bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of tolerance to the effects of vigabatrin (γ‐vinyl‐GABA) on GABA release from rat cerebral cortex, spinal cord and retina
Authors: Neal M.J. , Shah M.A.
Published: July 2012

The effects of acute and chronic vigabatrin (γ‐vinyl‐GABA) (GVG) administration on γ‐aminobutyric acid (GABA) levels and release in rat cortical slices, spinal cord slices and retinas were studied.

GVG (250 mg kg−1 i.p.) administered to rats 18 h before death (acute administration) produced an almost 3 fold increase in GABA levels of the cortex and spinal cord and a 6 fold increase in retinal GABA. The levels of glutamate, aspartate, glycine and taurine were unaffected.

When GVG (250 mg kg−1 i.p.) was administered daily for 17 days (chronic administration) a similar (almost 3 fold) increase in cortical GABA occurred but the increases in spinal and retinal GABA were reduced by approximately 40%.

Acute administration of GVG strikingly increased the potassium‐evoked release (KCl 50 mm) of GABA from all three tissues. This enhanced evoked release was reduced by about 50% in tissues taken from rats that had been chronically treated with GVG.

Acute administration of GVG reduced GABA‐transaminase (GABA‐T) activity by approximately 80% in cortex and cord and by 98% in the retina. Following the chronic administration of GVG, there was a trend for GABA‐T activities to recover (significant only in cortex). Acute administration of GVG had no effect on glutamic acid decarboxylase (GAD) activity in cortex or spinal cord. However, chronic treatment resulted in significant decreases in GAD activity in both the cortex and cord (35% and 50% reduction respectively).

The K‐evoked release of glutamate, aspartate, glycine and taurine from cortical slices and the K‐evoked release of glycine from spinal slices and retinas were not affected by either acute or chronic GVG treatment.

These experiments indicate that GVG treatment increases specifically the K‐evoked release of GABA and that tolerance can develop to this enhancing effect of GVG on central GABA release. This tolerance may result from increased feedback inhibition of GAD with a consequent reduction of presynaptic GABA stores.
No effect of pertussis toxin on peripheral prejunctional α2‐adrenoceptor‐mediated responses and on endothelium‐dependent relaxations in the rat
Authors: Docherty J.R.
Published: July 2012

We have investigated the effects of pertussis toxin treatment on a variety of peripheral tissues in the rat.

Incubation with pertussis toxin (1 μg ml−1) in vitro failed to alter the negative inotropic actions of acetylcholine in rat left atria.

Pretreatment with pertussis toxin (6 μg kg−1, i.v., 3–4 days) abolished the negative inotropic actions of acetylcholine in rat left atria.

Pretreatment with pertussis toxin (40 μg kg−l, i.v., 3–4 days) failed to alter the prejunctional inhibitory actions of the α2‐adrenoceptor agonist xylazine, either in terms of the isometric contraction to a single stimulus in rat vas deferens or in terms of stimulation‐evoked overflow of tritium in atria pre‐incubated with [3H]‐noradrenaline.

Pretreatment with pertussis toxin (6 μg kg−1, i.v., 3–4 days) failed to affect, and pertussis toxin (40 μg kg−1, i.v., 3–4 days) potentiated endothelium‐dependent relaxations of rat aorta to histamine and acetylcholine.

It seems unlikely that peripheral prejunctional actions of α2‐adrenoceptor agonists or endothelium‐dependent relaxations of rat aorta involve pertussis toxin‐sensitive G proteins.
Glibenclamide is a competitive antagonist of the thromboxane A2 receptor in dog coronary artery in vitro
Authors: Cocks Thomas M. , King Susannah J. , Angus James A.
Published: July 2012

Glibenclamide, a sulphonylurea oral hypoglycaemic agent is a widely used antagonist of cromakalim‐activated K+ channels in smooth muscle.

In isolated ring segments of the large circumflex coronary artery from the dog, glibenclamide (1–30 μm) caused a concentration‐dependent reduction in both spontaneous isometric force and contractions induced by U46619, a thromboxane A2‐mimetic.

Glibenclamide behaved as a competitive antagonist of U46619 with an estimated pKB (‐log KB) value of 6.2 by Schild regression analysis (slope 1.07).

Glibenclamide (30 μm) was apparently selective since it had no effect on the concentration‐contraction curves to endothelin‐1, noradrenaline or KCl.

We suggest that this additional property of glibenclamide should be considered in any smooth muscle study where active force is raised by either the exogenous application or endogenous generation of thromboxane A2.
Evaluation of the effect of azapropazone on neutrophil migration in regional myocardial ischaemia/reperfusion injury in rabbits
Authors: Mousa Shaker A. , Brown Reginald , Thoolen Martin J.M. , Smith Ronald D.
Published: July 2012

The purpose of the present study was to determine the myocardial cytoprotective efficacy of azapropazone (AZA) and its potential site of action on neutrophil infiltration into reperfused/ischaemic myocardium with or without in vivo activation of neutrophils in rabbits.

AZA, 100 mg kg−1, was administered i.v. 10 min after occlusion of the left circumflex (LCX) artery in rabbits with and without pretreatment with phorbol myristate acetate ester (PMA). The LCX occlusion was then released at 10 min after AZA administration. Haemodynamic parameters (heart rate, LV pressure, mean arterial blood pressure and dp/dt) were monitored throughout the experiment. After 60 min reperfusion, the area at risk was delineated and the heart was then excised and divided into epi‐ and endocardial pieces for analysis of myeloperoxidase activity.

AZA inhibited neutrophil infiltration into the reperfused/ischaemic rabbit myocardium with and without PMA treatment. The inhibition of neutrophil infiltration was more apparent in the epicardium than in the endocardium. Additionally, AZA inhibited to a similar extent the in vivo PMA‐stimulated neutrophil migration into the epicardium and endocardium area at risk. AZA had no significant effect on the haemodynamic parameters as compared to control.

AZA administered in an anaesthetized rabbit model of LCX occlusion/reperfusion resulted in the reduction of infarct size.

