bluuebunny/crossref_metadata_2025 huggingface dataset:
Cardioprotection by the calcium antagonist PN 200‐110 in the absence and presence of cardiodepression
Authors: Cook N.S. , Hof R.P.
Published: July 2012

The globally‐ischaemic Langendorff rabbit heart model has been used to study the cardioprotective effects of the dihydropyridine PN 200‐110 (PN) at two doses, one having no negative inotropic effect and a higher dose causing a 62 ± 5% reduction in contractility.

Following 45 min no‐flow global ischaemia, recovery was monitored for a period of 90 min reperfusion. Hearts were paced at a constant rate throughout experiments. Contractile force and coronary flow were recorded continuously. Tracer microspheres were injected at regular intervals to assess regional flow distributions, drill biopsies were taken to determine tissue high energy phosphate content, and enzyme leakage in the coronary effluent measured during the first 15 min of reperfusion.

Untreated hearts recovered 21 ±2% of their initial contractile force and flow to all heart regions was reduced. In particular, endocardial flow fell to 20% of its pre‐ischaemic level, with the ratio of flow to the endocardium (endo)/epicardium (epi) decreasing from ca. 1.0 to 0.4.

Hearts treated with 2 × 10−8 M PN (included in the perfusate from 30 min before ischaemia until 30 min after ischaemia) recovered 49 ± 2% of their initial, pretreatment contractile force, and following the ischaemia the endo/epi ratio was not significantly changed from the pre‐ischaemic value.

The lower PN dose (3 × 10−10 M) afforded a lesser degree of protection, contractility recovering to 29 ± 4% of the initial level, with an endo/epi ratio of 0.7 after 90 min reperfusion.

The two PN doses afforded a similar degree of protection against enzyme leakage which was in both cases significantly less than in untreated hearts.

Myocardial ATP and creatine phosphate content was markedly reduced by the ischaemic episode. Neither PN dose modified this depletion.

These results suggest that whilst cardiodepression may well offer protection against ischaemic damage, this is not the sole mechanism wherby PN (and possibly other calcium antagonists) can protect the heart. Preservation of blood flow to the inner layers of the left ventricular wall is likely to be one of the major factors underlying the enhanced recovery shown by PN.
Actions of ATP and α,β‐methylene ATP on neuromuscular transmission and smooth muscle membrane of the rabbit and guinea‐pig mesenteric arteries
Authors: Ishikawa Shiro
Published: July 2012

In the rabbit mesenteric artery, adenosine triphosphate (ATP), showed two actions on the membrane potential of muscle cells: low concentrations (1–10 μM) hyperpolarized and high concentrations (> 50 μM) depolarized the membrane. Both changes in the potential were accompanied by increases in ionic conductance.

In the rabbit mesenteric artery, α,β‐methylene ATP (MeATP), (> 30 nM) depolarized the muscle membrane at a lower concentration than ATP (> 50 μM), and increased the ionic conductance of the membrane. The depolarization induced by ATP was prevented by low concentrations of MeATP, but the hyperpolarization was retained. Furthermore, the hyperpolarization was not affected by theophylline (10 μM).

In the guinea‐pig mesenteric artery, ATP and MeATP depolarized and increased the ionic conductance of muscle membrane, but to depolarize the membrane, higher concentrations of both agents were required, compared to those in the rabbit mesenteric artery.

In the mesenteric arteries from both species, perivascular nerve stimulation evoked excitatory junction potentials (e.j.ps). In both tissues, MeATP inhibited the amplitude of e.j.ps at lower concentrations than did ATP, and both agents had more potent inhibitory actions on rabbit than on guinea‐pig. The inhibition of e.j.p. induced by low concentrations of these agents showed no relationship to depolarization, but the inhibition induced by high concentrations was paralleled by depolarization and increase in ionic conductance of the membrane.

In the rabbit mesenteric artery, overflow of noradrenaline (NA) and its metabolite (3,4‐dihydroxyphenylglycol; DOPEG) produced by perivascular nerve stimulation was examined. ATP (0.1 mM) but not MeATP (0.1 μM) reduced the overflow of NA, whereas both agents had no effect on the overflow of DOPEG.

Exogenously applied high concentrations of NA (> 3 μM) depolarized the muscle membrane in both species. These NA‐induced depolarizations were not affected by treatment with ATP or MeATP.

It is concluded that, in the rabbit mesenteric artery, ATP is more likely to be involved in generation of e.j.ps than is NA. A similar interpretation in the guinea‐pig mesenteric artery is complicated by the depolarization produced by high concentrations of ATP or MeATP.
Effects of diltiazem on electrical responses evoked spontaneously or by electrical stimulation in the antrum smooth muscle cells of the guinea‐pig stomach
Authors: Ishikawa Shiro , Komori Kimihiro , Nagao Tetsuhiko , Suzuki Hikaru
Published: July 2012

In circular smooth muscle cells of the guinea‐pig stomach (antrum), diltiazem (10−6 − 10−5 M) blocked the overshooting spike potential generated either spontaneously or by electrical stimulation in the presence of 2 mM tetraethylammonium chloride, but did not block the slow wave and the abortive spike potential.

The membrane was depolarized by high concentrations of diltiazem (more than 3 × 10−6 M), and this depolarization was associated with an increase in the membrane resistance.

The interval between slow waves was shortened to about 0.90 times the control (14.7 s) by 10−5 M diltiazem.

Transmural nerve stimulation evoked an inhibitory junction potential (i.j.p.) and enhanced the subsequently generated slow wave. Tetrodotoxin (3 × 10−7 M) blocked both responses but atropine (10−6 M) blocked only the latter.

Diltiazem (more than 10−6 M) increased the amplitude of the i.j.p. and depressed the enhancement of the slow wave produced by transmural nerve stimulation, presumably due to depolarization of the membrane. The latency for the i.j.p. remained the same in the presence of diltiazem (10−5 M).

