bluuebunny/crossref_metadata_2025 huggingface dataset:
Pharmacological evidence for a single bradykinin B2 receptor in the guinea‐pig
Authors: Pruneau D. , Luccarini J.M. , Defrêne E. , Paquet J.L. , Bélichard P.
Published: July 2012

The present study addresses the possibility of the existence of different kinin B2 receptor subtypes in the guinea‐pig by evaluating the affinity of peptide and nonpeptide receptor antagonists. For this purpose, jugular vein rings, ileum segments, lung parenchymal and trachea strips were set up in organ baths for isometric tension measurements. The experiments were conducted in the presence of indomethacin (3 μm), atropine (10 μm) and captopril (10 μm).

BK contracted jugular vein (JV), ileum (GPI), parenchyma (LP) and trachea (GPT) with an EC50 of 13.2 ± 1.4 nM (n = 27), 11.2 + 2.1 (n = 26), 23.6 ± 6.3 nM (n = 26) and 33.0 ± 6.5 (n = 27), respectively. Thiorphan, a neutral endopeptidase (EC 3.4.24.11) inhibitor and MERGETPA (DL‐2‐mercaptomethyl‐3‐guanidinoethylthiopropanoic acid), a carboxypeptidase inhibitor, had no effect on the BK‐induced contractions of JV, GPI and LP. In the GPT, thiorpan potentiated the contractile response to BK and was thus added in the corresponding experiments.

The peptide B2 receptor antagonist, Hoe 140 and the nonpeptide compound, WIN 64338, behaved as noncompetitive antagonists against contractile responses to cumulative BK in the four tissues although Hoe 140 appeared as a competitive inhibitor in the GPT only. In order to compare the inhibitory potency of these compounds between tissues, pKB values were determined. Mean values of pKB for Hoe 140 were 8.05 ± 0.07, 8.43 ± 0.11, 8.13 ± 0.18 and 8.52 ± 0.25 in the JV, GPI, GPT and LP, respectively. WIN 64338 gave mean pKB values of 6.89 ± 0.10, 7.57 ± 0.12, 7.36±0.12 and 7.51 ± 0.28 in the JV, GPI, LP and GPT, respectively.

D‐Arg [Hyp3, D‐Phe7, Leu8]BK and D‐Arg [Hyp3, D‐Phe7]BK (NPC 567) inhibited in a competitive fashion the concentration‐response curves to BK. Values of pA2 for each compound were not significantly different in the four tissues and were between 5.81 and 6.31 for D‐Arg [Hyp3, D‐Phe7, Leu8]BK and between 5.55 and 5.65 for NPC 567.

We conclude that the contractile response to BK in guinea‐pig vascular, intestine and lung tissue is mediated by a unique B2 receptor. Thus, our results do not support the existence of a B3 receptor in the trachea and we suggest that the previously reported B2B receptor subtype simply represents the guinea‐pig isoform.
Anxiolytic activity of adenosine receptor activation in mice
Authors: Jain Nisha , Kemp Nicola , Adeyemo Olasumbo , Buchanan Patricia , Stone Trevor W.
Published: July 2012

Purine analogues have been examined for anxiolytic‐ and anxiogenic‐like activity in mice, by use of the elevated plus‐maze.

The selective A1 receptor agonist, N6‐cyclopentyladenosine (CPA) had marked anxiolytic‐like activity at 10 and 50 μ kg−1, with no effect on locomotor performance at these doses.

The A1 selective adenosine receptor antagonist, 1,3‐dipropyl‐8‐cyclopentylxanthine (CPX) had no significant effect on anxiety‐related measures or locomotor behaviour, but blocked the anxiolytic‐like activity of CPA. The hydrophilk xanthine, 8‐(p‐sulphophenyl) theophylline did not prevent anxiolysis by CPA.

Caffeine had anxiogenic‐like activity at 30 mg kg−1 which was prevented by CPA at 50 μg kg−1.

The A2 receptor agonist, N6‐[2‐(3,5‐dimethoxyphenyl)‐2‐(2‐methylphenyl)‐ethyl]adenosine (DPMA) had no effect on anxiety behaviour but depressed locomotor activity at the highest dose tested of 1 mg kg−1. The A2 receptor antagonist, 1,3‐dimethyl‐l‐propargylxanthine (DMPX) had no effect on anxiety‐related measures or locomotion and did not modify the anxiolytic‐like activity of CPA.

Administration of DPMA in combination with anxiolytic doses of CPA prevented the anxiolytic‐like activity of the latter.

The results suggest that the selective activation of central A1 adenosine receptors induces anxiolytic‐like behaviour, while the activation of A2 sites causes locomotor depression and reduces the effects of A1 receptor activation. The absence of any effect of CPX alone suggests that the receptors involved in modulating behaviour in the elevated plus‐maze in mice are not activated tonically by endogenous adenosine.
Enhancement by cyclo‐oxygenase inhibitors of platelet‐activating factor production in thapsigargin‐stimulated macrophages
Authors: Watanabe Masako , Yamada Masateru , Mue Suetsugu , Ohuchi Kazuo
Published: July 2012

Thapsigargin stimulated the accumulation of cell‐associated platelet‐activating factor (PAF) and extracellular prostaglandin E2 (PGE2) in rat peritoneal macrophages. PAF in the conditioned medium was less than the detectable amount. To obtain further insight into the mechanism of PAF accumulation, the role of PGE2 in PAF accumulation was investigated.

When macrophages were incubated in medium containing thapsigargin (30 ng ml−1, 46.1 nM) and cyclo‐oxygenase inhibitors such as indomethacin, naproxen or ibuprofen, the PAF content of the cells at 10 min was increased in a concentration‐dependent manner in accordance with inhibition of PGE2 production. The stimulation of PAF accumulation by cyclo‐oxygenase inhibitors was significant at 10 min. Without stimulation by thapsigargin, cyclo‐oxygenase inhibitors did not increase PAF accumulation.

In thapsigargin‐stimulated macrophages, when PGE2 (10−7 m) was added to the medium, the cyclo‐oxygenase inhibitor‐induced stimulation of PAF accumulation at 10 min was markedly inhibited.