It is concluded that AZA has significant inhibitory effects on neutrophil migration which might contribute to its myocardial cytoprotective effect.
CGP 35348, a new GABAB antagonist, prevents antinociception and muscle‐relaxant effect induced by baclofen
Authors: Malcangio M. , Ghelardini C. , Giotti A. , Malmberg‐Aiello P. , Bartolini A.
Published: July 2012

CGP 35348, a new GABAB antagonist, was examined on antinociception induced by (±)‐baclofen by use of the hot plate and writhing tests in mice and the paw pressure test in rats. CGP 35348 was also studied in mice on (±)‐baclofen‐induced impairment of rota‐rod performance.

CGP 35348, injected either i.p. (60–100 mg kg−1 in mouse) or intracerebroventricularly (i.c.v.) (0.5–2.5 μg per mouse; 25 μg per rat) prevented (±)‐baclofen‐induced antinociception.

CGP 35348 did not modify oxotremorine‐ and morphine‐induced antinociception in mice and rats.

CGP 35348 (2.5 μg i.c.v. per mouse) also prevented (±)‐baclofen‐induced impairment of the rota‐rod test.

Two other GABAB antagonists, phaclofen (50 μg i.c.v. per mouse) and 2‐OH‐saclofen (2.5 μg‐10 μg i.c.v. per mouse) did not modify (±)‐baclofen‐induced antinociception.

These results suggest that, at present, CGP 35348 is the only compound able to antagonize (±)‐baclofen‐induced antinociception.
Effect of pertussis pretreatment on plasma glucose and insulin responses to lithium in rats
Authors: Hermida O. García , Fontela T. , Ghiglione M. , Uttenthal L.O.
Published: July 2012

Administration of lithium to rats causes a rise in plasma glucose and suppresses glucose‐stimulated insulin secretion. These effects are blocked by the α2‐adrenoceptor antagonist, yohimbine.

Pretreatment of rats with Bordetella pertussis toxin resulted in a reversal of the usual plasma glucose and insulin responses to intravenously administered lithium (4 mEq kg−1). There was a slow fall in plasma glucose, while plasma insulin rose to 267 ± 42% (± s.e.mean) of control values at 30 min. The effect of lithium on glucose‐stimulated insulin secretion was also reversed; there was a marked increase in the insulin response which contrasted with the suppression seen in normal controls.

In perifused islets of Langerhans isolated from pertussis pretreated rats, the previously described inhibition by lithium of the second phase of glucose‐stimulated insulin secretion from normal islets was almost completely abolished.

The results are consistent with the hypothesis that these effects of lithium are mediated by the influence of catecholamines on the islets. When the inhibitory effect of α2‐adrenoceptors is abolished by pertussis treatment, which blocks the action of the inhibitory guanine nucleotide‐binding protein Gi, effects of β‐adrenoceptor stimulation predominate, leading to an increased secretion of insulin.
Human interleukin‐1 induces a rapid relaxation of the rabbit isolated mesenteric artery
Authors: Marceau François , Petitclerc Eric , DeBlois Denis , Pradelles Philippe , Poubelle Patrice E.
Published: July 2012

Strips of rabbit superior mesenteric artery, precontracted with phenylephrine, relaxed when exposed to human recombinant interleukin‐1 (IL‐1) of the α or β types. The effect was observed within 10 min, was optimal 32 min after the application of the cytokines and concentration‐dependent (12–290 pm).

IL‐1α and IL‐1β were equipotent in relaxing the rabbit mesenteric artery. A synthetic fragment corresponding to IL‐1β 163–171 was approximately one million fold less active than IL‐1β. The tripeptide Lys‐d‐Pro‐Thr, an analogue of IL‐1β 193–195, was inactive as an antagonist of IL‐1β on the preparation.

Indomethacin (2.8 μm) prevented or acutely reversed IL‐1‐induced relaxations in the rabbit mesenteric artery. Purified haemoglobin (10 μm) or the removal of endothelium had no effect on relaxations elicited by IL‐1β.

The preparation exhibited some selectivity for IL‐1 as recombinant human tumour necrosis factor‐α (TNF‐α), IL‐2 or IL‐6 failed to influence it. TNF‐α was not synergistic with a subthreshold concentration of IL‐1β.

Immunoreactive 6‐keto‐prostaglandin F1α and prostaglandin E2 were increased in the bathing fluid of isolated mesenteric arteries exposed to IL‐1β as compared to controls.

A supernatant of lipopolysaccharide‐stimulated human monocytes produced a relaxation of the preparation with a profile similar to that produced with IL‐1s and there was a good quantitative agreement between the extent of the relaxation and the enzyme immunoassay measurements of IL‐1α and IL‐1β in the supernatant. Furthermore the relaxation of crude monocyte IL‐1 was prevented by preincubating with antibodies to IL‐1α and IL‐1β. This experiment illustrates the possible use of the preparation for bioassay of IL‐1.

It is concluded that either form of IL‐1 relaxes the precontracted rabbit mesenteric artery by a prostaglandin‐dependent, nitric oxide‐independent mechanism. The model is also useful for distinguishing the mechanism of IL‐1‐induced hypotension in vivo in rabbits.
Maintenance of functional activity of human pulmonary arteries after cryopreservation
Authors: Ellis P. , Müller‐Schweinitzer E.
Published: July 2012

Human intrapulmonary arteries have been investigated in vitro in fresh tissue or after storage at −190°C in foetal calf serum containing 1.8 m dimethyl sulphoxide.

After cryopreservation of the arteries, maximal contractile force was reduced to 76%. This was assessed by the responses (in g) to 10 nm of the thromboxane analogue, U 46619.

Constricting agonists such as noradrenaline, 5‐hydroxytryptamine, histamine and U 46619 stimulated fresh and frozen/thawed arteries producing pD2 values similar to the respective values determined on fresh tissues.

Endothelium‐independent relaxant responses of U 46619‐precontracted arteries to prostacyclin (PGI2), aminophylline and papaverine were generally unchanged after storage. The same was true for relaxant response to the potassium channel activator P‐1075 whereas the pD2 values for SDZ PCO 400, RP 49356 and cromakalim were somewhat diminished.

Nevertheless, a significant correlation was obtained when the apparent pD2 values for all agonists on fresh and frozen/thawed tissues were compared (P < 0.001).

