bluuebunny/crossref_metadata_2025 huggingface dataset:
Tachykinins activate guinea‐pig alveolar macrophages: involvement of NK2 and NK1 receptors
Authors: Brunelleschi Sandra , Vanni Lucia , Ledda Fabrizio , Giotti Alberto , Maggi Carlo Alberto , Fantozzi Roberto
Published: July 2012

The effects of substance P (SP), neurokinin A (NKA) and neurokinin B (NKB) were evaluated on superoxide anion () production by guinea‐pig alveolar macrophages (AM).

SP dose‐dependently (ED50 = 0.7 nm) evoked production from guinea‐pig AM; the N‐terminal heptapeptide, SP(1–7), was ineffective. In the presence of thiorphan (10−5 m), an enkephalinase inhibitor, the stimulating effects of SP were not significantly modified. NKA and NKB were both able to induce production from guinea‐pig AM, ED50 values being 0.1 and 1.3 nm, respectively. Therefore, the rank order of activity of natural tachykinins was NKA > SP > NKB. Tachykinin‐evoked effects were quantitatively similar to those elicited by the autacoid mediator PAF‐acether and less than those induced by the synthetic peptide N‐formylmethionyl‐leucyl‐phenylalanine (FMLP).

The NK2 receptor agonist [β‐Ala8]‐NKA (4–10) dose‐dependently evoked production from guinea‐pig AM; the NK1 receptor agonist [Pro9]‐SP sulphone acted only at high concentrations, while the NK3 receptor agonist [Me, Phe7]‐NKB was ineffective.

These findings indicate that guinea‐pig AM possess NK2 and possibly some NK1 tachykinin receptors and further suggest tachykinin involvement in lung pathophysiology.
Caffeine‐induced behavioural stimulation is dose‐ and concentration‐dependent
Authors: Kaplan Gary B. , Tai Nhan T. , Greenblatt David J. , Shader Richard I.
Published: July 2012

The relationship between plasma and brain caffeine and metabolite concentrations and behavioural stimulation was investigated over a 4 h time course.

CD‐1 mice receiving single intraperitoneal doses of caffeine‐sodium benzoate solution (caffeine doses: 0, 20, and 40 mg kg−1) were evaluated in an activity monitor, and their plasma and brain caffeine and metabolite concentrations were determined by high performance liquid chromatography (h.p.l.c.).

Kinetic variables for caffeine at low and high caffeine doses were: volume of distribution (Vd), 1.16 and 0.881 kg−1; plasma elimination half‐life (t1/2), 1.25 and 1.62 h; brain t1/2, 0.93 and 1.30h; clearance, 0.64 and 0.381 h−1 kg−1, respectively, with Vd and brain t1/2 differing significantly between the two caffeine doses.

Low‐dose caffeine stimulated vertical behaviours significantly more than high‐dose, during the first 150 min post‐dosage; both doses stimulated vertical behaviours significantly more than vehicle treatment.

Low‐dose and high‐dose caffeine stimulated horizontal and stereotypic behaviours equivalently, during the first 150 min post‐dosage; both doses stimulated these behaviours significantly more than vehicle.

Only later, 150 min post‐dosage, did high‐dose caffeine stimulate all behaviours significantly more than both low‐dose and vehicle treatment; this occurred when caffeine concentrations had fallen to approximately 10 μg g−1 in the high‐dose group.

The maximal stimulant effects of caffeine occurred in an intermediate concentration range, between 10–20 μg g−1, while lower and higher concentrations produced either no additional stimulation or decrements in activity.
Cationic factors affecting phospholipase activities from human lung
Authors: Yeats D.A. , Bakhle Y.S.
Published: July 2012

The effects of varying H+ and other cation concentrations on phospholipase activity were investigated on two particulate fractions from human lung, corresponding to the mitochondrial and microsomal fractions.

Three 14C‐labelled substrates, arachidonyl‐phosphatidylcholine (PC), ‐phosphatidylethanolamine (PE) and ‐phosphatidylinositol (PI) were used.

For two substrates, PE and PI, hydrolysis was maximal at pH 6, with either subcellular fraction.

Hydrolysis of all three substrates was strongly inhibited by EDTA and EGTA (10–25 mm). Addition of 2,2‐dipyridyl, o‐phenanthroline, 8‐hydroxyquinoline or desferrioxamine (10 μm‐1 mm) did not inhibit but often increased hydrolysis of all substrates.

Addition of Zn2+, as ZnCl2, (10 μm‐1 mm) inhibited PE and PI, but not PC, hydrolysis.

The phospholipase activities from human lung appear to be dependent on Ca2+ for maximal activity and to be inhibited by other metal ions including Zn2+.
The effects of granisetron, ICS 205–930 and ondansetron on the visceral pain reflex induced by duodenal distension
Authors: Moss Helen E. , Sanger Gareth J.
Published: July 2012

Distension of the duodenum in anaesthetized rats, by rapid application of intraluminal pressures (10–75 cmH2O), evoked falls in diastolic blood pressure and intragastric pressure.

The distension‐induced responses were blocked by pretreatment with morphine (20 mg kg−1, s.c.), an action reversible by injection of naloxone (5 mg kg−1, i.v.).

Bilateral cervical vagotomy reduced the distension‐evoked fall in intragastric pressure but had no effect on the corresponding fall in blood pressure.

Granisetron or ICS 205–930 (1–1000 μg kg−1, i.v.) had no effects on duodenal intraluminal pressure, but reduced the responses to distension with a bell‐shaped dose‐response relationship. Ondansetron (1–1000 μg kg−1, i.v.) did not reduce the reflex responses.

These results show that the 5‐HT3 receptor antagonists used exerted different effects on the reflex responses to duodenal distension.
Effects of tetraethylammonium and 4‐aminopyridine on outward currents and excitability in canine tracheal smooth muscle cells
Authors: Muraki K. , Imaizumi Y. , Kojima T. , Kawai T. , Watanabe M.
Published: July 2012

The effects of tetraethylammonium (TEA) and 4‐aminopyridine (4‐AP) on membrane currents and on single channel K currents in smooth muscle cells isolated from canine trachea were examined by use of tight seal whole cell‐ and patch‐clamp techniques.

