bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of putative neurotransmitters and related drugs on withdrawal contractures of guinea‐pig isolated ileum following brief contact with [Met5] enkephalin
Authors: Chahl Loris A.
Published: July 2012

Brief exposure for 2 min of guinea‐pig isolated ileum to [Met5]enkephalin (MEnk) and noradrenaline has been shown previously to produce withdrawal contractures on washout of the agonist or addition of naloxone (MEnk) or phentolamine (noradrenaline).

The present study was undertaken to investigate firstly, whether other putative neurotransmitters and/or related drugs which inhibit transmitter release also produced withdrawal responses following 2 min contact with the ileum and secondly, whether they affected the opioid withdrawal response.

Adenosine (1–5 μm), but not U‐50,488H (1–5 μm), somatostatin (0.01–5 μm), ocreotide (1–5 μm), baclofen (1–25 μm) or dopamine (5, 50 μm), produced a contracture on washout following 2 min contact with the ileum. The adenosine (5 μm) washout contracture, in common with MEnk and noradrenaline washout contractures, was inhibited by the substance P antagonist, spantide (10 μm).

Added 30 s before washout at a concentration of 5 μm, noradrenaline, U‐50,488H, adenosine, somatostatin and ocreotide significantly inhibited the washout withdrawal response following 2 min contact of the ileum with MEnk, 1 μm. A higher concentration of baclofen, 250 μm, also inhibited this response.

The naloxone (1 μm)‐precipitated withdrawal response following contact of the ileum with MEnk, 1 μm, for 2 min, was inhibited only by noradrenaline (5 μm) and U‐50,488H (5 μm).

It is concluded that during naloxone‐precipitated opioid withdrawal an additional population of enteric motor neurones is recruited which is not involved in the washout withdrawal response and these neurones have less diversity of presynaptic receptors mediating inhibition of transmitter release than cholinergic motor neurones.
Philanthotoxin blocks quisqualate‐, AMPA‐ and kainate‐, but not NMDA‐, induced excitation of rat brainstem neurones in vivo
Authors: Jones M.G. , Anis N.A. , Lodge D.
Published: July 2012

The effect of electrophoretic ejection of philanthotoxin (the polyamine toxin, from the Egyptian digger wasp) was tested on responses of brainstem and spinal neurones in the pentobarbitone‐anaesthetized rat to excitatory amino acids.

Philanthotoxin caused a dose‐dependent reduction of responses to quisqualate, α‐amino‐3‐hydroxy‐5‐phenyl‐4‐isoxazolepropionate (AMPA) and kainate with little effect on those to N‐methyl‐d‐aspartate (NMDA).

The time‐course of this antagonist action was slow. In particular the rate of recovery was dependent on frequency of ejection of the agonist. This agonist‐dependent recovery suggests that philanthotoxin has a channel blocking mode of action on mammalian central neurones.
Pharmacological characterization of polycation‐induced rat hind‐paw oedema
Authors: Antunes Edson , Mariano Mário , Cirino Giuseppe , Levi Silvio , DE Nucci Gilberto
Published: July 2012

The inflammatory response induced by poly‐l‐arginine in the rat hind‐paw was studied both by measuring paw oedema and histologically.

The paw volume was measured with a hydroplethysmometer at 0.5, 1, 2, 4, 6 and 18 h after the subplantar injection of the polycation. Protein extravasation was evaluated with Evans' blue and the histology studied by light microscopy.

Poly‐l‐arginine (12, 24, 43 and 115 kD) caused dose‐ and molecular weight‐dependent oedema which had a rapid onset and long duration. Evans' blue extravasation paralleled the oedema induced by poly‐l‐arginine. Microscopic examination of the paws at early stages of oedema formation showed exuberant liquid exudate with no inflammatory cells. After 18 h, a cellular infiltrate was present, consisting mainly of mononuclear cells.

Indomethacin, dexamethasone, BW755c or the PAF‐antagonist WEB 2086 caused no significant inhibition of the poly‐l‐arginine‐induced oedema. Cyproheptadine had inhibitory effects only on the early stages of the polycation‐induced oedema. Similar results were observed with rats depleted of histamine and 5‐hydroxytryptamine.

Heparin, a polyanion, injected in the rat paw caused a marked inhibition of the polycation‐induced oedema. NG‐monomethyl‐l‐arginine (LNMMA), an inhibitor of EDRF synthesis, injected locally also produced a marked inhibition, but this inhibition was reversed by iloprost.

These results suggest that the oedema induced by polycations was due to their cationic charge. The inhibitory effect of LNMMA is probably due to a decrease in vascular flow rather than a decrease in vascular permeability.
Tachykinin receptors in the circular muscle of the guinea‐pig ileum
Authors: Maggi Carlo Alberto , Patacchini Riccardo , Giachetti Antonio , Meli Alberto
Published: July 2012

We have studied the mechanical response of circular strips of the guinea‐pig ileum to tachykinins and characterized the receptors involved by means of receptor‐selective agonists.

The strips responded to both substance P (SP) and neurokinin A (NKA), as well as to [Pro9]‐SP sulphone (selective NK1‐receptor agonist), [βAla8]‐NKA(4–10) (selective NK2‐receptor agonist) and [MePhe7]‐neurokinin B (selective NK3‐receptor agonist). The ED50s of the various peptides (calculated as the concentration of agonist which produced 50% of the response to 10 μm carbachol) were similar, in the range of 40–200 nm, i.e. no clearcut rank order of potency was evident.

The response to a submaximal (10 nm) concentration of SP or NKA was unaffected in the presence of peptidase inhibitors (thiorphan, captopril and bestatin, 1 μm each).

The response to the NK1‐agonist was totally atropine‐resistant, but was reduced (about 30% inhibition) by tetrodotoxin. The response to the NK3‐receptor agonist was halved by atropine and abolished by tetrodotoxin. The response to the NK2‐agonist was unaffected by either atropine or tetrodotoxin.

The response to the selective NK2‐agonist was unchanged after desensitization of NK1‐ or NK3‐receptors.

