bluuebunny/crossref_metadata_2025 huggingface dataset:
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.
Haemodynamic and abdominal motor reflexes elicited by neurotensin in anaesthetized guinea‐pigs
Authors: Rioux Francis , Lemieux Margot
Published: July 2012

Single intraperitoneal (i.p.) injections of neurotensin (NT) (0.14–140 nmol kg−1) in anaesthetized guinea‐pigs were found to trigger transient abdominal wall contractions (TAWC) accompanied by relatively sustained increases of systemic blood pressure (BP) and heart rate (HR). The modification of the latter NT effects by various drugs and surgical manipulations was examined to obtain some insight into the nature of, and possible relationship between, these responses.

The abdominal motor response (i.e. TAWC) to i.p. NT (14 nmol kg−1) was inhibited by prior i.v. injection of the guinea‐pigs with pancuronium (0.27 μmol kg−1), morphine (1.5 and 15 μmol kg−1), clonidine (0.34 μmol kg−1), by concomitant i.p. injection of procaine 2% w/v, or by acute spinalization. It was potentiated by naloxone (2.8 and 28 μmol kg−1), but not affected by i.v. injection of autonomic drugs (i.e. pentolinium, prazosin, yohimbine and atropine), by capsaicin desensitization, or by acute bilateral cervical vagotomy. In spinalized animals a sustained abdominal wall contraction (SAWC) was unmasked, which was resistant to i.v. morphine, clonidine or baclofen but suppressed by i.v. pancuronium or i.p. lignocaine 2% w/v.

Haemodynamic responses to i.p. NT were not affected by i.v. pancuronium, morphine, naloxone, atropine, or by vagotomy. They were inhibited by i.v. pentolinium or clonidine (BP, HR), i.v. prazosin (BP), i.p. procaine 2% w/v (BP, HR), capsaicin desensitization or acute spinalization (BP, HR). Yohimbine (i.v.) potentiated BP and HR increases caused by i.p. NT.

These results suggest that: (1) the haemodynamic and TAWC responses to i.p. NT in this animal model, are two independent, neurally‐mediated reflexes which are likely to originate from the abdominal cavity and require a functionally intact spinal cord for their full expression; (2) the neural pathways subserving both types of responses appear to be different from each other. The nature and time‐response characteristics of the reflexes caused by i.p. NT, raise the possibility that i.p. NT is a noxious stimulus, at least in guinea‐pigs.
Biological activity and metabolism of 20‐hydroxyeicosatetraenoic acid in the human platelet
Authors: Hill Elizabeth , Fitzpatrick Frank , Murphy Robert C.
Published: July 2012

The cytochrome P‐450 metabolite of arachidonic acid, 20‐hydroxyeicosatetraenoic acid (20‐HETE), was found to be a potent, dose‐dependent inhibitor of platelet aggregation and inhibitor of thromboxane biosynthesis induced by arachidonic acid (IC50 5.2 ± 1.5 μm), A23187 (IC50 16.2 ± 5.4 μm), and U46619 (IC50 7.8 ± 2.4 μm). 20‐HETE did not inhibit thrombin‐induced aggregation.

The human platelet metabolized 20‐HETE to a series of novel metabolites formed by cyclo‐oxygenase as well as lipoxygenase pathways. The structures of the metabolites were identified by mass spectrometry as 20‐hydroxy‐thromboxane B2, 12,17‐dihydroxyheptadecatrienoic acid, 12,20‐dihydroxyeicosatetraenoic acid, and 11,20‐dihydroxyeicosatetraenoic acid.

The identification of the 11‐hydroxy metabolite of 20‐HETE suggests that 20‐HETE is less efficiently cyclized to an endoperoxide intermediate by cyclo‐oxygenase than is arachidonate.

Although some biological activity of 20‐HETE may be related to competition with endogenous arachidonate for cyclo‐oxygenase metabolism, the predominant mechanism of action of 20‐HETE appears to be through antagonism of the prostaglandin H2/thromboxane A2 receptor.
Structure‐activity relations of amiloride and its analogues in blocking the mechanosensitive channel in Xenopus oocytes
Authors: Lane John W. , McBride Don W. , Hamill Owen P.
Published: July 2012

Patch clamp recording techniques have been used to compare the block caused by amiloride and some of its structural analogues of the mechanosensitive (MS) cation selective channel in frog (Xenopus laevis) oocytes.

