bluuebunny/crossref_metadata_2025 huggingface dataset:
Neuroanatomical sites of action of 5‐HT3 receptor agonist and antagonists for alteration of aversive behaviour in the mouse
Authors: Costall B. , Kelly M.E. , Naylor R.J. , Onaivi E.S. , Tyers M.B.
Published: July 2012

The cerebral topography of the action of diazepam and the action of the 5‐hydroxytryptamine 5‐HT3 receptor antagonists GR38032F and ICS 205–930 in attenuating an aversive response was studied in the mouse.

Mice which had been cannulated to allow drug injection into the dorsal and median raphe nuclei, the amygdala, nucleus accumbens or caudate‐putamen were placed in a two compartment black (dimly illuminated) and white (brightly illuminated) test box. Measurements were made of the time spent, rearing and line crossings in the two sections and the latency of initial movement from the white to the black area.

The injection of diazepam (0.1–10 ng), GR38032F (0.01–1.0 ng) and ICS 205–930 (1.0–10 ng) into the dorsal raphe nucleus and amygdala, and the injection of diazepam (0.1–10 ng) into the median raphe nucleus, reduced an aversive response to the brightly illuminated white area, delaying the initial movement into the black section and increasing the time spent, rearings and line crossings in the white area. Concomitantly such activities were decreased in the black section.

The injection of the 5‐HT3 agonist 2‐methyl‐5‐hydroxytryptamine (0.1–10 ng) into the dorsal raphe nucleus and amygdala caused the opposite response, decreasing the time taken to move into the black section and increasing the time spent, rearings and line crossings in the black section, decreasing such activities in the white area.

The 5‐HT3 agonist and antagonists showed little or no effect following injection into the median raphe nucleus and there were no changes in exploratory behaviour following their injection, or injection of diazepam, into the nucleus accumbens or caudate‐putamen.

It is concluded that in the mouse the cerebral topography of action of GR38032F and ICS 205–930 in attenuating an aversive response follows that of diazepam in the dorsal raphe nucleus and amygdala but that diazepam may have additional effects mediated via the median raphe nucleus.
The effect of propranolol on the hyperaemic response of the hepatic artery to portal venous occlusion in the dog
Authors: Alexander B. , Blumgart L.H. , Mathie R.T.
Published: July 2012

It has been reported that activation of β‐adrenoceptors may be responsible for the hyperaemic response of the hepatic artery to portal venous blood flow reduction.

The effect of β‐adrenoceptor blockade on the hepatic arterial response to portal vein occlusion was investigated in 6 anaesthetized dogs. A side‐to‐side portacaval shunt was established to prevent loss of venous return and arterial blood pressure during periods of portal occlusion. Measurements of hepatic arterial and portal venous blood flows were made by use of electromagnetic flow probes.

Intravenous propranolol injection, at a dose sufficient to block the vasodilator effect of low doses of exogenous adrenaline, did not alter the magnitude of the hyperaemic response of the hepatic artery. Propranolol also produced no change in baseline portal venous pressure.

It is concluded that hepatic β‐adrenoceptors are unlikely to be involved in the arterial response to portal occlusion. The absence of any reduction in basal portal venous pressure by propranolol is of interest in view of the current application of the drug in the treatment of patients with portal hypertension.
A specific inhibitor of nitric oxide formation from l‐arginine attenuates endothelium‐dependent relaxation
Authors: Rees Daryl D. , Palmer Richard M.J. , Hodson Harold F. , Moncada Salvador
Published: July 2012

The role of l‐arginine in the basal and stimulated generation of nitric oxide (NO) for endothelium‐dependent relaxation was studied by use of NG‐monomethyl l‐arginine (l‐NMMA), a specific inhibitor of this pathway.

l‐Arginine (10–100 μm), but not d‐arginine (100 μm), induced small but significant endothelium‐dependent relaxations of rings of rabbit aorta. In contrast, l‐NMMA (1–300 μm) produced small, endothelium‐dependent contractions, while its enantiomer NG‐monomethyl‐d‐arginine (d‐NMMA; 100 μ) had no effect.

l‐NMMA (1–300 μm) inhibited endothelium‐dependent relaxations induced by acetylcholine (ACh), the calcium ionophore A23187, substance P or l‐arginine without affecting the endothelium‐independent relaxations induced by glyceryl trinitrate or sodium nitroprusside.

The inhibition of endothelium‐dependent relaxation by l‐NMMA (30 μm) was reversed by l‐arginine (3–300 μm) but not by d‐arginine (300 μm) or a number of close analogues (100 μm).

The release of NO induced by ACh from perfused segments of rabbit aorta was also inhibited by l‐NMMA (3–300 μm), but not by d‐NMMA (100 μm) and this effect of l‐NMMA was reversed by l‐arginine (3–300 μm).

These results support the proposal that l‐arginine is the physiological precursor for the basal and stimulated generation of NO for endothelium‐dependent relaxation.
Adenosine enhancement of adrenergic neuroeffector transmission in guinea‐pig pulmonary artery
Authors: Wiklund N. Peter , Cederqvist Bo , Gustafsson Lars E.
Published: July 2012

Adenosine and its derivatives N6‐[(R)−1‐methyl‐2‐phenylethyl]adenosine (R‐PIA) or 5′‐N‐ethylcarboxamideadenosine (NECA) enhanced nerve‐induced contractile responses and augmented the basal smooth muscle tone in transmurally stimulated isolated strips of the guinea‐pig pulmonary artery.

Adenosine, R‐PIA and NECA enhanced contractile responses induced by noradrenaline, whereas N6‐[(S)−1‐methyl‐2‐phenylethyl]‐adenosine (S‐PIA) was virtually inactive.

Adenosine, R‐PIA and NECA inhibited the nerve stimulation evoked release of [3H]‐noradrenaline. However, the total release of [3H]‐noradrenaline during the periods of NECA application was increased.

The nucleoside effects were blocked by the adenosine receptor antagonist 8‐p‐sulphophenyltheophylline.

8‐p‐Sulphophenyltheophylline inhibited nerve‐induced contractions and lowered basal muscle tone in preparations not having received any exogenous purines.

