bluuebunny/crossref_metadata_2025 huggingface dataset:
ELECTROPHYSIOLOGICAL EFFECTS OF IMPRAMINE ON BOVINE VENTRICULAR MUSCLE AND PURKINJE FIBRES
Authors: RODRIGUEZ SERGIA , TAMARGO JUAN
Published: July 2012

The effect of imipramine in concentrations between 0.01 μm and 50 μm has been studied on bovine Purkinje fibres and ventricular muscle transmembrane potentials.

In electrically stimulated fibres, imipramine had no effect on the resting membrane potential, but decreased the action potential amplitude, overshoot and maximum rate of depolarization (Vmax).

In Purkinje fibres, imipramine also decreased the conduction velocity and shifted the membrane responsiveness and recovery time curves downward and to the right.

In both Purkinje fibres and ventricular muscle, imipramine decreased the amplitude of phase 2 and prolonged phase 3. In Purkinje fibres, imipramine did not alter the action potential duration (APD) but prolonged the effective refractory period (ERP). In ventricular muscle, at concentrations higher than 1 μm imipramine shortened both the APD and the ERP and made the ERP long as compared to APD.

Imipramine decreased the slope of phase 4 diastolic depolarization in spontaneously beating Purkinje fibres.

These properties of imipramine are quite similar to those of quinidine or procainamide (class 1 antiarrhythmics). The mechanisms responsible for the cardiac effect of imipramine are discussed.
INFLUENCE OF TRACHEAL CONTRACTION ON RELAXANT EFFECTS in vitro OF THEOPHYLLINE AND ISOPRENALINE
Authors: KARLSSON J.‐A. , PERSSON C.G.A.
Published: July 2012

Relaxation by (−)‐isoprenaline (Iso) and theophylline (Theo) was measured in guinea‐pig isolated trachea, in the presence or absence of carbachol

With basal tone or with carbachol at a concentration of 5.4 × 10−7M, causing 70% maximal contraction, Iso and Theo relaxed the trachea to the same extent

With carbachol concentrations of 5.4×10−6M and 5.4×10−5M (96% and 100% maximal contractions) Iso caused no more than 63% and 34%, respectively, of the maximum relaxation to Theo

When calculated at 25% of the maximum Theo relaxation, the Iso/Theo potency ratio was gradually reduced from 14, 160 when evaluated at basal tone to 1, 560 at the highest carbachol concentration

In combination, at their maximally effective concentrations, Theo and Iso produced no larger a relaxation than did Theo alone

At the two highest concentrations of carbachol, concentration‐response curves to Theo were virtually superimposable whether determined in the absence or the presence of Iso at its maximally effective concentration. 7 It is concluded that Theo causes a greater relaxation of highly contracted tracheal muscle than Iso.
EVIDENCE FOR AN ACTION OF MORPHINE AND THE ENKEPHALINS ON SENSORY NERVE ENDINGS IN THE MOUSE PERITONEUM
Authors: BENTLEY G.A. , NEWTON S.H. , STARR JENNIFER
Published: July 2012

A modification of the abdominal constriction test in mice has been developed, and used to study the antinociceptive effects of morphine and several related drugs. In most experiments, acetic acid (0.6% i.p.) was used as the nociceptive stimulus, and in a few cases, acetylcholine (3.2mg/kgi.p.) was used. When the abdominal constriction response had reached a maximum, the drugs under test were given intraperitoneally, and their ability to decrease the number of abdominal constrictions was determined, beginning immediately after its administration. The aim of this study was to investigate the possibility that morphine and its congeners may produce an antinociceptive effect by an action within the peritoneum.

It was found that morphine was an extremely potent antinociceptive agent in this modified test, with an ID50 of 5.4 × 10−9 mol/kg (1.54 μg/kg). Codeine and pentazocine were about 40 times less active and oxymorphine was about twice as potent as morphine. Met‐ and Leu‐enkephalin were also potent but their action diminished very rapidly with time. Ketocyclazocine was the most potent substance tested, and had an ID50 value of 1.26 × 1010 mol/kg (0.036 μg/kg). All the drugs tested produced their maximal effect within 1 or 2 min of administration.

Pretreatment of the mice with naloxone caused a dose‐dependent shift to the right of the dose‐response curve to morphine. The pAx plot was linear over part of the range, with a slope of − 1.02 and the ‘apparent pA2’ value was 6.14. Naloxone was much less effective in antagonizing Met‐enkephalin, and caused a slight potentiation of ketocyclazocine and pentazocine and of cocaine, which was used for comparison.

Pretreatment of mice with morphine, 3 h earlier, caused a marked tolerance to a subsequent dose of morphine, and a potentiation of the antagonist potency of naloxone. However, there was little cross‐tolerance between morphine and Leu‐enkephalin.

It is concluded that morphine and its congeners can produce an antinociceptive effect by an action within the mouse peritoneum, presumably by interacting with one or more types of opioid receptors which may be situated on sensory nerve endings.
A STUDY ON THE INTERACTION OF CROTAPOTIN WITH CROTOXIN PHOSPHOLIPASE A2, NOTEXIN AND OTHER PRESYNAPTIC NEUROTOXINS
Authors: CHANG C.C. , SU M.J.
Published: July 2012

Crotapotin, the acidic subunit of crotoxin, greatly potentiated the presynaptic effect of isolated basic phospholipase A (PLA) of crotoxin in both mouse diaphragm and chick biventer cervicis muscles whereas the myotoxic effect was not affected significantly.

