bluuebunny/crossref_metadata_2025 huggingface dataset:
Interaction of palmitoyl carnitine with calcium antagonists in myocytes
Authors: Patmore Leslie , Duncan Greig P. , Spedding Michael
Published: July 2012

Beating of aggregates of embryonic chick myocytes, in primary culture, was quantified by use of a motion‐detector and video‐recorder technique. Interactions of palmitoyl carnitine, a putative endogenous ligand at Ca2+ channels, with calcium antagonists were investigated.

Bay K 8644 (1–100 nm) and palmitoyl carnitine (0.2–30 μm) increased edge movement of the aggregates; beats fused so that there was an increase in baseline ‘tone’. The concentrations required to produce a 50% increase in edge movement were 2.5 nm for Bay K 8644 and 2 μm for palmitoyl carnitine. Higher concentrations (20–30 μm) of palmitoyl carnitine caused tachycardia of abrupt onset but resulted in cessation of beating. The effects of palmitoyl carnitine were not stereo‐selective in that the (+)− and (−)‐isomers were equieffective. Lysophosphatidyl choline (LPC) had no effect in concentrations up to 10 μm but higher concentrations caused tachycardia followed by cessation of beating. High concentrations of both palmitoyl carnitine and LPC (100 μm) caused break‐up of the aggregates, presumably as a result of detergent effects.

Palmitoyl carnitine (1–100 μm) reversed the inhibitory effects of nisoldipine (0.3 μm), diltiazem (10 μm) and verapamil (1 μm). Ouabain was ineffective in reversing the effects of nisoldipine, differentiating the effects of palmitoyl carnitine from those of Na+/K+ATPase inhibition. In contrast, palmitoyl carnitine did not reverse the inhibitory effects of pimozide (2 μm) or lidoflazine (7 μm); palmitoyl carnitine showed a similar profile to Bay K 8644 in this respect.

These findings indicate that the effects of palmitoyl carnitine closely resemble those of Bay K 8644 and can be differentiated from those of lysophospholipids. As palmitoyl carnitine accumulates in the sarcolemma during myocardial ischaemia, the mode of action in the Ca2+ channel may have clinical relevance for the use of calcium antagonists in ischaemia.
Interference of WEB 2086 and BN 52021 with Paf‐induced effects on guinea‐pig trachea
Authors: Brunelleschi Sandra , Renzi Daniela , Ledda Fabrizio , Giotti Alberto , Fantozzi Roberto , Brink Charles , Benveniste Jacques
Published: July 2012

The thienotriazolodiazepine WEB 2086 and the gingkolide BN52021 have been evaluated as antagonists of Paf‐acether (Pal) by studying their effects on Paf‐induced relaxation and Paf‐induced prostaglandin E2 (PGE2) production in histamine‐contracted guinea‐pig tracheal preparations.

Relaxation induced by Paf 4 μm in histamine‐contracted guinea‐pig tracheal preparations was 39.67 ± 3.5% (n = 30). At the same concentration, Paf significantly increased PGE2 production from histamine‐contracted guinea‐pig tracheal preparations.

WEB 2086 inhibited in a dose‐related manner (IC50 = 21.2 nm) the relaxant effect induced by Paf and, at 1 μm, suppressed Paf‐induced release of PGE2.

BN 52021 100 μm inhibited to about 60% Paf‐induced relaxation of histamine‐contracted guinea‐pig tracheal preparations, but completely abolished Paf‐induced increase in PGE2.

Both antagonists had no effects on relaxations induced by arachidonic acid 10 μm or PGE2 0.1–1 μm in histamine‐contracted guinea‐pig tracheal preparations.

The results are consistent with the presence of specific Paf receptors in guinea‐pig trachea and indicate that a relaxant prostanoid, namely PGE2, at least partially mediates Paf‐induced relaxation in this experimental model.
m‐Octopamine injected into the paraventricular nucleus induces eating in rats: a comparison with noradrenaline‐induced eating
Authors: Fletcher P.J. , Paterson I.A.
Published: July 2012

The effects on food intake in rats of injection of m ‐and p‐octopamine into the paraventricular nucleus (PVN) of the hypothalamus were examined, and compared to the effects of noradrenaline (NA).

m‐Octopamine injected into the PVN induced a dose‐dependent increase in food intake, with the maximal effect occurring at a dose of 25 nmol. p‐Octopamine did not elicit eating unless it was administered to animals pretreated with the monoamine oxidase inhibitor, pargyline.

The effects of pretreatment with various adrenoceptor antagonists, injected into the PVN, on the eating responses induced by 25 nmol m‐octopamine and NA were examined. The α1‐adrenoceptor antagonist, corynanthine, and the β‐adrenoceptor antagonist, propranolol, failed to alter the eating induced by m‐octopamine or NA. The effects of these two amines were susceptible to blockade of α2‐adrenoceptors. Idazoxan reversed the eating induced by m‐octopamine and noradrenaline. However, yohimbine was effective only against the eating induced by m‐octopamine. Thus, both m‐octopamine and NA appear to act via α2, but not α1 or β‐adrenoceptors.

Injection of α‐methyl‐p‐tyrosine into the PVN attenuated the effect of m‐octopamine, but not of NA. This result suggests that m‐octopamine elicits eating, at least in part, by releasing endogenous NA.

The NA and octopamine uptake inhibitor, desipramine, significantly potentiated the eating induced by a low dose of m‐octopamine. This effect may occur because desipramine would prolong the synaptic activity of released NA.

The results indicate that m‐octopamine elicits a marked and reliable eating response which is mediated largely by a release of endogenous NA, which acts at α2‐receptors. These results are consistent with the view that octopamine may function as a modulator of NA activity in the central nervous system.
Inhibition of bradykinin‐induced bronchoconstriction in the guinea‐pig by a synthetic B2 receptor antagonist
Authors: Jin L.S. , Seeds E. , Page C.P. , Schachter M.
Published: July 2012

Intravenous bradykinin (Bk) elicited bronchoconstriction in the anaesthetized ventilated guinea‐pig which was not mimicked by the B1 receptor agonist, des‐Arg9‐Bk.

