bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of 7‐nitro indazole on neurotransmission in the rat vas deferens: mechanisms unrelated to inhibition of nitric oxide synthase
Authors: Allawi Hala S. , Wallace P. , Pitcher Ann , Gaffen Zoe , Bland‐Ward P.A. , Moore P.K. 
Published: July 2012

The effect of the nitric oxide synthase (NOS) inhibitor, 7‐nitro indazole (7‐NI), on sympathetic and purinergic neurotransmission in the rat isolated vas deferens preparation has been studied.
7‐NI (50–200 μm) caused a dose‐ and frequency‐dependent inhibition of the phasic (predominantly purinergic) contractile response of the rat vas deferens to electrical (field) stimulation (100 V, 0.5 ms). Greatest inhibition occurred at lower frequencies of stimulation (0.1–10 Hz). The sustained tonic contractile response (predominantly noradrenergic) was inhibited only at a high frequency of stimulation (60 Hz) and only at the highest concentration of 7‐NI studied (200 μm).
7‐NI (100 μm) significantly reduced the contractile response of the vas deferens to exogenous ATP (20 μm‐5mm) and the stable P2x purinoceptor agonist, α,β‐methylene ATP (2.5 and 25.0 μm) but was without effect on contractions due to noradrenaline (0.1–50 μm) indicating a lack of antagonist effect on post‐junctional α1 adrenoceptors.
The effect of 7‐NI (100 μm) on the phasic contractile response to field stimulation (0.1 and 2.0 Hz) was unaffected by preincubation of preparations with yohimbine (1.0 μm) or propranolol (0.01–10.0 μm) indicating the absence of involvement of α2– or β‐adrenoceptors in this response.
7‐NI (50–600 μm) caused dose‐related inhibition of contractions elicited by addition of a depolarizing concentration of KC1 (64 mm).
The effect of 7‐NI (100 μm) on the phasic contractile response to field stimulation (0.1 and 2.0 Hz) was unaffected by preincubation of preparations with l‐arginine (1 mm). Neither l‐arginine (1 mm) nor NG nitro l‐arginine methyl ester (l‐NAME, 100 μm) affected the response of the vas deferens to field stimulation at 0.1 or 2.0 Hz. Nitric oxide synthase (NOS) enzyme activity, measured as the conversion of [3H]‐l‐arginine to [3H]‐citrulline, was not detectable in rat vas deferens homogenates.
7‐Nr preferentially inhibits the purinergic component of the response of the rat vas deferens to field stimulation. The mechanism of action of 7‐NI is not known but is not related to NOS inhibition. It seems likely that 7‐NI combines an antagonist action at smooth muscle cell P2x‐purinoceptors with the ability to inhibit the cellular influx of calcium ions. Although these hitherto unrecorded effects of 7‐NI occur at relatively high concentrations, the effects described may contribute to the pharmacological effects of this NOS inhibitor.
The use of receptor desensitization to analyse CCKA and CCKB/gastrin receptors coupled to contraction in guinea‐pig stomach muscle
Authors: Bishop L.A. , Gerskowitch V.P. , Hull R.A.D. , Shankley N.P. , Black J.W. 
Published: July 2012