The accumulation of PAF induced by thapsigargin alone at 10 min was also inhibited by exogenous PGE2 (10−8 and 10−7 m), or arachidonic acid (10−6 and 10−5 m) in accordance with the increase in PGE2 production.

The accumulation of PAF induced by thapsigargin alone or by thapsigargin and indomethacin (10−6M) was inhibited by dibutyryl cyclic AMP.

These results indicate that the concurrently produced PGE2 in thapsigargin‐stimulated macrophages down‐regulates PAF accumulation by increasing intracellular cyclic AMP levels, and that cyclo‐oxygenase inhibitors increase PAF accumulation by inhibiting PGE2 production.
Enhancement of the hypotensive and vasodilator effects of endotoxaemia in conscious rats by the endothelin antagonist, SB 209670
Authors: Gardiner S.M. , March J.E. , Bennett T.
Published: July 2012

In conscious, chronically‐instrumented rats, the non‐selective endothelin antagonist, SB 209670 (10 μg kg−1 min−1), caused marked enhancement of the fall in mean arterial blood pressure during infusion of lipopolysaccharide (LPS) for 24 h (LPS alone=‐6 ± 3 mmHg; LPS + SB 209670 = −30 ±2 mmHg). This effect was accompanied by a conversion of the mesenteric vasoconstriction to a substantial mesenteric vasodilatation and an augmentation of the hindquarters vasodilatation, seen with LPS alone. Notably, the marked renal hyperaemic vasodilatation during LPS infusion was not affected significantly by SB 209670. These results indicate that endothelin, directly and/or indirectly, plays a pivotal role in the cardiovascular sequelae of endotoxaemia in conscious rats, and prevents marked hypotension, particularly by opposing mesenteric vasodilatation.
Inhibition by propofol (2,6 di‐isopropylphenol) of the N‐methyl‐D‐aspartate subtype of glutamate receptor in cultured hippocampal neurones
Authors: Orser Beverley A. , Bertlik Maria , Wang Lu‐Yang , MacDonald John F.
Published: July 2012

The effects of propofol (2,6 di‐isopropylphenol) on responses to the selective glutamate receptor agonists, N‐methyl‐D‐aspartate (NMDA) and kainate, were investigated in cultured hippocampal neurones of the mouse. Whole cell and single channel currents were recorded by patch‐clamp techniques. Drugs were applied with a multi‐barrel perfusion system

Propofol produced a reversible, dose‐dependent inhibition of whole cell currents activated by NMDA. The concentration of propofol which induced 50% of the maximal inhibition (IC50) was approximately 160 μm. The maximal inhibition was incomplete leaving a residual current of about 33% of the control response. This inhibitory action of propofol was neither voltage‐ nor use‐dependent

Analysis of the dose‐response relation for whole cell NMDA‐activated currents indicated that propofol caused no significant change in the apparent affinity of the receptor for NMDA

Outside‐out patch recordings of single channel currents evoked by NMDA (10 μm) revealed that propofol (100 HM) reversibly decreased the probability of channel opening but did not influence the average duration of channel opening or single channel conductance

Whole‐cell currents evoked by kainate (50 μ M) were insensitive to propofol (1 μm‐1 mM)

These results indicate that propofol inhibits the NMDA subtype of glutamate receptor, possibly through an allosteric modulation of channel gating rather than by blocking the open channel. Depression of NMDA‐mediated excitatory neurotransmission may contribute to the anaesthetic, amnesic and anticonvulsant properties of propofol.
β‐Adrenoceptor subtypes in young and old rat ventricular myocytes: a combined patch‐clamp and binding study
Authors: Cerbai E. , Guerra L. , Varani K. , Barbieri M. , Borea P.A. , Mugelli A.
Published: July 2012

We used electrophysiological and binding techniques to assess the presence of β1 and β2‐adrenoceptors (β1AR and β2AR) in rat cardiac myocytes and to determine their ratio during aging. Experiments were performed in left ventricular myocytes enzymatically dissociated from the heart of 3‐(young) or 22‐month‐old (old) Wistar Kyoto rats

In patch‐clamp experiments, myocytes from old rats showed a prolonged action potential duration (at −20 mV: 41.7±3.6 vs 26.2±3.1 ms; at −60 mV: 154.4 ± 17.7 vs 87.1 ±6.9 ms, P < 0.05) and an augmented membrane capacitance (an index of cell size) (271.7±20.2 vs 164.3± 14.6 pF, P < 0.05) compared to young rats. β2AR stimulation, achieved by superfusing myocytes with the selective β2AR agonist, zinterol (10 μm) or with (−)‐isoprenaline (1 μm) in the presence of the selective β1 AR antagonist, CGP 20712A (0.1 μm), significantly increased L‐type calcium current (Ica,L) in rat ventricular myocytes. The percentage increase was similar in both young and old rats, either with zinterol (26.9 ±3.6% and 24.2±2.8%, respectively) or isoprenaline plus CGP 20712A (30.4±3.7% and 22.4±4.1%, respectively). Isoprenaline alone (β1AR and β2AR stimulation) caused a much smaller increase in ICa,L in old rats (58.4±12.1%) than in younger ones (95.3±8.1%) (P=0.067)

The number of βAR mg−1 protein, measured with saturation binding assays of the non selective βAR antagonist [3H]‐CGP 12177 was 1989.4± 189.5 for 3‐ and of 1580.7± 161.5 for 22‐month‐old rats. Competition for [3H]‐CGP 12177 binding by CGP 20712A gave biphasic curves which demonstrated two classes of binding sites. Densities (as percentages of total PAR density), and affinities for the two binding sites were: 80.4 ±2.2% (Ki = 6.6 ±1.3 nM) β1AR and 19.6 ±2.2% (Ki = 6.9 ±2.2 μm) β2AR in young rats and 66.1 ±1.2% (Ki = 8.3 ±1.1 nM) β1 AR and 33.9 ±1.2% (Ki = 5.2 ± 0.6 μm) β2AR in old rats. The β1AR/β2AR ratio was significantly (P<0.01) reduced in old rats with respect to the younger ones