Bradykinin‐induced bronchoconstriction was inhibited by the B2 receptor antagonist B4881, but not by the B1 receptor antagonist des‐Arg9‐Leu8‐Bk. The effect of B4881 was short‐lived.

The B2 receptor antagonist as B4881 was selective for bradykinin as B4881 did not significantly inhibit bronchoconstriction induced by i.v. bombesin, platelet activating factor, acetylcholine, histamine or vagal stimulation.

These results suggest that bradykinin‐induced bronchoconstriction in the guinea‐pig is via activation of a B2 receptor population and that B4881 is a selective B2 antagonist that may be useful for investigating the involvement of bradykinin in the lung.
Subclassification of α1‐adrenoceptor recognition sites by urapidil derivatives and other selective antagonists
Authors: Hanft Gertraud , Gross Gerhard
Published: July 2012

The affinities of urapidil derivatives and other antagonists for α1‐adrenoceptors labelled by [3H]‐prazosin were determined on membranes of six different rat tissues.

Urapidil and its 5‐acetyl‐, 5‐formyl‐ and 5‐methyl‐derivative displaced [3H]‐prazosin from α1‐adrenoceptor binding sites in a concentration‐dependent manner which varied with tissue. IC50 values were lower in vas deferens, hippocampus and cerebral cortex than in heart, liver and spleen. For 5‐methyl‐urapidil, binding to two distinct sites could be demonstrated with mean K1 values of about 0.6 and 45 nM. Saturation binding studies with [3H]‐prazosin in the presence of 5‐methylurapidil indicated a competitive type of interaction between 5‐methyl‐urapidil and [3H]‐prazosin.

The proportion of [3H]‐prazosin binding sites with high affinity for 5‐methyl‐urapidil was 58% in vas deferens, 69% in hippocampus, 41% in cerebral cortex and 23% in myocardium. In liver and spleen virtually no high affinity sites were found. These values were in good agreement with the percentages of binding sites with high affinities for WB‐4101 and phentolamine, indicating that all these antagonists bind to the same subtype of α1 ‐recognition sites, whereas other α‐antagonists like BE 2254, yohimbine and unlabelled prazosin did not discriminate between two binding sites.

Preincubating membranes of the cerebral cortex with chloroethylclonidine preferentially inactivated [3H]‐prazosin binding sites with low affinity for 5‐methyl‐urapidil.

The antagonist potencies of 5‐methyl‐urapidil and WB‐4101 against α1‐adrenoceptor‐mediated contractile responses were higher in vas deferens than in myocardium. The α1‐mediated effects in vas deferens but not in the heart were highly susceptible to nitrendipine.

Using 5‐methyl‐urapidil, the existence of two distinct α1‐adrenoceptor recognition sites could be demonstrated which correspond to the proposed α1A‐ and α1B‐subtypes. Since 5‐methyl‐urapidil is one of the ligands with most selectivity between these subtypes in binding studies it may serve as a valuable tool for such investigations.
α1‐Adrenoceptor function and autoradiographic distribution in human asthmatic lung
Authors: Spina Dom , Rigby Paul J. , Paterson James W. , Goldie Roy G.
Published: July 2012

The autoradiographic distribution of α1‐adrenoceptors was investigated in non‐diseased and asthmatic human lung by use of [3H]‐prazosin (H‐PZ). To validate binding and autoradiographic methods, H‐PZ binding was also measured in rat heart.

Significant levels of specific H‐PZ binding were detected in sections of rat heart. This binding was associated with a single class of non‐interacting sites of high affinity (dissociation constant, Kd = 1.17 ± 0.26 nm). The maximum binding capacity (Bmax) was 59.5 ± 4.5 fmol mg−1 protein.

In sharp contrast, very low levels of specific H‐PZ binding were found in both human non‐diseased and asthmatic bronchus, although a high level of binding of [125I]‐iodocyanopindolol (I‐CYP, 50 pm) to β‐adrenoceptors was detected in these airways. Furthermore, very low levels of autoradiographic grains representing specific H‐PZ binding were found in all airway structures in human non‐diseased or asthmatic lung parenchyma.

Consistent with these data, the α‐adrenoceptor agonist phenylephrine failed to induce significant increases in tone in bronchi isolated from either non‐diseased or asthmatic human lung. Results indicate that asthma does not involve significant increases in airway α1‐adrenoceptor function.
κ‐Opioid‐induced changes in renal water and electrolyte management and endocrine secretion
Authors: Ashton N. , Balment R.J. , Blackburn T.P.
Published: July 2012

Subcutaneous injection of the κ‐opioid agonist U50,488 into conscious, saline‐loaded rats was associated with a diuresis, antinatriuresis and antikaliuresis which lasted for up to 3 h. Plasma renin activity and corticosterone levels were elevated but plasma vasopressin (AVP) and aldosterone levels were unaltered in similarly treated rats.

U50,488 administration to adrenal demedulated rats was not associated with a diuresis but produced an antinatriuresis, though sodium excretion rates were higher in demedullated than in sham‐operated animals. Plasma AVP and corticosterone levels were not affected by demedulation or subsequent U50,488 treatment. Sham‐operated, U50,488‐treated rats showed the expected increase in plasma corticosterone levels.

U50,488 administration resulted in an antidiuresis and an antinatriuresis in AVP‐deficient Brattleboro DI rats.

When coupled with fasting stress U50,488 administration resulted in similar but attenuated renal responses compared with those observed in unfasted rats. Basal plasma corticosterone levels were elevated in fasted animals and were further increased by U50,488.

