bluuebunny/crossref_metadata_2025 huggingface dataset:
The role of prostanoid TP‐ and DP‐receptors in the bronchoconstrictor effect of inhaled PGD2 in anaesthetized guinea‐pigs: effect of the DP‐antagonist BW A868C
Authors: Hamid‐Bloomfield S. , Payne A.N. , Petrovic A.A. , Whittle B.J.R.
Published: July 2012

In anaesthetized, pump‐ventilated guinea‐pigs, bolus intravenous injection of prostaglandin D2 (PGD2 5–160 μg kg−1) caused a dose‐dependent rise in both heart rate and systemic mean arterial blood pressure with only a small monophasic rise in pulmonary inflation pressure (PIP).

In contrast, inhaled PGD2 (0.1–1 mg ml−1, 30s) provoked a substantial concentration‐dependent Diphasic rise in PIP. The bronchoconstrictor action of inhaled PGD2 was accompanied by minimal cardiovascular effects.

The 3‐benzyl substituted hydantoin BW A868C (0.1–1 mg kg−1 i.v.) a novel prostanoid DP‐receptor antagonist, had no significant effect on the cardiovascular or bronchoconstrictor effects of intravenously administered or inhaled PGD2.

However, BW A868C (0.1–1 mg kg−1 i.v.) did inhibit the hypotensive actions of the DP‐receptor agonist, BW 245C (1–3 μg kg−1 i.v.).

The prostanoid TP‐receptor antagonist BM 13.177 (2.5 mg kg−1 i.v.) strongly inhibited the bronchoconstrictor effect of inhaled PGD2, abolishing the first phase of this response and reducing the peak increase in PIP provoked by PGD2 (0.1 or 1 mg ml−1 for 30s), by 67 ± 16% and 44 ± 5% respectively.

A combination of BW A868C (0.1 or 1 mg kg−1 i.v.) with BM 13.177 (2.5 mg kg−1 i.v.) produced no greater inhibition of the bronchoconstrictor effect of inhaled PGD2 than that seen with BM 13.177 (2.5 mg kg−1 i.v.) alone.

Neither bilateral vagotomy, nor selective inhibition of arachidonate cyclo‐oxygenase with indomethacin or 5‐lipoxygenase with the novel acetohydroxamic acid BW A4C, significantly reduced the bronchoconstrictor effect of inhaled PGD2.

These findings indicate that the bronchoconstrictor effect of inhaled PGD2 in guinea‐pigs in vivo is mediated primarily through direct TP‐receptor activation and not through actions on DP‐receptors.
Differential effects of petit mal anticonvulsants and convulsants on thalamic neurones: calcium current reduction
Authors: Coulter Douglas A. , Huguenard John R. , Prince David A.
Published: July 2012

Succinimide derivatives can be either convulsant (tetramethylsuccinimide (TMS)), or anticonvulsant (ethosuximide (ES); α‐methyl‐α‐phenylsuccinimide (MPS)). ES, an anticonvulsant succinimide, has previously been shown to block calcium currents of thalamic neurones, while the convulsant succinimide TMS blocks γ‐aminobutyric acid (GABA) responses in a similar fashion to the convulsant pentylenetetrazol (PTZ).

Using voltage‐clamp techniques, we analysed the effects of the anticonvulsant succinimides ES and MPS and the convulsants TMS and PTZ on calcium currents of acutely isolated thalamic relay neurones of the rat.

MPS and ES reduced low‐threshold calcium current (LTCC) in a voltage‐dependent manner, without affecting steady‐state inactivation. MPS was less potent than ES (IC50 of 1100 vs 200 μm) but greater in efficacy (100% maximal reduction vs 40% for ES).

PTZ had no effect on calcium currents, and TMS only reduced LTCC at very high concentrations, and did not occlude MPS effects when applied concurrently.

These results, which demonstrate that anticonvulsant, but not convulsant, succinimides block LTCC, provide additional support for the hypothesis that LTCC reduction is a mechanism of action of the anticonvulsant succinimides related to their effects in petit mal epilepsy.
Effect of propentofylline (HWA 285) on extracellular purines and excitatory amino acids in CA1 of rat hippocampus during transient ischaemia
Authors: Andiné Peter , Rudolphi Karl A. , Fredholm Bertil B. , Hagberg Henrik
Published: July 2012

The adenosine uptake blocker propentofylline (HWA 285) has previously been shown to protect hippocampal CA1 pyramidal cells from ischaemia‐induced delayed neuronal death. The influence of propentofylline, on the extracellular concentrations of purines, aspartate and glutamate in the CA1 of the rat hippocampus during transient forebrain ischaemia was investigated.

Twenty min of ischaemia was induced by four‐vessel occlusion in Wistar rats, extracellular compounds were sampled by use of microdialysis and EEG was recorded by a tungsten electrode attached to the dialysis probe.

Propentofylline (10 mgkg−1 i.p.) did not influence the basal levels of any of the compounds in the hippocampal dialysates.

The EEG became isoelectric within 20 s after induction of ischaemia.

Extracellular adenosine, inosine, hypoxanthine, aspartate and glutamate increased several fold during ischaemia and remained elevated during early reflow. Within 2 h of reperfusion the concentration of all compounds was normalized. Xanthine increased upon reperfusion and remained elevated after 2 h.

Propentofylline (10 mg kg−1 i.p.) administered 15 min before ischaemia significantly enhanced the ischaemia‐evoked increase of adenosine but attenuated the increases of the other purine catabolites and of glutamate.

In separate in vitro experiments, propentofylline did not inhibit adenosine deaminase activity.

The present data show that propentofylline enhances extracellular adenosine and lowers extracellular glutamate in vivo during ischaemia. These findings may be important in relation to the neuroprotective properties of propentofylline.
Aging differentially affects direct and indirect actions of endothelin‐1 in perfused mesenteric arteries of the rat
Authors: Dohi Yasuaki , Lüscher Thomas F.
Published: July 2012

The effects of age on the vascular action of endothelin‐1 were studied in mesenteric resistance arteries of 4,9 and 27 month old Fischer 344 rats.

