bluuebunny/crossref_metadata_2025_split huggingface dataset:
Inhibition of muscarinic receptor‐induced inositol phospholipid hydrolysis by caffeine, β‐adrenoceptors and protein kinase C in intestinal smooth muscle
Authors: Prestwich S.A. , Bolton T.B. 
Published: July 2012

The effects of caffeine, isoprenaline, dibutyryl cyclic AMP, isobutylmethylxanthine (IBMX), 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA) or 1‐oleoyl‐2‐acetylglycerol (OAG), (protein kinase C (PKC) activators), 2‐methoxy verapamil (D600), thapsigargin and ryanodine on muscarinic acetylcholine receptor (AChR)‐stimulated inositol phospholipid hydrolysis were studied in smooth muscle fragments from the longitudinal layer of the small intestine of the guinea‐pig.
Incubation of the fragments with the muscarinic agonist, carbachol (CCh) (100 μm) resulted in rapid increases in the levels of all the inositol phosphate isomers with maximal increases in the [3H]‐inositol (1,4,5) trisphosphate ([3H]‐Ins(1,4,5)P3) isomer occurring 10 s following incubation.
The β‐adrenoceptor agonist, isoprenaline (10 μm) and dibutyryl cyclic AMP (10 μm), a membrane permeant analogue of cyclic AMP both reduced the CCh stimulation, but not the basal levels of [3H]‐inositol phosphates. This inhibition by dibutyryl cyclic AMP was enhanced in the presence of the phosphodiesterase inhibitor, IBMX. CCh inhibited the isoprenaline‐induced increases in the levels of cyclic AMP and this was via a pertussi toxin (PTX)‐sensitive G‐protein mechanism.
TPA (1 μm) and OAG (100 μm) a 1,2‐diacylglycerol (DAG) analogue both reduced the CCh‐induced increases in [3H]‐inositol phosphates levels but neither affected basal values nor the basal levels of cyclic AMP.
D600 (10 μm), which blocks voltage‐dependent Ca2+ channels, also reduced the CCh‐stimulated levels of [3H]‐inositol phosphates suggesting that some of the agonist‐induced increases are due to a potentiating effect of Ca2+ entering the cell.
Caffeine (0.5–30 mm) significantly inhibited both the basal and CCh‐induced increases in all the [3H]‐inositol phosphate isomers. Its inhibitory action was not due to increases in cyclic AMP since caffeine had no effect on the levels of cyclic AMP at concentrations up to 30 mm.
Incubation with thapsigargin (1 μm) and ryanodine (10 μm) had no effect on either basal or CCh‐induced inositol phospholipid hydrolysis or cyclic AMP levels.
The results indicate a reciprocal inhibition by β‐adrenoceptors and muscarinic AChRs of their effects on cyclic AMP and inositol phosphate levels respectively. Ca2+ entering the cell (but not the action of ryanodine or thapsigargin) potentiates while caffeine inhibits muscarinic AChR‐induced rises in inositol phosphate levels. Diacylglycerols may exert a negative feed‐back inhibition on inositol phosphate production.
Interaction between methotrexate and indomethacin on a human normal haemopoietic cell line
Authors: Hollingsworth S.J. , Shankley N.P. , Anderson E.M. , Bennett A. 
Published: July 2012

The interaction between methotrexate and indomethacin has been examined, at a physiological folate concentration (20 nm), on a human normal lymphoblast‐like cell line (RPMI 1788) in vitro.
Indomethacin (1 μg ml−1) increased the reduction of lymphoblast growth caused by methotrexate (10–80 ng ml−1).
Indomethacin (0.1 and 1 μg ml−1) potentiated the cytotoxicity of methotrexate (20 and 40 ng ml−1) after 4 days in culture.
Indomethacin (0.4 μg ml−1) reduced the accumulation of tritium in lymphoblasts incubated with [3H]‐methotrexate after 30 min; therefore initial drug accumulation was not responsible for the potentiation seen after 4 days.
If indomethacin increases the killing of human cancer cells by methotrexate in vivo, with a smaller potentiation on lymphoblasts, this combination may be beneficial in treating human malignancy.
Differentiation by pyridoxal 5‐phosphate, PPADS and IsoPPADS between responses mediated by UTP and those evoked by α,β‐methylene‐ATP on rat sympathetic ganglia
Authors: Connolly Gerald P. 
Published: July 2012

