bluuebunny/crossref_metadata_2025 huggingface dataset:
Tachykininergic transmission to the circular muscle of the guinea‐pig ileum: evidence for the involvement of NK2 receptors
Authors: Bartho Lorand , Santicioli Paolo , Patacchini Riccardo , Maggi Carlo Alberto
Published: July 2012

The effect of newly developed, receptor‐selective tachykinin antagonists (GR 71,251 for NK1 receptors, MEN 10,376 and L 659,877 for NK2 receptors) on noncholinergic transmission to the circular muscle of the guinea‐pig ileum has been investigated.

In circular muscle strips of the ileum, electrical field stimulation in the presence of atropine (2 μm) and apamin (0.1 μm) evoked a complex motor response. The tonic primary contraction in this response was reduced by GR 71,251 (10 μm) and MEN 10,376 (3–10 μm) but not by L 659,877 (up to 10 μm). The presence of apamin was necessary in this experimental arrangement to unmask an atropine‐resistant primary contraction, sensitive to tachykinin antagonists. The motor response was abolished by tetrodotoxin.

In circular strips of the ileum GR 71,251 (10 μm) inhibited the tonic contraction produced by [Sar9] substance P sulphone, a selective NK1 receptor agonist but not that produced by [β Ala8] neurokinin A (4–10), a selective NK2 receptor agonist. By contrast, MEN 10,376 antagonized the effect of the NK2 agonist while leaving the response to the NK1 agonist unaffected.

In whole segments of the ileum, distension of the gut wall by an intraluminal balloon placed at about 1 cm from the point of recording of mechanical activity of the circular muscle produced atropine‐sensitive phasic contractions (ascending enteric reflex). In the presence of atropine (2 μm), a noncholinergic response was elicited, which required larger volumes of distension that the cholinergic one. The atropine‐resistant ascending enteric reflex was enhanced by apamin (0.1 μm) and abolished by tetrodotoxin, either in the presence or absence of apamin.

MEN 10,376 (3–10 μm) inhibited the atropine‐resistant ascending enteric reflex in the presence of apamin while GR 71,251 or L 659,877 (10 μm each) were ineffective. MEN 10,376 inhibited the atropine‐resistant ascending enteric reflex to a larger extent in the absence than in the presence of apamin and also slightly inhibited the ascending enteric reflex in the absence of atropine.

These findings provide evidence for an involvement of NK2 tachykinin receptors in excitatory transmission to the circular muscle of the guinea‐pig ileum. NK2 receptors are also involved in the physiological‐like circular muscle activation produced by stimulation of intramural neuronal pathways which subserve the atropine‐resistant ascending enteric reflex.
Effect of α‐human atrial natriuretic peptide on the synthesis of dopamine in the rat kidney
Authors: Soares‐da‐Silva P. , Fernandes M. Helena
Published: July 2012

The present study has examined the influence of α‐human atrial natriuretic peptide (α‐hANP) on the synthesis of dopamine and its deamination into 3,4‐dihydroxyphenylacetic acid (DOPAC) in rat kidney slices loaded with exogenous l‐dihydroxyphenylalanine (l‐DOPA).

α‐hANP (3.3 and 330 nm) was found to produce a marked reduction (63– 78% reduction) in the time‐dependent accumulation of newly‐formed dopamine and of its deaminated metabolite DOPAC in kidney slices loaded with 10 μm l‐DOPA. α‐hANP (330 nm) was also found to decrease the accumulation of newly‐formed dopamine (45– 66% reduction) and DOPAC (38– 61% reduction) in experiments in which increasing concentrations (1– 100 μm) of l‐DOPA were used. This inhibitory effect was found to be potentiated by zaprinast (M&B 22,948; 10 μm), a guanosine cyclic 3′,5′‐monophosphate (cyclic GMP) phosphodiesterase inhibitor. Alone, zaprinast also decreased the accumulation of both dopamine (54–71% reduction) and DOPAC (73– 92% reduction).

In kidney homogenates, α‐hANP (330 nm) was found to affect neither the formation of dopamine nor its deamination to DOPAC.

Both α‐hANP (330 nm) and zaprinast (10 μm) were found not to affect the formation of dopamine and DOPAC in kidney slices obtained from rats on a high salt diet during the previous 6 weeks. A similar situation was also found to occur when kidney slices obtained from 24‐months old rats were used.

The results obtained suggest that the inhibitory effect of α‐hANP on the renal synthesis of dopamine is dependent on the activation of a membrane‐operated mechanism, coupled to the enzyme guanylate cyclase, controlling the entry of l‐DOPA into the cells.
Direct and indirect stimulations of cyclic AMP formation in human brain
Authors: Kendall D.A. , Millns P.J. , Firth J.L.
Published: July 2012

Adenosine 3′:5′‐cyclic monophosphate (cyclic AMP) formation, by use of an [3H]‐adenine prelabelling assay, was measured in fragments of human cerebral cortex, taken in the course of various neurosurgical procedures.

Large accumulations of [3H]‐cyclic AMP due to isoprenaline, noradrenaline and adenosine and small effects due to forskolin were observed. Histamine, 5‐hydroxytryptamine (5‐HT) and the excitatory amino acids glutamate and quisqualate were ineffective.

The response to noradrenaline consisted of two components; a direct β‐adrenoceptor response and an enhancement mediated by an α.‐adrenoceptor which appears to be similar to that in rat cerebral cortex.

The response to isoprenaline was also potentiated by histamine H1 receptor stimulation but the direct effect of 2‐chloroadenosine was not altered by histamine, 5‐HT or quisqualate.

It is concluded that some, but not all, of the indirect modulations of cyclic AMP formation previously observed in experimental animal brain exist in human cerebral cortex.
Differences in neurokinin receptor pharmacology between rat and guinea‐pig superior cervical ganglia
Authors: Seabrook G.R. , Main M. , Bowery B. , Wood N. , Hill R.G.
Published: July 2012

The depolarizations elicited by seven neurokinin receptor agonists were examined in both rat and guinea‐pig superior cervical ganglia by use of grease‐gap methodology in the presence of tetrodotoxin (0.1 μm). Responses were normalised with respect to 1 μm eledoisin.

