bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanisms of positive inotropic effects and delayed relaxation produced by DPI 201–106 in mammalian working myocardium: effects on intracellular calcium handling
Authors: Kihara Yasuki , Gwathmey Judith K. , Grossman William , Morgan James P.
Published: July 2012

We used the bioluminescent protein aequorin, which emits light when it combines with Ca2+, to test the hypothesis that the inotropic and lusitropic actions of DPI 201–106 are due to changes in intracellular Ca2+ handling in papillary muscles from ferrets and guinea‐pigs.

DPI 201–106 increased peak isometric tension (T) in a dose‐dependent manner, with an 83% increase in T as the concentration of DPI 201–106 was increased to 1 × 10−5 m; however, peak [Ca2+]i did not increase significantly until the concentration of DPI 201–106 reached 3 × 10−6 m, suggesting a sensitization of the contractile apparatus to Ca2+.

Tetrodotoxin (1 × 10−6m), which did not reduce the tension response significantly before DPI 201–106, decreased both [Ca2+]i and T in the presence of 1 × 10−5m DPI 201–106, suggesting involvement of a sodium channel activation mechanism; however, tetrodotoxin did not completely reverse the calcium sensitization.

The shift of the [Ca2+]i versus T relationship was not observed in the presence of another sodium channel agonist, veratridine (3 × 10−7‐1 × 10−6m).

In the guinea‐pig, DPI 201–106 markedly prolonged relaxation of tension (increase of 60% in the time from peak to 50% tension regression), which was accompanied by the appearance of a second component in the aequorin light signal; effects on relaxation were less prominent in the ferret.

Tension prolongation and the second component of the [Ca2+]i transient in the guinea‐pig were exacerbated by increased [Ca2+]o and decreased by tetrodotoxin. Ryanodine (3 × 10−7 m) markedly diminished the calcium transient in controls and the initial component of the calcium transient in the presence of DPI 201–106, but had only a modest effect on the second component.

We conclude that although sodium agonism plays a role, sensitization of the contractile apparatus to Ca2+ is an important mechanism in the positive inotropic action of DPI 201–106.

The negative lusitropic action of DPI 201–106 varies between ferret and guinea‐pig, possibly reflecting differences between these two species in subcellular Ca2+ handling.
Role of endothelium in hypoxic contraction of canine basilar artery
Authors: Elliott D.A. , Ong B.Y. , Bruni J.E. , Bose D.
Published: July 2012

Reversible contraction of canine basilar artery, produced by hypoxia, persisted after mechanical and chemical removal of the endothelium. The removal of endothelium was confirmed by scanning electron microscopy as well as by the abolition or reversal of the relaxant response to acetylcholine or arginine8‐vasopressin.

Hydroquinone, believed to block selectively endothelium‐mediated relaxation, also preferentially attenuated hypoxic contractions even in the absence of endothelium but did not reduce responses to 5‐hydroxytryptamine (5‐HT) or high external potassium.

Contractions induced by red blood cell haemolysate, which occur independently of the endothelium, were also selectively attenuated by hydroquinone.

Contractions caused by hypoxia were inhibited by pretreatment with adenosine or by its application after contraction had developed.

Hypoxic contraction in canine basilar artery may result partly from a direct effect on smooth muscle as well as through the endothelium.

Hydroquinone may have an additional locus of action in smooth muscle cells besides its well known effect on the endothelium.
Effects of 5‐hydroxytryptamine on human isolated placental chorionic arteries and veins
Authors: Reviriego Jesús , Marín Jesús
Published: July 2012

Effects of 5‐hydroxytrypamine (5‐HT) on cylindrical segments of human chorionic arteries and veins were investigated. Concentrations of 5‐HT (up to 3 × 10−6 m) produced concentration‐dependent contractions; higher concentrations induced a reduction of the maximal response. These responses were antagonized by methysergide and ketanserin in a non‐competitive manner. The contractions elicited by low 5‐HT concentrations were more affected by methysergide (10−7m) than by ketanserin (10−7m). Ketanserin apparently increased the responses to high 5‐HT concentrations in veins. Arteries appeared to be more sensitive to both drugs than veins. Single concentrations of 5‐HT elicited transient contractions in both kinds of vessel.

Marked tachyphylaxis was seen in segments exposed to high concentrations of 5‐HT or in which a concentration‐response curve was determined.

Contractions induced by 5‐HT were reduced in a Ca2+‐free medium. Veins were more affected by the Ca2+ antagonists, nifedipine (10−7m), nicardipine (10−5m) and diltiazem (10−5m) than arteries.

5‐HT (10−6m) enhanced 45Ca2+ uptake in those vessels in which a concentration‐response curve had not been previously determined. In veins, this increase was reduced by the three Ca2+ antagonists.

The results indicate that 5‐HT responses in these vessels were greatly dependent on extracellular Ca2+. A type of 5‐HT1‐receptor may mediate responses to low 5‐HT concentrations, while higher concentrations may activate 5‐HT2‐receptors. 5‐HT may desensitize the latter by interconversion between a high affinity and low affinity state, as suggested by others, a change prevented in part by ketanserin.
The distribution of γ‐adrenoceptors and P2 purinoceptors in mesenteric arteries and veins of the guinea‐pig
Authors: Hirst G.D.S. , Jobling P.
Published: July 2012

Membrane potential changes and contractions were recorded from mesenteric arteries and veins of the guinea‐pig, during perivascular nerve stimulation or application of noradrenaline or adenosine triphosphate (ATP).

After α‐adrenoceptor blockade, noradrenaline activated low affinity adrenoceptors (γ‐adrenoceptors) causing depolarization and arterial contraction only in the presence of an inhibitor of catecholamine uptake.