The results of previous studies have been in conflict with respect to the involvement of specific cholecystokinin (CCKA) and CCKB/gastrin receptors in guinea‐pig gastric muscle. Here, in an in vitro, guinea‐pig gastric muscle assay, pentagastrin (PG) and tetragastrin (TG) behaved as high potency agonists and produced symmetrical concentration‐effect curves. In contrast, cholecystokinin‐octapeptide (CCK‐8), while also behaving as a high potency agonist, produced flat asymmetrical curves. Unlike recent data reported using this tissue (Boyle et al., 1993), the CCKA receptor‐selective antagonist, devazepide (3, 10, 30 nm) produced a rightward shift of the upper region of the CCK‐8 curve rendering it biphasic. The lower phase was abolished by the CCKB/gastrin receptor‐selective antagonist, L‐365260 (300 nm) indicating that the contractile effects of CCK‐8 in this tissue are mediated by both receptor types.
L‐365260 produced a concentration‐dependent, parallel rightward displacement of PG concentration‐effect curves. However, a flat Schild plot slope parameter (0.77 ± 0.06) was obtained. Therefore, an empirical pA2 value of 8.64 ± 0.21 was estimated from the smallest dose ratio. This value is consistent with published values characteristic of an interaction at CCKB/gastrin receptors.
TG (1 μm) was used to densensitize selectively the CCKB/gastrin receptors in the gastric muscle assay and thereby expose a population of receptors capable of responding to subsequent stimulation by CCK‐8 but not by PG. The selectivity of TG for CCKB/gastrin‐ over CCKA receptors was demonstrated by its low efficacy compared to CCK‐8 in the guinea‐pig gallbladder assay, a tissue shown previously to contain a homogeneous population of CCKA receptors. In TG‐desensitized gastric muscle, CCK‐8 concentration‐effect curves were symmetrical and could be displaced in a simple parallel fashion by devazepide at nanomolar concentrations consistent with an interaction at CCKA receptors (pKB ∼ 10).
These results indicate that the guinea‐pig gastric muscle contains both CCKA‐ and CCKB/gastrin receptors and the effects of CCK‐8 are mediated via both of these receptors. Notwithstanding the complexity of the behaviour of L‐365260, it was possible to obtain a reasonable description of the system using a simple 2‐receptor model in which the effects of individual receptor activation were assumed to be additive. The absence of a simple competitive interaction of PG with L‐365260 may indicate, for example, non‐homogeneity of CCKB/gastrin receptors or lack of concentration equilibrium between the bath and the receptor biophase.
Mediation by 5‐hydroxytryptamine2B receptors of endothelium‐dependent relaxation in rat jugular vein
Authors: Ellis Elizabeth S. , Byrne Clare , Murphy Olive E. , Tilford Nicholas S. , Baxter Gordon S. 
Published: July 2012

An ‘atypical’ 5‐HT2 receptor which is located on the endothelium of rat jugular vein has been described. In the present study we have further defined the nature of the 5‐HT2 receptor subtype present in this preparation.
In experiments conducted in the presence of ketanserin to preclude involvement of 5‐HT2 receptors, the mixed 5‐HT2B/2C antagonist, SB 200646, acted as an antagonist of 5‐HT at the endothelial 5‐HT receptor (pA2 = 7.2). Yohimbine, which exhibits negligible affinity for rat 5‐HT2C receptors but has high 5‐HT2B receptor affinity, acted as a potent but non‐surmountable antagonist (pA2 ≥ 7.3) in rat jugular vein. Neither yohimbine nor SB 200646 affected endothelium‐dependent relaxations induced by carbachol.
Mianserin also acted as a surmountable antagonist (pA2 = 7.3) and the 5‐HT2B agonist, BW 723C86, acted as a potent partial agonist (pEC50 [95% C L], intrinsic activity ± s.e.mean = 7.9 [7.6–8.3], 0.84 ± 0.04). Responses to BW 723C86 were antagonized by SB 200646 (0.3 μm) yielding an ‘apparent’ pA2 [95% CL] of 7.03 [6.76–7.32].
These data are consistent with the presence of 5‐HT2B receptors mediating endothelium‐dependent relaxation of rat jugular vein.
Species‐related differences in inotropic effects of angiotensin II in mammalian ventricular muscle: receptors, subtypes and phosphoinositide hydrolysis
Authors: Ishihata Akira , Endoh Masao 
Published: July 2012

