bluuebunny/crossref_metadata_2025_split huggingface dataset:
Signal transduction pathways involved in the acute potentiation of NMDA responses by 1S,3R‐ACPD in rat hippocampal slices
Authors: Harvey Jenni , Collingridge Graham L. 
Published: July 2012

A grease‐gap recording technique has been used to investigate the mechanisms underlying the acute potentiation of N‐methyl‐d‐aspartate (NMDA) responses by aminocyclopentane‐1S,3R‐dicarboxylic acid (1S,3R‐ACPD) in area CA1 of rat hippocampal slices.
1S,3R‐ACPD (10 μm), but not 1R,3S‐ ACPD (10 μm), potentiated submaximal responses to NMDA (dose‐ratio of 0.81 ± 0.02 (mean ± s.e.mean); n = 55), but not to α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid (AMPA), in a readily reversible manner. Potentiation also occurred in slices treated with 0.2 μm tetrodotoxin, and in slices perfused with Mg2+‐free medium.
1S,3R‐ACPD‐induced potentiation was unaffected by the protein kinase inhibitors K‐252b (0.1 μm) and staurosporine (1 μm) and the intracellular Ca2+ store depletor, thapsigargin (10 μm). Coapplication of staurosporine and thapsigargin was also without effect.
1S,3R‐ACPD‐induced potentiation was unaffected by inhibitors of arachidonic acid formation, bromophenacyl bromide (50 μm) and RG80267 (100 μm). Arachidonic acid (10–50 μm) depressed reversibly NMDA‐induced responses. The potentiation was unaffected by 8‐bromo cyclic AMP (500 μm) or the PKA inhibitor Rp‐adenosine 3,5‐cyclic monophosphothioate triethylamine (Rp‐cAMPS; 50 μm).
1S,3R‐ACPD‐induced potentiation was abolished in slices perfused with Ca2+‐free medium. The potentiation was also blocked by phorbol‐12,13‐diacetate (1 μm), in a staurosporine‐sensitive manner.
It is concluded that the potentiation of NMDA responses by 1S,3R‐ACPD is not mediated by protein kinase A or C., by release of Ca2+ from intracellular stores or by arachidonic acid. It involves a Ca2+‐sensitive process and is negatively regulated by protein kinase C.
Estimation of competitive antagonist affinity from functional inhibition curves using the Gaddum, Schild and Cheng‐Prusoíf equations
Authors: Lazareno S. , Birdsall N.J.M. 
Published: July 2012

The estimation of antagonist affinity from functional experiments in which the effect of a fixed agonist concentration is reduced by a range of antagonist concentrations (‘functional inhibition curves’) has been considered from both a theoretical and experimental viewpoint.
Theoretical predictions are compared with results obtained from the stimulation of [35S]‐GTPγS binding by acetylcholine to membranes of Chinese hamster ovary (CHO) cells stably transfected with human m1–m4 muscarinic receptors, and inhibition of the stimulated binding by pirenzepine and AQ‐RA 741.
The usual procedure of applying the Cheng‐Prusoff correction is shown to be theoretically invalid, and predictions are made of the size and distribution of errors associated with this procedure.
A different procedure for estimating antagonist affinity, using the principles of dose‐ratio analysis and analogous to use of the Gaddum equation, is found to be accurate and theoretically valid.
A novel method of analysis allows accurate estimation of both antagonist affinity and Schild slope, by fitting the combined data from an antagonist inhibition curve and an agonist activation curve directly to a form of the Schild equation (derived by Waud) using non‐linear regression analysis.
It is shown that the conventional Schild analysis can be enhanced by treating part of the data as a family of inhibition curves and including in the Schild plot dose‐ratios estimated from the inhibition curves.
Regional haemodynamic effects of angiotensin II (3–8) in conscious rats
Authors: Gardiner S.M. , Kemp P.A. , March J.E. , Bennett T. 
Published: July 2012

