bluuebunny/crossref_metadata_2025 huggingface dataset:
The action of amlodipine on voltage‐operated calcium channels in vascular smooth muscle
Authors: Hughes A.D. , Wijetunge S.
Published: July 2012

Amlodipine, a dihydropyridine derivative largely ionized at physiological pH, inhibited calcium channel currents in single vascular smooth muscle cells isolated from rabbit ear artery in a concentration‐dependent manner.

Amlodipine inhibited the current‐voltage relationship for calcium channel currents across the range of test potentials used. However, the effect of amlodipine was more marked on more depolarized test potentials. Amlodipine also shifted the steady‐state inactivation curve for calcium channel currents in a hyperpolarized direction.

The potency of amlodipine as determined from the steady‐state inhibition of calcium channel current induced by the drug was dependent on the holding potential of the cells. Use of a more depolarized holding potential increased the potency of amlodipine.

Onset of amlodipine‐induced inhibition was relatively rapid at both −60 mV and −40 mV holding potential. The use of a more depolarized holding potential increased the rate of association of amlodipine. No recovery from amlodipine‐induced inhibition was seen over a 20 min period following washout of the drug.

In addition to voltage‐dependence, the action of amlodipine showed use‐dependence, in that the effect of amlodipine was more marked when calcium channel currents were evoked frequently. Increasing the frequency of activation of calcium channel currents did not alter the apparent onset rate of amlodipine‐induced inhibition, but increased the degree of inhibition achieved by the drug.

The electrophysiological properties of amlodipine, particularly its voltage‐dependence are probably important determinants of its action in vivo.
Role of angiotensin AT1 and AT2 receptors in mediating the renal effects of angiotensin II in the anaesthetized dog
Authors: Clark Kenneth L. , Robertson Mark J. , Drew G. Michael
Published: July 2012

Experiments were performed using the selective AT1 receptor antagonist, GR117289, and the selective AT2 receptor antagonist, PD123177, to assess the relative importance of AT1 versus AT2 receptors in mediating the renal effects of angiotensin II (AII) in vivo, in salt‐replete pentobarbitone‐anaesthetized dogs.

The AT1 receptor antagonist, GR117289 (0.5 mg kg−1 + 1 μg kg−1 min−1, i.v.), caused renal vasodilatation, characterized by a mean increase of 21 ± 5% in renal blood flow, 45 min post‐dose. GR117289 also caused a fall in mean blood pressure (12 ± 4%), but despite this, sodium and urine excretion were not reduced. Indeed, there was a tendency for urine output and sodium excretion to increase, although the changes were not statistically significant. GR117289 caused a reduction in plasma aldosterone levels (−35 ± 16%) 45 min post‐dose, despite increasing plasma renin activity (+ 173 ± 42%). In contrast to GR117289, the AT2 receptor antagonist, PD123177 (20 μg kg−1 min−1 intra‐renal artery; i.r.a.) caused no significant change in blood pressure, renal blood flow, or sodium and urine excretion, indicating that the renal effects of endogenous AII in these salt‐replete animals are mediated predominantly by AT1 receptors.

Intra‐renal artery infusion of AII (1–300 ng kg−1 min−1) caused dose‐related renal vasoconstriction, and decreases in urine output, sodium excretion, fractional excretion of sodium, and glomerular filtration rate (GFR). The AT1 receptor antagonist, GR117289 (0.5 mg kg−1 + 1 μg kg−1 min−1, i.v.) antagonized these renal effects of AII, causing 15–38 fold rightward displacements of mean dose‐response curves for these parameters. In contrast, PD123177 (20 μg kg−1 min−1, i.r.a.) failed to antagonize the renal haemodynamic and excretory effects of lower doses of AII (1–10 ng kg−1 min−1, i.r.a.). However, at higher doses of AII (30–300 ng kg−1 min−1, i.r.a.), while PD123177 still failed to antagonize the effects of the peptide on urine output, sodium excretion and GFR, it did cause a small, but significant, degree of inhibition of AII‐induced renal vasoconstriction. In addition, at a higher dose (50 μg kg−1 min−1, i.r.a.), PD123177 caused a greater degree of antagonism of AII‐induced renal vasoconstriction, while renal excretory responses to AII remained unaffected.

This study shows that the renal haemodynamic and excretory effects of AII in salt‐replete anaesthetized dogs are mainly mediated by angiotensin AT1 receptors. However, the inhibitory effect of PD123177 on renal vasoconstrictor responses to high doses of AII, raises the possibility that functionally important AT2 receptors are present in the canine renal vasculature.
A comparison of rat brain amino acid and monoamine content in diazepam withdrawal and after exposure to a phobic stimulus
Authors: Andrews Nick , Barnes Nicholas M. , Steward Luanda J. , West Katie E. , Cunningham Jo , Wu Pei‐Ying , Zangrossi Helio , File Sandra E.
Published: July 2012

The content of amino acids (taurine, glycine, glutamic acid, γ‐aminobutyric acid (GABA) and aspartic acid) and monoamines (5‐hydroxytryptamine (5‐HT), 5‐hydroxyindoleacetic acid (5‐HIAA) and noradrenaline) in homogenates of rat cortical and hippocampal tissue were measured by high performance liquid chromatography (h.p.l.c.) with fluorescent and electrochemical detection respectively, after two anxiogenic treatments: exposure to a phobic stimulus (cat odour) and withdrawal from chronic diazepam treatment.

In neither of the two anxiogenic situations was there a significant change in any amino acid content, in either brain area.

In the group withdrawn from chronic diazepam, cortical 5‐HT and 5‐HIAA levels and hippocampal 5‐HT levels were significantly increased. Noradrenaline content was significantly decreased in the hippocampus.

The changes in 5‐HT and 5‐HIAA levels following cat odour exposure were area‐specific in that they decreased in the hippocampus, but increased in the cortex.

Following cat odour exposure, noradrenaline levels appeared not to change in either area studied. However during exposure to cat odour, it was found that half the animals avoided the odour source and half were indifferent. The animals showing marked avoidance had significantly higher cortical noradenaline content and this was significantly different from control, whereas hippocampal noradrenaline levels were not dependent upon the differences in avoidance of the odour source.