It is concluded that in the guinea‐pig stomach, diltiazem blocks Ca‐influx during the generation of the overshooting spike potential, but not the Ca‐influx related to generation of the abortive spike potential or the slow wave. The cholinergic excitatory and the non‐adrenergic, non‐cholinergic inhibitory transmission may not be much affected by diltiazem.
The effects of adrenoceptor agonists and antagonists on plasma potassium concentration in anaesthetized guinea‐pigs, rabbits and rats
Authors: Coats Rachel A.
Published: July 2012

An intravenous K+‐sensitive electrode has been used to monitor plasma [K+] changes induced by α‐ and β‐adrenoceptor agonists in anaesthetized guinea‐pigs, rabbits and rats. The effects of phentolamine and propranolol on these responses were studied.

In the guinea‐pig both α‐ and β‐adrenoceptor agonists produced a biphasic response consisting of an initial rapid increase in [K+] which was followed, within 1 min, by a fall below baseline. The antagonist studies indicated that in this species both phases of the response could be elicited by either α‐or β‐adrenoceptor activation.

In the rabbit the responses were both slower and smaller than those seen in the guinea‐pig and required larger agonist doses. In addition it was found that the increase in plasma [K+] was α‐adrenoceptor‐mediated while the subsequent fall was seen only with β‐adrenoceptor activation.

In the rat triphasic changes in plasma [K+] were seen consisting of an initial decrease which was α‐adrenoceptor‐mediated, followed by an increase and then a second fall which was elicited by β‐adrenoceptor stimulation. The increase in plasma [K+] was only slightly reduced by either α‐ or β‐adrenoceptor antagonists.

Apamin, a toxin from bee venom which blocks Ca2+‐activated K+‐channels, was found to block the hyperkalaemic phase of the response in the guinea‐pig and rabbit but had no effect in the rat.

It is concluded that there are marked species differences in the effects of adrenoceptor agonists on plasma [K+] in vivo.1
Cholinesterase activity and exposure time to acetylcholine as factors influencing the muscarinic inhibition of [3H]‐noradrenaline overflow from guinea‐ pig isolated atria
Authors: Fuder H. , Muscholl E. , Wolf K.
Published: July 2012

Guinea‐pig isolated atria were incubated and loaded with [3H]‐noradrenaline. The release of 3H and of [3H]‐noradrenaline was induced by field stimulation (6–9 trains of 150 pulses at 5 Hz). The stimulation‐evoked overflows of 3H and of [3H]‐noradrenaline were determined.

In the absence of an inhibitor of acetylcholinesterase, acetylcholine (12 min preincubation before nerve stimulation, up to 10 μM) failed to inhibit the evoked [3H]‐noradrenaline overflow. In the presence of atropine, an increase by acetylcholine of evoked release was observed in the same atria. In contrast, the selective muscarinic agonist methacholine significantly decreased the evoked overflow. The inhibition was antagonized by atropine. Methacholine did not enhance release in the presence of atropine.

When present for only 2 min, acetylcholine 10 μM inhibited the evoked overflow and no facilitation of release was observed in the presence of atropine.

In the presence of physostigmine, acetylcholine (12 min preincubation, 1 and 10 μM) inhibited evoked [3H]‐noradrenaline overflow, but the overflow was increased by acetylcholine 10 μM in the presence of atropine.

In the presence of cocaine, corticosterone, phentolamine, propranolol and hexamethonium together, acetylcholine 1 μM inhibited the evoked [3H]‐noradrenaline overflow. The inhibition was significantly enhanced in the presence of physostigmine. It decreased with preincubation time of the agonist, despite the presence of physostigmine and constant replacement by new drug. Neither inhibition nor facilitation of evoked release was observed in the presence of atropine.

It is concluded that a muscarinic inhibition by acetylcholine (upon prolonged exposure time) may be masked by a concomitant facilitation of release and/or desensitization of the muscarinic inhibitory mechanism. Furthermore, degradation by acetylcholinesterase contributes in part to the ineffectiveness of acetylcholine as a presynaptic inhibitor. When a distortion of the overflow/release ratio was excluded, adrenergic and nicotinic effects were prevented, and acetylcholinesterase was inhibited, the fading of muscarinic inhibition by acetylcholine may have been exclusively due to a slow and moderate desensitization of the presynaptic muscarinic mechanism.
Relationship between the stereoselective negative inotropic effects of verapamil enantiomers and their binding to putative calcium channels in human heart
Authors: Ferry D.R. , Glossmann H. , Kaumann A.J.
Published: July 2012

Ventricular preparations from patients with mitral disease and hypertrophic obstructive cardiomyopathy (HOCM) were set up to contract isometrically. Ventricular membrane particles were also prepared and putative calcium channels were labelled with [3H]‐nimodipine.

Positive staircase was induced by varying the rate of stimulation of isolated strips from 6 min−1 to 120 min−1 in the presence of 6–60 μm (—)‐adrenaline or (—)‐noradrenaline. (—)‐Verapamil 3–5 μm or (+)‐verapamil 20–30 μm reversed the force‐frequency relationship (i.e. caused negative staircase) in preparations from patients with mitral disease or HOCM.

In subendocardial strips of ventricular septum from 5 patients with HOCM paced at 60 min−1, both (—)‐verapamil and (+)‐verapamil caused cardiodepression. Half‐maximal cardiodepression was observed with 0.4 μm (—)‐verapamil and with 3 μm (+)‐verapamil.

[3H]‐nimodipine bound to ventricular membrane particles in a saturable, reversible fashion to a high affinity site with an equilibrium dissociation constant of 0.23 nm. The density of these sites was 95 fmol mg−1 of membrane protein. Binding of the tritiated 1,4‐dihydropyridine was stereoselectively inhibited by 1,4‐dihydropyridine enantiomers and nifedipine.

(—)‐Verapamil and (+)‐verapamil inhibited high affinity [3H]‐nimodipine binding in a negative heterotropic allosteric manner with (—)‐verapamil being 5 times more potent than (+)‐verapamil on an IC50 basis. At a given [3H]‐nimodipine concentration, (+)‐verapamil inhibited a greater fraction of specific [3H]‐nimodipine binding.

