bluuebunny/crossref_metadata_2025_split huggingface dataset:
The roles of spinal adenosine receptors in the control of acute and more persistent nociceptive responses of dorsal horn neurones in the anaesthetized rat
Authors: Reeve Alison J. , Dickenson Anthony H. 
Published: July 2012

We describe here the effects of intrathecal selective adenosine receptor agonists on acute and more persistent evoked responses of dorsal horn nociceptive neurones recorded in intact rats anaesthetized with halothane.
The effects of the A1 receptor agaonist, N6‐cyclopentyladenosine and the non‐selective agonist 2‐chloroadenosine as well as the A2a receptor agonist, 2‐p‐(2‐carboxyethyl) phenethylamino‐5″‐N‐ethylcarboxamidoadenosine hydrochloride were gauged on the C‐, Aδ‐, Aβ‐fibre, post‐discharge and wind‐up responses produced by peripheral tanscutaneous stimulation. The antagonists, theophylline and 8(p‐sulphophenyl) theophylline were also tested alone and to reverse the agonist effects.
Subcutaneous formalin (5%) was used to produce a more prolonged nociceptive response initiated by peripheral inflammation.
Both N6‐cyclopentyladenosine and 2‐chloroadenosine produced inhibitions of the C‐fibre evoked responses, wind‐up and post‐discharge of the neurones with no significant effects on the AP responses. By contrast, the Aδ evoked responses were facilitated over the same time course and dose‐range as the inhibitions. N6‐cyclopentyladenosine was more potent and effective than 2‐chloroadenosine. In marked contrast to these agonists, the A2a agonist produced only weak non‐specific inhibitions. Theophylline and 8(p‐sulphophenyl) theophylline alone had no effect on the acute responses but prevented or reversed inhibitory effects of N6‐cyclopentyladenosine.
The formalin response was markedly inhibited by spinal N6‐cyclopentyladenosine with both the acute first phase and more prolonged second phase being dose‐dependently inhibited. N6‐cyclopentyladenosine was considerably more potent on the formalin response than on the other neuronal measures.
The results suggest a role of adenosine A1 receptors in the modulation of both acute and inflammatory nociception in the spinal cord.
Effects of pinacidil on arterial and venous resistances and mean circulatory filling pressure in rats
Authors: Waite Robert P. , Lim Su Lin , Pang Catherine C.Y. 
Published: July 2012

The effects of the potassium channel opener, pinacidil, on mean arterial pressure (MAP), mean circulatory filling pressure (MCFP), total peripheral resistance (TPR), cardiac output (CO) and resistance to venous return (Rv) were studied in rats.
In pentobarbitone‐anaesthetized rats given mecamylamine (ganglionic blocker, 3.7 μg kg−1) and noradrenaline (1.5 μg kg−1 min−) to suppress autonomic reflexes, pinacidil (60 and 180 μg kg−1 min−1), relative to the vehicle, reduced MAP and TPR in a dose‐dependent manner but did not significantly alter CO, MCFP or Rv.
Pinacidil (10–300 μg kg−1 min−1) caused similar increases in MCFP, an inverse index of venous compliance, and similar dose‐dependent reductions in mean arterial pressure (MAP) in conscious, intact rats and rats infused with the ganglionic blocker, hexamethonium (150 μg kg−1 min−1). In rats with vasomotor tone elevated by the infusion of noradrenaline (1.5 μg kg−1 min−1), pinacidil caused markedly greater depressor responses but did not significantly alter MCFP.
Our results show that pinacidil is an efficacious vasodilator of arterial resistance blood vessels but has little venodilator activity.
Extrahepatic metabolism of frusemide in anaesthetized rabbits
Authors: Vergés José , Héroux Lucie , Maurice Hélène , du Souich Patrick 
Published: July 2012