The results show clearly different neurochemical changes in the rat following exposure to a phobic stimulus and withdrawal from diazepam. It is hoped comparative studies such as this will enable better understanding of anxiety states in the rat which could parallel the different classes of anxiety recognised in the clinic
Support of renal blood flow after ischaemic‐reperfusion injury by endogenous formation of nitric oxide and of cyclo‐oxygenase vasodilator metabolites
Authors: Cristol J.P. , Thiemermann C. , Mitchell J.A. , Walder C. , Vane J.R.
Published: July 2012

Ischaemia‐reperfusion injury in the kidney is associated with a loss of autoregulation, an increase in renal vascular resistance (RVR), a decrease of renal blood flow (RBF) and ultimately acute renal failure. The aim of this study was to investigate the role of the release of endogenous nitric oxide (NO) in the recovery of RBF after ischaemic injury of the renal vascular bed.

Anaesthetized rats (thiopentone sodium; 120 mg kg−1, i.p.) were submitted to acute renal ischaemia followed by 2 or 6 h of reperfusion (I/R). Reperfusion was associated with a significant reduction in RBF, an increase in RVR, and an impairment of the vasodilator effect of acetylcholine (ACh).

NG‐nitro‐l‐arginine methyl ester (l‐NAME, 30 μg kg−1 min−1, i.v., n = 5) significantly prevented the recovery of RBF after I/R injury. Similarly, inhibition of prostanoid formation with indomethacin (5 mg kg−1, i.v., n = 4) significantly enhanced the rise in RVR associated with I/R injury.

Infusion of l‐arginine (l‐Arg; 1 or 3 mg kg−1 min−1, i.v., n = 5 and 4, respectively) or d‐Arg (1 mg kg−1 min−1, i.v., n = 6), starting 30 min after occlusion, did not improve the recovery of RBF. Furthermore, infusion of l‐Arg (20 mg kg−1 min−1 for 15 min; n = 4) had no effect on the I/R‐induced impairment of the vasodilator responses to ACh.

To elucidate the relative importance of the constitutive and inducible NO synthase isoforms for the formation of NO after I/R, calcium‐dependent (constitutive) and calcium‐independent (inducible) NO synthase activities were measured in kidney homogenates obtained from ischaemic or non‐ischaemic kidneys. A calcium‐independent NO synthase activity was not detectable in kidney homogenates obtained from either sham‐operated control rats or from animals subjected to I/R. Moreover, dexamethasone (3 mg kg−1, i.v., 60 min prior to I/R, n = 6), an inhibitor of the induction of NO synthase, had no effect on either RBF or RVR in rats subjected to I/R. In contrast to I/R, lipopolysaccaride (LPS, endotoxin; 5 mg kg−1, i.p., n = 3) caused a significant induction of a calcium‐independent NO synthase activity in the kidney.

These results confirm the importance of the release of vasodilator cyclo‐oxygenase metabolites in the compromised renal circulation and indicate that the formation of NO derived from the constitutive, but not the inducible NO synthase, is also important for the maintenance of RBF after I/R injury of the renal vascular bed.
Effects of vasoactive intestinal polypeptide on antigen‐induced bronchoconstriction and thromboxane release in guinea‐pig lung
Authors: Ciabattoni Giovanni , Montuschi Paolo , Currò Diego , Togna Giuseppina , Preziosi Paolo
Published: July 2012

Exogenous vasoactive intestinal polypeptide (VIP) infused into the pulmonary artery of isolated and ventilated lungs of guinea‐pigs decreased, in a dose‐dependent fashion (1.0–10.0 nmol), airway resistance and thromboxane B2 (TXB2, the stable hydrolysis product of TXA2) release in the perfusion medium. Prostacyclin (PGI2) synthesis, as reflected by the release of its stable hydrolysis product 6‐oxo‐PGF1α, was unaffected. Pretreatment with the 5‐lipoxygenase inhibitor BWA4c (3.5 × 10−5 m) did not modify the bronchodilatory effect of VIP or its inhibitory action on TXB2 release.

Basal release of immunoreactive VIP from perfused lungs decreased from an initial value of 0.96 ± 0.10 ng min−1 (mean ± s.e.mean) in the first 2 min to an average of 0.58 ± 0.10 ng min−1 in the following 15–20 min.

Antigen challenge with ovalbumin (0.1%) in sensitized lungs caused an anaphylactic reaction in 45% of tested lungs, concomitant with a 5 fold increase in both VIP and TXB2 release. Tetrodotoxin pretreatment (10−6 m) reduced basal VIP release by > 80% and abolished the VIP increase observed during anaphylaxis, without modifying TXB2 release or the bronchoconstrictor response.

Indomethacin (10−6 m) inhibited TXB2 synthesis and release by > 90%, delayed the bronchoconstrictor response and blunted the increased VIP release during lung anaphylaxis, without influencing basal VIP release.

The 5‐lipoxygenase inhibitor BWA4c (3.5 × 10−5 m) blunted the increase of TXB2 and VIP release from guinea‐pig lung and attenuated the bronchoconstrictor response following ovalbumin challenge.

The administration of exogenous VIP as a continuous infusion (10−8 m) attenuated the bronchoconstriction and the release of cyclo‐oxygenase metabolites following antigen challenge.

Acetylcholine (10−6‐10−5 m) infused into the pulmonary artery induced a dose‐dependent bronchoconstriction not associated with enhanced VIP or TXB2 release.

The TXA2 mimetic U‐46619 (0.1–1.0 nmol) caused dose‐dependent increases in airway resistance, concomitant with an up to 10 fold increase in VIP release. VIP inhibited arachidonate‐induced in vitro aggregation of washed rabbit platelets in a dose‐dependent manner over a dose range 10−8‐10−6 M. Despite the antiaggregatory effect of VIP, TXB2 and PGE2 synthesis was reduced only to a minor extent, and there was no redirection of arachidonate metabolism from TXA2 to PGE2, indicating that VIP does not act as a TX synthase inhibitor in vitro.