Third order branches (about 200 μm in diameter) of mesenteric resistance arteries were dissected free and mounted on glass cannulae in organ chambers. Changes in intraluminal diameter of the perfused and pressurized vessels were continuously measured with a video dimension analyzer.

Endothelin‐1 (10−14−3 × 10−8 m.) caused contractions that were augmented after removal of the endothelium. The inhibitory effects of the endothelium were greater in young than in old rats.

The sensitivity of vascular smooth muscle to endothelin‐1 decreased with age, while the maximal response was maintained. In contrast, the contractions to noradrenaline were unaffected by aging.

Threshold concentrations of endothelin‐1 potentiated the contractions evoked by low and moderate concentrations of noradrenaline (10−7−10−6m) in old, but not in young, rats.

Endothelium‐dependent relaxations to acetylcholine inhibited maximal contractions to endothelin‐1 and this effect decreased with age. In contrast, the relaxations to the nitric oxide donor, 3‐morpholinosydnonimine (SIN‐1; the active metabolite of molsidomine), did not differ in the three age groups.

Aging specifically decreases the direct contractile effects of endothelin‐1 and the inhibitory effects of the endothelium against these contractions, while the indirect (potentiating) effects of the peptide become more pronounced.
Activities of endothelin‐1 in the vascular network of the rabbit ear: a microangiographic study
Authors: Randall Michael D. , Edwards David H. , Griffith Tudor M.
Published: July 2012

The effects of endothelin‐1 on perfusion pressure and on arterial and venous diameters were examined simultaneously in a rabbit isolated ear preparation perfused with physiological buffer. The effects of hypoxia and inhibition of endothelium‐derived relaxant factor (EDRF) activity on vascular responses to endothelin‐1 were also investigated.

Endothelin‐1 was potent at increasing perfusion pressure (ED50 = 46.7 ± 11.0 pmol; Rmax = 85.3 ± 5.3 mmHg). The potency and maximum reactivity were not significantly affected by hypoxia, inhibition of EDRF activity with 50 μm N‐nitro‐l‐arginine methyl ester (NAME) or a combination of hypoxia and NAME.

Endothelin‐1 caused equipotent dose‐dependent constrictions of the first four generations of arterial branch vessels (G1‐G4) but did not influence the diameter of the central ear artery except at high doses of the peptide when ‘paradoxical dilatation’ was observed. The peptide was also equipotent at causing constriction of the smaller venous vessels (V1‐V4) but did not affect the large veins (V0).

Under conditions of hypoxia the potency of endothelin‐1 was reduced in G2 and G3, was unaffected in G4 and the peptide did not significantly constrict either G0 or G1. Hypoxia reduced the potency of endothelin‐1 in the smaller venous vessels (V1‐V4), but conversely unmasked a marked constriction of the large veins (V0), which was not observed under normoxic conditions.

NAME 50 μm abolished the vasodilator effects of acetylcholine in this preparation. Inhibition of EDRF activity with NAME under normoxic conditions did not influence the constrictor activity of endothelin‐1 on the arterial or venous branch vessels. However, inhibition of EDRF activity under hypoxic conditions prevented the reduction of potency of endothelin‐1 as a constrictor of arterial and venous branch vessels which occurred in hypoxia. In the presence of NAME endothelin‐1 constricted V0 in both normoxia and hypoxia with equipotency but the maximum effect was greatest in hypoxia.

In conclusion, endothelin‐1 is a powerful vasoconstrictor which acts with greater potency in veins than arteries in the rabbit isolated ear. Although hypoxia does not influence pressor responses it nevertheless alters the spatial pattern of vasoconstriction. In particular hypoxia unmasks constriction of the large veins by endothelin‐1. Constriction of these veins was also observed in the absence of EDRF in normoxia, but to a much lesser degree so that the effect of hypoxia may only be partially due to reduced EDRF activity. Hypoxia may therefore directly or indirectly increase the sensitivity of the main veins to endothelin‐1.
Myocardial uptake of lignocaine: pharmacokinetics and pharmacodynamics in the isolated perfused heart of the rabbit
Authors: Mazoit Jean Xavier , Kantelip Jean‐Pierre , Orhant Edith Elisabeth , Talmant Jean‐Michel
Published: July 2012

The uptake kinetics and pharmacodynamics of lignocaine were studied in the isolated perfused heart of the rabbit.

Six hearts were perfused with increasing concentrations of lignocaine in a modified Krebs‐Henseleit buffer. The effluent concentration together with the increase in QRS duration were measured during lignocaine infusion and during 20 min after cessation of lignocaine infusion.

Lignocaine disposition and elimination were best described by a two‐compartment open model. Terminal half‐life was 11.0 ± 2.9 min. The unidirectional transfer was slower from central to peripheral compartment than from peripheral to central compartment (T1/2,12 = 42.6 ± 10.5 min whereas T1/2,21 = 10.7 ± 2.8 min). The myocardium/perfusate concentration‐ratio was 4.7 ± 0.4.

The pharmacodynamic effect was best described in the central compartment by using the Hill equation. Calculated maximum QRS duration (Emax) was 77 ± 8 ms. Emax was also directly measured in four additional rabbits by infusing ten times the dose of lignocaine used in the main experiment: the value of Emax measured in these conditions was 92.5 ± 9.6 ms, i.e. a QRS widening of 150%. The steady‐state perfusate concentration producing half the effect (C50) was 15.7 ± 7.6 μg ml−1.

In conclusion, the specific lignocaine binding leading to increase in QRS duration appeared to be more closely related to the vascular stream than non specific binding leading to a deeper accumulation process.
Sensitivity of hippocampal neurones to kainic acid, and antagonism by kynurenate
Authors: Stone T.W.
Published: July 2012

The sensitivity to kainic acid of neurones in the CA1 and CA3 regions of rat hippocampal slices has been examined by microiontophoresis and by superfusion methods.