Frusemide is removed from the body by biotransformation and renal secretion, but since frusemide metabolism is not altered in patients with hepatic cirrhosis, the role of the liver may be questioned. The aim of the study was to investigate which organs contribute to the first‐pass metabolism and systemic clearance of frusemide.
Groups of anaesthetized New Zealand rabbits were administered frusemide proximally (prox) and distally (dist) to different organs, and blood was sampled from the abdominal aorta. The area under frusemide plasma concentrations‐time curve (AUC0‐∞) was calculated and frusemide extraction by an organ was estimated from the ratio (AUCdist‐AUCprox)/AUCdist. The small intestine extracted 83% of the absorbed dose of frusemide but the first‐pass uptake by the liver and lungs was negligible.
To assess the contribution of the intestine and the kidneys to the systemic clearance of frusemide, it was injected into the jugular vein and blood was sampled proximal and distal to each organ. The kidneys extracted 24% of frusemide circulating in the renal arteries; on the other hand, the ability of the intestine to extract frusemide from the systemic circulation could not be detected.
The lungs did not metabolize frusemide in vitro; the rate of metabolism of frusemide in vitro by kidneys was similar to that estimated in the intestine, and both rates were faster (P<0.05) than that observed in the liver.
It is concluded that in rabbits, presystemic metabolism of frusemide is carried out by the intestine, and that systemic clearance of frusemide is mainly performed by the kidneys, although other organs, such as the intestine and the liver, must contribute to it.
PPADS: an antagonist at endothelial P2Y‐purinoceptors but not P2U‐purinoceptors
Authors: Brown Colin , Tanna Bhavna , Boarder Michael R. 
Published: July 2012

Bovine aortic endothelial (BAE) cells contain two co‐existing receptors for extracellular ATP, the P2Y and P2U‐purinoceptors. Here we have determined whether the proposed P2x‐purinoceptor antagonist, pyridoxalphosphate‐6‐azophenyl‐2″, 4″‐disulphonic acid (PPADS) could distinguish between these two receptor subtypes.
Cells labelled with myo‐[2‐3H]‐inositol were stimulated with increasing concentrations of either the P2Y‐agonist, 2MeSATP, or the P2U‐agonist, UTP in the absence or presence of 30 μm PPADS. The accumulation of total [3H]‐inositol (poly)phosphates mediated by 2MeSATP was markedly attenuated by PPADS, whereas the response to UTP was not significantly affected.
Stimulation of BAE cells with increasing concentrations of ATP showed a reduced response in the presence of 10 μm PPADS, but this effect of the antagonist was not significant. By contrast, inhibition of the response to ADP was profound and highly significant.
These observations show that PPADS is not a selective P2X‐purinoceptor antagonist, but is able to distinguish between P2Y‐ and P2U‐purinoceptors in BAE cells, and indicate that this compound may provide a useful tool in the study of multiple subtypes of P2‐purinoceptors. Furthermore the results are consistent with the hypothesis that ATP interacts with both receptor subtypes, but that the action of ADP is primarily at the P2Y‐purinoceptor in these endothelial cells.
Evidence for arginine vasopressin as the primary activator of the HPA axis during adjuvant‐induced arthritis
Authors: Chowdrey H.S. , Larsen P.J. , Harbuz M.S. , Jessop D.S. , Aguilera G. , Eckland D.J.A. , Lightman S.L. 
Published: July 2012

Adjuvant‐induced arthritis (AA) is an experimental inflammation of the joints that results in chronic activation of the hypothalamo‐pituitary‐adrenal (HPA) axis.
In this study the role of hypothalamic corticotrophin‐releasing factor (CRF) and arginine vasopressin (AVP) in the regulation of the HPA axis in this condition both in Sprague‐Dawley (SD), and Piebald‐Viral‐Glaxo (PVG) rats has been further characterized.
The increase in AVP peptide content of portal blood (as early as day 11), just prior to the onset of arthritis is confirmed and further increases, peaking at day 16 are shown, coincident with the progression of inflammation in the PVG rats.
The increase in AVP is associated with a significant increase in the expression of AVP but not CRF mRNAs in the medial parvocellular division of the hypothalamic paraventricular nucleus (PVN) of arthritic SD rats.
In the presence of maximal inflammation of SD rats there was a significant decrease in the maximum binding of [125I]‐Tyr‐oCRF to anterior pituitary membranes, whereas AVP receptor concentration in anterior pituitary membranes from both PVG and SD rats showed a significant increase with respect to controls.
The basal adrenocorticotrophin (ACTH) secretion in vitro was similar in both control and arthritic SD rats but that from arthritic PVG rat pituitaries was significantly greater than the respective controls (436±91 v 167±23 pg/tube). The ACTH response of pituitaries of arthritic PVG rats to CRF or the combination of CRF and AVP was significantly higher compared with the controls, although the ACTH response of arthritic SD rat pituitaries was unchanged.
The results are consistent with the view that activation of the parvocellular vasopressin system has an important role in the adaptation of the HPA axis to experimentally‐induced chronic stress of arthritis.
Reduction by prostaglandin E1 or prostaglandin E0 of myocardial infarct size in the rabbit by activation of ATP‐sensitive potassium channels
Authors: Hide Emma J. , Ney Peter , Piper Julie , Thiemermann Christoph , Vane John R. 
Published: July 2012

