bluuebunny/crossref_metadata_2025 huggingface dataset:
Pharmacological specificity of novel, synthetic, cyclic peptides as antagonists at tachykinin receptors
Authors: McKnight A.T. , Maguire J.J. , Elliott N.J. , Fletcher A.E. , Foster A.C. , Tridgett R. , Williams B.J. , Longmore J. , Iversen L.L.
Published: July 2012

The interaction at tachykinin receptors of a series of novel cyclic hexapeptides has been examined by use of radioligand binding assays (NK1 and NK3 sites in rat cortex, NK2 sites in hamster urinary bladder) and functional pharmacological assays (guinea‐pig ileum, rat vas deferens and rat portal vein for NK1, NK2 and NK3 receptors, respectively).

The compounds cyclc(GlnTrpPhe(R)Gly[ANC‐2]LeuMet) (L‐659,837) and cyclo(GlnTrpPheGlyLeuMet) (L‐659,877) were powerful and selective displacers of NK2 binding (pIC50 6.9 and 8.0, respectively), and were competitive antagonists of responses to stimulation of NK2 receptors in rat vas deferens (pKB for antagonism of responses to eledoisin 6.7 and 8.1, respectively). Responses in the NK1 and NK3 pharmacological assays were blocked only weakly, if at all.

In the longitudinal muscle of the small intestine of the rat, responses to stimulation of the putative NK2 receptor by eledoisin, neurokinin A or neurokinin B were antagonized by both cyclo(GlnTrpPhe(R)Gly[ANC‐2]LeuMet) and cyclo(GlnTrpPheGlyLeuMet) in a manner consistent with the presence in this tissue of a uniform population of receptors, indistinguishable from the NK2 receptor of the rat vas deferens.

The compounds cyclo(GlnTrpPheGlyLeuMet) and the lactam‐containing analogue are among the most selective antagonists for the NK2 receptor that have been described; their availability should be of value in the characterization of the receptors mediating responses to tachykinins, and in elucidating the physiological functions of the tachykinin receptors.
Modulation of agonist‐induced calcium mobilisation in bovine aortic endothelial cells by phorbol myristate acetate and cyclic AMP but not cyclic GMP
Authors: Buchan Kevin W. , Martin William
Published: July 2012

In bovine aortic endothelial cells (BAEC), thrombin (1 u ml−1), bradykinin (1–10 nm) and adenosine triphosphate (ATP) (0.3 μm–100 μm) each induced a biphasic elevation of cytosolic calcium ([Ca2+]i), consisting of an initial transient followed by a sustained plateau phase.

Pretreatment of BAEC with 4β‐phorbol 12‐myristate 13‐acetate (PMA; 100 nm) reduced the magnitude of the initial transient elevation of [Ca2+]i, induced by thrombin (1 u ml−1), low concentrations of bradykinin (1 nm) or ATP (0.3 μm, 3 μm), but not by higher concentrations of the latter two agonists. Addition of PMA (100 nm) during the plateau phase of the increase in [Ca2+]i induced by thrombin (1 u ml−1), bradykinin (10 nm) or ATP (30 μm) resulted in a fall in [Ca2+]i.

The inhibitory effects of PMA (100 nm) were inhibited by staurosporine (100 nm) but not mimicked by the inactive phorbol ester, 4α‐phorbol 12, 13‐didecanoate (4α‐PDD; 100 nm). Furthermore, staurosporine (100 nm) increased [Ca2+]i when added during the plateau phase of the increase in [Ca2+]i induced by thrombin or bradykinin. In contrast, staurosporine (100 nm) reduced [Ca2+]iWhen added during the plateau phase of the increase in [Ca2+]i induced by ATP (30 μm).

Pretreatment with forskolin (10 μm) had no effect on the magnitude of the initial transient elevation of [Ca2+]i induced by thrombin (1 u ml−1), bradykinin (1 nm and 10 nm) or ATP (30 μm). In contrast, forskolin (10 μm) and isoprenaline (10 μm) each induced biphasic elevations of [Ca2+]i when added during the plateau phase of the increase in [Ca2+]i induced by the three agonists. Furthermore, in the presence of the inhibitor of calcium influx, nickel chloride (4 mm), these biphasic elevations were reduced to monophasic transient elevations.

8 Bromo cyclic GMP (30 μm), a membrane‐permeant analogue of guanosine 3′: 5′‐cyclic monophosphate (cyclic GMP), had no effect on the magnitude of the initial transient elevation of [Ca2+]i induced by thrombin (1 u ml−1), bradykinin (10 nm) or ATP (3 μm). Furthermore, 8 bromo cyclic GMP (30 μm) and sodium nitroprusside (1 μm), had no effect when added during the plateau phase of the increase in [Ca2+]i induced by the three agonists.

NG‐nitro‐l‐arginine (50 μm), an inhibitor of nitric oxide synthase, had no effect on the magnitude of the initial transient elevation of [Ca2+]i induced by thrombin (1 u ml−1), bradykinin (1 nm) or ATP (3 μm), and had no effect on the plateau phase of the increase in [Ca2+]i induced by these agents.

These findings suggest that while activation of protein kinase C inhibits and elevation of adenosine 3′:5′‐cyclic monophosphate (cyclic AMP) augments calcium mobilisation in bovine aortic endothelial cells, elevation of cyclic GMP appears to have no effect.
Different pharmacological profiles of big‐endothelin‐3 and big‐endothelin‐1 in vivo and in vitro
Authors: D'Orléans‐Juste Pedro , Télémaque Sabine , Claing Audrey
Published: July 2012

Human big‐endothelin‐1 (big‐ET‐1) and endothelin‐1 (ET‐1) are equipotent as pressor agents and produce a significant change in mean arterial blood pressure (MAP) in anaesthetized guinea‐pigs (2 nmol kg−1: peak Δ MAP: 23 ± 6 mmHg and 26 ± 5 mmHg, respectively).

Unlike big‐ET‐1, big‐endothelin‐3 (big‐ET‐3) (10 and 20 nmol kg−1) induces no pressor responses whereas endothelin‐3 (ET‐3) at 2 nmol kg−1induces a significant increase of blood pressure in anaesthetized guinea‐pigs (peak Δ MAP: 27 ± 5 mmHg) with a shorter duration than ET‐1 and big‐ET‐1.

