bluuebunny/crossref_metadata_2025 huggingface dataset:
The neuroprotective effect of a nitric oxide inhibitor in a rat model of focal cerebral ischaemia
Authors: Buisson A. , Plotkine M. , Boulu R.G.
Published: July 2012

Recent data showed that glutamate toxicity in primary cortical cultures is mediated by nitric oxide. In order to investigate the effect of inhibition of NO synthase on focal cerebral ischaemia in rats, we studied the histological consequences of a middle cerebral artery (MCA) occlusion after post‐operative treatment with NG‐nitro‐l‐arginine methyl ester, an inhibitor of nitric oxide synthase. We found a significant reduction of cortical (−43%) and striatal (−25%) necrotic volumes induced by MCA occlusion, indicating that NO synthesis plays an important role in the neurotoxic cascade leading to neuronal damage after focal cerebral ischaemia in rats.
Induction of a calcium‐independent NO synthase by hypercholesterolaemia in the rabbit
Authors: Lang D. , Smith J.A. , Lewis M.J.
Published: July 2012

Endothelium‐dependent and ‐independent relaxation of aortic ring preparations was assessed and nitric oxide (NO) synthase activity measured in the lung, and cerebellum of cholesterol‐fed and normal rabbits. Endothelium‐dependent relaxation of acetylcholine and ATP was depressed while that to the calcium ionophore, A23187, was unaltered in the cholesterol‐fed group. Relaxation to sodium nitroprusside was however greater in aortae from the cholesterol‐fed animals. Neither Ca2+‐dependent nor Ca2+‐independent NO synthase activity could be detected in aortae or hearts taken from either group of animals. Activity of both enzymes was unaltered in cerebellae from both groups of animals. Activity of the Ca2+‐independent enzyme was however significantly greater (ca. 2 fold) in lungs from the cholesterol‐fed rabbits though the activity of the Ca2+‐dependent NO synthase was not significantly altered. This finding may account for the increased production of nitrogen oxides previously observed in this model of hypercholesterolaemia.
Ramiprilat increases bradykinin outflow from isolated hearts of rat
Authors: Baumgarten Claus R. , Linz Wolfgang , Kunkel Gert , Schölkens Bernward A. , Wiemer Gabriele
Published: July 2012

To establish that bradykinin is formed in the heart we measured bradykinin in the venous effluent from rat isolated hearts perfused with Krebs‐Henseleit buffer. In addition, we examined the effect on bradykinin outflow of the angiotensin converting enzyme (ACE) inhibitor, ramiprilat. From rat isolated normoxic hearts a bradykinin outflow of 0.85 ± 0.1 ng ml−1 perfusate g−1 wet weight was measured. Perfusion with ramiprilat increased the bradykinin concentration to 2.8 ± 0.3 ng ml−1 perfusate g−1 wet weight. During ischaemia bradykinin outflow maximally increased 8.2 fold to 7.0 ± 0.5 ng ml−1 perfusate g−1, and in ramiprilat‐perfused hearts 5.8 fold to 16.0 ± 1.8 ng ml−1 perfusate g−1. In the reperfusion period bradykinin outflow normalized to values measured in the respective pre‐ischaemic period.

The presents data show that bradykinin is continuously formed in the rat isolated heart. Ischaemia increases bradykinin outflow from the heart. Presumably by inhibiting degradation of kinins, ACE inhibition significantly increased the bradykinin concentration during normoxia, ischaemia and reperfusion.
Chloroethylclonidine: an irreversible agonist at prejunctional α2‐adrenoceptors in rat vas deferens
Authors: Bültmann Ralph , Starke Klaus
Published: July 2012

The possibility that chloroethylclonidine (CEC) activates prejunctional α2‐adrenoceptors was studied in the isolated vas deferens of the rat. Tissues were stimulated electrically and both the stimulation‐evoked overflow of tritium (after preincubation with [3H]‐noradrenaline) and the purinergic contraction component (isolated by prazosin 0.3 μm) were measured.

CEC (0.1–3 μm) concentration‐dependently reduced the overflow of tritium evoked by trains of 6 pulses/100 Hz. The inhibition by CEC was not altered by prazosin (0.3 μm) but was prevented by pre‐exposure to rauwolscine (0.3 μm). The inhibition, once established, did not fade upon washout of CEC, even when the washout fluid contained rauwolscine (0.3 μm).

CEC (0.1–3 μm) concentration‐dependently reduced the purinergic component of contractions elicited by single pulses. The inhibition, again, was prevented by pre‐exposure to rauwolscine (0.3 μm) and once established, did not fade upon washout of CEC, even when the washout fluid contained rauwolscine (0.3 μm).

CEC (3 μm) reduced the overflow of tritium evoked by 20 pulses/10 Hz, did not alter the overflow evoked by 100 pulses/10 Hz and increased the overflow evoked by 500 pulses/10 Hz.

CEC (3 μm) reduced the early peak, but increased the late plateau phase, of purinergic contractions elicited by 100 pulses/10 Hz.

It is concluded that CEC reduces the release of noradrenaline and a purinergic co‐transmitter by irreversible activation of prejunctional α2‐adrenoceptors. CEC seems to be a partial α2‐agonist with an efficacy lower than that of noradrenaline. The prejunctional inhibitory effect limits the suitability of CEC for the characterization of postjunctional α1‐adrenoceptors mediating responses to sympathetic nerve stimulation.
Lymphocyte β2‐adrenoceptors and adenosine 3′:5′‐cyclic monophosphate during and after normal pregnancy
Authors: von Mandach Ursula , Gubler Hans Peter , Engel Günther , Huch Renate , Huch Albert
Published: July 2012

The β2‐sympathomimetics, used to inhibit preterm labour, bind predominantly to β2‐adrenoceptors, activating adenylate cyclase to form adenosine 3′:5′‐cyclic monophosphate (cyclic AMP), a messenger substance which inhibits the enzyme cascade triggering smooth muscle contraction. β2‐Adrenoceptor density and cyclic AMP formation can be used as markers of β2‐adrenergic effect.

The present study addresses the influence of pregnancy on the β‐adrenoceptor system. β2‐Adrenoceptor density and cyclic AMP concentrations (basal and evoked by isoprenaline) in circulating lymphocytes were determined at three points in gestation (16, 29 and 37 weeks) and 9 weeks post partum in 22 normal pregnancies. (−)‐[125Iodo]‐cyanopindolol was used as the ligand to identify a homogeneous population of β2‐adrenoceptors on lymphocytes. B‐ and T‐cell fractions were estimated from the same samples.

