bluuebunny/crossref_metadata_2025_split huggingface dataset:
Development of a radioligand binding assay for 5‐HT4 receptors in guinea‐pig and rat brain
Authors: Grossman C.J. , Kilpatrick G.J. , Bunce K.T. 
Published: July 2012

The 5‐HT4 receptor antagonist, GR113808, has been radiolabelled to a high specific activity with tritium.
Characterization of specific [3H]‐GR113808 binding in homogenates of guinea‐pig striatum and hippocampus revealed a single site of high affinity (Kd values 0.20 and 0.13 nm respectively).
[3H]‐GR113808 binding was reversible and displayed rapid kinetics such that association and dissociation were complete within 3 min.
Specific [3H]‐GR113808 binding was potently and stereoselectively inhibited by agonists and antagonists acting at the 5‐HT4 receptor but not by compounds selective for other 5‐HT receptors or other neurotransmitter receptors.
Autoradiographic analysis revealed a discrete localization in both guinea‐pig and rat brain with high concentrations of binding in brain areas such as the striatum, substantia nigra and olfactory tubercle.
[3H]‐GR113808 binding to homogenates of guinea‐pig striatum meets the criteria for labelling of the 5‐HT4 receptor and, as such, represents the first characterization of this receptor in a radioligand binding assay.
Vasorelaxant mechanism of KRN2391 and nicorandil in porcine coronary arteries of different sizes
Authors: Miwa Atsushi , Kaneta Soichiro , Motoki Kazuhiro , Jinno Yasuhiro , Kasai Hideo , Okada Yuji , Fukushima Hideaki , Ogawa Nobuyuki 
Published: July 2012

The relaxant mechanisms of action of KRN2391, a novel vasodilator, and nicorandil on epi‐myocardial coronary artery (2.5–3.0 mm outer diameter) and mid‐myocardial coronary artery (0.8–1.0 mm outer diameter) were investigated in porcine isolated coronary arteries. In addition, the vasorelaxant responses of KRN2391 and nicorandil were compared with those of nitroglycerin and cromakalim, a K+ channel opener, in epi‐ and mid‐myocardial coronary arteries.
Nitroglycerin showed a more potent relaxant effect on epi‐myocardial coronary arteries than on mid‐myocardial coronary arteries, whereas cromakalim produced greater relaxation responses in mid‐myocardial coronary arteries. There was no difference between epi‐ and mid‐myocardial coronary arteries in terms of the relaxant effect of KRN2391 and nicorandil.
Relaxation induced by KRN2391 in epi‐ and mid‐myocardial coronary arteries was inhibited by oxyhaemoglobin, a pharmacological antagonist of nitrovasodilators, and glibenclamide, a pharmacological antagonist of K+ channel opening drugs. However, the inhibitory effect of glibenclamide on KRN2391‐induced relaxation was greater in mid‐myocardial coronary artery than in epi‐myocardial coronary artery.
Relaxation induced by nicorandil was inhibited by oxyhaemoglobin alone in epi‐myocardial coronary arteries and by both oxyhaemoglobin and glibenclamide in mid‐myocardial coronary arteries.
In epi‐ and mid‐myocardial coronary arteries, relaxation induced by cromakalim was inhibited by glibenclamide but not by oxyhaemoglobin, whereas relaxation induced by nitroglycerin was inhibited by oxyhaemoglobin but not by glibenclamide.
These results suggest that KRN2391 and nicorandil exhibit a dual mechanism of action acting partly as a nitrate and partly as a K+ channel opener. The mechanism of action of these drugs depend on the segment of coronary artery studied. Furthermore, the dual mechanism of action of KRN2391 and nicorandil seems to contribute to the equipotent relaxant effect between epi‐ and mid‐myocardial coronary arteries.
Modification by charybdotoxin and apamin of spontaneous electrical and mechanical activity of the circular smooth muscle of the guinea‐pig stomach
Authors: Suzuki Keiko , Ito Kaoru M. , Minayoshi Yukie , Suzuki Hikaru , Asano Masahisa , Ito Katsuaki 
Published: July 2012