The response to the NK2‐selective agonist was strongly inhibited by [Tyr5, d‐Trp6,8,9, Arg10]‐NKA(4–10) (MEN 10,207) a selective NK2‐receptor antagonist which did not modify the response to the NK1‐selective agonist.

Our findings indicate that all the three known types of tachykinin receptors mediate the contractile response of the circular muscle of the guinea‐pig ileum to peptides of this family. The response to activation of NK3‐receptors is totally neurogenic and partially mediated by endogenous acetylcholine, the response to activation of NK1‐receptors is partly neurogenic and largely myogenic and the response to activation of NK2‐receptors is totally myogenic.
Effects of hypomagnesia on transmitter actions in neocortical slices
Authors: El‐Beheiry H. , Puil E.
Published: July 2012

The effects of hypomagnesia on the neuronal responses induced by iontophoretically applied acetylcholine, glutamate, N‐methylaspartate (NMDA) and γ‐aminobutyric acid (GABA) were investigated using intracellular recording techniques in in vitro slices of sensorimotor cortex (guinea‐pigs).

Perfusion with Mg‐free media, with or without tetrodotoxin (TTX), induced a small hyperpolarization (∼4mV) and a small decrease (∼10%) in the input resistance of neurones. During TTX‐blockade of Na‐spike genesis, spontaneous depolarizing waves of low frequencies were observed in neurones of slices under Mg‐free conditions.

The effects of acetylcholine and to a lesser extent, GABA actions, were depressed in a dose‐dependent, reversible manner by decreases in the [Mg2+] of the perfusing media. In neurones of slices that had been incubated in Mg‐free artificial cerebrospinal fluid to ensure a maximal depletion, the responses to these transmitters were potentiated by each sequentially administered increase in extracellular [Mg2+]. The actions of NMDA were potentiated during perfusion of Mg‐free media. However, the responses to glutamate, which may activate receptors for NMDA, were either depressed or unchanged under these conditions.

A regulatory role for external Mg cations in the responses of neocortical neurones to the transmitter substances, acetylcholine and GABA, can be inferred from these investigations which simulate hypomagnesemia. The dose‐dependent depression of GABA actions by low extracellular [Mg2+] additionally provides a plausible mechanism that may contribute to the neuronal hyperexcitability that is observed during conditions of hypomagnesemia.
Evaluation of ZK110841 and AH6809, an agonist and an antagonist of prostaglandin DP‐receptors on human platelets, with a PGD2‐responsive cell line from bovine embryonic trachea
Authors: Ito Seiji , Okuda Emiko , Sugama Kazushige , Negishi Manabu , Hayaishi Osamu
Published: July 2012

ZK110841 and AH6809, an agonist and an antagonist of prostaglandin DP‐receptors on human platelets, were evaluated with a fibroblastic cell line from bovine embryonic trachea (EBTr) which specifically responds to prostaglandin D2 (PGD2). ZK110841, equipotent to PGD2, elevated the adenosine 3′: 5′‐cyclic monophosphate (cyclic AMP) level in EBTr cells dose‐dependently, being more than 100 fold over the basal level at 1 μm. The half‐maximally effective concentration of PGD2 or ZK 110841 was 10–30 nm. Increasing concentrations (10−7 − 10−4 m) of AH6809 (which possesses negligible intrinsic agonist activity) produced parallel shifts to the right of dose‐response curves to PGD2 and ZK110841. Schild plots of these data were linear (correlation close to unity) and pA2 values against PGD2 and ZK110841 were calculated to be 6.36 and 6.57, respectively, indicating that AH6809 is a simple and competitive antagonist. These results demonstrate that ZK110841, AH6809 and EBTr cells will be useful for characterization of DP‐receptors.
The effects of cromakalim on ATP‐sensitive potassium channels in insulin‐secreting cells
Authors: Dunne M.J. , Aspinall R.J. , Petersen O.H.
Published: July 2012

The single‐channel current recording technique has been used to investigate the effects of cromakalim, diazoxide and ATP, separately and combined, on the opening of ATP‐sensitive potassium channels in the insulin‐secreting cell‐line RINm5F. The actions of these drugs have been studied using the permeabilized open‐cell variation of the patch‐clamp technique.

In the absence of internal ATP, cromakalim (80–200 μm) was unable to open ATP‐sensitive K+ channels but when ATP was present both cromakalim and diazoxide caused channel openings.

Interactions between ATP and cromakalim seemed competitive. Concentrations of cromakalim in the range 80–200 μm readily activated channels inhibited by 0.1 mm ATP, but had no effects when the concentration of ATP was increased to 0.5–2 mm. Only when the concentration of cromakalim was increased to 400–800 μm could opening of 0.5–2 mm ATP‐inhibited channels be regularly observed. In the continued presence of cromakalim (400–800 μm), an increase in the internal concentration of ATP from either 0.25 to 0.5 mm or 1 to 2 mm, inhibited cromakalim‐activated K+ channels.

Activation of ATP‐inhibited K+ channels was abolished by replacing ATP with ATPγS and cromakalim had no effects on ATPγS‐inhibited channels. This suggests that cromakalim may open KATP channels in insulin‐secreting cells by a mechanism which involves protein phosphorylation.
K+‐stimulation of the phosphoinositide pathway in guinea‐pig ileum longitudinal smooth muscle is predominantly neuronal in origin and mediated by the entry of extracellular Ca2+
Authors: Watson Stephen P. , Lai Jeremy , Sasaguri Toshiyuki
Published: July 2012

K+ and scorpion toxin stimulate formation of inositol phosphates in guinea‐pig ileum longitudinal smooth muscle slices. The response to these two agents is not additive.

The response to K+ is inhibited partially by nifedipine and partially by ω‐conotoxin. When given together the effect of these two Ca2+ channel blockers is additive and the response to K+ is reduced by more than 80%.

The response to scorpion toxin is inhibited completely by tetrodotoxin, partially by ω‐conotoxin but not by atropine or nifedipine. Scorpion toxin induces a similar formation of inositol phosphates in collagenase‐dispersed cells to that seen in cross‐chopped slices.

The responses to scorpion toxin and K+ are inhibited completely when the extracellular Ca2+ concentration is reduced to below cytosolic levels (< 100 nm).