Noradrenaline did not cause depolarization or contraction of the vein after α‐adrenoceptor blockade even after catecholamine uptake was blocked.

Adenosine triphosphate caused depolarization and contraction of both arteries and veins. These responses were abolished by α‐,β‐,methylene adenosine triphosphate (Me‐ATP).

Me‐ATP abolished rapid excitatory junction potentials (e.j.ps) caused by perivascular nerve stimulation of arteries but had no effect on arterial responses mediated by γ‐adrenoceptors.

In veins, perivascular nerve stimulation evoked slow e.j.ps which persisted in the presence of Me‐ATP but were abolished after blockade of α‐adrenoceptors.

The observations indicate that P2 purinoceptors are present on both mesenteric artery and vein whilst γ‐adrenoceptors are localized near the neuromuscular junction of the artery. However γ‐adrenoceptors do not appear to be directly involved in the generation of arterial e.j.ps.
α1‐Adrenoceptor antagonist activity of novel pyrimidine derivatives (SHI437 and IK29) in rabbit aorta and trigone of the bladder
Authors: Azuma Hiroshi , Sugimoto‐Tokushima Mineko , Tanaka Kumi , Ikenoue Yoshiaki , Ito Shigeru , Ishikawa Masayuki
Published: July 2012

In the rabbit isolated aorta and trigone of the bladder, noradrenaline, phenylephrine and clonidine elicited concentration‐dependent contractions, which may be caused through activation of postsynaptic α1‐adrenoceptors.

SHI437, IK29, prazosin and yohimbine competitively antagonized the contractile responses induced by noradrenaline in the aorta and trigone. The pA2 values of SHI437, IK29, prazosin and yohimbine were 7.35 ± 0.09, 7.47 ± 0.10, 8.55 ± 0.02 and 6.28 ± 0.05 in the aorta, and 8.07 ± 0.04, 8.30 ± 0.03, 8.22 + 0.04 and 6.46 ± 0.04 in the trigone, respectively.

SHI437, IK29, prazosin and yohimbine also possessed competitive α2‐adrenoceptor blocking properties, judging from their antagonism of the clonidine‐induced inhibitory effect on the twitch responses in the electrically stimulated vas deferens of the rat. The pA2 values of SHI437, IK29, prazosin and yohimbine were determined to be 4.76 ± 0.02, 4.74 ± 0.02, 5.06 ± 0.03 and 7.86 ± 0.04, respectively.

SHI437, IK29 and prazosin inhibited the contractile responses elicited by transmural electrical stimulation without affecting the evoked 3H‐overflow from the [3H]‐noradrenaline‐preloaded rabbit aorta. Yohimbine augmented the contractile responses and 3H‐overflow.

SHI437 and IK29 at a concentration sufficient to inhibit noradrenaline‐induced contraction failed to attenuate the contractile responses of aorta to KCl, 5‐hydroxytryptamine and prostaglandin F2α, and of the trigone to acetylcholine and histamine.

The present results suggest that SHI437 and IK29 are highly selective α1‐adrenoceptor antagonists, especially in the trigone of the bladder.
Methylene blue but not changes in cyclic GMP inhibits resting and bradykinin‐stimulated production of prostacyclin by pig aortic endothelial cells
Authors: Martin William , Drazan Kveta M. , Newby Andrew C.
Published: July 2012

Primary cultures of pig aortic endothelial cells produced 6‐keto‐prostaglandin F1α (6‐keto PGF1α), the stable breakdown product of prostacyclin, both in the resting state and in response to bradykinin. The rise in 6‐keto‐PGF1α production induced by bradykinin (1–100 nm) was concentration‐dependent.

Treating endothelial cells with the inhibitor of soluble guanylate cyclase, methylene blue (0.1–20 μm) produced an irreversible reduction in resting and bradykinin (0.1 μm)‐stimulated production of 6‐keto‐PGF1α with an IC50 of 0.5 ± 0.1 μm. Treating endothelial cells with haemoglobin (10 μm) had no effect on resting or bradykinin (0.1 μm)‐stimulated production of 6‐keto‐PGF1α.

Two stimuli that elevate the level of guanosine 3′:5′‐cyclic monophosphate (cyclic GMP) in endothelial cells, 8‐bromo cyclic GMP (30 μm) and atriopeptin II (0.1 μm), each had no effect on resting or bradykinin (0.1 μm)‐stimulated production of 6‐keto‐PGF1α. Furthermore, treating endothelial cells with either 8‐bromo cyclic GMP (30 μm) or atriopeptin II (0.1 μm) had no effect on the ability of methylene blue (20 μm) to inhibit resting or bradykinin (0.1 μm)‐stimulated production of 6‐keto‐PGF1α.

Adding arachidonic acid (1 μm) to endothelial cells led to a marked stimulation of 6‐keto‐PGF1α production. Treating cells with either methylene blue (20 μm) or the cyclo‐oxygenase inhibitor, flurbiprofen (10 μm), inhibited both resting and arachidonic acid (1 μm)‐induced production of 6‐keto‐PGF1α.

In pig aortic endothelial cells methylene blue appears to block prostacyclin production by a mechanism independent of inhibition of soluble guanylate cyclase. Care should be exercised when using methylene blue as a selective inhibitor of endothelium‐derived relaxing factor due to its additional ability to block production of the other endothelium‐derived vasodilator, prostacyclin.
Interactions between the tachykinins and calcitonin gene‐related peptide lead to the modulation of oedema formation and blood flow in rat skin
Authors: Brain S.D. , Williams T.J.
Published: July 2012

The mechanisms involved in tachykinin‐induced oedema were investigated in rat skin and interactions between the tachykinins and calcitonin gene‐related peptide (CGRP) were studied.