Both water and electrolyte handling by the kidney are altered by U50,488. The diuretic effects of U50,488 were reversed by adrenal demedullation and in the absence of endogenous AVP, but the antinatriuretic actions were not altered, suggesting that the effects upon renal water and electrolyte excretion may be mediated by separate mechanisms.
The effect of atrial natriuretic peptide on human isolated resistance arteries
Authors: Hughes A.D. , Nielsen H. , Sever P.S.
Published: July 2012

The action of (1–28) α‐human atrial natriuretic peptide (ANP) was studied on human isolated resistance arteries.

Renal, skeletal muscle, omental and subcutaneous resistance arteries were taken from tissue removed at surgery and isometric tension responses were measured with a myograph.

ANP (10−9–10−6m) relaxed precontracted segments of renal and skeletal muscle arteries in a concentration‐dependent manner. ANP failed to relax isolated omental or subcutaneous arteries.

The effect of ANP on human isolated resistance arteries varies depending on the site of origin of the artery.
Sodium pentobarbitone enhances responses of thalamic relay neurones to GABA in rat brain slices
Authors: Sykes T.C.F. , Thomson Alex M.
Published: July 2012

In rat isolated thalamic slices, intracellular recordings were made of responses to electrophoretically applied γ‐aminobutyric acid (GABA) in the absence and presence of sodium pentobarbitone (NaPb).

Responses to electrophoretically applied GABA were biphasic in the majority of neurones studied. They consisted of an early, negative‐going and later, positive‐going phase, when recorded close to reversal potential.

An increase in the GABA ejection current caused an enhancement of the late positive‐going phase, along with a shift in the reversal potential of the whole response to a more positive value. These changes were accompanied by an increase in GABA‐induced conductance (decrease in resistance) and an increase in the duration of the response.

Application of NaPb to the GABA response produced similar effects, namely an enhancement of the late positive‐going phase, a shift in the reversal potential to a more positive value, an increase in conductance and an increase in duration.

GABA‐mediated inhibitory postsynaptic potentials (i.p.s.ps) were evoked by electrical stimulation of the nucleus reticularis thalami. Application of NaPb caused an increase in the duration of the i.p.s.p. and a shift in its reversal potential to a more positive value.
Sympathetic vascular control of the pig nasal mucosa: adrenoceptor mechanisms in blood flow and volume control
Authors: Lacroix Jean‐Silvain , Lundberg Jan M.
Published: July 2012

The adrenoceptor mechanisms influencing the total blood flow, volume and superficial blood flow in the nasal mucosa of pigs anaesthetized with pentobarbitone have been characterized by use of various agonists and antagonists.

Local intra‐arterial bolus injection of the selective α1‐agonist phenylephrine, the selective α2‐agonist UK 14.304, the mixed α1/α2‐agonist oxymetazoline and the mixed α/β‐agonists noradrenaline (NA) and adrenaline induced dosed‐related reduction of nasal arterial blood flow (BF), nasal mucosal volume (V, reflecting capacitance vessel function) and the laser Doppler flowmetry signal (LDF, reflecting superficial movement of blood cells). The rank order of α‐agonist potency regarding BF reduction was UK 14.304 > oxymetazoline > NA > phenylephrine = adrenaline. For the volume response the potency order was UK 14.304 > oxymetazoline = NA = adrenaline > phenylephrine while for the reduction of the LDF signal the potency was UK 14.304 = NA = adrenaline > oxymetazoline > phenylephrine. The selective β2‐agonist terbutaline caused dose‐dependent increase of BF whereas only a small augmentation of the V was obtained upon the highest dose (40 nmol) while no modification of the LDF signal was observed.

After pretreatment with the selective α1‐antagonist prazosin, the response to phenylephrine was abolished while the selective α2‐antagonist idazoxan attenuated the effect of UK 14.304. After pretreatment with α‐antagonists, both NA and adrenaline caused biphasic effects with constriction followed by vasodilatation for BF, but not for V or LDF. This vasodilatation was blocked by the β‐antagonist propranolol.

The reduction in nasal BF and V upon sympathetic nerve stimulation was attenuated both by prazosin and idazoxan. Propranolol enhanced the remaining reduction of BF but not of V in the presence of α‐antagonists.

It is concluded that α2‐adrenoceptor mechanisms in the pig nasal mucosa are dominating for the BF, V and LDF responses to exogenous agonists, α1‐Adrenoceptors also seem to be involved in the sympathetic control of BF, V and LDF. Activation of β2‐receptors increases mainly BF and does not influence the LDF signal.
Gastric damage following local intra‐arterial administration of reactive oxygen metabolites in the rat
Authors: Esplugues J.V. , Whittle B.J.R.
Published: July 2012

The effects of reactive oxygen metabolites on the rat gastric mucosa following close‐arterial infusion into the left gastric artery have been determined by macroscopic and histological assessment.

Local intra‐arterial infusion of hydrogen peroxide (0.6‐1.3 μmol kg−1 min−1) induced mucosal injury, characterised by areas of pronounced disruption and haemorrhage, which was prevented by concurrent intravenous administration of catalase.

Local infusion of the superoxide generating system xanthine‐oxidase and hypoxanthine likewise induced extensive haemorrhagic damage and necrosis of the mucosa. Prolonged incubation of this mixture (10 min) before administration, significantly reduced the degree of injury, indicating the lability of the products so formed.

The gastric mucosal injury induced by the superoxide generating system was inhibited by concurrent local infusion of superoxide dismutase (96 u kg−1 min−1), as was the associated increase in mucosal permeability to radiolabelled albumin.

Administration of catalase did not inhibit the gastric mucosal damage induced by infusion of xanthine oxidase‐hypoxanthine, yet augmented the protective effects of a low dose of superoxide dismutase (46 u kg−1 min−1 i.a.).