The allosteric mode of (+)‐verapamil inhibition of [3H]‐nimodipine binding was confirmed by kinetic studies. (—)‐Verapamil shifted (+)‐verapamil‐binding inhibition curves to the right in an apparently competitive fashion.

The inversion of staircase caused by both verapamil enantiomers suggests that they cause a use‐dependent channel blockade. The similar potency ratios for binding and for cardiodepression are indicative of a common locus of action for both verapamil enantiomers within the calcium channel.
Characterization of pre‐ and postsynaptic actions of (—)‐baclofen in the guinea‐pig hippocampus in vitro
Authors: Inoue Masumi , Matsuo Tadashi , Ogata Nobukuni
Published: July 2012

The effects of (—)‐baclofen on evoked potentials in the hippocampus were examined through intracellular recordings from guinea‐pig brain slices.

The evoked responses were recorded in two fibre connections within the hippocampus: the Schaffer collateral/commissural‐CA1 pyramidal cell, and the mossy fibre—CA3 pyramidal cell.

The Schaffer collateral/commissural‐CA1 response was suppressed by (—)‐baclofen in concentrations over 2 × 10−5m, whereas (+)‐baclofen, an inactive isomer, in a concentration of 10−4m had no effect on the response.

A compound action potential of Schaffer collateral/commissural axons was unaffected by (—)‐baclofen even at 10−4m, a concentration that almost completely depressed the evoked response in the CA1 pyramidal cell.

The mossy fibre—CA3 response was not inhibited by (—)‐baclofen (10−4m).

The depressant action of (—)‐baclofen on the Schaffer collateral/commissural—CA1 response was unaffected by bicuculline (10−4m), whereas the direct membrane effects of (—)‐baclofen were antagonized by bicuculline (10−5m).

It is suggested that (—)‐baclofen may modulate neuronal transmission through presynaptic recognition sites possibly by decreasing transmitter release from nerve terminals and also may directly regulate the endogenous neuronal excitability through an activation of the postsynaptic recognition sites.
Responses of the pig isolated renal artery to transmural electrical stimulation and drugs
Authors: Ferguson D.R. , Johnson B.I. , Price N.
Published: July 2012

Pig isolated renal arteries contract in response to addition of noradrenaline, 5‐hydroxytryptamine, histamine, angiotensin II, vasopressin and carbachol, whereas cholecystokinin, adenosine, and inosine produce relaxation.

Transmural stimulation of the tissue causes contraction of circular muscle in the arterial wall which produces apparent elongation of the vessel.

The effects of transmural stimulation are partially blocked by prazosin and potentiated by propranolol, indicating that noradrenaline acts through both α‐ and β‐adrenoceptors.

Guanethidine (10−5m) reduces the size of responses to transmural stimulation in the presence of both prazosin (10−6m) and propranolol (10−7m).

Both saralasin (10−7 m), and desensitization of angiotensin II receptors by prolonged contact with the peptide, produced a reduction in response to transmural stimulation, indicating that angiotensin II may be involved in neurotransmission. This effect was blocked by tetrodotoxin.

Transmural stimulation produces relaxation of renal arteries in the presence of maximal doses of saralasin, prazosin, and propranolol, suggesting that a third unidentified substance is also released from autonomic nerves.
On the type of receptor involved in the inhibitory action of adenosine at the neuromuscular junction
Authors: Ribeiro J. A. , Sebastião A.M.
Published: July 2012

The effects of adenosine and adenosine analogues (1‐N6‐phenylisopropyladenosine (1‐PIA), d‐N6‐phenylisopropyladenosine (d‐PIA), N6‐cyclohexyladenosine (CHA), N6‐methyladenosine, 5′‐N‐ethyl‐carboxamide adenosine (NECA) and 2‐chloroadenosine) on evoked endplate potentials (e.p.ps) and on twitch tension were investigated in innervated sartorius muscles of the frog.

Adenosine and its analogues decreased, in a concentration‐dependent manner, the amplitude of both the e.p.ps and the twitch responses evoked by indirect stimulation. The order of potencies in decreasing twitch tension was: 1‐PIA, CHA, NECA > 2‐chloroadenosine > d‐PIA > n6‐methyladenosine, adenosine. 1‐PIA was about ten fold more potent than d‐PIA.

None of the adenosine analogues tested affected the twitch responses of directly stimulated tubocurarine‐paralyzed muscles.

In concentrations that did not modify neuromuscular transmission, theophylline and 8‐phenylth‐eophylline (8‐PT) but not isobutylmethylxanthine (IBMX), antagonized the inhibitory action of 2‐chloroadenosine at the neuromuscular junction. 8‐PT behaved as a competitive antagonist and was about forty fold more potent than theophylline.

It is concluded that the R‐type adenosine receptor at the neuromuscular junction should not be classified in the A1/A2 system. The possibility of calcium‐linked adenosine receptors having pharmacological profiles distinct from those originally defined as modulating adenylate cyclase is discussed.
Effects of Bay K 8644 on contraction of the human isolated bronchus and guinea‐pig isolated trachea
Authors: Advenier Charles , Naline Emmanuel , Renier Annick
Published: July 2012

The effects of Bay K 8644, a dihydropyridine which increases calcium flux through the potential‐operated channels were studied on the contractions induced by histamine, acetylcholine, KCl and Ca2+ on human isolated bronchial strips and the results were compared to those obtained on guinea‐pig isolated tracheal spirals. Subsequently the contractant effects of Bay K 8644 in K+‐enriched medium and in the presence of Ca2+ 0.03 mM were investigated.

In Krebs normal calcium medium, Bay K 8644 did not significantly modify the EC50 of acetylcholine or histamine on the human bronchus, but in concentrations of 10−7 − 10−6 M it potentiated the effects of KCl on that preparation. It did not modify the EC50 of acetylcholine, histamine or KCl on the guinea‐pig trachea.

