bluuebunny/crossref_metadata_2025 huggingface dataset:
Differences in sensitivity of rat mesenteric small arteries to agonists when studied as ring preparations or as cannulated preparations
Authors: Buus N.H. , VanBavel E. , Mulvany M.J.
Published: July 2012

Pharmacological experiments on vascular tissue are normally performed on isometric ring or strip preparations. The aim of this study was to compare the isometric characteristics with the characteristics obtained if vessels were examined under the more physiologically appropriate isobaric condition.

Rat mesenteric small arteries were mounted either on two steel wires for isometric force measurement (wire‐myograph) or cannulated for measurement of the internal diameter under isobaric conditions (pressure‐myograph).

The passive pressure‐diameter characteristics of the small arteries were similar on the wire‐ and pressure‐myograph (using the Laplace relation to convert wall tension‐internal circumference data from the wire‐myograph to effective pressure‐diameter characteristics).

In cumulative concentration‐response experiments with noradrenaline and phenyelphrine, the threshold concentration was 8–10 times lower, and the EC50‐concentration was 4–5 times lower, in the pressure myograph compared to the wire‐myograph. Thus vessels were not only more sensitive on the pressure myograph, but the slopes of the concentration‐response curves were less steep. Similar experiments with vasopressin also showed this difference in the threshold‐concentration and slope, but EC50 concentrations were similar.

Cumulative concentration‐response experiments with K+ showed no difference either in EC50 or in slope on the wire‐ and pressure‐myographs.

On the wire‐myograph, some vessels were stretched longitudinally (to mimic the longitudinal stretch which had to be used in the pressure‐myograph to avoid buckling). Such stretch did not affect the passive characteristics.

The differences between the EC50 determined on the wire‐ and pressure‐myographs as regards noradrenaline and phenylephrine were eliminated when neuronal noradrenaline uptake was inhibited by denervation. However, the slope of the concentration‐response curves on the wire‐myograph was not affected by denervation.

When vessels were exposed to cocaine (3 μm) the noradrenaline concentration‐response curves were the same on the wire‐ and pressure‐myographs as regards both EC50 and slope.

On the wire‐myograph, the calcium antagonist, methoxyverapamil, (D600) reduced the maximal contractile effect of noradrenaline by 50%, but on the pressure‐myograph D600 did not affect the maximal response.

The present results show that results obtained from vascular tissue under isometric conditions may differ substantially from the characteristics which would be obtained under isobaric conditions.
Sensitivity to protein kinase C inhibitors of nicardipine‐insensitive component of high K+ contracture in rat and guinea‐pig aorta
Authors: Low A.M. , Loke J.C.P. , Kwan C.Y. , Daniel E.E.
Published: July 2012

In the rat and guinea‐pig aorta, we observed that the contraction to hypertonically‐added K+, unlike the isotonic K+‐induced contraction, was only partially sensitive to nicardipine (0.1, 1 and 10 μm), an L‐type Ca2+ channel blocker and occurred in Ca2+‐free medium containing 50 μm EGTA. We have characterized this nicarpidine‐insensitive hypertonically‐added K+ contraction.

The contraction induced by an equi‐osmolar concentration of mannitol was similar in size to that evoked by hypertonically‐added K+.

When the tissue was depleted of its internal Ca2+ stores with various agents such as phenylephrine (10 μm), cyclopiazonic acid (30 μm), thapsigargin (1 μm) or ryanodine (30 μm), or by incubation in Ca2+‐free medium over 30 min, little effect was observed on the high K+ contracture in the presence of L‐type Ca2+ channel blockade.

Phentolamine (10 μm) or indomethacin (10 μm) did not reduce the contraction induced by high K+.

Application of a protein kinase C inhibitor, H7 (10, 30 and 100 μm) or calphostin C (1 μm), reduced the high K+ contraction but not that caused by an equi‐osmolar concentration of mannitol.

The data suggest that hypertonic K+‐induced contraction differs from that caused by hypertonicity or depolarization per se and invokes membrane enzyme activation.
Measurement and pharmacokinetic analysis of imipramine and its metabolite by brain microdialysis
Authors: Sato Yuji , Shibanoki Shinji , Sugahara Megumi , Ishikawa Koichi
Published: July 2012

The feasibility of the brain microdialysis method for direct measurement and pharmacokinetic study of imipramine (Imip) and its metabolite desipramine (DMI) was investigated in the rat brain.

A dialysis tube was inserted into the right striatum of male Wistar rats, which were administered i.p. with 12.5 mg kg−1 Imip. Thirty μl dialysate was collected every 15 min, and the levels of Imip and DMI were measured by high‐performance liquid chromatography with electrochemical detection (h.p.l.c.–e.c.d.). SKF‐525A and aminopyrine were concomitantly administered in order to assess their respective effects on the pharmacokinetics of Imip and DMI in the brain.

The intracerebral half life (t1/2) of Imip was 2.4 ± 0.3 h with Imip alone. Premedication with SKF‐525A, an inhibitor of drug‐metabolizing enzymes, significantly prolonged the t1/2 of Imip, while at the same time production of DMI from Imip was accordingly inhibited. Concomitant administration of aminopyrine did not induce any significant change in the concentrations of Imip, but significantly inhibited the concentrations of DMI through its competitive antagonism in the demethylation pathway.

The present results suggest that the brain microdialysis method reflects the intracerebral pharmacokinetics of Imip and DMI well and may be applicable to further pharmacokinetic investigations of psychotropic agents.
Effects of isocarbacyclin, a stable prostacyclin analogue, on monkey isolated cerebral and peripheral arteries
Authors: Kawai Yasuaki , Ohhashi Toshio
Published: July 2012

The effects of isocarbacyclin (TEI 7165), a stable prostacyclin analogue, were examined in monkey isolated cerebral and peripheral arteries.