The effect of pyridoxal 5‐phosphate, and the 2′,4′ and 2′,5′‐disulphonic acid isomers of 6‐azophenyl‐pyridoxal 5‐phosphate (PPADS and IsoPPADS respectively) on depolarization of the rat superior cervical ganglion evoked by α,β‐methylene‐adenosine 5′‐triphosphate (α,β‐Me‐ATP) and uridine 5′‐triphosphate (UTP) were determined by a grease‐gap recording technique.
Pyridoxal 5‐phosphate (10–100 μm) and PPADS (10–100 μm) enhanced UTP‐ and depressed α,β‐Me‐ATP‐evoked depolarizations but did not significantly alter depolarizations evoked by potassium or hyperpolarizations evoked by adenosine. IsoPPADS (10 μm) depressed α,β‐Me‐ATP‐evoked depolarizations but did not alter depolarizations evoked by UTP. Depolarizations evoked by muscarine were depressed by IsoPPADS but not by pyridoxal 5‐phosphate.
It is concluded that pyridoxal 5‐phosphate, PPADS and IsoPPADS are antagonists at P2X‐purinoceptors but not at the receptors that mediate UTP‐evoked depolarization of the rat superior cervical ganglion. These observations substantiate the recent proposal that the rat superior cervical ganglia possess distinct receptors for purine and pyrimidine 5′‐nucleotides, i.e. P2X‐purinoceptors and pyrimidinoceptors respectively.
Endothelium‐dependent relaxation and hyperpolarization evoked by bradykinin in canine coronary arteries: enhancement by exercise‐training
Authors: Mombouli Jean‐Vivien , Nakashima Mikio , Hamra Mary , Vanhoutte Paul M. 
Published: July 2012

Kinins, which are produced locally in arterial walls, stimulate the release of endothelium‐derived vasodilator substances. Therefore, they may participate in the metabolic adaptation to chronic exercise that occurs in the coronary circulation. Experiments were designed to compare the reactivity to bradykinin in coronary arteries isolated from sedentary and exercised‐trained dogs (for 8–10 weeks).
The organ chambers used in this study were designed for measurement of isometric tension and cell membrane potential with glass microelectrodes. Rings of canine isolated coronary arteries with endothelium were suspended in the organ chambers filled with modified Krebs‐Ringer bicarbonate solution (37°C, gassed with 5% CO2 in 95 O2), and were all treated with indomethacin to prevent interference from prostaglandins.
Bradykinin evoked concentration‐dependent relaxations of the coronary arteries. However, the kinin was significantly less potent in relaxing coronary arteries from the sedentary dogs than those from the trained ones.
In the presence of NG‐nitro‐L‐arginine (an inhibitor of nitric oxide synthases), concentration‐relaxation curves to bradykinin were shifted to the right in both types of preparations. Nonetheless, the peptide was still significantly more potent in arteries from exercise‐trained animals.
In the electrophysiological experiments, concentration‐hyperpolarization curves to bradykinin obtained in arteries from sedentary dogs were also significantly to the right of those in vessels from exercise‐trained animals. Thus, in arteries from exercised animals, bradykinin more potently evoked the release of both nitric oxide (NO) and endothelium‐derived hyperpolarizing factor (EDHF).
The angiotensin converting enzyme (ACE)‐inhibitor, perindoprilat, shifted to the left the concentration‐relaxation curves to bradykinin obtained under control conditions and in the presence of NG‐nitro‐L‐arginine. The concentration‐hyperpolarization curves to bradykinin were also shifted to the left by perindoprilat. The shift induced by the ACE‐inhibitor in either type of preparation was not significantly different.
These findings demonstrate that exercise‐training augments the sensitivity of the coronary artery of the dog to the endothelium‐dependent effects of bradykinin. This sensitization to bradykinin may reflect an increased role of both NO and EDHF, and is not the consequence of differences in ACE activity in the receptor compartment.
Modulation of agonist‐induced phosphoinositide metabolism, Ca2+ signalling and contraction of airway smooth muscle by cyclic AMP‐dependent mechanisms
Authors: Hoiting B.H. , Meurs H. , Schuiling M. , Kuipers R. , Elzinga C.R.S. , Zaagsma J. 
Published: July 2012