Depolarizing current applied through a recording pipette did not elicit an action potential under current clamp. A strong outward rectification was observed.

In most cells under voltage‐clamp, only an outward current was observed upon depolarization from −60 mV when a pipette solution contained mainly KCl. The outward current consisted of three components; a large initial transient, a following sustained component and an additional component of irregular small transients on the sustained one. The two transient components were almost abolished when extracellular and pipette solutions contained 2.2 mm Cd2+ (0 mm Ca2+) and 10 mm EGTA, respectively. The sustained component was well maintained under these conditions.

TEA at low concentrations (<1 mm) effectively decreased the transient components and made the outward current smooth; it also suppressed the sustained component at higher concentrations. In outside‐out patches, external 1 mm TEA reduced the single channel conductance of Ca‐activated K channels by about 87% whereas 3 mm 4‐AP did not. 4‐AP at low concentrations (<3 mm) selectively reduced the sustained component of the outward current.

A Ca current recorded after the suppression of outward current by internal Cs+ had a peak of approximately 200 pA at + 10 mV (holding potential: −60 mV). The half inactivation voltage in the steady‐state was approximately −30 mV.

Simultaneous application of 1 mm TEA and 4‐AP reduced the outward current and unmasked a Ca current. Under these conditions, an action potential with overshoot was easily elicited under current clamp.

It is concluded that the low excitability of canine tracheal smooth muscle cell upon depolarization is due to a large outward K current which consists of Ca‐dependent and Ca‐independent components. The peak amplitude of the Ca current is similar to that in highly excitable smooth muscle cells such as those of the ureter.
Pharmacological analysis of established ventricular fibrillation
Authors: Carlisle Euan J.F. , Allen J. Desmond , Kernohan W. George , Leahey W. , Adgey A.A. Jennifer
Published: July 2012

The effects of antiarrhythmic drugs on the power spectrum of established ventricular fibrillation induced by endocardial electrical stimulation, have been studied in greyhounds anaesthetized with sodium pentobarbitone (35 mg kg−1, i.v.).

In dogs receiving no drug, initial recording of ventricular fibrillation showed a dominant frequency of 9.9 ± 0.7 Hz (lead II) and 10.0 ± 0.6 Hz (endocardium). After 3.3 min the frequency had fallen to 4.0 ± 0.4 Hz in lead II, but remained high in the endocardium (10.7 ± 0.5 Hz).

Lignocaine significantly reduced the dominant frequency for fibrillation recorded from lead II at (0–80 s), and for endocardial fibrillation at (0–200 s).

Pretreatment with propranolol or bretylium had little effect on the time course of the dominant frequency of fibrillation in lead II or the endocardium.

Verapamil prevented the fall in frequency seen in lead II after 80s in the no drug group. A significantly higher frequency was maintained in both lead II (14.7 ± 0.9 Hz) and the endocardium (14.8 ± 0.9 Hz) for 3.3 min, compared with the no drug group (P < 0.01).

Activation of fast sodium channels may determine the rapid frequency of the initial stages of ventricular fibrillation. The rapid fall in dominant frequency in lead II after fibrillation for 80s can be prevented by calcium channel blockade and may be due to intracellular accumulation of calcium.
The action of diazoxide and minoxidil sulphate on rat blood vessels: a comparison with cromakalim
Authors: Newgreen D.T. , Bray K.M. , McHarg A.D. , Weston A.H. , Duty S. , Brown B.S. , Kay P.B. , Edwards G. , Longmore J. , Southerton J.S.
Published: July 2012

The actions of diazoxide and minoxidil sulphate have been compared with those of cromakalim in rat aorta and portal vein.

Diazoxide and minoxidil sulphate hyperpolarized the rat portal vein in a similar manner to cromakalim.

Cromakalim, diazoxide and minoxidil sulphate increased 42K and 86Rb efflux from rat portal vein, although minoxidil sulphate had only a small effect on 86Rb efflux.

Cromakalim, diazoxide and minoxidil sulphate increased 42K efflux from rat aorta but only cromakalim and diazoxide increased 86Rb efflux from this tissue.

Glibenclamide inhibited the relaxant actions of cromakalim, diazoxide and minoxidil sulphate on rat aorta and the increase in 42K efflux produced by these agents in this tissue.

Diazoxide relaxed an 80 mm KCl‐induced contraction of rat aorta, whilst cromakalim and minoxidil sulphate were without effect.

Cromakalim, diazoxide and minoxidil sulphate had no effect on cyclic AMP or cyclic GMP concentrations in rat aorta.

It is concluded that diazoxide and minoxidil sulphate like cromakalim exhibit K+ channel opening properties in vascular smooth muscle. Diazoxide exerts an additional inhibitory action not related to the production of cyclic AMP or cyclic GMP. The action of minoxidil sulphate may be primarily located at a K+ channel which is relatively impermeable to 86Rb.
Co‐operation between interleukin‐1 and the fibrinolytic system in the degradation of collagen by articular chondrocytes
Authors: Cruwys S.C. , Davies D.E. , Pettipher E.R.
Published: July 2012

The interaction between interleukin 1 (IL‐1) and the fibrinolytic system in the control of collagen degradation by rabbit chondrocytes has been investigated in a tissue‐culture system where cells are grown on a 14C‐labelled collagen matrix.

Culture of rabbit chondrocytes in the presence of human recombinant IL‐1β at a concentration of 57 pm for 48 h led to the presence of procollagenase but not active collagenase in the medium. The latent collagenase could be activated by incubation with an organomercurial, aminophenylmercuric acetate (APMA).

