bluuebunny/crossref_metadata_2025_split huggingface dataset:
α2‐Adrenoceptor subtypes and imidazoline‐like binding sites in the rat brain
Authors: Brown C.M. , MacKinnon A.C. , McGrath J.C. , Spedding M. , Kilpatrick A.T. 
Published: July 2012

The binding of [3H]‐yohimbine and [3H]‐idazoxan to rat cortex and hippocampus is rapid, reversible and of high affinity. Saturation data indicate that a single population of binding sites exist for [3H]‐yohimbine in the cortex (Bmax 121 ± 10 fmol mg−1, protein; Kd 5.2 ± 0.9 nm) and hippocampus (Bmax 72 ± 6 fmol mg−1 protein; Kd 5.8 ± 0.7 nm). [3H]‐idazoxan labels one site in the cortex (Bmax 87 ± 8 fmol mg−1 protein; Kd 4.1± 0.9 nm) and hippocampus (Bmax 30 ± 6 fmol mg−1 protein; Kd 3.5 + 0.5 nm), when 3 μm phentolamine is used to define non‐specific binding. A second distinct [3H]‐idazoxan binding site (Bmax 110 ± 21fmolmg_1 protein; Kd 3.6 ± 0.07 nm) is identified in rat cortex if 0.3 μm cirazoline is used to define non‐specific binding and 3 μm yohimbine is included to prevent binding to α2‐adrenoceptors.
Displacement studies indicate that the α1‐adrenoceptor antagonist prazosin and the 5‐HT1 ligands 8‐OH‐DPAT, RU 24969 and methysergide differentiate [3H]‐yohimbine binding into two components; a high and low affinity site. In contrast the displacement of [3H]‐idazoxan by each ligand was monophasic.
The affinities of 8‐OH‐DPAT, RU 24969 and methysergide determined against [3H]‐idazoxan binding to the cortex and hippocampus correlate significantly with the binding site displaying low affinity for prazosin and previously designated α2A. In contrast, a poor correlation exists for the high affinity site for prazosin designated α2B.
[3H]‐idazoxan, in the presence of 3 μm yohimbine, labels a site that displays high affinity towards cirazoline, naphazoline and guanabenz, but low affinity towards clonidine, p‐aminoclonidine, adrenaline, noradrenaline and the α2‐adrenoceptor antagonists yohimbine, rauwolscine, WY 26703 and BDF 6143.
The results of this study indicate that [3H]‐yohimbine labels two sites; the α2A‐ and α2B‐adrenoceptors whereas [3H]‐idazoxan labels an α2‐adrenoceptor with a profile consistent with the α2A‐adrenoceptor subtype. In addition, [3H]‐idazoxan labels an imidazoline binding site in the rat cortex that is pharmacologically distinct from α2‐adrenoceptors. The low affinity of clonidine and p‐aminoclonidine indicates that the imidazoline‐like binding site in rat cortex is different from the site labelled by [3H]‐clonidine and [3H]‐p‐aminoclonidine in human, rat and bovine brain stem, providing evidence of potential heterogeneity within this class of binding sites.
The pharmacological characterization of 5‐HT3 receptors in three isolated preparations derived from guinea‐pig tissues
Authors: Butler A. , Elswood C.J. , Burridge J. , Ireland S.J. , Bunce K.T. , Kilpatrick G.J. , Tyers M.B. 
Published: July 2012