Addition of TEI 7165 (0.1 nm‐10 μm) produced a dose‐dependent relaxation in cerebral arteries pre‐contracted with 1 μm 5‐hydroxytryptamine (5‐HT). High concentrations (more than 1 μm) of TEI 7165 elicited a transient contraction followed by a sustained relaxation.

TEI 7165 also elicited a dose‐dependent relaxation in the peripheral (except popliteal) arteries. The maximum relaxation induced by 10 μm TEI 7165 was greater (P < 0.05) in the mesenteric artery than in the cerebral artery. The negative logarithm of the EC50 value for the mesenteric, 7.6 ± 0.3, was greater (P < 0.05) than that for the cerebral artery, 6.4 ± 0.3. The decreasing order of potency for the TEI 7165‐induced relaxation was as follows: mesenteric > renal > cerebral > coronary > popliteal.

Removal of the endothelium did not significantly affect TEI 7165‐induced relaxations.

The transient contraction produced by high concentrations of TEI 7165 was not observed in cerebral arteries precontracted with 1 nm U46619, a stable analogue of thromboxane A2 (TXA2). Furthermore, the TEI 7165‐induced contraction was markedly suppressed (P < 0.05) by treatment with 10 nm S1452, a TXA2 blocking agent.

These results suggest that TEI 7165 causes an endothelium‐independent relaxation in monkey cerebral and peripheral arteries, and that there is a marked regional difference in the TEI 7165‐induced relaxations. A high concentration of TEI 7165 also produces a transient contraction which is probably through activation of TXA2 (TP‐) receptors.
The differential effects of felodipine and nitrendipine on cerebral dihydropyridine binding ex vivo and the ethanol withdrawal syndrome in mice
Authors: Watson W.P. , Misra A. , Cross A.J. , Green A.R. , Little H.J.
Published: July 2012

The ability of two dihydropyridine calcium channel antagonists, felodipine and nitrendipine both to displace [3H]‐isradipine binding in CNS tissue measured ex vivo and to protect against the ethanol withdrawal syndrome has been investigated.

Mice were injected with various doses of felodipine or nitrendipine and [3H]‐isradipine binding measured in brain homogenates prepared 0.5, 3 or 5 h later. Inhibition versus dose curves were sigmoid and the dose required to produce 50% inhibition increased linearly with time after administration. Felodipine was approximately 10 times more potent than nitrendipine.

Nitrendipine (50 mg kg−1, i.p.) and felodipine (10 mg kg−1, i.p.) produced around a 75% inhibition of [3H]‐isradipine binding 3 h later. Binding of [3H]‐nitrendipine to cerebral tissues measured after in vivo injection of the ligand was decreased by nitrendipine (50 mg kg−1) and felodipine (10 mg kg−1) to a similar extent.

Nitrendipine (50 mg kg−1) prevented the behavioural signs of ethanol withdrawal as measured by handling induced convulsions, but felodipine (10 mg kg−1 or 2 mg kg−1) did not provide any protection against this effect of ethanol withdrawal. Felodipine (10 mg kg−1, twice daily) during the course of ethanol treatment also failed to attenuate the withdrawal syndrome.

The convulsive response to a mild audiogenic stimulus during ethanol withdrawal was increased following one dose of felodipine (5 mg kg−1, i.p.) but unaffected by nitrendipine.

Injection of Bay K 8644 (60 μg, i.c.v.) produced a significant increase in handling‐induced convulsive behaviour. Felodipine (10 mg kg−1, i.p.) reduced this behaviour both 60 and 120 min later, while nitrendipine (50 mg kg−1) showed a modest reduction only at 120 min.

In contrast, nitrendipine (50 mg kg−1) and felodipine (10 mg kg−1) produced similar effects on the hyperexcitability produced by handling following administration of bicuculline. Hexamethonium (8 mg kg−1) had no effect on this response.

No change was found in [3H]‐isradipine or [125I]‐ω‐conotoxin binding to cerebral tissue prepared from ethanol‐dependent mice.

These results demonstrate that while felodipine and nitrendipine have similar actions on some CNS‐mediated effects (raising seizure thresholds to several convulsant drugs), felodipine, in contrast to nitrendipine, has no effect on the ethanol withdrawal syndrome. Suggested explanations for the results include the possibility that nitrendipine may protect against the ethanol withdrawal syndrome via sites other than dihydropyridine receptors: that felodipine has partial agonist actions at dihydropyridine receptors in the CNS or that felodipine has actions which mask its protective effect in ethanol withdrawal.
Down‐regulation of bombesin binding to guinea‐pig pancreatic acinar cells during homologous desensitization
Authors: Sjödin L. , Gylfe E.
Published: July 2012

[125I]‐Tyr4‐bombesin exhibited saturable binding to pancreatic acinar cells.

Preincubation of cells at 37°C with 0.03 nM‐1 μm‐bombesin for 10 min followed by acid or neutral washes reduced subsequent binding of [125I]‐Tyr4‐bombesin in a concentration‐dependent manner by up to 90%.

In cell suspensions, bombesin raised the cytoplasmic Ca2+ concentration ([Ca2+]i) and the [Ca2+]i response was reduced by pre‐exposure to the agonist.

In individual superfused cells, bombesin at 1 nM normally caused a large [Ca2+]i transient followed by sustained [Ca2+]i oscillations. The cells exhibited a variable degree of desensitization when subsequently exposed to higher agonist concentrations.

Preincubation with bombesin for 10 min caused a concentration‐related reduction of subsequent amylase responses to bombesin.

Down‐regulation of receptor binding is a rapid phenomenon during bombesin exposure explaining, at least partially, tachyphylaxis of [Ca2+]i and amylase responses.
The imidazoline site involved in control of insulin secretion: characteristics that distinguish it from I1‐ and I2‐sites
Authors: Chan Susan L.F. , Brown Colin. A. , Scarpello Kay E. , Morgan Noel G.
Published: July 2012

The nature of the binding site mediating the insulin secretagogue activity of certain imidazoline compounds remains unclear and the pharmacology of the I1‐ and I2‐imidazoline sites, described in many tissues, does not correlate with the observed responses to imidazolines in islets. In the present paper, we describe further results which support the concept that the islet imidazoline site may represent a novel subtype of imidazoline receptor.

