bluuebunny/crossref_metadata_2025 huggingface dataset:
Differentiation by hydroquinone of relaxations induced by exogenous and endogenous nitrates in non‐vascular smooth muscle: role of superoxide anions
Authors: Hobbs Adrian J. , Tucker John F. , Gibson Alan
Published: July 2012

The influence of hydroquinone on relaxations induced by nitric oxide (NO), nitrovasodilator drugs, and non‐adrenergic, non‐cholinergic (NANC) field stimulation has been investigated in three tissues in which endogenous nitrates have been implicated in the NANC response; the mechanism of action of hydroquinone was also studied.

In mouse anococcygeus, hydroquinone (10–100 μm) produced a concentration‐dependent inhibition of relaxations induced by 15 μm NO. Hydroquinone, 100 μm, which reduced responses to NO by 85%, had no effect on relaxations induced by NANC field stimulation (10 Hz; 20s trains), hydroxylamine (10 μm), sodium nitroprusside (1 μm) or sodium azide (20 μm).

In guinea‐pig trachea, 100 μm hydroquinone reduced relaxations to 150 μm NO by 75%, but had no effect on those to NANC stimulation (10 Hz; 30 s trains) or sodium azide (5 μm).

In rat gastric fundus, 100 μm hydroquinone reduced relaxations to 1 μm NO by 85%, but had no effect on those to NANC stimulation (0.5 Hz; 15 s trains) or sodium azide (2 μm).

Superoxide dismutase (SOD; 50 u ml−1) had no effect on relaxations of the mouse anococcygeus in response to 15 μm NO or 10 Hz NANC stimulation. Further, the inhibition of responses to NO by hydroquinone was unaffected in the presence of SOD.

Hydroquinone (10–100 μm) failed to generate superoxide anions, as detected by a chemiluminescent assay. However, 100 μm hydroquinone, like SOD (50 u ml−1), produced almost complete inhibition of superoxide anion chemiluminescence induced by xanthine (500 μm): xanthine oxidase (0.07 u ml−1).

It is concluded that, in our system, hydroquinone inhibits NO by acting as a free radical scavenger rather than by generating superoxide anions. The ability of hydroquinone to block relaxations to NO, but not NANC stimulation, may suggest that the endogenous nitrate substance released by these NANC nerves may not be free NO, but may be an NO‐containing, or NO‐generating, molecule.
Pharmacological analysis of 5‐hydroxytryptamine effects on electrically stimulated human isolated urinary bladder
Authors: Corsi M. , Pietra C. , Toson G. , Trist D. , Tuccitto G. , Artibani W.
Published: July 2012

5‐Hydroxytryptamine (5‐HT) is able to potentiate the contractions induced by electrical field stimulation of pieces of human isolated urinary bladder. On the basis of available selective 5‐HT agonists and antagonists, we have further investigated the receptors involved and their site of action.

5‐HT produced a concentration‐dependent increase of the contractile response to electrical field stimulation from 0.1 nm to μm. At higher concentrations (up to 100 μm) the effect decreased. These activities were mimicked by a variety of 5‐HT agonists, for which the following rank order of potency was found: 5‐HT > α‐methyl 5‐HT > 5‐methoxytryptamine > 5‐carboxamidotryptamine > 2‐methyl 5‐HT ≫ GR 43175. In addition the gastro‐prokinetics agents metoclopramide, cisapride and the 5‐HT3 antagonist ICS 205–930 behaved as 5‐HT agonists, their EC50 values being 2.3, 0.3, and 0.5 (μm) respectively.

The 5‐HT potentiating effect was resistant to antagonism by ondansetron (1 μm) and cyanopindolol (1 μm), selective 5‐HT3 and 5‐HT1A/1B antagonists respectively. The 5‐HT2 antagonists ketanserin (1 μm), spiperone (1 μm) and methysergide (1 μm) also showed a weak inhibitory activity. Methiothepin (0.1–1 μm) antagonized only the inhibitory effect of 5‐HT. Metoclopramide (0.1–1 μm), cisapride (0.01–0.1 μm) and ICS 205–930 (0.3–3 μm) all produced a rightward displacement of the 5‐HT response curve with concomitant reduction of the maximum response. The pA2 values calculated were 7.4, 8.5 and 7.0 respectively. The antagonism of metoclopramide was receptor specific and was not apparently related to interactions with dopaminergic activity since domperidone showed no antagonism of 5‐HT, and metoclopramide, itself, did not antagonize the potentiating effect of prostaglandin F2α.

The receptor involved in the potentiating effect of 5‐HT may be located prejunctionally because 5‐HT did not potentiate responses to acetylcholine (ACh) or electrical field stimulation with the parameters of direct muscle excitation. Also, since the 5‐HT potentiating effect was blocked by atropine, it may be attributed to a release of ACh.

This study suggests that in the human urinary bladder 5‐HT causes two opposite effects on the contractile response to electrical field stimulation. A potentiating effect at low concentrations due to an interaction with an atypical receptor, different from the classical 5‐HT1, 5‐HT2 or 5‐HT3 subtypes and an inhibitory effect at greater concentrations probably due to an interaction with 5‐HT1‐like receptors. The possibility that this atypical receptor possesses some characteristics of those found in other isolated preparations like guinea‐pig ileum, rat oesophagus and mouse embryo colliculi neurones is discussed.
Interleukin‐8 as a mediator of sympathetic pain
Authors: Cunha F.Q. , Lorenzetti B.B. , Poole S. , Ferreira S.H.
Published: July 2012

The hyperalgesic effects of interleukin‐8 (IL‐8), interleukin‐1β (IL‐1β) and carrageenin were measured in a rat paw pressure test.

IL‐8 evoked a dose‐dependent hyperalgesia which was attenuated by a specific antiserum, the β‐adrenoceptor antagonists atenolol and propranolol, the dopamine1 receptor antagonist SCH 23390 and the adrenergic neurone‐blocking agent guanethidine. The hyperalgesia was not attenuated by the cyclo‐oxygenase inhibitor indomethacin or the IL‐1β analogue Lys‐d‐Pro‐Thr.

