bluuebunny/crossref_metadata_2025 huggingface dataset:
Endotoxin‐induced hyperreactivity of the guinea‐pig isolated trachea coincides with decreased prostaglandin E2 production by the epithelial layer
Authors: Folkerts Gert , Engels Ferdi , Nijkamp Frans P.
Published: July 2012

Pretreatment of guinea‐pigs with endotoxin (1 mg kg−1 b.w., i.p., 4 days before the experiments) results in respiratory airway hyperreactivity in vitro. Dose‐response curves with either arecoline or histamine on isolated tracheae from these animals display increased maximal contractions, and decreased EC50 values.

Tracheae denuded of epithelium respond with a similar hyperreactivity to histamine as observed in preparations from endotoxin pretreated animals. Removal of the epithelial layer of tracheae from endotoxin pretreated guinea‐pigs did not additionally affect the histamine dose‐response curve.

The cyclo‐oxygenase inhibitor indomethacin (10 μm) induces histamine hyperreactivity which is equal in intact and epithelium‐denuded tracheae from saline or endotoxin pretreated guinea‐pigs. Similar results are obtained with the combined lipoxygenase/cyclo‐oxygenase inhibitor nordihydroguaiaretic acid (10 μm).

Histamine (0.1 mm) induces an increase in prostaglandin E2 (PGE2) formation by the tracheal spiral in vitro, which is reduced by 34% by endotoxin pretreatment, and by about 60% following epithelium removal irrespective of endotoxin pretreatment.

Arachidonic acid (AA, 22 μm) stimulation of the guinea‐pig trachea in vitro induces a relaxation, and an increase in PGE2 production. In preparations lacking the epithelium, AA induces a contraction which coincides with a 60% reduced increase in PGE2 formation. These effects are not altered by endotoxin pretreatment.

It is concluded that the endotoxin‐induced respiratory airway hyperreactivity may be caused by a disturbed ability of epithelial cells to synthesize PGE2. The decreased formation of this prostaglandin is rather the consequence of a diminished liberation of AA from the phospholipid stores than a dysfunction of the cyclo‐oxygenase enzyme.
Monoamine oxidase activity and triiodothyronine biosynthesis in human cultured thyroid cells
Authors: Kraiem Z. , Sadeh O. , Youdim M.B.H.
Published: July 2012

The proposal that monoamine oxidase (MAO) is a source of peroxide in thyroid hormone biosynthesis has been examined by use of isolated cultured human thyroid cells which retain the ability to secrete triiodothyronine (T3) in response to thyroid stimulating hormone (TSH).

The results demonstrated the presence of MAO A and B in human thyroid cells which oxidized 5‐hydroxytryptamine and 2‐phenylethylamine, respectively, and were selectively inhibited by the MAO inhibitors clorgyline and (−)‐deprenyl.

Addition of propylthiouracil to the culture system induced a 61% reduction in TSH‐stimulated T3 secretion, indicating that the bulk of such secretion apparently derives from de novo iodothyronine synthesis.

The MAO A and B substrate, tyramine, was ineffective in stimulating T3 secretion.

The selective MAO inhibitors, clorgyline and (−)‐deprenyl, alone and in combination, and in the presence and absence of tyramine, failed to inhibit basal as well as TSH‐stimulated T3 secretion in cultured human thyrocytes.

It is therefore apparent that even though thyroid MAO A and B enzyme reactions result in the generation of H202, this H202 does not seem to play a significant role in T3 biosynthesis.
The effects of vasoactive intestinal peptide (VIP) antagonists, and VIP and peptide histidine isoleucine antisera on non‐adrenergic, non‐cholinergic relaxations of tracheal smooth muscle
Authors: Ellis James L. , Farmer Stephen G.
Published: July 2012

The effects of several drugs, including antagonists of vasoactive intestinal peptide (VIP), and antisera to VIP or peptide histidine isoleucine (PHI), on relaxation responses of guinea‐pig isolated trachea to electrical field stimulation (EFS) have been examined.

β‐Adrenoceptor blockade with propranolol only partially blocked the inhibitory response to EFS, but had no effect in tissues from animals pretreated with 6‐hydroxydopamine or reserpine.

Neither adenosine deaminase, in the presence of dipyridamole, nor the potent adenosine antagonist NPC205 (1,3‐n‐dipropyl‐8‐(4‐hydroxyphenyl)‐xanthine) had any effect on the inhibitory response to EFS.

The VIP antagonists, [Ac‐Tyr1, d‐Phe2]‐GRF(1–29)‐NH2 and [4‐Cl‐d‐Phe6, Leu17]‐VIP had no effect on the inhibitory response to EFS. Moreover, they were without effect on responses to exogenous VIP or PHI.

Overnight incubation with VIP antisera markedly reduced the inhibitory response to EFS. PHI antisera had a similar, but smaller effect.

In the presence of a concentration of VIP that is maximal for its relaxant effect, inhibitory responses to electrical stimulation were greatly inhibited.

Naloxone and reactive blue 2 each had no effect on inhibitory responses indicating that endogenous opioids and adenosine 5′‐triphosphate (ATP) respectively are not involved.

The results suggest that VIP and PHI, but not adenosine, contribute to non‐adrenergic, non‐cholinergic inhibitory nerve responses of guinea‐pig trachea. Moreover, the surprising lack of effect of both VIP antagonists on these responses, and in particular, on responses to exogenous VIP, suggests that the receptors mediating VIP‐induced tracheal relaxation are different from those that mediate pancreatic secretion.
α2‐Adrenoceptor agonists enhance responses to certain other vasoconstrictor agonists in the rat tail artery
Authors: Xiao Xiao‐Hui , Rand Michael J.
Published: July 2012

The effects of the α2‐adrenoceptor agonists clonidine, rilmenidine, TL99 and UK14304 on the vasoconstrictor response to sympathetic nerve stimulation and on the concentration‐response curves to noradrenaline and phenylephrine were compared in two isolated, perfused vascular tissues: the rat tail artery (which has both postjunctional α1‐ and α2‐adrenoceptors), and the rabbit ear artery (in which only α1‐adrenoceptors are present postjunctionally).