Culture of rat isolated islets in the presence of imidazoline secretagogues (either efaroxan or phentolamine) resulted in loss of responsiveness on subsequent re‐exposure to these agents. However, culture of islets with either idazoxan or UK 14,304 (imidazoline ligands that do not stimulate insulin secretion) did not lead to any loss of response when the islets were subsequently exposed to efaroxan. By contrast, islets cultured with UK 14,304 (a potent α2‐adrenoceptor agonist), displayed loss of sensitivity to noradrenaline, consistent with down‐regulation of α2‐adrenoceptors.

In order to characterize the imidazoline site further, radioligand binding studies were performed in membranes from RINm5F insulinoma cells using [3H]‐RX821002, an imidazoline insulin secretagogue that does not interact significantly with imidazoline sites in other tissues. [3H]‐RX821002 labelled α2‐adrenoceptors with high affinity (2.01 ± 0.7 nM) but also labelled a second, non‐adrenoceptor site with much lower affinity.

Under conditions of α2‐adrenoceptor blockade (in the presence of adrenaline), efaroxan displaced [3H]‐RX821002 binding to the low affinity site, in a dose‐dependent manner. Competition studies employing additional imidazoline compounds of varying secretagogue activity revealed that the pharmacological profile of the low affinity site correlates well with that observed in secretion experiments.

The results obtained from the down‐regulation experiments with isolated islets and from the radioligand binding studies suggest that the low affinity [3H]‐RX821002 binding site may represent the functional receptor responsible for the secretagogue activity of imidazoline compounds in the endocrine pancreas and that it has a pharmacological profile distinct from those of I1‐ and I2‐sites.
Adaptive changes in 5‐HT1A receptor‐mediated hippocampal inhibition in the alert rat produced by repeated 8‐OH‐DPAT treatment
Authors: Manahan‐Vaughan Denise , Anwyl Roger , Rowan Michael J.
Published: July 2012

The effect of acute and repeated treatment with 8‐hydroxy‐2‐(di‐n‐propylamino)tetralin (8‐OH‐DPAT), a 5‐HT1A receptor ligand, on excitatory amino acid‐mediated synaptic transmission was examined in the stratum radiatum CA1 region of the dorsal hippocampus of alert, gently restrained, rats.

Acute administration of 8‐OH‐DPAT transiently reduced the amplitude of the field excitatory postsynaptic potential (e.p.s.p.) in a dose‐dependent (25–75 μg kg−1, i.p.) manner. This effect was blocked by the postsynaptic 5‐HT1A receptor antagonist, MDL 73005EF (2 and 4 mg kg−1, i.p.).

8‐OH‐DPAT (25 μg kg−1, i.p.) administered daily for 7 days produced a gradual reduction in the 24 h pre‐injection baseline field e.p.s.p. amplitude. The reduction reached its lowest level after 7–8 days and was transiently reversed by acute injection of MDL 73005EF (2 mg kg−1, i.p.) on day 8. The field e.p.s.p. baseline amplitude recovered fully 5–8 days after cessation of drug treatment.

8‐OH‐DPAT (25 μg kg−1, i.p.) administered daily for 7 days produced a marked reduction in acute response to 8‐OH‐DPAT (25 and 50 μg kg−1, i.p.) which did not recover until between day 36 and day 80 of the study.

It was concluded that repeated treatment with 8‐OH‐DPAT produced adaptive changes which resulted in a reduction in the dynamic range of 5‐HT1A receptor‐mediated transmission in the hippocampus.
Sodium excretion following central administration of an I1 imidazoline receptor agonist, moxonidine
Authors: Penner S. Brian , Smyth Donald D.
Published: July 2012

Previously we have shown that an intrarenal infusion of moxonidine, an I1‐imidazoline receptor agonist, resulted in a natriuresis which was inhibited by intravenous idazoxan, a selective imidazoline receptor antagonist. Therefore we examined the effects on renal function of intracerebroventricular (i.c.v.) administration of moxonidine with or without i.c.v. idazoxan.

Seven days after unilateral nephrectomy, Sprague‐Dawley rats had i.c.v. cannulae implanted. Three days later the rats were anaesthetized (pentobarbitone), followed by cannulation of the jugular vein (fluid and drug administration), carotid artery (blood pressure) and the ureter (urine collection).

After a 45 min stabilization period, the effect of moxonidine was investigated by the i.c.v. administration of either isotonic saline or moxonidine (0.1, 0.3 or 1 nmol in isotonic saline) administered in 5 μl over 1 min. All doses of moxonidine resulted in an increase in urine flow with a concomitant increase in sodium excretion without affecting blood pressure. The highest dose of moxonidine (1 nmol) also increased free water clearance.

In a second series of experiments, the effects of idazoxan on the natriuretic response to i.c.v. moxonidine were determined. Moxonidine (0.3 nmol) again increased sodium and water excretion as compared to the i.c.v. saline control animals. Pretreatment with i.c.v. idazoxan (0.3 nmol), at a dose which alone failed to alter sodium and water excretion, completely attenuated the renal response to moxonidine. These results are consistent with central I1‐imidazoline receptors mediating a moxonidine‐induced increase in sodium and water excretion at doses that do not alter blood pressure.
Study of the effector mechanism involved in the production of haemorrhagic necrosis of the small intestine in rat passive anaphylaxis
Authors: Pellón María Isabel , Steil Ana Angelica , Furió Vicente , Crespo Mariano Sánchez
Published: July 2012

The effector mechanism of intestinal necrosis in rat anaphylaxis was studied following several complementary approaches: (i) the use of monoclonal antibodies (mAb) belonging to different classes (IgG1, IgG2b and IgE anti‐DNP), (ii) the assay of mediators, and (iii) the use of pharmacological tools.