In contrast to crotoxin PLA, the presynaptic effects of notexin and notechis‐5, self‐active single chain toxins, were antagonized by crotapotin while actions of β‐bungarotoxin were not affected.

By assaying PLA activity, crotoxin PLA was found to be unstable in physiological salt solution, especially when in contact with muscle, due to massive non‐specific binding to and destruction by the muscle.

The decline of crotoxin PLA was greatly reduced by the presence of crotapotin but not by another acidic protein, volvatoxin A2, or heparin.

Notechis‐5 was found to be stable even when in the presence of muscles.

[3H]‐acetylated crotoxin PLA, which retained about 40% of its original enzyme and presynaptic blocking activities, also bound rapidly to the mouse diaphragm on incubation and this binding was greatly hindered by the simultaneous addition of crotapotin.

The prevention of binding of crotoxin PLA by crotapotin occurred mostly at those sites where the binding was easily dissociable on washing. No antagonism of binding occurred at the firmly binding site.

The binding of [3H]‐acetylated crotapotin was much less than that of crotoxin PLA, and interestingly, the binding was increased by the latter, suggesting that crotapotin may be first bound to the diaphragm together with crotoxin PLA.

No specific binding at the endplate zone was found either for crotoxin PLA or for crotapotin.

It is concluded that crotapotin potentiates the presynaptic effect of crotoxin PLA by curtailing its non‐specific affinity with muscles, minimizing its dispersal and destruction en route to the nerve terminal, but not by acting as an affinity probe for the nerve terminal.
LEUKOTRIENES C4 AND D4 INDUCE PROSTAGLANDIN AND THROMBOXANE RELEASE FROM RAT PERITONEAL MACROPHAGES
Authors: FEUERSTEIN NILI , FOEGH MARIE , RAMWELL PETER W.
Published: July 2012

The present study examined the effect of leukotrienes C4 and D4, the products of the 5′ lipoxygenase pathway on prostaglandins and thromboxane release from rat peritoneal macrophages. Incubation of rat peritoneal macrophages with leukotrienes C4 and D4 enhanced the release of prostaglandin E2 (PGE2), 6‐keto PGF1α and thromboxane B2 (TxB2) in a dose‐dependent manner. The increase of PGE2 was more pronounced than that of 6‐keto‐PGF1α and TxB2. Lipopolysaccharide, a known stimulator of these cells elicited a similar pattern of increase of the arachidonate metabolites assayed. These results suggest that leukotrienes C4 and D4 are potential activators of macrophages. Since leukotrienes C4 and D4 are produced by these cells, it is suggested that endogenous leukotrienes may be involved in activation of macrophages.
α‐ADRENOCEPTORS CAN MEDIATE CHRONOTROPIC RESPONSES IN THE RAT HEART
Authors: FLAVAHAN N.A. , McGRATH J.C.
Published: July 2012

In the pithed rat, amidephrine, a ‘selective’ α1‐adrenoceptor agonist, evokes a positive chronotropic response. This response can be antagonized by prazosin but not by propranolol or by rauwolscine. Similarly, part of the chronotropic response to cardioaccelerator nerve stimulation is resistant to blockade by propranolol but is sensitive to prazosin or WB4101. We conclude that α1‐adrenoceptors can mediate a chronotropic response in the rat heart either to exogenous agonists or to the endogenous neurotransmitter noradrenaline.
β‐ADRENOCEPTOR AGONISTS ENHANCE 5‐HYDROXYTRYPTAMINE‐MEDIATED BEHAVIOURAL RESPONSES
Authors: COWEN P.J. , GRAHAME‐SMITH D.G. , GREEN A.R. , HEAL D.J.
Published: July 2012

The β‐adrenoceptor agonists, salbutamol, terbutaline and clenbuterol, were investigated for their effect on 5‐hydroxytryptamine‐mediated (5‐HT) hyperactivity.

The lipophilic β‐adrenoceptor agonist, clenbuterol (5 mg/kg) enhanced the behaviours induced by quipazine (25 mg/kg), including headweaving, forepaw treading and hind‐limb abduction and thus increased automated activity recording. Clenbuterol (5 mg/kg) also enhanced the hyperactivity syndrome produced by the 5‐HT agonist, 5‐methoxy N,N‐dimethyltryptamine (2 mg/kg) and the combination of tranylcypromine (10 mg/kg) and L‐tryptophan (50 mg/kg). Salbutamol and terbutaline potentiated quipazine‐induced hyperactivity only when given at the higher dose of 20 mg/kg.

The effect of clenbuterol in enhancing quipazine hyperactivity was blocked by the centrally acting β1‐adrenoceptor antagonist, metoprolol (5 mg/kg), but not by the β2‐adrenoceptor antagonist, butoxamine (5 mg/kg) or the peripherally acting β1‐adrenoceptor antagonist, atenolol (5 mg/kg).

Clenbuterol (5 mg/kg) did not enhance the circling responses produced by methamphetamine (0.5 mg/kg) in unilateral nigrostriatal‐lesioned rats.

The results suggest that β‐adrenoceptor agonists in common with some established antidepressant treatments produce enhancement of 5‐HT‐mediated behavioural responses.
PROTEASE INHIBITOR HOMOLOGUES FROM MAMBA VENOMS: FACILITATION OF ACETYLCHOLINE RELEASE AND INTERACTIONS WITH PREJUNCTIONAL BLOCKING TOXINS
Authors: HARVEY A.L. , KARLSSON E.
Published: July 2012

Five polypeptides, which were isolated from elapid snake venoms and which are structurally related to protease inhibitors, were tested for action on isolated biventer cervicis nerve‐muscle preparations of the chick.

