bluuebunny/crossref_metadata_2025_split huggingface dataset:
Interaction of human adrenomedullin 13–52 with calcitonin gene‐related peptide receptors in the microvasculature of the rat and hamster
Authors: Hall Judith M. , Siney Lynn , Lippton Howard , Hyman Albert , Kang‐Chang Jaw , Brain Susan D. 
Published: July 2012

Adrenomedullin (ADM), a recently discovered circulating hypotensive peptide, shares limited sequence homology with the sensory nerve‐derived vasodilator, calcitonin gene‐related peptide (CGRP). This study compared the vasodilator effect of sequence 13–52 of human adrenomedullin (ADM13–52) with that of human α CGRP (CGRP), in the microvasculature of the hamster cheek pouch and rat skin in vivo.
Single arterioles (20–40 μm diameter) in the hamster cheek pouch were visualised by intravital microscopy and video recording, and measured by image analysis. Both ADM13–52 (1 pmol–0.4 nmol) and CGRP (0.1 pmol–1 nmol) evoked dose‐related increases in the diameter of preconstricted arterioles (n = 6). ADM13–52 (ED50 14 pmol) was 20 fold less active than CGRP (ED50 0.71 pmol). The kinetics of onset and decline of vasodilator responses to both peptides were similar, with vasodilator responses to both peptides reaching a maximum at ca. 2 min, and reversing after 10–15 min (n = 5–7). The submaximal increase in blood flow evoked by ADM13–52 was significantly inhibited (P < 0.05; n = 6) by the CGRP1 receptor antagonist, CGRP8–37, at a dose (300 nmol kg−1, i.v.) that we have previously shown to inhibit significantly equivalent vasodilator responses to CGRP in this preparation.
In experiments measuring changes in local blood flow in rat skin by a 133xenon clearance technique, intradermal injection of both ADM13–52 (3–300 pmol) and CGRP (0.1–30 pmol) evoked dose‐related increases in local blood flow. ADM13–52 (ED50 27 pmol) was 17 fold less potent than CGRP (ED50 1.6 pmol) (n = 6). The submaximal increase in blood flow evoked by both peptides was significantly inhibited (P < 0.02; n = 5) by CGRP837 (100 nmol kg−1, i.v.).
We conclude that ADM13–52 is a potent vasodilator in the microvasculature of the hamster and rat in vivo. It mediates its vasodilator effect by arteriolar dilatation and this effect is due, at least in part, to the stimulation of CGRP1 receptors.
On the inhibition of prostanoid formation by SK&F 96365, a blocker of receptor‐operated calcium entry
Authors: Leis Hans J. , Zach Doris , Huber Evelyn , Ziermann Laszlo , Gleispach Helmut , Windischhofer W. 
Published: July 2012

The proposed blocker of receptor‐operated calcium channels, SK&F 96365 was shown to inhibit formation of prostaglandin E2 in two osteoblast‐like cell lines, MC3T3‐E1 and UMR‐106 in a dose‐dependent manner at an IC50 of 3–4 μm. Inhibition was observed with various stimuli (arachidonic acid, bradykinin and calcium ionophore A23187).
This effect was also observed in human platelets, where SK&F 96365 dose‐dependently blocked thromboxane biosynthesis and formation of 12‐hydroxy‐heptadecatrienoic acid after stimulation with arachidonic acid (IC50 = 4 μm).
The compound had no effect on 12‐hydroxy‐eicosatetraenoic acid production by human platelets. Additionally, linoleic acid oxidation by soybean 15‐lipoxidase was not impaired by SK&F 96365. The results thus provide evidence for cyclo‐oxygenase inhibition by SK&F 96365 at concentrations used to block receptor‐operated calcium influx.
Cardiovascular effects of the calcium sensitizer, levosimendan, in heart failure induced by rapid pacing in the presence of aortic constriction
Authors: Udvary Éva , Papp Julius Gy , Végh Ágnes 
Published: July 2012

The haemodynamic effects of a novel cardiotonic drug, levosimendan, which has both calcium‐sensitizing and phosphodiesterase III (PDE III) inhibitory properties, were studied in conscious dogs in which heart failure had been induced by prolonged cardiac pacing in the presence of aortic constriction. These effects were compared with those in sham‐operated dogs with essentially normal cardiac function.