This study examined whether pretreatment of rabbits with infusions of prostaglandin El (PGE1) or prostaglandin E0 (PGE0) (which were terminated prior to the onset of ischaemia) reduce myocardial infarct size arising from coronary artery occlusion (60 min) and reperfusion (120 min). In addition, we investigated whether the observed cardioprotective effects of these two prostaglandins were due to the activation of ATP‐sensitive potassium (KATP) channels.
In the anaesthetized rabbit, infarct size (expressed as a percentage of the area at risk) after 60 min of coronary artery occlusion followed by 2 h of reperfusion was 59±4% (n= 10). PGE1 or PGE0 treatment (1.0 μg kg−1 min−1), administered as 1 h pretreatments (0.05 ml min−1, i.v.), significantly reduced infarct size to 44±6% (n = 6) or 42±1% (n = 6), respectively. PGE1 or PGE0 pretreatment resulted in a significant reduction in mean arterial blood pressure, which returned to baseline within 15 min of discontinuation of the infusion (i.e. prior to LAL ligation).
The reduction in infarct size afforded by PGE1 was abolished by pretreatment of rabbits with the KATP channel blockers, glibenclamide (60±4%; n = 8) or 5‐hydroxydecanoate (58±6%; n = 6). Similarly, glibenclamide also largely attenuated the reduction in infarct size afforded by PGE0 (52±3%; n = 8).
We propose that a 1 h pretreatment of PGE1 or PGE0 reduces infarct size by activating protein kinase C resulting in the opening of KATP channels.
Endothelin ETA receptor expression in human cerebrovascular smooth muscle cells
Authors: Yu Julie C.M. , Pickard John D. , Davenport Anthony P. 
Published: July 2012

Endothelin (ET) has been implicated in cerebrovasospasm for example, following subarachnoid haemorrhage, and blocking the interaction of ET with its receptors on cerebral vessels, may be of therapeutic benefit. The aim of our study was to characterize endothelin receptor subtypes on medial smooth muscle cells of human cerebral vessels. Cultures of vascular smooth muscle cells were explanted from human cerebral resistance vessels and characterized as human brain smooth muscle cells (HBSMCs).
Over a 48 h incubation period, HBSMC cultures secreted comparable levels of immunoreactive (IR) big endothelin‐1 (big ET‐1) and IR endothelin (ET): 12.7± 10.3 and 8.3 + 5.6 pmol/106 cells, respectively (mean ± s.e.mean from three different individuals), into the culture medium.
Total RNA was extracted from cultures of human brain smooth muscle cells. Reverse‐transcriptase polymerase chain reaction (RT‐PCR) assays and subsequent product separation by agarose gel electrophoresis revealed single bands corresponding to the expected product sizes encoding cDNA for ETA (299 base pairs) and ETB (428 base pairs) (n = 3 different cultures).
Autoradiography demonstrated the presence of specific binding sites for [125I]‐ET‐1 which labels all ET receptors, and [125I]‐PD151242, an ETA subtype‐selective antagonist which exclusively labels ETA receptors, but no specific binding was detected using ETB subtype‐selective [125I]‐BQ3020 (n= 3 different cultures, in duplicate).
In saturation binding assays, [125I]‐ET‐1 bound with high affinity: KD = 0.8 ± 0.1 nm and Bmax = 690±108 fmol mg−1. A one‐site fit was preferred and Hill slopes were close to unity over the concentration range (10−12 to 10−8 m). [125I]‐PD151242 also bound with similar affinity: KD = 0.4 ± 0.1 nm and Bmax = 388 ± 68 fmol mg−l (mean ± s.e.mean, n = 3 different cultures). Again, a one‐site fit was preferred and Hill slopes were close to unity over the concentration range. Unlabelled PD151242 competed for the binding of [125I]‐ET‐I monophasically and analysis of the competition curves indicated that a one‐site fit was preferred over a two‐site model, implying that the cultures express mainly ETA receptors.
Although messenger RNA encoding both ETA and ETB receptors was detected, autoradiographical analysis, as well as binding studies indicate that human cultured brain smooth muscle cells express only ETA receptor protein. Antagonism of this subtype may be necessary to block the actions of ET‐1 in the human cerebral resistance vessels in the vasospasm observed subsequent to subarachnoid haemorrhage.
Endothelium‐dependent relaxations mediated by inducible B1 and constitutive B2 kinin receptors in the bovine isolated coronary artery
Authors: Drummond G.R. , Cocks T.M. 
Published: July 2012