By combining electrophysiological and binding measurements, we calculated β1AR and β2AR densities as number of receptors per μm2 of cell surface. In old rats, β1AR density was significantly decreased compared to young rats (8.4±2.0 vs 15.4±3.7 receptors μm−2, P<0.05), while β2AR density remained unchanged at both 3 and 22 months (3.8 ±0.7 and 4.2 ±1.1 receptors μm−2, respectively)

Our results demonstrate that both β1AR and β2AR are functionally present in rat ventricular myocytes of young and old rats. The decreased responsiveness to βAR stimulation during aging appears to be associated with a selective reduction in the density of β1AR.
Discrimination by the NO‐trapping agent, carboxy‐PTIO, between NO and the nitrergic transmitter but not between NO and EDRF
Authors: Rand M.J. , Li C.G.
Published: July 2012

The effects of carboxy‐PTIO, a scavenger of free radical nitric oxide (NO), were studied on endothelium‐dependent relaxations of rat aorta and nitrergic nerve stimulation‐induced relaxations of anococcygeus muscle and gastric fundus strips to test the hypothesis that endothelium‐derived relaxing factor (EDRF) and the transmitter released by nitrergic nerves is free radical NO

Carboxy‐PTIO (10–300 μm) produced concentration‐dependent reductions of relaxations elicited by exogenous NO, and relaxations mediated by EDRF released by acetylcholine and ATP in rings of rat aorta. The inhibitory effect of carboxy‐PTIO was removed by washing the tissues

In the rat anococcygeus muscle, carboxy‐PTIO (10–300 μm) produced concentration‐dependent reductions of relaxations to exogenous NO; however, in concentrations up to 2000 μm it did not reduce relaxations elicited by nitrergic nerve stimulation (1–2 Hz), in fact, concentrations of 300 μm or more slightly enhanced them

In rat gastric fundus strips, carboxy‐PTIO (100 and 300 μm) reduced relaxations to exogenous NO, but relaxations elicited by stimulation of the nitrergic component of non‐adrenergic, non‐cholinergic nerves were not affected

These results suggest that EDRF is free radical NO and may be designated EDNO, but the transmitter released from nitrergic nerves does not appear to be identical to EDNO and may not be free radical NO.
Enhanced sympathetic neurotransmission in the tail artery of 1,3‐dipropyl‐8‐sulphophenylxanthine (DPSPX)‐treated rats
Authors: Karoon Parastoo , Rubino Annalisa , Burnstock Geoffrey
Published: July 2012

Sympathetic neurotransmission and noradrenaline content of the tail artery of Wistar rats treated for 7 days with the adenosine antagonist, 1,3‐dipropyl‐8‐sulphophenylxanthine (DPSPX), were examined

Systolic blood pressure of the DPSPX‐treated rats (164.0 ± 2.9 mmHg; n = 6) was significantly greater than saline‐treated controls (140.0 ±2.8 mmHg; n = 5) after 7 days treatment

The pressor responses of the arterial rings to transmural nerve stimulation (65 V, 0.1 ms, 4–64 Hz, for 1 s) were markedly enhanced in the DPSPX‐treated compared with the saline‐treated animals. Both noradrenergic and purinergic components of perivascular sympathetic neurotransmission were enhanced during DPSPX‐induced hypertension

Vasoconstrictor responses to exogenous noradrenaline (0.1–300 μm) and adenosine 5′‐triphosphate (0.01–3 mM) were unaffected after DPSPX treatment, indicating prejunctional alteration of sympathetic cotransmission during DPSPX‐induced hypertension

Acute exposure to DPSPX (10 μm) did not modify vasoconstrictor responses to transmural nerve stimulation, thus supporting the claim that the enhancement of sympathetic neurotransmission only results from long‐term DPSPX treatment

The noradrenaline content of the tail arteries of DPSPX‐treated (4.498 ±0.26 ng cm−1; n = 4) was significantly greater than saline‐treated (3.440 ± 0.30 ng cm−1; n = 5) animals

These findings show that chronic inhibition of the actions of endogenous adenosine by DPSPX results in an elevation of systolic blood pressure accompanied by enhanced sympathetic cotransmission and enhanced noradrenaline content of the rat tail artery.
Effect of (8–32) salmon calcitonin, an amylin antagonist, on insulin, glucagon and somatostatin release: study in the perfused pancreas of the rat
Authors: Silvestre R.A. , Salas M. , Rodriguez‐Gallardo J. , Garcia‐Hermida O. , Fontela T. , Marco J.
Published: July 2012

The 8–32 fragment of salmon calcitonin ((8–32) sCT) has been proposed as a highly selective amylin receptor antagonist.

In the present study, we have studied the influence of (8–32) sCT on the inhibitory effect of both amylin and its structural congener, calcitonin gene‐related peptide (CGRP), on insulin secretion in the rat perfused pancreas.

Both amylin and CGRP, at 75 pM, clearly inhibited glucose‐induced insulin release (by 80% and by 70%, respectively). Simultaneous infusion of 10 μm (8–32) sCT reversed the inhibitory effect of amylin (by 80%; P<0.05 vs. amylin experiments) but did not significantly affect the inhibition of glucose‐induced insulin output elicited by CGRP. Furthermore, at the same concentration (10 μm), (8–32) sCT alone potentiated the insulin response to 7 mM glucose (2.5 fold; P<0.05) whilst it did not affect glucagon or somatostatin secretion.

The observation that infusion of an amylin antagonist into the rat pancreas potentiates the insulin response to glucose, favours the concept of endogenous amylin as an inhibitor of insulin release.

Finally, as an amylin antagonist at the level of the β‐cell, (8–32) sCT might be considered of potential interest in experimental and clinical pharmacology.
Oestradiol‐induced relaxation of rabbit basilar artery by inhibition of voltage‐dependent Ca channels through GTP‐binding protein
Authors: Ogata Rika , Inoue Yoshihito , Nakano Hitoo , Ito Yushi , Kitamura Kenji
Published: July 2012

Effects of oestradiol on the electrical and mechanical properties of the rabbit basilar artery were investigated by use of microelectrode, patch‐clamp and isometric tension recording methods.

