bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrical and mechanical effects of BRL34915 in guinea‐pig isolated trachealis
Authors: Allen S.L. , Boyle J.P. , Cortijo J. , Foster R.W. , Morgan G.P. , Small R.C.
Published: July 2012

BRL34915 (0.1–10 μM) suppressed the spontaneous tone of guinea‐pig isolated trachealis in a concentration‐dependent manner. BRL34915 was not antagonized by propranolol (1 μM).

In trachea where spontaneous tone was suppressed by indomethacin (2.8 μM) but subsequently restored to the same level with acetylcholine or histamine, the relaxant potency of BRL34915 was reduced.

In Krebs solution containing K+ (120 mM), isolated trachealis muscle developed near‐maximal tension. The relaxant effects of BRL34915 were virtually abolished in this medium.

Concentration‐effect curves for KCl, acetylcholine and histamine were constructed in tissues treated with indomethacin (2.8 μM). BRL34915 (10 μM) depressed the foot of the concentration‐effect curve for KCl and caused minor rightward shifts in the concentration‐effect curves of acetylcholine and histamine.

Four K+‐channel inhibitors were tested. Apamin (0.1 μM) did not modify the action of BRL34915. Tetraethylammonium (8 mM) had little effect but procaine (5 mM) and 4‐aminopyridine (5 mM) each significantly inhibited the relaxant action of BRL34915.

Intracellular electrophysiological recording showed that BRL34915 (0.1 μM) caused very minor relaxation and little, if any, electrical change. Higher concentrations (1–10 μM) evoked relaxation, suppression of spontaneous electrical slow waves and marked hyperpolarization of the trachealis cells. In the presence of TEA (8 mM) or procaine (5 mM) the hyperpolarization induced by BRL34915 was significantly reduced.

In trachealis skinned of its plasma membranes, tension development induced by Ca2+ (20 μM) was unaffected either by BRL34915 (10 μM) or by nicorandil (1 mM).

In studies of the efflux of 86Rb+ from muscle‐rich strips of trachea, BRL34915 (1 and 10 μM) increased the effux rate constant.

It is concluded that BRL34915 evokes relaxation of the trachealis by a mechanism that involves neither β‐adrenoceptor activation nor direct reduction of the sensitivity of the intracellular contractile machinery to cytosolic free Ca2+. The action of BRL34915 may depend on the opening of K+ channels in the plasma membrane which are permeable to 86Rb+. The opening of these channels, or the effects of their opening, may be reduced by K+‐channel inhibitors such as 4‐aminopyridine, procaine and TEA but not by apamin.
Effects of the calcium channel facilitator, CGP 28,392, on different modes of contraction in smooth muscle of rabbit and rat aortae and guinea‐pig taenia caeci
Authors: Karaki H. , Nagase H. , Ozaki H. , Urakawa N. , Weiss G.B.
Published: July 2012

Effects of a Ca2+ channel facilitator, CGP 28,392, on smooth muscle contractions were examined in order to delineate characteristics of Ca2+ channels in rabbit and rat aortae and guinea‐pig taenia caeci.

Application of increasing concentrations of KCl induced contractile responses in these smooth muscles and CGP 28,392 shifted the concentration‐response curve for KCl to the left. The maximum response was also increased in rat aorta and guinea‐pig taenia. CGP 28,392 also shifted the concentration‐response curves for noradrenaline in rat aorta and for histamine in taenia to the left and increased the maximum response in rat aorta. However, the corresponding curve for noradrenaline in rabbit aorta was not affected by CGP 28,392.

The sustained contractions induced by KCl were inhibited by cumulative application of verapamil in these smooth muscles. Pretreatment of the muscle with CGP 28,392 decreased the inhibitory effect of verapamil. The noradrenaline‐induced contraction in rat aorta and the histamine‐induced contraction in taenia were also inhibited by verapamil, and CGP 28,392 antagonized the effect of verapamil. The noradrenaline‐induced contraction in rabbit aorta was only slightly inhibited by verapamil, and CGP 28,392 did not modify the effect of verapamil.

In these smooth muscles, cumulative application of Ca2+ to the Ca2+‐depleted, KCl‐treated muscle induced contraction, and the concentration‐response curve for Ca2+ was shifted to the left by CGP 28,392 and to the right by verapamil. The concentration‐response curves for Ca2+ in Ca2+‐depleted, noradrenaline‐treated rabbit and rat aortae and in Ca2+‐depleted, histamine‐treated taenia were also shifted to the left by CGP 28,392 and to the right by verapamil. In some contractions, CGP 28,392 increased and verapamil decreased the maximum responses. CGP 28,392 antagonized the inhibitory effect of verapamil.

These results suggest that the Ca2+ channel facilitator, CGP 28,392, has a relatively selective activating effect on voltage‐dependent Ca2+ channels in rabbit aorta. However, it also activates receptor‐linked Ca2+ channels in rabbit aorta when Ca2+ concentrations are low. In rat aorta and guinea‐pig taenia this facilitator activates both types of Ca2+ channels.
The selectivity of the (−)‐and (+)‐forms of hyoscine methiodide and of hyoscyamine camphorsulphonate for muscarinic (M2) receptors
Authors: Barlow R.B. , Dawson Sally
Published: July 2012

The affinities of (−)‐S‐hyoscyamine (+)‐camphorsulphonate, (+)‐R‐hyoscyamine (−)‐camphorsulphonate, (−)‐S‐hyoscine methiodide and (+)‐R‐hyoscine methiodide for muscarinic acetylcholine receptors in guinea‐pig atria and ileum at 30°C and in ileum at 37°C have been measured in dose‐ratio experiments. The agonists were carbachol, arecaidine propargyl ester (APE) and ethoxyethyl trimethylammonium iodide (EOE).

The effects produced by the agonists confirmed that, relative to carbachol, arecaidine propargyl ester is more active on atria than on ileum whereas ethoxyethyl trimethylammonium iodide is more active on ileum than on atria.

