bluuebunny/crossref_metadata_2025_split huggingface dataset:
Scavenging of hydroxyl radicals but not of peroxynitrite by inhibitors and substrates of nitric oxide synthases
Authors: Rehman Almas , Whiteman Matthew , Halliwell Barry 
Published: January 2005

The nitric oxide synthase inhibitor NG‐nitro‐l‐arginine methyl ester (l‐NAME) is widely used to study the role of NO• in physiological and pathological processes, including its role in the generation of the cytotoxic species peroxynitrite (ONOO−) and of reactive oxygen radicals such as hydroxyl (OH•). Often l‐NAME is applied to tissues at mM concentrations. At such high concentrations, it might act as a free radical scavenger. A similar possibility might apply to the use of high levels of arginine to study the role of NO. in atherogenesis.
We therefore examined the rate of scavenging of OH• by l‐NAME and found that l‐NAME reacts more quickly with OH. than the established ‘OH. scavenger’ mannitol and the widely used ‘OH• trap’ salicylate. However, d‐NAME can scavenge OH• at rates equal to l‐NAME. Both l‐ and d‐arginine were also good OH• scavengers, comparable in effectiveness to mannitol.
Neither l‐NAME, d‐NAME, l‐arginine nor d‐arginine was able to inhibit ONOO−‐dependent nitration of tyrosine, suggesting that they are unlikely to be scavengers of ONOO−‐derived nitrating species.
Neither l‐NAME, d‐NAME, l‐arginine nor d‐arginine was able to inhibit the inactivation of α1‐antiproteinase by ONOO−, suggesting that they cannot prevent direct oxidations by peroxynitrite.
We conclude that l‐NAME has sufficient activity as an OH• scavenger to confound certain pharmacological experiments. However, this explanation of its biological effects can be ruled out if control experiments show that d‐NAME has no effect and that l‐arginine (also a free radical scavenger) antagonizes the action of l‐NAME.
Endothelin converting enzyme (ECE) activity in human vascular smooth muscle
Authors: Maguire Janet J. , Johnson Christopher M. , Mockridge James W. , Davenport Anthony P. 
Published: January 2005

We have characterized the human smooth muscle endothelin converting enzyme (ECE) present in the media of the endothelium‐denuded human umbilical vein preparation.
Endothelin‐1 (ET‐1) and ET‐2 were potent constrictors of umbilical vein with EC50 values of 9.2 nm and 29.6 nm, respectively. ET‐1 was at least 30 times more potent than ET‐3 suggesting the presence of constrictor ETA receptors. Little or no response was obtained to the ETB‐selective agonist sarafotoxin 6c. These data suggest that endothelin‐mediated vasoconstriction is via ETA receptors in this preparation.
Autoradiographical visualization of endothelin receptors with subtype selective ligands confirmed the predominance of the ETA receptor in the media of umbilical vein. High density of binding was obtained with the ETA selective [125I]‐PD151242, with much lower levels detected with the ETB selective [125I]‐BQ3020.
Big ET‐1 (EC50=42.7 nm) and big ET‐2(1–38) (EC50=99.0 nm) were less potent than ET‐1 and ET‐2, respectively. Big ET‐2(1–38) was more potent than its isoform big ET‐2(1–37) with concentration–response curves to big ET‐2(1–37) incomplete at 300 nm. No response was obtained to big ET‐3 at concentrations up to 700 nm. The C‐terminal fragments, big ET‐1(22–38) and big ET‐2(22–38) were inactive.
Responses to ET‐1 were unaffected by either the neutral endopeptidase (NEP) inhibitor thiorphan (10−5 m) or by the dual NEP/ECE inhibitor phosphoramidon (10−5 m). Big ET‐1 was also unaffected by thiorphan but antagonized in a concentration‐dependent manner by phosphoramidon (10−5 m and 10−4 m).
Addition of all four big endothelin peptides to human umbilical vein preparations resulted in detectable amounts of ET‐IR in the bathing medium. Therefore, although big ET‐3 was functionally inactive this reflects the low potency of ET‐3 at the ETA receptor rather than the lack of ability of this smooth muscle ECE to convert big ET‐3 to ET‐3.
To conclude we have demonstrated the presence of a phosphoramidon‐sensitive ECE on the smooth muscle layer of the human umbilical vein which can convert big ET‐1, big ET‐2(1–37), big ET‐2(1–38) and big ET‐3 to their mature biologically active forms. The precise subcellular localization of this enzyme and its physiological relevance remains to be determined.
Differential modulation of rat neuronal nicotinic receptor subtypes by acute application of ethanol
Authors: Covernton Patrick J. O. , Connolly John G. 
Published: January 2005