IL‐1β‐evoked hyperalgesia was attenuated by indomethacin and Lys‐d‐Pro‐Thr but not by atenolol or SCH 23390.

Carrageenin‐evoked hyperalgesia was attenuated by atenolol, indomethacin and anti‐IL‐8 serum. The effects of atenolol and anti‐IL‐8 serum were not additive. The effects of indomethacin and anti‐IL‐8 serum were additive: this combination abolished carrageenin‐evoked hyperalgesia.

A new biological activity of IL‐8 is described, namely the capacity to evoke hyperalgesia by a prostaglandin‐independent mechanism. IL‐8 is the first endogenous mediator to be identified as evoking hyperalgesia involving the sympathetic nervous system. Since IL‐8 is released by activated macrophages and endothelial cells it may be a humoral link between tissue injury and sympathetic hyperalgesia.
Effect of carbenoxolone on the biological activity of nitric oxide: relation to gastroprotection
Authors: Dembinska‐Kiec A. , Pallapies D. , Simmet Th. , Peskar B.M. , Peskar B.A.
Published: July 2012

The interactions between carbenoxolone and nitric oxide (NO) were examined by investigating their effects on human platelet aggregation, on rat aortic strips precontracted by phenylephrine and on protection of rat gastric mucosa against ethanol‐induced injury.

Carbenoxolone (100–300 μm) caused a significant and concentration‐dependent potentiation of rat peritoneal neutrophil (RPN)‐, 3‐morpholino‐sydnonimine (SIN‐1)‐ or iloprost‐induced inhibition of platelet aggregation. Higher concentrations (500 μm) of carbenoxolone alone markedly inhibited platelet aggregation. Pretreatment with carbenoxolone (100–300 μm) antagonized the reversal of the RPN‐ or SIN‐1‐induced antiaggregatory effect by oxyhaemoglobin (10 μm).

Rat aortic strips with intact endothelium precontracted by phenylephrine (0.1–0.3 μm) were relaxed by carbenoxolone (100–300 μm) in a concentration‐dependent manner. Relaxations were abolished by mechanical removal of the endothelium or by incubation with methylene blue (10 μm) or NG‐nitro‐l‐arginine (l‐NNA, 100 μm). Sodium nitroprusside (10 nm)‐induced relaxations of endothelium‐denuded rat aortic strips were potentiated by carbenoxolone (100 μm).

The carbenoxolone (200 mg kg−1, p.o.)‐induced gastroprotection against ethanol was antagonized by l‐NNA (5–40 mg kg−1) in a dose‐dependent manner. Pretreatment of rats with indomethacin (10 mg kg−1, s.c.) increased the effect of l‐NNA.

The results suggest that the activity of carbenoxolone in the experimental systems tested is due to phosphodiesterase inhibition, although radical scavenging properties of the drug could contribute to some of the effects observed. In the rat gastric mucosa both increased prostaglandin levels and effects on the NO system could contribute to the protective action of carbenoxolone.
Effect of respiratory tract viral infection on murine airway β‐adrenoceptor function, distribution and density
Authors: Henry Peter J. , Rigby Paul J. , Mackenzie John S. , Goldie Roy G.
Published: July 2012

The effects of a respiratory tract viral infection on β‐adrenoceptor density, distribution and function were investigated in murine airways.

Following intranasal inoculation of CBA/CaH mice with influenza A/PR‐8/34 virus, the virus proliferated rapidly in trachea (peak titres 2 days post‐inoculation) and lung (peak titres 4–6 days post‐inoculation). Respiratory tract viral infection was associated with a significant increase in lung weight (88% higher than control mice at day 6 post‐inoculation) that was related temporally to the development of peripheral lung inflammation and consolidation.

Analysis of specific binding of [125I]‐cyanopindolol to β‐adrenoceptors revealed that on days 2, 4 and 8 post‐inoculation with virus, mouse isolated tracheal sections contained, on average, 40% more β‐adrenoceptors than tracheal sections from time matched control mice. Subsequent quantitative autoradiographic studies demonstrated that this increase in total tracheal β‐adrenoceptors was due primarily to a 90% increase in the density of β‐adrenoceptors in the tracheal epithelium in virus‐infected mice.

In contrast, virus‐infection had no significant effect on the density of β‐adrenoceptors in tracheal airway smooth muscle, although within 2 days of inoculation with virus, mouse tracheal smooth muscle segments were approximately 2 fold less sensitive to the β‐adrenoceptor agonist, noradrenaline (mean pD2 = 6.57 ± 0.04, n = 24) and to the adenylyl cyclase‐activator forskolin (mean pD2 = 6.78 ± 0.04, n = 12) compared to segments from control mice (mean pD2 = 6.84 ± 0.06 for noradrenaline; mean pD2 = 7.03 ± 0.07 for forskolin). Similar values were obtained 8 days post‐inoculation. At day 2, but not day 8 post‐inoculation with virus, relaxation responses to theophylline were also marginally attenuated compared with controls.

Mouse isolated tracheal segments obtained 2 days after virus inoculation and segments from time‐matched control mice were equisensitive to the spasmogenic actions of the muscarinic cholinoceptor agonist, carbachol. However, tracheal segments from mice inoculated with virus were less responsive to carbachol on day 4 (mean pD2 = 6.45 ± 0.04, n = 8) and day 8 (mean pD2 = 6.45 ± 0.02, n = 12) compared to control preparations (day 4, mean pD2 = 6.73 ± 0.06, n = 8; day 8, mean pD2 = 6.65 ± 0.04, n = 12, P < 0.05). In contrast, endothelin‐1‐induced contractions of tracheal smooth muscle were not affected by virus‐infection.