The rank order of agonist potency in the rat ganglia was senktide > substance P > substance P methyl ester = eledoisin = Sar‐Met‐substance P > neurokinin B > neurokinin A, whereas in guinea‐pig superior cervical ganglion (SCG) the rank order was senktide > Sar‐Met‐substance P > neurokinin B = eledoisin = substance P methyl ester. The concentration‐effect curves for substance P and neurokinin A in guinea‐pig ganglia were biphasic which precluded the determination of meaningful potency values.

The maximal depolarization achieved by subtype selective ligands was different between these two species. On rat and guinea‐pig SCG, the NK3‐selective ligand, senktide, produced a maximal depolarization of 27% and 274% respectively, whereas the NK1‐selective ligand, substance P methyl ester, produced depolarizations of 77% and 64% respectively.

The depolarizations induced by substance P methyl ester and senktide in either species were unaffected by atropine (1 μm), suggesting a lack of involvement of presynaptic neurokinin receptors in the generation of the response.

The potency of substance P methyl ester, senktide, and neurokinin A were unaffected by pretreating ganglia with the peptidase inhibitors bacitracin (40 μg ml−1), leupeptin (4 μg ml−1), and chymostatin (2 μg ml−1). Similarly, these peptidase inhibitors had no effect on the maximal depolarizations achieved by any of these agonists.

It is evident that rat and guinea‐pig superior cervical ganglia possess both NK1 and NK3 receptors, but that their net contribution to depolarizations are different between the two species. The depolarizations in guinea‐pig SCG are mediated predominantly by an NK3 subtype and in rat SCG by an NK1 receptor subtype.
Studies on the cardiac actions of flosequinan in vitro
Authors: Gristwood R.W. , Beleta J. , Bou J. , Cardelús I. , Fernández A.G. , Llenas J. , Berga P.
Published: July 2012

We have investigated the in vitro cardiac actions of flosequinan and of its major metabolite in man, BTS 53554.

Positive inotropic activity was seen with flosequinan in guinea‐pig isolated ventricles, the threshold concentration for effect being less than 1 × 10−5 m. BTS 53554 was approximately half as potent as the parent compound.

In guinea‐pig working whole hearts flosequinan increased left ventricular dp/dtmax, indicating a positive inotropic action. This effect was accompanied by increases in heart rate, cardiac output and stroke volume.

The virtual complete inhibition of inotropic responses to flosequinan and BTS 53554 by carbachol suggests that these responses are adenosine 3′:5′‐cyclic monophosphate (cyclic AMP)‐mediated.

Flosequinan was shown to increase calcium inward current in guinea‐pig ventricle, an action consistent with a cyclic AMP involvement in the response.

The inotropic activity of flosequinan was not potentiated by the selective phosphodiesterase (PDE) III inhibitor SK&F 94120, a result which indicates that flosequinan does not increase cyclic AMP concentrations via stimulation of adenylate cyclase.

Flosequinan inotropic responses were potentiated by rolipram, a selective PDE IV inhibitor, a result consistent with flosequinan being itself a PDE III inhibitor.

Biochemical studies with purified enzymes confirmed that flosequinan and BTS 53554 are relatively selective inhibitors of PDE III.

A comparison of pharmacological and biochemical data for both flosequinan and BTS 53554 indicates that their PDE III inhibitory potency is sufficient to account for their inotropic activity.
Protein kinase C‐independent sensitization of contractile proteins to Ca2+ in α‐toxin‐permeabilized smooth muscle cells from the guinea‐pig stomach
Authors: Oishi Kazuhiko , Mita Mitsuo , Ono Teruaki , Hashimoto Takao , Uchida Masaatsu K.
Published: July 2012

Involvement of protein kinase C in receptor‐operated Ca2+ sensitization of cell shortening was investigated by use of α‐toxin‐permeabilized smooth muscle cells from the fundus of the guinea‐pig. Most of the isolated cells responded to 0.6 μm Ca2+ with a maximal shortening to approximately 65% of the resting cell length. Addition of acetylcholine (ACh) at a maximal concentration (10 μm) resulted in a marked decrease in the concentration of Ca2+ required to trigger a threshold response from 0.6 μm to 0.2 μm. The augmentation of Ca2+ sensitivity by ACh was not inhibited by specific protein kinase C inhibitors, calphostin C and K‐252b at a concentration of 1 μm. These findings suggest that protein kinase C is not involved in the muscarinic receptor‐operated augmentation of Ca2+ sensitivity.
The local intracoronary administration of methylene blue prevents the pronounced antiarrhythmic effect of ischaemic preconditioning
Authors: Vegh Agnes , Papp Julius Gy , Szekeres Laszlo , Parratt James
Published: July 2012

Short periods of coronary artery occlusion (2 × 5 min) markedly reduce the severity of arrhythmias and the changes in ST‐segment elevation and in the degree of inhomogeneity of conduction during a subsequent 25 min occlusion of the left anterior descending coronary artery in anaesthetized dogs. These changes were completely reversed if methylene blue (5 mg min−1) was infused into a side branch of the coronary artery throughout both the preconditioning and prolonged occlusions. These results suggest that the pronounced antiarrhythmic effects of preconditioning result from activation of guanylyl cyclase and result in increased levels of guanosine 3′:5′‐cyclic monophosphate.
Ramipril prevents left ventricular hypertrophy with myocardial fibrosis without blood pressure reduction: a one year study in rats
Authors: Linz Wolfgang , Schaper Jutta , Wiemer Gabriele , Albus Udo , Schölkens Bernward A.
Published: July 2012

Angiotensin converting enzyme (ACE)‐inhibitors have been demonstrated to be effective in the treatment of cardiac hypertrophy when used in antihypertensive doses. The aim of our one year study with an ACE‐inhibitor in rats was to separate local cardiac effects produced by a non‐antihypertensive dose from those on systemic blood pressure when an antihypertensive dose was used.

