bluuebunny/crossref_metadata_2025 huggingface dataset:
Differential effects of dopamine agonists upon stimulated limbic and striatal dopamine release: in vivo voltammetric data
Authors: Stamford Jonathan A. , Kruk Zygmunt L. , Millar Julian
Published: July 2012

Fast cyclic voltammetry at carbon fibre microelectrodes was used in rats anaesthetized with chloral hydrate to monitor dopamine release in the caudate and nucleus accumbens evoked by electrical stimulation of the median forebrain bundle. Stimulation trains (50 Hz sinusoidal current, 100 ± 10 μA r.m.s., 2 s duration) were repeated every 5 min throughout the experiment.

The actions of the dopamine agonists quinpirole, pergolide, SKF 38393, bromocriptine, (+)‐3‐(3‐hydroxyphenyl)‐N‐n‐propylpiperidine ((+)‐3PPP) and (−)‐3PPP were compared in the two nuclei.

Bromocriptine (10 mg kg−1, i.p.) did not affect release in either nucleus while SKF 38393 caused a fleeting decrease in limbic but not striatal dopamine release at a high dose (20 mg kg−1, i.p.).

Quinpirole and pergolide (both 1 mg kg−1, i.p.) decreased stimulated dopamine release in the nucleus accumbens while in the caudate the drugs each caused a transient, though not quite significant, elevation of stimulated dopamine release followed by decrease in release of the same magnitude as that seen in the nucleus accumbens.

The (−)‐enantiomer of 3PPP (20 mg kg−1, i.p.), a partial agonist at the dopamine autoreceptor, increased stimulated dopamine release in both nuclei although the action in the caudate was larger and more prolonged. (+)‐3PPP (20 mg kg−1, i.p.), a full agonist, decreased release in the nucleus accumbens. A small, transient and not significant increase in the caudate was followed by decreased release.

The results are interpreted as being evidence for differences in the dopamine autoreceptor in the two nuclei, possibly in the affinity state of the receptor in each nucleus.
Effects of cyclic nucleotides and phorbol myristate acetate on proliferation of pig aortic endothelial cells
Authors: Moodie Shonna Alexandra , Martin William
Published: July 2012

The role of cyclic nucleotides and protein kinase C in controlling proliferation of pig aortic endothelial cells (PAEC) in culture was investigated.

Dibutyryl cyclic AMP (30 μm), added twice daily, inhibited proliferation but 8 bromo cyclic GMP (30 μm) had no effect. Two other stimuli known to increase PAEC cyclic GMP content by stimulating particulate and soluble guanylate cyclase respectively, atriopeptin II (10 nm) and sodium nitroprusside (1 μm), were also without effect on proliferation.

Two agents known to inhibit soluble guanylate cyclase and lower intercellular cyclic GMP content, haemoglobin (10 μm) and methylene blue (10 μm), each inhibited proliferation of PAEC.

The inhibitory effect of haemoglobin (10 μm) was mediated by inhibition of soluble guanylate cyclase since it was reversed by agents known to increase cyclic GMP content, i.e. atriopeptin II (10 nm), 8 bromo cyclic GMP (30 μm) or sodium nitroprusside (1 μm). The inhibitory effect of methylene blue (10 μm) was not reversed by these agents.

Phorbol 12‐myristate 13‐acetate (PMA, 0.1 nm–1 μm), which activates protein kinase C, inhibited proliferation in a concentration‐dependent manner. No early stimulation of proliferation was seen wtih PMA. The inactive isomer, 4α‐phorbol 12, 13‐didecanoate (0.3 μm), lacked the ability of PMA to inhibit proliferation of PAEC.

PMA‐induced inhibition of proliferation appeared not to be due to stimulated production of destructive oxygen‐derived free radicals since it was unaffected by the radical scavengers, vitamin E (30 μm) or butylated hydroxytoluene (30 μm). The antiproliferative actions of paraquat (10 μm), an agent which generates free radicals intracellularly, was, in contrast, inhibited by vitamin E or butylated hydroxytoluene. Furthermore, neither dibutyryl cyclic AMP (30 μm) nor 8 bromo cyclic GMP (30 μm) had any effect on the ability of PMA to inhibit proliferation.

This study suggests that cyclic AMP, cyclic GMP and protein kinase C play a role in controlling the proliferation of PAEC.
Probing the molecular dimensions of general anaesthetic target sites in tadpoles (Xenopus laevis) and model systems using cycloalcohols
Authors: Curry S. , Moss G.W.J. , Dickinson R. , Lieb W.R. , Franks N.P.
Published: July 2012

The series of cycloalcohols C6, C7, C8 and C10 have been used to probe the molecular dimensions of a variety of general anaesthetic target sites.

The general anaesthetic EC50 concentrations of the cycloalcohols were determined for tadpoles (Xenopus laevis). All of the cycloalcohols tested were found to be potent general anaesthetics (on average EC50/Csat = 0.03).

The effects of the cycloalcohols on highly purified luciferase enzymes from fireflies (Photinus pyralis) and bacteria (Vibrio harveyi) were also investigated. Both enzymes were inhibited competitively, with the cycloalcohols competing with firefly luciferin for binding to the firefly enzyme and with n‐decanal for binding to the bacterial enzyme.

The binding site on the firefly enzyme could accommodate two molecules of cycloalcohols C6 and C7 but only a single molecule of the larger cycloalcohols (C8 and C10), implying a volume of the binding site of about 250 cm3 mol−1. In contrast, the binding site on the bacterial luciferase could bind only a single cycloalcohol molecule between C6 and C10.

While all of the cycloalcohols were potent inhibitors of the firefly luciferase enzyme (on average EC50/Csat = 0.015), they were very weak inhibitors of the bacterial luciferase enzyme (on average EC50/Csat = 0.12). Since both enzymes bind long‐chain aliphatic n‐alcohols tightly, the differing affinities of the cycloalcohols for the two enzymes is probably a consequence of geometrical factors.

The cycloalcohols produced very small effects on lipid bilayers. At EC50 concentrations which produce general anaesthesia, lipid bilayer phase transitions were shifted, on average, by only 0.43°C.