Addition of IL‐1β to chondrocytes grown on a 14C‐labelled collagen matrix did not increase the degradation of the matrix compared to control over a 48 h period. However, in the presence of plasmin (200 μg ml−1) or plasminogen (100 μg ml−1), IL‐1β (57 pm) caused almost complete degradation of the collagen matrix. Plasmin or plasminogen alone caused only slight degradation of the collagen matrix.

Tissue inhibitor of metalloproteinases (TIMP) or the selective metalloproteinase inhibitor, SC44463, inhibited the degradation induced by IL‐1β and plasminogen in a concentration‐related manner and at concentrations that were correlated with inhibition of collagenase.

When concentrations of IL‐1β which caused only minimal degradation of the matrix in the presence of plasminogen were combined with fibrin (1 μg ml−1), there was almost total degradation of the matrix by 48 h.

These results indicate there is a synergistic interaction between IL‐1 and the fibrinolytic system in the degradation of collagen by rabbit chondrocytes in culture.
Temperature‐dependence of desensitization induced by acetylcholine and histamine in guinea‐pig ileal longitudinal muscle
Authors: Horio Shuhei , Shima Masanori , Ueda Haruyasu , Ishida Yukio
Published: July 2012

The effects of temperature on the time course of desensitization induced by acetylcholine and histamine, and on the recovery from desensitization were studied in the longitudinal muscle of the guinea‐pig ileum.

Self‐ and cross‐desensitization produced by acetylcholine (10−5m) occurred rapidly in the first 10 min of exposure to the agonist, with the same time course and the same degree of desensitization over the temperature range of 11°C to 31°C.

Self‐desensitization produced by histamine (10−5m) also occurred rapidly in the first 10 min of exposure to the agonist, and showed great temperature‐dependence, especially at 11°C and 21°C, but scarcely occurred at 6°C.

Cross‐desensitization produced by histamine developed gradually with time and showed a moderate temperature‐dependence between 11°C and 31°C, but scarcely occurred at 6°C.

The recovery processes from desensitization showed marked temperature‐dependence. Recovery was halted completely at 11°C.

These studies suggest that acetylcholine‐induced desensitization may be attributed to a single nonspecific mechanism. Histamine‐induced desensitization may be due to at least two mechanisms: it occurs in both a specific and non‐specific manner. Each of these desensitizations can be characterized by its unique temperature‐dependence.
Ketamine potentiates 5‐HT3 receptor‐mediated currents in rabbit nodose ganglion neurones
Authors: Peters John A. , Malone Hilary M. , Lambert Jeremy J.
Published: July 2012

The interaction of ketamine with the 5‐HT3 receptor of rabbit nodose ganglion neurones is described. Ketamine (3–30 μm) enhanced 5‐HT3 receptor‐mediated currents recorded under voltage‐clamp conditions. This action did not appear to be related to the known effect of ketamine of inhibiting 5‐HT uptake.
Temporal changes in the calcium‐force relation during histamine‐induced contractions of strips of the coronary artery of the pig
Authors: Hirano Katsuya , Kanaide Hideo , Abe Shimako , Nakamura Motoomi
Published: July 2012

We examined temporal changes in the relationship between cytosolic calcium concentrations ([Ca2+]i) and developed tension during histamine‐induced contractions of strips of the coronary artery of the pig, by making use of simultaneous measurements of fura‐2 fluorescence and force.

The relationship between [Ca2+]i and developed tension observed with cumulative applications of extracellular Ca2+ ([Ca2+]o), ranging from 0 mm to 10 mm, during 118 mm K+‐depolarization was similar to that observed in chemically skinned strips of the porcine coronary artery, as noted by other investigators. [Ca2+]i at 0 mm [Ca2+]o, at 50% of maximum, and at maximum tension development were 76 nm, 424 nm, and 3050 nm, respectively.

Cumulative applications of histamine induced dose‐dependent increases in [Ca2+]i and tension and the extent of tension for a given change in [Ca2+]i increased, i.e. greater effectiveness of [Ca2+]i‐tension relationship, than seen with K+‐depolarization.

When histamine 10−5 m was applied, [Ca2+]i abruptly rose and reached the first peak within several seconds. After a slight dip at 30 s, [Ca2+]i reached a second peak at 3 min, and then gradually declined. On the other hand, tension developed rapidly reached a maximum at 4 min, then gradually declined. The relation between [Ca2+]i and tension in the early, rising phase of contraction was similar to that obtained during depolarization. At the time of maximum tension development, the relation was greater than that observed during depolarization, which persisted in the phase of declining tension.

To examine the role of protein kinase C in the increased effectiveness of [Ca2+]i‐tension relation of histamine‐induced contractions, we used 1‐(5‐isoquinolinesulphonyl)‐2‐methylpiperazine (H‐7), as an inhibitor. Exposure of strips to H‐7, 10−5 m, reduced the effectiveness of [Ca2+]i‐tension relation toward the level observed during depolarization, while it had no effect on the [Ca2+]i‐tension relation in the early phase of contraction either in the presence or absence of extracellular Ca2+.

In intact smooth muscle of the coronary artery of the pig, the relationship between [Ca2+]i and developed tension varies during contraction. Histamine, a receptor‐mediated stimulus, induced a greater tension for a given change in [Ca2+]i during the steady state of contraction than did depolarization. The greater effectiveness of contraction, particularly in the later phase, seems to be mediated by activation of an H‐7‐sensitive mechanisms.
Presynaptic inhibition by neuropeptide Y in rat hippocampal slice in vitro is mediated by a Y2 receptor
Authors: Colmers William F. , Klapstein Gloria J. , Fournier Alain , St‐Pierre Serge , Treherne Kerri A.
Published: July 2012

The action of analogues and C‐terminal fragments of neuropeptide Y (NPY) was examined on excitatory synaptic transmission in area CA1 of the rat hippocampal slice in vitro, by use of intracellular and extracellular recordings, to determine by agonist profile the NPY receptor subtype mediating presynaptic inhibition.