β2‐Adrenoceptor density decreased significantly during gestation until week 37 (P < 0.01), then increased post partum (P < 0.005). Cyclic AMP concentrations (basal and evoked by isoprenaline) were significantly lower after 16 weeks of gestation than post partum (P<0.05).

The results, which cannot be explained in terms of a shift in the lymphocyte (B‐ and T‐cell) ratio, indicate that β‐adrenoceptor density and function are reduced in normal pregnancy and only return to normal post partum. These findings may be of significance in devising future tocolytic therapy with β2‐adrenoceptor agonists.
NK2 receptors mediate plasma extravasation in guinea‐pig lower airways
Authors: Tousignant Christine , Chan Chi‐Chung , Guevremont Diane , Brideau Christine , Hale Jeffrey J. , MacCoss Malcolm , Rodger Ian W.
Published: July 2012

Neurokinin (NK) receptor‐mediated extravasation has been examined in guinea‐pig airways by use of a recently described marker for microvascular protein leakage, 125I‐labelled human fibrinogen.

Neurokinin A (NKA) caused a dose‐dependent increase in plasma [125I]‐fibrinogen extravasation in trachea, main bronchi, secondary bronchi and intraparenchymal airways. In contrast, the NK2 selective agonist [β‐Ala8]NKA(4–10) only caused extravasation in the secondary and intraparenchymal airways.

The NK2 selective antagonist, SR 48968, caused a dose‐dependent inhibition of NKA and [β‐Ala8]NKA(4–10)‐induced extravasation of fibrinogen in guinea‐pig secondary bronchi and intraparenchymal airways. SR 48968 was without effect on the NKA‐induced extravasation in trachea and main bronchi.

NKA‐ or [β‐Ala8]NKA(4–10)‐induced plasma extravasation was not modified by pretreatment with histamine H1‐ or H2‐receptor antagonists.

It is concluded that NK2 receptors mediate plasma [125I]‐fibrinogen extravasation in guinea‐pig secondary bronchi and intraparenchymal airways. This effect is direct and does not depend upon histamine released from mast cells.
α‐Sialyl cholesterol reverses AF64A‐induced deficit in passive avoidance response and depletion of hippocampal acetylcholine in mice
Authors: Abe Eiichi , Murai Shigeo , Masuda Yoshikatsu , Saito Hiroko , Itoh Tadanobu
Published: July 2012

The effect of α‐sialyl cholesterol (α‐SC; α‐d‐N‐acethylneuraminyl cholesterol) on disturbances of the central cholinergic system induced by ethylcholine mustard aziridinium ion (AF64A) and by scopolamine were studied by means of a step‐down passive avoidance response and locomotor activities in mice. The levels of acetylcholine (ACh) in certain regions of the brain were measured to assess the neurochemical recovery promoted by α‐SC.

Treatment with AF64A (2.5, 5 and 10 nmol, i.c.v.) impaired the 24 h retention latencies of animals in a dose‐dependent manner, and scopolamine (0.5 mg kg−1, i.p.) also impaired the retention performance. Administration of α‐SC (1 and 4 mg kg−1, p.o.) once daily for 13 days improved the retention performance in AF64A‐treated animals in a dose‐dependent manner, but not in the scopolamine‐treated animals.

Treatment with AF64A (2.5, 5 and 10 nmol, i.c.v.) and scopolamine (0.5 mg kg−1, i.p.) increased vertical and horizontal locomotor activities. α‐SC dose‐dependently attenuated the increase in locomotor activies induced by 2.5 nmol of AF64A, but not the locomotor activities caused by 5 or 10 nmol of AF64A, or scopolamine (0.5 mg kg−1, i.p.).

The deficit retention performance of AF64A‐treated animals was associated with depletion of ACh levels in the hippocampus, but not in the septum or cerebral cortex. Administration of α‐SC to AF64A‐treated animals dose‐dependently reversed the depletion of ACh levels in the hippocampus.

The results indicate that α‐SC had significant effects after oral administration of AF64A‐treated animals. The behavioural recovery promoted by α‐SC may be based on the reversal of ACh depletion in the hippocampus.
Possible action of cyclopiazonic acid on myocardial sarcoplasmic reticulum: inotropic effects on neonatal and adult rat heart
Authors: Agata Naoki , Tanaka Hikaru , Shigenobu Koki
Published: July 2012

Cyclopiazonic acid (CPA), a mycotoxin from Aspergillus and Penicillium, has been described as a highly selective inhibitor of Ca2+‐ATPase in the sarcoplasmic reticulum (SR) in skeletal and smooth muscles but no reports at present deal with the effect of CPA in cardiac muscle. In the present study, we examined the inotropic effect of CPA on adult and neonatal rat myocardia, the contractions of which are known to be highly dependent on Ca2+‐release from the sarcoplasmic reticulum and trans‐sarcolemmal Ca2+‐influx, respectively. CPA (30 μm) produced a negative inotropic effect in adult preparations, accompanied by marked prolongation of the contraction duration. In contrast, CPA had minimum effects on neonatal myocardium. Thus we have demonstrated that CPA exerts negative inotropic effects on adult myocardium probably through inhibition of SR function.
Adenosine A3 receptors1 mediate hypotension in the angiotensin II‐supported circulation of the pithed rat
Authors: Fozard J.R. , Carruthers A.M.
Published: July 2012

The cardiovascular effects of N6‐2‐(4‐aminophenyl)ethyladenosine (APNEA), which when radiolabelled with 125I shows high affinity for the newly described adenosine A3 receptor, have been investigated in the angiotension II‐supported circulation of the pithed rat. APNEA induces hypotensive responses which are unaffected by high doses (20–40 mg kg−1) of the broad spectrum, adenosine receptor antagonist, 8‐(p‐sulphophenyl)theophylline (8‐SPT). 8‐SPT‐resistant falls in blood pressure are also seen, in the absence of bradycardia, with 5′‐N‐ethylcarboxamidoadenosine (NECA) and the R‐ and S‐enantiomers of N6‐phenylisopropyladenosine (PIA). Xanthine insensitivity, high potencies of APNEA, NECA and R‐PIA, and an enantiomeric selectivity favouring R‐ over S‐PIA are distinguishing features of the adenosine A3 receptor. We suggest that hypotension in the pithed rat may be a functional correlate of this site.
Propofol stimulates nitric oxide release from cultured porcine aortic endothelial cells
Authors: Petros Andy J. , Bogle Richard G. , Pearson Jeremy D.
Published: July 2012