Experiments were carried out to clarify the mechanisms responsible for variations in the positive inotropic effect (PIE) of angiotensin II (AII) on ventricular muscles from various mammals. We examined the density of All receptors, the relative proportions of receptor subtypes and the acceleration of the hydrolysis of phosphoinositide that was induced by AII, as well as the PIE of AII in ventricular muscles from the rabbit, dog, rat and ferret.
In the rabbit, AII (1 μm) in the presence of bupranolol (0.3 μm) and prazosin (0.1 μm) elicited a concentration‐dependent PIE, which was antagonized by a selective AT1 subtype antagonist, losartan, but not by an AT2 antagonist, PD123319. AII did not have any inotropic effects in ventricular muscles from the dog, rat and ferret.
Specific high‐affinity binding of [125I]‐AII, with a similar Kd value in each case (1–2 nm), was observed with membrane fractions derived from ventricular muscle of all four species tested.
In the rabbit, losartan and PD123319 each displaced approximately 50% of [125I]‐AII specific binding having high affinity for the receptors, and indicating that AT1 and AT2 subtypes were present in equal numbers. In the other species the AT1 subtype of receptors was predominant.
In all four species AII caused a concentration‐dependent acceleration of the hydrolysis of phosphoinositide in ventricular slices that had been prelabelled with myo‐[3H]‐inositol.
The results indicate that the signal‐transduction process distal to acceleration of the hydrolysis of phosphoinositide may be responsible for the wide range of species variations in the inotropic action of AII on mammalian ventricular myocardium.
Electrophysiological effects of SD‐3212, a new antiarrhythmic agent with vasodilator action, on guinea‐pig ventricular cells
Authors: Kodama Itsuo , Suzuki Ryoko , Maruyama Kazuyasu , Toyama Junji 
Published: July 2012

The effects of SD‐3212 on transmembrane action potentials were examined in right ventricular papillary muscles and in single ventricular myocytes isolated from guinea‐pig hearts.
In papillary muscles, SD‐3212 ≥ 3 μm caused a significant decrease in the maximum upstroke velocity () of action potential without affecting resting membrane potential. The inhibition of was enhanced at higher stimulation frequencies.
In the presence of SD‐3212, trains of stimuli at rates ≥ 0.5 Hz led to a use‐dependent inhibition of . The time constant for the recovery of from the use‐dependent block was 1.3 s.
Voltage‐dependence of inhibition by SD‐3212 was investigated in single myocytes. The curves relating membrane potential and were shifted by SD‐3212 (10 μm) in a hyperpolarizing direction by 6.2 mV.
In myocytes treated with SD‐3212 (10 μm), the of test action potentials preceded by conditioning clamp to 0 mV was decreased progressively as the clamp pulse duration was prolonged. of test action potentials following a long (1 s) 0 mV clamp recovered at a time constant ranging from 1.01 to 1.22 s, being shorter at the more negative potential within a range from −70 to −90 mV.
These findings suggest that the primary electrophysiological effect of SD‐3212 is a use‐ and voltage‐dependent inhibition of sodium channels. From the onset and offset kinetics of the use‐dependent block, SD‐3212 is located between fast and intermediate kinetic Class‐I drugs. From the state‐dependence of sodium channel block, SD‐3212 belongs to inactivated channel blockers.
A reassessment of the modulatory role of cyclic AMP in catecholamine secretion by chromaffin cells
Authors: Parramón M. , González M.P. , Oset‐Gasque M.J. 
Published: July 2012