The effects of increased cellular cyclic AMP levels induced by isoprenaline, forskolin and 8‐bromoadenosine 3′:5′‐cyclic monophosphate (8‐Br‐cyclic AMP) on phosphoinositide metabolism and changes in intracellular Ca2+ elicited by methacholine and histamine were examined in bovine isolated tracheal smooth muscle (BTSM) cells.
Isoprenaline (pD2 (‐log10 EC50) = 6.32±0.24) and forskolin (pD2 = 5.6±0.05) enhanced cyclic AMP levels in a concentration‐dependent fashion in these cells, while methacholine (pD2 = 5.64±0.12) and histamine (pD2 = 4.90±0.04) caused a concentration‐related increase in [3H]‐inositol phosphates (IP) accumulation in the presence of 10 mM LiCl.
Preincubation of the cells (5 min, 37°C) with isoprenaline (1 μm), forskolin (10 μm) and 8‐Br‐cyclic AMP (1 mM) did not affect the IP accumulation induced by methacholine, but significantly reduced the maximal IP production by histamine (1 mM). However, the effect of isoprenaline was small (15.0±0.6% inhibition) and insignificant at histamine concentrations between 0.1 and 100 μm.
Both methacholine and histamine induced a fast (max. in 0.5‐2 s) and transient increase of intracellular Ca2+ concentration ([Ca2+]i) followed by a sustained phase lasting several minutes. EGTA (5 mM) attenuated the sustained phase, indicating that this phase depends on extracellular Ca2+.
Preincubation of the cells (5 min, 37°C) with isoprenaline (1 μm), forskolin (10 μm) and 8‐Br‐cyclic AMP (1 μm) significantly attenuated both the Ca2+‐transient and the sustained phase generated at equipotent IP producing concentrations of 1 μm methacholine and 100 μm histamine (approx. 40% of maximal methacholine‐induced IP response), but did not affect changes in [Ca2+]i induced by 100 μm methacholine (95.2±3.5% of maximal methacholine‐induced IP response).
Significant correlations were found between the isoprenaline‐induced inhibition of BTSM contraction and inhibition of Ca2+ mobilization or influx induced by methacholine and histamine, that were similar for each contractile agonist.
These data indicate that (a) cyclic AMP‐dependent inhibition of Ca2+ mobilization in BTSM cells is not primarily caused by attenuation of IP production, suggesting that cyclic AMP induced protein kinase A (PKA) activation is effective at a different level in the [Ca2+]i homeostasis, (b) that attenuation of intracellular Ca2+ concentration plays a major role in β‐adrenoceptor‐mediated relaxation of methacholine‐ and histamine‐induced airway smooth muscle contraction, and (c) that the relative resistance of the muscarinic agonist‐induced contraction to β‐adrenoceptor agonists, especially at (supra) maximal contractile concentrations is largely determined by its higher potency in inducing intracellular Ca2+ changes.
Inhibitory effect of noradrenaline uptake inhibitors on contractions of rat aortic smooth muscle
Authors: Huang Yu 
Published: July 2012