In the rabbit ear artery, the first observable effect of α2‐adrenoceptor agonists was inhibition of vasoconstrictor responses to sympathetic nerve stimulation. This occurred with concentrations of the α2‐adrenoceptor agonists which were far below those producing vasoconstriction. Responses to noradrenaline were not affected.

In contrast, in the rat isolated perfused tail artery, α2‐adrenoceptor agonists, in concentrations that produced no other observable effects, enhanced the vasoconstrictor responses to sympathetic nerve stimulation and to noradrenaline. Much higher concentrations of α2‐adrenoceptor agonists produced vasoconstriction in most preparations and only then reduced the response to sympathetic nerve stimulation. The enhancing effect of α2‐adrenoceptor agonists was blocked by idazoxan, but not by prazosin.

Vasoconstrictor responses in the rat tail artery to the relatively selective α1‐adrenoceptor agonist phenylephrine were enhanced by α2‐adrenoceptor agonists. The enhancement of the response to phenylephrine was greater than that to the mixed α1‐ and α2‐adrenoceptor agonist noradrenaline.

Vasoconstrictor responses in the rat tail artery to vasopressin, ATP and KCl, like those to α1‐adrenoceptor agonists, were enhanced by α2‐adrenoceptor agonists. However, vasoconstrictor responses to 5‐hydroxytryptamine and angiotensin II were not enhanced.
Measurement of 3‐methoxy‐4‐hydroxyphenylglycol (MHPG) in mouse brain by h.p.l.c. with electrochemical detection, as an index of noradrenaline utilisation and presynaptic α2‐adrenoceptor function
Authors: Heal D.J. , Prow M.R. , Buckett W.R.
Published: July 2012

A novel method for measurement of 3‐methoxy‐4‐hydroxyphenylglycol (MHPG) in mouse brain by use of high performance liquid chromatography (h.p.l.c.) with electrochemical detection is described. This technique incorporates an ethyl acetate purification procedure and uses 3‐hydroxy‐4‐methoxyphenylglycol (iso‐MHPG) as the internal standard.

Inhibition of monoamine oxidase by injection of tranylcypromine (5 and 10 mg kg−1) or pargyline (50 and 100 mg kg−1) markedly decreased brain MHPG concentrations. After injection of the tyrosine hydroxylase inhibitor, α‐methyl‐p‐tyrosine (200 mg kg−1), there were time‐dependent linear decreases in the concentrations of noradrenaline and MHPG in mouse brain. In addition, a very good correlation (r = 0.95, n = 30; P < 0.001) was found between the concentrations of noradrenaline and MHPG present in the brains of the same mice after α‐methyl‐p‐tyrosine treatment.

Mouse brain MHPG concentrations were dose‐dependently reduced after administration of the α2‐adrenoceptor agonist, clonidine (1–3000 μg kg−1), and elevated by the antagonists, idazoxan (1 and 5 mg kg−1), and yohimbine (1 and 5 mg kg−1). Intracerebroventricular injection of the α1‐adrenoceptor agonist, phenylephrine (5–50 μg) dose‐dependently increased MHPG levels. The α1‐adrenoceptor antagonist, prazosin, had no effect at the moderate dose of 1 mg kg−1, but increased MHPG concentrations at 5 mg kg−1. The β‐adrenoceptor agonist, clenbuterol (10–1000 μg kg−1) and the antagonist, pindolol (1 and 5 mg kg−1), were both without effect.

The decrease in brain MHPG concentrations induced by clonidine (100 μg kg−1) was prevented by prior injection of 1 mg kg−1 of idazoxan or yohimbine, but not by prazosin or pindolol.

MHPG levels were decreased after administration of the noradrenaline reuptake inhibitor desipramine (5 and 10 mg kg−1) and the non‐selective monoamine reuptake inhibitors, sibutramine HCl (BTS 54 524; 1 and 3 mg kg−1) and amitryptyline (5 mg kg−1). However, the selective 5‐hydroxytryptamine reuptake inhibitor, zimeldine (5 and 10 mg kg−1), was without effect. Dexamphetamine (1 and 5 mg kg−1) and methamphetamine (1 and 5 mg kg−1) both decreased brain MHPG concentrations in a dose‐related fashion.

Overall the data show that MHPG can be used as a functional index of both presynaptic α2‐adrenoceptor activity and noradrenaline turnover and utilisation.
Histamine release in the isolated vascularly perfused stomach of the rat: regulation by autoreceptors
Authors: Sandvik Arne K. , Lewin Miguel J.M. , Waldum Helge L.
Published: July 2012

In the isolated vascularly‐perfused stomach of the rat, gastrin 1–17 (520 pmol l−1) increased acid output from basal values of 13.7 ± 2.7 to 92.5 ± 11.4 μmol h−1 and venous histamine output from 10.1 ± 2.3 to 54.7 ± 7.9 nmol h−1 (mean ± s.e.mean).

The H1 receptor agonist 2‐methylhistamine (10 μmol l−1) increased acid output to 21.6 ± 2.9 μmol h−1 (P < 0.05) and reduced basal histamine output to 4.0 ± 0.8 nmol h−1 (P < 0.05). Gastrin‐stimulated acid secretion and vascular histamine output was not significantly affected by 2‐methylhistamine (10 μmol l−1).

The H2 receptor agonist, impromidine, dose‐dependently increased basal acid secretion, reaching a maximal value of 145.5 ± 11.7 μmol h−1 with impromidine (10 μmol l−1), and maximal gastrin‐stimulated acid secretion to 167.4 ± 15.1 μmol h−1 with impromidine (10 μmol l−1). Impromidine dose‐dependently inhibited basal and gastrin‐stimulated vascular histamine output.

The H3 receptor agonist R‐a‐methylhistamine, (1 and 10 μmol l−1) minimally increased basal acid secretion. R‐a‐methylhistamine (10 μmol l−1) did not significantly affect maximal gastrinstimulated acid secretion. Basal and gastrin‐stimulated vascular histamine outputs decreased to 4.0 ± 0.8 (P < 0.05) and 24.7 ± 4.7 nmol h−1 (P = 0.05) with R‐a‐methylhistamine (10 μmol 1−1).

