bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of the new A2 adenosine receptor antagonist 8FB‐PTP, an 8 substituted pyrazolo‐triazolo‐pyrimidine, on in vitro functional models
Authors: Dionisotti Silvio , Conti Annamaria , Sandoli Daniele , Zocchi Cristina , Gatta Franco , Ongini Ennio 
Published: July 2012

We have characterized the in vitro pharmacological profile of putative A2 adenosine antagonists, two non‐xanthine compounds, 5‐amino‐8‐(4‐fluorobenzyl)‐2‐(2‐furyl)‐pyrazolo [4,3‐e]‐1,2,4‐triazolo[1,5‐c] pyrimidine (8FB‐PTP) and 5‐amino‐9‐chloro‐2‐(2‐furyl 1,2,4‐triazolo [1,5‐c] quinazoline (CGS 15943), and the xanthine derivative (E)7‐methyl‐8‐(3,4‐dimethoxystyryl)‐1,3‐dipropyl‐xanthine (KF 17837).
In binding studies on bovine brain, 8FB‐PTP was the most potent (Ki = 0.074 nm) and selective (28 fold) drug on A2 receptors, whereas CGS 15943 and KF 17837 exhibited affinity in the low and high nanomolar range, respectively, and showed little selectivity.
In functional studies, 8FB‐PTP antagonized 5′‐N‐ethyl‐carboxamidoadenosine (NECA)‐induced vasorelaxation of bovine coronary artery (pA2 = 7.98) and NECA‐induced inhibition of rabbit platelet aggregation (pA2 = 8.20). CGS 15943 snowed weak activity in the platelet aggregation model (pA2 = 7.43) and failed to antagonize NECA‐induced vasodilatation. KF 17837 was ineffective in both models up to micromolar concentrations.
Antagonism of A1‐mediated responses was tested versus 2‐chloro‐N6‐cyclopentyladenosine (CCPA) in rat atria. 8FB‐PTP and CGS 15943 also antagonized competitively the negative chronotropic response induced by CCPA. Conversely, KF 17837 was unable to reverse A1‐mediated responses.
8FB‐PTP is a potent and competitive antagonist of responses mediated by A2 adenosine receptors. The data provided a basis to reduce, by further chemical modifications, the affinity at A1 receptor and therefore enhance A2 receptor selectivity.
Importance of the intestine as a site of metformin‐stimulated glucose utilization
Authors: Bailey C.J. , Mynett K.J. , Page T. 
Published: July 2012

The intestine has been implicated as a site of increased glucose utilization by the antihyperglycaemic drug, metformin. This study makes a quantitative assessment of this effect.
Glucose utilization by the intestine and hind limb region was determined by arterial‐venous glucose difference adjusted for blood flow rate in fasted rats receiving a hyperglycaemic hyperinsulinaemic infusion.
Intrajejunal administration of metformin, 250 mg kg−1, increased glucose disposal during the infusion procedure, associated with increased glucose utilization in the intestine by 69% and in the hind limb region by 40%.
Metformin, 250 mg kg−1, increased glucose disappearance during an intravenous glucose tolerance test. This was accompanied by increased uptake of tritiated 2‐deoxy‐d‐glucose into the intestinal mucosa to a greater extent than into skeletal muscles (per unit wet weight of tissue).
The results demonstrate that the intestinal mucosa is a quantitatively important site of increased glucose utilization during the blood glucose‐lowering effect of metformin.
Nitric oxide‐mediated inhibitory response of rat proximal colon: independence from changes in membrane potential
Authors: Suthamnatpong Naowarat , Hosokawa Muneaki , Takeuchi Tadayoshi , Hata Fumiaki , Takewaki Tadashi 
Published: July 2012