The evidence suggests that after cryopreservation of human intrapulmonary arteries at −190°C, mechanisms of both contraction and relaxation are well‐maintained.
Prejunctional modulatory action of neuropeptide Y on responses due to antidromic activation of peripheral terminals of capsaicin‐sensitive sensory nerves in the isolated guinea‐pig ileum
Authors: Takaki Miyako , Nakayama Sosogu
Published: July 2012

The effect of neuropeptide Y (NPY) on motor responses produced by activation of capsaicin‐sensitive primary afferents in the guinea‐pig isolated ileum was determined by use of capsaicin itself and electrical mesenteric nerve stimulation as stimuli.

NPY inhibited or suppressed the cholinergic contractile response produced by electrical mesenteric nerve stimulation while leaving the contractile response to a threshold concentration of capsaicin.

NPY had no effect on motor responses produced by a submaximal concentration of substance P, the putative endogenous mediator of the ‘efferent’ function of sensory fibres in this preparation.

It is concluded that NPY exerted a prejunctional inhibitory action on transmitter release from peripheral endings of capsaicin‐sensitive nerves at interneuronal synapses.
Regional haemodynamic effects of prolonged infusions of human α‐calcitonin gene‐related peptide in conscious, Long Evans rats
Authors: Gardiner S.M. , Compton A.M. , Kemp P.A. , Bennett T. , Foulkes R. , Hughes B.
Published: July 2012

Haemodynamic measurements were made in conscious, Long Evans rats chronically instrumented for the assessment of changes in regional blood flows (renal, mesenteric and hindquarters, or internal and common carotid) and systemic arterial blood pressure and heart rate, before, during and after 3 day infusions of vehicle or human α‐calcitonin gene‐related peptide (CGRP) (1.5 or 15 nmol kg−1 h−1).

In animals with renal, mesenteric and hindquarters flow probes (n = 8), during the first day of infusion of human α‐CGRP (1.5 nmol kg−1 h−1) there was sustained tachycardia and hypotension, a sustained reduction in renal flow, a transient reduction in mesenteric flow and a relatively well‐maintained increase in hindquarters flow. All these effects were significantly different from the changes seen in vehicle‐infused rats (n = 8), but calculation of vascular conductances showed only the late mesenteric vasodilatation and the sustained hindquarters vasodilatation were different from the changes in vehicle‐infused rats. However, by the second day of infusion and thereafter cardiovascular variables in the animals receiving vehicle and those receiving human α‐CGRP were not different.

Nine animals instrumented with probes to monitor changes in internal and common carotid haemodynamics initially received human α‐CGRP infused at a rate of 1.5 nmol kg−1 h−1. Three of these animals still showed some response to the human α‐CGRP (tachycardia, hypotension, hyperaemic vasodilatation) throughout the second day of infusion and hence were taken through the 3 day infusion protocol. When the infusion was stopped on the fourth day all these animals showed reversal of the effects of human α‐CGRP. The other 6 animals in the original group showed complete desensitization to the effects of human α‐CGRP by the end of the second day of infusion (as seen in the group instrumented with renal, mesenteric and hindquarter probes). Therefore, in order to assess the extent of desensitization, at the beginning of the third day the dose of human α‐CGRP was increased to 15 nmol kg−1 h−1. The resulting tachycardia, hypotension and hyperaemia in the carotid vascular beds were significant, (but no greater than the initial responses to human α‐CGRP at 1.5 nmol kg−1 h−1). These effects were maintained throughout the third infusion day, but there was some desensitization to the effects of this higher dose of human α‐CGRP by the beginning of the fourth infusion day. However, when the infusion was stopped there was clear reversal of the effects of human α‐CGRP.

The results indicate substantial inter‐individual variation in the haemodynamic effects of prolonged infusions of human α‐CGRP in conscious, Long Evans rats. However, since increasing the dose of human α‐CGRP overcame the desensitization, it is feasible that, in the clinical setting, maintained increases in internal carotid blood flow could be achieved by individually‐adjusted infusions of human α‐CGRP.
Effects of midaglizole, a new hypoglycaemic drug on the electrophysiological properties of guinea‐pig papillary muscle
Authors: Noguchi Noriyasu , Hasegawa Junichi , Mashiba Hiroto
Published: July 2012

The electrophysiological effects of midaglizole, a new oral hypoglycaemic agent which is an α2‐adrenoceptor antagonist, were assessed in the reserpinized ventricular myocardium of the guinea‐pig.

Midaglizole suppressed the maximal rate of rise (V̇max) and the amplitude of action potentials (APA) of the fast and the slow responses in a concentration‐dependent manner without influencing the resting potentials.

Voltage‐dependency of the V̇max block of the action potentials by midaglizole (10 μm) did not appear in solutions containing various concentrations of KCl.

It is concluded that midaglizole has inhibitory effects on the fast Na+ and slow Ca2+ currents of the membrane independent of the blockade of myocardial α‐adrenoceptors, and that these effects may be significant in some clinical uses of the drug.
A quantitative investigation into the dependence of Ca2+ mobilisation on changes in inositol 1,4,5‐trisphosphate levels in the stimulated neutrophil
Authors: Thompson Neil T. , Bonser Robert W. , Tateson James E. , Spacey Graham D. , Randall Roger W. , Hodson Harold F. , Garland Lawrence G.
Published: July 2012

The coupling of N‐formyl‐methionyl‐leucyl‐phenylalanine (fMet‐Leu‐Phe) receptor stimulation to Ca2+ mobilisation has been investigated in the human neutrophil by measuring the concentration‐effect curves for inositol 1,4,5‐trisphosphate (IP3) formation and Ca2+ mobilisation.

fMet‐Leu‐Phe‐dependent mobilisation of intracellular Ca2+ has been monitored in fluo‐3‐loaded human neutrophils by measuring increases in the cytoplasmic free Ca2+ concentration ([Ca2+]i) in the presence of extracellular EGTA. Fluo‐3 was used in preference to fura‐2 because it was found to be more sensitive to the high Ca2+ levels seen in stimulated neutrophils.

fMet‐Leu‐Phe induced a rapid mobilisation of intracellular Ca2+ (EC50 = 2.9 ± 0.1 nm) and increased [Ca2+]i to a maximum of 1286 ± 184 nm.