It is suggested that the observed stimulatory effects on muscle tone and on contractile responses to transmural nerve stimulation are mainly due to action at postjunctional stimulatory A1 adenosine receptors. In addition, actions at prejunctional inhibitory A1 and stimulatory A2 adenosine receptors are evident in this preparation.
Time course and extent of α1‐adrenoceptor density changes in rat heart after β‐adrenoceptor blockade
Authors: Steinkraus Volker , Nose Monika , Scholz Hasso , Thormählen Katrin
Published: July 2012

It has been suggested that impaired β‐adrenoceptor stimulation is a condition under which the functional role of cardiac α1‐adrenoceptors is enhanced. We therefore investigated the extent and time course of changes in α1‐adrenoceptor characteristics after chronic treatment with the β‐adrenoceptor blocker propranolol in rat heart. For comparison β‐adrenoceptors were also studied. The mechanism of the changes in adrenoceptor density was investigated with cycloheximide, an inhibitor of protein synthesis. The functional significance of an increased α1‐adrenoceptor density was tested by measuring isometric force of contraction in the presence of phenylephrine or isoprenaline in right ventricular papillary muscles.

Rats were treated with propranolol (9.9 mg kg−1 daily) or 0.9% NaCl, applied with osmotic minipumps for 1, 2, 3 or 7 days. Propranolol treatment resulted in a maximally 28% increase of α1‐adrenoceptor density after 3 days (NaCl 95.9 ± 3.5 vs. propranolol 123.0 ± 1.6 fmol mg−1 protein, n = 6, P < 0.01). This up regulation reached significant levels after 2 days of treatment and was reversible after cessation of treatment within two days. KD‐values were the same for NaCl‐ and propranolol‐treated rats. Changes of Bmax and KD in β‐adrenoceptor binding assays did not reach significant levels.

Cycloheximide (1.5 mg kg−1 i.p. daily for 3 days) inhibited the propranolol‐induced increase in Bmax of α1‐adrenoceptors completely. In addition, cycloheximide also decreased the density of α1‐ and β‐adrenoceptors also under control conditions.

pD2‐values for the positive inotropic effect of phenylephrine and isoprenaline in isolated electrically driven papillary muscle were similar in NaCl‐ and propranolol‐treated rats (phenylephrine: 5.41 ± 0.11 vs. 5.41 ± 0.19, n = 7; isoprenaline: 6.31 ± 0.18 vs. 6.65 ± 0.19, n = 7). The observed increase in α1‐adrenoceptor density in healthy rat heart may therefore not be high enough to enhance the phenylephrine‐induced increase in force of contraction.

In conclusion, time course and effects of cycloheximide indicate that the increase in Bmax of myocardial α1‐adrenoceptors is due to de novo synthesis of receptors. However, at least for the rat heart model, a functional significance of this increase could not be demonstrated.
Ouabain distinguishes between nicotinic and muscarinic receptor‐mediated catecholamine secretions in perfused adrenal glands of cat
Authors: Yamada Yutaka , Nakazato Yoshikazu , Ohga Akira
Published: July 2012

The effect of ouabain on catecholamine (adrenaline and noradrenaline) secretion induced by agents acting on cholinoceptors was studied in perfused cat adrenal glands. Acetylcholine (ACh) (5 × 10−7 to 10−3m), pilocarpine (10−5 to 10−3m) and nicotine (10−6 to 5 × 10−5m) caused dose‐dependent increases in catecholamine secretion. Both ACh and nicotine released more noradrenaline than adrenaline and the reverse was the case for pilocarpine.

Ouabain (10−5m) enhanced catecholamine secretion induced by ACh (10−5m), pilocarpine (10−3m) and nicotine (3 × 10−6m) during perfusion with Locke solution. The ratio of adrenaline to noradrenaline was not affected by ouabain.

In the absence of extracellular Ca2+, ACh and pilocarpine, but not nicotine, still caused a small increase in catecholamine secretions, which were enhanced by treatment with ouabain (10−5m) plus Ca2+ (2.2 mm) for 25 min. The effect of ouabain was much more significant on noradrenaline secretion than on adrenaline secretion. The enhanced response was blocked by atropine (10−6m) but not by hexamethonium (5 × 10−4m).

Nifedipine (2 × 10−6m) inhibited the responses to pilocarpine and nicotine. The treatment with ouabain (10−5 m) reversed only the response to pilocarpine and resulted in a significant increase in the proportion of noradrenaline released.

It is suggested that ouabain enhances evoked catecholamine secretions by facilitating Ca2+ entry through nicotinic receptor‐linked Ca2+ channels and by increasing the intracellular Ca2+ pool linked to muscarinic receptors.
An A2‐purinoceptor agonist, NECA, potentiates acetylcholine‐induced glucagon secretion
Authors: Bertrand G. , Gross R. , Petit P. , Loubatières‐Mariani M.M.
Published: July 2012

The effect of a stable structural analogue of adenosine, 5′‐N‐ethylcarboxamidoadenosine (NECA), was studied on glucagon secretion induced by acetylcholine (ACh) in the isolated perfused pancreas of the newborn dog. The perfusion solution contained a physiological concentration of glucose (4.2 mm). In the first set of experiments, ACh (0.5 μm) infused alone for 10 min induced a significant rise of glucagon secretion (370 ± 98%, 4 min after the beginning of infusion). In the second set, NECA (2.2 nm) infused 10 min before ACh administration, had no effect per se, but considerably increased the response to ACh (929 ± 262% of basal value within 3 min). So, the more specific A2 purinoceptor agonist, NECA, potentiated glucagon secretion induced by the cholinoceptor agonist, ACh.
Effect of a new potent CCK antagonist, lorglumide, on caerulein‐ and bombesin‐induced pancreatic secretion and growth in the rat
Authors: Scarpignato Carmelo , Varga Gábor , Dobronyi István , Papp Miklós
Published: July 2012

The effect of lorglumide, a new potent cholecystokinin (CCK) antagonist, on pancreatic secretion and growth induced by caerulein and bombesin was studied in the rat.

Pancreatic exocrine secretion was studied both in vitro (isolated and perfused pancreatic segments) and in vivo (anaesthetized animals with cannulation of the common bile duct) whereas the trophic effect was investiged after short‐term (5 days) administration of the peptides and/or lorglumide.