Big‐ET‐1 at concentrations 40 times higher than those required for ET‐1 (2.5 nm) releases prostacyclin (PGI2) (maximal release: 2.7 ± 0.8 ng ml−1; 2.9 ± 0.9 ng ml−1, respectively) and thromboxane B2 (TxB2) (maximal release: 6.7 ± 1.3 ng ml−1; 6.8 ± 1.1 ng ml−1, respectively) from guinea‐pig perfused lungs. ET‐3 (2.5 nm) is also a potent releaser of PGI2 and TxB2 from the guinea‐pig lungs (maximal release: PGI2: 2.4 ± 1.0 ng ml−1; TxB2: 3.8 ± 0.6 ng ml−1). Conversely, big‐ET‐3 (100 nm) does not increase basal release of eicosanoids.

Phosphoramidon (50 μm), a metalloprotease inhibitor, markedly reduced the eicosanoid releasing properties of big‐ET‐1 (n = 4, P < 0.01) in guinea‐pig perfused lungs without affecting the release stimulated by ET‐1.

Our results suggest that big‐ET‐1 is converted to ET‐1 via a phosphoramidon‐sensitive endothelin converting enzyme (ECE) to release eicosanoids. The ECE is present in the guinea‐pig pulmonary vasculature. Furthermore, our results suggest that the ECE activity is specific for big‐ET‐1 and may not convert big‐ET‐3 to its active metabolite, ET‐3.
l‐Glutamate diethyl ester and deaminated analogues as excitatory amino acid antagonists in rat cerebral cortex
Authors: Turner J.P. , Meldrum B.S.
Published: July 2012

The effects of l‐glutamate diethyl ester (GDEE) HCl, glutarate diethyl ester (GlrDEE) and glutarate dimethyl ester (GlrDME) on depolarizing responses to α‐amino‐3‐hydroxy‐5‐methyl‐4‐iso‐xazolepropionate (AMPA), kainate (Kain), N‐methyl‐d‐aspartate (NMDA) and quisqualate (Quis), and spontaneous paroxsymal discharges (SPDs) were examined. Experiments were performed on slices of rat cingulate cortex using the in vitro grease gap recording technique in nominally Mg2+‐free Krebs medium.

GDEE HCl (3–14 mm) caused a concentration‐dependent depolarization of the d.c. baseline potential. l‐Glutamate (0.1–0.5 mm), HCl (15 mm) and sucrose (30 mm) also depolarized the baseline. GlrDEE (3–12 mm) and GlrDME (4–26 mm) had no consistent effect on baseline potential.

GDEE HCl (10 mm) had no effect on depolarizing responses to AMPA, Kain and NMDA, but caused potentiation of those to Quis with a dose‐ratio of 0.53 (0.44–0.63) (n = 4). In two other experiments, where the depolarization of the baseline induced by GDEE HCl was large, a depression of Quis response amplitude was observed.

GlrDEE (10 mm) antagonized depolarizing responses to Kain, and to a lesser extent NMDA, with dose‐ratios of 2.14 (1.92–2.38) and 1.61 (1.39–1.87), respectively. This concentration of GlrDEE had no effect on AMPA responses, but potentiated Quis responses, with a dose‐ratio of 0.64 (0.58–0.71).

GlrDME (10 mm) antagonized depolarizing responses to Kain and to Quis, with dose‐ratios of 1.66 (1.48–1.85) and 1.22 (1.15–1.29), respectively, and had no effect on responses to NMDA.

The SPDs were inhibited by GDEE HCl (IC50 6.7 ± 0.37 mm), GlrDEE (IC50 5.6 ± 0.38 mm) and GlrDME (IC50 10.4 ± 0.73 mm).

In conclusion, there is little evidence that GDEE HCl is an antagonist of the postsynaptic excitatory amino acid receptors in the rat neocortex, and its effects may result from its contamination with l‐glutamate and increased osmolarity of the bathing medium at high concentrations. The deaminated analogues of GDEE are very weak Kain antagonists.
Effect of nedocromil sodium on allergen‐, PAF‐, histamine‐ and bradykinin‐induced airways vasodilatation and pulmonary obstruction in the pig
Authors: Alving K. , Matran R. , Lundberg J.M.
Published: July 2012

The influence of nedocromil sodium on the nasal and bronchial effects induced by allergen, platelet‐activating factor (PAF), capsaicin, histamine and bradykinin aerosol challenge in ascaris‐sensitized and pentobarbitone‐anaesthetized pigs was studied. Blood flow changes in the bronchial and nasal circulation were measured with ultrasonic flow probes around the supplying arteries, and vascular resistance was calculated. Changes in pulmonary resistance (Rpulm), dynamic compliance (Cdyn), mean arterial pressure (MAP) and heart rate (HR) were also determined.

Allergen and PAF aerosol challenge in the lung produced similar effects consisting of both bronchial and nasal vasodilatation, bronchoconstriction (increase in Rpulm and decrease in Cdyn) and increases in MAP and HR. Local pretreatment with nedocromil sodium (80 mg, aerosol) reduced the peak and duration of both the bronchial vasodilatation and increase in Rpulm, while only the duration of the change in Cdyn was significantly decreased. Nedocromil sodium did not alter the increases in MAP and HR. The nasal vasodilatation evoked by PAF, but not allergen, challenge in the lung was reduced by nedocromil sodium.

Allergen challenge in the nose induced vasodilatation of long duration which was reduced by local nedocromil sodium pretreatment (50 μg kg−1, intra‐arterially).

The vasodilator response to histamine aerosol was attenuated in the nasal, but not the bronchial circulation by local nedocromil sodium pretreatment. Histamine‐induced bronchoconstriction was not altered by nedocromil sodium.

Bradykinin aerosol‐induced vasodilatation in the nasal and bronchial circulation was markedly and equally reduced by local nedocromil sodium and systemic capsaicin (50 mg kg−1, s.c. 2 days before) pretreatment. The vasodilatation caused by i.v. bradykinin challenge was not reduced by capsaicin pretreatment. Capsaicin aerosol‐induced vasodilatation in the nasal and bronchial circulation was not affected by local nedocromil sodium pretreatment.