Intradermal injections of the tachykinins, substance P, neurokinin A and neurokinin B, stimulated local oedema formation which was in each case potentiated by co‐injection of the vasodilator CGRP. Oedema induced by substance P, in the presence and absence of CGRP, was significantly inhibited by pretreatment of rats with a combination of the histamine H1 antagonist, mepyramine, and the 5‐hydroxytryptamine antagonist, methysergide. Oedema induced by neurokinin A or B was not inhibited by this pretreatment.

Intradermally‐injected CGRP induced a long lasting increase in local blood flow, which was measured with a laser Doppler blood flow meter. The simultaneous injection of substance P, but not of the structurally‐related neurokinins, caused a loss of the prolonged vasodilator activity of CGRP.

These results show that oedema induced by substance P is partially dependent on mast cell amines and that only substance P causes a loss of the prolonged vasodilator activity of CGRP.

We suggest that the ability of substance P to prevent the persistent vasodilator activity of CGRP may be a direct consequence of substance P‐induced activation of mast cells.
Effect of changing extracellular levels of magnesium on spontaneous activity and glutamate release in the mouse neocortical slice
Authors: Smith D.A.S. , Connick J.H. , Stone T.W.
Published: July 2012

The mouse neocortical slice preparation, maintained in a two compartment, grease gap bath, exhibits spontaneous depolarizing activity (with or without rhythmic after potentials) after perfusion with magnesium‐free artificial cerebrospinal fluid.

If the magnesium concentration is decrementally lowered over an extended time period, then incrementally raised following a similar time course, the spontaneous depolarizing shift activity shows a hysteresis (with regard to both frequency and amplitude), the depolarizing shifts being more resistant to magnesium during the the incremental period.

The amino acid content of the perfusing fluid was analysed by high performance liquid chromatography (h.p.l.c.). Although a basal efflux of 6 amino acids was quantifiable, only glutamate levels increased following superfusion of the preparation with magnesium‐free, artificial cerebrospinal fluid.

Glutamate release increased to 266% of the resting release in the presence of magnesium within the first 12 min of the change into magnesium‐free artificial cerebrospinal fluid. This increase in release preceded the onset of spontaneous depolarising activity. The release of glutamate remained elevated at 182% of control up to 60 min after perfusion with magnesium‐free buffer, when depolarizing activity was well established.

A model is presented and discussed for the genesis and maintenance of the spontaneous depolarizing shifts. It is suggested that the maintenance of this spontaneous activity reflects a long term enhancement of neocortical neurone excitability which may be related to long term potentiation in the hippocampus.
Differential control and calcium‐dependence of production of endothelium‐derived relaxing factor and prostacyclin by pig aortic endothelial cells
Authors: White David G. , Martin William
Published: July 2012

Production of endothelium‐derived relaxing factor (EDRF) by primary cultures of pig aortic endothelial cells was assessed indirectly by measuring endothelial cyclic GMP content, and prostacyclin production was measured by radioimmunoassay of 6‐keto prostaglandin F1α (6‐keto PGF1α).

The resting level of cyclic GMP fell significantly following removal of extracellular calcium (1 mM EGTA present), but elevations of cyclic GMP content induced by sodium azide (10 μm) or atriopeptin II (10 nm) were similar in the absence and presence of extracellular calcium.

Haemoglobin (10 μm) reduced the resting level of cyclic GMP in the presence, but not the absence of extracellular calcium. M&B 22,948 (100 μm), superoxide dismutase (30 u ml−1), bradykinin (0.1 μm), ATP (10 μm) and ionophore A23187 (0.1 μm) each induced an increase in endothelial cyclic GMP content that was reduced in the absence of extracellular calcium.

In cascade bioassay experiments using endothelial cells on microcarrier beads and perfused in columns, continuous infusion of bradykinin (0.1 μm) induced release of EDRF, assayed on rabbit aortic rings, that was maximal after 2 min and still detectable up to about 16 min.

In the presence of extracellular calcium, the time course of bradykinin (0.1 μm)‐stimulated production of EDRF, assessed as endothelial cyclic GMP content was maximal within 1 min, declined thereafter, but was still significant after 30 min. Production of 6‐keto PGF1α, measured simultaneously, rose rapidly but was complete within 3 min.

In the absence of extracellular calcium the resting endothelial content of cyclic GMP fell, but resting production of 6‐keto PGF1α was unaffected. The rise in cyclic GMP content stimulated by bradykinin (0.1 μm) was lower than when calcium was present and was complete within 3 min, but the magnitude and time course of bradykinin (0.1 μm)‐stimulated production of 6‐keto PGF1α was unaffected.

In the presence of TMB‐8 (100 μm) resting endothelial content of cyclic GMP rose slightly, but production of 6‐keto PGF1α fell. The bradykinin (0.1 μm)‐stimulated increase in cyclic GMP content was augmented, but the stimulation of 6‐keto PGF1α production was blocked. Results from cascade bioassay experiments confirmed that TMB‐8 (100 μm) did not inhibit bradykinin‐induced production of EDRF.

The data suggest that resting production of EDRF but not prostacyclin is dependent upon the presence of extracellular calcium. Bradykinin‐stimulated production of EDRF is sustained and requires the presence of extracellular calcium, but stimulated production of prostacyclin is transient and may result from discharge of an intracellular pool of calcium.

The vascular endothelial cell appears therefore to control differentially production of EDRF and prostacyclin.
Effects of propafenone on electrical and mechanical activities of single ventricular myocytes isolated from guinea‐pig hearts
Authors: Honjo Haruo , Watanabe Toshifumi , Kamiya Kaichiro , Kodama Itsuo , Toyama Junji
Published: July 2012

The effects of propafenone on the transmembrane action potential and sarcomere shortening during twitch contraction were investigated in single ventricular myocytes isolated from guinea‐pig hearts.