Neither nifedipine nor ω‐conotoxin, either alone or in combination, inhibited formation of inositol phosphates by substance P or carbachol. Both of these agonists induced a significant formation of inositol phosphates even when the extracellular Ca2+ concentration was reduced to 10 nm.

These results indicate that K+ and scorpion toxin induce formation of inositol phosphates through the mobilisation of extracellular Ca2+. The response to K+ appears to occur predominantly in neuronal cells.
Endothelin‐1 inhibits platelet aggregation in vivo: a study with 111indium‐labelled platelets
Authors: Thiemermann Christoph , May Gillian R. , Page Clive P. , Vane John R.
Published: July 2012

A non‐invasive technique for the scintigraphic determination of 111indium‐labelled platelet aggregation stimulated with submaximal doses of adenosine diphosphate (ADP, 56 μg kg−1 i.v.), collagen (100 μg kg−1 i.v.), platelet‐activating factor (PAF, 0.1 μg kg−1 i.v.) or thrombin (18 iu kg−1 i.v.) was used to investigate the platelet‐inhibitory effects of endothelin 1 (ET‐1) in anaesthetized rabbits in vivo.

ET‐1 (1 nmol kg−1 i.v.) inhibited ADP‐stimulated platelet aggregation in vivo; a maximum inhibition of 78% of the control value was reached at 3 min, with 45% inhibition at 15 min, and a return to control values at 30 min after injection of the peptide.

ET‐1 (1 nmol kg−1 i.v.) inhibited in vivo platelet aggregation in response to collagen or PAF by 86% and 52%, respectively, but had no effect on thrombin‐induced platelet aggregation.

Indomethacin (5 mg kg−1 i.v.) abolished the ET‐1‐induced inhibition of ADP‐stimulated platelet aggregation and significantly potentiated and prolonged the pressor response brought about by ET‐1.

In conclusion, the data demonstrate that ET‐1 potently inhibits platelet aggregation in the anaesthetized rabbit in vivo by releasing a hypotensive and anti‐aggregatory cyclo‐oxygenase product, presumably prostacyclin, into the circulation.
Enhancement by neuropeptide Y (NPY) of the dihydropyridine‐sensitive component of the response to α1‐adrenoceptor stimulation in rat isolated mesenteric arterioles
Authors: Andriantsitohaina Ramaroson , Stoclet Jean Claude
Published: July 2012

The mechanism by which neuropeptide Y (NPY) potentiates the vasoconstriction induced by α1‐adrenoceptor agonists was investigated in 3rd generation mesenteric arterioles of the rat.

At a maximally active concentration, nitrendipine (10−6 m) displaced to the right the concentration‐response curves to noradrenaline (pD2 decreased from 6.2 ± 0.06 to 5.7 ± 0.03) and phenylephrine (pD2 decreased from 5.6 ± 0.03 to 5.3 ± 0.03). Diltiazem (10−5 m) also shifted to the right the concentration‐response curve to phenylephrine (pD2 decreased from 6.0 ± 0.06 to 5.5 ± 0.04). In addition, the maximal response to phenylephrine was significantly decreased in the presence of either nitrendipine or diltiazem.

In the absence of a calcium channel blocking agent, NPY (100 nm) produced a leftward shift of the concentration‐response curves to noradrenaline (pD2 increased from 6.2 ± 0.06 to 6.5 ± 0.05) and phenylephrine (pD2 increased from 5.6 ± 0.03 to 6.0 ± 0.06 and from 6.0 ± 0.06 to 6.3 ± 0.11). In the presence of either nitrendipine (10−6 m) or diltiazem (10−5 m), NPY (100 nm) did not alter the concentration‐response curves to either noradrenaline or phenylephrine.

NPY was added to arterioles brought to the same level of tension (40% of the maximal contraction) either by phenylephrine alone (1.5 × 10−6 m) or by a higher concentration of phenylephrine (3 × 10−6 m) followed by the addition of prazosin (1.3 × 10−9 m; a concentration at which it partially blocks α1‐adrenoceptors). In these conditions, the response to phenylephrine was completely abolished by nitrendipine (10−6 m) or by diltiazem (10−5m). Furthermore, NPY (10−10 to 10−7 m) increased the arteriolar tension up to the maximal contractile capacity of the vessels with pD2 values of 8.6 ± 0.02 and 8.7 ± 0.01, in the absence and presence of prazosin, respectively.

Prazosin was replaced in the above protocol by other vasodilator agents acting through different mechanisms. Whether in the presence of 2 × 10−7m forskolin, 6 × 10−7m sodium nitroprusside (which stimulate adenylate cyclase or guanylate cyclase, respectively) or 2 × 10−7m diltiazem (a concentration at which calcium entry is partially blocked), NPY enhanced phenylephrine‐induced contraction to the maximum level with an identical potency (pD2 values of the peptide ranged from 8.3 to 8.7).

The results show that, in rat mesenteric arterioles, NPY potentiates only the calcium entry blocker‐sensitive component of contraction induced by stimulation of α1‐adrenoceptors. In addition, they provide evidence that the peptide counteracts with an equal potency the inhibitory effect of partial block of α1‐adrenoceptors and of relaxing agents acting through different mechanisms. It is suggested that NPY enhances calcium entry induced by stimulation of α1‐adrenoceptors in this tissue.
l‐NG‐nitro arginine (l‐NOARG), a novel, l‐arginine‐reversible inhibitor of endothelium‐dependent vasodilatation in vitro
Authors: Moore P.K. , Al‐Swayeh O.A. , Chong N.W.S. , Evans R.A. , Gibson A.
Published: July 2012

The effect of l‐NG‐nitro arginine (l‐NOARG) was compared with that of l‐NG‐monomethyl arginine (l‐NMMA) on vasodilatation of the isolated aorta of the rabbit and perfused mesentery of the rat in response to acetylcholine (ACh) and sodium nitroprusside (NP).

l‐NOARG (1.5–100 μm) and l‐NMMA (3–100 μm) produced concentration‐related contraction of the rabbit aorta precontracted with phenylephrine (700–900 nm). Similarly, l‐NOARG (10–200 μm) and l‐NMMA (30–100 μm) elevated perfusion pressure of the noradrenaline (NA, 0.6–2.5 mm)‐preconstricted rat mesentery preparation.

