bluuebunny/crossref_metadata_2025 huggingface dataset:
Neuroprotective efficacy of ebselen, an anti‐oxidant with anti‐inflammatory actions, in a rodent model of permanent middle cerebral artery occlusion
Authors: Takasago T. , Peters E. E. , Graham D. I. , Masayasu H. , Macrae I. M.
Published: January 2005

The aim of this study was to investigate whether delayed treatment with the anti‐oxidant and anti‐inflammatory agent ebselen reduces the volume of infarction in a rodent model of permanent focal cerebral ischaemia.

Ebselen (10 or 30 mg kg−1) or vehicle was administered by gavage 30 min and 12 h after the induction of cerebral ischaemia by permanent occlusion of the left middle cerebral artery (MCA). Animals were killed 24 h following MCA occlusion, and the volumes of ischaemic damage in the ebselen and control groups were evaluated by quantitative histopathology.

Ebselen was quickly absorbed following oral (gavage) administration and reached peak levels in the plasma by 1 h post‐administration (plasma selenium level of 0.68±0.04 and 0.84±0.1 μg ml−1 for 10 and 30 mg kg−1, respectively, compared to control level of 0.51±0.02 μg kg−1).

Treatment with the lower dose of ebselen (10 mg kg−1) significantly (P<0.01) reduced the volume of infarction in the cerebral hemisphere and cerebral cortex (by 31.8% and 36.7%, respectively compared with the placebo group).

The neuroprotective efficacy of the higher dose ebselen (30 mg kg−1) was less than that of the lower dose ebselen (10 mg kg−1). The volume of ischaemic damage in the cerebral hemisphere was reduced by 23.7% (P<0.02), and cerebral cortex by 27.5% (P<0.01).

Both doses of ebselen (10, 30 mg kg−1) had no therapeutic efficacy on the caudate nucleus, where ischaemia was most severe, in this model.

Free radical‐mediated injury is normally associated with reperfusion of ischaemic tissue. The present results suggest that oxidative injury is also a significant contributor to brain damage in models of maintained (permanent) ischaemia and that ebselen is effective in attenuating this free radical‐induced damage.

British Journal of Pharmacology (1997) 122, 1251–1256; doi:10.1038/sj.bjp.0701426
Involvement of nitric oxide in the inhibition of angiogenesis by interleukin‐2
Authors: Sakkoula Eleni , Pipili‐Synetos Eva , Maragoudakis M. E.
Published: January 2005

Interleukin‐2 (IL‐2), an immunoregulatory cytokine possessing antitumour activity, is an inducer of nitric oxide (NO) synthesis in mice and man. In this study, the possibility that IL‐2 possesses antiangiogenic properties that account for its antitumour effects in vivo was examined. IL‐2 caused a dose‐dependent inhibition of angiogenesis in the chick embryo chorioallantoic membrane (CAM). This inhibition was completely reversed by the NO synthase inhibitor NG‐nitro‐L‐arginine methylester (L‐NAME). Furthermore, IL‐2 was capable of stimulating NO synthase activity in the CAM in vitro and this effect was suppressed by L‐NAME. Addition of IL‐2 to human umbilical vein endothelial cells (HUVECs) in culture, had no effect on their growth characteristics. These results suggest that IL‐2 may be an important antiangiogenic molecule causing its effect via nitric oxide synthesis. The antiangiogenic activity of IL‐2 may be, at least in part, responsible for its antitumour properties.

British Journal of Pharmacology (1997) 122, 793–795; doi:10.1038/sj.bjp.0701436
Analysis of the pulmonary hypertensive effects of the isoprostane derivative, 8‐iso‐PGF2α, in the rat
Authors: John Gareth W. , Valentin Jean‐Pierre
Published: January 2005

We analysed the pulmonary hypertensive effects of the F2‐isoprostane derivative, 8‐iso‐prostaglandin F2α (8‐iso‐PGF2α), in comparison with those of the high efficacy thromboxane A2/prostanoid (TP) receptor agonist, U‐46619, in pentobarbitone‐anaesthetized, open‐chest rats (n=4–15 per group).

8‐iso‐PGF2α produced dose‐dependent increases in mean pulmonary arterial pressure, with an ED50 of 39.0 (31.4–50.6) μg kg−1, i.v. (geometric mean with 95% confidence limits in parentheses) compared to 1.4 (1.1–2.3) μg kg−1, i.v., for U‐46619. The maximum responses evoked by U‐46619 and 8‐iso‐PGF2α were not statistically significantly different (21.0±1.0 and 25.8±1.9 mmHg at 10 μg kg−1 of U‐46619 and 630 μg kg−1 of 8‐iso‐PGF2α, respectively).

The TP receptor antagonist, SQ 29,548 (0.63 mg kg−1, i.v. + 0.63 mg kg−1 h−1) fully antagonised both U‐46619 and 8‐iso‐PGF2α‐induced pulmonary hypertensive responses.

Further experiments were carried out to determine whether 8‐iso‐PGF2α antagonized the pulmonary hypertensive responses evoked by U‐46619, or those induced by itself, as would be predicted for a partial agonist. However, ED10 or ED25 doses of 8‐iso‐PGF2α (10 or 20 μg kg−1, i.v.) failed to reduce the pulmonary hypertensive responses induced either by U‐46619 or by itself.

The data suggest that in the pulmonary vascular bed of the rat, 8‐iso‐PGF2α acts as an agonist of high intrinsic activity at SQ 29,548‐sensitive (probably TP) receptors.

British Journal of Pharmacology (1997) 122, 899–905; doi:10.1038/sj.bjp.0701441
PNU‐107484A with α isoform‐dependent functional changes in αxβ2γ2 subtypes of rat recombinant GABAA receptors
Authors: Im Haesook K. , Im Wha Bin , Carter Donald B. , Schwartz Theresa M. , Bundy Gordon L. , Von Voigtlander Philip F.
Published: January 2005

We discovered a novel γ‐aminobutyric acidA (GABAA) receptor ligand displaying seemingly opposite functionalities, depending on the α isoform of the αxβ2γ2 subtypes. PNU‐107484A enhanced GABA‐induced Cl− currents in the α1β2γ2 subtype, but inhibited the currents in the α3β2γ2 and α6β2γ2 subtypes, and its half‐maximal concentrations in the subtypes were 3.1±0.5, 4.2±1, and 3.5±0.2 μM, respectively, without showing much dependency on α isoforms.