The amount of IP3 in fMet‐Leu‐Phe‐stimulated neutrophils was determined by competition with [3H]‐IP3 for a specific IP3 binding protein isolated from bovine adrenocortical microsomes. Basal IP3 levels of 13.3 ± 2.0 pmol per 107 cells were increased nearly 4 fold by maximally effective concentrations of fMet‐Leu‐Phe.

The EC50 for the IP3 response (95 ± 18 nm) was much higher than that for mobilisation of intracellular Ca2+, such that only a doubling in the concentration of IP3 was required to fully mobilise intracellular Ca2+.

As a result of this relationship IP3 production was more sensitive than Ca2+ mobilisation to inhibition by demethoxyviridin, an inhibitor of phospholipase activation.
(+)‐Isradipine but not (−)‐Bay‐K‐8644 exhibits voltage‐dependent effects on cat adrenal catecholamine release
Authors: López Manuela G. , Michelena Pedro , Gandía Luis , García Antonio G.
Published: July 2012

Catecholamine release from cat adrenal glands perfused at a high rate (4 ml min−1) at 37°C with polarizing (1.2 or 5.9 mm K+) or depolarizing (17.7, 35, 59 or 118 mm K+) solutions, was triggered by 5 or 10 s pulses of Ca2+ (0.5 or 2.5 mm) in the presence of various concentrations of K+.

In polarized glands, secretion was greater the higher the K+ concentration present during the secretory K+/Ca2+ test pulse. Thus, in 17.7 mm K+, catecholamine released was 162 ± 27 ng per pulse, while in 118 mm K+ secretion rose to 1839 ± 98 ng per pulse. In depolarized glands, secretion reached a peak of around 1000 ng per pulse in 35–59 mm K+; in 118 mm K+, secretion did not increase further, suggesting that voltage changes are implicated in the control of the secretory process.

Blockade of secretion by increased concentrations of (+)‐isradipine was much more manifest in polarized glands. The higher the degree of depolarization was (35, 59 or 118 mm K+), the lower the IC50s were. So, the ratios between the IC50s in polarized and depolarized glands rose from 3.92 in 35 mm K+ to 26.7 in 118 mm K+.

In contrast, the Ca2+ channel activator (−)‐Bay K 8644 potentiated catecholamine release evoked by K+/Ca2+ pulses equally well in polarized or depolarized glands. The ratios between EC50s in polarized or depolarized glands were, respectively, 0.30,0.59 and 0.69 for 17.7, 35 and 118 mm K+.

In simultaneous experiments, the two enantiomers of Bay K 8644 exhibited opposite effects on secretion. (+)‐Bay K 8644 (a Ca2+ channel blocker) inhibited secretion better in depolarized than in polarized glands, whilst (−)‐Bay K 8644 potentiated secretion in a voltage‐independent manner.

Potentiation of secretion by (−)‐Bay K 8644 was concentration‐dependent from 10−8 to 10−6 m. At 10−5 m, such potentiation largely disappeared in both polarized and depolarized glands. However, this dual effect of (−)‐Bay K 8644 was better seen in depolarizing conditions, suggesting that using the same enantiomer, the voltage‐dependence is only seen when blockade of secretion dominates.

In the presence of increasing concentrations of (−)‐Bay K 8644 (3 × 10−9, 3 × 10−8 and 3 × 10−7 m), the concentration‐response curves for (+)‐isradipine to inhibit secretion were displaced to the right. However, a Schild plot of (dose ratio −1) against (−)‐Bay K 8644 concentrations gave a slope of 0.6, suggesting that the interactions between (+)‐isradipine and (−)‐Bay K 8644 were non‐competitive in nature. The pA2 for (−)‐Bay K 8644 was 9.13.

Overall, the results suggest that potentiation of secretion by (−)‐Bay K 8644 (a voltage‐independent phenomenon), and blockade by (+)‐isradipine or (+)‐Bay K 8644 (a voltage‐dependent phenomenon) might be exerted through binding of the dihydropyridines activators and blockers to separate sites on chromaffin cell L‐type Ca2+ channels.
Evidence that the unilateral activation of 5‐HT1D receptors in the substantia nigra of the guinea‐pig elicits contralateral rotation
Authors: Higgins G.A. , Jordan C.C. , Skingle M.
Published: July 2012

The effects of various 5‐hydroxytryptamine (5‐HT) receptor agonists were examined following unilateral infusion into the substantia nigra (SN) of the guinea‐pig.

The 5‐HT1 receptor agonists, 5‐carboxamidotryptamine (5‐CT) (2–25 μg), sumatriptan (10–25 μg) and RU24969 (25 μg) all induced a marked contralateral rotation. In contrast, the selective 5‐HT1A receptor agonist 8‐hydroxy‐2‐(di‐n‐propylamino)tetralin (8‐OH DPAT, 10–25 μg) produced only a very small response, whilst the selective 5‐HT1C/5‐HT2 receptor agonist (±)‐1‐(4‐iodo‐2,5‐dimethoxyphenyl)‐2‐aminopropane hydrochloride ((±)‐DOI) (25 μg) and the 5‐HT3 receptor agonist, 2‐methyl 5‐HT (2‐Me5‐HT, 25 μg) were without effect.

The contralateral rotation induced by 5‐CT (10 μg) was attenuated following pretreatment with the non‐selective 5‐HT1/5‐HT2 receptor antagonists methiothepin (1 mg kg−1, s.c.) and metergoline (5–10 mg kg−1, s.c.) but not the 5‐HT1C/5‐HT2 antagonist ritanserin (1 mg kg−1, s.c.) or the 5‐HT3 antagonist, ondansetron (0.5 mg kg−1, s.c). An involvement of dopaminergic systems in the rotational response to 5‐CT was implied by the antagonism of 5‐CT‐induced rotation by haloperidol (0.3 mg kg−1, s.c).

At doses lower than those required to produce contralateral rotation, 5‐CT (0.08–0.4 μg) and sumatriptan (2 μg) induced a small, but nonetheless consistent, ipsilateral rotation.