The effects of noradrenaline (NA) uptake inhibitors on contractions induced by NA, high K+, and 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA) in rat isolated aorta were investigated.
Protriptyline (0.3 μm) and amitriptyline (0.3 μm) produced an approximately parallel shift to the right in the dose‐response curve to NA. Protriptyline (>0.3 μm), amitriptyline (>0.3 μm) and xylamine (0.01‐1 μm) significantly reduced the maximal contractile response to NA. The IC50 values for inhibition of the contractile response to 3 μm NA were 1.58 μm for xylamine, 1.70 μm for amitriptyline and 2.57 μm for protriptyline.
Protriptyline and amitriptyline dose‐dependently inhibited the high K+ (60 mM)‐induced contraction (IC50 = 0.69 μm for protriptyline and IC50 = 3.15 μm for amitriptyline). In contrast, xylamine did not affect the high K(+‐induced contraction.
Protriptyline and amitriptyline dose‐dependently inhibited TPA (1 μm)‐induced contraction in calcium‐free solution; xylamine (up to 30 μm) was without effect. Staurosporine (10 nM) completely inhibited the TPA‐ and NA‐induced contraction.
Protriptyline (3 μm) and amitriptyline (3 μm) caused about 54% and 60% inhibition, respectively, of aortic contractions caused by endothelin‐1 (10 nM) in the absence of endothelium. Xylamine (10 μm) was without effect.
Inhibitory effects of NA uptake inhibitors on contractions were independent of the presence of endothelium and were unaffected by the K+ channel blockers, tetraethylammonium ions (up to 3 mM) and glibenclamide (up to 30 μm).
These results indicate that tricyclic antidepressant drugs such as protriptyline and amitriptyline could act as both postsynaptic adrenoceptor antagonists and direct inhibitors of muscle contraction; whereas, xylamine, a structurally distinct NA uptake blocker might principally exert its action only at α‐adrenoceptors on rat aortic smooth muscle.
The effects of anticonvulsants on 4‐aminopyridine‐induced bursting: in vitro studies on rat peripheral nerve and dorsal roots
Authors: Lees G. 
Published: July 2012

Aminopyridines have been used as beneficial symptomatic treatments in a variety of neurological conditions including multiple sclerosis but have been associated with considerable toxicity in the form of abdominal pain, paraesthesias and (rarely) convulsions.
Extracellular and intracellular recording was used to characterize action potentials in rat sciatic nerves and dorsal roots and the effects of 4‐aminopyridine (4‐AP).
In sciatic nerve trunks, 1 mM 4‐AP produced pronounced after potentials at room temperature secondary to regenerative firing in affected axons (5–10 spikes per stimulus). At physiological temperatures, after potentials (2–3 spikes) were greatly attenuated in peripheral axons.
4‐AP evoked more pronounced and prolonged after discharges in isolated dorsal roots at 37°C (3–5.5 mV and 80–100 ms succeeded by a smaller inhibitory/depolarizing voltage shift) which were used to assess the effects of anticonvulsants.
Phenytoin, carbamazepine and lamotrigine dose‐dependently reduced the area of 4‐AP‐induced after potentials at 100 and 320 μm but the amplitude of compound action potentials (evoked at 0.5 Hz) was depressed in parallel.
The tonic block of sensory action potentials by all three drugs (at 320 μm) was enhanced by high frequency stimulation (5–500 Hz).
The lack of selectivity of these frequency‐dependent Na+ channel blockers for burst firing, compared to low‐frequency spikes, is discussed in contrast to their effects on 4‐AP‐induced seizures and paroxysmal activity in CNS tissue (which is associated with large and sustained depolarizing plateau potentials).
In conclusion, these in vitro results confirm the marked sensitivity of sensory axons to 4‐AP (the presumptive basis for paraesthesias). Burst firing was not preferenitally impaired at relatively high concentrations suggesting that anticonvulsants will not overcome the toxic peripheral actions of 4‐AP in neurological patients.
A comparative study of the reversal by different α2‐adrenoceptor antagonists of the central sympatho‐inhibitory effect of clonidine
Authors: Vayssettes‐Courchay Christine , Bouysset Françoise , Cordi Alex A. , Laubie Michel , Verbeuren Tony J. 
Published: July 2012