It has been reported that angiotensin II (AII) (3–8) causes endothelium‐dependent renal cortical vasodilatation, in anaesthetized rats, through interaction with a novel receptor that shows no affinity for the AT1‐receptor antagonist, losartan. Therefore in order to get a fuller profile of the regional haemodynamic effects of AII (3–8) in conscious rats we assessed its renal, mesenteric and hindquarters vascular effects, and compared them to the responses elicited by AII and AIII.
AII and AIII (1.25, 12.5 and 125 pmol kg−1) caused dose‐dependent pressor and renal and mesenteric vasoconstrictor effects. At doses up to 125 pmol kg−1, AII (3–8) was without any cardiovascular effects, but with doses of 1.25 and 12.5 nmol kg−1 there were dose‐dependent increases in mean arterial blood pressure and reductions in renal and mesenteric flows and vascular conductances. The responses to AII (3–8) (12.5 nmol kg−1) were abolished by losartan (20 μmol kg−1).
Since it has been found that pretreatment with l‐arginine can reveal a vasodilator effect of AII (3–8) on rabbit pial arterioles, we assessed responses to AII (3–8) (12.5 nmol kg−1) before and 5 min after onset of a primed infusion of l‐arginine (1.4 mmol kg−1 bolus, 1.4 mmol kg−1 h−1 infusion). Responses to AII (3–8) were unchanged by l‐arginine.
The results are consistent with AII (3–8) being a less effective agonist than AII (or AIII) at the AT1‐receptor, but provide no evidence for AII (3–8) interacting with a novel receptor that shows no affinity for losartan.
Effects of the central analgesic tramadol and its main metabolite, O‐desmethyltramadol, on rat locus coeruleus neurones
Authors: Sevcik Jan , Nieber Karen , Driessen Bernd , Illes Peter 
Published: July 2012

Tramadol is a centrally acting analgesic with low opioid receptor affinity and, therefore, presumably additional mechanisms of analgesic action. Tramadol and its main metabolite O‐desmethyltramadol were tested on rat central noradrenergic neurones of the nucleus locus coeruleus (LC), which are involved in the modulation of nociceptive afferent stimuli.
In pontine slices of the rat brain the spontaneous discharge of action potentials of LC cells was recorded extracellularly. (−)‐Tramadol (0.1–100μm), (+)‐tramadol (0.1–100 μm), (−)‐O‐desmethyltramadol (0.1–100 μm) and (+)‐O‐desmetnyltramadol (0.01–1 μm) inhibited the firing rate in a concentration‐dependent manner. (+)‐O‐desmetnyltramadol had the highest potency, while all other agonists were active at a similar range of concentrations.
(−)‐Tramadol (10, 100 μm) was less inhibitory in brain slices of rats pretreated with reserpine (5 mg kg−1, 5 h before decapitation) than in controls.
The effect of (−)‐tramadol (10 μm) was abolished in the presence of the α2‐adrenoceptor antagonist, rauwolscine (1 μm), whilst that of (+)‐O‐desmetnyltramadol (0.3 μm) virtually disappeared in the presence of the opioid antagonist, naloxone (0.1 μm). (+)‐Tramadol (30 μm) and (−)‐O‐desmethyltramadol (10 μm) became inactive only in the combined presence of naloxone (0.1 μm) and rauwolscine (1 μm).
In another series of experiments, the membrane potential of LC neurones was determined with intracellular microelectrodes. (−)‐Tramadol (100 μm) inhibited the spontaneous firing and hyperpolarized the cells; this effect was abolished by rauwolscine (1 μm). (+)‐O‐desmethyltramadol (10 μm) had a similar but somewhat larger effect on the membrane potential than (−)‐tramadol. The (+)‐O‐desmethyltramadol‐ (10 μm) induced hyperpolarization was abolished by naloxone (0.1 μm).
The hyperpolarizing effect of noradrenaline (30 μm) was potentiated in the presence of (−)‐tramadol (100 μm), but not in the presence of (+)‐O‐desmethyltramadol (10 μm). There was no potentiation of the noradrenaline (30 μm) effect, when the cells were hyperpolarized by current injection to an extent similar to that produced by (−)‐tramadol (100 μm).
Both noradrenaline (100 μm) and (−)‐tramadol (100 μm) decreased the input resistance.
The results confirm that the analgesic action of tramadol involves both opioid and non‐opioid components. It appears that (−)‐tramadol inhibits the uptake of noradrenaline and via a subsequent increase in the concentration of endogenous noradrenaline indirectly stimulates α2‐adrenoceptors. (+)‐O‐desmethyltramadol seems to stimulate directly opioid μ‐receptors. The effects of (+)‐tramadol and (−)‐O‐desmetnyltramadol consist of combined μ‐opioid and α2‐adrenergic components.
Role of tumour necrosis factor in the induction of nitric oxide synthase in a rat model of endotoxin shock
Authors: Thiemermann Christoph , Wu Chin‐Chen , Szabó Csaba , Perretti Mauro , Vane John R. 
Published: July 2012

