bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mediation by M3‐muscarinic receptors of both endothelium‐dependent contraction and relaxation to acetylcholine in the aorta of the spontaneously hypertensive rat
Authors: Boulanger Chantal M. , Morrison Keith J. , Vanhoutte Paul M. 
Published: July 2012

Experiments were designed to characterize the subtype(s) of endothelial muscarinic receptor that mediate(s) endothelium‐dependent relaxation and contraction in the aorta of spontaneously hypertensive rats (SHR).
Rings of SHR aorta with endothelium were suspended in organ baths for the measurement of isometric force. Ecothiopate (an inhibitor of acetylcholinesterase) was present throughout the experiments. Endothelium‐dependent contraction to acetylcholine was studied in quiescent aortic rings in the presence of NG‐nitro‐l‐arginine (to prevent the formation of nitric oxide). Endothelium‐dependent relaxation to acetylcholine was obtained during contraction to phenylephrine and in the presence of indomethacin (to inhibit cyclo‐oxygenase activity). Responses to acetylcholine were assessed against the non‐preferential muscarinic receptor antagonist, atropine, and the preferential antagonists pirenzepine (M1), methoctramine (M2) and 4‐diphenylacetoxy‐N‐methylpiperidine methobromide (4‐DAMP; M3).
The potency of acetylcholine in inducing endothelium‐dependent contraction was 6.54 ± 0.07 (EC50). Atropine, pirenzepine, methoctramine and 4‐DAMP displayed competitive antagonism towards the endothelium‐dependent contraction to acetylcholine. The pA2 values for these muscarinic receptor antagonists were estimated from Arunlakshana‐Schild plots to be (– log m) 9.48 ± 0.07, 6.74 ± 0.22, 6.30 ± 0.20 and 9.39 ± 0.22 respectively. The potency of acetylcholine in inducing endothelium‐dependent relaxation was 7.82 ± 0.09 (IC50). Atropine, pirenzepine and 4‐DAMP displayed competitive antagonism towards the endothelium‐dependent relaxation to acetylcholine but methoctramine had no effect. The pA2 values for atropine and 4‐DAMP for the relaxation to acetylcholine were estimated from Arunlakshana‐Schild plots to be (– log m) 9.15 ± 0.23 and 9.63 ± 0.28, respectively. These results suggest that the muscarinic M3 receptor subtype mediates both endothelium‐dependent relaxation and contraction to acetylcholine in SHR aorta.
Pilocarpine‐induced relaxation of rat tail artery by a non‐cholinergic mechanism and in the absence of an intact endothelium
Authors: Tonta M.A. , Partington Helena C. , Tare M. , Coleman H.A. 
Published: July 2012

The partial muscarinic agonist, pilocarpine, evoked concentration‐dependent relaxation with an EC50 of 2.4 × 10−3 m in isolated segments of rat tail artery that were constricted with phenylephrine (10−8 to 2 × 10−7 m). Acetylcholine also evoked concentration‐dependent relaxation but was more potent than pilocarpine (EC50, 6.5 × 10−7 m).
The concentration‐relaxation curves for pilocarpine were not affected by the muscarinic antagonists, atropine (10−9 m) or pirenzepine (5 × 10−7 m), while the concentration‐relaxation curves for acetylcholine‐evoked relaxation of the same tissues were shifted some 10 fold to the right by these concentrations of atropine and pirenzepine.
Acetylcholine failed to evoke relaxation following removal of the endothelium. The smooth muscle of the rat tail artery was some 10 fold more sensitive to the relaxing action of pilocarpine following denudation of the endothelium.
The effects of pilocarpine and acetylcholine on membrane potential were studied in tissues that were depolarized to − 39 ± 1 mV with phenylephrine (5 × 10−8 to 2 × 10−7 m). In intact tissues, pilocarpine caused hyperpolarization, an effect that persisted in the presence of muscarinic antagonists. Acetylcholine also evoked hyperpolarization.
