bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of γ‐mangostin through the inhibition of 5‐hydroxytryptamine2A receptors in 5‐fluoro‐α‐methyltryptamine‐induced head‐twitch responses of mice
Authors: Chairungsrilerd Nattaya , Furukawa Ken‐Ichi , Tadano Takeshi , Kisara Kensuke , Ohizumi Yasushi
Published: January 2005

Intracerebronventricular (i.c.v.) injection of γ‐mangostin (10–40 nmol/mouse), a major compound of the fruit hull of Garcinia mangostana Lin., like ketanserin (10, 20 nmol/mouse, i.c.v.) inhibited 5‐fluoro‐α‐methyltryptamine (5‐FMT) (45 mg kg−1, i.p.)‐induced head‐twitch response in mice in the presence or absence of citalopram (a 5‐hydroxytryptamine (5‐HT)‐uptake inhibitor).

Neither the 5‐FMT‐ nor the 8‐hydroxy‐2‐(di‐n‐propylamino)tetralin (5‐HT1A‐agonist)‐induced 5‐HT syndrome (head weaving and hindlimb abduction) was affected by γ‐mangostin or ketanserin.

The locomotor activity stimulated by 5‐FMT through the activation of α1‐adrenoceptors did not alter in the presence of γ‐mangostin.

5‐HT‐induced inositol phosphates accumulation in mouse brain slices was abolished by ketanserin. γ‐Mangostin caused a concentration‐dependent inhibition of the inositol phosphates accumulation.

γ‐Mangostin caused a concentration‐dependent inhibition of the binding of [3H]‐spiperone, a specific 5‐HT2A receptor antagonist, to mouse brain membranes.

Kinetic analysis of the [3H]‐spiperone binding revealed that γ‐mangostin increased the Kd value without affecting the Bmax value, indicating the mode of the competitive nature of the inhibition by γ‐mangostin.

These results suggest that γ‐mangostin inhibits 5‐FMT‐induced head‐twitch response in mice by blocking 5‐HT2A receptors not by blocking the release of 5‐HT from the central neurone. γ‐Mangostin is a promising 5‐HT2A receptor antagonist in the central nervous system.

British Journal of Pharmacology (1998) 123, 855–862; doi:10.1038/sj.bjp.0701695
CGRP and nitric oxide of neuronal origin and their involvement in neurogenic vasodilatation in rat skin microvasculature
Authors: Merhi Merhi , Dusting Greg J. , Khalil Zeinab
Published: January 2005

Sensory nerves are important for the initiation of neurogenic inflammation and tissue repair. Both calcitonin gene‐related peptide (CGRP) and nitric oxide (NO) have been implicated in neurogenic vasodilatation and inflammatory responses.

A blister model in the rat hind footpad was used as a site to induce neurogenic vasodilatation in response to antidromic electrical stimulation of the sciatic nerve. Blood flux was monitored with a laser Doppler flow monitor.

The quantitative contributions of CGRP and NO to vasodilatation were examined by use of the CGRP receptor antagonist CGRP8–37 and NO synthase inhibitors 7‐nitroindazole (7‐NI), 3‐bromo 7‐NI and NG‐nitro L‐arginine methyl ester (L‐NAME). The potential modulatory role of endothelin was examined by use of the ETA receptor antagonist BQ‐123.

CGRP8–37 (10 μM) was perfused over the blister base before nerve stimulation and continuously throughout the post‐stimulation period, resulting in a significant reduction (41%) in the blood flux vascular response.

Pretreatment with the specific neuronal NO synthase inhibitors, 7‐NI and 3‐bromo 7‐NI (10 mg kg−1, i.v.), and of the non‐specific L‐NAME (100 μM), resulted in significant inhibition of the blood flux response (36%, 72% and 57% decrease, respectively). In contrast, 7‐NI treatment in young rats pretreated with capsaicin had no further effect on the vascular response, suggesting that the source of NO is the sensory nerves.

BQ‐123 (10 μM) significantly enhanced the stimulation‐induced blood flux response (61% increase). When 7‐NI was co‐administered with either CGRP8–37 or BQ‐123, the drug actions were additive, suggesting that there was no interaction between NO and CGRP or endothelin.

These data suggest that both NO and CGRP participate in neurogenic vasodilatation in rat skin microvasculature and that this response is modulated by endogenous endothelin.

British Journal of Pharmacology (1998) 123, 863–868; doi:10.1038/sj.bjp.0701696
Elevated plasma endothelin‐1 level in streptozotocin‐induced diabetic rats and responsiveness of the mesenteric arterial bed to endothelin‐1
Authors: Makino Ayako , Kamata Katsuo
Published: January 2005

Both the plasma endothelin‐1 (ET‐1) levels and the plasma glucose levels were markedly elevated in streptozotocin (STZ)‐induced diabetic rats.

The maximum contractile response of the mesenteric arterial bed to ET‐1 was significantly reduced, and the vasodilatation induced by the ETB‐receptor agonist IRL‐1620 in the mesenteric arterial bed was significantly reduced in STZ‐induced diabetic rats.

ET‐1 (10−8 M) caused a transient vasodilatation followed by a marked vasoconstriction in methoxamine‐preconstricted mesenteric arterial beds. The ET‐1‐induced vasodilatation was significantly larger in beds from diabetic rats than in those from age‐matched controls. By contrast, the ET‐1‐induced vasoconstriction was significantly smaller in STZ‐induced diabetic rats than in the controls.

Both removal of the endothelium with Triton X‐100 and preincubation with BQ‐788 (10−6 M) (ETB‐receptor antagonist) abolished the ET‐1‐induced vasodilatation. Preincubation with BQ‐485 (10−6 M) or BQ‐123 (3×10−6) (ETA‐receptor antagonist) significantly augmented the ET‐1‐induced vasodilatation in control mesenteric arterial beds, but not that in beds from diabetic rats.

These results demonstrate that marked increases not only in plasma glucose, but also in plasma ET‐1 occur in STZ‐induced diabetic rats. We suggest that the decreased contractile response and the increased vasodilator response of the mesenteric arterial bed to ET‐1 may both be due to desensitization of ETA receptors, though ETB receptors may also be desensitized. This desensitization may result from the elevation of the plasma ET‐1 levels seen in STZ‐induced diabetic rats.