The pharmacological characterization of the 5‐HT3 receptors in guinea‐pig isolated tissues is described. The tissues used were ileum (longitudinal muscle‐myenteric plexus), colon and vagus nerve. The guinea‐pig isolated colon is a novel preparation.
In the guinea‐pig isolated ileum, 5‐hydroxytryptamine (5‐HT, 1 × 10−8−3 × 10−5 m) and the selective 5‐HT3 receptor agonist 2‐methyl‐5‐HT (3 × 10−7−1 × 10−4 m) caused concentration‐related contractions. The 5‐HT concentration‐response curve was biphasic whilst the 2‐methyl‐5‐HT curve was monophasic. The EC50 value for the low potency portion of the 5‐HT curve was 4.1 × 10−6 m. The EC50 for 2‐methyl‐5‐HT was 1.23 × 10−5 m. Selective 5‐HT3 receptor antagonists caused rightward shifts of the 2‐methyl‐5‐HT curve and the lower potency portion of the 5‐HT curve. Neither ketanserin (1 × 10−6 m) nor methysergide (1 × 10−5 m) antagonized the responses to 5‐HT or 2‐methyl‐5‐HT.
In the guinea‐pig isolated colon, 5‐HT (3 × 10−7−3 × 10−5 m; EC50 2.4 × 10−6 m) caused contractions which were mimicked by 2‐methyl‐5‐HT (1 × 10−6−1 × 10−4 m; EC50 7.2 × 10−6 m). Selective 5‐HT3 receptor antagonists caused rightward displacements of the 5‐HT concentration‐response curves. Neither ketanserin (1 × 10−6 m) nor methysergide (1 × 10−5 m) had any effect on responses to 5‐HT or 2‐methyl‐5‐HT.
In the guinea‐pig isolated vagus nerve, 5‐HT (1 × 10−6−3 × 10−4 m) and 2‐methyl‐5‐HT (1 × 10−5−1 × 10−3 m; EC50 7.6 × 10−5 m) caused depolarizations; at higher concentrations there were afterhyperpolarizations. The maximum response to 2‐methyl‐5‐HT was less than half that to 5‐HT. Selective 5‐HT3 receptor antagonists caused rightward displacements of the 5‐HT concentration‐response curves. Antagonists at other 5‐HT receptors (ketanserin, 1 × 10−5 m and methysergide, 1 × 10−6 m) had no effect.
The estimated affinity values of 5‐HT3 receptor antagonists correlated well between the three models. Phenylbiguanide was inactive as an agonist or antagonist (up to 1 × 10−4 m) in each preparation.
Comparisons with antagonist affinity values obtained in the rat isolated vagus nerve revealed marked differences. Antagonists were generally more potent on the rat isolated vagus nerve, although the differences varied considerably between antagonists.
The results are discussed in terms of species‐related receptor differences.
Pharmacological and biochemical comparison of thyrotropin releasing hormone (TRH) and di‐methyl proline‐TRH on pituitary GH3 cells
Authors: McDermott Alison M. , Wilkin Graham P. , Dickinson Stephen L. 
Published: July 2012

The binding of [3H]‐thyrotropin releasing hormone ([3H]‐TRH) and [3H]‐RX77368 (di‐methyl proline TRH) and the ability of these peptides to stimulate phosphoinositide hydrolysis were investigated in the GH3 pituitary cell line.
For both peptides binding was found to be saturable with a single component (Hill slopes were, for TRH, 0.98 and for RX77368, 1.13). TRH bound with greater affinity than RX77368 Kd values were 16 nm and 144 nm respectively. Bmax values were 227 fmol mg−1 protein for TRH and 123 fmol mg−1 protein for RX77368.
The rank order of potency of a series of TRH analogues to inhibit binding was the same versus each peptide. However, unlike with saturation analysis, Hill slopes of all displacing ligands were less than 1.0 against both TRH and RX77368 suggeting either multiple binding sites, alteration of affinity state, negative co‐operativity or some allosteric interaction.
Both peptides stimulated phosphoinositide hydrolysis in a dose‐dependent fashion. TRH was more potent than RX77368, EC50 values were 7.9 ± 1 nm and 96.3 ± 3 nm respectively.
These in vitro data suggest that the greater in vivo potency of RX77368 is not the result of enhanced receptor affinity but is more probably due to its greater metabolic stability.
Characterization of P2x‐receptors in rabbit isolated ear artery
Authors: O'Connor S.E. , Wood B.E. , Leff P. 
Published: July 2012

