bluuebunny/crossref_metadata_2025_split huggingface dataset:
Role of β‐adrenoceptor‐adenylate cyclase system in the developmental decrease in sensitivity to isoprenaline in foetal and neonatal rat heart
Authors: Tanaka Hikaru , Shigenobu Koki 
Published: July 2012

The inotropic and chronotropic sensitivity to noradrenaline and isoprenaline (Iso) of foetal and neonatal rat heart decreases as the heart becomes sympathetically innervated. In the present study, we have examined adenylate cyclase (AC) activation and β‐adrenoceptor binding to determine whether a developmental decrease in sensitivity was demonstrable in the β‐receptor‐AC system of atrial and ventricular membranes from the 15 day foetus and 1 day and 7 day neonates.
While the maximum activation of AC by Iso increased with age, the sensitivity expressed in terms of pD2 values decreased from the 15th foetal day to the first day after birth in the atria, and from the first day to the 7th day after birth in the ventricle.
In contrast, activation of AC by forskolin was almost identical at all ages both in atria and ventricle.
The maximum equilibrium binding of [3H]‐dihydroalprenolol decreased with age, the dissociation constant being about the same at all ages in both the atria and ventricle.
In conclusion, we have demonstrated a developmental decrease in the sensitivity of AC to Iso in myocardial membrane fractions consistent with the developmental decrease in chronotropic and inotropic sensitivity to β‐adrenoceptor agonists. Although a reduction in β‐adrenoceptor number partly accounts for the decrease in sensitivity, some other factors such as decreased coupling to AC may largely be responsible.
Effects of indomethacin on the regional haemodynamic responses to low doses of endothelins and sarafotoxin
Authors: Gardiner Sheila M. , Compton Alix M. , Bennett Terence 
Published: July 2012

Regional haemodynamic responses to i.v. bolus injections of low doses (4 pmol and 40 pmol) of endothelin‐1, −2, −3 and sarafotoxin‐S6b were assessed in conscious, Long Evans rats in the absence and presence of indomethacin.
Both doses of endothelin‐3 and sarafotoxin‐S6b caused early renal vasodilatations that were not affected by indomethacin. Endothelin‐1 caused an initial renal vasodilatation only in the presence of indomethacin, indicating that this peptide produced concurrent release of cyclo‐oxygenase products that caused renal vasoconstriction. Neither dose of endothelin‐2 produced an increase in renal conductance.
The 4 pmol dose of all four peptides caused mesenteric vasoconstrictions only. With the 40 pmol dose of the peptides, none caused early mesenteric vasoconstriction except in the presence of indomethacin. Thus, in this vascular bed the primary vasoconstrictor effects of the peptides (seen with the 4 pmol dose) were offset, following the 40 pmol dose, by release of vasodilator cyclo‐oxygenase products. Indomethacin alone caused significant vasoconstriction only in the mesenteric vascular bed, indicating that in this region of the circulation, vasodilator prostanoids might be involved also in the tonic control of vascular conductance.
All four peptides at both doses caused early hindquarters vasodilatation. However, only the initial hypotensive and hindquarters vasodilator effects of the 40 pmol dose of sarafotoxin‐S6b were attenuated by indomethacin. Under these conditions the hindquarters vasodilator effects of sarafotoxin‐S6b were similar to those of the other peptides, indicating that the more marked effects of sarafotoxin‐S6b in the absence of indomethacin were contributed to by vasodilator cyclo‐oxygenase products in the hindquarters.
Influence of plasma protein content and platelet number on the potency of PAF and its antagonist RP 59227 in rabbit platelet preparations
Authors: Floch Anne , Cavero Icilio 
Published: July 2012