Both caerulein and bombesin stimulated amylase release from in vitro pancreatic segments in a concentration‐dependent manner. Although the efficacy of both peptides was virtually identical, the potency of caerulein was higher than that of bombesin. Lorglumide displaced the concentration‐response curves to caerulein to the right without affecting the maximum response, suggesting a competitive antagonism. The Schild plot analysis of data gave a straight line with a slope not significantly different from unity. The calculated pA2 for lorglumide was 7.31 ± 0.45. The antagonist, however, was completely ineffective when tested against bombesin‐induced amylase release.

In vivo experiments confirmed results from in vitro studies since lorglumide (5 and 10 mg kg−1) significantly reduced pancreatic exocrine secretion induced by caerulein without affecting the response to bombesin.

Administration of either peptide increased the weight of the pancreas, the total pancreatic protein and DNA, trypsin and amylase content. Lorglumide (10 mg kg−1), administered together with caerulein, reduced the peptide‐induced increase in pancreatic weight, protein and enzyme content. On the contrary, when lorglumide was given together with bombesin, all the parameters that were examined were not altered by concomitant administration of the antagonist.

These results have demonstrated the ability of lorglumide to antagonize the effects on the pancreas of a CCK‐analogue, caerulein, and its inability to affect bombesin‐induced pancreatic secretion and growth, suggesting that lorglumide is a potent and selective antagonist of CCK‐receptors in the pancreas.
Electrophysiological and antiarrhythmic effects of UK 52,046–27 during ischaemia and reperfusion in the guinea‐pig heart
Authors: Flores Nicholas A. , Sheridan Desmond J.
Published: July 2012

We studied the antiarrhythmic and electrophysiological effects of UK 52,046–27 (10−8 m and 5 × 10−8 m), a highly selective α1‐adrenoceptor antagonist, during global ischaemia (flow reduced to 10% of control for 30 min) and reperfusion, in isolated, buffer‐perfused hearts of guinea‐pigs.

The compound had few electrophysiological effects during normal perfusion, although action potential amplitude and were reduced with 10−8 m (by 9% and 22%) and refractory period was increased with 5 × 10−8 m (by 13%) compared to control hearts.

Perfusion with 5 × 10−8 m UK 52,046–27 reduced the incidence of ventricular tachycardia during ischaemia from 67% to 25%, and during reperfusion reduced the incidence of ventricular tachycardia (from 83% to 17%) and ventricular fibrillation (from 67% to 8%).

The compound prolonged significantly action potential duration and refractory period during ischaemia and reperfusion. was reduced to a greater extent during reperfusion in the treated hearts, while greater increases in QRS width and stimulation threshold occurred during ischaemia in the treated group.

These results confirm that blockade of the α1‐adrenoceptor subpopulation during myocardial ischaemia and reperfusion decreases the incidence of arrhythmias and alters cellular electrophysiology during ischaemia and reperfusion.
Capsaicin and nicotine‐sensitive afferent neurones and nasal secretion in healthy human volunteers and in patients with vasomotor rhinitis
Authors: Stjärne P. , Lundblad L. , Lundberg J.M. , Änggård A.
Published: July 2012

Applications of capsaicin, nicotine and methacholine were made locally onto the nasal mucosa in human controls and patients suffering from hyperreactive nasal disorders. Perception of sensation was registered as a sympton score and secretion quantified. The sensory reaction (irritation ‐pain) to capsaicin was similar in the three groups studied, i.e. controls, a group of patients with the diagnosis of vasomotor rhinitis and a group of patients with increased nasal secretion as the main symptom of the hyperreactive disorder. Nicotine induced only a mild itching sensation in the three groups. However, capsaicin and nicotine challenge caused a significantly larger secretory response in the last group than in the unselected vasomotor rhinitis group and in the control group.

Pretreatment with muscarinic receptor antagonists almost completely abolished the secretory response to both capsaicin and nicotine, and blocked methacholine‐induced secretion. Furthermore, pretreatment with a combination of local anaesthetic and vasoconstrictor agent abolished the capsaicin‐induced irritation, as well as the capsaicin‐ and nicotine‐induced secretion on both the ipsilateral and the contralateral side. Therefore, no clearcut contribution seems to be exerted by locally released peptides from sensory neurones as direct trigger substances for the secretory response to capsaicin.

In conclusion, the nasal secretory response, in man, to both capsaicin and nicotine, seems to be mediated via cholinergic parasympathetic reflexes. In patients with hyperreactive non‐allergic disorders of the nasal mucosa with rhinorrhea as the main complaint, the enhanced secretion may be due to a hyperreactive efferent cholinergic mechanism rather than hypersensitive irritant receptors on capsaicin‐ and nicotine‐sensitive sensory neurones. Challenge with irritant agents seems a useful test for the evaluation of both afferent and efferent reflexogenic responses in hyperreactive disorders of the nasal mucosa.
Effects of benzodiazepines and non‐benzodiazepine compounds on the GABA‐induced response in frog isolated sensory neurones
Authors: Yakushiji Takashi , Fukuda Takemi , Oyama Yasuo , Akaike Norio
Published: July 2012

The effects of benzodiazepines and non‐benzodiazepine compounds on the γ‐aminobutyric acid (GABA)‐induced chloride current (ICl) were studied in frog isolated sensory neurones by use of a concentration‐jump (termed ‘concentration‐clamp’) technique, under single‐electrode voltage‐clamp conditions. The drugs used were classified into four categories as follows: full benzodiazepine receptor agonists (diazepam, clonazepam, nitrazepam, midazolam, clotiazepam and etizolam), partial agonists (CL 218,872, Ro 16–6028, Ro 17–1812 and Ro 23–0364), inverse agonists (Ro 15–3505, FG 7142 and β‐CCE) and a benzodiazepine receptor antagonist, Ro 15–1788 (flumazenil).