The data with agonists and antagonists taken together suggest that 5‐CT‐induced contralateral rotation may be mediated by 5‐HT1D receptor activation but definitive classification of the receptor will not be possible until selective 5‐HT1D‐antagonists become available. This may therefore represent the first model to study this receptor subtype in vivo.
Effect of thyrotropin releasing hormone (TRH) on acetylcholine release from different brain areas investigated by microdialysis
Authors: Giovannini M.G. , Casamenti F. , Nistri A. , Paoli F. , Pepeu G.
Published: July 2012

The effect of thyrotropin releasing hormone (TRH) administration upon acetylcholine (ACh) release in freely moving rats was investigated by means of transversal microdialysis coupled to h.p.l.c. TRH administered either s.c. or via local perfusion increased the ACh release from the cortex and hippocampus but not from the striatum. The increase in ACh release was maintained after 7 days of s.c. administration of TRH.

After s.c. injection of the neuropeptide, the increase in ACh release was dose‐dependent and reached a maximum at 40 min after administration. The maximal percentage increases were 18, 52, 66 and 89% at doses of 1, 2.5, 5 and 10 mg kg−1 and 35, 48 and 54% at doses of 2.5, 5 and 10 mg kg−1 in the cortex and hippocampus, respectively. The effect of TRH was dependent on neuronal activity since it was completely inhibited by perfusion with tetrodotoxin (TTX), 5 × 10−7 m.

Perfusion with TRH, 2.5 μg μl−1, caused 198% and 150% increase in ACh release 60 and 80 min after the beginning of the perfusion in the cortex and hippocampus, respectively. After this initial peak, a 100% increase in ACh release persisted throughout the perfusion.

Systemic TRH administration was followed by marked hyperactivity and stereotyped behaviour that showed a time course shorter than that of the increase in ACh release.

These findings demonstrate that TRH exerts a strong stimulant action on cortical and hippocampal cholinergic pathways.
Studies of three non‐peptide cholecystokinin antagonists (devazepide, lorglumide and loxiglumide) in human isolated alimentary muscle and guinea‐pig ileum
Authors: D'Amato M. , Stamford I.F. , Bennett A.
Published: July 2012

Three recently described non‐peptide cholecystokinin (CCK) antagonists (devazepide, lorglumide, loxiglumide) have been studied for their antagonism of the contraction to cholecystokinin‐octapeptide (CCK‐OP) in human alimentary muscle and guinea‐pig intestine.

Each antagonist caused a concentration‐dependent inhibition of the contraction induced by CCK‐OP, regardless of regional and species differences.

The potencies of each drug, estimated by use of an adaptation of the Cheng & Prusoff equation, were similar in the different regions of human alimentary tract (weighted mean apparent pKB, ± s.e.mean: devazepide, 5.76 ± 0.08, n = 20; lorglumide, 5.82 ± 0.04, n = 25; loxiglumide, 5.87 ± 0.07, n = 24).

In contrast, the potencies differed markedly in the guinea‐pig ileum. Apparent pKB values obtained by the same method as with human tissues were, mean ± s.e.mean: devazepide, 10.61 ± 0.61; lorglumide, 7.43 ± 0.20; loxiglumide, 6.67 ±0.12. pKB values obtained from classical competition experiments were: devazepide, 10.09 ± 0.09; lorglumide 7.70 ± 0.12; loxiglumide 6.08 ± 0.22.

The CCK receptors in human gut muscle from different regions seem to be similar, but there appear to be species differences.
Pharmacological profile of various κ‐agonists at κ‐, μ‐ and δ‐opioid receptors mediating presynaptic inhibition of neurotransmitter release in the rat brain
Authors: Mulder A.H. , Burger D.M. , Wardeh G. , Hogenboom F. , Frankhuyzen A.L.
Published: July 2012

The potency, relative efficacy and selectivity of a series of κ‐opioid receptor agonists at the μ‐, δ‐ and κ‐opioid receptors mediating inhibition of electrically‐induced (radiolabelled) neurotransmitter release from superfused rat brain slices was determined.

With regard to their potencies at κ‐receptors mediating inhibition of striatal [3H]‐dopamine release, the highest pD2 value (8.7) was found for bremazocine and the lowest (7.1) for U50488; the pD2 values for ethylketocyclazocine (EKC), tifluadom, U69593 and PD117302 were between 8.0 and 8.3. There were no marked differences between the relative efficacies of the κ‐agonists (maximum inhibition being 60–70%). In contrast to the other κ‐agonists, at a concentration of 1 μm, PD117302 caused a significant (25–40%) increase of the spontaneous efflux of tritium.

None of the κ‐agonists significantly affected striatal [14C]‐acetylcholine (ACh) release, with the exception of a slight inhibitory effect of EKC. The δ‐receptor‐mediated inhibitory effect of [d‐Ala2, d‐Leu5] enkephalin (DADLE) on [14C]‐ACh release was antagonized in a concentration‐dependent manner by bremazocine (0.1 and 1.0 μm) and also partially by EKC (1 μm), but not by the other κ‐agonists. The pA2 value for bremazocine as an antagonist at the δ‐receptors involved was 8.0, compared to 7.6 for naloxone.

None of the κ‐agonists significantly affected cortical [3H]‐noradrenaline (NA) release, with the notable exception of tifluadom, which strongly inhibited release by activating μ‐receptors. The μ‐receptor‐mediated inhibitory effect of Tyr‐d‐Ala‐Gly‐(NMe)Phe‐Gly‐ol (DAMGO) on [3H]‐NA release was antagonized in a concentration‐dependent manner by bremazocine and EKC, but not by the other κ‐agonists. The pA2 value for bremazocine as an antagonist at the μ‐receptors involved was 8.2, compared to 8.6 for naloxone.