In the α1β2 subtype, the drug at concentrations up to 40 μM showed no effect on GABA‐induced Cl− currents, suggesting the requirement of the γ subunit for its action.

PNU‐107484A behaved like a positive allosteric modulator of the α1β2γ2 subtype with its binding site distinct from those for benzodiazepines, barbiturates and neurosteroids. With the α3β2γ2 subtype, the drug behaved like a non‐competitive inhibitor of GABA, thus blocking Cl− currents by GABA alone or in the presence of pentobarbitone and neurosteroids.

It appears that PNU‐107484A is a unique GABAA receptor ligand with α isoform‐dependent functionalities, which may provide a basis for development of α isoform‐selective ligands, and it could be useful as a probe to investigate the physiological roles of the various α isoform subtypes.

British Journal of Pharmacology (1997) 122, 821–824; doi:10.1038/sj.bjp.0701450
Investigation of α1‐adrenoceptor subtypes mediating vasoconstriction in rabbit cutaneous resistance arteries
Authors: Smith K. M. , Macmillan J. B. , McGrath J. C.
Published: January 2005

Cutaneous resistance arteries (c.r.a.) (internal diameter=240.94±5.42 μm, n=67/25 (number arteries/number animals)) from New Zealand white rabbits were mounted in wire myographs and a normalization procedure followed.

Cumulative concentration‐response curves (CCRCs) were constructed for the α‐adrenoceptor agonists noradrenaline (NA), (R)A61603 and phenylephrine (PE) in the presence of cocaine (3 μM), propranolol (1 μM) and corticosterone (10 μM). The effects of competitive α1‐adrenoceptor antagonists, prazosin, WB4101, 5‐methyl‐urapidil, HV723, BMY7378 and the irreversible α1B selective compound chloroethylclonidine (CEC) were examined versus the potency and maximum response of the c.r.a.s to noradrenaline.

The high potency of A‐61603 relative to PE has been shown to differentiate both functional and binding site α1A‐ or α1B‐adrenoceptors from α1D‐adrenoceptors: A‐61603 was 944 times more potent than phenylephrine (at EC50) suggesting the presence of a functional α1A or α1B as opposed to an α1D‐subtype.

Exposure to chloroethylclonidine (CEC; 100 μM) decreased the maximum response to noradrenaline but did not significantly change noradrenaline sensitivity indicating that a substantial part of noradrenaline‐induced vasoconstriction in rabbit cutaneous arteries is CEC‐insensitive.

The potencies of prazosin (pA2=9.14) and WB4101 (pA2=9.30) indicate the involvement of prazosin‐sensitive functional α1‐adrenoceptors. The slopes of corresponding Schild plots for prazosin and WB4101 did not include negative unity which implies the possible involvement of more than one functional α1‐adrenoceptor subtype in noradrenaline‐induced vasoconstriction in rabbit cutaneous resistance arteries. In contrast to this, in the case of 5‐methyl‐urapidil and HV723, the Schild plot slope parameters were not significantly different from negative unity over the range of concentrations used; the low pA2 value for 5‐methylurapidil (7.27) suggests the non‐involvement of an α1A‐ or an α1D‐adrenoceptor; the low pA2 value for HV723 (8.47) was similar to that against responses postulated as α1L.

We conclude that rabbit cutaneous resistance arteries express a prazosin‐sensitive functional α1‐adrenoceptor resembling the α1B and another low affinity site for prazosin which on the basis of the functional antagonism produced by HV723 most closely resembles the α1L‐adrenoceptor; the low pA2 value for HV723 (8.47) is similar to that against responses postulated as α1L.

British Journal of Pharmacology (1997) 122, 825–832; doi:10.1038/sj.bjp.0701451
Multiple effects of nordihydroguaiaretic acid on ionic currents in rat isolated type I carotid body cells
Authors: Hatton C. J. , Peers C.
Published: January 2005

The effects of the lipoxygenase inhibitor nordihydroguaiaretic acid (NDGA) on the ionic currents of rat carotid body type I cells were investigated by use of whole‐cell and outside‐out patch clamp techniques.

NDGA (5–50 μM) produced a concentration‐dependent inhibition of whole‐cell K+ currents at all activating test potentials (holding potential −70 mV). The time‐course of the inhibition was also concentration‐dependent and the effects of NDGA were only reversible following brief periods of exposure (<2 min). Another lipoxygenase inhibitor, phenidone (5 μM), was without effect on whole‐cell K+ currents in carotid body type I cells.

NDGA (5–50 μM) also inhibited whole‐cell Ca2+ channel currents (recorded with Ba2+ as charge carrier) in a concentration‐dependent manner.

Isolation of voltage‐gated K+ channels by use of high [Mg2+] (6 mM), low [Ca2+] (0.1 mM) solutions revealed a direct inhibition of the voltage‐sensitive component of the whole‐cell K+ current by NDGA (50 μM).

In excised, outside‐out patches NDGA (20–50 μM) increased large conductance, Ca2+ activated K+ channel activity approximately 10 fold, an effect which could be reversed by either tetraethylammonium (10 mM) or charybdotoxin (30 nM).

It is concluded that NDGA activates maxi‐K+ channels in carotid body type I cells and over the same concentration range inhibits voltage‐sensitive K+ and Ca2+ channels. The inhibition of whole cell K+ currents seen is most likely due to a combination of direct inhibition of the voltage‐sensitive K+ current and indirect inhibition of maxi‐K+ channel activity through blockade of Ca2+ channels.