Dendrotoxin from the Eastern green mamba (Dendroaspis angusticeps) and toxins K and I from the black mamba (Dendroaspis polylepis polylepis) increased responses to indirect stimulation without affecting responses to exogenous acetylcholine, carbachol or KCl.

The two other protease inhibitor homologues, HHV‐II from Ringhals cobra (Hemachatus haemachatus) and NNV‐II from Cape cobra (Naja nivea) did not increase responses to nerve stimulation. Trypsin inhibitor from bovine pancreas also had no facilitatory effects on neuromuscular transmission.

The facilitatory toxins from mamba venoms interacted with the prejunctional blocking toxins, β‐bungarotoxin, crotoxin and notexin, but not with taipoxin. The blocking effects of β‐bungarotoxin were reduced by pretreatment with the mamba toxins, whereas the blocking actions of crotoxin and notexin were enhanced.

The results indicate that protease inhibitor homologues from mamba venoms form a new class of neurotoxin, which acts to increase the release of acetylcholine in response to motor nerve stimulation.

From the interaction studies it is concluded that the facilitatory toxins bind to motor nerve terminals at sites related to those occupied by the prejunctional blocking toxins. However, differences in interactions with individual toxins suggest that there must be several related binding sites on the nerve terminals.
Heat loss reaction to capsaicin through a peripheral site of action
Authors: Donnerer Josef , Lembeck Fred
Published: July 2012

The intravenous injection of 15 fig capsaicin produced an increase in the temperature of tail skin and paw pad and a fall in the colon temperature in conscious rats. These reactions reflect increased heat dissipation.

The increase in skin temperature induced by intravenous capsaicin was absent when the function of small diameter primary afferent neurones was impaired by treatment of the rats with capsaicin as neonates. Thus it appears that intravenous capsaicin triggered the thermoregulatory response predominantly by stimulation of peripheral heat receptors.

By means of local application of capsaicin to the nerves of the hind leg and by their chronic denervation, by treatment with phenoxybenzamine and guanethidine, evidence was obtained that reflex withdrawal of sympathetic vasoconstrictor tone mediates the heat loss reaction to intravenous capsaicin.
Effects of cocaine and desipramine on the neurally evoked overflow of endogenous noradrenaline from the rat heart
Authors: Dart A.M. , Dietz R. , Kübier W. , Schömig A. , Strasser R.
Published: July 2012

Stimulation of postganglionic cardiac sympathetic nerves produced a stimulation frequency‐dependent overflow of endogenous noradrenaline from the otherwise isolated rat heart.

Such nerve stimulation also produced increases in heart rate. There was significant correlation between heart rate increases and corresponding noradrenaline concentrations in the coronary venous effluent.

Cocaine (3 × 10−5 M) caused a significant reduction in both the noradrenaline overflow and the heart rate increase, produced by nerve stimulation for 1 min at 4 Hz.

Desipramine (10−6M) caused a significant increase in the noradrenaline overflow produced by stimulation for 1 min (4 Hz) with a mean increase of approximately 60%. There was no significant effect on the heart rate increase produced by such stimulation.

The opposite effects of cocaine (3 × 10−5M) and desipramine (10−6M) on noradrenaline overflow are attributed to differences in the local anaesthetic properties of these agents.
Extracellular chloride replacement by isethionate induces abnormal spontaneous release of transmitter at the frog neuromuscular junction
Authors: Ashford M.L.J. , Wann K.T.
Published: July 2012

Replacement of chloride by isethionate in Ringer solution bathing frog skeletal muscle fibres induces, after a delay of about 30 min, marked mechanical activity which was blocked by tubocurarine. This effect is reversed by washing out the isethionate.

Miniature end plate potentials (m.e.p.ps) and giant potentials (potentials >2 × modal value) were recorded intracellularly in normal Ringer and isethionate Ringer solution.

The frequency of m.e.p.ps was unaltered by isethionate. The proportion of giant potentials increased from 3% in normal Ringer to 24.5% in isethionate Ringer after 90 min. This effect is usually reversible if the exposure to isethionate does not exceed 2 h.

The giant potentials were large enough to initiate trains of action potentials and still occurred in the presence of tetrodotoxin or Ca2+‐free Ringer. Isethionate produced no change in the τD of miniature endplate currents.

Chloride replacement by propionate produced no change in the proportion of giant potentials.

It is suggested that the isethionate anion can induce giant potentials and the possible mechanism of action is discussed.
Different α‐adrenoceptors modulate the release of 5‐hydroxytryptamine and noradrenaline in rat cortex
Authors: Ennis Christine
Published: July 2012

The potassium‐evoked release of [3H] ‐noradrenaline from slices of rat occipital cortex and the potassium‐evoked release of [3H]‐5‐hydroxytryptamine from slices of rat frontal cortex were measured using a superfusion system.

The rank order of potency for a number of α‐adrenoceptor agonists was different for the two neuronal systems, Clonidine and azepexole being the most potent inhibitors of noradrenaline release and methoxamine and phenylephrine being the most potent against 5‐hydroxytryptamine release.

The rank order of potency for a series of α‐adrenoceptor antagonists in reversing the inhibition of noradrenaline release produced by Clonidine was: phentolamine > rauwolscine = yohimbine = corynanthine >> WB4101, whereas against methoxamine‐inhibition of 5‐hydroxytryptamine release the rank order of potency was: WB4101 > phentolamine > corynanthine > yohimbine > rauwolscine.

