bluuebunny/crossref_metadata_2025_split huggingface dataset:
5‐HT4 receptors mediating enhancement of contractility in canine stomach; an in vitro and in vivo study
Authors: Prins N H , Grijn A van der , Lefebvre R A , Akkermans L M A , Schuurkes J A J 
Published: January 2005

We aimed to study 5‐HT4 receptors in canine stomach contractility both in vivo and in vitro.
In anaesthetized Beagle dogs, the selective 5‐HT4 receptor agonist prucalopride (i.v.) induced dose‐dependent tonic stomach contractions under isobaric conditions, an effect that was antagonized by the selective 5‐HT4 receptor antagonist GR 125487 (10 μg kg−1, i.v.).
Electrical field stimulation (EFS) of corpus longitudinal muscle strips resulted in atropine‐ and tetrodotoxin‐sensitive contractions (L‐NOARG (0.1 mM) present in all organ bath solutions). Prucalopride increased these contractions (maximal response after single‐dose addition (0.3 μM): 165% of initial value, or after cumulative addition: 188%). In the presence of methysergide (3 μM), 5‐HT also increased EFS‐contractions (after single‐dose addition (0.3 μM): increase to 192%, after cumulative addition: 148%).
The selective 5‐HT4 receptor antagonists GR 113808 (0.1 μM) or GR 125487 (10 nM) antagonized the prucalopride (0.3 μM)‐induced contraction increments. When EFS‐induced contractions were blocked by atropine or tetrodotoxin, prucalopride was ineffective. In the presence of methysergide (3 μM), the contraction increases to 5‐HT (0.3 μM) were prevented by GR 113808 (0.1 μM).
The prucalopride curve (pEC50 7.9) was shifted in parallel to the right by GR 113808 3 nM (pA2 9.4). In the presence of methysergide (3 μM), the curve to 5‐HT (pEC50 8.1) was competitively antagonized by GR 113808, yielding a Schild slope of 0.8±0.2 (pKB of 9.1 with unit Schild slope).
In corpus circular muscle strips, the prucalopride (0.3 μM)‐induced augmentation of EFS‐contractions (258%) was also prevented by GR 113808 (0.1 μM) (124%).
In conclusion, the effects of 5‐HT4 receptor agonists on proximal stomach motor activity in vivo can be explained by an effect on 5‐HT4 receptors on cholinergic nerves within the gastric muscle wall.

British Journal of Pharmacology (2001) 132, 1941–1947; doi:10.1038/sj.bjp.0703985
Rat arterial smooth muscle devoid of ryanodine receptor function: effects on cellular Ca2+ handling
Authors: Dreja Karl , Nordström Ina , Hellstrand Per 
Published: January 2005

The roles of intracellular Ca2+ stores and ryanodine (Ry) receptors for vascular Ca2+ homeostasis and viability were investigated in rat tail arterial segments kept in organ culture with Ry (10 – 100 μM) for up to 4 days.
Acute exposure to Ry or the non‐deactivating ryanodine analogue C10‐Oeq glycyl ryanodine (10 μM) eliminated Ca2+ release responses to caffeine (20 mM) and noradrenaline (NA, 10 μM), whereas responses to NA, but not caffeine, gradually returned to normal within 4 days of exposure to Ry.
Ry receptor protein was detected on Western blots in arteries cultured either with or without Ry.
Brief Ca2+ release events (sparks) were absent after culture with Ry, whereas Ca2+ waves still occurred. The propagation velocity of waves was equal (∼19 μm s−1) in tissue cultured either with or without Ry.
Inhibition of Ca2+ accumulation into the sarcoplasmic reticulum (SR) by culture with caffeine (5 mM), cyclopiazonic acid or thapsigargin (both 10 μM) decreased contractility due to Ca2+‐induced cell damage. In contrast, culture with Ry did not affect contractility.
Removal of Ca2+ from the cytosol following a Ca2+ load was retarded after Ry culture. Thapsigargin reduced the rate of Ca2+ removal in control cultured rings, but had no effect after Ry culture.
It is concluded that intracellular Ca2+ stores recover during chronic Ry treatment, while Ry receptors remain non‐functional. Ry receptor activity is required for Ca2+ sparks and for SR‐dependent recovery from a Ca2+ load, but not for Ca2+ waves or basal Ca2+ homeostasis.