All full agonists at concentrations of 3 × 10−6 m. or less increased dose‐dependently the peak amplitude of ICl elicited by 3 × 10−6 m. GABA to twice to three times larger than the control. However, no further augmentation of the GABA response was observed at concentrations of 1 × 10−5 m. or higher. Partial agonists also showed a dose‐dependent augmentation of the GABA response at concentrations ranging from 3 × 10−8 m. to 3 × 10−5 m., but their efficacies of augmentation of the GABA response were only about half or less of those of full agonists. Of the inverse agonists, β‐CCE had a unique dose‐dependent effect on the GABA response. β‐CCE reduced dose‐dependently the GABA response at concentrations of less than 3 × 10−6 m., but augmented it at concentrations of 3 × 10−5 m. and 6 × 10−5 m. The inverse agonists reduced dose‐dependently the GABA response. The benzodiazepine antagonist, flumazenil, slightly augmented the GABA response at concentrations between 3 × 10−7 m. and 3 × 10−5 m.

These results show clear differences in the effects on the GABA response between these four categories of compounds known to affect the benzodiazepine recognition site of the GABA/benzodiazepine receptor‐chloride channel complex. Our experimental system of frog isolated sensory neurones and a ‘concentration‐clamp’ technique appears to be useful for evaluating efficacy of compounds on responses mediated by the GABA/benzodiazepine receptor‐chloride channel complex.
5‐Hydroxytryptamine is a possible neurotransmitter of the non‐cholinergic excitatory nerves in the longitudinal muscle of rainbow trout stomach (Salmo gairdneri)
Authors: Kitazawa Takio
Published: July 2012

The neurotransmitter of the non‐cholinergic excitatory nerves in the rainbow trout stomach was identified on the basis of the pharmacological properties of the contractile responses to transmural stimulation (TMS) and nicotine.

TMS caused tetrodotoxin‐sensitive contractions of rainbow trout stomach strips in a frequency‐dependent manner (0.5–50 Hz). Atropine (1 μm) significantly decreased the contractile response to low‐frequency stimulation (0.5–2 Hz), but did not affect that to high‐frequency stimulation (3–20 Hz).

The atropine‐resistant contractile response to TMS (20 Hz) was unaffected by hexamethonium (100 μm), phentolamine (5.4 μm), pyrilamine (1 μm), naloxone (1 μm) or substance P‐induced desensitization.

5‐Hydroxytryptamine (5‐HT, 3 nm‐3 μm) caused atropine‐resistant contractions in a concentration‐dependent manner. In the presence of atropine, methysergide (1 μm) decreased the contractile responses to TMS and 5‐HT.

Nicotine (3 μm‐500 μm) induced atropine‐resistant contractions that were completely abolished by tetrodotoxin or hexamethonium. Also methysergide inhibited the contractile responses to nicotine.

An acid extract of rainbow trout stomach exhibited atropine‐resistant contractions that were decreased by methysergide, in both rainbow trout stomach and guinea‐pig ileum longitudinal smooth muscle preparations.

The present results indicate that, in longitudinal muscle strips of the rainbow trout stomach, 5‐HT is one of the mediators (neurotransmitters) of the non‐cholinergic excitatory contractions induced by TMS and nicotine.
GABA receptors on the somatic muscle cells of the parasitic nematode, Ascaris suum: stereoselectivity indicates similarity to a GABAA‐type agonist recognition site
Authors: Holden‐Dye Lindy , Krogsgaard‐Larsen Povl , Nielsen Lone , Walker Robert J.
Published: July 2012

The γ‐aminobutyric acid (GABA) receptors on the somatic muscle cells of Ascaris, which mediate muscle cell hyperpolarization and relaxation, have been characterized by use of intracellular recording techniques.

These receptors are like mammalian GABAA‐receptors in that the response is mediated by an increase conductance to chloride ions. The GABAA‐mimetic, muscimol, has a relative potency of 0.40 ± 0.02 (n = 3) compared to GABA.

The stereoselectivity of the GABA receptor on Ascaris is identical to that for the mammalian GABAA‐receptor, as determined from the relative potency of three pairs of enantiomers of structural analogues of GABA.

The most potent agonist is (S)‐(+)‐dihydromuscimol which is 7.53 ± 0.98 (n = 5) times more potent than GABA.

The Ascaris GABA receptor is not significantly blocked, at concentrations below 100 μm by the potent, competitive GABAA‐receptor antagonist, SR95531.

The Ascaris GABA receptor does not recognise agents that are known to block the GABA gated chloride channel in mammalian preparations such as t‐butylbicyclophosphorothionate (TBPS, 10 μm, n = 2) or the insecticide dieldrin (100 μm, n = 3).

GABAergic responses in Ascaris are not potentiated by pentobarbitone (100 μm, n = 3) or flurazepam (100 μm, n = 3).

The potencies of various GABA‐mimetics in the Ascaris preparation have been compared with their potency at displacing GABAA‐receptor binding in mammalian brain. Excluding the sulphonic acid derivatives of GABA, the correlation coefficient (r) between the potencies of compounds in the two systems is 0.74 (P < 0.01). The significance of this correlation is discussed.

The pharmacology of the Ascaris GABA receptor is discussed in relation to other invertebrate systems and the mammalian subclassification of GABA receptors.
In favour of the vesicular hypothesis: neurochemical evidence that vesamicol (AH5183) inhibits stimulation‐evoked release of acetylcholine from neuromuscular junction
Authors: Vizi E.S.
Published: July 2012

The effects of optical isomers of vesamicol (2‐(4‐phenylpiperidino) cyclohexanol), an inhibitor of acetylcholine (ACh) storage, on stimulation‐evoked release of [3H]‐acetylcholine ([3H]‐ACh) from the neuromuscular junction have been studied in the region of the mouse hemidiaphragm which contains the motor endplates, and which can easily be loaded with [3H]‐choline. This method made it possible to detect exclusively the Cao‐dependent release of [3H]‐ACh in response to stimulation, and therefore to test the vesicular hypothesis.

(−)−Vesamicol was approximately 20 times more potent than (+)‐vesamicol in reducing stimulation‐evoked release of [3H]‐ACh.

4‐Aminopyridine, a potassium channel blocker, enhanced the release of ACh in response to stimulation, but failed to increase release from hemidiaphragm which had been pretreated with (−)−vesamicol.