We have studied the effects of acute ethanol (EtOH) exposure on the agonist responses of rat neuronal nicotinic receptors expressed in Xenopus oocytes by means of voltage clamp techniques.
In some cells, agonist‐induced current responses with the α3β4 subunit combination could be either significantly potentiated or inhibited (range 25% to 237% of control response) by low ethanol concentrations (1–30 mm). At high ethanol concentrations (100–300 mm) robust potentiations were observed (range 135% to 305% of control).
The low EtOH concentration effects on the α3β4 subtype exhibited tolerance with repeated EtOH exposure.
In general, the α3β2, α4–1β2 and α4–1β4 subunit combinations were less sensitive to low concentrations of ethanol, but respectively showed potentiations of up to 178%, 226% and 154% at high EtOH concentrations.
The α7 homomeric receptor was also relatively insensitive at low EtOH concentrations. At high EtOH concentrations, potentiations, inhibitions or no alteration of control agonist response were observed (range 88% to 141% of control).
We conclude that all the neuronal nicotinic receptor subunit combinations tested here can be modulated by high concentrations of EtOH in a rapidly reversible manner. This modulation may underlie some of the behavioural effects of ethanol. The α3β4 subunit combination may be especially sensitive to modulation by low EtOH concentrations. This remarkable sensitivity and plasticity of nicotinic receptors may contribute to a process of mutual reinforcement in nicotine and alcohol addiction.
Release of the antioxidants ascorbate and urate from a nitrergically‐innervated smooth muscle
Authors: Lilley Elliot , Gibson Alan 
Published: January 2005

The main object of the present study was to determine whether ascorbate, an antioxidant which has been shown to protect nitric oxide (NO) from attack by scavenger molecules, might be released from nitrergically‐innervated smooth muscle; ascorbate release from the rat anococcygeus was measured by use of h.p.l.c. with electrochemical detection.
Incubation of rat anococcygeus muscles in normal physiological salt solution (PSS; 30 min) resulted in release of ascorbate into the bathing medium (7.7±0.9 nmol g−1 tissue). This release was increased by 96% when muscles were incubated in high K+ (70 mm) PSS. The resting release of ascorbate was unaffected by tetrodotoxin (TTX; 1 μm), ω‐conotoxin GVIA (10 nm) or omission of calcium ions from the PSS (with addition of 0.2 mm EGTA), but all three procedures attenuated the increased release observed under depolarizing conditions. Resting release of ascorbate was unaffected by glutamate (100 μm), aspartate (100 μm), γ‐aminobutyric acid (100 μm) or carbachol (50 μm).
A second h.p.l.c. peak, which always preceded the ascorbate peak, was identified as urate. Urate release from the anococcygeus, following 30 min incubation in normal PSS, was 64.6±12.7 nmol g−1 tissue but, unlike ascorbate, urate release was unchanged in high K+ PSS. In functional experiments, urate (100–400 μm) partially protected NO (15 μm)‐induced relaxations of the rat anococcygeus from inhibition by 2‐(4‐carboxyphenyl)‐4,4,5,5‐tetramethylimidazoline‐1‐oxyl‐3‐oxide (carboxy‐PTIO; 50 μm), but not from inhibition by hydroquinone or duroquinone (both 100 μm).
Muscles chemically sympathectomized with 6‐hydroxydopamine (6‐OHDA, 500 μm; 2 h) still exhibited release of ascorbate (2.5±0.4 nmol g−1 tissue) and urate (22.2±2.9 nmol g−1 tissue); in both cases the release was similar to that observed in time‐matched control tissues not exposed to 6‐OHDA. High K+ PSS produced a TTX‐sensitive increase in release of ascorbate, but not urate, from 6‐OHDA‐treated muscles.
The results demonstrate that significant amounts of ascorbate and urate are released from the rat anococcygeus muscle. Ascorbate, but not urate, release appears to be enhanced by activation of nerves which are resistant to 6‐OHDA pretreatment. Since both antioxidants can protect NO from attack by scavenger molecules, their release in nitrergically‐innervated tissues may be important for the provision of the correct redox environment to allow NO to fulfill its proposed neurotransmitter role.
Preferential expression of the neuropeptide Y Y1 over the Y2 receptor subtype in cultured hippocampal neurones and cloning of the rat Y2 receptor
Authors: St‐Pierre Jacques‐André , Dumont Yvan , Nouel Dominique , Herzog Herbert , Hamel Edith , Quirion Rémi 
Published: January 2005