The isolated central ear artery of the rabbit contracts in response to adenosine 5′‐triphosphate (ATP) and analogues, effects proposed to be mediated by stimulation of P2x‐receptors. We have extended the characterization of the purinoceptor in this tissue by examining the effects of a series of receptor agonists. The study was designed in such a way as to avoid factors which normally limit attempts to classify receptors on the basis of agonist potency orders.
d‐α,β‐methylene ATP (d‐α,β‐meATP), d‐β,γ‐methylene ATP (d‐β,γ‐meATP), l‐β,γ‐methylene ATP (l‐β,γ‐meATP), 2‐methylthio‐d‐ATP (2‐MeSATP) and ATP produced concentration‐related contractions of the ear artery with similar maximum responses, suggesting that they were full agonists. Selective desensitization of P2x‐receptors abolished or greatly reduced responses to d‐α,β‐meATP, l‐β,γ‐meATP, d‐β,γ‐meATP and 2‐MeSATP. Responses to ATP were inhibited by desensitization but a significant resistant component was still apparent.
d‐α,β‐meATP was the most potent agonist tested (pA50 6.47 ± 0.04) being 2138 times more potent than ATP and approximately 9 times more potent than l‐β,γ‐meATP. The agonist potency order was: d‐α,β‐meATP > l‐β,γ‐meATP > d‐β,γ‐meATP ≥ 2‐MeSATP > ATP. This is generally consistent with the order proposed for P2x‐receptors. The relative potencies of P2x‐agonists in the rabbit ear artery show both similarities to and differences from data obtained in other smooth muscle preparations.
Haemodynamic profile of an inhibitor of phosphodiesterase III, adibendan (BM 14.478): comparison with nitroprusside and dobutamine in conscious dogs
Authors: Dorszewski A. , Müller‐Beckmann B. , Kling L. , Sponer G. 
Published: July 2012

This study was performed to investigate whether cardiac positive inotropic as well as peripheral vasodilator properties of adibendan contribute to its overall haemodynamic profile in conscious dogs.
Haemodynamic measurements were carried out in conscious chronically instrumented dogs after administration of adibendan, sodium nitroprusside or dobutamine.
The cardiovascular changes induced by adibendan (0.01 and 0.03 mg kg−1) resembled those of dobutamine (1.0–4.0 μg kg−1 min−1): left ventricular dP/dt60 (LV dP/dt60), stroke volume (SV) and cardiac output (CO) increased to a similar extent, but mean arterial pressure (MAP) and heart rate (HR) remained unchanged.
In contrast to dobutamine, higher doses of adibendan (0.1–1.0 mg kg−1) decreased MAP and LVEDP. These effects were of a similar magnitude to those observed following nitroprusside administration (0.5–12.5 μg kg−1 min−1). In contrast to nitroprusside, adibendan still showed additional effects on LV dP/dt60 and CO.
From these results, it is concluded that both the peripheral vasodilator and the cardiac positive inotropic action of adibendan contribute to its overall haemodynamic profile.
Interleukin‐1 potentiates histamine‐induced release of prostacyclin from human endothelial cells
Authors: Bull Helen A. , Dowd Pauline M. 
Published: July 2012

In human cultured umbilical vein endothelial cells, interleukin‐1 potentiated histamine‐induced release of prostacyclin in a time‐ and concentration‐dependent manner.
In cells incubated with interleukin‐1 for 24 h, maximal potentiation was observed when cells were pre‐incubated with 0.5 u ml−1 interleukin‐1 before stimulation with histamine (1 μm‐1 mm).
In cells incubated with 0.5 u ml−1 interleukin‐1, 20 min pre‐incubation was sufficient to induce a statistically significant potentiation of prostacyclin release induced by 1 μm histamine (P > 0.05).
Nifedipine but not cycloheximide, significantly (P > 0.05) inhibited histamine‐induced release of prostacyclin and interleukin‐1 potentiation of histamine‐induced release of prostacyclin (P > 0.05).
Incubation with 1 u ml−1 interleukin‐1 induced a two fold increase in cellular prostaglandin synthetase activity within 30 min. The enzyme activity increased up to 6 h and was maintained up to 24 h. In cells co‐incubated with cycloheximide and 1 u ml−1 interleukin 1, prostaglandin synthetase activity at 24 h was the same as that in unstimulated cells. Prostacyclin release was not significantly inhibited in cells co‐incubated with cycloheximide and interleukin 1.
These results suggest that interleukin‐1 potentiates histamine‐induced release of prostacyclin by rapid up‐regulation of prostaglandin synthetase activity as well as by inducing synthesis of enzyme protein. These mechanisms may act to potentiate/regulate vascular endothelial responses in inflammatory reactions.
Characterization of three inhibitors of endothelial nitric oxide synthase in vitro and in vivo
Authors: Rees D.D. , Palmer R.M.J. , Schulz R. , Hodson H.F. , Moncada S. 
Published: July 2012