Oestradiol (10 μm‐100 μm) relaxed arterial tissue pre‐contracted by excess [K]0 solution (30 mM) in a concentration‐dependent manner. In Ca‐free solution, histamine (10 μm) and caffeine (20 mM) each produced a phasic contraction, but oestradiol (10 μm) did not significantly affect their amplitude.

Oestradiol (≥ 100 μm) did not change the resting membrane potential of the artery whether in the presence or absence of TEA (10 mM). Action potentials observed in the presence of 10 mM TEA were abolished by oestradiol (100 μm).

Oestradiol (1 μm‐100 μm) inhibited the voltage‐dependent Ba current in a concentration‐dependent manner. Oestradiol (100 μm) inhibited the Ba current observed in the presence of nicardipine (1 μm) more than that in the absence of nicardipine (to 31.0% vs 62.0% of control).

GTPγS (30 μm) in the pipette enhanced the inhibitory actions of oestradiol on the Ba current. On the other hand, with GDPβS (1 mM) in the pipette, oestradiol failed to inhibit the Ba current. Pertussis toxin (PTX 3 μg ml−1) in the pipette totally prevented the inhibitory action of oestradiol on the Ba current.

Oestradiol (≷ 100 μm) had no significant effect on the outward K currents evoked by a membrane depolarization.

These results strongly suggest that oestradiol relaxes arterial tissue by inhibition of voltage‐dependent Ca channels and that it inhibits both nicardipine‐sensitive and‐resistant Ca currents via a PTX‐sensitive GTP‐binding protein. The main target of oestradiol among the arterial Ca channels seems to be the nicardipine‐resistant Ca channel, rather than the nicardipine‐sensitive one.
Regulation of nitric oxide‐like activity by prostanoids in smooth muscle of the canine saphenous vein
Authors: Illiano Stephane , Marsault Robert , Descombes Jean‐Jacques , Verbeuren Tony , Vanhoutte Paul M.
Published: July 2012

Organ bath experiments and measurements of prostanoids were performed to investigate the presence of nitric oxide synthase in venous smooth muscle and its interaction with cyclo‐oxygenase.

In rings of canine saphenous vein without endothelium, the inhibitor of cyclo‐oxygenase, indomethacin (10 μm), induced contraction. NG‐nitro‐L‐arginine (100 μm) (L‐NOARG), an inhibitor of nitric oxide synthase did not affect the tone of rings of canine saphenous vein when administered alone. However, in the presence of indomethacin L‐NOARG (100 μm) induced further contraction.

Similar results were obtained in response to NG‐monomethyl‐L‐arginine (L‐NMMA)(300 μm or NG‐nitro‐L‐arginine methylester (L‐NAME)(100 μm).

When rings of canine saphenous vein without endothelium were contracted with phenylephrine (1 μm) instead of indomethacin, neither L‐NOARG or L‐NMMA induced further contraction.

When rings of canine saphenous vein without endothelium were contracted with noradrenaline (0.3 μm) in the presence of indomethacin (10 μm) plus L‐NOARG (100 μm), a relaxation to L‐arginine was observed. Transient relaxations to superoxide dismutase (150 u ml−1) were observed in all rings.

When rings of saphenous vein without endothelium were incubated with lipopolysaccharide (LPS) (100 μg ml−1) or interleukin −1β (10 u ml−1) the concentration‐contraction curve to noradrenaline was not affected.

Rings without endothelium released prostaglandin E2 and prostaglandin I2, as measured by radiommunoassay. The basal production was abolished by indomethacin and not affected by L‐NOARG.

These results suggest that when cyclo‐oxygenase is inhibited, a nitric oxide synthase activity is revealed in rings of canine saphenous vein without endothelium.
Mechanism of butyrate‐induced vasorelaxation of rat mesenteric resistance artery
Authors: Aaronson P.I. , McKinnon W. , Poston L.
Published: July 2012

The vasorelaxant effect of the sodium salt of the short chain fatty acid, butyrate, on preconstricted rat small mesenteric arteries (mean inner diameter approximately 300 μm) was characterized. Isometric force development was measured with a myograph, and intracellular pH (pHi) was simultaneously monitored, in arteries loaded with the fluorescent dye BCECF in its acetomethoxy form. Sodium butyrate (substituted isosmotically for NaCl) was applied to arteries after noradrenaline (NA) or high K+ contractures were established.

Arteries preconstricted with a concentration of NA inducing an approximately half maximal contraction were relaxed by 91.5±6.3% by 50 mmol 1−1 butyrate. This concentration of butyrate did not, however, cause a significant relaxation of contractures to a maximal (5 μmol 1−1) NA concentration, and also failed to relax signifcantly contractures stimulated by high (45 and 90 mmol 1−1) K+ solutions. Contractures elicited with a combination of NA (at a submaximal concentration) and 45 mmol 1−1 K+ were, however, markedly relaxed by butyrate.

Investigation of the concentration‐dependency of the butyrate‐induced relaxation of the half maximal NA response revealed an EC50 for butyrate of approximately 22 mmol 1−1.

Sodium butyrate (50 mmol 1−1) caused pHi to decrease from 7.25±0.02 to 6.89±0.08 (n=4, P<0.001). However, the vasorelaxant effect of butyrate on the submaximal NA contracture was not significantly modified when this fall in intracellular pH was prevented by the simultaneous application of NH4Cl.

Butyrate‐induced relaxation was also unaffected by endothelial denudation and inhibition of NO synthase with Nω‐nitro‐L‐arginine methyl ester (100 μmol 1−1).

The relaxation of the NA contracture by 50 mmol 1−1 sodium butyrate was abolished in arteries pretreated with the cyclic AMP antagonist Rp‐cAMPS (25 μmol 1−1).