Lethality and haemorrhagic necrosis of the small intestine were observed in IgE‐sensitized rats, whereas IgG mAb produced milder physiological disturbances.

Inhibition of leukotriene biosynthesis reduced the drop of systemic blood pressure (BP) and the extent of protein‐rich plasma exudation but it did not influence the haemorrhagic component of intestinal necrosis.

The antihistamine, pyrilamine, partially diminished the haemorrhagic component of the intestinal necrosis.

The involvement of mediators related to platelet‐activating factor (PAF) was studied by examining the pharmacological effects of these autacoids and of PAF‐receptor antagonists (PCA4248, UR12460 and BB823). PAF induced intestinal lesions similar to those observed in IgE‐sensitized rats and PAF‐receptor antagonists markedly decreased haemorrhage in IgE‐sensitized rats.

PAF levels were transiently increased after dinitrophenol (DNP)‐ bovine serum albumin (BSA) challenge in the small intestine of IgE‐sensitized rats.

These data stress differences in the outcome of anaphylaxis related to the type of receptors for the Fc portion of immunoglobulins that are involved. IgE is the antibody class that elicits the most severe response due to the activation of mast cells via FceRI (surface receptors that bind IgE antibodies with high affinity), and the only one able to produce intestinal haemorrhagic necrosis.

The mast‐cell‐derived mediators PAF/acyl‐PAF and histamine, most probably associated with tumour necrosis factor α/cachectin (TNF‐α), seem to play a central role in the production of the vascular changes required for the extravasation of erythrocytes in the small intestine mucosa.
Modulatory effects of endothelin‐1 on purinergic and adrenergic components of sympathetically‐mediated contractile activity of rabbit saphenous artery
Authors: Mutafova‐Yambolieva Violeta N. , Radomirov Radomir G.
Published: July 2012

The present study has been performed to evaluate the modulatory effects of endothelin‐1 (ET‐1) on the purinergic and adrenergic components of sympathetically‐mediated contractile responses of endothelium‐free rabbit saphenous artery preparations.

ET‐1 increased the smooth muscle tone, the pD2 value being 7.77 ± 0.05.

Postjunctionally, ET‐1 enhanced the responses to exogenous adenosine 5′‐triphosphate (ATP) and did not influence those to exogenous noradrenaline (NA).

ET‐1 increased the contractile responses to short‐lasting and to long‐lasting electrical field stimulation at a frequency of 5 or 10 Hz, showing a tendency towards decreasing the prazosin‐sensitive component and increasing the mATP‐sensitive component of the contractile responses.

In prazosin‐treated preparations ET‐1 increased the residual mATP‐sensitive responses and this effect was more pronounced after yohimbine.

In mATP‐treated preparations ET‐1 increased the residual electrically‐induced contractions and this increase was abolished after yohimbine.

It is suggested that ET‐1 modulates co‐transmission in the rabbit saphenous artery by potentiating postjunctionally the purinergic component of the contractile responses to both exogenous ATP or electrical stimulation.
Heterogeneity of α1‐adrenoceptor subtypes involved in adrenergic contractions of dog blood vessels
Authors: Kohno Yoko , Saito Hitoshi , Takita Manabu , Kigoshi Shigeru , Muramatsu Ikunobu
Published: July 2012

We determined the α1‐adrenoceptor subtypes involved in adrenergic contractions of eight different blood vessels isolated from the dog.

Noradrenaline produced concentration‐dependent contractions in all the blood vessels tested, which were competitively inhibited by prazosin, WB4101, HV723 and 5‐methylurapidil. However, there was considerable difference between the vessels with regard to the pKB values for all the antagonists. The α1‐adrenoceptors of dog vertebral and carotid arteries had high affinity for prazosin (pKB > 9.0) but low affinity for WB4101 (< 8.5), 5‐methylurapidil (< 7.5) and HV723 (≤ 8.5). By contrast, HV723 had higher affinity (> 9.0) than prazosin (< 8.3), WB4101 (< 8.7) and 5‐methylurapidil (< 8.2) in the portal vein, mesenteric artery and vein, and renal artery. In the femoral artery and vein, however, the four antagonists showed pKB values in the range 8.0–8.7.

Chloroethylclonidine (10 μm) produced a remarkable reduction of the contractile responses to noradrenaline in the vertebral and carotid arteries as compared with those in the other vessels. Nifedipine inhibited the responses to noradrenaline in all the tissues tested, and had marked effects in the portal vein.

Sympathetic adrenergic contractions induced by transmural electrical stimulation were also inhibited by prazosin and HV723 at different potencies among tissues. The relative potencies of both the antagonists paralleled the relationship in inhibiting the responses to exogenous noradrenaline in each vessel.

According to recent α1‐adrenoceptor subclassification, the present results suggest that the contractions of blood vessels induced by endogenous and exogenous noradrenaline are mediated through different α1‐adrenoceptor subtypes heterogeneously distributed in each vessel; presumably, the α1B subtype in the carotid and vertebral arteries, the α1N subtype in the visceral region and the α1L subtype in the femoral region. Regionally different expression of α1‐adrenoceptor subtypes may be in part associated with the regional heterogeneity of sympathetic responses in the blood vessels.
Characterization of the angiotensin II AT1 receptor subtype involved in DNA synthesis in cultured vascular smooth muscle cells
Authors: Briand V. , Riva L. , Galzin A.M.
Published: July 2012

This study was undertaken in cultured vascular smooth muscle cells to characterize the angiotensin II (AII) AT1 receptor subtype involved in DNA synthesis because (i) the AII receptor involved in vascular proliferation has previously been characterized in vitro in rat aortic cells and identified as an AT1 subtype and (ii) molecular cloning and biochemical studies have provided evidence for the existence of different AT1 receptor subtypes.