Following removal of the endothelium, pilocarpine (10−5 to 10−3 m) evoked hyperpolarization in 6 of 15 preparations and a decrease in the frequency of action potentials in the remainder. Both of these responses were associated with relaxation.
The effects of pilocarpine were compared with other agents that evoke endothelium‐independent relaxation. The concentration‐relaxation curves in response to pilocarpine and nitroprusside were shifted to the right by ferricyanide (10−5 m) and methylene blue (10−5 m). Glibenclamide (10−6 m) was without effect on the hyperpolarization and relaxation evoked by pilocarpine (10−4 to 10−3 m).
Thus, pilocarpine evokes relaxation of rat tail artery independently of the cholinergic system and it is suggested that this is achieved by decreasing the frequency of action potentials in the smooth muscle.
Relationship between plasma lipids and palmitoyl‐CoA hydrolase and synthetase activities with peroxisomal proliferation in rats treated with fibrates
Authors: Alegret M. , Ferrando R. , Vázquez M. , Adzet T. , Merlos M. , Laguna J.C. 
Published: July 2012

The time‐course of the effect of clofibrate (CFB), bezafibrate (BFB) and gemfibrozil (GFB) on lipid plasma levels and palmitoyl‐CoA hydrolase and synthetase activities, as well as the correlations with the peroxisomal proliferation phenomenon have been studied in male Sprague‐Dawley rats.
The administration of the three drugs caused a significant reduction in body weight gain, accompanied with a paradoxical increase in food intake in groups treated with BFB and GFB.
Drug treatment produced gross hepatomegaly and increase in peroxisomal β‐oxidation, and these parameters were strongly correlated. The order of potency was BFB > CFB ≥ GFB.
Both plasma cholesterol (BFB ∼ CFB > GFB) and triglyceride (BFB ∼ GFB > CFB) levels were reduced in treated animals. There was an inverse correlation between these parameters and peroxisomal β‐oxidation, although the peroxisomal proliferation seemed to explain only a small part of the hypolipidemic effect observed.
Cytosolic and microsomal (but not mitochondrial) palmitoyl‐CoA hydrolase activities were increased by the three drugs (BFB > CFB > GFB), probably by inducing the hydrolase I isoform, which is insensitive to inhibition by fibrates in vitro. The increased hydrolase activities were directly and strongly correlated with peroxisomal β‐oxidation.
Palmitoyl‐CoA synthetase activity was also increased by the treatment with fibrates (BFB > CFB >GFB), probably as a consequence of the enhancement of hydrolase activities.
Some of the effects of fibrate treatment can be explained, at least in part, in terms of peroxisomal induction and caution should be exercised in the extrapolation of these results to species, such as man, that are insensitive to peroxisomal proliferation.
Effects of chronic intravenous infusions of dopexamine and isoprenaline to rats on D1‐, β1‐ and β2‐receptor‐mediated responses
Authors: Martin S.W. , Broadley Kenneth J. 
Published: July 2012

Rats received intravenous infusions of dopexamine, an agonist with selectivity for D1‐dopamine receptors and β2‐adrenoceptors (240 μg kg−1 h−1), isoprenaline, a β1‐ and β2‐adrenoceptor agonist (40 μg kg−1 h−1) or vehicle (isotonic saline at pH 2.5) for 7 days via subcutaneously implanted osmotic minipumps. Tissues were then removed for determination of functional responsivenss to β1‐adrenoceptor, β2‐adrenoceptor and dopamine D1‐receptor stimulation.
The β1‐adrenoceptor‐mediated responses of the spontaneously beating right atrium (increase in rate) and paced left atrium (increase in tension) showed significant reductions in sensitivity to isoprenaline following isoprenaline infusion. The EC50 values were significantly increased from 5.6 to 17.7 nm in right atria and from 7.4 to 27.1 nm in left atria. The maximum rate increase of right atria was also significantly less after isoprenaline infusion compared with controls (164.0 and 251.9 beats min−1, respectively) but the maximum tension responses of left atria were not significantly different. After infusion with dopexamine, however, there was no change in sensitivity of the left or right atria to β1‐adrenoceptor stimulation by isoprenaline.
