bluuebunny/crossref_metadata_2025 huggingface dataset:
Impairment of Ca release from mammalian ventricular sarcoplasmic reticulum by the calcium channel agonist Bay K 8644
Authors: Hryshko L.V. , Bose D.
Published: July 2012

Positive inotropic concentration of the Ca‐channel agonist, Bay K 8644, depressed contraction of canine right ventricular trabecula immediately after a rest period of 8 min, without decreasing action potential plateau amplitude. In contrast, high external Ca and ouabagenin caused only a slight decrease in post‐rest contraction. Bay K 8644‐induced post‐rest depression was inversely related to the extracellular Ca concentration. Hence it could not be due to cellular Ca overload. Since post‐rest potentiation is due to increased contribution of Ca from the sarcoplasmic reticulum, these results suggest that Bay K 8644 decreases the amount of releasable Ca from this structure during rest.
Noradrenaline stimulation of the phosphoinositide system: evidence for a novel hydrophobic inositol‐containing compound in resistance arterioles
Authors: Ollerenshaw J.D. , Heagerty A.M. , Swales J.D.
Published: July 2012

Five inositol phosphates were extracted from adult rat resistance arterioles and separated by ion‐exchange high performance liquid chromatography.

By use of this technique, inositol phosphates liberated were identified as inositol 1‐phosphate, inositol 1,4‐bisphosphate, inositol 1,3,4‐trisphosphate, inositol 1,4,5‐trisphosphate and inositol 1,3,4,5‐tetrakisphosphate. Stimulation of phosphoinositide hydrolysis with noradrenaline produced increases in inositol phosphate production.

Three inositol‐containing phospholipids extracted from resistance arterioles were measured as their glycerol esters following deacylation, thereby permitting an analysis of both membrane and cytosolic components of the phosphoinositide signalling system.

A substantial agonist‐sensitive pool of a previously undescribed inositol but not glycerol‐containing lipid extract component was also identified in this tissue.

These experiments for the first time allow a precise description of phosphoinositide metabolism in resting and agonist‐stimulated resistance arterioles and provide data on a novel compound possibly similar to that recently described in other tissues.
Mechanism of action of α‐adrenoceptor activation in single cells freshly dissociated from the rabbit portal vein
Authors: Byrne N.G. , Large W.A.
Published: July 2012

The action of noradrenaline was studied in freshly dispersed cells of the rabbit portal vein using microelectrode techniques.

In normal physiological salt solution, the ionophoretic application of noradrenaline evoked an α‐adrenoceptor‐mediated depolarization and sometimes a β‐adrenoceptor‐mediated hyperpolarization. Experiments were carried out in the presence of propranolol to study the membrane mechanism associated with α‐adrenoceptor activation.

In the current clamp mode of recording, the equilibrium potential of the noradrenaline‐evoked depolarization was −1.9 mV. The depolarization was brought about by an increase in membrane conductance.

Under voltage clamp conditions, noradrenaline produced an inward current with a reversal potential of −7 ± 3 mV (mean ± s.e. mean).

The relationship between the noradrenaline‐induced inward current and clamp potential was non‐linear. Depolarization enhanced the conductance elicited by noradrenaline.

Evidence is presented which suggests that an additional conductance mechanism (probably an increase in potassium conductance) is also evoked by α‐adrenoceptor stimulation in dispersed cells of rabbit portal vein.
Influence of halothane on electrical coupling in cell pairs isolated from guinea‐pig ventricle
Authors: Terrar D.A. , Victory J.G.G.
Published: July 2012

The actions of halothane on electrical coupling between cells were investigated in cell pairs isolated from guinea‐pig ventricular muscle.

Under voltage‐clamp conditions a step depolarization applied to one cell caused a similar change in potential in the second. Application of halothane led to the appearance of double peaks in inward current evoked by step depolarizations. These observations were interpreted in terms of uncoupling of the cells leading to escape of the second cell from the influence of the voltage‐clamp in the first cell.

This suggestion that uncoupling in the presence of halothane led to differences in electrical activity in the two cells was confirmed in experiments in which independent electrodes were used to measure membrane potential in the two cells.

The voltage responses of both cells of the pair were recorded in response to constant current pulses. Administration of halothane led to abolition of the response recorded from the second cell while that of the first was enhanced. The actions are consistent with an action of halothane on gap junctions to block electrical coupling.

Qualitatively similar observations, consistent with electrical uncoupling, were observed with isoflurane.

These findings may be significant in relation to the arrhythmogenic actions of halothane.
Calcium and the activation of the α1‐adrenoceptors in the guinea‐pig taenia caeci
Authors: Rusko J. , Bauer V.
Published: July 2012

The actions of phenylephrine (0.1–100 μmol l−1) and methoxamine (0.1–100 μmol l−1) were compared with that of adrenaline (0.01–10 μmol l−1) using the single sucrose gap method and mechanical recording in the guinea‐pig taenia caeci. Drugs were applied for variable periods of time.

The characteristics of the inhibitory effects of α‐adrenoceptor agonists were the same when exposure time did not exceed 5 min. When the exposure was prolonged, in contrast to the sustained effects of adrenaline (0.1–3 μmol l−1), phenylephrine and methoxamine (1–10 μmol l−1) produced a transient inhibitory action.

During the delayed recovery phase of phenylephrine, adrenaline preserved its ability to suppress the spontaneous electrical and mechanical activities of the taenia both when phenylephrine was replaced by adrenaline or when adrenaline was applied in addition to phenylephrine. All the above effects were found in untreated preparations, as well as during blockade of muscarinic cholinoceptors by atropine (1.4 μmol 1−1), β‐adrenoceptors by propranolol (3 μmol l−1) and release of endogenous catecholamines by guanethidine (2.5μmol l−1).

In the presence of phorbol 12,13‐dibutyrate adrenaline ceased to be effective, while the inhibitory action of phenylephrine was converted to a contraction.