Rats made hypertensive by aortic banding were subjected to chronic oral treatment for one year with an antihypertensive dose of the ACE inhibitor, ramipril 1 mg kg−1 daily, (RA 1 mg) or received a low dose of 10 μg kg−1 daily (RA 10 μg) which did not affect high blood pressure.

Chronic treatment with the ACE‐inhibitor prevented left ventricular hypertrophy in the antihypertensive rats as did the low dose which had no effects on blood pressure. Similar effects were observed on myocardial fibrosis. Plasma ACE activity was inhibited in the RA 1 mg but not in the RA 10 μg group although conversion of angiotensin (Ang) I to Ang II in isolated aortic strips was suppressed in both treated groups. Plasma catecholamines were increased in the untreated control group, but treatment with either dose of ramipril normalized the values. The myocardial phosphocreatine to ATP ratio (an indicator of the energy state in the heart) was reduced in the vehicle control group whereas the hearts from treated animals showed a normal ratio comparable to hearts from sham‐operated animals.

After one year, five animals were separated from each group, treatment withdrawn, and housed for additional six months. In the RA 1 mg group, blood pressure did not reach the value of the control vehicle group and surprisingly, left ventricular hypertrophy and myocardial fibrosis did not recur in animals during withdrawal of treatment.

These data show that long term ACE inhibitor treatment with ramipril in antihypertensive and non‐antihypertensive doses prevented cardiac hypertrophy and myocardial fibrosis. This protective effect was still present after 6 months treatment withdrawal.
Phosphoramidon blocks big‐endothelin‐1 but not endothelin‐1 enhancement of vascular permeability in the rat
Authors: Lehoux Stéphanie , Plante Gérard E. , Sirois Martin G. , Sirois Pierre , D'Orléans‐Juste Pedro
Published: July 2012

Changes in vascular permeability following intravenous injections of human big‐endothelin‐1 (big‐ET‐1) and endothelin‐1 (ET‐1) were measured by extravasation of Evans blue dye (EB, 20 mg kg−1) in selected tissues.

A low dose of big‐ET‐1 (40 pmol kg−1) failed to alter vascular permeability but a dose of 400 pmol kg−1 increased EB extravasation in the trachea, upper and lower bronchi, and lung parenchyma by 55 to 69% (P < 0.05). Vascular permeability was also enhanced in the liver, spleen, kidney, heart, and diaphragm by 20, 14, 41, 25, and 67%, respectively (P < 0.05).

Upon injection of ET‐1 (400 pmol kg−1), EB extravasation increased in the upper and lower bronchi, lung parenchyma, liver, pancreas, kidney, heart, and diaphragm.

Administration of ET‐1 and big‐ET‐1 was not associated with significant systemic responses.

Pretreatment with phosphoramidon (PA) blocked the response to big‐ET‐1 in all tissues examined but this inhibitor failed to alter the response to ET‐1.

We conclude from these results that the dose‐dependent increase in vascular permeability induced by big‐ET‐1 in various tissues follows its conversion to ET‐1 by the endothelin converting enzyme, a PA‐sensitive process.
Potentiation of the vasorelaxant activity of nitric oxide by hydroxyguanidine: implications for the nature of endothelium‐derived relaxing factor
Authors: Zembowicz Artur , Swierkosz Tomasz A. , Southan Garry J. , Hecker Markus , Vane John R.
Published: July 2012

We recently demonstrated that NG‐hydroxy‐l‐arginine (l‐HOArg) is a substrate for the constitutive nitric oxide (NO) synthase present in bovine aortic endothelial cells cultured on microcarrier beads (EC). Furthermore, l‐HOArg reacts chemically with NO released from these cells to form a potent and more stable vasodilator. This is most likely through a reaction with the hydroxyguanidino group.

Here, we studied the interaction of a simpler molecule, hydroxyguanidine (HOG) with NO.

HOG (10 μm), like l‐HOArg (10 μm) or NG‐hydroxy‐d‐arginine (d‐HOArg, 10 μm), potentiated and stabilized the relaxant activity of authentic NO.

When NO was bubbled through the solution of HOG, a new compound was formed. It had similar physicochemical properties to those of the previously described l‐HOArg/NO adduct. It was also a potent vasodilator and its action was inhibited by oxyhaemoglobin (10 μm), indicating formation of a NO‐containing substance.

Moreover, HOG (10 μm) was not a substrate for the constitutive NO synthase present in the microsomal fraction of EC and did not affect the flow‐induced or bradykinin‐stimulated generation of prostacyclin, as measured by 6‐ketoPGF1α.

We also studied the effect of HOG on the endothelium‐derived relaxing factor (EDRF) released from the column of EC. HOG (10 μm) potentiated and stabilized the relaxations of rabbit aortic strips induced by EDRF released by bradykinin (5–20 pmol) or ADP (5–10 nmol). These relaxations were inhibited by NG‐nitro‐l‐arginine methyl ester (l‐NAME, 10 μm) and l‐arginine (l‐Arg, 1 mm) reversed the inhibitory effects of l‐NAME.

HOG (10 μm) augmented the basal (flow‐induced) EC‐dependent relaxations which were also inhibited by l‐NAME (10 μm) and the effects of l‐NOArg were reversed by l‐Arg (1 mm).

Thus, the hydroxyguanidino moiety of l‐HOArg is involved in the reaction with NO. Moreover, the comparable reaction of the hydroxyguanidino compounds with NO on the one hand and with flow‐induced and agonist‐triggered EDRF on the other, strongly supports their common identity.
Analysis of the agonist activity of fenoldopam (SKF 82526) at the vascular 5‐HT2 receptor
Authors: Christie Mark I. , Harper Diane , Smith George W.
Published: July 2012

The 5‐HT2 receptor agonist activity of fenoldopam (SKF 82526) was characterized in the rabbit isolated aorta preparation.

Fenoldopam was an agonist at the vascular 5‐HT2 receptor with lower affinity and efficacy than the naturally occurring agonist 5‐hydroxytryptamine (5‐HT). Fenoldopam had an affinity (pKA) of 5.84 ± 0.04 and efficacy (τ) of 0.57 ± 0.04, whereas 5‐HT had a pKA of 6.65 ± 0.12 and τ of 2.66 ± 0.41.