British Journal of Pharmacology (1998) 123, 1065–1072; doi:10.1038/sj.bjp.0701704
Characterization of the recombinant human prostanoid DP receptor and identification of L‐644,698, a novel selective DP agonist
Authors: Hamish Wright D. , Metters Kathleen M. , Abramovitz Mark , Ford‐Hutchinson Anthony W.
Published: January 2005

A human embryonic kidney cell line [HEK 293(EBNA)] stably expressing the human recombinant prostaglandin D2 (PGD2) receptor (hDP) has been characterized with respect to radioligand binding and signal transduction properties by use of prostanoids and prostanoid analogues. Radioligand binding studies included saturation analyses, the effects of nucleotide analogues, the initial rate of ligand‐receptor association and equilibrium competition assays. In addition, adenosine 3′:5′‐cyclic monophosphate (cyclic AMP) generation in response to ligand challenge was also measured, as this is the predominant hDP signalling pathway.

L‐644,698 ((4‐(3‐(3‐(3‐hydroxyoctyl)‐4‐oxo‐2‐thiazolidinyl) propyl) benzoic acid) (racemate)) was identified as a novel ligand having high affinity for hDP with an inhibitor constant (Ki) of 0.9 nm. This Ki value was comparable to the Ki values obtained in this study for ligands that have previously shown high affinity for DP: PGD2 (0.6 nm), ZK 110841 (0.3 nm), BW245C (0.4 nm), and BW A868C (2.3 nm).

L‐644,698 was found to be a full agonist with an EC50 value of 0.5 nm in generating cyclic AMP following activation of hDP. L‐644,698 is, therefore, comparable to those agonists with known efficacy at the DP receptor (EC50): PGD2 (0.5 nm), ZK 110841 (0.2 nm) and BW245C (0.3 nm).

L‐644,698 displayed a high degree of selectivity for hDP when compared to the family of cloned human prostanoid receptors: EP1 (>25,400 fold), EP2 (∼300 fold), EP3‐III (∼4100 fold), EP4 (∼10000 fold), FP (>25,400 fold), IP (>25,400 fold) and TP (>25,400 fold). L‐644,698 is, therefore, one of the most selective DP agonists as yet described.

PGJ2 and Δ12‐PGJ2, two endogenous metabolites of PGD2, were also tested in this system and shown to be effective agonists with Ki and EC50 values in the nanomolar range for both compounds. In particular, PGJ2 was equipotent to known DP specific agonists with a Ki value of 0.9 nm and an EC50 value of 1.2 nm.

British Journal of Pharmacology (1998) 123, 1317–1324; doi:10.1038/sj.bjp.0701708
The effect of a secreted form of β‐amyloid‐precursor protein on intracellular Ca2+ increase in rat cultured hippocampal neurones
Authors: Koizumi Schuichi , Ishiguro Mariko , Ohsawa Ikuroh , Morimoto Takako , Takamura Chizuko , Inoue Kazuhide , Kohsaka Shinichi
Published: January 2005

The effects of secreted forms of β‐amyloid‐precursor proteins (APPSs) on the intracellular Ca2+ concentration ([Ca2+]i) were investigated in rat cultured hippocampal neurones. APP695S, a secretory form of APP695, attenuated the increase in [Ca2+]i evoked by glutamate. In addition, APP695S itself evoked an increase in [Ca2+]i in 1 or 2 day‐cultured hippocampal cells, but not in 7 to 13 day‐cultured cells.

Eighty‐one percent of neurones which were immunocytochemically positive for microtubule‐associated protein 2 responded to APP695S with an increase in [Ca2+]i.

APP695S induced a transient rise in [Ca2+]i even in the absence of extracellular Ca2+ and produced an elevation in inositol‐1,4,5‐trisphosphate (IP3) in a concentration‐dependent manner from 100 to 500 ng ml−1. In the presence of extracellular Ca2+, APP695S caused a transient rise in [Ca2+]i followed by a sustained phase at high [Ca2+]i, suggesting Ca2+ entry from the extracellular space.

The [Ca2+]i elevation was mimicked by amino terminal peptides of APPS, but not by carboxy terminal peptides.

These results taken together suggest that APP695S induces an increase in [Ca2+]i in hippocampal neurones through an IP3‐dependent mechanism that changes according to the stage of development.

British Journal of Pharmacology (1998) 123, 1483–1489; doi:10.1038/sj.bjp.0701712
Zn2+ modulation of ATP‐responses at recombinant P2X2 receptors and its dependence on extracellular pH
Authors: Wildman S S. , King B F. , Burnstock G
Published: January 2005

Using recombinant P2X2 receptors expressed in Xenopus oocytes, the modulatory effects of zinc (Zn2+) on ATP‐responses were studied under voltage‐clamp conditions and at different levels of extracellular pH.

Zn2+ (0.3–300 μM) added to the bathing medium potentiated ATP‐activated membrane currents, increasing ATP‐responses by up to 20 fold. This potentiating effect was reversed on washout. Zn2+‐potentiation was reduced in an exponential manner (decaying 1/e in 42 s) as the interval was lengthened between adding Zn2+ then ATP to the superfusate.

The potentiating effect of Zn2+ was progressively diminished by acidic shifts in extracellular pH (pHe) which, of itself, also potentiated ATP‐responses at P2X2 receptors. The maximal potentiating effects of Zn2+ and H+ were not additive.

Neither Zn2+ nor H+ potentiation of ATP‐responses was abolished by diethylpyrocarbonate (DEPC, 0.3–3 mM), which irreversibly denatures histidyl residues. Nine histidyl residues are present in the extracellular loop of P2X2 receptors.

Zn2+ also enhanced the blocking activity of the P2 receptor antagonist suramin at P2X2 receptors. Therefore, Zn2+ also mimics H+ in increasing suramin‐activity at P2X2 receptors.