Three analogues of l‐arginine were characterized as inhibitors of endothelial nitric oxide (NO) synthase by measuring their effect on the endothelial NO synthase from porcine aortae, on the vascular tone of rings of rat aorta and on the blood pressure of the anaesthetized rat.
NG‐monomethyl‐l‐arginine (l‐NMMA), N‐iminoethyl‐l‐ornithine (l‐NIO) and NG‐nitro‐l‐arginine methyl ester (l‐NAME; all at 0.1–100 μm) caused concentration‐dependent inhibition of the Ca2+‐dependent endothelial NO synthase from porcine aortae.
l‐NMMA, l‐NIO and l‐NAME caused an endothelium‐dependent contraction and an inhibition of the endothelium‐dependent relaxation induced by acetylcholine (ACh) in aortic rings.
l‐NMMA, l‐NIO and l‐NAME (0.03–300 mg kg−1, i.v.) induced a dose‐dependent increase in mean systemic arterial blood pressure accompanied by bradycardia.
l‐NMMA, l‐NIO and l‐NAME (100 mg kg−1, i.v.) inhibited significantly the hypotensive responses to ACh and bradykinin.
The increase in blood pressure and bradycardia produced by these compounds were reversed by l‐arginine (30–100 mg kg−1 i.v.) in a dose‐dependent manner.
All of these effects were enantiomer specific.
These results indicate that l‐NMMA, l‐NIO and l‐NAME are inhibitors of NO synthase in the vascular endothelium and confirm the important role of NO synthesis in the maintenance of vascular tone and blood pressure.
Effects of inhibitors of protein kinase C and Na +/H + exchange on α1‐adrenoceptor‐mediated inotropic responses in the rat left ventricular papillary muscle
Authors: Otani Hitomi , Otani Hajime , Uriu Toshiko , Hara Mitsuyoshi , Inoue Masafumi , Omori Kyoko , Cragoe Edward J. , Inagaki Chiyoko 
Published: July 2012

α1‐Adrenoceptor stimulation of rat left ventricular papillary muscle produced a triphasic inotropic response: an initial transient positive inotropic effect (PIE) followed by a transient negative inotropic effect (NIE) and a sustained PIE.
The protein kinase C inhibitor, staurosporine, at concentrations ranging from 30 nm to 100 nm inhibited the sustained PIE, but had no significant effect on the transient PIE and NIE.
H‐7, 1‐(5‐isoquinoline sulphonyl)‐2‐methylpiperazine, a less specific inhibitor of protein kinase C than staurosporine, at a concentration of 100 μm inhibited both the transient NIE and the sustained PIE without affecting the transient PIE.
Amiloride, an inhibitor of Na+/H+ exchange, at concentrations ranging from 0.1 mm to 1 mm inhibited the sustained PIE and, at higher concentrations, also inhibited the transient NIE.
An amiloride analogue, 5‐(N‐methyl‐N‐isobutyl)amiloride (MIBA), inhibited only the sustained PIE with an IC50 of 0.3 μm which is approximately two orders of magnitude lower than amiloride.
The receptor‐linked stimulation of Na+/H+ exchange through protein kinase C activation may be a mechanism for α1‐adrenoceptor‐mediated sustained PIE.
Local formation of angiotensin II in the rat aorta: effect of endothelium
Authors: Eglème Cécile , Cressier Floriane , Wood Jeanette M. 
Published: July 2012