Neither NPY, analogues nor fragments of NPY affected the passive or active properties of the postsynaptic CA1 pyramidal neurones, indicating their action is at a presynaptic site.

The full‐sequence analogues, peptide YY (PYY) and human NPY (hNPY), were equipotent with NPY at the presynaptic receptor, while desamido hNPY was without activity.

NPY2–36 was equipotent with NPY. Fragments as short as NPY13–36 were active, but gradually lost activity with decreasing length. NPY16–36 had no effect on extracellular field potentials, but still significantly inhibited excitatory postsynaptic potential amplitudes. Fragments shorter than NPY16–36 had no measurable effect on synaptic transmission.

The presynaptic NPY receptor in hippocampal CA1 therefore shares an identical agonist profile with the presynaptic Y2 receptor at the peripheral sympathetic neuroeffector junction.
Actions of dipyridamole on endogenous and exogenous noradrenaline in the dog mesenteric vein
Authors: Li Yajun , Zhang Guoliang , Suzuki Hikaru , Kuriyama Hirosi
Published: July 2012

In the isolated mesenteric vein of the dog, dipyridamole inhibited both the excitatory junction potential (e.j.p.) and the slow depolarization evoked by perivascular nerve stimulation, to 60–70% of control, with no change in the postjunctional membrane potential. These inhibitory actions of dipyridamole were not modified by 8‐phenyltheophylline or phentolamine, suggesting that the inhibition did not involve either the actions of endogenous adenosine or the prejunctional α‐autoregulation mechanism.

Dipyridamole did not produce any detectable effects on either the facilitation process of the e.j.ps or the postjunctional membrane depolarization produced by exogenously applied noradrenaline (NA).

Dipyridamole reduced the outflow of both the NA and the 3,4‐dihydroxyphenylglycol (DOPEG) evoked by perivascular nerve stimulation to below 10% of control, the effect being much greater than that of exogenously applied adenosine (to about 90% of the control).

Exogenously‐added NA was degraded by incubation with a segment of the vein. Dipyridamole itself produced degradation of NA and accelerated the NA‐induced degradation. By contrast, pyrogallol, but not pargyline or imipramine, prevented the NA‐induced degradation.

It is suggested that dipyridamole degrades NA directly, and also indirectly through activation of catechol‐O‐methyl transferase, with no alteration of the activity of monoamine oxidase or of the uptake mechanisms of NA into nerve terminals.
Ion transport in cultured epithelia from human sweat glands: comparison of normal and cystic fibrosis tissues
Authors: Brayden D.J. , Pickles R.J. , Cuthbert A.W.
Published: July 2012

Cultured epithelia derived from whole human sweat glands, isolated secretory coils, isolated reabsorptive ducts and whole glands from cystic fibrosis (CF) subjects have been used to examine drug sensitivity by use of short circuit current recording.

Short circuit current increases were observed with lysylbradykinin, carbachol and histamine in epithelia of different origins. All responses were due to stimulation of electrogenic sodium absorption, evidenced by the inhibition of these responses by amiloride. The latter also abolished the basal current. The terpenes, thapsigargin and forskolin had no effect on transport.

The stimulation of a sodium current by agonists was dependent upon calcium, responses being inhibited by lanthanum ions and EGTA. Further A23187 induced a sodium current.

Pronounced oscillations in the sodium currents were a feature of the responses, implying synchronous, regulated cell activity.

Forskolin produced a ten fold increase in adenylate cyclase activity. All agonists listed in 2 except forskolin caused an increase in intracellular calcium [Ca]i, [Ca]i responses in CF cells were not different from those of normal cells, except with thapsigargin where the responses were smaller.

It is concluded that in culture, cells develop ductal characteristics, whether derived from normal or CF glands, coils or ducts. An increase in [Ca]i followed by activation of calcium‐sensitive potassium channels and apical membrane hyperpolarization may be the major mechanism for increasing sodium influx.
Evidence that part of the NANC relaxant response of guinea‐pig trachea to electrical field stimulation is mediated by nitric oxide
Authors: Li Chun Guang , Rand Michael J.
Published: July 2012

The nitric oxide (NO) synthesis inhibitors NG‐monomethyl l‐arginine (l‐NMMA) and l‐nitroarginine methyl ester (l‐NAME) reduced relaxations of guinea‐pig tracheal smooth muscle elicited by stimulation of intramural non‐adrenergic, non‐cholinergic (NANC) nerves, but d‐NMMA had no effect. l‐NAME was 10–30 times more potent than l‐NMMA. Relaxations produced by sodium nitroprusside and vasoactive intestinal polypeptide (VIP) were not affected by l‐NMMA or l‐NAME.

The inhibitory effect of l‐NMMA on NANC‐mediated relaxations was partially reversed by l‐arginine but was not affected by d‐arginine.

VIP antibody and α‐chymotrypsin abolished or greatly reduced the relaxant action of VIP and reduced relaxations elicited by stimulation of NANC nerves; the residual NANC relaxation was further reduced by l‐NAME.

The results suggest that NO and VIP are mediators of NANC‐induced relaxations of guinea‐pig tracheal smooth muscle. We propose the term ‘nitrergic’ to describe transmission processes which are mediated by NO.
Protection induced by cholecystokinin‐8 (CCK‐8) in ethanol‐induced gastric lesions is mediated via vagal capsaicin‐sensitive fibres and CCKA receptors
Authors: Evangelista S. , Maggi C.A.
Published: July 2012

We have investigated the effect of intravenous injection of cholecystokinin‐8 (CCK‐8) and other peptides on gastric lesion formation in response to an intragastric perfusion with 25% ethanol in rats anaesthetized with urethane.

Intravenous injection of CCK‐8 (50–100 nmol kg−1), but not bombesin (1–100 nmol kg−1), calcitonin gene‐related peptide (1–50 nmol kg−1), neurokinin A (1 μmol kg−1) or substance P (100 nmol kg−1), induced protection against gastric haemorrhagic lesions produced by ethanol.