Like amiloride, the amiloride analogues dimethylamiloride (DMA), benzamil and bromohexa‐methyleneamiloride (BrHMA) block the MS channel in a highly voltage‐dependent manner.

All analogues tested were more potent blockers than amiloride with IC50's of 500 μm (amiloride), 370 μm (DMA), 95 μm (benzamil) and 34 μm (BrHMA).

Hill plots gave Hill coefficients of 2 (amiloride), 1.8 (DMA), 1 (benzamil) and 1.2 (BrHMA) indicating that the binding of two ligand molecules may be necessary for the block caused by amiloride, DMA and possibly BrHMA whereas only a single ligand molecule may be required for the block by benzamil.

The potential use of BrHMA as a light‐activated, covalent label of the MS channel protein is discussed.

The amiloride analogue ‘fingerprinting’ of the blocking site on the MS channel indicates it is structurally different from previously described amiloride‐sensitive ion transport pathways but may be related to the amiloride binding site on outer hair cells of the ear.
Effects of BRL 38227, sodium nitroprusside and verapamil on collateral perfusion following acute arterial occlusion in the rabbit isolated ear
Authors: Randall Michael D. , Griffith Tudor M.
Published: July 2012

We have used an isolated, buffer‐perfused, rabbit ear model of acute arterial occlusion to investigate the effects of the nitrovasodilator sodium nitroprusside, the potassium channel activator BRL 38227 (the active (−)‐enantiomer of cromakalim) and the calcium antagonist, verapamil, on collateral perfusion in the absence of pharmacological tone.

Verapamil was the most potent vasodilator (EC50 = 72.6 ± 32.0 nm) of 5‐hydroxytryptamine/histamine‐induced tone in the rabbit isolated perfused ear. Sodium nitroprusside and BRL 38227 were less potent with respective EC50 values of 488 ± 75 nm and 296 ± 40 nm. Following inhibition of endothelium‐derived relaxing factor (EDRF) synthesis, the potency of BRL 38227 was significantly (P < 0.001) increased with an EC50 of 55.6 ± 5.0 nm.

BRL 38227 at 500 nm and 3 μm induced substantial increases in collateral perfusion following arterial ligation in the absence of pharmacological tone compared to control. Furthermore 3 μm BRL 38227 completely reversed the attenuation of collateral perfusion which followed inhibition of EDRF synthesis with 100 μm NG‐nitro‐l‐arginine methyl ester (l‐NAME).

Sodium nitroprusside (500 nm and 3 μm) induced modest improvements in collateral perfusion in the early stages after arterial occlusion.

Verapamil did not influence collateral perfusion at either of the concentrations used (50 nm and 3 μm), even though it was a potent vasodilator.

The results of this study indicate that BRL 38227, and to a much lesser extent sodium nitroprusside, selectively improve collateral perfusion following arterial occlusion, even in the presence of effects of EDRF on acute collateralization, while verapamil has no effect. Furthermore, BRL 38227 also improves collateral perfusion following inhibition of EDRF synthesis. It remains to be established whether BRL 38227 has beneficial actions in acute arterial occlusion in vivo.
Developmental changes in endothelium‐dependent pulmonary vasodilatation in pigs
Authors: Liu S.F. , Hislop A.A. , Haworth S.G. , Barnes P.J.
Published: July 2012

We compared in vitro endothelium‐dependent vasorelaxant responses to acetylcholine (ACh) and the endothelium‐independent vasodilator response to sodium nitroprusside (SNP) in prostaglandin F2α (PGF2α)‐precontracted muscular pulmonary arteries (PA) from pigs aged 5 min to 2 h (neonatal), 3–10 days, 3–8 weeks and adults.

In the pulmonary artery (PA) rings from neonatal animals, the vasodilator response to ACh was negligible. However, responses to ACh were present in all PA rings from older animals, being greatest at 3–10 days and then decreasing with age (P < 0.001, ANOVA). ACh (30 μm) induced a 1 ± 1%, 92 ± 9%, 62 ± 5% and 51 ± 6% reduction of the PGF2α‐generated tension in neonatal, 3–10 days, 3–8 weeks and adult groups, respectively.