The constrictor effects of fenoldopam and 5‐HT were competitively antagonized by the 5‐HT2 antagonist, ketanserin, with pKB values of 8.81 ± 0.11 and 8.83 ± 0.10 respectively.

Prior incubation with fenoldopam produced a concentration‐related rightward shift of a subsequent 5‐HT concentration‐response curve. This inhibition was specific for 5‐HT since constrictor responses to angiotensin II were unaffected.

This study indicates that the D1 receptor agonist, fenoldopam, acts as an agonist at the vascular 5‐HT2 receptor, but with an affinity and efficacy less than that of the naturally occurring agonist, 5‐HT.
Mechanisms of the biphasic responses to endothelin‐3 in dog coronary arteries
Authors: Okamura Tomio , Matsumoto Tetsuya , Ikemoto Fumihiko , Toda Noboru
Published: July 2012

Endothelin‐3 (ET‐3) elicited relaxations at low concentrations (up to 10−8 m) and contractions at higher concentrations in dog isolated coronary arteries precontracted with prostaglandin F2α (PGF2α). The relaxation by ET‐3 was not affected by endothelium denudation nor treatment with NG‐nitro‐l‐arginine, but was abolished or reversed to a contraction by treatment with indomethacin and markedly suppressed by tranylcypromine, a PGI2 synthetase inhibitor, or diphloretin phosphate, a prostaglandin receptor antagonist. ET‐1 produced only concentration‐dependent contractions.

BQ‐123, a new selective ETA receptor antagonist, caused relaxation of the strips contracted with ET‐3 in a dose‐dependent manner and prevented the ET‐3‐induced contraction but did not affect the contraction produced by PGF2α. The relaxation caused by ET‐3 was enhanced by treatment with BQ‐123.

It is concluded that the relaxations elicited by ET‐3 in dog coronary arteries are mediated via liberation of PGI2 by activation of non‐ETA receptors, located in subendothelial tissues, possibly smooth muscle cells, whereas the peptide‐induced contractions are mediated via ETA receptors.
Potassium channel openers, NIP‐121 and cromakalim, enhance the relaxation induced by sodium nitroprusside in the guinea‐pig isolated trachea
Authors: Shikada Ken‐ichi , Tanaka Sakuya
Published: July 2012

The effect of the potassium channel openers, NIP‐121 and cromakalim, on agonist‐induced relaxation of the guinea‐pig isolated trachea was investigated and the results were compared with those in the epithelium‐denuded trachea.

Tracheal strips were incubated with a potassium channel opener or vehicle for 30 min in the presence of 5 μm indomethacin and then contracted with 30 nm leukotriene D4 (LTD4). Relaxant agents were added to the organ bath after the LTD4‐elicited contraction had reached a plateau.

In epithelium‐intact trachea, NIP‐121 0.1 μm and cromakalim 1 μm, which did not modify the LTD4 (30 nm)‐induced contraction, significantly enhanced the sodium nitroprusside (SNP)‐induced relaxation. This enhancement of relaxation was not seen in the case of relaxation induced by the cyclic AMP‐dependent bronchodilators isoprenaline, vasoactive intestinal peptide or prostaglandin E2. The enhancement of SNP‐induced relaxation by NIP‐121 and cromakalim was abolished in the presence of the ATP‐sensitive potassium channel blocker, glibenclamide (1 μm). NIP‐121 and cromakalim did not produce any significant changes in the relaxation induced by 8‐bromoguanosine‐cyclic monophosphate (8‐Br‐cyclic GMP), a cyclic GMP analogue.

In epithelium‐denuded trachea, SNP‐induced relaxation alone was significantly enhanced but that induced by 8‐Br‐cyclic GMP was not changed. Neither NIP‐121 nor cromakalim enhanced SNP‐induced relaxation in denuded trachea.

These results suggest that in the presence of an intact epithelium the enhancement by NIP‐121 and cromakalim of the relaxation of guinea‐pig tracheal smooth muscle induced by SNP may be associated with the opening of glibenclamide‐sensitive potassium channels.
Effects of cicletanine on haemodynamics, arrhythmias and extent of necrosis during coronary ligation in rabbits
Authors: Burton T. , Chakrabarty S. , Fluck D.S. , Flores N.A. , Sheridan D.J.
Published: July 2012

The effects of cicletanine on arrhythmias, haemodynamics and extent of necrosis during myocardial ischaemia were investigated in rabbits subjected to coronary ligation.

Cicletanine increased cardiac output prior to coronary occlusion (P < 0.01) but had no other significant haemodynamic effects at this time and did not significantly alter heart rate, blood pressure or cardiac output during 30 min of ischaemia or 30 min of reperfusion.

Ventricular fibrillation and mortality were greater in control (65% and 60% respectively) than treated animals (15.4% and 15.4%, P < 0.01).

The extent of myocardial necrosis expressed as a percentage of the area at risk was also reduced by cicletanine from 61 ± 8% in controls to 37 ± 6% (P < 0.05).

These findings indicate that cicletanine attenuates arrhythmias and preserves myocardium in the early phase of ischaemia and this effect appears to be independent of an established antihypertensive action.
Involvement of nitric oxide in the regional haemodynamic effects of perindoprilat and captopril in hypovolaemic Brattleboro rats
Authors: Gardiner Sheila M. , Bennett Terence
Published: July 2012

Male, homozygous Brattleboro (i.e. vasopressin‐deficient) rats were chronically instrumented with pulsed Doppler flow probes and intravascular catheters, and were studied 5 h after a subcutaneous injection of an hyperoncotic solution of polyethylene glycol to render them hypovolaemic, and hence dependent on the renin‐angiotensin system for maintenance of haemodynamic status. Pilot experiments showed that, in this model, primed infusion of perindoprilat (0.05 mg kg−1 bolus, 0.05 mg kg−1 h−1 infusion) or captopril (0.2 mg kg−1 bolus, 0.2 mg kg−1 h−1 infusion) just abolished the pressor effect of angiotensin I (120 pmol), and had similar initial hypotensive and renal hyperaemic vasodilator effects.