The fact that (−)−vesamicol inhibited the release of [3H]‐ACh in response to electrical stimulation only when it was administered prior to the loading of the tissue with [3H]‐choline, and had no effect when the stores had already been filled with labelled [3H]‐ACh indicates that the stimulation‐evoked release of [3H]‐ACh is of vesicular origin and (−)−vesamicol has no effect on the release process. This is the first neurochemical evidence for the vesicular origin of stimulation‐evoked release of ACh from the neuromuscular junction.
Effects of putative activators of K+ channels in mouse pancreatic β‐cells
Authors: Garrino M.G. , Plant T.D. , Henquin J.C.
Published: July 2012

The vasodilator and antihypertensive properties of pinacidil, cromakalim (BRL 34915), nicorandil and minoxidil sulphate may be due, at least in part, to their ability to open K+ channels in vascular smooth muscles. In this study, mouse pancreatic islets were used to determine whether these drugs affect insulin release by acting on K+ channels of β‐cells. Their effects were compared to those of diazoxide.

Diazoxide caused a dose‐dependent inhibition of insulin release by islets incubated with 15 mm glucose (93% at 100 μm). Pinacidil inhibited release by 36 and 72% at 100 and 500 μm, respectively. Cromakalim and nicorandil were less effective (35 and 25% inhibition at 500 μm). Minoxidil sulphate increased insulin release at 500 μm.

In the presence of 7 mm glucose and in the absence of Ca2+ (to avoid activation of Ca2+‐dependent K+ channels), 86Rb efflux from islet cells was increased by 100–500 μm pinacidil and 500 μm nicorandil, which were, however, less potent than diazoxide. Cromakalim was ineffective, whereas 500 μm minoxidil sulphate decreased the efflux rate. In the absence of glucose and presence of Ca2+, 500 μm cromakalim and minoxidil sulphate inhibited 86Rb efflux.

Like diazoxide, pinacidil (500 μm) abolished glucose‐induced electrical activity in β‐cells and hyperpolarized the membrane.

ATP‐sensitive K+ currents were studied in single β‐cells by the whole cell patch‐clamp technique. Pinacidil increased the current less than did diazoxide. In contrast, cromakalim and minoxidil sulphate decreased K+‐currents whilst nicorandil was without effect.

It is concluded that pinacidil, like diazoxide, inhibits insulin release from β‐cells by opening ATP‐sensitive K+ channels, whereas the smaller inhibitory effects of cromakalim and nicorandil may involve actions other than on K+ channels in these cells. Minoxidil sulphate potentiates glucose‐induced insulin release, probably by inhibiting ATP‐sensitive K+ channels. However, all these effects of the vasodilators are only seen at high concentrations and are thus unlikely to occur in vivo.
Myenteric 5‐HT‐containing neurones activate the descending cholinergic excitatory pathway to the circular muscle of guinea‐pig ileum
Authors: Jin Ji‐Guang , Neya Toshiaki , Nakayama Sosogu
Published: July 2012

Participation of myenteric 5‐hydroxytryptamine (5‐HT)‐containing neurones in the ascending and descending pathways of the guinea‐pig isolated ileum was investigated in a new preparation. Transmural electrical stimulation of the longitudinal muscle‐myenteric plexus (LM‐MP) portion of the preparation caused ascending and descending contractions of circular or longitudinal muscle in the attached, intact segments situated orally or anally to the point of stimulation

All contractions to LM‐MP stimulation were abolished by tetrodotoxin (0.2 μm). The ascending and descending contractions of circular muscles were also abolished by atropine and inhibited to about 50% by hexamethonium. They were not affected by desensitization to substance P (SP) or by the SP antagonist, (D‐Pro2,D‐Trp7,9)‐substance P. The contractions of longitudinal muscles were inhibited by about 45% by hexamethonium and abolished by a combination of atropine with SP desensitization or the SP antagonist, (D‐Pro2,D‐Trp7,9)‐substance P.

Desensitization to 5‐HT, ICS 205–930 (1 μm) or cocaine (1 μm) reduced the descending contraction of circular muscle by 80–90%, without significantly affecting the ascending contraction. Methysergide (0.2 μm) failed to alter either contraction.

5‐HT desensitization, ICS 205–930 and cocaine only partially reduced the descending contraction of longitudinal muscle. A similar reduction of the ascending contraction (20–30%) was also observed. Methysergide had no effects on either contraction.

Contractions of either circular or longitudinal muscle produced by field stimulation of the intact segment were not significantly affected by any of the 5‐HT receptor antagonists tested.

The results imply that 5‐HT‐containing neurones, as interneurones, are involved mainly in the descending cholinergic excitatory pathway to the circular muscles.
α2‐Adrenoceptor agonists enhance vasoconstrictor responses to α1‐adrenoceptor agonists in the rat tail artery by increasing the influx of Ca2+
Authors: Xiao X.‐H. , Rand M.J.
Published: July 2012

The α2‐adrenoceptor agonists TL99 (2‐(NN‐dimethyl)amino‐6,7‐dihydroxy‐1,2,3,4‐tetrahydronaphthalene) and UK14304 (5‐bromo‐6‐[2‐imidazoline‐2‐yl‐aminol]‐quinoxaline), in concentrations that are less than 1% of those producing vasoconstriction, enhance vasoconstrictor responses to noradrenaline and phenylephrine in isolated perfused preparations of the rat tail artery.

The enhancing effect was abolished when Ca2+ was absent and by the calcium channel blocking drug diltiazem.

α2‐Adrenoceptor agonists had no effect on the component of the responses to noradrenaline and phenylephrine that is attributable to mobilization of intracellular Ca2+, but enhanced the component attributable to influx of extracellular Ca2+.