The relaxant response to SNP was present in the PA rings from all age groups and increased with age (P < 0.001, ANOVA). SNP (1 μm)‐induced relaxation was 55 ± 9%, 73 ± 7%, 97 ± 5% and 93 ± 6% in neonatal, 3–10 days, 3–8 week and adult groups, respectively.

Removal of the vascular endothelium abolished the relaxant response to ACh but had no effect on the response to SNP in any groups.

NG‐monomethyl‐l‐arginine (30 μm), a nitric oxide synthesis inhibitor, inhibited the response to ACh but not to SNP. The lipoxygenase inhibitor, nordihydroguaiaretic acid, had no significant effect on responses to ACh or SNP in any group.

These findings suggest that the nitric oxide pathway may not play a part in dilating the pig pulmonary arteries at birth, but may be important during the transitional period of establishing a stable post‐natal pulmonary circulation. The increase in response to SNP with age parallels the increase in smooth muscle cell myofilaments to which it may be related.
Selective and full β1‐adrenoceptor agonist action of a catechol derivative of denopamine (T‐0509) in the guinea‐pig cardiac muscle and trachea: comparison with denopamine, xamoterol and isoprenaline
Authors: Yabana Hideo , Watanabe Hirofumi , Narita Hiroshi , Nagao Taku
Published: July 2012

The pharmacological actions of T‐0509, a 3‐hydroxy derivative of denopamine, were studied in various guinea‐pig tissues; these effects were compared with those of isoprenaline, denopamine and xamoterol.

The intrinsic activities of the positive inotropic actions of T‐0509, denopamine and xamoterol compared with isoprenaline (= 100%) in the papillary muscle were 99%, 83% and 28%, respectively, while their relative potencies (EC50 agonist EC50 isoprenaline) were 0.23, 33 and 1.4, respectively. The intrinsic activities of T‐0509, denopamine and xamoterol as positive chronotropic agents in the right atria were 98%, 69% and 48%, respectively, and their equipotent concentrations (isoprenaline = 1) were 0.24, 50 and 4, respectively.

The positive chronotropic actions of T‐0509 and denopamine were antagonized by bisoprolol (3 × 10−8 m), but not by ICI 118,551 (3 × 10−8 m).

The intrinsic activity of T‐0509 in histamine‐contracted tracheae was similar to that of isoprenaline, but its equipotent concentration was 38; the effects of both agents were antagonized by ICI 118,551 (3 × 10−8 m), but not by bisoprolol (3 × 10−8 m). Denopamine and xamoterol did not show any agonist activity on guinea‐pig trachea.

Denopamine and xamoterol antagonized the positive chronotropic (pA2, denopamine: 6.98, xamoterol: 7.75) and tracheal relaxant (pA2, denopamine: 5.39, xamoterol: 6.25) effects of isoprenaline.

Isoprenaline, T‐0509 and denopamine, but not xamoterol, contracted the guinea‐pig aorta in a decreasing order in the presence of propranolol (10−6 m).

Based on the above studies, T‐0509 appears to be a highly selective β1‐adrenoceptor agonist with full agonist properties, while denopamine and xamoterol appear to be selective, but partial ft ‐adrenoceptor agonists.
Effects of acute and chronic electroconvulsive shock on noradrenaline release in the rat hippocampus and frontal cortex
Authors: Thomas D.N. , Nutt D.J. , Holman R.B.
Published: July 2012

Changes in the extracellular content of endogenous noradrenaline (NA) in frontal cortex and hippocampus were determined by in vivo microdialysis following acute and chronic electroconvulsive shock (ECS) in rats anaesthetized with chloral hydrate.

Basal release of NA in the frontal cortex (4.9 ± 0.3 pg/sample) did not differ significantly from that in the hippocampus (4.6 ± 0.2 pg/sample).

A single ECS resulted in an increase of NA release in the hippocampus (21.1 ± 1.3 pg/sample) and in the frontal cortex (11.6 ± 1.2 pg/sample). In both brain regions extracellular NA had returned to basal values within 30 min.