We conclude that VIP may play a role in regulating bronchial smooth muscle reactivity in lung anaphylaxis by inhibiting the synthesis and release of TXA2, a potent vasoactive and bronchoconstrictor agent. TXA2, on the other hand, strongly enhances neuronal VIP release.
Effects of the κ‐opioid agonist U50,488 on parturition in rats
Authors: Douglas A.J. , Clarke G. , MacMillan S.J.A. , Bull P.M. , Neumann I. , Way S.A. , Wright D.M. , McGrory B.G. , Russell J.A.
Published: July 2012

The effects of the K‐opioid agonist U50,488 on parturition were studied in the rat.

Given directly after the birth of the second pup U50,488 (5 mg or 10 mg kg−1, i.p.) delayed the birth of the subsequent 4 pups by ca. 100 min, acting like morphine (10 mg kg−1, i.p.). In controls given the vehicle i.p., the birth of the 4 pups after treatment took 45.4 ± 4.6 min. The effects of U50,488 could be prevented by simultaneous naloxone injection (10 mg kg−1). Injection of either U50,488 or morphine at 1 mg kg−1, i.v. also significantly delayed parturition. The effects of U50,488 but not of morphine were fully prevented by preinjection with nor‐binaltorphimine (0.5 mg kg−1, i.v.) showing selective κ‐opioid receptor‐mediated inhibition by U50,488 of established parturition.

In rats with an indwelling jugular venous cannula, i.v. injection of U50,488 (5 mg kg−1) after the birth of the second pup slowed parturition in a similar way to i.p. injection and significantly reduced blood plasma oxytocin concentration measured by radioimmunoassay compared with vehicle‐injected controls.

Bolus i.v. injections of oxytocin (4 mu once per 5 min) significantly reduced the delay in parturition caused by i.v. U50,488, but continuous i.v. infusion of oxytocin (4 mu 5 min−1) was less effective.

Since i.v. oxytocin did not immediately reverse the effects of U50,488 on parturition, direct effects of U50,488 on isometric uterine contractions in vitro were sought. U50,488 inhibited spontaneous or oxytocin‐stimulated contractions of uteri from rats within 24 h after parturition in a dose‐related manner; the inhibitory effect was not naloxone‐reversible.

Thus U50,488 inhibited established parturition in the rat in a κ‐opioid selective manner by reducing oxytocin secretion. The inhibitory effect may well have been potentiated by a direct non‐opioid depressant action on contractile activity of the uterus.
Effect of tienoxolol, a new diuretic β‐blocking agent, on urinary prostaglandin excretion in the rat
Authors: Caussade François , Cloarec Alix
Published: July 2012

The effects of tienoxolol, (ethyl 2‐[3‐[(1,1‐dimethylethyl)amino]‐2‐hydroxypropoxy]‐5‐[(2‐thienylcarbonyl) amino] benzoate, hydrochloride), a novel drug exhibiting both diuretic and β‐adrenoceptor blocking properties, were investigated on urinary 6‐keto‐prostaglandin F1α (6‐keto‐PGF1α) and PGE2 excretion in the rat and compared to those of reference diuretic (furosemide) and β‐adrenoceptor antagonists (acebutolol, propranolol). Since tienoxolol was shown to bind to A1 and A2 adenosine receptors, the action of theophylline was also evaluated.

Tienoxolol (8–128 mg kg−1, p.o.) induced a dose‐related increase of 6‐keto‐PGF1α excretion from 32 mg kg−1 but a significant elevation of urinary PGE2 levels was only reached after administration of 128 mg kg−1. However, renal prostaglandin concentrations were not modified by tienoxolol.

Furosemide (32 mg kg−1) displayed a strong diuretic activity but did not enhance 6‐keto‐PGF1α excretion. Likewise, the latter was unaffected by acebutolol and propranolol (128 mg kg−1) and no significant diuresis was observed following administration of these two β‐blocking agents. Theophylline (64 mg kg−1), like tienoxolol, was able to induce both diuresis and urinary prostaglandin excretion. Furthermore, they bound with similar affinities to A1 and A2 adenosine receptors. This led to the suggestion that a relationship between P1‐purinoceptors, prostaglandin release, diuresis and natriuresis could exist.

Oral co‐administration of NECA (0.2 mg kg−1) with tienoxolol markedly reduced the urinary 6‐keto‐PGF1α excretion observed when tienoxolol was administered alone. However, neither diuresis nor natriuresis were modified, demonstrating that the proposed relationship was untenable.

In conclusion, PGI2 probably does not participate in the diuretic and natriuretic activity of tienoxolol. The increase of urinary 6‐keto‐PGF1α excretion may result not only from the haemodynamic properties of the drug but also from the rise of the urinary flow induced by tienoxolol.
Characterization of the binding of [3H]‐l‐NG‐nitro‐arginine in rat brain
Authors: Michel Anton D. , Phul Ravinder K. , Stewart Tracy L. , Humphrey Patrick P.A.
Published: July 2012

In the present study tritiated l‐NG‐nitro‐arginine (l‐NOARG) has been shown to label specific binding sites in rat brain cytosol. We conclude that this ligand is directly labelling nitric oxide synthase (NOS). This conclusion is based on our observations (i) that binding was stereoselectively inhibited by l‐arginine, in preference to d‐arginine, and (ii) that a number of different NOS inhibitors were able to displace [3H]‐l‐NOARG binding at similar concentrations to those required to inhibit the activity of rat brain cytosol NOS in functional studies.
Mg2+ and caffeine‐induced intracellular Ca2+ release in human vascular endothelial cells
Authors: Zhang Aimin , Cheng Toni P.‐O. , Altura Bella T. , Altura Burton M.
Published: July 2012