We conclude that the general anaesthetic effects of the cycloalcohols can most economically be explained by assuming that the cycloalcohols act at protein binding sites in the central nervous system. These target sites would have binding properties similar to those of the anaesthetic‐binding site on firefly luciferase, but their average volume would be somewhat smaller than 250 cm3 mol−1.
Effects of a novel smooth muscle relaxant, KT‐362, on contraction and cytosolic Ca2+ level in the rat aorta
Authors: Sakata Kiyoshi , Karaki Hideaki
Published: July 2012

Inhibitory effects of a novel smooth muscle relaxant, KT‐362 (5‐[3‐([2‐(3,4‐dimethoxyphenyl)‐ethyl]amino)‐1‐oxopropyl]‐2,3,4,5‐tetrahydro‐1,5‐benzothiazepine fumarate), on contraction and the cytosolic Ca2+ level ([Ca2+]cyt) in isolated vascular smooth muscle of rat aorta were examined.

KT‐362 inhibited the contractions induced by high K+ and noradrenaline. The inhibitory effect was antagonized by an increase in external Ca2+ concentration. A Ca2+ channel activator, Bay K 8644, did not change the effect of KT‐362 on high K+‐induced contraction.

[Ca2+]cyt, measured with fura‐2‐Ca2+ fluorescence, increased during the contractions induced by high K+ or noradrenaline. KT‐362 decreased [Ca2+]cyt and muscle tension stimulated by high K+ or noradrenaline. By contrast, a Ca2+ channel blocker, verapamil, inhibited the noradrenaline‐induced increase in [Ca2+]cyt with only partial inhibition of the noradrenaline‐induced contraction and KT‐362 inhibited the verapamil‐insensitive portion of the contraction without changing [Ca2+]cyt.

In a Ca2+‐free solution, noradrenaline and caffeine induced a transient contraction following a transient increase in [Ca2+]cyt. KT‐362 inhibited the increments due to noradrenaline but not those induced by caffeine.

These results suggest that KT‐362 inhibits vascular smooth muscle contraction by inhibiting Ca2+ channels, receptor‐mediated Ca2+ mobilization, and receptor‐mediated Ca2+ sensitization of contractile elements.
Furosemide inhibits the centrally‐mediated pressor response to clonidine in conscious, normotensive rats
Authors: Kawasaki Hiromu , Nakamura Shigeru , Takasaki Koichiro
Published: July 2012

The effect of furosemide on the pressor response induced by intracerebroventricular (i.c.v.) injection of clonidine was investigated in freely moving, normotensive rats with chronically implanted arterial catheters.

When injected i.c.v., clonidine at doses of 5 and 10 μg produced a dose‐dependent pressor response and a decrease in heart rate. No depressor response was induced by clonidine.

Systemic (i.v.) pretreatment with furosemide (2–10 mg kg−1) increased urine volume and dose‐dependently inhibited the pressor response to i.c.v. clonidine (10 μg), and a long‐lasting depressor response to clonidine was observed. However, furosemide treatment did not alter the bradycardia produced in response to clonidine.

The systemic treatment with furosemide (10 mg kg−1, i.v.) had no effect on the pressor response to i.v. noradrenaline.

These results suggest that reduction of body fluid volume inhibits the centrally‐mediated pressor response to clonidine and leads to the hypotensive effect. We also suggest that combined treatment with a diuretic increases the hypotensive efficacy of clonidine.
Salmeterol: a potent and long‐acting inhibitor of inflammatory mediator release from human lung
Authors: Butchers P.R. , Vardey C.J. , Johnson M.
Published: July 2012

The effects of salmeterol, a novel long‐acting β2‐adrenoceptor agonist, have been investigated on antigen‐induced mediator release from passively sensitized fragments of human lung in vitro.

Salmeterol was a potent inhibitor of the release of histamine (–log IC50 = 8.54), leukotriene C4 (LTC4)/LTD4 (–log IC50 = 9.07) and prostaglandin D2 (–log IC50 = 8.81). It was slightly less potent (1–3 fold) than isoprenaline, but significantly more potent (10–35 fold) than salbutamol.

Propranolol competitively antagonized the inhibitory effects of salmeterol on histamine release (pA2 = 8.41) and LTC4/LTD4 release, (pA2 = 8.40) indicating an action via β‐adrenoceptors.

The inhibitory effects of isoprenaline (20 nm) and salbutamol (200 nm) were removed after washing the lung tissue for 2 h and 4 h respectively. In contrast, the inhibitory effects of salmeterol (40 nm) were much longer‐lasting, and were still evident after 20 h.

Salmeterol therefore exhibits potent and persistent inhibition of anaphylactic mediator release from human lung. This anti‐inflammatory effect may be important for the therapeutic potential of salmeterol in the treatment of bronchial asthma.
Effects of NG‐nitro‐l‐arginine methyl ester on vasodilator responses to adrenaline or BRL 38227 in conscious rats
Authors: Gardiner S.M. , Kemp P.A. , Bennett T.
Published: July 2012

Conscious, Long Evans rats, chronically instrumented for the measurement of regional haemodynamics, were used to assess responses to 3 min infusions of the potassium channel opener, BRL 38227 (1 and 10 μg kg−1 min−1) or adrenaline (0.05 and 0.5 μg kg−1 min−1) in the absence and in the presence of NG‐nitro‐l‐arginine methyl ester (l‐NAME; 3 mg kg−1 h−1), an inhibitor of nitric oxide biosynthesis.

In the absence of l‐NAME, the low dose of BRL 38227 caused slight hypotension and tachycardia, accompanied by small increases in mesenteric and hindquarters blood flow only. However, there were increases in renal, mesenteric and hindquarters vascular conductances. l‐NAME had no effect on any of these responses.

The high dose of BRL 38227 caused substantial hypotension and tachycardia. Renal and hindquarters flows did not change significantly, but there was a marked increase in mesenteric flow. There were only modest increases in renal and hindquarters vascular conductances but a substantial mesenteric vasodilatation. In the presence of l‐NAME, there was a slight reduction of the latter but no other changes in the responses to BRL 38227.

In the absence of l‐NAME, the low dose of adrenaline caused slight hypotension but a marked tachycardia. There were no changes in renal or mesenteric blood flow but a clear‐cut increase in hindquarters flow. Renal and mesenteric vascular conductances showed only small rises, in contrast to the substantial hindquarters vasodilatation. In the presence of l‐NAME, there was significant attenuation of the tachycardia and of the increases in hindquarters flow and vascular conductance in response to adrenaline.