Animals were treated chronically with ECS (once per day for seven days). Twenty‐four h later (day 8), basal release of NA into dialysis samples from the frontal cortex was significantly increased (50%) as compared to chronic sham controls. Basal release in the hippocampus was not significantly different from the sham controls. In the chronic ECS animals the increase in NA released in both brain areas following an ECS on day 8 did not differ from either the chronic sham controls or from animals given acute ECS.

Animals were challenged 24 h after eight ECS or sham control treatments (once per day) with the α2‐adrenoceptor antagonist, idazoxan (10 mg kg−1, s.c). Idazoxan increased NA release in the hippocampus in both groups. There was no difference in the magnitude of the response in ECS‐ and in sham‐treated rats. In the frontal cortex, idazoxan increased the extracellular NA content in the chronic sham controls, but the response to idazoxan was significantly attenuated in the chronic ECS animals.

Chronic but not acute ECS was found to elicit a sustained (> 24 h) increase in the release of NA in the frontal cortex, but not in the hippocampus. The idazoxan data suggest that the increase may be due to a downregulation of presynaptic α2‐adrenoceptors in the frontal cortex. The difference in response of these two brain regions to chronic ECS is discussed in terms of differences in the regulation of extracellular NA content by uptake and autoreceptor activation.
Investigations of the subtype of α2‐adrenoceptor mediating contractions of the human saphenous vein
Authors: Smith Karen , Connaughton Sonia , Docherty James R.
Published: July 2012

We have examined the effects of a series of α2‐adrenoceptor antagonists against isometric contractions to noradrenaline in human saphenous vein, and correlated these potencies with affinities for the α2A‐ligand binding site of human platelet and the α2B‐ligand binding site of rat kidney.

The α2B‐selective adrenoceptor antagonists, prazosin, ARC 239 and HV 723 showed high, and the α2A‐selective antagonist BRL 44408 showed low, potency in human saphenous vein.

Potency in human saphenous vein correlated better with affinity for the α2B‐ligand binding site (r =0.71, n = 12, P < 0.01) than with affinity for the α2A‐ligand binding site (r = 0.56, n = 12, non significant).

It is concluded that the postjunctional α2‐adenoceptor of human saphenous vein resembles an α2B‐ligand binding site more than an α2A‐ligand binding site.
Differences in evoked dopamine efflux in rat caudate putamen, nucleus accumbens and tuberculum olfactorium in the absence of uptake inhibition: influence of autoreceptors
Authors: Trout Stephen J. , Kruk Zygmunt L.
Published: July 2012

Dopamine efflux following single pulse or train of pulse stimulations was measured in slices of rat caudate putamen, nucleus accumbens and tuberculum olfactorium, using fast cyclic voltammetry at a carbon fibre microelectrode; 1, 5, 10, 20 or 50 pulses were applied at each location at frequencies varying from 10 Hz to 500 Hz.

There are significant differences in the ability of the different regions to increase dopamine efflux following single or repeated electrical stimulation.

Highest release in response to a single pulse is observed in the caudate putamen (approximately 250 nm dopamine), but the ratio of the peak dopamine overflow following a train of 20 pulses (50 Hz) when compared to a single pulse is rarely greater than three.

Release following single pulse stimulation in the nucleus accumbens (approximately 185 nm dopamine) is often slightly less than in the caudate putamen, but the ratio of peak release when trains of 20 pulses (50 Hz) are compared to single pulse stimulation has been as great as seven fold.

The tuberculum olfactorium releases the least dopamine of the three regions following a single pulse stimulation (approximately 40 nm dopamine), but the ratio of peak dopamine release following trains of 20 pulses (50 Hz) when compared to single pulse can result in a value approaching 20.

When 20 pulses are applied to the caudate putamen at frequencies ranging from 10 to 500 Hz, the peak efflux is essentially the same (frequency/release profile is flat), with the maximum increase only 140% that of a single pulse.

By contrast, in the nucleus accumbens and the tuberculum olfactorium, well defined frequency‐release relationships are seen following 20 pulses applied at 10, 20 and 50 Hz; at higher frequencies the dopamine release decreases as frequency is increased.