The results suggest that the α‐adrenoceptors which modulate potassium‐evoked 5‐hydroxytryptamine release are not identical with the α2‐adrenoceptors located on noradrenergic nerve terminals and may more closely resemble α1‐than α2‐adrenoceptors.
The effects of 2‐nicotinamidoethyl nitrate on smooth muscle cells of the dog mesenteric artery and trachea
Authors: Inoue Toshiro , Ito Yushi , Takeda Kazuo
Published: July 2012

The effects of 2‐nicotinamidoethyl nitrate (nicorandil; 2‐NN), a synthesized coronary vasodilator, on smooth muscle cells of dog mesenteric artery or trachea were investigated using microelectrode, double sucrose gap and isometric tension recording methods.

Nicorandil hyperpolarized the smooth muscle membrane of the mesenteric artery (5 × 10−6m) and the trachea (5 × 10−5 m).

In both these smooth muscle cells, the nicorandil‐induced hyperpolarization remained constant in various concentrations of [Cl−1]o, but changed with various concentrations of [K+]o. This hyperpolarization was partly inhibited following pretreatment with tetraethylammonium (TEA > 1 mm) and was completely inhibited following pretreatment with procaine (1 mm or 5 mm), indicating that the nicorandyl‐induced hyperpolarization is due to increase in the K‐conductance, in both these membranes.

Following pretreatment with TEA (5 mm), outward current pulses evoked an action potential in tracheal smooth muscle cells. Nicorandil inhibited the generation of action potential due to the hyperpolarization of the membrane but not due to inhibition of the spike generating mechanism.

Nicorandil (10−6m) inhibited the contracture evoked by excess [K]o, in both tissues. The contracture evoked by noradrenaline or repetitive field stimulation with short duration (50 μs) pulses was also inhibited in the mesenteric artery, while a higher dose of nicorandil (10−5m) was required to inhibit the contracture evoked by acetylcholine or repetitive field stimulation in the trachea.

Excitatory junction potentials (e.j.ps) evoked by field stimulation in the mesenteric artery due to the release of noradrenaline, or in the trachea due to release of acetylcholine, were suppressed by 10−5 m or 5 × 10−5 m nicorandil, respectively. The reduction in the amplitude of e.j.p. was mainly due to the hyperpolarization of the membrane with increase in the membrane conductance.

In the mesenteric artery, following pretreatment with TEA (1 mm) an action potential was generated on the e.j.p. Nicorandil suppressed the generation of the action potential by reduction in the amplitude of the e.j.p., below the threshold required for generation of the action potential.

These results indicate that nicorandil hyperpolarizes the membrane by increasing K‐conductance and inhibits the generation of contraction, in both tissues. Higher concentrations of nicorandil are required to suppress the mechanical response in the trachea than in the mesenteric artery. Depression of the mechanical responses in both tissues is partly due to suppression of Ca‐mobilization inside the muscle cells and partly to hyperpolarization of the membrane.
Inflammatory actions of platelet activating factor (Paf‐acether) in guinea‐pig skin
Authors: Morley J. , Page C.P. , Paul W.
Published: July 2012

Cutaneous responses to synthetic platelet activating factor (Paf‐acether) have been studied in guinea‐pigs by means of radioisotopic marker techniques.

Intradermal injection of Paf‐acether elicited increased plasma protein extravasation (IPPE) (0.2–200 pmol/site), platelet accumulation (PA) (20–200 pmol/site) and red blood cell accumulation (RBCA) (200 pmol/site), whereas lyso‐Paf (up to 2 nmol/site) was inactive in all these respects.

Following intradermal injection, the IPPE responses to Paf‐acether (2 and 20 pmol/site) were complete within 15 and 30 min respectively, although in response to 200 pmol/site, IPPE was detectable up to 1.5 h. The PA and RBCA responses to Paf‐acether (200 pmol/site) were complete within 1 h.

IPPE induced by Paf‐acether (3 pmol/site) was potentiated by concomitant intradermal injection of a cutaneous vasodilator prostaglandin E2 (PGE2, 1 nmol/site) and inhibited by the β‐adrenoceptor agonist, isoprenaline (4.5 nmol/site) or the α‐adrenoceptor agonist, phenylephrine (6 nmol/site). Such observations are consistent with Paf‐acether effecting increased vessel wall permeability.

Intradermal injection of PGEx (3 nmol/site) significantly reduced PA in response to Paf‐acether (200 pmol/site), whilst significantly enhancing IPPE. This dissociation of increased vascular permeability from PA is consistent with Paf‐acether eliciting IPPE via a platelet‐independent mechanism.

These results indicate that a direct effect on vessel wall permeability contributes to the inflammatory response to Paf‐acether in guinea‐pig skin. It is suggested that Paf‐acether is a potential mediator of allergy and inflammation.
Compared myocardial and vascular effects of captopril and dihydralazine during hypertension development in spontaneously hypertensive rats
Authors: Freslon J.L. , Giudicelli J.F.
Published: July 2012

When administered to young spontaneously hypertensive rats (SHRs), dihydralazine (25 mg kg−1, daily) and captopril (100 mg kg−1, daily) prevent with the same efficacy genetic hypertension development (GHD).

Dihydralazine treatment increased vascular mesenteric compliance, as shown by a significant decrease in the stiffness of the vessels (‐27%), and induced slight reductions in contractility (‐12%) and in wall to lumen (W/L) ratio (‐15%). After treatment withdrawal, all these parameters returned to control values within 7 weeks, as did blood pressure.