There was no striking difference between estimates of affinity based on the effects of agonists on atrial size and the effects on atrial rate nor was there any striking difference between the affinities measured with the different agonists.

With the isomers of hyoscyamine there was no striking difference between the affinity for receptors in atria and those in ileum, which is consistent with the low selectivity reported for atropine (racemic hyoscyamine). (−)‐S‐Hyoscine methiodide had greater affinity for muscarinic receptors in ileum than for those in atria, though the difference is smaller than has been previously observed. (+)‐R‐Hyoscine methiodide had no detectable selectivity. The phenomenon of selectivity cannot be wholly ascribed to differences in physicochemical properties of the antagonists: the three‐dimensional structures with which the antagonists interact cannot be identical.
Inotropic effects of Ca2+ channel agonist and antagonists in neuraminidase‐treated left atria of rats
Authors: Hattori Yuichi , Hazama Setsuro , Kanno Mono , Nakao Yasuo
Published: July 2012

The effects of removal of sialic acid from cardiac sarcolemma on contractile functions and on inotropic responses to Ca2+ channel agonist and antagonists were investigated in rat left atria.

About 64% of the total sialic acid content of the left atria was removed during a 90 min exposure to neuraminidase (2 u ml−1).

The removal of sialic acid neither affected the development of twitch tension induced by stimulation at a frequency of 0.5 Hz, nor altered the interval‐dependent changes in contractility such as the force‐frequency relationship and post rest contractions.

The positive inotropic effects produced by isoprenaline, and by an increase in extracellular Ca2+ concentration were the same in the neuraminidase‐treated preparations as those in the untreated preparations. Bay K 8644, a Ca2+ channel agonist, induced an increase in conractility in the neuraminidase‐treated preparations comparable to that in the untreated ones.

Neuraminidase treatment significantly attenuated the negative inotropic effects of verapamil and diltiazem, whereas it had no effect on that of nifedipine.

The results indicate that sialic acid removal modifies neither the basal contractile functions nor the positive inotropism which is associated with an enhancement of the slow inward Ca2+ current. However, sialic acid, which constitutes the glycocalyx of the cardiac sarcolemma, may be involved in the mechanism of the Ca2+ channel antagonistic actions of verapamil and diltiazem, but not that of nifedipine. Thus, our results provide pharmacological evidence that verapamil and diltiazem behave differently from the dihydropyridine compounds.
The effects of thyroxine treatment of rats on neuronal and extraneuronal uptake and metabolism of catecholamines in the heart
Authors: Bryan Lesley J. , O'Donnell Stella R. , Williams Adrienne M.
Published: July 2012

The effects of thyroxine (T4) treatment of rats on the neuronal and extraneuronal uptake and subsequent metabolism of catecholamines in the heart were examined, to determine whether changes in the local dissipation of catecholamines might contribute to the enhanced sympathetic cardiac responses that occur when thyroid hormone levels are elevated.

T4‐treated rats were injected subcutaneously with L‐thyroxine sodium 1 mg kg−1 on days 1, 3 and 5, and controls were injected with the normal saline vehicle on the same days. The experiments on isolated, perfused hearts were carried out on day 8. The T4‐treated rats had only 50% of the growth rate of the controls and their heart weights were 18% greater than the controls. The experimental data were adjusted to allow for the increase in heart weight caused by the T4 treatment.

The initial rates of neuronal uptake of noradrenaline and of extraneuronal uptake of noradrenaline and isoprenaline in the hearts from T4‐treated rats were not significantly different from those in hearts from control rats.

The steady‐state rates of extraneuronal O‐methylation of isoprenaline and of extraneuronal deamination of noradrenaline in hearts from T4‐treated rats were not significantly different from those in hearts from control rats.

The steady‐state rate of neuronal deamination of noradrenaline was significantly lower and the accumulation of unmetabolized noradrenaline in the hearts was significantly greater in T4‐treated rats than in the controls. These findings could be explained by a decrease in neuronal monoamine oxidase activity or by an increase in intraneuronal binding of noradrenaline in hearts from T4‐treated rats. If the first of these two speculations should be correct, the changes in neuronal dissipation could contribute to cardiac supersensitivity to noradrenaline or adrenaline, since these amines are substrates for neuronal uptake. However, it could not explain cardiac supersensitivity to isoprenaline in T4‐treated rats.

The study has shown that it is unlikely that increased plasma thyroid hormone levels cause cardiac supersensitivity to catecholamines by affecting the local dissipation processes for those amines in the heart.
B‐HT 958 lowers blood pressure and heart rate in the rat through stimulation of dopamine receptors
Authors: Brown Morris J. , Harland Deborah
Published: July 2012

To investigate whether the hypotensive and bradycardiac effects of B‐HT 958 (2‐amino‐6‐(p‐chlorobenzyl)‐4H‐5,6,7,8‐tetrahydrothiazolo‐(5,4‐d) azepine) are due to the stimulation of peripheral prejunctional α2‐adrenoceptors, the selective α2‐adrenoceptor antagonist idazoxan was given either intravenously (i.v.) or intracerebroventricularly (i.c.v.) to anaesthetized rats before the administration of i.v. B‐HT 958. Plasma noradrenaline was used as an approximate index of peripheral sympathetic nervous activity.

B‐HT 958 350 μg kg−1 i.v. caused significant falls in blood pressure and heart rate which were maximal 5 min after dosing (− 29.25 ± 3.2 mmHg and − 52 ± 6.8 beats min−1 respectively, mean of all control animals). The hypotension and bradycardia were accompanied by significant falls in plasma noradrenaline concentration of 30–40%.

Idazoxan 300 μg kg−1 i.v. caused a marked, but transient tachycardia and a large sustained rise in plasma noradrenaline concentration. Idazoxan 300 μg kg−1 and 1000 μg kg−1 i.v. did not prevent B‐HT 958‐induced falls in mean arterial pressure, heart rate and plasma noradrenaline concentration. Responses to B‐HT 958 were unaffected by idazoxan 20 μg i.c.v.