In Ca2+‐free Krebs medium with additional K + (30 mM), Ca2+ concentration‐response curves were displaced to the left by Bay K 8644 in the two preparations. Shifts were 0.52 ± 0.11 and 0.72 ±0.16 log units respectively with Bay K 8644 10−8 and 10−7 M on human bronchus (n = 4) and 0.67 ± 0.16 and 1.06 ± 0.19 log units respectively with Bay K 8644 10−7 and 10−6 M on the guinea‐pig trachea (n = 5).

In Krebs medium with Ca2+ 0.03 mM and K+ 30 mM, Bay K 8644 (10−8 to 10−6 M) contracted both the human bronchus and the guinea‐pig isolated trachea. This effect was competitively antagonized by nicardipine.

These results demonstrate the presence of dihydropyridine sites of action on human bronchus and confirm the minor role played by Ca2+ influx through potential‐operated channels in the contractile effects of acetylcholine or histamine. They also demonstrate the similar reactivity of human bronchus and guinea‐pig isolated trachea to Bay K 8644.
Comparison of the effects of BRL 34915 and verapamil on electrical and mechanical activity in rat portal vein
Authors: Hamilton T.C. , Weir Sheila W. , Weston A.H.
Published: July 2012

The effects of the novel anti‐hypertensive agent BRL 34915, (±) 6‐cyano‐3,4‐dihydro‐2,2‐dimethyl‐trans‐4‐(2‐oxo‐1‐pyrrolidyl)‐2H‐benzo[b]pyran‐3‐ol, have been compared with those of verapamil on rat isolated portal vein.

BRL 34915 produced a concentration‐dependent reduction in mechanical responses to noradrenaline but had relatively little inhibitory effect on K+‐induced contractions. Verapamil reduced the magnitude of both noradrenaline and K+‐induced mechanical responses.

BRL 34915 delayed the appearance of the reduced noradrenaline contractions, a property not shared by verapamil.

BRL 34915 abolished spontaneous electrical and mechanical discharges and hyperpolarized the portal vein cells close to their calculated potassium equilibrium potential. Verapamil inhibited spontaneous electrical and mechanical discharges, effects associated with a small depolarization.

BRL 34915 produced a significant increase in the 86Rb efflux rate coefficient whilst verapamil was without effect on this parameter.

The inhibitory effects of BRL 34915 were rapid in onset and readily reversible by washing, whilst those of verapamil were slower in onset and only slowly reversible.

It is concluded that the inhibitory effects of BRL 34915 in rat portal vein are produced by the opening of potassium channels in the smooth muscle cells. This inhibits spike activity and in sufficient concentration holds the membrane potential at or close to the potassium equilibrium potential, thereby reducing the effects of excitatory agents.
The effect of clonidine on venous haemodynamics in cats and dogs
Authors: Bentley G.A. , Cullen L.K. , Reynoldson J.A. , Widdop R.E.
Published: July 2012

Experiments were undertaken to investigate a possible action of clonidine on venous haemodynamics, using cats and dogs with autoperfused hindquarters. This provided an arterial input to the region independent of cardiac output. Venous capacitance in the hindquarters was indicated by blood flow in the abdominal vena cava, as measured by an electromagnetic flow probe around this vessel.

It was found that in both cats and dogs, clonidine given intravenously (5 μg kg−1 i.v.) or into the cisterna magna (1 μg kg−1 i.c.m.) reduced mean arterial pressure and heart rate, but did not decrease hindquarter perfusion pressure. With the exception of dogs given i.v. clonidine, this drug caused a decrease in inferior vena cava (IVC) blood flow and this closely paralleled the hypotensive effect. However, when clonidine was given i.v. to dogs, the decrease in IVC blood flow preceded the hypotension. At the doses used, the reduction in IVC blood flow was larger following i.v. than i.c.m. clonidine in both species, and in all cases, it remained below control levels for at least 30 min, in spite of the constant arterial input to the region.

In cats, dose‐response curves were constructed to noradrenaline and adrenaline given into the perfusion circuit (i.a.) before and after clonidine. Following i.v. and i.c.m. clonidine, there was a selective depression of the venoconstrictor actions of the catecholamines, but no change in the arterial pressor action.

Radiographic and latex studies in the dog and cat respectively were performed in order to visualize collateral blood flow that could account for the persistent decreases in IVC blood flow. In both species, intraspinal collateral flows were demonstrated which returned blood to the heart after ligation of the inferior vena cava below the renal veins. However, it was not possible to demonstrate radiographically any changes produced by clonidine in the collateral flow because of technical difficulties.

These results suggest that clonidine causes a selective reduction in sympathetic tone to the veins that is mediated at least partly by a central action, as well as an expansion of the collateral venous routes. This, together with the selective impairment of venoconstrictor responses to both noradrenaline and adrenaline, may account for the decrease in cardiac output that is most often reported following clonidine.
Effects of Bay K 8644 and nifedipine on femoral arteries of spontaneously hypertensive rats
Authors: Aoki Kyuzo , Asano Masahisa
Published: July 2012

Vasoconstrictor effects of Bay K 8644 (an agonist known to increase Ca2+ influx through the voltage‐dependent Ca2+ channels) on femoral arteries of 6 week old spontaneously hypertensive rats (SHR) were investigated, and data compared with findings in age‐matched normotensive Wistar‐Kyoto rats (WKY).

The addition of Bay K 8644 (1 × 10−10 − 3 × 10−7 M) elicited a dose‐dependent contraction in SHR femoral artery in the absence of any contractile agent. Maximum contraction induced by this agonist was the same as the maximum induced by either K+‐depolarization or α‐adrenoceptor stimulation.

Bay K 8644 was less effective in eliciting a contraction in the WKY femoral artery.

Increased sensitivity to K+ was also observed in the SHR femoral artery. In contrast, contractions in response to α‐adrenoceptor stimulation were the same in the SHR as those in the WKY.