Captopril treatment also strongly increased the mesenteric vessels compliance, vessel stiffness being decreased by 16%, and reduced their contractility (‐15%) and their W/L ratio (—30%). These effects as well as those exerted on blood pressure persisted up to 7 weeks after treatment ceased although there was a slight trend to a progressive reduction in the intensity of both phenomena.

These experiments show that captopril but not dihydralazine has a long‐lasting effect in opposing the functional and morphological vascular alterations occurring during GHD in SHRs and this phenomenon probably contributes to a large extent to the sustained preventive effects of the drug against GHD.
Substance P inhibits the M‐current in bullfrog sympathetic neurones
Authors: Adams P.R. , Brown D.A. , Jones S.W.
Published: July 2012

Substance P (SP, 2.5–10 μm) was applied by rapid bath perfusion to bullfrog lumbar sympathetic neurones in vitro, voltage‐clamped through a single micro‐electrode. In unclamped cells, SP produced a depolarization accompanied by an increase in apparent input resistance. Under voltage‐clamp a voltage‐dependent inward current was induced by SP, during which the time‐dependent relaxations induced by square voltage commands were inhibited. It is concluded that SP inhibits the M‐current (IM), a species of voltage‐dependent K+‐current, and that IM‐inhibition was the primary cause of the inward current and membrane depolarization in the cells tested.
Effects of modification of the membranes of intact erythrocytes on the anti‐haemolytic action of chlorpromazine
Authors: Born G.V.R. , Housley G.M.
Published: July 2012

Fresh human erythrocytes were washed and incubated at 37°C in physiological saline buffered with Tris, containing calcium and either neuraminidase or trypsin or both enzymes together.

Each enzyme alone, as well as both together, released similar amounts of sialic acids without haemolysis, apparently therefore from the same accessible sites on the surface of the cells.

Exposure to neuraminidase or/and trypsin did not affect the osmotic fragility of red cells in hypotonic saline.

The anti‐haemolytic effect of low concentrations of chlorpromazine or thioridazine was diminished by previous exposure of red cells to neuraminidase and/or trypsin. The diminution in the anti‐haemolytic effect of chlorpromazine was proportional to the release of sialic acids.

The observations suggest that positively charged drugs such as chlorpromazine interact strongly with the negatively charged sialic acid moieties of glycoproteins on cell surfaces, removal of which increases the drugs' access to and disruption of the lipid bilayer in cell membranes.
Endothelium‐dependent relaxation of the pig aorta: relationship to stimulation of 86Rb efflux from isolated endothelial cells
Authors: Gordon John L. , Martin William
Published: July 2012

Bradykinin, adenosine triphosphate (ATP) and acetylcholine each relaxed histamine‐contracted strips of pig aorta in a dose‐dependent manner. These relaxations were abolished when the endothelium was removed.

Relaxation induced by ATP was mimicked by adenosine diphosphate (ADP) but adenosine monophosphate (AMP) and adenosine were about 120 times less potent.

Relaxation induced by acetylcholine was antagonized by atropine in a competitive manner, and carbachol induced the same degree of relaxation as acetylcholine, but was about 10 times less potent.

The calcium ionophore, A23187, also induced a dose‐dependent relaxation of pig aortic strips provided the endothelium was present, suggesting that a rise in the level of ionized calcium within the endothelial cells is one means by which vascular smooth muscle relaxation can be triggered.

Bradykinin, ATP, ADP, AMP, adenosine and A23187 each induced a dose‐dependent increase in 86Rb efflux from preloaded pig aortic endothelial cells. The dose‐response curves for stimulation of 86Rb efflux and for endothelium‐dependent relaxation were similar for each individual compound. ADP was equipotent with ATP, but AMP and adenosine were about 120 times less potent.

Neither acetylcholine nor carbachol, in concentrations that induce endothelium‐dependent relaxation, had any effect on 86Rb efflux from isolated aortic endothelial cells.

Lanthanum, which blocks calcium influx, abolished the increases in 86Rb efflux induced by bradykinin and ATP, and the calcium ionophore A23187 was the most effective stimulant of 86Rb efflux, suggesting that the potassium transport induced by these agents is calcium‐activated.

It is concluded that endothelial responses to bradykinin and ATP can be assessed by monitoring 86Rb efflux, which probably reflects a calcium‐activated efflux of potassium associated with the endothelium‐dependent vascular relaxation induced by these agents. This pathway is apparently not involved in endothelial responses to acetylcholine.
Coexistence of GABAA and GABAB receptors on Aδ and C primary afferents
Authors: Désarmenien Michel , Feltz Paul , Occhipinti Guiseppe , Santangelo Francesca , Schlichter Remy
Published: July 2012

Intracellular recordings from adult rat dorsal root ganglion neurones were performed in vitro and the coexistence of two γ‐aminobutyric acid (GABA) receptors on the membrane of identified Aδ and C primary afferents was demonstrated.

Transient applications of GABA (10−6 − 10−2m) evoked dose‐dependent depolarizations and increased membrane conductance. The responses were mimicked by muscimol, isoguvacine, THIP and 3 amino propane sulphonic acid (3 APS); they were blocked by bicuculline and picrotoxin. Pentobarbitone induced an increase of GABA‐induced depolarizations.

Perfusion of tetraethylammonium (TEA, 7.5 mm) and intracellular injection of Cs+ ions unmasked the Ca2+ component of action potentials, which appeared as long‐lasting plateau depolarizations. Such action potentials were shortened in the presence of methoxyverapamil (D600, 5 × 10−6‐ 10−5m) and in a medium without Ca+ ions.