Rings of bovine left anterior descending coronary artery (LAD) were contracted with the thromboxane A2‐mimetic, U46619 (1–30 nM), to approximately 40% of their maximum contraction to 125 mM KCl Krebs solution (KPSSmax) for comparison of responses to the B1 and B2 kinin receptor agonists, des‐Arg9‐bradykinin (des‐Arg9‐BK) and bradykinin (BK), respectively. Relaxation responses were normalized as percentages of the initial U46619‐induced contraction level, while contractile responses were expressed as percentages of KPSSmax.
After 6 h of in vitro incubation in Krebs solution at 37°C, des‐Arg9‐BK (pEC50, 8.00 ±0.08; maximum response (Rmax), 93.9 ±1.9%) and BK (pEC50, 9.75 ±0.07; Rmax, 100.1 ±0.7%) caused endothelium‐dependent relaxations in precontracted rings of bovine LAD which were competitively and selectively antagonized by the B. receptor antagonist, des‐Arg9‐[Leu8]‐BK (pA2, 6.27 ±0.11) and the B2 receptor antagonist Hoe‐140 (pA2, 9.63 +0.14), respectively.
At 3 h of in vitro incubation, the sensitivity (pEC50, 7.45 ±0.10) and Rmax (84.6 ±3.3%) to des‐Arg9‐BK were significantly less than those obtained in the same tissues at 6 h (pEC50, 7.94 ± 0.06; Rmax, 91.4±2.5%), whereas endothelium‐dependent relaxations to BK and ACh were unaffected by incubation time.
Relaxation responses to des‐Arg9‐BK, but not BK, at both 3 h and 6 h were significantly attenuated by the protein synthesis inhibitors, cycloheximide (30 and 100 μm) and actinomycin D (2 μm).
At 6 h, the nitric oxide (NO) synthase inhibitor, NG‐nitro‐L‐arginine (L‐NOARG, 100 μm), caused a significant 2 fold decrease in pEC50 (9.58 ±0.03) but had no effect on Rmax for BK. For des‐Arg9‐BK, L‐NOARG (100 μm) caused a marked and significant decrease in both the pEC50 and Rmax and revealed contractions to low concentrations of des‐Arg9‐BK. In both cases, L‐NOARG inhibition was reversed in the presence of L‐arginine (10 mM).
At 6 h, removal of the endothelium abolished relaxation responses to des‐Arg9‐BK and BK, and for des‐Arg9‐BK, but not BK, unmasked concentration‐dependent contractions (pEC50, 7.57 ±0.09; Rmax, 83.4±9.1%). The sensitivity of contractions to des‐Arg9‐BK increased slightly from 3h (pEC50, 7.37 ±0.08) to 6 h (pEC50, 7.62 ±0.12) of in vitro incubation; however, there was a small but significant depression in the maximum response over this time (Rmax, 126.8 ±8.5% and 103.3 ±8.6% for 3 h and 6 h of incubation respectively).
In conclusion, the bovine LAD contains inducible B1 and constitutive B2 endothelial cell kinin receptors, both of which mediate endothelium‐dependent relaxation partly via the release of NO. B1 receptors were also present on the smooth muscle layer of the bovine LAD.
Enhancement of immobility in a forced swimming test by subacute or repeated treatment with phencyclidine: a new model of schizophrenia
Authors: Noda Y. , Yamada K. , Furukawa H. , Nabeshima T. 
Published: July 2012