The H2 receptor antagonist ranitidine (2 μmol l−1) did not inhibit basal acid secretion, but acid outputs with gastrin and all histamine agonists were reduced. Ranitidine did not affect histamine release in the basal state, with gastrin or with any histamine agonist tested.

We conclude that gastric histamine release in the rat is regulated via a histamine H2 receptor sensitive to the histamine agonists tested, but not to ranitidine. It is unlikely that the inhibition of histamine release is secondary to increased gastric acidity.
Nedocromil sodium inhibits the A23187‐ and opsonized zymosan‐induced leukotriene formation by human eosinophils but not by human neutrophils
Authors: Bruijnzeel P.L.B. , Hamelink M.L. , Kok P.T.M. , Kreukniet J.
Published: July 2012

Inflammatory cells such as eosinophils and neutrophils are thought to contribute actively to the pathogenesis of asthma by the release of bronchoconstrictor mediators including leukotrienes. Previous studies have revealed the almost exclusive synthesis of leukotriene C4 (LTC4) by human eosinophils and of leukotriene B4 (LTB4), 20‐OH‐LTB4 and the non‐enzymatically formed LTB4‐isomers by neutrophils when stimulated in vitro with the calcium ionophore A23187 or opsonized zymosan (OZ). In this study we have investigated whether nedocromil sodium, a new anti‐asthma drug, was capable of inhibiting A23187‐ and OZ‐induced leukotriene formation by these cells.

Nedocromil sodium inhibited A23187‐ and OZ‐induced LTC4 formation by eosinophils in a concentration‐dependent manner (mean IC30 for A23187: 5.6 × 10−5m; mean IC30 for OZ: 6.3 × 10−5 m), whereas it did not inhibit A23187‐ and OZ‐induced LTB4 formation by neutrophils.

Extension of the preincubation time of the cells with the drug did not alter the observed inhibitory capacity. The optimal preincubation time was 5 min.

The in vitro inhibition of LTC4 formation by eosinophils by nedocromil sodium may be a valuable property of this drug in the treatment of asthma.
A comparison of vasodilator activity of agents activating cyclic nucleotides with those inhibiting their metabolism in rabbit isolated ear artery
Authors: Wood L.M. , Owen D.A.A.
Published: July 2012

The effects of forskolin, a direct activator of adenylate cyclase and sodium nitroprusside, a direct activator of guanylate cyclase, were studied on rabbit isolated ear arteries preconstricted with 80 mm potassium.

Bolus injection of these two compounds resulted in vasodilatation. They had similar potencies in this tissue but forskolin had a significantly longer duration of action than sodium nitroprusside.

In the same tissue, perfusion with isobutylmethylxanthine (IBMX), a non‐selective phosphodiesterase (PDE) inhibitor, or zaprinast, selective for the PDE primarily responsible for the metabolism of guanosine 3′:5′‐cyclic monophosphate (cyclic GMP), resulted in vasodilatation. However, SK&F 94120 selective for cyclic AMP‐PDE (PDE III), primarily responsible for the metabolism of adenosine 3′:5′‐cyclic monophosphate (cyclic AMP), resulted in vasodilatation only at very high concentrations. The rank order of potency for the compounds was IBMX > zaprinast > SK&F 94120.

The effects of these three PDE inhibitors were studied on the vasoconstriction produced by perivascular sympathetic nerve stimulation in the absence of raised potassium. IBMX and zaprinast, caused a reduction in the response at 50 Hz stimulation frequency and a shift in the frequency‐response curve to the right. SK&F 94120 did not displace the frequency‐response curve but did reduce the response at 50 Hz. The same order of potency for the inhibition of the vasoconstrictor responses to perivascular sympathetic nerve stimulation was found as for vasodilatation i.e. IBMX > zaprinast > SK&F 94120.

These results indicate that in the same tissue direct activation of adenylate and guanylate cyclase results in vasodilatation. Non‐specific PDE and cyclic GMP‐PDE inhibition also resulted in vasodilatation and inhibition of vasoconstrictor responses to sympathetic nerve stimulation. However a selective cyclic AMP‐PDE (PDE III) inhibitor did not result in vasodilatation, except at very high concentrations, or inhibit sympathetic vasoconstrictor responses except to reduce the response at 50 Hz stimulation. These findings provide further support for the ability of PDE inhibitors to be tissue selective.
Inhibition of N‐methyl‐D‐aspartate‐ and kainic acid‐induced neurotransmitter release by ω‐conotoxin GVIA
Authors: Keith Richard A. , Mangano Thomas J. , Salama Andre I.
Published: July 2012

The role of voltage‐sensitive calcium channels (VSCC) in N‐methyl‐D‐aspartate (NMDA)‐ and kainic acid (KA)‐evoked neurotransmitter release from rat cortical and hippocampal brain slices was evaluated by determining the effects of ω‐conotoxin GVIA, an inhibitor of neuronal L‐ and N‐type VSCC, and PN 200–110, a selective inhibitor of L‐type VSCC.

Selective antagonists of the NMDA receptor ionophore complex, Mg2+, CPP and MK‐801, inhibited NMDA‐ but not KA‐evoked release of [3H]‐noradrenaline from hippocampal and cortical brain slices. This suggests that cortical and hippocampal receptors are similar and that NMDA and KA act at distinct excitatory amino acid receptor subtypes.

[3H]‐noradrenaline release induced by both NMDA and KA was similarly inhibited (approximately 30%) by ω‐conotoxin GVIA. In contrast, PN 200–110 had no significant effect, although there was a tendency towards inhibition.

The results suggest that although NMDA‐ and KA‐receptors are pharmacologically distinct, the N‐type, but not the L‐type, VSCC plays a small but significant role in neurotransmitter release induced by both NMDA and KA. It remains to be determined whether the N‐type VSCC are involved in the physiological and/or pathological manifestations of excitatory amino acid receptor stimulation.
Cromakalim‐induced relaxation of guinea‐pig isolated trachealis: antagonism by glibenclamide and by phentolamine
Authors: Murray M.A. , Boyle J.P. , Small R.C.
Published: July 2012

Tested against the spontaneous tone of guinea‐pig isolated trachealis, cromakalim (0.1–100 μm), isoprenaline (1 nm‐1 μm) and theophylline (1 μm‐1 mm) each produced concentration‐dependent relaxation.