These findings directly confirm that reactive oxygen metabolites can induce extensive gastric mucosal injury, supporting their role in the pathogenesis of gastric damage following ischaemia and hypotensive shock.
Postnatal changes in response to adenosine and adenine nucleotides in rat duodenum
Authors: Furukawa Kyoko , Nomoto Teruko
Published: July 2012

The effects of adenosine and adenine nucleotides were studied in rat duodenum from postnatal day 1 to day 70. The mechanical activity of duodenal segments was recorded through an isotonic transducer connected to a polygraphic recorder.

In rat duodenal segments, adenosine‐5′‐triphosphate (ATP, 10−4m) and adenosines‐5′‐diphosphate (ADP, 10−4m) produced a contractile response on postnatal day 1. This response increased with age, peaking on day 7, followed by a gradual decrease and was non‐existent by day 21. In contrast, a relaxant response to ATP and ADP was apparent on day 21, and continued to increase up to day 70.

The contraction caused by ATP was inhibited by indomethacin or the P2y‐purinoceptor antagonist, reactive blue‐2 but not by tetrodotoxin or hyoscine. Thus, it may be mediated by production of prostaglandin through the P2y‐purinoceptor. The relaxation produced by ATP was inhibited by reactive blue‐2 but not by tetrodotoxin, guanethidine or the P1‐purinoceptor antagonist, 8‐phenyltheophylline indicating that ATP acts on smooth muscle directly through the P2y‐purinoceptor. The pD2 for the contractile response to ATP was 5.15 on day 7 and that for the relaxant response, 6.64 on day 70.

Adenosine (10−4m) and adenosine‐5′‐monophosphate (AMP, 10−4m) elicited no response before day 14. On day 14, both adenosine and AMP produced a small relaxant response which increased with age. The relaxation produced by adenosine was inhibited by 8‐phenyltheophylline but not by tetrodotoxin or guanethidine, indicating that it is mediated by an action on the P1‐purinoceptor of smooth muscle.

It is evident from these results that in neonatal rat, a contractile response to ATP and ADP occurs initially in the duodenum, followed by a relaxant response to adenosine and AMP on day 14 and to ADP and ATP on day 21.

The smooth muscle of rat duodenum may tentatively be concluded to contain separate purinoceptors for adenosine and AMP (P1) and ADP and ATP (P2) and the responses to P1‐ and P2‐agonists change during the course of development.
Inhibition of neurally‐evoked transmitter release by calcium channel antagonists in rat parasympathetic ganglia
Authors: Seabrook Guy R. , Adams David J.
Published: July 2012

Excitatory postsynaptic potentials (e.p.s.ps) were recorded from the submandibular parasympathetic ganglia of newborn rats (10–20 days old), by intracellular microelectrode recording and a suction electrode to deliver stimulus trains to the lingual nerve (15 stimuli at 0.1, 0.3, 1, 3, and 10 Hz, 22°C). Only evoked responses without voltage‐dependent action potentials were analyzed (observed at membrane potentials negative to −70 mV), and e.p.s.p. amplitudes were determined for the plateau responses during each train (5‐15th response).

Cadmium, an inorganic calcium channel antagonist, reduced e.p.s.p. amplitudes in a dose‐dependent manner (Kd 74 μm, P < 0.01). Nickel (1–300 μm) did not attenuate the amplitude of evoked responses.

Verapamil (0.1–30 μm), a phenylamine, had no significant effects upon e.p.s.p. amplitudes at any frequency examined. Higher concentrations of verapamil (100 μm) blocked neurally evoked responses in a manner consistent with the antagonism of voltage‐sensitive sodium currents.

Diltiazem, a benzothiazepine, reduced e.p.s.p. amplitudes in a dose‐dependent manner, the depression being accentuated at high stimulation frequencies (80% block at 30 μm and 10 Hz). The pure (−)‐cis enantiomer of diltiazem (10–30 μm) was without effect.

Amlodipine, a 1,4‐dihydropyridine, did not antagonize synaptic transmission at any stimulus frequency examined (10–30μm, 0.1–10 Hz, n = 3).

Amiloride, a potassium‐sparing diuretic, depressed the amplitudes of evoked responses in a dose‐dependent manner (one‐site Kd 31 μm, P < 0.005), although the extent of the block was alleviated with high stimulus frequencies. The effects of 30 μm amiloride were unlikely to be of postsynaptic origin as both the amplitudes of miniature e.p.s.ps, and the iontophoretic potentials induced by exogenous acetylcholine, were not attenuated by treatment with this compound. The amiloride derivative, 3′,4′‐dichlorobenzamil was ineffective in reducing the amplitude of e.p.s.ps (30–100 μm).

ω‐Conotoxin GVIA, a marine neurotoxin, which depressed whole cell calcium currents recorded from cultured rat parasympathetic cardiac neurones (up to 90% block at 10 nm), was ineffective at blocking synaptic transmission in submandibular ganglia (0.1–1 μm).

The differential effects of these calcium channel antagonists upon synaptic transmission in rat parasympathetic ganglia, suggest that either more than one type of calcium channel may be involved in transmitter release, or that the presynaptic calcium channels possess pharmacological sensitivities different from those of channel types described in neuronal cell bodies.
Inhibitory effects of AH 21–132 in guinea‐pig isolated ileum and taenia caeci
Authors: Small R.C. , Boyle J.P. , Elliott K.R.F. , Foster R.W. , Watt A.J.
Published: July 2012

AH 21–132 is being investigated as a potential chemotherapeutic agent for bronchial asthma. The present experiments were designed to determine whether AH 21–132 shares the activity of theophylline as an antagonist at adenosine A1 receptors and to assess its potency as a relaxant in intestinal smooth muscle.

In the transmurally‐stimulated guinea‐pig ileum, theophylline (1 mm), but not AH 21–132 (1 and 10 μm), antagonized twitch depression induced by adenosine. Higher concentrations (100 μm and 1 mm) of AH 21–132 themselves had a depressant effect. Neither theophylline (1 mm) nor AH 21–132 (1 and 10 μm) antagonized twitch depression induced by noradrenaline.