We conclude that the butyrate‐induced relaxation of the NA contracture is independent of intracellular acidification. The ability of Rp‐cAMPS to abolish the butyrate relaxation indicates that stimulation of the cyclic AMP second messenger system may play an important role in mediating this effect.
Functional characterization of the 5‐HT terminal autoreceptor in the guinea‐pig brain cortex
Authors: Roberts Claire , Watson; Jeannette , Burton; Melanie , Price; Gary W. , Jones Brian J.
Published: July 2012

In guinea‐pig cerebral cortical slices in vitro we have shown that the rank order of potency of 5‐hydroxytryptamine (5‐HT), 5‐carboxamidotryptamine and sumatriptan for inhibition of electrically stimulated [3H]‐5‐HT release correlates well with published data on their 5‐HT1D receptor binding affinites.

Both the non‐selective 5‐HT1D receptor antagonist, methiothepin and the selective 5‐HT1D receptor antagonist, N‐[4‐methoxy‐3‐(4‐methyl‐1‐piperazinyl]phenyl]‐2′‐methyl‐4′‐(5‐methyl‐1,2,4‐oxadiazole‐3‐yl) [1,1‐biphenyl]4‐carboxamide (GR127935) increased stimulated [3H]‐5‐HT release per se and also attenuated agonist‐induced inhibition of [3H]‐5‐HT release. GR127935 (10nM‐100nM) produced a pA2 of 9.0 against 5‐HT, which is consistent with its 5‐HT1D receptor binding affinity.

From these findings we conclude that, in guinea‐pig cerebral cortex, the 5‐HT terminal autoreceptor is of the 5‐HT1D receptor subtype. However, three observations suggest the presence of multiple terminal autoreceptors: shallow inhibition curves to the agonists; a shallow Schild slope of GR127935 antagonism and differences in the maximal responses to 5‐HT between whole cortex and frontal cortex.
Selection of distinct conformational states of the 5‐HT3 receptor by full and partial agonists
Authors: van Hooft Johannes A. , Vijverberg Henk P.M.
Published: July 2012

5‐Hydroxytryptamine 5‐HT3 receptor‐mediated ion currents evoked by 5‐HT, quaternary 5‐HT (5‐HTQ), meta‐chlorophenylbiguanide (mCPBG), dopamine and tryptamine in N1E‐115 mouse neuroblastoma cells have been investigated in whole‐cell voltage clamp and single channel patch clamp experiments.

The concentration‐dependent activation and desensitization of the ion currents evoked by the agonists yield the potency order: mCPBG > 5‐HTQ  5‐HT > > tryptamine > dopamine, and the efficacy order: 5‐HT  mCPBG  5‐HTQ > > dopamine  tryptamine. Thus, 5‐HT, 5‐HTQ and mCPBG are full agonists, whereas dopamine and tryptamine are partial agonists at the 5‐HT3 receptor.

Full and partial agonists cause complete cross‐desensitization and activate single channels with similar conductances and open lifetimes. This shows that full and partial agonists act on the same population of 5‐HT3 receptors.

The time course of recovery from desensitization depends on the agonist used. Recovery from partial agonist‐induced desensitization is single exponential, whereas the desensitization induced by full agonists recovers with sigmoid kinetics, suggesting at least 3 steps between 4 states.

During the process of recovery from cross‐desensitization, the full agonists activate a larger fraction of the 5‐HT3 receptors than the partial agonists, irrespective of the agonist used to induce desensitization.

It is concluded that full and partial agonists induce distinct desensitized states and, during recovery from desensitization, recognize distinct conformations of unoccupied 5‐HT3 receptors. This conformational selection is likely to account for the different efficacies of full and partial 5‐HT3, receptor agonists.
Effects of levodropropizine on vagal afferent C‐fibres in the cat
Authors: Shams H. , Daffonchio L. , Scheid P.
Published: July 2012

Levodropropizine (LVDP) is an effective antitussive drug. Its effects on single‐unit discharge of vagal afferent C‐fibres were tested in anaesthetized cats to assess whether an inhibition of vagal C‐fibres is involved in its antitussive properties. Vagal C‐fibres, identified by their response to phenylbiguanide (PBG), were recorded via suction electrodes from the distal part of the cut vagus. Based on their response to lung inflation, C‐fibres were classified as pulmonary (19 fibres) or non‐pulmonary (6 fibres).

PBG increased the discharge rate of both C‐fibre types and activated a respiratory reflex causing apnoea. This reflex was abolished when the second vagus nerve was cut as well, while PBG‐mediated stimulation of the C‐fibres was not affected by vagotomy.

LVDP was administered intravenously and the C‐fibre response to PBG was compared with that before administration of the drug. LVDP reduced both the duration of apnoea and the response of the C‐fibre to PBG.

Comparison of the C‐fibre responses to PBG and to a mixture of PBG and LVDP revealed that the period of apnoea was shortened and the discharge rate of the C‐fibre reduced when LVDP was present.

The LVDP‐induced inhibition of the C‐fibre response to PBG was on average 50% in pulmonary and 25% in non‐pulmonary fibres.

These results suggest that LVDP significantly reduces the response of vagal C‐fibres to chemical stimuli. It is, thus, likely that the antitussive effect of LVDP is mediated through its inhibitory action on C‐fibres.
Mediation of the positive chronotropic effect of CGP 12177 and cyanopindolol in the pithed rat by atypical β‐adrenoceptors, different from β3‐adrenoceptors
Authors: Malinowska Barbara , Schlicker Eberhard
Published: July 2012

The influence of β1, β2, and β3‐adrenoceptor agonists and of CGP 12177 and cyanopindolol on heart rate and diastolic blood pressure was studied in the pithed rat.

The β1‐adrenoceptor agonist, prenalterol, increased heart rate and the β2‐adrenoceptor agonist, fenoterol, caused a fall in blood pressure. The effect of prenalterol was antagonized by the β1‐adrenoceptor antagonist, CGP 20712 0.1 μmol kg−1 and the action of fenoterol was attenuated by the β2‐adrenoceptor antagonist, ICI 118551 0.1 μmol kg−1. Both effects were markedly diminished by the non‐selective β‐adrenoceptor antagonist, bupranolol 0.1 μmol kg−1.