The high dose of adrenaline caused marked hypotension and tachycardia. Renal flow did not change, but there was a fall in mesenteric and a marked rise in hindquarters flow. Renal vascular conductance showed a slight increase but mesenteric vascular conductance did not change significantly, whereas there was a substantial hindquarters vasodilatation. In the presence of l‐NAME, adrenaline caused an increase in blood pressure but no significant change in heart rate; the renal vasodilatation was abolished, there was a mesenteric vasoconstriction, and the hindquarters vasodilatation was markedly reduced. l‐NAME also attenuated the tachycardia induced by adrenaline in animals with no cardiac baroreflexes.

The present results indicate that l‐NAME‐sensitive mechanisms are involved in the vasodilator and tachycardic effects of adrenaline. The relative lack of effect of l‐NAME on responses to BRL 38227 indicates that the changes in the responses to adrenaline were not non‐specific or due to changes in haemodynamic status caused by l‐NAME. The results raise the possibility that the ‘hypertensinogenic’ properties of endogenous adrenaline could be amplified when nitric oxide biosynthesis is impaired.
Neuropeptide Y, peptide YY and C‐terminal fragments release histamine from rat peritoneal mast cells
Authors: Grundemar Lars , Håkanson Rolf
Published: July 2012

Neuropeptide Y (NPY) and peptide YY (PYY) seem to act on at least two receptor sybtypes, Y1 and Y2. The Y1‐receptor requires the whole C‐terminally amidated NPY/PYY molecule whereas the Y2‐receptor in addition recognizes C‐terminal fragments of the two peptides. The present study was designed to elucidate whether NPY and related peptides were able to release histamine from isolated peritoneal mast cells of the rat.

NPY, NPY 15–36, NPY 22–36, NPY 26–36 and desamido‐NPY evoked a concentration‐dependent release of mast‐cell histamine. The pEC15 values for NPY 15–36 and NPY 22–36 were higher, while the pEC15 value for NPY 26–36 was lower than that for NPY. At the highest concentration tested (0.1 mm), NPY and its C‐terminal fragments released between 30 and 40% of the total histamine content. At the same concentration desamido‐NPY released about 20%.

PYY and PYY 15–36 also evoked a concentration‐dependent release of mast‐cell histamine. PYY was more effective than PYY 15–36 since, at 0.1 mm, PYY released about 33%, while PYY 15–36 released about 15% of the total histamine content. Pancreatic polypeptide (PP) and the Y1‐receptor‐selective agonist [Pro34]NPY were virtually inactive.

The effect profile of the NPY/PYY‐related peptides suggests that they act on the mast cells by a mechanism that does not involve either of the receptor subtypes hitherto described. The kinetics of the NPY‐evoked histamine release may suggest that positively charged amino acid residues of NPY/PYY release mast‐cell histamine by a non‐receptor mechanism, as has been suggested for substance P and other basic peptides.
Variations in potassium concentration modify the inhibitory effect of lorcainide on myocardial Na+‐K+‐ATPase activity
Authors: Almotrefi Abdulrahman A. , Dzimiri Nduna
Published: July 2012

The inhibitory action of lorcainide on the myocardial Na+‐K+‐ATPase (EC 3.6.1.3) activity was studied in guinea‐pig heart preparations at medium K+ concentrations of 2.5, 5.0 and 10 mm.

Lorcainide exhibited characteristically similar concentration‐dependent inhibitory effects at all three K+ concentrations tested. However, the inhibitory potencies were significantly increased at decreased K+ concentrations.

The IC50 values were 10.4 ± 3.2 μm at 2.5 mm, 28.3 ± 7.9 μm at 5.0 mm and 40.7 ± 9.2 μm at 10.0 mm K+ respectively. Thus, reduction in the K+ concentration from the ‘standard’ 5.0 to 2.5 mm enhanced the inhibitory potency of lorcainide, the effective concentrations being shifted towards much lower ranges, while increasing it to 10 mm on the other hand produced opposite but less marked effects.

These results show that the inhibition of myocardial Na+‐K+‐ATPase activity by lorcainide depends on the K+ concentration of the incubation medium. These effects are probably related to the mechanism by which lorcainide interferes with the electrogenic Na+/K+ pump activity of the enzyme, and hence may contribute to some of its cardiac actions.
Effects of endothelin‐1 on vascular permeability in the conscious rat: interactions with platelet‐activating factor
Authors: Filep János G. , Sirois Martin G. , Rousseau Anne , Fournier Alain , Sirois Pierre
Published: July 2012

The objectives of the present experiments were to assess the effects of endothelin‐1 on the macrovascular permeability in selected vascular beds, to study the involvement of platelet‐activating factor (PAF) in vascular responses to endothelin‐1 and to examine the vascular effects of combined administration of endothelin‐1 and PAF in conscious rats.

Intravenous bolus injection of endothelin‐1 (0.1–2 nmol kg−1) resulted in a dose‐dependent biphasic change in mean arterial blood pressure (MABP) with initial transient hypotension followed by a prolonged pressor action. These changes were accompanied by a dose‐dependent increase in haematocrit values.

Endothelin‐1 (0.1 and 1 nmol kg−1) increased dose‐dependently the vascular permeability of the trachea, upper and lower bronchi, stomach, duodenum, spleen and kidney (up to 240%) as measured by the extravasation of Evans blue dye. The permeability of pulmonary parenchyma, liver and pancreas was not affected significantly by endothelin‐1 treatment.

Pretreatment of animals with the specific PAF receptor antagonist, WEB 2086 (1 mg kg−1, i.v.) or BN 52021 (10 mg kg−1, i.v.) reduced the endothelin‐1 (1 nmol kg−1)‐induced rise in haematocrit by about 50 and 30%, respectively. Both antagonists were highly effective at inhibiting protein extravasation in the stomach, duodenum and kidney. On the other hand, BN 52021, but not WEB 2086, significantly attenuated the effect of endothelin‐1 on permeability in the lower bronchi and spleen. Neither WEB 2086 nor BN 52021 modified the changes in MABP evoked by endothelin‐1.

When low doses of endothelin‐1 (0.1 nmol kg−1) and PAF (0.19 nmol kg−1) were administered simultaneously, enhanced protein extravasation was detected in the upper and lower bronchi, whereas neither endothelin‐1 nor PAF by themselves affected vascular permeability in these tissues. These changes occurred in the absence of significant changes in MABP.