Prolonged (5–10 min) perfusion of GABA (10−9‐10−5m) shortened the Ca2+ component of action potentials. This effect was mimicked by baclofen (10−7‐5 × 10−6m) and muscimol (5 × 10−7‐10−5m) and was not affected by bicuculline perfusion (5 × 10−6‐10−5m). Isoguvacine (2.5 × 10−5m) did not affect action potential duration.

It is concluded that two GABA receptors coexist on the membrane of slow conducting primary afferents: the bicuculline‐sensitive GABAA receptor mediates depolarizations and the bicuculline‐insensitive GABAB receptor shortens the calcium component of action potentials.
Nitroglycerine‐induced biphasic relaxation in vascular smooth muscle of rat aorta
Authors: Karaki H. , Murakami K. , Nakagawa H. , Urakawa N.
Published: July 2012

Nitroglycerine induced biphasic relaxation in the rat aorta, previously contracted by noradrenaline; a rapid decrease in tension was followed by a gradual increase reaching a steady level below the control contractile tension. No initial transient relaxation was induced by nitroglycerine in high K‐stimulated muscle.

The initial transient relaxation, but not the sustained relaxation, was dependent on the concentration of external K; maximum relaxation was observed in the presence of 2.7 mm K solution and only a slight relaxation was observed in 0 mm or 10.8 mm K solution. The initial transient relaxation was also inhibited by ouabain or low Na solution.

On an appropriate increase in the concentration of external K, noradrenaline‐induced contraction was transiently relaxed. Previous application of nitroglycerine potentiated this K‐induced relaxation.

Pretreatment of the muscle with methylene blue, an inhibitor of guanylate cyclase, inhibited both the initial transient and the sustained relaxations induced by nitroglycerine, but not the K‐induced transient relaxation.

It is suggested that the nitroglycerine‐induced initial transient relaxation, but not the sustained relaxation, may be due to a stimulation of an electrogenic Na pump. Both relaxation phases may be mediated by cyclic GMP.
Antagonism of Ca2+ and other actions of verapamil in guinea‐pig isolated trachealis
Authors: Foster R.W. , Okpalugo B.I. , Small R.C.
Published: July 2012

In trachealis bathed by a K+‐rich, Ca2+‐free physiological salt solution, calcium chloride (CaCl2) at 0.01 to 10 mmol l−1 evoked concentration‐dependent spasm. Verapamil (0.1 to 10 μmol l−1) was an effective antagonist of CaCl2.

Spasm evoked by acetylcholine, histamine, potassium chloride (KCl) and tetraethylammonium (TEA) was studied in trachealis bathed by normal Krebs solution. Verapamil (0.1 to 10 μmol l−1) markedly suppressed spasm evoked by KCl and TEA. In contrast the actions of acetylcholine and histamine were much less affected by verapamil.

Spasm evoked by prostaglandin E2 was studied in trachealis bathed by Krebs solution containing indomethacin (2.8 μmol l−1). Verapamil (0.1 to 10 μmol l−1) had little or no effect against prostaglandin E2‐induced spasm.

Verapamil (0.1 to 10 μmol l−1) had relatively little effect on the tone of trachealis bathed by normal Krebs solution. In contrast bathing in Krebs solution lacking CaCl2 caused almost complete tone loss.

Extracellular electrophysiological recording showed that verapamil (10 μmol l−1) suppressed not only TEA‐evoked spasm but also TEA‐evoked slow waves and spike potentials. Verapamil also abolished the transient period of slow wave activity associated with the spasm evoked by KCl.

Intracellular electrophysiological recording showed that TEA‐induced spike activity was resistant to tetrodotoxin (3 μmol l−1). However, verapamil (10 μmol l−1) abolished the tetrodotoxin‐resistant spikes without increasing the resting membrane potential.

It is concluded that verapamil suppresses TEA‐ or KCl‐induced spasm, slow waves or spikes by inhibition of Ca2+ influx. Spasm evoked by acetylcholine, histamine and prostaglandin E2 depends on mechanisms for increasing the cytoplasmic concentration of free Ca2+ which are resistant to verapamil. The failure of verapamil markedly to depress tissue tone is consistent with the proposal that tone results from the activity of endogenous prostaglandins.
Evidence that the P1‐purinoceptor in the guinea‐pig taenia coli is an A2‐subtype
Authors: Burnstock Geoffrey , Hills Judith M. , Hoyle Charles H. V.
Published: July 2012

The effects of 5′‐N‐ethylcarboxamidoadenosine (NECA), l‐NECA, 2‐chloroadenosine, N6‐phenylisopropyladenosine (l‐PIA and d‐PIA), cyclohexyladenosine (CHA), and adenosine were examined on the guinea‐pig taenia coli.

All the analogues except l‐NECA caused relaxations; the order of potency for the series was: NECA > 2‐chloroadenosine > l‐PIA > CHA > d‐PIA > adenosine.

l‐PIA was twice as potent as d‐PIA in inducing relaxations of the guinea‐pig taenia coli.

Adenosine and its analogues that induce relaxation all caused a slow membrane hyperpolarization; differences in the rates of hyperpolarization and latencies were apparent, although not statistically significant.

The duration of the response to adenosine was significantly less than that for any adenosine analogue.

Ion studies, using the sucrose gap, revealed that responses to the analogues were attenuated in elevated extracellular potassium or reduced extracellular chloride.