Glibenclamide (0.1–10 μm) did not itself alter the spontaneous tone of the trachea nor did it modify the relaxant actions of isoprenaline or theophylline. In contrast, glibenclamide (0.1 and 1 μm) caused a concentration‐dependent rightward shift of the log concentration‐effect curve of cromakalim. Glibenclamide (10 μm) reduced the slope of the log concentration‐effect curve of cromakalim and moved the foot of the curve back towards the control position.

Phentolamine (1, 10 and 100 μm) did not itself alter the spontaneous tone of the trachea nor did it modify the relaxant actions of isoprenaline or theophylline. In contrast phentolamine caused concentration‐dependent depression of the log concentration‐effect curve of cromakalim.

Neither prazosin (1 μm) nor yohimbine (10 μm) modified the spontaneous tone of the trachea. Prazosin and yohimbine each failed to antagonise the effects of cromakalim, isoprenaline and theophylline.

Intracellular electrophysiological recording showed that glibenclamide (1 μm) and phentolamine (100 μm) caused minor change in the resting membrane potential of trachealis cells. Slow wave activity was slightly depressed by these agents. In contrast tetraethylammonium (TEA; 8 mm) caused marked depolarisation, and promoted the conversion of slow waves into regenerative action potentials. These electrical changes were accompanied by tonic tension development.

Phentolamine (100 μm) and glibenclamide (1 μm) reduced and reversed both the relaxation and the hyperpolarisation induced by cromakalim (10 μm).

It is concluded that glibenclamide and phentolamine each provide selective antagonism of the relaxant action of cromakalim in guinea‐pig trachealis. These agents also inhibit the plasmalemmal hyperpolarisation induced by cromakalim. The effect of phentolamine is unrelated to the blockade of α1 or α2‐adrenoceptors. If either glibenclamide or phentolamine act to block the K+ channels opened by cromakalim, then such channels are not identical to those which endow the trachealis plasmalemma with its powerful rectifying behaviour.
Effects of extracellular adenine nucleotides on the electrical, ionic and secretory events in mouse pancreatic β‐cells
Authors: Petit P. , Bertrand G. , Schmeer W. , Henquin J.C.
Published: July 2012

The mechanisms whereby extracellular adenine nucleotides modulate pancreatic β‐cell function were studied with mouse islets stimulated by 15 mm glucose.

Adenosine 5′‐triphosphate (ATP) and adenosine 5′‐diphosphate (ADP) (100 μm) inhibited insulin release, 45Ca efflux and 86Rb efflux from islet cells, and decreased electrical activity in β‐cells. These changes were rapid but small and transient.

α,β‐Methylene ADP caused a rapid and sustained inhibition of insulin release, 45Ca efflux and 86Rb efflux from islet cells. It also produced a slight hyperpolarization of the β‐cell membrane, with sustained modification of the pattern but only transient decrease of the intensity of the electrical activity. In the absence of extracellular Ca2+, α,β‐methylene ADP increased 45Ca and 86Rb efflux without changing insulin release. Most effects of α,β‐methylene ATP were qualitatively similar but quantitatively smaller than those of the ADP‐analogue.

Adenylylimido‐diphosphate (AMP‐PNP) slightly increased 45Ca and 86Rb efflux and potentiated insulin release in the presence of extracellular Ca2+. However, its effects on electrical activity in β‐cells were qualitatively similar to those of the α,β‐methylene analogues.

The small effects of ATP and ADP could result from their degradation into adenosine. α,β‐Methylene ADP appears to increase K+ permeability of the β‐cell membrane and to produce a second, intracellular, effect which largely contributes to the inhibition of insulin release. Another recognition site, with higher affinity for triphosphate derivatives, could mediate the small stimulatory effects of AMP‐PNP.
Identification of a single α1‐adrenoceptor corresponding to the α1A‐subtype in rat submaxillary gland
Authors: Michel Anton D. , Loury Dana N. , Whiting Roger L.
Published: July 2012

The α1‐adrenoceptors present in membranes of rat liver, cortex and submaxillary gland were labelled with [3H]‐prazosin and the affinity of 15 ligands for these receptors was determined.

In saturation studies, [3H]‐prazosin bound with high affinity (Kd = 30–39 pM) to a single population of sites in all three preparations.

In competition studies using rat cortex, evidence for heterogeneity of the α1‐adrenoceptor binding sites was obtained. Displacement isotherms for amidephrine, benoxathian, oxymetazoline, phentolamine and WB 4101 were biphasic and were consistent with the presence of both α1A‐ and α1B‐adrenoceptor subtypes as described by Morrow & Creese (1986) and Han et al. (1987).

The rat liver and submaxillary gland membrane preparations both possessed homogeneous populations of α1‐adrenoceptors. However, there were pharmacological differences between the receptors in these two preparations. Rat submaxillary gland α1‐adrenoceptors displayed high affinity for amidephrine, benoxathian, oxymetazoline, phentolamine and WB 4101 and therefore appeared to represent α1A‐adrenoceptors. Rat liver α1‐adrenoceptors possessed lower affinity for these ligands (6–65 fold) suggesting that these receptors were of the α1B‐subtype.

Spiperone exhibited 12.9 fold higher affinity for rat liver α1B‐adrenoceptors than for rat submaxillary gland α1A‐adrenoceptor and may therefore represent the first α1B‐adrenoceptor selective ligand.
Differential cardiovascular and respiratory responses to central administration of selective opioid agonists in conscious rabbits: correlation with receptor distribution
Authors: May C.N. , Dashwood M.R. , Whitehead C.J. , Mathias C.J.
Published: July 2012

The effects of intracerebroventricular (i.c.v.) and intracisternal (i.c.) administration of a range of doses (0.01, 0.1 and 1.0 nmol kg−1) of specific μ‐ δ‐ and κ‐opioid agonists on cardiovascular and respiratory function and on plasma catecholamines have been studied in conscious rabbits. The distribution of μ‐ δ‐ and κ‐opioid receptors was localized in rabbit brain by in vitro autoradiography.