British Journal of Pharmacology (1997) 122, 923–929; doi:10.1038/sj.bjp.0701452
Enhancement by exogenous and locally generated angiotensin II of purinergic neurotransmission via angiotensin type 1 receptor in the guinea‐pig isolated mesenteric artery
Authors: Onaka Uran , Fujii Koji , Abe Isao , Fujishima Masatoshi
Published: January 2005

Angiotensin II is known to enhance sympathetic neurotransmission in the vasculature by increasing the release of noradrenaline, but little is known about the effect on the co‐released transmitter, adenosine 5′‐triphosphate (ATP). In the present study we have examined the effect of angiotensin II on the excitatory junction potential (e.j.p.) elicited by repetitive field stimulation in the guinea‐pig isolated mesenteric artery, to establish the angiotensin II receptor subtype involved in modulating the release of ATP and the role of the endothelium in converting angiotensin I to angiotensin II.

Suramin (300 μM), a P2 purinoceptor antagonist, abolished both the e.j.ps and depolarizing response to α,β‐methylene‐ATP, a stable analogue of ATP, without affecting the resting membrane potential and noradrenaline‐induced depolarization.

Angiotensin II (0.1 μM) affected neither the resting membrane potential nor the amplitude of the first e.j.p., but increased the amplitudes of the subsequent e.j.ps. This enhancing effect of angiotensin II was abolished by CV‐11974 (0.1 μM), an angiotensin II type 1 (AT1) receptor antagonist, but unaffected by PD 123319 (1 μM), an angiotensin II type 2 (AT2) receptor antagonist, or CGP 42112A (1 μM), AT2 receptor ligand.

Angiotensin I (0.1 μM) exerted a similar effect on e.j.ps to that of angiotensin II. CV‐11974 (0.1 μM) or temocaprilat (10 μM), an angiotensin converting enzyme (ACE) inhibitor, abolished the effect of angiotensin I. Removal of the endothelium did not alter the action of angiotensin I.

The results of the present study indicate that the release of ATP from sympathetic nerves innervating the guinea‐pig isolated mesenteric artery, as determined from the magnitude of the e.j.p., can be enhanced by angiotensin II via activation of prejunctional AT1 receptors. Qualitatively similar effects were observed with angiotensin I, which appears to be converted into angiotensin II by a subendothelial process.

British Journal of Pharmacology (1997) 122, 942–948; doi:10.1038/sj.bjp.0701458
Dilatation by angiotensin II of the rat femoral arterial bed in vivo via pressure/flow‐induced release of nitric oxide and prostaglandins
Authors: Heinemann Akos , Wachter Christof H. , Peskar Bernhard A. , Holzer Peter
Published: January 2005

The haemodynamic effects of angiotensin II (AII) and, for comparison, arginine vasopressin (AVP) in the femoral and superior mesenteric artery of urethane‐anaesthetized rats were analysed with the ultrasonic transit time shift technique.

I.v. bolus injection of AII (0.1–3 nmol kg−1) and AVP (0.03–1 nmol kg−1) increased blood pressure which was accompanied by a decrease in blood flow through the superior mesenteric artery and an increase in femoral blood flow. The femoral hyperaemia was in part due to vasodilatation as indicated by a rise of femoral vascular conductance up to 200% relative to baseline. The femoral vasodilatation caused by AVP, but not AII, was followed by vasoconstriction.

Blockade of angiotensin AT1 receptors by telmisartan (0.2–20 μmol kg−1) prevented all haemodynamic responses to AII.

The femoral dilator responses to AII and AVP depended on the increase in vascular perfusion pressure since vasodilatation was reversed to vasoconstriction when blood pressure was maintained constant by means of a gravity reservoir. However, the AII‐evoked femoral vasodilatation was not due to an autonomic or neuroendocrine reflex because it was not depressed by hexamethonium (75 μmol kg−1), prazosin (0.25 μmol kg−1) or propranolol (3 μmol kg−1).

The AII‐induced femoral vasodilatation was suppressed by blockade of nitric oxide (NO) synthesis with NG‐nitro‐L‐arginine methyl ester (L‐NAME, 40 μmol kg−1) and reversed to vasoconstriction when L‐NAME was combined with indomethacin (30 μmol kg−1), but was left unaltered by antagonism of endothelin ETA/B receptors with bosentan (37 μmol kg−1).

These results demonstrate that the effect of AII to increase systemic blood pressure and the resulting rise of perfusion pressure in the femoral artery stimulates the formation of NO and prostaglandins and thereby dilates the femoral arterial bed. This local vasodilator mechanism is sufficient to mask the direct vasoconstrictor response to AII.

British Journal of Pharmacology (1997) 122, 975–984; doi:10.1038/sj.bjp.0701460
Characterization of α1‐adrenoceptor subtypes mediating contractions to phenylephrine in rat thoracic aorta, mesenteric artery and pulmonary artery
Authors: Hussain Monira B. , Marshall Ian
Published: January 2005

The subtype of α1‐adrenoceptor mediating contractions to phenylephrine of the rat thoracic aorta, mesenteric artery and pulmonary artery were investigated by use of antagonists which show selectivity between the cloned α1‐adrenoceptor subtypes in binding studies.

Cumulative concentration‐contraction curves for phenylephrine were competitively antagonized in the rat thoracic aorta by prazosin (pA2 9.9), WB4101 (pA2 9.6), 5‐methylurapidil (pA2 8.1), benoxathian (pA2 9.2) and indoramin (pA2 7.4). These compounds were also competitive antagonists in the mesenteric and pulmonary arteries (except for 5‐methylurapidil in the pulmonary artery), (prazosin pA2 9.9 and 9.7; WB4101 pA2 9.8 and 9.6; 5‐methylurapidil pA2 7.9 and pKB estimate 8.0; benoxathian pA2 8.8 and 9.3; indoramin pA2 7.2 and 7.5, respectively).

RS 17053 was not a competitive antagonist in any blood vessel as Schild plot slopes were greater than unity. The pKB estimates for RS 17053 were 7.1 in aorta, 7.0 in the mesenteric artery and 7.7 in the pulmonary artery.