When the iontophoretic currents needed to produce comparable plateaux of firing were compared, neurones in the pyramidal cell layer of the CA3 region were approximately 5 times more sensitive than cells in the CA1 region. No difference was noted in sensitivity to N‐methyl‐d‐aspartate (NMDA) or quisqualate.

When kainate was superfused at known concentrations, the threshold for eliciting excitation in CA1 was 2.1 μm. The threshold concentration in CA3 was 0.24 μm.

Two weeks after the stereotaxic intrahippocampal injection of colchicine, the granule cells of the dentate gyrus and thus the mossy fibre projections to CA3 were destroyed. In slices prepared from animals thus treated the threshold concentration of kainate for eliciting excitation had risen to 1.64 μm.

Kainate was less effective in promoting the development of epileptiform bursts of neuronal firing in colchicine‐treated slices than in controls.

Kynurenic acid antagonized the excitation of CA1 neurones elicited by kainate, NMDA or quisqualate. In the CA3 region kynurenate antagonized selectively responses to microiontophoretic NMDA, with little effect on responses to kainate or quisqualate.

In slices taken from colchicine‐treated rats kynurenate was able to block responses to kainate in the CA3 area in parallel with responses to NMDA.

Taken together the results suggest that the excitatory responses to kainate in the CA3 region may be partly due to a presynaptic action on mossy fibre terminals to release endogenous amino acids. The differential action of kynurenate in normal and lesioned slices may, therefore, indicate that the postsynaptic kainate receptors are sensitive to antagonism by this compound whereas the presynaptic receptors are resistant to kynurenate.
Effects of repeated infusions of substance P and vasoactive intestinal peptide on the weights of salivary glands subjected to atrophying influences in rats
Authors: Månsson Bengt , Nilsson Bengt‐Olof , Ekström Jörgen
Published: July 2012

The long‐term influence of substance P (SP) and vasoactive intestinal peptide (VIP) on rat salivary gland weight was investigated after parasympathetic denervation or on feeding soft food.

The parotid gland lost about one‐third of its weight within 4–5 days following parasympathetic postganglionic denervation or change in dietary regimen, from pellets to liquid diet, thought to reduce nerve reflex activity.

Daily i.v. infusions with SP or VIP diminished or largely prevented the fall in parotid gland weight, whereas infusions with pentagastrin, bethanechol and saline had no effect. The infusions were preceded by administration of α‐ and β‐adrenoceptor antagonists; these antagonists were also given to the control animals.

The effect of SP and VIP on the parotid gland weight appeared to be related to cell size rather than to cell number, as judged by measurements of RNA and DNA.

Observations on the two other major salivary glands underlined the fact that different gland types in the same animal behave differently. Parasympathetic preganglionic denervation (decentralization) lowered the weights of the sublingual and submandibular glands, whereas liquid diet only reduced the weight of the sublingual gland. SP and VIP did not affect the weights of the submandibular glands, but VIP prevented the slight fall in sublingual gland weight induced by liquid diet.

The present results suggest a trophic role in rats for SP and VIP on parotid glands and for VIP on sublingual glands. Such an influence may be exerted naturally as a result of their release from nerves containing these peptides around acini.
Rabbit brain contains an endogenous inhibitor of endothelium‐dependent relaxation
Authors: Moore P.K. , Al‐Swayeh O.A. , Evans R.
Published: July 2012

Supernatants prepared from the rabbit brain, lung and liver caused an endothelium‐dependent and volume‐related contraction of the phenylephrine‐pretreated rabbit aorta and inhibited relaxation due to acetylcholine (ACh).

Perfusion in situ of the rabbit lung or liver with Krebs solution substantially reduced or removed the endothelium‐dependent inhibitor. Spectrophotometric analysis revealed the presence of substantial amounts of haemoglobin (1.8–2.1 μm) in these organ supernatants.

Supernatants prepared from the Krebs‐perfused rabbit brain retained the ability to contract the phenylephrine‐pretreated rabbit aorta and to inhibit relaxation due to ACh and substance P (SP). Rabbit brain supernatant did not reduce the vasodilator effect of sodum nitroprusside (NP) or nitric oxide (NO).

Rabbit brain supernatant contained low (< 0.35 μm) concentrations of haemoglobin.

The inhibitory effect of rabbit brain supernatant was reversed by l‐arginine (500 μm) but not d‐arginine (500 μm).

The inhibitor of endothelium‐dependent vasodilatation present in rabbit brain was not removed by dialysis (24 h, 4°C) but was partially precipitated by ammonium sulphate (30% w/v).

Rabbit brain contains an endogenous inhibitor of vascular NO biosynthesis. The identity of this inhibitor is not known although it seems likely to be a large peptide or protein.
Role of eicosanoids in PAF‐induced increases of the vascular permeability in rat airways
Authors: Sirois M.G. , Plante G.E. , Braquet P. , Sirois P.
Published: July 2012

Platelet activating factor (PAF; 1.0 and 5.0 μg kg−1) injected in the tail vein of unanaesthetized rats dose‐dependently increased the vascular permeability of the trachea, upper and lower bronchi (up to 400%) as measured by the extravasation of Evans blue dye. The permeability of the parenchyma was not affected by PAF treatment.

Pretreatment of the animals with an intravenous injection of the PAF antagonist BN‐52021 (10 mg kg−1) abolished almost totally the vascular permeability changes elicited by PAF injection (5.0 μg kg−1).

Pretreatment of the animals with intravenous injections of inhibitors of thromboxane formation, indomethacin (10 mg kg−1) and compound OKY‐046 (10 mg kg−1), and thromboxane antagonist, compound L‐655,240 (5 mg kg−1), partially reduced PAF effects in the airways (from 28 to 69%). The thromboxane mimic U‐44069 (5.0 μg kg−1) did not modify the vascular permeability of rat airways. The effect of a low dose of PAF (0.1 μg kg−1) on the vascular permeability of the trachea and bronchi (but not of the parenchyma) was potentiated by compound U‐44069 (5.0 μg kg−1) or noradrenaline (400 ng kg−1) whereas the effect of a high dose of PAF (5.0 μg kg−1) was not affected.

