bluuebunny/crossref_metadata_2025_split huggingface dataset:
Metabolism of methylarginines by human vasculature; implications for the regulation of nitric oxide synthesis
Authors: MacAllister Raymond J. , Fickling Sara A. , Whitley Guy St. J. , Vallance Patrick 
Published: July 2012

The metabolism of methylarginines by human cultured endothelial cells and human saphenous vein was studied in vitro. The human endothelial cell line (SGHEC‐7), primary cultures of human umbilical vein endothelial cells (HUVEC) and human saphenous vein were incubated with [14C]‐monomethyl‐l‐arginine ([14C]‐l‐NMMA) and the cytosolic extract analysed by high performance liquid chromatogaphy (h.p.l.c.) with on‐line radioisotope detection.
SGHEC‐7, HUVEC and human saphenous vein metabolized [14C]‐l‐NMMA to a compound which co‐eluted with [14C]‐citrulline. A second metabolite which co‐eluted with [14C]‐arginine was evident on the radiochromatograms of HUVEC cytosol and saphenous vein extracts.
The intracellular levels of [14C]‐l‐NMMA and [14C]‐citrulline in SGHEC‐7 cells incubated with [14C]‐l‐NMMA (0.5 μCi ml−1: 8.9 μm) for 1 h were 113 ± 22 and 67.6 ± 6.2 pmol mg−1 cell protein respectively (n = 7). Co‐incubation with NGNGdimethyl‐l‐arginine (ADMA; 100 μm) but not NGN′Gdimethyl‐l‐arginine (SDMA; 100 μm) reduced the intracellular level of [14C]‐citrulline to 26.3 ± 3.7 pmol mg−1 cell protein (P < 0.01; n = 3) without reducing the intracellular level of [14C]‐l‐NMMA.
The intracellular levels of [14C]‐citrulline in SGHEC‐7 cells incubated with [14C]‐l‐NMMA for 1 h were reduced following co‐incubation with NGnitro‐l‐arginine methylester (l‐NAME; 1 mm), NGnitro‐l‐arginine (l‐NOARG; 1 mm) and l‐canavanine (1 mm) to 47.1 ± 6.2, 24.7 ± 3.6 and 12.5 ± 2.8% of control levels (P < 0.001; n = 9). ADMA (1 mm; n = 3) reduced intracellular [14C]‐citrulline levels to 4 ± 4% of control (P < 0.01) but SDMA (1 mm; n = 3) had no effect.
The accumulation of endogenously synthesized ADMA in the culture supernatant of SGHEC‐7 cells was increased by co‐incubation with l‐NMMA (1 mm) from 1.98 ± 0.08 to 2.74 ± 0.36 nmol mg−1 cell protein, an increase of 40%.
These results demonstrate that human vasculature possesses an enzyme which has similar properties to dimethylarginase; human endothelial cells and human saphenous vein metabolize l‐NMMA to citrulline via a process inhibited by ADMA but not SDMA. The increase in endothelium‐derived ADMA following co‐incubation with l‐NMMA is consistent with competition between ADMA and l‐NMMA for dimethylarginase. Inhibition of this enzyme might increase the intracellular concentration of ADMA, an endogenously produced compound that inhibits nitric oxide synthesis.
Modulation of vasodilatation to levcromakalim by adenosine analogues in the rabbit ear: an explanation for hypoxic augmentation
Authors: Randall Michael D. , Ujiie Hiroshi , Griffith Tudor M. 
Published: July 2012