Propafenone at low concentrations (3–5 × 10−7 m) slightly lengthened action potential duration (APD), but shortened it at higher concentrations. The shortening of APD was accompanied by an attenuation of sarcomere shortening during twitch contraction.

Propafenone (>10−6 m) caused a concentration‐dependent decrease in the maximum upstroke velocity () of the action potential. In the presence of propafenone (3 × 10−6 m), trains of stimuli led to an exponential decline in A time constant for the recovery of from the use‐dependent block was 4.8 s.

In myocytes treated with propafenone (3 × 10−6 m), the of test action potentials preceded by the conditioning clamp pulses to 0mV was progressively decreased by increasing the duration of single clamp pulse or by increasing the number of multiple brief clamp pulses.

These findings suggest that propafenone has use‐dependent inhibitory action on the sodium channel by binding to the channel during both activated and inactivated states, and that the unbinding rate is comparable to that of Class‐I antiarrhythmic drugs with intermediate kinetics. Propafenone may also have an inhibitory action on calcium and potassium channels.
GR32191, a highly potent and specific thromboxane A2 receptor blocking drug on platelets and vascular and airways smooth muscle in vitro
Authors: Lumley P. , White B.P. , Humphrey P.P.A.
Published: July 2012

The thromboxane A2 (TP)‐receptor blocking activity and specificity of action of GR32191 ([1R‐[1α(Z),2β,3β,5α]]‐(+)−7‐[5‐([1,1′‐biphenyl]‐4‐ylmethoxy)−3‐hydroxy‐2‐(1‐piperidinyl)cyclopentyl]‐4‐heptonoic acid has been evaluated in human platelets and various smooth muscle preparations, both vascular and non‐vascular, from a range of species including man.

Utilising a platelet counting method to assess aggregation the drug was found to antagonise, in a surmountable manner, human platelet aggregation produced by the TP‐receptor agonists, U‐46619, EP171 and SQ26655, in whole blood and physiological buffer, with pA2 values of approximately 8.3 and 8.7 in the two media respectively. In the presence of GR32191 the rate of aggregation induced by U‐46619 was slowed.

The effect of GR32191 upon U‐46619‐induced platelet shape change and aggregation in plateletrich plasma was evaluated utilising a turbidometric technique. Both shape change and aggregation were antagonised by GR32191. At relatively high concentrations of the drug a slowing of aggregation and shape change to U‐44619 was seen and an unsurmountable antagonism became apparent.

The action of GR32191 upon human platelets was specific with platelet aggregation induced by adenosine 5′‐diphosphate, platelet activating factor, vasopressin and adrenaline and the inhibitory effects of prostacylin (PGI2), prostaglandin D2 (PGD2) and N‐ethylcarboxamide‐adenosine (NECA) being unaffected by concentrations of the drug as high as 10 μm. Furthermore, at concentrations of up to 100 μm, the drug itself produced no shape change or aggregation, of human platelets.

GR32191 also specifically and potently antagonised in a competitive, surmountable manner the contractile actions of U‐46619 upon human vascular smooth muscle and antagonised U‐46619‐induced contractions of vascular and airways smooth muscle preparations from rat, dog, guinea‐pig and rabbit with varying potency. This is discussed in terms of possible heterogeneity of TP‐receptors.

GR32191 therefore represents a highly potent and specific TP‐receptor blocking drug. This profile of action, coupled to its long duration of effect in man described elsewhere, make it an ideal drug tool for elucidating the physiological and pathophysiological role of thromboxane A2.
Investigation of the central sites at which morphine acts to cause hypertension in conscious rabbits
Authors: May C.N. , Whitehead C.J. , Dashwood M.R. , Mathias C.J.
Published: July 2012

In conscious rabbits intracerebroventricular (i.c.v.) morphine (10 and 50 μg kg−1) caused a dose‐related increase in plasma noradrenaline and adrenaline, respiratory depression and sedation. The increase in sympatho‐adrenal outflow resulted in hypertension accompanied by bradycardia and the increase in adrenaline secretion caused hyperglycaemia. Morphine (1 μg kg−1 i.c.v.) and i.c.v. saline had no effect.

The same doses of morphine given intracisternally (i.c.) caused bradycardia and a similar degree of respiratory depression to i.c.v. morphine, but no significant increase in blood pressure and only a small, gradual rise in plasma adrenaline.

Intravenous naloxone (1 mg kg−1) did not block the hypertension, hyperglycaemia or increase in plasma catecholamines that followed i.c.v. morphine, but prevented the respiratory depression and sedation.

Ganglionic blockade with pentolinium prevented the rise in plasma catecholamines, blood pressure and plasma glucose induced by i.c.v. morphine.

These findings demonstrate that the increased sympathoadrenal outflow following i.c.v. morphine results from an action on periventricular structures. The resultant increase in plasma catecholamines, which is largely naloxone resistant, accounts for the hypertension and hyperglycaemia. The bradycardia is probably partly baroflex mediated and partly due to an increase in vagal tone as a result of stimulation of brainstem opioid receptors. The respiratory depression is probably due to an action of morphine on brainstem opioid receptors.
Effects of adenosine on polymorphonuclear leucocyte function, cyclic 3′:5′‐adenosine monophosphate, and intracellular calcium
Authors: Nielson Christopher P. , Vestal Robert E.
Published: July 2012

Inhibition of human polymorphonuclear leucocyte (PMN) function by adenosine was studied with respect to effects of adenosine on intracellular cyclic AMP and calcium during the PMN respiratory burst.