These data demonstrate that respiratory tract viral infection can produce significant tissue‐selective changes in airway β‐adrenoceptor density as well as small reductions in airway smooth muscle muscarinic cholinoceptor and β‐adrenoceptor function.
Effects of porcine relaxin on contraction, membrane response and cyclic AMP content in rat myometrium in comparison with the effects of isoprenaline and forskolin
Authors: Osa Takuro , Inoue Hiroyoshi , Okabe Koji
Published: July 2012

The longitudinal muscle from the uterus of oestrogen‐treated rats was quiescent in Mg‐free Krebs solution. Electrical stimulation generated phasic contraction, which was depressed to 35% and 18% by 50 mu and 150 mu porcine relaxin, respectively.

The phasic contractions were more strongly depressed to 26% by 50 mu relaxin in solution containing 0.6 mm Mg, and the depression lasted for more than 4 h after the removal of relaxin. During the persisting depression, raising the external Ca to 7.5 mm did not restore the contraction, but the contraction was restored by removal of Mg.

The depression of the phasic contraction by relaxin, examined in Mg‐free solution, was enhanced and reduced by pretreatment of the tissue with 0.6 mm Mg and 0.6 mm Mn, respectively, for about 15 min. In contrast, the depression of contraction by isoprenaline or forskolin was enhanced by pretreatment with either Mg or Mn.

The cellular content of cyclic AMP was measured in Krebs solution containing 0.6 mm Mg. The values were 1.24 (pmol mg−1 protein) in control solution, and 2.31 and 1.56 when the tissues were treated with 150 mu relaxin and 10−9 m isoprenaline, respectively.

The cyclic AMP production in response to 10−7 m forskolin measured in Mg‐free solution was enhanced when the tissue was pretreated with either 0.6 mm Mg or Mn for 15 min. The cyclic AMP production in response to 100 mu relaxin was increased when the tissue was pretreated with 0.6 mm Mg, and was unchanged by pretreatment with Mn. The cyclic AMP production in response to 10−9 m isoprenaline was unchanged by pretreatment with the divalent cations.

The membrane potential of the muscle was −60.8 mV in Krebs solution containing 0.3 mm Mg, and electrical stimulation induced an action potential which consisted of spike and plateau components. Application of 150 mu relaxin reduced the duration of the plateau; the contractions were progressively depressed. The resting membrane potential and membrane resistance were unchanged by application of 150 mu relaxin. The membrane was hyperpolarized by 2.8 mV, accompanied by a decrease in membrane resistance, when 10−9 m isoprenaline was applied.

Although there were several differences between the effects of relaxin and isoprenaline, it is probable that some process, which is cyclic AMP‐dependent, accelerated by Mg and depressed by Mn, is involved in the depressant action of relaxin on contraction.
The effect of CCKB/gastrin antagonists on stimulated gastric acid secretion in the anaesthetized rat
Authors: Hayward N.J. , Harding M. , Lloyd S.A.C. , McKnight A.T. , Hughes J. , Woodruff G.N.
Published: July 2012

The urethane‐anaesthetized, vagotomised rat preparation was used to investigate the effects of the histamine H2‐antagonist ranitidine, the proton pump inhibitor omeprazole and the CCKB/gastrin antagonists CI‐988, PD 136450 and L‐365,260 on pentagastrin‐, histamine‐ and bethanechol‐induced gastric acid secretion.

The novel CCKB/gastrin antagonists CI‐988 and PD 136450, and L‐365,260 dose‐dependently inhibited pentagastrin‐induced secretion. The ED50 value for PD 136450 was 0.05 μmol kg−1, the same following intravenous or subcutaneous administration.

CI‐988 and PD 136450 administered subcutaneously at dose levels highly effective for antagonism of pentagastrin responses had no effect on basal acid secretion.

Ranitidine inhibited pentagastrin‐, bethanechol‐, and histamine‐induced acid secretion, whereas the CCKB/gastrin antagonists inhibited only the secretory response to pentagastrin.

The selective CCKA antagonist, devazepide, was inactive at up to 300 μmol kg−1 i.p. against the three stimulants of acid secretion.

CI‐988 and PD 136450 will be useful research tools with which to investigate the role of CCKB/gastrin receptors in gastric acid secretion and the trophic activities of gastrin and cholecystokinin (CCK) on the gastrointestinal tract.
Increased endothelin excretion in rats with renal failure induced by partial nephrectomy
Authors: Brooks David P. , Contino Lisa C. , Storer Barbara , Ohlstein Eliot H.
Published: July 2012

Six weeks following partial nephrectomy in rats, significant increases in serum urea nitrogen and serum creatinine concentration and a significant decrease in creatinine clearance were observed.

Measurement of systolic blood pressure by tail plethysmography indicated that animals that had undergone partial nephrectomy were hypertensive.

Compared to sham‐operated animals, there were 4 fold increases in both urinary protein excretion and urinary endothelin excretion.

There was a significant correlation between urinary protein and urinary endothelin excretion (r = 0.77). There was also a correlation (r = 0.65) between urinary endothelin excretion and systolic blood pressure.

Plasma endothelin concentrations were not different in sham‐operated and partially nephrectomized rats.

The data indicate that there is an increased renal endothelin production in rats with chronic renal failure.
Protective action of clonidine against the arrhythmogenic and lethal effects of ouabain in guinea‐pigs
Authors: Thomas George P. , Stephen P.M.
Published: July 2012

Clonidine (1.25, 2.5 and 5.0 μg kg−1) was studied for its effect on the cardiac arrhythmias and lethality induced by slow intravenous infusion of ouabain in guinea‐pigs.

Clonidine produced significant delays in the onset of the arrhythmic stages and lethality. However, clonidine did not offer any such protection in reserpinised guinea‐pigs, whereas its effects were unaltered in atropinized guinea‐pigs.

Idazoxan (100 μg kg−1, i.v.) abolished the antiarrhythmic effect of clonidine whereas corynanthine (1 mg kg−1, i.v.) had no such effect.

Clonidine inhibited the rate of the ouabain‐induced rise in blood pressure and the peak pressor response.

In isolated paced left atria of the guinea‐pig, clonidine (3.75 × 10−4 m) did not offer any protection against rapid and/or irregular extrasystolic contractions induced by ouabain.