Experiments with sulpiride or metoclopramide (dopamine D2 receptor antagonists) indicate that dopamine release in the caudate putamen is not regulated by dopamine autoreceptor activation by endogenous dopamine under our experimental conditions (in the absence of reuptake inhibtion). By contrast, in the nucleus accumbens and in the tuberculum olfactorium, we present evidence to show that at frequencies of stimulation up to 20 Hz, endogenous dopamine acts at dopamine autoreceptors to inhibit further release of dopamine but a minimum exposure time of between 500 and 1000 ms is needed for the response to D2 autoreceptor activation by endogenously released dopamine to be seen.
5‐Hydroxyindole slows desensitization of the 5‐HT3 receptor‐mediated ion current in N1E‐115 neuroblastoma cells
Authors: Kooyman André R. , van Hooft Johannes A. , Vijverberg Henk P.M.
Published: July 2012

Effects of 5‐hydroxyindole (5‐OHi) on 5‐HT3 receptor‐operated ion current were investigated in voltage‐clamped N1E‐115 neuroblastoma cells. In the presence of 1 mm 5‐OHi, the amplitudes of inward currents induced by the agonists 5‐hydroxytryptamine (5‐HT), 2‐methyl‐5‐HT and dopamine were enhanced and desensitization of the responses was markedly slowed down. The results indicate that 5‐OHi selectively modifies the desensitization of the 5‐HT3 receptor‐mediated ion current.
Localization and characterization of neuropeptide Y binding sites in porcine and human colon
Authors: Walsh David A. , Wharton John , Blake David R. , Polak Julia M.
Published: July 2012

We have used quantitative receptor autoradiography to investigate the localization and characteristics of binding sites for 125Iodine‐Bolton Hunter‐labelled human neuropeptide Y ([125I]‐BH‐NPY) in porcine and human colon, and compared the binding characteristics with those found in porcine spleen.

Saturable, specific, high affinity [125I]‐BH‐NPY binding was localized to myenteric ganglia in porcine and human colons, and to submucosal ganglia in porcine colon.

Specific [125I]‐BH‐NPY binding to porcine myenteric ganglia was reversible in the presence of guanosine 5′‐O‐(3‐thiotriphosphate) and was inhibited by related peptides with the rank order of potency; porcine NPY = human NPY = peptide tyrosine tyrosine (PYY) ≫ pancreatic polypeptide.

The Y2 selective analogue, NPY(13–36), competed for [125I]‐BH‐NPY binding to porcine myenteric ganglia with greater potency than the Y1 selective analogue, [Leu31, Pro34]NPY, the difference being small, but significant.

The characteristics of [125I]‐BH‐NPY binding to porcine myenteric ganglia were similar to those observed concurrently to porcine splenic red pulp.

The small difference in inhibitory potencies between NPY(13–36) and [Leu31, Pro34]NPY observed in this study in comparison with previous studies was not explained by differential ligand depletion during incubations, but may be due to differences in methodology between binding studies performed on tissue sections and on membranes.

We conclude that specific [25I]‐BH‐NPY binding sites are present in the myenteric and submucosal ganglia of the colon and that these sites may act as functional receptors by which NPY and PYY modulate colonic motility and electrolyte transport.
Stimulation of insulin secretion by imidazoline compounds is not due to interaction with non‐adrenoceptor idazoxan binding sites
Authors: Brown Colin A. , Loweth Anne C. , Smith Stephen A. , Morgan Noel G.
Published: July 2012

The potency of interaction of several imidazoline compounds with non‐adrenoceptor idazoxan binding sites (NAIBS) in rat liver membranes was compared with their ability to alter insulin secretion from rat pancreatic islets.

NAIBS could be labelled specifically with [3H]‐idazoxan in both rat liver membranes and in rat islet homogenates. Liver binding sites exhibited a KD for [3H]‐idazoxan of 24 nm and a Bmax of 264 fmol mg−1 protein.

Binding of [3H]‐idazoxan to NAIBS in rat liver membranes was displaced effectively by unlabelled idazoxan (IC50 0.1 μm) and by UK14304 (IC50 0.5 μm). However, two other imidazoline compounds efaroxan and RX821002, which are related in structure to idazoxan, were much less effective as displacers.