We have used a rabbit isolated ear, buffered‐perfused preparation to investigate the effects of adenosine analogues on the vasodilatation to the potassium channel opener, levcromakalim (the active (−)‐enantiomer of cromakalim). We have examined the effects of 8‐cyclopentyl‐1,3‐dipropylxanthine (DPCPX), a selective adenosine A1 antagonist, on vasodilatation to levcromakalim under hypoxic conditions and also following inhibition of nitric oxide synthesis.
Levcromakalim relaxed preconstricted preparations with an EC50 = 369 ± 48 nm and maximum relaxation of tone (Rmax) = 81.0 ± 3.2%. In the presence of 1 μm N6‐cyclohexyladenosine (CHA) a selective adenosine A1 agonist, there was a significant (P < 0.01) leftward shift in the concentration‐response curve with an EC50 = 194 ± 54 nm and Rmax = 93.2 ± 2.0%. Conversely, the presence of CHA did not influence vasodilatation to either pinacidil or sodium nitroprusside.
Hypoxia also significantly (P < 0.001) increased the vasodilator potency of levcromakalim (EC50 = 134 ± 22 nm), and this enhancement was completely reversed (EC50 = 380 ± 107nm, P<0.01) by pretreatment of the preparations with 5 μm DPCPX, a selective A1 adenosine antagonist. However, under normoxic conditions DPCPX did not influence vasodilatation to levcromakalin.
Inhibition of nitric oxide synthesis with 100 μm NG‐nitro‐l‐arginine methyl ester (l‐NAME) caused a significant (P < 0.001) leftward shift in the concentration‐response curve to levcromakalim (EC50 = 73.0 ± 7.6 nm). Pretreatment of preparations with DPCPX partially reversed the increase in potency found in the absence of nitric oxide synthesis (EC50 = 153 ± 18 nm, P < 0.001).
We have shown that an adenosine A1 agonist may increase the potency of levcromakalim indicating that adenosine receptor activation may augment the vasodilator activity of levcromakalim. That responses to levcromakalim but not those to pinacidil were affected by CHA points to further differences in the pharmacology of these potassium channel openers. The reversal by the adenosine A1 antagonist of the hypoxic‐potentiation of vasodilatation to levcromakalim, and also augmentation following inhibition of nitric oxide synthesis, suggests that under these conditions there is an endogenous release of adenosine which may enhance responses to levcromakalim. The findings of this study suggest that levcromakalim may selectively dilate vessels where there is elevated adenosine release.
Prevention by specific chemical classes of α1‐adrenoceptor antagonists of veratrine‐contractures in rat left atria independently of α1‐adrenoceptor blockade
Authors: Grand Bruno Le , Marty Aline , Vié Bruno , Patoiseau Jean‐François , John Gareth W. 
Published: July 2012

The putative direct protective effects of a series of chemically diverse α1‐adrenoceptor antagonists against veratrine alkaloid‐induced tetanic contractures in rat isolated left atria have been investigated.
Atria were mounted in organ baths containing normal, oxygenated physiological salt solution (20 ml, pH 7.4), for isometric tension recording. Atria were electrically driven at 4 Hz and were maintained at 34°C. Veratrine (100 μg ml−1) was applied to the atria to elicit tetanic (diastolic) contracture.
Concentration‐dependent protective effects against veratrine‐contractures, in the absence of negative inotropic responses, were observed with the quinazoline congeners, prazosin and doxazosin and with the benzodioxane‐related compounds, WB 4101 and its thio analogue, benoxathian. IC50 concentrations and apparent Hill coefficients of all four drugs ranged from 0.27 to 0.93 μm, and from 0.86 to 1.09, respectively, and are consistent with interaction at a single site.
In contrast, no protective activity versus veratrine‐contractures was observed with corynanthine, 5‐methyl‐urapidil, phenoxybenzamine, phentolamine or chloroethylclonidine (10 μm).
Contractures were prevented by prazosin at concentrations 2–3 log units higher than those which antagonized methoxamine‐evoked inotropic responses. In addition, concommitant α1‐adrenoceptor occupancy by high concentrations of methoxamine (100 μm), phentolamine (10 μm, inactive per se in preventing contracture), or both drugs together, failed, in each case, to modify significantly the protective effects of prazosin or WB 4101 against veratrine‐contractures.
Our findings demonstrate that α1‐adrenoceptor antagonists which prevent veratrine‐contractures belong to specific chemical classes of the quinazoline‐ and benzodioxane‐type. The mechanism by which these drugs afford protection is apparently independent of an interaction with defined α1‐adrenoceptors.
Attenuated renal response to moxonidine and rilmenidine in one kidney‐one clip hypertensive rats
Authors: Li Ping , Penner S. Brian , Smyth Donald D. 
Published: July 2012