It is concluded that the antiarrhythmic effect of clonidine is due to its effects on the indirect neural components of digitalis toxicity mediated by the stimulation of α2‐adrenoceptors, without any direct antiarrhythmic effect on the myocardium.
Mechanisms of the anticholinergic effect of SUN 1165 in comparison with flecainide, disopyramide and quinidine in single atrial myocytes isolated from guinea‐pig
Authors: Inomata Norio , Ishihara Takafumi , Akaike Norio
Published: July 2012

The mechanism of the anticholinergic effect of SUN 1165 on the acetylcholine (ACh)‐induced K+ current (IK.ACh) was examined and compared with those of flecainide, disopyramide and quinidine in single atrial myocytes, in a whole‐cell configuration by use of the concentration‐jump technique. This technique combines an intracellular perfusion and a rapid exchange of external solution surrounding the voltage‐clamped single myocyte within 2 ms.

In the cells loaded with guanosine‐5′‐triphosphate (GTP), 100 μm, the muscarinic ACh response, (IK.ACh), was mediated by GTP‐binding proteins. The concentrations of the test drugs that produced a half‐maximal inhibition of ACh (1 μm)‐induced IK.ACh (IC50) were 29 μm for SUN 1165, 3.6 μm for flecainide, 1.7 μm for disopyramide, and 1.6 μm for quinidine. The blockade of IK.ACh by SUN 1165 and its recovery from the inhibition occurred within a few seconds. Disopyramide had a similar rapid action, while the effects of flecainide and quinidine occurred much more slowly within a few tens of seconds.

In cells loaded with 100 μm guanosine‐5′‐O‐(3‐thio triphosphate) (GTPγS, a nonhydrolysable GTP analogue), the K+ channel was uncoupled from the muscarinic receptors and activated irreversibly due to direct activation of GTP‐binding proteins by GTPγS. SUN 1165 and disopyramide had a weak inhibitory effect (IC50 > 100 μm for both), while flecainide and quinidine depressed the GTPγS‐induced K+ current with similar potencies to the cases of ACh‐induced currents; IC50 was 5.3 μm for flecainide and 4.4 μm for quinidine.

These results suggest that the mechanisms underlying the anticholinergic effects of these antiarrhythmic drugs are different; disopyramide and high concentrations of SUN 1165 mainly block muscarinic ACh receptors in atrial myocytes, while flecainide and quinidine inhibit the K+ channel itself and/or GTP‐binding proteins.
A specific B2‐bradykinin receptor antagonist HOE 140 abolishes the antihypertrophic effect of ramipril
Authors: Linz Wolfgang , Schölkens Bernward A.
Published: July 2012

To evaluate the role of bradykinin in the antihypertrophic effect of the angiotensin‐converting enzyme (ACE) inhibitor, ramipril, we investigated the influence of HOE 140, a specific B2‐receptor antagonist, on the effects of ramipril on left ventricular hypertrophy (LVH) in rats with aortic banding. Ramipril at a dose of 1 mg kg−1 day−1 for 6 weeks prevented the increase in blood pressure and development of LVH after aortic banding; plasma ACE activity was significantly inhibited. A lower dose of ramipril (10 μg kg−1 May−1 for 6 weeks) had no effect on the increase in blood pressure or on plasma ACE activity, but prevented LVH after aortic banding. The antihypertrophic effects of the higher and the lower dose ramipril, as well as the antihypertensive action of the higher dose of ramipril were abolished by the coadministration of HOE 140 (500 μg kg−1 day−1). The present data show for the first time that the beneficial effects of an ACE‐inhibitor on LVH in rats with hypertension caused by aortic banding can be prevented by a specific B2‐receptor antagonist.
Inhibition by salmeterol of increased vascular permeability and granulocyte accumulation in guinea‐pig lung and skin
Authors: Whelan C.J. , Johnson M.
Published: July 2012

The long‐acting β2‐adrenoceptor agonist, salmeterol has been evaluated for its anti‐inflammatory effects in the guinea‐pig lung and skin.

Salmeterol, administered in bronchodilator doses to conscious guinea‐pigs by both oral (0.01–1.0 mg kg−1) and inhaled (nebulizer concentration, 0.001–1.0 mg ml−1) routes, inhibited histamine‐induced plasma protein extravasation (PPE) into the airway lumen.

Inhibition of PPE by salmeterol was long‐lasting (>6 h) and was inhibited by prior administration of propranolol (1 mg kg−1, s.c.), indicating an effect mediated by β‐adrenoceptors.

Inhaled salbutamol (nebulizer concentration, 0.001 — 1.0 mg ml−1) also inhibited PPE in guinea‐pig lung but, in contrast to salmeterol, this effect was short‐lived with substantial loss of activity 2 h after administration.

Inhaled salmeterol (0.1 mg ml−1) and salbutamol (1.0 mg ml−1) inhibited the accumulation of neutrophils in guinea‐pig lung in response to lipopolysaccharide (100 μg ml−1). Salmeterol, but not salbutamol, inhibited the infiltration of eosinophils into the airway lumen in response to platelet activating factor (100 μg ml−1). These effects of salmeterol were blocked by prior administration of propranolol (5 mg kg−1, s.c.), indicating that they were also β‐adrenoceptor‐mediated.

Oral salmeterol (10 mg kg−1, p.o.), but not salbutamol (10 and 100 mg kg−1, p.o.), inhibited zymosan‐induced granulocyte accumulation and PPE in guinea‐pig skin. Lower doses of salmeterol (0.1 and 1 mg kg−1) inhibited PPE, but not granulocyte accumulation. The effects of salmeterol were blocked by prior administration of propranolol (1 mg kg−1, s.c.). Both salmeterol and salbutamol inhibited histamine‐induced PPE in guinea‐pig skin.

Intradermal salmeterol (10−8 mol per site), but not salbutamol, was also effective in inhibiting zymosan‐induced granulocyte accumulation and PPE in guinea‐pig skin.