Perindoprilat had more sustained hypotensive, and mesenteric and hindquarters vasodilator effects than captopril in the presence of saline. In the presence of NG‐nitro‐l‐arginine methyl ester (l‐NAME 3 mg kg−1 h−1), the renal vasodilator effects of perindoprilat were unchanged, whereas the other haemodynamic effects of perindoprilat and captopril were reduced. Hence, in the presence of l‐NAME, all haemodynamic effects of perindoprilat were greater than those of captopril.

The renal hyperaemic vasodilator effects of acetylcholine were abolished by l‐NAME and by perindoprilat, and were markedly reduced by captopril. However, since perindoprilat and captopril caused such marked renal hyperaemic vasodilatation themselves, it is feasible this change in baseline status contributed to their effects. It is unlikely this could be a full explanation of the results, because the haemodynamic effects of lemakalim were unchanged under any experimental conditions.

Bradykinin alone, or in the presence of saline, caused mesenteric hyperaemic vasodilatation whereas, in the presence of perindoprilat or captopril, bradykinin caused marked renal and mesenteric vasoconstrictions. However, in the additional presence of l‐NAME, the mesenteric vasoconstriction was reduced, yet the hypotensive effect of bradykinin was augmented. One possible explanation of these observations is that, in the presence of l‐NAME and either perindoprilat or captopril, bradykinin caused marked coronary vasoconstriction, leading to a reduction in cardiac output.

Neither perindoprilat nor captopril impaired the pressor, or renal, mesenteric, or hindquarters vasoconstrictor effects of l‐NAME. Indeed, in their presence, the effects of l‐NAME were generally enhanced, consistent with perindoprilat and captopril causing activation of nitric oxide‐dependent mechanisms that were subsequently inhibited by l‐NAME.
Characteristics of the contractile response of rabbit aorta produced by cromakalim in calcium‐free solution
Authors: Duty S. , Weston A.H.
Published: July 2012

The effect of potassium channel opening compounds has been investigated in the smooth muscle of rabbit aorta under Ca‐free conditions. Examination of the characteristics of the response has been performed using cromakalim as the prototype compound.

In order of potency, Ro 31–6930, cromakalim, minoxidil sulphate and pinacidil each produced a contraction in rabbit aortic strips bathed in Ca‐free MOPS‐buffered physiological salt solution (PSS). In contrast, forskolin, glyceryl trinitrate and nifedipine each failed to increase tension under identical conditions. Cromakalim also evoked contraction of bovine trachealis muscle bathed in Ca‐free PSS.

The contractile response to cromakalim in rabbit aortic strips was of delayed onset (15–20 min) and reached a plateau after approximately 120 min (1.8 g maximum with 1 μm cromakalim). No cromakalim‐induced tension changes were observed in either 1 mm or 2.5 mm Ca‐containing PSS.

Raising the [KCl] of the Ca‐free PSS to 65.9 mm fully inhibited the cromakalim‐induced contraction in rabbit aortic strips. In addition, pretreatment of aortic strips with the sulphonylurea glibenclamide antagonized the subsequent mechanical response to cromakalim.

In Ca‐free PSS, cromakalim (1 μm) stimulated 42K‐efflux with a time‐course corresponding to the contractile event. Glibenclamide (1 μm) inhibited this cromakalim‐induced 42K‐efflux.

In sharp microelectrode studies in bovine trachealis, cromakalim (10 μm) produced a sustained membrane hyperpolarization in normal PSS. In contrast, the cromakalim‐induced hyperpolarization in Ca‐free PSS was not sustained. The fading of the hyperpolarization was temporally correlated with the increase in tension under these experimental conditions.

It is concluded that the K‐channel opener‐induced smooth muscle contractile response revealed in Ca‐free PSS is the consequence of K‐channel opening. The nature of the detailed mechanism which underlies this contractile phenomenon remains to be determined.
Effects of acromelic acid A on the binding of [3H]‐kainic acid and [3H]‐AMPA to rat brain synaptic plasma membranes
Authors: Smith Adam L. , McIlhinney R.A. Jeffrey
Published: July 2012

The ability of acromelic acid A to inhibit [3H]‐kainic acid and [3H]‐(RS)‐α‐amino‐3‐hydroxy‐5‐methyloxazole‐4‐propionic acid ([3H]‐AMPA) binding to rat brain synaptic plasma membranes was investigated by equilibrium radioligand binding assay.

Kinetic analysis of [3H]‐kainic acid binding demonstrated the existence of two kainate binding sites in this tissue preparation and yielded equilibrium dissociation constants for [3H]‐kainic acid of KD = 0.4 nm and KD = 20.8 nm.

Kainic acid and domoic acid both appeared to displace [3H]‐kainic acid from a single binding site with equilibrium binding constants of KD = 19.4 nm and Ki= 14.5 nm respectively. Acromelic acid A exhibited a biphasic inhibition of [3H]‐kainic acid binding to synaptic membranes with binding affinities of Ki = 15.1 nm and Ki = 1.49 μm.

In the absence of chaotropic ions, the order of potency of inhibition of [3H]‐AMPA binding was acromelic acid A (Ki = 26 nm) > AMPA (KD = 184 nm) > domoic acid (Ki = 499 nm).

The inclusion of 100 mm thiocyanate ion in the [3H]‐AMPA binding assay resulted in a change in the order of potency to: AMPA (KD = 160 nm) > acromelic acid A (Ki = 289 nm) > domoic acid (Ki = 9.02 μm).

These results show that acromelic acid A distinguishes two kainate binding sites in rat brain synaptic plasma membranes and in addition, that in the absence of chaotropic ions, acromelic acid A is the most potent displacer of [3H]‐AMPA binding yet described.
Subtype classification of the presynaptic α‐adrenoceptors which regulate [3H]‐noradrenaline secretion in guinea‐pig isolated urethra
Authors: Alberts Pèteris
Published: July 2012

The following experiments were carried out to investigate the presence and type of functional presynaptic receptors in adrenergic nerves of the guinea‐pig urethra.

