bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cytoprotection by iloprost against paracetamol‐induced toxicity in hamster isolated hepatocytes
Authors: Nasseri‐Sina P. , Fawthrop D.J. , Wilson J. , Boobis A.R. , Davies D.S. 
Published: July 2012

The ability of iloprost (ZK36374) to protect hamster isolated hepatocytes from the toxic effects of paracetamol and its reactive metabolite N‐acetyl‐p‐benzoquinoneimine (NABQI) was investigated. The cytoprotection provided by iloprost was compared with that of N‐acetyl‐l‐cysteine.
Treatment of hepatocytes with either NABQI (0.4 mm) or paracetamol (2 mm) alone resulted in a considerable loss of cell viability, as assessed by trypan blue exclusion or leakage of lactate dehydrogenase, accompanied by an increase in the percentage of viable cells that were blebbed. N‐acetyl‐l‐cysteine (1.25 mm) pretreatment diminished the loss of cell viability and the percentage of blebbed cells resulting from exposure to NABQI or paracetamol, whereas iloprost (10−16 m to 10−10 m) pretreatment reduced only the loss of cell viability, not the percentage of viable cells exhibiting blebbing. Pretreatment with N‐acetyl‐l‐cysteine significantly attenuated the depletion by paracetamol of glutathione and decreased the covalent binding of [14C]‐paracetamol to cellular proteins, whereas iloprost was without any such effects.
The effects of iloprost and N‐acetyl‐l‐cysteine were also investigated by use of a model of paracetamol toxicity in which it is possible to study the biochemical events leading to cell injury separate from the generation of toxic metabolites. Hamster hepatocytes were incubated with paracetamol (4 mm) for 90 min at 37°C during which metabolism of paracetamol occurs with minimal loss of cell viability. Following washing of cells, to remove paracetamol and its metabolites, there was a progressive loss of viability and increase in the percentage of cells exhibiting blebbing when incubated in buffer alone. Addition of either N‐acetyl‐l‐cysteine (1.25 mm) or iloprost (10−14 m to 10−8 m), following washing, significantly reduced the expected loss of cell viability. Iloprost at concentrations outside this range was without effect.
Paracetamol toxicity to isolated hepatocytes could be prevented or delayed by treatment with either N‐acetyl‐l‐cysteine or iloprost, but whereas the former prevented or even reversed plasma membrane blebbing with a resultant reduction in the percentage of viable cells that were blebbed, the prostanoid appeared only to delay the progression from plasma membrane blebbing to loss of viability. Hence, the percentage of viable cells that were ultimately blebbed following exposure to paracetamol was not significantly reduced by addition of iloprost.
Aspirin or ibuprofen exacerbated the loss of viability induced by prior incubation with paracetamol. Thus, there may be a role for endogenous prostaglandins in protecting hepatocytes from paracetamol toxicity.
Iloprost is cytoprotective without any effect upon toxin metabolism or detoxication. The mechanism of action of iloprost probably does not involve induction of prostaglandin synthesis or activation of the previously‐characterized prostacyclin receptor.
Pharmacological characterization of a receptor for calcitonin gene‐related peptide on rat, L6 myocytes
Authors: Poyner David R. , Andrew David P. , Brown Derek , Bose Christopher , Hanley Michael R. 
Published: July 2012