These results suggest that the enhancing effect of α2‐adrenoceptor agonists on responses of the rat tail artery to α1‐adrenoceptor agonists involves an increase in Ca2+‐influx into smooth muscle cells through Ca2+ channels that are opened when α2‐adrenoceptors are activated.
l‐NG‐nitro arginine inhibits non‐adrenergic, non‐cholinergic relaxations of guinea‐pig isolated tracheal smooth muscle
Authors: Tucker John F. , Brave Sandra R. , Charalambous Litsa , Hobbs Adrian J. , Gibson Alan
Published: July 2012

The effects of l‐NG‐nitro arginine (l‐NOARG) on α‐chymotrypsin‐resistant, non‐adrenergic, non‐cholinergic (NANC) relaxations of guinea‐pig tracheal smooth muscle have been examined. l‐NOARG (1–100 μm), but not d‐NOARG (100 μm), inhibited the NANC relaxations in a concentration‐related manner. The effects of l‐NOARG were partially reversed by l‐arginine but not d‐arginine.l‐NOARG was without effect on acetylcholine‐induced contractile responses of the trachea or on relaxations produced by vasoactive intestinal peptide, sodium nitroprusside or isoprenaline. These results suggest that an endogenous nitrate may contribute to NANC relaxations of tracheal smooth muscle.
Mediation of 5‐hydroxytryptamine‐induced tachycardia in the pig by the putative 5‐HT4 receptor
Authors: Villalón Carlos M. , den Boer Marien O. , Heiligers Jan P.C. , Saxena Pramod R.
Published: July 2012

Intravenous bolus Injections of 5‐hydroxytryptamine (5‐HT; 3, 10 and 30 μg kg−1), 5‐methoxytryptamine (5‐MeO‐T; 3, 10 and 30 μg kg−1), renzapride (BRL 24924; 3, 10, 30 and 100μgkg−1) and isoprenaline (0.03, 0.1 and 0.3 μg kg−1) to anaesthetized pigs increased heart rate by, respectively, 22 ± 3, 44 ± 3 and 65 ± 4 beats min−1 (5‐HT; n = 17); 12 ± 1, 26 ± 2 and 44 ± 4 beats min−1 (5‐MeO‐T; n = 15), 5 ± 2, 11 ± 2, 18 ± 4 and 37 ± 5 beats min−1 (renzapride; n = 8) and 17 ± 2, 46 ± 3 and 75 ± 3 beats min−1 (isoprenaline; n = 13). The responses to 5‐HT, 5‐MeO‐T and renzapride were antagonized by ICS 205–930 (1 and 3 mg kg−1, i.v.), which did not modify the increases in heart rate by isoprenaline. Renzapride showed tachyphylaxis and attenuated the responses to 5‐HT. These findings indicate that 5‐HT elicits tachycardia in the pig by acting on a novel receptor, either similar or identical to the 5‐HT4 receptor identified in mouse brain colliculi.
Role of Na‐H exchange in the inotropic action of Bay K 8644 and of ouabain in guinea‐pig isolated atria
Authors: Ghysel‐Burton Josiane , Godfraind Théophile
Published: July 2012

The inotropic effects of two concentrations of ouabain and of Bay K 8644 have been studied in isolated left atria of the guinea‐pig in physiological solutions at pH lowered from 7.4 to 6.0 and in the presence of ethylisopropylamiloride (EIPA) an inhibitor of Na+/H+ exchange. The low concentration of ouabain (300 nm) was chosen to saturate the high affinity binding sites (it occupied about 7% of the low affinity sites). The high concentration of ouabain saturated both high and low binding sites. Bay K 8644 evoked a positive inotropic effect of a magnitude similar to ouabain (300 nm).

When comparing the positive inotropic effects of equi‐effective concentrations of ouabain (300 nm) and of Bay K 8644 (100 nm), it was observed that extracellular acidification specifically depressed the inotropic effect of ouabain 300nm; the positive inotropic effect of the high concentration of ouabain (3 μm) was barely affected by extracellular acidification.

EIPA 10 μm depressed the positive inotropic effect of ouabain 300 nm, but did not affect the peak response to Bay K 8644. The depressant action of EIPA on the positive inotropic effect of ouabain was concentration‐dependent and was much more obvious on the effect of ouabain 300 nm than on ouabain 3 μm.

An increase in diastolic tension was evoked by 3 μm but not by 300 nm ouabain. This increase in tone was reduced dose‐dependently by EIPA (10–30 μm). It was also significantly reduced when the extracellular pH was equal to 6.4 or 6.0.

Ouabain (300 nm) evoked a gain in tissue Na and an equivalent loss in tissue K. Acidification of the extracellular pH down to pH 6.0 evoked a pH‐dependent reduction of Na gain but left K loss unaltered. EIPA 10, 20 and 30 μm evoked a significant reduction of Na gain without significantly affecting K loss.

Ouabain (3 μm) evoked a large gain in tissue Na and an equivalent loss of K. Tissue Ca content was also increased. Acidification of the extracellular pH from pH 7.4 to pH 6.9 evoked a significant reduction of Na and Ca gain; changes in tissue K were not significant. Acidification down to pH 6.0 increased reduction of Na and Ca gain, but not that of K loss which nevertheless became statistically significant.

These results show that tissue Na gain observed after inhibition of the sodium pump by ouabain may be related to activation of Na‐H exchange. They also indicate that blockade of Na‐H exchange selectively reduced the inotropic effect of ouabain in guinea‐pig atria resulting from interaction of the glycoside with high affinity binding sites. This confirms previous observations in rat heart.
Lithium amplifies inhibitions of inositol phospholipid hydrolysis in mammalian brain slices
Authors: Kendall David A. , Whitworth Paul
Published: July 2012

We have examined the effects of lithium chloride (LiCl) on inhibitions of inositol phospholipid hydrolysis in guinea‐pig and rat brain slices by assessing the accumulation of [3H]‐inositol phosphates ([3H]‐InsP), in vitro.

In guinea‐pig and rat cerebral cortex slices the accumulation of total [3H]‐inositol phosphates due to the cholinoceptor agonist carbachol was inhibited by the excitatory amino acid l‐glutamate, but only when LiCl was present.

The effects of LiCl were time and concentration‐dependent. Significant inhibitions of the carbachol response by glutamate (in the presence of LiCl) being evident only after 20–30 min of stimulation at LiCl concentrations above 1.2 mm.

N‐methyl‐d‐aspartate (NMDA), in the absence of LiCl, enhanced the response to carbachol at low concentrations of the amino acid and inhibited the response at higher concentrations. In the presence of 5 mm LiCl, only the inhibitory phase was observed.

In rat cerebral cortex slices, aluminium fluoride inhibited [3H]‐InsP accumulation in the presence of carbachol, noradrenaline and a depolarising concentration of KC1 and these inhibitions were more marked when LiCl was present. The response to histamine was unaffected.