Eighteen mongrel dogs were instrumented for the measurement of left ventricular pressure (LVSP, LVEDP) and contractile function (dP/dt; dP/dt/P). In twelve dogs a balloon catheter, positioned in the thoracic aorta, was inflated producing an approximate 60% reduction in effective aortic diameter. Twenty min later rapid ventricular pacing (240 beats mean−1) was commenced and maintained for 48 h by means of a bipolar pacing electrode introduced into the right ventricle. This electrode served also for recording changes in the endocardial electrogram in the absence of pacing. Six of these dogs were used to evaluate the haemodynamic changes of pacing‐induced heart failure; a further six of these dogs the haemodynamic changes elicited by levosimendan under these conditions. Six sham‐operated dogs (group 2) served as controls.
In six dogs (group 1) the haemodynamic alterations were assessed after the development of heart failure. In the presence of aortic constriction, 48 h continuous rapid cardiac pacing resulted in a marked deterioration in left ventricular function which remained stable for at least 48 h after cessation of pacing. Thus, there was a marked reduction in LVSP (15%), + dP/dtmax (35%), ‐dP/dtmax (36%) and also in dP/dt/P (29%), whereas LVEDP was increased considerably (from 6.4 ± 1.4 to 20.0 ± 2.2 mmHg). A marked elevation occurred in endocardial ST‐segment (138%), lasting for 20 min.
Levosimendan was administered intravenously in doses of 0.005, 0.01 and 0.03 μmol kg−1 to 2 groups of conscious dogs. In the sham‐operated dogs (group 2), only the higher dose (0.03 μmol kg−1) produced significant increases in LVSP (19%), + dP/dtmax (37%), and in dP/dt/P (32%). In dogs with heart failure (group 3) doses of 0.005, 0.01 and 0.03 μmol kg−1 levosimendan resulted in an improvement in + dP/dtmax (26%, 38% and 49%), ‐dP/dtmax (20%, 25% and 38%) and in dP/dt/P (19%, 34% and 50%) and reduction in the elevated LVEDP (from 20 ± 2.2 mmHg to 16 ±1.0, 10 ± 1.3 and 9± 1.0 mmHg, respectively).
Levosimendan proved to be a potent cardiotonic drug at the doses used, and was approximately three times more effective under conditions of impaired left ventricular function than in normal hearts.
Nitric oxide‐donating properties of mesoionic 3‐aryl substituted oxatriazole‐5‐imine derivatives
Authors: Kankaanranta H. , Rydell E. , Petersson A.‐S. , Holm P. , Moilanen E. , Corell T. , Karup G. , Vuorinen P. , Pedersen S.B. , Wennmalm ÅR. , Metsä‐Ketelä T. 
Published: July 2012

The nitric oxide (NO)‐releasing properties of two new mesoionic 3‐aryl substituted oxatriazole‐5‐imine derivatives (GEA 3162 and GEA 3175) were characterized and compared with the known NO‐donors 3‐morpholino‐sydnonimine (SIN‐1) and S‐nitroso‐N‐acetylpenicillamine (SNAP).
GEA 3162, GEA 3175, SIN‐1 and SNAP inhibited adenosine 5′‐diphosphate‐induced platelet aggregation (IC50 values 0.18, 0.39, 3.73 and 2.12 μm, respectively). All four compounds induced a dose‐dependent and more than 4 fold increase in cyclic GMP in platelets. The increase in cyclic GMP concentration was potentiated more than 1.5 fold by a phosphodiesterase inhibitor, zaprinast (10 μm) and inhibited 38–97% by oxyhaemoglobin (10–45 μm).
All of the four compounds studied converted oxyhaemoglobin to methaemoglobin and formed a paramagnetic NO‐haemoglobin complex. All but GEA 3175 formed nitrite and nitrate in phosphate buffer. During a 40 min incubation, GEA 3162, SIN‐1 and SNAP (100 μm) produced 50–70 μm NO2−+NO3− as determined by high performance liquid chromatography. The release of NO and NO2 by GEA 3175 was increased 140 fold in the presence of human plasma (0.14 and 19.7 ppb in the absence and presence of 1% human plasma, respectively) as analyzed by ozone chemiluminescence.