The CCKA‐antagonist L‐364,718 (2.45 μmol kg−1, i.v.) increased the lesion index induced by ethanol and reversed the protective effect of CCK‐8 (50 nmol kg−1, i.v.). The CCKB‐antagonist L‐365,260 (5 μmol kg−1, i.v.) and a lower dose of L‐364,718 (0.25 μmol kg−1, i.v.) were ineffective.

The gastric protective effects afforded by CCK‐8 (50 nmol kg−1, i.v.) were not observed in vagotomized‐rats and were reduced by capsaicin pretreatment. In capsaicin‐pretreated rats there was a worsening of gastric lesions induced by ethanol‐perfusion as compared to those observed in vehicle‐pretreated rats.

These results demonstrate that the mucosal protective effect of CCK‐8 involves, at least in part, the activation of CCKA‐receptors and is mediated by vagal capsaicin‐sensitive fibres.
Phorbol dibutyrate enhances local anaesthetic action
Authors: Austin S. , McGivern J. , Scholfield C.N.
Published: July 2012

Synaptically‐evoked field responses were elicited by stimulation of the lateral olfactory tract of rat olfactory cortex slices maintained in vitro.

Various concentrations of lignocaine (5–500 μm) were applied to the solution bathing the slices. These produced dose‐dependent depressions of the synaptically‐evoked potential over the concentration range 20–500 μm. The responses completely recovered on washing out the lignocaine. Similar depressions were also noted for procaine (100–1000 μm).

In the 47 slices tested, application of β‐phorbol 12, 13‐dibutyrate (1 μm) increased the amplitude of the synaptic response (from 0.99 ± 0.05 to 1.36 ± 0.06 mV). β‐Phorbol 13‐monbutyrate (1 μm) had no effect.

In the presence of phorbol dibutyrate the depressant effect of lignocaine was increased: the EC50 changed from 91 ± 10 to 24 ± 2 μm (a mean potency increase of 3.47 ± 0.14). A similar increase in potency for procaine was observed with phorbol dibutyrate (from 264 ± 23 to 49 ± 9 μm: a 5.49 ± 0.82 increase in potency). If the tissue was pre‐equilibrated in a concentration of lignocaine which produced a 60–80% depression, addition of phorbol ester caused a complete abolition of the evoked potential.

β‐Phorbol 13‐monobutyrate (1 μm) had no effect on the potency of lignocaine.

The Na and K currents generating the action potential in the presynaptic nerve terminals were unaffected by phorbol dibutyrate. The depressant effect of lignocaine on these currents was not modified by phorbol dibutyrate.

The potentiation of lignocaine could not be accounted for by membrane depolarization or by non‐specific actions of phorbol dibutyrate, and was distinct from the action on transmitter release. Therefore, it seems likely that protein kinase C activation was responsible for the modified action of lignocaine, although the mechanism for this is unclear.
Relation between adrenergic neurogenic contraction and α1‐adrenoceptor subtypes in dog mesenteric and carotid arteries and rabbit carotid arteries
Authors: Muramatsu Ikunobu
Published: July 2012

We examined the distribution of α1‐adrenoceptor subtypes and their relation to adrenergic neurogenic contraction induced by electrical transmural stimulation in the dog mesenteric and carotid arteries and the rabbit carotid artery.

In the dog mesenteric artery, contraction to noradrenaline was competitively inhibited by HV723 (pKB = 9.37) and prazosin (pKB = 8.40). Pretreatment with chlorethylclonidine (CEC) slightly attenuated only the contractions induced by low concentrations of noradrenaline. Contraction induced by electrical transmural stimulation was inhibited at lower concentrations of HV723 than of prazosin.

In the dog carotid artery, contraction to noradrenaline was inhibited with higher affinity by prazosin (pKB = 9.82) than by HV723 (pKB = 8.47). Prozosin was also more potent than HV723 in inhibiting the contraction to electrical stimulation. Pretreatment with CEC markedly attenuated or abolished contraction to noradrenaline and electrical stimulation.

In the rabbit carotid artery, prazosin inhibited noradrenaline‐induced contraction biphasically (pKB = 9.91 and 8.60). After CEC pretreatment, contraction to noradrenaline was attenuated moderately and the high affinity site for prazosin was abolished. HV723 competitively inhibited the noradrenaline response with a similar pKB value (approximately 8.5) regardless of CEC treatment. Contraction to electrical stimulation was inhibited by prazosin more effectively than by HV723 in preparations not treated with CEC, while it was equipotently inhibited by both antagonists in CEC‐treated preparations.

These results suggest that the contractions induced by endogenous and exogenous noradrenaline are mediated through the same subtypes of α1‐adrenoceptor distributed in each artery; according to our recent subclassification: α1N subtype in the dog mesenteric artery, α1H subtype in the dog carotid artery and α1H and α1L subtypes in the rabbit carotid artery. Different susceptibility to α1‐adrenoceptor antagonists of sympathetic adrenergic responses in various blood vessels may be related to heterogeneous involvement of distinct α1‐adrenoceptor subtypes in the sympathetic response.
Existence of two components in the tonic contraction of rat aorta mediated by α1‐adrenoceptor activation
Authors: Nishimura Kanami , Ota Mikio , Ito Katsuaki
Published: July 2012

The mechanisms involved in the contraction of rat aorta induced by the activation of α1‐adrenoceptors were studied. Phenylephrine induced a phasic contraction in the aorta incubated in Ca2+‐free medium containing 0.5 mm EGTA. Subsequent addition of Ca2+ induced a tonic contraction, which exhibited a stepwise development, an initial phase lasting 3 to 6 min (tonic‐I) followed by a superimposing second phase (tonic‐II).

2‐Nitro‐4‐carboxyphenyl‐N,N‐diphenylcarbamate, which has been reported to inhibit phosphatidylinositol turnover, and H‐7, a protein kinase C inhibitor, inhibited the tonic‐I phase more effectively than the tonic‐II phase. On the other hand, the tonic‐II phase was more sensitive to nifedipine and cromakalim.