Interaction of ionized magnesium ([Mg2+]o) and caffeine in regulation of intracellular free calcium concentration ([Ca2+]i) in human aortic endothelial cells was studied using fura‐2 and digital imaging microscopy. In 1.2 mm [Mg2+]o, basal [Ca2+]i was 73.7 ± 22.4 nm, with a heterogeneous distribution within the cells. No significant changes of basal [Ca2+]i were found either when cells were treated with 10 mm caffeine or when [Mg2+]o was lowered from 1.2 mm to 0.3 mm. However, a combined superfusion of the cells with 0.3 mm [Mg2+]o and 10 mm caffeine resulted in a significant elevation of [Ca2+]i to 382.8 ± 57.1 nm, probably by release of Ca2+ from internal stores, which was attenuated by NiCl2 (1 mm). These results suggest that a Ca2+‐induced Ca2+ release mechanism is involved in regulation of [Ca2+]i in endothelial cells, which may be either regulated or modulated by Mg2+.
Inhibition by the adenosine analogue, (R‐)‐N6‐phenylisopropyl‐adenosine, of kainic acid neurotoxicity in rat hippocampus after systemic administration
Authors: MacGregor D.G. , Stone T.W.
Published: July 2012

Binding of the peripheral benzodiazepine receptor ligand, [3H]‐PK 11195, to rat hippocampal membranes has been used to quantify the reactive gliosis resulting from neuronal death induced by intraperitoneally administered kainic acid.

Intraperitoneal administration of kainic acid (10 mg kg−1) caused a 350–500% increase in [3H]‐PK 11195 binding measured in rat hippocampal P2 membranes 7 days later. Co‐treatment with the adenosine derivative R‐phenylisopropyladenosine (R‐PIA) (100, 25 or 10 μg kg−1, i.p.) abolished this elevation. The protective action of R‐PIA could itself be abolished by co‐treatment with 8‐phenyltheophylline (1 mg kg−1).

Body temperatures were recorded in the antagonist experiments and no significant changes were recorded, suggesting that the protective action of R‐PIA was not mediated by hypothermia.

Since systemic kainic acid‐induced neurotoxicity has been claimed as a good model of neuronal death in temporal lobe epilepsy, the results suggest that the systemic administration of purines in low doses may provide protection against certain neurodegenerative insults.
Mechanisms of vasodilatation in pregnancy: studies of the role of prostaglandins and nitric‐oxide in changes of vascular reactivity in the in situ blood perfused mesentery of pregnant rats
Authors: Chu Z.M. , Beilin L.J.
Published: July 2012

To examine the possible mechanisms of the vasodilatation and blunted pressor responses in late pregnancy, we have studied vascular reactivity of the in situ blood perfused mesenteric resistance vessels of 18–20 day pregnant Wistar‐Kyoto rats (WKY).

Intra‐arterial mean blood pressure (MBP) was lower in pregnant rats than in nonpregnant controls. There was no significant difference in basal mesenteric perfusion pressure (BPP) between groups.

Vascular reactivity to electrical stimulation (ES) or intra‐arterial noradrenaline (NA), angiotensin II (AII) and arginine vasopressin (AVP) was decreased in the preparations from pregnant rats compared to that from nonpregnant controls. Noradrenaline spillover into mesenteric venous blood following ES was similar in pregnant and nonpregnant animals.

Indomethacin (5 mg kg−1, i.v.), an inhibitor of cyclo‐oxygenase, induced significant increases in reactivity to ES in both pregnant and nonpregnant groups while potentiating the responses to NA and AII in nonpregnant animals only and having no effect on AVP‐induced contractions in the preparations from either pregnant or nonpregnant animals.

NG‐nitro‐l‐arginine (l‐NOARG) (5 mg kg−1, i.v.), an inhibitor of nitric‐oxide synthase, increased MBP and BPP in both pregnant and nonpregnant animals, but the difference in MBP between groups was still evident.

l‐NOARG enhanced mesenteric vascular responses to ES, NA and AII in both pregnant and nonpregnant groups. Only the difference in NA responses between groups was abolished after pretreatment with l‐NOARG.

These data show that vasoconstrictor responses to a variety of agonists are decreased in the in situ blood‐perfused mesenteric resistance vessels of pregnant rats. Increase in endothelial‐dependent nitric‐oxide generation could contribute to the vasodilatation seen in pregnancy but other mechanisms might also be involved. Cyclo‐oxygenase products are not responsible for any decreased contractile responses in this preparation.
Interactions between responses mediated by activation of adenosine A2 receptors and α1‐adrenoceptors in the rabbit isolated aorta
Authors: Wiener Harvey L. , Thalody George P. , Maayani Saul
Published: July 2012

This paper describes aspects of the functional antagonism between the responses mediated by activated α1‐adrenoceptors and adenosine A2 receptors in the adventitia‐ and endothelium‐denuded aorta of the rabbit.

Adenosine A2 receptor agonists relaxed aortic rings pre‐contracted with phenylephrine. The relaxation response was agonist concentration‐dependent and saturable. The respective contractile and relaxation responses were stable, reproducible, and reversible.

Increasing the phenylephrine concentration caused a progressive attenuation of the action of adenosine A2 receptor agonists, consisting of a decreased maximal response and a dextral shift of the adenosine agonist concentration‐response curve. This functional antagonism could be completely reversed upon removal of adenosine by either the addition of adenosine deaminase or by wash‐out of the adenosine agonist from the tissue. The relaxation response to the adenosine A2 receptor partial agonists, N6‐cyclohexyladenosine and R‐(−)‐N6‐(2‐phenylisopropyl)adenosine, was abolished at higher phenylephrine concentrations (e.g. 30 EC50).

A 1000 fold increase in the adenosine concentration was required to shift the value of the EC50 of phenylephrine six fold, while a similar increase in the value of the EC50 of adenosine could be elicited by only a 32 fold increase in the phenylephrine concentration. A 30 fold increase in the phenylephrine concentration shifted the value of the EC50 of 5′‐N‐ethylcarboxamidoadenosine four fold.

Analysis of the functional antagonism between the responses mediated by these receptors using the Black & Leff (1983) operational model of agonism allowed for the estimation of the agonist dissociation constant, KA, and the apparent efficacy, τ, for both phenylephrine and adenosine A2 receptor agonists. Increasing the concentration of phenylephrine reduced the value of τ for adenosine agonists in a concentration‐dependent and saturable manner. Similarly, increasing the concentration of adenosine reduced the value of τ for phenylephrine in a concentration‐dependent and saturable manner. The phenylephrine KA value obtained by the method of functional antagonism (1.9 μm) was similar to that obtained by the receptor inactivation method (2.1 μm).