The adenosine analogue 5′‐N‐ethylcarboxamide‐adenosine (NECA) and L‐N6‐phenyl‐isopropyladenosine (L‐PIA) inhibited PMN oxygen metabolite generation with relative potencies (NECA > adenosine > L‐PIA) characteristic of an A2 receptor.

The respiratory burst was inhibited by adenosine when PMN were activated by calcium ionophore or chemotactic peptide but not when cells where activated by oleoyl‐acetyl‐glycerol (OAG).

Adenosine increased intracellular cyclic AMP during the PMN respiratory burst regardless of whether cells were stimulated by ionophore, chemotactic peptide or OAG.

To determine whether the differences in cell inhibition by adenosine were related to differences in intracellular calcium mobilization by each activating agent, calcium was evaluated with the fluorescent probe, indo‐1. Adenosine suppressed the increase in intracellular calcium following PMN activation by calcium ionophore or chemotactic peptide. In contrast, calcium did not increase in PMN activated by OAG and adenosine did not affect intracellular calcium changes following this stimulus.

These results demonstrate that physiological concentrations of adenosine inhibit the PMN respiratory burst in association with an increase in intracellular cyclic AMP and reduction of intracellular calcium.
The ability of denbufylline to inhibit cyclic nucleotide phosphodiesterase and its affinity for adenosine receptors and the adenosine re‐uptake site
Authors: Nicholson C.D. , Jackman S.A. , Wilke R.
Published: July 2012

Denbufylline has been examined for its ability to inhibit cyclic nucleotide phosphodiesterase isoenzymes from rat cardiac ventricle and cerebrum, as well as for its affinity for adenosine A1 and A2 receptors and the re‐uptake site. For comparison, SK&F 94120, theophylline and 3‐isobutyl‐1‐methyl‐xanthine (IBMX) were examined as phosphodiesterase inhibitors whilst N6‐cyclohexyladenosine, R(−)‐N6‐(2‐phenylisopropyl)‐adenosine, 5′‐N‐ethylcarboxamido‐adenosine, 2‐nitrobenzylthioinosine, theophylline and IBMX were examined for their affinity for adenosine binding sites.

This investigation confirmed the presence of four phosphodiesterase activities in rat cardiac ventricle; in rat cerebrum only three were present.

Denbufylline selectively inhibited one form of Ca2+‐independent, low Km cyclic AMP phosphodiesterase. The form inhibited was one of two present in cardiac ventricle and the sole one in cerebrum. This form was not inhibited by cyclic GMP. The inotropic agent SK&F 94120 selectively inhibited the form of cyclic AMP phosphodiesterase which was inhibited by cyclic GMP present in cardiac ventricle. Theophylline and IBMX were relatively non‐selective phosphodiesterase inhibitors.

Denbufylline was a less potent inhibitor of ligand binding to adenosine receptors than of cyclic AMP phosphodiesterase. This contrasted with theophylline, which had a higher affinity for adenosine receptors, and IBMX which showed no marked selectivity. Denbufylline, theophylline and IBMX all had a low affinity for the adenosine re‐uptake site.

Denbufylline is being developed as an agent for the therapy of multi‐infarct dementia. The selective inhibition of a particular low Km cyclic AMP phosphodiesterase may account for the activity of this compound.
Phentolamine and structurally related compounds selectively antagonize the vascular actions of the K+ channel opener, cromakalim
Authors: McPherson Grant A. , Angus James A.
Published: July 2012

The effects of cromakalim, a novel vasodilator agent believed to open K+ channels, were studied in a range of large and small arteries in vitro. In dog isolated coronary artery, precontracted with U46619 (a thromboxane A2‐mimetic), cromakalim caused concentration‐dependent relaxation which could be inhibited by phentolamine (10–100 μm).

The ability of phentolamine to antagonize cromakalim was selective since it did not affect responses to a number of other vasodilators including isoprenaline, nitroprusside or nicorandil.

The effect of phentolamine was not related to its α‐adrenoceptor blocking actions since other α‐adrenoceptor antagonists (prazosin 10 μm, rauwolscine 10 μm and phenoxybenzamine 1 μm) failed to influence the action of cromakalim.

A number of compounds structurally related to phentolamine were also able to block the vasorelaxant response to cromakalim in the dog isolated coronary artery. The rank order of potency was alinidine = phentolamine = ST91 > tramazoline = naphazoline. Clonidine and tolazoline were inactive. The most potent compounds (alinidine and phentolamine) were effective only at concentrations above 1 μm.

Electrophysiological studies, in which resting membrane potential and tension were measured simultaneously, were carried out on rat isolated femoral artery. Phentolamine (30 μm) antagonized both the vasorelaxation and hyperpolarization caused by cromakalim.

These results suggest that phentolamine and some structurally related compounds, may inhibit K+ channel opening, an action which would account for their ability to antagonize the actions of cromakalim. Such compounds may prove useful in determining the role of K+ channels in regulating vascular smooth muscle tone in vivo and in vitro.
The dihydropyridine niguldipine modulates calcium and potassium currents in vascular smooth muscle cells
Authors: Klöckner U. , Isenberg G.
Published: July 2012

Vascular smooth muscle cells were isolated from the portal vein and from pial vessels of the cow. They were voltage‐clamped with a single patch electrode technique (whole cell recording) in order to analyse the effects of niguldipine on ionic membrane currents. Due to adsorption of niguldipine to plastic and glass, the effective concentrations are lower than the nominal concentrations by a factor of about 3.

Niguldipine reduced Ca‐currents (ICa of the L‐type, voltage operated) at nominal concentrations > 0.1 μm up to a complete block at 1 μm (50% block at 0.4 μm). Nominal concentrations between 50 and 200 nm facilitated ICa (‘Ca‐agonistic effect’). The Ca‐agonistic effects of niguldipine showed modest use‐ but strong voltage‐dependence.