AH 21–132 (100 μm and 1 mm) depressed maximum contractions of ileum induced by both acetylcholine (ACh) and histamine.

In ileum treated with hyoscine (1 μm), AH 21–132 (>10 μm) caused a concentration‐dependent depression of the log concentration‐effect curve for potassium chloride.

Simultaneous extracellular electrophysiological and mechanical recording from taenia caeci showed that AH 21–132 (100 μm‐1 mm) inhibited spontaneous tension waves and their associated bursts of electrical spike activity.

Intracellular electrophysiological recording from taenia caeci showed that the mechano‐inhibitory effect of 1 mM AH 21–132 was accompanied by abolition of spontaneous spike activity. Following spike abolition, the membrane potential assumed a value very close to that observed during periods of electrical quiescence prior to drug exposure.

AH 21–132 inhibited the activity of cyclic AMP‐dependent and cyclic GMP‐dependent phosphodiesterases derived from homogenates of ileal smooth muscle. The effective concentration ranges were 0.1–1000 μm and 1–1000 μm, respectively. Theophylline, too, inhibited these enzymes but in each case was less potent than AH 21–132.

It is concluded that AH 21–132 is devoid of antagonist activity at adenosine A1 receptors which modulate ACh release from intramural cholinergic nerves in the ileum. At concentrations greater than 10 μm, AH 21–132 has a relaxant effect on intestinal smooth muscle characterized by suppression of spontaneous action potentials but by minor change in resting membrane potential. AH 21–132 previously has been reported to depress the spontaneous tone of trachealis muscle with an EC50 value of less than 10 μm and the present experiments therefore show that this agent is much less potent in inhibiting intestinal muscle. This potency difference cannot be attributed to a tissue‐related difference in the potency of AH 21–132 as an inhibitor of cyclic AMP‐ or cyclic GMP‐dependent phosphodiesterases.
Inhibition of platelet‐activating factor‐ and zymosan‐activated serum‐induced chemotaxis of human neutrophils by nedocromil sodium, BN 52021 and sodium cromoglycate
Authors: Bruijnzeel P.L.B. , Warringa R.A.J. , Kok P.T.M.
Published: July 2012

Inflammatory cells such as eosinophils and neutrophils are thought to contribute actively to the pathogenesis of asthma since they infiltrate into the lung tissue. These cells are mobilized by lipid‐like and protein‐like chemotactic factors. As illustrative examples of both groups, platelet‐activating‐factor (Paf) and zymosan‐activated‐serum (ZAS) were used in this study. The inhibitory effects of nedocromil sodium, the Paf antagonist BN 52021 and sodium cromoglycate on Paf‐ and ZAS‐induced neutrophil chemotaxis were evaluated.

All tested drugs inhibited Paf‐induced neutrophil chemotaxis with approximately the same potency (IC50 ≅ 1 nm).

Nedocromil sodium and sodium cromoglycate were equally potent in inhibiting ZAS‐induced neutrophil chemotaxis (IC50 = 0.1–1 μm), whereas BN 52021 was considerably less potent (IC30=10 μm).

To find out whether the drugs tested could inhibit early events in cell activation, their capacity to inhibit Paf‐ and ZAS‐induced cytosolic free Ca2+‐mobilization was investigated. BN 52021, at a concentration of 100 μm, completely inhibited Paf‐induced Ca2+‐mobilization and inhibited ZAS‐induced Ca2+‐mobilization by about 50%. Nedocromil sodium and sodium cromoglycate were ineffective.
Activation of the human neutrophil 5‐lipoxygenase by exogenous arachidonic acid: involvement of pertussis toxin‐sensitive guanine nucleotide‐binding proteins
Authors: McColl Shaun R. , Krump Eric , Naccache Paul H. , Caon Adriana C. , Borgeat Pierre
Published: July 2012

The mechanism by which incubation of human peripheral blood neutrophils with exogenous arachidonic acid leads to 5‐lipoxygenase product synthesis was investigated.

Incubation of neutrophils with arachidonic acid caused a concentration‐ and time‐dependent synthesis of leukotriene B4, its Ω‐oxidation products, and 5‐hydroxyeicosatetraenoic acid.

The threshold concentration of arachidonic acid required for this effect was equal to, or greater than 3.3 μm and the synthesis increased with up to 33 μm arachidonic acid, the highest concentration used. Synthesis induced by arachidonic acid increased with time for up to 15 min and the major products detected were the Ω‐oxidation products of leukotriene B4.

Pre‐incubation of neutrophils with pertussis toxin inhibited the synthesis of 5‐lipoxygenase products induced by arachidonic acid by 75% or more, but had no effect on either arachidonic acid‐induced synthesis of the 15‐lipoxygenase product, 15‐hydroxyeicosatetraenoic acid, or activation of the 5‐lipoxygenase induced by the calcium ionophore A23187.

Pre‐incubation of neutrophils with granulocyte‐macrophage colony‐stimulating factor lead to enhanced leukotriene synthesis in response to arachidonic acid.

These results imply that exogenous arachidonic acid is not only used as a substrate, but also activates the 5‐lipoxygenase. Possible mechanisms of action are discussed.
3‐Aminopropylphosphinic acid—a potent, selective GABAB receptor agonist in the guinea‐pig ileum and rat anococcygeus muscle
Authors: Hills Judith M. , Dingsdale Rhona A. , Parsons Michael E. , Dolle Roland E. , Howson William
Published: July 2012

3‐Aminopropylphosphinic acid, a γ‐aminobutyric acid (GABA) analogue, was tested for activity on guinea‐pig isolated ileum and rat isolated anococcygeus muscle preparations. The effects of 3‐aminopropylphosphinic acid were compared with those of GABA and baclofen.