British Journal of Pharmacology (2001) 132, 1957–1966; doi:10.1038/sj.bjp.0703986
Enhanced acetylcholine release in the hippocampus of cannabinoid CB1 receptor‐deficient mice
Authors: Kathmann Markus , Weber Bernd , Zimmer Andreas , Schlicker Eberhard 
Published: January 2005

We examined whether acetylcholine release in the hippocampus and striatum and noradrenaline release in the hippocampus is altered in CB1 receptor‐deficient mice. The electrically evoked tritium overflow from hippocampal slices preincubated with [3H]‐choline was increased by about 100% in CB1−/− compared to CB1+/+ mice whereas the electrically evoked tritium overflow from striatal slices preincubated with [3H]‐choline and from hippocampal slices preincubated with [3H]‐noradrenaline did not differ. The cannabinoid receptor agonist, WIN 55,212‐2, inhibited, and the CB1 receptor antagonist, SR 141716, facilitated, the evoked tritium overflow from hippocampal slices (preincubated with [3H]‐choline) from CB1+/+ as opposed to CB1−/− mice. Both drugs did not affect the evoked tritium overflow from striatal slices (preincubated with [3H]‐choline) and from hippocampal slices (preincubated with [3H]‐noradrenaline) from CB1+/+ and CB1−/− mice. The selective increase in acetylcholine release in CB1−/− mice may indicate that the presynaptic CB1 receptors on the cholinergic neurones of the mouse hippocampus are tonically activated and/or constitutively active in vivo.British Journal of Pharmacology (2001) 132, 1169–1173; doi:10.1038/sj.bjp.0703987
Dose‐related neuroprotective effects of chronic nicotine in 6‐hydroxydopamine treated rats, and loss of neuroprotection in α4 nicotinic receptor subunit knockout mice
Authors: Ryan R E , Ross S A , Drago J , Loiacono R E 
Published: January 2005

The present study examined the effect of a range of doses of chronic nicotine (0.75, 1.5, 3.0 and 30.0 mg kg−1 day−1, s.c., 14 days) upon striatal dopaminergic nerve terminal survival following 6‐hydroxydopamine (6‐OHDA; 10 μg intrastriatal unilaterally) in rats; and the effects of acute nicotine (1 mg kg−1, s.c.) pretreatment upon striatal neurodegeneration induced by methamphetamine (5 mg kg−1, i.p., three doses at 2 h intervals) in wild‐type and α4 nicotinic receptor (nAChR) subunit knockout mice.
In both models of Parkinsonian‐like damage, loss of striatal dopaminergic nerve terminals was assessed by [3H]‐mazindol autoradiography.
In rats, chronic nicotine infusion delivered by osmotic minipump implanted subcutaneously 7 days prior to intrastriatal 6‐OHDA injection produced significant and dose‐related protection against 6‐OHDA‐induced neurodegeneration. Low (0.75 and 1.5 mg kg−1 day−1) but not high (3.0 and 30.0 mg kg−1 day−1) nicotine doses significantly inhibited 6‐OHDA‐induced degeneration.
In wild‐type mice, acute nicotine treatment produced significant inhibition of methamphetamine‐induced neurodegeneration. In α4 nAChR subunit knockout mice, acute nicotine treatment failed to inhibit methamphetamine‐induced neurodegeneration.
Nicotine is capable of protecting dopaminergic neurons against Parkinsonian‐like neurodegeneration in vivo. In rats, this neuroprotective effect is critically dependent upon nicotine dose and is consistent with the activation of nAChRs, as high, desensitizing doses of nicotine fail to be neuroprotective. Further, neuroprotection is absent in α4 nAChR subunit knockout mice. The current results therefore suggest that activation of α4 subunit containing nAChRs constitutes a major component of the neuroprotective effect of nicotine upon Parkinsonian‐like damage in vivo.