Niguldipine increased the outward currents at nominal concentrations >10nM. The extra outward currents reversed at −85 mV, the result suggesting that niguldipine had increased potassium currents, IK. Maximal facilitation of IK by niguldipine was about 400% and was obtained at 1 μm, half‐maximal facilitation was obtained with a nominal concentration of 20 nm.

Both reduction of ICa and facilitation of IK may contribute to vasodilatation by niguldipine. Due to its greater sensitivity, the effects on IK may dominate.
Streptozotocin‐induced diabetes reduces the density of [125I]‐endothelin‐binding sites in rat cardiac membranes
Authors: Nayler Winifred G. , Liu Jianjun , Panagiotopoulos Sianna , Casley David J.
Published: July 2012

The effect of acute, streptozotocin‐induced diabetes on the affinity (KD), density (Bmax) and selectivity of specific, high affinity binding sites for [125I]‐endothelin ([125I]‐ET) in rat cardiac membrane fragments was determined. Three days after a single i.v. bolus dose of streptozotocin (60 mg kg−1), the density of [125I]‐ET binding sites was reduced (P < 0.01) without changes in affinity or selectivity.
Effects of α‐ and β‐calcitonin gene‐related peptides upon ion transport in rat descending colon
Authors: Cox H.M. , Ferrar J.A. , Cuthbert A.W.
Published: July 2012

Both α‐ and β‐calcitonin gene‐related peptide (CGRP) exhibit concentration‐dependent dual actions upon rat colonic epithelia. At low concentrations (i.e. 0.03–10 nm) both CGRPs produce antisecretory effects that are abolished by pretreating tissues with tetrodotoxin (TTX). At higher concentrations (30–200 nm) secretory responses predominate and these effects are not abolished by TTX. It is suggested that the mediator of the antisecretory actions of CGRPs is somatostatin.
Classification of tachykinin receptors in muscularis mucosae of opossum oesophagus
Authors: Daniel E.E. , Cipris S. , Manaka Y. , Bowker P. , Regoli D.
Published: July 2012

Muscularis mucosae of the distal oesophagus of the opossum contracts in response to substance P and to a variety of tachykinins. To delineate the nature of the receptors present in this tissue, we evaluated contractile responses to substance P, neurokinin A, neurokinin B, eledoisin and analogues believed to be highly selective for NK‐1, NK‐2 and NK‐3 receptors. In addition, the effects of prolonged exposure to each of these agents (10−6 m or 10−5m) on contractile responses to substance P and to itself were evaluated. Similarly effects of prolonged exposure to the various tachykinins and their analogues on the field‐stimulated responses of this muscle were studied.

All naturally occurring tachykinins were full agonists and differed in potency (comparing ED50 values) by less than ten fold. In nearly all cases there was cross tachyphylaxis between substance P and the other tachykinins and each reduced tonic responses to field stimulation, a response previously shown to be mediated by a substance P like agent. Eledoisin failed to cause tachyphylaxis under the conditions of these experiments.

When highly selective tachykinin analogues were used, only that believed to activate NK‐1 receptors was a full agonist. [β‐Ala4,Sar9,MetO211]SP(4–11) was also only slightly less potent than substance P. In contrast, an agonist selective for NK‐2 (NK‐A) receptors, [Nle10]NKA(4–10), and one selective for NK‐3 (NK‐B) receptors, [β‐Asp4,MePhe7]NKB(4–10) were unable to produce a response equal to 50% of the maximum even at 10−5m. However, all three selective tachykinin analogues reduced responses to substance P but not to carbachol. They usually reduced both phasic and tonic responses to field stimulation.

We conclude, based on this and earlier study, that the tachykinin receptors of opossum oesophagus muscularis mucosae recognize all naturally occurring tachykinins but may represent only NK‐1 receptors. The ability of analogues selective for other types of tachykinin receptors to reduce responses to substance P raises the possibility that their selectivity depends in part on diminished efficacy rather than totally on diminished affinity at some classes of receptor.
Effects of capsaicin pretreatment on neuropeptides and salivary secretion of rat parotid glands
Authors: Ekström Jörgen , Ekman Rolf , Håkanson Rolf , Luts Anders , Sundler Frank , Tobin Gunnar
Published: July 2012

‘Atropine‐resistant’ secretion of saliva in response to parasympathetic stimulation may reflect antidromic activation of sensory nerve fibres. In this investigation, the effect of pretreatment in the rat with capsaicin (total dose of 125 mg kg−1, s.c.), was determined.

In the parotid glands substance P (SP)/calcitonin gene‐related peptide (CGRP)‐containing nerve fibres around ducts and blood vessels disappeared after capsaicin, while periacinar SP‐containing fibres (devoid of CGRP) and CGRP‐containing fibres (devoid of SP) remained. Vasoactive intestinal peptide (VIP)‐containing nerve fibres seemed to be unaffected. The parotid content of SP and CGRP was reduced by 11 and 36% respectively, while that of VIP remained unchanged.

The weights of the parotid glands and their sensitivity to the secretagogues methacholine and SP, injected intravenously, were unchanged as was the response to stimulation of the auriculo‐temporal nerve in the presence and absence of atropine.

In contrast to capsaicin pretreatment, parasympathetic denervation of the parotid gland reduced the weight of the gland and produced an increase in the response to methacholine and SP.

For comparison, the effectiveness of the capsaicin treatment on neuropeptide content was determined in the urinary bladder. The bladder of capsaicin‐pretreated rats increased in weight (21%) and in VIP content (31%), while the content of SP and CGRP was reduced by 86 and 94%, respectively. SP‐ and CGRP‐containing nerve fibres were virtually eliminated, while VIP‐containing nerve fibres seemed unaffected.