The μ‐agonist [D‐Ala2, MePhe4‐Gly5‐ol]enkephalin (DAGOL) given i.c.v. caused a large rise in plasma noradrenaline and adrenaline, hypertension accompanied by an initial bradycardia followed by tachycardia, respiratory depression and sedation. After i.c. administration there were similar changes in heart rate (HR) and respiration, but no significant changes in mean arterial pressure (MAP) or plasma catecholamines.

The δ‐agonist [D‐Pen2,5]enkephalin (DPDPE) increased MAP and HR after both i.c.v. and i.c. administration, caused a small increase in noradrenaline but had no effect on adrenaline and did not alter respiration rate or blood gases. After i.c.v. DPDPE the rabbits became more alert and active.

The κ‐agonist U69593 given i.c.v. or i.c. had no effect on MAP or HR. After i.c.v. U69593, Paco2 fell, but there were no other respiratory effects. The responses to dynorphin 1–13, an endogenous κ‐agonist, were similar to those of U69593.

The opioid antagonist naloxone (30 nmol kg−1) given intravenously (i.v.) blocked the effects of i.c.v. DAGOL (1 nmol kg−1). A 100 fold higher dose of i.v. naloxone (3 μmol kg−1) was required to abolish the effects of i.c.v. DPDPE (1 nmol kg−1).

Autoradiographic studies demonstrated a high density of μ‐ and δ‐opioid receptors in hypothalamic sites. In the brainstem μ‐receptors were demonstrated in the nucleus tractus solitarius (NTS) and δ‐receptors in the dorsal motor nucleus of the vagus. κ‐Receptors were not detected in either the hypothalamus or brainstem.

These findings demonstrate that DAGOL increases sympatho‐adrenal outflow, probably by stimulation of hypothalamic μ‐receptors. The effects on HR are probably partly through a baroreflex and partly through an action of DAGOL on μ‐receptors in the dorsal motor nucleus of the vagus. DPDPE probably acts on δ‐receptors in the NTS to increase MAP and HR. Respiratory depression resulted from stimulation of μ‐receptors in the brainstem with no evidence of δ‐ or κ‐receptors being involved.
Capsaicin evokes secretion of nasal fluid and depletes substance P and calcitonin gene‐related peptide from the nasal mucosa in the rat
Authors: Petersson G. , Malm L. , Ekman R. , Håkanson R.
Published: July 2012

The secretion of nasal fluid was studied in anaesthetized rats after topical application of capsaicin, and of calcitonin gene‐related peptide (CGRP) alone or CGRP in combination with substance P (SP). The flow of nasal fluid was stimulated and the secretions collected by a filter paper technique. The concentrations of SP and CGRP in nasal biopsies were determined after topical or systemic administration of capsaicin.

Capsaicin (single dose administration) stimulated nasal secretion in a dose‐dependent manner. The effect was inhibited by hexamethonium, lignocaine, or by the tachykinin antagonist (D‐Pro2, D‐Trp7,9)‐SP, but not by atropine, or by a combination of the histamine H1‐receptor antagonist chlorpheniramine and the H2‐receptor antagonist ranitidine.

When applied cumulatively, capsaicin rapidly produced desensitization. The concentrations of SP and CGRP in the nasal mucosa were reduced by capsaicin 6 days after topical or s.c. administration but not 15 min after topical application of desensitizing doses.

CGRP did not stimulate the secretion of nasal fluid and did not alter SP‐evoked nasal secretion.

The inhibition by hexamethonium of the capsaicin‐evoked nasal secretion suggests the involvement of ganglionic reflexes. In addition, the inhibition of the response to capsaicin by (D‐Pro2,D‐Trp7,9)‐SP and lidocaine and the depletion of SP and CGRP after capsaicin indicate the involvement of tachykinin‐mediated axon reflexes.
Amelioration of glycerol‐induced acute renal failure in the rat with 8‐cyclopentyl‐1,3‐dipropylxanthine
Authors: Kellett R. , Bowmer C.J. , Collis †M.G. , Yates M.S.
Published: July 2012

Previous studies have shown that 8‐phenyltheophylline (8‐PT), a non‐selective antagonist at adenosine A1‐ and A2‐receptors, can ameliorate the severity of glycerol‐induced acute renal failure (ARF) in the rat. In the present study we have examined the effects of an antagonist with selectivity for adenosine A1‐receptors (8‐cyclopentyl‐1,3‐dipropylxanthine, CPX) on the development of ARF.

In the anaesthetised rat 8‐PT (4 mg kg−1, i.v.) and CPX (0.1 mg kg−1, i.v.) antagonised adenosine‐evoked responses which are thought to be mediated via A1‐receptors (bradycardia and decrease in renal blood flow). The agonist dose‐ratio produced by CPX was equal to or greater than that found with 8‐PT (heart rate and renal blood flow respectively). The hypotensive response to adenosine which is predominantly due to A2‐receptor activation was also antagonised by 8‐PT, whereas CPX was a much less effective antagonist of this response.

Administration of CPX (0.1 mg kg−1, i.v.; twice daily for two days) significantly attenuated the increase in plasma levels of urea and creatinine, the increased kidney weight and the renal tubule damage observed in rats 2 days following induction of ARF with intramuscular glycerol injection. In addition treatment with CPX significantly enhanced the clearances of inulin and p‐aminohippurate.

After glycerol injection, the mortality rate over 7 days in untreated and vehicle‐treated rats was 43% and 21% respectively. In contrast, all animals treated with CPX survived over the 7 day observation period.