The results suggest that the mesoionic 3‐aryl substituted oxatriazole‐5‐imine derivatives GEA 3162 and GEA 3175 as well as SIN‐1 and SNAP release nitric oxide.
Ontogenic aspects of liver and kidney catechol‐O‐ methyltransferase sensitivity to tolcapone
Authors: Vieira‐Coelho M.A. , Soares‐da‐Silva P. 
Published: July 2012

The present work describes the catechol‐O‐methyltransferase (COMT) activities in the liver and kidney of developing and adult rats (aged 3, 6, 9, 18, 30 and 60 days; n = 5 per group) and evaluates the enzyme sensitivity to inhibition by tolcapone, a reversible COMT inhibitor.
COMT activity, evaluated by the ability to methylate adrenaline to metanephrine, was determined in liver and kidney homogenates prepared in 0.5 mM phosphate buffer (pH = 7.8) containing pargyline (0.1 mM), MgC12 (0.1 mM), EGTA (1 mM) and S‐adenosyl‐L‐methionine (0.1 mM). Vmax (in nmol mg−1 protein h−1) of liver COMT was found to decrease gradually with age, from 5.3±0.5 at the age of 3 days up to 2.9±0.2 at the age of 60 days; for the same age range, Km values (in μm; geometric means with 95% confidence limits) increased from 3.3 (1.0, 7.5) up to 13.1 (2.1, 24.1). At the age of 3 days, Vmax values for kidney COMT (2.6±0.1) were lower than those for the liver COMT. However, Vmax values for kidney COMT were found to increase up to 6.2±0.6 at the age of 18 days and then declined by 44% at the age of 30 and 60 days. In kidney, aging was also accompanied by an increase in Km values for COMT (from 2.7 [1.1, 4.3] up to 24.0 [11.7, 36.3]).
The sensitivity of liver and renal COMT activity to tolcapone was markedly dependent on the age, 3‐days old rats being more sensitive to tolcapone than older animals. The IC50 values (in nM) for inhibition of liver COMT by tolcapone increased gradually with age, from 41 (26, 65) at the age of 3 days up to 720 (640, 800) at the age of 60 days. As was found in the liver, IC50 values (in nM) for inhibition of kidney COMT by tolcapone also increased with age, from 8 (6, 10) at the age of 3 days up to 177 (131, 240) at the age of 60 days. In all experimental groups, the IC50 values for inhibition of liver COMT by tolcapone was higher than those for kidney COMT.
In conclusion, these results suggest that aging is accompanied by a decrease in liver and kidney COMT affinity for the substrate (evidenced by the increase in Km values) and a decrease in sensivity towards inhibition by tolcapone (evidenced by the increase in IC50 values). Furthermore, kidney COMT is shown to be more sensitive to inhibition by tolcapone than liver COMT, irrespective of the age of the animal.
Barbiturate interactions at the human GABAA receptor: dependence on receptor subunit combination
Authors: Thompson S.A. , Whiting P.J. , Wafford K.A. 
Published: July 2012

Human GABAA receptors containing different α and β subunits with a γ2s subunit were expressed in Xenopus oocytes and the effects of pentobarbitone on these subunit combinations were examined by electrophysiological recording of GABA currents with the two‐electrode voltage‐clamp method.
Pentobarbitone has previously been shown to have three actions on GABAA receptors: a potentiation of GABA responses, a direct activation of GABAA receptors and, at high concentrations, a block of the GABA chloride channel. In this study pentobarbitone activity consisted of the above mentioned three components on all the subunit combinations tested. However, the affinities and efficacies varied with receptor subtype.
Potentiation of GABA by pentobarbitone occurred over the same concentration‐range for all the subunits with affinities in the range of 20–35 μm. The degree of potentiation obtained, however, varied from 236% of GABA EC20 on α1β2γ2s to 536% on α6β2γ2s.
Examination of the direct effect of pentobarbitone revealed that the type of α subunit present determines both the degree of affinity and efficacy obtained. Receptors containing an α6 subunit produced maximum direct responses to pentobarbitone larger than that obtainable with maximum GABA (150% to 170% of maximum GABA). The maximum direct pentobarbitone response obtainable with other α subunits ranged between 45% of maximum GABA for α5β2γ2s to 82% for α2β2γ2s. The affinity of the direct action of pentobarbitone on α6β2γ2s was 58 μm compared to affinities for the other α subunits ranging from 139 μm on α2β2γ2s to 528 μm on α5β2γ2s.