The recovery of the clonidine‐induced hypotension, bradycardia and sympatho‐inhibition produced by several putative α2‐adrenoceptor antagonists was investigated in pentobarbitone anaesthetized rats. The activity of four substances containing an imidazoline structure: idazoxan, methoxy‐idazoxan, BRL44408 and atipamezole was compared with the effect of fluparoxan, yohimbine and L‐657,743; in addition the effect of the α1‐adrenoceptor antagonist, prazosin, was also studied.
Prazosin (0.03‐1 mg kg−1, i.v.) failed to alter the sympatho‐inhibitory and hypotensive effects of clonidine (10 μg kg−1, i.v.). L‐657,743 (0.01‐1 mg kg−1, i.v.) induced a recovery of blood pressure, heart rate and renal sympathetic nerve activity. Yohimbine (0.03‐3 mg kg−1, i.v.) completely reversed the sympatho‐inhibitory effect of clonidine but did not alter its hypotensive effect.
The four imidazoline drugs: idazoxan (10–300 μg kg−1, i.v.), methoxy‐idazoxan (1–100 μ kg−1, i.v.), BRL44408 (0.1–3 mg kg−1, i.v.) and atipamezole (0.03‐1 mg kg−1, i.v.) and fluparoxan (10–300 μ kg−1, i.v.) reversed the clonidine‐induced hypotension but produced only a partial recovery of the renal sympathetic nerve activity and of the heart rate. After pretreatment with prazosin (0.1 mg kg−1, i.v.), the recovery of the sympathetic nerve activity elicited by these compounds was significantly higher. In hexamethonium (10 mg kg−1, i.v.) pretreated rats, these five drugs induced dose‐related hypertension which was reduced by pretreatment with prazosin (0.1 mg kg−1, i.v.).
Our results indicate that the putative α2‐adrenoceptor antagonists idazoxan, methoxy‐idazoxan, BRL44408, atipamezole and fluparoxan also have a peripheral hypertensive effect which is mediated through activation of vascular α1‐adrenoceptors; this property of the compounds may be partly responsible for the reversal of the hypotensive action of clonidine. Considering the structure and the affinities of the drugs tested, our data indirectly suggest that α2A‐adrenoceptors may be implicated in the central sympatho‐inhibitory effects of clonidine.
Myocardial protection after monophosphoryl lipid A: studies of delayed anti‐ischaemic properties in rabbit heart
Authors: Baxter G. F. , Goodwin R.W. , Wright M.J. , Kerac M. , Heads R. J. , Yellon D.M. 
Published: July 2012

Monophosphoryl lipid A (MLA) is a non‐pyrogenic derivative of Salmonella lipopolysaccharide. Administration of this agent at high doses to rats and at low doses to dogs was previously shown to confer marked protection against ischaemia‐reperfusion 24 h later, although the cellular mechanisms of this delayed protection are obscure. We hypothesized that MLA pretreatment causes the induction of the 70 kDa cytoprotective stress protein HSP70i in the myocardium. If this were the case, protection against ischaemia‐reperfusion injury would be observed both in vitro and in vivo.
Rabbits were pretreated with MLA 0.035 mg kg−1, i.v. or vehicle solution. For the in vitro study, hearts were isolated 24 h later and Langendorff‐perfused with Krebs‐Henseleit buffer at 37°C. Global ischaemia was induced for 20 min followed by 120 min reperfusion. Recovery of post‐ischaemic left ventricular function and lactate dehydrogenase efflux was similar in MLA and vehicle pretreated hearts and there was no significant difference in the percentage of infarction of the left ventricle determined by triphenyltetrazolium staining (MLA 22.4±5.2%, vehicle 24.8±5.1%).
When 30 min regional ischaemia and 120 min reperfusion was instituted in pentobarbitone‐anaesthetized rabbits 24 h after pretreatment with MLA or vehicle, the percentage infarction within the risk zone was reduced from 42.6±5.7% in vehicle pretreated animals to 19.6±4.4% in MLA pretreated animals (P<0.01).
Determination of myocardial HSP70i content by Western blot analysis showed that MLA treatment did not increase HSP70i immunoreactivity.
We conclude that MLA at this dose confers protection only against ischaemia‐reperfusion injury in vivo and that this protection is not related to induction of HSP70i. Because protection was observed only in vivo it seems possible that the delayed protection conferred by MLA is mediated by effects on humoral or blood‐borne factors.
Pharmacological and biochemical characterization of purified A2a adenosine receptors in human platelet membranes by [3H]‐CGS 21680 binding
Authors: Varani Katia , Gessi Stefania , Dalpiaz Alessandro , Borea Pier Andrea 
Published: July 2012