We studied the relation of nitric oxide‐mediated relaxation of smooth muscle to changes in membrane potential of cells in the proximal colon of rats.
The resting membrane potential and electrical field stimulation (EFS)‐induced junction potentials were recorded from the circular and longitudinal muscle cells.
Localized distension with a small balloon caused relaxation of the circular muscle on the anal side of the distended region (descending relaxation). Relaxation of the longitudinal muscle was also induced by EFS.
Inhibitory junction potentials (i.j.ps) were recorded from all circular muscle cells tested, but rarely from the longitudinal muscle cells.
The i.j.ps were recorded only in the presence of atropine but relaxations of both muscles were induced even in the absence of atropine.
Apamin (100 nm) completely abolished the i.j.ps recorded in both circular and longitudinal muscle cells, but had no significant effect on the relaxations of either.
In contrast to apamin, NG nitro‐l‐arginine (10 μm) inhibited the relaxations of both muscles, but did not affect the i.j.ps.
Exogenously added nitric oxide (0.1–10 μm) induced relaxations of both muscles concentration‐dependently, but did not affect the membrane potentials at these concentrations.
These data strongly suggest that nitric oxide‐mediated relaxation of rat proximal colon is not associated with the i.j.ps of the cell membrane.
Evidence for a differential location of vasoconstrictor endothelin receptors in the vasculature
Authors: Moreland Suzanne , McMullen Diane , Abboa‐Offei Benoni , Seymour Andrea 
Published: July 2012

There are at least two subtypes of vascular endothelin (ET) receptors. Stimulation of the ETA receptors on vascular smooth muscle cells leads to vasoconstriction, whereas activation of the ETB receptors on endothelial cells elicits vasodilatation. Several reports in the literature have suggested the presence of a vasoconstrictor non‐ETA receptor on vascular smooth muscle which has pharmacological similarities to the ETB receptor. The present study was undertaken to determine the location of this ETB‐like receptor within the vascular system.
Fourteen vascular smooth muscle preparations from six species were used to determine the effect of the ETA receptor antagonist, BQ‐123, on concentration‐response curves elicited by ET‐1 and the ability of the ETB receptor agonist, sarafotoxin S6c, to cause contraction. The vessels fell into two categories. One group was sensitive to BQ‐123 and insensitive to sarafotoxin S6c and, thus, probably contained ETA receptors. The other group, with vasoconstrictor ETB‐like receptors, was insensitive to BQ‐123 and sensitive to sarafotoxin S6c.
Vessels from cynomolgus monkeys, when studied in vitro, appeared to contain primarily ETA receptors, although the potency of BQ‐123 was quite variable, suggesting the possibility of ETA receptor subtypes. In contrast, both ET‐1 and sarafotoxin S6c, given as intravenous injections in conscious monkeys, produced transient, equipotent, and dose‐related increases in blood pressure. The highest dose of sarafotoxin S6c (1 nmol kg−1, i.v.) also caused a marked secondary depressor response (‐80± 6 mmHg) that lasted approximately 10 min. The pressor responses suggest that the vasoconstrictor ETB‐like receptors are present in cynomolgus monkeys.
The data suggest the presence of two distinct vasoconstrictor ET receptor subtypes on smooth muscle cells. The ETA receptors are primarily located on the high pressure side of the circulation. The vasoconstrictor ETB‐like receptors appear to be concentrated on the low pressure side.
Adenosine‐sensitive α1‐adrenoceptor effects on reperfused ischaemic hearts: comparison with phorbol ester
Authors: Khandoudi Nassirah , Moffat Margaret P. , Karmazyn Morris 
Published: July 2012