In calcium‐free conditions in the presence of EGTA (0.4 mmol l−1) the initial hyperpolarization induced by adrenaline and phenylephrine was significantly reduced and with repeated applications of the agonists the inhibitory response disappeared. Similar results were obtained using tissues treated with nifedipine (1 and 10 μmol l−1). When caffeine (30 mmol l−1) was present in the calcium‐free solution the α‐agonists studied were unable to produce any membrane potential changes.

The present results imply that the inhibitory effect of α1‐adrenoceptor agonists is mediated by the opening of potassium channels, which are activated by calcium derived from an intercellular source supplied from the extracellular space via a nifedipine‐sensitive mechanism.
Inhibitory effects of procaine on contraction and calcium movement in vascular and intestinal smooth muscles
Authors: Ahn H.Y. , Karaki H.
Published: July 2012

The effects of procaine on muscle tension and 45Ca2+ movements were investigated in vascular smooth muscle of the rabbit aorta and intestinal smooth muscle of the taenia isolated from guinea‐pig caecum.

Procaine (10 mm) induced a contraction in the taenia but had little effect on the resting tension in the aorta.

Procaine, 0.5–10 mM, relaxed the sustained contractions induced by 65.4 mM KCl and 10−6 m noradrenaline in the aorta, and by 45.4 mM KCl, 10−6 m carbachol and 10−6 m histamine in the taenia. The inhibitory effect of procaine on the high K+‐induced contractions was antagonized by external Ca2+ but not by the Ca2+ channel activators, Bay K 8644 and CGP 28,392.

45Ca2+ uptake was increased by high K+ or noradrenaline in the aorta and by high K+ or carbachol in the taenia. The increments were inhibited by procaine at the concentrations needed to inhibit the muscle contractions.

In a Ca2+‐free solution, noradrenaline and caffeine induced a transient contraction in the aorta, whereas a second application of each stimulant was almost ineffective. Addition of 1–10 mM procaine shortly before the first application of the stimulant inhibited the contraction. After washing the muscle with a Ca2+‐free solution without procaine, the second application of the stimulant induced a greater contraction than that in control muscle without procaine pretreatment.

Noradrenaline and caffeine released 45Ca2+ from a cellular site in the aorta. Procaine inhibited the effects of these stimulants.

It was concluded that procaine may inhibit both the opening of Ca2+ channels and the release of Ca2+ from cellular stores and the former but not the latter effect may be attributable to a local anaesthetic action.
α‐Methyldopa produces mydriasis in the rat by stimulation of CNS α2‐adrenoceptors
Authors: Hey John A. , Ito Takashi , Koss Michael C.
Published: July 2012

The effects of i.v. administration of α‐methyldopa (MD) on rat pupil diameter were investigated. All experiments were carried out in rats in which vagosympathetic nerve trunks were sectioned bilaterally at the cervical level.

In anaesthetized rats MD produced a marked dose‐related increase in pupil diameter. The onset of pupillary response to MD was gradual and reached maximal levels 2–3 h after administration.

Pretreatment with α2‐adrenoceptor antagonists yohimbine (1.5 mg kg−1, i.v.) or idazoxan (0.5 mg kg−1, i.v.) blocked the pupillary response to MD. In contrast, the α1‐antagonists prazosin (1.0 mg kg−1, i.v.) and phenoxybenzamine (1.5 mg kg−1, i.v.) did not significantly alter the pupillary effects of MD.

Selective enzymatic blockade with 3‐hydroxy‐benzyl‐hydrazine (NSD‐1015; 25 mg kg−1, i.p.), a dopa‐decarboxylase inhibitor, as well as bis (4‐methyl‐homopiperazinyl‐thiocarbonyl) disulphide (FLA‐63, 5.0 mg kg−1, i.p.), a dopamine‐β‐hydroxylase inhibitor, prevented the mydriatic effect of MD.

The above findings support the hypothesis that MD produces a clonidine‐like CNS mydriasis in the rat. This effect appears to be mediated primarily by the MD metabolite, α‐methylnoradrenaline.

These results indicate that MD produces mydriasis in the rat by a CNS action. The mydriatic action of MD appears to be produced by its metabolite α‐methylnoradrenaline which in turn stimulates CNS postsynaptic α2‐adrenoceptors.
Effects of anterior hypothalamic lesions and sham‐operations on bacterial endotoxin‐induced non‐specific airway hyperreactivity in vivo and in vitro
Authors: Van Oosterhout Antoon J.M. , Woutersen‐van Nijnanten Felice M.A. , Folkerts Gert , Nijkamp Frans P.
Published: July 2012

In the present study the effects of anterior hypothalamic (AHA) lesions and sham‐operations were investigated on the endotoxin‐induced airway hyperreactivity in guinea‐pigs. Unoperated, sham‐operated and AHA‐lesioned guinea‐pigs were injected intraperitoneally with Escherichia coli endotoxin and the airway reactivity tested four days later in isolated tracheal spirals and in spontaneously breathing anaesthetized animals. Control animals were given sterile saline.

Sham‐operated control animals demonstrated a diminished responsiveness of the tracheal spirals in vitro and of the lung resistance (ΔR1) in vivo to histamine receptor and cholinoceptor‐muscarinic agonists as compared to unoperated control animals.

AHA‐lesioned control animals showed a responsiveness of the respiratory airways in vitro and in vivo between the values of unoperated and sham‐operated control animals, suggesting that lesions partially restored the diminished responsiveness.

In unoperated and sham‐operated guinea‐pigs, endotoxin administration induced hyperreactivity of the tracheal spirals and ΔR1 to histamine receptor and cholinoceptor‐muscarinic agonists with respect to the control groups.

In AHA‐lesioned animals, the endotoxin‐induced airway hyperreactivity in vitro and in vivo to histamine receptor and cholinoceptor‐muscarinic agonists was absent.
Contribution of galanin to non‐cholinergic, non‐adrenergic transmission in rat ileum
Authors: Muramatsu Ikunobu , Yanaihara Noboru
Published: July 2012

We examined the possibility that the neuropeptide, galanin, may act as a transmitter in longitudinal muscle isolated from the rat ileum.