In summary, Zn2+ and H+ potentiate agonist and antagonist activity at P2X2 receptors but their effects are not wholly alike for receptor agonism. There, the potentiating effects of Zn2+ are time‐dependent and gradually convert to inhibition while those of H+ are time‐independent, persistent and more potent, suggesting that either these modulators interact in a different way with a single allosteric site or with different allosteric sites.

British Journal of Pharmacology (1998) 123, 1214–1220; doi:10.1038/sj.bjp.0701717
Cholecystokinin‐8 regulation of NGF concentrations in adult mouse brain through a mechanism involving CCKA and CCKB receptors
Authors: Tirassa Paola , Stenfors Carina , Lundeberg Thomas , Aloe Luigi
Published: January 2005

Nerve growth factor (NGF), a powerful agent for the growth, differentiation and regeneration of lesioned cells of the central and peripheral nervous systems, has in recent years been indicated as a potential therapeutic agent capable of reversing the processes of cell damage in neurodegenerative events in man. Since NGF does not cross the blood‐brain barrier and central NGF administration requires invasive surgical procedures, the discovery of substances modulating in vivo NGF synthesis in the brain will be extremely useful for a possible clinical use of NGF.

The aim of the present study to analyse if the content of NGF in the brain of adult mice can be affected by peripheral administration of cholecystokinin‐8 (CCK‐8), a well known neuropeptide which has stimulant actions on neurons in the brain and promotes a variety of neurobehavioural effects both in man and rodents.

The dose‐response and time course effects of an i.p. injection of CCK‐8 on the NGF concentrations in the hippocampus, cortex, hypothalamus and pituitary of adult male mice were analysed by use of a sensitive immunoenzymatic assay for NGF. The effects of pretreatment with selective CCKA and CCKB receptor antagonists and atropine on the NGF response to CCK injection were also studied.

The effects of CCK‐8 were dose‐ and time‐dependent and the injection of 8 nmol kg−1 resulted in a 3 fold increase of NGF levels in the hypothalamus and pituitary, and about a 60% increase in the hippocampus. No effects were observed in the cortex. Pretreatment with a selective CCKA receptor antagonist blocked the CCK‐induced NGF increase in the hypothalamus and pituitary. In the hippocampus the same effect was obtained with a CCKB receptor antagonist. Pretreatment with atropine suppressed the CCK‐induced effects on NGF levels in all the brain regions examined.

Our results showing that i.p. injection with CCK‐8 can modulate NGF levels in the brain through a mechanism which seems, in part, to be mediated via the vagal afferents, indicate that this neuropeptide may represent a useful pharmacological approach to enhance endogenous NGF levels in neuropathologies associated with a neurotrophin deficit.

British Journal of Pharmacology (1998) 123, 1230–1236; doi:10.1038/sj.bjp.0701718
SB‐205384: a GABAA receptor modulator with novel mechanism of action that shows subunit selectivity
Authors: Meadows H J. , Kumar C S. , Pritchett D B. , Blackburn T P. , Benham C D.
Published: January 2005

SB‐205384, and its (+) enantiomer (+)‐SB‐205384 were tested for their modulatory effects on human GABAA receptor subunit combinations expressed in Xenopus oocytes by electrophysiological methods.

The slowing of the decay rate induced by SB‐205384 on native GABA‐activated currents in rat neurones was also seen on GABAA currents in oocytes expressing human GABAA subunits. This temporal effect was observed for the α3β2γ2 subunit combination with little effect in subunit combinations containing either α1 or α2.

Potentiation of the peak amplitude of the GABA‐activated currents by SB‐205384 or (+)‐SB‐205384 was less specific for a particular subunit combination, although the greatest effect at 10 μM drug was seen on the α3β2γ2 subunit combination.

In contrast, zolpidem, a benzodiazepine site modulator, did not significantly slow decay rates of GABAA currents in oocytes expressing the α3β2γ2 subunit combination. Zolpidem, as expected, did selectively potentiate GABA‐activated currents on oocytes expressing the γ2 subunit compared to those containing the γ1.

The results show that the novel kinetic modulatory profile of SB‐205384 is selective for the α3β2γ2 subunit combination. This suggests that the compound is binding to a novel regulatory site on the subunit complex.

British Journal of Pharmacology (1998) 123, 1253–1259; doi:10.1038/sj.bjp.0701721
The possible mechanisms of the antiproliferative effect of fullerenol, polyhydroxylated C60, on vascular smooth muscle cells
Authors: Lu Liang‐Huei , Lee Yuan‐Teh , Chen Huei‐Wen , Chiang Long Y. , Huang Huei‐Chen
Published: January 2005

The possible mechanisms of the antiproliferative effect of polyhydroxylated fullerene (fullerenol), a novel free radical trapper, were studied in rat vascular smooth muscle cells (A7r5 cells) and compared with the effect of ascorbic acid.

Fullerenol‐1 and ascorbic acid inhibited the proliferative responses in a number of cells, including rat aortic smooth muscle cells (A7r5 cells), human coronary artery smooth muscle cells, and human CEM lymphocytes (CEM cells) in a concentration dependent manner.

At the concentration range of 10−6 to 10−2 M, fullerenol‐1 and ascorbic acid concentration‐dependently inhibited the proliferative responses stimulated by serum in A7r5 cells. Fullerenol‐1 was more potent than ascorbic acid.

The production of O2− induced by alloxan, a diabetogenic compound, was reduced by fullerenol‐1 (10−4 M) in the presence of A7r5 cells.

The cytosolic protein kinase C activity of A7r5 cells stimulated by phorbol ester was reduced by 10−3 M fullerenol‐1, but not ascorbic acid (10−4–10−2 M) and fullerenol‐1 at lower concentrations (10−6–10−4 M).

In contrast, the membraneous protein tyrosine kinase activity of A7r5 cells stimulated by foetal calf serum was significantly reduced by fullerenol‐1 (10−6–10−3 M) and ascorbic acid (10−4–10−2 M). Again, the inhibitory activity of fullerenol‐1 was greater than that of ascorbic acid.