Partial occlusion of the α1‐adrenoceptor by the alkylating agent, dibenamine, demonstrated that the magnitude of the adenosine A2 receptor‐mediated relaxation was inversely proportional to the number of functional α1‐adrenoceptors.

It is concluded that the magnitude of functional antagonism is proportional to the stimulus elicited through either receptor. We propose that this tissue preparation and pair of receptors is a good model to study quantitative aspects of functional antagonism between activated receptors.
Interaction between the effects of 5‐hydroxytryptamine and adrenaline on the growth of platelet thrombi in the coronary artery of the anaesthetized dog
Authors: McAuliffe S.J.G. , Snow H.M. , Cox B. , Smith C.C.T. , Noble M.I.M.
Published: July 2012

The interaction between adrenaline and 5‐hydroxytryptamine (5‐HT) has been quantitated on the rate of thrombus formation, in the stenosed coronary artery with damaged endothelium of the anaesthetized dog.

Changes in the plasma concentration of adrenaline were produced by varying the rate of an intravenous infusion of adrenaline and in the effects of 5‐HT, by intravenous injections of the selective 5‐HT2 receptor antagonist, ICI 170809.

Increases in the plasma concentration of adrenaline, which did not cause significant changes in blood pressure and heart rate, increased the rate of thrombus formation.

Antagonism of the 5‐HT2 receptor by ICI 170809, in the absence of an infusion of adrenaline, abolished thrombus formation (mean ED50 0.41 μg kg−1, i.v.).

The effects of adrenaline were non‐competively antagonized by ICI 170809; maximum effects were obtained in the dose‐range 50–200 μg kg−1, i.v., when the mean dose‐ratio increase in adrenaline required to restore equivalent rates of thrombus formation was 39 fold.

These results are consistent with a synergism between adrenaline and 5‐HT and emphasize the importance of both on thrombus formation.
Interactions of nitric oxide synthase inhibitors and dexamethasone with α‐adrenoceptor‐mediated responses in rat aorta
Authors: Adeagbo Ayotunde S.O. , Triggle Christopher R.
Published: July 2012

The effects of NG‐nitro‐l‐arginine methyl ester (l‐NAME) and NG‐monomethyl‐l‐arginine (l‐NMMA), their d‐isomers, and dexamethasone on noradrenaline (NA)‐induced contractions and antagonism by α‐adrenoceptor antagonists, have been investigated in rat isolated thoracic aortic rings with/without endothelium.

NA produced concentration‐dependent contractions of isolated aortic rings with EC50 values of 2.41 ± 0.54 (n = 21) and 28.00 ± 8.50 (n = 25) nm for endothelium‐denuded and ‐intact preparations respectively. Acetylcholine (ACh) relaxed NA‐precontracted rings with intact, but not those denuded of endothelium.

Treatment with l‐NAME (1–30 μm), or l‐NMMA (10–500 μm), but not their d‐isomers, resulted in an endothelium‐dependent enhancement of NA‐induced contractions. Pre‐treatment, in vitro, with 0.5 μm dexamethasone neither directly potentiated, nor influenced l‐NAME‐induced potentiation of NA‐mediated contractions in endothelium‐intact rings; however, dexamethasone pretreatment reduced EC50 values for NA, and also prevented l‐NAME‐induced potentiation, in denuded rings equilibrated for 5 h under resting tension.

In both intact and denuded rings, phentolamine, prazosin and WB 4101 shifted NA concentration‐response curves to the right; l‐NAME, and also l‐NMMA, but not their d‐isomers, reversed the blockade as indicated by significant decreases in NA dose‐ratios. In denuded rings, reversal by l‐NAME or l‐NMMA was prevented following pretreatment with dexamethasone.

Following treatment with 5 or 50 nm phenoxybenzamine (PBZ), NA concentration‐response (C‐R) curves were shifted to the right with marked depression of maximal responses; 100 μm l‐NAME reversed the antagonism in both endothelium intact and denuded rings. However, 500 nm PBZ treatment resulted in complete abolition of the responses to NA, and contractions were not restored by either l‐NAME or l‐NMMA.

5‐Hydroxytryptamine (5‐HT)‐induced contractions of aortic rings were potentiated by endothelium denudation and also by l‐, but not d‐, NAME. 5‐HT‐induced contractions were non‐competitively antagonized by 10 nm ritanserin, and 100 μm l‐NAME partially reversed the antagonism in intact but not denuded rings.

It is concluded that the inhibition of constitutive endothelial NO synthase and inducible smooth muscle NO synthase accounts for the ability of l‐NAME, and l‐NMMA, to potentiate the effects of agonists and reduce α‐adrenoceptor antagonism in endothelium‐intact and denuded rings. Furthermore, endothelial cell removal/damage triggers the induction of a smooth muscle NO synthase.
Comparison between carvedilol and captopril in rats with partial ablation‐induced chronic renal failure
Authors: Brooks David P. , Short Brian G. , Cyronak Matthew J. , Contino Lisa C. , DiCristo Martin , Wang Yi‐Xin , Ruffolo Robert R.
Published: July 2012

The effect of the novel β‐adrenoceptor antagonist and vasodilator, carvedilol (SK&F 105517, ∼ 70 mg kg−1 daily in the food), and captopril (∼ 38 mg kg−1 daily in the drinking fluid) on the progression of chronic renal failure in rats was studied.

Six weeks following partial renal ablation, the urinary protein excretion of the carvediol‐ (60 ± 21 mg day−1) and captopril‐treated (35 ± 9mgday−1) animals was less than 50% that of control rats (133 ± 27 mg d−1).