British Journal of Pharmacology (2001) 132, 1650–1656; doi:10.1038/sj.bjp.0703989
Characterization of β1‐selectivity, adrenoceptor‐Gs‐protein interaction and inverse agonism of nebivolol in human myocardium
Authors: Maack C , Tyroller S , Schnabel P , Cremers B , Dabew E , Südkamp M , Böhm M 
Published: January 2005

Intrinsic activity and β1‐selectivity are important features of β‐blockers in the treatment of patients with coronary syndromes and heart failure. In human myocardium, intrinsic activity and β1‐selectivity of the novel β‐adrenoceptor antagonist nebivolol have not yet been determined.
The study examines intrinsic activity, β‐adrenoceptor‐G‐protein coupling and β1‐selectivity of nebivolol and bisoprolol in human ventricular myocardium. Furthermore, intrinsic activity of both compounds is compared to the one of bucindolol, carvedilol and metoprolol in human atrial myocardium.
Radioligand binding studies ([125I]‐lodocyanopindolol) were performed on membrane preparations of human failing and nonfailing myocardium and on COS‐7 cells transfected with human β1‐ and β2‐adrenoceptors, respectively. Functional experiments were carried out on isolated muscle preparations of human left ventricular and right atrial myocardium from failing and nonfailing hearts.
Radioligand binding studies reveal 3 – 4 fold β1‐selectivity for nebivolol and 16 – 20 fold β1‐selectivity for bisoprolol in human myocardium. In COS‐7‐cells, β1‐selectivity is 3 fold for nebivolol and 15 fold for bisoprolol.
Neither the binding of nebivolol nor of bisoprolol is affected by the presence of guanylylimidodiphosphate (Gpp(NH)p).
Nebivolol and bisoprolol exert similar inverse agonist activity in human ventricular as well as atrial myocardium. In atrial myocardium, inverse agonism of both compounds is higher compared to bucindolol, equal to carvedilol and lower compared to metoprolol.
Favourable haemodynamic effects of nebivolol in humans are not due to β1‐selectivity or partial agonist activity of this agent. Other mechanisms, i.e. the production of nitric oxide, may thus be responsible for its unique haemodynamic profile.

British Journal of Pharmacology (2001) 132, 1817–1826; doi:10.1038/sj.bjp.0703992
In vivo steady‐state pharmacokinetic outcome following clinical and toxic doses of racemic citalopram to rats
Authors: Kugelberg Fredrik C , Apelqvist Gustav , Carlsson Björn , Ahlner Johan , Bengtsson Finn 
Published: January 2005

The thymoleptic drug citalopram (CIT) belongs to the selective serotonin reuptake inhibitors (SSRIs) and is today extensively used in psychiatry. Further clarification of the enantiomer‐selective distribution of racemic CIT in both clinical and toxic doses is highly warranted.
By a steady‐state in vivo paradigm, rats underwent chronic systemic exposure for 10 days by using osmotic pumps and the total as well as the individual distributions of the S‐ and R‐enantiomers of CIT, and its metabolites in serum and two different brain regions, were analysed.
In serum, the S/R ratios in the groups treated with 10, 20, or 100 mg kg−1 day−1 were 0.94, 0.83, and 0.34, respectively. The ratios were almost the same in the brain regions.
In the group treated with 100 mg kg−1 day−1, the serum and brain total CIT levels were found to be 20 times and 6 – 8 times higher than in the rats treated with 10 or 20 mg kg−1 day−1, respectively. In all groups, the CIT levels were higher in brain tissue as compared to serum.
In a spontaneous open‐field behavioural test, a correlation between clinical and toxic drug concentrations was observed.
In conclusion, the R‐enantiomer was present in an increased proportion compared with the S‐enantiomer when higher steady‐state CIT concentration was prevailing. This is of particular interest, since the S‐enantiomer is responsible for the inhibition of serotonin reuptake in vitro. The present data may be of importance, as full understanding on where different racemic or enantiomeric drug effects of CIT and its main metabolites are unravelled.