The potency of platelet activating factor (PAF) as a pro‐aggregatory agent and of RP 59227, a selective antagonist of PAF‐induced platelet aggregation, was determined in several types of rabbit platelet preparations.
PAF produced concentration‐dependent responses irrespective of whether the suspension medium for the platelets (200,000 per μl) was undiluted plasma (PRP), saline‐diluted plasma (dil. PRP) or a salt solution (WP: washed platelets). The potency of PAF, expressed as pD2, was 3 fold higher in WP than PRP or diluted PRP (dil. PRP) for which the ratio (v/v) of total plasma to saline was 1:1.5. In PRP and WP preparations, an increase in the number of platelets in the reaction medium from 200,000 to 600,000 enhanced the potency of PAF slightly (2.3 fold). Furthermore, PAF was 3 times more potent in WP than PRP when studied in preparations containing either 200,000, 400,000 or 600,000 platelets per μl.
RP 59227, like the reference compounds WEB 2086 and CV‐6209, behaved as a competitive antagonist against PAF‐evoked platelet aggregation in PRP, WP and dil. PRP (200,000 platelets per μl). Their potency was slightly greater (1.6 to 2.6 fold more) in dil. PRP than in WP, but in PRP it was 3.5 to 4.3 times lower than in WP. RP 59227 was 2.3 and 5.0 times less potent when the platelet number of the PRP suspension was increased from 200,000 to 400,000 and 600,000 per μl, respectively, whereas the potency of RP 59227 in WP was not modified by these changes in platelet number. Furthermore, CV‐6209, RP 59227 and WEB 2086 were found to be 2.8 to 3.3 times more potent when studied after 10 rather than 1 min incubation time.
In conclusion, methodological variables such as platelet number, plasma protein content and incubation time can modify the potency not only of PAF, as an aggregatory agent, but also of its antagonists. Thus, only platelet aggregation studies carried out by using well‐defined experimental conditions afford an appropriate investigational approach to establish a potency rank order for PAF‐receptor antagonists. Furthermore, dil. PRP which can be easily and rapidly prepared appears to be as appropriate as WP to determine pA2 values for PAF antagonists.
Investigation of the mechanism(s) of 8‐OH‐DPAT‐mediated inhibition of plasma insulin in spontaneously hypertensive rats
Authors: Bouhelal Rochdi , Loubatières‐Mariani Marie‐Madelaine , Mir Anis K. 
Published: July 2012

Effects of the prototype selective 5‐HT1A receptor agonist, 8‐hydroxy‐2‐(di‐n‐dipropylamino)tetralin (8‐OH‐DPAT), were studied on the glycaemia and insulinaemia in conscious spontaneously hypertensive (SH) rats concurrently with blood pressure (BP) and heart rate (HR); underlying mechanism(s) were investigated in anaesthetized and pithed SH rats and in the perfused rat pancreas.
Intravenous (i.v.) injections of 8‐OH‐DPAT (150 μg kg−1, i.v.) into fasted conscious but not anaesthetized SH rats increased glycaemia; glucose‐stimulated (i.v. glucose tolerance test) plasma insulin levels were significantly inhibited in both cases without significant changes in glucose tolerance. Metabolic changes were associated with prominent decreases in BP and HR.
No inhibitory effect of 8‐OH‐DPAT, 150 μg kg−1 i.v., on glucose‐stimulated plasma insulin was observed in pithed SH rats; in contrast, clonidine (8 μg kg−1 i.v.), produced marked inhibition of insulin levels in association with glucose intolerance. Neither compound decreased BP; rather, pronounced vasopressor effects were observed.
In the isolated perfused pancreas of the rat, 8‐OH‐DPAT, at 10−8 and 10−7m, concentrations known to activate 5‐HT1A receptors in vitro, failed to modify glucose‐stimulated insulin release. Inhibition (39 ± 7%) was seen only at a high concentration of 10−6 m.
The present data suggest that like the cardiovascular effects of 8‐OH‐DPAT, the inhibition of glucose‐stimulated insulin release is mediated via the central nervous system. However, it is suggested that different mechanisms are involved in the cardiovascular actions and metabolic effects of 8‐OH‐DPAT in the SH rat; the latter are likely to reflect a consequence of activation of the hypothalamic‐adrenal axis.
Anaesthetic suppression of transmitter actions in neocortex
Authors: Puil E. , El‐Beheiry H. 
Published: July 2012