The non‐selective β‐adrenoceptor agonist, isoprenaline, three β3‐agonists as well as CGP 12177 and cyanopindolol elicited a positive chronotropic effect, exhibiting the following pEDA60 values (negative log values of the doses increasing heart rate by 60 beats min−1): isoprenaline 10.4, CGP 12177 8.3, cyanopindolol 7.2, BRL 37344 6.9, ZD 2079 5.2 and CL 316243 <5.

CGP 20712 0.1 μmol kg−1, given together with ICI 118551 0.1 μmol kg−1, markedly attenuated the positive chronotropic effect of isoprenaline, BRL 37344, ZD 2079 and CL 316243 without affecting the increase in heart rate produced by CGP 12177 and cyanopindolol.

The positive chronotropic effect of CGP 12177 and cyanopindolol was attenuated by CGP 20712, 1 and 10 μmol kg−1 and bupranolol, 10 μmol kg−1 but was not affected by ICI 118551, 10 μmol kg−1. The effect of CGP 12177 was also not changed by BRL 37344 1 μmol kg−1, ZD 2079 10 μmol kg−1, CL 316243 10 μmol kg−1, the α1‐adrenoceptor antagonist, prazosin 1 μmol kg−1 and the 5‐hydroxytryptamine 5‐HT2A receptor antagonist, ketanserin 3 μmol kg−1.

CGP 12177 0.002 μmol kg−1 and cyanopindolol 0.003 μmol kg−1 shifted to the right the dose‐response curve of prenalterol for its positive chronotropic effect. The ‐log values of the doses causing a twofold shift to the right were 9.6 and 9.5, respectively.

Isoprenaline 0.00001‐0.001 μmol kg−1, BRL 37344 0.01‐1 μmol kg−1 and CGP 12177 0.1 μmol kg−1 caused a fall in diastolic blood pressure which was markedly attenuated by combined administration of CGP 20712 and ICI 118551, 0.1 μmol kg−1 each.

CGP 12177 0.01 and 0.1 μmol kg−1 and cyanopindolol 1 μmol kg−1 elicited an increase in diastolic blood pressure. CGP 20712, ICI 118551, bupranolol and, in the case of CGP 12177, also BRL 37344, ZD 2079, CL 316243, prazosin and ketanserin did not influence this effect.

In conclusion, the positive chronotropic effect of CGP 12177 and cyanopindolol is not mediated via β1‐, β2‐, β3‐, α1‐adrenoceptors or 5‐HT2A receptors. This effect may involve atypical β‐adrenoceptors, similar or identical to those described by Kaumann (1989) in isolated heart preparations.
Hyperpolarization and inhibition of contraction mediated by nitric oxide released from enteric inhibitory neurones in guinea‐ pig taenia coli
Authors: Ward Sean M. , Dalziel Hugh H. , Khoyi Mohammed A. , Westfall Alison S. , Sanders Kenton M. , Westfall David P.
Published: July 2012

. Inhibition of nitric oxide synthase by NG‐nitro‐L‐arginine (L‐NNA) reduced the neurogenic relaxation of precontracted taenia coli only in the absence of atropine. The membrane hyperpolarization associated with the neurogenic relaxation was also reduced by inhibition of NOS only when atropine was absent.

. The membrane hyperpolarization associated with the neurogenic relaxation of the taenia coli was inhibited by oxyhaemoglobin only in the absence of atropine. In the presence of atropine, oxyhaemoglobin did not reduce the i.j.p. or nerve‐evoked relaxation.

. Inhibition of NOS by L‐NNA did not affect the overflow of [3H]‐ACh in response to electrical field stimulation (EFS), suggesting that, under the conditions of our experiments, endogenous NO did not modulate release of ACh. Sodium nitroprusside also had no effect on the neurogenic overflow of [3H]‐ ACh; however, noradrenaline significantly reduced [3H]‐ACh overflow.

. In summary, the postjunctional effects of neurally‐released NO are not apparent in guinea‐pig taenia coli when atropine is present. This implies muscarinic regulation of NO release or muscarinic regulation of another excitatory substance, such as tachykinin(s), that, when blocked, masks the postjunctional effects of NO. These data, together with previous studies, suggest a possible regulatory role for NO in enteric neurotransmission that may be more prominent in some species or tissues than others.
Enhanced contractile responses of arteries from streptozotocin diabetic rats to sodium fluoride
Authors: Weber Lynn P. , Chow Wing Lim , Abebe Worku , MacLeod Kathleen M.
Published: July 2012

. Previous studies from this laboratory have demonstrated that α1‐adrenoceptor‐mediated increases in tension and phosphoinositide metabolism are enhanced in the aorta and mesenteric arteries from diabetic rats. The purpose of the present investigation was to determine whether contractile responses to sodium fluoride (NaF), which directly stimulates GTP‐binding proteins (G‐proteins), are also enhanced in diabetic arteries.

. NaF (1–20 mM) in the presence of 10 μm aluminium chloride produced slowly developing, concentration‐dependent contractions in mesenteric arteries from three month streptozotocin‐diabetic (60 mg kg−1, i.v.) male Wistar rats and age‐matched control rats. The maximum contractile response but not the sensitivity to NaF was significantly greater in mesenteric arteries from diabetic than from control rats, as was the response to noradrenaline (NA). Maximum contractile responses of aorta and caudal artery from diabetic rats to NaF were also significantly enhanced.

. Removal of the endothelium and denervation with 6‐hydroxydopamine did not significantly alter the maximum contractile response of mesenteric arteries from either control or diabetic rats to NaF. Similarly, NaF had no effect on cyclic AMP levels in aorta, and no difference in cyclic AMP levels, either basally or in the presence of NaF, was detected between control and diabetic rat aorta.

. Contractile responses of mesenteric arteries from both control and diabetic rats to NaF were diminished in calcium‐free Krebs solution, but the NaF response remained significantly elevated in mesenteric arteries from diabetic rats compared to control.

. Ryanodine (30 μm) which depletes intracellular calcium stores, nifedipine (3 μm) which blocks dihydropyridine‐sensitive calcium channels and calphostin C (0.5 μm) which selectively inhibits protein kinase C, all significantly inhibited maximum contractile responses of mesenteric arteries from control and diabetic rats to NaF. There were no significant differences between control and diabetic arteries in the relative magnitude of the inhibition produced by the three antagonists.