We have examined the effects of the α1‐adrenoceptor agonists, phenylephrine or methoxamine, on contractility in rat and rabbit isolated hearts as well as their effects on postischaemic ventricular recovery. We compared these effects to those of 12‐phorbol 13‐myristate acetate (PMA), a direct activator of protein kinase C (PKC).
The positive inotropic effect of α1‐receptor agonists was significantly attenuated in the presence of the Na/H exchange inhibitor, methylisobutyl amiloride (MIA, 1 μm), whereas the positive inotropic effect of PMA was unaffected.
Reperfusion of rat hearts subjected to either 30 or 60 min of zero‐flow ischaemia, resulted in recovery of contractility to 91 ± 2% and 57 ± 7% of the preischaemic values, respectively which was unaffected by phenylephrine. In contrast, PMA at a concentration (10 pM) devoid of direct depressant effects, significantly decreased recovery following 60 min of ischaemia to 31 ± 4% of pre‐ischaemic value (P < 0.05 from control); an effect which was completely prevented by the PKC inhibitor, bisindolyl‐maleimide. A similar inhibitory effect of PMA and lack of effect of phenylephrine were seen in reperfused rabbit hearts.
As α1‐receptor activation has been shown previously to stimulate cardiac adenosine production, we assessed whether blockade of adenosine A1 receptors with the specific antagonist, 1,3‐dipropyl‐8‐cyclopentylxanthine (DPCPX, 0.5 μm) would unmask the actions of phenylephrine in hearts subjected to 30 min ischaemia and reperfusion. In the presence of DPCPX, phenylephrine reduced recovery to 44 ± 9% compared to 82 ± 10% recovery in the absence of phenylephrine (P < 0.05). Identical results were observed in rabbit hearts treated with DPCPX in which recovery was reduced from 57.1 ± 11.2% to 17.8 ± 6.8% by phenylephrine (P < 0.05). Another A1 receptor antagonist, (±)‐N6‐endonorbornan‐2‐yl‐9‐methyladenine (N‐0861, 0.5 μm) produced virtually identical results to those observed with DPCPX.
MIA failed to modulate the inhibition of postischaemic recovery by phenylephrine. Bisindolyl‐maleimide, on the other hand, partially prevented the effects of phenylephrine on postischaemic contractile dysfunction. The inhibitory effect of either PMA or phenylephrine on postischaemic recovery of both rat and rabbit hearts was generally dissociated from alterations in energy metabolism, although in the case of rat hearts, inhibition by phenylephrine was associated with diminished high energy phosphate content.
Our results demonstrate that both α1‐receptor activation as well as direct activation of PKC with phorbol ester can attenuate post‐ischaemic ventricular recovery. Moreover, our results strongly suggest that endogenous adenosine protects the heart against the deleterious effects of α1‐receptor activation during ischaemia and reperfusion.
Permeation properties and modulation of volume‐activated Cl−‐currents in human endothelial cells
Authors: Nilius Bernd , Sehrer Jan , Droogmans Guy 
Published: July 2012

We have studied the permeation and pharmacological properties of a recently described volume‐activated, calcium‐insensitive, small‐conductance Cl−‐channel in endothelial cells from human umbilical vein.
The relative permeability for various anions was I− > Cl− ∼ Br− > F− > gluconate− (1.63 ± 0.36: 1:0.95 ± 0.16:0.46 ± 0.04:0.19 ± 0.07, n = 10).
5‐Nitro‐2‐(3‐phenylpropylamino)‐benzoic acid (NPPB) induced a fast and reversible block of the current (K1 = 29 μmol l−1).
Extracellular ATP induced a low‐affinity block of the current, that showed a small voltage‐dependence (K1 = 4.9 mmol l−1 at + 80 mV and K1 = 8.2 mmol l−1 at − 80 mV).
Extracellularly applied arachidonic acid (10 μmol l−1) irreversibly blocked the current in 5 out of 9 cells. This block seems to be non‐specific, because other ionic currents, e.g. inwardly rectifying K+ currents, were blocked as well.
Tamoxifen induced a high affinity block of the current (K1 = 2.9 μmol l−1). Block and reversal of block were however much slower than with NPPB.
Cytotoxic compounds, which are substrates of the P‐glycoprotein multidrug transporter, loaded into endothelial cells via the patch pipette, exerted only minor effects on the volume‐activated current. Vinblastine and colcemid did not affect the volume‐activated current, whereas daunomycin and vincristine induced a slow ‘run‐down’ of the current.
The similarity between permeation and pharmacological properties of volume‐activated Cl−‐currents in endothelial cells and those in many other cell types may suggest that they all belong to the same family of volume‐activated small‐conductance Cl−‐channels. Evidence that they belong to the class of P‐glycoprotein associated Cl−‐channels is however only marginal, whereas their biophysical characteristics differ significantly from those of the CIC‐2 volume‐activated Cl−‐channels.
Blockade of the inward rectifier potassium current by the Ca2+‐ATPase inhibitor 2′,5′‐di(tert‐butyl)‐1,4‐benzohydroquinone (BHQ)
Authors: Hasséssian Haroutioun , Vaca Luis , Kunze Diana L. 
Published: July 2012