l‐NOARG (1.5–100 μm) and l‐NMMA (3–100 μm) caused concentration‐related inhibition of the vasodilator effect of ACh (0.01–1.0 μm) on the rabbit aorta without influencing responses to NP (0.03–0.5 μm). l‐NOARG methyl ester (30 μm) also inhibited ACh‐induced vasorelaxation with similar potency to NOARG. l‐arginine (30–150 μm) but not d‐arginine (100 μm) caused graded reversal of the inhibitory effect of both l‐NOARG (15 μm) and l‐NMMA (30 μm). Complete reversal of the effect of both inhibitors was achieved with 150 μm l‐arginine. l‐Alanine (50 μm), l‐arginosuccinic acid (5 μm), l‐citrulline (50 μm), l‐methionine (50 μm) and l‐ornithine (50 μm) failed to reverse the inhibitory effect of l‐NOARG (15 μm).

l‐NOARG (10–200 μm) and l‐NMMA (30–100 μm) inhibited the vasodilator effect of ACh (0.006–18.0 nmol) in the rat mesentery without affecting vasodilatation due to NP (1.1–11.1 nmol). l‐Arginine (100 μm) but not d‐arginine (100 μm) produced partial reversal of the effect of l‐NOARG (30 μm) and l‐NMMA (30 μm).

l‐ and d‐Nα‐butyloxycarbonyl NG‐nitro arginine (100 μm) produced modest (approximately 20%) inhibition of the effect of ACh on the rabbit aorta; this effect was not reversible with l‐arginine (100 μm). l‐Nα‐monocarbobenzoxy arginine (l‐NMCA, 50 μm), l‐Nα‐NG‐dicarbobenzoxy arginine (l‐NDCA, 5 μm) and l‐NG‐tosyl arginine (50 μm) were inactive.

These results identify l‐NOARG as a potent, l‐arginine reversible inhibitor of endothelium‐dependent vasodilatation. The available data suggests that l‐NOARG, like l‐NMMA, inhibits endothelial nitric oxide (NO) biosynthesis.
4‐DAMP analogues reveal heterogeneity of M1 muscarinic receptors
Authors: Micheletti R. , Giudici L. , Turconi M. , Donetti A.
Published: July 2012

The muscarinic receptors responsible for two effects elicited by McN‐A‐343, i.e. the relaxation of the rat duodenum and the inhibition of the twitch contraction of rabbit vas deferens, were investigated by use of derivatives of 4‐diphenyl acetoxy‐N‐methyl piperidine methobromide (4‐DAMP). Both receptors had been previously identified as M1 on the basis of the high affinity shown towards pirenzepine. Schild analysis of antagonism revealed that the affinities of 4‐DAMP and three of its analogues in the rat duodenum were significantly different from those estimated in rabbit vas deferens. These data indicate that distinct receptor subtypes mediate duodenal relaxation and vas deferens inhibition of twitch contraction and suggest that receptors classified as M1 by means of pirenzepine affinity constitute a heterogeneous population.
Pretreatment with rh‐GMCSF, but not rh‐IL3, enhances PAF‐induced eosinophil accumulation in guinea‐pig airways
Authors: Sanjar S. , Smith D. , Kings M.A. , Morley J.
Published: July 2012

Intraperitoneal injections of recombinant human granulocyte‐macrophage colony stimulating factor (rh‐GMCSF, 50 μg kg−1 daily) or interleukin‐3 (rh‐IL3, 50 μg kg−1 daily) for two days, induced an increase in the percentage of bone marrow and pulmonary airway eosinophils in the guinea‐pig. In addition, rh‐IL3‐treated animals exhibited an increase (21%) in blood neutrophils. Exposure of guinea‐pigs to an aerosol of platelet activating factor (PAF) gives rise to a selective pulmonary eosinophil accumulation, maximal at 48 h. The eosinophilic response to PAF was significantly enhanced in rh‐GMCSF‐treated guinea‐pigs but was suppressed in rh‐IL3‐treated animals.
Phenthonium, a quaternary derivative of (−)−hyoscyamine, enhances the spontaneous release of acetylcholine at rat motor nerve terminals
Authors: Fann Meei Liy , Souccar Caden , Lapa Antonio J.
Published: July 2012

A quaternary derivative of (−)−hyoscyamine, phenthonium (Phen) induced a concentration‐dependent increase in the rate of spontaneous quantal release of acetylcholine (ACh) at the mammalian neuromuscular junction, as shown by intracellular recordings of the miniature endplate potentials (m.e.p.ps) in rat diaphragm muscles.

The prejunctional effect of Phen (10–50 μm) was reversible, unrelated to temperature (22°‐35°C), unaltered by either changes in [Ca2+]o or by high [Mg2+]o, and was not induced by membrane depolarization.

Simultaneously, Phen reduced the amplitude of m.e.p.ps by a postjunctional action.

The muscarinic agonist oxotremorine did not prevent the increase in m.e.p.p. frequency induced by Phen. Cholinesterase inhibition with neostigmine potentiated the prejunctional effect induced by a low (20 μm) but not a high (50 μm) concentration of Phen.

The increase in m.e.p.p. frequency induced by Phen was not influenced by previous incubation with either atropine (0.01–10 μm) or (+)‐tubocurarine (0.05‐0.1 μm). Each antagonist however, intensified the postjunctional effect of Phen.

Phen (20 μm) did not influence the quantal contents of e.p.ps in cut‐muscle preparations or in the presence of high [Mg2+]o. A high concentration of Phen (50 μm) increased the rundown of e.p.p. trains evoked at 10–50 Hz.

The results indicate that the facilitatory prejunctional action of Phen cannot be explained by an antimuscarinic activity. A possible interaction of the antagonist with putative prejunctional nicotinic cholinoceptors however, was not excluded.
Neuropeptide Y neuromodulation of sympathetic co‐transmission in the guinea‐pig vas deferens
Authors: Ellis James L. , Burnstock Geoffrey
Published: July 2012

We examined the neuromodulatory effects of neuropeptide Y (NPY) on purinergic and adrenergic co‐transmission in the guinea‐pig vas deferens.