β2‐Adrenoceptor‐mediated relaxation responses to isoprenaline of the pulmonary artery, constricted with noradrenaline (6 × 10−8 m), showed no significant difference in maximum response or EC50 in tissue from isoprenaline‐ or dopexamine‐infused rats compared with vehicle‐infused controls. β2‐Adrenoceptor‐mediated vasodilator responses were also examined in the kidney perfused with the thromboxane A2 analogue, U46619 (7.1 × 10−8 m) to raise perfusion pressure. As with the pulmonary artery, there was no significant difference in ED50 or maximum response to isoprenaline in kidneys from isoprenaline‐infused animals compared with vehicle controls.
The D1‐receptor‐mediated vasodilator responses to dopamine of the kidney perfused with U46619 were reduced after infusion of rats with dopexamine. The maximum fall in perfusion pressure (16.0 mmHg) and ED50 value (5.2 μg) were significantly different from those after vehicle infusion (31.5 mmHg; 1.5 μg).
These results show that functional responses mediated via β1‐adrenoceptors and D1‐receptors are reduced by intravenous infusions of isoprenaline and dopexamine, respectively. In contrast, the β2‐adrenoceptor‐mediated vasodilator responses of the pulmonary artery and kidney are not reduced by these agonists. Thus, under identical conditions, there appears to be selective down‐regulation of peripheral β1‐ and D1‐receptors, but not of β2‐adrenoceptors.
Block by capsaicin of voltage‐gated K+ currents in melanotrophs of the rat pituitary
Authors: Kehl S.J. 
Published: July 2012

Whole‐cell recordings of macroscopic K+ currents were made from acutely dissociated and cultured melanotrophs isolated from the pars intermedia of the adult rat pituitary.
In acutely dissociated cells, external capsaicin reversibly decreased the amplitude both of the fast‐activating, fast‐inactivating potassium current IK(f) and the slowly‐activating, slowly‐inactivating potassium current IK(s). To simplify the investigation of the mechanism of action of capsaicin experiments were conducted on cultured melanotrophs that express only IK(s).
In control cells the activation rate and the amplitude of IK(s) increased with depolarization and the current showed very little inactivation at any voltage during pulses lasting for 100–300 ms. In capsaicin, the decrease of the current amplitude was associated with an increased rate of current decay (‘inactivation’). At a given voltage, the extent and the rate of the capsaicin‐induced inactivation was proportional to the capsaicin concentration; and, at a given concentration, the extent and rate of the inactivation increased with membrane depolarization.
The fit of the Hill equation to data derived from the steady‐state block of IK(s) evoked at 10 mV indicated an equilibrium dissociation constant (KD) of 17.4 μm (95% confidence limits 15.8–19.0) and a Hill coefficient of 1.8 (95% Cl 1.5–2.2) suggesting that at least two molecules of capsaicin must bind to the channel to block it.
Analysis of the voltage‐dependence of the steady‐state block in 100 μm capsaicin showed that half‐maximal block occurred at − 29 ± 2 mV (n = 10). Two‐pulse experiments designed to study the time‐dependence of channel block in 100 μm capsaicin indicated that the blocking kinetics were well fitted by a single exponential and that the rate of block increased with depolarization. The value for τblock at 0 mV was 24 ± 7 ms (n = 4).
Recovery from block in 100 μm capsaicin was also well fitted by a single exponential. The recovery time constant (τrecovery) was 708 ± 140 ms at − 50 mV, 70 ± 6 ms at − 70 mV and 19 ± 1.3 ms at − 90 mV (n = 4).
In 50–100 μm capsaicin, the decay of the tail current was biexponential, the values for τfast and τslow being, respectively, less than and greater than the single time constant fitted to the control tail current. Inward and outward K+ currents were equally affected by capsaicin.
Most of these effects of capsaicin on the IK(s) of melanotrophs can be accounted for by a kinetic scheme in which capsaicin binds to and blocks open K+ channels.