The local formation of angiotensin II (AII) from its precursors, angiotensin I (AI) and tetradecapeptide (TDP) renin substrate, was studied in intact (with endothelium) and rubbed (without endothelium) aortic rings of the rat.
AI and TDP renin substrate maximally contracted intact tissues in a similar way to AII. The same observations were made in rubbed tissues.
The maximal response and the sensitivity of the aorta to these agonists were greater in rubbed than in intact tissues.
In intact preparations, methylene blue increased the contractile response to AII and TDP to the same extent as endothelium removal.
In intact preparations, AII receptor blockade completely suppressed all contractile responses, converting enzyme inhibition completely blocked the responses to AI and TDP, and renin inhibition partially blocked the responses to TDP.
In rubbed preparations, AII receptor blockade completely inhibited all contractile responses, converting enzyme inhibition completely suppressed the responses to AI but only partially inhibited those to TDP, and renin inhibition partially blocked the responses to TDP.
In conclusion, the formation of AII from TDP and its blockade by a converting enzyme inhibitor and a renin inhibitor shows that converting enzyme and a renin‐like aspartic proteinase are present in the aortic wall. Furthermore, the results show that the endothelium is not essential for the conversion of the TDP to AII, but modulates the responses to locally formed AII through the release of endothelium‐derived relaxing factor (EDRF).
2‐Chloroadenosine induction of vagally‐mediated and atropine‐resistant bronchomotor responses in anaesthetized guinea‐pigs
Authors: Manzini Stefano , Ballati Lido 
Published: July 2012

The bronchoconstrictor effects of intravenous administration of adenosine derivatives in anaesthetized non‐curarized guinea‐pigs have been studied.
2‐Chloroadenosine (2‐Cl‐Ade), 5′‐N‐ethylcarboxamideadenosine (NECA) and l‐N6‐phenylisopropyl‐adenosine (l‐PIA) all produced dose‐dependent, transient increases in tracheal insufflation pressure, with an order of potency (NECA ≤ 2‐Cl‐Ade ≫ l‐PIA) typical of A2‐receptor mediated biological responses.
2‐Chloroadenosine‐induced bronchoconstrictor responses disappeared after vagotomy or topical application of tetrodotoxin (TTX) on cervical vagal trunks.
2‐Chloradenosine‐induced bronchospasm was unaffected by atropine (1 mg kg−1 i.v.), physostigmine (50 μg kg−1 i.v.) and hexamethonium (30 mg kg−1 i.v.) but was significantly reduced by theophylline (25 mg kg−1 i.v.).
The magnitude of 2‐Cl‐Ade‐induced bronchospasm was significantly reduced by acute (10 μg kg−1 i.v.) or chronic (55 mg kg−1 s.c. four days before the experiment) pretreatment with capsaicin.
Guanethidine (20 mg kg−1 s.c. on two consecutive days), prazosin (10 μg kg−1 i.v.), diphenhydramine (1 mg kg−1 i.v.) and indomethacin (1 mg kg−1 i.v.) failed to block the bronchomotor response to 2‐Cl‐Ade. In contrast, cyproheptadine (1–5 mg kg−1 i.v.) markedly reduced, but did not abolish the bronchospasm elicited by the purine derivative.
We conclude that in anaesthetized non‐curarized guinea‐pigs, a transient vagally‐mediated bronchospasm can be induced by stimulation of A2‐purinoceptors. This effect is complex and involves, at least in part, stimulation of capsaicin‐sensitive sensory nerves and 5‐hydroxytryptamine release. This experimental model might be useful for the further study of the potential role of adenosine in asthma, and for the evaluation of new antiasthma drugs.
Role of adrenoceptors in vitro and in vivo in the effects of lithium on blood glucose levels and insulin secretion in the rat
Authors: Fontela T. , Hermida O. García , Gómez‐Acebo J. 
Published: July 2012

Pretreatment of rats with the non‐selective α‐adrenoceptor antagonist dihydroergotamine counteracts the inhibition of glucose‐induced insulin secretion caused by lithium both in vitro and in vivo. The present study was therefore carried out to specify further which type of adrenoceptor is involved in lithium‐induced hyperglycaemia and inhibition of insulin secretion.
The lithium‐induced effects were reversibly blocked by pretreatment of rats with the α2‐adrenoceptor antagonist yohimbine or a combination of yohimbine and the non‐selective β‐receptor antagonist propranolol, whereas the α1‐receptor antagonist prazosin and propranolol alone were ineffective in blocking these effects.
These findings suggest that the effects of lithium on plasma glucose and insulin levels are mediated mainly by the stimulation of α2‐adrenoceptors.
FPL 63012AR: a potent D1‐receptor agonist
Authors: Smith G.W. , Farmer J.B. , Ince F. , Matu K. , Mitchell P.D. , Naya I. , Springthorpe B. 
Published: July 2012