In superfused vas deferens preparations, NPY (0.3 μm) inhibited the stimulus‐evoked overflow of both ATP and [3H]‐noradrenaline ([3H]‐NA) at 2 Hz, but only the stimulus‐evoked release of [3H]‐NA at 20 Hz.

Postjunctionally, NPY greatly enhanced responses to α,β‐methylene ATP and to a lesser extent to exogenous NA.

Preparations stimulated in organ baths showed frequency‐dependent contractions to field stimulation. NPY abolished responses to field stimulation at low frequency and a small number of pulses. At high frequency (20 Hz), NPY abolished responses elicited by 10 pulses, inhibited responses by 50% at 20 pulses and had little effect on preparations stimulated for 240 pulses.

Our study suggests that NPY neuromodulates co‐transmission in the vas deferens by inhibiting the release of ATP and NA and that these effects predominate over the postjunctional enhancement by NPY. These results also show that the physiological effect of NPY will be determined both by the frequency at which the nerves are discharging and the duration of their firing.
Cardiovascular effects of central injection of acetylcholine in anaesthetized dogs: a role for vasopressin release
Authors: Rascol Olivier , Montastruc Jean‐Louis , Gauquelin Guillemette , Tran Marie‐Antoinette , Geelen Ghislaine , Gharib Claude , Montastruc Paul
Published: July 2012

The effect of an intracisternal injection of 20 μg kg−1 of acetylcholine was studied on systolic and diastolic blood pressures, heart rate, and plasma levels of noradrenaline, adrenaline, vasopressin, plasma renin activity and atrial natriuretic factor in chloralose‐anaesthetized dogs, 8 of which were normal and 7 with diabetes insipidus (deprived of vasopressin secretion by surgical lesion of the hypothalamoneurohypophysial system).

Acetylcholine significantly increased systolic and diastolic blood pressures in both groups of animals. However, the rise in blood pressure was significantly shorter lived in the dogs with diabetes insipidus.

Acetylcholine significantly increased plasma levels of noradrenaline but not adrenaline in control animals and in dogs with diabetes insipidus. Noradrenaline and adrenaline responses after acetylcholine were not different in the two groups of animals.

Acetylcholine induced a significant increase in vasopressin plasma levels only in control animals while in dogs with diabetes insipidus vasopressin remained at nearly undetectable levels.

Acetylcholine significantly increased atrial natiuretic factor plasma levels only in control dogs.

Although plasma renin activity increased in both groups of animals after the i.c. injection of acetylcholine, this change was not significant in any group.

These results suggest that, in the anaesthetized dog, the central injection of acetylcholine induces a rise in blood pressure through both an increase in sympathetic outflow and a release of vasopressin.
Effect of capsaicin‐sensitive sensory nerves on plasma glucose and catecholamine levels during 2‐deoxyglucose‐induced stress in conscious rats
Authors: Zhou Xin‐Fu , Livett Bruce G.
Published: July 2012

Sensory fibres innervate the adrenal medulla but their function is not known. In this paper we have studied the effect of capsaicin‐sensitive sensory fibres on the adrenal catecholamine (CA) response and blood glucose response to 2‐deoxyglucose (2‐DG)‐induced glucopenic stress in conscious rats.

2‐DG at 500 mg kg−1 (i.v.) induced a 2.5 fold increase in plasma glucose levels, a 3.5 fold increase in inferior vena caval (i.v.c.) plasma noradrenaline (NA) levels and a 7 fold increase in i.v.c. plasma adrenaline (Ad) levels over 60 min. The hyperglycaemia in response to 2‐DG was attenuated by pentolinium and by left splanchnicotomy plus right adrenalectomy. These procedures also caused a complete inhibition of the increase in plasma CA.

The hyperglycaemia in response to 2‐DG was attenuated by pretreatment of rats with capsaicin as neonates, suggesting that capsaicin‐sensitive sensory fibres are required for regulation of plasma glucose in response to glucopenic stress.

The increase in i.v.c. plasma CA levels in response to 2‐DG during the early phase of glucopenia (first 30 min) in the conscious rats pretreated with capsaicin was the same as in the rats pretreated with vehicle alone. During the later phase of glucopenia (after 45 min), the increase in plasma CA levels in rats pretreated with capsaicin was higher than in the rats pretreated with vehicle alone.

In vehicle‐pretreated rats and capsaicin‐pretreated rats the tissue NA and Ad levels in the adrenal medulla after 8 h of stress were depleted to the same extent. However, tissue CA levels in the capsaicin group recovered faster over 24 h than in the vehicle group.

These results indicate that capsaicin‐sensitive sensory fibres are not required to maintain adrenal CA secretion during glucopenic stress in the conscious rat but are required for maintenance of blood glucose levels.
Inhibition by ibudilast of leukotriene D4‐induced formation of inositol phosphates in guinea‐pig lung
Authors: Etoh Susumu , Ohashi Mitsuo , Baba Akemichi , Iwata Heitaroh
Published: July 2012

The effects of a novel anti‐asthmatic drug, 3‐isobutyryl‐2‐ isopropylpyrazolo [1,5‐a]pyridine (ibudilast, KC‐404) on leukotriene D4 (LTD4)‐induced formation of inositol phosphates were studied in slices of guinea‐pig lung and hippocampus.

In guinea‐pig lung, ibudilast inhibited LTD4 (0.01‐1 μm)‐induced formation of inositol monophosphate (IP1) in a concentration‐dependent manner (IC50 = 10 μm) without affecting LTD4 receptor binding.

Ibudilast (10 μm) inhibited histamine (0.1‐1 mm)‐induced formation of IP1 in guinea‐pig lung slices but not in hippocampal slices.

Inhibition of agonist‐induced formation of IP1 by ibudilast was non‐competitive.

Ibudilast had no effect on either GTP‐ or calcium‐stimulated phosphatidylinositol specific‐phospholipase C activity of lung membranes.