The α1D‐subtype selective antagonist BMY 7378 appeared to be non‐competitive with shallow Schild plot slopes. The data were better fitted with two lines in all tissues, with Schild plot slopes that were no longer different from unity, except in the pulmonary artery. The higher affinity site for BMY 7378 in the aorta had a pA2 of 9.0, while it was 8.8 and 8.9 in the mesenteric and pulmonary arteries, respectively.

MDL73005EF acted in a non‐competitive manner in all three blood vessels, with shallow Schild plot slopes. The pKB estimates for MDL73005EF were 8.4 in aorta, 7.5 in the mesenteric artery and 8.0 in the pulmonary artery.

In all three blood vessels the functionally determined antagonist affinity estimates correlated best with published pKi values for their displacement of [3H]‐prazosin binding on membranes expressing cloned α1d‐adrenoceptors compared with α1a‐ or α1b‐adrenoceptors. The antagonist affinity estimates in the aorta, mesenteric and pulmonary arteries correlated highly with their previously published pA2 values in rat aorta (α1D) and less well with those for α1A‐ and α1B‐adrenoceptors mediating contraction of the rat epididymal vas deferens and rat spleen, respectively.

The results of this study suggest that the contraction to phenylephrine of the rat thoracic aorta, mesenteric artery and pulmonary artery are mediated in part via the α1D‐subtype of adrenoceptor. The data for both BMY 7378 and MDL73005EF in all three blood vessels are consistent with receptor heterogeneity. However, the identity of the second site is unclear.

British Journal of Pharmacology (1997) 122, 849–858; doi:10.1038/sj.bjp.0701461
Modulation of nicotinic ACh‐, GABAA‐ and 5‐HT3‐receptor functions by external H‐7, a protein kinase inhibitor, in rat sensory neurones
Authors: Hu Hong‐Zhen , Li Zhi‐Wang
Published: January 2005

The effects of external H‐7, a potent protein kinase inhibitor, on the responses mediated by γ‐aminobutyric acid A type (GABAA)‐, nicotinic acetylcholine (nicotinic ACh)‐, ionotropic 5‐hydroxytryptamine (5‐HT3)‐, adenosine 5′‐triphosphate (ATP)‐, N‐methyl‐D‐aspartate (NMDA)‐ and kainate (KA)‐receptors were studied in freshly dissociated rat dorsal root ganglion neurone by use of whole cell patch‐clamp technique.

External H‐7 (1–1000 μM) produced a reversible, dose‐dependent inhibition of whole cell currents activated by GABA, ACh and 5‐HT.

Whole‐cell currents evoked by ATP, 2‐methylthio‐ATP, NMDA and KA were insensitive to external H‐7.

External H‐7 shifted the dose‐response curve of GABA‐activated currents downward without changing the EC50 significantly (from 15.0±4.0 μM to 18.0±5.0 μM). The maximum response to GABA was depressed by 34.0±5.3%. This inhibitory action of H‐7 was voltage‐independent.

Intracellular application of H‐7 (20 μM), cyclic AMP (1 mM) and BAPTA (10 mM) could not reverse the H‐7 inhibition of GABA‐activated currents.

The results suggest that external H‐7 selectively and allosterically modulates the functions of GABAA‐, nicotine ACh‐ and 5‐HT3 receptors via a common conserved site in the external domain of these receptors.

British Journal of Pharmacology (1997) 122, 1195–1201; doi:10.1038/sj.bjp.0701462
Effect of chronic ethanol treatment in vivo on excitability in mouse cortical neurones in vitro
Authors: Ibbotson T. , Field M. J. , Boden P. R.
Published: January 2005

The effects of cessation of chronic ethanol ingestion on seizure activity in vivo and on the characteristics of the evoked synaptic potentials in cortical neurones in vitro have been investigated in mice. Withdrawal from chronic ethanol treatment increased handling seizure ratings in mice between 4 and 16 h post‐withdrawal. This ethanol‐induced increase in seizure rating was unaffected by carbamazepine (30 mg kg−1) but significantly reduced at a higher concentration (130 mg kg−1).

Intracellular recordings were made from cortical layer II neurones in vitro from control mice and from mice following chronic ethanol ingestion. Evoked synaptic potentials were generated in these neurones through intralaminar stimulation.

Neurones from control mice displayed an evoked potential consisting of a fast excitatory postsynaptic potential (e.p.s.p.) mediated by AMPA‐type glutamate receptors and an inhibitory postsynaptic potential (i.p.s.p.) mediated via GABAA receptors. Application of pentylenetetrazole (PTZ) or bicuculline onto these neurones inhibited the i.p.s.p., caused a large increase in both the amplitude and duration of the e.p.s.p. and initiated spontaneous excitatory activity. The resulting large evoked e.p.s.p. was mediated via both NMDA‐ and AMPA‐type glutamate receptors.

Most neurones (77%) from ethanol treated mice displayed an evoked potential which comprised a large e.p.s.p. and no i.p.s.p. The e.p.s.p. consisted of several distinct components and in addition these neurones displayed spontaneous paroxysmal depolarizing shifts. This multi‐component e.p.s.p. was mediated through both NMDA‐ and AMPA‐type glutamate receptors. A population (23%) of neurones from ethanol treated mice exhibited evoked potentials which possessed both inhibitory and excitatory components and these neurones were effectively identical to those obtained from control mice.

Carbamazepine reduced the duration of the e.p.s.p. in neurones from ethanol treated mice and in PTZ‐treated control neurones.

Prolonged ethanol ingestion is known to create a neurochemical imbalance in cortical neurones resulting in abnormal neurotransmission. The present study highlights the functional consequences that arise as a result of these neurochemical changes leading to over‐excitation of neurones and pronounced epileptiform activity.