I1 non‐adrenoceptor, imidazoline receptor agonists, such as moxonidine, increase urine flow rate and sodium excretion following infusion into the renal artery. The functions of these agonists in genetic and acquired models of hypertension have not been determined.
We therefore studied the renal effects of two known non‐adrenoceptor, imidazoline receptor agonists, rilmenidine and moxonidine, in 1K‐1C hypertensive and 1K‐sham normotensive rats. Rilmenidine (0, 3, 10, 30 nmol kg−1 min−1) or moxonidine (0, 1, 3, 10 nmol kg−1 min−1) was infused directly into the renal artery (30 gauge needle) of 1K‐sham normotensive and 1K‐1C hypertensive rats.
In 1K‐sham normotensive rats, rilmenidine and moxonidine produced dose related increases in urine flow rate, sodium excretion and osmolar clearance. Both rilmenidine and moxonidine failed to increase urine flow rate, sodium excretion and osmolar clearance in 1K‐1C hypertensive rats to the same extent as in 1K‐sham animals. At comparable doses, rilmenidine had no effect, while moxonidine (3 and 10 nmol kg−1 min−1) did result in a small increase in urine volume and osmolar clearance which was less than that observed in the 1K sham control animals.
These studies indicate that the renal effects of non‐adrenoceptor, imidazoline receptor stimulation are diminished in 1K‐1C hypertensive rats compared with 1K‐sham normotensive rats. Whether this decrease in activity of the natriuretic non‐adrenoceptor, imidazoline receptors contributes to the increase in blood pressure in the 1K‐1C acquired model of hypertension remains to be determined.
Dual effects of mastoparan on intracellular free Ca2+ concentrations in human astrocytoma cells
Authors: Nakahata Norimichi , Ishimoto Hiromi , Mizuno Kohichi , Ohizumi Yasushi , Nakanishi Hironori 
Published: July 2012

The effect of mastoparan, a wasp venom toxin, on intracellular free Ca2+ concentration ([Ca2+]i) was examined in human astrocytoma cells. Mastoparan inhibited [Ca2+]i induced by carbachol (100 μm) in a concentration‐dependent manner in the absence of extracellular Ca2+, consistent with our previous results showing that mastoparan inhibits phosphoinositide hydrolysis in human astrocytoma cells.
In contrast, mastoparan itself increased [Ca2+]i and augmented carbachol‐induced increase in the [Ca2+]i in the presence of extracellular Ca2+, suggesting that mastoparan elicited Ca2+ influx from the extracellular medium. The increase appeared to be maximum at extracellular Ca2+ concentrations of 0.1–0.2 mm. The higher concentrations of extracellular Ca2+ depressed the influx.
Pertussis toxin did not affect mastoparan‐induced inhibition of [Ca2+]i in the absence of extracellular Ca2+, consistent with the previous results that pertussis toxin did not affect mastoparan‐induced inhibition of phosphoinositide hydrolysis.
Pertussis toxin augmented mastoparan‐induced increase in [Ca2+]i in the presence of extracellular Ca2+, suggesting that pertussis toxin substrate(s) seems to be inhibitory for Ca2+ influx induced by mastoparan.
Verapamil, nifedipine and diltiazem (each 10 μm), L‐type Ca2+ antagonists, did not affect mastoparan‐induced Ca2+ influx. However, verapamil (10 μm) slightly inhibited the increase in [Ca2+]i induced by carbachol in the presence of mastoparan.
The results obtained in the present study indicate that mastoparan has two opposite effects on [Ca2+]i in human astrocytoma cells and possibly has at least two sites of action.
Regulation by hypoxia of endothelin‐1‐stimulated phospholipase D activity in sheep pulmonary artery cultured smooth muscle cells
Authors: Plevin Robin , Kellock Nicola A. , Wakelam Michael J.O. , Wadsworth Roger 
Published: July 2012