Serum creatinine (Scr) and urea nitrogen (SUN) concentrations of the carvedilol‐(Scr, 0.63 ± 0.09 mg dl−1; SUN, 11.3 ± 1.2 mg dl−1) and captopril‐treated (Scr, 0.82 ± 0.05 mg dl−1; SUN, 14.1 ± 1.5 mg dl−1) animals were also significantly (P < 0.05) lower than that observed in control animals (Scr, 1.4 ± 0.3 mg dl−1; SUN, 19.2 ± 3.9 mg dl−1), indicating that glomerular filtration rate was improved by both drugs. Plasma renin activity was significantly (P < 0.05) higher in captopril‐treated rats (24.7 ± 4.6 ng angiotensin I ml−1 h−1) than in either carvedilol‐treated (7.9 ± 1.4 ng angiotensin I ml−1 h−1) or control animals (7.4 ± 1.0 ng angiotensin I ml−1 h−1).

Histological examination of the kidneys demonstrated a significantly reduced glomerular hypertrophy and glomerulosclerosis in those animals receiving carvedilol or captopril compared to controls.

Serum carvedilol concentration measured every 6 h for 24 h was variable and ranged on average from 57 ± 13 ng ml−1 at 16 h 00 min to 121 ± 31 ng ml−1 at 03 h 00 min. These data indicate that the rats probably had 24 h systemic exposure to carvedilol.

The present study indicates that carvedilol is effective in attenuating the progression of chronic renal failure in rats.
Evidence for the involvement of both ATP and nitric oxide in non‐adrenergic, non‐cholinergic inhibitory neurotransmission in the rabbit portal vein
Authors: Brizzolara Antonia L. , Crowe Rahima , Burnstock Geoffrey
Published: July 2012

The NANC inhibitory innervation of the longitudinal muscle of the rabbit portal vein has been examined. Neurogenic relaxations were partially inhibited by the P2‐purinoceptor antagonist, suramin. Addition of the NO‐synthase inhibitor NG‐nitro‐l‐arginine methyl ester (l‐NAME) also significantly reduced responses to electrical stimulation and the addition of l‐arginine reversed this effect. A combination of both suramin and l‐NAME abolished the neurogenic relaxation. A maximum relaxation of the vein was evoked by sodium nitroprusside which was not affected by l‐NAME or suramin. Histochemical staining demonstrated the presence of NADPH‐diaphorase containing nerves between the longitudinal and circular muscle coats of the media and also in the adventitia. It is concluded that both ATP and NO are inhibitory neurotransmitters in the NANC nerves of the rabbit portal vein.
Role of neuronal and vascular Ca2+‐channels in the ACTH‐induced reversal of haemorrhagic shock
Authors: Guarini Salvatore , Bazzani Carla , Bertolini Alfio
Published: July 2012

In a rat model of volume‐controlled haemorrhagic shock causing the death of all control (saline‐treated) animals within 30 min, the intravenous (i.v.) bolus injection of ACTH‐(1–24) at a dose of 160 μg kg−1 produced an impressive and sustained restoration of arterial pressure, pulse pressure and respiratory function, with 100% survival at the end of the observation period (2 h).

Both intracerebroventricular (i.c.v., 0.015–0.06 μg kg−1) and i.v. (5 μg kg−1) pretreatment with the N‐calcium channel blocker, ω‐conotoxin GVIA, and i.v. (but not i.c.v.) pretreatment with the L‐calcium channel blocker, nicardipine (125–500 μg kg−1) dose‐dependently prevented the ACTH‐induced shock reversal.

These results further indicate that the effect of ACTH in haemorrhagic shock may involve a neuronal link and the eventual restoration of vascular tone mediated by N‐ and L‐type calcium channels, respectively.
Effect of delayed weaning on opioid receptor control of swim stress‐induced antinociception in the developing rat
Authors: Muhammad Bala Y. , Kitchen Ian
Published: July 2012

The opioid type of swim‐stress induced antinociception (SIA) is mediated via μ‐sites in preweanling rats and predominantly by δ‐sites in postweanling animals. We have studied the effect of delay of weaning on the receptor transition of this behaviour in the developing rat.

Litters were weaned normally at day 21 or allowed to remain with their mothers until assessment of swim SIA. Animals were stressed by warm water (20°C) swimming for 3 min periods and antinociception assessed by the tail immersion test (50°C).

Naloxone (10 mg kg−1) partially reversed swim SIA in both 25 day old weaned and non‐weaned rats.

Naltrindole (1 mg kg−1) partially reversed swim SIA in 25 day old weaned rats but had no effect in non‐weaned animals. Naltrindole (5 mg kg−1) completely abolished swim SIA in weaned rats but was without effect in non‐weaned groups. Antinociceptive responses to the μ‐agonist, alfentanil (60 μg kg−1) were unaffected by naltrindole at 1 mg kg−1 but were partially reversed at 5 mg kg−1.

In 30 day old non‐weaned rats, naltrindole (5 mg kg−1) abolished the swim SIA.

In conclusion, transition from μ‐ to δ‐receptor control of swim SIA in rat pups can be delayed by between 5 and 10 days by delay of weaning. The environmental stimulus of weaning can activate opioid receptor subtype operation of biological responses in the developing animal.
Effect of nafamostat mesilate on Na+ and K+ transport properties in the rabbit cortical collecting duct
Authors: Muto Shigeaki , Imai Masashi , Asano Yasushi
Published: July 2012

To determine the mechanism(s) of hyperkalemia caused by nafamostat mesilate (NM), a serine‐protease inhibitor, we investigated the effects of the drug on Na+ and K+ transport properties of the collecting duct (CD) cell in the isolated and perfused cortical collecting duct from rabbit kidneys.

NM at 10−4 m in the lumen, hyperpolarized the apical membrane in parallel with increases in transepithelial resistance (RT) and fractional apical membrane resistance (fRA).

These effects were completely inhibited by pretreatment with 50 μm luminal amiloride, whereas they were not affected by luminal addition of 2 mm Ba2+.

NM at 10−4 m in the bath slightly but significantly depolarized the basolateral membrane without any changes in RT or fRA, although NM at 10−5 m in the bath had no effect on the electrical parameters.