. These data suggest that there may be increased activation of the same signalling processes that mediate NA‐stimulated vasoconstriction, perhaps contraction‐associated G‐proteins or the effectors coupled to these G‐proteins, in response to NaF in mesenteric arteries from diabetic rats. This may also be responsible for the enhanced contractile responses of these arteries to α1‐adrenoceptor stimulation.
Spinal 5‐HT2 receptor‐mediated facilitation of pudendal nerve reflexes in the anaesthetized cat
Authors: Danuser Hansjorg , Thor Karl B.
Published: July 2012

. 5‐Hydroxytryptamine (5‐HT) is intimately associated with central sympathetic and somatic control of the lower urinary tract. The sympathetic and somatic innervation of the lower urinary tract is conveyed through efferent axons of the hypogastric and pudendal nerves, respectively.

. The present study examined the effects of 2,5‐dimethoxy‐4‐iodophenylisopropylamine (DOI), a 5‐HT2 receptor subtype‐selective agonist, on evoked potentials recorded from the central ends of the hypogastric and pudendal nerves in response to electrical stimulation of afferent fibres in the pelvic and pudendal nerves, respectively. Various spinalization paradigms were employed to localize the site of action. All cats were pretreated with xylamidine (1 mg kg−1), a peripherally‐restricted 5‐HT2 receptor antagonist.

. In acute spinal cats, DOI (0.01–3 mg kg−1, i.v.) reliably produced dose‐dependent increases in the pudendal nerve reflex (to 228±31% of control). These increases were reversed by the 5‐HT2 receptor‐selective antagonist, LY53857 (0.3‐3 mg kg−1, i.v.). On the other hand, in spinally‐intact cats, DOI produced no significant changes in the pudendal reflex. However, within minutes of spinalization of DOI‐pretreated cats, a marked increase (to 221±16% of control) in the pudendal reflex was observed which could be reversed by LY53857. No significant effects were observed on hypogastric reflexes in either acute spinal or spinally‐intact cats following DOI administration. No effects were seen in either spinally‐intact or acute spinal animals when LY53857 was administered as the initial drug.

. These results indicate that activation of spinal 5‐HT2 receptors facilitates pudendal reflexes. In spinally‐intact cats, it is hypothesized that DOI activates supraspinal pathways that mediate inhibition of the pudendal reflexes and counteracts the facilitatory effects of spinal 5‐HT2 receptor activation.
Nitric oxide inhibition of basal and neurogenic mucus secretion in ferret trachea in vitro
Authors: Ramnarine S.I. , Khawaja A.M. , Barnes P.J. , Rogers D.F.
Published: July 2012

In order to examine the role of nitric oxide (NO) on airway mucus secretion we studied the effects of the nitric oxide synthase (NOS) inhibitor l‐NG‐monomethyl‐l‐arginine (l‐NMMA), a novel nitric oxide donor, (±)‐(E)‐ethyl‐2‐[(E)‐hydroxyimino]‐5‐nitro‐3‐hexeneamide (FK409), and the NO precursor l‐arginine on basal mucus secretion in the ferret trachea in vitro in Ussing chambers. We also determined the effects of these agents upon secretion induced by electrical stimulation of nerves or by acetylcholine (ACh). We used 35SO4 as a mucus marker.

l‐NMMA (0.01‐1 mM) increased basal output of 35SO4‐labelled macromolecules with a maximal increase above baseline of 248% at 0.1 mM l‐NMMA. l‐Arginine (1 mM) alone had no significant effect on basal secretion but reversed the potentiating effect of l‐NMMA on basal secretion. l‐NMMA‐induced increases in basal mucus secretion were sustained for at least 30 min in the continuing presence of the NOS inhibitor. In contrast to the potentiating effects of l‐NMMA, FK409 (100 nM) reduced basal secretion by 60% (at 1 nM and at 10 nM it was without effect).

Electrical stimulation (50 V, 10 Hz, 0.5 ms for 5 min) increased 35SO4 output by 174%. l‐NMMA (1 and 10 mM) present during stimulation of tracheal segments resulted in significant potentiations of 214% and 116%, respectively, of the neurogenic response. The potentiated response to 10 mM l‐NMMA was reversed by l‐arginine (1 mM). At this dose l‐arginine had no effect itself on basal secretion. In contrast to the potentiating effects of l‐NMMA on neurogenic secretion, FK409 at 10 nM and 100 nM inhibited the neurogenic response by 98% and 99%.

At all concentrations tested, neither l‐NMMA (0.01 mM − 1 mM) nor FK409 (1 − 100 mM) had any significant effect on ACh‐induced mucus secretion.

These observations lead us to conclude that nitric oxide, derived from constitutive NO synthase, acts as an endogenous inhibitor of both basal and neurogenic mucus secretion in ferret trachea in vitro.
Mode of action of bradycardic agent, S 16257, on ionic currents of rabbit sinoatrial node cells
Authors: Bois Patrick , Bescond Jocelyn , Renaudon Barbara , Lenfant Jacques
Published: July 2012

The effect of the bradycardic agent S 16257 on the main ionic mechanisms of diastolic depolarization in sinoatrial node cells isolated from rabbit heart, was investigated by the patch‐clamp technique in whole‐cell and macro‐patch recordings.

In whole‐cell conditions, S 16257 induced a marked exponential use‐dependent blockade of the hyperpolarization‐activated If current, without shift of the voltage range of its activation curve. The rate of block increased with the drug concentration. The IC50 for the block of If was 2.8 × 10−6 m.

A similar use‐dependent decline of If was obtained with 3 μm S 16257, in cell‐attached and in inside‐out macro‐patch configurations, suggesting that the bradycardic agent interacts with If channels from the inside of the cell.

A high concentration of S 16257 (10 μm) had no detectable effect on T‐type calcium current and slightly decreased L‐type calcium current (−18.12±0.66%), without significant use‐dependent blockade.

S 16257 had no effect on the delayed outward potassium current IK at 3 μm and slightly decreased it only at high concentrations, −16.3±1.2% at 10 μm. In contrast, zatebradine, another bradycardic agent, reduced IK by 20.3±2.5% at 3 μm.