The binding properties of human platelet A2a adenosine receptors, assayed with the A2a‐selective agonist, [3H]‐2‐[p‐(2‐carboxyethyl)‐phenethylamino]‐5′‐N‐ethylcarboxamidoadenosine ([3H]‐CGS 21680), are masked by a non‐receptorial component, the adenotin site. In order to separate A2a receptors from adenotin sites, human platelet membranes were solubilized with 1% 3‐[(3‐cholamidopropyl)dimethylammonio]‐1‐propanesulphonate (CHAPS). The soluble platelet extract was precipitated with polyethylene glycol (PEG) and the fraction enriched in adenosine receptors was isolated from the precipitate by differential centrifugation.
The present paper describes the binding characteristics of the selective A2a agonist, [3H]‐CGS 21680, to this purified platelet membrane preparation. In addition, receptor affinity and potency of several adenosine agonists and antagonists were determined in binding and adenylyl cyclase studies.
Saturation experiments revealed a single class of binding site with Kd and Bmax values of 285 nM and 2.07 pmol mg−1 of protein respectively. Adenosine receptor ligands competed for the binding of 50 nM [3H]‐CGS 21680 to purified protein, showing a rank order of potency consistent with that typically found for interactions with the A2a adenosine receptors. In the adenylyl cyclase assay the compounds examined exhibited a rank order of potency very close to that observed in binding experiments.
Thermodynamic data indicated that [3H]‐CGS 21680 binding to the purified receptor is totally entropy‐driven in agreement with results obtained in rat striatal A2a adenosine receptors.
It is concluded that in the purified platelet membranes there is a CGS 21680 binding site showing the characteristic properties of the A2a receptor. This makes it possible to use this compound for reliable radioligand binding studies on the A2a adenosine receptor of human platelets.
Protection of the aged substantia nigra of the rat against oxidative damage by (−)−deprenyl
Authors: de la Cruz Cristina P. , Revilla Elisa , Steffen Vera , Rodríguez‐Gómez Jose A. , Cano Josefina , Machado Alberto 
Published: July 2012

We have studied the effect of (−)−deprenyl on the oxidative damage that the rat substantia nigra suffers during aging.
(−)−Deprenyl (2 mg kg−1, three times a week) administered for two months, beginning at 22 months of age, produced a significant increase in tyrosine hydroxylase (TH) activity (2.67±0.40 and 3.64±0.38 nmol mg−1 protein h−1 in untreated aged rats and treated aged rats respectively, P<0.05) and in TH amount (0.072±0.012 and 0.128±0.38 absorbance 405 nm in untreated aged and treated aged rats respectively, P<0.05).
The proteins of aged rat substantia nigra showed a significant decrease of carbonyl groups in treated animals compared with saline‐injected control rats (136.2±21.8 and 71.5±13.2 c.p.m. μg−1 protein in untreated aged and treated aged rats respectively, P<0.05).
The carbonyl groups measured in TH enzyme showed a statistically significant decrease (42.3%) after (−)−deprenyl treatment (471.4±73.0 and 271.9±50.00 c.p.m. in untreated aged and treated aged rats respectively, P<0.001).
All these results suggest that oxidative damage produced during aging is prevented by (−)−deprenyl treatment and could explain the effect of this drug in Parkinson's disease (PD) and other degenerative diseases such as Alzheimer's disease.