The urethra from male guinea‐pigs was incubated with [3H]‐noradrenaline and superfused with Tyrode solution in vitro. The fractional secretion of [3H]‐noradrenaline evoked by 300 electrical pulses was measured.

The [3H]‐noradrenaline secretion was positively frequency‐dependent, yielding a half‐maximal secretion at 8 ± 5 Hz. Stimulation was usually applied at 5 Hz.

The [3H]‐noradrenaline secretion was not altered by noradrenaline (1 or 100 μm), norephedrine (1 μm), isoprenaline (0.1 μm), 5‐hydroxytryptamine (10 μm), oxotremorine (10 μm), adenosine (0.2 mm), propranolol (1 μm), atropine (1 μm) or 8‐phenyltheophylline (10 μm).

The [3H]‐noradrenaline secretion was enhanced by clonidine (3 μm), chlorpromazine (10 μm), metitepine (1 μm), 4‐aminopyridine (0.5 mm), tetraethylammonium (2 mm), 3‐isobutyl‐1‐methylxanthine (4 mm), 8‐bromo cyclic AMP (1 mm) and forskolin (25 μm).

The α‐adrenoceptor antagonists rauwolscine, yohimbine, phentolamine, prazosin and AR‐C 239 maximally enhanced the [3H]‐noradrenaline secretion to about 300% of control. The partial α‐adrenoceptor agonist oxymetazoline maximally enhanced the secretion to about 200% of control. The order of apparent EC50 values was rauwolscine < yohimine < phentolamine < oxymetazoline < prazosin < AR‐C 239.

The enhancing effects of yohimbine (1 μ m) with tetraethylammonium (2 mm), 8‐bromo cyclic AMP (1 mm), or forskolin (25 μm) were additive, but not those of yohimbine (1 μm) with prazosin (10 μm), 4‐aminopyridine (0.5 mm), or 3‐isobutyl‐1‐methylxanthine (4 mm).

These results suggest that the [3H]‐noradrenaline secretion in the guinea‐pig urethra is regulated by presynaptic α2A‐adrenoceptors which may, in a cyclic AMP‐independent manner, be coupled to a 4‐aminopyridine‐sensitive potassium channel. The secretion is not influenced by compounds acting at β‐adrenoceptors, muscarinic cholinoceptors or adenosine receptors.
Responses to vasodilator drugs on pulmonary artery preparations from pulmonary hypertensive rats
Authors: Wanstall Janet C. , O'Donnell Stella R.
Published: July 2012

Relaxant responses to six vasodilator drugs, with different mechanisms of action, were examined on noradrenaline (0.1 μm)‐contracted ring preparations of pulmonary artery and aorta taken from rats with pulmonary hypertension induced by monocrotaline or chronic hypoxia.

On pulmonary artery preparations from monocrotaline‐treated rats, compared with controls, (a) the maximum relaxation to pinacidil and cromakalim was significantly increased, but their potency (negative log EC50) was unchanged, (b) the potencies of nitroprusside and sodium nitrite were significantly reduced (10 fold and 3 fold respectively), but there was no change in the maxima, (c) for nicorandil there was an increase in maximum relaxation and a decrease in potency (3 fold), and (d) for atriopeptin II there was no change in potency or maximum.

The increase in maximum relaxation for pinacidil and the decrease in potency for nitroprusside were also demonstrated in pulmonary artery preparations from rats with chronic hypoxic pulmonary hypertension. The other four drugs were not examined in preparations from hypoxic rats.

In both models of pulmonary hypertension, no change in maximum response or potency was seen on aortic preparations for any of the vasodilator drugs.

In control preparations, none of the drugs was more potent on pulmonary artery than on aorta (i.e. they were not pulmonary‐selective). In preparations from pulmonary hypertensive rats, pinacidil was selective for pulmonary artery, in contrast to nitroprusside which was selective for aorta.

It is concluded that the development of pulmonary hypertension in rats is accompanied by changes in the responsiveness of the pulmonary arteries to some vasodilator drugs; whether or not these changes occur depends on the mechanism of action of the vasodilator drug; but they are independent of the method of inducing pulmonary hypertension.

It is postulated that the reduction in potency seen for nitroprusside, sodium nitrite and nicorandil may be due to desensitization of soluble guanylate cyclase in pulmonary vascular smooth muscle in pulmonary hypertension.
Interference of cetirizine with the late eosinophil accumulation induced by either PAF or compound 48/80
Authors: Martins Marco A. , Pasquale Claudia P. , e Silva Patrícia M.R. , Pires Ana L.A. , Ruffié Claude , Rihoux Jean P. , Cordeiro Renato S.B. , Vargaftig B. Boris
Published: July 2012

The effect of topical or systemic treatment with the histamine H1‐receptor antagonist, cetirizine, on the rat pleural eosinophil accumulation induced by PAF or compound 48/80 was investigated. The number of pleural resident eosinophils increased 6 h after the intrathoracic (i.t.) injection of PAF (1 μg/cavity), peaked within 24 h and persisted significantly augmented for at least 96 h. Compound 48/80 (25 μg/cavity) also produced a long lasting pleural eosinophilia but this was first noted only 24 h after stimulation.

Intraperitoneal pretreatment with cetirizine inhibited eosinophilia induced by either PAF (ED50 = 19 mg kg−1) or compound 48/80 (ED50 = 14 mg kg−1) whereas meclizine, another histamine H1‐receptor antagonist, was inactive.

Administered locally, cetirizine (5 and 15 μg/cavity) also dose‐dependently inhibited both PAF‐ and compound 48/80‐induced eosinophilia, providing evidence that its inhibitory effect is not due to any action upon circulating eosinophils. Consistent with this result, incubation of isolated peritoneal eosinophils with cetirizine failed to modify in vitro eosinophil migration caused by PAF.

Since the late eosinophilia induced by PAF may depend on the synthesis of a transferable protein mediator, cetirizine was administered to donor or recipient rats in order to determine whether it interferes with the generation or with the expression of this protein. We showed that only the treatment of recipient rats abolished the transfer of the eosinophilotactic activity, indicating that cetirizine does not modify the generation but inhibits the expression of this activity.