The effects of general anaesthetics were investigated on neuronal sensitivities to transmitter substances, which were determined by iontophoretic applications of acetylcholine, glutamate, N‐methyl‐d‐aspartate (NMDA) and γ‐aminobutyrate (GABA) during intracellular recording in in vitro slice preparations of neocortex (guinea‐pig).
In most of the 65 neurones studied, perfusion of isoflurane (0.5–2.5 minimum alveolar concentration (MAC)) or Althesin (25–200 μm) and, in some cases, halothane (0.5–2 MAC), markedly reduced the depolarizing responses and associated membrane conductance changes evoked by dendritic applications of acetylcholine, glutamate, NMDA and GABA.
The order of depression was acetylcholine > glutamate or NMDA ≫ GABA. This selectivity could also be assessed from the EC50 for the isoflurane‐induced depression of the just‐maximal responses to acetylcholine, which was 0.9 MAC compared with an EC50 =1.9 MAC for the suppression of glutamate responses. The selectivity was less pronounced in the case of the actions of Althesin, where the EC50s were 75 μm for the depression of acetylcholine responses and 90 μm for the depression of glutamate responses.
The hyperpolarizing responses observed when GABA was applied near the perikaryon in 7 neurones, were slightly reduced (∼ 15%) in 4, and unchanged in 3 neurones during anaesthetic application.
The pronounced depression of the responsiveness to the putative arousal transmitters and an observed blockade of acetylcholine‐induced potentiation of glutamate actions suggest that anaesthetics produce unconsciousness, at least in part, by interfering with subsynaptic mechanisms of neocortical activation.
Inhibition of endothelial‐bound angiotensin converting enzyme, in vivo
Authors: Catravas John D. , Ryan James W. , Chung Alfred Y.K. , Quinn Nancy E. , Anthony Betty L. 
Published: July 2012

We determined apparent Ki constants of two inhibitors, captopril and CL242,817, for pulmonary endothelial‐bound angiotensin converting enzyme (ACE) in anaesthetized rabbits. [3H]‐benzoyl‐Phe‐Ala‐Pro was used as the substrate. The apparent kinetic parameters Km and Amax (product of Vmax and microvascular plasma volume) were measured, as was the ratio (Amax/Km) (measured under first order reaction conditions) before and 30s after the i.v. administration of captopril 10 nmol kg−1 or CL242,817, 35 nmol kg−1.
Under mixed order reaction conditions, ([S] ≥ Km), apparent Km values increased from 12.2 ± 1.9 μm to 32.9 ± 3.3 μm (P < 0.05) in the captopril‐treated rabbits and from 9.3 ± 2.3 μm to 45.8 ± 9.8 μm (P < 0.05) in the CL242,817‐treated rabbits, indicative of competitive inhibition. However, apparent Amax values decreased from 10.3 ± 2.1 to 4.5 ± 0.8 μmol min−1 (P < 0.05) and 8.9 ± 1.7 to 4.8 ± 0.5 μmol min−1 (P < 0.05), respectively.
Under first order reaction conditions ([S] ≪ Km), the Amax/Km ratio decreased from 763 ± 100 to 125 ± 38 ml min−1 (P < 0.05) and 1009 ± 149 to 126 ± 44 ml min−1 (P < 0.05) in the captopril‐ and CL242,817‐treated groups respectively.
When the single pass transpulmonary binding of 80 pmol [3H]‐RAC‐X‐65 (an ACE inhibitor) was measured in additional rabbits, a significant (P < 0.05) decrease in RAC‐X‐65 binding was observed 30 s after captopril (80% decrease) or CL242,817 (85% decrease), a result expected for a loss of catalytically active enzyme mass due to tightly bound captopril or CL242,817.
These results indicate that, in vivo, both captopril and CL242,817 are competitive, tight binding inhibitors of lung ACE. Furthermore, they suggest means for evaluating the interaction of other potential ACE inhibitors with the pulmonary endothelial membrane‐bound enzyme, in vivo, possibly in phase I clinical trials.
Studies of receptor‐mediated inhibition of 45Ca accumulation into synaptosomes
Authors: Xiang Jian‐Zhong , Brammer Michael J. , Campbell Iain C. 
Published: July 2012