The role of adenosine 3′:5′‐cyclic monophosphate (cyclic AMP) in the regulation of catecholamine (CA) secretion in chromaffin cells remains equivocal from previous studies.
In the present study the effect of this cyclic nucleotide on basal CA secretion, as well as on intracellular calcium and membrane potential has been examined.
Forskolin and the permeable cyclic AMP analogue, 8‐(4‐chlorphenylthio)‐adenosine‐3′‐5′ monophosphate cyclic (pClpcAMP), increased basal CA secretion in a dose‐dependent manner. The EC50S were 0.43 ± 0.10 μm for forskolin and 39 ± 9 μm for pClpcAMP. Other agonists with adenylate cyclase activity such as stimulants of adenosine receptors, β‐adrenoceptors, GABAB receptors and intestinal vasoactive peptide (VIP), also increased basal CA secretion in a highly significant manner. However, when they were added together with forskolin, CA secretion was not affected although an additive increase in cyclic AMP levels was produced.
Statistical analysis of the correlation between cyclic AMP levels and CA secretion evoked by these cyclic AMP increasing compounds showed that a significant direct correlation between both parameters existed only when low levels of cyclic AMP were produced by secretogogue stimulation. When the increase in intracellular cyclic AMP concentrations exceeded approximately 8 times the basal cyclic AMP levels the correlation was not significant. These results indicate a dual dose‐dependent effect of cyclic AMP on basal CA secretion.
The stimulatory effect of low cyclic AMP on basal CA secretion was accompanied by an increase in membrane potential and in intracellular calcium concentrations ([Ca2+]i), the latter mainly being due to an increase in intracellular Ca2+ entry through L‐type voltage‐dependent Ca2+ channels.
The possible mechanisms involved in these cyclic AMP effects are discussed.
Different effects of endothelin‐3 on the Ca2+ discharge induced by agonists and Ca2+‐ATPase inhibitors in human platelets
Authors: Astarie‐Dequeker Catherine , Korichneva Irina , Devynck Marie‐Aude 
Published: July 2012

The present study demonstrates that endothelin‐3 (ET‐3), previously shown to attenuate thrombin‐evoked aggregation of human platelets, delayed the dose‐dependent aggregatory response to thapsigargin (Tg). As this Ca2+‐ATPase inhibitor induces platelet activation in part through the depletion of internal Ca2+‐stores, we examined the influence of ET‐3 on Ca2+ discharge from internal pools.
Cytosolic Ca2+ concentration was evaluated with Fura‐2 in the absence of Ca2+ influx. Platelet preincubation for 15 min with 5 times 10−7 m ET‐3 decreased the Ca2+ release evoked by thrombin and U46619, a thromboxane‐mimetic. However, ET‐3 did not affect Ca2+ movements induced by 1 μm ADP. Addition of Tg (0.5 to 5 μm) to resting platelets induced a cytosolic [Ca2+] rise with concentration‐dependent increase of the initial rate and decrease of the time to reach the peak. ET‐3 slowed down these dose‐dependent effects with a more marked influence on the responses induced by low concentrations of Tg.
ET‐3 did not modify the Ca2+ response to another Ca2+‐ATPase inhibitor, 2,5‐di‐(tert‐butyl)‐1,4‐benzohydroquinone(tBuBHQ). The thromboxane A2 receptor antagonist, SQ 29548, reduced by 53% the calcium signal evoked by 1 μm Tg, which became similar to that induced by 15 μm tBuBHQ. Under these conditions, the ET‐3 effects were suppressed. A subsequent addition of thrombin induced a substantial further Ca2+ increase which was again sensitive to ET‐3.
ET‐3 attenuates Ca2+ mobilization from an internal pool dependent on the stimulation of thrombin and thromboxane A2 receptors and insensitive to the direct effect of Ca2+‐ATPase inhibitors. The small but significant inhibitory effect of ET‐3 leads us to propose that endothelin‐3 acts as a modulator of platelet activation.
Differences between 5‐HT3 receptor antagonists in modulation of visceral hypersensitivity
Authors: Banner S.E. , Sanger G.J. 
Published: July 2012