Thus, whereas U69593 and PD117302 display high potency and selectivity towards κ‐opioid receptors, the potent benzomorphan κ‐agonists bremazocine and EKC also appear to be strong μ‐opioid receptor antagonists.
Selective and competitive antagonism by suramin of ATP‐stimulated catecholamine‐secretion from PC12 phaeochromocytoma cells
Authors: Inoue Kazuhide , Nakazawa Ken , Ohara‐Imaizumi Mica , Obama Tomoko , Fujimori Kannosuke , Takanaka Akira
Published: July 2012

Suramin, a putative P2‐antagonist, (10 to 300 μm) inhibited the adenosine 5′‐triphosphate (ATP)‐stimulated secretion of [3H]‐noradrenaline or endogenous dopamine from phaeochromocytoma PC12 cells in a concentration‐dependent manner. Suramin (300 μm) did not affect the dopamine‐secretion stimulated by high K+ or nicotine.

Suramin shifted the concentration‐response curve for ATP to the right. The antagonism was competitive with a pA2 value of 4.52.

ATP also stimulated an increase in intracellular Ca2+ concentration as determined by fura‐2 methods. Suramin antagonized this effect over the same concentration range that antagonized the ATP‐stimulated catecholamine secretion.

These results suggest that suramin can be used as a selective and competitive antagonist of ATP in experiments concerning mechanisms of catecholamine‐secretion.
A comparison of the relative activities of a number of GABAB antagonists in the isolated vas deferens of the rat
Authors: Hills Judith M. , Larkin Madelene M. , Howson William
Published: July 2012

A series of GABAB receptor antagonists were tested against (±)‐baclofen for activity on the presynaptic GABAB receptor in the rat vas deferens.

All the antagonists tested caused a rightward shift in the concentration‐response curve to (±)‐baclofen.

pA2 values calculated from full Schild analysis were as follows: phaclofen, pA2 = 4.3; δ‐amino valeric acid, pA2 = 4.4; 3‐aminopropyl(diethoxymethyl)phosphinic acid (CGP 35348), pA2 = 5.0; 3‐aminopropyl(n‐hexyl)phosphinic acid (3‐APHPA), pA2 = 4.5.

These results show that none of the above compounds possess potent antagonist activity at the GABAB receptor (i.e. pA2 > 6) in this peripheral tissue. In addition, the more recently available phosphinic acid antagonists, appear to offer no great advance over the GABAB antagonists previously available.
Pharmacology of a cholecystokinin receptor on 5‐hydroxytryptamine neurones in the dorsal raphe of the rat brain
Authors: Boden P.R. , Woodruff G.N. , Pinnock R.D.
Published: July 2012

The effect of bath application of sulphated cholecystokinin octapeptide (CCK‐8) was studied on neurones in slices containing rat raphe nucleus.

Intracellular recordings were made from neurones in the dorsal raphe nucleus. Some of the neurones with the characteristics of 5‐hydroxytryptamine (5‐HT)‐containing cells which were inhibited by 5‐HT and excited by noradrenaline were excited by cholecystokinin. The response to cholecystokinin was dose‐dependent over the range 10 to 1000 nm.

The response to CCK‐8 persisted in the presence of tetrodotoxin. Either reduction of extracellular calcium or addition of 25 mm magnesium did not block the CCK response, suggesting it was mediated by receptors located on the membrane of the raphe neurones.

The agonist and antagonist specificity of the CCK response was determined. The CCKB selective agonist, pentagastrin, was inactive when applied at concentrations up to 10 μm. the CCKA receptor antagonist L‐364,718 (1 to 100 nm) blocked the response to cholecystokinin. Much higher (1–10 μm) concentrations of the CCKB receptor antagonist L‐365,260 were required for inhibition of the CCK response.

These data support the existence of a CCK receptor, located on raphe neurones in the rat, with a pharmacological profile very similar to that described for the CCKA type.
Differential effect of R 56865 on ouabain binding to isolated sarcolemma and intact atrial tissue of guinea‐pig
Authors: Heers Cara , Scheufler Eckhard , Wilhelm Doris , Wermelskirchen Detlef , Wilffert Bob , Peters Thies
Published: July 2012

R 56865 (N‐[1‐[4‐(4‐fluorophenoxy)‐butyl]‐4‐piperidinyl]‐N‐methyl‐2‐benzothiazolamine) is a compound known to antagonize cardiac glycoside intoxication. Therefore, the effect of the compound on ouabain binding to intact cardiac tissue as well as cardiac membrane preparations was investigated.

The binding of ouabain to highly purified sarcolemmal membranes was not influenced by R 56865 1 × 10−6 mol l−1 (ouabain: KD = 1.3 × 10−7 mol l−1, Bmax = 160 pmol mg−1; ouabain + R 56865: KD = 1.4 × 10−7 mol l−1, Bmax = 168 pmol mg−1).

In contrast to the results in purified membranes, the binding of ouabain (10−8 mol l−1 to 5 × 10−7 mol l−1) to intact atria was significantly reduced.

Ouabain, 5 × 10−7 mol l−1, led to a transient positive inotropic effect of about 220% followed by a developing negative inotropic effect after 3 h. R 56865, 10−7 mol l−1, led to a maximal positive inotropic effect of about 290% also followed by a delayed decline of contractile force. A tenfold higher concentration of R 56865 led to sustained positive inotropic effect of about 250% in the same time interval.

The different effects of R 56865 on ouabain binding in subcellular preparations and intact tissue do not support the view that R 56865 interferes directly with the action of ouabain on Na/K‐ATPase. An indirect effect, which may be mediated by a lowered intracellular sodium load is discussed.
Anti‐arrhythmic activities of opioid agonists and antagonists and their stereoisomers
Authors: Sarne Y. , Flitstein A. , Oppenheimer E.
Published: July 2012

A series of opioid agonists, antagonists and their (+)‐stereoisomers were tested for antiarrhythmic activity in the rat coronary artery occlusion model.

Naloxone (0.01–2 mg kg−1) significantly reduced the incidence and severity of cardiac arrhythmias, in accordance with previous published studies.

The non‐opioid stereoisomer, (+)‐naloxone, was equipotent with naloxone against occlusion‐induced arrhythmia.

Similar non‐stereospecific antiarrhythmic effects were induced by another opioid antagonist, Win 44,441–3 and its stereoisomer Win 44,441–2.

The opioid agonists, morphine and levorphanol, protected against occlusion‐induced arrhythmia as did the opioid antagonists, and the (+)‐stereoisomer, dextrorphan, was equipotent to levorphanol.

