bluuebunny/crossref_metadata_2025_split huggingface dataset:
The effect of forskolin on 5‐HT1‐like and angiotensin II‐induced vasoconstriction and cyclic AMP content of the rabbit isolated femoral artery
Authors: Randall V.A. , MacLennan S.J. , Martin G.R. , Wilson V.G. 
Published: July 2012

A characteristic feature of vasoconstrictor 5‐HT1‐like receptors in vitro is that responses mediated by these receptors are enhanced by other vasoconstrictor agents. In the present study, we have examined the influence of cellular cyclic AMP on vasoconstrictor responses to activation of 5‐HT1‐like receptors in isolated ring segments of the rabbit femoral artery (RbFA), and determined whether modulation of this second messenger underlies the ability of angiotensin II, an endogenous vasoconstrictor, to enhance 5‐HT1‐like responses.
In the presence of 0.1 μm ketanserin (to antagonize 5‐HT2‐receptors) and 0.3 μm prazosin (to antagonize α1‐adrenoceptors), 5‐HT produced a concentration‐related contraction, which was significantly augmented by pre‐contraction of the vessel with 0.1‐0.45 nM ([A30]) angiotensin II. Responses to 5‐HT in the presence of angiotensin II were inhibited by the 5‐HT1‐like/5‐HT2 antagonist, metergoline (1 μm).
The directly‐acting adenylyl cyclase activator, forskolin (1 μm), abolished responses to angiotensin II and caused a rightward shift and concomitant depression of the 5‐HT concentration‐effect (E/[A]) curve. Higher concentrations of forskolin (> 10 μm) abolished responses to 5‐HT and 1 μm sodium nitroprusside abolished responses to 5‐HT and angiotensin II (n = 7).
In the presence of angiotensin II (0.1‐0.45 nM), however, 1 μm forskolin failed to inhibit 5‐HT‐induced contractions; the E/A curve for 5‐HT (in the presence of forskolin and angiotensin II) was not significantly different from that produced in the presence of angiotensin II alone. Similarly, the presence of angiotensin II (0.1‐0.45 nM) was also able to overcome partially the inhibitory effect of 1 μm sodium nitroprusside against 5‐HT‐induced contractions (n = 7). In marked contrast, 5‐HT failed to elicit a contraction in the presence of angiotensin II and 10 μm forskolin (n = 5).
5‐HT (1 μm) significantly reduced basal cyclic AMP accumulation by 35%, whereas angiotensin II (0.45 nM) was without effect. The combination of angiotensin II and 5‐HT failed to alter significantly the reduction in cyclic AMP produced by 5‐HT alone. Forskolin (1 μm) increased cyclic AMP levels 7 fold above basal, but neither 1 μm 5‐HT nor a combination of 1 μm 5‐HT and 0.45 nM angiotensin II produced a significant decrease in cyclic AMP content.
Whilst moderate concentrations of forskolin can inhibit the reponses to either agent, simultaneous activation of angiotensin II and 5‐HT1‐like receptors can overcome the inhibitory effect of elevated levels of cyclic AMP. Since the potentiating effect of angiotensin II, in either the presence or absence of forskolin, occurs without significant alteration of cellular cyclic AMP, it seems likely that a cyclic AMP‐independent pathway is implicated in the synergistic interaction between angiotensin II and vasoconstrictor 5‐HT1‐like receptors.
ATP and nitric oxide: inhibitory NANC neurotransmitters in the longitudinal muscle‐myenteric plexus preparation of the rat ileum
Authors: Smits Geert J.M. , Lefebvre Romain A. 
Published: July 2012

The nature of neurotransmitter(s) involved in non‐adrenergic non‐cholinergic (NANC) relaxations induced by electrical stimulation (10 s trains, 1–8 Hz) was investigated in the precontracted longitudinal muscle‐myenteric plexus preparation of the rat ileum.
Electrical stimulation of the tissue induced complex responses, consisting of a primary contraction, a primary relaxation, an off‐relaxation and a rebound contraction, which were all tetrodotoxin(TTX)‐sensitive.
Vasoactive intestinal polypeptide (VIP) and carbon monoxide (CO) did not induce relaxations. α‐Chymotrypsin did not reduce the relaxations induced by electrical stimulation, while zinc protoporphyrin IX had non‐specific effects.
Nitric oxide (NO) induced concentration‐dependent relaxations. NG‐nitro‐l‐arginine methylester (L‐NAME) abolished the primary contractions and off‐relaxations, while it partially reduced the primary relaxations.
ATP induced relaxations and ATP‐desensitization of the tissues partially reduced the primary relaxations. Suramin and reactive blue 2 did not consistently influence the primary relaxations.
The ATP‐induced relaxations were not influenced by L‐NAME or TTX. The inhibitory effect of ATP‐desensitization and L‐NAME did not summate.
The cyclic AMP content of the tissue did not increase upon electrical stimulation or after addition of NO or ATP. The cyclic GMP content of the tissue increased upon electrical stimulation and addition of NO, but not after addition of ATP.
It is concluded that the relaxation induced by electrical stimulation consists of two types of responses. The off‐relaxation is completely nitrergic, while the primary relaxation is mediated by NO, ATP and an as yet unknown transmitter which is not VIP or CO.
Effects of selective phosphodiesterase 3 inhibition in the perfused liver of the rat after endotoxin treatment
Authors: Weidenbach H. , Beckh K. , Schricker T. , Georgieff M. , Adler G. , Burger M. 
Published: July 2012