British Journal of Pharmacology (2001) 132, 1683–1690; doi:10.1038/sj.bjp.0704015
Allosteric modulation of [3H]‐CGP39653 binding through the glycine site of the NMDA receptor: further studies in rat and human brain
Authors: Mugnaini Manolo , Meoni Paolo , Bunnemann Bernd , Corsi Mauro , Bowery Norman G 
Published: January 2005

Binding of D,L‐(E)‐2‐amino‐4‐[3H]‐propyl‐5‐phosphono‐3‐pentenoic acid ([3H]‐CGP39653), a selective antagonist at the glutamate site of the NMDA receptor, is modulated by glycine in rat brain tissue. We have further investigated this phenomenon in rodent and human brain by means of receptor binding and quantitative autoradiography techniques.
In rat cerebral cortical membranes the glycine antagonist 3‐[2‐(Phenylaminocarbonyl)ethenyl]‐4,6‐dichloro‐indole‐2‐carboxylic acid sodium salt (GV150526A) did not change basal [3H]‐CGP39653 binding, but competitively reversed the high affinity component of [3H]‐CGP39653 binding inhibition by glycine, with a pKB value of 8.38, in line with its affinity for the glycine site (pKi=8.49 vs [3H]‐glycine). Glycine (10 μM) significantly decreased [3H]‐CGP39653 affinity for the NMDA receptor (with no change in the Bmax), whereas enhanced L‐glutamate affinity (P<0.05, paired‐samples Student's t‐test).
In rat brain sections the addition of GV150526A (30 μM) to the incubation medium increased [3H]‐CGP39653 binding to 208% of control (average between areas), indicating the presence of endogenous glycine. The enhancement presented significant regional differences (P<0.05, two‐way ANOVA), with striatum higher than cerebral cortex (282 and 187% of control, respectively; P<0.05, Fisher's LSD). On the contrary, there was not any significant variation in affinity values of [3H]‐CGP39653, L‐glutamate, glycine and GV150526A in striatal and cortical membranes. These results confirmed the existence of regionally distinct NMDA receptors subtypes with different glycine/glutamate allosteric modulation.
Whole brain autoradiography revealed an uneven distribution of [3H]‐CGP39653 binding sites in human brain. High levels of binding were determined in hippocampus and in cingulate, frontoparietal and insular cortex. Intermediate to low levels of binding were found in diencephalic nuclei and basal ganglia. [3H]‐CGP39653 binding was increased to 216% of control (mean between areas) by 30 μM GV150526A. The enhancement, however, did not present significant regional differences.
These results introduce GV150526A as a useful tool to identify NMDA receptor subtypes by means of receptor autoradiography; moreover, they demonstrate that the allosteric inhibition of [3H]‐CGP39653 binding by glycine parallels an increase in receptor affinity to the endogenous ligand L‐glutamate. Finally, this study provides the first detailed anatomical description of the regional distribution of [3H]‐CGP39653 binding sites in human brain.

British Journal of Pharmacology (2001) 132, 1883–1897; doi:10.1038/sj.bjp.0704017
Incorporation of sodium channel blocking and free radical scavenging activities into a single drug, AM‐36, results in profound inhibition of neuronal apoptosis
Authors: Callaway Jennifer K , Beart Philip M , Jarrott Bevyn , Giardina Sarah F 
Published: January 2005