In cultured rat aortic vascular smooth muscle (VSMC), exposure to AII (0.1 to 100 nM) resulted in a concentration‐dependent increase in [3H]‐thymidine incorporation with an EC50 of 1.41 ± 0.51 nM. Maximal stimulation was observed in the presence of 100 nM AII and corresponded to 271 ± 40% of basal [3H]‐thymidine incorporation.

To characterize the AII AT1 receptor subtype involved in this effect, cells were exposed to AII (3 nM) in the absence or presence of increasing concentrations of various AII receptor antagonists. The stimulatory effect of AII (3 nM) on [3H]‐thymidine incorporation in VSMC was antagonized by the non‐selective AT1/AT2 receptor antagonist, [Sar1,Ile8]‐AII (IC50 = 5.6 nM), by the AT1A/AT1B receptor antagonist, losartan (IC50 = 10.5 nM) and the AT1 receptor antagonist, L‐158809 (IC50 = 0.20 nM). The selective AT2 receptor ligand, CGP 42112A, antagonized AII‐induced [3H]‐thymidine incorporation with an IC50 of 6.3 ± 1.3 μm while the AT2/AT1B receptor antagonist, PD 123319, was found to be almost inactive (IC50 > 10 μm).

Under the same experimental conditions, angiotensin III (AIII) was found to be at least 50 times less potent than AII with an apparent EC50 of 81.6 ± 7.7 nM. At the highest concentration tested (10 μm), the effect of AIII corresponded to 327 ± 61% of basal [3H]‐thymidine incorporation.

These results confirm that AII can stimulate DNA synthesis in VSMC through an AT1 receptor. Furthermore, the pharmacological characterization of this AT1 receptor is compatible with the AT1A receptor subtype recently described on cultured mesangial cells since (i) the AT1A/AT1B receptor antagonist losartan is active at nanomolar concentrations, (ii) micromolar concentrations of the AT2/AT1B receptor antagonist PD 123319 are ineffective at antagonizing the AII‐induced [3H]‐thymidine incorporation and (iii) AII is at least 50 times more potent than AIII in stimulating DNA synthesis.
Functional expression of human D3 dopamine receptors in differentiated neuroblastoma × glioma NG108–15 cells
Authors: Seabrook Guy R. , Kemp John A. , Freedman Stephen B. , Patel Shil , Sinclair Heather A. , McAllister George
Published: July 2012

This study describes the depression of calcium currents caused by activation of human D3 dopamine receptors which have been stably expressed in the neuroblastoma × glioma NG108–15 cell line. Transfected cells, which had been differentiated with prostaglandin E1 and isobutylmethylxanthine, exclusively expressed D3 receptor mRNA, which was demonstrated by reverse transcription polymerase chain reaction techniques. Transfected cells had high affinity binding sites for iodosulpiride, with a Kd of 0.8 nm and receptor density of 240 fmolmg−1 protein. Calcium currents were recorded using nystatinperforated patch clamp techniques. In contrast to untransfected cells that had been differentiated, high‐threshold calcium currents in differentiated hD3‐NG108–15 cells were depressed by application of dopamine and quinpirole. These responses were abolished by the dopamine receptor antagonist S‐(–)‐sulpiride (1 μm), demonstrating that they were caused by the activation of the transfected dopamine receptors. Coupling of human D3 receptors to calcium currents was sensitive to the action of pertussis toxin, suggesting the involvement of G‐proteins of the Gi and/or Go subtype. These results demonstrate that human D3 receptors represent a functional class of dopamine receptor.
Contribution of ATP and nitric oxide to NANC inhibitory transmission in rat pyloric sphincter
Authors: Soediono Prajitno , Burnstock Geoffrey
Published: July 2012

Changes in isometric tension were recorded from circular muscle strips of rat pyloric sphincter in vitro, in response to electrical field stimulation and exogenously applied muscle relaxants.

Concentration‐response relationships were studied for relaxations to exogenously applied adenosine 5′‐triphosphate (ATP) and two analogues, 2‐methylthioATP (2‐MeSATP) and α,β‐methylene ATP (α,β‐MeATP). These drugs evoked concentration‐dependent relaxation of rat pyloric sphincter with an order of potency 2‐MeSATP > ATP > > α,β‐MeATP, indicating the presence of P2Y‐purinoceptors. The IC50 value of each nucleotide was: 2‐MeSATP, 5.0 × 10−8 m; ATP, 7.9 × 10−6 m; α,β‐MeATP showed only slight activity at a concentration of 0.1 mm.

Frequency‐response relationships for relaxations evoked by electrical field stimulation (EFS) were studied in the absence and presence of 10 μm NG‐nitro‐L‐arginine methyl ester (L‐NAME, an inhibitor of nitric oxide (NO) synthesis) and 20 μm reactive blue 2 (a P2y‐purinoceptor antagonist). It was found that these substances significantly reduced the relaxant response of rat pyloric sphincter to EFS by 40% and 50% respectively. In the presence of both L‐NAME and reactive blue 2 the responses were reduced by 75%.

Concentration‐response relationships were studied for ATP and 2‐MeSATP in the presence of L‐NAME. It was found that L‐NAME did not significantly inhibit the relaxant responses to these drugs.

Concentration‐response relationships for ATP and noradrenaline were studied in the presence of reactive blue 2 (20 μm); the P2Y‐antagonist significantly inhibited the relaxant response to ATP, but not that to noradrenaline.

The distribution of nitric oxide synthase in rat pyloric sphincter was investigated immunohis‐tochemically, with immunoreactive nerve fibres found throughout the circular muscle layer and myenteric plexus of the sphincter.

While abundant vasoactive intestinal polypeptide (VIP)‐containing nerve fibres were demonstrated immunohistochemically in the pyloric sphincter, relaxations to VIP (1 nm‐0.3 μm) were not observed in this preparation.