In conclusion, nedocromil sodium blocks some local vascular and bronchial effects, but not increases in MAP and HR, induced by allergen and PAF aerosol in the pig. Bradykinin‐induced vasodilatation in the airways, which seems to be largely dependent on capsaicin‐sensitive sensory nerves, is markedly inhibited by nedocromil sodium pretreatment, whereas capsaicin‐induced vasodilatation is not affected by nedocromil sodium. It may be suggested that nedocromil sodium acts by inhibiting some common process involved in the release of mediators from inflammatory cells (when stimulated by allergen and PAF) and sensory nerves (when stimulated by bradykinin and histamine, but not capsaicin).
Characterization of the interaction of R 56865 with cardiac Na‐ and L‐type Ca channels
Authors: Wilhelm D. , Himmel H. , Ravens U. , Peters T.
Published: July 2012

In isolated cardiac muscle, submicromolar concentrations of R 56865 (N‐[1‐[4‐(4‐fluorophenoxy)‐butyl]‐4‐piperidinyl]‐N‐methyl‐2‐benzothiazolamine) have been shown to attenuate the toxicity of cardiac glycosides.

We studied the influence of R 56865 on calcium and sodium currents in single isolated ventricular cardiomyocytes. The effect of R 56865 on action potential and contractile force in the presence of increased sodium load was also tested by exposing papillary muscles to veratridine or Anemonia sulcata toxin ATX II.

The calcium current was not affected by R 56865 as assessed in slow action potentials of papillary muscles and current measurements in ventricular cardiomyocytes.

In papillary muscles, R 56865 (1 μmol l−1) abolished veratridine‐induced aftercontractions and afterdepolarizations without affecting the profound prolongation of the action potential. When pretreated with R 56865, the occurrence of afterdepolarizations was prevented and the decline of the resting membrane potential was attenuated.

Pretreatment with R 56865 (1 μmol l−1) did not counteract the ATX II‐induced prolongation of the action potential.

The sodium current (Nao 30 mmol l−1) was concentration‐dependently decreased by R 56865 (0.1–10 μmol l−1). The blocking effect was more pronounced at less negative holding potentials.

Our results demonstrate that the protective effect of R 56865 against veratridine‐induced electrical and mechanical oscillations is not due to a direct effect on the calcium current. A potential‐dependent inhibition of the sodium current may contribute. Additional sites of action, like interference with intracellular calcium release and inhibition of potassium currents, remain to be investigated.
Non‐adrenergic, non‐cholinergic neural activation stabilizes smooth‐muscle tone independently of eicosanoid factors in guinea‐pig isolated airways
Authors: Lindén A. , Ullman A. , Löfdahl C‐G. , Skoogh B‐E.
Published: July 2012

We examined the effect of variations in resting smooth‐muscle tone induced by eicosanoid inhibitors on the direction and magnitude of the non‐adrenergic, non‐cholinergic (NANC) nervous response in guinea‐pig isolated airways.

NANC responses (in the presence of 1 μm atropine, 10 μm guanethidine) to electrical field stimulation (1200 mA; 0.5 ms; 240 s; 3 Hz) were studied in guinea‐pig isolated airway preparations (n = 4–7) taken from the proximal trachea, the distal trachea and the main bronchus. Tissues were treated with either the cyclo‐oxygenase‐blocker, indomethacin (10 μm), or the leukotriene receptor antagonist, FPL 55712 (11.5 μm), to modulate the resting tone.

Depending on the level of resting tone prior to electrical field stimulation, NANC activation induced either a contraction or a relaxation converging towards a similar level of tone, a ‘tonus equilibrium’. This tonus equilibrium displayed an increasing level towards the periphery (3 ± 3 (s.e.mean) % for the proximal trachea, 28 ± 3% for the distal trachea and 54 ± 4% for the main bronchus, in % of maximum active tension). After NANC activation, the tonus returned to a level similar to the resting tone.

We conclude that changes in resting smooth‐muscle tone not only affect the magnitude but also the direction of the NANC response. It is suggested that the NANC nervous system is a stabilizing factor in the regulation of airway smooth‐muscle tone, independent of eicosanoid factors. An increasing contractile component and a decreasing relaxant component of the NANC system towards the peripheral airways is indicated.
A comparative study of the prostanoid receptor profile of 9α11β‐prostaglandin F2 and prostaglandin D2
Authors: Giles H. , Bolofo M.L. , Lydford S.J. , Martin G.R.
Published: July 2012

The aim of this study was to determine the receptor profile of 9α11β‐prostaglandin F2 (PGF2) and compare it with that of its parent, prostaglandin D2 (PGD2). The experiments were designed to overcome the problems associated with the presence of multiple prostanoid receptor sub‐types in most tissues; the lack of selective antagonists for each receptor means that conclusions regarding efficacy at FP and EP2 receptors must remain provisional.

At DP receptors in human platelets and rabbit jugular vein, PGD2 was a full agonist, p[A50] 7.02 ± 0.09 and 6.60 ± 0.12 respectively. 9α11β‐PGF2 was approximately 30–60 fold less potent than PGD2.

9α11β‐PGF2 was a full agonist in the FP receptor containing preparation, cat iris sphincter (p[A50] 7.35 ± 0.09) comparable in potency to PGD2 (p[A50] 7.15 ± 0.19). Likewise the two prostanoids showed similar potency at the TP receptor in guinea‐pig aorta (9α11β‐PGF2 p[A50] 6.00 ± 0.07; PGD2 6.24 ± 0.08).

9α11β‐PGF2 and PGD2 had efficacy but low potency at EP1 receptors (guinea‐pig oesophageal muscularis mucosa) and demonstrated 2000–3000 fold lower potency than PGE2 (p[A50] 8.35 ± 0.09). Similarly, in the EP2 receptor‐containing preparation, cat trachea, 9α11β‐PGF2 was 3500 fold less potent and PGD2 700 fold less potent than PGE2 (p[A50] 8.06 ± 0.26).

9α11β‐PGF2 and PGD2 (10 μm) were without affinity at the IP receptors on human platelets and had no agonist action in the EP3 receptor containing preparation, guinea‐pig vas deferens.