The addition of nifedipine, a Ca2+ channel antagonist, to an unstimulated preparation produced a dose‐dependent relaxation in femoral arteries from SHR, but not from WKY. When the arteries were contracted with 60 mM K+, nifedipine produced similar relaxations in the SHR as those in the WKY, suggesting that the Ca2+ channels in the SHR femoral arteries are more activated than those in the WKY femoral arteries.

Contractile responses of SHR femoral arteries to Bay K 8644 were antagonized competitively by nifedipine.

Contractile responses to Ca2+ determined in K+‐depolarized strips were also antagonized competitively by nifedipine. However, Schild plot analysis clearly demonstrated a different pA2 value for nifedipine, suggesting that there may be a difference in the state of voltage‐dependent Ca2+ channels in SHR femoral artery between the stimulation with Bay K 8644 and K+‐depolarization.
A comparison of the binding of σ opioids and phencyclidine, and the interaction with antipsychotic drugs in rat brain membranes
Authors: Downes C.P. , Lewis P.E. , Stone M.A.
Published: July 2012

The present study investigates the relationship between binding at the s̀ site labelled by the prototypic s̀ ligand (+)‐[3H]‐N‐allylnormetazocine ((+)‐[3H]‐SKF10,047) and binding at the phencyclidine (PCP) site labelled by [3H]‐phencyclidine in rat whole brain membranes.

(+)‐[3H]‐SKF10,047 bound with a KD of 251 ± 66 nM. [3H]‐PCP bound with a KD of 180 ± 35 nM (KD ± asymptotic s.e.).

The potencies of a range of compounds to displace these ligands were only poorly correlated (r = 0.3). Furthermore selective displacement of (+)‐[3H]‐SKF10,047 but not of [3H]‐PCP was demonstrated using the non‐selective dopamine ligand haloperidol and the dopamine2‐selective ligand 3‐(3‐hydroxyphenyl)N‐n‐propylpiperidine (3PPP). These results indicate that the s̀ and PCP sites are different entities.

The relationship between binding at the s̀ site and dopamine receptors was investigated in rat whole brain membranes and in striatal membranes.

(±)‐SKF10,047 displaced [3H]‐haloperidol bound to whole brain membranes with a greater potency than it displaced [3H]‐haloperidol bound to striatal membranes. The opposite was true for the dopamine antagonist, clozapine, which showed greater potency in striatal membranes.

Comparison of [3H]‐haloperidol binding in whole brain and striatum gave only a poor correlation (r = 0.6). Hence, different binding sites would appear to exist in these brain regions, the binding of [3H]‐haloperidol to whole brain being predominantly to s̀ sites and the binding to striatum being predominantly to dopamine receptors.
Autonomic responses of the isolated, innervated trachea of the guinea‐pig: interaction with autonomic drugs, histamine and 5‐hydroxytryptamine
Authors: McCaig Dorothy J.
Published: July 2012

Intraluminal pressure was measured in the isolated, fluid‐filled trachea of the guinea pig, with autonomic innervation on the right side intact. Increases or decreases in intraluminal pressure reflected excitatory or inhibitory responses respectively, in the tracheal smooth muscle.

Stimulation of the cervical vagus nerve evoked a cholinergic excitatory response. After cholinergic blockade with atropine, a non‐adrenergic, non‐cholinergic inhibitory response was obtained.

Stimulation of the cervical sympathetic trunk, or stellate ganglion, evoked β‐adrenergic inhibitory responses. In the presence of propranolol, sympathetic stimulation evoked α‐adrenergic excitatory responses which were of low amplitude (< 5% of cholinergic excitatory responses). In the presence of phentolamine but not prazosin, β‐adrenergic inhibitory responses were potentiated.

Neostigmine potentiated responses to vagal stimulation, increasing the amplitude and duration of response. At higher concentrations neostigmine (i) raised intraluminal pressure, a response blocked by atropine, and (ii) attenuated sympathetic inhibitory responses, an effect largely blocked by atropine.

Histamine increased intraluminal pressure and this response was attenuated by atropine. In the presence of histamine, vagal excitatory responses were attenuated. Sympathetic inhibitory responses at low frequencies of stimulation (up to 10 Hz) were inhibited by histamine.

5‐Hydroxytryptamine (5‐HT) increased intraluminal pressure also, an effect partially blocked by atropine. 5‐HT had no effect on vagal excitatory responses. Like histamine, 5‐HT attenuated sympathetic inhibitory responses at lower frequencies of stimulation.
A comparison of the effects of three substance P antagonists on tachykinin‐stimulated [3H]‐acetylcholine release in the guinea‐pig ileum
Authors: Featherstone R.L. , Fosbraey P. , Morton I.K.M.
Published: July 2012

The potencies of three tachykinin antagonists [D‐Pro4,D‐Trp7,9,10]SP(4–11), [D‐Arg1,D‐Pro2,D‐Trp7,9,Leu11]SP(1–11) and [D‐Arg1,D‐Trp7,9,Leu11]SP(1–11) (spantide) against eledoisin were examined in the guinea‐pig ileum myenteric plexus, where a continuous superfusion system was employed to examine evoked release of [3H]‐acetylcholine ([3H]‐ACh]); effects on mechanical activity of the preparations were also measured.

Eledoisin was chosen as the standard tachykinin agonist since the rank order of potency observed in evoking release was eledoisin, kassinin, substance P, physalaemin; on this basis is may be presumed that an ‘SP‐E’ type receptor was involved in the release process.

The two undecapeptide antagonists both significantly reduced the response to eledoisin (10 nM) as assessed by both [3H]‐ACh release and mechanical activity which under these conditions was largely dependent on ACh release, and the response levels could be restored by increasing the concentration of eledoisin to 100 nM. The pA2 values for the two antagonists were estimated as 5.3 for [D‐Arg1,D‐Pro2,D‐Trp7,9,Leu11]SP(1–11) and 5.2 for [D‐Arg1,D‐Tip7,9,Leu11]SP(1–11). [D‐Pro4,D‐Trp7,9,10]SP(4–11) was markedly less potent with a pA2 value of < 4.8.