Neuropeptide Y (NPY) and NPY receptors are most abundant in the hippocampal formation where they modulate cognitive functions. Expression of NPY receptors in rat cultured primary hippocampal cells was investigated in the present study by use of combined molecular, pharmacological and immunohistochemical approaches, including the cloning of the rat Y2 receptor described here for the first time.
More than 70% of the hippocampal neurones were endowed with [125I]‐[Leu31,Pro34]PYY Y1‐like receptor silver grain accumulations and Y1 receptor immunostaining. These radio‐ and immuno‐labelling signals were distributed over cell bodies and processes of bipolar, stellate and pyramidal‐like neuronal cells, as confirmed by neurone‐specific enolase and MAP‐2 staining.
Competition binding profiles revealed that specific [125I]‐[Leu31,Pro34]PYY binding was competitively displaced according to a ligand selectivity pattern prototypical of the Y1 receptor sub‐type with [Leu31,Pro34]substituted NPY/PYY analogues>>C‐terminal fragments=pancreatic polypeptides, with the non‐peptide antagonist BIBP3226 being most potent. This profile excludes the possible labelling by [125I]‐[Leu31,Pro34]PYY of the newly cloned Y4, Y5 and Y6 receptors.
The expression of the genuine Y1 receptor was confirmed by RT–PCR in hippocampal cultures. In contrast, negligible levels of Y2‐like/[125I]‐PYY3–36 binding were detected in these cultures in spite of the presence of its mRNA, as characterized by RT–PCR. The expression of both the Y1 and the Y2 receptor mRNAs was also noted in normal embryonic hippocampal tissues showing that signals expressed in cultured neurones were also present in utero.
Taken together, these results suggest that the Y1 receptor subtype may be of critical importance in the normal functioning of the rat hippocampus, especially during brain development and maturation.

British Journal of Pharmacology (1998) 123, 183–194; doi:10.1038/sj.bjp.0701589
Influence of dietary salts on the cardiovascular effects of low‐dose combination of ramipril and felodipine in spontaneously hypertensive rats
Authors: Mervaala Eero M A , Malmberg Lena , Teräväinen Terttu‐Liisa , Laakso Juha , Vapaatalo Heikki , Karppanen Heikki 
Published: January 2005

In spontaneously hypertensive rat (SHR) we examined over a 4‐week period the influence of control low sodium diet, common salt‐enriched diet (sodium chloride 6% of the dry weight of the chow) and a novel mineral salt‐enriched diet (potassium‐, magnesium‐, and l‐lysine‐enriched mineral salt added at a 75% higher level of 10.5% to produce the same sodium chloride concentration of 6%) on the cardiovascular effects produced by a low‐dose combination of an angiotensin converting enzyme inhibitor ramipril (0.25 mg kg−1 day−1 in the food) and a calcium channel blocker felodipine (0.4 mg kg−1 day−1 subcutaneously via an osmotic minipump).
Common salt, but not the mineral salt, accelerated the development of hypertension and induced left ventricular and renal hypertrophy in SHR. Neither common salt nor mineral salt significantly affected heart rate.
The combination of ramipril and felodipine decreased systolic blood pressure and prevented the development of left ventricular hypertrophy effectively during the common salt diet without any significant effect on the heart rate. The cardiovascular effects of the drug combination were improved by the low sodium diet or by replacement of high common salt in the diet by mineral salt.
Responses of endothelium‐intact mesenteric arterial rings in vitro were examined at the end of the four‐week study. The combination of ramipril and felodipine markedly improved the endothelium‐dependent vascular relaxation responses to acetylcholine and enhanced the endothelium‐independent vascular relaxation responses to sodium nitroprusside in SHR on control and common salt diets. Replacement of common salt in the diet by mineral salt improved the endothelium‐dependent vascular relaxation responses to acetylcholine. The drug combination attenuated the α‐adrenoceptor‐mediated vascular contractile responses to noradrenaline during the common salt diet.
Ramipril and felodipine in combination increased plasma renin activity by 1.9–3.2 fold without affecting serum aldosterone levels.
Our findings suggest that the cardiovascular effect of the low‐dose combination of ramipril and felodipine was maintained during high salt intake. However, salt restriction or replacement of common salt in the diet by the potassium‐ and magnesium‐enriched mineral salt improved the cardiovascular effects of the drug combination. In the face of a high intake of sodium, a part of the beneficial cardiovascular effects of the drug combination is apparently mediated by improved endothelium‐dependent and endothelium‐independent vascular relaxation responses and attenuated α‐adrenoceptor‐mediated vascular contractile responses.