It is concluded that salmeterol, at bronchodilator doses in the guinea‐pig, inhibits granulocyte accumulation and PPE, possibly by an action on the vasculature. As this profile of activity is not shared by the shorter‐acting compound, salbutamol, it would seem that anti‐inflammatory activity is associated with β‐adrenoceptor agonism of long duration. The implications of these findings for the use of salmeterol in the treatment of bronchial asthma are discussed.
Evidence for an atypical, or β3‐adrenoceptor in ferret tracheal epithelium
Authors: Webber S.E. , Stock M.J.
Published: July 2012

A preparation of the ferret trachea in vitro was used to examine the effects of three selective β‐adrenoceptor agonists on lysozyme secretion from submucosal gland serous cells and epithelial albumin transport into tracheal mucus following sustained, submaximal stimulation of mucus production with methacholine (20 μm)

Prenalterol, salbutamol and BRL 37344 all enhanced methacholine‐induced albumin output. BRL 37344 was 10,000 times more potent than salbutamol, and salbutamol was slightly more potent than prenalterol. The concentrations required to increase albumin output by 100% (EC100%) were 1.4 nm, 0.7 mm and approximately 1.0 mm for BRL 37344, salbutamol and prenalterol, respectively. All three agonists inhibited methacholine‐induced lysozyme output, with salbutamol being 60 times more potent than BRL 37344, and BRL 37344 being approximately 100 times more potent than prenalterol.

The selective β2‐adrenoceptor antagonist, ICI 118551, inhibited the increase in albumin output produced by BRL 37344, but was much more potent at inhibiting the response to salbutamol; the pA2 for ICI 118551 was 5.55 and 7.18 (P < 0.001) when the agonist was BRL 37344 and salbutamol, respectively. ICI 118551 also attentuated the inhibition of lysozyme output produced by the two agonists, but was 10–30 times more potent at inhibiting this response than the albumin response to BRL 37344 and salbutamol.

The greater potency (4–5 orders of magnitude) of BRL 37344, compared to the β1‐ (prenalterol) and β2 ‐ (salbutamol) adrenoceptor selective agonists, in stimulating methacholine‐induced albumin transport suggests that tracheal epithelium possess an atypical, or β3‐adrenoceptor similar to that previously reported for adipocytes and gastrointestinal smooth muscle. The weak antagonism of the response to BRL 37344 by ICI 118551 would also be consistent with an atypical adrenoceptor mediating the albumin transport response. Inhibition of methacholine‐induced serous cell lysozyme output would appear to be mediated predominantly by β2‐adrenoceptors.

In view of the possible beneficial protective effects of albumin in airway surface liquid, selective β3‐agonists like BRL 37344 might have potential value in the prevention and/or treatment of inflammatory airway disease.
Characterization of the receptor mediating relaxation to substance P in canine middle cerebral artery: no evidence for involvement of substance P in neurogenically mediated relaxation
Authors: Stubbs C.M. , Waldron G.J. , Connor H.E. , Feniuk W.
Published: July 2012

The aim of this study was to characterize the neurokinin receptor which mediates relaxation of dog isolated middle cerebral artery by the use of selective agonists and antagonists and to establish whether substance P is involved in the neurogenically mediated relaxant response in this vessel.

Substance P caused concentration‐related, endothelium‐dependent relaxations of dog isolated middle cerebral artery, contracted with prostaglandin F2α. The selective NK1 receptor agonists, GR73632 and substance P methyl ester (SPOMe), also caused relaxation with similar maximum effects to those of substance P. GR73632 and SPOMe were approximately 20 times and 6 times less potent respectively than substance P. The selective NK2 and NK3 receptor agonists, GR64349 and senktide, were only weakly active in causing relaxation being at least 425 times and 245 times less potent respectively than substance P.

The selective NK1 receptor antagonist, GR82334, was a potent, specific, competitive antagonist of the relaxant effects of substance P. In contrast, the selective NK2 receptor antagonist, R396 (10 μm) had no effect on the response to substance P.

Electrical field stimulation of dog isolated middle cerebral artery, contracted with prostaglandin F2α, caused neurogenically mediated, non‐adrenergic non‐cholinergic (NANC) relaxations. These NANC relaxations were unaffected by endothelium removal, GR82334 (10 μm) or by capsaicin (10 μm) treatment. However, the nitric oxide synthesis inhibitor, L‐NG‐monomethyl arginine methyl ester (L‐NMMA) (100 μm) markedly attenuated the response to electrical stimulation.

These results suggest that substance P causes relaxation of dog isolated middle cerebral artery via activation of NK1 receptors. However, substance P does not appear to be involved in NANC neurotransmission. In contrast, the marked inhibitory effect of L‐NMMA on NANC relaxations implicates nitric oxide in NANC neurotransmission in this vessel.
Bradykinin stimulation of phosphoinositide hydrolysis in guinea‐pig ileum longitudinal muscle
Authors: Ransom Richard W. , Goodman Carl B. , Young Gretchen S.
Published: July 2012

Bradykinin (BK)‐induced contraction of ileal smooth muscle is assumed to be due to phosphoinositide hydrolysis but this has never been reported. We have investigated whether BK receptors are linked to this transduction mechanism in guinea‐pig ileum longitudinal muscle and determined whether these receptors are equivalent to those labelled in [3H]‐BK binding assays.

In membranes prepared from longitudinal muscle, [3H]‐BK bound to a single class of sites with high affinity. Characterization of the binding with BK analogues indicated that the radioligand selectivity labelled a B2 type receptor.

BK significantly elevated tissue levels of [3H]‐inositol phosphates in longitudinal muscle slices preincubated with [3H]‐myo‐inositol. The agonists potencies of BK, Lys‐BK, Met‐Lys‐BK, Tyr5‐BK and Tyr8‐BK were in agreement with their relative potencies in the binding assay. The B1 receptor agonist des‐Arg9‐BK, did not stimulate inositol phosphate production. The response to BK was blocked by known B2 receptor antagonists but not by the B1 antagonist des‐Arg9, Leu8‐BK.