Our results demonstrate that fullerenol‐1 and ascorbic acid exhibit inhibitory effects on transduction signals in addition to their antioxidative property. It is suggested that the antiproliferative effect of fullerenol‐1 on vascular smooth muscle cells may partly be mediated through the inhibition of protein tyrosine kinase.

British Journal of Pharmacology (1998) 123, 1097–1102; doi:10.1038/sj.bjp.0701722
Effect of RX 821002 at 5‐HT1A‐receptors in rabbit spinal cord in vivo
Authors: Ogilvie Jane , Clarke Rob W.
Published: January 2005

The activity of RX 821002 (2‐methoxy idazoxan) at 5‐HT1A‐receptors in the spinal cord has been investigated in decerebrated, spinalized rabbits. Reflexes evoked in medial gastrocnemius motoneurones by electrical stimulation of the sural nerve were unaffected by intrathecal (i.th.) administration of RX 821002 (111 and 664 nmol cumulative, n=7), although the highest dose of this drug did produce a significant increase in heart rate of 28±7 beats min−1. Subsequent administration of the 5‐HT1A‐receptor agonist (±)‐8‐hydroxy‐2‐(di‐n‐propylamino)tetralin (8‐OH‐DPAT) at 300 nmol, i.th., facilitated reflexes to a median of 144% of pre‐drug controls, an effect that was partially reversed (to a median value of 120% of pre‐drug values) by subsequent administration of the 5‐HT1A‐receptor antagonist WAY‐100635, at 185 nmol i.th.

In a separate set of experiments, 8‐OH‐DPAT was given at 30 nmol i.th. and potentiated reflexes to a median of 170% of pre‐drug levels (n=8). Subsequent administration of RX 821002 (at a cumulative dose of 1.11 μmol, i.th., n=5) significantly reduced gastrocnemius responses to a median of 154% of control values.

After a 3 h recovery period, 8‐OH‐DPAT was re‐administered at 30 nmol, i.th., and increased reflexes to a median value of 151% of pre‐drug levels, an effect not significantly different from when it was given alone. WAY‐100635 dose‐dependently antagonized this effect, causing significant reductions in reflexes at a cumulative dose of 0.55 nmol, i.th., and complete reversal of the effects of 8‐OH‐DPAT at a cumulative dose of 5.5 nmol.

These data show that, at intrathecal doses up to 664 nmol, RX 821002 is devoid of agonist activity at 5‐HT1A‐receptors. It appears to be a very weak antagonist at these sites in vivo, being some 2000 times less potent than WAY‐100635. The inability of WAY‐100635 to block completely the effects of high doses of 8‐OH‐DPAT has been noted previously and can be explained by non‐selective actions of the agonist. However, it would appear that a 30 nmol i.th. dose of 8‐OH‐DPAT is selective for 5‐HT1A receptors in this preparation.

British Journal of Pharmacology (1998) 123, 1138–1142; doi:10.1038/sj.bjp.0701729
Neurogenic and non‐neurogenic responses in the urinary bladder of hibernating hamster
Authors: Pinna Christian , Knight Gillian E. , Puglisi Lina , Burnstock Geoffrey
Published: January 2005

Purinergic and cholinergic components of parasympathetic neurotransmission and contractile responses to exogenous α,β‐methylene ATP, acetylcholine, substance K, substance P, calcitonin gene‐related peptide, vasoactive intestinal polypeptide and capsaicin have been investigated in the urinary bladder of hibernating hamsters (4 weeks), cold exposed (4 weeks) and age‐matched controls.

Electrical field stimulation (EFS) evoked increased frequency‐dependent contractions in the detrusor strips from hibernating hamsters compared with those obtained from cold‐exposed and age‐matched animals. Tetrodotoxin (10−6 M) completely blocked the frequency‐dependent contractions in all groups.

The purinergic component of the parasympathetic neurotransmission was not affected in hibernating and cold‐exposed animals while the cholinergic component was increased with respect to age‐matched animals. The neurogenic response to EFS, still present after incubation with atropine (10−6 M) and suramin (10−4 M), was attenuated by indomethacin (10−6 M) and blocked by tetrodotoxin (10−6 M).

Exogenous administration of α,β‐methylene ATP elicited a significantly reduced contraction in strips from hibernating and cold‐exposed hamsters relative to age‐matched animals. The contractile response to exogenous acetylcholine was greater in the detrusors from hibernating hamsters than in cold‐exposed and age‐matched animals. Substance K elicited reduced contractions in preparations from hibernating animals compared with cold‐exposed and control animals. Calcitonin gene‐related peptide, vasoactive intestinal polypeptide, substance P and capsaicin did not elicit any relaxant or contractile response either at resting tone or in carbachol (5×10−7 M)‐precontracted tissues.

In summary, our findings indicate that 4 weeks of hibernation can significantly increase neurogenic responses in the hamster urinary bladder. This appears to be due to an increase in postjunctional responses to acetylcholine. In contrast, there was a decrease of the postjunctional responses to the parasympathetic cotransmitter ATP and also to the sensory‐motor neurotransmitter substance K.

British Journal of Pharmacology (1998) 123, 1281–1287; doi:10.1038/sj.bjp.0701734
Effect of the triaminopyridine flupirtine on calcium uptake, membrane potential and ATP synthesis in rat heart mitochondria
Authors: Zimmer Guido , Balakirev Maxim , Zwicker Klaus , Hofmann Michael , Woodcock Barry G. , Pergande Gabriela
Published: January 2005

Flupirtine is an analgesic agent which exhibits neuronal cytoprotective activity and may have value in the treatment of conditions involving cell injury and apoptosis. Since flupirtine has no action on known receptor sites we have investigated the effect of this drug on mitochondrial membrane potential, and the changes in intramitochondrial calcium concentration in particular.

The findings show that flupirtine increases Ca2+ uptake in mitochondria in vitro. At clinically relevant flupirtine concentrations, corresponding to flupirtine levels in vitro of 0.2 to 10 nmol mg−1 mitochondrial protein, there was a 2 to 3 fold increase in mitochondrial calcium levels (P<0.01). At supra‐physiological flupirtine concentrations of 20 nmol mg−1 mitochondrial protein and above, the mitochondrial calcium concentrations were indistinguishable from those in untreated mitochondria.