This study investigates the role of tumour necrosis factor (TNF) in the induction of nitric oxide synthase (NOS) by bacterial endotoxin (lipopolysaccharide; LPS) in a rat model of endotoxin shock.
In anaesthetized rats, pretreatment with a monoclonal antibody for TNF (TNFab; 20 mg kg−1, s.c., at 16 h prior to LPS) ameliorated the fall in mean arterial blood pressure (MAP) in response to LPS (2 mg kg−1, i.v.). For instance, endotoxaemia for 180 min resulted in a fall in MAP from 114 ± 6 (control) to 84 ± 5 mmHg (P < 0.01; n = 7). In contrast, animals pretreated with TNFab prior to LPS injection maintained significantly higher MAP when compared to LPS‐control (MAP at 180 min; 118 ± 3 mmHg; P < 0.01, n = 5).
Three hours of endotoxaemia was also associated with a significant reduction of the contractile effects of noradrenaline (NA) (10−1–10−6 m) on the thoracic aorta ex vivo. This hyporeactivity to NA was partially restored by in vitro treatment of the vessels with NG‐nitro‐l‐arginine methyl ester (l‐NAME, 20 min, 3 × 10−4 m). Pretreatment of rats with TNFab (20 mg kg−1; at 16 h prior to LPS) significantly (P < 0.05) attenuated the LPS‐induced hyporeactivity of rat aortic rings ex vivo. l‐NAME did not enhance the contractions of aortic rings obtained from TNFab pretreated LPS‐rats.
At 180 min after LPS there was a significant elevation of the induced NOS activity in the lung (5.14 ± 0.57 pmol citrulline mg−1 min−1, n = 8). TNFab pretreatment significantly attenuated this induction of NOS in response to LPS by 37 ± 6% (n = 5; P < 0.05).
We conclude that the formation of endogenous TNF contributes to the induction of the calcium‐independent isoform of NOS in response to LPS in vivo. Thus, the beneficial effects of agents which inhibit either the release or the action of TNF in circulatory shock may be, in part, due to inhibition of NOS induction.
Use‐dependent block of Na+ currents by mexiletine at the single channel level in guinea‐pig ventricular myocytes
Authors: Sunami Akihiko , Fan Zheng , Sawanobori Tohru , Hiraoka Masayasu 
Published: July 2012

The mechanism of use‐dependent block of Na+ current by mexiletine was studied at the single channel level in guinea‐pig ventricular myocytes by the patch‐clamp techniques. All experiments were performed using stimulation protocols to enable us to analyze the strict dependence of changes in channel properties on channel use.
In cell‐attached patches, bath or pipette application of mexiletine (40 μm) produced a use‐dependent reduction of the peak average current without changes in single channel conductance. Null sweeps were increased and the number of openings per sweep decreased with successive pulses, whereas no significant change in the mean open time was detected during the train.
Block by mexiletine became greater when pulse duration was extended beyond the period in which channels were open, suggesting that block progressed without channel opening.
At near threshold potentials, mexiletine decreased the later occurrence of first openings. Additionally, late openings were reduced in a use‐dependent way.
We conclude that mexiltine binds to the inactivated closed states of the Na+ channel and then causes a failure of late openings as well as early, which results in null sweeps on subsequent depolarization.
Characterization of the novel nitric oxide synthase inhibitor 7‐nitro indazole and related indazoles: antinociceptive and cardiovascular effects
Authors: Moore P.K. , Wallace P. , Gaffen Z. , Hart S.L. , Babbedge R.C. 
Published: July 2012

