses of guinea‐pig isolated atria to (−)‐N6‐phenylisopropyladenosine (R‐PIA), a stable adenosine A1‐receptor agonist, and to carbachol, a muscarinic agonist. R‐PIA and carbachol showed the same negative inotropic effects over a similar range of concentrations (3–300 μm), both in spontaneously beating and in electrically driven atria.

TEA (0.1 to 20 mm) and 4‐AP (0.3 to 3 mm), both antagonized the negative inotropic and chronotropic effects of carbachol in a concentration‐dependent manner. In contrast, these compounds failed to inhibit the effects induced by R‐PIA. Apamin, a specific blocker of a low conductance Ca2+‐activated K+ channel, was ineffective in accordance with the absence of these channels in atrial tissue.

TEA (0.1 to 20 mm) inhibited the negative inotropic effect of carbachol, but not that of R‐PIA, in atria paced and depolarized by a high K+ medium (22mm). In this preparation Na+ current is abolished and the contraction induced by noradrenaline and electrical stimulation is solely dependent on Ca2+ influx currents.

Stepwise addition of Ca2+ to a calcium‐depleted perfusing medium of electrically driven atria, induced a positive inotropic effect which was inhibited by R‐PIA. In contrast, carbachol had no effect.

In agreement with our previous study, the data suggest that R‐PIA acts on isolated atria by inhibiting Ca2+ influx through L‐channels.
Differential release of histamine and eicosanoids from human skin mast cells activated by IgE‐dependent and non‐immunological stimuli
Authors: Benyon R. Christopher , Robinson Clive , Church Martin K.
Published: July 2012

Cells were dispersed from human foreskin using a mixture of collagenase and hyaluronidase and separated into mast cell‐depleted (<1%) or enriched (>75%) preparations by density‐gradient centrifugation.

Challenge of gradient fractions with ∍‐chain‐specific anti‐human IgE stimulated the release of histamine, prostaglandin D2 (PGD2) and leukotriene C4 (LTC4). The release of eicosanoids was significantly correlated with that of histamine, suggesting that they are derived from the mast cell population of the dispersate. In highly purified (76.2 ± 4.2%) mast cell preparations, maximum net release of histamine, PGD2 and LTC4 was 3432 ± 725, 84.9 ± 10.8 and 6.6 ± 1.2 pmol/106 nucleated cells.

The non‐immunological stimuli substance P, vasoactive intestinal peptide (VIP), somatostatin, compound 48/80, morphine and poly‐L‐lysine released similar amounts of histamine to anti‐IgE, but 12 to 21 fold less PGD2 and LTC4.

These studies suggest that IgE‐dependent and non‐immunological stimuli activate human skin mast cells by different secretory mechanisms, a hypothesis supported by our previous findings of differences in Ca2+ requirements and time‐course of histamine release. Activation by the non‐immunological mechanism may be of importance in vivo due to the close anatomical association between skin mast cells and dermal nerve‐terminals containing neuropeptides.
Block of sodium channels by psychotropic drugs in single guinea‐pig cardiac myocytes
Authors: Ogata Nobukuni , Narahashi Toshio
Published: July 2012

Effects of imipramine and haloperidol on voltage‐gated sodium channels were investigated in guinea‐pig isolated ventricular myocytes by the whole‐cell patch clamp technique. Some additional experiments were also performed with chlorpromazine for the purpose of comparison.

All test drugs in micromolar concentrations suppressed the amplitude of peak sodium current associated with step depolarization from a holding potential of −140 mV in a reversible manner. The order of potency was chlorpromazine > imipramine > haloperidol.

Dose‐response curves obtained with a holding potential of −140 mV were best fitted by 2:1 stoichiometry in all three drugs and were shifted in the direction of lower concentrations when a holding potential of −90 mV was used.

The drug‐induced block was not associated with any change in the time courses of sodium current activation and inactivation.

Steady‐state sodium channel inactivation curve was shifted in the direction of more negative potentials by the drugs.

All three drugs also produced marked use‐dependent block as demonstrated by a cumulative increase in the block during a train of depolarizing pulses.

The use dependence was due to a higher affinity of the drugs for the inactivated state of sodium channels than the resting state and to a very slow repriming of the drug‐bound sodium channels from inactivation.

The steady‐state and use‐dependent block of voltage‐gated sodium channels by psychotropic drugs may contribute to their cardiotoxic and perhaps antiarrhythmic effect.
5‐HT1‐like receptors requiring functional cyclo‐oxygenase and 5‐HT2 receptors independent of cyclo‐oxygenase mediate contraction of the human umbilical artery
Authors: MacLennan S.J. , Whittle M.J. , McGrath J.C.
Published: July 2012

The interactions between 5‐hydroxytryptamine (5‐HT) and the antagonists ketanserin, methysergide and phentolamine were studied in isolated preparations of human umbilical artery (HUA) at physiological oxygen tension (Po2 ∽ 15 mmHg) and at high Po2 (∽ 120 mmHg).