The effects of α2‐adrenoceptor and κ‐opiate receptor activation on 45Ca accumulation into rat cortical synaptosomes were examined.
Clonidine (1μm) and U50488H (1μm) significantly reduced 45Ca accumulation under both resting (5 mM K+) and depolarizing (15–30 mM K+) conditions.
The inhibitory effects of the agonists on 45Ca accumulation into synaptosomes were enhanced in the presence of the Na+‐Ca2+ exchange inhibitor sodium orthovanadate (vanadate, 2mm), and were not present in mitochondrial preparations.
When the agonists were used together, their inhibitory effects were not additive but were, in fact, attenuated.
In the presence of the α2‐adrenoceptor antagonist idazoxan (1 μm), the inhibitory effect of U50488H on 45Ca accumulation was enhanced. A similar increase in the inhibitory effectiveness of clonidine was observed in the presence of naloxone (20 μm).
When synaptosomes were pretreated with 3‐isobutyl‐1‐methylxanthine (IBMX, 0.5 mm), dibutyrylcyclic AMP (db‐cyclic AMP, 10 μm) or 8‐bromo‐cyclic AMP (8Br‐cyclic AMP, 10μm), the inhibitory effects of clonidine and U50488H were abolished, suggesting that a decrease in cyclic AMP production is part of the receptor‐effector coupling mechanism of both receptor systems.
The phorbol ester, 12‐O‐tetradecanoylphorbol 13‐acetate (TPA, 0.05 μm) increased 45Ca accumulation but did not alter the inhibitory effects of clonidine or U50488H, thus showing that the effects of the agonists are not mediated by protein kinase C.
We conclude that a2‐adrenoceptor and κ‐opiate receptor activation dramatically reduce 45Ca influx through Ca2+ channels (e.g., by 50%), that there is a functional antagonism between the two receptor systems and that in both cases, the receptor effector mechanism involves a decrease in cyclic AMP production.
l‐Arginine and arginine analogues: effects on isolated blood vessels and cultured endothelial cells
Authors: Schmidt Harald H.H.W. , Baeblich Sören E. , Zernikow Bettina C. , Klein Marcus M. , Böhme Eycke 
Published: July 2012

The present study examined effects of arginine (Arg) and various Arg analogues on the vascular tone of rabbit and rat aortic rings, the release of nitrite from cultured bovine aortic endothelial cells and the metabolism of l‐Arg in bovine and porcine endothelial cell homogenates. The respective d‐enantiomers or N‐α‐benzoyl‐l‐arginine ethyl ester did not substitute for l‐Arg.
In bovine aortic endothelial cells, the release of nitrite was only observed in the presence of l‐Arg or l‐Arg methyl ester in the cell culture medium.
In dialyzed homogenates of porcine and bovine aortic endothelial cells, l‐Arg was metabolized independently of NADPH and Ca2+ to yield l‐ornithine (l‐Orn) and l‐citrulline (l‐Cit). No concomitant nitrite formation was detected.
Pretreatment of rabbit and rat aortic rings with l‐canavanine (l‐Can) or NG‐monomethyl‐l‐Arg (l‐NMMA) inhibited ATP‐ and acetylcholine‐induced relaxations (endothelium‐dependent) but not glyceryltrinitrate‐induced relaxations (endothelium‐independent).
In rabbit aortic rings, Arg and monomeric Arg analogues induced endothelium‐independent relaxations. l‐Arg methyl ester induced an endothelium‐independent contraction, and l‐NMMA induced a relaxation in the absence of endothelium and a contraction in the presence of endothelium. Polymeric basic amino acids such as poly l‐Arg induced endothelium‐dependent relaxations (inhibited by l‐Can), a subsequent refractoriness to endothelium‐dependent vasodilatators (not prevented by l‐Can) and endothelial cell death.
We suggest that extracellular l‐Arg is essential for the formation of endothelium‐derived nitrogen oxides (EDNO). However, Arg and Arg analogues do not exert endothelium‐dependent relaxation. l‐Can and l‐NMMA inhibit endothelium‐dependent relaxation, consistent with an inhibition of EDNO formation from l‐Arg, but also exert endothelium‐independent effects on vascular tone.
Cytoplasmic calcium and the relaxation of canine coronary arterial smooth muscle produced by cromakalim, pinacidil and nicorandil
Authors: Yanagisawa Teruyuki , Teshigawara Tadashi , Taira Norio 
Published: July 2012