It is concluded that NM mainly acts on the apical membrane of the CD cell and inhibits the amiloride‐sensitive Na+ conductance in the apical membrane.
Effects of KRN2391, nicorandil and diltiazem on the changes in the electrocardiogram caused by endothelin‐1 in anaesthetized rats
Authors: Harada Katsuhiko , Miwa Atsushi , Kaneta Soichiro , Izawa Toshio , Fukushima Hideaki , Ogawa Nobuyuki
Published: July 2012

The effect of KRN2391, a novel vasodilator, on the changes of electrocardiogram caused by endothelin‐1 (ET‐1) was studied in anaesthetized rats and compared with the effects of nicorandil and diltiazem. In addition, the effect of KRN2391 on the action potential of guinea‐pig papillary muscle was studied.

The intracoronary administration (i.c.) of ET‐1 (5 μg) induced not only ST segment elevation of the electrocardiogram due to contraction of the coronary artery, but also arrhythmias involving atrioventricular block (A‐V block), ventricular premature contraction (VPC) and ventricular fibrillation (VF), and resulted in death in most animals. However, the administration of methacholine (3 μg, i.c.) produced ST segment elevation alone without developing arrhythmias.

Pretreatment with intravenous administration of KRN2391 (30 μg kg−1) inhibited the ST segment elevation and the development of arrhythmias induced by ET‐1, and decreased the incidence of death.

Nicorandil (1000 μg kg−1) prevented the ST segment elevation without suppression of the occurrence of VF. Diltiazem (100 μg kg−1) suppressed both the ST segment elevation and the occurrence of VF but not other arrhythmias. Nicorandil at 3000 μg kg−1 and diltiazem at 300 μg kg−1 produced not only a suppression of ST segment elevation and VF incidence but also a decrease in the occurrence of arrhythmias. These doses of nicorandil and diltiazem produced a decrease in death in a dose‐dependent manner.

KRN2391 (10 and 30 μg kg−1), nicorandil (1000 and 3000 μg kg−1) and diltiazem (100 and 300 μg kg−1) significantly decreased mean blood pressure in a dose‐dependent manner. Heart rate was decreased by nicorandil (3000 μg kg−1) and diltiazem (100 and 300 μg kg−1) but was not affected by KRN2391 (10 and 30 μg kg−1).

KRN2391 (30 μm) significantly shortened the action potential duration of guinea‐pig ventricle at 50% and 90% repolarization (APD50 and APD90). The effect of KRN2391 was inhibited by a K+ channel blocker, glibenclamide (30 μm).

These results suggest that the occurrence of ST segment elevation and arrhythmias induced by ET‐1 are due to a dual direct action on both coronary vascular smooth muscle and myocardium. Therefore, the protective effects of KRN2391, nicorandil and diltiazem on ET‐1‐induced heart disorders appear to be due to their direct actions on coronary vascular smooth muscle and the myocardium.
Intracellular cross‐talk between receptors coupled to phospholipase C via pertussis toxin‐sensitive and insensitive G‐proteins in DDT1MF‐2 cells
Authors: Dickenson John M. , Hill Stephen J.
Published: July 2012

The effect on intracellular free calcium concentration ([Ca2+]i) of simultaneous activation of receptors coupled to phospholipase C via pertussis toxin (PTX)‐sensitive and ‐insensitive G‐proteins has been investigated in the hamster vas deferens smooth muscle cell line, DDT1MF‐2.

In fura‐2‐loaded DDT1MF‐2 cells, activation of adenosine A1‐receptors (which are linked to PTX‐sensitive G‐proteins) with a maximal concentration of N6‐cyclopentyladenosine (CPA; 300 nm) increased [Ca2+]i from 121 ± 5 nm to 254 ± 20 nm (n = 8). These experiments were performed in the presence of extracellular Ca2+. Stimulation of histamine H1‐receptors (which are linked to PTX‐insensitive G‐proteins) with a low concentration of histamine (1 μm) increased [Ca2+]i from 128 ± 8 nm to 150 ± 13 nm (n = 8). When combined, CPA (300 nm) and histamine (1 μm) synergistically raised [Ca2+]i from 134 ± 6 nm to 607 ± 61 nm (n = 8).

Removal of extracellular Ca2+ (experiments performed in Ca2+‐free buffer containing 0.1 mm EGTA) had no effect on the synergistic interaction between CPA (300 nm) and histamine (1 μm).

The addition of maximal concentrations of CPA (300 nm) and histamine (100 μm) resulted in a rise in [Ca2+]i which was additive when compared to the Ca2+ responses obtained with the two agonists alone. Low (30 nm) and subthreshold (3 nm) concentrations of CPA did not alter the Ca2+ response elicited by maximal concentrations of histamine (100 μm).

Subthreshold concentrations of CPA (3 nm) and low concentrations of histamine (1 μm) elicited synergistic rises in [Ca2+]i.

Synergistic Ca2+ responses were not observed between histamine H1‐ and ATP‐receptors when cells were simultaneously stimulated with either 1 μm or 10 μm of each agonist.

These data suggest that adenosine A1‐receptors linked to PTX‐sensitive G‐protein(s) and histamine H1‐receptors linked to PTX‐insensitive G‐proteins interact synergistically to raise [Ca2+]i. In contrast, activation of ATP‐receptors which are linked to PTX‐insensitive G‐protein(s) do not interact synergically with histamine H1‐receptors.
In vivo release of dopamine from rat striatum, substantia nigra and prefrontal cortex: differential modulation by baclofen
Authors: Santiago Marti , Machado Alberto , Cano Josefina
Published: July 2012

The effect of baclofen, a GABAB receptor agonist, on the release of dopamine from the striatum (ST), substantia nigra (SN) and prefrontal cortex (PFC) of the rat was examined by intracerebral microdialysis.

Perfusion of baclofen 50 μm did not affect the striatal release of dopamine. However, dopamine release was markedly reduced in the SN and PFC.

3,4‐Dihydroxyphenylacetic acid and homovanillic acid output increased in the ST and decreased in the SN and PFC when baclofen was perfused through the microdialysis probe. 5‐Hydroxyindoleacetic acid levels were not affected in any experimental condition by baclofen perfusion.