The type of β subunit present did not influence the direct action of pentobarbitone to the same extent as the α subunit. There were no significant differences between affinity or efficacy on oocytes expressing α6 and γ2s with β1, β2 or β3. Affinities and efficacies on oocytes expressing α1 and γ2s with β1, β2 or β3 were significantly different with pentobarbitone having a higher affinity and efficacy on α1β3γ2s followed by α1β2γ2s and then α1β1γ2s.
The direct effect of pentobarbitone was blocked by picrotoxin but not by competitive antagonists, such as bicuculline or SR95531, indicating that the direct agonist activity of pentobarbitone was not mediated via the GABA binding site.
For the first time the influence of the various α and β subunits on the effects of pentobarbitone were demonstrated. The results indicate that GABAA receptors containing α6 subunits have both a higher affinity and efficacy for direct activation by pentobarbitone, and reveal that pentobarbitone binds to more than one site on the GABAA receptor, and these are dependent on receptor subunit composition.
Investigation into the 5‐hydroxytryptamine‐induced atropine‐resistant neurogenic contraction of guinea‐pig proximal colon
Authors: Kojima Shu‐Ichi , Shimo Yasuo 
Published: July 2012

The aim of this study was to characterize the receptors mediating the atropine‐resistant neurogenic contraction to 5‐hydroxytryptamine (5‐HT) in the longitudinal muscle of the guinea‐pig proximal colon and to determine the type of tachykinin receptors involved in the contractile response to 5‐HT by the use of selective antagonists.
In the presence of atropine (0.3 μm), guanethidine (5 μm), hexamethonium (100 μm), ketanserin (0.1 μm) and indomethacin (3 μm), 5‐HT (0.01–3 μm) produced concentration‐dependent neurogenic contractions of colonic strips and at 0.3 μm produced a maximal effect (pEC50 = 7.39±0.09, n = 18). The 5‐HT4 receptor stimulant, 5‐methoxytryptamine (5‐MeOT, 0.03–10 μm) also produced neurogenic contractions with similar maximum effect to those of 5‐HT (pEC50 = 6.89±0.16).
The 5‐HT4 receptor antagonist, DAU 6285 (3 μm) shifted the concentration‐response curves to both 5‐HT and 5‐MeOT to the right without significant depression of the maximum, but the 5‐HT1/5‐HT2 receptor antagonist, metitepine (0.1 μm) and the 5‐HT3 receptor antagonist, ondansetron (0.3 μm) had no effect on the control curves to 5‐HT and 5‐MeOT.
The selective NK1 receptor antagonist, FK 888 (1 μm) markedly attenuated the contractions to 5‐HT and 5‐MeOT. In contrast, the selective NK2 receptor antagonist, SR 48968 (10 nM) and the selective NK3 receptor antagonist, SR 142801 (10 nM) had no effect on the contractions to 5‐HT and 5‐MeOT.
These results indicate that the 5‐HT‐induced atropine‐resistant neurogenic contraction of guinea‐pig proximal colon is due to activation of 5‐HT4 receptors, presumably located on excitatory motor neurones, innervating the longitudinal muscle. The contraction evoked by activation of the 5‐HT4 receptors is mediated primarily via NK1 receptors but not NK2 or NK3, suggesting that the 5‐HT4 receptor‐mediated contraction is evoked indirectly via tachykinin release from tachykinin‐releasing excitatory neurones.
Operational characteristics of somatostatin receptors mediating inhibitory actions on rat locus coeruleus neurones
Authors: Chessell I.P. , Black M.D. , Feniuk W. , Humphrey P.P.A. 
Published: July 2012

In order to characterize somatostatin (SRIF) receptor inhibiting spontaneous firing of rat locus coeruleus neurones, and their transduction mechanism(S), extracellular recordings were obtained from a pontine slice preparation of rat brain containing the locus coeruleus (LC). LC neurones were identified by electrophysiological and pharmacological properties; spontaneous firing (characteristically 0.5‐5 Hz) was reversibly and concentration‐dependently inhibited by exogenously applied noradrenaline.