British Journal of Pharmacology (1997) 122, 956–962; doi:10.1038/sj.bjp.0701471
Subtypes of endothelin receptors that mediate venous effects of endothelin‐1 in anaesthetized rats
Authors: Palacios Beatriz , Lin Lim Su , Pang Catherine C. Y.
Published: January 2005

The subtypes of endothelin receptors that mediate the effects of endothelin‐1 (ET‐1) on mean arterial pressure (MAP), heart rate (HR), mean circulatory filling pressure (MCFP), arterial resistance (RA), cardiac output (CO) and venous resistance (RV) were characterized in 9 groups of pentobarbitone‐anaesthetized rats via the injection of ET‐1 in the absence and presence of bosentan (Ro 47‐0203, ETA‐ and ETB‐receptor antagonist), PD 142893 (ETA‐ and ETB‐receptor antagonist) or FR 139317 (ETA‐receptor antagonist), as well as injection of the ETB‐receptor agonist, IRL 1620.

Cumulative i.v. bolus injections of ET‐1 or IRL 1620 (0.5, 1 and 2 nmol kg−1) dose‐dependently increased MAP (ET: by 22, 34 and 44; IRL: 8, 17 and 28 mmHg), RA (ET: 62, 108 and 162; IRL: 51, 63 and 86% over baseline), RV (ET: 70, 132 and 179; IRL: 81, 89 and 98% over baseline) and MCFP (ET: 1.1, 1.8 and 1.9; IRL: 0.9, 1.0 and 1.2 mmHg) and reduced CO (ET: −18, −35 and −44; IRL: −24; −26; −25% below baseline). Equimolar doses of ET‐1 and IRL 1620 caused similar initial transient depressor responses. Saline did not modify any haemodynamic variables in the time‐control group.

Bosentan (10 mg kg−1, i.v.) inhibited ET‐induced increases in MAP, RV, RA and MCFP and decrease in CO. PD 142893 (22 mg kg−1, i.v.) abolished ET‐induced changes on MAP, RV, RA and CO, but did not alter effects on MCFP. Bosentan alone did not cause haemodynamic changes, but PD 142893 alone elevated MCFP (0.9±0.3 mmHg at 1 h after injection) and did not alter other variables. Both antagonists abolished the initial depressor effects of ET‐1.

FR 139317 (1 mg kg−1, i.v.) partially inhibited the increases in MAP, RV, RA and MCFP and decreases in CO elicited by ET‐1, but did not alter the transient depressor response of ET‐1.

The results show that both ETA‐ and ETB‐receptors mediate the arterial and venous constrictor effects of ET‐1. Bosentan is more efficacious than PD 142893 in inhibiting the venous effects of ET‐1.

British Journal of Pharmacology (1997) 122, 993–998; doi:10.1038/sj.bjp.0701474
Inhibition by levetiracetam of a non‐GABAA receptor‐associated epileptiform effect of bicuculline in rat hippocampus
Authors: Margineanu Doru Georg , Wülfert Ernst
Published: January 2005

Extracellular recording of field potentials, evoked by commissural stimulation in hippocampal area CA3 of anaesthetized rats, was performed in order to study the mode of action of the novel antiepileptic drug levetiracetam (ucb LO59).

The amplitude of orthodromic field population spike (PS2) markedly increased and repetitive population spikes appeared when the recording micropipette contained either bicuculline methiodide (BMI), or the specific GABAA antagonist gabazine (SR‐95531).

BMI‐induced increases in PS2 were reduced in a dose‐dependent manner by 1 to 320 μmol kg−1 levetiracetam i.v., with a U‐shape dose‐response relationship. However, levetiracetam did not reduce the increases in PS2 produced by gabazine.

Clonazepam (1 mg kg−1, i.p.), carbamazepine (20 mg kg−1, i.p.) and valproate (200 mg kg−1, i.v.) were ineffective in preventing BMI‐induced increases in PS2, while the calcium channel antagonist flunarizine, 50 μmol kg−1, i.p., reduced PS2 increments caused by BMI. The L‐type calcium channel blocker nifedipine, 100 μmol kg−1, i.p., was without effect. Similar to levetiracetam, flunarizine did not reduce the increases in PS2 induced by gabazine.

These data suggest that the increased excitability of CA3 neurones, caused by BMI administered in situ, involves calcium‐dependent processes not associated with blockade of GABAA receptors. The inhibition by levetiracetam of this calcium‐dependent effect of BMI might contribute to the antiepileptic effects of the drug.

British Journal of Pharmacology (1997) 122, 1146–1150; doi:10.1038/sj.bjp.0701476
Effect of thromboxane A2 antagonists on bronchial hyperresponsiveness induced immediately after interleukin‐8 inhalation in guinea‐pigs
Authors: Fujimura Masaki , Myou Shigeharu , Nomura Masaharu , Matsuda Tamotsu , Harada Akihisa , Mukaida Naofumi , Matsushima Kouji , Nonomura Akitaka
Published: January 2005

Although repeated intranasal administration of interleukin‐8 (IL‐8) causes bronchial hyperresponsiveness (BHR) mediated via thromboxane A2 (TXA2) and airway neutrophil accumulation in guinea‐pigs, the acute effect of inhaled IL‐8 is unclear. We performed this study to clarify the acute effect of IL‐8 on bronchial responsiveness and the role of TXA2.

The effects of inhaled IL‐8 on bronchial responsiveness and of the TXA2 antagonists, S‐1452 (0.01 and 0.1 mg kg−1) and ONO‐NT‐126 (1.0 or 10 μg kg−1), on IL‐8‐induced BHR were examined by use of a modified Konzett‐Rössler method in guinea‐pigs.

Inhaled IL‐8 at 100 ng ml−1, which failed to induce significant changes in Pao (pressure at the airway opening), enhanced an increase in Pao induced by subsequent inhalations of ascending doses (50–200 μg ml−1) of methacholine and histamine, suggesting the potentiating effect of IL‐8 on bronchial responsiveness. No significant leukocyte infiltration was observed histologically sixteen minutes after the IL‐8 inhalation. Both S‐1452 and ONO‐NT‐126 reduced the IL‐8‐induced BHR.

In conclusion, IL‐8 rapidly causes BHR via TXA2 release in guinea‐pigs.