The L6 myocyte cell line expresses high affinity receptors for calcitonin gene‐related peptide (CGRP) which are coupled to activation of adenylyl cyclase. The biochemical pharmacology of these receptors has been examined by radioligand binding or adenosine 3′:5′‐cyclic monophosphate (cyclic AMP) accumulation.In intact cells at 37°C, human and rat α‐ and β‐CGRP all activated adenylyl cyclase with EC50s of about 1.5 nm. A number of CGRP analogues containing up to five amino acid substitutions showed similar potencies. In membrane binding studies at 22°C in 1 mmMg2+, the above all bound to a single site with IC50s of 0.1–0.4 nm.The fragment CGRP(8–37) acted as a competitive antagonist of CGRP stimulation of adenylyl cyclase with a calculatedKdof 5 nm. TheKddetermined in membrane binding assays was lower (0.5 nm).The N‐terminal extended human α‐CGRP analogue Tyro‐CGRP activated adenylyl cyclase and inhibited [125I]‐iodohistidyl‐CGRP binding less potently than human α‐CGRP (EC50for cyclase = 12 nm, IC50for binding = 4 nm).The pharmacological profile of the L6 CGRP receptor suggests that it most closely resembles sites on skeletal muscle, cardiac myocytes and hepatocytes. The L6 cell line should be a stable homogeneous model system in which to study CGRP mechanisms and pharmacology.
Different patterns of release of endothelium‐derived relaxing factor and prostacyclin
Authors: Mitchell Jane A. , DE Nucci Gilberto , Warner Timothy D. , Vane John R. 
Published: July 2012

Release of endothelium derived relaxing factor (EDRF) and prostacyclin (PGI2) from endothelial cells (EC) cultured from bovine aortae was measured by bioassay and radioimmunoassay, respectively, during infusions (10 min) of bradykinin (BK), adenosine diphosphate (ADP), arachidonic acid (AA), alkaline buffers and the free‐bases (FB) of l‐arginine or d‐arginine. Release of EDRF from the luminally perfused rabbit aorta was also measured during infusions (10 min) of acetylcholine (ACh), substance P and ADP.
Bradykinin (10 or 30 nm) infused through the column of EC induced release of both EDRF and PGI2, neither of which was maintained for the duration of the infusion.
ADP (1.6 or 4 μm) infused through the column of EC induced release of a EDRF which was maintained for the duration of the infusion and a release of PGI2 which lasted for a much shorter period.
Arachdonic acid (30 or 90 μm) infused through the column of EC caused a sustained release of EDRF and PGI2, both of which outlasted the infusion of AA.
l‐Arginine FB, d‐arginine FB or alkaline buffer infused through the column of EC released EDRF, but only small amounts of PGI2. The release of EDRF outlasted the period of infusion and was due to an increase in the pH of the Krebs solution perfusing the EC.
Infusions of ACh (0.25–1 μm) or ADP (4–16 μm) caused a sustained release of EDRF from the luminally‐perfused rabbit aorta, whereas infusion of substance P (3.3–10 μm) caused only a transient release of EDRF.
These results show that distinct patterns of EDRF release exist to different agonists in both cultured and in situ EC, and that EDRF and PGI2 do not necessarily follow the same time course of release. Furthermore, sustained release of EDRF does not require the constant infusion of the precursor, l‐arginine, whereas sustained release of PGI2 only occurs when AA, the precursor of PGI2, is present in the extracellular medium.
Alterations in cellular cholesterol metabolism following administration of 6‐hydroxydopamine to rabbits
Authors: O'Meara Niall M.G. , Devery Rosaleen A.M. , Owens Daphne , Collins Patrick B. , Johnson Alan H. , Tomkin Gerald H. 
Published: July 2012