The data presented provide evidence that LiCl amplifies inhibitions of inositol phospholipid hydrolysis due to receptor and non‐receptor mediated stimuli, although the mechanism underlying the effect is, as yet, obscure.
Pharmacological and biochemical effects of the cardiotonic agent Org10325 in isolated cardiac and vascular tissue preparations
Authors: Shahid M. , Martorana M.G. , Cottney J.E. , Marshall R.J.
Published: July 2012

The pharmacological and biochemical effects of a novel cardiotonic agent, Org10325 have been studied in isolated cardiac and vascular tissue preparations.

Org10325 produced concentration‐dependent (0.15–4.8 mm) positive inotropic, positive chronotropic and vascular relaxant responses in rabbit isolated papillary, atrial and aortic preparations, respectively. The maximal chronotropic effect (45%) was significantly less than the isoprenaline maximum. The inotropic effects of Org10325 were not modified by α‐ or β‐adrenoceptor blockade or by pretreatment with reserpine. Org10325 was at least 23 times more potent at relaxing aortic strips pre‐contracted with phenylephrine than with KCl.

Org10325 (74 μm) potentiated (10–14 fold) the positive inotropic effects of isoprenaline in rabbit isolated papillary muscles. Carbachol inhibited the positive inotropic effect of Org10325. Both the positive inotropic and vasorelaxant effects of Org10325 were accompanied by increases in cyclic AMP but not cyclic GMP.

In rat perfused heart preparation Org10325 increased phosphorylase a, cyclic AMP‐dependent protein kinase activities and stimulated phosphorylation of contractile proteins (troponin‐I and C‐protein).

Org10325 selectively inhibited the cyclic AMP hydrolytic activity of cyclic AMP high affinity cyclic nucleotide phosphodiesterase (PDE) isoenzymes, PDE III (IC50 65 μm) and PDE IV (IC50 71 μm), from rabbit cardiac ventricle. Weak inhibition (IC50 > 250μm) of PDE I and PDE II was observed.

The results show that the cardiac and vascular effects of Org10325 are mediated by an increase in cellular cyclic AMP due to inhibition of PDE III and PDE IV activities. However, in contrast to other PDE‐inhibitors Org10325 produced a marked increase in relaxation time of isolated papillary muscle suggesting the involvement of additional cyclic AMP‐independent mechanisms of action.
L‐NG‐nitro‐arginine and its methyl ester are potent inhibitors of non‐adrenergic, non‐cholinergic transmission in the rat anococcygeus
Authors: Hobbs Adrian J. , Gibson Alan
Published: July 2012

The effects of l‐NG‐nitro‐arginine (l‐NOARG) and some other arginine analogues on non‐adrenergic, non‐cholinergic (NANC) relaxations of the rat anococcygeus muscle were investigated.

l‐NOARG (5–200 μm) produced concentration‐related inhibition of the NANC response; 100 μm l‐NOARG produced 90% inhibition.

l‐Arginine (5–200 μm) produced a concentration‐related reversal of the inhibitory effect of 20 μm l‐NOARG; a five fold excess of l‐arginine (100 μm) was required to obtain the maximum reversal of 90%. d‐Arginine (100 μm) produced no such reversal, but significant reversal was produced by l‐citrulline, l‐arginine‐l‐aspartate, l‐homoarginine and l‐arginine‐methyl‐ester (all at 100 μm).

l‐NG‐nitro‐arginine‐methyl‐ester (l‐NAME; 5–200 μm) also reduced NANC relaxations, with a potency similar to that of l‐NOARG; both l‐NOARG and l‐NAME were some ten times more potent than l‐NG‐monomethyl‐arginine (l‐NMMA). Like l‐NOARG, the effects of l‐NAME (20 μm) were reversed by 100 μm l‐ but not d‐arginine.

Neither l‐NOARG nor l‐NAME (both 20 μm) affected submaximal relaxations induced by 10 μm sodium nitroprusside or 20 μm hydroxylamine.

d‐NOARG, l‐NG‐tosyl‐arginine and l‐Nα‐(t‐butyl‐oxycarbonyl)‐NG‐nitroarginine (all at 100 μm) had no effect on NANC relaxations.

Thus, in the rat anococcygeus, l‐NOARG and l‐NAME are more potent than l‐NMMA as prejunctional inhibitors of NANC transmission. The reversibility of the effect of l‐NOARG by arginine analogues suggests that the NANC system of the anococcygeus shows similarities to the endogenous nitrate system recently described in the brain.
A study of the purinoceptors mediating contraction in the rat colon
Authors: Bailey S.J. , Hourani S.M.O.
Published: July 2012

The effects of a number of purine analogues were examined on the rat isolated colon muscularis mucosae. Adenosine, adenosine 5′‐monophosphate (AMP), adenosine 5′‐diphosphate (ADP), adenosine 5′‐triphosphate (ATP), 2‐methylthioATP (MeSATP), adenosine 5′‐(2‐fluorodiphosphate) (ADPβF), adenosine 5′‐(β,γ‐methylene)triphosphonate (AM PPCP) and adenosine 5′‐(α,β‐methylene)triphosphonate (AMPCPP) each contracted the muscularis mucosae in the concentration range 1–100 μm.

MeSATP was the most potent purine agonist, with a threshold concentration for contraction of 0.05 μm and an EC50 of approximately 0.3 μm, and AMPCPP was less potent than ATP. The enantiomer of AMPPCP, l‐AMPPCP, was inactive at concentrations up to 100 μm.

The adenosine receptor antagonist 8‐(p‐sulphophenyl)theophylline (8‐SPT, 50 μm) produced approximately 50 fold shifts of the dose‐response curves to adenosine, AMP and AMPPCP, whereas those to ATP, MeSATP and substance P (SP) were unaffected. Intermediate shifts were observed for the dose‐response curves to ADP, AD$1βF and AMPCPP. With a lower concentration of 8‐SPT (10 μm) a dose ratio of approximately 11 was observed for the inhibition of the effects of both adenosine and AMPPCP.

ATP was rapidly degraded by the tissue to ADP, AMP and adenosine, AD$1βF was more slowly degraded to AMP and adenosine, and no significant degradation of AMPPCP was detected during 20 min incubation.