BK‐induced phosphoinositide hydrolysis was unaffected by exposure of muscle slices to either atropine or indomethacin.

The results indicate that the B2 receptors linked to phosphoinositide turnover in ileal longitudinal muscle exhibit properties similar to those involved in contractile responses. Also, the receptor mediating the phosphoinositide response is likely to be that labelled in the [3H]‐BK binding studies.
Phosphoramidon potentiates the contractile response to endothelin‐3, but not endothelin‐1 in isolated airway tissue
Authors: McKay K.O. , Black J.L. , Armour C.L.
Published: July 2012

Phosphoramidon (10 μm) markedly increased the contractile response to endothelin‐3 in human and rabbit bronchus in vitro. In human tissue the contractile response to 0.3 μm endothelin‐3 was significantly increased from 54 ± 12% to 137 ±34% (of the response to 1 mm acetylcholine) in the presence of phosphoramidon. Similarly, in rabbit isolated bronchus, the endothelin‐3‐induced response was increased from 34 ± 5% to 61 ± 7%.

In addition, the potency (as measured by EC30 values) of this peptide in human and rabbit airways was significantly augmented in the presence of the enzyme inhibitor. The geometric mean EC30 value was decreased from 53 nm (95% CI:15, 190) to 8 nm (95% CI:3, 23) in human bronchus and from 150 nm (95% CI:89, 250) to 23 nm (95% CI:11, 50) in rabbit tissue.

Neither the potency nor the response (at 0.3 μm) to endothelin‐3 in canine bronchial rings was altered after incubation of the tissue in phosphoramidon.

A previous study carried out in human airways has implied that the difference in potency between endothelin‐1 and endothelin‐3 may be attributed to a heterogeneous endothelin receptor population. The results of our study, while also demonstrating this difference in potency, have shown that this marked difference, as well as that obvious in rabbit airway tissue can be abolished in the presence of phosphoramidon.

Phosphoramidon produced no change in the cumulative concentration‐response curve for endothelin‐1 in airway tissue from the three species studied.

These results suggest that a phosphoramidon‐sensitive enzyme (probably neutral endopeptidase) found in lung, may be responsible for local degradation of endothelin‐3, but not endothelin‐1 in human and rabbit isolated bronchus.
Effects of monoamine uptake inhibitors on extracellular and platelet 5‐hydroxytryptamine in rat blood: different effects of clomipramine and fluoxetine
Authors: Ortiz Jordi , Artigas Francesc
Published: July 2012

The concentration of 5‐hydroxytryptamine (5‐HT) in rat platelet‐free plasma increased significantly 30 min after a single i.p. injection (10 mg kg−1) of each of six inhibitors of the high‐affinity 5‐HT uptake (fluvoxamine, fluoxetine, alaproclate, paroxetine, sertraline and clomipramine). The increases ranged from 226% to 776% of control values. In contrast, imipramine, desipramine and femoxetine had no significant effect. The increase elicited by paroxetine was dependent on the dose (1, 5 and 10 mg kg−1) and returned to control values after 4 h. That observed after clomipramine was also transient and paralleled the plasma concentration of the drug (Spearman‐rank correlation r = 0.43).

In vivo, the rat pulmonary vascular endothelium removed trace amounts (8.8 nmol in a bolus) of intravenously injected [14C]‐5‐HT. Paroxetine pretreatment (10 mg kg−1, 30 min before‐hand) reduced this uptake by 73%.

Repeated fluoxetine treatments reduced rat whole blood 5‐HT concentration (ca. − 60% after daily 2× 5 mg kg−1, i.p. during 14 days). However, plasma (extracellular) 5‐HT was not increased.

Various repeated treatments with clomipramine (i.p. injections or osmotic minipumps, up to 30 mg kg−1 day−1), failed to decrease rat whole blood 5‐HT concentrations. Platelet‐free plasma 5‐HT was also unchanged, even after treatments yielding plasma clomipramine levels 2.7 times higher than those that increased it acutely.

These results indicate that the extracellular pool of 5‐HT in rat blood (measured in the platelet‐free plasma) is physiologically under the control of high‐affinity 5‐HT uptake systems. The sustained 5‐HT uptake inhibition does not result in an increase of 5‐HT in platelet‐free plasma, suggesting that adaptative mechanisms are triggered. The distinct long‐term effects of the two antidepressants clomipramine and fluoxetine on rat whole blood 5‐HT suggest a differential in vivo action on the rat 5‐HT uptake.
Potassium channel modulation in rat portal vein by ATP depletion: a comparison with the effects of levcromakalim (BRL 38227)
Authors: Noack Thomas , Edwards Gillian , Deitmer Petra , Weston Arthur H.
Published: July 2012

The effects of levcromakalim and of adenosine 5′‐triphosphate (ATP) depletion on membrane potential and ionic currents were studied in freshly‐dispersed smooth muscle cells of rat portal vein by use of combined voltage‐ and current‐clamp techniques.

Levcromakalim (1 μm) induced a glibenclamide‐sensitive, non‐inactivating K‐current (IKCO) and simultaneously inhibited the slow, transient outward, delayed rectifier K‐current (ITO). Levcromakalim also hyperpolarized the portal vein cells by approximately 20 mV.

Reduction of intracellular ATP by removal of glucose and carboxylic acids from the recording pipette and of glucose from the bath fluid, induced a slowly‐developing, non‐inactivating and glibenclamide‐sensitive K‐current (Imet) within 60–300 s after breaking the membrane patch. Imet reached peak amplitude after 300–900 s, remained at a plateau for 200–800 s and then slowly ran down. At the peak of Imet, the cells were hyperpolarized by approximately 20 mV and their input conductance was increased by 42%.

At the time of maximum development of Imet, the delayed rectifier current, ITO, was reduced by 48%.

In the absence of glucose and carboxylic acids, addition of 1 μm free ATP to the recording pipette almost doubled the magnitude of Imet. At a holding potential of −10 mV, Imet was increased from 124 ± 11 pA to 228 ± 54 pA whereas the time‐course of development and run‐down of Imet was unaffected.