In insulin secretion experiments, the ATP‐sensitive potassium channel agonist diazoxide (250 μm) was able to suppress the rise in insulin secretion induced by 20 mm glucose. Both efaroxan and RX821002 (100 μm) antagonized the inhibitory effect of diazoxide on glucose‐induced insulin secretion. By contrast, neither idazoxan (100 μm) nor UK14304 (50 μm), was able to overcome significantly the inhibitory effect of diazoxide.

The ability of 100 μm efaroxan to antagonize the suppression of insulin secretion mediated by diazoxide, was not prevented by idazoxan (up to 100 μm) or by UK14304 (up to 50 μm).

The results indicate that the stimulatory effects of imidazoline compounds on insulin secretion are not due to interaction with NAIBS similar to those present in rat liver.
Nitric oxide modulates vascular permeability in the rat coronary circulation
Authors: Filep János G. , Földes‐Filep Éva , Sirois Pierre
Published: July 2012

The objective of the present study was to assess whether inhibition of nitric oxide (NO) production could modulate vascular permeability in the coronary circulation in conscious rats.

Intravenous injection of NG‐nitro‐l‐arginine methyl ester (l‐NAME, 2 mg kg−1) resulted in a slowly developing hypertension and evoked twofold increases in vascular permeability in the left ventricle and right atrium as measured by the extravasation of Evans blue dye. Maintenance of mean arterial blood pressure at the level observed following l‐NAME injection by infusion of noradrenaline (620–820 ng kg−1 min−1) did not induce significant protein extravasation in the coronary circulation.

l‐NAME treatment markedly enhanced (up to 490%) protein extravasation both in the left ventricle and right atrium in response to platelet‐activating factor (PAF, 1.9 nmol kg−1, i.v.) and endothelin‐1 (1 nmol kg−1, i.v.). Noradrenaline infusion potentiated (up to 69%) endothelin‐1‐induced protein extravasation. The permeability effect of PAF was only slightly enhanced by noradrenaline.

The present findings indicate that inhibition of endogenous NO synthesis leads to an increase in protein extravasation and to potentiation of the permeability effects of PAF and endothelin‐1 in the coronary circulation. These results also suggest that NO may be an important regulator of vascular permeability under physiological and pathological conditions.
Pharmacological differentiation by pertussis toxin of the in vivo acute responses to fMLP and PAF in guinea‐pig lungs
Authors: Arreto C.D. , Bureau M.F. , Imaizumi A. , Vargaftig B.B.
Published: July 2012

The effects of pertussis toxin on the N‐formyl‐l‐methionyl‐l‐leucyl‐l‐phenylalanine (fMLP) and platelet‐activating factor (PAF)‐induced variations in pulmonary capillary albumin exchanges, blood volume, leucocyte or platelet sequestration were studied in the guinea‐pig, by use of radioactive tracers. The effects of pertussis toxin on pulmonary insuflation pressure were studied in parallel.

The i.v. administration of fMLP and PAF to the guinea‐pig was followed by bronchoconstriction, increased lung capillary albumin exchanges (vasopermeability) sequestration of leucocytes, leucopenia and reduction of blood volume (vasoconstriction). PAF also induced platelet sequestration in lungs and thrombocytopenia.

Pertussis toxin (10 μg kg−1, i.v., 72 h before the experiment) prevented all the studied fMLP‐induced effects, but failed to modify PAF‐induced bronchoconstriction, lung vasoconstriction, platelet sequestration, thrombocytopenia and the increased capillary vasopermeability. In the same conditions the lung leucocyte sequestration was not significantly affected when leucopenia was partially reduced.

It is suggested that the effects of fMLP, but not those of PAF, involve a Gi‐like protein.
Characterization of 5‐HT3 receptors of N1E‐115 neuroblastoma cells by use of the influx of the organic cation [14C]‐guanidinium
Authors: Bönisch H. , Barann M. , Graupner J. , Göthert M.
Published: July 2012

The 5‐HT3 receptor‐mediated cation influx into N1E‐115 mouse neuroblastoma cells has been studied by the use of the organic cation [14C]‐guanidinium.

5‐Hydroxytryptamine (5‐HT, 30 μm) caused a time‐dependent influx of [14C]‐guanidinium which, in contrast to the influx elicited by veratridine (100 μm), was not inhibited by tetrodotoxin (TTX, 10 μm). The 5‐HT‐induced influx was potentiated by substance P and inhibited by ondansetron.