AM‐36 is a novel neuroprotective agent incorporating both antioxidant and Na+ channel blocking actions. In cerebral ischaemia, loss of cellular ion homeostasis due to Na+ channel activation, together with increased reactive oxygen species (ROS) production, are thought to contribute to neuronal death. Since neuronal death in the penumbra of the ischaemic lesion is suggested to occur by apoptosis, we investigated the ability of AM‐36, antioxidants and Na+ channel antagonists to inhibit toxicity induced by the neurotoxin, veratridine in cultured cerebellar granule cells (CGC's).
Veratridine (10 – 300 μM) concentration‐dependently reduced cell viability of cultured CGC's. Under the experimental conditions employed, cell death induced by veratridine (100 μM) possessed the characteristics of apoptosis as assessed by morphology, TUNEL staining and DNA laddering on agarose gels.
Neurotoxicity and apoptosis induced by veratridine (100 μM) were inhibited to a maximum of 50% by the antioxidants, U74500A (0.1 – 10 μM) and U83836E (0.03 – 10 μM), and to a maximum of 30% by the Na+ channel blocker, dibucaine (0.1 – 100 μM). In contrast, AM‐36 (0.01 – 10 μM) completely inhibited veratridine‐induced toxicity (IC50 1.7 (1.5 – 1.9) μM, 95% confidence intervals (CI) in parentheses) and concentration‐dependently inhibited apoptosis.
These findings suggest veratridine‐induced toxicity and apoptosis are partially mediated by generation of ROS. AM‐36, which combines both Na+ channel blocking and antioxidant activity, provided superior neuroprotection compared with agents possessing only one of these actions. This bifunctional profile of activity may underlie the potent neuroprotective effects of AM‐36 recently found in a stroke model in conscious rats.

British Journal of Pharmacology (2001) 132, 1691–1698; doi:10.1038/sj.bjp.0704018
Existence of different α1‐adrenoceptor subtypes in junctional and extrajunctional neurovascular regions in canine splenic arteries
Authors: Yang Xiao‐Ping , Chiba Shigetoshi 
Published: January 2005

The present study attempted to characterize the α1‐adrenoceptor subtypes mediating vasoconstrictor responses to administered and nerve stimulation‐evoked noradrenaline (NA) release in the isolated and perfused canine splenic artery.
A previous study demonstrated that periarterial electrical nerve stimulation (30 s trains of pulses at a frequency of 1, 4 or 10 Hz) induced a double peaked vasoconstriction consisting of an initial transient, predominantly P2X‐purinoceptor‐mediated constriction followed by a prolonged, mainly α1‐adrenoceptor‐mediated response in the canine splenic artery.
The effects of α1‐adrenoceptor subtype antagonists on neuronally‐mediated second peaked vasoconstrictions were analysed. BMY 7378 (10 – 100 nM), a selective α1D‐adrenoceptor antagonist produced a dose‐dependent inhibition of the second peak responses at all frequencies used. BMY 7378 (100 nM) reduced these responses by approximately 30%. Exposure of tissues to chloroethylclonidine (CEC, 60 μM), a selective α1B‐adrenoceptor antagonist attenuated the second peak response by approximately 60%, even in the presence of BMY 7378 (100 nM). On the other hand, WB 4101 (100 nM), a selective α1A‐adrenoceptor antagonist potentiated nerve‐stimulation‐evoked double peaked vasoconstrictions, especially at low frequencies (1 and 4 Hz).
Vasoconstrictor responses to administered NA were dose‐dependently antagonized by WB 4101 (10 – 100 nM), but were not significantly affected by either BMY 7378 (10 – 100 nM) or by CEC (60 μM).
The present results indicate that NA released from sympathetic nerves may junctionally exert its vasoconstrictor effect via activation of postjunctional α1B‐ and in part α1D‐adrenoceptors, whereas exogenous NA extrajunctionally activates α1A‐adrenoceptors to produce its vascular action in canine splenic arteries.

British Journal of Pharmacology (2001) 132, 1852–1858; doi:10.1038/sj.bjp.0704020
Selective inhibition of human inducible nitric oxide synthase by S‐alkyl‐L‐isothiocitrulline‐containing dipeptides
Authors: Park Jung‐Min , Higuchi Tsunehiko , Kikuchi Kazuya , Urano Yasuteru , Hori Hiroyuki , Nishino Takeshi , Aoki Junken , Inoue Keizo , Nagano Tetsuo 
Published: January 2005