Mitochondrial membrane potential closely paralleled the changes in mitochondrial calcium levels showing a 20% (P<0.01) increase when the flupirtine concentration was raised from 0.2 nmol to 10 nmol mg−1 mitochondrial protein and a return to control values at 20 nmol mg−1 protein.

The increase in mitochondrial calcium uptake and membrane potential were accompanied by an increase in mitochondrial ATP synthesis (30%; P<0.05) and a similar percentage reduction in mitochondrial volume.

Calcium at 80 and 160 nmol mg−1 mitochondrial protein decreased ATP synthesis by 20–25% (P<0.001). This decrease was prevented or diminished if flupirtine at 10 nmol mg−1 protein was added before the addition of calcium.

Since intracellular levels of flupirtine in intact cells never exceeded 10 nmol mg−1 mitochondrial protein, these findings are supportive evidence for an in vivo cytoprotective action of flupirtine at the mitochondrial level.

British Journal of Pharmacology (1998) 123, 1154–1158; doi:10.1038/sj.bjp.0701736
Nitric oxide‐related cyclic GMP‐independent relaxing effect of N‐acetylcysteine in lipopolysaccharide‐treated rat aorta
Authors: Muller Bernard , Kleschyov Andrei L. , Malblanc Sophie , Stoclet Jean‐Claude
Published: January 2005

We have recently demonstrated the formation of protein‐bound dinitrosyl‐iron complexes (DNIC) in rat aortic rings exposed to lipopolysaccharide (LPS) and shown that N‐acetylcysteine (NAC) can promote vasorelaxation in these arteries, possibly via the release of nitric oxide (NO) as low molecular weight DNIC from these storage sites. The aim of the present study was to investigate further the mechanism of the relaxation induced by NAC in LPS‐treated vessels.

In rings incubated with LPS (10 μg ml−1 for 18 h) and precontracted with noradrenaline (NA, 3 μM) plus Nω‐nitro‐L‐arginine methylester (L‐NAME, 3 mM), the relaxation evoked by NAC (0.1 to 10 mM) was abolished by 1H‐[1,2,4]oxadiazolo[4,3‐a]quinoxalin‐1‐one (ODQ, 1 μM, a selective inhibitor of soluble guanylyl cyclase) but not affected by Rp‐8‐bromoguanosine 3′5′‐cyclic monophosphorothioate (Rp‐8BrcGMPS, 60 μM a selective inhibitor of cyclic GMP‐dependent protein kinase). Tetrabutylammonium (TBA, 3 mM, as a non selective K+ channels blocker) or elevated concentration of external KCl (25 or 50 mM) significantly attenuated the NAC‐induced relaxation. Selective K+ channels blockers (10 μM glibenclamide, 0.1 μM charybdotoxin, 0.5 μM apamin or 3 mM 4‐aminopyridine) did not affect the NAC‐induced relaxation. The relaxing effect of NAC (10 mM) was not associated with an elevation of guanosine 3′ : 5′ cyclic monophosphate (cyclic GMP) in LPS‐treated rings.

In aortic rings precontracted with NA (0.1 μM), low molecular weight DNIC (with thiosulphate as ligand, 1 nM to 10 μM) evoked a concentration‐dependent relaxation which was antagonized by ODQ (1 μM) and Rp‐8BrcGMPS (150 μM) but not significantly affected by TBA (3 mM) or by the use of KCl (50 mM) as preconstricting agent. The relaxation produced by DNIC (0.1 μM) was associated with an 11 fold increase in aortic cyclic GMP content, which was completely abolished by ODQ (1 μM).

Taken together with our previous data, the main finding of the present study is that the vascular relaxation induced by NAC in LPS‐treated aorta, although probably related to NO through an interaction via preformed NO stores, was not mediated by activation of the cyclic GMP pathway. It may involve the activation of TBA‐sensitive K+ channels. The differences in the mechanism of relaxation induced by NAC and by exogenous DNIC suggest that the generation of low molecular weight DNIC from protein‐bound species does not play a major role in the NAC‐induced relaxation observed in LPS‐treated rat aorta. In addition, it is suggested that ODQ may display other properties than the inhibition of soluble guanylyl cyclase.

British Journal of Pharmacology (1998) 123, 1221–1229; doi:10.1038/sj.bjp.0701737
Role of nitric oxide in the development and partial reversal of allergen‐induced airway hyperreactivity in conscious, unrestrained guinea‐pigs
Authors: Schuiling Martin , Zuidhof Annet B. , Bonouvrie Monique A. A. , Venema Nicolette , Zaagsma Johan , Meurs Herman
Published: January 2005

Using a conscious, unrestrained guinea‐pig model of allergic asthma, we investigated the role of endogenous nitric oxide (NO) in the regulation of airway (hyper)reactivity to histamine before and after the allergen‐induced early and late asthmatic reactions, by examining the effect of inhalation of the NO synthase inhibitor Nω‐nitro‐l‐arginine methyl ester (l‐NAME, 12 mm, 15 min) on the histamine‐induced airway obstruction of ovalbumin‐sensitized guinea‐pigs before, and at 5.5 h and 23.5 h after allergen challenge.

Before allergen challenge, inhaled l‐NAME caused a significant 2.02±0.25 fold increase (P<0.01) in airway reactivity to histamine; this effect was reversed within 2.5 to 6 h after administration.

After the allergen‐induced early asthmatic reaction at 5 h after ovalbumin provocation, a significant 3.73±0.67 fold increase (P<0.01) of the airway reactivity to histamine was observed; subsequent inhalation of l‐NAME at 5.5 h had no effect on the airway hyperreactivity, reassessed at 6 h.

After the late asthmatic reaction, at 23 h after ovalbumin provocation, a reduced, but still significant airway hyperreactivity to histamine (2.18±0.40 fold; P<0.05) was observed. Subsequent inhalation of l‐NAME now significantly potentiated the partially reduced airway hyperreactivity 1.57±0.19 fold (P<0.05) to the level observed after the early asthmatic reaction.