These results support the suggestion that adenosine is an important factor in the development of ARF and indicate that this effect of the purine is likely to be mediated via an adenosine A1‐receptor.
The relationship between neutrophils and increased microvascular permeability in a model of myocardial ischaemia and reperfusion in the rabbit
Authors: Williams Frances M. , Collins Paul D. , Tannière‐Zeller Marianne , Williams Timothy J.
Published: July 2012

111In‐labelled neutrophils and 125I‐labelled albumin were used to measure neutrophil accumulation and microvascular plasma protein leakage in the ischaemic/reperfused myocardium of anaesthetized rabbits.

A period of 30 min coronary artery occlusion followed by 3h reperfusion resulted in an increase in both 111In and 125I counts in the area at risk (AR) of the myocardium.

Pretreatment of 111In‐neutrophils in vitro with monoclonal antibody 60.3 directed against the CD18 antigen on neutrophils, followed by intravenous administration, significantly suppressed their accumulation into the AR myocardium.

Depletion of circulating neutrophils by use of anti‐neutrophil serum or mustine hydrochloride did not affect plasma protein leakage into the AR myocardium.

Administration of the platelet activating factor (PAF) antagonist WEB 2086 (10 mg kg−1, i.v.) had no effect on the accumulation of 111In‐neutrophils or on plasma protein leakage in the AR myocardium.
The effect of benserazide on the peripheral and central distribution and metabolism of levodopa after acute and chronic administration in the rat
Authors: Kent A.P. , Stern G.M. , Webster R.A.
Published: July 2012

The effects of levodopa alone (50 mg kg−1) and levodopa (10 mg kg−1) plus benserazide (50 mg kg−1) were tested on the levels of dopa, dopamine, 3‐methoxytyrosine (3‐MT), 3,4‐dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), measured by h.p.l.c with electrochemical detection, in samples of plasma, CSF, urine, striatum and hypothalamus of rats taken 30 min after injection. Levodopa plus benserazide produced significantly higher levels of dopa in plasma and brain than levodopa alone and reduced the peripheral synthesis and metabolism of dopamine.

When given chronically over 6 weeks the advantages of adding benserazide (50 mg kg−1 day−1) to levodopa (40 mg kg−1 day−1) were less marked and although more dopamine was present in the striatum than with levodopa given alone (200 mg kg−1 day−1) there was no evidence of any increase in its metabolites (HVA and DOPAC) and therefore of its turnover and utilisation.

The most striking effect of chronic treatment with levodopa plus benserazide was the appearance of large quantities of 3‐MT in plasma, CSF and brain.

When levodopa alone, or levodopa plus benserazide, was given as an acute challenge to animals receiving the same treatment chronically, it was found that levodopa alone still produced increases in striatal dopamine, DOPAC and HVA in those animals dosed chronically on levodopa, but it was less effective in this respect when given with benserazide to the animals dosed with levadopa plus benserazide.

It is concluded that this difference in levodopa distribution may depend on the persistence in benserazide‐treated animals of 3‐MT, which has a long half‐life and may compete with dopa for transport into the blood and brain.

The implication of these findings to the treatment of Parkinsonism is discussed.
Effect of neuropeptide Y on α2‐adrenoceptor‐mediated cardiovascular responses in the pithed rat
Authors: Vila E. , Macrae I.M.
Published: July 2012

The effects of neuropeptide Y (NPY) on the cardiovascular responses induced by stimulation of pre‐ and postjunctional α2‐adrenoceptors were studied in the pithed normotensive rat.

The increase in diastolic blood pressure induced by cumulative injection of xylazine (1–1000 μgkg−1, i.v.) were potentiated by NPY (5 μg kg−1) but not affected by a lower dose (0.75 μg kg−1) of this peptide.

Xylazine (1–100 μg kg−1) inhibited in a dose‐dependent manner the tachycardia induced by continuous electrical stimulation (0.2 Hz, 2 ms, 60 V) of the spinal cord (C7‐Thl).

NPY (5 μg kg−1 but not 0.75 μg kg−1) enhanced the inhibitory effect of xylazine on the tachycardia induced by electrical stimulation without having any direct effect on heart rate.

These results suggest that there may be a positive interaction between NPY receptors, postjunctional α2‐adrenoceptors and between NPY receptors and prejunctional α2‐adrenoceptors in the cardiovascular system of the rat.
Identification of human platelet a2‐adrenoceptors with a new antagonist [3H]‐RX821002, a 2‐methoxy derivative of idazoxan
Authors: Galitzky Jean , Senard Jean Michel , Lafontan Max , Stillings Mike , Montastruc Jean Louis , Berlan Michel
Published: July 2012

The binding of a new α2‐adrenoceptor antagonist, [3H]‐RX821002 (2‐(2‐methoxy‐l,4‐benzodioxan‐2‐yl)‐2‐imidazoline), was investigated in human platelet membranes and compared with [3H]‐yohimbine binding parameters.

Analysis of kinetic data revealed association and dissociation time courses consistent with a simple bimolecular reaction. Saturation isotherms showed that [3H]‐RX821002 labelled a higher total number of α2‐binding sites (224 ± 31 vs 168 ± 24 fmol mg−1 protein) than [3H]‐yohimbine and with higher affinity (Kd: 0.92 ± 0.06 vs 1.51 ± 0.08nm). Moreover [3H]‐RX821002 exhibited a lower percentage of nonspecific binding.

The difference in total binding is due to a better labelling of the α2‐adrenoceptors in the low affinity state by [3H]‐RX821002 since the labelled receptors number in high affinity state was identical with the two radioligands.

[3H]‐RX821002 binding displayed a specificity similar to that obtained with [3H]‐yohimbine. The potency of various compounds acting on adrenoceptors was: yohimbine > oxymetazoline > UK 14304 > (−)−adrenaline > prazosin ≥ (+)‐adrenaline > isoprenaline. This order of potency is classical for an α2A‐adrenoceptor.

RX821002 is a more potent α2‐adrenoceptor antagonist than yohimbine on adrenaline‐induced platelet aggregation.