These results suggest that ibudilast has no direct effect on LTD4 receptors, GTP binding proteins (G proteins) or phospholipase C, but inhibits inositol phosphate formation, possibly by interfering with the coupling between receptors and G proteins.
Action of cromakalim on potassium membrane conductance in isolated heart myocytes of frog
Authors: Pilsudski Richard , Rougier Oger , Tourneur Yves
Published: July 2012

The effects of cromakalim on membrane currents were studied at 20°C in frog atrial and ventricular cells in patch clamp recording using the whole cell configuration.

When cromakalim (1 μm) was applied in the external medium, a time‐independent current was activated in a few minutes. Cromakalim induced a weak increase of inward membrane currents recorded during hyperpolarization and a large increase of outward membrane currents recorded during depolarization.

The current voltage relationship of the cromakalim‐induced current reversed near EK and rectified in the outward direction.

The cromakalim‐activated current was inhibited by external application of cesium (20 mm), barium (1.8 mm), tolbutamide (1 mm) and glibenclamide (1 μm).

The effects of cromakalim were insensitive to a cytosolic increase in adenosine 5′‐triphosphate (ATP, 3–5 mm). Cromakalim had no effects when applied in the cell.

Our results confirm that cromakalim activates an IK(ATP)‐like conductance and suggest that the effects of the drug are due to an action on the external side of the membrane and are independent of the ATP cell content.
The properties of the ATP‐induced depolarization and current in single cells isolated from the guinea‐pig urinary bladder
Authors: Inoue R. , Brading A.F.
Published: July 2012

The actions of exogenously applied ATP were investigated with the whole‐cell patch clamp method in single cells isolated from guinea‐pig urinary bladder with a modified concentration jump technique.

Rapid application of ATP (threshold ca. 100 nm) depolarized the cell membrane with superimposition of action potentials which was followed by transient hyperpolarization. In the presence of D600, the amplitude of the ATP‐induced depolarization was a function of the ATP concentration (EC50:0.5‐1 μm).

ATP activated a dose‐dependent inward current with a short latency (18 ms with 10 μm ATP; measured as the time between the start of application and 10% of the peak). The relationship of the peak current versus ATP concentration was well fitted by a Michaelis‐Menten equation with a Hill coefficient (n) of 1.7 and a dissociation constant (Kd) of 2.3 μm. The current desensitized rapidly and the time course of desensitization was a function of the ATP concentration and could be fitted by two exponentials.

The reversal potential of the ATP‐activated current was near 0 mV. Replacement of extracellular Na by other monovalent or divalent cations indicated that the current flows through nonselective cation channels.

α,β‐Methylene ATP also produced a dose‐dependent inward current but was less potent than ATP (n: 1.6, Kd: 10.4 μm). α,β‐Methylene ATP blocked the response to ATP by desensitization of the receptor.

α,β‐Methylene ATP was 50–100 times more potent than ATP at eliciting a contractile response of strips of detrusor smooth muscle.

The relevance of the above results to the possible role of ATP as the fast excitatory transmitter is discussed.
Phosphinic acid analogues of GABA are antagonists at the GABAB receptor in the rat anococcygeus
Authors: Hills Judith M. , Sellers Andrew J. , Mistry Jayshree , Broekman Marianne , Howson William
Published: July 2012

CGP 35348 (3‐aminopropyl(diethoxymethyl)phosphinic acid) and 3‐aminopropyl(n‐hexyl)phosphinic acid (3‐APHPA) were tested in the rat anococcygeus muscle against CGP 27492 (3‐aminopropylphosphinic acid), a selective GABAB agonist, for their antagonist activity. Their antagonist potency was compared with that of 2‐hydroxysaclofen. The pA2 values for CGP 35348, 3‐APHPA and 2‐hydroxysaclofen were 5.38, 4.86, 4.45 respectively in the rat anococcygeus muscle. These results confirm the previous reports of GABAB antagonist activity for these compounds and show a marginal improvement in potency over 2‐hydroxysaclofen.
Influence of angiotensin II on the α‐adrenoceptors involved in mediating the response to sympathetic nerve stimulation in the rabbit isolated distal saphenous artery
Authors: Dunn W.R. , McGrath J.C. , Wilson V.G.
Published: July 2012

Under normal experimental conditions, sympathetic nerve‐mediated responses to electrical field stimulation in the isolated distal saphenous artery of the rabbit are sensitive to prazosin (0.1 μm) and so, by definition, are mediated by α1‐adrenoceptors. In the presence of angiotensin II (A II, 0.05 μm) however, a component of the response to nerve stimulation became resistant to prazosin. This ‘uncovered’ response was virtually abolished by the selective α2‐adrenoceptor antagonist rauwolscine (1 μm), a concentration that in the absence of A II had enhanced nerve‐mediated responses. Exposure to A II therefore, allows the clear demonstration of a role for postjunctional α2‐adrenoceptors in mediating the contractile response to sympathetic nerve stimulation in this arterial preparation.
Bicuculline blocks nicotinic acetylcholine response in isolated intermediate lobe cells of the pig
Authors: Zhang Zhong‐Wei , Feltz Paul
Published: July 2012

The effect of bicuculline on nicotinic acetylcholine (ACh) responses in isolated intermediate lobe (IL) cells of the pig was investigated by use of patch‐clamp techniques. Bicuculline was found to reduce AChevoked whole‐cell currents (IACh) in all cells tested (n = 40).

The blocking effect of bicuculline on IACh was dose‐dependent, the concentration producing half‐maximal blockade being 43.8 μm.

The blockade of IACh by bicuculline was not voltage‐dependent at membrane potentials above −60 mV, but a slight voltage‐dependence was observed at holding potentials (HP) of −80 and −100 mV.

The inhibitory effect of bicuculline on IACh was partially competitive at a HP of −60 mV.

Neither SR 95531, a pyridazinyl γ‐aminobutyric acid derivative, nor t‐butylbicyclophosphorothionate (TBPS) blocked IACh in IL cells.