In order to investigate the vasodilator mechanisms of the K+ channel openers, cromakalim, pinacidil and nicorandil, we measured changes in cytoplasmic Ca2+ concentration ([Ca2+]i) simultaneously with force by a microfluorimetric method using fura‐2, a calcium indicator, in canine coronary arterial smooth muscle cells.
The three K+ channel openers all produced a concentration‐dependent reduction of [Ca2+]j in 5 and 30mM KCl physiological salt solution (PSS) but failed to affect [Ca2+]i in 45 and 90 mM KC1‐PSS.
Cromakalim only partly inhibited (‐45%) the 30 mM KCl‐induced contractures, whereas pinacidil and nicorandil nearly abolished contractions produced by 45 mM, 90 mM and 30 mM KC1‐PSS.
Tetrabutylammonium (TBA), a nonselective K+ channel blocker, or glibenclamide, a supposed adenosine 5′‐triphosphate (ATP)‐sensitive K+ channel blocker, abolished the reduction of [Ca2+]i caused by the three K+ channel openers and the relaxant effect of cromakalim, whereas they only slightly attenuated the relaxant effects of pinacidil and nicorandil.
The increase in [Ca2+]i produced by 45 or 90 mM KCl‐PSS in the presence of pinacidil or nicorandil was abolished by 10−5m verapamil, indicating that the increase in [Ca2+]i was caused by the influx of extracellular Ca2+ and that pinacidil and nicorandil did not affect the voltage‐dependent Ca2+ channel directly.
The [Ca2+]i‐force relationship in the presence of cromakalim was not distinguishable from that of control.
The [Ca2+]i‐force curve was shifted to the right by pinacidil and nicorandil.
These results show that cromakalim is a more specific K+ channel opener than pinacidil and nicorandil, and that vasodilatation produced by cromakalim in this study is predominantly a result of a reduction of [Ca2+]i due to the closure of voltage‐dependent Ca2+ channels by hyperpolarization. In contrast, additional mechanisms are involved in the vasodilator actions of pinacidil and nicorandil. One of these is related to a reduction in the sensitivity of contractile proteins to Ca2+. The latter mechanism of nicorandil is akin to that of nitroglycerin. K+ channels opened by these K+ channel openers may be ATP‐sensitive ones which are blocked by glibenclamide.
Inhibitory role of endothelium‐derived relaxing factor in rat and human pulmonary arteries
Authors: Crawley D.E. , Liu S.F. , Evans T.W. , Barnes P.J. 
Published: July 2012

The inhibitory role of endothelium‐derived relaxing factor was studied in both rat and human pulmonary arteries in vitro by inhibiting its synthesis with the L‐arginine analogue NG‐monomethyl‐l‐arginine (l‐NMMA).
In rat pulmonary arteries, l‐NMMA pretreatment (10–300 μm) dose‐dependently inhibited acetylcholine‐induced relaxation (which is endothelium‐dependent). NG‐monomethyl‐d‐arginine (d‐NMMA, 100 μm) was without effect, l‐Arginine, but not d‐arginine, dose‐dependently reversed this inhibition. l‐NMMA had no effect on relaxation induced by sodium nitroprusside.
In human small pulmonary arteries l‐NMMA (100 μm) pretreatment similarly inhibited the acetylcholine‐induced relaxation but had no effect on the sodium nitroprusside‐induced relaxation.
In both rat and human pulmonary arteries, l‐NMMA, but not d‐NMMA, always caused contraction of preconstricted tissues whereas it had no effect on baseline tone. In the rat this contraction was completely prevented by prior treatment with l‐arginine.
l‐NMMA (100 μm) pretreatment mimicked the effect of endothelium removal on phenylephrine‐induced vasoconstriction, both resulting in an increase in tension development at each concentration of phenylephrine. This enhancement was greatest at low concentrations of phenylephrine but was still present even at the highest concentrations. Pretreatment with l‐NMMA (100 μm) also significantly increased the responses to single doses of phenylephrine.
These results suggest that endothelium‐derived relaxing factor from endothelial cells both mediates the relaxation response to acetylcholine and also acts as a physiological brake against vasoconstriction in pulmonary vessels.
Reduction of NMDA receptors with dithiothreitol increases [3H]‐MK‐801 binding and NMDA‐induced Ca2+ fluxes
Authors: Reynolds Ian J. , Rush Elizabeth A. , Aizenman Elias 
Published: July 2012