The effects of charybdotoxin and apamin, putative blockers of Ca2+‐activated K+ channels, on spontaneous electrical and mechanical activity of circular smooth muscle of the guinea‐pig stomach antrum were examined in the presence of 1 μm tetrodotoxin and 1 μm atropine.
Both charybdotoxin (> 3 nm) and apamin (> 3 nm) dose‐dependently increased the amplitude of spontaneous contractions without altering their frequency. The maximum effect of charybdotoxin was much greater than that of apamin. Both toxins increased the amplitude of intracellular Ca2+ oscillations measured with fura‐2.
When the extracellular Ca2+ concentration was lowered to 1.5 mm or less, apamin did not significantly potentiate the contractions whereas charybdotoxin still potentiated them but with less potency.
Charybdotoxin (30 nm) increased the amplitude of spikes and slow waves, and slightly decreased the resting membrane potential. On the other hand, apamin (100 nm) preferentially increased the slow wave amplitude with no effect on the resting membrane potential.
These results suggest that both toxins affect the spontaneous contraction by modifying the electrical activity and that charybdotoxin‐sensitive K+ channels and apamin‐sensitive ones are differently involved in the spontaneous electrical activity.
Cellular mechanism of the positive inotropic effect of hydralazine in mammalian myocardium
Authors: Hurrell David G. , Perreault Cynthia L. , Miao Lin , Ransil Bernard J. , Morgan James P. 
Published: July 2012

The purpose of this study was to elucidate the cellular mechanism of the positive inotropic effect of hydralazine, a vasodilator widely used for afterload reduction in patients with heart failure that has also been reported to have positive inotropic effects on the heart. After isolation, right ventricular papillary muscles from the ferret were maintained in bicarbonate‐buffered salt solution (30°C). A concentration‐response relationship was obtained for hydralazine (10−6 to 10−3 m). In order to mimic different levels of catecholamine release found in heart failure, we utilized two methods of stimulation: (a) threshold punctate pulses and (b) suprathreshold punctate stimulation with voltage approximately 10% above threshold.
In a first group of muscles (n = 16), a maximally effective concentration of hydralazine (10−3 m) increased peak isometric tension by 39 ± 9% (P < 0.05). Doses lower than 10−5 m had no significant effect. The bioluminescent Ca2+ indicator, aequorin, was loaded into a subset of these muscles (n = 7). A significant increase in peak light (i.e., intracellular Ca2+) developed, concurrently with an increase in peak tension (38 ± 5% to 66 ± 8%). This inotropic response was associated with a decrease in time to peak tension (ms), 221 ± 7 to 186 ± 5 (P < 0.05), and time to peak light, 65 ± 4 to 52 ± 2 (P < 0.05). These effects were markedly attenuated by pretreatment with autonomic blocking agents.
In a second group of muscles (n = 12), histamine was used to stimulate cyclic AMP production in the presence of propranolol. Hydralazine (3 × 10−4 m) led to a shift in the pD2 (i.e. the negative log of the concentration of histamine producing 50% of the maximal response) from 6.1 ± 0.1 to 5.9 ± 0.1 (P < 0.05), thus increasing the sensitivity of the muscles to histamine. Hydralazine also increased maximum tension from 160 ± 77% to 195 ± 57% (P < 0.05) above baseline. Thus, hydralazine altered the potency and efficacy of histamine despite the presence of β‐adrenoceptor blockade.
A third group of muscles were chemically skinned to examine the effects of hydralazine on myofilament Ca2+ responsiveness. Pretreatment of ferret papillary muscles with hydralazine (10−3 m) before skinning did not shift the force‐pCa curve after skinning (n = 16). However, hydralazine added to previously skinned fibres desensitized the myofilaments, as indicated by a rightward shift of the force‐pCa curve (n = 12). Maximum tension development was not changed.
The pharmacological effects of hydralazine are characteristic of inotropic drugs that act mainly via cyclic AMP; however, the increase in peak tension demonstrated with histamine in the presence of hydralazine also suggests an effect on cyclic AMP‐independent second messenger pathways. These data are consistent with reports that large doses of hydralazine may increase cellular levels of cyclic AMP, as well as other second messengers, by direct cardiac and indirect neuronal mechanisms.
The novel 5‐HT1A receptor antagonist, SDZ 216–525, decreases 5‐HT release in rat hippocampus in vivo
Authors: Sharp T. , McQuade R. , Fozard J.R. , Hoyer D. 
Published: July 2012