8‐Phenyltheophylline, a potent P1‐purinoceptor antagonist, caused a rightward shift of all the adenosine and analogue concentration‐response curves.

Dipyridamole, an adenosine uptake inhibitor, potentiated the relaxations to adenosine but had no significant effect on the relaxations induced by the analogues.

It is concluded that NECA, 2‐chloroadenosine, l‐PIA, CHA, d‐PIA and adenosine mediate their relaxant effects via an extracellular P1‐purinoceptor which displays characteristics of the A2‐subtype as determined by the rank order of agonist potency. Electrophysiological analysis of the responses to each of the analogues did not reveal any marked differences in the modes of action even between NECA and l‐PIA (preferential A2‐and A1‐receptor agonists, respectively).
Is Ro 03–7894 an irreversible antagonist at β‐adrenoceptor sites?
Authors: Krstew E. , MCPherson G. A. , Malta E. , Molenaar P. , Raper C.
Published: July 2012

Ro 03–7894 (0.6 mm) produced a non‐parallel shift to the right of dose‐response curves to (‐)‐isoprenaline in K+ depolarized uterine preparations from the guinea‐pig. The displacement of the curves was readily reversed by washing. A rightward shift of similar magnitude was also produced by Ro 03–7894 in transmurally stimulated ileal preparations. The relaxant effects of fenoterol in carbachol‐contracted guinea‐pig tracheal preparations (in the presence of 2 μm atenolol) were not altered by 0.6 mm Ro 03–7894. In the three tissues there was no evidence of a reduction in the maximal inhibitory response to the agonists.

In uterine and tracheal preparations, Ro 03–7894 (0.6 mm) depressed contractile responses to exogenous calcium. The depression of responses was enhanced after washout of Ro 03–7894 for 80 min. Contractile responses of ileal preparations to transmural stimulation were also depressed by Ro 03–7894.

Concentration‐effect curves for the positive inotropic effects of (‐)‐isoprenaline in guinea‐pig left atrial preparations were markedly shifted to the right and the maximum response depressed by 0.6 mm Ro 03–7894. Although the rightward shift of the curves was fully reversed during the 120 min washout period, the maximal responses remained depressed. In similar experiments, Ro 03–7894 produced a washout‐resistant depression of inotropic responses to histamine and calcium.

The results of radioligand binding studies in left atria using (‐)‐[125I]‐iodocyanopindolol indicated that, when compared to the untreated atria, there was no reduction in the maximal density of binding sites 120 min after washout of 0.6 mm Ro 03–7894.

On the basis of the present results it is concluded that Ro 03–7894 induces a non‐specific depressant effect on smooth and cardiac muscle preparations during exposure to the drug. This depressant effect persists following washout of the drug. There is no evidence for an irreversible effect of Ro 03–7894 at β‐adrenoceptor sites.
An investigation of presynaptic α‐adrenoceptor subtypes in the pithed rat heart and in the rat isolated vas deferens
Authors: Docherty James R.
Published: July 2012

The presynaptic cardio‐inhibitory effects of the α‐adrenoceptor agonists xylazine, cirazoline and amidephrine and their interaction with the antagonists yohimbine and prazosin were investigated in the pithed rat.

The presynaptic inhibitory effects of the α2‐selective agonist xylazine were antagonized by the α2‐antagonist yohimbine but not by the α2‐antagonist prazosin, thus demonstrating the lack of α2‐adrenoceptor antagonism by prazosin.

The presynaptic inhibitory effects of cirazoline were antagonized equally by yohimbine and prazosin, and the presynaptic inhibitory effects of the selective α1‐agonist amidephrine were antagonized by prazosin more potently than by yohimbine.

In the nifedipine‐treated isolated epididymal portion of the rat vas deferens, both xylazine and amidephrine produced concentration‐dependent inhibition of the isometric contraction to single pulse electrical stimulation. The α2‐antagonist rauwolscine antagonized the inhibitory effects of xylazine but not of amidephrine.

It is concluded that inhibitory α1‐adrenoceptors, as well as the already established α2‐receptors, are present presynaptically in the pithed rat heart and in the rat vas deferens.
Mechanisms of reflex bradycardia and hypotension by metabolites of arachidonic acid in the cat
Authors: Hintze Thomas H. , Kaley Gabor , Panzenbeck Maret J.
Published: July 2012

In the cat, intravenous injections of arachidonic acid or prostaglandin (PG)F2α caused significant reductions in mean arterial pressure and heart rate which were eliminated or significantly lessened, respectively, by previous administration of indomethacin. The bradycardia to intravenous prostacyclin (PGI2) was unaffected by indomethacin.

In cats with bilateral ligation of the carotid arteries to eliminate competition between systemic baroreflexes and cardiopulmonary reflexes, PGI2, PGF2α and arachidonic acid caused significantly greater hypotension and bradycardia than in cats with intact carotid baroreflexes.

The bradycardia to PGI2, PGF2α and arachidonic acid was eliminated by bilateral vagal section or atropine.

PGE1, PGE2 and nitroprusside caused dose‐related falls in mean arterial pressure and a small tachycardia.

In a small group of cats (7 of 67) nitroprusside also caused a reduction in heart rate which was eliminated by indomethacin.