All three antagonists possessed considerable inherent stimulatory activity as measured both by [3H]‐ACh release and mechanical activity, [D‐Pro4,D‐Trp7,9,10]SP(4–11) being the most active in this respect, a 10 μM concentration producing 50% of the response seen with 10 nM eledoisin.

These findings are discussed both in relation to tachykinin receptor classifications and limitations in the use of such antagonists in the study of the role of tachykinins in neurotransmission.
Dermorphin analogues containing D‐kyotorphin: structure‐antinociceptive relationships in mice
Authors: Kisara Kensuke , Sakurada Shinobu , Sakurada Tsukasa , Sasaki Yusuke , Sato Takumi , Suzuki Kenji , Watanabe Hiromi
Published: July 2012

The antinociceptive effects of synthetic dermorphin and its analogues containing D‐Arg in position 2 injected into the lateral cerebroventricle were examined in conscious mice.

Intracerebroventricular (i.c.v.) administration of dermorphin and [D‐Arg2] dermorphin produced potent and long‐lasting antinociceptive activity as assayed by the tail‐pressure test.

Dermorphin and [D‐Arg2] dermorphin were 210 and 52 times more potent than morphine, respectively.

The antinociceptive effects produced by these heptapeptides were antagonized by a low dose (0.5 mg kg−1, i.p.) of the opioid antagonist naloxone.

The ED50 values for [D‐Arg2] dermorphin (1–6), (1–5) and (1–4) were not significantly different from that for [D‐Arg2] dermorphin. The potency of the shortest fragment, [D‐Arg2] dermorphin (1–2) was found to possess a severely reduced activity, whilst [D‐Arg2] dermorphin (1–3) maintained activity and was 10 times more potent than morphine.

[D‐Arg2] dermorphin analogues showed almost identical effects when tested on the electrically‐induced contractions of the guinea‐pig isolated ileum.

These results led us to conclude that the presence of the N‐terminal tripeptide in the structure of [D‐Arg2] dermorphin is of crucial importance for the manifestation of the full intrinsic opioid‐like antinociceptive activity of [D‐Arg2] dermorphin, which is presumably mediated through opioid receptors in the brain.
The role of endothelial and non‐endothelial prostaglandins in the relaxation of isolated blood vessels of the rabbit induced by acetylcholine and bradykinin
Authors: Förstermann Ulrich , Hertting Georg , Neufang Brigitte
Published: July 2012

Strips of rabbit extrapulmonary, coeliac and mesenteric arteries were mounted in organ baths for isotonic recording of changes in tissue length. The formation by the strips of the vasodilator prostaglandins PGI2 (measured as 6‐keto‐PGF1α) and PGE2 was determined by specific radioimmunoassays.

Removal of vascular endothelium initially increased and then permanently decreased the basal prostaglandin release of the tissues.

Acetylcholine (ACh) relaxed strips of all three arteries if the endothelium was intact. ACh also stimulated the formation of PGI2 and PGE2 from all three tissues; about 60% of these prostaglandins originated from endothelial cells. Indomethacin caused complete inhibition of prostaglandin formation and a slight inhibition of the ACh‐relaxation (not statistically significant). Complete inhibition of the ACh relaxation was achieved with nordihydroguaiaretic acid (NDGA). NDGA also partially inhibited prostaglandin formation. These data suggest that in blood vessels that are also prostaglandin‐sensitive, the ACh relaxation is predominantly mediated by a non‐prostaglandin endothelium‐derived relaxing factor.

Bradykinin was more potent that ACh in releasing prostaglandins from the same arteries. This release was activated in subendothelial components of the vascular wall. Neither this prostaglandin release nor the bradykinin‐induced relaxations were significantly reduced in endothelium‐denuded arteries. Indomethacin completely blocked the bradykinin‐induced prostaglandin release and the bradykinin relaxation. NDGA caused a moderate inhibition of the bradykinin‐induced prostaglandin release and slightly attenuated the bradykinin relaxation (neither effect of NDGA was statistically significant).

Under all experimental conditions (control, indomethacin, NDGA) and with all three arteries there was a good correlation between the bradykinin‐induced prostaglandin release and the respective mechanical response. No such correlation could be found for ACh.

Prostaglandin‐dependent relaxations of the coeliac and mesenteric artery are probably mediated by endogenous PGI2. The extrapulmonary artery is rather insensitive to PGI2 and is probably relaxed mainly by endogenous PGE2.
Adrenoceptor blocking properties of atropine‐like agents anisodamine and anisodine on brain and cardiovascular tissues of rats
Authors: Varma D.R. , Yue T.L.
Published: July 2012

The cholinoceptor antagonists anisodamine and anisodine are widely used in the People's Republic of China for the management of acute circulatory shock but the mechanism of their beneficial effects is not fully known; we therefore investigated if these agents possessed adrenoceptor blocking properties.

The antagonistic effect of anisodamine and anisodine against the specific binding of the α1‐adrenoceptor ligand [3H]‐WB‐4101 to cardiac and brain tissue membrane preparations and against the effects of phenylephrine on isolated aortic strips and left atria of rats were compared with classical muscarinic receptor and adrenoceptor blocking agents.

Both anisodamine and anisodine possessed α1‐adrenoceptor blocking properties; the order of potency of various agents in displacing the binding of [3H]‐WB‐4101 to receptors and in antagonizing the effects of phenylephrine on aortic strips and left atria was: prazosin > atropine > anisodamine > scopolamine > anisodine.

It is concluded that both anisodamine and to a lesser extent anisodine possess α‐adrenoceptor blocking properties; this antagonistic activity of anisodamine may contribute to its salutary effects on the microcirculation. However, it is unlikely that anisodine produces a significant adrenoceptor blockade in the clinically used dose‐range.
Autoradiographic analysis of the distribution of β‐adrenoceptors in the dog splenic vasculature
Authors: Lipe Suzanne , Summers Roger J.
Published: July 2012

The technique of in vitro labelling and autoradiography has been used to localize β‐adrenoceptors in sections of the splenic vascular bundle of the dog.