Spontaneous firing of LC neurones was reversibly and concentration‐dependently inhibited by SRIF and the N‐terminally extended form, somatostatin‐28 (SRIF‐28), with EC50 values of 15.1 and 19.4 nM, respectively. The synthetic SRIF analogues (octreotide, MK‐678, BIM‐23027 and L‐362,855) also caused concentration‐dependent inhibition of LC neurone firing with a rank order of agonist potencies compatible with actions at a receptor resembling the recombinant sst2 receptor. The putative sst3 selective agonist, BIM‐23056, was without agonist or antagonist effect.
Addition of 100 nM desipramine significantly increased the efficacy of exogenously applied noradrenaline (EC50 values, 2.96 and 0.13 μm, absence and presence of desipramine, respectively) but did not significantly affect SRIF‐induced inhibition (EC50 values, 15.6 and 8.0 nM, respectively). Furthermore, application of phenoxybenzamine (3 μm) abolished responses to NA, but did not affect responses to SRIF (EC50=14.1 nM).
Application of the cyclic AMP analogue, 8‐bromoadenosine‐cyclic monophosphate (8‐Br‐cyclic AMP; 500 μm), significantly increased the spontaneous firing rate of all neurones tested (223±24% over basal rate). Concentration‐effect curves for SRIF constructed in the absence and presence of 8‐Br‐cyclic AMP had similar threshold concentrations, maxima and EC50 values.
Incubation of pontine slices in a modified artificial CSF containing 500 ng ml−1 pertussis toxin (PTX) for 18 h prior to extracellular recording affected neither the spontaneous firing of LC neurones, nor the inhibitory responses to muscimol (EC50 2.2 and 1.2 μm, absence and presence of PTX). However, inhibitory responses to SRIF were markedly attenuated.
We conclude that the inhibitory actions of SRIF on spontaneous firing of LC neurones are mediated directly by activation of somatodendritic SRIF receptors, and not indirectly by release of noradrenaline. The SRIF receptors involved appear to couple via a pertussis toxin sensitive G‐protein, and elicit their response by a mechanism apparently independent of inhibition of cyclic AMP formation. The agonist profile of several selective and novel SRIF analogues suggests the identity of this receptor to be similar to the recombinant sst2 receptor.
5‐HT3 and 5‐HT4 receptor‐mediated facilitation of the emptying phase of the peristaltic reflex in the marmoset isolated ileum
Authors: Tuladhar B.R. , Costall B. , Naylor R.J. 
Published: July 2012

The patterns of intestinal motility and the effect of an increase in intraluminal pressure were studied in vitro on segments obtained from the marmoset small intestine.
Segments obtained from the distal half of the marmoset small intestine exhibited segmentation, consisting of narrow annular contractions (lasting for 2–3 s) interposed between the relaxed segments of varying length. The subsequent contractions occurred slightly distal to the previous contraction, with ring‐like contractions appearing to move in the aboral direction. Such segmentation was infrequent or absent in the segments obtained from the proximal half of the small intestine. An increase in intraluminal pressure inhibited segmentation and finally produced peristalsis in most of the tissues.
The influence of 5‐hydroxytryptamine (5‐HT) receptor agonists and antagonists on the threshold of the peristaltic reflex was investigated in the segments obtained from the distal half of the intestine after segmentation had subsided. The effect of drug application to the serosal surface was measured as a change in threshold pressure required to trigger the peristaltic reflex. A facilitation was defined in two ways (a) as a reduction in the threshold pressure required to trigger the reflex and (b) in those tissues that failed to respond with peristalsis on raising intraluminal pressure to the maximum attainable (1 kPa), as a reduction in threshold pressure compared to this value.
5‐HT (7.85±0.19), 5‐methoxytryptamine (7.79±0.24), 5‐carboxamidotryptamine (6.66±0.13) and 2‐methyl‐5‐HT (6.24±0.16) caused a concentration related facilitation of the peristaltic reflex, the pD2 values (mean±s.e.mean) being shown in parentheses.
The concentration‐response curves to both 5‐HT and 5‐methoxytryptamine were dextrally shifted in a surmountable manner in the presence of GR 113808 (30 nM). pD2 values for 5‐HT and 5‐methoxytryptamine were significantly decreased to 6.98±0.24 and 6.83±0.36 respectively in the presence of GR 113808 (30 nM).