5‐HT and the selective 5‐HT3 receptor agonists, m‐chloro‐phenylbiguanide, phenylbiguanide and 2‐methyl‐5‐HT caused bell‐shaped concentration‐response curves; the rank order of potency was m‐chlorophenylbiguanide > 5‐HT > phenylbiguanide = 2‐methyl‐5‐HT. Among these agonists, 5‐HT elicited the highest influx of [14C]‐guanidinium. 5‐Methoxytryptamine, an agonist at 5‐HT4 receptors, showed no effect.

The [14C]‐guanidinium influx induced by 100 μm 5‐HT was not affected by methysergide (10 μm) and ketanserin (10 μm) but was inhibited by 5‐HT3 receptor antagonists with the following rank order of potency: ICS 205–930 > ondansetron > MDL 72222 ≫ metoclopramide.

The 5‐HT‐induced [14C]‐guanidinium influx was increased in the absence of Ca2+ and/or Na+ and by a reduction of the temperature from 36° to 20°C.

Preincubation with 5‐HT (100 μm) caused a time‐dependent and rapidly reversible decrease of the 5‐HT‐induced [14C]‐guanidinium influx.

It is concluded that [14C]‐guanidinium influx measurement in N1E‐115 cells is a convenient method to study properties of the cation channel of the 5‐HT3 receptor. This influx is independent of the fast sodium channel.
Activation of ion channels by lysylbradykinin in the HCA‐7 colony 29 human adenocarcinoma cell line
Authors: Henderson R.M. , Cuthbert A.W.
Published: July 2012

The patch‐clamp technique, both cell attached and inside‐out patches, was used to examine the effects of lysylbradykinin (LBK) and A23187 on ion channels in cultured Colony 29 epithelial cells derived from a human adenocarcinoma.

LBK and A23187 applied directly to the intact cell stimulated the opening of a number of types of ion channel including Ca2+‐activated K+ channels.

By use of inside‐out patches, anion channels could be stimulated to open by application of protein kinase A and ATP to the cytosolic surface. Ca2+‐activated K+ channels were also identified in isolated membrane patches.

The results suggest that the anion secretion which is stimulated by LBK is a complex event, involving the activation of a number of different types of ion channel, and that part of the response is the result of hyperpolarization of the cell by activation of Ca2+‐activated K+ channels. From the data presented in this and the accompanying papers it appears that the Ca2+‐sensitive K+ channels would be equally effective in either the apical or basolateral membranes.
Evidence against vasoactive intestinal polypeptide as the relaxant neurotransmitter in human cavernosal smooth muscle
Authors: Pickard R.S. , Powell P.H. , Zar M.A.
Published: July 2012

The putative role of vasoactive intestinal polypeptide (VIP) as the relaxant neurotransmitter in human cavernosal smooth muscle has been studied in isolated tissue preparations.

Consistent neurogenic relaxations were evoked by electrical field stimulation (EFS; 2–64 pulses/train, 0.8 ms pulse duration, 10 Hz). VIP (0.1–3 μm) relaxed cavernosal smooth muscle in a dose‐dependent fashion. Relaxant responses to both EFS and VIP were reduced in tissue from impotent men.

Neurogenic relaxant responses were not diminished in the presence of the VIP‐inactivating peptidase, α‐chymotrypsin (α‐CT, 2 units ml−1). In contrast VIP‐induced relaxations were completely abolished.

Inhibition of nitric oxide synthase by NG‐nitro‐l‐arginine (30 μm), and of guanylate cyclase by methylene blue (50 μm) caused highly significant reductions of neurogenic relaxant responses whereas VIP‐evoked relaxations were unaffected.

It is concluded that VIP‐evoked relaxations are not mediated by the NO‐guanosine 3′:5′‐cyclic monophosphate (cyclic GMP) pathway and that VIP release is not essential for neurogenic relaxation of human cavernosal smooth muscle. VIP does not therefore act as the major relaxant neurotransmitter in this tissue.
Modulation of central noradrenergic function by RS‐15385‐197
Authors: Redfern W.S. , MacKinnon A.C. , Brown C.M. , Martin A.B. , Kilpatrick A.T. , Clague R.U. , Spedding M.
Published: July 2012

RS‐15385‐197, a highly potent and selective α2‐adrenoceptor antagonist, was examined in a variety of in vitro and in vivo functional tests to assess the selectivity of its interaction with central noradrenergic neurones in the rat.