Propofol, an intravenous anaesthetic agent, causes marked vasodilatation in vivo. In the present study the effects of propofol on the release of nitric oxide (NO) from vascular endothelial cells was determined in vitro. Application of propofol to co‐cultures of porcine aortic endothelial and smooth muscle cells resulted in a rapid increase in cyclic GMP formation. This increase was significantly inhibited following pretreatment of the cells with either NG‐nitro‐l‐arginine (l‐NOARG) or in the presence of haemoglobin. When applied to smooth muscle cells alone, propofol did not result in an increase in cyclic GMP levels. These results demonstrate that propofol stimulates the production and release of NO from cultured endothelial cells and suggest that the vasodilatation and hypotension observed when propofol is given in vivo may be due to NO release.
Acetylcholine‐induced relaxation in bovine isolated mesenteric arteries is suppressed by polymorphonuclear leukocytes
Authors: De Kimpe Sjef J. , Van Heuven‐Nolsen Dicky , Nijkamp Frans P.
Published: July 2012

The endothelium plays a critical role in maintaining vascular tone via generation of potent vasoconstrictor and dilator substances. We examined the effect of bovine purified polymorphonuclear leukocytes (PMN) on the endothelium‐dependent relaxation to acetylcholine in isolated mesenteric arteries.

In the presence of PMN (2.5 × 106 cells ml−1) the maximal relaxation to acetylcholine was decreased from 76.1 ± 2.4% to 44.9 ± 7.4% of the precontraction (P < 0.001). This effect was inhibited by superoxide dismutase and NG‐mono‐methyl‐l‐arginine, but not by catalase or indomethacin.

PMN were not able to influence significantly the endothelium‐independent relaxation to nitroprusside.

Removal of PMN after preincubation and prior to precontraction and relaxation did not influence the acetylcholine‐induced relaxation, indicating that no irreversible vascular damage had occurred.

Superoxide anion production by unstimulated PMN was less than 10% compared to phorbol myristate acetate‐activated PMN, measured by chemiluminescence and reduction of ferricytochrome c.

We conclude that small amounts of superoxide anions produced by unstimulated PMN contribute to a decrease in relaxation to acetylcholine by interfering with endothelium‐derived nitric oxide.
Withdrawal contractures of guinea‐pig isolated ileum after acute activation of κ‐opioid receptors
Authors: Morrone L.A. , Romanelli L. , Amico M.C. , Valeri P.
Published: July 2012

The present study was undertaken to investigate firstly whether a brief exposure for 5 min of guinea‐pig isolated ileum to the κ‐opioid agonist, U‐50,488H produced a withdrawal contracture on addition of naloxone and secondly to ascertain whether the response was due to the activation of κ‐opioid receptors.

Naloxone (10−6 m) did not elicit a response in preparations exposed to U‐50,488H (5 × 10−7 M‐2 × 10−6 m). However, after exposure to U‐50,488H (5 × 10−7 m), naloxone (10−6 m) produced a strong contracture if the agonist was washed out 1 min before the addition of the antagonist.

The addition of naloxone (10−6 m) to the ileum preparation exposed to U‐50,488H (10−7 m or lower) caused a response of similar intensity irrespective of whether the agonist had been washed out.

The selective κ‐opioid antagonist, nor‐binaltorphimine (2.7 × 10−9 m and 2.7 × 10−7 m), injected before the opioid agonists, prevented the naloxone‐induced contracture after exposure to U‐50,488H (8 × 10−8 m) but did not affect the contracture after exposure to morphine (5 × 10−7 m).

Nor‐binaltorphimine (2.7 × 10−9 m) caused a contraction of the ileum preparation when injected

min after exposure to U‐50,488H (8 × 10−8 m) but not after morphine (5 × 10−7 m).

The α2‐adrenoceptor agonist, clonidine (3 × 10−8 m) and the calcium channel blocker, nifedipine (3 × 10−8 m), injected 1 min before naloxone, blocked the ileum contraction to naloxone after exposure to U‐50,488H (8 × 10−8 m). The results demonstrate that the stimulation of K‐opioid receptors can induce a similar dependence in guinea‐pig ileum to that produced by activation of μ receptors.
Functional characterization of muscarinic receptors in murine airways
Authors: Garssen J. , Van Loveren H. , Gierveld C.M. , Van Der Vliet H. , Nijkamp F.P.
Published: July 2012

The effects of muscarinic receptor antagonists considered to be selective for M1 receptors (pirenzepine; PZ), M2 receptors (AFDX‐116), and for M3 receptors (4‐diphenyl acetoxy N‐methylpiperidine (4‐DAMP)) were used to investigate the existence of muscarinic receptor subtypes in murine airways. Atropine was used as a nonselective antagonist. The effects of these antagonists were studied upon tracheal contractions induced either by EFS (electric field stimulation) or by application of an exogenous cholinoceptor agonist (arecoline).

The muscarinic receptor antagonists tested inhibited arecoline‐induced tracheal contractions with the following rank order of potency: 4‐DAMP = atropine > pirenzepine = AFDX‐116. The rank order of potency of the muscarinic antagonists used in inhibiting EFS‐induced tracheal contractions was: 4‐DAMP = atropine > PZ > AFDX‐116. The pA2 values for these antagonists were similar when compared to the pA2 values determined in guinea‐pig and bovine airway smooth muscle.

In addition to in vitro studies, the effects of inhalation of the different muscarinic antagonists on lung function parameters in vivo were investigated. Inhalation of 4‐DAMP induced a decrease in airway resistance and an increase in lung compliance. In contrast, inhalation of AFDX‐116 induced an increase in airway resistance and almost no change in lung compliance. Apart from some minor effects of atropine on airway resistance, atropine, PZ, and pilocarpine failed to induce changes in lung mechanics as determined by in vivo lung function measurements.