9α11β‐PGF2 is a major metabolite of PGD2 in vivo and this conversion clearly represents an inactivation step since 9α11β‐PGF2 is of considerably lower potency than PGD2 at DP receptors. However, it is of similar potency to PGD2 at TP, FP, EP1 and EP2 receptors and it may, therefore, contribute to the biological effects which follow PGD2 administration or endogenous synthesis; its actions at these receptors are likely to be similar to those of PGD2 itself.
Dissociation between the effects of zymosan on the systemic and pulmonary vessels of the rat
Authors: Damas Jacques , Lagneaux Denise
Published: July 2012

Zymosan, an activator of the alternative complement pathway, (2 to 16 mg kg−1) injected intravenously via the tail vein of anaesthetized rats, dose‐dependently increased the vascular permeability of lung parenchyma, as measured by the accumulation of 125I‐labelled albumin in lungs.

Pretreatment of the animals with cyclo‐oxygenase inhibitors, indomethacin or ketoprofen (3 mg kg−1) or with the lipoxygenase and cyclo‐oxygenase inhibitor, BW755C (40 mg kg−1) abolished the vascular permeability changes induced by zymosan (16 mg kg−1). Neither, the PAF antagonist, WEB 2086 (10 mg kg−1) nor the antagonists of mast cell amines, mepyramine and methysergide (3 mg kg−1) affected the plasma exudation in lungs. Zymosan did not induce any accumulation of labelled albumin in lungs of rats made leucopenic by rabbit anti‐neutrophil serum.

Zymosan (16 mg kg−1) increased the haematocrit. This increase was not modified by indomethacin but reduced by WEB 2086.

Intravenous injection of zymosan (3 and 8 mg kg−1) in anaesthetized rats transiently increased right ventricular blood pressure and pulmonary arterial pressure, accelerated respiratory rate and decreased systemic blood pressure.

WEB 2086 largely reduced the systemic hypotension but did not affect the increase of pulmonary vascular resistance. Indomethacin inhibited the increase of blood pressure in the right ventricle and the modification of the respiratory rate. This drug did not inhibit but increased the systemic hypotension induced by zymosan.

Zymosan (16 mg kg−1) reduced serum complement haemolytic activity by 46%.

These data suggest that the pulmonary vascular changes induced by intravascular complement activation with zymosan in rats are mediated by neutrophils and prostanoids while the systemic vascular effects depend mainly on PAF.
Cardiovascular actions of the κ‐agonist, U‐50,488H, in the absence and presence of opioid receptor blockade
Authors: Pugsley M.K. , Penz W.P. , Walker M.J.A. , Wong T.M.
Published: July 2012

The cardiovascular actions of U‐50,488H, a κ‐receptor agonist, were studied in rat isolated perfused hearts, and in anaesthetized rats, over concentrations or doses generally above those required to produce κ‐receptor‐mediated effects.

U‐50,488H dose‐dependently decreased left‐ventricular peak systolic pressure and beating rate in vitro and reduced blood pressure and heart rate in vivo.

Over the concentration range of 1–30 μm in vitro, and the dose‐range of 0.5–32 μmol kg−1 in vivo, U‐50,488H prolonged the P—R, QRS and Q—T intervals of the ECG.

The effects of U‐50,488H were not antagonized by an opioid receptor antagonist, naloxone (1 μm or 8 μmol kg−1). Similarly, the opioid receptor antagonist, MR 2266, at 8 μmol kg−1 did not significantly reduce the cardiovascular actions of U‐50,488H in vivo.

The actions of U‐50,488H on responses to electrical stimulation were also studied. Over the dose range of 0.5–32 μmol kg−1, U‐50,488H altered thresholds and effective refractory period. It had a biphasic action on thresholds for induction of ventricular fibrillation. Thresholds were decreased at lower doses (0.5–4 μmol kg−1) but increased at higher doses (8–32 μmol kg−1). The effects of lower doses were blocked by naloxone. Effective refractory period and threshold pulse width only increased with dose.

In conclusion, U‐50,488H at high concentration, had direct depressant actions on cardiac contractility, electrical excitability and the ECG. These depressant effects were not antagonized by the opioid receptor antagonists, naloxone and MR 2266, and probably do not involve opioid receptors. Furthermore, some of the observed effects were those expected to result from sodium channel blockade.
Inhibition of endothelium‐dependent vasorelaxation by arginine analogues: a pharmacological analysis of agonist and tissue dependence
Authors: Martin G.R. , Bolofo M.L. , Giles H.
Published: July 2012

Isolated rings of rabbit external jugular vein (RbJV) and rat thoracic aorta (RA) were used to study the effect of the NO synthase inhibitor l‐NG‐nitroarginine methyl ester (l‐NAME) on muscarinic and 5‐hydroxytryptamine (5‐HT) receptor‐stimulated, endothelium‐dependent vascular relaxations.

In RbJV relaxations produced by the endothelial 5‐HT receptor agonist α‐methyl‐5‐HT were potently and non‐surmountably inhibited by l‐NAME (10 μm), whereas acetylcholine relaxations in this tissue were unaffected by this concentration of inhibitor. By contrast, acetylcholine relaxations in RA were virtually abolished by 10 μm l‐NAME. In each case an equivalent concentration of d‐NAME was without effect on agonist‐induced relaxations.

The different effect of l‐NAME on acetylcholine relaxations in RbJV and RA was not due to muscarinic receptor differences. Affinity estimates for acetylcholine (pKA = 6.12 ± 0.09; 6.09 ± 0.08 respectively) and for 4‐diphenyl‐acetoxy‐N‐methylpiperidine methobromide (4‐DAMP, pKB = 9.01 ± 0.12; 9.24 ±0.16 respectively) indicated that the receptors in both tissues belong to the same M3 class. Tissue differences resulting from the release of a cyclo‐oxygenase product or a glibenclamide‐sensitive K+‐channel‐linked hyperpolarizing factor were also ruled out by selective inhibition of these pathways.

When phenoxybenzamine was used to reduce the efficacy of acetylcholine in RbJV so that it behaved as a partial agonist in this tissue, l‐NAME (10 μm) now produced non‐surmountable inhibition of relaxation responses. In untreated tissues the same concentration of l‐NAME also profoundly inhibited responses produced by butyrylcholine and pilocarpine, both of which behave as partial agonists at the M3 receptor in RbJV.