Combined administration of higher doses of endothelin‐1 (1 nmol kg−1) and PAF (1.9 nmol kg−1) resulted in marked increases (up to 530%) in protein extravasation in the airways, pancreas, stomach and duodenum. The effect of endothelin‐1 on permeability was not affected by PAF in the spleen, whereas it was completely inhibited by PAF in the kidney. Combined injection of endothelin‐1 and PAF resulted in a slight, but significant increase in MABP.

The present findings show that endothelin‐1 is capable of increasing vascular permeability in selected vascular beds including the airways, gastrointestinal tract and kidney, and suggest that PAF may mediate, in part, its action on permeability, but not its hypotensive action. The present data also suggest that endothelin‐1 and PAF can act in concert to increase vascular permeability in rat airways and gastrointestinal tract.
Selective inhibition of K+ ‐stimulation of Na,K‐ATPase by bretylium
Authors: Tiku Patience E. , Nowell Peter T.
Published: July 2012

The effects of bretylium were investigated on purified Na,K‐ATPase from guinea‐pig heart and on the Na/K pump in trout erythrocytes, with a view to further identifying the mechanism(s) associated with its antiarrhythmic effects.

Na,K‐ATPase activity of the thiocyanate‐dispersed enzyme was determined by the measurement of inorganic phosphate produced by ATP hydrolysis.

When the concentrations of each of the Na,K‐ATPase activating components were varied in turn, bretylium (1–5 mmol l−1) exhibited competitive‐type effects against K+ with a Ki of 1.4 mmol l−1 and noncompetitive‐type effects against Na+, Mg2+ and ATP.

In K+ influx studies in trout erythrocytes with 86Rb+ used as the marker, the inhibition of total influx observed with bretylium (5 and 10 mmol l−1) was attributable to the bretylium cation selectively inhibiting the Na/K pump‐mediated influx with the associated tosylate anion inhibiting Na/K cotransport.

The observed inhibition kinetics indicated that the bretylium cation (2–15 mmol l−1) competitively inhibited K+ stimulation of the Na/K pump at 6 and 1.25 mmol l−1 external K+ with a mean K1 of 2.3 mmol l−1.

The effects demonstrated on the functioning Na/K pump in erythrocytes confirmed the Na,K‐ATPase findings, with bretylium selectively inhibiting K+ stimulation of the pump mechanism in both cases.

It is suggested that Na,K‐ATPase inhibition may contribute to the antiarrhythmic and positive inotropic effects of bretylium with the cardiac accumulation of bretylium also possibly being a further important factor.
Inositol 1,4,5‐trisphosphate‐ and guanosine 5′‐O‐(3‐thio triphosphate)‐induced Ca2+ release in cultured airway smooth muscle
Authors: Chopra Lorna C. , Twort Charles H.C. , Cameron Ian R. , Ward Jeremy P.T.
Published: July 2012

The interaction between inositol 1,4,5‐trisphosphate (InsP3) and guanosine 5′‐O‐(3‐thio triphosphate) (GTPγS) releasable calcium (Ca2+) pools was examined using 45Ca effluxes in permeabilized cultured airway smooth muscle cells from rabbit trachea.

Addition of InsP3 or GTPγS caused a concentration‐dependent release of intracellular Ca2+. The release of Ca2+ by InsP3 was much greater than with GTPγS. Pretreatment with maximally effective InsP3 (10 μm) abolished the GTPγS‐induced Ca2+ release, whereas pretreatment with 100 μm GTPγS reduced the InsP3‐induced Ca2+ release by 25%.

Ryanodine (100 μm), also gave a large release of intracellular Ca2+. After pretreatment with 100 μm ryanodine, GTPγS did not induce Ca2+ release, and InsP3‐induced Ca2+ release was reduced by 76%.

Caffeine (50 mm), produced a slow release of intracellular Ca2+. Pre‐exposure to 50 mm caffeine had no effect on the GTPγS‐induced Ca2+ release but reduced the InsP3 releasable Ca2+ by 58%.

Pretreatment with ryanodine abolished the caffeine‐induced Ca2+ release, and addition of caffeine before ryanodine reduced the ryanodine‐induced Ca2+ release by 64.4%.

These results suggest that there are at least three pools of Ca2+ present within airway smooth muscle cells. The largest pool is released by InsP3 or ryanodine, another is released either by a high concentration of InsP3 or on application of GTPγS, and the third by InsP3 alone. Ca2+ may be able to move from the GTPγS‐sensitive pool into the InsP3‐ and ryanodine‐sensitive pool when this becomes depleted. In contrast, the opposite movement of Ca2+ cannot occur.
Three distinct binding sites for [3H]‐prazosin in the rat cerebral cortex
Authors: Oshita Masafumi , Kigoshi Shigeru , Muramatsu Ikunobu
Published: July 2012

The putative α1‐adrenoceptor subtypes of rat cerebral cortex membranes were characterized in binding experiments with [3H]‐prazosin.

Specific binding of [3H]‐prazosin was saturable between 20–5000 pm. Scatchard plots of the binding data were non‐linear, indicating the presence of two distinct affinity sites for prazosin (pKD, high = 10.18, Rhigh = 308 fmol mg−1 protein; pKD, low = 8.96, Rlow = 221 fmol mg−1 protein).

In the membranes pretreated with chlorethylclonidine (CEC) two affinity sites for prazosin were also observed: the affinities were similar to those without CEC pretreatment, but the maximum numbers of binding sites were reduced by CEC pretreatment to 23 and 62% for prazosin‐high (Rhigh) and low affinity sites (Rlow), respectively.

The prazosin‐high affinity sites were further subdivided into two subclasses by WB4101(2‐(2,6‐dimethoxyphenoxyethyl)aminomethyl‐1,4‐benzodioxane) and phentolamine; the low affinity sites for WB4101 and phentolamine were more potently inactivated by CEC as compared with the high affinity sites. On the other hand, prazosin, HV723 (α‐ethyl‐3,4,5‐trimethoxy‐α‐(3‐((2‐(2‐methoxyphenoxy)ethyl)‐amino)‐propyl)benzeneacetonitrile fumarate) and yohimbine inhibited [3H]‐prazosin binding to prazosin‐high affinity sites monophasically.