The role of adrenergic mechanisms in the regulation of cholesterol metabolism was investigated by studying the effects of 6‐hydroxydopamine (6‐OHDA) on serum cholesterol levels and on the activities of 3‐hydroxy‐3‐methylglutaryl coenzyme A (HMGCoA) reductase, acyl coenzyme A: cholesterol‐O‐acyltransferase (ACAT) in the livers and intestines, and cholesterol 7α‐hydroxylase in the livers of male New Zealand White rabbits.
Total serum cholesterol levels were significantly reduced (P < 0.01) in 6‐OHDA‐treated animals. This was reflected in the very low density lipoprotein, low density lipoprotein and high density lipoprotein fractions. The reduction in lipoprotein cholesterol levels reflected reduced cholesterol proportions in the lipoprotein fractions.
The 6‐OHDA‐treated animals also had significantly lower activities of intestinal (P < 0.001) and hepatic (P < 0.01) HMGCoA reductase. The specific activities of intestinal ACAT, hepatic ACAT and cholesterol 7α‐hydroxylase were comparable in both groups.
In contrast to the results observed in vivo, 6‐OHDA did not have any in vitro effect on cholesterol biosynthesis in cultured human leucocytes.
This latter finding suggests that the effects of 6‐OHDA on cellular cholesterol biosynthesis in vivo are indirect, possibly resulting from the known toxic effect of this drug in sympathetic nerve terminals, and imply a potential role for the sympathetic nervous system in the regulation of cellular cholesterol biosynthesis in vivo.
Agonist interactions with 5‐HT3 receptor recognition sites in the rat entorhinal cortex labelled by structurally diverse radioligands
Authors: Barnes J.M. , Barnes N.M. , Costall B. , Jagger S.M. , Naylor R.J. , Robertson D.W. , Roe S.Y. 
Published: July 2012

The pharmacological properties of 5‐HT3 receptor recognition sites labelled with [3H]‐(S)‐zacopride, [3H]‐LY278,584, [3H]‐granisetron and [3H]‐GR67330 in membranes prepared from the rat entorhinal cortex were investigated to assess the presence of cooperativity within the 5‐HT3 receptor complex.
In rat entorhinal cortex homogenates, [3H]‐(S)‐zacopride, [3H]‐LY278,584, [3H]‐granisetron and [3H]‐GR67330 labelled homogeneous densities of recognition sites (defined by granisetron, 10 μm) with high affinity (Bmax = 75 ± 5, 53 ± 5, 92 ± 6 and 79 ± 6 fmol mg−1 protein, respectively; pKd = 9.41 ± 0.04, 8.69 ± 0.14, 8.81 ± 0.06 and 10.14 ± 0.04 for [3H]‐(S)‐zacopride, [3H]‐LY278,584, [3H]‐granisetron and [3H]‐GR67330, respectively, n = 3–8).
Quipazine and granisetron competed for the binding of each of the radioligands in the rat entorhinal cortex preparation at low nanomolar concentrations (pIC50; quipazine 9.38–8.51, granisetron 8.62–8.03), whilst the agonists, 5‐hydroxytryptamine (5‐HT), phenylbiguanide (PBG) and 2‐methyl‐5‐HT competed at sub‐micromolar concentrations (pIC50; 5‐HT 7.16–6.42, PBG 7.52–6.40, 2‐methyl‐5‐HT 7.38–6.09).
Competition curves generated with increasing concentrations of quipazine, PBG, 5‐HT and 2‐methyl‐5‐HT displayed Hill coefficients greater than unity when the 5‐HT3 receptor recognition sites in the entorhinal cortex preparation were labelled with [3H]‐LY278,584, [3H]‐granisetron and [3H]‐GR67330. These competing compounds displayed Hill coefficients of around unity when the sites were labelled with [3H]‐(S)‐zacopride. Competition for the binding of [3H]‐(S)‐zacopride, [3H]‐LY278,584, [3H]‐granisetron and [3H]‐GR67330 by granisetron generated Hill coefficients around unity.
The nature of the interaction of competing compounds (quipazine, granisetron, PBG, 5‐HT, 2‐methyl‐5‐HT) for the [3H]‐(S)‐zacopride binding site in the rat entorhinal cortex preparation was not altered by the removal of the Krebs ions or the addition of the monoamine oxidase inhibitor, pargyline, to the HEPES/Krebs buffer.
In conclusion, the present studies provide further evidence towards the presence of cooperativity within the 5‐HT3 receptor macromolecule and indicate that either [3H]‐(S)‐zacopride labels a different site on the receptor complex from [3H]‐LY278,584, [3H]‐granisetron or [3H]‐GR67330, or it binds in such a manner as to prevent the conformatory change in the receptor protein responsible for the cooperative binding of agonists (and quipazine).
Morphine 6‐glucuronide: a metabolite of morphine with greater emetic potency than morphine in the ferret
Authors: Thompson P.I. , Bingham S. , Andrews P.L.R. , Patel N. , Joel S.P. , Slevin M.L. 
Published: July 2012