When administered 30 min before allergen exposure, l‐NAME significantly enhanced the allergen‐induced early asthmatic reaction. However, when administered at 5.5 h after allergen provocation, l‐NAME did not affect the subsequent late asthmatic reaction.

These results indicate that endogenous NO is involved the regulation of histamine‐ and allergen‐induced bronchoconstriction and that a deficiency of cNOS‐derived NO contributes to the allergen‐induced airway hyperreactivity to histamine after the early asthmatic reaction, while a recovery of NO deficiency may account for the partial reversal of the allergen‐induced airway hyperreactivity after the late asthmatic reaction.

British Journal of Pharmacology (1998) 123, 1450–1456; doi:10.1038/sj.bjp.0701738
The expression of functional postsynaptic α2‐adrenoceptors in the corpus cavernosum smooth muscle
Authors: Gupta Sandeep , Moreland Robert B. , Yang Stone , Gallant Cynthia M. , Goldstein Irwin , Traish Abdulmaged
Published: January 2005

The purpose of this study was to determine if corpus cavernosum smooth muscle expresses functional postsynaptic α2‐adrenoceptors (AR).

The α2‐adrenoceptor agonist UK 14,304 elicited concentration‐dependent contractions in rabbit corpus cavernosum smooth muscle (CCSM). The half‐maximal response occurred at 0.32±0.03 μM and the maximum contraction at 10 μM UK 14,304.

Pretreatment of CCSM strips with selective α2‐adrenoceptor antagonists, rauwolscine and RS‐15385, produced rightward shifts in the dose‐response curves to UK 14,304 (pA2 values 7.1 and 8.5, respectively). In contrast, these antagonists did not alter contraction induced by the α1‐adrenoceptor agonist phenylephrine (PE) or oxymetazoline. UK 14,304‐induced contractions were also inhibited by prazosin (pA2=9.08).

UK 14,304‐induced contractions, unlike those to PE, were highly dependent on the presence of extracellular Ca2+.

[3H]‐rauwolscine bound to CCSM membranes with high affinity (Kd=1.5 nM). [3H]‐rauwolscine binding was displaced by unlabelled rauwolscine, RS‐15385, UK 14,304 and prazosin, but not by PE.

UK 14,304 inhibited forskolin and prostaglandin E1 (PGE1)‐induced increases in intracellular cyclic AMP concentration in primary cultures of rabbit CCSM cells.

These results demonstrate that CCSM expresses Gi‐coupled postsynaptic α2‐adrenoceptors, and activation of these receptors causes contraction of trabecular smooth muscle.

British Journal of Pharmacology (1998) 123, 1237–1245; doi:10.1038/sj.bjp.0701739
Antidepressant‐like effects of endogenous histamine and of two histamine H1 receptor agonists in the mouse forced swim test
Authors: Lamberti Claudia , Ipponi Alessandro , Bartolini Alessandro , Schunack Walter , Malmberg‐Aiello Petra
Published: January 2005

Effects of substances which are able to alter brain histamine levels and two histamine H1 receptor agonists were investigated in mice by means of an animal model of depression, the forced swim test.

Imipramine (10 and 30 mg kg−1, i.p.) and amitriptyline (5 and 15 mg kg−1, i.p.) were used as positive controls. Their effects were not affected by pretreatment with the histamine H3 receptor agonist, (R)‐α‐methylhistamine, at a dose (10 mg kg−1, i.p.) which did not modify the cumulative time of immobility.

The histamine H3 receptor antagonist, thioperamide (2–20 mg kg−1, s.c.), showed an antidepressant‐like effect, with a maximum at the dose of 5 mg kg−1, which was completely prevented by (R)‐α‐methylhistamine.

The histamine‐N‐methyltransferase inhibitor, metoprine (2–20 mg kg−1, s.c.), was effective with an ED50 of 4.02 (2.71–5.96) mg kg−1; its effect was prevented by (R)‐α‐methylhistamine.

The histamine precursor, l‐histidine (100–1000 mg kg−1, i.p.), dose‐dependently decreased the time of immobility [ED30 587 (499–712) mg kg−1]. The effect of 500 mg kg−1 l‐histidine was completely prevented by the selective histidine decarboxylase inhibitor, (S)‐α‐fluoromethylhistidine (50 mg kg−1, i.p.), administered 15 h before.

The highly selective histamine H1 receptor agonist, 2‐(3‐trifluoromethylphenyl)histamine (0.3–6.5 μg per mouse, i.c.v.), and the better known H1 agonist, 2‐thiazolylethylamine (0.1–1 μg per mouse, i.c.v.), were both dose‐dependently effective in decreasing the time of immobility [ED50 3.6 (1.53–8.48) and 1.34 (0.084–21.5) μg per mouse, respectively].

None of the substances tested affected mouse performance in the rota rod test at the doses used in the forced swim test.

It was concluded that endogenous histamine reduces the time of immobility in this test, suggesting an antidepressant‐like effect, via activation of H1 receptors.

British Journal of Pharmacology (1998) 123, 1331–1336; doi:10.1038/sj.bjp.0701740
Involvement of bradykinin B1 and B2 receptors in relaxation of mouse isolated trachea
Authors: Li Liang , Vaali Kirsi , Paakkari Ilari , Vapaatalo Heikki
Published: January 2005

The aim of the present study was to investigate the effects of bradykinin and [des‐Arg9]‐bradykinin and their relaxant mechanisms in the mouse isolated trachea.

In the resting tracheal preparations with intact epithelium, bradykinin and [des‐Arg9]‐bradykinin (each drug, 0.01–10 μm) induced neither contraction nor relaxation. In contrast, bradykinin (0.01–10 μm) induced concentration‐dependent relaxation when the tracheal preparations were precontracted with methacholine (1 μm). The relaxation induced by bradykinin was inhibited by the B2 receptor antagonist, d‐Arg0‐[Hyp3,Thi5,d‐Tic7,Oic8]‐bradykinin (Hoe 140, 0.01–1 μm) in a concentration‐dependent manner whereas the B1 receptor antagonist, [des‐Arg9,Leu8]‐bradykinin (0.01–1 μm), had no inhibitory effect on bradykinin‐induced relaxation. [des‐Arg9]‐bradykinin (0.01–10 μm) also caused concentration‐dependent relaxation after precontraction with methacholine. The relaxation induced by [des‐Arg9]‐bradykinin was concentration‐dependently inhibited by the B1 receptor antagonist, [des‐Arg9,Leu8]‐bradykinin (0.01–1 μm), whereas the B2 receptor antagonist, Hoe 140 (0.01–1 μm) was without effect.