Recent evidence suggests that the novel compound SDZ 216–525 is a selective and possibly silent 5‐HT1A receptor antagonist. Here we have examined the action of SDZ 216–525 on central 5‐HT1A autoreceptor function. The experiments involved measurement of drug effects on extracellular 5‐HT in the ventral hippocampus of the chloral hydrate anaesthetized rat by use of microdialysis.
Acute injection of SDZ 216–525 (0.1, 0.3, 1.0 and 3 mg kg−1, s.c.) caused a dose‐related decrease in 5‐HT output with an estimated ED50 of at least 0.3 mg kg−1. This ED50 value is 20–30 times greater than ED50 values previously obtained for 8‐hydroxy‐2‐(di‐n‐propylamino) tetralin (8‐OH‐DPAT) and NAN‐190. In comparison, SDZ 216–525 is reported to have slightly higher affinity for the 5‐HT1A site than 8‐OH‐DPAT and NAN‐190.
The inhibitory effect of SDZ 216–525 (1 mg kg−1, s.c.) on 5‐HT was blocked by the 5‐HT1/β‐adrenoceptor antagonist, (−)‐pindolol (8 mg kg−1, s.c.) but not by a combination of the β1 and β2‐selective adrenoceptor antagonists metoprolol and ICI 118,551 (4 mg kg−1, each).
Although in several experimental models SDZ 216–525 has high affinity, selectivity and lacks intrinsic activity at the 5‐HT1A receptor, our experiments show that the drug decreases extracellular 5‐HT in ventral hippocampus of the chloral hydrate anaesthetized rat via a pindolol‐sensitive mechanism. We conclude that either SDZ 216–525 promotes (with low potency in vivo) 5‐HT1A receptor/G‐protein interactions, or that the 5‐HT1A autoreceptor is a 5‐HT1A receptor subtype different from the postsynaptic 5‐HT1A receptor.
Inhibition of nitric oxide synthesis reveals non‐cholinergic excitatory neurotransmission in the canine proximal colon
Authors: Shuttleworth C. William , Sanders Kenton M. , Keef Kathleen D. 
Published: July 2012

Neuromuscular transmission in the circular muscle of the canine proximal colon was examined, in the presence and absence of nitric oxide synthase inhibitors, by use of mechanical and intracellular microelectrode recording techniques.
Electrical field stimulation (EFS; 0.1–20 HZ) produced frequency‐dependent contractions of circular muscle strips which reached a maximum at 15 Hz. These reponses were enhanced by NG‐monomethyl‐l‐arginine (l‐NMMA; 300 μm) and reduced by atropine (1 μm). The effects of l‐NMMA were reversed by l‐arginine (3 mm). All responses to EFS were abolished by tetrodotoxin (1 μm).
In the presence of atropine, phentolamine and propranolol (all at 1 μm; ‘non‐adrenergic, non‐cholingergic (NANC) conditions’), EFS evoked frequency‐dependent inhibition of phasic contractions which reached a maximum at 5 Hz. At higher frequencies of EFS, inhibition diminished, and these responses were followed by post‐stimulus excitation.
Under NANC conditions and in the presence of l‐NG‐nitroarginine methyl ester (l‐NAME; 200 μm), EFS evoked contractions at frequencies of 5 Hz or greater. These contractions were reduced by co‐incubation with l‐arginine (2 mm) and abolished by tetrodotoxin (1 μm).
In the presence of atropine (1 μm), EFS (5–20 Hz) caused frequency‐dependent inhibition of electrical slow waves. In the presence of l‐NAME (100 μm) and atropine, the inhibitory response to EFS was abolished and an increase in slow wave duration was seen at stimulation frequencies greater than
Hz. The effects of EFS on slow wave duration were abolished by tetrodotoxin (1 μm).
Atropine‐resistant contractions to EFS were enhanced by indomethacin (10 μm) and reduced or abolished by the non‐selective NK1/NK2 tachykinin receptor antagonist d‐Pro2, d‐Trp7,9 SP, and by the selective NK2 receptor antagonist MEN 10,376 (10 μm).
Exogenous tachykinins mimicked non‐cholinergic excitatory electrical and mechanical responses. The rank order of potency for contraction was neurokinin A > neurokinin B > substance P, suggesting a predominance of the NK2 sub‐type of tachykinin receptors on colonic smooth muscle cells. Low concentrations of neurokinin A also increased the amplitude and duration of electrical slow waves.
These results suggest that: (i) in previous studies, non‐cholinergic excitatory responses were masked by the simultaneous release of NO; (ii) non‐cholinergic excitatory responses occur throughout the period of stimulation and are not manifest only as ‘rebound’ excitation; (iii) one or more tachykinins, possibly, acting via NK2 receptors, may mediate non‐cholinergic excitatory responses.
Protective effects of ranolazine in guinea‐pig hearts during low‐flow ischaemia and their association with increases in active pyruvate dehydrogenase
Authors: Clarke B. , Spedding M. , Patmore L. , McCormack J.G. 
Published: July 2012