The emetic potencies of morphine and its metabolite morphine 6‐glucuronide have been determined in the ferret by constructing dose‐response curves for mean total retches and vomits for subcutaneous doses of 0.05 mg kg−1 to 5 mg kg−1. Morphine 6‐glucuronide induced retching and vomiting at lower doses than morphine and at a maximal dose induced more retching and vomiting than morphine.
The emesis induced by both morphine and morphine 6‐glucuronide was abolished by the pre‐ administration of naloxone (0.5 mg kg−1 s.c.).
The 5‐HT3 receptor antagonists granisetron and ondansetron (1 mg kg−1, s.c.) failed to abolish or reduce emesis induced by either compound.
At a high‐dose (5 mg kg−1), morphine but not morphine 6‐glucuronide failed to induce emesis and abolished the emesis induced by the cytotoxic drug, cyclophosphamide (200 mg kg−1, i.p.).
Preliminary pharmacokinetic studies of intravenous and subcutaneous morphine and morphine 6‐glucuronide revealed that morphine 6‐glucuronide accounts for less than 1% of the metabolic product of morphine in the ferret. Peak plasma levels of the two compounds after their subcutaneous administration were obtained within 10 min. The metabolic profile of morphine was not dose‐dependent. There was no relationship between plasma level and emetic response for either compound.
Modulation by peripheral opioids of basal and distension‐stimulated gastric acid secretion in the rat
Authors: Esplugues J.V. , Barrachina M.D. , Esplugues J. 
Published: July 2012

The influence of opioids in modulating gastric acid secretory responses has been investigated in the continuously perfused stomach of the anaesthetized rat.
Intravenous administration of morphine (0.75–3 mg kg−1) or the peripherally acting enkephalin analogue, BW443C (0.75–3 mg kg−1), substantially augmented acid secretion in basal conditions. These effects were significantly inhibited by the opioid antagonists naloxone (1 mg kg−1) and the peripherally acting N‐methylnalorphine (2 mg kg−1). When administered alone, neither opioid antagonist influenced basal acid output.
Acid secretory responses to different levels of gastric distension (5–20 cmH2O) were significantly and dose‐dependently reduced in rats pretreated with morphine (3 mg kg−1) or BW443C (1.5 mg kg−1). Previous administration of either naloxone or N‐methyl nalorphine reversed the inhibitory effects of opioids on gastric acid secretion stimulated by distension. Likewise, blockade of opioid receptors with naloxone or N‐methylnalorphine significantly increased acid output induced by distension.
Levels of serum gastrin in control animals were not increased after intragastric distension (20 cm H2O). Pretreatment with BW443C (1.5 mg kg−1) did not modify the levels of gastrin present during basal or distension stimulated conditions.
Pretreatment with morphine or BW443C did not influence the acid responses to i.v. injection of pentagastrin (100 μg kg−1), histamine (5 mg kg−1) or carbachol (4 μg kg−1). Acid secretion induced by i.v. administration of 2‐deoxy‐d‐glucose (150 mg kg−1) was reduced in rats pretreated with morphine but not with BW443C. Gastric secretory responses to insulin (0.3 i.u. kg−1) were not modified by i.v. morphine.
These observations support a role for peripherally acting opioids in the regulation of gastric acid secretion during basal and distension‐stimulated conditions.
Apparent block of K+ currents in mouse motor nerve terminals by tetrodotoxin, μ‐conotoxin and reduced external sodium
Authors: Braga M.F.M. , Anderson A.J. , Harvey A.L. , Rowan E.G. 
Published: July 2012