The results provide evidence for the existence of M3 receptors on murine tracheae that are involved in the contraction of tracheal smooth muscle. This is in agreement with other animal species such as the guinea‐pig and bovine. In vivo experiments also demonstrated that in the mouse, M3 receptors play an important role in bronchial smooth muscle contraction and thus in bronchoconstriction. Interestingly we have also demonstrated that M2 receptors can play a role in bronchodilatation. Inhalation of an M2 receptor antagonist induced an increase in airway resistance whereas inhalation of an M3 receptor antagonist induced a decrease in airway resistance. It is therefore likely that an M3/M2 receptor balance plays an important role in the regulation of airway function.
Effects of MS‐551, a new class III antiarrhythmic drug, on action potential and membrane currents in rabbit ventricular myocytes
Authors: Nakaya Haruaki , Tohse Noritsugu , Takeda Youji , Kanno Morio
Published: July 2012

Electrophysiological effects of MS‐551, a new class III antiarrhythmic drug, were examined and compared with those of (+)‐sotalol in rabbit ventricular cells.

In rabbit ventricular muscles stimulated at 1.0 Hz, MS‐551 (0.1–10 μm) and (+)‐sotalol (3–100 μm) prolonged action potential duration (APD) and effective refractory period without affecting the maximum upstroke velocity of phase 0 depolarization . The class III effect of MS‐551 was approximately 30 times more potent than that of (+)‐sotalol.

Class III effects of MS‐551 and (+)‐sotalol showed reverse use‐dependence, i.e., a greater prolongation of APD at a longer cycle length.

In rabbit isolated ventricular cells, 3 μm MS‐551 and 100 μm sotalol inhibited the delayed rectifier potassium current (IK) which was activated at more positive potentials than −50 mV and saturated around + 20 mV.

MS‐551 at a higher concentration of 10 μm decreased the transient outward current (Ito) and the inward rectifier potassium current (IK1) although 100 μm sotalol failed to inhibit these currents.

MS‐551 is a non‐specific class III drug which can inhibit three voltage‐gated K+ channels in rabbit ventricular cells.
Effects of propafenone on calcium currents in single ventricular myocytes of guinea‐pig
Authors: Fei Lü , Gill Jaswinder S. , McKenna William J. , Camm A. John
Published: July 2012

The effects of propafenone on the inward calcium current (ICa) were investigated in isolated single ventricular myocytes of the guinea‐pig by the whole‐cell clamp method. Propafenone inhibited ICa in a dose‐dependent manner at concentrations of propafenone ranging from 1 × 10−8 to 1 × 10−3 m and half maximal block of ICa occurred at a propafenone concentration of 1.5 × 10−6 m. Propafenone did not change the current‐voltage relation of ICa other than a reduction in amplitude and showed no clear use‐ or frequency‐dependent effects upon ICa (stimulation frequencies from 0.03 to 2 Hz). Propafenone did not alter the steady‐state inactivation process: the half maximal activation potentials were 18.5 ± 2.2 mV in the control state and 20.9 ± 5.0 mV in the presence of 1×10−6 m propafenone (n = 12, NS). Propafenone (1 × 10−6 m) increased the half‐time of reactivation by 73.9% (n = 6, 212.3 ± 1.2 ms vs 369.2 ± 1.5 ms, P < 0.05).

We conclude that propafenone blocks ICa in a concentration‐dependent and a channel state‐, use‐ or frequency‐independent manner. The ICa, blockade elicited by propafenone at clinically therapeutic plasma concentration is significant and may be involved in its anti‐arrhythmic effects.
Characterization of the increase in vascular permeability induced by vascular permeability factor in vivo
Authors: Collins P.D. , Connolly D.T. , Williams T.J.
Published: July 2012

Vascular permeability factor (VPF) is a protein secreted from a variety of human and rodent tumour and normal tissue cells. In addition to mediating angiogenesis and endothelial cell growth, VPF has been reported to be a potent mediator of increased microvascular permeability in vivo. In this study we have investigated these permeability changes in vivo using a quantitative model of local plasma leakage in rabbit skin.

Our results reveal that VPF is a potent mediator of plasma leakage which, in the rabbit, depends on a synergistic interaction with arteriolar vasodilators such as prostaglandin E2. The requirement for an exogenous vasodilator further suggests that VPF does not act to increase blood flow in this model.

We show that this response does not require the presence of circulating neutrophils and in this respect is similar to direct‐action permeability increasing mediators such as histamine and bradykinin. Similarly, the time course of plasma leakage induced by VPF resembles that of direct‐action mediators, where the greatest response occurs over the first 30 min. In contrast, the neutrophil‐dependent plasma leakage induced by the active component of zymosan‐activated plasma, C5ades arg, was maintained at a similar level over 2.5 h.

Further, using mediator antagonists and enzyme inhibitors we demonstrate that the mechanism of action of VPF is not via activation of histamine, kinin, or platelet‐activating factor pathways.
Counteraction of the rapid tolerance to 8‐OH‐DPAT‐induced corticosterone secretion in rats by activation of the GABAA receptor‐chloride channel complex
Authors: Kelder Diana , Ross Svante B.
Published: July 2012

The effect of various classes of compounds on the rapidly developed tolerance to 8‐hydroxy‐2‐(di‐n‐propylamino)tetralin (8‐OH‐DPAT)‐induced corticosterone secretion was examined.

Compounds activating the γ‐aminobutyric acidA (GABAA) receptor‐chloride complex, i.e. muscimol (3 mg kg−1), diazepam (5 mg kg−1), flunitrazepam (1 mg kg−1), sodium pentobarbitone (10–30 mg kg−1) and chlormethiazole ethane disulphonate (50 mg kg−1) counteracted the development of tolerance when injected before or simultaneously with, but not 15 min after 8‐OH‐DPAT.

At these doses the compounds produced an acute increase in serum corticosterone but had, with the exception of muscimol, no effect on the response to the challenge dose of 8‐OH‐DPAT 24 h later. Muscimol significantly decreased the response.

The GABAA chloride channel antagonist, picrotoxin (1 mg kg−1, s.c.), but not bicuculline (1 mg kg−1, i.p.) potentiated the development of tolerance to 8‐OH‐DPAT‐induced corticosterone secretion.