A simple model was developed which describes the theoretical behaviour of receptor‐stimulated synthesis and release of NO. The model predicts that competitive inhibition of NO formation results in parallel displacements of the agonist response curve in the case of high efficacy agonist, but right‐shift with concomitant depression of the curve maximum in the case of low efficacy agonists. Simulations based on the model showed reasonable agreement with the experimental data.

It is concluded that analogues of l‐arginine demonstrate tissue‐ and agonist‐dependence in terms of their ability to inhibit receptor‐mediated events involving the liberation of NO. This behaviour can reflect differences in agonist efficacy in the receptor systems being studied, a possibility that should be ruled out before apparent resistance to inhibition is taken as evidence for the involvement of heterogeneous endothelium‐derived relaxing factors (EDRFs).
Anpirtoline, a novel, highly potent 5‐HT1B receptor agonist with antinociceptive/antidepressant‐like actions in rodents
Authors: Schlicker E. , Werner U. , Hamon M. , Gozlan H. , Nickel B. , Szelenyi L , Göthert M.
Published: July 2012

The purpose of the present study was to relate the effects of the novel drug, anpirtoline, on 5‐hydroxytryptamine (5‐HT) receptor subtypes to its antinociceptive and antidepressant‐like actions in rodents.

Binding assays with rat brain membranes have shown that anpirtoline bound with a much higher affinity to 5‐HT1B receptors (Ki = 28 nm) than to 5‐HT1A (Ki = 150 nm) and 5‐HT2 (Ki = 1.49 μm) receptors.

Like 5‐HT, anpirtoline concentration‐dependently inhibited forskolin‐stimulated adenylate cyclase activity in homogenates from the rat substantia nigra. Both effects were not additive, and could be prevented by 5‐HT1B receptor antagonists such as propranolol and penbutolol.

In superfused rat and pig brain cortex slices preincubated with [3H]‐5‐HT, the electrically evoked tritium overflow was inhibited by anpirtoline and 5‐HT. Whereas 5‐HT was equipotent in both tissues (EC50 = 69 nm), anpirtoline was markedly less potent in pig brain cortex slices (EC50 = 1190 nm) than in rat brain cortex slices (EC50 = 55 nm). The concentration‐response curve for anpirtoline was shifted to the right by metitepine in both preparations.

In the social behaviour deficit test, anpirtoline and trifluoromethylphenyl‐piperazine were effective in reversing the isolation‐induced impairments in mice, an effect shown only by compounds with agonist properties at the 5‐HT1B receptor.

In the electrostimulated pain test using mice, anpirtoline dose‐dependently increased the pain threshold with an ED50 of 0.52 mg kg−1, i.p. The antinociceptive activity of anpirtoline was abolished by pretreatment with cyproheptadine or propranolol.

In the forced swimming test in rats, anpirtoline induced a dose‐related increase in swimming activity. With an ED50 value of 4.6 mg kg−1, i.p., anpirtoline was 4 times more potent than the two standard compounds imipramine and desipramine. The decrease of immobility time or the increase of active periods in this model of behavioural despair is suggested to be characteristic of antidepressant drugs.

Anpirtoline exhibits both antinociceptive and antidepressant‐like activities in animals. It is probable that anpirtoline elicits these pharmacological effects via its agonist effect on 5‐HT1B and 5‐HT1A receptors.
The role of nitric oxide in the regional vasodilator effects of endothelin‐1 in the rat
Authors: Fozard John R. , Part Marie‐Louise
Published: July 2012

The role of nitic oxide (NO) derived from l‐arginine in the regional vasodilator effects of endothelin‐1 has been investigated in anaesthetized, spontaneously hypertensive (SH) rats in which autonomic reflexes were abolished by ganglion blockade. The experimental design incorporated animals infused with phenylephrine to mimic the peripheral vasoconstrictor effects of the NO biosynthesis inhibitors and a single dose per animal paradigm to obviate problems of tachyphylaxis to the vasodilator effects of endothelin‐1.

Infusion of the inhibitor of NO synthase, N‐monomethyl‐l‐arginine (l‐NMMA) at a dose (5 mg kg−1 min−1) which maximally raised blood pressure did not influence either the fall in blood pressure or the vasodilator responses induced in the hindquarters and carotid vascular beds by endothelin‐1 (1 nmol kg−1, i.v.). The duration (but not the initial magnitude) of the vasodepressor response to endothelin‐1 was however significantly attenuated (by 49%) during infusion of the more potent inhibitor of NO synthase, NG‐nitro‐l‐arginine methyl ester (l‐NAME), 2 mg kg−1 min−1.

Increasing the dose of l‐NAME to 10 and 25 mg kg−1 min−1 significantly attenuated, but did not abolish, the falls in blood pressure and hindquarters vasodilator responses to acetylcholine, 1 μg kg−1, and endothelin‐1, 1 nmol kg−1 min−1. The effects were selective in that vasodepressor responses to the endothelium‐independent vasodilator, sodium nitroprusside, 1–10 μg kg−1 min−1, were unaltered.

The data indicate that NO generated de novo from l‐arginine mediates a significant component of the vasodilator effect of endothelin‐1 in the anaesthetized, ganglion‐blocked SH rat. However, a major component of the vasodepressor effects of both endothelin‐1 and acetylcholine may occur independently of this mechanism.
Platelet‐activating factor (PAF) plays an important role in the immediate asthmatic response in guinea‐pig by augmenting the response to histamine
Authors: Morooka Shigeaki , Uchida Masako , Imanishi Noriaki
Published: July 2012

To investigate the role of platelet activating factor (PAF) in the immediate asthmatic response, we examined the bronchial reactivity to histamine after administration of PAF to guinea‐pigs or antigen challenge to passively sensitized guinea‐pigs.

A bolus injection of PAF (20–40 ng kg−1), which did not cause a significant increase in intrathoracic pressure (ITP), augmented the bronchial response to histamine almost 8 fold. This airway hyperreactivity was observed even 1 min after PAF treatment.

A subthreshold dose of antigen (0.01 mg kg−1, i.v.) also provoked hyperreactivity to histamine, which became significant 6 and 11 min after the antigen treatment.

The specific PAF‐antagonists, SM‐10661 and CV‐6209 (i.v.) dose‐dependently inhibited both PAF‐and antigen‐induced airway hyperreactivities to histamine.