Galanin at nanomolar concentrations produced a phasic contraction with a concomitant increase in rhythmic activity. At concentrations in excess of 3 × 10−8 m, the contraction was followed by a rapid desensitization; hence, with the cumulative re‐addition of galanin, there was no response. This desensitization was probably selective for galanin because there was no attenuation of the contractile responses to substance P, neurokinin A and B, bradykinin or carbachol.

The phasic contraction induced by galanin was not inhibited by atropine, guanethidine, hexamethonium, naloxone, tetrodotoxin or [D‐Pro2, D‐Trp7,9]‐substance P.

Electrical stimulation of intramural nerves at low frequencies (1–5 Hz) led to an augmentation of spontaneous rhythmic contractions, which were completely or partially inhibited by atropine. However, guanethidine, hexamethonium, naloxone, [D‐Pro2, D‐Trp7,9]‐substance P and desensitization to galanin were without effect on the response to such electrical stimulation.

In contrast, transmural electrical stimulation at higher frequencies in the presence of atropine and guanethidine produced biphasic contractile responses with transient and slow components. The slow component was selectively attenuated by galanin desensitization.

The slow component induced by high frequency stimulation was markedly attenuated by repeated electrical stimulation at short intervals (2.5 min between 30 s trains). Following repeated stimulation, the contractile response to galanin was also attenuated. Thus, a cross‐desensitization between the mediator of the slow component and galanin had to be considered. In contrast, responses to tachykinins and the transient component induced by electrical stimulation were without effect.

Somatostatin, vasoactive intestinal polypeptide and α,β‐methylene ATP were without effect on the tone of the muscle. Calcitonin gene‐related peptide, neurotensin, gastrin‐releasing peptide, neuropeptide Y and capsaicin produced either a transient arrest of the spontaneous rhythmic activity or a transient relaxation.

These results suggest that the slow component of the non‐cholinergic non‐adrenergic contraction, as induced by intramural nerve stimulation is apparently due to the endogenous release of galanin, presumably released from galanin‐containing nerves in the rat ileum.
Facilitation of noradrenaline release from sympathetic nerves in rat anococcygeus muscle by activation of prejunctional β‐adrenoceptors and angiotensin receptors
Authors: Li Chunguang , Majewski Henryk , Rand Michael J.
Published: July 2012

Isolated preparations of rat anococcygeus muscle were incubated with [3H]‐noradrenaline and the efflux of radioactivity induced by stimulation of intramural sympathetic nerves was used as a measure of release of transmitter noradrenaline. Isometric contractile responses were also measured.

Angiotensin I (0.03 μm) and angiotensin II (0.03 μm) produced non‐sustained contractile responses and enhanced the stimulation‐induced (S‐I) effluxes of radioactivity as well as the contractile responses to electrical stimulation. These effects were blocked by the angiotensin II receptor antagonist saralasin (0.03 μm), and the effect of angiotensin I, but not angiotensin II, was blocked by the angiotensin converting enzyme inhibitor captopril (0.1 μm).

The findings indicate that there are both pre‐ and postjunctional receptors for angiotensin II and that angiotensin I is converted to angiotensin II in the anococcygeus muscle preparation.

Isoprenaline (0.1 μm) slightly enhanced the S‐I efflux of radioactivity, and produced a greater enhancement after neuronal uptake blockade with desipramine (0.03 μm) and α‐adrenoceptor blockade with phentolamine (1 μm).

The facilitatory effect of isoprenaline on S‐I efflux of radioactivity was abolished by propranolol (0.3 μm), but was not affected by low concentrations of saralasin (0.03 μm) or captopril (0.1 μm) which abolished the effect of angiotensin I. The findings suggest that isoprenaline acts directly on prejunctional β‐adrenoceptors to enhance S‐I noradrenaline release, rather than indirectly by releasing angiotensin II from within the tissue. Higher concentrations of saralasin (0.1 μm) or captopril (5 μm) did block the facilitatory effect of isoprenaline. The significance of this finding is not clear.
Effects of 5‐hydroxytryptamine agonists and antagonists on the responses of rat spinal motoneurones to raphe obscurus stimulation
Authors: Roberts M.H.T. , Davies M. , Girdlestone D. , Foster G.A.
Published: July 2012

The excitability of lumbar spinal motoneurones was studied in halothane‐anaesthetized rats by recording with microelectrodes the amplitude of the population spike evoked antidromically by stimulation of the cut ventral roots.

Electrical stimulation of the nucleus raphe obscurus for 1 min at 20 Hz increased the population spike amplitude and, as shown by intracellular recording, depolarized motoneurones. This response could be mimicked by microinjection of dl‐homocysteic acid into raphe obscurus but the response was not present in animals pretreated wtih the 5‐hydroxytryptamine (5‐HT) neurotoxin 5,7‐dihydroxytryptamine (5,7‐DHT).

Microiontophoretically applied 5‐HT had very similar effects on the extracellularly recorded population spike to those caused by stimulation of the raphe obscurus. These responses to 5‐HT were larger in 5,7‐DHT‐pretreated animals.

The effects of 5‐HT were potently mimicked by iontophoretically applied 5‐carboxamidotryptamine but 8‐hydroxy‐2‐(di‐n‐propylamino) tetralin (8‐OH‐DPAT) was without effect.

Antagonists were applied by microiontophoresis and also by intravenous injection. Ketanserin, the selective 5‐HT2 antagonist, did not antagonize the effects of 5‐HT. Neither did the 5‐HT3‐receptor antagonist MDL 72222 or the selective 5‐HT1 binding ligand cyanopindolol.

The non‐selective 5‐HT1/5‐HT2‐receptor antagonist methysergide was an effective antagonist of both the effects of 5‐HT and the response to raphe obscurus stimulation. Methysergide did not reduce the excitatory effects of noradrenaline.