British Journal of Pharmacology (1998) 123, 195–204; doi:10.1038/sj.bjp.0701591
Comparison of the effects of drugs on hyperexcitability induced in hippocampal slices by withdrawal from chronic ethanol consumption
Authors: Bailey C P , Molleman A , Little H J 
Published: January 2005

The effects of drugs, previously demonstrated to have a range of effects on the behavioural signs of ethanol withdrawal hyperexcitability, were examined in area CA1 in isolated hippocampal slices prepared after withdrawal from chronic ethanol in vivo.
The decreases seen after the ethanol treatment in the thresholds for production of single and multiple population spikes were prevented when the dihydropyridine calcium channel antagonist, isradipine, was included in the perfusion medium at 4 μM.
Another dihydropyridine, felodipine, which had no activity against withdrawal signs in vivo, did not affect the changes in field potentials, at concentrations up to 10 μM.
Diltiazem, which increased withdrawal hyperexcitability in vivo, had no effect on the withdrawal changes in field potentials at 30 μM; higher concentrations affected the control slices.
The novel anticonvulsant, gabapentin, at 1 μM but not at 100 nM, significantly decreased the signs of withdrawal hyperexcitability in the hippocampal slices. When the CCKB antagonist, CI988, was added to the bathing medium, at 1 μM, there were small, but significant decreases in the withdrawal hyperexcitability.
The results showed that the actions of these drugs on the changes in the field potentials in isolated hippocampal slices were very similar to their previously demonstrated effects on the convulsive signs of ethanol withdrawal in vivo, but differences were seen in the corresponding comparison with anxiolytic actions in vivo.

British Journal of Pharmacology (1998) 123, 215–222; doi:10.1038/sj.bjp.0701596
Ethanol‐induced inhibition of a neuronal P2X purinoceptor by an allosteric mechanism
Authors: Li Chaoying , Peoples Robert W , Weight Forrest F 
Published: January 2005

Ethanol inhibits a neuronal P2X purinoceptor by shifting the ATP concentration–response curve to the right in an apparently competitive manner. However, the underlying mechanism has not been determined. We investigated the effects of ethanol on the activation and deactivation time constants for ATP‐activated current in bullfrog dorsal root ganglion neurones. Ethanol decreased the time constant of deactivation of ATP‐gated ion channels without affecting the time constant of activation. The observations are not consistent with a competitive mechanism of inhibition by ethanol, but may be explained by an allosteric action of ethanol to decrease apparent agonist affinity. This represents a novel mechanism of action of ethanol on a neurotransmitter‐gated ion channel.British Journal of Pharmacology (1998) 123, 1–3; doi:10.1038/sj.bjp.0701599
Efficacy of inverse agonists in cells overexpressing a constitutively active β2‐adrenoceptor and type II adenylyl cyclase
Authors: Stevens Patricia A , Milligan Graeme 
Published: January 2005

Maximal stimulant output from the adenylyl cyclase cascade in neuroblastoma × glioma hybrid, NG108‐15, cells is limited by the levels of expression of isoforms of adenylyl cyclase. Stable expression in these cells of a constitutively active mutant (CAM) version of the human β2‐adrenoceptor resulted in higher basal adenylyl cyclase activity than following expression of the human wild type β2‐adrenoceptor. Isoprenaline acted as a full agonist in membranes from both wild type and CAM β2‐adrenoceptor expressing clones.
Expression of type II adenylyl cyclase resulted in a substantially elevated capacity of isoprenaline to stimulate [3H]‐forskolin binding, whereas in CAM β2‐adrenoceptor expressing cells the basal high affinity [3H]‐forskolin binding represented a markedly greater % of the maximal effect which could be produced by addition of isoprenaline, and the EC50 for isoprenaline was some 10 fold lower than in cells expressing the wild type β2‐adrenoceptor.
Further transfection of the CAM β2‐adrenoceptor expressing cells with type II adenylyl cyclase greatly increased both absolute basal and agonist‐stimulated levels of adenylyl cyclase activity.
Betaxolol, ICI 118,551, sotalol and timolol acted as inverse agonists with varying degrees of efficacy, whereas propranolol functioned as a neutral antagonist and alprenolol as a partial agonist.
Pretreatment of the CAM β2‐adrenoceptor and type II adenylyl cyclase expressing clones with the irreversible alkylating agent BAAM (1 μM) did not reduce the efficacy of isoprenaline but eliminated efficacy from all the inverse agonist ligands. This effect was dependent upon the concentration of BAAM employed, with half‐maximal effects being produced between 10 nM and 100 nM of the alkylating agent, which is similar to the concentrations required to prevent subsequent ligand access to some 50% of the CAM β2‐adrenoceptor population.
These data demonstrate that inverse agonist efficacy can be modulated by receptor availability and also indicate why in physiological systems, inverse agonism can be difficult to detect.