These results suggest that PAF plays an important role in antigen‐induced acute airway responses by augmenting the activities of spasmogens.
Inhibition by adrenergic neurone blocking agents of the relaxation induced by BRL 38227 in vascular, intestinal and uterine smooth muscle
Authors: Berry J.L. , Small R.C. , Hughes S.J. , Smith R.D. , Miller A.J. , Hollingsworth M. , Edwards G. , Weston A.H.
Published: July 2012

The adrenergic neurone blocking agents, guanethidine and bretylium, have been tested for inhibitory activity against the actions of some relaxant drugs (BRL 38227, noradrenaline, sodium nitroprusside, theophylline) in vascular, intestinal and uterine smooth muscle.

In guinea‐pig isolated taenia caeci pre‐contracted with KCl (25 mm), BRL 38227 (0.1–10 μm) and noradrenaline (10 nm‐100 μm) each caused concentration‐dependent relaxation. Guanethidine and bretylium (50 μm) each antagonized the relaxation to BRL 38227 but not that to noradrenaline. At high concentration (500 μm), the adrenergic neurone blocking agents antagonized the action of BRL 38227 and, to some extent, that of noradrenaline.

In rat isolated aorta pre‐contracted with noradrenaline (300 nm), BRL 38227 (0.0125–3.2 μm) and sodium nitroprusside (0.3–100 nm) each produced concentration‐dependent smooth muscle relaxation. Guanethidine and bretylium (5–500 μm) each antagonized the action of BRL 38227 without antagonizing that of sodium nitroprusside.

Rats were pretreated with 17‐β oestradiol benzoate. Tension waves were then induced from segments of isolated, oestrogen‐dominated uterus by transmural electrical stimulation or by oxytocin (0.2 nm). These tension waves were inhibited by BRL 38227 (0.025–3.2 μm) or theophylline (0.05–0.8 mm) in a concentration‐dependent manner. Guanethidine (50 μm) antagonized the action of BRL 38227 in both the electrically‐ and oxytocin‐driven tissues. In the electrically‐driven tissues, guanethidine (50 μm) did not antagonize the inhibition to theophylline.

In KCl (25 mm)‐treated guinea‐pig taenia caeci, guanethidine (50 μm) inhibited the efflux of 86Rb+ evoked by BRL 38227 (10 μm) but not that evoked by noradrenaline (10 μm). In contrast, apamin (100 nm) reduced the efflux of 86Rb+ which was promoted by noradrenaline, but did not affect efflux induced by BRL 38227.

6 It is concluded that the adrenergic neurone blocking agents, guanethidine and bretylium (each at 50 μm), selectively inhibit the relaxant action of BRL 38227 in vascular, intestinal and uterine smooth muscle. If this inhibition reflects direct blockade of the K+‐channel (KKCO) which is opened by BRL 38227, then the adrenergic neurone blocking agents act as inhibitors selective for KKCO as opposed to the small, apamin‐sensitive (SKCa) and large (BKCa) conductance, Ca2+‐dependent K+‐channels.
The actions of two sensory neuropeptides, substance P and calcitonin gene‐related peptide, on the canine hepatic arterial and portal vascular beds
Authors: Withrington P.G.
Published: July 2012

The two peptides, calcitonin gene‐related peptide (CGRP) and substance P (SP) were administered individually as bolus injections into the separately perfused hepatic arterial and portal vascular beds of the anaesthetized dog to assess their actions and relative molar potencies at these sites.

CGRP caused an immediate dose‐related increase in hepatic arterial flow when injected close‐arterially, reflecting a fall in resistance. This vasodilator effect was slightly increased by the prior administration of the selective β2‐adrenoceptor antagonist, ICI 118,551.

On a molar basis, CGRP was more potent as an hepatic arterial vasodilator than the non‐selective β‐adrenoceptor agonist, isoprenaline (Iso).

Intra‐portal injection of CGRP also evoked hepatic arterial vasodilatation unaccompanied by other cardiovascular changes.

CGRP in doses up to 10 nmol had no effect on portal vascular resistance when administered intra‐portally.

6 SP evoked a rapid, dose‐related increase in hepatic arterial flow when injected intra‐arterially. The molar ED50 for this hepatic vasodilatation was 40.2 fmol, significantly less than the ED50 for either CGRP or Iso. SP was the most potent hepatic arterial vasodilator yet examined. The vasodilator effect of SP was slightly potentiated by prior β2‐adrenoceptor blockade.

7 SP caused hepatic arterial vasodilatation when administered by intra‐portal injection; its absolute and relative potency was much reduced.

8 SP when injected intra‐portally caused a graded increase in hepatic portal inflow resistance. The molar potency for this portal vasoconstriction was significantly greater than that for noradrenaline (NA); however, the maximum increase in portal resistance was significantly less to SP than to NA.

9 In view of the location of the peptides CGRP and SP within the afferent innervation of the liver, it is proposed that they play an important function in controlling the hepatic microvasculature in response to sensory stimuli, particularly those arising from changes in portal blood composition secondary to change in metabolic activity within the gastrointestinal tract (GIT).

10 Since the peptides are released from the GIT into the hepatic portal inflow, they may modify hepatic arterial blood flow, the extent of which is related to events within the GIT.
A perfusion system for the long term study of macrophage activation
Authors: Assreuy Jamil , Moncada Salvador
Published: July 2012

A closed system was developed for perfusing J774 macrophages in columns. The cells were perfused for up to 100 h, at which time they were still viable.

Stimulation with increasing concentrations (0.01–10 μg ml−1) of bacterial lipopolysaccharide (LPS) caused the cells to produce increasing amounts of nitrite in the perfusion medium. This production was time‐dependent, reaching a plateau by 48–50 h.

The nitrite accumulation caused by 0.1 μg ml−1 of LPS was augmented by priming the cells for 2 h with increasing amounts of interferon‐γ. The nitrite accumulation also reached a plateau under these conditions.

N‐iminoethyl‐l‐ornithine (l‐NIO, 30 μm) completely inhibited the accumulation of nitrite whereas dexamethasone (0.3 μm) caused 60–70% inhibition.

Perfusion of the cells without l‐arginine prevented the nitrite accumulation. Replacement of this amino acid after 20 or 50 h of perfusion led to a rapid generation of nitrite, the levels of which continued to increase for the duration of the experiment.