The aim of this study was to investigate the structure‐activity relationship of S‐alkyl‐L‐isothiocitrulline‐containing dipeptides towards three partially purified recombinant human nitric oxide synthase (NOS) isozymes, as well as the effects of these compounds on cytokine‐induced NO production by human DLD‐1 cells.
In an in vitro assay, S‐methyl‐L‐isothiocitrulline (L‐MIT) was slightly selective for human neuronal NOS (nNOS) over the inducible (iNOS) or endothelial (eNOS) isozyme, but the combination of a hydrophobic L‐amino acid (L‐Phe, L‐Leu or L‐Trp) with L‐MIT dramatically altered the inhibition pattern to give selective iNOS inhibitors. Introduction of a hydroxy, nitro, amino or methoxy group at the para position of the aromatic ring of L‐MIT‐L‐Phe (MILF) decreased the selectivity and inhibitory potency. A longer or larger S‐alkyl group also decreased the selectivity and potency. Dixon analysis showed that all of the dipeptides were competitive inhibitors of the three isoforms of human NOS. The enzymatic time course curves indicated that MILF was a slow binding inhibitor of human iNOS.
These results suggest that the human NOS isozymes have different‐sized cavities in the binding site near the position to which the C‐terminal of L‐arginine binds, and the cavity of iNOS is hydrophobic. Interestingly, L‐MIT‐D‐Phe (MIDF) showed little inhibitory activity or selectivity, suggesting that the cavity of human iNOS is located in a well‐defined direction from the α carbon atom.
NO production in cytokine‐stimulated human DLD‐1 cells was measured with a fluorescent indicator, DAF‐FM. MILF, L‐MIT‐L‐Trp(‐CHO) (MILW) and L‐MIT‐L‐Tyr (MILY) showed more potent activity than L‐MIT in this whole‐cell assay.
Thus, S‐alkyl‐L‐isothiocitrulline‐containing dipeptides are selective inhibitors of human iNOS, and work efficiently in cell‐based assay.

British Journal of Pharmacology (2001) 132, 1876–1882; doi:10.1038/sj.bjp.0704023
The polycationic aminoglycosides modulate the vasoconstrictive effects of endothelin: relevance to cerebral vasospasm
Authors: Wickman Grant , Nessim Mourad A , Cook David A , Vollrath Bozena 
Published: January 2005

The vasoactive peptide endothelin (ET) has been implicated in the pathogenesis of cerebral vasospasm following subarachnoid haemorrhage. In these studies we investigated the involvement of protein kinase C (PKC) in sustained vasoconstriction induced by ET‐1 in canine cerebral arteries. We also examined the ability of the aminoglycoside antibiotics to reverse the effects mediated by ET‐1 in canine cerebrovascular smooth muscle cells (CVSMC).
The ETA receptor antagonist, BQ‐123, showed a competitive inhibition of the ET‐1 responses.
The vasoconstrictor action of both ET‐1 (0.5 nM) and phorbol myristate acetate (PMA) (160 nM) was reversed by a selective PKC inhibitor, Ro‐32‐0432.
In cerebral arteries precontracted with ET‐1 the aminoglycosides caused a concentration‐dependent relaxation. The EC50s for the relaxation were as follows: 0.54±0.05, 0.63±0.01, 1.88±0.46 and 2.3±0.92 mM for gentamicin, neomycin, streptomycin and kanamycin, respectively.
Gentamicin caused a concentration‐dependent decrease of the PMA‐induced responses in calcium free medium.
PKC activity was elevated in CVSMC exposed to ET‐1 (170%) and PMA (167%) for a period of time (60 min) corresponding to maximum tonic contraction induced by these agents in arterial rings.
The administration of the aminoglycosides to CVSMC, in concentrations corresponding to the EC50s from contractility studies, reduced the effects of both ET‐1 and PMA on PKC activity to the levels not different from controls.
These results show that the aminoglycosides are able to inhibit sustained vasoconstriction induced by ET‐1, an effect which is due, at least in part, to the inhibition of PKC.

British Journal of Pharmacology (2001) 133, 5–12; doi:10.1038/sj.bjp.0704025