British Journal of Pharmacology (1998) 123, 335–343; doi:10.1038/sj.bjp.0701600
Interactions between P‐glycoprotein substrates and other cationic drugs at the hepatic excretory level
Authors: Smit Johan W. , Duin Erik , Steen Herman , Oosting Roelof , Roggeveld Jan , Meijer Dirk K F. 
Published: January 2005

In the present study it was tested whether known P‐glycoprotein (P‐gp) substrates/MDR reversal agents interact with small (type 1) and bulky (type 2) cationic drugs at the level of biliary excretion in the rat isolated perfused liver model (IPRL). The studies were performed with model compounds tri‐n‐butylmethylammonium (TBuMA) (a relatively small type 1 organic cation), rocuronium (Roc) (a bulky type 2 organic cation) and the classical P‐gp substrate doxorubicin (Dox).
Inhibitors were given in a 4 fold molar excess to the substrate studied. To minimize an interaction of the substrates at the hepatic uptake level, the competing compounds were added when over 55% to 85% of the administered dose of the model compounds had been removed from the perfusate and taken up by the liver.
We found a mutual interaction between TBuMA and procainamidethobromide (PAEB), both type 1 cationic compounds during biliary excretion. Interestingly, type 2 compounds, such as rocuronium, clearly inhibited type 1 cationic drugs as well as Dox secretion into bile, whereas type 1 compounds did not significantly inhibit type 2 drug excretion into bile. The type 1 cations PAEB and TBuMA only moderately inhibited Dox biliary excretion. Dox did not inhibit the biliary excretion of the type 2 agent rocuronium whereas rocuronium reduced Dox biliary excretion by 50% compared to controls.
MDR substrates/reversal agents like verapamil, quinine, quinidine and vinblastine strongly reduced both type 1 and type 2 organic cation excretion into bile. Dox secretion into bile was also profoundly reduced by these drugs, vinblastine being the most potent inhibitor in general.
The lack of mutual inhibition observed in some combinations of substrates may indicate that major differences in affinity of the substrates for a single excretory system exist. Alternatively, multiple organic cation transport systems with separate substrate specificities may be involved in the biliary excretion of amphiphilic drugs. Furthermore, the present study revealed a clear positive correlation between the lipophilicity of the potential inhibitors studied and their respective inhibitory activity on the biliary excretion of the model drugs investigated.
Our data are compatible with a potential involvement of P‐glycoprotein in the hepatobiliary excretion of doxorubicin as well as of some type 1 and type 2 organic cations. Furthermore we postulate that the hydrophobic properties of the amphiphilic cationic drugs studied play a crucial role in the accommodation of these agents by P‐glycoprotein and/or other potential cationic drug carrier proteins in the canalicular membrane.

British Journal of Pharmacology (1998) 123, 361–370; doi:10.1038/sj.bjp.0701606
Effect of a monoclonal antibody against interleukin‐4 on collagen‐induced arthritis in mice
Authors: Yoshino Shin 
Published: January 2005

The present study was undertaken to investigate the effect of a monoclonal antibody (11B11 mAb) against interleukin‐4 (IL‐4) on collagen‐induced arthritis (CIA) in mice.
11B11 mAb was daily injected intraperitoneally over a period of 10 days, commencing on the day of immunization with type II collagen (CII).
The results showed that the anti‐IL‐4 mAb markedly augmented both the incidence and the severity of CIA. The augmentation of the disease was associated with a significant increase in anti‐CII IgG2a antibody production, proliferative responses of lymph node cells to CII and interferon‐γ (IFN‐γ) secretion from the lymphoid cells. The production of anti‐CII IgG1 antibodies the secretion of IL‐4 was markedly reduced in the mAb‐treated mice.
Thus, the neutralization of IL‐4 by 11B11 mAb appears to be effective in augmenting CIA.

British Journal of Pharmacology (1998) 123, 237–242; doi:10.1038/sj.bjp.0701607