7‐Nitro indazole (7‐NI, 10–50 mg kg−1), 6‐nitro indazole and indazole (25–100 mg kg−1) administered i.p. in the mouse produce dose‐related antinociception in the late phase of the formalin‐induced hindpaw licking and acetic acid‐induced abdominal constriction assays. The ED50 values (mg kg−1) were as follows: 7‐NI (27.5 and 22.5), 6‐nitro indazole (62.5 and 44.0) and indazole (41.0 and 48.5) in the two assays respectively. 3‐Indazolinone, 6 amino indazole and 6‐sulphanilimido indazole (all 50 mg kg−1) were without effect. With the exception of 5‐nitro indazole (50 mg kg−1) which produced sedation, none of the other indazole derivates examined caused overt behavioural changes.
The antinociceptive effect of 7‐NI (25 mg kg−1, i.p.) in the late phase of the formalin‐induced hindpaw licking assay was partially (46.7 ± 16.2%, n = 18) reversed by pretreatment with l‐ but not d‐arginine (both 50 mg kg−1, i.p.).
The time course of 7‐NI induced antinociception in the mouse was correlated with inhibition of brain (cerebellum) nitric oxide synthase (NOS) activity. Maximum antinociceptive activity and NOS inhibition were detected 18–30 min following i.p. administration. In contrast, no antinociceptive effect or inhibition of cerebellar NOS was detected 75 min post‐injection.
7‐NI, 6‐nitro indazole, indazole, 3‐indazolinone and 6‐amino indazole (all 50 mg kg−1) failed to influence mean arterial pressure (MAP) over the 45 min after i.p. administration in the anaesthetized mouse. Similarly, 7‐NI (25 mg kg−1) administered i.v. in the anaesthetized rat did not increase MAP or influence the vasodepressor effect of i.v. injected acetylcholine (ACh) over the same period.
7‐NI (100 μm) did not influence the vasorelaxant effect of ACh (IC50, 0.2 ± 0.04 μm, cf. 0.16 ± 0.06 μm, n = 6) in phenylephrine‐precontracted rabbit aortic rings.
These data provide further evidence that antinociception following administration of 7‐NI in the mouse results from inhibition of central NOS activity and is not associated with inhibition of in vivo vascular endothelial cells NOS. Accordingly, 7‐NI (or a derivative thereof) may provide an alternative approach to the development of novel antinociceptive drugs.
Pharmacological characterization of the novel nonpeptide angiotensin II receptor antagonist, BIBR 277
Authors: Wienen W. , Hauel N. , Van Meel J.C.A. , Narr B. , Ries U. , Entzeroth M. 
Published: July 2012

The pharmacological profile of BIBR 277, 4′‐[(1,4′‐dimethyl‐2′‐propyl[2,6′‐bi‐1H‐benzimidazol]‐1′‐yl)methyl]‐[1,1′‐biphenyl]‐2‐carboxylic acid, a novel, nonpeptide angiotensin II receptor antagonist has been investigated by use of receptor binding studies, enzymatic assays, functional in vitro assays in rabbit aorta as well as in vivo experiments in pithed, anaesthetized and conscious rats.
BIBR 277 potently interacted with rat AT1 receptors (Ki 3.7 nm). Competitive receptor interaction was shown by radioligand saturation experiments performed in the presence of BIBR 277. The failure to inhibit radioligand binding to AT2 sites demonstrates the selectivity of BIBR 277 for AT1 receptors. This is further substantiated by the findings that BIBR 277 neither interacted with other receptor systems investigated nor affected the activity of components of the human renin‐angiotensin system, such as plasma renin or serum converting enzyme.
In rabbit aorta, BIBR 277 had no agonistic properties and was shown to be an insurmountable antagonist of angiotensin II‐induced contractions (KB 0.33 nm). The antagonistic effect persisted even after several wash‐out procedures. However, this interaction was not irreversible since the insurmountable antagonism was concentration‐dependently reversed when BIBR 277 (0.1 μm) and the surmountable antagonist, losartan (0.1 and 1.0 μm) were incubated simultaneously. The specificity of BIBR 277 for the AT1 receptor was further substantiated in this preparation since micromolar concentrations of BIBR 277 neither affected potassium chloride and noradrenaline‐induced contractions nor acetylcholine‐mediated tissue relaxation.
In pithed rats, i.v. administration of BIBR 277 (0.1, 0.3 and 1.0 mg kg−1) shifted the dose‐pressor response curve to angiotensin II dose‐dependently to the right with ED50 values of 0.23 μg kg−1 (control) and 1.4 μg kg−1, 4.7 μg kg−1 and 20 μg kg−1, respectively. As observed in the in vitro experiments no agonistic effect was detected and the maximum of the blood pressure response to angiotensin II at the highest dose of BIBR 277 was decreased by 29%.
In anaesthetized rats, bolus i.v. administration of 0.1, 0.3 and 1.0 mg kg−1 BIBR 277 attenuated the blood pressure response to bolus i.v. injections of angiotensin II (0.1 μg kg−1). At the highest dose an almost complete blockade was observed even after 2 h.
Single oral administration of BIBR 277 (0.3 and 1.0 mg kg−1) to conscious, chronically instrumented renovascular hypertensive rats dose‐dependently decreased the mean arterial blood pressure by 15 and 30 mmHg, respectively. At the higher dose a significant antihypertensive effect was maintained for more than 24 h. Moreover, consecutive daily dosing of 1 mg kg−1 orally resulted in a sustained reduction in blood pressure over the 4 day observation period.
It is concluded that BIBR 277 is an effective and selective angiotensin II antagonist with antihypertensive activity after oral administration.
Dissociation of the anti‐ischaemic effects of cloricromene from its anti‐platelet activity
Authors: Lidbury Paul S. , Cirillo Rocco , Vane John R. 
Published: July 2012