In the presence of the cyclo‐oxygenase inhibitor, indomethacin (0.01–1 μm), the relaxations induced by bradykinin and [des‐Arg9]‐bradykinin were inhibited concentration‐dependently.

Two nitric oxide (NO) biosynthesis inhibitors NG‐nitro‐l‐arginine methyl ester (l‐NAME, 100 μm) and NG‐nitro‐l‐arginine (l‐NOARG, 100 μm) had no inhibitory effects on the relaxations induced by bradykinin and [des‐Arg9]‐bradykinin. Neither did the selective inhibitor of the soluble guanylate cyclase, 1H‐[1,2,4]oxadiazolo[4,3‐a]quinoxalin‐1‐one (ODQ, 10 μm) inhibit the relaxations induced by bradykinin and [des‐Arg9]‐bradykinin.

Prostaglandin E2 (PGE2, 0.01–33 μm) caused concentration‐dependent relaxation of the tracheal preparations precontracted with methacholine. Indomethacin (1 μm) and ODQ (10 μm) exerted no inhibitory effects on the relaxation induced by PGE2.

The NO‐donor, sodium nitroprusside (SNP; 0.01–100 μm) also caused concentration‐dependent relaxation of the tracheal preparations precontracted with methacholine. ODQ (0.1–1 μm) concentration‐dependently inhibited the relaxation induced by SNP.

These data demonstrate that bradykinin and [des‐Arg9]‐bradykinin relax the mouse trachea precontracted with methacholine by the activation of bradykinin B2‐receptors and B1‐receptors, respectively. The stimulation of bradykinin receptors induces activation of the cyclo‐oxygenase pathway, leading to the production of relaxing prostaglandins. The NO pathway is not involved in the bradykinin‐induced relaxation. The relaxation caused by NO‐donors in the mouse trachea is likely to be mediated via activation of soluble guanylate cyclase.

British Journal of Pharmacology (1998) 123, 1337–1342; doi:10.1038/sj.bjp.0701741
Validation of Furchgott's method to determine agonist‐dependent A1‐adenosine receptor reserve in guinea‐pig atrium
Authors: Morey Timothy E. , Belardinelli Luiz , Dennis Donn M.
Published: January 2005

The ubiquitous distribution of A1‐adenosine receptors (A1AdoR) represents an impediment to achieve organ and/or response selectivity of A1AdoR agonists. Differential receptor reserve may be exploited to overcome this problem. We hypothesize that A1AdoR reserve is agonist‐dependent and can be accurately estimated with Furchgott's method.

Concentration‐response curves were constructed from measurement of the atrial monophasic action potential duration in guinea‐pig, isolated hearts treated with R(−) N6‐(2‐phenylisopropyl)adenosine (R‐PIA) or 2‐chloro‐N6‐cyclopentyl‐adenosine (CCPA) before and after treatment with the selective, irreversible A1AdoR antagonist 8‐cyclopentyl‐3‐[3‐[[4‐(fluorosulphonyl)benzoyl]oxy]propyl]‐1‐propyl‐xanthine (FSCPX). Using Furchgott's method, we determined the equilibrium dissociation constant (KA) of R‐PIA and CCPA, and the fraction of non‐inactivated A1AdoRs remaining after FSCPX treatment (qfunctional). Values of qfunctional were correlated to the fraction of specific binding sites after FSCPX treatment labelled by [3H]‐8‐cyclopentyl‐1,3‐dipropylxanthine ([3H]‐CPX) derived from saturation binding normalized to control (qbinding).

Both R‐PIA and CCPA are full A1AdoR agonists, but have significantly different potencies (pD2 [EC50]=6.84±0.04 [145 nm] vs 7.36±0.04 [44 nm], respectively), receptor affinities (pKA [KA]= 6.54±0.10 [288 nm] vs 6.13±0.03 [734 nm]), and pharmacological shift ratios defined as KA/EC50 (2.2±0.6 vs 15.9±1.5). Values for qfunctional and qbinding were highly correlated (r2=0.96). The ratio between the intrinsic efficacies of CCPA and R‐PIA derived from Furchgott's analysis was 5.9, a value similar to the ratio of 6.2–6.6 calculated from previously obtained binding data.

Radioligand binding studies validated the use of Furchgott's method to estimate A1AdoR reserve. A1AdoR reserve was agonist‐dependent. CCPA was shown to be a high intrinsic efficacy, low affinity agonist, whereas R‐PIA was found to be a low intrinsic efficacy, high affinity agonist.

British Journal of Pharmacology (1998) 123, 1425–1433; doi:10.1038/sj.bjp.0701747
Exogenous NPY modulation of cardiac autonomic reflexes and its pressor effect in the conscious rabbit
Authors: Serone Adrian P. , Angus James A. , Wright Christine E.
Published: January 2005

Neuropeptide Y (NPY) may inhibit sympathetic and vagal transmission via presynaptic Y2 receptors and cause vasoconstriction via postsynaptic Y1 receptors. We examined the effects of NPY and related peptides on cardiovascular parameters and autonomic reflexes in the conscious rabbit. Further, the postjunctional effects of NPY and related peptides were assessed on acetylcholine (ACh) and isoprenaline agonist dose‐chronotropic response curves.

In conscious rabbits the cardiac baroreceptor‐heart rate reflex (baroreflex), Bezold‐Jarisch like and nasopharyngeal reflexes were assessed in control, propranolol‐treated or methscopolamine‐treated (baroreflex only) groups, before and 30 min after i.v. administration of NPY (10 μg kg−1+ 5 μg kg−1min−1) or vehicle (saline, 10 ml h−1). The effects of equivalent pressor doses of [Leu31, Pro34]NPY or methoxamine on the baroreflex were also examined. In separate animals, dose‐heart rate (HR) response curves to isoprenaline or ACh were constructed before and 15 min after administration of NPY, [Leu31,Pro34]NPY (ACh only) or [Leu31,Pro34]NPY + sodium nitroprusside (ACh only).