During the development and after the run‐down of Imet, levcromakalim (1–10 μm) failed to induce IKCO.

Stationary fluctuation analysis of the current noise associated with Imet revealed a unitary conductance of between 10–20 pS in a physiological potassium gradient. A second contaminating current with an underlying unitary conductance of approximately 150 pS remained after Imet had run down.

It is concluded that IKCO induced by levcromakalim and Imet are carried by the same population of relatively small conductance, glibenclamide‐sensitive K‐channels. The open state of these is increased by procedures designed to lower intracellular ATP concentrations.

The simultaneous inhibition of the delayed rectifier current (ITO) by both levcromakalim and during the development of Imet is highly significant. It suggests that levcromakalim could modify the interaction of ATP with sites linked to more than one type of K‐channel. This results in the opening of those channels which underlie IKCO (and which are normally inhibited by ATP binding) together with the modulation of phosphorylation‐dependent channels such as those which underlie ITO.
Inhibitors of nitric oxide synthase selectively reduce flow in tumour‐associated neovasculature
Authors: Andrade Silvia P. , Hart Ian R. , Piper Priscilla J.
Published: July 2012

The effects of l‐arginine analogues, NG‐nitro‐l‐arginine methyl ester (l‐NAME) and NG‐monomethyl‐l‐arginine (l‐NMMA) and methylene blue on blood flow in a murine adenocarcinoma and melanoma have been investigated.

Sponge implants in Balb/c and C57/BL mice were used to host proliferating tumour cells while the washout of 133Xe was employed to assess local blood flow in the implanted sponges.

Pharmacological inhibition of nitric oxide (NO) reduced blood flow in both tumours but this effect was reversed by administration of l‐arginine.

In marked contrast, the effect of these same NO inhibitors on the blood flow in sponge‐induced non‐neoplastic granulation tissue was negligible.

These results strongly suggest that: (a) flow in tumour vessels is modulated by nitric oxide which maintains a dilator tone in neoplastic tissue; (b) the constrictor activity (as monitored by an increase in t½ of 133Xe) of NO inhibitors may be attributed to the removal of such dilator tone; (c) many of the abnormalities described in tumour vasculature, such as hyporeactivity or unresponsiveness to vasoactive mediators and maximum vasodilatation, may be due to an increase in NO synthesis in cancers.
The selective NK3 receptor agonist senktide excites a subpopulation of dopamine‐sensitive neurones in the rat substantia nigra pars compacta in vitro
Authors: Keegan K.D. , Woodruff G.N. , Pinnock R.D.
Published: July 2012

Intra‐ and extracellular recordings were made from substantia nigra zona compacta neurones from an in vitro rat brain slice preparation. A subpopulation of dopamine‐sensitive neurones were encountered which were potently excited by bath application of the NK3 receptor agonist, senktide. On these senktide‐sensitive neurones, NK1 and NK2 receptor agonists were inactive. The excitatory action of senktide supports a role for tachykinins as putative neurotransmitters in the basal ganglia.
Indirect inhibitory effect of succinylcholine on acetylcholine‐activated channel activities and its modulation by external Ca2+ in mouse skeletal muscles
Authors: Nojima Hiroshi , Muroi Masashi , Kimura Masayasu
Published: July 2012

The effect of extracellular calcium on single acetylcholine (ACh)‐activated channel activities when desensitizing concentrations of succinylcholine (SuCh) were applied to the surrounding endplate membrane was investigated by the cell‐attached patch‐clamp technique at endplates of single skeletal muscle (flexor digitorum brevis) fibres of adult mice.

Bath‐applied SuCh (0.1–3 μm, in 2.5 mm Ca2+) increased in a concentration‐dependent manner the mean open time of ACh‐activated channel currents recorded at membrane potentials which cancelled the SuCh‐induced depolarizations.

In the presence of 0.5 and 2.5 mm external Ca2+, SuCh (3 μm) applied outside the patch pipette prolonged the mean open time of ACh‐activated channel currents in a time‐dependent manner (by 45% and 52%, respectively), and simultaneously significantly decreased the single channel conductance (by 14% and 10%, respectively). These SuCh‐induced effects did not occur in a nominally Ca2+‐free extracellular medium.

Under the same conditions, SuCh (3 μm) augmented the time‐dependent decline in the opening frequency of ACh‐activated channel currents obtained in nominally Ca2+‐free medium.

These results suggest that external calcium ions act to modulate nicotinic ACh receptor channel activity, and accelerate desensitization of the receptor.
Pharmacological characterization of RP 62203, a novel 5‐hydroxytryptamine 5‐HT2 receptor antagonist
Authors: Doble A. , Girdlestone D. , Piot O. , Allam D. , Betschart J. , Boireau A. , Dupuy A. , Guérémy C. , Ménager J. , Zundel J.L. , Blanchard J.C.
Published: July 2012

RP 62203 (2‐[3‐(4‐(4‐fluorophenyl)‐piperazinyl)propyl]naphto[1,8‐cd]isothiazole‐1,1‐dioxide) is a novel naphtosultam derivative which shows very high affinity for 5‐HT2 receptors in the rat cerebral cortex (Ki = 50.0 pm).

RP 62203 is relatively selective for this sub‐type of 5‐hydroxytryptamine (5‐HT) receptor, having lower affinity for the 5‐HT1A receptor and very low affinity for the 5‐HT3 receptor. RP 62203 displayed low to moderate affinity for α1‐adrenoceptors, dopamine D2 receptors and histamine H1 receptors.

In vivo binding experiments demonstrated that oral administration of low doses of RP 62203 led to a long‐lasting (> 6 h) occupation of cortical 5‐HT2 receptors (ID50 = 0.39 mg kg−1).

In cortical slices from the neonatal rat, RP 62203 potently inhibited inositol phosphate formation evoked by 5‐HT, with an IC50 of 7.76 nm.