6 Thus, the perfusion system can be used to study the kinetics of the activation of the NO synthase and most likely other parameters in J774 cells and probably other cells in culture. An observation already of interest is that the ‘disappearance’ of the NO synthase after its activation can be prevented or reduced by removal of l‐arginine from the medium.
Rabbit isolated renal artery contractions by some tryptamine derivatives, including 2‐methyl‐5‐HT, are mediated by a 5‐HT1‐like receptor
Authors: Tadipatri Sreekanth , Feniuk Wasyl , Saxena Pramod R.
Published: July 2012

Despite the fact that 5‐hydroxytryptamine (S‐HT)‐induced contractions of the rabbit isolated renal artery are mediated by a receptor belonging to the heterogeneous 5‐HT1‐like category, we observed that the so‐called selective 5‐HT3 receptor agonist, 2‐methyl‐5‐HT, caused a concentration‐dependent contraction of this vessel. This study was therefore undertaken to analyze the effects of 2‐methyl‐5‐HT in the renal artery segments, either quiescent or precontracted with U46619 (10−7 m). α‐Methyl‐5‐HT and 5‐methoxytryptamine, which have high affinities for 5‐HT2 and 5‐HT4 receptors, respectively, were used for comparison.

In the precontracted vessel segments, the maximum contractile responses obtained with 2‐methyl‐5‐HT, α‐methyl‐5‐HT, 5‐methoxytryptamine and 5‐HT were similar to those in the quiescent segments. However the pD2 values were higher in the precontracted segments, making them about 4–100 fold more sensitive.

Neither MDL 72222 (10−6 m) nor tropisetron (3 × 10−6 m) suppressed renal artery contractions elicited by 5‐HT, 2‐methyl‐5‐HT, α‐methyl‐5‐HT or 5‐methoxytryptamine, thus ruling out the involvement of 5‐HT3 as well as 5‐HT4 receptors.

On the other hand, both methiothepin (10−8 and 10−7 m) and ketanserin (10−7 and 10−6 m) caused a rightward shift of agonist concentration‐effect curves. The two antagonists had similar pA2 values against the different agonists tested on either quiescent or precontracted vessels, but ketanserin (apparent pA2: 6.6 to 7.0) was between 20–100 fold less potent than methiothepin (apparent pA2: 8.4 to 8.8).

The results of this functional study permit us to conclude that the contractile effects of 2‐methyl‐5‐HT as well as α‐methyl‐5‐HT and 5‐methoxytryptamine on the rabbit isolated renal artery are mediated by a 5‐HT1‐like receptor. Since, in addition, the reported ligand binding affinity of 2‐methyl‐5‐HT at 5‐HT3 receptors is similar to both the ligand binding affinity and the functional pD2 at 5‐HT1 sites, this compound cannot be regarded as a selective 5‐HT3 receptor agonist. Similarly, α‐methyl‐5‐HT and 5‐methoxytryptamine have only a limited selectivity for 5‐HT2 and 5‐HT4 receptors, respectively.
Investigations into neuropeptide Y‐mediated presynaptic inhibition in cultured hippocampal neurones of the rat
Authors: Bleakman David , Harrison Neil L. , Colmers William F. , Miller Richard J.
Published: July 2012

We have examined the effects of neuropeptide Y (NPY) on synaptic transmission and [Ca2+]i signals in rat hippocampal neurones grown in culture. [Ca2+]i in individual neurones displayed frequent spontaneous fluctuations often resulting in an elevated plateau [Ca2+]i. These fluctuations were reduced by tetrodotoxin (1 μm) or combinations of the excitatory amino acid antagonists 6‐cyano‐7‐dinitroquinoxaline (CNQX) (10 μm) and aminophosphonovalerate (APV) (50 μm), indicating that they were the result of glutamatergic transmission occurring between hippocampal neurones.

[Ca2+]i fluctuations were also prevented by Ni2+ (200 μm), by the GABAB receptor agonist, baclofen (10 μm) and by NPY (100 nm) or Y2 receptor‐selective NPY agonists. Following treatment of cells with pertussis toxin, NPY produced only a brief decrease in [Ca2+]i fluctuations which rapidly recovered.

Perfusion of hippocampal neurones with 50 mm K+ produced a large rapid increase in [Ca2+]i. This increase was slightly reduced by NPY or by a combination of CNQX and APV. The effects of CNQX/APV occluded those of NPY. NPY had no effect on Ba2+ currents measured in hippocampal neurones under whole cell voltage‐clamp even in the presence of intracellular GTP‐γ‐S. On the other hand, Ba2+ currents were reduced by both Cd2+ (200 μm) and baclofen (10 μm).

Current clamp recordings from hippocampal neurones demonstrated the occurrence of spontaneous e.p.s.ps and action potential firing which were accompanied by increases in [Ca2+]4. This spontaneous activity and the accompanying [Ca2+]i signals were prevented by application of NPY (100 nm). When hippocampal neurones were induced to fire trains of action potentials in the absence of synaptic transmission, these were accompanied by an increase in cell soma [Ca2+]i. NPY (100 nm) had no effect on these cell soma [Ca2+]i signals. NPY (100 nm) also had no effect on inward currents generated in hippocampal neurones by micropipette application of glutamate (50 μm).

Thus, NPY is able to abolish excitatory neurotransmission in hippocampal cultures through a pertussis toxin‐sensitive mechanism. However, no effect of NPY on Ca2+ influx into the cell soma of these hippocampal neurones could be discerned. These results are consistent with a localized presynaptic inhibitory effect of NPY on glutamate release in hippocampal neurones in culture.
Antagonism of synaptic potentials in ventral horn neurones by 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione: a study in the rat spinal cord in vitro
Authors: King A.E. , Lopez‐Garcia J.A. , Cumberbatch M.
Published: July 2012

The rat spinal cord in vitro has been used to assess the effect of 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX) on the dorsal root evoked extracellular ventral root reflex (DR‐VRR) and the intracellular excitatory postsynaptic potential (e.p.s.p.) in ventral horn neurones and motoneurones.

CNQX (1–5 μm) produces a selective and dose‐dependent reduction in the amplitude of the monosynaptic component of the DR‐VRR recorded from lumbar spinal segments.