It is concluded that 5‐HT application and stimulation of raphe obscurus increase the excitability of motoneurones by an action on a 5‐HT1‐like receptor which appears to be different from the 5‐HT1A‐and the 5‐HT1B‐binding sites characterized by others.
Endothelium‐derived relaxing factor and the effects of acetylcholine and histamine on resistance blood vessels
Authors: Bhardwaj R. , Moore P.K.
Published: July 2012

The role of endothelium‐derived relaxing factor (EDRF) in the action of vasodilator (acetylcholine, histamine, nitroprusside) and vasoconstrictor (noradrenaline, vasopressin) drugs on vascular resistance in the isolated perfused kidney and mesentery of the rat was studied.

Acetylcholine (EC50 = 0.18 ± 0.05 nmol and 3.1 ± 0.06 nmol, n = 8) and histamine (EC50 = 31.2 ± 4.9 nmol and 46.2 ± 3.9 nmol, n = 8) produced dose‐related vasodilatation in noradrenaline‐preconstricted (i.e. ‘high tone’) rat renal and mesenteric blood vessels. The response to both vasodilators (but not nitroprusside) was abolished by infusion of CHAPS (4.7 mg ml−1, 30 s). By use of an immunocytochemical staining procedure CHAPS was demonstrated to remove vascular endothelial cells lining intrarenal blood vessels.

Gossypol (3 μm), metyrapone (10 μm) and nordihydroguaiaretic acid, (NDGA, 30 μm), presumed inhibitors of EDRF biosynthesis, reduced or abolished the response to acetylcholine and histamine in perfused kidney and mesentery of the rat without affecting vasodilatation due to nitroprusside. Mepacrine (10 μm) similarly abolished the response to acetylcholine and histamine but in addition, reduced the response to nitroprusside in both preparations.

Methylene blue (100 μm), a presumed antagonist of the effect of EDRF, abolished vasodilatation due to acetylcholine and histamine and reduced the response to nitroprusside in perfused rat kidney and mesentery. Superoxide dismutase, SOD (15 u ml−1), was without effect.

While CHAPS treatment significantly augmented the vasoconstrictor response to both noradrenaline and vasopressin in perfused renal and mesenteric vessels this effect was not mimicked by metyrapone or gossypol suggesting that the enhanced effect of vasopressor agents in CHAPS‐perfused rat organs is due to the removal of a permeability barrier rather than impaired EDRF formation.

Responses to vasoconstrictor and vasodilator drugs in the perfused kidney and mesentery were obtained in the presence of indomethacin (8/XM) which produced in excess of 90% inhibition of prostacyclin (PGI2) release as measured by radioimmunoassay of 6‐oxo‐prostaglandin F1α (6‐oxo‐PGF1α) in the Krebs effluent.

We provide evidence that EDRF mediates the vasodilator response to acetylcholine and histamine in resistance blood vessels in perfused rat kidney and mesentery. The possibility that EDRF has a physiological role to play in regulating the calibre of resistance blood vessels is discussed.
Agonists at μ‐opioid, M2 ‐muscarinic and GABAB ‐receptors increase the same potassium conductance in rat lateral parabrachial neurones
Authors: Christie M.J. , North R.A.
Published: July 2012

Intracellular recordings of membrane potential and current were made from neurones in the lateral parabrachial nucleus in slices of rat brain in vitro.

The membrane was hyperpolarized by the opioid peptides Tyr‐d‐Ala‐Gly‐MePhe‐Gly‐ol (DAGOL, 0.01–1μm) and [Met5]enkephalin (3–30μm), though not by Tyr‐d‐Pen‐Gly‐Phe‐d‐Pen and U50488. In two experiments, naloxone competitively antagonized the effects of DAGOL and [Met]enkephalin with equilibrium dissociation constants of 0.8 and 3.2 nM, respectively.

Baclofen (0.3–30 μm) also hyperpolarized the neurones; this action was unaffected by naloxone.

DAGOL, [Met5]enkephalin and baclofen caused outward currents at the resting potential. These currents reversed polarity at a membrane potential which changed with the logarithm of the extracellular potassium concentration.

Muscarine has been shown previously to increase the potassium conductance by an action at M2‐receptors: the potassium currents induced by maximal concentrations of muscarine, baclofen and [Met5]enkephalin were non‐additive, indicating that these agonists opened the same population of potassium channels.

Noradrenaline, UK14304, carboxamidotryptamine, dopamine, adenosine and somatostatin had little or no effect on membrane potential.

It is concluded that rat lateral parabrachial neurones express μ‐opioid, γ‐aminobutyric acidB (GABAB), and M2‐muscarinic receptors: activation of any of these receptors increases the potassium conductance of the membrane and inhibits the neurones through hyperpolarization.
The effects of endothelium‐dependent vasodilators on cardiac output and their distribution in the anaesthetized rat: a comparison with sodium nitroprusside
Authors: Thomas G. Roger , Thiemermann Christoph , Walder Claire , Vane John R.
Published: July 2012

The effects of sodium nitroprusside, acetylcholine and bradykinin on cardiac output and its distribution were studied in the anaesthetized, vagotomised rat preparation by use of 113Sn‐labelled microspheres.

All three vasodilators lowered peripheral arterial blood pressure, but only bradykinin significantly reduced total peripheral resistance without reducing cardiac output. Bradykinin caused tachycardia, but this was offset by a reduction in stroke volume. These effects of bradykinin were not altered by indomethacin (4 mg kg−1). Acetylcholine and sodium nitroprusside both caused significant (P > 0.05) reductions in stroke volume and cardiac output.

Bradykinin reduced vascular resistance in the liver, stomach, small intestine, large intestine, pancreas/mesentery, epididimides, skeletal muscle and fat. These responses were not affected by indomethacin, whereas, the reduction in vascular resistance in the brain induced by bradykinin was abolished by indomethacin.

Acetylcholine caused a reduction in renal vascular resistance, where bradykinin had no effect. However, acetylcholine did not cause any haemodynamic changes in the bradykinin‐sensitive intestinal vasculature.

Acetylcholine caused vasoconstriction in the coronary and epididymal vasculature. Bradykinin in the presence of indomethacin induced vasoconstriction in the skin.