In the electrically stimulated ileum, 3‐aminopropylphosphinic acid, like GABA and baclofen, caused a concentration‐dependent inhibition of the cholinergic twitch contraction, the IC50 value being 1.84 ± 0.23 μm (n = 12). Unlike GABA, but like baclofen, 3‐aminopropylphosphinic acid did not produce an initial contraction.

The inhibitory effects of 3‐aminopropylphosphinic acid and baclofen in the guinea‐pig ileum were not significantly antagonized by bicuculline (10 μm), phentolamine plus propranolol (both 1 μm), yohimbine (1 μm), naloxone (1 μm), impromidine (1 μm) or 8‐phenyltheophylline (10 μm). The inhibitory effects of 3‐aminopropylphosphinic acid, but not of baclofen, were however antagonized by phaclofen (500 μm). In addition the effects of 3‐aminopropylphosphinic acid were abolished by baclofen desensitization in the guinea‐pig ileum.

3‐Aminopropylphosphinic acid, GABA and baclofen reduced the twitch contraction evoked by electrical field stimulation in the rat anococcygeus muscle. The IC50 for 3‐aminopropylphosphinic acid inhibition of the anococcygeus contraction was 0.89 ± 0.15 μm (n = 8).

It is concluded that 3‐aminopropylphosphinic acid is a potent, selective GABAB agonist, being seven times more potent than baclofen in the guinea‐pig ileum and five times more potent than baclofen in the rat anococcygues muscle preparations.
Antagonism of responses to excitatory amino acids on rat cortical neurones by the spider toxin, argiotoxin636
Authors: Priestley T. , Woodruff G.N. , Kemp J.A.
Published: July 2012

Several low molecular weight spider toxins have recently been shown to block potently glutama‐tergic neuromuscular transmission at the invertebrate neuromuscular junction. The aim of the present investigation was to evaluate the effects of one such toxin, argiotoxin636, on excitatory amino acid receptor‐mediated responses in mammalian neurones.

Membrane currents were recorded from rat cortical neurones after 2–6 weeks in cell culture, by the whole‐cell variant of the patch‐clamp technique. N‐methyl‐D‐aspartate (NMDA) and kainate were used as selective agonists for their respective receptor subtypes. α‐Amino‐3‐hydroxy‐5‐methyl‐4‐isoxazole‐propionic acid (AMPA) was used as a selective agonist for the quisqualate receptor subtype.

Responses to these agonists were characterised with respect to their concentration and voltage‐dependence. Argiotoxin636 (3–30 μm) was found to attenuate markedly responses to NMDA in an agonist‐ and voltage‐dependent manner. Thus, argiotoxin636 progressively reduced successive responses to NMDA when membrane potentials were voltage clamped between −40 mV to −100 mV. The more negative the membrane potential the more rapid the development of the block of inward current.

The antagonism of NMDA‐induced currents by argiotoxin636 could be reversed by clamping the membrane at positive potentials (+ 20 to + 60 mV) and reapplying NMDA.

Responses to AMPA and kainate were less affected by argiotoxin636, with an antagonist action only becoming evident at a concentration of 100 μm

These results suggest that argiotoxin636 is an open‐channel blocker of the NMDA activated ion‐channel in mammalian neurones. Furthermore, our results indicate at least a 30 fold selectivity for NMDA over the quisqualate‐ and kainate‐activated ion‐channels.
The effect of a single dose of oestradiol on tamoxifen‐induced uterine hyperaemia and growth in the rat
Authors: Marshall K. , Senior J.
Published: July 2012

The effect of oestradiol on tamoxifen ‐ (single doses of each agent) induced responses in the uterus of the mature ovariectomized rat was investigated. The parameters examined were uterine blood flow (measured by the microsphere technique), weight and oestrogen receptor concentrations.

Initially the addition of oestradiol to the tamoxifen regimen produced a reduction in uterine blood flow and dry weight which was reflected by a reduction in nuclear oestrogen receptor. However, as the tamoxifen response became more established from 48 h onwards the addition of oestradiol produced an additive effect. These changes were not mirrored by increases in nuclear oestrogen receptor.

The results suggest that tamoxifen and oestradiol may, in part, act via different mechanisms; the role of possible mediatory systems such as histamine release and eosinophil migration is discussed. Heterogeneous control systems may also be involved in the early and late uterine response.
Nitroglycerin relaxes canine coronary arterial smooth muscle without reducing intracellular Ca2+ concentrations measured with fura‐2
Authors: Yanagisawa Teruyuki , Kawada Mitsuo , Taira Norio
Published: July 2012

Changes in cytoplasmic Ca2+ concentration ([Ca2+]i) were measured simultaneously with force by a microfluorometric method using a calcium indicator, fura‐2, in canine coronary arterial smooth muscle cells.

Depolarization by high (30–90 mm) KCl‐physiological salt solution (PSS) produced concentration‐dependent increases in force and [Ca2+]i.

The KCl‐induced increase in [Ca2+]i was abolished by Ca2+‐free conditions and almost abolished by verapamil 10−5m, suggesting that it was entirely due to the increased Ca2+ influx through voltage‐dependent Ca2+ channels.

The [Ca2+]i‐force relationship in the presence of verapamil was not distinguishable from that of control.

Nitroglycerin produced a concentration‐dependent, reversible contraction of the coronary artery that had been contracted by high KC1‐PSS, without reduction of the increased [Ca2+]i.

The KCl‐induced increase in [Ca2+]i was not affected by nitroglycerin and in the presence of nitroglycerin it was abolished by 10−5m verapamil suggesting that it was caused by the influx of extracellular Ca2+.

The [Ca2+]i‐force curve was shifted to the right by nitroglycerin.

It is likely that nitroglycerin relaxes the coronary arterial smooth muscle by reducing the amount of myosin light chain phosphorylation even in the presence of raised [Ca2+]i produced by increased Ca2+ influx following depolarization.
Effects of endothelin on the mechanical activity and cytosolic calcium levels of various types of smooth muscle
Authors: Sakata K. , Ozaki H. , Kwon S.‐C. , Karaki H.
Published: July 2012

Effects of porcine/human endothelin (endothelin‐1), a novel vasoconstrictor peptide, on various smooth muscles were examined.