We have investigated the effect of 2′,5′‐di (tert‐butyl)‐1,4‐benzohydroquinone (BHQ) and thapsigargin, inhibitors of the intracellular Ca2+‐ATPase, on ionic currents in rat basophilic leukaemia (RBL‐2H3) cells under whole cell voltage clamp.
The whole cell current was inwardly rectifying and reversed at − 35 ± 6 mV (n = 16). The conductance of the inward current increased as the concentration of extracellular K+ was raised from 2.7 to 5.4, 10.8 and 21.6 mM. BaCl2 (100 μm) reduced the current to a small linear component and shifted the reversal potential to − 4 ± 3 mV (n = 6). A concentration of 50 μm BaCl2 produced 45 ± 10% (n = 4) blockade of the inward current.
BHQ and thapsigargin were examined for their effects on the inwardly rectifying current. A maximal blockade of inward current was obtained within 6 min after perfusion with 10 μm BHQ. The small current remaining after blockade with BHQ had a linear voltage‐dependence and reversed direction at − 6 ± 9 mV (n = 6). Thapsigargin (up to 3 μm) was without effect on the inward rectifier.
In contrast to the blockade of the inward rectifier produced by BaCl2 which was predominantly on the steady state current, particularly at the very hyperpolarized holding potentials (− 120 mV), blockade by BHQ was equally strong on the instantaneous as well as the steady state current.
Blockade of the inward rectifier by BHQ may cause depolarization of the cell which will affect Ca2+ influx during investigations with BHQ. Thapsigargin does not block the inward rectifier and will not inhibit Ca2+ influx in this way.
Effects of bipyridylium compounds on calcium release from triadic vesicles isolated from rabbit skeletal muscle
Authors: Kang J.J. , Hsu K.S. , Lin‐Shiau S.Y. 
Published: July 2012

The effects of 1,1′‐diheptyl‐4,4′‐bipyridinium dibromide (DHBP), a viologen for electrochromic memory display agent, on calcium release and ryanodine binding were studied with triad‐rich sarcoplasmic reticulum (SR) vesicles isolated from rabbit skeletal muscle.
DHBP inhibited the calcium release induced by 2 mM caffeine and 2 μg ml−1 polylysine with an IC50 value of 5 μg ml−1 and 4 μg ml−1 respectively.
DHBP inhibited [3H]‐ryanodine binding in a dose‐dependent manner with an IC50 of 2.5 μg ml−1 and 90–100% inhibition at 20–30 μg ml−1.
Calcium uptake by SR was inhibited in the presence of caffeine and this inhibition was antagonized by concomitant addition of DHBP.
The effect of DHBP on muscle twitches was studied on the mouse diaphragm. Muscle twitches elicited by direct electrical muscle stimulation and contractions induced by either 10 mM caffeine or 1 μm ryanodine were blocked by pretreatment with DHBP.
Data from this study provided evidence that DHBP blocked the calcium release from SR by direct interaction with the calcium release channel, also known as the ryanodine receptor. A possible use of this agent as a specific inhibitor for calcium release and as a muscle relaxant was suggested.
Strain‐dependency of leukotriene C4 generation from isolated lungs of immunized mice
Authors: Zuany‐Amorim Claudia , Vargaftig B. Boris , Maclouf Jacques , Pretolani Marina 
Published: July 2012