In isolated Langendorff‐perfused, electrically‐paced, hearts of guinea‐pigs, global low‐flow‐ischaemia (LFI; at 0.7 ml min−1) resulted in marked increases in the rates of release of lactate, lactate dehydrogenase (LDH) and creatine kinase (CK) over a 30 min period. At the end of the LFI period, tissue ATP content was significantly reduced from a control value of 11.8 ± 0.8 (5) to 5.6 ± 0.8 (5) μmol g−1 dry weight.
The presence of ranolazine [(±)‐N‐(2,6‐dimethyl‐phenyl)‐4[2‐hydroxy‐3‐(2‐methoxy‐phenoxyl)‐propyl]‐1‐piperazine acetamide dihydro‐chloride; RS‐43285‐193] at 10 μm, from 20 min prior to and during LFI, resulted in significant reductions in the release of lactate, LDH and CK during the ischaemic period and a significant preservation of tissue ATP (9.0 ± 1.1 (6) μmol g−1 dry wt.). Ranolazine did not prevent the reductions in creatine phosphate or glycogen observed in LFI, nor did it have any significant effects on any contractile parameters before or during the LFI period.
Neither ranolazine nor LFI affected the total amounts of tissue pyruvate dehydrogenase (PDH) activity; however, the significant reduction in the amount of active, non‐phosphorylated PDH caused by LFI (from 88.2 ± 5.5 to 44.2 ± 3.2% of total activity) was partially but significantly prevented by ranolazine (67.2 ± 6.8%). This effect of ranolazine on PDH may be part of the mechanism whereby the compound reduces lactate release and preserves tissue ATP during ischaemia.
Binding of angiotensin antagonists to rat liver and brain membranes measured ex vivo
Authors: Marshall Fiona H. , Clark Samantha A. , Michel Anton D. , Barnes Julie C. 
Published: July 2012

The effects of the angiotensin antagonists GR117289, losartan and Sar1Ala8‐angiotensin II on the ex vivo binding of [125I]‐Sar1Ile8‐angiotensin II to rat liver and cortex/hippocampus (Cx/H) membranes have been investigated.
GR117289 (0.1–30 mg kg−1, s.c., 2 h pretreatment) caused a dose‐dependent reduction in [125I]‐Sar1Ile8‐angiotensin II binding to both liver and cortex/hippocampus membranes.
Administration of a submaximal dose of GR117289 (1 mg kg−1, s.c.) indicated that the peak inhibition of binding in the liver occurred within 0.5 h, whereas the peak inhibition of binding in the Cx/H occurred 2 h after drug treatment.
The effect of GR117289 was long lasting. Binding was still reduced in the Cx/H 48 h after drug treatment (10 mg kg−1, s.c.) but had returned to normal 72 h after drug treatment. In the liver binding was still reduced 72 h after treatment with the same dose.
Losartan (1 − 30 mg kg−1, s.c.) was equipotent with GR117289 in its ability to reduce liver binding, but was less effective at inhibiting binding to central receptors.
The non‐peptide antagonist Sar1Ala8‐angiotensin II (3 and 10 mg kg−1) reduced binding in the liver but not in the Cx/H membranes.
These results suggest that, unlike the peptide antagonist Sar1Ala8‐angiotensin II, the non‐peptide angiotensin antagonists, GR117289 and losartan, are able to cross the blood brain barrier and occupy central angiotensin II receptors.
Postjunctional inhibitory effect of the NK2 receptor antagonist, SR 48968, on sensory NANC bronchoconstriction in the guinea‐pig
Authors: Lou Ya‐Ping , Lee Lu‐Yuan , Satoh Hiroyuki , Lundberg Jan M. 
Published: July 2012