It is concluded that the antiarrhythmic effects of opioid drugs are not mediated by opioid receptors. A direct effect on ionic currents in cardiac muscle is suggested as the mechanism of opioid antiarrhythmic activity.
Comparison of the effects of intra‐arterial and aerosol administration of endothelin‐1 (ET‐1) in the guinea‐pig isolated lung
Authors: Pons Françoise , Touvay Caroline , Lagente Vincent , Mencia‐Huerta Jean Michel , Braquet Pierre
Published: July 2012

Intra‐arterial injection of endothelin‐1 (ET‐1, 400 pmol; 1 μg) in guinea‐pig isolated perfused lungs, induced increases in pulmonary inflation pressure (PIP) and perfusion pressure (PPP), associated with oedema formation and thromboxane B2 (TxB2) release but not with the generation of sulphidopeptide leukotrienes or release of histamine. In contrast, aerosol administration of ET‐1 (3, 6, 10 μg ml−1, for 2 min) evoked a dose‐dependent increase in PIP, without significant changes in PPP, oedema formation or TxB2 release.

Addition of indomethacin (5 μm) or BW 755C (10 or 100 μm), but not nordihydroguaiaretic acid (NDGA, 50 μm) or FPL 55712 (10 μm), to the perfusion medium led to a significant inhibition of the increases in PIP and PPP, TxB2 release and oedema formation evoked by intra‐arterial injection of 400pmol ET‐1. In contrast, indomethacin (5 μm), BW 755C (100 μm) or FPL 55712 (10 μm), added to the perfusion medium 10 min prior to challenge, did not affect the increase in PIP induced by a 2‐min aerosol of a solution of ET‐1 10 μg ml−1.

In vivo aerosol administration of indomethacin (100 mg ml−1, for 20 min) to non‐anaesthetized guinea‐pigs, 15 min before lung removal, did not modify the bronchopulmonary response evoked in isolated perfused lungs by an aerosol of ET‐1 10 μg ml−1. However, under the same experimental conditions, indomethacin significantly inhibited TxB2 release evoked by aerosolized arachidonic acid (2 mg ml−1).

In conclusion, the present study shows that when injected by the intra‐arterial route, ET‐1 effects are mediated primarily via the generation of cyclo‐oxygenase metabolites of arachidonic acid, whereas when the aerosol route is used, the peptide appears to act on airway smooth muscle cells, through an indomethacin‐insensitive process which may involve some other, as yet unidentified, mediator(s).
Effect of the leukotriene receptor antagonists FPL 55712, LY 163443, and MK‐571 on the elimination of cysteinyl leukotrienes in the rat
Authors: Denzlinger C. , Grimberg M. , Kapp A. , Haberl C. , Wilmanns W.
Published: July 2012

Leukotriene elimination via bile and urine is an important mechanism of inactivation for these potent lipid mediators. We investigated whether the elimination of cysteinyl leukotrienes is a target for the action of leukotriene receptor antagonists.

Experiments were performed in male rats under deep thiopentone anaesthesia. The bile duct and the urinary bladder were cannulated. Tritium labelled leukotrienes and leukotriene receptor antagonists were given via central venous catheters. Elimination of leukotrienes produced in vivo was studied following stimulation of endogenous leukotriene biosynthesis by operative trauma. 3H‐leukotriene metabolites were identified by h.p.l.c. analysis. Leukotrienes produced in vivo were measured by combined use of h.p.l.c. and RIA.

Under control conditions, 49 ± 12% of the injected 3H‐leukotriene radioactivity was recovered in bile and 1 ± 0.8% in urine within 90 min. Operative trauma resulted in initial hepatobiliary secretion of 887 ± 206 pmol kg−1 h−1 of the endogenous leukotriene metabolite N‐acetyl leukotriene E4 (LTE4NAc).

FPL 55712 strongly inhibited hepatobiliary elimination of 3H‐leukotriene radioactivity in a dose‐dependent manner after i.v. injection of [3H]‐LTC4, [3H]‐LTD4 or [3H]‐LTE4, respectively. Biliary [3H]‐LTD4 was reduced most effectively. The leukotriene antagonist potently prevented biliary elimination of LTE4NAc produced in vivo. Bile flow and elimination from blood into bile of [3H]‐ouabain were also impaired by FPL 55712, but to a lesser extent.

LY 163443 reduced biliary [3H]‐LTD4 after i.v. administration of [3H]‐LTD4. However, the total elimination of 3H‐leukotriene metabolites into bile was not significantly inhibited by the drug.

MK‐571 reduced the biliary concentration of tracer after administration of 3H‐leukotrienes most potently with respect to [3H]‐LTD4. In contrast, the total recovery of 3H‐leukotrienes in bile tended to increase. This is explained by a drug‐induced increase in bile flow.

Urinary elimination of 3H‐leukotrienes, quantitatively less important in the rat, was not significantly influenced by the leukotriene receptor antagonists. Recovery of 3H‐leukotriene radioactivity in liver and kidneys was quantitatively insignificant.

From our data, we conclude that leukotriene receptor antagonists have the potential to affect leukotriene elimination by a mechanism not necessarily related to receptor blockade. Inhibition of elimination by the receptor antagonists may prolong the biological half life of leukotrienes. This effect may counteract the antagonistic properties of these drugs.
The pharmacology of fluparoxan: a selective α2‐adrenoceptor antagonist
Authors: Halliday C.A. , Jones B.J. , Skingle M. , Walsh D.M. , Wise H. , Tyers M.B.
Published: July 2012

This paper describes the pharmacology of the novel α2‐adrenoceptor antagonist fluparoxan (GR 50360) which is currently being studied clinically as a potential anti‐depressant. Idazoxan and yohimbine were included in many studies for comparison.

In the rat isolated, field‐stimulated vas deferens and the guinea‐pig isolated, field‐stimulated ileum preparations, fluparoxan was a reversible competitive antagonist of the inhibitory responses to the α2‐adrenoceptor agonist UK‐14304 with pKB values of 7.87 and 7.89 respectively. In the rat isolated anococcygeus muscle, fluparoxan was a much weaker competitive antagonist of the contractile response to the α1‐adrenoceptor agonist phenylephrine with a pKB of 4.45 giving an α2:α1‐adrenoceptor selectivity ratio of greater than 2500.