B‐HT 958‐induced falls in mean arterial pressure, heart rate and plasma noradrenaline concentration were significantly attenuated by i.v. administration of the dopamine receptor antagonist, sulpiride 300 μg kg−1. Sulpiride 10 μg and 50 μg i.c.v. caused inhibition of B‐HT 958 hypotension and bradycardia similar to that of intravenous sulpiride. After i.c.v. sulpiride, B‐HT 958 did not cause a significant fall in plasma noradrenaline concentration.

A combination of idazoxan 1000 μg kg−1 i.v. and sulpiride 300 μg kg−1 i.v. did not cause further significant inhibition of B‐HT 958 hypotension and bradycardia compared with sulpiride 300 μg kg−1 i.v. alone. This combination however had a significantly greater effect in inhibiting B‐HT 958 hypotension than had idazoxan 1000 μg kg−1 alone, and almost completely blocked the B‐HT 958‐induced fall in plasma noradrenaline concentration.

These results suggest that in the anaesthetized rat the cardiovascular effects of B‐HT 958 are due to stimulation of dopamine receptors, probably located within the central nervous system, and not to stimulation of peripheral prejunctional α2‐adrenoceptors.
The mode of vasorelaxant action of 2‐ aminoisoquinoline, 1.3 (2H.4H)‐dione, a novel ‘intracellular calcium inhibitor’
Authors: Hester R.K. , Satake N. , Shibata S. , Ueda S. , Yamahara J.
Published: July 2012

In rabbit aorta, pretreatment with 2‐aminoisoquinoline, 1.3 (2H.4H)‐dione (AQ, 10−5 M and 10−4 M) shifted the concentration‐response relationship to noradrenaline (NA, 10−9 M to 10−4 M) in a parallel manner whereas the agent (10−4 M) failed to affect the response to potassium and only slightly depressed Ca2+‐induced contractions in a Ca2+‐free medium in the presence of K+ (40 mM).

Ca2+‐entry blockers such as nifedipine and diltiazem (10−6 M and 10−5 M) had very weak or no apparent effects on the response to NA but markedly attenuated or abolished the K+‐ and Ca2+‐induced contractions.

Following incubation of tissues for 15 min in a Ca2+‐free medium with low EGTA (0.01 mM) and methoxyverapamil (D600, 10−5 M), NA (3 × 10−7 M) caused a phasic (transient) contraction and the subsequent application of Ca2+ (2mM) resulted in a tonic contraction. This NA‐induced, Ca2+‐dependent, D600‐insensitive contraction was inhibited by AQ (10−5 M and 10−4 M) in a concentration‐dependent manner. This suggests that the inhibitory action of AQ may be related to Ca2+ entry through specific receptor activated pathways.

Following incubation of tissues for 30 min in a Ca2+‐free medium with high EGTA (2.0 mM), NA (10−5 M) caused a contraction of rabbit aorta which is dependent upon release of intracellular Ca2+, but the response was 50% to 60% less than that in a normal medium. This contraction was inhibited by AQ (10−5 M and 10−4 M) and nitroglycerin (10−5 M) but not by nifedipine or diltiazem. The inhibitory action of combined treatment with AQ and nitroglycerin (10−5 M) on the response to NA was not different from that of either agent alone.

These results suggest that AQ may have inhibitory actions on the release of intracellular Ca2+ and also on Ca2+‐entry through D600‐insensitive, receptor‐activated Ca2+ pathways in rabbit aorta.
α2‐Adrenergic hyperpolarization is not involved in slow synaptic inhibition in amphibian sympathetic ganglia
Authors: Rafuse Paul E. , Smith Peter A.
Published: July 2012

The adrenaline‐induced hyperpolarization (AdH), slow inhibitory postsynaptic potential (slow i.p.s.p.) and hyperpolarizing phase of the response to methacholine (MChH) in Rana pipiens sympathetic ganglia were studied by means of the sucrose‐gap technique.

Desmethylimipramine (DMI, 0.5 μM) lowered the EC50 for adrenaline from 1.65 μM (1.23–2.21 μM, n = 10) to 0.30 μM (0.21–0.41 μM, n = 8). DMI did not potentiate the slow i.p.s.p. or the MChH.

Propranolol, sotalol or prazosin (1 μM) did not antagonize the AdH. The response was antagonised by phentolamine (IC50 = 0.53 μM), yohimbine (IC50 = 6.2 nM) and idazoxan (IC50 = 0.59 μM). Yohimbine (0.1 μM) did not reduce the amplitude of the slow i.p.s.p. or the MChH.

The slow i.p.s.p. was eliminated in Ringer solution containing Cd2+ (100 μM): This concentration of Cd2+ did not reduce the amplitude of the MChH.

α‐Methylnoradrenaline produced a concentration‐dependent hyperpolarization with an EC50 of 0.31 μM (0.13–0.73 μM, n = 5), in the presence of DMI (0.5 μM).

These results are consistent with the hypothesis that the AdH may be generated by activation of a receptor similar to the mammalian α2‐adrenoceptor. No evidence was found in support of the hypothesis that an adrenergic interneurone is involved in the synaptic pathway for the slow i.p.s.p.
Attenuation by isosorbide dinitrate of coronary occlusion‐induced acidosis in the dog myocardium
Authors: Abiko Yasushi , Fukushi Yukio , Haga Naomi , Matsumura Hisao
Published: July 2012

In dogs anaesthetized with pentobarbitone, the thorax was opened and myocardial pH measured continuously by the use of a glass pH electrode inserted in the left ventricular wall.

The left anterior descending coronary artery (LAD) was partially occluded so that the LAD flow could be reduced to a half or one‐third of the original flow (partial occlusion). LAD partial occlusion was continued for 90 min, drug or saline being infused for the last 60 min of this period.

LAD occlusion decreased myocardial pH significantly by 0.41 to 0.67 pH units, and increased ST segment of the surface electrocardiogram from 11.7 to 12.1 mV.