In conclusion, the data show that, with the possible exception of the brain and the skin, the vasodilator actions of bradykinin can adequately be transduced (presumably by endothelium‐derived relaxing factor, EDRF) in the absence of prostacyclin synthesis. Additionally, these results indicate that the vasculature of the stomach, pancreas/mesentery, epididimides and skeletal muscle are equally sensitive to both acetylcholine and bradykinin, whereas the kidneys showed selectivity towards acetylcholine and the intestines towards bradykinin. These results may indicate differential receptor populations.
Facilitation of noradrenaline release from sympathetic nerves through activation of ACTH receptors, β‐adrenoceptors and angiotensin II receptors
Authors: Costa Mary , Majewski Henryk
Published: July 2012

In rabbit pulmonary artery and left atrial strips previously incubated with [3H]‐noradrenaline, the active fragment of adrenocorticotropic hormone (ACTH1–24, 0.1 μm) significantly enhanced the stimulation‐induced (S‐I) outflow of radioactivity when a cocktail containing corticosterone (40 μm), cocaine (30 μm) and propranolol (4 μm) was present, but not in the absence of these drugs. In rabbit pulmonary artery a facilitatory effect of ACTH1–24 (0.1μm) was also observed when only cocaine (30 μm) was present.

ACTH1–24 (0.1 μm) did not affect the S‐I outflow of radioactivity from rat atria, rat pulmonary artery or guinea‐pig pulmonary artery, either in the presence or in the absence of the cocktail containing corticosterone (40 μm), cocaine (30 μm) and propranolol (4 μm). These results suggest that the presence of facilitatory prejunctional ACTH receptors may be restricted to rabbit sympathetic nerve endings.

Angiotensin II (0.01 μm), but not isoprenaline (0.1 μm) or ACTH1–24 (0.1μm), significantly enhanced the S‐I outflow of radioactivity from rabbit pulmonary artery. In the presence of phentolamine (1 μm) to block inhibitory α2‐adrenoceptors, the facilitatory effect of angiotensin II (0.01 μm) was significantly enhanced, and a significant facilitatory effect of isoprenaline (0.1 μm) and of ACTH1–24 (0.1 μm) was then revealed. These results suggest that feedback inhibition of noradrenaline release, mediated through the prejunctional α2‐adrenoceptor mechanism, buffers increases in noradrenaline release during activation of facilitatory prejunctional receptors.

In rabbit pulmonary artery, two concentrations of 8‐Br‐cyclic AMP, (270 or 540 μm), enhanced the S‐I outflow of radioactivity in the presence of phentolamine (1 μm) to a similar extent. In the presence of 8‐Br‐cyclic AMP (270 μm) and phentolamine, the facilitatory effects of isoprenaline (0.1 μm) and of ACTH1–24 (0.1 μm) were blocked, whereas that of angiotensin II (0.01 μm) was not changed. These results suggest that both prejunctional β‐adrenoceptors and ACTH receptors enhance noradrenaline release by generating cyclic AMP. The mechanism by which angiotensin II facilitates noradrenaline release is probably independent of the cyclic AMP second messenger pathway.
N,N‐diallyl‐tyrosyl substitution confers antagonist properties on the κ‐selective opioid peptide [D‐Pro10]dynorphin A(1–11)
Authors: Gairin Jean Edouard , Mazarguil Honoré , Alvinerie Paul , Botanch Catherine , Cros Jean , Meunier Jean‐Claude
Published: July 2012

In the search for κ‐opioid antagonists, we have designed two N,N‐diallyl substituted analogues of the κ‐selective peptide [D‐Pro10]dynorphin A (1–11)(DPDYN). In this study, we have examined (i) the binding properties of N,N‐diallyl‐DPDYN (analogue 1) and N,N‐diallyl‐[Aib2,3]DPDYN (analogue 2) at the three main types (μ, δ, κ) of opioid binding sites, (ii) their binding sensitivity to Na+ ions (120 mM NaCl) and guanine nucleotide (50 μm Gpp(NH)p) at μ‐ and κ‐binding sites and (iii) their biological activity in two pharmacological bioassays specific for μ‐ and κ‐(guinea‐pig ileum) and κ‐(rabbit vas deferens) opioid receptors.

Steric hindrance resulting from incorporation of two bulky allyl groups at the tyrosyl nitrogen atom greatly altered the binding properties of DPDYN. A dramatic fall in apparent affinity for the three types (μ, δ, κ) of site as well as selectivity for κ‐sites was observed for the two N,N‐diallyl‐substituted peptide analogues.

At κ‐sites of guinea‐pig cerebellum and μ‐sites of rabbit cerebellum, N,N‐diallyl‐substitution led to a complete loss of binding sensitivity to the inhibitory effect of 120 mM NaCl + 50 μm Gpp(NH)p compared to the high sensitivity of DPDYN. This may therefore suggest that the N,N‐diallyl‐DPDYN analogues are endowed with opioid antagonist properties.

No agonist activity of the analogues was observed in guinea‐pig myenteric plexus and rabbit vas deferens organ preparations. In contrast, both of the diallyl‐substituted peptides displayed similar antagonist properties against the κ‐agonist DPDYN in both preparations. In the guinea‐pig ileum, the affinities of the antagonist peptides against the μ‐agonist Tyr‐D‐Ala‐Gly‐MePhe‐NH(CH2)2OH(DAGOL) were approximately half that observed against DPDYN.

These results show that N,N‐diallyl‐tyrosyl substitution leads to analogues of DPDYN which act in vitro as pure opioid antagonists and exhibit a reasonable affinity at, but a weak selectivity for, the κ‐opioid receptors.
Electrical and mechanical effects of new aminosteroids on guinea‐pig isolated ventricular muscle
Authors: Adamantidis M.M. , Honoré E.R. , Dupuis B.A.
Published: July 2012

LND 623 and LND 796 are two aminosteroid derivatives which exert similar positive inotropic effects to digitalis. Their electrophysiological, toxic and inotropic effects were investigated in both normal and partially K+‐depolarized ventricular muscle.