Effects of DAU 6215, a novel 5‐hydroxytryptamine3 (5‐HT3) antagonist on electrophysiological properties of the rat hippocampus
Authors: Passani M.B. , Pugliese A.M. , Azzurrini M. , Corradetti R. 
Published: July 2012

The aim of the present study was to test the effects of DAU 6215 (endo‐N‐(8‐methyl‐8‐azabicyclo‐[3.2.1]‐octo‐3‐yl)‐2,3‐dihydro‐2‐oxo‐1H‐benzimidazole‐1‐carboxamide hydrochloride), a newly synthesized, selective 5‐hydroxytryptamine3 (5‐HT3) antagonist, on the cell membrane properties and on characterized 5‐HT‐mediated responses of pyramidal neurones in the hippocampal CA1 region.
Administration of DAU 6215, even at concentrations several hundred fold its Ki, did not affect the cell membrane properties of pyramidal neurones, nor modify extracellularly recorded synaptic potentials, evoked by stimulating the Schaffer's collaterals.
Micromolar concentrations (15–30 μm) of 5‐HT elicited several responses in pyramidal neurones that are mediated by distinct 5‐HT receptor subtypes. DAU 6215 did not antagonize the 5‐HT1A‐induced membrane hyperpolarization and conductance increase, a response that was blocked by the selective 5‐HT1A antagonist NAN‐190 (1‐(2‐methoxyphenyl)‐4‐[4‐(2‐phtalamido)butyl‐piperazine). Similarly, DAU 6215 did not affect the membrane depolarization and decrease in amplitude of the afterhyperpolarization, elicited by the activation of putative 5‐HT4 receptors.
5‐HT increased the frequency of spontaneous postsynaptic potentials (s.p.s.ps) recorded in pyramidal neurones loaded with chloride. In agreement with previous observations, most of the s.p.s.ps were reversed GABAergic events, produced by the activation of 5‐HT3 receptors on interneurones, because they persisted in the presence of the glutamate NMDA and non NMDA antagonists, d‐aminophosphonovaleric acid (APV; 50 μm) and 6,7‐dinitroquinoxaline‐2,3‐dione (DNQX; 25 μm), and were elicited by the selective 5‐HT3 agonist, 2‐methyl‐5‐HT (2‐Me‐5‐HT, 50 μm).
The increase in frequency of s.p.s.ps induced by 5‐HT was significantly antagonized by DAU 6215 in 70% of the cases, whereas the 5‐HT3 antagonist always suppressed the effect of 2‐Me‐5‐HT, at concentrations as low as 60 nm.
The antagonistic effect of DAU 6215 was also tested on the 5‐HT3‐mediated block of induction of long‐term potentiation (LTP), elicited by a primed burst (PB) stimulation. Extracellular recordings showed that low concentrations (60 nm) of DAU 6215 suppressed the inhibitory action of 5‐HT on PB‐induced LTP, without affecting the 5‐HT1A‐induced reduction in the amplitude of the population spike.
These results provide evidence that DAU 6215 is an effective antagonist of the 5‐HT3‐mediated responses in the central nervous system and may offer a cellular correlate for the pharmacological effects of DAU 6215 as an anxiolytic and cognition enhancer.
Anti‐inflammatory and analgesic activity of the bradykinin antagonist, icatibant (Hoe 140), against an extract from Porphyromonas gingivalis
Authors: Griesbacher Thomas , Sutliff Roy L. , Lembeck Fred 
Published: July 2012

Porphyromonas gingivalis is one of the bacteria likely to be related to pain in periodontitis. Several enzymes isolated from P. gingivalis have been reported to have kininogenase activity. Since kinin release could be held responsible for inflammatory symptoms and pain in periodontitis, we investigated whether the inflammatory and algesic effects of a sonic extract from P. gingivalis (PGSE) could be inhibited by the potent bradykinin B2 receptor antagonist, icatibant (Hoe 140).