In dogs with non‐ischaemic normal hearts, isosorbide dinitrate (ISDN; 1 mg kg−1) did not change markedly either the LAD flow, myocardial pH or heart rate, whereas it decreased myocardial contractile force (determined by a strain gauge arch) slightly and both the systolic and diastolic blood pressure markedly.

In dogs with partial LAD occlusion, ISDN (1 mg kg−1) increased myocardial pH significantly and decreased blood pressure, but did not change ST segment elevation in an epicardial lead.

These results indicate that ISDN attenuates ischaemia‐induced acidosis without attenuating ischaemia‐induced ST elevation in the dog myocardium.
Dopamine‐induced amylase secretion from rat parotid salivary gland in vitro: an effect mediated via noradrenergic and cholinergic nerves.
Authors: Hata Fumiaki , Ishida Hajime , Kondo Etsuo
Published: July 2012

The effect of dopamine on amylase secretion by rat parotid tissue was examined in vitro.

Dopamine induced marked amylase secretion from the tissue in a dose‐dependent manner. Its EC50 value was about 4 μM and the maximal response was obtained at a concentration of 100 μM.

The dopamine‐induced secretion was inhibited by the dopamine‐antagonists haloperidol, (+)‐butaclamol and spiroperidol.

Atropine reduced the dopamine‐induced secretion significantly, and physostigmine enhanced the secretion.

Parasympathectomy of the gland resulted in a significant decrease in the dopamine‐induced secretion, but did not reduce the secretion induced by dopamine with atropine.

Dopamine‐induced ACh release from parasympathetic nerve terminals in the tissue was studied in tissue preparations that had been loaded with [3H]‐choline. Dopamine elicited Ca2+‐sensitive tritium release, and dopamine antagonists or parasympathectomy prevented this release.

Sympathectomy or reserpine treatment of rats resulted in significant decrease in the dopamine‐induced secretion, but increase in noradrenaline (NA)‐ or isoprenaline‐induced secretion.

Dopamine‐induced NA release was studied by preloading the parotid tissue with [3H]‐NA. Dopamine induced Ca2+‐sensitive tritium release, and dopamine antagonists or sympathectomy prevented the release.

Several lines of circumstantial evidence strongly suggested that dopamine has a specific site for action in the parotid tissue that is independent of NA receptors.

In sympathectomized or reserpine‐treated glands, atropine completely inhibited the dopamine‐induced amylase secretion, suggesting that dopamine did not have a direct effect on postsynapses.

These findings indicate that dopamine induces amylase secretion in two indirect ways mediated through ACh and NA released from parasympathetic and sympathetic nerve terminals, respectively.
P2‐purinoceptors regulate surfactant secretion from rat isolated alveolar Type II cells
Authors: Rice Ward R. , Singleton Fannie M.
Published: July 2012

Rat isolated alveolar Type II cells were utilized to examine the effect of purine and pyrimidine analogues on secretion of pulmonary surfactant.

ATP potently stimulated [3H]‐phosphatidylcholine ([3H]‐PC) secretion in a time‐ and dose‐dependent manner. The effect of ATP was noted by one hour of exposure and persisted for three hours. The EC50 (concentration producing 1/2 the maximal response) for ATP‐induced [3H]‐PC secretion was 100 nM.

ADP was also a potent secretagogue for surfactant secretion, but AMP and adenosine had no significant effect on surfactant secretion at concentrations < 250 μM. The EC50 for ADP‐induced [3H]‐PC secretion was 250 nM.

Other purine and pyrimidine nucleotides (ITP, GTP, CTP, TTP) were examined for their effect on [3H]‐PC secretion. All purine and pyrimidine triphosphates examined significantly augmented [3H]‐PC secretion, but were much less potent than ATP. The EC50s were ITP = 10 μM; GTP = 100 μM; CTP = 250 μM; TTP = 100 μM.

Neither 8‐phenyltheophylline (10 μM, a P1‐purinoceptor antagonist), propranolol (100 μM, a β‐adrenoceptor antagonist), nor indomethacin (10 μM, a prostaglandin synthetase inhibitor) inhibited ATP‐induced [3H]‐PC secretion from isolated Type II cells.

These data provide evidence for regulation of surfactant secretion from alveolar Type II cells by a P2‐purinoceptor.
The classification of peripheral 5‐HT2‐like receptors using tryptamine agonist and antagonist analogues
Authors: Leff P. , Martin G.R. , Morse J.M.
Published: July 2012

In a previous study, we attempted to verify the classification of 5‐hydroxytryptamine2 (5‐HT2) receptors in three vascular tissues, by use of the conventional antagonists, ketanserin, spiperone, methysergide and trazodone. However, it was not possible to conclude homogeneity of the receptor type in the three tissues due to the inconsistent behaviour of these antagonists, in particular, their apparently variable affinities between the tissues. These results led to the reliability of the conventional antagonists being questioned as receptor probes.

In the present study, a set of tryptamine analogues were investigated in two of the tissues, the rabbit aorta and the rat jugular vein. Unlike the conventional antagonists, these compounds bear a close chemical relation to the natural agonist, 5‐HT.

In both tissues, α,α‐dimethyltryptamine demonstrated apparently simple competitive antagonism of 5‐HT‐induced constrictions. Its affinity was estimated to be the same in each case.

The affinities and relative efficacies of 5‐HT, 5‐cyanotryptamine, N,N‐dimethyltryptamine and N‐benzyl‐5‐methoxytryptamine were also found to be indistinguishable between the two tissues.

Unlike the conventional 5‐HT2 receptor antagonists, these tryptamine analogues failed to distinguish between the 5‐HT receptors in the rabbit aorta and rat jugular vein implying that they truly belong to the same class. In view of this result, it is suggested that simple tryptamine analogues are more reliable probes for 5‐HT receptor classification than ligands which bear little or no chemical relation to the natural agonist.
Cytostatic action of two nitrosoureas derived from cysteamine
Authors: Bourut Charlotte , Chenu Evelyne , Godenèche Denise , Madelmont Jean‐Claude , Marla René , Mathé Georges , Meyniel Gaston
Published: July 2012

2‐Chloroethyl nitrosocarbamoylcystamine or ICIG‐1325 (CNCC) is a lipid‐soluble isomeric mixture of nitrosoureas.