These results indicate that [3H]‐RX821002 is a suitable ligand for the identification of human platelet α2‐adrenoceptors.
Ethanol inhibition of baroreflex bradycardia: role of brainstem GABA receptors
Authors: Varga Karoly , Kunos George
Published: July 2012

Ethanol administered i.v. or into the nucleus tractus solitarii (NTS) of rats anaesthetized with urethane inhibits baroreflex bradycardia elicited by phenylephrine. This effect is prevented or reduced by pretreatment of rats with 3‐mercaptopropionic acid, bicuculline, or RO 15–4513. Intra‐NTS injection of muscimol also inhibits baroreflex bradycardia and causes a pressor response which is potentiated by intra‐NTS ethanol. It is proposed that ethanol inhibits baroreflex bradycardia, at least in part, by potentiating the action of endogenous γ‐aminobutyric acid (GABA) at GABAA receptors in the NTS or its vicinity.
Enhancement of the endothelial production of prostacyclin by inhibitors of protein synthesis
Authors: Boeynaems J.‐M. , Boutherin‐Falson O. , Lagneau C. , Galand N.
Published: July 2012

Pretreatment of bovine aortic endothelial cells with cycloheximide enhanced their capacity to release prostacyclin in response to adenosine 5′‐triphosphate (ATP) and bradykinin.

The action of cycloheximide was time‐dependent; it became detectable after a 1 h exposure to the cells and was maximal after 3 h.

Puromycin mimicked the effect of cycloheximide. For these two agents, the enhancement of prostacyclin release was obtained at concentrations producing a partial inhibition of protein synthesis.

Cycloheximide increased the mobilization of free arachidonic acid induced by ATP in bovine aortic endothelial cells.

In conclusion, the synthesis of new proteins is not involved in the stimulatory action of ATP and bradykinin on prostacyclin production by bovine aortic endothelial cells. Despite the short half‐life of prostaglandin H synthase in endothelial cells, cycloheximide and puromycin enhanced the release of prostacyclin induced by agonists. Our data suggest that this release might be under the control of rapidly turning‐over phospholipase inhibitory proteins.
Effects of carbachol and (−)‐N6‐phenylisopropyladenosine on myocardial inositol phosphate content and force of contraction
Authors: Kohl Claudia , Linck Bettina , Schmitz Wilhelm , Scholz Hasso , Scholz Jens , Tóth Mathias
Published: July 2012

The effects of carbachol and the A1‐adenosine receptor agonist (−)‐N6‐phenylisopropyladenosine (PIA) on force of contraction and inositol lipid metabolism were studied in electrically driven left auricles and papillary muscles isolated from guinea‐pig hearts. Both carbachol and PIA (0.01–10 μm) had concentration‐dependent negative inotropic effects in auricles. In papillary muscles PIA had no inotropic effect. Carbachol also had no inotropic effect at low concentrations (0.01–1 μm) but at 10–100 μm it exerted a slight positive inotropic effect.

In auricles and papillary muscles both carbachol and PIA concentration‐dependently increased inositol trisphosphate (IP3; significant at 1 μm). Accordingly phosphatidylinositol bisphosphate (PIP2), the precursor of IP3, was reduced. All effects of carbachol and PIA were antagonized by atropine (10 μm) and 1,3‐dipropyl‐8‐cyclopentylxanthine (DPCPX; 20 μm) respectively, indicating receptor‐mediated effects.

In auricles the negative inotropic effects of carbachol and PIA preceded the increase in IP3.

In papillary muscles the increase in IP3 preceded the slight positive inotropic effect of carbachol, indicating that the M‐cholinoceptor‐mediated increase in IP3 and force of contraction may be related. However, PIA showed a comparable increase in IP3 but no inotropic effect, indicating a dissociation between those parameters.

In conclusion, in previous studies a close relation between increases in IP3 and force of contraction has been shown after α1‐adrenoceptor stimulation. The present study with carbachol supports this view. However, the present data for PIA could not show such a close relationship, questioning the role of IP3 as an endogenous regulator of force of contraction.
Different profiles of desensitization dynamics in guinea‐pig jejunal longitudinal smooth muscle after stimulation with histamine and methacholine
Authors: Leurs R. , Smit M.J. , Bast A. , Timmerman H.
Published: July 2012

In the present study we investigated desensitization phenomena of guinea‐pig jejunal longitudinal smooth muscle responses after stimulation with 100 μm histamine or methacholine, using a superfusion method.

Histamine H1‐receptor‐mediated contractions appear to be rapidly reduced after application of 100 μm histamine. Muscarinic responses were not affected following desensitization with 100 μm histamine, indicating a homologous desensitization.

Initial contractions to 0.3 μm histamine were reduced by 90%, recovered quickly, but did not reach control levels within 1 h. Desensitization of histamine responses could be separated into two phases; a rapid, but transient, desensitization and a more sustained desensitization. As a consequence of this sustained effect the pD2 for histamine shifted from 6.7 ±0.1 (control) to 6.1 ±0.1 (desensitized).

Desensitization with 100 μm methacholine caused a heterologous desensitization, reflected by the development of a refractory period, in which neither histamine nor methacholine was able to elicit a contraction. After a few minutes responses to both agents recovered to control levels.

During the refractory period after methacholine desensitization, muscle strips were still responsive to 40 mm KCl but did not contract in response to 10 mm caffeine, suggesting that the heterologous desensitization is caused by a modification of an intracellular Ca2+‐store, which is used by both histamine and methacholine.

The recovery of the responses after methacholine desensitization was not dependent on extracellular Ca2+, suggesting that the recovery is not dependent on refilling of the intracellular Ca2+ store with extracellular Ca2+.

The protein kinase C activator, phorbol‐12,13‐dibutyrate, concentration‐dependently inhibited histamine‐ and methacholine‐induced contractions. Protein kinase C seems therefore not to be implicated in the observed homologous H1‐receptor desensitization.