In anaesthetized rats, the subplantar injection of PGSE (0.1 and 1.0 mg) caused a dose‐dependent oedema of the hind paws. The net increase of the paw volume 60 min after the injection was 23 ± 5% and 77 ± 12%, respectively. The oedema was rich in plasma proteins as determined by the Evans blue method. Pretreatment with icatibant (300 nmol kg−1, s.c.) significantly reduced the effect of 1.0 mg of PGSE whereas the effects of 0.1 mg of PGSE remained unaffected.
The subplantar injection of 1.0 mg of PGSE in unanaesthetized rats caused nociceptive behavioural responses which started about 5 min after the injection and lasted for about 10–15 min. These responses were completely prevented by pretreatment with icatibant (300 nmol kg−1, s.c.).
The present results show that the plasma extravasation induced by non‐algesic doses of a sonic extract from P. gingivalis are caused by mechanisms other than B2 kinin receptor activation whereas inflammatory effects of algesic doses are due to the action of kinins. The pain elicited by the extract is solely mediated by kinins and can be prevented by icatibant. The bradykinin antagonist could thus have a potential for a clinical use against pain associated with periodontal inflammation.
(−)‐Discretamine, a selective α1D‐adrenoceptor antagonist, isolated from Fissistigma glaucescens
Authors: Ko Feng‐Nien , Guh Jih‐Hwa , Yu Sheu‐Meei , Hou Yu‐Sheng , Wu Yang‐Chang , Teng Che‐Ming 
Published: July 2012

The selectivity of (−)‐discretamine for α1‐adrenoceptor subtypes was investigated by use of functional and binding studies in rat vas deferens, spleen and aorta, and in cultured DDT1MF‐2 and A10 cells.
In prostatic portions of rat vas deferens, the competitive antagonists (−)‐discretamine, 5‐methyl‐urapidil (5‐MU) and prazosin inhibited contractions to noradrenaline (NA) with pA2 values of 6.21, 8.71 and 9.27, respectively. The irreversible antagonist, chloroethylclonidine (CEC, 100 μm) failed to affect contractions to NA while nifedipine (1 μm) blocked them almost completely.
In rat spleen, the competitive antagonists (−)‐discretamine, 5‐MU and prazosin inhibited contractions to phenylephrine with pA2 values of 6.44, 7.19 and 9.45, respectively. CEC (100 μm) significantly reduced the maximum contraction to phenylephrine while nifedipine (1 μm) did not affect it.
In rat aorta, the competitive antagonists (−)‐discretamine, 5‐MU and prazosin inhibited contractions to NA with pA2 values of 7.60, 8.00 and 9.40, respectively. CEC also antagonized the contractions to NA in a competitive manner with a pA2 value of 6.10.
The specific binding of [3H]‐prazosin to DDT1MF‐2 and A10 cells was concentration‐dependent and saturated at 3–5 nM with KD values of 0.24 ± 0.02 and 0.20 ± 0.02 nM, respectively. (−)‐Discretamine, 5‐MU, CEC and prazosin inhibited specific [3H]‐prazosin binding to DDT1MF‐2 and A10 cells in a concentration‐dependent manner with IC50 values of 390.8 ± 20.6, 43.6 ± 3.9, 200.0 ± 30.0 and 0.8 ± 0.1 nM, respectively in DDT1MF‐2 cells, and 25.0 ± 3.2, 8.6 ± 1.4, 1000.0 ± 30.8 and 0.52 ± 0.03 nM, respectively in A10 cells.
Pretreatment of A10 cells with CEC (10 μm) for 30 min and then washed out thoroughly, reduced specific [3H]‐prazosin binding by 30%. The CEC‐insensitive [3H]‐prazosin binding was inhibited by (−)‐discretamine with an IC50 value of 7.0 ± 0.3 nM.
5‐MU (100 nM), CEC (1 μm) and prazosin (10 nM) markedly inhibited NA (3 μm)‐induced [3H]‐inositol monophosphate formation in DDT1MF‐2 and A10 cells, while (−)‐discretamine (100 nM) inhibited NA‐induced [3H]‐inositol monophosphate formation only in A10 cells.
In conclusion, (−)‐discretamine is a selective α1D‐adrenoceptor antagonist in vascular smooth muscle. Its selectivity among various α1‐adrenoceptor subtypes is α1A:α1B:α1D = 0.04:0.07:1.0.