Noxious colo‐rectal distension was applied in conscious rats by acute balloon inflation and the effects observed as abdominal muscle contraction with the threshold typically between 10–40 mmHg. The effects of 5‐HT3 receptor antagonists on responses to noxious colo‐rectal distension were then studied in both normal rats and those pretreated with 5‐hydroxytryptophan (5‐HTP).
Granisetron and ondansetron (10 μg kg−1 and 1 mg kg−1, s.c.) had no effect on visceromotor thresholds to colo‐rectal distension in normal rats.
Hypersensitivity of the colo‐rectum was achieved by systemic administration of a low dose of 5‐HTP (10 mg kg−1, s.c.) which lowered the distension pressure required to induce the visceromotor reflex; analysis of variance showed a highly significant treatment effect (F1,11 = 84.26, P<0.001).
Granisetron, zatosetron, bemesetron and renzapride equi‐potently increased the threshold values at which distension evoked a visceromotor reflex after dosing with 5‐HTP, with a maximal response 3.6 to 4.2 fold above saline controls, at 10 μg kg−1, s.c. Metoclopramide (10 μg kg−1) also raised the level of distension required to elicit a response. By comparison, tropisetron caused a small, non‐significant increase in visceromotor threshold values and only at high doses (1 mg kg−1), whilst ondansetron and BRL 46470 had no signficant effects at doses up to 10 mg kg−1.
The response to granisetron (10 μg kg−1, s.c.) in 5‐HTP‐treated rats was unaltered by pre‐administration of naloxone (5 mg kg−1, s.c).
These results suggest that a 5‐HT3‐like receptor modulates 5‐HTP‐ evoked visceral hypersensitivity. However, the rank order of antagonist potency does not correlate with their order of potency against the classically defined 5‐HT3 receptor.
A new class of furoxan derivatives as NO donors: mechanism of action and biological activity
Authors: Ferioli R. , Folco G.C. , Ferretti C. , Gasco A.M. , Medana C. , Fruttero R. , Civelli M. , Gasco A. 
Published: July 2012

The mechanism of action and biological activity of a series of R‐substituted and di‐R‐substituted phenylfuroxans is reported.
Maximal potency as vasodilators on rabbit aortic rings, precontracted with noradrenaline (1 μm), was shown by phenyl‐cyano isomers and by the 3,4‐dicyanofuroxan, characterized by a potency ratio 3–10 fold higher than glyceryl trinitrate (GTN). This effect was reduced upon coincubation with methylene blue or oxyhaemoglobin (10 μm).
The furoxan derivatives showing maximal potency as vasodilators were also able to inhibit collagen‐induced platelet aggregation, with IC50 values in the sub‐micromolar range.
The furoxan derivatives were able to stimulate partially purified, rat lung soluble guanylate cyclase; among the most active compounds, the 3‐R‐substituted isomers displayed a higher level of stimulatory effect than the 4‐R analogues.
Solutions (0.1 mm) of all the tested furoxans, prepared using 50 mm phosphate buffer, pH 7.4, (diluting 10 mm DMSO stock solutions) did not release nitric oxide (NO) spontaneously; however in presence of 5 mm l‐cysteine, a significant NO‐releasing capacity was observed, which correlated significantly with their stimulation of the guanylate cyclase activity.
Pharmacological characterization of RS 25259‐197, a novel and selective 5‐HT3 receptor antagonist, in vivo
Authors: Eglen R.M. , Lee C.‐H. , Smith W.L. , Johnson L.G. , Clark R. , Whiting R.L. , Hegde S.S. 
Published: July 2012