The rate of 45Ca2+ influx during the tonic‐I phase in phenylephrine‐treated muscles was not different from that in untreated muscles, while that during the tonic‐II phase was significantly greater. Nifedipine inhibited the increased 45Ca2+ influx during the tonic‐II phase, whereas H‐7 did not affect the uptake during either phase.

These results suggest that the tonic contraction of rat aorta following α1‐adrenoceptor activation involves two different mechanisms: one is directly related to consequences of the polyphosphoinositide cascade, probably to protein kinase C, and the other dependent on Ca2+ influx through nifedipine‐sensitive Ca2+ channels.
Inhibitory effects of BAY u3405 on prostanoid‐induced contractions in human isolated bronchial and pulmonary arterial muscle preparations
Authors: Norel X. , Labat C. , Gardiner P.J. , Brink C.
Published: July 2012

The thromboxane‐mimetic, U46619, was a more potent contractile agonist than prostaglandin D2 (PGD2), PGF2α or histamine in human isolated bronchial and pulmonary arterial muscle preparations.

Human isolated proximal bronchial muscles were less sensitive to contractile agents than distal bronchial preparations. However, the former tissues developed a greater contractile force (Emax) when compared with results obtained in the latter tissues.

BAY u3405 attenuated the contractions induced by U46619, PGF2α and PGD2 in both human isolated bronchial and pulmonary arterial muscle preparations.

BAY u3405 did not alter histamine concentration‐effect curves nor the relaxation induced by Butaprost (TR4979) in human isolated bronchial muscle preparations. In addition BAY u3405 did not modify the relaxation induced by PGI2 in isolated pulmonary arterial muscle preparations.

The contractions induced by different prostaglandins were blocked by BAY u3405, suggesting a common functional site for these agents found both on human bronchial and pulmonary arterial muscles.
Contraction of vascular smooth muscle induced by phorbol 12, 13 dibutyrate in human and rat pulmonary arteries
Authors: Savineau Jean‐Pierre , Marthan Roger , Crevel Huguette
Published: July 2012

The effect of phorbol 12,13 dibutyrate (PDB) on vascular tone was studied in both human and rat isolated pulmonary arterial strips (HPA and RPA, respectively).

PDB (1 nm to 2 μm) produced slowly developing, sustained and concentration‐dependent contractions in HPA (mean EC50 = 3.5 nm, n = 5) and RPA (mean EC50 = 120 nm, n = 5). The maximal response was 185.6 ± 25% and 207 ± 27.5% (n = 5) of that induced by K+‐rich (80 mm) solution, and 223 ± 34.5% and 176.5 ± 38.6% of the noradrenaline (10 μm)‐induced contraction in HPA and RPA, respectively.

PDB‐induced contractions were not altered either by the presence of atropine (10 μm), propranolol (5 μm), phentolamine (5 μm) or tetrodotoxin (10 μm) in the bathing solution, or by the removal of endothelium from pulmonary arteries.

In HPA, the amplitude of PDB‐induced contractions was significantly reduced by removal of external calcium ions, addition of verapamil (10 μm) or trifluoperazine (TFP, 5 μm) and significantly increased by Bay K 8644 (0.5 μm). In contrast, in RPA, calcium‐free solution and verapamil had only a moderate effect on the maximal PDB‐induced contraction (approximately 20% reduction), whereas Bay K 8644 and TFP had no significant effect. In both HPA and RPA, PDB‐contractions in calcium‐free solutions were not modified by ryanodine (25 μm) or by 8‐(N,N diethylamino)octyl‐3,4,5, trimethoxybenzoate hydrochloride (TMB‐8, 50 μm).

PDB‐induced contractions were inhibited by protein kinase C (PKC) antagonists. The maximal response was decreased by 60 ± 10.5% and 35 ± 11.5% (n = 5) by 1‐(5‐isoquinolinesulphonyl)‐2‐methyl‐piperazine (H7, 50 μm), 70.5 ± 12.2% and 56 ± 18% (n = 5) by phloretin (100 μm) and 80.7 ± 8.4% and 71 ± 14% (n = 5) by staurosporine (25 nm) in HPA and RPA, respectively.

Long term treatment (15–20 h) of arterial strips with phorbol esters (phorbol 12,13 didecanoate, or PDB) abolished the contractile response to subsequent addition of PDB.

These results show that PDB is a potent vasoconstrictor agent in human and rat pulmonary arteries. Unlike the rat, part of the PDB response depends on calcium influx in human preparations. PDB action appears mainly mediated by the activation of protein kinase C. PKC could thus play a major role in the control of vascular pulmonary reactivity.
Sequential release of tumour necrosis factor, platelet activating factor and eicosanoids during endotoxin shock in anaesthetized pigs; protective effects of indomethacin
Authors: Mózes Tibor , Zijlstra Freek J. , Heiligers Jan P.C. , Tak Corné J.A.M. , Ben‐Efraim Shlomo , Bonta Iván L. , Saxena Pramod R.
Published: July 2012

The effects of indomethacin were investigated on haemodynamics, haematological and blood glucose values, and the release of tumour necrosis factor (TNF), platelet activating factor (PAF) and eicosanoids in anaesthetized pigs receiving 5 μg kg−1 E. coli lipopolysaccharide (LPS) over 60 min into the superior mesenteric artery. The animals were observed for an additional period of 2 h after the termination of LPS infusion.

Eight of the 17 animals infused with LPS and not treated with indomethacin died within 30 min after the beginning of LPS infusion (non‐survivors), while the other 9 survived the experimental period of 3 h though in a state of shock (survivors).

No alterations were observed in plasma concentrations of PAF and eicosanoids (thromboxane B2 (TXB2), 6‐keto prostaglandin F1α (6‐keto PGF1α) and leukotriene B4 (LTB4)) in non‐survivors. However, a marked increase was detected in TNF release. A significant, though transient, increase in concentrations of PAF, TNF and eicosanoids occurred in the survivors. The peak in the concentrations of PAF and TXB2 preceded the maximum in TNF values in survivors.