In addition to the high affinity sites, the prazosin‐low affinity sites were labelled at high concentrations of [3H]‐prazosin. Thus, prazosin and WB4101 showed shallow displacement curves. On the other hand, HV723 and yohimbine did not discriminate between prazosin‐high and low affinity sites.

Two distinct α1‐adrenoceptor subclassifications have been recently proposed (α1A, α1B subtypes and α1H, α1L, α1N subtypes). According to the criteria defined with competitive antagonists in both the subclassifications, the present results indicate that the α1‐adrenoceptors of rat cerebral cortex consist of three different subtypes, presumably α1A, α1B and α1L, and suggest that the α1A and α1B subtypes are identified as a single affinity site for prazosin (α1H). The results also indicate that care must be taken in the use of CEC for α1‐adrenoceptor subclassification because of its low selectivity.
Ca2+ channel activation and membrane depolarization mediated by Cl− channels in response to noradrenaline in vascular myocytes
Authors: Pacaud Pierre , Loirand Gervaise , Baron Anne , Mironneau Chantal , Mironneau Jean
Published: July 2012

The effects of noradrenaline (NA) were studied on vascular smooth muscle cells isolated from rat portal vein.

Two types of single‐Ca2+ channel currents with conductances of 17 pS and 8 pS were obtained in cell‐attached configuration. Bath application of NA increased the open probability of both channels during depolarizing pulses without a change of background membrane conductance. However, NA did not open Ca2+ channels when the membrane patch potential was held at −50 mV, which is about the resting potential in physiological conditions.

In the whole‐cell configuration, studies of voltage‐dependent Ca2+ channel currents showed that the peak conductance curve was not shifted to more negative potentials by NA.

Measurements of internal Ca2+‐concentration ([Ca2+]i) with Indo‐1 indicated that NA increased [Ca2+]i at a holding potential of −50 mV and evoked a Ca2+‐activated Cl− current. These effects were blocked when heparin was included in the pipette solution.

A Cl− channel blocker without effect on Ca2+ channels (anthracene‐9‐carboxylic acid) inhibited the contractions of portal vein strips induced by NA in a manner similar to that produced by a Ca2+ channel inhibitor (isradipine). The NA‐induced contraction was completely suppressed in the presence of ryanodine which depletes intracellular Ca2+ stores.

The present study suggests that activation of Cl− channels by Ca2+ release produces a membrane depolarization which is a prerequisite for enhanced opening of voltage‐dependent Ca2+ channels in response to NA in venous smooth muscle.;
Endothelium‐independent relaxation of rabbit coronary artery by 17β‐oestradiol in vitro
Authors: Jiang Canwen , Sarrel Philip M. , Lindsay David C. , Poole‐Wilson Philip A. , Collins Peter
Published: July 2012

We assessed the relaxant effect of 17β‐oestradiol (10−7, 10−6 and 10−5 m) on rabbit isolated coronary arteries precontracted with prostaglandin F2α (3 × 10−6 m), high extracellular potassium (30 mm) and Bay K 8644 (10−6 m) plus high extracellular potassium (15 mm) by measuring isometric tension. 17β‐Oestradiol (10−6 and 10−5 m) induced significant relaxation in coronary arteries from male and female rabbits. No differences were seen between arteries with or without endothelium. There were also no differences between coronary arteries isolated from male and female rabbits.

Inhibitors of endothelium‐derived relaxing factor and vasodilator prostanoids, namely, reduced haemoglobin, Nω‐nitro‐l‐arginine methyl ester and indomethacin, did not affect the relaxation induced by 17β‐oestradiol in endothelium‐intact coronary arteries.

Methylene blue, an inhibitor of guanylate cyclase, did not affect the coronary artery relaxation induced by 17β‐oestradiol.

The calcium concentration‐dependent contraction curve in potassium‐depolarization medium was shifted to the right by 17β‐oestradiol (10−6 and 10−5 m) in the rabbit coronary artery and rat aorta. The −log EC50 s of calcium in control and after incubation with 17β‐oestradiol (10−6 and 10−5 m) were 3.7 ± 0.09, 3.1 ± 0.10 and 2.8 ± 0.08 respectively in rabbit coronary arteries and 3.8 ± 0.11, 3.3 ± 0.14 and 2.9 ±0.15 in rat aorta.

The results indicate that 17β‐oestradiol induces rabbit coronary artery relaxation by an endothelium‐independent mechanism in vitro. A calcium antagonistic property may be involved in the mechanism of rabbit coronary arterial relaxation by 17β‐oestradiol.;
Dexamethasone‐induced gastric mucosal damage in the rat: possible role of platelet‐activating factor
Authors: Filep János G. , Hermán Ferenc , Földes‐Filep Éva , Schneider Ferenc , Braquet Pierre
Published: July 2012

The aim of the present experiments was to study the possible role of platelet‐activating factor (PAF) in mediating gastric mucosal damage induced by dexamethasone in the rat by measuring gastric tissue levels of PAF during dexamethasone‐treatment and by investigating the effects of specific PAF receptor antagonists on dexamethasone‐induced gastric lesions. PAF‐like bioactivity extracted from the rat glandular stomach was determined by a platelet aggregation assay.

Dexamethasone treatment (0.4– 4 mg kg−1, daily for 1– 6 days) produced time‐ and dose‐dependent damage to the glandular mucosa of the stomach as characterized by extensive, uniform hyperaemia with multiple, focal petechiae and erosions.

These changes were accompanied by a time‐, and dose‐dependent increase in PAF content of the glandular stomach. Control rat stomach contained small amounts of PAF (0.14 ± 0.04 ng per g wet weight), which increased over 40 fold in response to dexamethasone treatment (4 mg kg−1, daily for 6 consecutive days). The presence of PAF‐like material in the stomach extract was ascertained by thin‐layer chromatography, high performance liquid chromatography and by alkaline hydrolysis.

Pretreatment of the animals with one or other of the structurally unrelated PAF receptor antagonists, BN 52021 (10 mg kg−1, i.p.) or BN 50727 (1 mg kg−1, i.p.) significantly reduced dexamethasone‐induced gastric damage. In these animals neither petechiae nor erosions were observed.