It is concluded that ATP, acting through P2Y‐purinoceptors, and NO contribute to NANC inhibitory neurotransmission in rat pyloric sphincter. NO appeared to contribute to the later component of NANC relaxation. The action of ATP was not mediated by NO, and VIP did not contribute to the NANC inhibitory responses in this preparation.
Atypical β‐adrenoceptors in the rat isolated common carotid artery
Authors: Oriowo Mabayoje Ayotunde
Published: July 2012

The possible existence of atypical β‐adrenoceptors in vascular smooth muscle of the rat common carotid artery was examined in this study.

Isoprenaline produced concentration‐dependent relaxation of noradrenaline (10−7 m) precontracted ring segments of the carotid artery. The relaxation was not affected by endothelial denudation.

Propranolol (10−8 m‐3 × 10−7 m) shifted the isoprenaline curve to the right without suppressing the maximum response. However, the slope (0.74) of the Schild plot was significantly (P < 0.05) less than 1.

Salbutamol (fe), CGP 12177 and BRL 37344 (ft) also concentration‐dependently relaxed noradrenaline precontracted artery segments. These relaxations were not affected by propranolol (10−7 m). Pretreatment of the artery segments with BRL 37344 did not desensitize the tissue to the relaxant effect of isoprenaline, CGP 12177 and salbutamol.

It is concluded that atypical β‐adrenoceptors exist in vascular smooth muscle of the common carotid artery.
Electrophysiological subtypes of inhibitory P1 purinoceptors on myenteric neurones of guinea‐pig small bowel
Authors: Christofi F.L. , Wood J.D.
Published: July 2012

Conventional intracellular microelectrode techniques were used to subclassify P1 purinoceptors linked to reduction of cell input resistance, steady‐state hyperpolarization of the membrane potential, or inhibition of fast e.p.s.ps, in neurones of microdissected myenteric plexus preparations from guinea‐pig ileum. The potencies of P1 purinoceptor agonists were estimated in neurones that were current clamped to a fixed membrane potential.

In AH/Type 2 neurones, the A2 agonist, CGS 21680, the A1 agonist, CCPA or the mixed A1‐A2 agonist, NECA, suppressed excitability by reducing input resistance (40–50% max.) and causing hyperpolarization (20–25 mV max.). CGS 21680 (0.1‐1 μm) enhanced the after‐hyperpolarizing potential.

From cumulative dose‐response data, the potency order for reducing input resistance was CCPA (IC50 = 5.1 ± 2.2nM) > > > CGS 21680 (IC50 = 5.6 ± 2.5 μm). This effect was reversed by the A1 antagonist, CPT (EC50 = 65 ± 11 nm).

In contrast, the potency order for membrane hyperpolarization was CCPA (IC50 = 61 ± 23 nm) = CGS 21680 (IC50 = 290 ± 90 nm) ≥ NECA (IC50 = 450 ± 100 nm). Hyperpolarization elicited by CCPA was sensitive to the A1‐A2 antagonist, DPSPX.

Agonists suppressed fast e.p.s.ps, but not DMPP responses, with an order of CCPA (IC50 = 8.1 ± 3.0 nm) > > > CGS 21680 (IC30 = 10 ± 2.9 μm).

In conclusion, the excitability of AH/Type 2 neurones is suppressed by activation of high affinity A1 receptors that may be linked to a cyclic AMP‐dependent pathway, leading to increase in calcium‐dependent potassium conductance and enhancement of the after‐hyperpolarizing potential. Activation of lower affinity non A1 receptors linked to a cyclic AMP‐independent pathway reduces excitability and leads mainly to a steady‐state hyperpolarization. Adenosine also suppresses nicotinic cholinergic transmission by activating presynaptic high affinity A1 receptors.
Enhancement of retinal acetylcholine release by DAMGO: possibly a direct opioid receptor‐mediated excitatory effect
Authors: Neal M.J. , Paterson S.J. , Cunningham J.R.
Published: July 2012

An eye‐cup preparation in anaesthetized rabbits was used to examine opioid modulation of acetylcholine (ACh) release from cholinergic neurones in the retina.

The μ‐opioid receptor agonist, [D‐Ala2, MePhe4, Gly‐ol5]‐enkephalin (DAMGO), when applied locally to the retina at concentrations between 1–30 μm significantly increased the light‐evoked release of ACh. The effect of DAMGO was completely blocked by the selective μ‐receptor antagonist CTOP but the k‐receptor antagonist nor‐binaltorphimine (norBNI) did not affect the action of DAMGO on ACh release indicating that the opioid produced its effect by activation of μ‐receptors (the rabbit retina has negligible δ‐receptors).

Blockade with bicuculline and strychnine of GABAergic and glycinergic inputs to the cholinergic neurones did not affect the action of DAMGO on ACh release. Also DAMGO did not reduce the potassium‐evoked release of either GABA or glycine from rat isolated retinas.

Exposure of the rabbit retina to a combination of an A1‐adenosine receptor antagonist, 8‐cyclopentyl‐1,3 dipropylxanthine (DPCPX), and adenosine deaminase did not affect the enhancing action of DAMGO on the light‐evoked release of ACh.

When the retina in the rabbit eye‐cup was exposed to kainate, the release of ACh was increased by approximately three times the resting release. In the presence of DAMGO the kainate‐evoked release of ACh was enhanced by 44%.

These experiments show that activation of μ‐opioid receptors by DAMGO increases the release of ACh elicited by physiological stimulation (flickering light). Since we could find no evidence that DAMGO reduces inhibitory inputs to the cholinergic neurones, it seems that the enhancing action of DAMGO on the light‐evoked release of ACh involves a direct excitatory effect rather than disinhibition. This conclusion is supported by the enhancing action of DAMGO on the kainate‐evoked release of ACh because kainate is thought to act directly on the cholinergic neurones.
Role of endogenous endothelin in myocardial and coronary endothelial injury after ischaemia and reperfusion in rats: studies with bosentan, a mixed ETA‐ETB antagonist
Authors: Richard Vincent , Kaeffer Nathalie , Hogie Manuela , Tron Christophe , Blanc Thierry , Thuillez Christian
Published: July 2012

Previous studies suggested that endothelin‐1 (ET‐1) may play a role in myocardial ischaemia and reperfusion. This study was designed to test the effect of a new nonpeptide antagonist of endothelin ETA and ETB receptors, bosentan, on myocardial infarct size, ventricular arrhythmias, and coronary endothelial dysfunction after ischaemia and reperfusion.