Immobility induced by forced swimming is well known as an animal model of depression. To develop an animal model for the negative symptoms of schizophrenia, in particular the depressive symptoms, the effect of phencyclidine (PCP) on immobility in the forced swimming test was investigated in mice, since PCP produces such negative symptoms in humans.
Repeated treatment with PCP (10 mg kg−1 day−1, s.c., once a day for 14 days) prolonged the immobility time in the forced swimming test 24 h after the final injection compared with saline treatment; the effect was not obtained by single or 5 treatments with PCP (10 mg kg−1, s.c.), or by repeated treatment with methamphetamine (0.5 and 1 mg kg−1 day−1, s.c., once a day for 14 days).
The enhancing effect of PCP (10 mg kg−1 day−1, s.c.) on the immobility persisted for at least 21 days after the withdrawal of the drug.
Haloperidol (0.3 and mg kg−1, p.o.), ritanserin (3 and 10 mg kg−1, p.o.), risperidone (0.1‐1 mg kg−, p.o.), and clozapine (3 and 10 mg kg−1, p.o.) failed to attenuate the immobility induced by the forced swimming in mice repeatedly treated with saline when the drugs were administered 1 h before the forced swimming test. However, ritanserin (30 mg kg−1) and clozapine (30 mg kg−1) did attenuate this immobility.
The enhancing effect of PCP on the immobility was attenuated by ritanserin (3 and 10 mg kg−1, p.o.), risperidone (0.3 mg kg−1, p.o.), and clozapine (3 and 10 mg kg−1, p.o.), whereas haloperidol (0.3 and 1 mg kg−1, p.o.) had no effect.
These results suggest that the enhancement of immobility in the forced swimming test brought about by repeated PCP treatment could be used as a model of the negative symptoms, particularly the depression, of schizophrenia. This effect of PCP appeared to be mediated, at least in part, via 5‐HT2A receptors.
Multiple pathways underlying endothelium‐dependent relaxation in the rabbit isolated femoral artery
Authors: Plane Frances , Pearson Timothy , Garland Christopher J. 
Published: July 2012

In isolated segments of the rabbit femoral artery stimulated with noradrenaline, both acetylcholine (1nM‐10μM) and the calcium ionophore A23187 (1nM‐100 μM) evoked endothelium‐dependent smooth muscle relaxation and hyperpolarization while bradykinin (0.01–100 nM) had no effect.
The nitric oxide synthase inhibitors, NG‐nitro‐L‐arginine (L‐NOARG; 100 μM; 20 min) or NG‐nitro‐L‐arginine methyl ester (L‐NAME; 100 μM; 20 min) each abolished the hyperpolarization and the majority of the relaxation to acetylcholine (maximal response reduced from 96.8 ±2.3% to 2.0 ± 1.4%).
The potassium channel blocker, glibenclamide (10 μM; 10 min) also abolished the change in membrane potential to acetylcholine but did not modify the smooth muscle relaxation.
In contrast, neither L‐NAME nor glibenclamide modified the comparable responses of the femoral artery to A23187, which were also unaffected by the cyclo‐oxygenase inhibitor, indomethacin (10 μM).
In artery segments stimulated with potassium chloride (25 mM), the maximal change in tension and membrane potential evoked by A23187 (100 μM) was significantly reduced from 95.0 ±4.5% and 23.0±2.0mV to 69.0 ±10.1% and 12.0±1.5 mV, respectively. Under these conditions L‐NAME further reduced the relaxation but not the accompanying hyperpolarization to A23187.
Endothelium‐denuded arterial segments sandwiched with endothelium‐intact ‘donor’ segments gave qualitatively similar relaxant responses to those described above for acetylcholine and A23187.
Exogenous nitric oxide (0.5–10μM) stimulated a transient relaxation in precontracted artery segments, which at concentrations above 5 μM was accompanied by smooth muscle hyperpolarization (maximum 8.5 ± 3.2 mV; n = 4). The hyperpolarization but not the relaxation to nitric oxide was abolished by either glibenclamide or 25 mM potassium.
These data indicate that in the femoral artery, acetylcholine‐induced relaxation can be attributed solely to the release of nitric oxide from the endothelium, which then stimulates relaxation independently of a change in smooth muscle membrane potential. In contrast, both the relaxation and hyperpolarization evoked by A23187 appear to be mediated predominantly by nitric oxide‐independent pathways which appear to involve a diffusible factor released from the endothelium. The results suggest that this diffusible hyperpolarizing factor can be released from endothelial cells in the femoral artery by A23187 but not by acetylcholine.
Regulation of cytosolic calcium by collagen in single human platelets
Authors: Poole Alastair W. , Watson Stephen P. 
Published: July 2012