Neither the peptidoleukotriene antagonist MK‐571 (10 mg kg−1) nor the 5‐lipoxygenase inhibitor, L‐663,536 (10 mg kg−1) given before the injection of PAF (5.0 μg kg−1) affected the protein extravasation in rat lung tissues.

These data suggest that the effect of PAF on rat vascular permeability is partly modulated by thromboxane formation although thromboxanes have no direct effect on the permeability. Thromboxane may act via a vasoconstriction that increases hydrostatic pressure and potentiates the extravasation elicited by PAF effect on endothelial cells.

Leukotrienes do not appear to be involved in the changes of rat airway permeability induced by PAF.
Differential effects of calcium antagonists and Bay K 8644 on contractile responses to exogenous noradrenaline and adrenergic nerve stimulation in the rabbit ear artery
Authors: Skärby Tor V. Ch. , Högestätt Edward D.
Published: July 2012

The effects of three calcium antagonists (nifedipine, verapamil, diltiazem) and the calcium agonist Bay K 8644 were compared on contractile responses of similar amplitude elicited by noradrenaline (NA) and electrical nerve stimulation (ENS) in the rabbit isolated ear artery.

Contractions induced by both NA (3 × 10−7 m) and ENS (10 Hz, 10 s) were almost exclusively mediated by α1‐adrenoceptors, since 10−7 m prazosin abolished (NA) or almost abolished (ENS) the responses, and prazosin was more than three orders of magnitude more potent than rauwolscine on both types of response.

ENS‐induced contractions were considerably less inhibited by nifedipine, verapamil and diltiazem than were those elicited by NA. Bay K 8644 enhanced responses to NA more than those to ENS.

The inhibitory effect of nifedipine and Ca2+ deprivation on NA‐induced contractions decreased with increasing NA concentration. Reduction of the NA response by prazosin or phenoxybenzamine increased the nifedipine inhibition.

Reduction of the ENS‐induced contractions by prazosin or phenoxybenzamine, or by use of a lower stimulation frequency did not increase the inhibitory effect of nifedipine.

In conclusion, the differential effects of the calcium antagonists on NA‐ and ENS‐induced contractions were not related to differences in α‐adrenoceptor subtype (α1/α2), receptor reserve or response amplitude, but may rather reflect temporal and spatial differences in α‐adrenoceptor activation between the responses.
Impaired induction of nerve ornithine decarboxylase activity in the streptozotocin‐diabetic rat is prevented by the aldose reductase inhibitor ponalrestat
Authors: Pekiner C. , McLean W.G.
Published: July 2012

The present study was designed to investigate if the aldose reductase inhibitor ponalrestat is capable of preventing the impairment of the response of ornithine decarboxylase (ODC) to nerve crush in streptozotocin (STZ)‐diabetic rats.

ODC activity was measured in the dorsal root ganglia of crushed and uncrushed contralateral sciatic nerve of non‐diabetic, ponalrestat‐treated non‐diabetic, STZ‐diabetic and ponalrestat‐treated STZ‐diabetic rats.

Twenty four hours after crush, a significant (P > 0.001) increase in the ratio of ODC activity in ganglia of crushed relative to uncrushed nerves was found in non‐diabetic but not in diabetic rats, as expected. In the ponalrestat‐treated diabetic rats the ratio was significantly higher (P > 0.001) than that in the untreated diabetic rats and was not different from that in the non‐diabetic group.

Ponalrestat also significantly decreased absolute levels of ODC activity in ganglia of uncrushed nerves from diabetic and non‐diabetic animals. Despite the near‐normal induction of ODC activity by nerve crush in the ponalrestat‐treated diabetic animals, absolute ODC activity remained lower than that in ganglia of uncrushed nerves from non‐diabetics.

We conclude that ponalrestat is able to prevent the impaired induction of ODC in experimental diabetes. The results, however, call into question the relationship between impaired ODC induction and diabetes‐induced defects in nerve regeneration, which are insensitive to ponalrestat.
Synaptosomal tryptophan uptake and efflux following lesion of central 5‐hydroxytryptaminergic neurones
Authors: Wilkinson Lawrence S. , Collard Keith J.
Published: July 2012

This study attempted to determine whether the activation of the tryptophan carrier in rat forebrain synaptosomes caused by depolarization or by extracellular sodium depletion occurred exclusively in 5‐hydroxytryptaminergic nerve endings.

Ascending 5‐hydroxytryptaminergic neurones were lesioned either electrolytically or by intraventricular administration of 5,7‐dihydroxytryptamine. The extent of the lesion was assessed by comparing the uptake of [3H]‐5‐hydroxytryptamine (5‐HT) in lesioned animals and in sham‐operated controls. [3H]‐5‐HT uptake was reduced by 85.9 ± 1.63% (mean ± s.e.mean) in animals receiving electrolytic lesions, and by 87.4 ± 4.51% in those receiving 5,7‐dihydroxytryptamine.

The uptake of [3H]‐tryptophan by synaptosomes from lesioned animals incubated in standard Na+‐rich media was slightly lower (278.8 ± 27.3 pmol mg−1 protein min−1) than that observed in sham‐operated controls (360.6 ± 30.3 pmol mg−1 protein min−1). However, uptake in the absence of extracellular Na+ was increased to a similar extent in both the sham‐operated (539 ± 54.5 pmol mg−1 protein min−1) and lesioned animals (507.2 ± 42.4 pmol mg−1 protein min−1).

The efflux of [3H]‐tryptophan in response to extracellular Na+ depletion was similar in sham‐operated and lesioned animals. Release expressed as a percentage of tissue [3H]‐tryptophan released in response to the pulse of Na+‐free medium was 6.691 ± 0.585 (n = 4) in sham‐operated controls and 8.195 ± 0.906 in lesioned animals.

The efflux of [3H]‐tryptophan in response to K+ depolarization was also unchanged in lesioned animals when compared with sham‐operated controls. Release, expressed as described above was, in sham‐operated controls 3.76 ± 0.41 (n = 4) and 4.09 ± 0.30 in lesioned animals.