This study was designed to investigate the role of rat phosphodiesterase 3 (RPDE3) in regulation of liver metabolism in sepsis. We studied the effects of the phosphodiesterase 3 inhibitor (PDI), enoximone, alone and in combination with regulating factors of hepatic carbohydrate metabolism and bile secretion in the perfused liver of rats treated 4 h earlier with endotoxin. In addition, cyclic AMP and cyclic GMP levels were determined in the effluate and bile by radio immunoassay methods.
After endotoxin treatment, infusion of enoximone at three concentrations (1 μm, 10 βM) resulted in an increased glucose output from −1.4 ± 0.9 to 7.8 ± 2.5 μmol 1g−1 20 min−1. Bile acid‐independent bile flow increased also, in a dose‐dependent manner.
In untreated livers, cyclic AMP release increased in the effluate from 1000 ± 73 fmol g−1 min−1 to 1710 ± 143 fmol g−1 min−1 when enoximone (10 μm) was administered. In bile from untreated livers, the level of cyclic AMP was also significantly increased by enoximone. After endotoxin treatment, the enoximone (10 μm) effect on cyclic AMP levels in effluate and bile was greatly reduced. Levels of cyclic GMP in the effluate and bile appeared unchanged in the presence of enoximone.
During co‐infusion of glucagon (1 nM) and enoximone (10 μm), cyclic nucleotide levels in the effluate and bile of livers after endotoxin treatment were determined. In the effluate, cyclic AMP release increased from 827 ± 144 fmol g−1 min−1 to 17802 ± 2821 fmol g−1 min−1 when glucagon was administered. The presence of enoximone enhanced cyclic AMP further to 41696 ± 920 fmol g−1 min−1. The same changes in cyclic AMP release were found in bile. Levels of cyclic GMP in the effluate and bile were not significantly affected by the administration of glucagon and the PDI.
Glucose release was determined during glucagon, sympathetic nerves stimulation and phenylephrine administration in the presence and absence of enoximone. The addition of enoximone to glucagon increased glucose release by 8.2 ± 2.8 μmol g−1 20 min−1, without alteration of lactate balance. The PDI enhanced the glycogenolytic effects of nerve stimulation and of phenylephrine, accompanied by a reduction in lactate production.
Enoximone significantly enhanced the bile acid independent bile flow after glucagon, nerves stimulation and after administration of phenylephrine. Bile acid secretion was unaffected by the PDI. The vasoconstrictor effect of nerve stimulation was reduced by the PDI.
We conclude that endotoxin treatment reduces the ability of the PDI, enoximone, to increase cyclic AMP release in the perfused liver. The significant increase in cyclic AMP release after stimulation with glucagon and enoximone favours the view that RPDE3 is involved in the degradation of cyclic AMP in the liver after exposure to endotoxin. Additionally, the inhibition of the RPDE3 results in glucose release, vasodilatation and choleresis in endotoxin pretreated livers.
Heterogeneous distribution of benzodiazepine receptors among rat neostriatal neurones
Authors: Munakata Mitsutoshi , Nakanishi Ryoji , Akaike Norio 
Published: July 2012