Its dose‐effect relationship on L1210 leukaemia is characterized by a large maximally efficient dose‐range (MEDR), greater than that of other nitrosoureas. CNCC also demonstrated significant therapeutic activity on intracerebrally (i.c.) transplanted L1210 leukaemia and on six transplanted solid tumours, TM2 mammary carcinoma, M555 ovarian carcinoma, B16 melanoma, glioma 26, 3LL, Lewis lung carcinoma and colon 26 carcinoma. It was inactive on fibrosarcoma ICIG‐Ci4. Its antitumour activity spectrum is wider than that of the related compounds 2‐[3‐(2‐chloroethyl) 3‐nitrosoureido]D‐glucopyranose (CZT), (chloro‐2‐ethyl)‐1 (ribofuranosyl‐isopropylidene‐2′‐3′paranitrobenzoate‐5′)‐3 nitrosourea (RFCNU), and (chloro‐2‐ethyl)‐1 (ribopyranosyl triacetate‐2′‐3′‐4′)‐3 nitrosourea (RPCNU).

A study of its metabolic disposition in animals has shown that CNCC undergoes extensive first‐pass metabolism leading to the formation of four main plasma metabolites.

These metabolites are water‐soluble nitrosoureas that arose from the bioreduction of the disulphide bridge followed by the methylation and the oxidation of the thiol groups.

Experimental screening was performed with these chemically synthesized metabolites. Both N'‐(2‐chloroethyl)‐N‐[2‐(methylsulphinyl)ethyl]‐N'‐nitrosourea (CMSOEN2) and N'‐(2‐chloroethyl)‐N‐[2‐(methylsulphonyl)ethyl]‐N'‐nitrosourea (CMSO2EN2) are very active on L1210 leukaemia grafted intraperitoneally (i.p.) and i.c., L40 leukaemia, B16 melanoma, glioma 26 and Lewis lung carcinoma. Their effectiveness is better than that of the parent compound CNCC. In addition, the percentage of mice cured after CMSOEN2 or CMSO2EN2 treatment is increased especially on B16 melanoma and glioma 26.

Haematological toxicity of both active metabolites is lower than that of CNCC, particularly on platelets which is the main toxicity location due to nitrosoureas.
A comparison between mechanisms of action of different nicotinic blocking agents on rat submandibular ganglia
Authors: Large W.A. , Sim J.A.
Published: July 2012

The blocking properties of tubocurarine, decamethonium, hexamethonium and trimetaphan on nicotinic agonists applied by repetitive ionophoretic pulses were examined in rat submandibular ganglion cells using a two‐microelectrode voltage‐clamp technique at 30°C.

Hexamethonium, a proposed slowly dissociating, open‐channel blocker at concentrations of 2–20 μM did not produce a ‘use‐dependent’ run‐down of responses, but its antagonism was clearly dependent on membrane potential.

The voltage‐dependent reduction of agonist response by hexamethonium was not dependent on the nature of agonist used. Similar results were obtained with acetylcholine (ACh) and carbamylcholine (CCh) ionophoresis.

(+)‐Tubocurarine (5 μM) and decamethonium (10 μM) produced ‘use‐dependent’ run‐down of agonist responses which became more pronounced at higher frequency and as the cell was hyperpolarized, consistent with open‐channel blockade. In contrast, trimetaphan (2.5 μM), a receptor antagonist did not cause ‘use‐dependent’ run‐down of responses.

Hence, the antagonism produced by hexamethonium, unlike tubocurarine and decamethonium, could not be accounted for in terms of open‐channel blockade but requires an alternative mechanism, the nature of which is discussed.
Evidence against VIP as the inhibitory transmitter in non‐adrenergic, non‐cholinergic nerves supplying the longitudinal muscle of the mouse colon
Authors: Fontaine J. , Grivegnee A.R. , Robberecht P.
Published: July 2012

Vasoactive intestinal peptide (VIP) had two types of effects on the longitudinal muscle of the mouse distal colon.

At low concentrations (10−8 M) VIP induced a contraction which seemed to be related to the production of prostaglandins as it was abolished after preincubation with indomethacin (10−6 M).

At higher concentrations (3 × 10−8 and 10−7 M) VIP induced relaxations which developed slowly and were related to stimulation of the adenylate cyclase activity of the smooth muscle cells.

There is no evidence that VIP is the non‐adrenergic, non‐cholinergic transmitter released by electrical stimulation in this preparation and responsible for rapid relaxation of the smooth muscle.
Comparative antiarrhythmic and electrophysiological effects of drugs known to inhibit calmodulin (TFP, W7 and bepridil)
Authors: Barron E. , Marshall R.J. , Martorana M. , Winslow E.
Published: July 2012

The potential antiarrhythmic and electrophysiological actions of drugs known to inhibit calmodulin, i.e. trifluoperazine (TFP) and N‐(6‐aminohexyl)‐5‐chloro‐1‐naphthalene sulphonamide (W7) have been compared with bepridil, whose antiarrhythmic actions have previously been ascribed to blockade of the fast inward sodium current in cardiac tissue.

Like bepridil, both TFP and W7 reduced the severity of arrhythmias evoked by 30 min of coronary artery occlusion in tha anaesthetized rat.

TFP (2.5–10 mg kg−1, i.v.), W7 (2.5–10 mg kg−1, i.v.) and bepridil (1–5 mg kg−1, i.v.) also antagonized the development of ventricular fibrillation induced by 5 min of occlusion followed by reperfusion. All three drugs also reduced mortality. TFP and bepridil also reduced the incidence of reperfusion‐induced ventricular tachycardia whilst all 3 drugs reduced its duration.

Although TFP was shown to possess α‐adrenoceptor blocking properties, the classical α‐blocker, phentolamine, failed to reduce significantly the incidence or severity of reperfusion arrhythmias.