The results of this study show that the tryptophan carrier which is activated by depolarization or by extracellular Na+ depletion is not located exclusively on 5‐hydroxytryptaminergic nerve endings. Moreover the contribution made by 5‐hydroxytryptaminergic neurones appears to be only minor.
Impairment of pulmonary endothelium‐dependent relaxation in patients with Eisenmenger's syndrome
Authors: Xuan A.T. Dinh , Higenbottam T.W. , Clelland C. , Pepke‐Zaba J. , Cremona G. , Wallwork J.
Published: July 2012

A comparison has been made between the endothelium‐dependent relaxation of pulmonary arteries (PA) obtained at heart‐lung transplantation from 4 patients with Eisenmenger's syndrome and secondary pulmonary hypertension, and PA obtained at lobectomy from 4 patients with lung carcinoma, the controls. All vascular rings were studied immediately after lung excision. PA rings from control patients dose‐dependently relaxed to cumulative doses of acetylcholine (ACh, 10−10 to 10−5 m), achieving a maximal relaxation of 80 ± 5% (mean ± s.e.mean) from precontraction with phenylephrine. By contrast, PA rings from Eisenmenger's syndrome patients achieved a maximal relaxation of only 34 ± 12% (P < 0.05, unpaired t test), with even paradoxical contraction at high doses of ACh (10−6 to 10−5 m). Sodium nitroprusside (10−4 m) relaxed all PA rings, with and without endothelium (carefully removed before study), obtained from both control and Eisenmenger's syndrome patients. These results provide the first evidence that endothelium‐dependent relaxation of PA mediated by endothelium‐derived relaxing factors is impaired in Eisenmenger's syndrome patients with secondary pulmonary hypertension.
The effects of Ca2+ antagonists and hydralazine on central 5‐hydroxytryptamine biochemistry and function in rats and mice
Authors: Green A.R. , DeSouza R.J. , Davies E.M. , Cross A.J.
Published: July 2012

The effects of calcium antagonists on behaviour mediated by 5‐hydroxytryptamine (5‐HT) have been studied in rats and mice together with an investigation of the effects of these drugs on 5‐HT synthesis in rat brain and endogenous 5‐HT release from brain slices.

Administration of felodipine (35 mg kg−1 i.p.) to rats pretreated with tranylcypromine (20 mg kg−1, i.p.) resulted in the animals displaying the complete 5‐HT‐mediated behavioural syndrome (including head weaving, reciprocal forepaw treading and hind limb abduction) 75 min later. No evidence was obtained for the rate of 5‐HT synthesis in brain regions differing between control and felodipine‐treated rats.

Pretreatment with felodipine (10 or 35 mg kg−1) enhanced the 5‐HT‐mediated behavioural syndrome induced by injection of tranylcypromine and l‐tryptophan. The rate of 5‐HT accumulation in the brain was similar in both groups. Administration of Bay K 8644 (1 mg kg−1, i.p.) did not prevent the enhanced behaviour induced by felodipine (10 mg kg−1).

The 5‐HT behavioural syndrome induced by injection of the 5‐HT1A agonist 8‐hydroxy‐2‐(di‐n‐propylamino)tetralin (8‐OH‐DPAT) was unaltered by either acute injection of felodipine (35 mg kg−1) or administration of felodipine twice daily for 3 days.

Felodipine (10 μm), verapamil (10 μm) and Bay K 8644 (10 μm) did not alter either basal release of endogenous 5‐HT from slices prepared from frontal cortex or hind brain, or release following addition of K+ at a concentration of 20 mm, or 35 mm.

Verapamil (25 mg kg−1, i.p.), nicardipine (25 mg kg−1, i.p.) and nifedipine (20 mg kg−1, i.p.) all markedly inhibited the 5‐HT2 receptor‐mediated head twitch response in mice produced by injection of 5‐methoxy‐N,N‐dimethyl‐tryptamine (5‐MeODMT). Felodipine had the same effect with an ED50 of 2.6 mg kg−1. Bay K 8644 did not reverse this effect. Both verapamil (IC50:2.5 μm) and nicardipine (IC50:8 μm) were 5‐HT2 antagonists as indicated by inhibition of [3H]‐ketanserin binding in mouse frontal cortex. However felodipine and nifedipine antagonized 5‐HT2 receptor binding only in the millimolar range.

Hydralazine (5 mg kg−1, i.p.) induced the 5‐HT behavioural syndrome in tranylcypromine pretreated rats, enhanced the tranylcypromine/l‐tryptophan behavioural syndrome, inhibited 5‐MeODMT‐induced head twitch behaviour in mice and was not a 5‐HT2 receptor antagonist.

These data indicate that at a high dose, Ca2+ antagonists produce complex changes in 5‐HT function in rodents which are similar to those produced by lithium administration. The data with hydralazine suggest that the effects seen are not related to an action at Ca2+ channels.
Effects of basal and acetylcholine‐induced release of endothelium‐derived relaxing factor on contraction to α‐adrenoceptor agonists in a rabbit artery and corresponding veins
Authors: McGrath J.C. , Monaghan S. , Templeton A.G.B. , Wilson V.G.
Published: July 2012

The effects of an endothelium‐dependent (acetylcholine) and an endothelium‐independent (sodium nitroprusside) relaxant against noradrenaline‐induced contractions were compared in three isolated superficial blood vessels of the rabbit, the lateral saphenous vein, plantaris vein and distal saphenous artery. Both produced concentration‐related relaxations of all three vessels and were more effective against sub‐maximal than maximal contractions to noradrenaline. Transient contractions to high concentration of acetylcholine occurred only in endothelium‐intact preparations of saphenous vein and were inhibited by flurbiprofen.

In endothelium‐denuded preparations sodium nitroprusside was 3 times more effective than in endothelium‐intact preparations, while acetylcholine (< 3 μm) was inactive. Sensitivity was similar for each relaxant: lateral saphenous vein ≥ plantaris vein > distal saphenous artery. The similar profile of sodium nitroprusside and acetylcholine suggests that differences in susceptibility to endothelium‐derived relaxing factor (EDRF) are caused by inter‐vessel variations in the excitation‐coupling process for noradrenaline.