In mouse triangularis sterni nerve‐muscle preparations, reduced extracellular Na+ concentrations and low concentrations of the Na+ channel blocking toxins tetrodotoxin (TTX, 18–36 nm) and μ‐conotoxin GIIIB (0.4–2.0 μm) selectively decreased the amplitude of the component of perineural waveforms associated with nerve terminal K+ currents, without affecting the main Na+ spike.
Intracellular recording of endplate potentials (e.p.ps) and miniature endplate potentials (m.e.p.ps) from triangularis sterni preparations revealed that TTX and μ‐conotoxin GIIIB depressed the evoked quantal release of acetylcholine without significant effects on m.e.p.p. amplitude, frequency or time constant of decay.
The apparent block of K+ current by low concentrations of TTX and μ‐conotoxin is probably not a direct effect on K+ channels but results from a decrease in the passive depolarization of nerve terminals following blockade of a small proportion of axonal Na+ channels.
Imidazoline binding sites in human placenta: evidence for heterogeneity and a search for physiological function
Authors: Diamant Sophia , Eldar‐Geva Talia , Atlas Daphne 
Published: July 2012

An α2‐adrenoceptor antagonist, idazoxan, that binds to both α2‐adrenoceptors and to imidazoline sites (IR), has been used to characterize human placental IR. Human placenta is shown to be the richest source of IR (1800 ± 100 fmol mg−1 protein; Kd 38.9 ± 3.4 nm).
Primary cells derived from human placenta and grown in monolayers, also displayed a high density of receptors (3209 ± 136 fmol mg−1 in cytotrophoblasts and 3642 ± 144 fmol mg−1 protein in syncytiotrophoblast enriched cell culture).
[3H]‐idazoxan did not show binding characteristics of α2‐adrenoceptors in human placental membranes or human trophoblastic cells, thus making it a ligand of choice to study the imidazoline site. The tissue appeared to be lacking α2‐adrenoceptors in that other α2‐adrenoceptor ligands, [3H]‐rauwolscine and [3H]‐clonidine, do not bind to α2‐adrenoceptors in human placenta.
IRs are localized on the cell surface, as determined by the release of bound [3H]‐idazoxan from cells, when washed with high ionic/acidic medium.
Imidazoline receptors of human placenta display high affinity for amiloride (72 ± 27 nm). The high affinity was used as a criterion to classify IR to IRa subtype (placenta, rabbit kidney, rabbit liver and rabbit adipose cells) as opposed to the IRb subtype which display low affinity for amiloride (> 2 μm, in all the other tissues).
Several novel ligands comprising a guanido functional group attached to an aromatic residue (e.g. benziliden‐amino‐guanidine (BAG), guanido pyrole) display pronounced selectivity for IR over the α2‐adrenoceptors as the affinity of BAG is about 40 fold higher (Kd = 18.9 ± 13.8 nm in human placenta), than the affinity for α2‐adrenoceptors (Kd = 768 ± 299 nm in human platelets). Imidazoline sites bind selectively BAG and other guanido ligands thus indicating a distinct structural requirement at its site of binding.
K+ channel blockers and monovalent ions (e.g. Cs+ and NH4+) interfere with idazoxan binding to IR, indicating a possible involvement of IR in K+ transport.
The pharmacological modulation of thrombin‐induced cerebral thromboembolism in the rabbit
Authors: May G.R. , Paul W. , Crook P. , Butler K.D. , Page C.P. 
Published: July 2012