Binding of (−)‐[125I]‐cyanopindolol (Cyp) to sections of splenic vascular bundle equilibrated within 150 min and slowly dissociated after addition of (−)‐propranolol. The process was saturable with a dissociation constant (KD) of 40.3 ± 4.4 pM and Bmax of 18.9 ± 1.7 fM (in 6 sections).

Binding to sections was stereoselective, the (−)‐isomer of propranolol being 90 times more effective than the (+)‐isomer in competing for (−)‐[125I]‐Cyp binding.

Delineation of β‐adrenoceptor subtypes using the selective antagonists betaxolol (β1) and ICI 118,551 (β2) indicated that the receptors present were almost exclusively of the β2‐subtype.

Autoradiographic studies under the conditions evaluated in the biochemical experiments showed that β‐adrenoceptors are unevenly distributed in the dog splenic vein, artery and associated nerve bundles. High concentrations of receptors are associated with the splenic nerves and lower but still significant concentrations in the vasculature.

Higher resolution studies with nuclear emulsion coated coverslips revealed concentrations of β‐adrenoceptors over cells adjacent to the lumen in veins. In arteries most β‐adrenoceptors were found associated with the medial layer with fewer receptors towards the intima or adventitia. Serial sections of either artery or vein incubated with (−)‐[125I]‐Cyp in the presence of (−)‐propranolol showed low levels of non‐localized binding.
The effects of Bay K 8644 and nifedipine on the neural responses of the rabbit ear artery
Authors: Cheung D.W. , MacKay M.J.
Published: July 2012

The effects of Bay K 8644 and nifedipine on the electrical and mechanical responses of the distal ear artery of the rabbit to stimulation of the perivascular nerves were studied.

Neural stimulation elicited excitatory junction potentials (e.j.ps) in the smooth muscle cells of the artery. An action potential was generated when the e.j.p. reached a threshold of about − 53 mV. Contraction was always triggered by the action potential.

Bay K 8644 at low concentrations (7 × 10−8 M) had no significant effect on the resting membrane potential and the e.j.p. However the amplitudes of the action potential, and the contraction were potentiated by Bay K 8644. Multiple action potentials could also be generated from a single e.j.p.

At higher concentrations, Bay K 8644 (3 × 10−6 M) caused membrane depolarization, development of vascular tone and spontaneous action potentials. All the effects of Bay K 8644 could be reversed by exposure to light.

Nifedipine (3 × 10−7 M) inhibited the action potential and the resulting contraction. The effect of nifedipine could be reversed by Bay K 8644 but not by light.

These results demonstrate that the excitatory and inhibitory effects of Bay K 8644 and nifedipine on vascular smooth muscle are associated with changes in the electrical responses.
Isothiouronium compounds as γ‐aminobutyric acid agonists
Authors: Allan Robin D. , Dickenson Helena W. , Hiern Barry P. , Johnston Graham A.R. , Kazlauskas Rymantas
Published: July 2012

Analogues of γ‐aminobutyric acid (GABA) incorporating an isothiouronium salt as a replacement for a protonated amino functional group have been investigated for activity on: GABA receptors in the guinea‐pig ileum; [3H]‐GABA and [3H]‐diazepam binding to rat brain membranes; and GABA uptake and transamination.

For the homologous series of α‐isothiouronium alkanoic acids, maximum GABA‐mimetic activity was found at 3‐[(aminoiminomethyl)thio]propanoic acid.

Introduction of unsaturation into this compound gave two isomeric conformationally restricted analogues. The trans isomer was inactive at GABA receptors while the cis compound ((Z)‐3‐[(aminoiminomethyl)thio]prop‐2‐enoic acid (ZAPA)) was more potent than muscimol and GABA as a GABA agonist with respect to low affinity GABA receptor sites.

Both isomers were moderately potent at inhibiting the uptake of [3H]‐GABA into rat brain slices.

Comparison of possible conformations of the two unsaturated isomers by interactive computer graphics modelling and comparison with muscimol has led to a plausible active conformation of ZAPA, which may be a selective and potent agonist for low affinity GABA binding sites.
The effects of amiodarone on the electrocardiogram of the guinea‐pig are not explained by interaction with thyroid hormone metabolism alone
Authors: Stäubli M. , Studer H.
Published: July 2012

The iodine‐containing contrast medium iopanoic acid induces alterations of thyroid hormone metabolism comparable to those observed with the iodine‐containing antiarrhythmic drug amiodarone. Both compounds inhibit the intracellular conversion of thyroxine (T4) to triiodothyronine (T3). Using iopanoic acid, the question was investigated, in guinea‐pigs, whether inhibition of T4→T3 conversion is by itself associated with the same changes in the electrocardiogram, i.e. QT prolongation and bradycardia, as those observed during amiodarone treatment.

At a dose of 4 g kg−1, iopanoic acid induced maximal inhibition of the T4→T3 conversion. Although these changes were even more pronounced than those in a control group of animals treated with 2.12 g amiodarone kg−1, neither prolongation of the QT nor a slowing of the heart rate was observed. QT prolongation and bradycardia were induced only by amiodarone treatment but not by iopanoic acid.

Iopanoic acid at the high toxic dose of 12 g kg−1 induced the same degree of inhibition of T4 → T3 conversion as the 4 g kg−1 dose. QT prolongation and slowing of the heart rate were apparent at this dose in parallel with a loss of weight.

It is concluded that even a maximal inhibition of the T4 → T3 conversion has no effect on the ECG of guinea‐pigs. The inhibition of the T4 → T3 conversion alone does not explain the QT prolongation and bradycardia observed with amiodarone treatment. The amiodarone effects on the ECG may represent a combination of interactions with thyroid hormones and antiadrenergic activity.
Neuropeptide Y: a powerful modulator of epithelial ion transport
Authors: Friel David D. , Miller Richard J. , Walker Mary W.
Published: July 2012

Neuropeptide Y (NPY) is a major gut peptide localized in the intestinal mucosa of several mammalian species. Ileal mucosa from rabbit and guinea‐pig was mounted in Ussing chambers in order to study the effect of NPY on short circuit current.