FPL 63012AR is a D1‐receptor agonist in the dog kidney, 10 times as potent as dopamine, reducing renal vascular resistance by 20% with an intra‐arterial dose of 0.42 nmol kg−1.
No prejunctional inhibitory D2‐receptor agonist activity was detected in either the isolated ear artery of the rabbit or in the conscious dog as D2‐receptor‐mediated emesis.
Unlike dopamine, FPL 63012AR had no significant agonist activity at α1‐, α2‐, β1‐ or β2‐adrenoceptors.
FPL 63012AR is a potent inhibitor of [3H]‐noradrenaline uptake (Uptake1) into brain synaptosomes, with an IC50 of 29.5 nm, i.e. 9.2 times more potent than dopamine.
The ability to block Uptake1 in the anaesthetised dog was confirmed by inhibition of the tyramine‐induced pressor and inotropic responses.
Intravenous infusion of FPL 63012AR in anaesthetized and conscious dogs (0.3 to 3 nmol kg−1 min−1) reduced vascular resistance and increased blood flow to the kidney which was accompanied by hypotension and tachycardia.
It is concluded that FPL 63012AR is an example of a novel class of potent agonists at the D1‐receptor. Such compounds may have the potential for use clinically in improving renal perfusion and reducing afterload.
On the blockade of acetylcholine release at mouse motor nerve terminals by β‐bungarotoxin and crotoxin
Authors: Rowan E.G. , Pemberton K.E. , Harvey A.L. 
Published: July 2012

β‐Bungarotoxin and crotoxin are phospholipose A2 neurotoxins, which block irreversibly the evoked release of acetylcholine from motor nerve terminals of mouse triangularis sterni preparations.
Extracellular recording of nerve terminal action potentials reveal that inhibition of transmitter release is not associated with failure of the action potential to invade nerve terminals.
When evoked transmitter release (measured as intracellularly recorded endplate potentials) was blocked by β‐bungarotoxin, spontaneous acetylcholine release was stimulated as in control experiments by K+‐induced depolarization and by the Ca2+‐ionophore A23187.
The site of action of the toxins remains to be elucidated but would appear to be associated with the coupling of action potential induced‐depolarization to the release mechanism, rather than with the release mechanism itself.
Effects of platelet activating factor on contractile force and 45Ca fluxes in guinea‐pig isolated atria
Authors: Diez J. , Delpón E. , Tamargo J. 
Published: July 2012

The effects of platelet activating factor (PAF) were studied on the electromechanical properties and 45Ca2+ fluxes of guinea‐pig isolated atria.
Both in spontaneously beating and electrically driven atria, PAF (10−12‐10−7m) increased atrial rate but produced a biphasic effect on contractile force. At low concentrations (up to 10−10m) it produced a positive inotropic effect, while at higher concentrations PAF exerted a negative inotropic effect. A similar biphasic effect was observed in the slow contractions elicited by isoprenaline in K+‐depolarized atrial fibres.
The positive inotropic effect of PAF was prevented by verapamil, whereas pretreatment of atria with propranolol, phentolamine, indomethacin or atropine did not modify its positive and negative inotropic actions. BN 52021, a specific PAF antagonist, abolished both the positive and negative inotropic effects.
PAF had no effect on the characteristics of the action potentials recorded in either normally polarized or K+‐depolarized (slow action potential) atrial fibres.
At concentrations at which it increased contractile force, PAF potentiated the contractile responses to Ca2+ (0.9‐9 mm), whereas at negative inotropic concentrations it inhibited them. The negative inotropic effect of PAF was partially reversed in 70% Na+ medium.
At 10−11 m, PAF increased 45Ca2+ uptake and reduced the rate coefficient (kcm for the 45Ca2+ efflux. This increase in 45Ca2+ uptake was abolished in atria pretreated with verapamil or BN 52021. However, 10−7 μ PAF modified neither 45Ca2+ uptake nor efflux in atrial muscle.
These results suggest that in guinea‐pig atria the biphasic inotropic effects of PAF cannot be explained through modifications in the slow inward Ca2+ current or in Na+‐Ca2+ exchange, but may be related to changes in trans‐sarcolemmal Ca2+ entry mediated by specific PAF receptors.