Our findings indicate that cetirizine is able to inhibit eosinophil accumulation by acting locally. The mechanism is neither related to its recognized ability to antagonize histamine H1‐receptors nor to a direct action upon circulating eosinophils.
Effects of inhibiting nitric oxide biosynthesis on the systemic and splanchnic circulation of rats with portal hypertension
Authors: Pizcueta M.P. , Piqué J.M. , Bosch J. , Whittle B.J.R. , Moncada S.
Published: July 2012

The effects of inhibiting endogenous nitric oxide (NO) synthesis with NG‐monomethyl‐l‐arginine (l‐NMMA) on the systemic and splanchnic circulation have been investigated in rats with experimental chronic portal hypertension, anaesthetized with ketamine.

Portal hypertension was induced by partial portal vein ligation, 2 weeks prior to study. This procedure induced a reduction in systemic arterial blood pressure (MAP), an increase in cardiac output as measured by radiolabelled microspheres, a reduction in peripheral and splanchnic vascular resistance and an increased portal venous inflow (PVI) and portal pressure, as compared to control non‐ligated rats.

l‐NMAA (6.25 and 50 mg kg−1, i.v.) dose‐dependently increased MAP, reduced cardiac output and PVI, and increased peripheral and splanchnic vascular resistance. With l‐NMMA (50 mg kg−1), PVI and the vascular resistances returned to values comparable to those determined in control non‐ligated anaesthetized rats under resting conditions.

Porto‐collateral resistance was also increased by these doses of l‐NMMA, whereas portal pressure was unchanged. The increase in renal blood flow and decrease in renal vascular resistance also seen in portal‐hypertensive rats was reversed by l‐NMMA (50 mg kg−1).

These effects of l‐NMMA (50 mg kg−1) were inhibited by prior administration of l‐arginine (300 mg kg−1, i.v.).

These findings indicate that the chronic hyperdynamic circulatory characteristics following portal vein stenosis can be attenuated by l‐NMMA. Thus, the excessive formation of endogenous NO may be implicated in the pathogenesis of the haemodynamic disturbances and splanchnic vasodilatation associated with chronic portal hypertension.
PAF‐induced muscarinic cholinoceptor hyperresponsiveness of ferret tracheal smooth muscle and gland secretion in vitro
Authors: Webber S.E. , Morikawa T. , Widdicombe J.G.
Published: July 2012

The effects of exposure of the ferret trachea in vitro to platelet activating factor (PAF) were examined on methacholine‐induced smooth muscle contraction, mucus volume and lysozyme outputs, and albumin transport across the tracheal epithelium.

Methacholine (0.1–30 μm) produced concentration‐dependent increases in tracheal smooth muscle tone and mucus volume, lysozyme and albumin outputs from the trachea.

The concentration‐response curves for methacholine‐induced smooth muscle contraction, mucus volume and lysozyme outputs were all shifted upwards after exposure of the trachea to PAF (1 μm) with a significant increase in maximum response for each variable. The EC50 values for methacholine‐induced smooth muscle contraction and mucus volume output were significantly reduced after PAF exposure suggesting an increase in the potency of methacholine. The concentration‐response curve for methacholine‐induced albumin output was shifted downwards after PAF exposure with a greatly reduced maximum but no change in the EC50 for methacholine.

PAF‐induced hyperresponsiveness of methacholine‐induced smooth muscle contraction, mucus volume and lysozyme outputs was not affected by indomethacin, FPL55712, or mepyramine and cimetidine, but was prevented by catalase and superoxide dismutase (SOD), and by WEB2086. Similarly, PAF‐induced inhibition of methacholine‐stimulated albumin output was prevented by catalase and SOD, and by WEB2086.

We conclude that PAF induces hyperresponsiveness of ferret tracheal smooth muscle and submucosal gland secretion (including lysozyme secretion from serous cells) to methacholine. This hyperresponsiveness is probably produced by receptor‐mediated release of oxygen free‐radicals. The inhibition of methacholine‐induced albumin flux suggests a loss of epithelial function which is also probably mediated by release of free‐radicals. The mechanism by which the free‐radicals produce the changes in responsiveness to methacholine, and the cellular source of the free‐radicals, remain to be established.
Adenosine receptors in post‐mortem human brain
Authors: James Stephen , Xuereb John H. , Askalan Rand , Richardson Peter J.
Published: July 2012

Adenosine A2‐like binding sites were characterized in post‐mortem human brain membranes by examining several compounds for their ability to displace [3H]‐CGS 21680 (2[p‐(2 carboxyethyl)‐phenethylamino]‐5′‐N‐ethylcarboxamido adenosine) binding.

Two A2‐like binding sites were identified in the striatum.

The more abundant striatal site was similar to the A2a receptor previously described in rat striatum, both in its pharmacological profile and striatal localization.

The less abundant striatal site had a pharmacological profile similar to that of the binding site characterized in the other brain regions examined. This was intermediate in character between A1 and A2 and may represent another adenosine receptor subtype.

The co‐purification of [3H]‐CGS 21680 binding during immunoisolation of human striatal cholinergic membranes was used to assess the possible cholinergic localization of A2‐like binding sites in the human striatum. Only the more abundant striatal site co‐purified with cholinergic membranes. This suggests that this A2a‐like site is present on cholinergic neurones in the human striatum.
Effect of neuropeptide Y on adrenergic and non‐adrenergic, non‐cholinergic responses in the rat anococcygeus muscle
Authors: Vila E. , Tabernero A. , Fernandes F. , Salaices M.
Published: July 2012

The effects of neuropeptide Y (NPY) were examined on adrenergic and non‐adrenergic, non‐cholinergic (NANC) neurotransmission in the rat anococcygeus muscle.

NPY (0.1–0.3 μm) greatly potentiated the contractile responses induced by field stimulation. Prazosin (0.1 μm) completely abolished the stimulation‐induced responses either in the absence or presence of NPY.

NPY (0.1–0.3 μm) enhanced only the contractile responses to low doses of noradrenaline (NA, 0.003–0.01 μm). Responses to tyramine were unaffected by the same concentrations of NPY.