A number of compounds with widely differing pharmacological actions were examined and found to have no effect on the development of tolerance to 8‐OH‐DPAT‐induced corticosterone secretion.
Effects of chronic treatment with nitric oxide synthase inhibitors on regional haemodynamic responses to vasodilators in conscious Brattleboro rats
Authors: Gardiner Sheila M. , Kemp Philip A. , Bennett Terence
Published: July 2012

The effects of acute inhibition of nitric oxide (NO) synthase on cardiovascular responses to vasodilator challenges have already been described. We now report the responses to vasodilators during and after chronic NO synthase inhibition.

In conscious Brattleboro rats, the regional haemodynamic effects of 3 min infusions of acetylcholine (4 μg min−1), sodium nitroprusside (15 μg min−1) or adrenaline (0.2 μg min−1) were assessed (from areas under or over curves (AUC, AOC)) under control conditions, 6 and 72 h after the addition of the NO synthase inhibitor, NG‐monomethyl‐l‐arginine (l‐NMMA) to the drinking water (1 mg ml−1), and 6, 24 and 48 h after the withdrawal of l‐NMMA. In a separate group of Brattleboro rats, responses to acetylcholine, sodium nitroprusside and adrenaline were assessed before and 6 h after the onset of oral ingestion of the more potent nitric oxide synthase inhibitor, NG‐nitro‐l‐arginine methyl ester (l‐NAME; 0.05 mg ml−1).

Acetylcholine caused renal vasodilatation (87 ± 11 units) and mesenteric vasoconstriction (−31 ± 5 units), sodium nitroprusside caused vasodilatation in renal (96 ± 12 units), mesenteric (222 ± 13 units) and hindquarters (49 ± 15 units) vascular beds, whereas adrenaline caused hindquarters vasodilatation (92 ± 8 units). Seventy two h after the onset of oral ingestion of l‐NMMA, acetylcholine had a decreased renal vasodilator (59 ± 9 units) effect, sodium nitroprusside had an increased renal vasodilator (142 ± 23 units) action, while adrenaline had a decreased hindquarters vasodilator (55 ± 6 units) influence. Twenty four h after withdrawal of l‐NMMA, the renal vasodilator effect of acetylcholine was greater than the control response (106 ± 14 units), but the regional haemodynamic effects of sodium nitroprusside and adrenaline were not different from those under control conditions. Hence, the increased renal vasodilator response to acetylcholine was probably due to changes in muscarinic receptor‐mediated mechanisms rather than to any increase in guanylyl cyclase or its sensitivity to NO.
Contractile and relaxant effects of phorbol ester in the intestinal smooth muscle of guinea‐pig taenia caeci
Authors: Mitsui Minori , Karaki Hideaki
Published: July 2012

Effects of phorbol esters on the cytosolic Ca2+ level ([Ca2+]i) and muscle tension in the intestinal smooth muscle of guinea‐pig taenia caeci were examined.

12‐Deoxyphorbol 13‐isobutyrate (DPB, 1 μm) did not change the [Ca2+]i and tension in resting muscle.

In high K+‐stimulated muscle, 1 μm DPB transiently augmented the contraction and decreased [Ca2+]i. 12‐Deoxyphorbol 13‐isobutyrate 20‐acetate (1 μm) and phorbol 12, 13‐dibutyrate (1 μm) showed similar effects to DPB whereas phorbol 12‐myristate 13‐acetate (1 μm) and phorbol 12, 13‐didecanoate (1 μm) were ineffective.

DPB (1 μm) inhibited both [Ca2+]i and tension stimulated by 300 nm carbachol or 3 μm histamine. In the presence of a higher concentration of carbachol (1 μm), DPB decreased [Ca2+]i and transiently increased muscle tension.

In the muscle strips permeabilized with bacterial α‐toxin, 1 μm DPB shifted the Ca2+‐tension curve to the left. An inhibitor of protein kinase C, H‐7 (30 μm), inhibited the effect of DPB.

DPB did not change the high K+‐induced contraction in the muscle strips pretreated with 3 μm phorbol 12‐myristate 13‐acetate for 24 h.

These results suggest that activation of protein kinase C has dual effects; it augments contraction by increasing the Ca2+ sensitivity of the contractile elements and it inhibits contraction by decreasing [Ca2+]i.
S‐nitrosocysteine, but not sodium nitroprusside, produces apamin‐sensitive hyperpolarization in rat gastric fundus
Authors: Kitamura Kenji , Lian Qishen , Carl Andreas , Kuriyama Hirosi
Published: July 2012

To investigate the pharmacological properties of the membrane hyperpolarization induced by electrical field stimulation (EFS), sodium nitroprusside (SNP) and S‐nitrosocysteine (NO‐Cys) in circular smooth muscle cells of the rat gastric fundus (forestomach), the effects of various potassium channel blockers on these hyperpolarizations were investigated.

EFS (50 μs, 20 Hz, 3 pulses, 10–50 V) produced inhibitory junction potentials (i.j.ps), in the presence of atropine (1 μm) and guanethidine (1 μm). NO‐Cys and SNP produced hyperpolarization of the membrane in the rat gastric fundus. l‐NG‐nitroarginine (l‐NNA) inhibited the i.j.ps, but not the hyperpolarization induced by NO‐Cys and SNP. This inhibitory action of l‐NNA on the i.j.ps was partly reversed by subsequent application of l‐arginine (1 mm) but not by d‐arginine.

Oxyhaemoglobin (Oxy‐Hb; 5 μm) inhibited these hyperpolarizations, although a higher concentration of Oxy‐Hb was required to inhibit the SNP‐induced hyperpolarization. Hydroquinone (50 μm) inhibited only the hyperpolarization induced by NO‐Cys.

Apamin (1 μm) partly inhibited i.j.ps and NO‐Cys‐induced hyperpolarization, but not the SNP‐induced hyperpolarization. Tetraethylammonium (TEA; 1 mm), 4‐aminopyridine (4‐AP; 1 mm) or glibenclamide (1 μm) did not affect hyperpolarization induced by NO‐Cys and SNP.

8‐Bromo cyclic guanosine 3′:5′‐monophosphate (1 mm) also produced hyperpolarization. Apamin (1 μm), TEA (1 mm) and glibenclamide (5 μm) all failed to inhibit this hyperpolarization.