These data suggest that different forms of desensitization can be distinguished in this model, each with a different time course and dependent on the applied stimulus.
The use of oxyhaemoglobin to explore the events underlying inhibition of platelet aggregation induced by NO or NO‐donors
Authors: Salvemini Daniela , Radziszewski Waldemar , Korbut Richard , Vane John
Published: July 2012

Full inhibition of thrombin‐induced platelet aggregation was elicited by the least maximal platelet inhibitory concentrations of nitric oxide (NO; 7 ± 1 μm) or NO‐donors which included sodium nitroprusside (NaNp; 80 ± 13 μm), 3‐morpholinosydnonimine (SIN‐1; 3 ± 0.1 μm) or endothelial cells (EC; 2.36 ± 0.12 × 105) added 1 min before thrombin. Oxyhaemoglobin (oxyHb; 10 μm) administered 30s to 10 min after stimulation with thrombin caused a time‐dependent reversal of the inhibition induced by these agents. OxyHb was ineffective when these agents were co‐incubated with the non‐selective phosphodiesterase inhibitor 3‐isobutyl‐1‐methylxanthine (IBMX, 0.05 mm).

OxyHb did not reverse the platelet inhibition with IBMX (0.2 mm) or that caused by a selective guanosine 3′: 5′‐cyclic monophosphate (cyclic GMP) phosphodiesterase inhibitor 2‐O‐propoxyphenyl‐8‐azapurin‐6‐one, (M & B 22948; 20 μm). In addition, oxyHb did not reverse the inhibition with iloprost (1 nm) which inhibits platelet aggregation through stimulation of adenylate cyclase.

The inhibition of platelet aggregation by NO (7 ± 1 μm) or NaNp (80 ± 13 μm) was accompanied by a 13 fold increase in cyclic GMP levels occurring within 15 s of addition of these agents. In the continued presence of NO or NaNp, the reversing effect of oxyHb given 1 min after thrombin was associated with a pronounced decrease in cyclic GMP levels.

We conclude that the inhibition of platelet aggregation by activators of guanylate cyclase depends in the first few minutes on continuous stimulation of the enzyme in order to maintain intracellular concentrations of cyclic GMP, except when its breakdown is inhibited.

The addition of agents such as oxyHb after the inhibition of platelet aggregation offers another way of investigating the biochemical changes involved in maintaining platelets in an inactive state.
Pharmacological characterization of tachykinin‐stimulated inositol phospholipid hydrolysis in peripheral tissues
Authors: Suman‐Chauhan N. , Guard S. , Williams B.J. , Watling K.J.
Published: July 2012

Tachykinin‐stimulated inositol phospholipid hydrolysis was examined in slices of rat parotid gland, hamster urinary bladder and guinea‐pig ileum longitudinal muscle.

In the presence of lithium, substance P and other naturally‐occurring and synthetic tachykinins induced large, dose‐dependent increases in [3H]‐inositol monophosphate accumulation.

In slices of rat parotid gland, [pGlu6,l‐Pro9]SP(6–11) was considerably more potent in stimulating inositol phospholipid hydrolysis than [pGlu6,d‐Pro9]SP(6–11).

In contrast, in slices of hamster urinary bladder, [pGlu6,d‐Pro9]SP(6–11) exhibited greater potency in evoking inositol phospholipid breakdown than [pGlu6,l‐Pro9]SP(6–11).

The differential selectivity of these C‐terminal fragments of substance P suggests that they may be useful tools for distinguishing between NK1 and NK2 receptors.

L‐659,837 and L‐659,874 antagonized eledoisin‐stimulated inositol phospholipid hydrolysis in slices of hamster urinary bladder. Neither compound significantly reduced substance‐P evoked inositol phospholipid breakdown in slices of rat parotid gland, or senktide‐induced inositol phospholipid hydrolysis in slices of guinea‐pig ileum.

L‐659,837 and L‐659,874 had no effect on the atropine‐sensitive, carbachol‐stimulated inositol phospholipid hydrolysis in slices of rat parotid gland.

These data further support the notion that L‐659,837 and L‐659,874 are potent and selective NK2 receptor antagonists.
Differences in hepatic drug accumulation and enzyme induction after chronic amiodarone feeding of two rat strains: role of the hydroxylator phenotype?
Authors: Pirovino M. , Honegger U. , Müller O. , Zysset Th. , Küpfer A. , Tinel M. , Pessayre D.
Published: July 2012

It has previously been shown that the extent of hepatic phospholipidosis induced by chronic amiodarone treatment correlates with the degree of drug accumulation in liver tissue.

To investigate a possible influence of pharmacogenetic factors, biochemical and morphological investigations were carried out in two rat strains differing in debrisoquine hydroxylation.

Plasma and liver tissue concentrations of amiodarone and its main metabolite, desethyl‐amiodarone, were significantly higher in rats with deficient hydroxylation. Microsomal enzyme induction, drug cytochrome P‐450 complex formation and typical ultrastructural features of phospholipidosis were only seen in rats with deficient hydroxylation and in a more sensitive species, the guinea‐pig.

It remains to be seen whether deficient debrisoquine hydroxylation in man is associated with an increased susceptibility to amioadarone side effects.
Cardiac β‐adrenoceptor binding characteristics with age following adrenal demedullation
Authors: Turner Nihal , Houck Wayne T. , Boehm Cheryl , Roberts Jay
Published: July 2012

The role of adrenal medullary catecholamines in the regulation of cardiac function becomes more important when adrenergic neural influences in the heart are decreased. Since adrenergic nervous input to the heart decreases with age, it would be expected that catecholamine influence on cardiac neuroeffector junction would increase.

Fischer‐344 rats of 6‐, 12‐ and 24‐months were adrenal demedullated or sham‐operated and the animals were killed at the end of two weeks. β‐Adrenoceptors were studied in the membrane preparations from the ventricles of rat hearts. [125I]‐iodopindolol was used as the radioligand. The density of β‐receptors (Bmax), dissociation constant (KD) and the ratio of cardiac β‐adrenoceptor subtypes were studied. The relative percentages of β‐receptor subtypes were determined by use of ICI 89,406 (β1‐selective antagonist) and ICI 118,551 (β2‐selective antagonist).

In 24‐month‐old animals which were adrenal demedullated, hydrocortisone replacement was employed for one week; the animals were killed one week later.

The data indicate that there was a diminution of the Bmax following adrenal demedullation at all ages but that the ratios of β1:β2‐adrenoceptors remain the same as in the controls (67:33). The effect of adrenal medullary catecholamines on cardiac β‐receptor binding characteristics did not seem to be influenced by age.