In superfused anococcygeus, previously loaded with [3H]‐NA, NPY (0.1–0.3 μm) failed to modify the basal, as well as the stimulation‐evoked, release of tritium at 2 and 4 Hz.

NANC relaxations induced by electrical stimulation were significantly reduced, in a concentration‐related manner, by 0.1–0.3 μm NPY.

6 l‐NG‐nitro‐arginine (l‐NOARG, 30 μm) enhanced the stimulation (0.25–1 Hz)‐induced motor responses. In the presence of l‐NOARG (30 μm), NPY (0.1 μm) did not modify the motor responses induced by field stimulation (0.25–0.5 Hz). l‐Arginine did not reverse the NPY‐induced potentiation of stimulation‐induced motor responses.

7 The relaxations of anococcygeus muscle induced by sodium nitroprusside (SNP, 0.01–0.3 μm) were diminished by NPY (0.1–0.3 μm).

8 Our study suggests that NPY, at concentrations devoid of contractile effect, potentiates the motor responses of rat anococcygeus muscle as a consequence, at least in part, of the inhibition of NANC relaxing responses by a different mechanism from l‐NOARG.
Vasopressin‐stimulated [3H]‐inositol phosphate and [3H]‐phosphatidylbutanol accumulation in A10 vascular smooth muscle cells
Authors: Plevin Robin , Stewart Allison , Paul Andrew , Wakelam Michael J.O.
Published: July 2012

The characteristics of vasopressin‐stimulated phosphatidylinositol 4,5 bisphosphate (PtdIns(4,5)P2) and phosphatidylcholine (PtdCh) hydrolysis were examined in A10 vascular smooth muscle cells (VSMC), by assessing the formation of [3H]‐inositol phosphates ([3H]‐IP) and the accumulation of the phospholipase D (PLD) specific product, [3H]‐phosphatidylbutanol ([3H]‐PtdBuOH).

Vasopressin ([Arg8]‐VP) and a number of related analogues stimulated the accumulation of [3H]‐IP and [3H]‐PtdBuOH with similar EC50 values, generating the same rank order of potency for each response (Arg8‐VP = vasotocin = Lys8‐VP ≫ oxytocin).

Inhibition of vasopressin‐stimulated [3H]‐IP and [3H]‐PtdBuOH accumulation by the V1a receptor antagonists, Des‐Gly9[β‐mercapto‐β,β,‐cyclopentamethylene propionyl, O‐Et‐Tyr2,Val4,Arg8]‐vasopressin generated similar IC50 values suggesting that both these responses are mediated through the activation of a single V1a receptor subtype.

The onset of vasopressin‐stimulated inositol‐1,4,5‐trisphosphate (Ins(1,4,5)P3) mass formation proceeded [3H]‐PtdBuOH accumulation indicating that PtdCh hydrolysis was activated subsequent to PtdIns(4,5)P2 breakdown.

The protein kinase C (PKC) activator, tetradecanoylphorbol acetate (TPA) also stimulated [3H]‐PtdBuOH accumulation. Preincubation with the PKC inhibitor Ro‐31–8220 abolished both TPA‐ and vasopressin‐stimulated [3H]‐PtdBuOH, suggesting that the intermediate activation of protein kinase C is involved in the regulation of PLD by vasopressin.

6 Pretreatment of the A10 VSMC with Ro‐31–8220 (100 μm) also potentiated vasopressin‐stimulated Ins(1,4,5)P3 mass formation. Therefore stimulation of PKC may have opposing roles in the regulation of agonist activation of PLC and PLD.

7 Preincubation of the cells with EGTA, verapamil, or the receptor‐operated calcium channel antagonist, SK&F 96365, reduced vasopressin‐stimulated [3H]‐PtdBuOH accumulation by approximately 30%, suggesting that influx of calcium has a significant role to play in the regulation of vasopressin‐stimulated PLD activity.
GH4ZD10 cells expressing rat 5‐HT1A receptors coupled to adenylyl cyclase are a model for the postsynaptic receptors in the rat hippocampus
Authors: Fowler C.J. , Ahlgren P.C. , Brännström G.
Published: July 2012

Vasoactive intestinal polypeptide (VIP) stimulated adenosine 3′:5′‐cyclic monophosphate (cyclic AMP) production by cultured GH4ZD10 cells with an EC50 value of about 7 nm. The extracellularly recovered cyclic AMP predominated, and was reduced by co‐incubation with 8‐hydroxy‐2‐(di‐n‐propylamino) tetralin (8‐OH‐DPAT) and 5‐hydroxytryptamine (5‐HT), whereas dopamine (0.1–30 μm) did not reduce VIP‐stimulated cyclic AMP production.

The responses to 5‐HT and 8‐OH‐DPAT were blocked by (−)‐alprenolol and NAN 190. The antagonism by (−)‐alprenolol was competitive in nature with a pA2 value of 7.0.

The responsiveness of the cells to 5‐HT agonists was highly dependent upon the culturing conditions used. Thus, 8‐OH‐DPAT inhibition of VIP (30 nm)‐stimulated cyclic AMP production decreased with increasing passage number of the cells. Reduction of the zinc concentration used to promote expression of the 5‐HT1A receptor gene produced a greater sensitivity of the cells to 5‐HT agonists.

Under such conditions, the following efficacies (5‐HT = 100) were found: lisuride 106, (+)‐lysergic‐acid diethylamide 100, 5‐methoxy‐N,N‐dimethyltryptamine 98, RU 24949 98, 5‐carboxamidotryptamine 97, (±)‐8‐OH‐DPAT 90, (+)‐8‐OH‐DPAT 87, 1‐[2‐(4‐aminophenyl)ethyl]‐4‐(3‐trifluoromethylphenyl)‐piperazine 86, flesinoxan 79/88, (−)‐8‐OH‐DPAT 62, buspirone 43/50, ipsapirone 46. Spiroxatrine and spiperone had a low intrinsic activity, but reduced the response to 5‐HT. These efficacies are similar to those reported in the literature for post‐synaptically localized 5‐HT1A receptors in the rat hippocampus. Thus, the GH4ZD10 cells serve as a useful in vitro model system for these receptors.