In guinea‐pig myocardial fibres, LND 623 and LND 796 required tenfold higher concentrations than digoxin to induce the same signs of toxicity; e.g. triggered activities generated from delayed afterdepolarizations, leading to the marked depression of action potential characteristics and inexcitability. These abnormal rhythms and delayed afterdepolarizations were abolished by 1 mM caffeine. The toxic effects were reversed by washout, particularly in the case of LND 796.

In normal‐K+ solution, LND 623 and LND 796 exhibited concentration‐dependent positive inotropic effects on guinea‐pig papillary muscle and increased concomitantly resting membrane potential and action potential amplitude. The range of active concentrations (0.1 to 1 μm) of LND 623 was larger than that of digoxin (0.3 to 1 μm). Like digoxin, LND 796 exerted negative inotropic effects at the lowest concentrations (0.01 to 0.03 μm) and positive inotropic effects at high concentrations (1 and 3 μm).

In partially K+‐depolarized papillary muscle, in the presence of 2 μm histamine, LND 623 (3 and 10μm) and LND 796 (10 and 30μm) enhanced the two components P1 and P2 of the contraction and increased slow action potential amplitude, resting potential and maximal rate of depolarization. Low concentrations (0.03 to 0.3 μm) of LND 796 induced negative inotropic effects. β‐Adrenoceptor blockade with atenolol (1 μm) did not modify the activity of LND 623 but significantly enhanced the negative inotropic effect on P2 induced by 1 and 3 μm LND 796 and reduced the positive inotropic effect on P1 and P2 of the highest concentration (30 μm) studied.

In the presence of either caffeine (1 mm) or Ca2+‐free, Sr2+‐rich (3.6 mm) solution, LND 623 and LND 796 produced a positive inotropic effect which was stronger with LND 623.

It is suggested that two mechanisms are involved in the inotropic effects of these aminosteroids: (i) an enhanced Ca2+ entry via the slow calcium channels partially brought about by a local release of endogenous catecholamines in the case of LND 796, (ii) an inhibitory effect on Na+‐K+ ATPase which, at the highest concentrations, lead to similar signs of cellular toxicity to those described for digitalis drugs. Because of their enlarged positive inotropic range, both aminosteroids may be of interest in the treatment of congestive heart failure.
Vasoconstrictor and vasodilator effects in normal and atherosclerotic conscious rabbits
Authors: Hof Robert P. , Hof Akiko
Published: July 2012

Rabbits were fed a cholesterol‐rich diet for 5 two‐week intervals. Polyvinyl catheters were then implanted into the femoral artery and vein. Dose‐response curves to acetylcholine (ACh), noradrenaline (NA), phenylephrine (Phen) and angiotensin II (AII), were obtained in 6 cholesterol‐fed and 6 control rabbits before and after isradipine (code name PN200–110) 100μgkg−1. After these experiments the animals were killed and aortic rings were suspended in an organ bath. ACh but not nitroprusside‐induced relaxation was impaired in atherosclerotic but not in control preparations.

ACh decreased blood pressure dose‐dependently in both groups of rabbits even though ACh did not relax the aortae of the same rabbits in vitro.

Blood pressure effects reflect mostly changes in resistance vessels. The pressor effects of NA, Phen and AII were enhanced in atherosclerotic compared with normal rabbits.

After a dose of 100μgkg−1 isradipine the dose‐response curves of all agents were shifted to the right. The differences between atherosclerotic and control rabbits disappeared, except for the AII‐induced pressor response, which remained enhanced in atherosclerotic animals. The calcium antagonist thus only partly corrected the atherosclerosis‐associated hyperresponsiveness to vasoconstrictor agents.
Chronotropic effect of nizofenone fumarate in rabbit sino‐atrial node in vitro
Authors: Kotake Hiroshi , Nawada Takahiro , Matsumoto Tatsuhiko , Kitamura Hideyuki , Kaneda Takafumi , Hasegawa Junichi , Mashiba Hiroto
Published: July 2012

The effects of nizofenone fumarate were studied on the membrane potentials and currents of rabbit sino‐atrial node preparations by means of the double‐microelectrode voltage clamp method.

In spontaneously firing pacemaker cells, nizofenone (above 1 μm) decreased the heart rate. Above 3 μm, nizofenone reduced the maximum upstroke velocity, the amplitude of the action potential and the slope of the phase 4 depolarization, and prolonged the action potential duration at 50% repolarization.

Under voltage clamp conditions, nizofenone decreased the slow inward current and the time‐dependent potassium outward current in a dose‐dependent manner.

These findings suggest that nizofenone exerts an inhibitory action on the automaticity of sinoatrial node preparations via effects on both inward and outward currents.
β ‐Adrenoceptor stimulation inhibits histamine‐stimulated inositol phospholipid hydrolysis in bovine tracheal smooth muscle
Authors: Hall I.P. , Hill S.J.
Published: July 2012

Histamine and carbachol produced concentration‐related increases in the accumulation of 3Hinositol phosphates in slices of bovine tracheal smooth muscle.

Noradrenaline alone produced a small stimulation of 3H‐inositol phosphate accumulation which was inhibited by the α‐adrenoceptor antagonist phentolamine. In contrast, when noradrenaline (0.1 mm) was added simultaneously with histamine it significantly reduced the inositol phosphate response to high (≥0.1mm) concentrations of histamine. However, noradrenaline had no inhibitory effect on the carbachol‐induced inositol phosphate response.

The non‐selective β‐agonist isoprenaline (IC50 = 0.08 μm) and the β2‐selective agonist salbutamol (IC50 = 0.29 μm) both produced a dose‐related inhibition of the inositol phosphate response to 0.1 mM histamine. The inhibitory effect of salbutamol was antagonized by propranolol (KA = 2.4 × 109M−1) and the β2‐selective adrenoceptor antagonist ICI 118551 (KA = 1.7 × 109 M−1).

The accumulation of 3H‐inositol phosphates induced by histamine increased steadily over a 40 min period after an initial lag period of 3–4 min. Following the simultaneous addition of histamine and salbutamol there was a further delay of 3–4 min before the appearance of the inhibitory effect of salbutamol.