Cloricromene is a non‐anticoagulant coumarin derivative with anti‐platelet and anti‐leukocyte properties, which has beneficial effects in various models of ischaemia and shock.
We have assessed the effects of cloricromene on (a) ex vivo platelet aggregation, and (b) infarct size using a model of myocardial ischaemia in the anaesthetized rabbit.
Cloricromene (1–1000 μg kg−1 min−1 for 15 min) induced a dose‐dependent inhibition of ex vivo platelet aggregation, causing only a minimal increase in heart rate and no change in mean arterial blood pressure. The inhibitory activity was considerably stronger when platelet aggregation was induced by collagen than by ADP.
Cloricromene inhibited ex vivo platelet aggregation in rabbits pretreated with indomethacin (5 mg kg−1) and this inhibition persisted for 30–60 min.
The model of myocardial ischaemia involved 1 h occlusion of the first antero‐lateral branch of the left coronary artery followed by 2 h of reperfusion. Infusion of cloricromene (30 or 300 μg kg−1 min−1), ibuprofen (80 μg kg−1 min−1) or vehicle began 15 min prior to occlusion, and continued throughout the experiment.
While area at risk was similar for all groups studied, cloricromene (30 or 300 μg kg−1 min−1) or ibuprofen caused a reduction in infarct size, and decreased myeloperoxidase activity in the tissue of the infarcted myocardium.
Cloricromene at 300 μg kg−1 min−1 also reduced the occlusion‐induced elevation of the ST‐segment of the rabbit electrocardiogram, and inhibited platelet aggregation ex vivo. Ibuprofen or cloricromene at 30 μg kg−1 min−1 had no effect on either the ST‐elevation or platelet reactivity.
Thus, cloricromene exhibits a cardioprotective activity via an inhibition of leukocyte infiltration, in the presence (300 μg kg−1 min−1) or absence (30 μg kg−1 min−1) of inhibition of platelet activity ex vivo. The anti‐aggregatory activity of cloricromene acts via a mechanism that is either different from, or in addition to, inhibition of cyclo‐oxygenase, and is of long duration.
A facilitatory effect of anti‐angiotensin drugs on vagal bradycardia in the pithed rat and guinea‐pig
Authors: Rechtman M. , Majewski H. 
Published: July 2012