These results indicate that NO‐Cys and EFS hyperpolarize the membrane by activating apamin‐sensitive and TEA‐resistant K+ channels and favour the hypothesis that a NO‐liberating substance may act as a neurotransmitter in non‐adrenergic, non‐cholinergic (NANC) neurones in the rat forestomach. Our results also suggest that increase in cyclic GMP may cause apamin‐resistant hyperpolarization but the apamin‐sensitive hyperpolarization is mediated by another mechanism.
A2‐purinoceptor‐mediated relaxation in the guinea‐pig coronary vasculature: a role for nitric oxide
Authors: Vials Amanda , Burnstock Geoffrey
Published: July 2012

The Langendorff heart preparation was used to investigate the mechanism of action of the endothelium‐dependent vasodilatation evoked by adenosine and its analogues in the guinea‐pig coronary vasculature.

The relative order of potency of adenosine and its analogues in causing a reduction in perfusion pressure was d‐5′‐(N‐ethylcarboxamide)adenosine (NECA) = 2‐[p‐(2‐carboxyethyl)phenylethylamino]‐5′‐N‐ethylcarboxamidoadenosine (CGS 21680)>R‐N6‐(2‐phenylisopropyl)adenosine (R‐PIA) = adenosine = 2‐chloroadenosine (2‐CA)>S‐N6‐(2‐phenylisopropyl)adenosine (S‐PIA) = N6‐cyclopentyl‐adenosine (CPA); thus suggesting the presence of A2‐purinoceptors in this preparation.

8‐(p‐Sulphophenyl)theophylline (8‐PSPT; 3 × 10−5 m) significantly reduced both the maximum amplitude and area of the vasodilatation produced in response to adenosine (5 × 10−10 − 5 × 10−8 mol) without having any effect on the response to the P2‐purinoceptor agonist, 2‐methylthioATP. The relaxation induced by adenosine (5 × 10−12 − 5 × 10−8 mol) was unaffected by the selective A1‐purinoceptor antagonist 1,3‐dipropyl‐8‐cyclopentylxanthine (DPCPX; 10−8 m). This antagonist profile suggests that only A2‐purinoceptors are present in the guinea‐pig coronary vasculature.

The areas of the vasodilator response to adenosine (5 × 10−10 − 5 × 10−7 mol), NECA (5 × 10−12 − 5 × 10−7 mol) and CGS 21680 (5 × 10−12 − 5 × 10−10 mol) were significantly reduced by NG‐nitro‐l‐arginine methyl ester (l‐NAME; 3 × 10−5 m). The amplitude of the responses to low concentrations of adenosine (5 × 10−10 − 5 × 10−9 mol), NECA (5 × 10−11 mol) and CGS 21680 (5 × 10−11 − 5 × 10−9 mol) were significantly reduced by l‐NAME (3 × 10−5 m).

l‐Arginine (1.5 × 10−3m) significantly reversed the inhibition, by l‐NAME (3 × 10−5m), of the relaxant response to adenosine (5 × 10−8 mol), NECA (5 × 10−9 mol) and CGS 21680 (5 × 10−11 mol).

Indomethacin (10−6 m) did not inhibit the response to adenosine, except at low doses (5 × 10−11 − 5 × 10−10 mol).

It is concluded that in the guinea‐pig coronary vasculature, while a major part of the vasodilator action of adenosine is probably directly via A2‐receptors on the smooth muscle, activation of a subpopulation of A2‐purinoceptors on endothelial cells by adenosine and its analogues induces relaxation via production of nitric oxide; prostanoids appear to play a minimal role in the relaxation induced by adenosine as in most other preparations.
Effects of prolonged application of isoprenaline on intracellular free magnesium concentration in isolated heart of rat
Authors: Nishimura H. , Matsubara T. , Ikoma Y. , Nakayama S. , Sakamoto N.
Published: July 2012

The effect of prolonged application of isoprenaline on intracellular free‐Mg2+ concentration ([Mg2+]i) was examined by use of 31P‐nuclear magnetic resonance (31P‐n.m.r.) in rat isolated hearts. Left ventricular pressure (LVP) was simultaneously measured.

[Mg2+]i was estimated from the separation of the α‐ and β‐ATP peaks, using the dissociation constant of MgATP 38 μm (established previously). In normal (phosphate‐free, Krebs‐Henseleit) solution, [Mg2+]i was approximately 0.4 mm.

When isoprenaline was applied for 100 min, a transient increase in [Mg2+]i was observed during the initial 25 min, whilst concentrations of ATP ([ATP]) and phosphocreatine ([PCr]) decreased and [Pi] correspondingly increased. During the subsequent 75 min of isoprenaline application, [Mg2+]i decreased below its resting levels. Washout of isoprenaline restored [Mg2+]i and [PCr], but [ATP] remained low. These changes elicited by isoprenaline were not observed in the presence of propranolol, a typical α‐adrenoceptor blocker.

Isoprenaline increased both LVP and heart rate. The increased LVP and heart rate slowly returned to lower values during prolonged application of isoprenaline, but remained higher than those before application.

The transient rise in [Mg2+]i elicited by isoprenaline could be attributed to the decrease in [ATP] resulting in a release of Mg2+. The subsequent decrease in [Mg2+]i during the prolonged applications suggests that β‐adrenoceptor stimulation itself facilitates Mg2+‐extruding mechanism(s).
Functional importance of cholinergic and purinergic neurotransmission for micturition contraction in the normal, unanaesthetized rat
Authors: Igawa Yasuhiko , Mattiasson Anders , Andersson Karl‐Erik
Published: July 2012

The cholinergic and purinergic neurotransmission involved in micturition in the normal, unanaesthetized rat was investigated by means of continuous cystometry.

ATP (1 and 5 mg kg−1), administered intra‐arterially (i.a.) close to the bladder, produced rapid, phasic, dose‐dependent increases in bladder pressure with micturition immediately after injection. The micturition pressure of the following spontaneous voidings increased, and bladder capacity, micturition volume, and residual volume decreased. Pretreatment with α,β‐methylene ATP (1 mg kg−1, i.a.) blocked the effects of ATP (5 mg kg−1).

α,β‐Methylene ATP (0.25, 0.5 and 1 mg kg−1, i.a.) produced rapid, phasic, increases in bladder pressure with micturition immediately after injection. The effects of α,β‐methylene ATP (0.25 mg kg−1, i.a.) were not affected by pretreatment with indomethacin (0.5–2 mg kg−1, i.a.). The micturition pressure of the subsequent spontaneous voidings decreased, and bladder capacity and residual volume increased.