The effect of histamine on inositol phosphate accumulation was accompanied by a stimulation of [3H]‐inositol incorporation into membrane phospholipids which was reduced by the presence of salbutamol. However, when histamine was used to stimulate maximally [3H]‐inositol incorporation during the prelabelling period, salbutamol produced a marked inhibition of histamine‐stimulated 3H‐inositol phosphate accumulation under conditions in which there was no change in the level of incorporation.
α2‐Adrenoceptor‐mediated inhibition of histamine release from rat cerebral cortical slices
Authors: Hill S.J. , Straw R.M.
Published: July 2012

Depolarization of rat cerebral cortical slices, prelabelled with [3H]‐histidine, in high potassium (40 mM KCl) medium stimulated the release of [3H]‐histamine. The K+‐evoked release of [3H]‐histamine was attenuated by incubation in calcium‐free medium and prevented by prior incubation of brain slices with the selective histidine decarboxylase inhibitor S‐(α)‐fluoromethylhistidine.

The K+‐evoked release of [3H]‐histamine was significantly (P < 0.001) reduced following stimulation of histamine H3‐receptors with R‐(α)‐methylhistamine (1 μm) and this effect was antagonized by the H3‐antagonist thioperamide (1 μm).

Noradrenaline and the α2‐selective adrenoceptor agonists clonidine and UK‐14,304 inhibited the K+‐evoked release of [3H]‐histamine in a concentration‐dependent manner yielding EC50 values of 2.5, 0.8 and 1.2 μm, respectively. However, the maximum response to clonidine was only 52 ± 8% of that obtained with noradrenaline.

The inhibitory effect of noradrenaline was antagonized by the non‐selective α‐antagonist phentolamine and by the selective α2‐antagonists yohimbine and idazoxan. However, the response to noradrenaline was not inhibited by the α1‐antagonist prazosin at concentrations up to 1 μm.

These results suggest that both histamine H 3‐receptors and α2‐adrenoceptors are present on histamine‐containing nerve terminals in rat cerebral cortex and can exert an inhibitory influence on neurotransmitter release.
Inhibition of leukotriene release in anaphylactic guinea‐pig hearts by a 5‐lipoxygenase inhibitor, CGS 8515
Authors: Yaacob H.B. , Piper Priscilla J.
Published: July 2012

Ovalbumen (100μg)‐induced coronary vasoconstriction and decrease in cardiac developed tension were studied in isolated perfused hearts from sensitized guinea‐pigs. Leukotriene‐like material released in the cardiac effluent was assayed against synthetic leukotriene C4 (LTC4).

LTC4 was released in a time‐dependent fashion, and release was enhanced when hearts were challenged in the presence of indomethacin (2.8 μm). The release was maximal at 2–3 min and detectable for as long as 10 min following ovalbumen challenge. Immunoreactive (ir) thromboxane‐B2 (TxB2) was also detected in cardiac effluent which had been partially purified using C18 Sep‐Paks.

CGS 8515 (0.03–1.0 μm), an inhibitor of 5‐lipoxygenase, dose‐dependently inhibited ovalbumen‐induced coronary vasoconstriction and leukotriene‐C4 release. CGS 8515 inhibited ovalbumen‐induced decreases in cardiac developed tension at 0.3 and 1.0 μm, but did not antagonize coronary vasoconstriction induced by synthetic LTC4.

The release of cyclo‐oxygenase products following ovalbumen challenge was not inhibited by CGS 8515, but was markedly inhibited by indomethacin (2.8 μm) pretreatment.

We conclude that leukotrienes have a major role in guinea‐pig cardiac anaphylaxis, and that CGS 8515 has a cardio‐protective action. The results obtained in these experiments in vitro show that CGS 8515 is a potent and selective 5‐lipoxygenase inhibitor.
A 5‐HT1‐like receptor mediates a pertussis toxin‐sensitive inhibition of rat ventromedial hypothalamic neurones in vitro
Authors: Newberry Nigel R. , Priestley Tony
Published: July 2012

5‐ Hydroxytryptamine (5‐HT), 5‐carboxamidotryptamine and 8‐hydroxy‐2‐(di‐n‐propylamino)‐tetralin inhibited rat ventromedial hypothalamic neurones in vitro in a concentration‐dependent manner. The agonist‐induced inhibition was reduced by spiperone (1 μM) and by pertussis toxin, but not by MDL 72222 (10 μM) or ketanserin (1 μM). The inhibition appeared to be mediated via 5‐HT1A‐receptors and a pertussis toxin‐sensitive pathway.
Pinacidil opens K+‐selective channels causing hyperpolarization and relaxation of noradrenaline contractions in rat mesenteric resistance vessels
Authors: Videbæk Lars M. , Aalkjær Christian , Mulvany Michael J.
Published: July 2012

The effects of pinacidil on noradrenaline‐induced tone, smooth muscle membrane potential and42 K‐ and86 Rb‐efllux from isolated mesenteric resistance vessels (internal diameter 200 μm) of the rat have been studied.

Pinacidil (0.3–10 μM) produced concentration‐dependent suppression of noradrenaline‐induced tone.

Pinacidil (0.3–10 μM) caused concentration‐dependent hyperpolarization of the smooth muscle.

In rat resistance vessels loaded with42 K, pinacidil (1–10 μM) significantly increased the42 K‐efllux rate constant.

With the use of86 Rb as a marker for K+, 1 μM pinacidil did not affect the86 Rb‐efflux rate constant, while 10 μM pinacidil transiently increased the86 Rb rate constant.

The results indicate that the relaxant action of pinacidil in these vessels is due to the opening of K+‐channels and consequent hyperpolarization. The K+‐channels opened are selective for42 K over86 Rb.
Possible mechanism of acetaldehyde‐induced noradrenaline release from sympathetic nerve terminals in isolated blood vessels
Authors: Chiba S. , Tsukada M.
Published: July 2012

Vasoconstrictor responses to acetaldehyde were investigated in isolated and perfused canine intermediate auricular (ear) arteries.