Haemoglobin inhibited acetylcholine‐induced relaxations in the endothelium‐intact preparation of the lateral saphenous vein and distal saphenous artery, which suggests a similar EDRF in each preparation and the likelihood that this is a single substance, presumably nitric oxide.

The influence of basal, spontaneously released EDRF on α‐adrenoceptor function was tested either by mechanical disruption of the endothelium or by adding haemoglobin to endothelium‐intact segments. Endothelial disruption slightly reduced contractions to noradrenaline (NA) in distal saphenous artery but increased response size of lateral saphenous and plantaris veins, in the latter also increasing sensitivity to NA: haemoglobin mimicked endothelial disruption. Thus, basal release of EDRF like acetylcholine and nitroprusside was more effective in the veins than in the corresponding artery.

In lateral saphenous vein responses to phenylephrine were enhanced by endothelial disruption, but without change in sensitivity: responses to UK‐14304, B‐HT 920 and cirazoline, which had a relatively slow speed of onset of contraction were not affected. There was no correlation between enhancement and α‐adrenoceptor sub‐type although the agonists which were enhanced all activate α1‐adrenoceptors. Competitive antagonists failed to reveal an α‐adrenoceptor subtype enhanced by endothelial disruption. However, effects of phenoxybenzamine suggest that α1‐adrenoceptors are necessary for the influence of basal EDRF.
The combined electrophysiological effects of lignocaine and sotalol in canine isolated cardiac Purkinje fibres are rate‐dependent
Authors: Lathrop David A. , Varró András
Published: July 2012

The frequency‐dependent electrophysiological effects of lignocaine, sotalol, and their combination were studied in dog isolated cardiac Purkinje fibres, both at various constant rates of stimulation and following abrupt changes in pacing cycle length.

The combined effect of 18 μm lignocaine and 30 μm sotalol selectively lengthened duration of premature action potentials evoked at a diastolic interval of 40 ms (from 172.2 ± 5.4 to 201.7 ± 4.9 ms, n = 6, P > 0.01) without significantly changing the durations of action potentials evoked at the basic cycle length of 500 ms (259.1 ± 7.7 vs 251.9 ± 3.9 ms, n = 11).

The combination of lignocaine with sotalol, like lignocaine alone, displayed a use‐dependent depression of and revealed a slow component for a recovery of (τ = 173.5 ± 16.0 ms, n = 5).

The kinetics for restitution of action potential duration were also slowed by the combination of the two dwo drugs (τf = 173.6 ± 16.7, before, vs 268.5 ± 8.5 ms, after; n = 5, P > 0.01), while the maximum action potential duration attained in this relation was not increased as it was by sotalol alone.

Lignocaine, therefore, appeared to inhibit the sotalol‐induced lengthening of action potential duration at slow pacing rates and at long diastolic intervals. The combination of lignocaine with sotalol also completely abolished the occurrence of sotalol‐induced early afterdepolarizations.

Finally, sotalol alone moderately increased the range of premature action potential durations, while the combination of the two drugs significantly decreased this parameter.

These findings indicate that the combination of lignocaine with sotalol may provide important, and unique, beneficial electrophysiological alterations that might be expected to provide enhanced antiarrhythmic efficacy in patients.
Dual effects of capsaicin on responses of the rabbit ear artery to field stimulation
Authors: Moritoki Hideki , Takase Hideshi , Tanioka Asao
Published: July 2012

The effects of capsaicin (Cap) on contractions of ring segments of rabbit ear artery induced by field stimulation were studied.

At low concentrations (0.3–3 μm) Cap caused transient enhancement and at higher concentrations (above 3 μm) inhibition of stimulation‐induced contractions, without affecting noradrenaline (NA)‐induced contractions.

In the continuous presence of high concentrations of Cap, rebound facilitation was observed after inhibition, and at this stage, Cap elicited less inhibition of the response.

Repeated application of Cap at 60 min intervals irreversibly desensitized the artery to the inhibitory effect of Cap.

Functional removal of the endothelium enhanced the facilitatory effect of low concentrations of Cap and attenuated its inhibitory effect.

Pretreatment with indomethacin abolished the facilitatory effect of Cap and enhanced its inhibitory effect, indicating that prostaglandins are involved in the action of Cap. The effect of indomethacin was more marked in preparations from which the endothelium had been removed.

Desensitization to substance P (SP) or substance K (SK), did not affect either the inhibitory or the facilitatory effect of Cap.

These results suggest that the dual effects of Cap on stimulation‐induced contractions of rabbit ear artery may arise from the release of multiple mediators that act prejunctionally to modulate NA release. The stimulant effect seems to be mediated by prostanoids, while the inhibitory effect seems to be caused by a substance(s) that is not SP or SK. The possibility that the mediator is calcitonin gene‐related peptide requires further study.
Effect of the nootropic drug oxiracetam on field potentials of rat hippocampal slices
Authors: Pugliese Anna Maria , Corradetti Renato , Ballerini Laura , Pepeu Giancarlo
Published: July 2012

The effect of the nootropic drug oxiracetam on hippocampal neurotransmission was investigated in the CA1 region of the rat hippocampal slice in vitro by use of extracellular recordings.

Superfusion of oxiracetam (0.1–100 μm) produced a concentration‐dependent, wash‐resistant (>90 min), increase in initial slope and amplitude of the dendritic field excitatory postsynaptic potential (e.p.s.p.). This increase was maximal at a concentration of 1 μm (70%).

Input‐output curves relating the initial slope to the amplitude of the afferent volley were significantly (P < 0.05) steeper and showed a greater maximal response in the presence of 1 μm oxiracetam than in control conditions.

Two trains of high frequency stimulation (100 Hz, 0.4 s, 5 min apart) delivered in the stratum radiatum 30 min after washout of oxiracetam (1 μm) still elicited a long‐term potentiation (LTP) of the field e.p.s.p. However, the absolute magnitude of the LTP produced did not differ from that obtained in untreated slices.