We have investigated the modulation of N‐methyl‐d‐aspartate (NMDA) receptor activation by the sulphydryl redox reagents dithiothreitol (DTT) and 5,5‐dithio‐bis‐2‐nitrobenzoic acid (DTNB).
Increases in [3H]‐MK‐801 binding produced by glutamate, glycine and spermidine were enhanced by DTT (2 mm) and diminished by DTNB (0.5 mm).
The inhibition of [3H]‐MK‐801 binding by CGS 19755 and 7‐chlorokynurenate was not altered by 2 mM DTT. However, the potency of the competitive polyamine antagonist, arcaine, was decreased by DTT.
NMDA‐induced Ca2+ fluxes into primary cultures of rat forebrain neurones were enhanced by DTT in a DTNB‐reversible fashion. In addition to augmenting the magnitude of NMDA‐induced increase in intracellular free Ca2+, 10mM DTT also prolonged the duration of the Ca2+ signal. However, DTT had no effect on the increase in Ca2+ produced by depolarizing neurones with 50 mM KCl.
These studies show that the reduction of disulphide bonds on the NMDA receptor complex by DTT increases activation. The precise site of these groups remains unclear but they are unlikely to form an integral part of the glutamate, glycine or polyamine binding domains. The enhancement of the activation of the NMDA receptor by DTT is associated with increased Ca2+ fluxes. The possible pathophysiological consequences of receptor reduction are discussed.
Carbamylcholine‐ and 5‐hydroxytryptamine‐induced contraction in rat isolated airways: inhibition by calcitonin gene‐related peptide
Authors: Cadieux Alain , Lanoue Chantal , Sirois Pierre , Barabe Jean 
Published: July 2012

The effects of rat and human α‐calcitonin gene‐related peptide (α‐CGRP) were investigated in isolated smooth muscle preparations obtained from three levels of the rat respiratory tract.
Neither peptide (10−10–10−6m) had any effect on resting tension or on carbamylcholine (10−6m)‐induced tone of trachea or main bronchus. In contrast, CGRP sometimes reduced spontaneous or carbamylcholine‐induced tone of lung parenchymal strips.
CGRP produced a significant rightward shift of the log concentration‐response curves to carbamylcholine and 5‐hydroxytryptamine (5‐HT) in the main bronchus. A rightward shift was also seen in trachea and parenchymal strips but this did not achieve the level of significance. The maximal response to 5‐HT was reduced in the main bronchus and lung parenchyma whereas the maximal contraction to carbamylcholine was decreased in parenchymal strip only.
In all three airway preparations, CGRP caused concentration‐dependent inhibition of responses elicited by challenges with 10−7m carbamylcholine or 5 × 10−7m 5‐HT. The inhibitory effect of the peptide was inversely related to the size of the airways: the smaller the calibre, the greater the inhibition.
The inhibitory action of CGRP was not modified by pretreatment with tetrodotoxin (10−6m), propranolol (10−6m) or indomethacin (10−6m).
The results strongly suggest that (a) CGRP has a nonspecific inhibitory action on airway smooth muscle cells, (b) CGRP may act as a potent inhibitor of responses elicited by bronchoconstrictor substances and (c) its inhibitory activity may be most powerfully expressed in peripheral regions of the respiratory tract.