British Journal of Pharmacology (1997) 122, 1015–1020; doi:10.1038/sj.bjp.0701478
Hexamethonium‐ and methyllycaconitine‐induced changes in acetylcholine release from rat motor nerve terminals
Authors: Tian Lijun , Prior Chris , Dempster John , Marshall Ian G.
Published: January 2005

The neuronal nicotinic receptor antagonists hexamethonium and methyllycaconitine (MLA) have been used to study the putative prejunctional nicotinic ACh receptors (AChRs) mediating a negative‐feedback control of ACh release from motor nerve terminals in voltage‐clamped rat phrenic nerve/hemidiaphragm preparations.

Hexamethonium (200 μM), but not MLA (0.4–2.0 μM), decreased the time constant of decay of both endplate currents (e.p.cs) and miniature endplate currents (m.e.p.cs), indicating endplate ion channel block with hexamethonium. However, driving function analysis and reconvolution of e.p.cs and m.e.p.cs indicated that this ion channel block did not compromise the analysis of e.p.c. quantal content.

At low frequencies of stimulation (0.5–2 Hz), hexamethonium (200 μM) and MLA (2.0 μM) increased e.p.c. quantal content by 30–40%. At high frequencies (50–150 Hz) neither compound affected e.p.c. quantal content. All effects on quantal content were paralleled by changes in the size of the pool of quanta available for release.

The low frequency augmentation of e.p.c. quantal content by hexamethonium was absent when extracellular [Ca2+] was lowered from 2.0 to 0.5 mM.

At the concentrations studied, MLA and hexamethonium produced a small (10–20%) decrease in the peak amplitude of m.e.p.cs.

Neither apamin (100 nM) nor charybdotoxin (80 nM) had effects on spontaneous or nerve evoked current amplitudes at any frequency of stimulation. Thus the ability of nicotinic antagonists to augment e.p.c. quantal content is not due to inhibition of Ca2+‐activated K+‐channels.

We suggest that hexamethonium and MLA increase evoked ACh release by blocking prejunctional nicotinic AChRs. These receptors exert a negative feedback control over evoked ACh release and are probably of the α‐bungarotoxin‐insensitive neuronal type.

British Journal of Pharmacology (1997) 122, 1025–1034; doi:10.1038/sj.bjp.0701481
Electrophysiological characterisation of tachykinin receptors in the rat nucleus of the solitary tract and dorsal motor nucleus of the vagus in vitro
Authors: Maubach Karen A. , Jones Roland S. G.
Published: January 2005

Recent studies have shown antagonists at the NK1 subtype of receptor for tachykinins are anti‐emetics and suggested that this may result from blockade of tachykinin‐mediated synaptic transmission at a central site in the emetic reflex.

We have used intracellular recording in vitro to study the pharmacology of tachykinins in the nucleus of the solitary tract (NST) and dorsal motor nucleus of the vagus (DMNV).

Neurones in the NST were depolarized by substance P (SP), the presumed endogenous ligand for the NK1 receptor and these effects were mimicked by the NK1 agonists, SP‐O‐methylester (SPOMe), GR73632 and septide; however, SP was nearly an order of magnitude less potent than the latter two agonists.

In the DMNV, SP and NK1 receptor agonists evoked similar depolarising responses but SP appeared to be more potent than in the NST and was closer in potency to the other agonists.

NK1‐receptor antagonists blocked responses to septide and GR73632 in the NST but had little effect on responses to SP and SPOMe. In contrast, in the DMNV the NK1‐receptor antagonists blocked responses to septide and GR73632 but also reduced responses to SP and SPOMe.

Neurokinin A (NKA) was almost equipotent with septide and GR73632 in depolarizing both NST and DMNV neurones but these effects were not mimicked by a specific NK2‐receptor agonist. Responses to NKA were unaffected by an NK2‐receptor antagonist; however, the depolarizing effects of NKA were blocked by NK1‐receptor antagonists.

Neurones in both DMNV and NST were unaffected by the endogenous NK3‐receptor ligand, neurokinin B and by a specific agonist for this site, senktide.

The results with NK1 receptor agonists and antagonists suggest that the septide‐sensitive NK1 site is involved in the excitation of both NST and DMNV neurones. The ‘classical’ NK1 receptor may play more of a role in the DMNV and a third unknown site may be responsible for the depolarizing response to SP in the NST. The effects of NKA are best interpreted as an action at the septide‐sensitive NK1 site. This raises the possibility that anti‐emetic action of the NK1 antagonists may be due to blockade of NKA transmission at the septide‐sensitive site.

British Journal of Pharmacology (1997) 122, 1151–1159; doi:10.1038/sj.bjp.0701482
Ethanol inhibition of N‐methyl‐D‐aspartate‐activated current in mouse hippocampal neurones: whole‐cell patch‐clamp analysis
Authors: Peoples Robert W. , White Geoffrey , Lovinger David M. , Weight Forrest F.
Published: January 2005

The action of ethanol on N‐methyl‐D‐aspartate (NMDA)‐activated ion current was studied in mouse hippocampal neurones in culture using whole‐cell patch‐clamp recording.

Ethanol inhibited NMDA‐activated current in a voltage‐independent manner, and did not alter the reversal potential of NMDA‐activated current.

Concentration–response analysis of NMDA‐ and glycine‐activated current revealed that ethanol decreased the maximal response to both agonists without affecting their EC50 values.

The polyamine spermine (1 μM) increased amplitude of NMDA‐activated current but did not alter the percentage inhibition of ethanol.

Compared to an extracellular pH of 7.0, pH 6.0 decreased and pH 8.0 increased the amplitude of NMDA‐activated current, but these changes in pH did not significantly alter the percentage inhibition by ethanol.

The sulphydryl reducing agent dithiothreitol (2 mM) increased the amplitude of NMDA‐activated current, but did not affect the percentage inhibition by ethanol.

Mg2+ (10, 100, 500 μM), Zn2+ (5, 20 μM) or ketamine (2, 10 μM) decreased the amplitude of NMDA‐activated current, but did not affect the percentage inhibition by ethanol.