Anaesthetized male Wistar rats were subjected to 20min ischaemia (left coronary artery occlusion) followed by 1 h (for the evaluation of coronary endothelial dysfunction) or 2 h (for the evaluation of infarct size) reperfusion, or 5 min ischaemia followed by 15 min reperfusion (for the evaluation of reperfusion arrhythmias). Vascular studies were performed on 1.5‐2 mm coronary segments (internal diameter 250–300 μm) removed distal to the site of occlusion and mounted in wire myographs for isometric tension recording. Area at risk and infarct size were determined by Indian ink injection and triphenyl tetrazolium staining, using computerized analysis of enlarged sections after colour video acquisition.

Bosentan, administered at a dose which virtually abolished the pressor response to big ET‐1 (3 mg kg−1, i.v. before ischaemia) did not affect heart rate, arterial pressure or the rate pressure product before ischaemia, during ischaemia and during reperfusion. Bosentan did not affect the incidence of reperfusion‐induced ventricular fibrillation (controls: 86%, n = 14; bosentan: 93%, n = 15), and did not modify infarct size (% of area at risk: controls: 63 ± 4, n = 10; bosentan: 60 ± 6, n = 8). Ischaemia followed by reperfusion markedly reduced the endothelium‐dependent relaxations to acetylcholine (maximal response: sham: 59 ± 4%, n = 9; ischaemia‐reperfusion: 26 ± 6%, n = 8; P < 0.01), characteristic of reperfusion‐induced endothelial dysfunction, and this dysfunction was not prevented by bosentan (maximal response to acetylcholine: 25 ± 5%, n = 9; P < 0.01 vs sham; P = NS vs ischaemia/reperfusion).

These experiments suggest that endogenous endothelin does not contribute to myocyte or coronary endothelial injury in this rat model of ischaemia and reperfusion.
Regional and species differences in glyburide‐sensitive K+ channels in airway smooth muscles as estimated from actions of KC 128 and levcromakalim
Authors: Kamei Kenshi , Yoshida Shohshin , Imagawa Jun‐Ichi , Nabata Hiroyuki , Kuriyama Hirosi
Published: July 2012

The purpose of the present experiments was to elucidate the differences in actions of two K+ channel openers, KC 128 and levcromakalim, on the carbachol‐induced contraction, membrane potential and 86Rb+ efflux of the dog tracheal and bronchial smooth muscles. Furthermore, we compared the effects of these agents on guinea‐pig and human airway smooth muscles.

In the dog tracheal and bronchial smooth muscle tissues, levcromakalim induced a concentration‐dependent relaxation of the carbachol‐induced contraction. The IC50 values were 0.35 μm (pIC50: 6.46 ± 0.10, n = 9) and 0.55 μm (pIC50: 6.26 ± 0.07, n = 5), respectively. KC 128 relaxed bronchial smooth muscles precontracted by carbachol with an IC50 value of 0.19 μm (pICso: 6.73 ± 0.10, n = 7). However, KC 128 had almost no effect on the contraction evoked by carbachol in the trachea (IC50 > 10 μm). The relaxations induced by levcromakalim and KC 128 were antagonized by glyburide (0.03‐1 μm) but not by charybdotoxin (100 nm).

Levcromakalim (1 μm) hyperpolarized the membrane of both dog tracheal and bronchial smooth muscle cells, whereas KC 128 (1 μm) hyperpolarized the membrane of bronchial but not of tracheal smooth muscle cells.

Levcromakalim (10 μm) increased 86Rb+ efflux rate from both tracheal and bronchial smooth muscle tissues but KC 128 (10 μm) increased 86Rb+ efflux rate only from bronchial and not tracheal smooth muscle tissues. Glyburide (1 μm) prevented the hyperpolarization and the 86Rb+ efflux induced by these agents at the same concentration as observed for mechanical responses.

Both KC 128 and levcromakalim relaxed the guinea‐pig isolated tracheal smooth muscles precontracted by carbachol (100 nm), histamine (3μm) or U46619 (10 nm). KC 128 was approximately 10 times more potent than levcromakalim for each agonist.

In human bronchial smooth muscles, levcromakalim but not KC 128 induced a concentration‐dependent relaxation of the carbachol‐induced contraction.

It is concluded that KC 128 has relaxant and hyperpolarizing effects in the dog bronchial and guinea‐pig tracheal smooth muscles, but not in the dog tracheal and human bronchial smooth muscles. On the other hand, levcromakalim acts consistently on all the above airway smooth muscle tissues. These results indicate that there are regional and species differences in distribution of K+ channels, and at least two different K+ channel opener‐ and glyburide‐sensitive K+ channels are present in the dog airway smooth muscles.
Inhibition by gomisin C (a lignan from Schizandra chinensis) of the respiratory burst of rat neutrophils
Authors: Wang Jih P. , Raung Shue L. , Hsu Mei F. , Chen Chien C.
Published: July 2012

The possible mechanisms of action of the inhibitory effect of gomisin C on the respiratory burst of rat neutrophils in vitro was investigated.

The peptide formyl‐Met‐Leu‐Phe (FMLP) induced superoxide anion (O2−) formation and O2 consumption, which was inhibited by gomisin C in a concentration‐dependent manner (IC50 21.5 ± 4.2 μg ml−1 for O2− formation). Gomisin C also suppressed O2− formation and O2 consumption at low concentrations of phorbol myristate acetate (PMA) with an IC50 value of 26.9 ± 2.1 μg ml−1 for O2− formation. However, gomisin C did not affect the responses induced by a high concentration of PMA.