The effects of a selective NK2 receptor antagonist, SR 48968, on non‐adrenergic non‐cholinergic (NANC) bronchoconstriction in the guinea‐pig were investigated in both in vitro and in vivo studies.
In isolated bronchus, the electrical field stimulation (EFS, 1 Hz for 1 min)‐induced NANC bronchoconstriction was inhibited by 83% after preincubation with SR 48968 (10−7 m) for 1 h. The selective NK1 receptor antagonist, CP 96,345 (10−6 m), together with SR 48968 completely abolished the remaining EFS‐evoked NANC bronchial contraction. ST 48968 (10−7 m) totally blocked the bronchial contraction caused by neurokinin A (NKA), but reduced only slightly the bronchoconstriction caused by high concentrations of substance P (SP) and did not influence the response to acetylcholine (ACh).
In the guinea‐pig isolated perfused lung, SR 48968 (5 × 10−7 m) perfusion for 30 min markedly reduced, by 95% and 68% respectively, the increase in lung resistance (RL) and the decrease in dynamic compliance (CDyn) evoked by vagal stimulation (1 Hz for 1 min). Capsaicin (10−8 m)‐evoked bronchoconstriction was also significantly inhibited by SR 48968 (5 × 10−7 m). However, the same concentration of SR 48968 did not affect the release of neuropeptide calcitonin gene‐related peptide (CGRP)‐like immunoreactivity (LI) evoked by either vagal stimulation or capsaicin in the isolated perfused lung, suggesting no prejunctional action. SR 48968 (5 × 10−7 m) caused a parallel shift of the concentration‐response curve to the right by a factor of 10 for the bronchoconstriction evoked by NKA (10−9 − 3 × 10−7 m) in the isolated lung, while it abolished the contraction induced by the selective NK2 receptor agonist, Nle10 NKA(4–10) (10−9 − 3 × 10−7 m).
In in vivo studies, ST 48968 (0.3 mg kg−1, i.v.) also greatly inhibited the increase in insufflation pressure evoked by either capsaicin (10 μg kg−1, i.v.) or NKA (1 μg kg−1, i.v.), without any measurable effect on the accompanying hypotensive responses.
The results suggest: (i) ST 48968 is a selective and potent NK2 postjunctional receptor antagonist both in vitro and in vivo in the guinea‐pig, and (ii) the NANC bronchoconstriction evoked by sensory nerve activation either by antidromic nerve stimulation or by capsaicin is mediated mainly via NK2 receptors and only to a minor extent via NK1 receptors.
Inhibition by sumatriptan of central trigeminal neurones only after blood‐brain barrier disruption
Authors: Kaube Holger , Hoskin Karen L. , Goadsby Peter J. 
Published: July 2012

The 5‐hydroxytryptamine (5‐HT1)‐like agonist, sumatriptan, is highly efficient in the relief of migraine headache and its accompanying symptoms.
Experimental evidence has indicated that its site of action may be on the cranial vessels or on the trigeminal innervation of the cranium, or both, since sumatriptan does not pass the blood‐brain barrier easily under normal circumstances. It is, however, not clear whether the blood‐brain barrier is normal or abnormal during a migraine attack.
In this study, single unit activity and trigeminal somatosensory evoked potentials in central trigeminal neurones were monitored during electrical stimulation of the superior sagittal sinus.
Intravenous administration of sumatriptan (100 μg kg−1) did not alter trigeminal evoked activity unless the permeability of the blood‐brain barrier had been increased by infusion of an hyperosmolar mannitol solution. After blood‐brain barrier disruption, sumatriptan decreased the peak‐to‐peak amplitude of evoked potentials by 40 ± 6% and the probability of firing of single units by 30 ± 9%. Mannitol infusions alone in control animals caused no changes in evoked potentials or single unit activity.
The data suggest that in normal circumstances sumatriptan does not have sufficient access to trigeminal neurones to alter their function.
Hypercholesterolaemia severely impairs EDRF‐dependent collateral perfusion following acute arterial occlusion in rabbit isolated ear
Authors: Randall Michael D. , Smith Jerry A. , Griffith Tudor M. 
Published: July 2012

We have used a rabbit isolated buffer‐perfused ear as a model of acute arterial occlusion to investigate the effects of dietary‐induced hypercholesterolaemia on EDRF‐dependent collateral perfusion. The effects of hypercholesterolaemia on endothelium‐dependent relaxations to acetylcholine were also investigated in the unligated isolated buffer‐perfused ear of the rabbit.
In rabbits receiving a high cholesterol diet (1%) for 4 weeks, blood cholesterol levels were significantly (P < 0.001) increased (26.0 ± 3.6 vs. 2.6 ± 0.6 mmol 1−1), EDRF‐dependent collateral perfusion was similar to that in age‐matched controls for the first 15 min after occlusion but then decreased and was significantly (P < 0.01) less than control during the maintenance phase of collateral perfusion.
Cholesterol feeding for 8 weeks (blood cholesterol = 56.2 ± 3.8 vs. 1.3 ± 0.1 mmol 1−1) was associated with almost complete impairment of collateral perfusion, an effect previously observed following inhibition of EDRF synthesis.
Endothelium‐dependent relaxations to acetylcholine in isolated perfused ears were impaired in the rabbits fed the diet for 8 weeks but not those fed for 4 weeks. In the 8 week group, the maximum relaxation of tone was 32.6 ± 11.6% and was significantly (P < 0.01) less than that in the controls (77.9 ± 5.7%).
We conclude that EDRF‐dependent collateral perfusion is severely impaired in hypercholesterolaemia and that the level of impairment is related to the duration of feeding.