In conclusion, S 16257 may lower heart rate without significant negative inotropic action. In comparison with zatebradine, S 16257 had less effect on IK suggesting less prolongation of repolarization time.
A comparative study of the antithrombotic effect of aurintricarboxylic acid on arterial thrombosis in rats and guinea‐pigs
Authors: Takiguchi Yoshiharu , Shimazawa Masamitsu , Nakashima Mitsuyoshi
Published: July 2012

. The antithrombotic effect of aurintricarboxylic acid (ATA) which inhibits binding of von Willebrand factor (vWF) to platelet glycoprotein lb (GPlb) receptor was evaluated in photochemically‐induced thrombosis models in the femoral artery of rats and guinea‐pigs.

. ATA at a dose of 10 mg kg−1 significantly prolonged the time required for thrombotic occlusion of the artery in rats. The antithrombotic efficacy was associated with a significant inhibition of platelet retention and ex vivo botrocetin‐induced platelet aggregation.

. On the other hand, in guinea‐pigs, ATA at the same dose inhibited the platelet retention and the platelet aggregation, but did not prevent thromboocclusion.

. ATA inhibited aggregation of washed platelets from rats or guinea‐pigs in response to botrocetin and thrombin in a dose‐dependent manner (1–30 μm), and to the same extent.

. ATA moderately increased activated partial thromboplastin time and bleeding time in both species.

. These results indicate that vWF may play a role in the development of occlusive arterial thrombosis in the rat, but not in the guinea‐pig.

. The antithrombotic activity of ATA may partly arise from its inhibitory effect on thrombin, in addition to that on the vWF‐GPlb pathway.
Direct positive chronotropic effects of angiotensin II and angiotensin III in pithed rats and in rat isolated atria
Authors: Li Q. , Zhang J. , Pfaffendorf M. , van Zwieten P.A.
Published: July 2012

. The direct positive chronotropic effects of angiotensin II (AII) and its degradation products angiotensin III (AIII) and angiotensin IV (AIV) were established in pithed rats and in rat spontaneously beating right atria.

. In pithed rats, AII, AIII and AIV caused dose‐dependent tachycardia with similar maximal responses (110 beats min−1). The β‐adrenoceptor antagonist propranolol (3.37 × 10−6 mol kg−1) but not the α1‐adrenoceptor antagonist prazosin (2.38 × 10−7 mol kg−1) significantly reduced these effects (P < 0.05; n = 7–8), but 20–25% of the responses could not be blocked by propranolol.

. In isolated atria, AII, AIII and AIV caused concentration‐dependent increases in beating rate with similar maximal responses to AII and AIII (34.3 ± 0.4 and 34.7 ± 0.4 beats min−1; n = 9–10), and a lower maximal response to AIV (26.8 ± 0.6 beats min−1; P < 0.05; n = 8). AIII was about 9 times less potent than AII, whereas AIV proved approximately 3800 times less potent than AII. Neither propranolol (1 μm) nor prazosin (1 μm) could influence the effects of the angiotensin peptides.

. In isolated atria, the selective AT1‐receptor antagonist, losartan (10, 100 and 300 nM) caused parallel rightward shifts of the concentration‐response curves for AII and AIII, whereas the selective AT2‐receptor antagonist PD123177 (1 μm) did not influence the effects of AII and AIII. The aminopeptidase‐A and ‐M inhibitor amastatin (10 μm), significantly steepened the slope of the AIII curves and increased the potency of AIII about 6 fold. Amastatin did not influence the responses to AII.

. Our results indicate that both in vivo and in vitro, exogenous AII and AIII induced a direct dose‐dependent chronotropic effect, which is independent of the adrenergic system. This chronotropic effect is mediated by AT1‐subtype receptors.
Inhibitory action of nociceptin on spinal dorsal horn neurones of the rat, in vivo
Authors: Stanfa L.C. , Chapman V. , Kerr N. , Dickenson A.H.
Published: July 2012

Intrathecally administered nociceptin (5, 50, 225 μg) dose‐relatedly inhibited the C‐fibre evoked wind‐up and post‐discharge of dorsal horn neurones, but not the baseline C‐fibre evoked responses. Spinal naloxone 50 μg, but not 10 μg, reversed the effects of nociceptin. Thus the antinociceptive role of nociceptin in the spinal cord differs from that of classical opioids.
The effect of the calcium‐antagonist nitrendipine on intracellular calcium concentration in endothelial cells
Authors: Salameh Aida , Schomecker Gunhild , Breitkopf Katja , Dhein Stefan , Klaus Wolfgang
Published: July 2012

Nitrendipine induces NO‐release from coronary vascular endothelium presumably by activating endothelial NO‐synthase. We have investigated whether this effect may be mediated by an influence on the intracellular calcium in endothelial cells.

Bovine aortic endothelial cells (BAEC) were incubated with Fura‐2/AM (1 μm) for 30 min and Fura‐2 fluorescence was measured at 510 nm in response to chopped excitation with both 340 and 380 nm. The ratio 340/380 nm (known to reflect changes in intracellular calcium) was calculated from these data.

Nitrendipine (0.1 to 100 μm) led to a significant, concentration‐dependent, monophasic increase in [Ca2+]iin suspended BAEC by 11±2 nM (0.1 μm), 23±3 nM (1 μm), 34±4 nM (10 μm) and by 47±5 nM (100 μm) from a control level of 118±10 nM.

This elevation of intracellular calcium was prevented by pretreatment of BAECs with gadolinium (100 μm) or by incubation with calcium free saline solution. In contrast, the application of 0.3 μmthapsigargin did not abolish the nitrendipine‐induced calcium signal. In additional experiments it was shown that the nitrendipine‐induced NO‐release (as measured with the oxy‐haemoglobin‐method could also be inhibited by gadolinium and was absent in calcium‐free solution.

Thus, nitrendipine elevates intracellular calcium in suspended BAECs in a concentration‐dependent manner. This elevation is mainly due to a gadolinium‐sensitive calcium influx from the extracellular space rather than a calcium release from intracellular stores.