The results suggest that GABAB receptors modulate the release of dopamine in the SN and PFC, but do not affect the striatal release of dopamine, which indicates that the role of GABA receptor activation is different in the dopaminergic terminals of the ST and PFC.
Species‐selective binding of [3H]‐idazoxan to α2‐adrenoceptors and non‐adrenoceptor, imidazoline binding sites in the central nervous system
Authors: Hussain J.F. , Kendall D.A. , Wilson V.G.
Published: July 2012

We have used the imidazoline derivative [3H]‐idazoxan to define α2‐adrenoceptors and non‐adrenoceptor, imidazoline binding sites in cerebral cortex membranes of calf, mouse, rat, guinea‐pig and man.

Competition experiments using the selective α‐adrenoceptor drugs, rauwolscine and corynanthine, indicated that [3H]‐idazoxan bound to a single population of sites in the calf and mouse membranes. However, [3H]‐idazoxan also labelled non‐adrenoceptor, imidazoline binding sites in the rat (15%), guinea‐pig (30%) and human (40%) cerebral cortex membranes.

Competition experiments with adrenaline and cirazoline in the guinea‐pig cortex, verified [3H]‐idazoxan binding to both α2‐adrenoceptors and to non‐adrenoceptor, imidazoline binding sites.

It has been postulated by several groups that [3H]‐idazoxan may possess partial agonist activity. To investigate this further, saturation experiments were performed in the cerebral cortex membranes of all five species in the absence and presence of 300 μm guanosine triphosphate (GTP). GTP had no effect on [3H]‐idazoxan binding in guinea‐pig cerebral cortex; in both rat and mouse membranes 300 μm GTP increased the dissociation constant for [3H]‐idazoxan by 2–3 fold without significantly affecting the Bmax. GTP reduced the Bmax by approximately 30% and 60% in calf and human cerebral cortex membranes, respectively, without significantly altering the Kd.

Saturation experiments were performed in the calf cerebral cortex membranes in the absence and presence of 300 μm GTP with the selective α2‐adrenoceptor agonist [3H]‐clonidine and the selective muscarinic antagonist [3H]‐quinuclidinyl benzilate (QNB). GTP reduced the Bmax for [3H]‐clonidine without altering the Kd, but failed to affect either the Bmax or the Kd for [3H]‐QNB.

Saturation experiments were performed in human cerebral cortex membranes in the presence of α2‐adrenoceptor blockade with and without GTP. GTP 300 μm reduced the Bmax for [3H]‐idazoxan at the non‐adrenoceptor, imidazoline binding sites, without affecting the Kd. GTP did not affect [3H]‐QNB binding to muscarinic sites.

Thus, there is a need to investigate further the pharmacological actions of [3H]‐idazoxan in view of its ability to recognise both α2‐adrenoceptors and non‐adrenoceptor, imidazoline binding sites and because it might possess agonist activity at some of these sites.
Attenuation of contractions to acetylcholine in canine bronchi by an endogenous nitric oxide‐like substance
Authors: Gao Yuansheng , Vanhoutte Paul M.
Published: July 2012

The involvement was assessed of an endogenous nitric oxide‐like substance in contractions of canine bronchi to acetylcholine.

Canine third order bronchial rings, in some of which the epithelium was removed mechanically, were suspended in organ chambers and isometric tension was recorded. In some experiments, the content of guanosine 3′,5′‐cyclic monophosphate (cyclic GMP) of the bronchi was also measured.

Acetylcholine induced concentration‐dependent contractions. The contractions were potentiated by nitro‐l‐arginine (an inhibitor of the synthesis of nitric oxide), oxyhaemoglobin (a scavenger of nitric oxide), and methylene blue (an inhibitor of soluble guanylate cyclase). The magnitude of the potentiation to acetylcholine‐induced contractions by these inhibitors were not significantly different between tissues with and without epithelium.

Acetylcholine induced a concentration‐dependent increase in intracellular content of cyclic GMP, which was similar in bronchi with and without epithelium. These increases were abolished by nitro‐l‐arginine and methylene blue.

During contractions to acetylcholine, exogenous nitric oxide relaxed the canine bronchi. The relaxations were not affeced by nitro‐l‐arginine, but were augmented by superoxide dismutase plus catalase, and were abolished by methylene blue.

These observations suggest that, during contraction evoked by acetylcholine, the production of an endogenous nitric oxide‐like substance increases and in turn attenuates the response of the airways to the muscarinic agonist. However, the endogenous nitric oxide‐like substance does not play a major role in the epithelium‐dependent attenuation of the contraction to acetylcholine in canine bronchi.
Characterization of CCK receptors in a novel smooth muscle preparation from the guinea‐pig stomach by use of the selective antagonists CI‐988, L‐365,260 and devazepide
Authors: Boyle Stephen J. , Tang Kim‐Wah , Woodruff Geoffrey N. , McKnight Alexander T.
Published: July 2012

The cholecystokinin receptors mediating motor responses in a novel smooth muscle preparation from the corpus region of the guinea‐pig stomach have been characterized by use of five agonist peptides and the antagonists CI‐988, L‐365,260 and devazepide.

Mucosa‐denuded strips of circular muscle were contracted in a concentration‐dependent manner by the five cholecystokinin (CCK)‐related peptides CCK‐8S, pentagastrin, gastrin‐I, CCK‐8US and CCK‐4.

CI‐988 was a powerful antagonist of the response to pentagastrin with an affinity (pKB = 9.49) similar to that obtained in CCKB receptor binding assays. With CCK‐8S as the agonist, CI‐988 was approximately 1000 fold less powerful as an antagonist.

Devazepide powerfully blocked responses to CCK‐8S with an affinity (pKB = 9.54) that was in agreement with reported functional data obtained in pancreatic amylase secretion studies, a system exhibiting CCKA receptor activity. Devazepide displayed lower affinity against pentagastrin than against CCK‐8S.

CI‐988 blocked responses to pentagastrin in an insurmountable manner in the presence of 3 nm devazepide; a concentration previously shown to block the CCKA receptor. The nature of the antagonism observed with L‐365,260 was unaltered by the presence of devazepide.

The guinea‐pig stomach corpus smooth muscle preparation contains both subtypes of CCK receptor and will be useful as a pharmacological tool for investigating the functional effects of novel CCK ligands.