The pharmacological effects in vivo, of RS 25259‐197, a selective 5‐HT3 receptor antagonist, have been investigated.
In anaesthetized rats, RS 25259‐197, administered by the intravenous, intraduodenal or transdermal route, dose‐dependently inhibited the von Bezold‐Jarisch reflex induced by 2‐methyl 5‐HT (ID50 = 0.04 μg kg−1, i.v., 3.2 μg kg−1, i.d. and 32.8 μg per chamber, respectively). In this regard, when administered intraduodenally, RS 25259‐197 was more potent and exhibited a longer duration of action than either ondansetron or granisetron.
In conscious ferrets, RS 25259‐197, administered intravenously or orally, dose‐dependently inhibited emesis induced by cisplatin. The ID50 estimates of RS 25259‐197 were 1.1 μg kg−1, i.v. and 3.2 μg kg−1, p.o. In this respect, RS 25259‐197 was more potent than ondansetron and equipotent with granisetron.
In conscious dogs, RS 25259‐197, administered intravenously or orally, dose‐dependently inhibited emesis induced by cisplatin (ID50 = 1.9 μg kg−1, i.v. and 8.5 μg kg−1, p.o.), dacarbazine (ID50 = 4.1 μg kg−1, i.v. and 9.7 μg kg−1, p.o.), actinomycin D (ID50 = 4.9 μg kg−1, i.v. and 2.5 μg kg−1, p.o.) and mechlorethamine (ID50 = 4.4 μg kg−1, i.v. and 3.0 μg kg−1, p.o.). Against each of the emetogenic agents, RS 25259‐197 was very much more potent than ondansetron. When tested at equi‐effective intravenous doses against cisplatin‐induced emesis in dogs, RS 25259‐197 had a longer duration of anti‐emetic activity (7 h) than ondansetron (4 h). At doses up to and including 1000 μg kg−1, p.o., neither RS 25259‐197 nor ondansetron was capable of inhibiting apomorphine‐induced emesis.
At doses up to 1000 μg kg−1, i.v., RS 25259‐197 produced no meaningful haemodynamic changes in anaesthetized dogs.
In summary, RS 25259‐197 is a novel, highly potent and orally active 5‐HT3 receptor antagonist in vivo. With respect to its anti‐emetic activity, RS 25259‐197 appears to be a significant improvement over ondansetron in terms of potency and duration of action.
Group B Streptococcus and E. coli LPS‐induced NO‐dependent hyporesponsiveness to noradrenaline in isolated intrapulmonary arteries of neonatal piglets
Authors: Villamor Eduardo , Pérez‐Vizcaíno Francisco , Ruiz Teresa , Leza Juan C. , Moro Manuel , Tamargo Juan 
Published: July 2012

The effects of endotoxin (E. coli lipopolysaccharide, LPS) and heat inactivated group B Streptococcus (GBS) were studied on the contractile responses to noradrenaline (NA) in isolated pulmonary arteries and on the activity of the constitutive and inducible nitric oxide synthase (NOS) in lung fragments of neonatal piglets.
Short‐term (≤ 5 h) incubation with LPS (1 μg ml−1) or GBS (3 × 107 colonies forming units ml−1) did not modify the vascular responsiveness to NA (10−8 M‐10−4 m) in isolated intrapulmonary arteries. However, long‐term incubation (20 h) with LPS or GBS produced a significant reduction in the maximal contractile responses and shifted the concentration‐response curve for NA downwards.
Endothelium removal or the cyclo‐oxygenase inhibitor meclofenamate (10−5 m) did not affect the GBS‐ and LPS‐induced hyporesponsiveness to NA.
The presence of the nitric oxide (NO) precursor, l‐arginine (10−5 m), 30 min prior to the contractility challenge increased the LPS‐ and GBS‐induced pulmonary vascular hyporesponsiveness to NA. In contrast, the addition, prior to the challenge with NA, of the NOS inhibitor NG‐nitro‐l‐arginine methyl ester (l‐NAME, 10−4m) or coincubation with dexamethasone (3 × 10−6m), a potent inhibitor of the induction of NOS, or with the protein synthesis inhibitor cycloheximide (10−5 m) completely restored the reactivity to NA in LPS‐ and GBS‐treated pulmonary arteries.
The incubation for 20 h of lung fragments with LPS and GBS produced a significant increase in the Ca2+‐independent (inducible) NOS activity determined by the conversion of radiolabelled l‐arginine to citrulline, but did not modify the constitutive NOS activity. This NOS induction was abolished by coincubation with dexamethasone (3 × 10−6 m).
These results demonstrated that prolonged incubation with GBS and LPS causes an induction of NOS activity which results in a reduced vascular responsiveness to NA in pulmonary arteries of neonatal piglets. Thus, induction of NOS seems to be responsible for the delayed pulmonary vascular hyporesponsiveness induced by GBS (a Gram‐positive) and E. coli (a Gram‐negative), the most common causal agents of neonatal sepsis.