The aim of the study was to characterize the effects of hypoxia on agonist‐stimulated phospholipase D (PLD) and phospholipase C activity of sheep pulmonary artery cultured smooth muscle cells.
Endothelin‐1 (ET‐1), 5‐hydroxytryptamine (5‐HT) and the protein kinase C (PKC) activator tetradecanoylphorbol acetate (TPA), stimulated a time‐ and concentration‐dependent increase in [3H]‐phosphatidylbutanol accumulation. This was abolished by pretreatment of the cells with the PKC inhibitor, Ro‐318220, suggesting that agonist‐stimulated phospholipase D activity is dependent upon the activation of PKC.
Hypoxia (Po2 20 mmHg for 30 min) stimulated basal [3H]‐phosphatidylbutanol accumulation by approximately 2 fold and this activity was abolished by preincubation of the cells with 10 μm Ro‐318220.
In cells preincubated in low O2 containing medium for 30 min, the subsequent agonist‐stimulated accumulation of [3H]‐phosphatidylbutanol was reduced. However, the decrease in stimulation was greater for ET‐1 and 5‐HT than for TPA.
ET‐1 and TPA stimulated a time‐dependent increase in protein kinase C‐ mediated psuedosubstrate phosphorylation. Following preincubation for 30 min in low O2 containing media, basal pseudosubstrate phosphorylation increased whilst the fold stimulation by TPA and ET‐1 decreased.
In cells preincubated in low O2 containing medium, ET‐1‐stimulated [3H]‐inositol phosphate accumulation was reduced by approximately 30– 40%. This reduction was reversed by preincubation of the cells with Ro‐318220.
These results suggest a role for PKC in the effects of hypoxia on PLD in pulmonary artery smooth muscle cells.
The effect of calcium removal on the suppression by adenosine of epileptiform activity in the hippocampus: demonstration of desensitization
Authors: Hosseinzadeh H. , Stone T.W. 
Published: July 2012

Previous work has suggested that presynaptic effects of adenosine may be dependent on divalent cations. The present study was undertaken to determine whether a similar requirement existed at postsynaptic sites.
Extracellular recordings were made in the CA1 pyramidal cell layer of rat hippocampal slices following orthodromic stimulation of Schaffer collateral fibres in stratum radiatum or antidromic stimulation of the alveus. In antidromic stimulation experiments, CaCl2 was omitted (calcium‐free medium) or reduced to 0.24 mm (low calcium medium) and in some experiments MgS04 was increased to 2 mm. Kynurenic acid at concentrations of 1 and 5 mm in calcium‐free medium and 1 mm in low calcium medium had no effect on secondary spike size.
Adenosine and baclofen induced a concentration‐dependent reduction in the amplitude of orthodromic potentials with maximum effects at 20 and 5 μm respectively.
In nominally calcium‐free medium, bursts of multiple population spikes were obtained in response to antidromic stimulation. Adenosine had little effect in reducing the secondary spike amplitude. At high concentration (2 mm) an initial depression was seen which declined within 3–5 min.
Sensitivity to adenosine was restored in low calcium medium or by raising magnesium. Although raising the divalent cation concentration increased the inhibitory effect of adenosine, desensitization was still seen.
2‐Chloroadenosine (100–500 μm) and R‐PIA (50 μm), which are not substrates for either the nucleoside transporters or adenosine deaminase, were inactive in the absence of calcium. S‐(2‐hydroxy‐5 nitrobenzyl)‐6‐thioinosine, an adenosine uptake blocker, at a concentration 100 μm had no effect on secondary potential size and did not restore adenosine sensitivity in calcium‐free medium.
Thapsigargin, which discharges intracellular calcium stores, had no significant effect at 1 μm on the bursts of action potentials and did not change the effect of 0.5 mm adenosine in calcium‐free medium.
Unlike adenosine, baclofen concentration‐dependently reduced the secondary spike size in calcium‐free medium and no sign of recovery was observed during maintained superfusion for up to 45 min. No cross‐desensitization was seen between baclofen and adenosine.
Applications of adenosine locally by pressure to neuronal somata or dendrites still resulted in desensitized responses in calcium‐free medium.
It is concluded that the postsynaptic sensitivity to adenosine is dependent on the concentration of divalent cations in the extracellular space implying an effect of cations on adenosine receptor activation or transduction processes.
Benzodiazepine/cholecystokinin interactions at functional CCK receptors in rat brain
Authors: Boden P.R. , Woodruff G.N. 
Published: July 2012