These observations suggest that PAF is a likely endogenous mediator of glucocorticoid‐induced gastric mucosal damage in the rat.
α.‐Adrenoceptor modulation of the efferent function of capsaicin‐sensitive sensory neurones in guinea‐pig isolated atria
Authors: Amerini Sandra , Rubino Annalisa , Mantelli Laura , Ledda Fabrizio
Published: July 2012

Transmural nerve stimulation of guinea‐pig atria, obtained from animals pretreated with reserpine (5 mg kg−1, i.p.), in the presence of atropine 1 μm and of the β‐adrenoceptor blocker CGP 20712A 1 μm, induced a positive inotropic effect which was reduced by the calcitonin gene‐related peptide (CGRP) antagonist hCGRP‐(8–37) and abolished by pretreatment with capsaicin 1 μm.

Noradrenaline concentration‐dependently (0.01– 10 μm) reduced the increase in cardiac contractility induced by transmural nerve stimulation. The inhibitory effect of noradrenaline was antagonized by yohimbine (0.5– 1 μm), in a dose‐dependent manner. Prazosin (0.5–1 μm) antagonized the effect of noradrenaline and this effect was independent of concentration.

In the presence of yohimbine, the lower part of the inhibitory‐response curve for noradrenaline was slightly but significantly shifted by prazosin. A similar degree of antagonism was observed in the presence of 1 μm phenoxybenzamine.

The selective α.2 agonists BHT 920 and clonidine reduced, in the same concentration‐range (0.01–1 μm), the cardiac response to transmural nerve stimulation in a yohimbine‐sensitive fashion.

Phenylephrine (0.1– 100 μm) and methoxamine (1– 300 μm) also induced an inhibitory effect on transmural nerve stimulation. The effect of phenylephrine was antagonized by yohimbine (1 μm) more efficiently than by prazosin (0.5 μm).

These results are in keeping with the presence of inhibitory prejunctional α.2‐adrenoceptors on cardiac sensory nerve endings which modulate the efferent function of capsaicin‐sensitive neurones.
Synergism between the contractile effect of epidermal growth factor and that of des‐Arg9‐bradykinin or of α.‐thrombin in rabbit aortic rings
Authors: deBlois Denis , Drapeau Guy , Petitclerc Eric , Marceau François
Published: July 2012

Rabbit aortic rings were used to test the possible contractile effects of growth factors and their interaction with other stimuli. A rapid potentiation of kinin‐induced contraction by epidermal growth factor (EGF) has been previously observed in this preparation.

EGF (5–1500 ng ml−1) and the isoform BB of platelet‐derived growth factor (PDGF‐BB; 1–126 ng ml−1) exerted modest but sustained contractile effects in rabbit aortic rings.

EGF pretreatment (100 ng ml−1) potentiated the contractile responses to des‐Arg9‐bradykinin (des‐Arg9‐BK), an agonist of the B1 receptors for kinin found in this preparation, and to human α.‐thrombin but not to several other contractile stimuli. The interaction appeared also relatively selective for the growth factor, because PDGF‐BB pretreatment potentiated neither des‐Arg9‐BK nor α.‐thrombin‐induced contraction.

EGF, applied on a contraction plateau induced by des‐Arg9‐BK or α.‐thrombin, exerted a synergistic contractile effect, with a time course and a half‐maximal concentration for EGF‐induced contraction similar to the ones recorded in resting tissues (between 67 and 220 ng ml−1, depending on the series of experiments).

The direct or synergistic contractile effects of EGF were not modified by the removal of the endothelium or by treatment with indomethacin. However, the tyrosine kinase inhibitors, erbstatin or genistein, inhibited the synergistic effect of EGF with des‐Arg9‐BK. The small direct contractile effect of EGF was significantly reduced by genistein. The synergistic effect of EGF with α.‐thrombin was comparatively more resistant to the tested tyrosine kinase inhibitors.

An inhibitor of the catalytic activity of α.‐thrombin, d‐Phe‐Pro‐Arg‐CH2Cl, prevented the contractile effect of α.‐thrombin in the aortic rings. In this system, a tetradecapeptide derived from a recently cloned α.‐thrombin receptor was a contractile stimulus at and above 10 μm. Consistent with the hypothesis that this peptide could behave as an α.‐thrombin receptor agonist, its contractile effect was potentiated by EGF pretreatment. Pharmacological evidence was provided to show that the receptors for α.‐thrombin were distinct from the B1 receptors for kinins. Together, these findings suggest that a model of a cleavable receptor recently elaborated to account for α.‐thrombin effects on human platelets is valid in blood‐free vascular smooth muscle preparations such as the rabbit isolated aorta.

The synergism between EGF and kinin‐ or α.‐thrombin‐induced contractions constitutes a novel mode of myotropic action for growth factors. The synergism is probably dependent on the tyrosine kinase activity of receptors for EGF. These combinations of stimuli could occur in various types of vascular disease and account for abnormal vascular reactivity often associated with atheroma lesions or vascular wound healing.
Effects of PAF on excitatory neuro‐effector transmission in dog airways
Authors: Tashiro Kazuhiro , Xie Zhuoqiu , Ito Yushi
Published: July 2012

Effects of PAF on excitatory neuro‐effector transmission in smooth muscle cells of mucosa‐free trachea and epithelium‐intact bronchiole of the dog were investigated, by isometric tension recording, microelectrode and double sucrose‐gap methods.

PAF (10−11 − 10−7 m) dose‐dependently enhanced the amplitude of contraction evoked by repetitive field stimulations (10 stimuli at 20 Hz) in both tracheal and bronchiolar tissues. At higher concentrations PAF (> 10−8 m) increased the amplitude of contraction to a greater extent in the bronchiole than in the trachea.

In both muscle tissues, in parallel to the amplitude of contraction, PAF markedly enhanced the amplitude of excitatory junction potentials (e.j.ps) evoked by a single field stimulation in a dose‐dependent manner, with no change in the resting membrane potential or input membrane resistance of the smooth muscle cells. PAF (5 × 10−7 m) enhanced the amplitude of e.j.p. to a greater extent in the bronchiole than in the trachealis. In contrast, lyso‐PAF (10−10 − 10−7 m) showed no effect on e.j.p. amplitude in bronchiolar tissues. At a high concentration (10−7 m) lyso‐PAF slightly enhanced the e.j.p. amplitude in tracheal tissue, however the lyso‐PAF induced stimulation of e.j.p. amplitude in the trachea was small compared to that of PAF.