Carbachol (5–50 μg kg−1, i.a.) produced rapid, sustained, dose‐dependent increases in bladder pressure with micturition, and then increased basal pressure, threshold pressure, and micturition pressure, and decreased bladder capacity and micturition volume during the following spontaneous voidings.

Atropine (1 mg kg−1, i.a.) decreased micturition pressure and micturition volume, but did not induce dribbling incontinence. Micturition contractions still occurred after the injection, but changed in appearance and were of shorter duration than before. In the presence of atropine (1mg kg−1, i.a.), α,β‐methylene ATP (1 mg kg−1, i.a.) produced initially a phasic increase in bladder pressure with micturition and then dribbling incontinence in all animals tested.

After blockade of the micturition reflex with morphine (10 μg intrathecally), ATP (5 mg kg−1, i.a.), α,β‐methylene ATP (0.25–1 mg kg−1, i.a.), and carbachol (5–500 μg kg−1, i.a.) were unable to empty the bladder.

The results suggest that drug‐induced bladder emptying in the normal, unanaesthetized rat requires an intact micturition reflex and they support the view that the two physiologically important transmitters involved in micturition are acetylcholine and ATP.
Investigations of the dual contractile/relaxant properties showed by antioquine in rat aorta
Authors: Ivorra M. Dolores , Lugnier Claire , Catret Maria , Anselmi Elsa , Cortes Diego , D'Ocon Pilar
Published: July 2012

In the present study we assessed the activity of antioquine, a bisbenzyltetrahydroisoquinoline alkaloid isolated from Pseudoxandra sclerocarpa, by examining its effects on the contractile activity of rat isolated aorta, specific binding of [3H]‐(+)‐cis‐diltiazem, [3H]‐nitrendipine and [3H]‐prazosin to cerebral cortical membranes and the different molecular forms of cyclic nucleotide phosphodiesterases (PDE) isolated from bovine aorta.

Contractions in rat aorta induced by high concentrations of KCl (80 mm) and noradrenaline (1 μm) were inhibited by antioquine in a concentration‐dependent manner (0.1 μm– 300 μm). The alkaloid appeared more potent against KCl‐induced contractions. This inhibitory effect was observed at both 37°C and 25°C.

Paradoxically, at the highest concentration tested (300 μm) antioquine induced a contractile response of similar magnitude in the presence and absence of extracellular calcium, at 37°C. This activity was greatly attenuated at 25°C. Antioquine‐induced contractions were not inhibited by prazosin (0.1 μm), nifedipine (1 μm) or diltiazem (100 μm). On the contrary, prazosin and nifedipine slightly increased the contractions in the presence of extracellular calcium. Papaverine (100 μm) partially inhibited the contractile response to antioquine both in the presence and absence of extracellular calcium.

At 25°C, in Ca2+‐free solution, antioquine (300 μm) did not modify the contractile response (phasic and tonic) evoked by noradrenaline, but increased the phasic contraction induced by caffeine. At 37°C, the contraction elicited by antioquine made it impossible to observe the noradrenaline‐induced one.

Antioquine showed affinity for the [3H]‐prazosin binding site and for the [3H]‐(+)‐cis‐diltiazem binding site of the Ca2+‐channel receptor complex, but had no effect at the dihydropyridine binding site in rat cerebral cortex.

Antioquine weakly inhibited some PDE forms isolated from bovine aorta: a CaM‐PDE (PDE I) which preferentially hydrolyzes cyclic GMP and is activated by calmodulin, and a rolipram‐sensitive cyclic AMP‐PDE (PDE IV) which hydrolyzed cyclic AMP. Antioquine did not exert any inhibitory effect on the other forms of PDE, a cyclic GMP selective form (PDE V) and a low Km cyclic AMP‐PDE that is inhibited by cyclic GMP (CGI‐PDE, PDE III).

The present work provides evidence that antioquine has properties both as a calcium entry blocker (possibly through the benzodiazepine recognition site in the calcium channel) and as a contractile agent. Its mechanism of action as a contractile agent is not related to Ca2+‐entry and is hypothetically similar to that of calyculin‐A or okadaic acid. The possible involvement of α‐adrenoceptors in this paradoxical effect cannot be excluded. The rigidity of the molecule provides an interesting model for analyzing this contractile mechanism and the intracellular processes involved.
On the high affinity binding site for [3H]‐1,3‐dipropyl‐8‐cyclopentylxanthine in frog brain membranes
Authors: Oliveira J.C. , Sebastião A.M. , Ribeiro J.A.
Published: July 2012

Radioligand binding properties of the adenosine receptor ligands, [3H]‐1,3‐dipropyl‐8‐cyclopentylxanthine ([3H]‐DPCPX), and [3H]‐R‐phenylisopropyladenosine ([3H]‐R‐PIA) were investigated in frog brain membranes.

The specific binding of the adenosine antagonist, [3H]‐DPCPX to frog brain membranes showed one binding site with Kd and Bmax values of 43.8 nm and 0.238 ± 0.016 pmol mg−1 protein, respectively. Guanosine 5′‐triphosphate (GTP, 100 μm) decreased to 72 ± 7% and Mg2+ (8 mm) increased to 121 ± 3% [3H]‐DPCPX (40 nm) binding to frog brain membranes.

[3H]‐DPCPX saturation binding experiments performed in the presence of Mg2+ (8 mm), or in the presence of GTP showed that Mg2+ ions decreased the Kd value of [3H]‐DPCPX to 14 nm, and GTP increased this value to 65.6 nm. Bmax values were not significantly (P > 0.05) modified (0.261 ± 0.018 pmol mg−1 protein, with Mg2+, and 0.266 ± 0.026 pmol mg−1 protein, in presence of GTP) by the presence of Mg2+ or GTP.

The specific binding of [3H]‐R‐PIA (15 nm) was decreased to 37 ± 6% by GTP (100 μm) and increased to 123 ± 4% by Mg2+ (8 mm). [3H]‐R‐PIA saturation binding experiments performed in the presence of Mg2+ (8 mm) showed one binding site with Kd and Bmax values of 0.9 nm and 0.229 ± 0.008 pmol mg−1 of protein, respectively.