Intracarotid (i.c.) administration of thrombin induced a marked accumulation of 111indium‐labelled platelets and 125I‐labelled fibrinogen within the cranial vasculature of anaesthetized rabbits.
Thrombin (100 iu kg−1, i.c.) — induced platelet accumulation was completely abolished by pretreatment with desulphatohirudin (CGP 39393; 1 mg kg−1 i.c., 1 min prior to thrombin). Administration of CGP 39393 1 or 20 min after thrombin produced a significant reduction in platelet accumulation.
Intravenous (i.v.) administration of the platelet activating factor (PAF) receptor antagonist BN 52021 (10 mg kg−1) 5 min prior to thrombin (100 iu kg−1, i.c.) had no effect on platelet accumulation.
An inhibitor of NO biosynthesis, l‐NG‐nitro arginine methyl ester (l‐NAME; 100 mg kg−1, i.c.), had no significant effect on the cranial platelet accumulation response to thrombin (10 iu kg−1, i.c.) when administered 5 min prior to thrombin.
Defibrotide (32 or 64 mg kg−1 bolus i.c. followed by 32 or 64 mg kg−1 h−1, i.c., infusion for 45 min) treatment begun 20 min after thrombin (100 iu kg−1, i.c.) did not significantly modify the cranial platelet accumulation response.
Cranial platelet accumulation induced by thrombin (100 iu kg−1, i.c.) was significantly reversed by the fibrinolytic drugs urokinase (20 iu kg−1, i.e., infusion for 45 min), anisoylated plasminogen streptokinase activator complex (APSAC) (200 μg kg−1, i.v. bolus) or recombinant tissue plasminogen activator (rt‐PA; 100 μg kg−1, i.c. bolus followed by 20 μg kg−1 min−1, i.c., infusion for 45 min) administered 20 min after thrombin. APSAC had no significant effect when administered 3 h after thrombin.
APSAC (200 μg kg−1, i.v. bolus) significantly reversed thrombin (100 iu kg−1, i.c.) — induced intracranial accumulation of 125I‐fibrinogen when administered 20 min after thrombin.
These results suggest that neither endogenous PAF nor NO modulate thrombin‐induced intracranial platelet accumulation in the rabbit. However, fibrin deposition appears to play an important role as shown by the ability of fibrinolytic agents to reverse platelet and fibrinogen accumulation induced by i.c. thrombin.
Endothelium‐dependent relaxation to acetylcholine in the rabbit basilar artery: importance of membrane hyperpolarization
Authors: Rand Victoria E. , Garland C.J. 
Published: July 2012

Muscarinic stimulation of isolated, preconstricted segments of the basilar artery, with either acetylcholine or carbachol, was followed by endothelium‐dependent smooth muscle relaxation and membrane hyperpolarization.
Smooth muscle relaxation to acetylcholine was stimulated in the presence of lower concentrations than the associated hyperpolarization (EC50 values 3.2 μm and 31.6 μm, respectively), and was sustained during agonist application, while the hyperpolarization was relatively transient.
Repeated exposure to acetylcholine was associated with loss of membrane hyperpolarization, while smooth muscle relaxation was unaltered. Following a second exposure to 100 μm acetylcholine, mean hyperpolarization was markedly depressed from 8.5 to 2 mV, and subsequent exposures failed to induce any hyperpolarization. Relaxations with a similar amplitude and rate of development, were recorded with each subsequent addition of acetylcholine.
The competitive substrate inhibitors for nitric oxide synthase, l‐NG‐monomethyl arginine (100 μm l‐NMMA) or l‐NG‐nitro arginine methyl ester (100 μm l‐NAME), modified the form and amplitude of both the relaxation and the hyperpolarization to acetylcholine. In the majority of experiments, both the hyperpolarization and the relaxation were almost totally abolished.
Neither nitric oxide, applied directly in physiological salt solution, nor sodium nitroprusside, produced smooth muscle hyperpolarization except in high concentrations. Reproducible, small amplitude (around 2 mV) hyperpolarization followed the application of either NO gas (15 μm) or sodium nitroprusside (100 μm), both of which induced almost maximal smooth muscle relaxation.
These data show that muscarinic stimulation of endothelial cells in the rabbit basilar artery is followed by both smooth muscle hyperpolarization and relaxation. They indicate that nitric oxide is involved in both of these responses, but that the smooth muscle hyperpolarization is not an essential component of the relaxation.