Single injections of small doses of acetaldehyde (1–3 μmol) induced vasoconstriction in a dose‐related manner and showed no tachyphylaxis. On the other hand, large doses of acetaldehyde (10–30 μmol) frequently caused tachyphylaxis when injected at 10 min intervals.

After tyramine treatment, constrictions induced by a large dose of acetaldehyde were consistently restored temporarily.

The acetaldehyde‐induced vasoconstriction was inhibited by bunazosin, a potent α1‐adrenoceptor antagonist.

A small dose of imipramine blocked tyramine‐induced vasoconstriction, but had no significant influence on noradrenaline (NA)‐induced constrictions, and caused slight potentiation of acetaldehyde‐induced constrictions.

Hydrocortisone treatment did not modify tyramine‐induced vasoconstrictions and slightly suppressed NA‐ and acetaldehyde‐induced constrictions but not significantly.

It is suggested that acetaldehyde causes a release of NA from a NA store of the sympathetic nerve terminals which is different from the tyramine‐sensitive NA store, and that the acetaldehyde‐sensitive NA store may be readily filled up with NA from the tyramine‐sensitive store.
Evidence that the histamine sensitivity and responsiveness of guinea‐pig isolated trachea are modulated by epithelial prostaglandin E2 production
Authors: Braunstein Guy , Labat RCarlos , Brunelleschi Sandra , Benveniste Jacques , Marsac Jean , Brink Charles
Published: July 2012

Guinea‐pig isolated tracheal preparations in which the epithelium had been removed exhibited a greater contractile response to histamine (intact: 1.91 ± 0.12g; n = 6 and rubbed: 2.76 ± 0.15g; n = 11; P < 0.001). The histamine sensitivity (pD2 value) of these preparations was also significantly greater (intact: 4.80 ± 0.04 and rubbed: 5.40 ± 0.08; P < 0.01).

Indomethacin suppressed the basal tone of both intact and rubbed preparations but was more effective in the former tissues (intact: −0.70 ± 0.14g; n = 22 and rubbed: −0.17 ± 0.05g; n = 12; P < 0.02).

Arachidonic acid (AA; 10 μM) suppressed the basal tone of intact tissues but contracted such preparations following indomethacin treatment (1.7 μM; 30 min). However, in rubbed tissues AA (10 μM) induced a contraction which was attenuated following indomethacin treatment.

Prostaglandin E2 (PGE2; 0.01 and 0.1 μM) suppressed the basal tone of intact preparations and always evoked contraction of rubbed tissues. Following indomethacin treatment PGE2 (0.01 and 0.1 μM) generally evoked spasm of intact and rubbed tissues while at higher concentrations (1 μM) relaxant effects were observed.

Removal of the epithelium did not alter the relaxant effect of PGE2 (pD2 value) on histamine (50 μM)‐contracted tissues (intact: 6.86 ± 0.08 and rubbed: 7.10 ± 0.3; n = 4; P > 0.1).

In rubbed preparations treated with indomethacin, PGE2 (0.01 and 0.1 μM) evoked spasm. However, when added to preparations contracted with 5 μM histamine, PGE2 always caused relaxation.

The release of immunoreactive PGE2 by rubbed preparations during histamine and/or AA stimulation was significantly less than that produced by intact stimulated tissues.

Exogenous PGE2 (0.01‐1 μM) decreased the maximal response and sensitivity of rubbed tracheal preparations to histamine.

These results suggest that release of an epithelial derived cyclo‐oxygenase product, namely PGE2, may regulate basal tone, histamine response and sensitivity of the guinea‐pig isolated trachea.
Release‐regulating autoreceptors of the GABAB‐type in human cerebral cortex
Authors: Bonanno Giambattista , Cavazzani Paolo , Andrioli Gian Carlo , Asaro Daniela , Pellegrini Graziella , Raiteri Maurizio
Published: July 2012

The depolarization‐evoked release of γ‐aminobutyric acid (GABA) and its modulation mediated by autoreceptors were investigated in superfused synaptosomes prepared from fresh human cerebral cortex.

The release of [3H]‐GABA provoked by 15 mM K+ from human cortex nerve endings was almost totally (85%) calcium‐dependent.

In the presence of the GABA uptake inhibitor SK&F 89976A (N‐(4,4‐diphenyl‐3‐butenyl)‐nipecotic; acid), added to prevent carrier‐mediated homoexchange, GABA (1–10 μm) decreased in a concentration‐dependent manner the K+‐evoked release of [3H]‐GABA. The effect of GABA was mimicked by the GABAB receptor agonist (−)‐baclofen (1–100 μm) but not by the GABAA receptor agonist muscimol (1–100 μm). Moreover, the GABA‐induced inhibition of [3H]‐GABA release was not affected by two GABAA receptor antagonists, bicuculline or SR 95531 (2‐(3′‐carbethoxy‐2′‐propenyl)−3‐amino‐6‐paramethoxy‐phenyl‐pyridazinium bromide).

(−)‐Baclofen also inhibited the depolarization‐evoked release of endogenous GABA from human cortical synaptosomes.

It is concluded that GABA autoreceptors regulating the release of both newly taken up and endogenous GABA are present in human brain and appear to belong to the GABAB subtype.
A local circuit neocortical synapse that operates via both NMDA and non‐NMDA receptors
Authors: Thomson Alex M. , Girdlestone Debbie , West David C.
Published: July 2012

In slices of rat neocortex, spike triggered averaging was employed to record in one neurone the excitatory postsynaptic potential (e.p.s.p.) generated by a spike in another, neighbouring neurone. When recorded at different membrane potentials, some of these e.p.s.ps exhibited a voltage relation typical of neuronal responses to N‐methyl‐d‐aspartate (NMDA).

Selective NMDA antagonists reduced the amplitude of these e.p.s.ps, but had little effect on their early rising phase. In contrast, a less selective excitatory amino acid antagonist reduced all phases of the e.p.s.p.

By analyzing single axon e.p.s.ps we have been able to establish that the synaptic input to one cortical cell, delivered by a single presynaptic cortical cell, operates simultaneously via NMDA and non‐NMDA amino acid receptors.