The effects of benzodiazepine receptor (BZR) agonist were investigated in dissociated rat neostriatal neurones by a conventional whole‐cell patch recording configuration at room temperature.
The dissociated neurones, with a longest somatic diameter of larger than 25 μm, were classified as ‘large neurones’, while those having soma measuring less than 15 μm were described as ‘small neurones’. Large neurones were intensely positive for acetylcholinesterase staining, whereas the small ones were not.
CL218,872 enhanced the GABA response in both the large and small neurones with similar EC50s. However, the potentiation efficacy of CL218,872 in large neurones was larger than that of small ones.
Zolpidem also potentiated the GABA response in both neuronal populations with similar EC50s. This compound also enhanced the GABA response more strongly in large neurones than in small ones.
Zopiclone exerted a prominent potentiation in large neurones, although no difference was seen in the EC50s in the large and small neurones.
It was concluded that the BZR in large neurones had a different pharmacological property from that in small ones and that the BZR agonists showed a prominent difference, not in EC50, but in the potentiation efficacy between these neuronal populations.
Inhibition of PAF synthesis by stimulated human polymorphonuclear leucocytes with cloricromene, an inhibitor of phospholipase A2 activation
Authors: Ribaldi E. , Mezzasoma A.M. , Francescangeli E. , Prosdocimi M. , Nenci G.G. , Goracci G. , Gresele P. 
Published: July 2012

A phospholipase A2 (PLA2) represents the key enzyme in the remodelling pathway of platelet‐activating factor (PAF) synthesis in human polymorphonuclear (PMN) leucocytes.
PLA2 activation is also the rate‐limiting step for the release of the arachidonic acid utilized for the synthesis of leukotrienes in stimulated leucocytes; however, it is unknown whether the PLA2s involved in the two biosynthetic pathways are identical.
Cloricromene (8‐monochloro‐3‐β‐diethylaminoethyl‐4‐methyl‐7‐ethoxy‐carbonylmethoxy coumarin) is an antithrombotic coumarin derivative which inhibits platelet and leucocyte function and suppresses arachidonic acid liberation by interfering with PLA2 activation.
The aim of the present study was to assess whether chloricromene inhibits PAF synthesis by stimulated human polymorphonuclear leucocytes (PMNs).
Cloricromene (50–500 μm) inhibited in a concentration‐dependent manner the release of PAF, as measured by h.p.l.c. bioassay, from A23187‐stimulated PMNs. Significant inhibition (45%) of PAF‐release was obtained with 50 μm cloricromene and the IC50 was 85 μm. Mepacrine (500 μm), a non‐specific PLA2 inhibitor, strikingly reduced PAF release.
The incorporation of [3H]‐acetate into [3H]‐PAF induced by serum‐treated zymosan in human PMNs was also inhibited concentration‐dependently by cloricromene, with an IC50 of 105 μm. Mepacrine also suppressed [3H]‐acetate incorporation into [3H]‐PAF.
Cloricromene did not affect the activities of the enzymes involved in PAF‐synthesis acetyltransferase or phosphocholine transferase.
Our data demonstrate that cloricromene, an inhibitor of PLA2‐activation in human leucocytes, reduces the synthesis of PAF by stimulated PMNs. This finding has a twofold implication: the PLA2s (or the mechanisms that regulate their activation) involved in PAF synthesis and arachidonate release in human leucocytes are either identical or else indistinguishable by their sensitivity to cloricromene; the inhibition of PAF release by activated leucocytes may contribute to the antithrombotic and anti‐ischaemic activities exerted by cloricromene.
Cardiovascular effects of a novel, potent and selective phosphodiesterase 5 inhibitor, DMPPO: in vitro and in vivo characterization
Authors: Delpy Eric , de Gouville Anne‐Charlotte le Monnier 
Published: July 2012