It is concluded that bicuculline interacts directly with the ACh receptor‐ionophore complex on porcine IL cells.
Identification of N‐iminoethyl‐l‐ornithine as an irreversible inhibitor of nitric oxide synthase in phagocytic cells
Authors: McCall T.B. , Feelisch M. , Palmer R.M.J. , Moncada S.
Published: July 2012

The synthesis of nitric oxide (NO) from l‐arginine by rat peritoneal neutrophils (PMN) and the murine macrophage cell‐line J774 and the inhibition of this synthesis by N‐iminoethyl‐l‐ornithine (l‐NIO), NG‐monomethyl‐l‐arginine (l‐NMMA), NG‐nitro‐l‐arginine (l‐NNA) and its methyl ester (l‐NAME) were investigated.

l‐NIO was the most potent inhibitor in both types of cells while l‐NMMA was less active. l‐NNA and l‐NAME had no significant effect in PMN and l‐NNA produced only approximately 40% inhibition of the generation of NO in the J774 cells at the highest concentration tested (300 μm).

The inhibitory effect of l‐NIO was rapid in onset, requiring 10 min pre‐incubation to achieve its full inhibitory activity, while the other compounds required 20–60 min pre‐incubation to achieve their full effect.

The inhibitory effect of l‐NIO (10 μm) on intact cells could not be reversed by l‐arginine (300 μm) but could be prevented by concomitant incubation with this compound (300 μm), while the effect of the other inhibitors could be reversed by a 3–5 fold molar excess of l‐arginine.

The NO synthase from both PMN and J774 cells was cytosolic and NADPH‐ but not Ca2+‐dependent, with Km values for l‐arginine of 3.3 ± 0.8 and 4.2 ± 1.1 μm respectively.

l‐NIO was the most potent inhibitor of the neutrophil and J774 enzymes with IC50 values of 0.8 ± 0.1 and 3 ± 0.5 μm respectively. Furthermore, the effect of l‐NIO was irreversible. The other three compounds were less potent, reversible inhibitors.

The inhibitory effects of all these compounds were enantiomerically specific.

These data indicate that l‐NIO is a novel, potent, rapid in onset and irreversible inhibitor of NO synthase in phagocytic cells. The rapid uptake of l‐NIO compared with the other compounds indicates that phagocytic cells have different uptake mechanisms for l‐arginine analogues.
Selectivity profile of the novel muscarinic antagonist UH‐AH 37 determined by the use of cloned receptors and isolated tissue preparations
Authors: Wess J. , Lambrecht G. , Mutschler E. , Brann M.R. , Dörje F.
Published: July 2012

Functional in vitro experiments were carried out to determine the antimuscarinic potencies of the pirenzepine derivative UH‐AH 37 (6‐chloro‐5,10‐dihydro‐5‐[(1‐methyl‐4‐piperidinyl)acetyl]‐11H‐dibenzo‐[b,e] [1,4] diazepine‐11‐one hydrochloride) at M1 muscarinic receptors of rabbit vas deferens, M2 receptors of rat left atria and M3 receptors of rat ileum. Furthermore, N‐[3H]‐methylscopolamine competition binding experiments were performed to obtain its affinities for the five cloned human muscarinic receptors (m1‐m5) stably expressed in CHO‐K1 cells. Pirenzepine served as a reference drug throughout all experiments.

In all preparations used, UH‐AH 37 interacted with muscarinic receptors in a fashion characteristic of a simple competitive antagonist.

In the functional studies, UH‐AH 37, like pirenzepine, showed high affinity for M1 (pA2 8.49) and low affinity for M2 muscarinic receptors (pA2 6.63). In contrast to pirenzepine, UH‐AH 37 also displayed high affinity for M3 receptors (pA2 8.04).

In agreement with its functional profile, UH‐AH 37 bound with highest affinity to m1 (pKi 8.74) and with lowest affinity to m2 receptors (pKi 7.35). Moreover, it showed a 7 fold higher affinity for m3 (pKi 8.19) than for m2 receptors, whereas pirenzepine bound to both receptors with low affinities.

The binding affinity of UH‐AH 37 for m4 and m5 receptors (pKi 8.32 for both receptors) was only ca. 2.5 fold lower than that for m1 receptors, while the corresponding affinity differences were 6 and 13 fold in case of pirenzepine.

In conclusion, the receptor selectivity profile of UH‐AH 37 differs clearly from that of its parent compound, pirenzepine, in both functional and radioligand binding studies, the major characteristics being its pronounced M2 (m2)/M3 (m3) selectivity. UH‐AH 37 thus represents a useful tool for the further pharmacological characterization of muscarinic receptor subtypes.
Ageing is associated with increased 5‐HT2‐receptor affinity and decreased receptor reserve in rat isolated coronary arteries
Authors: Nyborg Niels C. Berg
Published: July 2012

The 5‐hydroxytryptamine (5‐HT)‐receptor subtype and affinity for 5‐HT was determined in large and small coronary arteries isolated as ring segments from the proximal and distal part of the left coronary artery of 3 month (young) and 2‐year old (old) rats.

Ketanserin induced a rightward shift of the 5‐HT concentration‐response curve in both proximal and distal coronary arteries from young rats. The slopes of the Schild‐plots were indistinguishable from unity and the estimated pA2 values were 9.11 and 9.27 for proximal and distal coronary arteries, respectively. These data indicate a homogeneous population of 5‐HT2‐like receptors in the coronary arteries.

The contractile effect of 5‐HT as well as the sensitivity to 5‐HT was greater in proximal and distal coronary arteries from old than from young rats.

The apparent 5‐HT2‐receptor affinity, −log(KA[m]), and fractional receptor‐occupancy for relative responses between 10% and 90% of maximum was determined by partial irreversible inhibition of the 5‐HT2‐receptors with phenoxybenzamine.

Ageing was associated with an increase in 5‐HT2‐receptor affinity for 5‐HT in both proximal and distal coronary arteries, whereas the fractional receptor occupancy for half‐maximal response to 5‐HT decreased with age.

5‐HT2‐receptor affinity for 5‐HT could account for the 5‐HT sensitivity of distal coronary arteries in both young and old rats but not in proximal coronary arteries as the slope of the regression line of plots of 5‐HT2‐receptor affinity vs. sensitivity was indistinguishable from unity in only the distal vessels.

The 5‐HT2‐receptor affinity for 5‐HT was linearly correlated to the fractional receptor occupancy for half maximal response, suggesting that the 5‐HT2‐receptor reserve or density down‐regulates the receptor affinity for 5‐HT.