In the conscious mouse, fluparoxan (0.2–3.0 mg kg−1) was effective by the oral route and of similar potency to idazoxan in preventing clonidine‐induced hypothermia and antinociception. In the rat, UK‐14304‐induced hypothermia (ED50 = 1.4 mg kg−1, p.o. or 0.5 mg kg−1, i.v.) and rotarod impairment (ED50 = 1.1 mg kg−1 p.o. or 1.3 mg kg−1, i.v.) were antagonized by fluparoxan. Fluparoxan, 0.67–6 mg kg−1, p.o., also prevented UK‐14304‐induced sedation and bradycardia in the dog.

In specificity studies fluparoxan had low or no affinity for a wide range of neurotransmitter receptor sites at concentrations up to at least 1 × 10−5 m. It displayed weak affinity for 5‐HT1A (pIC50 = 5.9) and 5‐HT1B (pKi = 5.5) binding sites in rat brain.

We conclude that fluparoxan is a highly selective and potent α2‐adrenoceptor antagonist. The density of rat brain [3H]‐dihydroalprenolol binding sites was reduced by 26% when fluparoxan was administered chronically for 6 days at a dose of 12 mg kg−1 orally twice daily. The down‐regulation of β‐adrenoceptors by fluparoxan is consistent with its antidepressant potential.
α2‐Adrenoceptor blocking profile of SK&F 104078: further evidence for receptor subtypes
Authors: Akers I. , Coates J. , Drew G.M. , Sullivan A.T.
Published: July 2012

The ability of the putative, selective post‐junctional α2‐adrenoceptor antagonist, SK&F 104078 to antagonize the effects of structurally‐diverse agonists at pre‐junctional α2‐adrenoceptors in the guinea‐pig ileum and rat vas deferens in vitro and in the rat heart in vivo, and at post‐junctional α2‐adrenoceptors in the rabbit ear vein in vitro, was examined. Results obtained with SK&F 104078 were compared with those obtained with yohimbine.

Xylazine and B‐HT933 each caused a concentration‐dependent inhibition of the field‐stimulation‐evoked twitch responses of the guinea‐pig ileum and rat vas deferens. SK&F 104078 did not antagonize either agonist in the guinea‐pig ileum and exerted only minimal blocking activity against xylazine in the rat vas deferens. In contrast, SK&F 104078 competitively antagonized B‐HT933 in the rat vas deferens (pA2 = 6.45). Yohimbine competitively antagonized both agonists in each tissue (pA2 values ranged between 7.46 and 7.88).

In the pithed rat xylazine and B‐HT933, injected intravenously, caused a dose‐dependent reduction in the tachycardia elicited by stimulation of the cardiac preganglionic sympathetic nerves. SK&F 104078 (10 mg kg−1, i.v.) caused a 20–30 fold rightward displacement of the dose‐response curve to xylazine, but did not affect responses to B‐HT933. Yohimbine (1 mg kg−1, i.v.) antagonized both agonists to a similar degree.

In the rabbit ear vein xylazine, B‐HT933, noradrenaline and UK14304 elicted vasoconstrictor responses. Prazosin was without effect, but in contrast, SK&F 104078 was a competitive antagonist of each of the agonists (pA2 values ranged between 6.63 and 6.72). Yohimbine also competitively antagonized each of the agonists in this preparation (pA2 values ranged between 7.81 and 8.07).

SK&F 104078 was also a competitive antagonist (pA2 = 6.20) against noradrenaline at post‐junctional α1‐adrenoceptors in the rabbit aorta.

These data show that SK&F 104078 is a competitive antagonist at post‐junctional α1‐ and α2‐adrenoceptors. Its antagonist potency at pre‐junctional α2‐adrenoceptors is agonist‐ and tissue‐dependent. Yohimbine does not discriminate between pre‐ and post‐junctional α2‐adrenoceptors. The findings are discussed in terms of the possible existence of subclasses of α2‐adrenoceptors.
The involvement of endothelium‐derived relaxing factor in the regulation of renal cortical blood flow in the rat
Authors: Walder Claire E. , Thiemermann Christoph , Vane John R.
Published: July 2012

In the present study the role of endogenous nitric oxide (NO) was investigated, in the regulation of renal cortical blood flow (RCBF) in vivo in anaesthetized rats under conditions in which prostacyclin involvement had been eliminated.

Infusions of the NO synthesis inhibitor NG‐monomethyl‐l‐arginine (MeArg) at 1 or 3 mg kg−1 min−1, i.v., produced significant decreases in RCBF of 29 ± 7% and 35 ± 5%, respectively. These effects were reversed by co‐infusion of a 3 fold excess of l‐arginine (l‐Arg).

Similarly, intravenous infusion of Nω‐nitro‐l‐arginine methyl ester (NO2Arg) at 30 or 300 μg kg−1 min−1 attenuated RCBF by 21 ± 4% or 53 ± 4%, respectively, and these effects were reversed by l‐Arg (3 or 10 mg kg−1 min−1, i.v.). Most importantly, a low dose of NO2Arg (30 μg kg−1 min−1, i.v.), while having no pressor effect, considerably reduced RCBF, indicating that basal release of NO is important for the maintenance of renal cortical blood flow.

MeArg (3 mg kg−1 min−1, i.v.) or NO2Arg (300 μg kg−1 min−1, i.v.) inhibited endothelium‐dependent acetylcholine (ACh, 10 μg kg−1 min−1, i.v. for 3 min) increases in RCBF in an l‐Arg reversible manner, but did not affect endothelium‐independent (dopamine 10 μg kg−1 min−1, i.v., for 3 min) increases. Endothelin‐1 (1 nmol kg−1, i.v.), when given as a control for the vasoconstrictor effects of MeArg and NO2Arg, produced a slight inhibition of the ACh‐induced increase in RCBF, but this effect was significantly weaker than that produced by MeArg or NO2Arg.

Our findings suggest that MeArg and NO2Arg inhibit basal and ACh‐stimulated release of NO in the renal cortical vasculature. Thus, endogenous NO formation may play an important role in the local regulation of renal cortical blood flow.