With low intensity dorsal root stimulation CNQX selectively attenuates the amplitude of the short latency intracellular e.p.s.p. (70% reduction, P < 0.005) and its rise‐time (75%, P < 0.01) without affecting the half‐time to decay.

When high intensity stimulation is used CNQX significantly attenuates the amplitude of the e.p.s.p. (56%, P < 0.005), rise‐time (76%, P < 0.01) and abolishes the short latency spike. In addition longer latency synaptic components are attenuated and the half‐time to decay significantly reduced (47%, P < 0.005).

The results with CNQX are compared to d‐aminophosphonovalerate and discussed in relation to the recruitment of low versus high threshold afferents. The data supports an involvement of non‐NMDA receptors in transmission through both mono‐ and polysynaptic pathways in the ventral horn.
Calmidazolium, a calmodulin inhibitor, inhibits endothelium‐dependent relaxations resistant to nitro‐l‐arginine in the canine coronary artery
Authors: Illiano Stephane , Nagao Tetsu , Vanhoutte Paul M.
Published: July 2012

The role of calmodulin in endothelium‐dependent relaxations in the canine coronary artery, was investigated by use of the inhibitor of calmodulin, calmidazolium.

The endothelium‐dependent relaxations to adenosine diphosphate (ADP) and nebivolol, a β‐adrenoceptor antagonist, in control solution, and to bradykinin in high potassium solution (to inhibit endothelium‐dependent hyperpolarization), were abolished by nitro‐l‐arginine (30 μm), an inhibitor of nitro oxide‐synthase. Calmidazolium (10 μm) did not inhibit these relaxations.

Calmidazolium did not affect the endothelium‐independent relaxations to SIN‐1, an exogenous donor of nitric oxide (NO).

The relaxations to bradykinin and to the calcium ionophore A23187 in control solution were inhibited to a small extent by calmidazolium (10 μm).

Bradykinin and A23187 induced relaxations in the presence of nitro‐l‐arginine (30 μm) that were abolished by calmidazolium (10 μm) but not affected by glibenclamide (10 μm), an inhibitor of ATP‐sensitive K+ channels.

6 The endothelium‐independent relaxations to lemakalim, an ATP‐sensitive K+ channel opener, were not affected by calmidazolium (10 μm) but were inhibited by glibenclamide (10 μm).

7 These results suggest that calmidazolium does not inhibit the endothelium‐dependent relaxations due to endothelium‐derived NO in the canine coronary artery but inhibits either the production of endothelium‐derived hyperpolarizing factor (EDHF) from endothelial cells or its effects on vascular smooth muscle cells. Furthermore these results suggest that EDHF contributes to endothelium‐dependent relaxations in the canine coronary artery.
Reduced relaxant potency of nitroprusside on pulmonary artery preparations taken from rats during the development of hypoxic pulmonary hypertension
Authors: Wanstall Janet C. , Hughes Ian E. , O'Donnell Stella R.
Published: July 2012

Relaxant responses to nitroprusside were examined on U46619‐contracted pulmonary artery ring preparations from rats exposed to hypoxia, in chambers containing 10% oxygen, for 1, 3, or 14 days, or for 14 days followed by 12 days in room air. Control rats were housed in room air.

After 3 days of hypoxia (but not 1 day), rats had elevated pulmonary artery pressure, right ventricular hypertrophy and polycythemia. After 14 days of hypoxia there was, in addition, hypertrophy of the pulmonary artery. In rats returned to room air for 12 days after 14 days of hypoxia, there was still some right ventricular and vascular hypertrophy but no increase in pulmonary artery pressure or polycythemia.

The potency (neg log EC50) of nitroprusside on pulmonary arteries taken from rats after 3 or 14 days of hypoxia was significantly less than on preparations from control rats (3 and 11 fold, respectively). This was not seen after 1 day of hypoxia or after 14 days of hypoxia followed by 12 days in room air. Removal of the endothelium from the preparations had no effect on the potency of nitroprusside in control or hypoxic rats (14 days).

In preparations from hypoxic, but not control, rats (14 days), the maximum response to nitroprusside was > 100% (177% reversal of the U46619 contraction) in the absence, but not in the presence, of the endothelium, indicating that pulmonary arteries from hypoxic rats had inherent tone which could be counteracted by a relaxing factor from the endothelium.

Exposure of rats to hypoxia (14 days) did not affect the potency of nitroprusside on aorta or trachea.

6 It is concluded that exposure of rats to hypoxia results in reversible desensitization of the vascular smooth muscle of pulmonary artery to nitroprusside. The time course of this desensitization suggests that it is probably associated with the elevated pulmonary artery pressure or maintained hypoxaemia rather than with the vascular hypertrophy.

7 It is postulated that the increase in pulmonary artery pressure and/or the maintained hypoxaemia may cause chronic release of nitric oxide from the pulmonary vascular endothelium or smooth muscle resulting in desensitization of soluble guanylate cyclase to the action of nitroprusside.
Effect of the thromboxane A2‐mimetic U46619 on 5‐HT1‐like and 5‐HT2 receptor‐mediated contraction of the rabbit isolated femoral artery
Authors: MacLennan Stephen J. , Martin Graeme R.
Published: July 2012

The influence of the thromboxane A2‐mimetic U46619 (11α,9α‐epoxymethano PGH2) on 5‐hydroxytryptamine (5‐HT)‐induced contractions of the rabbit isolated femoral artery has been examined.

In the absence of U46619, 5‐HT responses were mediated predominantly by 5‐HT2‐receptors as judged by potent, surmountable antagonism by the selective 5‐HT2 receptor antagonists, spiperone and ketanserin. Both antagonists unmasked a population of 5‐HT1‐like receptors which accounted for approximately 10–15% of the 5‐HT maximum response.

In the presence of U46619 (3–10 nm), 5‐HT‐induced contractions were largely resistant to blockade by 5‐HT2 receptor antagonists since 5‐HT1‐like receptor‐mediated contraction now accounted for approximately 60% of the 5‐HT maximum response.

These results show that activation of thromboxane A2 receptors in a tissue possessing both 5‐HT2 and 5‐HT1‐like receptors can convert 5‐HT‐induced contraction from one mediated predominantly by 5‐HT2 receptors to one which is mediated predominantly by 5‐HT1‐like receptors.