PAF (10−7 m) had no effect on the membrane depolarization induced by acetylcholine (ACh, 10−9 − 10−5 m) and carbachol (10−9 − 10−5 m) in tracheal smooth muscle cells.

The PAF‐antagonists CV3988 (5 × 10−7 m) or WEB2086 (5 × 10−7 m) significantly enhanced the e.j.p. amplitude themselves, PAF (5 × 10−8 m) further enhanced the e.j.p. amplitude in the presence of WEB2086 (5 × 10−7 m) but not CV3988 (5 × 10−7 m). In contrast, the new PAF‐antagonist, E 6123 (5 × 10−8 m), did not affect the e.j.p. amplitude itself, and completely inhibited the increase in e.j.p. amplitude caused by 5 × 10−8 m PAF. On the other hand, in the presence of the H1‐antagonist, mepyramine, PAF (5 × 10−8 m) further enhanced the e.j.p. amplitude.

The leukotriene synthesis inhibitor AA‐861 (10−6 m) or leukotriene antagonist ONO1078 (10−7 m) inhibited the increase in e.j.p. amplitude caused by 5 × 10−8 m PAF, respectively.

In the presence of AA‐861 (10−6 m), leukotriene B4 (LTB4, 10−8 m) or LTD4 (10−8 m) slightly, and LTC4 (10−8 m) markedly enhanced the e.j.p. amplitude. In contrast, LTE4 (10−8 m) significantly suppressed the e.j.p. amplitude.

PAF (5 × 10−8 m) attenuated the depression phenomena of e.j.ps observed during double stimulus experiments at different time intervals (5–10 s), but had no effect on the summation of e.j.ps during repetitive field stimulation at a high frequency (20 Hz) in the trachealis.

These results indicate that PAF potentiates excitatory neuro‐effector transmission mainly through stimulating the release of lipoxygenase products, mainly LTC4 in the dog airway smooth muscle tissues.
Role of the l‐arginine‐NO pathway and of cyclic GMP in electrical field‐induced noradrenaline release and vasoconstriction in the rat tail artery
Authors: Bucher Bernard , Ouedraogo Sylvin , Tschöpl Martin , Paya Dominique , Stoclet Jean‐Claude
Published: July 2012

The possible roles of the l‐arginine‐NO pathway and of guanosine 3′:5′‐cyclic monophosphate (cyclic GMP) in regulating the prejunctional release of noradrenaline and neurogenic vasoconstriction were investigated in the perfused rat tail artery.

In the presence of Nω‐nitro‐l‐arginine methyl ester (l‐NAME; 30 μm), an inhibitor of NO formation, the vasoconstrictor responses to perivascular nerve stimulation (24 pulses at 0.4 Hz, 0.3 ms, 200 mA) and to exogenous noradrenaline (1 μm) were significantly enhanced, whereas the stimulation‐evoked tritium overflow from [3H]‐noradrenaline preloaded arteries was not modified. The vasoconstriction enhancing effect of l‐NAME was prevented by l‐arginine (1 mm) but not d‐arginine (1 mm) and was abolished by removal of the endothelium.

The NO donor, 3‐morpholinosydnonimine‐N‐ethylcarbamide (SIN‐1; 0.1–30 μm), and the cyclic GMP phosphodiesterase inhibitor, zaprinast (0.1–30 μm) both induced a concentration‐dependent inhibition of the electrical field stimulation‐induced vasoconstriction, while atrial natriuretic peptide (ANP; 100 nm) produced only a slight decrease of the vasoconstrictor response. Methylene blue (3μm), a known inhibitor of soluble guanylate cyclase increased the electrical field stimulation‐induced vasoconstriction. SIN‐1 and methylene blue when administered simultaneously, antagonized each others effect. None of the compounds tested (SIN‐1, zaprinast, ANP or methylene blue) had any significant effect on the stimulation‐evoked [3H]‐noradrenaline overflow.

8‐Bromo‐cyclic GMP, a potent activator of cyclic GMP‐dependent protein kinase, markedly and concentration‐dependently (3–300 μm) increased [3H]‐noradrenaline overflow but decreased field stimulation‐induced vasoconstriction. Dibutyryl‐cyclic GMP (100 μm), a weak activator of cyclic GMP‐dependent protein kinase, affected neither the pre‐ nor the postjunctional response to electrical field stimulation.

These data show that an NO‐like substance of endothelial origin, derived from l‐arginine, attenuates vasoconstriction in the rat tail artery, whether neurally‐induced or evoked by exogenous noradrenaline. Since noradrenaline release was unaltered by compounds modifying NO production, this NO‐like compound acted through a postjunctional mechanism. The lack of prejunctional effects of both soluble and membrane‐associated guanylate cyclase activators, despite a large effect of 8‐bromo‐cyclic GMP, suggests that endogenous cyclic GMP production, if present in sympathetic nerves, may not be involved in the regulation of noradrenaline release in the rat tail artery.
BK1 and BK2 bradykinin receptors in the rat duodenum smooth muscle
Authors: Feres Teresa , Paiva Antonio C.M. , Paiva Therezinha B.
Published: July 2012

The dual action of bradykinin (relaxation and contraction) on the rat duodenum was investigated by studying its effect on adenosine 3′:5′‐cyclic monophosphate (cyclic AMP) levels in cultured duodenal smooth muscle cells, and the effects of apamin on the isolated muscle responses to agonists and antagonists of BK1 and BK2 receptors.

No change was observed in the cyclic AMP content of cultured cells incubated with up to 100 nm bradykinin.

Apamin (100–500 nm) inhibited the relaxant component and enhanced the contractile component of the responses to bradykinin and to the BK2‐specific analogue [Thi5,8,d‐Phe7]‐bradykinin.

Apamin (100–500 nm) did not affect the contractile response of stretched duodenum preparations to the BK1‐specific agonist des‐Arg9‐bradykinin.

The BK2 antagonist, [d‐Arg0Hyp3Thi5,8,d‐Phe7]‐bradykinin, at a concentration which completely inhibited the relaxant response to bradykinin and to [Thi5,8,d‐Phe7]‐bradykinin, also prevented the contraction in response to either agonist in the presence of apamin.