After induction and establishment of LTP, oxiracetam (1 μm) had a smaller (27%) and reversible effect on the evoked field e.p.s.p.

d‐2‐Amino‐5‐phosphonopentanoic acid (AP‐5), at the same concentration (50 μm) which in our conditions prevented the induction of LTP, blocked the action of 1 μm oxiracetam and strongly depressed the effect of higher concentrations of the nootropic drug.

It is concluded that oxiracetam provokes an enduring increase of neurotransmission in the CA1 rat hippocampal region. This action appears to share some features with LTP as indicated by its persistence, sensitivity to AP‐5 and lack of additivity with electrically‐induced LTP.
The effects of pyrogallol and hydroquinone on the response to NANC nerve stimulation in the rat anococcygeus and the bovine retractor penis muscles
Authors: Gillespie John S. , Sheng Hong
Published: July 2012

The effects of pyrogallol and hydroquinone on the bovine retractor penis (BRP) and rat anococcygeus muscles to non‐adrenergic, non‐cholinergic (NANC) nerve stimulation have been examined. Both drugs at a concentration of 10−4 m significantly reduced the response in the rat anococcygeus muscle but had no effect in the BRP muscle.

The inhibition of the NANC response in the rat anococcygeus muscle by pyrogallol was completely reversed by superoxide dismutase suggesting it was due to the generation of superoxide anions.

Pyrogallol inhibited the response to nitric oxide (NO) in the rat anococcygeus muscle but not that to 3‐isobutyl‐1‐methyl‐xanthine (IBMX) which confirmed a selective action.

These results suggest that the NANC neurotransmitter in the rat anococcygeus muscle is susceptible to superoxide anions and may be NO or a substance that can liberate NO.
Effects of a selective 5‐HT2 agonist, DOI, on 5‐HT neuronal firing in the dorsal raphe nucleus and 5‐HT release and metabolism in the frontal cortex
Authors: Wright Ian K. , Garratt Jeni C. , Marsden C.A.
Published: July 2012

Systemic administration of the 5‐HT2 agonist 1‐(2,5‐dimethoxy‐4‐iodophenyl)‐2‐aminopropane (DOI) (50 and 100 μg kg−1, i.v.) inhibited dorsal raphe neuronal firing. DOI (100 μg kg−1, i.v.) also produced a decrease in extracellular 5‐hydroxytryptamine (5‐HT) and 5‐hydroxyindoleacetic acid (5‐HIAA) in the frontal cortex measured by microdialysis. However, local administration of DOI into the frontal cortex produced no change in extracellular 5‐HT and 5‐HIAA at any dose given (1, 10 and 100 ng). The results demonstrate that DOI is a potent inhibitor of 5‐HT neuronal firing and terminal release and that the effects on release are not mediated by an action within the terminal region. The site of action and the receptor involved in the inhibition remains to be determined.
Caffeine acting on pregnant rat myometrium: analysis of its relaxant action and its failure to release Ca2+ from intracellular stores
Authors: Savineau Jean‐Pierre , Mironneau Jean
Published: July 2012

The effect of caffeine on mechanical activity was studied in pregnant rat myometrium.

In muscle cells with intact plasmalemmae, caffeine (0.1–50 mm) produced no contraction whatever the experimental conditions.

Caffeine (0.1–10 mm) inhibited, in a concentration‐dependent manner, contractions induced by electrical stimulation, potassium‐rich (60 mm K+) solution, sodium‐free solution or oxytocin (22.5 nm).

In Ca2+‐free solution, various substances (oxytocin, sodium orthovanadate and prostaglandin E2) evoked sustained contractions that were suppressed by caffeine (5–10 mm). When caffeine (> 5 mm) was applied during Ca2+‐loading of the tissue (2.1 mm Ca2+, 5 min) in the presence of a K+‐rich solution, the subsequent transient contraction induced by a short application (10 s) of oxytocin (22.5 nm) in Ca‐free solution was reduced (63 ± 3.5% reduction for 20 mm caffeine, n = 4).

In saponin‐skinned strips, application of caffeine (5–10 mm) during loading of the Ca2+‐store increased the subsequent contraction induced by myo‐inositol 1,4,5 trisphosphate (IP3, 10 μm). Caffeine (10–30 mm) decreased calcium‐activated contractions in skinned fibres lacking a functional internal Ca‐store. This effect was reduced by the cyclic AMP‐dependent protein kinase inhibitor Thr‐Thr‐Tyr‐Ala‐Asp‐Phe‐Ile‐Ala‐Ser‐Gly‐Arg‐Thr‐Gly‐Arg‐Arg‐Asn‐Ala‐Ile‐His‐Asp (8 μm).

In conclusion, it is suggested that the inability of caffeine to cause spasm of rat myometrium is due to the absence of a caffeine‐sensitive calcium‐release channel in the sarcoplasmic reticulum. Relaxant effects of caffeine can be explained by mechanisms leading to a decrease in both the cytoplasmic free Ca2+ concentration and the Ca2+‐sensitivity of the contractile machinery.
Characterisation of stereospecific binding sites for inositol 1,4,5‐trisphosphate in airway smooth muscle
Authors: Chilvers E.R. , Challiss R.A.J. , Willcocks A.L. , Potter B.V.L. , Barnes P.J. , Nahorski S.R.
Published: July 2012

A ‘P2’ membrane fraction of bovine tracheal smooth muscle displays high affinity (KD 3.8 ± 0.2 nm), saturable (Bmax 1003 ± 170 fmol mg−1 protein) and reversible binding of d‐myo[3H]‐inositol 1,4,5‐trisphosphate ([3H]‐Ins(1,4,5)P3).

This binding site shows strict stereo‐ and positional specificity for the d‐Ins(1,4,5)P3 isomer with l‐Ins(1,4,5)P3, dl‐Ins(1,3,4,5)P4 and d‐Ins(1,3,4)P3 displacing [3H]‐Ins(1,4,5)P3 with Ki values of 20 μm, 0.35 μm and 2.4 μm, respectively.