In hypothalamic slices, RS‐15385‐197 was potent in augmenting K+‐evoked release of [3H]‐noradrenaline, with an EC50 of 9 nm. Idazoxan and yohimbine showed 100 fold less activity. This was due to its antagonist action at presynaptic α2‐adrenoceptors, as RS‐15385‐197 (10 μm), did not directly release [3H]‐noradrenaline from cortical slices unlike reserpine (10 μm), and did not inhibit noradrenaline re‐uptake into cortical synaptosomes.

In vivo, RS‐15385‐197 (0.5 mg kg−1, p.o.) increased levels of 3‐methoxy‐4‐hydroxy‐phenylglycol (MHPG) in the cerebral cortex without modifying levels of 5‐hydroxyindoleacetic acid (5‐HIAA). This dose, but not a lower dose (0.1 mg kg−1, p.o.) caused β‐adrenoceptor down‐regulation in the cortex when administered once daily for 14 days whereas 5‐HT2 receptor number was unaltered, indicating a selective effect on noradrenergic transmission.

Selective depletion of cortical 5‐HT by administration of p‐chlorophenylalanine (PCPA; 100 mg kg−1, i.p. for 14 days) or 5,7‐dihydroxytryptamine (5,7‐DHT; 150 μg i.c.v.) prevented the β‐adrenoceptor down‐regulation caused by RS‐15385‐197, indicating that a tonic 5‐hydroxytryptaminergic input was required for it to elicit β‐adrenoceptor down‐regulation. It was not possible to prevent the loss of activity of RS‐15385‐197 in these 5‐HT‐depleted animals by co‐administration with the 5‐HT1A partial agonist, 8‐hydroxy‐n‐dipropyl aminotetralin (8‐OH‐DPAT, 0.3 mg kg−1, i.p. twice daily for final 3 days).

At a dose (1 mg kg−1, p.o.) which completely prevented the hypoactivity produced by clonidine (0.1 mg kg−1, p.o.), RS‐15385‐197 did not affect behavioural stereotypy induced by 8‐OH‐DPAT (0.3 mg kg−1, s.c.). Similarly, following chronic dosing with the racemate, RS‐15385‐196 (3 mg kg−1, p.o., once daily for 14 days), there was no effect on the behavioural and hypothermic response to 8‐OH‐DPAT (0.5 mg kg−1, s.c.). Therefore, RS‐15385‐197 was selective for central α2‐adrenoceptors over 5‐HT1A receptors in in vivo functional tests.

Thus, RS‐15385‐197 was highly selective in interacting with central noradrenergic neurones in the rat in vitro and in vivo. It is therefore currently the agent of choice for investigations of the role of α2‐adrenoceptors in the CNS.
Endothelin (16–21): biphasic effect and no desensitization on the guinea‐pig isolated ileum
Authors: Miasiro N. , Nakaie C.R. , Paiva A.C.M.
Published: July 2012

In the guinea‐pig ileum the C‐terminal hexapeptide of the endothelins, endothelin (16–21), induced a biphasic effect (relaxation followed by contraction) qualitatively similar to that seen in the responses to endothelins 1 and 3. Both components of the response were concentration‐dependent in the range studied (2–100 μm).

The response induced by endothelin (16–21) was inhibited in low‐sodium (80 mm) medium.

Repeated administration of endothelin (16–21) induced no desensitization of the preparation, contrasting with the tachyphylaxis induced by endothelin‐1 and endothelin‐3 in the guinea‐pig ileum.

Tissues rendered tachyphylatic to endothelin‐1 or endothelin‐3 responded normally to endothelin (16–21).

The results suggest that the C‐terminal tail of the endothelins contains the message for the biphasic response, whereas the N‐terminal domain may be responsible for the strong binding to the receptor and for the tachyphylactic properties of endothelin‐1 and endothelin‐3, in the guinea‐pig isolated ileum. However, the possibility that endothelin (16–21) may be acting on a site other than the endothelin receptor cannot be ruled out.