The effects of benzodiazepines on cholecystokinin (CCK) responses produced following activation of CCKB receptors by pentagastrin in the ventromedial hypothalamus (VMH) or CCKA receptors by CCK‐8S in the dorsal raphe of the rat brain in vitro have been investigated.
The benzodiazepine agonist, flurazepam, at high concentrations, blocked pentagastrin‐induced excitations in the rat VMH yielding an equilibrium constant (Ke) value of 12.5 μm.
In the rat dorsal raphe, where activation of CCKA receptors leads to neuronal depolarization, flurazepam also produced a weak block of the CCK response.
Flurazepam blocked CCK responses but not carbachol‐induced excitations of VMH neurones. The inhibition of CCK responses by flurazepam was not blocked by the benzodiazepine antagonist, flumazenil.
These data suggest that flurazepam is a weak antagonist at central CCKB receptors.
At central CCKA receptors, flurazepam blocked CCK‐8S responses but the inhibition was not competitive, with a reduction in the peak CCK‐8S obtainable in the presence of flurazepam. These results suggest that flurazepam acts at a site other than the CCKA receptor itself to block CCK responses in the dorsal raphe.
Enhancement of noradrenergic constriction of large coronary arteries by inhibition of nitric oxide synthesis in anaesthetized dogs
Authors: Woodman Owen L. , Pannangpetch Patchareewan 
Published: July 2012

Coronary vascular responses to bilateral carotid occlusion (BCO) and the intravenous infusion of tyramine (Tyr, 20 μg kg−1 min−1) and noradrenaline (NA, 0.5 μg kg−1 min−1) were examined after bilateral vagotomy and antagonism of β‐adrenoceptors. BCO, Tyr and NA decreased large coronary artery diameter and increased mean coronary resistance and systemic arterial pressure without affecting heart rate.
Inhibition of nitric oxide (NO) synthase with NG‐nitro‐l‐arginine (l‐NNA, 5 and 15 mg kg−1) significantly increased mean arterial pressure and decreased heart rate and large coronary artery diameter. Mean coronary resistance was unaffected by either dose of l‐NNA. l‐NNA significantly reduced depressor and coronary vasodilator responses to the endothelium‐dependent vasodilator acetylcholine (ACh, 10 μg kg−1, i.v.). Systemic and coronary vasodilator responses to sodium nitroprusside (SNP, 5 μg kg−1) were unaffected by l‐NNA with the exception that the dilatation of the large coronary artery was significantly enhanced by the higher dose.
−1‐NNA significantly enhanced constriction of the large coronary arteries caused by BCO, Tyr and NA but did not affect the increases in mean coronary resistance or systemic arterial pressure.
Inhibition of NO synthesis enhances adrenergic constriction of large coronary arteries caused by both neuronally released and exogenous noradrenaline. In contrast, l‐NNA did not affect adrenergic constriction of coronary or systemic resistance vessels. Endothelium‐derived NO may play an important role in the modulation of noradrenergic vasoconstriction in coronary conductance arteries.
Effects of a novel nonpeptide bradykinin B2 receptor antagonist on intestinal and airway smooth muscle: further evidence for the tracheal B3 receptor
Authors: Farmer Stephen G. , DeSiato Mark A. 
Published: July 2012