Another group of 7 LPS‐infused pigs was treated with indomethacin (2 mg kg−1, i.v. bolus 60 min before the start of LPS infusion, followed by a continuous infusion of 3 mg kg−1 h−1). This treatment prevented death and shock despite the high concentrations of circulating TNF and PAF. Concentrations of cyclo‐oxygenase enzyme products were reduced, whereas LTB4 release was not affected. The effect of indomethacin on haemodynamic changes occurred earlier than on cyclo‐oxygenase products.

In another group of 6 pigs indomethacin (2 mg kg−1, i.v.) was given 20–25 min after the start of LPS infusion at which time mean arterial blood pressure (MABP) had decreased below 40 mmHg indicating imminent death. This indomethacin treatment immediately reversed the hypotension, restored the organ perfusion, delayed the haemoconcentration and thrombocytopenia and prevented death. However, TNF and PAF concentrations remained elevated. Concentrations of cyclo‐oxygenase products studied were reduced by the end of the observation period, whereas LTB4 production was unaffected.

The decrease in MABP induced by exogenous PAF was temporarily prevented by indomethacin.

These data indicate that the beneficial effect of indomethacin in LPS‐induced septic shock is related to cyclo‐oxygenase inhibition as well as to a direct vasoconstrictor property of the drug.
Effects of flecainide on isolated vascular smooth muscles of rat
Authors: Pérez‐Vizcaino Francisco , Duarte Juan , Tamargo Juan
Published: July 2012

The inhibitory effects of flecainide were studied on contractile responses in rat isolated aortae and caudal artery and on spontaneous mechanical activity in portal vein segments.

In rat isolated aorta flecainide, 10−6 m‐5 × 10−4 m, inhibited in a dose‐dependent manner the contractile responses induced by high K (80 mm) and noradrenaline (NA, 10−5 m). These inhibitory actions were observed when flecainide was added before or after the induced contractions and were similar in aortae with or without endothelium.

Contractile responses induced by addition of Ca to Ca‐free high‐K solution were also dose‐dependently inhibited by flecainide (IC50 = 2.5 ± 0.3 × 10−5 m). Moreover, flecainide inhibited the contractile responses elicited by NA in rings incubated in Ca‐free solution.

Flecainide also inhibited the spontaneous mechanical activity in portal vein segments (IC50 = 6.5 ± 0.9 × 10−5 m).

Flecainide, 10−4 m, inhibited 45Ca uptake stimulated by high K or NA without altering 45Ca uptake in resting aortae.

These results indicated that in rat isolated aortae, caudal arteries and portal veins, flecainide inhibited Ca entry through voltage‐operated channels and NA‐induced Ca uptake as well as Ca release from intracellular stores, thus decreasing the availability of intracellular free Ca required for vascular smooth muscle contraction.
Contraction of rat thoracic aorta strips by endothelin‐1 in the absence of extracellular Ca2+
Authors: Itoh Hiroo , Higuchi Haruyuki , Hiraoka Naoto , Ito Masaaki , Konishi Tokuji , Nakano Takeshi , Lederis Karl
Published: July 2012

Endothelin‐1 (ET‐1) caused a concentration‐dependent contraction of helical strips from rat thoracic aorta in the absence of extracellular Ca2+. The Ca2+‐depleted muscle strips, prepared by three repeated applications of 10−2 m caffeine or 10−6 m noradrenaline in Ca2+‐free buffer, were contracted by 10−8 m ET‐1 in the same manner as non‐treated strips.

In the absence of extracellular Ca2+, 10−7 m phorbol 12‐myristate 13‐acetate (PMA), an activator of protein kinase C, induced a small but sustained contraction of the rat thoracic aorta strips within 60 min. Preincubation of the strips with 10−7 m PMA for 60 min in Ca2+‐free buffer, did not affect the 10−8 m ET‐1‐induced contraction, but decreased the 5 × 10−8 m phorbol 12,13‐dibutyrate (PDB)‐, or the 10−7 m PMA‐induced contraction, and potentiated the contraction induced by 10−8 m urotensin II. Preincubation with 10−8 m ET‐1 (which induced maximum contraction) for 25 min in Ca2+‐free buffer did not change the subsequent contraction induced by PMA (10−7 m) or urotensin II (10−8 m) but gave a somewhat lower maximum tension than in non‐treated strips.

Calyculin‐A, a potent inhibitor of phosphatase, also induced a contraction of the Ca2+‐depleted muscle strips in Ca2+‐free buffer. Preincubation of the strips with ET‐1 (10−8 m) or PMA (10−7 m) decreased the calyculin‐A (3 × 10−8 m)‐induced contraction.

These results suggest that ET‐1 may induce phosphorylation of an unknown protein either without an increase in myoplasmic Ca2+ concentration or, alternatively, with mobilization of intracellular Ca2+ from noradrenaline‐ and caffeine‐insensitive Ca2+ sources, through a mechanism different from that of phorbol ester.
Effects of Org 7797 on early, late and inducible arrythmias following coronary artery occlusion in rats and dogs
Authors: Winslow E. , Campbell J.K. , Barron E. , Marshall R.J. , Muir A.W.
Published: July 2012

The class Ic steroidal antiarrhythmic agent, Org 7797, was compared with two other Ic agents, flecainide and propafenone for intravenous activity against ischaemia‐related cardiac arrhythmias and for electrophysiological actions in vivo. In addition the haemodynamic effects of Org 7797 were assessed in greyhounds.

Org 7797 (0.5 mg kg−1) significantly reduced the expected incidence of early ischaemia‐induced ventricular fibrillation (VF) in rats and greyhound dogs and at doses of 0.5–1.0 mg kg−1 antagonized reperfusion‐induced arrhythmias. Comparative studies in rats showed Org 7797 to be 2–4 times more potent than flecainide or propafenone.