In contrast to bepridil (2–20 μM), which markedly reduced the maximum rate of depolarization (Vmax) of guinea‐pig isolated papillary muscle, W7 (5–50 μM) showed only weak effects on Vmax and was at least 10 times less potent than bepridil whilst TFP only reduced Vmax in high concentrations (40–100 μM) which lowered resting membrane potential.

Unlike bepridil, neither TFP (4–40 μM) nor W7 prolonged the absolute refractory period.

The results suggest that drugs which inhibit calmodulin confer protection against both ischaemia ‐ and reperfusion‐induced arrhythmias in the rat. Although the electrophysiological actions of bepridil would adequately account for its antiarrhythmic activity, the same cannot be said of W7 and especially TFP.

In conclusion, calmodulin antagonism may constitute a mechanism of antiarrhythmic activity.
Changes in cardiovascular sensitivity of alloxan‐treated diabetic rats to arachidonic acid
Authors: Boura A.L.A. , Hodgson W.C. , King R.G.
Published: July 2012

Arachidonic acid (AA, 0.125‐2.0 mg kg−1) administered intravenously to male Wistar rats produced a dose‐dependent fall in diastolic blood pressure. However AA (0.125‐1.0 mg kg−1) injected into the autoperfused hindquarters via the aorta produced a dose‐dependent increase in perfusion pressure. Both these responses to AA were inhibited by indomethacin (5 mg kg−1).

The thromboxane A2 receptor antagonist AH23848 (5 mg kg−1, i.v.) inhibited pressor responses to AA in the autoperfused hindquarters, but potentiated depressor responses to AA (0.125‐0.5 mg kg−1) in the whole animal.

Alloxan‐treated diabetic rats (14 days after a single s.c. injection of alloxan, 175 mg kg−1) displayed reduced sensitivity to the depressor effects of AA (1–2 mg kg−1) in the whole animal, increased sensitivity to the pressor effects of AA (0.5‐1.0 mg kg−1) in the perfused hindquarters, and reduced sensitivity to the pressor effects of the thromboxane A2 mimetic U46619 (0.5–8.0 μg kg−1, i.a.) in the perfused hindquarters.

These results suggest that AA can be predominantly converted to either pressor or depressor metabolites depending on the vasculature. In the diabetic state the ratio of the metabolites formed appears to change favouring a major pressor metabolite, which is probably thromboxane A2.
Prevention of physostigmine‐induced lethality by the opioid analgesic meptazinol in the mouse
Authors: Bottoncetti Anna , Galli Alessandro
Published: July 2012

The prophylactic action of meptazinol against physostigmine‐and neostigmine‐induced lethality was evaluated in mice. Meptazinol proved to be effective against physostigmine (1 mg kg−1 i.p.), but not against neostigmine (0.5 mg kg−1 i.p.).

The antagonism by meptazinol of physostigmine‐induced poisoning was maximal when the drug was administered 15 min before physostigmine. Under these conditions the ED50 (95% confidence limits) of meptazinol was 24 (22.0–26.1) mg kg−1 s.c. A 30 mg kg−1 dose of the drug prevented lethality in 89% of the animals.

The action of meptazinol was not antagonized by naloxone hydrochloride (2 mg kg−1 i.p.), injected 10 min before meptazinol.

Pretreatment of mice with 30 mg kg−1 meptazinol 15 min before physostigmine (1 mg kg−1) poisoning increased brain acetylcholinesterase (AChE) activity on average, from 8 to 31% of control values.

The protection of cholinesterases against physostigmine‐and neostigmine‐induced inactivation was demonstrated in vitro directly on purified preparations of the enzymes using a dilution method. The ED50 values (95% confidence limits) for the protective effect of meptazinol of electric eel AChE against 1 and 3 μm physostigmine and 1 μm neostigmine were 2.6 (1.4‐4.9), 9.5 (5–18) and 3 (1.6‐5.7) μm, respectively, while for protection of horse serum butyrylcholinesterase (BuChE) against the same inhibitors, the ED50 values were 12 (5.4–26.4), 42 (27–65.1) and 8 (3.6–17.6) μm, respectively.

It is suggested that prevention of physostigmine‐induced lethality by meptazinol is a consequence of its protective action on AChE in the central nervous system.
Differential classification of vascular smooth muscle and endothelial cell 5‐HT receptors by use of tryptamine analogues
Authors: Leff P. , Martin G.R. , Morse J.M.
Published: July 2012

In ring preparations of the rabbit external jugular vein contracted with the thromboxane‐mimetic U‐46619, submicromolar concentrations of 5‐hydroxytryptamine (5‐HT) and chemically related analogues produced relaxations that were dependent on the integrity of the vascular endothelium.

The receptor mediating endothelium‐dependent relaxations was evidently similar to previously described endothelial 5‐HT receptors since relaxation responses to α‐methyl‐5‐HT were not blocked by atropine, (±)‐propranolol, yohimbine, indomethacin, ketanserin or MDL‐72222, but were noncompetitively antagonized by methysergide, methiothepin and cyproheptadine.

The activities of some tryptamine agonists and antagonists at the endothelial 5‐HT receptor in rabbit jugular vein were compared with their activities at the smooth muscle 5‐HT2‐receptor in rabbit aortic rings. Differences in the tryptamines' affinities and relative efficacies showed that the endothelial 5‐HT receptor was not of the 5‐HT2‐type.

The high agonist potencies of 5‐HT and 5‐carboxamidotryptamine, the susceptibility to antagonism by both methiothepin and methysergide and the resistance to blockade by selective 5‐HT2 and 5‐HT3 (‘M’) receptor antagonists implies that the endothelial receptor belongs to the ‘5‐HT,‐like’ class. However, the agonist potency order 5‐HT = α‐methyl‐5‐HT > 5‐carboxamidotryptamine suggested that the receptor is not the same as the peripheral ‘5‐HT1‐like’ receptors reported to mediate directly contraction of the dog saphenous vein or relaxation of vascular and non‐vascular smooth muscles. At these receptors, the potency order is 5‐carboxamidotryptamine > 5‐HT > α‐methyl‐5‐HT.