In rat aorta, endothelin (1 pM‐30 nm) induced contraction in a concentration‐dependent manner. Removal of endothelium shifted the concentration‐response curve to the left. When added during the sustained contraction induced by 0.1 μm noradrenaline, endothelin (1 nm) induced a relaxation that was inhibited by removing endothelium or by methylene blue.

In rat aorta without endothelium, endothelin (1–30 nm) increased cytosolic Ca2+ level ([Ca2+]cyt) followed by contraction. Endothelin induced less contraction than high K+ at a given [Ca2+]cyt when the concentration of endothelin was lower (1–3 nm) and/or during the early phase of the contraction (< 10 min). In contrast, endothelin induced a greater contraction than KCl after prolonged exposure to high concentrations (> 10 nm).

The increase in [Ca2+]cyt due to endothelin was strongly inhibited by 10 μm verapamil or 0.3 μm nicardipine although muscle contraction was only partially inhibited.

In Ca2+‐free solution, endothelin (30 nm) induced a transient increase in [Ca2+]cyt and a slow increase in muscle tension. After a prolonged incubation in Ca2+‐free solution, endothelin (30 nm) still induced a slow increase in tension without changing [Ca2+]cyt. This contraction was inhibited by 1 μm sodium nitroprusside or 10 μm forskolin.

In canine trachea and guinea‐pig uterus, endothelin (30 nm) induced sustained contraction with an increase in [Ca2+]cyt. In the absence of external Ca2+, endothelin (30 nm) induced a sustained contraction in canine trachea without changing [Ca2+]cyt. In guinea‐pig vas deferens, taenia caeci and ileal longitudinal muscle, endothelin induced small increases in [Ca2+]cyt and tension.

In permeabilized smooth muscles, endothelin (30 nm) did not change the muscle tone.

These results suggest that endothelin acts on the endothelium and increases the synthesis or release of endothelium‐derived relaxing factor (EDRF). These results also suggest that endothelin acts directly on smooth muscle and increases [Ca2+]cyt by releasing Ca2+ from storage sites and increasing Ca2+ influx through the verapamil‐ and 1,4‐dihydropyridine‐sensitive pathway. Endothelin seems to decrease Ca2+‐sensitivity of contractile elements at lower concentrations and/or during the early phase of the contraction, whereas it increases Ca2+‐sensitivity at higher concentrations during the sustained phase of the contraction. Furthermore, endothelin induces a contraction that is not dependent on [Ca2+]cyt.
The influence of amine metabolizing enzymes on the pharmacology of tyramine in the isolated perfused mesenteric arterial bed of the rat
Authors: Elliott Jonathan , Callingham Brian A. , Sharman Dennis F.
Published: July 2012

The pressor response to the infusion of tyramine (Tyr) into the isolated perfused mesenteric arterial bed of the rat has been studied at both a low and a high dose (0.2 and 2.0 μmol) and the effect of monoamine oxidase‐A (MAO‐A) and semicarbazide‐sensitive amine oxidase (SSAO) inhibition was examined. Very little MAO‐B activity is found in homogenates of this tissue when Tyr is used as substrate.

Inhibition of SSAO by treating rats with 1 mg kg−1 (E)‐2‐(3′,4′‐dimethoxyphenyl)‐3‐fluoroally lamine (MDL 72145) 1 h before dissection, had no significant effect on the maximum pressure attained or the area under the curve (AUC) of the response to both low and high doses of Tyr. Inhibition of MAO‐A, by inclusion of 10 μm clorgyline in the perfusing fluid, resulted in no significant potentiation at both low or high doses of Tyr. The inhibition of both these enzymes together substantially increased the AUC of the pressor response.

Cocaine (3 μm) significantly potentiated the responses to adrenaline (Ad). At this dose, cocaine significantly reduced the peak height and the AUC of the responses to both doses of Tyr.

Inhibition of extraneuronal uptake mechanisms with corticosterone (29 μm) did not potentiate the response to Ad and did not significantly alter the response to Tyr (low dose).

The effects of MDL 72145 and clorgyline on the directly acting amine, Ad, were studied. MDL 72145 caused a small but significant increase in the EC50 and in the maximum response to Ad, whilst clorgyline (10 μm) increased the EC50 value slightly and decreased the maximum response. When the two inhibitors were used in combination, a significant increase in the maximum response but with no change in the EC50 was seen.

These data indicate that the action of Tyr in this vascular bed is, at least, partly indirect. Inactivation of Tyr is effected by both MAO‐A and SSAO in the blood vessel wall. Inhibition of both enzymes seems to be necessary to achieve a significant potentiation of the pressor response. The effects of these enzyme inhibitors on directly acting amines may mask any potentiation of the response when MAO‐A or SSAO alone are inhibited.
Spinal antinociceptive actions of μ‐ and κ‐opioids: the importance of stimulus intensity in determining ‘selectivity’ between reflexes to different modalities of noxious stimulus
Authors: Parsons Chris G. , Headley P. Max
Published: July 2012

In electrophysiological experiments in spinalized rats, μ‐ and κ‐opioids were tested intravenously on the responses of single motoneurones to electronically controlled, alternating noxious heat and noxious pinch stimuli. The effects of μ‐ and κ‐opioids were compared with those of the general anaesthetic α‐chloralose and the dissociative anaesthetic/PCP ligand ketamine.

The κ‐opioids U‐50,488 (0.5–16 mg kg−1 i.v.) and tifluadom (0.05‐1.6 mg kg−1 i.v.) had very similar actions to the μ‐opioid fentanyl (0.5–16 μg kg−1 i.v.). Thus all three agonists reduced thermal and mechanical nociceptive reflexes in parallel and in a dose‐dependent manner, but only so long as neuronal responses to the alternating stimuli elicited similar excitability levels in the neurone under study. Ketamine (0.5–16 mg kg−1 i.v.) had similar actions to the opioids whereas α‐chloralose (20 mg kg−1 i.v.) had very little effect on neuronal responsiveness.