Specific binding of [3H]‐Ins(1,4,5)P3 is enhanced at alkaline pH values (maximal at pH 7.75) and, in distinct contrast to [3H]‐Ins(1,4,5)P3 binding in rat cerebellum membranes, is not inhibited by Ca2+ (5–500 μm).

Heparin displaces [3H]‐Ins(1,4,5)P3 specific binding with an IC50 of 7.6 ± 1.0 μg ml−1.

Comparative studies demonstrated specific [3H]‐Ins(1,4,5)P3 binding in bovine cardiac atrial preparations (Bmax 75 ± 5 fmol mg−1 protein) and very low specific [3H]‐Ins(1,4,5)P3 binding in bovine cardiac ventricle and skeletal muscle membranes (≤ 25 fmol mg−1 protein).
The action of atriopeptin III on renal function in two models of chronic renal failure in the rat
Authors: Johns Edward J. , Rutkowski Bolesław
Published: July 2012

The natriuretic and diuretic effects of atriopeptin III (125, 250 and 500 ng kg−1, i.v.) were studied in groups of rats anaesthetized with pentobarbitone which were either sham controls, unilaterally nephrectomized controls, adenine‐fed or subtotal nephrectomy chronic renal failure models.

Atriopeptin III given at these doses to the sham control animals had no effect on blood pressure, renal blood flow or glomerular filtration rate but reversibly increased urine flow, between 46% to 54%, absolute sodium excretion, between 52% to 61%, and fractional sodium excretion, between 48% to 54% (all P values <0.05) from the lowest to the highest dose. The adenine‐fed chronic renal failure group of rats had a reduced renal blood flow of between 30 and 75%, and glomerular filtration rate of approximately 20%, compared to the sham controls. Administration of atriopeptin at 125, 250 and 500 ng kg−1 to the animals with renal failure increased water and sodium excretion to the same degree as observed in the sham group of rats.

In the group of unilaterally nephrectomized rats, atriopeptin III, at 125, 250 and 500 ng kg−1 increased urine flow by 36%, 47% and 72%, respectively, absolute sodium excretion by 37%, 57% and 106%, respectively, and fractional sodium excretion by 46%, 45% and 102%, respectively. A similar pattern of responses was observed in the subtotal nephrectomy, chronic renal failure group in which filtration rate was approximately 4 times less than the controls. Although the magnitude of the urine flow and absolute sodium excretion responses were the same, the increases in fractional sodium excretion were all significantly larger than in the unilaterally nephrectomized control group.

These results show that in two different models of chronic renal failure, atriopeptin III still caused a natriuresis and diuresis. This suggests that the nephrons retain sensitivity to the atrial natriuretic peptides in diseases such as chronic renal failure and that these compounds may be useful in mobilizing body fluids in this situation.
The role of the endothelium in mediating the actions of ATP, adenosine and acetylcholine on flow through blood vessels in the rabbit knee joint
Authors: Ferrell W.R. , Khoshbaten A.
Published: July 2012

An in vitro preparation of the rabbit knee joint, perfused with oxygenated Locke solution, was used to investigate the presence of purinoceptors and the role of endothelium within articular blood vessels.

The basal tone of the blood vessels was not affected by adenosine or acetylcholine. Adenosine 5′‐triphosphate (ATP) injection produced vasoconstriction which was unaffected by removal of the endothelial layer, but diminished by α, beta methylene ATP, a compound which desensitizes P2‐purinoceptors.

When knee joint blood vessel tone was raised by perfusion with vasopressin (10−8m) or 5‐hydroxytryptamine (10−5 m), acetylcholine, ATP and adenosine were all found to induce concentration‐dependent relaxation of these vessels. ATP was found to have a dual effect of transient constriction followed by longer‐lasting dilatation.

3‐Methylxanthine, a P1‐purinoceptor antagonist significantly reduced the relaxation response to adenosine but had no effect on the vasodilator effect of ATP.

Removal of the endothelial layer virtually abolished the vasodilator effects of acetylcholine and ATP but not adenosine.

These results demonstrate that articular blood vessels supplying the rabbit knee contain P1‐purinoceptors located on the vascular smooth muscle which mediate vasodilatation. P2‐purinoceptors mediating a constrictor effect are also present on this smooth muscle. It is likely that the vasodilator effect of ATP is mediated via P2‐purinoceptors located on the endothelial layer.
Specific but differential antagonism by glibenclamide of the vasodepressor effects of cromakalim and nicorandil in spinally‐anaesthetized dogs
Authors: Yamada Hiroaki , Yoneyama Fumiya , Satoh Keisuke , Taira Norio
Published: July 2012

Whether the vasodepressor effects of cromakalim and nicorandil, potassium channel openers, were differentially antagonized by glibenclamide, a supposed specific antagonist of potassium channel openers, was investigated in spinally‐anaesthetized dogs in which arterial pressure was maintained elevated by i.v. infusion of noradrenaline.

Cumulative administration of cromakalim (3–100 μg kg−1, i.v.), nicorandil (30–1000 μg kg−1, i.v.), diltiazem (3–300 μg kg−1, i.v.) and nitroglycerin (0.3–100 μg kg−1, i.v.) caused dose‐dependent decreases in mean arterial pressure. In dogs which received glibenclamide (3 mg kg−1, i.v.), the dose‐vasodepressor response curves for cromakalim and nicorandil were located on the right in parallel to the respective curves determined in control dogs, but those for diltiazem and nitroglycerin were not different. ED50% values increased about 6.7 fold for cromakalim and 2.2 fold for nicorandil.

The depression of LV dP/dtmax produced by a high dose of cromakalim (100 μg kg−1 i.v.) was abolished by glibenclamide and that produced by nicorandil was not only antagonized but converted to an increase.

These results suggest that the vasodepressor action of cromakalim is due predominantly to potassium channel opening, but that of nicorandil involves not only potassium channel opening but its action as a nitrate.