Cutaneous vasodilatation induced by nitric oxide‐evoked stimulation of afferent nerves in the rat
Authors: Holzer P. , Jocič M. 
Published: July 2012

The site of action at which nitric oxide (NO) may contribute to neurogenic vasodilatation in the hindpaw skin of urethane‐anaesthetized rats was examined by the use of NG‐nitro‐l‐arginine methyl ester (l‐NAME), an inhibitor of NO synthase.
Skin blood flow was measured by laser Doppler flowmetry, and neurogenic vasodilatation was evoked either by topical application of mustard oil (5%) or antidromic electrical stimulation of the saphenous nerve (antidromic vasodilatation).
l‐NAME (60 μmol kg−1, i.v.) attenuated the hyperaemia evoked by mustard oil in an enantiomer‐specific manner but failed to reduce antidromic vasodilatation and the vasodilatation due to i.v. injected calcitonin gene‐related peptide (CGRP) and substance P (0.1–1 nmol kg−1 each), two proposed mediators of neurogenic vasodilatation.
Pretreatment of rats with capsaicin (125 mg kg−1, s.c. 2 weeks beforehand), to defunctionalize afferent neurones, reduced the hyperaemic response to mustard oil and prevented l‐NAME from further decreasing the vasodilatation evoked by mustard oil.
Intraplantar infusion of sodium nitroprusside (SNP, 0.15 nmol in 1 min), a donor of NO, induced hyperaemia which was significantly diminished by the CGRP antagonist CGRP8–37 (50 nmol kg−1, i.v.) and by capsaicin pretreatment. The ability of CGRP8–37 to inhibit the vasodilator response to SNP was lost in capsaicin‐pretreated rats.
Taken together, these data indicate that NO does not play a vasorelaxant messenger role in neurogenic vasodilatation but can contribute to activation of, and/or transmitter release from, afferent nerve fibres in response to irritant chemicals.
Role of R‐type calcium channels in the response of the perfused arterial and venous mesenteric vasculature of the rat to platelet‐activating factor
Authors: Claing Audrey , Bkaily Ghassan , Berthiaume Nathalie , Sirois Pierre , Rola‐Pleszczynski Marek , D'Orléans‐Juste Pedro 
Published: July 2012

The vasoactive properties of platelet‐activating factor (PAF) were studied in the arterial and venous vasculature of the rat double‐perfused mesenteric bed. Although PAF (0.01–0.3 pmol) induced a dose‐dependent vasodilatation of the arterial mesenteric vasculature, it triggered only vasoconstrictions on the venous side, with an intact endothelium as bradykinin induced a significant venodilatation.
NG‐nitro‐l‐arginine methyl ester (l‐NAME, 100 μm), a nitric oxide synthase inhibitor, markedly reduced the vasodilatation induced by PAF in the arterial mesenteric vasculature and potentiated the contractile responses of the venous side to the same agent.
The PAF antagonist, WEB‐2170, markedly reduced the response to PAF on both sides of the mesenteric vasculature. However, the IC50 of WEB‐2170 against PAF was reached at a much higher concentration (1 × 10−8 M) on the arterial side than on the venous side (5.3 × 10−11 M). Furthermore, a second antagonist of PAF receptors, SRI‐63441, although being less potent on the venous vasculature than WEB‐2170, was equipotent in antagonizing the venoconstriction and the arterial dilatation induced by PAF (IC50 of SRI‐63441, arterial side: 2.9 × 10−9 M; venous side: 3.1 × 10−9 M).
The dual L‐ and R‐calcium channel blocker, isradipine (PN 200–110), but not the L‐type calcium channel blocker, nifedipine, markedly reduced the PAF‐induced vasoactive properties on both sides of the mesenteric vasculature.
Our results illustrate the differential vasoactive properties of PAF in the mesenteric vasculature of the rat. These vasoactive responses occur following activation of specific receptors for PAF or, alternatively, through activation of R‐type calcium channels.