Apparently ‘selective’ depressions by both μ‐ and κ‐opioids could be orchestrated by a deliberate mismatch of the intensities of alternating noxious heat and pinch stimuli; as measured by neuronal firing rate, the weaker of the responses to either type of stimulus was invariably reduced to a greater degree.

Similar ‘selectivity’ could be demonstrated for both μ‐ and κ‐ligands when the weaker and stronger responses were of the same modality, being applied by the same pincher device but with alternating applied force.

It is concluded that the ‘selective’ spinal actions of κ‐opioids seen in non‐thermal over thermal behavioural models of nociception is likely to be related to the relative intensities, rather than the modalities, of the noxious stimuli used. The validity of the interpretation of results obtained in such behavioural studies is discussed.
Inhibitory effect of a toxin okadaic acid, isolated from the black sponge on smooth muscle and platelets
Authors: Karaki Hideaki , Mitsui Minori , Nagase Hiromi , Ozaki Hiroshi , Shibata Shoji , Uemura Daisuke
Published: July 2012

Effects of okadaic acid, a toxin isolated from marine sponges, on smooth muscle contraction and platelet activation were examined.

Contractions in rabbit aorta induced by high concentrations of K+ and noradrenaline were inhibited by 0.1–1 μm okadaic acid in a concentration‐dependent manner. Spontaneous rhythmic contractions as well as high K+‐induced contraction in guinea‐pig taenia caeci were also inhibited by 1 μm okadaic acid.

High K+‐induced contraction in rabbit aorta was accompanied by increased Ca2+ influx measured with 45Ca2+ and increased cytosolic Ca2+ ([Ca2+]cyt) measured with fura‐2‐Ca2+ fluorescence. Okadaic acid inhibited the contraction without inhibiting Ca2+ influx and produced only a small decrease in [Ca2+]cyt.

In a saponin‐skinned taenia, Ca2+‐induced contraction was not inhibited but rather potentiated by okadaic acid.

Okadaic acid, 1 μm, inhibited aggregation, ATP release and increase in [Ca2+]cyt induced by thrombin in washed rabbit platelets. Okadaic acid itself did not change the platelet activities.

Okadaic acid did not change the cyclic AMP content of rabbit aorta although the inhibitory effects of okadaic acid were similar to those of cyclic AMP.

Although the mechanism of the inhibitory effect of okadaic acid was not clarified in the present experiments, it is suggested that okadaic acid acts by inhibiting protein phosphatases resulting in an indirect activation of cyclic AMP‐dependent protein phosphorylation.
Enhancement of leukotriene C4 release from primate airway macrophages by cellular interactions
Authors: Campbell A.M. , Harper S.T. , Hallam C. , Wells E. , Mann J. , Robinson C.
Published: July 2012

Cells were obtained from the lungs of Macaque monkeys by bronchoalveolar lavage in order to study the role of cellular interactions in the release of leukotriene C4 (LTC4).

In normal monkeys, macrophages were the most abundant cell type recovered, whereas in monkeys sensitized with Ascaris suum there was an increase in the numbers of eosinophils and mast cells recovered.

Challenge of cells from both groups of animals with an optimal concentration of opsonized zymosan (OPZ) resulted in the time‐dependent release of LTC4 from macrophages. However, release was significantly greater in cells obtained from sensitized donors compared to normal donors.

Density‐gradient centrifugation of cells lavaged from sensitized donors was used to prepare fractions containing both eosinophils and mast cells. Addition of these cells to macrophage populations obtained from non‐sensitized donors caused a significant enhancement of OPZ‐induced LTC4 release. In the absence of macrophages no significant release of LTC4 was detected from eosinophil/mast cell‐containing fractions stimulated with OPZ, despite the fact that the zymosan had been phagocytosed by the eosinophils.

There was a significant correlation between the percentage enhancement of LTC4 release and the number of eosinophils added. However, there was not a significant correlation with the number of mast cells added.

These results suggest that a cellular interaction between macrophages and eosinophils may be important in the regulation of mediator synthesis and release. The precise mechanism of this effect remains to be elucidated.
Effect of acute and subchronic nicotine treatment on cortical acetylcholine release and on nicotinic receptors in rats and guinea‐pigs
Authors: Nordberg A. , Romanelli L. , Sundwall A. , Bianchi C. , Beani L.
Published: July 2012

The effect of acute and chronic (16 days) administration of nicotine on cortical acetylcholine (ACh) release, gross behaviour and brain nicotinic binding sites was investigated in rats and guinea‐pigs.

The drug, injected either subcutaneously (0.45‐0.90 mg kg−1) or intracerebroventricularly (1, 3 and 5 μg) increased the cortical ACh release, in a dose‐dependent manner, through mecamylamine‐sensitive receptors for 1–2 h in both species.

Chronic treatment significantly increased basal ACh release in the rat and slightly lowered it in the guinea‐pig, but the response to a challenging dose of nicotine was proportionally maintained in both species.

The number of nicotinic receptors was four times higher in the rat than in the guinea‐pig and was not dependent on the radioligand used ([3H]‐nicotine or [3H]‐ACh, in the presence of atropine) to determine this. The nicotinic binding sites showed an apparent increase in chronically treated rats but no change in guinea‐pigs.

Tolerance to the inhibitory effect of the drug, assessed with the T maze test, was found in the rat. No apparent change in gross behaviour was detected in the guinea‐pig.

It is concluded that chronic nicotine treatment causes evident tolerance to its inhibitory effect on behaviour in the rat, but no adaptation to its excitatory properties on the cholinergic brain structures in rats and guinea‐pigs.