At physiological Po2 ketanserin, methysergide and phentolamine behaved as silent competitive antagonists of the 5‐HT‐induced contraction of HUA. pA2 values calculated by Schild analysis were 8.92, 8.52 and 6.37, respectively.

At high Po2, 5‐HT‐induced contractions were antagonised in a biphasic manner by ketanserin (0.1 μm); the response to low but not to high concentrations of 5‐HT was resistant to blockade by ketanserin. The ketanserin‐resistant component was abolished following cyclo‐oxygenase inhibition by indomethacin (1 μm).

At high Po2, methysergide behaved as a partial agonist. Methysergide‐induced contractions were inhibited but not abolished by indomethacin, and resistant to 5‐HT2 receptor and α1‐adrenoceptor blockade.

At high Po2 the component of the response to 5‐HT mediated by the ketanserin‐resistant receptor was mimicked by the selective 5‐HT1‐like receptor agonist 5‐carboxamidotryptamine (5‐CT): 5‐CT was 7 fold more potent than 5‐HT.

At high Po2 the component of the response to 5‐HT mediated by the ketanserin‐resistant receptor was antagonised by phentolamine and the selective α2‐adrenoceptor antagonist Wy 26703.

These results suggest that (i) at physiological Po2 5‐HT2 receptors almost exclusively mediate contractions induced by 5‐HT, and (ii) at high Po2 the agonist potency order of 5‐CT > 5‐HT > methysergide suggests that ketanserin‐resistant responses are mediated by 5‐HT1‐like receptors which require functional cyclo‐oxygenase.
A purified lipocortin shares the anti‐inflammatory effect of glucocorticosteroids in vivo in mice
Authors: Errasfa Mourad , Russo‐Marie Françoise
Published: July 2012

The injection of a suspension of a polyacrylamide gel (bio gel) into the dorsal subcutaneous area of mice induced an inflammatory reaction and the migration of neutrophils towards the inflamed site.

The intravenous administration of anti‐inflammatory drugs (dexamethasone, indomethacin and lysine‐acetylsalicylate) to Polyacrylamide gel‐treated mice inhibited the accumulation of neutrophils in the inflamed site.

A similar administration of a 36 K mouse lipocortin, induced a strong dose‐dependent inhibition of neutrophil accumulation in the inflamed site.

Dexamethasone and lipocortin inhibited the production of eicosanoids, prostaglandin E2 (PGE2) and leukotriene B4 (LTB4) in the inflamed site of Polyacrylamide gel‐treated mice.

Lipocortin impaired both phospholipase A2 (PLA2) activity and chemotaxis of isolated inflammatory neutrophils.

The present studies show an in vivo anti‐inflammatory effect of lipocortin similar to that of glucocorticosteroids. In agreement with recent data on the extracellular effects of various lipocortins, these results might implicate lipocortin(s) in the anti‐inflammatory effects of glucocorticosteroids.
Non classical, multiple‐site interaction of [3H]‐prazosin with the α1‐adrenoceptor of intact BC3H1 cells
Authors: Sladeczek Fritz , Kirk Christopher J. , Bockaert Joël , Schmidt Bernard H.
Published: July 2012

In intact BC3H1 cells the EC50 of noradrenaline (NA) for the inositol phosphate response measured at 37°C (EC50 = 193 nm) was much lower than its apparent dissociation constant (Ki37°c = 83.211 μm) determined at this temperature by [3H]‐prazosin binding.

After pretreatment of the cells with NA at 37°C for 45 min, the time used in binding assays at this temperature, this difference between EC50 and Ki37°c did not decrease significantly. An agonist‐induced reduction in α1‐adrenoceptor affinity can therefore not explain the very high Ki37°C value.

NA pretreatment at 37°C decreased the number of [3H]‐prazosin binding sites (assessed by whole cell binding at 2°C) by only 49%; not by 100%, the value expected if agonist‐induced receptor internalization were the origin of the very low Ki37°C.

The EC50 of NA for the inositol phosphate response in the presence of 156 pM [3H]‐prazosin was 1.841 μm but the IC50 of NA for the inhibition of [3H]‐prazosin binding (126 pm) was 316 μm. As there is no α1‐adrenoceptor reserve in these cells we propose that at 37°C [3H]‐prazosin interacts, not only with the catecholamine recognition site (site 1) of the receptor, but also reacts weakly with another site from which it cannot be directly displaced by catecholamine‐like substances (site 2).
Nitric oxide synthesized from L‐arginine regulates vascular tone in the coronary circulation of the rabbit
Authors: Amezcua J.L. , Palmer R.M.J. , de Souza B.M. , Moncada S.
Published: July 2012

The role of nitric oxide (NO) in the regulation of the vascular tone of the coronary circulation of the Langendorff‐perfused rabbit heart was investigated.