The observations are consistent with ethanol inhibiting the function of NMDA receptors by a non‐competitive mechanism that does not involve several modulatory sites on the NMDA receptor–ionophore complex.

British Journal of Pharmacology (1997) 122, 1035–1042; doi:10.1038/sj.bjp.0701483
Release of 5‐hydroxytryptamine by hypoxia from epithelioid cells of chicken thoracic aorta
Authors: Ito Shigeo , Ohta Toshio , Nakazato Yoshikazu
Published: January 2005

Epithelioid cells in the chicken thoracic aorta are shown to contain 5‐hydroxytryptamine (5‐HT) in immunocytochemical studies. To determine whether these cells act as chemoreceptors, as do type I cells of the carotid body, we examined the effects of hypoxia and acidosis on the release of 5‐HT from the chicken thoracic aorta. Hypoxia caused the output of 5‐HT in incubation medium. A reduction of pH to 6.8 failed to evoke 5‐HT release. The response to hypoxia was inhibited by the removal of extracellular Ca2+ and by nifedipine and ω‐conotoxin GVIA. These results suggest that epithelioid cells in the chicken thoracic aorta are chemoreceptors which sense a decrease in PO2 and then release 5‐HT by Ca2+ influx through voltage‐dependent L‐ and N‐type Ca2+ channels. The epithelioid cells in the chicken aorta may be a useful model for pharmacological and physiological studies of 5‐HT‐containing cells.

British Journal of Pharmacology (1997) 122, 799–801; doi:10.1038/sj.bjp.0701489
Cardiovascular effects of the novel Ca2+‐sensitiser EMD 57033 in pigs at rest and during treadmill exercise
Authors: Stubenitsky René , Van Der Weerd Rick W. P. , Haitsma David B. , Verdouw Pieter D. , Duncker Dirk J.
Published: January 2005

To date no study has described the cardiovascular effects of increased myofilament Ca2+ responsiveness in awake animals both under resting conditions and during treadmill exercise. In the present study we therefore investigated the systemic, pulmonary and coronary haemodynamic actions of the Ca2+ sensitizer EMD 57033 in 16 chronically instrumented awake pigs at rest and during treadmill exercise, and compared these to the haemodynamic actions of the Ca2+ sensitizer/phosphodiesterase inhibitor pimobendan.

Under resting conditions EMD 57033 (0.2, 0.4 and 0.8 mg kg−1 min−1, i.v.) produced dose‐dependent increases in LVdP/dtmax (up to 65±17% (mean ±s.e.mean), P0.05) and stroke volume (up to 20±3%, P0.05), with an increase in heart rate only after the highest dose (22±5%, P0.05), while mean aortic blood pressure and LVdP/dtmin were not altered. EMD 57033 had also no effect on pulmonary vascular resistance, but produced dose‐dependent decreases in systemic vascular resistance (32±4%, P0.05), and coronary vascular resistance (44±2%, P0.05). These effects were essentially unchanged when animals were pretreated with non‐selective β‐adrenoceptor blockade, indicating that phosphodiesterase inhibition did not contribute to the positive inotropic actions of EMD 57033.

During exercise at 2, 3, and 4 km h−1, the positive inotropic actions of EMD 57033 gradually waned at higher levels of exercise. This may have been caused by the exercise‐induced increase in β‐adrenergic activity, because after pretreatment with propranolol the positive inotropic actions of EMD 57033 were preserved at all levels of exercise. In contrast, the positive inotropic and chronotropic effects of pimobendan were amplified during exercise, but were abolished (at rest) or markedly attenuated (during exercise) after pretreatment with propranolol.

The responses to EMD 57033 during exercise after combined α‐ and β‐adrenergic receptor blockade were not different from those after β‐adrenergic receptor blockade alone, indicating that the positive inotropic actions of EMD 57033 were not mediated via or did not depend on intact α‐adrenergic receptor activity.

In conclusion, EMD 57033 increases left ventricular myocardial contractility in awake pigs. During exercise this effect is partially offset by the increased β‐adrenergic activity, with no effect of α‐adrenergic activity, suggesting that EMD 57033 may be most effective in patients with severe loss of β‐adrenergic responsiveness.
Cyclic GMP‐dependent protein kinase activation in the absence of negative inotropic effects in the rat ventricle
Authors: MacDonell Karen L. , Diamond Jack
Published: January 2005

It has been suggested that activation of cyclic GMP‐dependent protein kinase (PKG) is a necessary step in the chain of events leading to the production of negative inotropy by muscarinic receptor agonists in mammalian ventricles, and that some cyclic GMP‐elevating agents, such as sodium nitroprusside (SNP), fail to exert a negative inotropic effect because they elevate cyclic GMP levels in a pool that does not activate the kinase. This hypothesis was tested in the present study by monitoring the effects of carbachol, SNP and atrial natriuretic peptide (ANP) on contractility, cyclic GMP content and PKG activity in rat intact ventricular preparations and freshly isolated ventricular cardiomyocytes.

The presence of PKG in both the intact vehicle and in isolated ventricular cardiomyocytes was confirmed by MonoQ anion exchange chromatography and Western blotting. The elution profile indicated that the conditions of the PKG assay were selective for measuring PKG activity.

Carbachol induced a marked negative inotropic effect in intact, perfused hearts and ventricular strips in the presence of isoproterenol. The negative inotropic effect of carbachol was not associated with significant changes in cyclic GMP content or PKG activity in intact ventricular tissue, or in PKG activity in isolated cardiomyocytes.

SNP and ANP significantly increased cyclic GMP levels and activated PKG in intact ventricular preparations. Both drugs also activated PKG in isolated cardiomyocytes. However, neither drug had any negative inotropic effect in isoprenaline‐stimulated perfused hearts and ANP did not change the contractility of isoprenaline‐stimulated isolated cardiomyocytes.

The results of this study demonstrate that the negative inotropic effects of muscarinic receptor agonists can occur in the absence of significant activation of PKG. Conversely, marked increases in ventricular cyclic GMP content and PKG activity caused by SNP or ANP were not accompanied by a negative inotropic effect.