The activity of neurones in the raphé and their responses to microiontophoretically applied 5‐HT were studied with extracellular recording electrodes in the anaesthetized rat. RP 62203 potently and dose‐dependently blocked excitations evoked by 5‐HT when administered at doses of 0.5–4.0 mg kg−1, i.p. In contrast, neither 5‐HT‐evoked depressions nor glutamate‐evoked excitations of raphé neuronal firing were blocked by RP 62203 at doses as high as 8.0 mg kg−1 i.p.

Head twitches induced by 1‐(2,5‐dimethoxy‐4‐iodophenyl)‐2‐aminopropane (DOI) could be abolished by low doses of RP 62203 in mice (ED50 = 0.44 mg kg−1, p.o.) and in rats (ED50 = 1.54 p.o.). Similar results were obtained with mescaline and 5‐hydroxytryptophan (5‐HTP).

The potency of RP 62203 was compared with that of three other 5‐HT2 receptor antagonists, ritanserin, ICI 169,369 and ICI 170,809. In all models, RP 62203 showed similar activity to ritanserin, whilst either ICI 169,369 or ICI 170,809 was several fold less active.

It is concluded that RP 62203 is a potent and selective antagonist at 5‐HT2 receptors in the rodent central nervous system.
Changes in adrenoceptors and monoamine metabolism in neonatal and adult rat brain after postnatal exposure to the antihypertensive labetalol
Authors: Erdtsieck‐Ernste E.B.H.W. , Feenstra M.G.P. , Botterblom M.H.A. , DE Barrios J. , Boer G.J.
Published: July 2012

The purpose of the present study was to investigate the acute (single injection), direct (chronic treatment) and the long‐lasting effects after exposure to the α1/β‐adrenoceptor antagonist labetalol during rat brain development on adrenoceptors and monoamine metabolism.

In 10‐day‐old rat pups, subcutaneously administered labetalol (10 mg kg−1) passed the blood‐brain barrier, reaching a level of 2.1 μg g−1 tissue in the brain 90 min after injection.

Chronic labetalol treatment (10 mg kg−1, s.c., twice daily) during the first 10 days of life significantly increased α1‐adrenoceptor binding in the hypothalamus (+39%), but not in the occipital cortex.

This chronic postnatal labetalol treatment did not result in long‐lasting changes in α1 and β‐receptors measured on day 60.

A single labetalol injection (10 mg kg−1, s.c.) on postnatal day 10 significantly increased noradrenaline (NA) metabolism in all brain regions tested (+25 to 105%), but had no effects on 5‐hydroxytryptamine (5‐HT) or dopamine metabolism.

Chronic labetalol treatment between postnatal (PN) days 1 and 10 also increased NA metabolism on PN 10 (3‐methoxy‐4‐hydroxyphenylglycol (MHPG)/NA, +20 to 100%), suggesting that tolerance to the acute effect of labetalol did not occur. A slight increase in 5‐HT metabolism (20%) was induced by the chronic labetalol treatment in the hippocampus and meso‐limbic system.

In general, long‐lasting effects on NA metabolism could not be detected on day 60, more than one month after the treatment. However, 5‐HT metabolism was significantly increased in all four brain regions measured (+20 to 70%).

We conclude that chronic labetalol exposure during early postnatal rat brain development does not cause long‐lasting changes in β‐receptor number or NA metabolism, but appears to be critical for the rate of 5‐HT metabolism in later life.
Characterization of vascular neuropeptide Y receptors
Authors: Grundemar Lars , Jonas S.E. , Mörner N. , Högestätt Edward D. , Wahlestedt Claes , Håkanson Rolf
Published: July 2012

In the present study we compared neuropeptide Y (NPY) and NPY‐related analogues for their ability to activate or bind to vascular NPY receptors in four experimental set‐ups. Previous results have suggested the existence of different receptor subtypes, Y1 receptors requiring full‐length NPY (1–36) or [Pro34]‐NPY, and Y2 receptors recognizing also N‐terminally truncated forms of NPY but not [Pro34]‐NPY.

NPY 1–36 and [Pro34]‐NPY dose‐dependently increased arterial pressure in the anaesthetized rat with a similar magnitude and potency. NPY 2–36 was much less potent than NPY 1–36. NPY 4–36 and NPY 11–36 were inactive even at a dose as high as 10 nmol kg−1.

NPY 1–36, [Pro34]‐NPY, NPY 2–36 and NPY 5–36 concentration‐dependently increased the coronary resistance in the Langendorff preparation of the rat. NPY 1–36 and [Pro34]‐NPY were equipotent, while NPY 2–36 and NPY 5–36 were about 7 and 20 times less potent. At 0.3 μm, NPY 11–36, NPY 20–36 and NPY 22–36 induced a slight contraction while NPY 23–36 was inactive.

NPY 1–36, [Pro34]‐NPY, NPY 2–36, NPY 4–36, NPY 5–36 and NPY 11–36 evoked concentration‐dependent contractions in the isolated inferior caval vein of the rat and guinea‐pig. [Pro34]‐NPY was more potent than NPY 1–36. NPY 2–36 was equipotent with NPY 1–36, while NPY 4–36, NPY 5–36 and NPY 11–36 were approximately 30 times less potent.

[Pro34]‐NPY was equipotent with NPY 1–36 in displacing the 125I‐labelled gut hormone peptide ([125I]‐PYY) from rat aortic smooth muscle cells, while NPY 2–36 and shorter forms of NPY were much less potent or inactive.

In caval vein smooth muscle cells of the rat, the displacement pattern was more complex than in aortic smooth muscle cells, in that both [Pro34]‐NPY and NPY 13–36 effectively displaced the radioligand, albeit none of them completely.

In conclusion, the NPY‐evoked pressor response in the whole rat and coronary vessels seems to be mediated by vascular Y1 receptors and the binding characteristics of the NPY‐related peptides in the aortic smooth muscle cells correspond to a population of such receptors. In the caval vein, the profile of the bioactivity and the binding affinity of the NPY‐related peptides suggest a mixed population of Y1/Y2 receptors.