Administration of NPY‐receptor agonists caused sustained bradycardia (in the absence of methscopolamine) and rightward shifts of the barocurves in all 3 groups. The range of sympathetically‐mediated tachycardia was significantly decreased by NPY or [Leu31,Pro34]NPY in the methscopolamine‐treated group. However, these changes in the baroreflex were no different from those elicted by equipressor doses of methoxamine. There was no vagal inhibition by any NPY‐receptor agonist in all three autonomic reflexes examined. ACh or isoprenaline dose‐HR response curves were not affected by NPY peptide administration.

We conclude that in the conscious rabbit, at a single dose that elicits a significant pressor response, exogenous NPY has no direct effect on modulation of cardiac and autonomic reflexes. Non‐specific effects of exogenous NPY on the baroreflex may be fully explained by its pressor action. There was no effect of NPY on postjunctional ACh or isoprenaline agonist dose‐response curves. Therefore, it is unlikely that endogenous NPY has a functional role in directly modulating cardiac autonomic neurotransmission in the rabbit.

British Journal of Pharmacology(1998)123, 1375–1384; doi:10.1038/sj.bjp.0701752
Ca2+ mobilization in the aortic endothelium in streptozotocin‐induced diabetic and cholesterol‐fed mice
Authors: Kamata Katsuo , Nakajima Masato
Published: January 2005

Experiments were performed to compare Ca2+ mobilization in the aortic endothelium in streptozotocin (STZ)‐induced diabetic and cholesterol‐fed mice with that in age‐matched controls.

The intracellular free Ca2+ ([Ca2+]i) in the fura PE‐3 loaded endothelium of aortic rings was dose‐dependently increased by cumulative administration of acetylcholine (ACh). ACh caused a transient rise in [Ca2+]i in Ca2+‐free medium. The ACh‐induced increase in [Ca2+]i in normal or Ca2+‐free medium was significantly weaker in both STZ‐induced diabetic and cholesterol‐fed mice.

The weaker [Ca2+]i response in Ca2+‐containing medium in STZ‐induced diabetic and cholesterol‐fed mice was normalized by chronic administration of cholestyramine.

The increased low density lipoprotein (LDL) levels seen in both STZ‐induced diabetic and cholesterol‐fed mice were normalized by the same chronic administration of cholestyramine (300 mg kg−1, p.o. daily for 10 weeks). Chronic administration of cholestyramine had no effect on the plasma glucose level.

Lysophosphatidylcholine (LPC) decreased the [Ca2+]i responses to ACh in the aortic endothelium from normal mice.

These results suggest that ACh increases both Ca2+ influx and Ca2+ release from storage in the aortic endothelium. The weaker [Ca2+]i influx seen in the endothelium of aortae from both STZ‐induced diabetic and cholesterol‐fed mice was improved by the chronic administration of cholestyramine, and we suggest that this improvement is due, at least in part, to a lowering of the plasma LDL level. It is further suggested that LPC may have an important influence over Ca2+ mobilization in the endothelium.

British Journal of Pharmacology (1998) 123, 1509–1516; doi:10.1038/sj.bjp.0701754
Characterization of calcitonin gene‐related peptide(CGRP) receptors in intramural coronary arteries from male and female Sprague Dawley rats
Authors: Sheykhzade Majid , Berg Nyborg Niels C.
Published: January 2005

In this study we characterized the CGRP‐receptor subtype by Schild‐plot analysis using the C‐terminal fragment, human‐αCGRP(8–37), a putative competitive CGRP1‐receptor selective antagonist. In addition, the effect of rat‐αCGRP was compared with that of homologous peptides rat‐βCGRP, rat‐amylin, rat‐adrenomedullin and [Cys(Acm)2,7]‐human‐αCGRP, a putative selective CGRP2‐receptor agonist, in the left coronary arteries of 3 months old male and female Sprague Dawley rats.

Isolated rings from the distal, intramural part of the left anterior descending (LAD) coronary artery in both groups of rats were mounted on a double wire‐myograph. The arteries were then stretched to their optimal lumen diameter for active tension development and precontracted with 10−5 m prostaglandin F2α (PGF2α), after which agonists were added to the organ bath in a cumulative manner.

Rat‐αCGRP induced endothelium‐independent relaxations in male and female Sprague‐Dawley rats. Rat‐βCGRP concentration‐response relations (10−11–10−7 m) were similar to those of rat‐αCGRP in either sex. The maximal relaxations induced by rat‐amylin and rat‐adrenomedullin, both at 10−6 m, were significantly (P<0.05) lower than those induced by rat‐α‐ and rat‐βCGRP. In contrast, the selective CGRP2‐receptor agonist [Cys(Acm)2,7]‐human‐αCGRP failed to induce significant relaxations at the highest concentration used (10−7 m) in the coronary arteries of male and female rats.

The C‐terminal fragment, human‐αCGRP(8–37) blocked concentration‐dependently (10−7–10−6 m) the rat‐αCGRP‐induced relaxation in 10−5 m PGF2α‐precontracted coronary arteries. The slopes of the regression lines of the Schild‐plots for both male and female rats were not significantly (P>0.05) different from unity and the pA2 values for human‐αCGRP(8–37) were 6.93 and 6.98 in arteries from male and female rats, respectively. There was no significant (P>0.05) difference in estimated pKB values for human‐αCGRP(8–37) between male (6.99±0.10, n=13) and female (6.95±0.08, n=13) rats.

The concentration‐response relationships for rat‐α‐ and rat‐βCGRP were similar in male and female Sprague Dawley rats. The predominant CGRP receptor subtype in small intramural coronary arteries appeared to belong to the CGRP1‐receptor subtype in both sexes.

British Journal of Pharmacology (1998) 123, 1464–1470; doi:10.1038/sj.bjp.0701760