Gomisin C had no effect on O2− generation and uric acid formation in the xanthine‐xanthine oxidase system, and failed to alter O2− generation during dihydroxyfumaric acid (DHF) autoxidation, indicating that it does not scavenge superoxide.

Like trifluoperazine (TFP), gomisin C attenuated the activity of PMA‐activated neutrophil particulate NADPH oxidase in a concentration‐dependent manner.

Gomisin C reduced the elevations of cytosolic free Ca2+ in neutrophils stimulated by FMLP in the presence or absence of EDTA. Cyclopiazonic acid (CPA) induced the release of Ca2+ from intracellular stores and this was also reduced by gomisin C. However, the Ca2+ influx pathway activated by CPA was not affected by gomisin C.

The cellular cyclic AMP level was markedly increased by forskolin, but not by gomisin C. Moreover, the inositol phosphate levels in FMLP‐activated neutrophils were not affected by gomisin C.

These results show that the inhibitory action of gomisin C on the respiratory burst is not mediated by changes in cellular cyclic AMP or in inositol phosphates, or by scavenging O2− released from neutrophils, but may be mediated partly by the suppression of NADPH oxidase and partly by the decrease of cytosolic Ca2+ released from an agonist‐sensitive intracellular store.
Role of 5‐HT3 receptors in basal and K+‐evoked dopamine release from rat olfactory tubercle and striatal slices
Authors: Zazpe A. , Artaiz I. , Del Río J.
Published: July 2012

The present study was aimed at examining the role of 5‐HT3 receptors in basal and depolarization‐evoked dopamine release from rat olfactory tubercle and striatal slices. [3H]‐dopamine ([3H]‐DA) release was measured in both brain regions and endogenous dopamine release from striatal slices was also studied.

The selective 5‐HT3 receptor agonist 2‐methyl‐5‐HT (0.5–10μm) produced a concentration‐dependent increase in [3H]‐DA efflux evoked by K+ (20 μm) from slices of rat olfactory tubercle. 1‐Phenylbiguanide (PBG) and 5‐HT also increased K+‐evoked [3H]‐DA efflux.

5‐HT (1–100 μm) increased in a concentration‐dependent manner basal [3H]‐DA release from olfactory tubercle and striatal slices as well as endogenous DA release from striatal slices. The selective 5‐HT3 receptor agonists 2‐methyl‐5‐HT and 1‐phenylbiguanide were weaker releasing agents. In all cases, the release was Ca2+ independent and tetrodotoxin insensitive.

5‐HT3 receptor antagonists such as ondansetron, granisetron and tropisetron (0.2 μm) significantly blocked the enhanced K+‐evoked [3H]‐DA efflux from rat olfactory tubercle slices induced by 2‐methyl‐5‐HT. A ten fold higher concentration of the 5‐HT2 receptor antagonist ketanserin was ineffective.

Much higher concentrations, up to 50 μm, of the same 5‐HT3 receptor antagonists did not block the increase in basal [3H]‐DA release from striatal or olfactory tubercle slices induced by 5‐HT or the release of endogenous DA induced by 5‐HT from striatal slices.

The DA uptake blocker nomifensine (10 μm) did not modify the enhancement in K+‐evoked [3H]‐DA efflux from rat olfactory tubercle slices induced by 2‐methyl‐5‐HT. However, both nomifensine and cocaine significantly blocked the increase in basal dopamine release, either tritiated or endogenous, induced by 5‐HT.

These results indicate that 5‐HT3 receptors only modulate DA release when the terminal fields of dopaminergic systems have been activated. In basal conditions, 5‐HT3 receptor agonists enhance DA release through a carrier‐mediated mechanism. This may be of therapeutic relevance for the possible use of 5‐HT3 receptor antagonists under conditions of abnormal activation of the dopaminergic system.
The transhepatic action of ATP on the hepatic arterial and portal venous vascular beds of the rabbit: the role of nitric oxide
Authors: Browse Dominic J. , Mathie Robert T. , Benjamin Irving S. , Alexander Barry
Published: July 2012

The effect of bolus administration of adenosine 5′‐triphosphate (ATP) into the portal vein on hepatic arterial pressure (the transhepatic action of ATP) and portal venous pressure, and the contribution of nitric oxide towards these responses, was studied in the in vitro dual‐perfused rabbit liver.

At basal tone, hepatic arterial and portal venous vasoconstriction followed ATP injection, while at a tone raised with methoxamine (10−6‐10−5m) ATP caused hepatic arterial vasodilatation, and a phasic vasodilatation followed by vasoconstriction in the portal venous vascular bed.

To determine whether the transhepatic arterial dilatation was due to the diffusion of nitric oxide (NO) from the portal venous vasculature, NG‐nitro‐L‐arginine methyl ester (L‐NAME, 100 μm), an inhibitor of NO synthesis, was infused selectively into the portal vein. L‐NAME infusion potentiated portal venous vasoconstriction to ATP (‐log M ED50 5.32 ± 0.31 to 6.51 ± 0.43, P < 0.05, Student's paired / test) indicating the possible inhibition of a NO‐mediated vasodilator component of the portal venous response to ATP. There was, however, no demonstrable difference in the transhepatic arterial vasodilatation induced by ATP during this infusion.

Simultaneous perfusion of both the hepatic arterial and portal venous inflows with L‐NAME (100 μm) resulted in a significant decrease in the amplitude of hepatic arterial responses to ATP demonstrating that these responses were ultimately mediated by an NO‐dependent mechanism.

This study has thus demonstrated a vasodilator component of the portal venous response to ATP that is NO‐mediated. It also provides evidence that it is not portally‐derived NO, but NO released from the hepatic arterial vascular bed, that accounts for the hepatic arterial vasodilatation to intra‐portal administration of ATP. This implies that ATP itself, and not a second messenger, diffuses from the portal venous to hepatic arterial vascular bed to elicit the hepatic arterial response.