NG‐monomethyl‐L‐arginine (L‐NMMA; 10–100 μm), a specific inhibitor of NO formation from L‐arginine (L‐Arg), but not its D‐enantiomer (D‐NMMA; 100 μm) produced a dose‐related, sustained increase in the coronary perfusion pressure (CPP). In addition, L‐NMMA inhibited the vasodilator responses of acetylcholine (ACh), unmasking in some instances its direct vasoconstrictor effect. These effects of L‐NMMA were attenuated by L‐Arg.

L‐NMMA (10 and 30 μm), but not D‐NMMA (30 μm), caused a long‐lasting inhibition of NO formation which was reversed by L‐Arg (30 and 100 μm), but not by D‐Arg (100 μm).

This study indicates that the formation of NO from L‐Arg in the coronary circulation of the rabbit plays a role both as a regulator of vascular tone and as a mediator of the vasodilatation induced by ACh.
Characterization of adenosine receptors in guinea‐pig isolated left atria
Authors: Jahnel Ulrich , Nawrath Hermann
Published: July 2012

The effects of purinergic stimulation on action potential, force of contraction, 86Rb efflux and 45Ca uptake were investigated in guinea‐pig left atria.

Adenosine exerted a negative inotropic effect which was antagonized by adenosine deaminase but enhanced by dipyridamole.

The negative inotropic effect of adenosine was mimicked by 5′‐(N‐ethyl)‐carboxamido‐adenosine (NECA) and the isomers of N6‐(phenyl‐isopropyl)‐adenosine, R‐PIA and S‐PIA. NECA and R‐PIA were about 1000 times more potent than adenosine, whereas R‐PIA was about 100 times more potent than S‐PIA.

The inotropic effects of adenosine (in the presence of dipyridamole), NECA, R‐PIA and S‐PIA were competitively antagonized either by theophylline (pA2 about 4.5) or 8‐phenyltheophylline (pA2 about 6.3).

NECA and R‐PIA shortened the action potential duration and increased the rate constant of the efflux of 86Rb in a concentration‐dependent manner with no differences in potency; the effects were competitively antagonized by 8‐phenyltheophylline.

Barium ions reduced the efflux of 86Rb under control conditions and antagonized the increase induced by NECA and R‐PIA.

NECA and R‐PIA significantly reduced 45Ca uptake in beating preparations.

It is concluded that adenosine, NECA and R‐PIA activate a common receptor population (P1 or A3) on the outside of the cell membrane of atrial heart muscle to increase the potassium conductance and to reduce the action potential and, thereby, calcium influx and force of contraction.
Effect of age and methacholine on the rate and coronary flow of isolated hearts of diabetic rats
Authors: Li Xiaojiang , Tanz Ralph D. , Chang K.S.K.
Published: July 2012

Isolated hearts perfused by the method of Langendorff from 6, 12 and 24 week streptozotocin (STZ) diabetic rats displayed a significant bradycardia following 60 min equilibration. The rate of hearts from 12‐week diabetic rats (164 ± 17) displayed the greatest bradycardia compared to age‐matched controls (268 ± 15; P < 0.001), and diabetics treated with insulin (232 ± 17; P < 0.01), but by 52 weeks the heart rate of the 3 groups was similar. With advancing age the effect of STZ diabetes on the rate of rat isolated perfused hearts remained unchanged but the rate of the control and diabetic + insulin groups declined.

Hearts from 6–52 week STZ‐treated rats were found to be more sensitive to the negative chronotropic effect of methacholine, the greatest difference occurring in hearts from the 12 week animals. Atropine (10−7m) did not affect the resting heart rate of age‐matched controls or diabetics but blocked methacholine (2.6 × 10−6m)‐induced bradycardia in both, suggesting that the site of action of diabetic bradycardia is not the muscarinic receptors.

At the end of equilibration there was a significant decrease in coronary flow in hearts from 12 week diabetic animals. In spontaneously beating diabetic rat hearts administration of methacholine (2.6 × 10−6m) produced a significantly greater decrease in coronary flow in the 12, 24 and 52 week diabetic hearts. When electrically paced (5 Hz) however, there was no difference in response to methacholine between the three groups except at 52 weeks between the age‐matched control and diabetic groups. This suggests that the more pronounced reduction induced by methacholine on the coronary flow of diabetic hearts is secondary to its negative chronotropic effect.

In general, hearts from diabetic animals treated with insulin respond similarly to their age‐matched controls in the presence and absence of methacholine.