These results constitute preliminary evidence that peripheral ‘5‐HT1‐like’ receptors, like central 5‐HT1 recognition sites, are a heterogeneous population. Further comparative studies with a wider range of receptor probes are necessary to establish whether or not these receptors represent functional counterparts of the ligand binding sites in the brain.
A role for corticosterone in the in vivo regulation of the extraneuronal uptake of [3H]‐isoprenaline into rat atria
Authors: Morton A.J.
Published: July 2012

The role of corticosterone, a potent in vitro inhibitor of extraneuronal uptake, in the regulation of the extraneuronal accumulation of [3H]‐isoprenaline into rat atria was examined.

Procedures which increased plasma corticosterone levels resulted in a decrease in the corticosterone‐sensitive component of extraneuronal accumulation of [3H]‐isoprenaline (64% after reserpine treatment and 25% after chronic cold exposure).

Procedures which decreased levels of plasma corticosterone resulted in an increase in the corticosterone‐sensitive component of extraneuronal accumulation of [3H]‐isoprenaline (approximately 20% after adrenalectomy and 32% after hypophysectomy). This increase was partially prevented by the in vivo administration of dexamethasone (40 μg kg−1).

There was a strong inverse correlation between the plasma corticosterone concentration and the level of extraneuronal uptake into atria (P < 0.01).

Corticosterone appears to play a major role in the regulation of extraneuronal uptake into tissues of the rat.
Relationship between β‐adrenoceptors and calcium channels in human ventricular myocardium
Authors: Ferry D.R. , Kaumann A.J.
Published: July 2012

The stoichiometric relationship between adrenoceptors and saturable binding sites for 1,4‐dihydropyridines in calcium channels was investigated in human ventricular myocardium. Membrane particles were prepared from heart specimens of patients undergoing open heart surgery. The patients suffered from hypertrophic obstructive cardiomyopathy (HOCM) or mitral valve disease.

Using [3H]‐prazosin and [125I]‐2‐β‐hydroxy‐3‐iodiphenyl‐ethyl‐aminoethyl tetralone ([125I]‐HEAT) as labels we detected only a marginal density of α1‐adrenoceptors, regardless of disease. No α2‐adrenoceptors were detected with [3H]‐rauwolscine.

In HOCM patients we estimated 72 ± 10 fmol mg−1 (n = 12) β‐adrenoceptors labelled with [3H]‐(‐)‐dihydroalprenolol and 74 ± 5 fmol mg−1 (n = 2) β‐adrenoceptors labelled with [125I]‐(‐)‐iodocyanopindolol; the equilibrium dissociation constants KD, were 1.2 ± 0.2 nmol l−1 for [3H]‐(‐)‐dihydroalprenolol and 7 ± 1 pmol l−1 for [125I]‐(‐)‐iodocyanopindolol. In patients with mitral valve disease we estimated 84 ± 11 fmol mg−1 (n = 3) labelled with [3H]‐(‐)‐dihydroalprenolol and 66 ± 13 fmol mg−1 (n = 2) labelled with [125I]‐(‐)‐iodocyanopindolol. The KD values were 1.8 ± 0.6 nmol l−1 for [3H]‐(‐)‐dihydroalprenolol and 8 ± 2 pmol l−1 for [125I]‐(‐)‐iodocyanopindolol.

In 14 HOCM patients we estimated 107 ± 12 fmol mg−1 calcium channel sites labelled with [3H]‐nimodipine with a KD of 280 ± 4 pmol l−1. In 5 patients with mitral valve disease the density of calcium channel sites labelled with [3H]‐nimodipine was 78 ± 5 fmol mg−1 with a KD of 290 ± 20 pmol l−1, In HOCM patients the density of calcium channel sites labelled with the benzoxadiazol 1, 4‐dihydropyridine ([3H]‐(+)‐PN 200–110) was 1.6 fold of that labelled with [3H]‐nimodipine with a KD of 84 ± 11 pmol l−1.

In a group of 4 HOCM patients in which calcium channels were labelled with [125I]‐iodipine, the density of sites was 1.37 ± 0.07 fold the density of sites labelled by [3H]‐(+)‐PN 200‐11‐. The KD value of [125I]‐iodipine was 246 ± 16 pmol−1. (+)‐PN 200‐110 was approximately 100 fold more potent than (‐)‐PN 200‐110 as a competitor of [125I]‐iodipine binding.

For the HOCM group a significant correlation was found between β‐adrenoceptor density and calcium channel density, whereas in the mitral valve group no such correlation was found. This does not prove that there is causal interaction leading to a relationship between the density of β‐adrenoceptors and calcium channels. However, because positive inotropic effects of catecholamines mediated by β‐adrenoceptors are associated with opening of calcium channels, this suggests that the density of both β‐adrenoceptors and calcium channels could be co‐regulated.
The antianaphylactic action of histamine H2‐receptor agonists in the guinea‐pig isolated heart
Authors: Blandina P. , Brunelleschi Sandra , Fantozzi R. , Giannella Eliana , Mannaioni P.F. , Masini Emanuela
Published: July 2012

The effects of histamine and of H1‐and H2‐receptor agonists on the response to specific antigen were studied in isolated hearts taken from actively sensitized guinea‐pigs.

Histamine and H2‐receptor agonists (dimaprit, impromidine) dose‐dependently decrease the positive chronotropic and inotropic effects, and the severity of arrhythmias evoked by the challenge of sensitized hearts with specific antigen.

Nordimaprit and the selective H1‐receptor agonist 2‐pyridyl‐ethyl‐amine (2‐PEA) did not modify the patterns of cardiac anaphylaxis.

The positive inotropic and chronotropic responses of the isolated heart to exogenous histamine appear to be partly reduced in the presence of dimaprit.