The aim of this study was to investigate the cardiovascular effects of a novel, potent and specific phosphodiesterase 5 (PDE 5) inhibitor, 1,3 dimethyl‐6‐(2‐propoxy‐5‐methane sulphonylamidophenyl)‐pyrazolo[3,4‐d]pyrimidin‐4‐(5H)‐one (DMPPO) in phenylephrine‐precontracted rat aortic rings and different in vivo rat preparations.
DMPPO elicited a concentration‐dependent relaxation of rat aortic rings with functional endothelium. DMPPO‐induced relaxation was abolished by endothelium removal or pretreatment with the soluble guanylate cyclase inhibitor, methylene blue (10 μm).
In aortic rings without endothelium, the potency (pD2 = ‐log10 EC50) of atrial natriuretic peptide (ANP) to induce relaxation increased from 8.13 ± 0.05 in the absence of DMPPO to 8.32 ± 0.05 and 8.52 ± 0.08 in the presence of 30 nM and 100 nM DMPPO, respectively. Similarly, the potency of sodium nitroprusside (SNP) in inducing relaxation increased from 7.38 ± 0.07 in the absence of the PDE 5 inhibitor to 8.07 ± 0.11 and 8.15 ± 0.08 in the presence of 30 nM and 100 nM DMPPO, respectively. In contrast, relaxation to the adenylate cyclase activator, forskolin, was unchanged by DMPPO (100μm).
In rings without endothelium, DMPPO (100 nM) increased by 2.5 fold intracellular levels of guanosine 3′:5′‐cyclic monophosphate (cyclic GMP). Moreover, DMPPO (100 nM) potentiated the increases in cyclic GMP levels induced by ANP (30 nM) by 3 fold and SNP (30 nM) by 2.7 fold. Adenosine 3′:5′‐cyclic monophosphate (cyclic AMP) levels were not modified by DMPPO.
In anaesthetized normotensive or spontaneously hypertensive rats (SHR), DMPPO (2 and 5 mg kg−1, i.v.) lowered blood pressure without affecting heart rate. Similarly, in conscious SHR, orally administered DMPPO (5 mg kg−1) induced a 25 mmHg decrease in blood pressure for at least 7 h without modifying heart rate. Meanwhile, urinary cyclic GMP was increased by 50% whereas cyclic AMP remained unchanged.
In normotensive anaesthetized rats, sodium nitroprusside (SNP) (i.v. bolus) induced a decrease in blood pressure which rapidly returned to baseline. In DMPPO (1 mg kg−1, i.v.)‐treated rats, the hypotensive effects of SNP (10 to 100 μg kg−1) were prolonged over time whereas the peak effect was unchanged.
In pithed rats, phenylephrine (i.v. bolus) induced dose‐dependent increases in blood pressure. Pretreatment with DMPPO (5 mg kg−1, i.v.) partially inhibited the pressor response to phenylephrine (0.3 to 100 μg kg−1).
In conclusion, the potent and selective PDE 5 inhibitor, DMPPO, produces relaxation in isolated vessels in the presence of a cyclic GMP drive and reduces blood pressure of intact animals. Its high oral bioavailability and long duration of action should make it a useful tool to study the role of cyclic GMP in various biological systems.
Biphasic effect of pentobarbitone on chick myotube nicotinic receptor channel kinetics
Authors: Liu Guo Jun , Madsen Barry W. 
Published: July 2012

The modulatory action of pentobarbitone on chick myotube nicotinic acetylcholine receptor kinetics was studied by the patch clamp technique, particularly focussing on effects at low concentrations.
Open time sojourn distributions of foetal‐type receptors recorded at room temperature (22–24°C) in cell‐attached mode in the presence of 0.2 μm acetylcholine were well described by two exponentials, with fast and slow time constants of 0.53 ± 0.12 and 16.7 ± 2.2 ms (mean ± s.e.mean) respectively.
The duration of the slow open time constant was increased by low concentrations of pentobarbitone (up to 1 μm), and thereafter decreased with higher concentrations (10–50 μm) in a concentration‐dependent manner.
Complementary evidence for the stimulatory effect of pentobarbitone on open time was obtained (i) by using a backfill technique where drug concentration at the patch gradually increases over time, and (ii) through use of perfused outside‐out preparations where receptors in the same patch were successively exposed to acetylcholine in the absence and presence of pentobarbitone.
The dual action of pentobarbitone on channel kinetics probably indicates that an allosteric interaction mechanism is involved rather than simple steric channel blockade.
Sulprostone‐induced reduction of myocardial infarct size in the rabbit by activation of ATP‐sensitive potassium channels
Authors: Hide Emma J. , Thiemermann Christoph 
Published: July 2012

This study examined whether (i) a 1 h pretreatment with or (ii) a continuous infusion of sulprostone reduces myocardial infarct size arising from coronary artery occlusion (60 min) and reperfusion (120 min) in the anaesthetized rabbit. In addition, we investigated whether the observed cardioprotective effect of this selective agonist of prostanoid EP1/EP3 receptors were due to the activation of ATP‐sensitive potassium (KATP) channels.
In anaesthetized rabbits pretreated with vehicle (5% ethanol in 0.9% saline; 0.05 ml min−1, i.v.) infarct size (expressed as a percentage of the area at risk) after 60 min of coronary artery occlusion followed by 120 min of reperfusion was 59 ± 4% (n = 10). Pretreatment of rabbits with sulprostone (1.0 μg kg−1 min−1 for 1 h, discontinued immediately prior to coronary artery occlusion) did not reduce infarct size (60 ± 4%; n = 4). In contrast, a continuous infusion of sulprostone (1.0 μg kg−1 min−1) starting 10 min prior to the onset of LAL occlusion and continued throughout the experiment, significantly reduced infarct size (41 ± 5%, n = 6) when compared to the respective vehicle‐treated controls (57 ± 4%, n = 10; P < 0.05). Sulprostone (pretreatment or continuous infusion) had no effect on any of the haemodynamic parameters measured.
The reduction in infarct size afforded by continuous infusion of sulprostone was abolished by pretreatment of rabbits with the KATP channel blocker 5‐hydroxydecanoate (5‐HD 5 μg kg−1; 63 ± 4%; n = 6). When administered alone, 5‐HD had no effect on infarct size when compared to control (52 ± 6, n = 10).
We propose that a continuous infusion of the selective EP1/EP3 prostanoid receptor agonist, sulprostone, reduces infarct size in the anaesthetized rabbit by a mechanism that involves the opening of KATP channels.
Actions of the digitalis analogue strophanthidin on action potentials and L‐type calcium current in single cells isolated from the rabbit atrioventricular node
Authors: Hancox Jules C. , Levi Allan J. 
Published: July 2012