Our results demonstrate two populations of bradykinin receptors in rat duodenum: a BK2 subtype responsible for the biphasic response of the non‐stretched duodenum, and a BK1 subtype responsible for the contractile effect on the stretched tissue.
Central administration of 5‐HT activates 5‐HT1A receptors to cause sympathoexcitation and 5‐HT2/5‐HT1C receptors to release vasopressin in anaesthetized rats
Authors: Anderson Ian K. , Martin Graeme R. , Ramage Andrew G.
Published: July 2012

The effects of intracerebroventricular injections to the right lateral ventricle (i.c.v.) of 5‐hydroxytryptamine (5‐HT, 40 and 120 nmol kg−1), N,N‐di‐n‐propyl‐5‐carboxamidotryptamine (DP‐5‐CT; 3 nmol kg−1), 5‐carboxamidotryptamine (5‐CT; 3 nmol kg−1), 8‐hydroxy‐2‐(di‐N‐propylamino) tetralin (8‐OH‐DPAT; 3, 40 and 120 nmol kg−1) and 1‐(2,5‐di‐methoxy‐4‐iodophenyl)‐2‐aminopropane (DOI; 40 and 120 nmol kg−1) on renal sym pathetic nerve activity, blood pressure, heart rate and phrenic nerve activity were investigated in normotensive rats anaesthetized with α‐chloralose.

5‐HT caused a long lasting pressor response which was associated with an initial bradycardia and renal sympathoinhibition followed by a tachycardia and renal sympathoexcitation. Pretreatment with the 5‐HT2/5‐HT1C receptor antagonists, cinanserin (300 nmol kg−1, i.c.v.) or LY 53857 (300 nmol kg−1, i.c.v.) reversed the initial bradycardia and sympathoinhibition to tachycardia and sympathoexcitation. Combined pretreatment with LY 53857 (300 nmol kg−1, i.c.v.) and the 5‐HT1A antagonist, spiroxatrine (300 nmol kg−1, i.c.v.), blocked the effects of 5‐HT on all the above variables.

Pretreatment with the vasopressin V1‐receptor antagonist, β‐mercapto‐β,β‐cyclopentamethylenepropionyl1, O‐Me‐Tyr2, Arg8‐vasopressin [(d(CH2)5Tyr(Me)AVP, 10 μg kg−1, i.v.] did not affect the magnitude but reduced the duration of the pressor response produced by i.c.v. 5‐HT and reversed the initial bradycardia and renal sympathoinhibition to tachycardia and sympathoexcitation.

1‐(2,5‐Di‐methoxy‐4‐iodophenyl)‐2‐aminopropane (DOI) caused a pressor effect which was associated with a bradycardia and sympathoinhibition. These effects were blocked by pretreatment with BW501C67 (0.1 mg kg−1, i.v.), a peripherally acting 5‐HT2/5‐HT1C receptor antagonist. However, BW501C67 (0.1 mg kg−1, i.v.) failed to block the effects of i.c.v. 5‐HT.

DP‐5‐CT, 5‐CT and 8‐OH‐DPAT (3 nmol kg−1, i.c.v.) caused sympathoexcitation, tachycardia and a rise in blood pressure. Pretreatment with methiothepin (1 mg kg−1, i.v.) or spiroxatrine (300 nmol kg−1, i.c.v.) attenuated the response to i.c.v. DP‐5‐CT.

It is concluded that i.c.v. administration of 5‐HT activates 5‐HT1A receptors to cause sympathoexcitation and 5‐HT2 or 5‐HT1C receptors to cause the release of vasopressin.
Stereospecific antiarrhythmic effects of naloxone against myocardial ischaemia and reperfusion in the dog
Authors: Lee Andrew Ying‐Siu
Published: July 2012

The effects of both the (−)‐ and (+)‐stereoisomers of naloxone in anaesthetized dogs with arrhythmias induced by acute coronary artery occlusion followed by reperfusion were investigated.

Following coronary artery occlusion and reperfusion, all dogs in the control group developed ischaemia‐ and reperfusion‐induced cardiac arrhythmias, bradycardia and hypotension.

The opiate antagonist (−)‐naloxone prevented the arrhythmias, bradycardia and hypotension due to myocardial ischaemia and reperfusion.

The (+)‐stereoisomer of naloxone, which is inactive as an opiate antagonist, was without beneficial effects.

These results indicate a possible involvement of endogenous opioid peptides in the cardiac effects due to myocardial ischaemia and reperfusion, mediated by opiate receptors through opiate antagonism.
ATP activates P2x‐contracting and P2y‐relaxing purinoceptors in the smooth muscle of mouse vas deferens
Authors: Boland Benoit , Himpens Bernard , Vincent M. Françoise , Gillis Jean‐Marie , Casteels Rik
Published: July 2012

The mechanism for the low potency of exogenous ATP in producing contraction at the P2x‐purinoceptors in the smooth muscle of the mouse vas deferens (VD) was examined.

The measure of the breakdown of ATP in contact with the VD showed that its degradation was limited and did not account for its weak contractile effect.

Externally applied, ATP induced a small and transient contraction but a marked and prolonged increase of the cytosolic Ca2+ concentration ([Ca2+]i), which suggests an efficient binding to the P 2x‐purinoceptors. Such a calcium‐force dissociation was not observed with β,γ‐methylene ATP (β,γ‐Me‐ATP), a structural ATP analogue.

The force response of precontracted VD to ATP was biphasic, consisting of a small initial contraction followed by a sustained marked relaxation. In contrast, β,γ‐Me‐ATP elicited a pronounced contraction without ensuing relaxation.

ATP was more potent than adenosine in producing relaxation, and the relaxation was not antagonized by 8‐phenyltheophylline, suggesting the activation of P2‐purinoceptors.

For this relaxation, the rank order of potency was 2‐methyl‐thio‐ATP (2‐MeSATP) > ATP>β,γ‐Me‐ATP, which is characteristic for the P2y‐purinoceptors.

Reactive Blue 2, a P2y‐purinoceptor antagonist, was found to reduce the relaxation mediated by ATP.

These results indicate that ATP acts in VD not only on contracting but also on relaxing P2‐purinoceptors, eliciting thereby overlapping opposite effects. In VD, the classical low potency of ATP for contraction is thus not explained by its low bioavailability or its low binding, but rather by its low specificity for the contracting P2x‐purinoceptors, leading to the activation of the relaxing P2y‐purinoceptors.