Org 7797 (0.5 mg kg−1) slowed intracardiac conduction in anaesthetized beagles and again was at least 2–4 times more potent than flecainide or propafenone.

Org 7797 (0.5 and 2.0 mg kg−1), flecainide (1.0 and 2.0 mg kg−1) or propafenone (0.5 and 2.0 mg kg−1), did not significantly prevent induction of tachyarrhythmias (VT) in dogs with 5–6 day old myocardial infarcts although all 3 drugs appeared to prevent induced VF. All 3 drugs (notably fecainide) did however reduce the VT rate.

All 3 drugs (1–2 mg kg−1) suppressed spontaneous tachyarrhythmias in conscious beagle dogs with 1–2 day old infarcts. Propafenone was the least effective.

In an antifibrillatory dose (0.5 mg kg−1), the major haemodynamic effect of Org 7797 was a 10% increase in peripheral vascular resistance. Stroke volume, cardiac output and coronary blood flow were unchanged. In therapeutic doses, Org 7797 was also less negatively chronotropic than flecainide.

It was concluded that Org 7797 is a potent antifibrillatory agent which is haemodynamically well tolerated. Higher doses are required to suppress late ischaemia‐induced tachyarrhythmias which suggest that its antifibrillatory effects are the consequence of an action other than, or in addition to, sodium channel block.
Staurosporine inhibits the extent of acetylcholine receptor recovery from carbachol‐induced desensitization in snake twitch fibres
Authors: Hardwick Jean C. , Coniglio Lisa M. , Parsons Rodney L.
Published: July 2012

The effect of the protein kinase inhibitor, staurosporine, on the extent and time course of recovery following carbachol‐induced desensitization was studied in snake twitch‐muscle fibres maintained in an isotonic potassium propionate solution and voltage‐clamped to +30mV.

Pretreatment with staurosporine (0.5 μm) decreased the extent of recovery of spontaneous miniature endplate current (m.e.p.c.) amplitudes following desensitization by a sustained application of 540 μm carbachol. Recovery was inhibited by approximately 50% without altering the time course of m.e.p.c. recovery.

Staurosporine also produced a concentration‐dependent (10 nm to 0.5 μm) decrease in the amplitude of a second carbachol‐induced current, following a wash period, as compared to the amplitude of the current produced by the initial carbachol application. Pretreatment with 0.5 μm K252a, another wide spectrum protein kinase inhibitor, also decreased the extent of recovery of the response to a second carbachol application following desensitization.

Staurosporine pretreatment (0.5 μm) had no effect on either the kinetics of receptor‐channel gating or the initial endplate sensitivity to agonist. This was determined by comparing the amplitude of the carbachol (540 μm)‐induced currents and the amplitude and decay rate of m.e.p.cs in control and staurosporine‐treated fibres.

Staurosporine had no effect on the time course of desensitization onset produced during the initial application of 540 μm carbachol or the depth of desensitization produced by the end of a 2–3 min exposure to 540 μm carbachol.

Elevation of the external calcium concentration from 1 to 10 mm during the 540 μm carbachol application completely antagonized the decreased extent of recovery of m.e.p.c. amplitude produced by pretreatment with 0.5 μm staurosporine.

We suggest that phosphorylation of a population of acetylcholine receptors is required for complete recovery from desensitization, and that staurosporine inhibits the protein kinases responsible for this phosphorylation.

We further propose that a transient increase in intracellular calcium, produced by an increase in calcium influx through agonist‐activated endplate channels, stimulates additional protein kinase activity, which in turn, antagonizes the effect of staurosporine‐treatment on recovery.
Cromakalim (BRL 34915) counteracts the epileptiform activity elicited by diltiazem and verapamil in rats
Authors: Popoli P. , Pezzola A. , Sagratella S. , Zeng Y.C. , de Carolis A. Scotti
Published: July 2012

The effects of BRL 34915 (cromakalim), a potassium channel opener, have been tested on the epileptiform activity elicited by high doses/concentrations of some calcium antagonists in in vivo (diltiazem) and in vitro (diltiazem and verapamil) experiments in rats.

Diltiazem (150–300 mg kg−1, i.p.) induced behavioural and electroencephalographic (EEG) seizures that were completely prevented by cromakalim (10 nmol/10μl, i.c.v.). Whereas, pentobarbitone (5–10 mg kg−1, i.p.) only prevented the behavioural component of the seizures.

In hippocampal slices, verapamil (1.5–2.0 mm) produced, within 30–60 min of perfusion, a CAl epileptiform bursting in 80% of the experiments. This epileptiform activity was prevented by the cromakalim concentration (50 μm) that did not affect the control CAl synaptic transmission per se. Pentobarbitone also prevented verapamil‐induced epileptiform bursting only at the concentration (100 μm) that also reduced control CAl synaptic transmission.

Diltiazem (1.5 mm) produced a biphasic excitatory‐depressant effect within 60 min of perfusion. A CAl epileptiform bursting appeared in 100% of the experiments within 30 min of perfusion. These excitatory effects were followed by a depression phase, characterized by a reduction of the magnitude of CAl excitatory postsynaptic potentials (e.p.s.ps) and population spike.

The diltiazem‐induced epileptiform bursting was prevented by cromakalim at a concentration (50 μm) that did not affect the control CAl synaptic transmission per se. Pentobarbitone also prevented the diltiazem‐induced epileptiform bursting only at a concentration (100 μm) that also reduced the control CAl synaptic transmission. Both cromakalim (50 μm) and pentobarbitone (100 μm) failed to affect the depressant effects of diltiazem on CAl hippocampal area. On the contrary, high (3.3 mm) calcium solutions prevented both the excitatory and the depressant effects of 1.5 mm diltiazem within 60 min.

These data indicate an involvement of potassium currents in the epileptiform activity elicited by high doses of diltiazem and verapamil.