In conclusion, antidromic activation of primary afferent (capsaicin‐sensitive) C‐fibres does not contribute significantly to the ‘atropine‐resistant’ secretory response of the parotid gland to stimulation of the parasympathetic nerve.
Dual effects of diazoxide on ATP‐K+ currents recorded from an insulin‐secreting cell line
Authors: Kozlowski R.Z. , Hales C.N. , Ashford M.L.J.
Published: July 2012

The effects of diazoxide on ATP‐K+ channel currents, recorded from the insulin‐secreting cell line, CRI‐G1, were studied using patch‐clamp techniques.

Under current‐clamp recording conditions diazoxide (0.6 mm), inhibited action potential activity and hyperpolarized CRI‐G1 cells with a concomitant increase in membrane conductance. Recordings from voltage‐clamped whole‐cells and isolated patches indicate that activation of ATP‐K+ channel currents underlie these effects.

Diazoxide elicited an activation of ATP‐K+ channels which had been partially inhibited by ATP, on application to either surface of the plasma membrane, although it was more effective when applied directly to the cytoplasmic side. Activation of the ATP‐K+ currents involves an increase in the single channel open‐state probability and an apparent increase in the number of functional channels.

Activation was observed only when Mg‐ATP was present in the cytoplasmic bathing solution. There was no activation of currents by diazoxide when ATP, in the absence of Mg2+ ions, or Mg‐AMP‐PNP was present to inhibit the ATP‐K+ channels.

In the absence of ATP and Mg2+ ions in the cytoplasmic bathing solution, diazoxide (0.6 mm) produced an inhibition of ATP‐K+ currents.

Cromakalim (BRL 34915) at 10 μm and 100 μm had no significant effects on ATP‐K+ currents.

It is concluded that diazoxide‐induced activation of ATP‐K+ channel currents probably involves phosphorylation of the channel or some closely associated membrane protein.
Superoxide anions enhance platelet adhesion and aggregation
Authors: Salvemini Daniela , de Nucci Gilberto , Sneddon John M. , Vane John R.
Published: July 2012

Superoxide dismutase (SOD, 60 u ml−1) or ferricytochrome c (70 μm) significantly inhibited thrombin‐stimulated platelet adhesion to gelatin‐coated plastic, whereas catalase (1000 u ml−1) or mannitol (1 mm) had no effect.

The platelet aggregation induced by low concentrations of thrombin (causing less than 45% maximal change in light transmission) was inhibited by SOD. Catalase or mannitol had no effect on platelet aggregation.

Pyrogallol (an O2− generator) enhanced both platelet adhesion to gelatin‐coated plastic and platelet aggregation induced by thrombin; this enhancement was neutralized by SOD.

These results indicate that O2− increase both platelet adhesion and aggregation, whereas other free radicals such as hydrogen peroxide or hydroxyl radicals are not involved.
Angiotensin neuromodulation of adrenergic and purinergic co‐transmission in the guinea‐pig vas deferens
Authors: Ellis James L. , Burnstock Geoffrey
Published: July 2012

The effects of angiotensin II (AII) and angiotensin III (AIII) on the isolated vas deferens of the guinea‐pig were studied via three parameters: the overflow of adenosine 5′‐triphosphate (ATP) and tritiated noradrenaline (NA), the mechanical response to field stimulation and the mechanical response to exogenous NA and α,β‐methylene ATP (α,β‐mATP).

At 2Hz, All enhanced the overflow of ATP and NA, whereas at 20 Hz, All enhanced the overflow of NA but was without significant effect on ATP overflow. AIII, at 2 Hz, inhibited the overflow of ATP, but enhanced NA overflow, whereas at 20 Hz ATP overflow was unaffected, but NA overflow was still enhanced.

At 2 Hz, AII enhanced both phases of the response to field stimulation and at 20 Hz the overall response. AIII at 2 Hz enhanced the adrenergic response, but was without effect on the purinergic response to field stimulation. At 20 Hz, AIII was without effect on the overall response.

AII enhanced responses to exogenous NA and α,β‐mATP, whereas AIII was without effect.

These results provide evidence that both ATP and NA release are capable of being modulated by angiotensins. Furthermor, modulation of ATP release is frequency‐dependent, whereas [3H]‐NA release is not. These results raise questions about the mechanisms of storage and release of the sympathetic co‐transmitters NA and ATP; they also show that angiotensin receptors in the guinea‐pig vas deferens are not a homogeneous population.
Pronounced cholinergic but only moderate purinergic effects in isolated atrial and ventricular heart muscle from cats
Authors: Kemmer Michael , Jakob Helga , Nawrath Hermann
Published: July 2012

The effects of cholinergic and purinergic stimulation on action potential, force of contraction and 86Rb efflux were investigated in cat atrial and/or ventricular heart muscle.

Acetylcholine and carbachol exerted a concentration‐dependent negative inotropic effect in cat atrial heart muscle. Carbachol 10 μmol l−1 completely abolished the force of contraction and increased the rate constant of 86Rb efflux 2–3 fold, whereas the action potential duration was shortened to about 1/10 of its length under control conditions.

The effects of acetylcholine and carbachol in cat atrial heart muscle were mimicked, qualitatively, by adenosine and its analogues 5′‐(N‐ethyl)‐carboxamido‐adenosine (NECA) and (−)‐N6‐(R‐phenyl‐isopropyl)‐adenosine (R‐PIA). Maximal purinergic effects, however, amounted to about 15–50% in comparison to those of cholinergic stimulation.