We examined the effects of phosphonium, [[4‐[[2‐[[bis(cyclohexylamino)methylene] amino]‐3‐(2‐naphthalenyl) 1‐oxopropyl]amino]‐phenyl]‐tributyl, chloride, monohydrochloride (WIN 64338), a novel, nonpeptide bradykinin B2 receptor antagonist, on bradykinin‐induced contractions of guinea‐pig isolated ileum, and guinea‐pig and ferret trachea.
WIN 64338 potently and competitively antagonized ileal contractions, in response to bradykinin, exhibiting a pA2 value of 7.97 ± 0.10. The compound was without effect on contractions elicited by methacholine, a muscarinic receptor antagonist. Thus, WIN 64338 is a competitive and selective antagonist of ileal B2 receptors.
In contrast, WIN 64338 was completely without effect on bradykinin‐induced contractions of guinea‐pig or ferret trachea. Thus, even at a concentration of 1 μm, which was sufficient to cause a 100 fold decrease in ileal sensitivity to bradykinin, WIN 64338 failed to shift the bradykinin log concentration‐response curves in trachea isolated from either species.
These data confirm that WIN 64338 represents the first reported nonpeptide antagonist of guinea‐pig ileal B2 receptors. They also provide additional evidence for heterogeneity of bradykinin receptors within the same species (guinea‐pig) and, furthermore, indicate that the tracheal bradykinin receptor (B3?) is different from that in ileal tissue (B2).
Binding and functional properties of hexocyclium and sila‐hexocyclium derivatives to muscarinic receptor subtypes
Authors: Waelbroeck M. , Camus J. , Tastenoy M. , Feifel R. , Mutschler E. , Tacke R. , Strohmann C. , Rafeiner K. , de Miranda J.F. Rodrigues , Lambrecht G. 
Published: July 2012

We have compared the binding properties of several hexocyclium and sila‐hexocyclium derivatives to muscarinic M1 receptors (in rat brain, human neuroblastoma (NB‐OK 1) cells and calf superior cervical ganglia), rat heart M2 receptors, rat pancreas M3 receptors and M4 receptors in rat striatum, with their functional antimuscarinic properties in rabbit vas deferens (M1/M4‐like), guinea‐pig atria (M2), and guinea‐pig ileum (M3) muscarinic receptors.
Sila‐substitution (C/Si exchange) of hexocyclium (→ sila‐hexocyclium) and demethyl‐hexocyclium (→ demethyl‐sila‐hexocyclium) did not significantly affect their affinities for muscarinic receptors. By contrast, sila‐substitution of o‐methoxy‐hexocyclium increased its affinity 2 to 3 fold for all the muscarinic receptor subtypes studied.
The p‐fluoro‐ and p‐chloro‐derivatives of sila‐hexocyclium had lower affinities than the parent compound at the four receptor subtypes, in binding and pharmacological studies.
In binding studies, o‐methoxy‐sila‐hexocyclium (M1 = M4 ≥ M3 ≥ M2) had a much lower affinity than sila‐hexocyclium for the four receptor subtypes, and discriminated the receptor subtypes more poorly than sila‐hexocyclium (M1 = M3 > M4 > M2). This is in marked contrast with the very clear selectivity of o‐methoxy‐sila‐hexocyclium for the prejunctional M1/M4‐like heteroreceptors in rabbit vas deferens.
The tertiary amines demethyl‐hexocyclium, demethyl‐sila‐hexocyclium and demethyl‐o‐methoxy‐sila‐hexocyclium had 10 to 30 fold lower affinities than the corresponding quaternary ammonium derivatives.