The results are consistent with the existence in the rat colon muscularis mucosae of a mixed population of purine receptors of P2Y and P1 types. The colon thus contains the first documented incidence of a P2Y‐receptor mediating contraction. The powerful inhibition by the P1‐purinoceptor antagonist 8‐SPT of the effects of AMPPCP suggests that its action in this tissue is mediated by P1‐purinoceptors, although 8‐SPT was more potent here than has previously been demonstrated.
Effect of 6‐cyano‐2,3‐dihydroxy‐7‐nitro‐quinoxaline (CNQX) on dorsal root‐, NMDA‐, kainate‐ and quisqualate‐mediated depolarization of rat motoneurones in vitro
Authors: Long S.K. , Smith D.A.S. , Siarey R.J. , Evans R.H.
Published: July 2012

Mature in vitro rat spinal cord preparations have been used to compare the depressant effects of 6‐cyano‐2,3‐dihydroxy‐7‐nitroquinoxalinedione (CNQX) and kynurenate on transmission from low threshold myelinated primary afferents in dorsal roots. EC50 values ± s.e.mean (number of preparations in parentheses) for depression of the monosynaptic ventral root reflex were respectively 1.0 ± 0.3 μm (5) and 135 ± 15μm (3) for CNQX and kynurenate. Transmission through superior cervical ganglia was not significantly affected by concentrations of CNQX up to 100 μm or kynurenate up to 5 mm.

Immature in vitro rat spinal cord preparations were used to measure dose‐ratios for antagonism of depolarizations induced by N‐methyl‐d‐aspartate (NMDA), kainate or quisqualate by 4, 10 and 25 μm CNQX. In the presence of 0.75 mm Mg2+ pA2 values + s.e.mean were respectively 4.62 ± 0.05 (16), 5.79 ± 0.01 (4) and 5.59 ± 0.05 (16) for each agonist. These values were not significantly altered in the absence of added Mg2+. The mean pA2 values for kainate were significantly higher than those for quisqualate (P < 0.01).

Antagonism of NMDA‐induced depolarizations was evident at 10 and 25 but not 4 μm CNQX. The antagonism of NMDA was reversed by d‐serine (100 and 200 μm).

A similarity between the relative potencies of both CNQX and kynurenate for depression of synaptic transmission and antagonism of amino acid‐induced depolarizations indicates that monosynaptic transmission from myelinated primary afferents to motoneurones is mediated by kainate and/or quisqualate sub‐types of non‐NMDA receptors.
A 5‐hydroxytryptamine receptor in human atrium
Authors: Kaumann Alberto J. , Sanders Louise , Brown Anthony M. , Murray Kenneth J. , Brown Morris J.
Published: July 2012

The effects of 5‐hydroxytryptamine (5‐HT) were investigated on right atrial appendages obtained from patients treated with β‐adrenoceptor blocking agents who were undergoing open heart surgery. Atrial strips were paced under isometric conditions.

5‐HT increased contractile force to approximately one half of the force produced by a saturating concentration of (−)−isoprenaline. Both 5‐HT and (−)−isoprenaline accelerated the onset of relaxation, as indicated by an abbreviation of time to peak force.

The effects of 5‐HT were resistant to blockade by 0.4 μm (±)‐propranolol, 1μm (−)−pindolol, 0.4 μm methiothepin, 4 μm yohimbine, 0.4 μm ketanserin, 10 μm phenoxybenzamine, 1μm methysergide, 2 μm MDL 72222 and 20 μm granisetron.

Cocaine 6 μm potentiated the effects of 5‐HT, increasing the pEC50 from 6.6 to 7.4. The inotropic potency of 5‐HT is five times greater than that of (−)−noradrenaline.

ICS 205930 antagonized competitively the effects of 5‐HT with a pKB of 6.7.

In the presence of 0.4 μm (±)‐propranolol, 10 μm 5‐HT increased both adenosine 3′:5′ cyclicmonophosphate (cyclic AMP) levels and cyclic AMP‐dependent protein kinase activity by approximately one half and two thirds respectively, of the corresponding effects of 200 μm (−)−isoprenaline.

Both the increase in cyclic AMP levels and the stimulation of protein kinase activity are consistent with the inotropic effects of 5‐HT being mediated by cyclic AMP‐dependent phosphorylation of Ca2+ channels and of proteins involved in contraction and relaxation.

The human atrial 5‐HT receptor resembles the neuronal ‘so called’ 5‐HT4 receptor of rodents both in increasing cyclic AMP levels and in its affinity for ICS 205930.
A salivary vasodilator in the blood‐sucking bug, Rhodnius prolixus
Authors: Ribeiro José M.C. , Marinotti Osvaldo , Gonzales Rafael
Published: July 2012

Salivary gland homogenates of the blood‐sucking bug, Rhodnius prolixus induced transient, dose‐dependent relaxation of rabbit aortic preparations pre‐constricted with 200 ng ml−1 noradrenaline, 1 μg ml−1 histamine or 20 ng ml−1 angiotensin II. Such relaxations were less marked when the aorta was constricted by 60 mm KCl. These effects were observed with as little as 0.2 μg ml−1 of crude salivary gland protein.

The vasodilator effect was endothelium‐independent, abolished by 50 μm hydroquinone or 50 μm methylene blue, and potentiated by 30 u ml−1 superoxide dismutase.

Salivary homogenates generated a coloured compound when reacted with sulfanilic acid in the presence of N‐(1‐naphtyl)‐ethylediamine, indicating the presence of reactive nitrogen groups, equivalent to 35 ± 3 ng of sodium nitrite per pair of glands.

Molecular sieving high performance liquid chromatography of salivary gland homogenates generated a single peak of vasorelaxant activity which coincided with the presence of platelet antiaggregating and spasmolytic (guinea‐pig ileum contracted with histamine) activities, as well as with reactive nitrogen groups.

It is concluded that a protein of molecular weight 16,500 daltons in the salivary glands of R. prolixus contains reactive nitrogen groups which assist the bug during a blood meal. It is suggested that saliva of blood sucking arthropods is a natural resource of novel pharmacological activities.