There is controversy in the literature as to whether collagen is able to induce directly a rise in cytosolic calcium concentration ([Ca2+]i) in human platelets. We have addressed this question by observing the cytosolic calcium response of single fura‐2‐loaded human platelets settling onto a collagen‐coated surface using dynamic fluorescence ratio imaging.
Following a short lag phase after adherence to collagen fibres, platelets underwent a rapid rise in cytosolic calcium from basal values of 80 ± 13 nM (n = 24) to a peak of 475 ± 42 nM (n = 24) which was sustained for the remaining period of the experiment.
The tyrphostin protein tyrosine kinase inhibitor, ST271, reduced substantially the proportion of platelets which exhibited a rise in [Ca2+]i on adherence to collagen and transformed the response in remaining cells to one of oscillations.
In contrast, and as a control for collagen, laminin‐coated surfaces induced adherence of human platelets without elevating intracellular [Ca2+]; the cells however remained responsive to ADP.
We conclude that collagen directly induces a rise in cytosolic calcium in single human platelets through a tyrosine kinase‐mediated pathway.
Drug‐induced defaecation in rats: role of central 5‐HT1A receptors
Authors: Croci Tiziano , Landi Marco , Bianchetti Alberto , Manara Luciano 
Published: July 2012

We investigated the acute effects of 5‐hydroxytryptamine (5‐HT), and of the 5‐HT1A receptor agonists, 8‐hydroxy‐2‐(di‐n‐propylamino)tetralin (8‐OH‐DPAT), buspirone and SR 57746A, on rat faecal pellet output and water content.
5‐HT, 8‐OH‐DPAT, buspirone and SR 57746A, a new selective 5‐HT1A receptor agonist, displaced [3H]‐8‐OH‐DPAT from specific binding sites in rat hippocampus membranes (Ki, nM: 1.8, 1.2, 15, 3.1 respectively) and stimulated rat defaecation dose‐dependently. SR 57746A and buspirone induced 1 g dry weight of faeces at 1.3 and 6.1 mgkg−1, p.o. (ADO respectively. 8‐OH‐DPAT and 5‐HT stimulated defaecation after s.c. injection (ADl5 0.07 and 7.5mgkg−1, respectively). All these agents increased faecal water content.
The putative 5‐HTlA receptor antagonist, pindolol, injected s.c. or i.c.v., significantly reduced the defaecation induced by systemically administered 8‐OH‐DPAT, buspirone or SR 57746A, but not 5‐HT.
Pretreatment with p‐chlorophenylalanine (i.p.) or 5,7‐dihydroxytryptamine (i.c.v.), according to protocols designed to cause either generalized or CNS‐limited 5‐HT depletion respectively, also reduced the defaecation induced by buspirone or SR 57746A.
No specific 5‐HT1A binding sites could be labelled by incubating rat colon membranes with [3H]‐8‐OH‐DPAT, and in vitro preparations of rat colon segments showed no response to 8‐OH‐DPAT or SR 57746A up to 5 μM.
After eight days' repeated daily treatment, complete tolerance developed to the stimulant effects of SR 57746A and buspirone on faecal water content, but not on faecal pellet output. This suggests that faecal mass excretion and water exchange through the gut wall are affected by independent mechanisms.
The present findings support the involvement of central 5‐HT1A receptors in intestinal propulsion and regulation of luminal fluid content, presumably accounting for the drug‐induced defaecation in rats.