The concentration‐inhibition curves of adenosine agonists and antagonists versus [3H]‐DPCPX binding showed the following order of potencies: CPA > R‐PIA ≃ NECA > S‐PIA > > CGS 21680, for the agonists, and XAC ≃ DPCPX > > XCC > PACPX, for the antagonists.

The present results suggest that the adenosine binding site in the frog brain membranes is G‐protein coupled, but that the antagonist affinities and the pharmacological profile is different from the A1 or A2 adenosine receptors.
The antiarrhythmic effects of the nucleoside transporter inhibitor, R75231, in anaesthetized pigs
Authors: Wainwright C.L. , Parratt J.R. , Van Belle H.
Published: July 2012

The effect of R75231, an inhibitor of purine nucleoside transport, were examined on ischaemic arrhythmias in anaesthetized pigs.

In closed chest pigs (n = 4), R75231 exerted a moderate dose‐dependent decrease in mean arterial blood pressure (from 97 ± 4 mmHg to 95 ± 4, 90 ± 1 and 83 ± 2 mmHg at 25, 50 and 100 μg kg−1 respectively) and produced a dose‐related shift to the left of the blood pressure dose‐response curve to intravenous bolus doses of adenosine. The degree of inhibition of adenosine uptake by R75231, assessed ex vivo in erythrocyte suspensions, was 43 ± 5%, 64 ± 13 and 114 ± 15% at doses of 25, 50 and 100 μg kg−1 respectively.

In open chest pigs, intravenous injection of R75231 (50 μg kg−1; n = 6 and 100 μg kg−1; n = 10) induced a dose‐related decrease in both systolic and diastolic arterial blood pressure which was more marked than in closed‐chest pigs (mean pressure 86 ± 4 to 70 ± 2 mmHg and 88 ± 6 to 60 ± 6 mmHg with 50 and 100 μg kg−1 respectively), without affecting heart rate or myocardial contractility. Coronary artery occlusion in these pigs caused a secondary decrease in blood pressure. This was not observed in controls (n = 10). The lower dose of R75231 did not exert any antifibrillatory effects, whereas the higher dose significantly reduced the incidence of ventricular fibrillation, from 80% in control pigs to 30%. Neither dose modified the incidence of ventricular tachycardia (33% and 40% with 50 and 100 μg kg−1 respectively, compared to 30% in controls) or had any effect on the total number of ventricular ectopic beats (85 ± 47 and 130 ± 31 vs 110 ± 19 in controls). R75231, at a dose of 100 μg kg−1, also attenuated the ischaemia‐induced shortening of QRS‐interval, but neither dose modified the ST‐segment depression seen following occlusion.

These results show that the nucleoside transport inhibitor, R75231, exerts an antifibrillatory effect in a model of severe myocardial ischaemia in a dose which completely inhibits adenosine uptake ex vivo. However, while this agent has minimal haemodynamic effects in closed chest animals, the reduction in blood pressure induced by R75231 in open‐chest pigs cannot be excluded as a possible contributory mechanism of the antiarrhythmic effects of this drug.
Prevention of nitric oxide synthase induction in vascular smooth muscle cells by microtubule depolymerizing agents
Authors: Marczin Nándor , Papapetropoulos Andreas , Jilling Tamás , Catravas John D.
Published: July 2012

We investigated the role of microtubules in the induction of nitric oxide synthase in cultured vascular smooth muscle cells. We found that like interleukin‐1α, lipopolysaccharide elicited a time and concentration‐dependent accumulation of cyclic GMP via induction of nitric oxide synthase. Nocodazole and colchicine, two chemically distinct microtubule depolymerizing agents, completely prevented lipopolysaccharide‐ and interleukin‐induced (and nitric oxide‐mediated) cyclic GMP generation. In contrast to lipopolysaccharide and interleukin‐1α, cyclic GMP accumulation in response to sodium nitroprusside, an exogenous nitrovasodilator, was not altered by either nocodazole or colchicine. Our findings demonstrate that microtubule depolymerizing agents inhibit nitric oxide synthase induction and suggest a prominent role for microtubules in mediating the activation of the inducible nitric oxide pathway in smooth muscle cells.
5‐HT1B receptors mediate potent contractile responses to 5‐HT in rat caudal artery
Authors: Craig Douglas A. , Martin Graeme R.
Published: July 2012

5‐Hydroxytryptamine (5‐HT) evoked potent contractile responses in phenoxybenzamine‐treated ring segments of rat caudal artery, partially contracted with U46619. Responses were mimicked by 5‐HT1‐selective agonists with the potency order: RU24969 > 5‐carboxamidotryptamine > 5‐HT = CP 93,129 > > sumatriptan. 8‐Hydroxy‐N,N‐dipropylaminotetralin was virtually inactive. Responses were unaffected by spiperone (0.1 μm) and mesulergine (1.0 μm), but were antagonized competitively by (±)‐cyanopindolol affording agonist‐independent pKB estimates of 8.4 to 8.9. The pharmacological profile of this receptor is consistent with that of the 5‐HT1B subtype. Since the 5‐HT1B receptor is the rodent homologue of the 5‐HT1Dβ subtype, it might be anticipated that 5‐HT1Dβ receptors will be found to mediate vasoconstrictor responses in non‐rodent species.
Development of a radioligand binding assay for 5‐HT4 receptors in guinea‐pig and rat brain
Authors: Grossman C.J. , Kilpatrick G.J. , Bunce K.T.
Published: July 2012

The 5‐HT4 receptor antagonist, GR113808, has been radiolabelled to a high specific activity with tritium.

Characterization of specific [3H]‐GR113808 binding in homogenates of guinea‐pig striatum and hippocampus revealed a single site of high affinity (Kd values 0.20 and 0.13 nm respectively).

[3H]‐GR113808 binding was reversible and displayed rapid kinetics such that association and dissociation were complete within 3 min.

Specific [3H]‐GR113808 binding was potently and stereoselectively inhibited by agonists and antagonists acting at the 5‐HT4 receptor but not by compounds selective for other 5‐HT receptors or other neurotransmitter receptors.

Autoradiographic analysis revealed a discrete localization in both guinea‐pig and rat brain with high concentrations of binding in brain areas such as the striatum, substantia nigra and olfactory tubercle.

[3H]‐GR113808 binding to homogenates of guinea‐pig striatum meets the criteria for labelling of the 5‐HT4 receptor and, as such, represents the first characterization of this receptor in a radioligand binding assay.