In pithed rats, preganglionic vagal nerve stimulation (at 5 Hz) elicited a bradycardia. This bradycardia was potentiated by the angiotensin converting enzyme inhibitor, captopril (1 mg kg−1, i.v.) by about 40%. Subsequent angiotensin II infusion (0.03 μg kg−1 min−1) reversed this effect. A similar facilitatory effect was also seen with the angiotensin receptor antagonist, losartan (10 mg kg−1, i.v.). These results suggest a tonic inhibitory effect of endogenous angiotensin II on vagal transmission.
The effect of captopril in potentiating vagal bradycardia appears to be at the level of vagal neurones, since the bradycardia elicited by the muscarinic agonist, methacholine was unaffected.
After the pithed rats were nephrectomized, captopril had no effect on vagally‐induced bradycardia, suggesting that the formation of the endogenous angiotensin II responsible for the effect was dependent on renin release from the kidney.
When the sympathetic nerves of the pithed rat were electrically stimulated there was a tachycardia, and this was unaffected by captopril. However, when the sympathetic and vagus nerves were activated concurrently, the resulting tachycardia was inhibited by captopril.
In pithed guinea‐pigs, captopril also potentiated the bradycardia caused by vagal nerve stimulation. This appears to be a tissue‐selective effect since the bronchoconstriction due to the vagal stimulation was not affected by captopril.
These results suggest that endogenous angiotensin II can have a tonic inhibitory effect on cardiac vagal transmission. Disruption of this mechanism by anti‐angiotensin drugs may attenuate the reflex tachycardia associated with the fall in blood pressure in anti‐hypertensive therapy.
Comparison of contractile responses to 5‐hydroxytryptamine and sumatriptan in human isolated coronary artery: synergy with the thromboxane A2‐receptor agonist, U46619
Authors: Cocks T.M. , Kemp B.K. , Pruneau D. , Angus J.A. 
Published: July 2012

The interaction between the thromboxane A2 receptor agonist, U46619 and two 5‐hydroxytryptamine (5‐HT) receptor agonists, the non‐selective, naturally occurring agonist, 5‐HT and the selective 5‐HT1‐like agonist, sumatriptan were studied in human epicardial coronary arteries in vitro.
Coronary artery rings (2–4 mm in diameter) were prepared from epicardial arteries from explant hearts of patients undergoing heart transplant (cardiomyopathy, n = 13; ischaemic heart disease, n = 10) and unused donor hearts (n = 5). Each ring of artery was set at optimal resting conditions to record changes in isometric force.
The majority of artery rings developed phasic, rhythmic contractions either spontaneously or in response to all vasoconstrictor agonists tested. Both the spontaneous and agonist‐induced phasic contractions were abolished by nifedipine (0.1 μm).
Concentration‐contraction curves to 5‐HT‐receptor agonists and noradrenaline (NA), were first constructed in artery rings that did not develop phasic activity. 5‐HT and ergometrine were the most potent agonists with EC50 values of 6.8 ± 0.2 and 7.7 ± 0.2 (−log m) respectively. Potencies (EC50's) to sumatriptan, methysergide and noradrenaline could not be determined due to their poor ability to contract the coronary artery. Maximum contractions (Emax; normalized as a percentage of the contraction to a maximum‐depolarizing concentration of K+ in physiological salt solution (KPSS)) for 5‐HT, ergometrine, sumatriptan, methysergide and noradrenaline were 40 ± 10, 9 ± 3, < 5, < 5 and < 5% respectively.
In arteries without phasic activity, U46619 (1 nm) caused an increase in force of 3.8 ± 1% KPSS. With U46619 present, the Emax values for 5‐HT, ergometrine, sumatriptan and methysergide were all markedly increased. For 5‐HT and sumatriptan, Emax values were 92 ± 4% and 49 ± 14% KPSS respectively. The presence of U46619 did not significantly change the sensitivity (EC50) to 5‐HT.
In a separate series of arteries, nifedipine (0.1 μm) was used to block phasic, contractile activity. The synergy observed between U46619 and 5‐HT or sumatriptan still occurred although the Emax values for each agonist were depressed but the EC50 values were again unaffected.
In conclusion, these in vitro studies indicate that the normally poor contractions to sumatriptan, in human coronary arteries are significantly enhanced when active force is induced with a thromboxane A2‐receptor agonist, U46619. The enhanced response is not specific for either sumatriptan or 5‐HT1‐like receptors since contractions to 5‐HT, ergometrine and methysergide were also potentiated by U46619.