The H2‐receptor agonists decrease the amount of histamine released during cardiac anaphylaxis which is increased by cimetidine, while nordimaprit and PEA were ineffective, indicating an inhibitory function afforded by H2‐receptors in cardiac anaphylaxis.
Release of γ‐aminobutyric acid and acetylcholine by neurotensin in guinea‐pig ileum
Authors: Nakamoto Mitsuharu , Tanaka Chikako , Taniyama Kohtaro
Published: July 2012

The release of γ‐aminobutyric acid (GABA) and acetylcholine (ACh) from the strips of guinea‐pig ileum was investigated in the presence of neurotensin.

Neurotensin evoked the release of [3H]‐GABA from the strips preloaded with [3H]‐GABA, and the evoked release was Ca2+‐dependent and tetrodotoxin‐sensitive.

Hexamethonium, scopolamine, [D‐Pro2, d‐Trp7,9] substance P and pretreatment with substance P did not alter the neurotensin‐evoked release of [3H]‐GABA.

Pretreatment with neurotensin inhibited the release of [3H]‐GABA evoked by neurotensin but not by high K+, thereby indicating that neurotensin induced a specific desensitization of its own receptor. These observations indicate that neurotensin may stimulate the GABAergic neurone through its own receptor.

Neurotensin evoked the release of [3H]‐ACh from strips preloaded with [3H]‐choline and this release was Ca2+‐dependent and tetrodotoxin‐sensitive.

The evoked release of [3H]‐ACh was not affected by hexamethonium, scopolamine and [D‐Pro2, d‐Trp7,9] substance P.

Bicuculline partly inhibited the neurotensin‐evoked release of [3H]‐ACh; thus neurotensin seems to induce a release of ACh partly through the release of endogenous GABA.

All this evidence indicates that neurotensin induces release of GABA as well as ACh from the myenteric neurones of the guinea‐pig ileum.
Changes in tissue blood flow and β‐receptor density of skeletal muscle in rats treated with the β2‐adrenoceptor agonist clenbuterol
Authors: Rothwell Nancy J. , Stock Michael J. , Sudera Deepak K.
Published: July 2012

Rats injected with the β2‐adrenoceptor agonist clenbuterol (2 mg kg−1per day) for 18 days gained significantly more weight than controls.

Tissue blood flow assessed 24 h after the last injection from the distribution of radiolabelled microspheres was increased in white (5 fold) and brown (3 fold) adipose tissue of clenbuterol‐treated rats but was unaffected in kidney, brain and diaphragm, and was reduced by about 80% in skeletal muscle.

Acute injection of clenbuterol one hour before measuring blood flow, increased blood flow to brown fat (20 fold) in both treated and control groups. Blood flow to skeletal muscle increased more in the rats treated chronically with clenbuterol (6 fold increase) than in control rats (2 fold increase), but absolute flow rates were still significantly lower in the rats treated chronically with clenbuterol.

Skeletal muscle β‐adrenoceptor density and subtype were assessed from ligand binding and displacement studies using [3H]‐dihydroalprenolol. Rats treated with clenbuterol for 18 days showed a 50% reduction in β‐receptor density, but the ratio of β1/β2‐receptors was unaffected (15% β1/85% β2).

The results indicate that, although clenbuterol produces acute increases in muscle blood flow, chronic treatment results in lower flow rates immediately (1 h) and 24 h after the previous injection. The attenuated response following chronic treatment is associated with a marked reduction in skeletal muscle β‐adrenoceptor density.

The data suggest that any anabolic effects of clenbuterol on muscle which may require, or may be mediated by increases in blood supply, cannot be sustained by chronic treatment. Conversely, blood flow to white and brown adipose tissue would appear to be potentiated by chronic treatment, possibly reflecting increases in lipolytic and/or thermogenic activity.
The consequences of loss followed by recovery of noradrenergic nerve function on muscarinic receptors in the chick expansor secundariorum muscle
Authors: Lot Theodore Y.
Published: July 2012

The effects of chemical sympathectomy with 6‐hydroxydopamine on the response of the expansor secundariorum muscle to noradrenergic nerve stimulation, noradrenaline and acetylcholine have been investigated.

Expansor muscles from 60 day old chicks were sensitive to noradrenergic nerve stimulation and exogenous noradrenaline but virtually unresponsive to acetylcholine.

Chemical sympathectomy with 6‐hydroxydopamine caused loss of function of noradrenergic nerves of the expansor muscle, induced supersensitivity to exogenous noradrenaline and gradually increased the response of the expansor muscle to acetylcholine.

As the patency of noradrenergic nerves reappeared there was a decline in the extent of supersensitivity to noradrenaline and the response to acetylcholine gradually declined.

The time courses of these changes differed, indicating that the mechanisms responsible for changes in response to noradrenaline and acetycholine are different.
Competitive and non‐competitive antagonism exhibited by ‘selective’ antagonists at atrial and ileal muscarinic receptor subtypes
Authors: Eglen R.M. , Whiting R.L.
Published: July 2012

The affinity of a number of ‘selective’ agonists and antagonists has been assessed at atrial or ileal muscarinic receptors by use of in vitro functional analysis.

The most selective compound for ileal muscarinic receptors was silabenzhexol (approx. 50 fold), and to a lesser extent benzhexol (approx. 5 fold). Conversely, the most selective compound for the atrial muscarinic receptors was AF‐DX 116 (approx. 6 fold).

The novel M1‐receptor antagonist, telenzepine and other antagonists such as propantheline and isopropamide did not distinguish between atrial and ileal receptors.

Dicyclomine, adiphenine, hexahydroadiphenine and oxyphenonium exhibited competitive antagonism at atrial receptors but non‐competitive antagonism at ileal receptors. No conclusions could, therefore, be drawn with regard to their selectivity.

The agonists, arecaidine propargyl ester (APE), ethoxyethyltriethylammonium (EOE) and carbachol, exhibited some selectivity in potency but little difference in affinity.

It is concluded that the study supports the existence of ileal and atrial muscarinic receptor subtypes. However, the use of dicyclomine and related compounds in receptor classification is limited.