In the presence of a high concentration of (10 μm) 5‐methoxytryptamine the subsequent addition of 2‐methyl‐5‐HT (3–10 μm) but not 5‐methoxytryptamine (10 μm) facilitated peristalsis; the effect of 3 μm 2‐methyl‐5‐HT was significantly decreased by 2 μm ondansetron.
It is concluded that the facilitation of the peristaltic reflex in the marmoset intestine induced by 5‐HT at submicromolar concentrations involves a 5‐HT4 receptor stimulation with an additional 5‐HT3 receptor activation at higher concentrations.
Differences in agonist and antagonist activities for two indices of metabotropic glutamate receptor‐stimulated phosphoinositide turnover
Authors: Mistry Rajendra , Challiss R.A. John 
Published: July 2012

The abilities of the four diastereoisomers of 1‐aminocyclopentane‐1,3‐dicarboxylic acid (ACPD) to stimulate, and the metabotropic glutamate receptor (mG1uR) antagonist (±)‐α‐methylcarboxyphenylglycine (MCPG) to inhibit, phosphoinositide turnover in neonatal rat cerebral cortex have been studied. Two indices of phosphoinositide cycle activity were assessed; inositol 1,4,5‐trisphosphate (Ins(1,4,5)P3) mass accumulation, and total inositol phosphate [3H]‐InsPx accumulation (in the presence of Li+) in myo‐[3H]‐inositol prelabelled slices.
The diastereoisomers of ACPD stimulated each response with a rank order of potency of 1S, 3R > 1R, 3R > 1S, 3S > > 1R, 3S. The response to 1R, 3R‐ACPD was largely prevented by pre‐addition of the NMDA‐receptor antagonist, MK‐801, or omission of extracellular Ca2+, suggesting that this isomer acts indirectly on phosphoinositide responses through activation of NMDA‐type ionotropic glutamate receptors. In contrast, the responses to 1S, 3R‐ and 1S, 3S‐ACPD were unaffected by prior addition of MK‐801, but were blocked by MCPG.
The concentration of 1S, 3R‐ACPD required to half‐maximally stimulate the Ins(1,4,5)P3 response (‐log EC50 (M), −4.09 ± 0.10) was significantly higher than that required to exert a similar effect on [3H]‐InsPx accumulation (‐log EC50 (M), −4.87 ±0.07; P<0.01; n=4). A similar marked 8–9 fold discrepancy between these two values was observed for the 1S, 3S isomer, which elicited similar maximal responses to those caused by 1S, 3R‐ACPD.
Significant differences were also observed with respect to the ability of (±)‐MCPG (1 mM) to cause a rightward shift in the concentration‐response relationships for 1S, 3R‐ACPD‐stimulated Ins(1,4,5)P3 (5.59±0.24 fold shift) and [3H]‐InsPx (3.04±0.34 fold shift; P<0.01; n=4) responses, giving rise to Kd values of 218 and 490 μm for (±)‐MCPG antagonism of the respective responses.
The potency difference between the 1S, 3R‐ACPD‐stimulated Ins(1,4,5)P3 and [3H]‐InsPx responses was reduced when experiments were performed in nominally calcium‐free medium ([Ca2+]e = 2–5 μm) and EC50 values were almost identical when extracellular calcium was reduced further by EGTA addition ([Ca2+]e≤ 100 nM). Similarly, the Kd value for (±)‐MCPG antagonism of the 1S, 3R‐ACPD‐stimulated [3H]‐InsPx response decreased under [Ca2+]e‐free conditions, approaching those obtained for the 1S, 3R‐ACPD‐stimulated Ins(1,4,5)P3 response in the presence of normal [Ca2+]e.
These data suggest that estimates of the activities of mGluR agonists and antagonists, derived by measuring phosphoinositide turnover, can differ significantly depending on whether Ins(1,4,5)P3 mass or [3H]‐InsPx responses are measured. In particular, the possibility that the mGluR‐mediated [3H]‐InsPx response may not simply reflect direct receptor/G protein/phosphoinositidase C (PIC) activation, but may also be the consequence of stimulation of a facilitatory Ca2+‐influx pathway is discussed.