The results indicate that the increase in 5‐HT sensitivity and contractile effect in rat coronary arteries rely upon an increase in both 5‐HT2‐receptor agonist affinity and efficiency of the excitation‐contraction coupling process in the vascular smooth muscle.
Interaction of 1‐methyl‐4‐phenylpyridinium ion and tyramine with a site putatively involved in the striatal vesicular release of dopamine
Authors: Vaccari A. , Del Zompo M. , Melis F. , Gessa G.L. , Rossetti Z.L.
Published: July 2012

The neurotoxin MPP+ potently inhibited the striatal binding of [3H]‐tyramine, a putative marker for the vesicular transporter of dopamine, and provoked a massive in vivo release of striatal dopamine. Tetrabenazine, an established ligand for the vesicular catecholamine carrier, potently inhibited [3H]‐tyramine binding, tyramine‐provoked striatal efflux of dopamine and the fast component of MPP+‐induced dopamine release. It is concluded that MPP+ in the striatum, besides interacting with additional intracellular targets, avidly binds at a vesicular site functionally involved with the outward transport of dopamine.
BAY u3405, a potent and selective thromboxane A2 receptor antagonist on airway smooth muscle in vitro
Authors: McKenniff M.G. , Norman P. , Cuthbert N.J. , Gardiner P.J.
Published: July 2012

BAY u3405 (3(R)‐[[(4‐fluorophenyl) sulphonyl]amino]‐1,2,3,4‐tetrahydro‐9H‐carbazole‐9‐propanoic acid) has been evaluated on airway smooth muscle, from a number of species including man, for its thromboxane A2 (TXA2) antagonist activity.

BAY u3405 was a potent, and competitive, antagonist of the TXA2‐mimetic U46619‐induced contractions of human, guinea‐pig, rat and ferret airway smooth muscle with pA2 values between 8.0 and 8.9 and with no inherent contractile activity (10−9–10−4 m).

The TXA2 antagonist activity of BAY u3405 was stereoselective. Its (S)‐enantiomer, BAY u3406, was approximately 50 fold less effective against U46619 on guinea‐pig and human airway smooth muscle.

BAY u3405 also competitively antagonized contractions of guinea‐pig airway smooth muscle induced by prostaglandin D2 (PGD2) or its metabolite 9α, 11β‐PGF2. On human and ferret airway smooth muscle it abolished contractions induced by PGD2, PGF2α and 16, 16‐dimethyl‐PGE2.

A high concentration (10−6 m) of BAY u3405 had no effect on the contraction, or relaxation, of airway smooth muscle induced by a range of other agonists, nor did BAY u3405 have any effect on other prostanoid receptor types (DP, EP1, EP2, FP or IP).

BAY u3405, in contrast to some other TXA2 antagonists, is a potent and selective antagonist on a wide range of airways including human. This high affinity, and the oral activity of the compound described elsewhere, suggest it may be an appropriate tool to investigate the role of prostanoids in airway diseases such as asthma.
The change in the threshold for short‐term desensitization in isolated smooth muscle cells showing an all‐or‐none response to acetylcholine
Authors: Mita Mitsuo , Uchida Masaatsu K.
Published: July 2012

Isolated smooth muscle cells from guinea‐pig taenia caecum were prepared by collagenase digestion. The cells showed an all‐or‐none response to acetylcholine (ACh) under our experimental conditions.

Desensitized cells showed an all‐or‐none response but required a higher concentration of ACh for induction of contraction, indicating that the desensitization was due to a change in the threshold concentration.

In [3H]‐quinuclidinyl benzilate ([3H]‐QNB) binding to the desensitized cells, KD and Bmax were not significantly different from those estimated in the control cells. The competitive inhibition curve for specific binding of [3H]‐QNB by ACh in the desensitized cells was in agreement with that of control cells.

The ACh‐stimulated increase of the 45Ca2+ influx was very rapid and correlated well with the contraction of the cells. The concentrations of ACh inducing the maximal 45Ca2+ influx were increased by desensitization.

These results indicated that although the binding of ACh to the receptor was not changed by desensitization, the threshold concentration of ACh for their contraction was raised by desensitization, and the 45Ca2+ influx accompanying the contraction was shifted to the side of high concentration of ACh.

These results suggest that the development of short‐term desensitization is due to an uncoupling of the receptor from the mechanism for initiation of the contraction.
Response of rabbit ear artery to endothelin‐1 during cooling
Authors: Monge L. , García‐Villalón A.L. , Montoya J.J. , García J.L. , Gómez B. , Diéguez G.
Published: July 2012

The effects of cooling on the response of rabbit central ear artery to endothelin‐1 and the role of the endothelium in these effects were studied in 2 mm long cylindrical arterial segments.

Concentration‐response curves for endothelin‐1 (10−10–3 × 10−7 m) were recorded isometrically in arteries with and without endothelium at 37°C and during cooling (24°C). To analyze further the endothelial mechanisms of the response to endothelin‐1 during cooling, the effects of this peptide in the presence of NG‐nitro‐l‐arginine methyl ester (l‐NAME) (10−4 m) or meclofenamate (10−5 m) were also determined.

In every condition tested, endothelin‐1 produced a marked, concentration‐dependent arterial contraction. Sensitivity of intact arteries to this peptide was consistently lower at 24°C than at 37°C. At 37°C there were comparable responses of arteries with and without endothelium, but at 24°C arteries without endothelium showed a higher sensitivity than intact arteries to endothelin‐1.

l‐NAME (10−4 m) increased the maximal contraction at 37°C, and both the sensitivity and maximal contraction at 24°C of intact arteries to endothelin‐1. Meclofenamate (10−5 m) did not affect the arterial response to endothelin‐1.

Sensitivity of arteries with and without endothelium to nitroprusside (10−9–10−3 m) was significantly decreased during cooling, and endothelium removal did not affect the relaxation to this nitrovasodilator.

These results suggest that cooling decreases sensitivity of cutaneous arteries (ear artery) to endothelin‐1 probably by increasing the availability of endothelial nitric oxide.