These results suggest that increases in cyclic GMP levels and activation of PKG do not play important roles in the regulation of rat ventricular contractility by muscarinic receptor agonists.
Calcium mobilization in Jurkat cells via A2b adenosine receptors
Authors: Mirabet Maribel , Mallol Josefa , Lluis Carmen , Franco Rafael
Published: January 2005

A functional study of cell surface A2b adenosine receptors was performed on the T cell leukaemia line, Jurkat.

A2b receptors were coupled both to the adenylate cyclase system and to intracellular calcium channels. In fact, the agonist of A2b receptors, 5′‐N‐ethylcarboxamidoadenosine (NECA), led to a transient accumulation of intracellular calcium by an inositol phosphate‐independent mechanism.

The NECA‐induced accumulation of cGMP was not responsible for the calcium mobilization via A2b receptors.

The calcium response elicited by activation of A2b receptors was independent of that evoked by activation of the T cell receptor.

These findings not only delineate a novel transduction mechanism for adenosine but also support a specific role for adenosine in modulating signals elicited via the T cell receptor.

British Journal of Pharmacology (1997) 122, 1075–1082; doi:10.1038/sj.bjp.0701495
Effect of peroxynitrite on plasma extravasation, microvascular blood flow and nociception in the rat
Authors: Ridger V. C. , Greenacre S. A. B. , Handy R. L. C. , Halliwell B. , Moore P. K. , Whiteman M. , Brain S. D.
Published: January 2005

Peroxynitrite (ONOO−) is a cytotoxic species, formed by the reaction between nitric oxide and superoxide free radicals, that may be involved in inflammation. In this study we have investigated the effect of peroxynitrite on plasma extravasation and microvascular blood flow in the dorsal skin and on nociceptive responses in the hind paw of the rat.

Male Wistar rats were anaesthetized and their dorsal skin shaved. Plasma extravasation was measured by the extravascular accumulation of 125I‐labelled albumin over 0–45 min and 0–240 min. Blood flow was measured by laser‐Doppler flowmetry over 0–240 min. Studies in the hind paw were carried out in the conscious rat. Hind paw weight changes were determined by volume displacement and nociception by a mechanical hyperalgesia technique.

Intradermal (i.d.) peroxynitrite (100–200 nmol site−1) produced a significant (P<0.01) dose‐dependent increase in plasma extravasation in dorsal skin over 0–45 min which was not increased over 45–240 min. Plasma extravasation was significantly (P<0.001) decreased in rats pretreated with the anti‐inflammatory steroid dexamethasone (1 mg kg−1, i.v.; −180 min), but not modulated by treatment with the hydrogen peroxide deactivator catalase (2200 u site−1), or the superoxide scavenger superoxide dismutase (500 u site−1), effective doses of the tachykinin NK1 antagonist SR140333 (1 nmol site−1), the cyclo‐oxygenase inhibitor indomethacin (358 μmol site−1), or combined pretreatment with mepyramine (histamine H1‐receptor antagonist; 2.8 nmol site−1) and methysergide (5‐HT antagonist; 1.9 nmol site−1).

Microvascular blood flow was significantly (P<0.05) increased 30 and 120 min after i.d. peroxynitrite (100 nmol site−1) in dorsal skin and remained raised until the end of the recording period (240 min). The increase in blood flow was unaffected by dexamethasone (1 mg kg−1, i.v.; −180 min) or indomethacin (10 mg kg−1, s.c.; −30 min).

Hind paw volume was significantly (P<0.001) increased 30 min after intraplantar peroxynitrite (87.5 and 175 nmol paw−1) and remained raised for the duration of the experiment (360 min). By comparison, nociception was not altered by intraplantar peroxynitrite.

These data indicate that peroxynitrite can cause an increase in both plasma extravasation and blood flow, suggesting that peroxynitrite could be of biological relevance to microvascular responses. These findings may be of importance in the pathology of inflammatory diseases in which peroxynitrite formation occurs.

British Journal of Pharmacology (1997) 122, 1083–1088; doi:10.1038/sj.bjp.0701498
Lipopolysaccharide induces expression of tumour necrosis factor alpha in rat brain: inhibition by methylprednisolone and by rolipram
Authors: Buttini M. , Mir A. , Appel K. , Wiederhold K. H. , Limonta S. , Gebicke‐Haerter P. J. , Boddeke H. W. G. M.
Published: January 2005

We have investigated the effects of the phosphodiesterase (PDE) type IV inhibitor rolipram and of the glucocorticoid methylprednisolone on the induction of tumour necrosis factor alpha (TNF‐α) mRNA and protein in brains of rats after peripheral administration of lipopolysaccharide (LPS).

After intravenous administration of LPS, a similar time‐dependent induction of both TNF‐α mRNA and protein was observed in rat brain. Peak mRNA and protein levels were found 7 h after administration of LPS.

In situ hybridization experiments with a specific antisense TNF‐α riboprobe suggested that the cells responsible for TNF‐α production in the brain were microglia.

Intraperitoneal administration of methylprednisolone inhibited the induction of TNF‐α protein in a dose‐dependent manner. A maximal inhibition of TNF‐α protein production by 42.9±10.2% was observed at a dose regimen consisting of two injections of each 30 mg kg−1 methylprednisolone.

Intraperitoneal administration of rolipram also inhibited the induction of TNF‐α protein in a dose‐dependent manner. The maximal inhibition of TNF‐α protein production was 96.1±12.2% and was observed at a dose regimen of three separate injections of each 3 mg kg−1 rolipram.

In situ hybridization experiments showed that the level of TNF‐α mRNA induced in rat brain by LPS challenge was reduced by intraperitoneal administration of methylprednisolone (2×15 mg kg−1) and of rolipram (3×3 mg kg−1).

We suggest that peripheral administration of LPS induces a time‐dependent expression of TNF‐α in rat brain, presumably in microglial cells, and that methylprednisolone and rolipram inhibit LPS‐induced expression of TNF‐α in these cells via a decrease of TNF‐α mRNA stability and/or TNF‐α gene transcription.