The antigen‐induced leukotriene C4 (LTC4)‐like‐material release from isolated perfused lungs of actively sensitized Swiss, Balb/C and CBA/J mice was compared. The intra‐tracheal (i.t.) instillation of 1 and 100 μg ovalbumin to lungs from Swiss mice was followed by a dose‐dependent generation of LTC4‐like material into the effluent, as detected by radio‐immunoassay and h.p.l.c., followed by an enzyme‐immunoassay. In contrast, lungs from sensitized Balb/C and CBA/J mice failed to exhibit LTC4‐like‐material release in amounts above the basal values. No histamine secretion was observed when lungs of the three strains of mice were challenged with ovalbumin.
The i.t. instillation of 1 or 10 μg platelet‐activating factor (PAF) or of 100 μg arachidonic acid to lungs from non‐sensitized mice, induced the release of comparable amounts of LTC4‐like‐material in the effluent, irrespective to the strain. However, N‐formyl‐l‐methionyl‐l‐leucyl‐l‐phenylalanine (fMLP, 0.1, 10 μg), was more effective in inducing the release of LTC4‐like‐material from lung from Swiss and CBA, than from Balb/C, mice.
The intraplantar injection of 0.01 μg ovalbumin to sensitized Swiss mice induced an intense oedema formation, as measured plethysmographically, while Balb/C mice required a dose of antigen at least 10 fold higher for a similar response. CBA/J mice did not respond to antigen challenge in terms of oedema formation. The intraplantar injection of PAF or fMLP to non‐immunized mice induced an oedema of similar intensity in all the strains considered. Accordingly, the different responses to ovalbumin of the three strains of mice is not accounted for by different paw responsiveness to inflammatory mediators.
Swiss and CBA/J mice exhibited higher titers of circulating IgG antibodies, as measured by passive cutaneous anaphylaxis (PCA), than Balb/C mice. Conversely, lower IgE titers were measured in the serum of sensitized Swiss and CBA/J mice, as compared to Balb/C.
Our results demonstrate a strain‐dependency of antigen‐induced LTC4 release from lungs from sensitized mice. This difference is related to the ability of sensitized animals to develop immediate hypersensitivity responses, such as paw oedema formation, but not to the antibody subclass involved in the immunization. Strain‐dependent factors may influence the intensity of the response to antigen stimulation. It is thus essential to characterize the different components of the immune response when mouse models for studying hypersensitivity reactions are developed.
Effects of cyclopiazonic acid on contractility and ecto‐ATPase activity in guinea‐pig urinary bladder and vas deferens
Authors: Ziganshin Airat U. , Hoyle Charles H.V. , Ziganshina Lilia E. , Burnstock Geoffrey 
Published: July 2012

Cyclopiazonic acid (CPA), an inhibitor of sarcoplasmic ATPase, was tested on guinea‐pig urinary bladder and vas deferens for its ability: (1) to modify contractile responses to electrical field stimulation (EFS), exogenous ATP, α,β‐methylene ATP (α,β‐meATP), carbachol, noradrenaline (NA), histamine, and KCl; (2) to affect ecto‐ATPase activity; (3) to modify the release of ATP evoked by EFS.
In the urinary bladder, CPA (10 μm) potentiated contractile responses to EFS, exogenous ATP (100 μm), α,β‐meATP (1 μm), carbachol (0.5 μm), histamine (30 μm) and KCl (30 μm). In the vas deferens, CPA (10 μm) potentiated responses to EFS, ATP, α,β‐meATP, NA (100 μm) and KCl. CPA at a concentration of 1 μm had no effect on ATP‐induced relaxation of carbachol‐precontracted guinea‐pig taenia coli, and at a concentration of 10 μm it markedly increased spontaneous contractile activity of taenia.
Ecto‐ATPase was estimated to have Vmax and Km values of 0.98 nmol Pi 30 min−1 mg−1 wet tissue and 881 μm ATP in the urinary bladder, and 0.75 nmol Pi 30 min−1 mg−1 wet tissue and 914 μm ATP in the vas deferens, respectively. CPA at a concentration of 10 μm significantly inhibited ecto‐ATPase activity by 18% in the urinary bladder and by 24% in the vas deferens.
In the guinea‐pig vas deferens, CPA significantly potentiated ATP release evoked by EFS from 2.2 ± 0.8 (6) pmol ATP min−1 g−1 wet tissue to 35.2 ± 4.8 (6) pmol ATP min−1 g−1 wet tissue (P < 0.01).
In conclusion, the potentiation of contractile responses of the guinea‐pig urinary bladder and vas deferens by CPA has a non‐specific character. CPA inhibited ecto‐ATPase activity and increased ATP release, but these effects do not appear to contribute to the potentiation of P2x‐purinoceptor‐mediated responses since the contractile actions of all the agonists studied were potentiated to the same extent.
Modulation by endogenous prostanoids of the vasoconstrictor activity of endothelin‐1 in the canine isolated, perfused spleen
Authors: Grassi‐Kassisse Dora M. , Antunes Edson , Withrington Peter G. , de Nucci Gilberto 
Published: July 2012