The atrioventricular node (AVN) of the heart is vital to normal cardiac function and is a major site of antiarrhythmic drug action. This study describes the effects of the cardiac glycoside analogue strophanthidin on spontaneous action potentials and L‐type calcium current recorded from single AVN cells isolated from the rabbit heart.
With a standard KCl‐based internal dialysis solution, exposure to 50 μm strophanthidin produced a progressive depolarization of the maximum diastolic potential and a reduction in action potential amplitude and upstroke velocity. Sustained application resulted in the loss of action potentials and occurrence of spontaneous ‘bell‐shaped’ depolarizations.
Cells were whole‐cell voltage clamped at −40 mV and depolarizing voltage clamps applied. With a standard KCl‐based internal dialysis solution, exposure to 50 μm strophanthidin caused a large reduction of ICa,L at all potentials between −30 and +40 mV (n = 4). At +10 mV, the mean ICa,L amplitude was reduced from −232 ± 65 pA to −48 ± 26 pA (P < 0.05; t test; n = 5 cells).
To record ICa,L more selectively, cells were dialysed with a Cs‐based pipette solution. A short strophanthidin exposure reduced ICa,L amplitude from −250 ± 31 pA to −88 ± 19 pA (P < 0.001; n = 8 cells). For both KCl and CsCl‐based solutions it was observed that sustained exposure to strophanthidin for several minutes caused spontaneous inward fluctuations in the membrane current record similar to the ‘ITI’ (arrhythmogenic oscillatory transient inward) current shown for other cardiac cells.
When the calcium chelator BAPTA was added to the pipette solution (10 mM), the reduction in ICa,L by strophanthidin was largely eliminated (P > 0.1), and no spontaneous inward current fluctuations were observed after sustained exposure to strophanthidin (n = 8 cells).
When external Ca in the perfusate was replaced with Ba, strophanthidin did not significantly reduce the Ba current through L‐type calcium channels (n = 5 cells).
We conclude that strophanthidin reduces ICa,L by an indirect action, mediated by the rise in intracellular calcium (Cai) which follows inhibition of the Na/K pump caused by cardiac glycosides. The appearance of spontaneous ITI with strophanthidin would also seem to be mediated by a rise in Cai, and may contribute to the spontaneous oscillations in membrane potential observed after prolonged strophanthidin exposure.
Effects of neuropeptide Y on L‐type calcium current in guinea‐pig ventricular myocytes
Authors: Bryant S.M. , Hart G. 
Published: July 2012

Neuropeptide Y (NPY) reduces cell shortening at high concentrations in guinea‐pig ventricular myocytes. We have studied the effects of the peptide on calcium current in cardiac myocytes.
We have recorded L‐type calcium current in guinea‐pig ventricular myocytes under conditions in which the effects of other overlapping currents have been minimised by using Na+‐free, K+‐free external solution and patch‐clamp electrodes containing Cs+.
Peak inward calcium current is reduced by NPY at concentrations in excess of 1 nM, and maximal inhibition (31%) was found at and above concentrations of 100 nM. The IC50 value for NPY inhibition of peak calcium current was 1.72 nM.
NPY had no effect on the voltage‐dependence of calcium current amplitude, on the time course of current inactivation, or on the voltage‐dependence of the steady‐state gating variables.
NPY did not reduce the calcium current in the presence of 8‐Br‐cyclic AMP, and it was also without effect when GTP‐γ‐S or GDP‐β‐S were included in the patch pipette.
We conclude that in guinea‐pig ventricular myocytes NPY acts at low concentration to reduce L‐type calcium current, via a G‐protein‐mediated pathway and reduction in intracellular cyclic AMP.