In cat ventricular heart muscle, cholinergic or purinergic stimulation had no significant effects on the force of contraction in the absence of a cyclic AMP‐dependent positive inotropic effect. Carbachol antagonized the positive inotropic effect elicited by either 3‐isobutyl‐1‐methylxanthine, isoprenaline or cyclic 8‐(4‐chlorphenylthio)adenosine‐3′:5′‐monophosphate; NECA and R‐PIA were less effective. The inhibition by carbachol of the effects of isoprenaline was not related to a change in the rate constant of 86Rb efflux.

It is concluded that the effects of cholinoceptor and purinoceptor agonists in the cat heart involve a change in the potassium conductance in the atrium, whereas the effects in the ventricle may be related to changes of intracellular cyclic AMP levels. It seems reasonable to assume that, in comparison to cholinergic stimulation, a low density of purinoceptors in the cat heart is responsible for the relatively weak effects of adenosine agonists in this species.
The effects of alterations in electrogenic Na+/K+‐pumping in guinea‐pig isolated trachealis: their modulation by the epithelium
Authors: Raeburn David , Fedan Jeffrey S.
Published: July 2012

An examination was made of the effect of epithelium removal on mechanical responses of guinea‐pig isolated tracheal strips after inhibition or activation of electrogenic Na+/K+‐pumping.

The Na+/K+‐pump inhibitor ouabain (0.1–10 μm) evoked concentration‐dependent contractions which were potentiated by epithelium removal.

K+‐free solution, which inhibits Na+/K+‐pumping, produced a slow, sustained relaxation in intact preparations. In epithelium‐free preparations the relaxation was transient and of lesser magnitude.

The addition of K+ (10 or 30 mm), which activates Na+/K+‐pumping, to preparations bathed in K+‐free solution caused a relaxation of preparations under spontaneous tone or contracted with methacholine; the magnitude and duration of relaxation was greater in the epithelium‐free preparations. Ouabain (0.1 μm) attenuated the relaxation to K+ in intact preparations and converted the response of epithelium‐free preparations to a contraction. In the presence of a higher concentration of ouabain (1 μm), intact preparations contracted in response to K+.

In normal K+ solution, ouabain (0.1 μm) increased the sensitivity of intact preparations to methacholine but reduced their sensitivity to K+. Ouabain was without these effects in epithelium‐free preparations.

Thus, responses of intact preparations to perturbations which affect electrogenic Na+/K+‐pumping in trachealis are influenced by an epithelium‐derived factor. The production of the factor may be linked to an epithelial Na+/K+‐pump, or the factor may modulate the activity of an electrogenic Na+/K+‐pump in the muscle.
Endothelin‐induced contractions of tracheal smooth muscle and identification of specific endothelin binding sites in the trachea of the rat
Authors: Turner N.C. , Power R.F. , Polak J.M. , Bloom S.R. , Dollery C.T.
Published: July 2012

The presence of specific binding sites and the contractile activity of the novel peptide, endothelin have been investigated in rat trachea.

Endothelin (10−8–10−5m) induced long‐lasting contraction of rat tracheal rings superfused with Krebs solution (EC50 5.4 × 10−6m). Contractions of the tissue to 10−6m endothelin were attenuated in Ca2+‐free medium containing 0.1 mM EGTA but unaffected by nicardipine (10−7m).

After equilibration in Ca2+‐free medium (without EGTA) a return to normal Ca2+ concentrations (2.5 mm), 30 min or 60 min following endothelin (10−6m), produced a sustained contraction of the tissue.

Specific binding sites for endothelin were identified on rat tracheal smooth muscle (KD 1.34 × 10−10m, maximal binding 1.2 fmol mm−2). Specific binding sites were also identified on nerve trunks. Endothelin binding was unaffected by co‐incubation with nicardipine (10−7m) or verapamil (10−7m).

The discrepancy between the apparent KD for endothelin binding and the EC50 for endothelin‐induced contraction suggests that the endothelin binding sites identified in this study may not be associated with the receptors mediating contraction.

These results indicate that endothelin binding sites are present on tracheal smooth muscle. The mechanism of endothelin‐induced contraction, whilst being dependent on extracellular calcium, does not appear to involve binding to the dihydropyridine‐ or verapamil‐sensitive sites on the voltage‐dependent Ca2+ channel. Its long duration of action may be associated with a sustained increase in Ca2+ permeability.
Possible therapeutic effect of naftidrofuryl oxalate on brain energy metabolism after microsphere‐induced cerebral embolism
Authors: Miyake Keiko , Tanonaka Kouichi , Minematsu Reiko , Inoue Kiyoshi , Takeo Satoshi
Published: July 2012

The present study was designed to determine whether naftidrofuryl oxalate exerts a possible therapeutic effect on brain energy metabolism impaired by microsphere‐induced cerebral embolism in vitro.

Injection of microspheres into the right carotid canal resulted in a decrease in tissue high‐energy phosphates both in the right and left hemispheres, and an increase in tissue lactate in the right hemisphere, on the 3rd and the 5th day after the embolism. The embolism also induced a marked reduction in mitochondrial oxidative phosphorylation ability and succinate dehydrogenase activity. The results suggest that severe ischaemia was induced in the brain by the microsphere administration.

Treatment of microsphere‐injected rats with naftidrofuryl oxalate (15 mg kg−1) for 3 or 5 days elicited a significant recovery of tissue high‐energy phosphate and lactate levels. The recovery was associated with a significant restoration of mitochondrial succinate dehydrogenase activity on the both days and of mitochondrial oxidative phosphorylation rate on the 5th day.

The results suggest that naftidrofuryl oxalate is beneficial in the recovery of cerebral energy metabolism impaired by microsphere‐induced cerebral ischaemia, presumably through a mechanism involving its direct effect on the cerebral mitochondrial enzyme activities.