Endothelin‐1 (ET‐1, 0.4–200 pmol) was injected into the arterial circuit of the isolated perfused spleen of the dog in which splenic arterial perfusion pressure and spleen weight were recorded continuously.
Serial collection was made of splenic venous effluent before and after intra‐arterial injection of ET‐1 and assayed by direct radioimmunoassay for prostaglandin E2 (PGE2), 6‐oxo‐PGF1α and thromboxane B2 (TXB2).
ET‐1 caused graded arterial vasoconstriction of prolonged duration with small reductions in spleen weight at higher doses.
ET‐1 cause a dose‐related release of PGE2, 6‐oxo‐PGF1α and TXB2 into the splenic venous effluent. The mean peak increase above the basal levels following 200 pmol of ET‐1 was 800% for PGE2, 233% for 6‐oxo‐PGF1α and 205% for TXB2.
Intra‐arterial infusion of indomethacin significantly reduced the basal release of all three eicosanoids and significantly elevated the basal splenic vascular resistance. The release of all three eicosanoids in response to ET‐1 and adrenaline (Ad) was significantly reduced by indomethacin and the accompanying increases in the splenic arterial vascular resistance were significantly potentiated at low doses of ET‐1. The splenic arterial vascular responses to Ad were unchanged by indomethacin infusion.
These results indicate that the release of eicosanoids may modulate the splenic vascular responses to ET‐1.
The interaction between salmeterol and β2‐adrenoceptor agonists with higher efficacy on guinea‐pig trachea and human bronchus in vitro
Authors: Källström Britt‐Louise , Sjöberg Jacob , Waldeck Bertil 
Published: July 2012

In guinea‐pig tracheal preparations precontracted with 1 μmol 1−1 carbachol, formoterol, procaterol, fenoterol, salmefamol, salbutamol and terbutaline (in that order of potency) caused a concentration‐dependent and almost complete, relaxation. However, under these conditions, the maximum relaxation by salmeterol was approximately 30% of the maximum attainable relaxation.
We have therefore explored the ability of salmeterol to inhibit the relaxant response to β2‐adrenoceptor agonists of different chemical structure and relatively higher efficacy in smooth muscle preparations from guinea‐pig trachea and human bronchus.
With 1 μmol 1−1 salmeterol in the organ bath, the concentration‐effect curves for the other agonists were shifted to the right in a variable way by 1.8‐2.8 log units, fenoterol and salbutamol being the extremes.
When 20 μmol 1−1 sulfonterol, another low efficacy β2‐adrenoceptor agonist, was substituted for salmeterol, the difference in the magnitude of the rightward shift between fenoterol and salbutamol was eliminated.
In the human bronchus, formoterol and terbutaline had a higher apparent efficacy than salmeterol. With 1 μmol 1−1 salmeterol in the organ bath, the concentration‐effect curve for formoterol was shifted 2.7 log units to the right.
Salmeterol inhibits, competitively, relaxant responses to β2‐adrenoceptor agonists with higher efficacy. The degree of inhibition seems to be dependent on the agonist used. This contrasts with results obtained with sulfonterol and suggests that salmeterol interacts with the β2‐adrenoceptor in a complex way.