Neuropeptide Y inhibited the short circuit current when applied to the serosal side of the tissue. The maximum change in short circuit current was − 50 ± 6 μA cm−2 in the rabbit ileum and − 49 ± 14 μA cm−2 in the guinea‐pig ileum. The EC50 was 3 × 10−8 M in both species.

Pretreatment of rabbit ileum with the α2‐adrenoceptor antagonist, yohimbine (1 × 10−6 M) for 10 min did not reduce the response of the tissue to neuropeptide Y (1 × 10−7 M).

When applied serosally to rabbit ileal mucosa, the related peptide YY caused a maximum change in short circuit current of − 60 ± 13 μA cm−2; the EC50 was 2 × 10−9 M.

Isotopic flux studies in rabbit ileum showed that 1 × 10−7 M neuropeptide Y enhanced mucosal‐toserosal Na+ and Cl− fluxes and reduced serosal‐to‐mucosal Cl− flux.

Replacement of chloride with gluconate on both sides of the tissue significantly reduced the change in short circuit current produced by neuropeptide Y (1 × 10−7 M), as did a similar replacement of bicarbonate.

It is concluded that neuropeptide Y and peptide YY are the most potent neurotransmitters or hormones so far described in their ability to attenuate electrogenic transport in the small intestine.
Effects of verapamil on the response of the guinea‐pig tracheal muscle to carbachol
Authors: Baba K. , Satake T. , Takagi K. , Tomita T.
Published: July 2012

The effects of verapamil on the contraction of the guinea‐pig tracheal smooth muscle induced by calcium (Ca2+) or barium (Ba2+) were investigated in three different conditions: (a) in excess K solution, (b) in the presence of carbachol, and (c) in excess K solution containing carbachol. In order to clarify the contractions, the effects of removal and readdition of the divalent cations were also investigated.

In Ca2+‐loaded tissues, application of carbachol in Ca‐free medium produced a transient contraction, the magnitude of which decreased the longer the duration of exposure to Ca2+‐free solution.

In Ca2+‐depleted, Ba2+‐loaded tissues, application of carbachol in a Ba2+‐ and Ca2+‐free medium produced a transient contraction the magnitude of which decreased the longer the duration of exposure to the Ba2+‐ and Ca2+‐free solution.

After exposure to Ca2+‐free solution for 40 min, the sensitivity of the tissue to Ca2+ was greater in the presence of 30 μM carbachol (ED50 = 0.06 mM) than in the presence of 40 mM K+ (ED50 = 0.3 mM). The Ca2+‐sensitivity in the presence of 30 μM carbachol plus K+ (40 mM) was not different from that in the presence of 30 μM carbachol alone.

In Ca2+‐free solution, the sensitivity of the tissue to Ba2+ in the presence of 40 mM K+ (ED50 = 1.4 mM) was not different from that observed in the presence of 30 μM carbachol (ED50 = 1.3 mM).

After exposure to Ca2+‐free solution, verapamil produced a parallel rightward shift in the concentration‐response curves to added Ca2+ and Ba2+ in the presence of either 40 mM K+, 30 μM carbachol or 40 mM K+ plus 30 μM carbachol.

The pA2 values of verapamil against Ca2+ responses in the presence of 40 mM K+, 30 μM carbachol and 40 mM K+ plus 30 μM carbachol were 7.0, 6.5 and 6.5, respectively. The pA2 values of verapamil against Ba2+ responses under these conditions were 7.1, 7.0 and 7.1, respectively.

It is concluded that the sustained contraction produced by carbachol requires the influx of Ca2+ and that Ba2+ can substitute for Ca2+ in this process. Furthermore, the ionic channels which admit Ca2+ may be modified by carbachol to different degrees depending on the presence of Ca2+ or Ba2+. Such changes alter the affinity of the channel to verapamil.
Inhibition of neutrophil activation by p‐bromophenacyl bromide and its effects on phospholipase A2
Authors: Duque Ricardo E. , Fantone Joseph C. , Kramer Craig , Marasco Wayne A. , Phan Sem H.
Published: July 2012

In an effort to elucidate the nature of the inhibitory effects of p‐bromophenacyl bromide (pBPB) on neutrophil stimulation, we have examined its effects on several stages of stimulus‐response coupling.

Pretreatment of rat neutrophils with pBPB resulted in a dose‐ and time‐dependent irreversible inhibition of both N‐formylmethionyl‐leucylphenylalanine (fMet‐Leu‐Phe)‐induced lysosomal enzyme release and change in transmembrane potential.

Inhibition of the biological responses to the chemotactic peptide f Met‐Leu‐Phe was not due to receptor inactivation since f Met‐Leu‐[3H]‐Phe binding to the formyl peptide receptor was not significantly altered by pBPB pretreatment.

Inhibition by pBPB of phorbol myristate acetate (PMA)‐induced changes in transmembrane potential and the generation of superoxide (0–2) was also observed.

pBPB treatment appeared to inhibit activation of the NADPH oxidase without a direct effect on the oxidase itself.

This inhibitory effect was not accompanied by cell death or decrease in cellular titratable sulphydryl groups (at least at doses < 20 μM).

There was, however, significant inhibition of a membranous fraction of f Met‐Leu‐Phe‐induced phospholipase A2 activity by pretreatment with 10 μM pBPB, although total cellular phospholipase A2 was only minimally (< 20% inhibition) affected.

These data would indicate that pBPB inhibits an early event associated with stimulus‐response coupling in rat polymorphonuclear leukocytes (i.e. change in transmembrane potential). The inhibitory effects of pBPB may be secondary to the inhibition of a critical membranous fraction of cell bound phospholipase A2 activity or its activation, necessary for the initiation of cell activation.