We conclude that the reflex bradycardia to PGF2α, like that to arachidonic acid is, at least in part, the result of the stimulation of synthesis of another prostaglandin, most likely PGI2.
Effect of nonselective and selective inhibitors of monoamine oxidases A and B on pethidine toxicity in mice
Authors: Boden R. , Botting Regina , Coulson P. , Spanswick Gillian
Published: July 2012

The LD50 of pethidine was determined in mice pretreated (4 h) either with the nonselective monoamine oxidase (MAO) inhibitor, phenelzine or with clorgyline, a selective inhibitor of MAO A or deprenyl, a selective inhibitor of MAO B.

Phenelzine or combined clorgyline plus deprenyl pretreatments decreased pethidine LD50.

Clorgyline or deprenyl alone did not affect pethidine toxicity.

Whole brain 5‐hydroxytryptamine (5‐HT) concentrations were measured in the pretreated mice. 5‐HT levels were approximately doubled (P < 0.001) after phenelzine or clorgyline plus deprenyl treatment, but not after clorgyline or deprenyl given alone.

These results indicate that both MAO A and MAO B need to be inhibited to increase pethidine toxicity and brain 5‐HT levels. They support the involvement of 5‐HT in the toxic interaction between pethidine and MAO inhibitors.
Some pharmacological and biochemical interactions of the enantiomers of adenylyl 5′‐(β, γ‐methylene)‐diphosphonate with the guinea‐pig urinary bladder
Authors: Cusack N.J. , Hourani S.M.O.
Published: July 2012

Adenosine 5′‐triphosphate (ATP) and adenylyl 5′‐(β,γ methylene)‐diphosphonate (AMP‐PCP) both contracted the guinea‐pig urinary bladder, but the response to AMP‐PCP was much greater. We synthesized the enantiomer of AMP‐PCP, L‐adenylyl 5′‐(β,γ‐methylene)‐diphosphonate (L‐AMP‐PCP), and tested it on the guinea‐pig bladder.

L‐AMP‐PCP contracted the guinea‐pig bladder, and was more potent than AMP‐PCP and much more potent than ATP. The potential breakdown product of L‐AMP‐PCP, L‐adenosine, unlike adenosine (the breakdown product of AMP‐PCP), did not inhibit contractions of the guinea‐pig bladder.

ATP and its enantiomer L‐adenosine 5′‐triphosphate (L‐ATP) were rapidly degraded by the muscle, and AMP‐PCP was also degraded, but more slowly. L‐AMP‐PCP, however, was completely resistant to degradation.

L‐AMP‐PCP would appear to be a useful ATP analogue, as it is potent and resistant to degradation, and its potential breakdown product, L‐adenosine, is inactive.
Purine involvement in morphine antinociception
Authors: Mantegazza Paolo , Tammiso Remigio , Zambotti Fernanda , Zecca Luigi , Zonta Nerina
Published: July 2012

The effects of a series of adenosine derivatives on morphine antinoceptive effect were investigated in rats by the ‘tail‐flick’ method.

2‐Chloroadenosine (CADO) and L‐N6‐phenylisopropyladenosine (L‐PIA), given intraperitoneally, caused decreased morphine antinociception.

Intracerebroventricular injections of CADO, L‐PIA and 5′‐N‐ethylcarboxamide adenosine (NECA), but not of 2′‐deoxyadenosine, antagonized morphine antinociception.

The effects of both central and peripheral injections of CADO and L‐PIA on morphine antinociception were partially reversed by caffeine.

Intracerebroventricular injection of dibutyryl‐cyclic 3′,5′ adenosine monophosphate (db cyclic AMP) had no effect on morphine antinociception.

These data indicate that adenosine plays a role in morphine‐induced antinociception. The results are discussed in terms of postulated effects of adenosine derivatives on adenylate cyclase.
Phentolamine‐induced rhythmic contractions in bladder detrusor muscle of guinea‐pig
Authors: Satake Nobuhiro , Shibata Shoji , Ueda Shoichi
Published: July 2012

Phentolamine caused a rhythmic contraction concentration‐dependently without affecting resting tone in the detrusor muscle.

Prazosin, yohimbine, propranolol, noradrenaline, Clonidine or isoprenaline failed to cause the rhythmic contraction. These agents did not modify the response to phentolamine suggesting no involvement of α‐or β‐adrenoceptors in the response to phentolamine.

Chlorpheniramine, Cimetidine, methysergide, SK&F 83566, atropine, bretylium, hemicholinium or tetrodotoxin failed to inhibit the response to phentolamine. These results suggest that the effect of phentolamine is not mediated through histaminergic, 5‐hydroxytryptaminergic, dopaminergic or cholinergic systems, or through transmitter release from nerve endings.

Prostaglandin F2α (PGF2α), arachidonic acid but not ATP caused rhythmic contractions which resembled the response to phentolamine. Potassium also caused a contraction with increasing resting tone.

Following treatment with nifedipine, or incubation in a Ca2+‐ free medium, the responses to phentolamine, PGF2α, arachidonic acid and potassium were markedly inhibited or abolished.

Cyclo‐oxygenase inhibitors such as indomethacin, aspirin and corticosterone inhibited or abolished the responses to phentolamine and arachidonic acid but did not inhibit the response to PGF2α.

The results suggest that the phentolamine‐induced rhythmic contraction may, at least in part, result from the cyclo‐oxygenase metabolite of arachidonic acid in guinea‐pig detrusor muscles and a consequent increase in the transmembrane Ca2+‐influx.
Muscarinic inhibitory receptors in pulmonary parasympathetic nerves in the guinea‐pig
Authors: Fryer Allison D. , Maclagan Jennifer
Published: July 2012

In anaesthetized guinea‐pigs, gallamine produced a dose‐related potentiation of the bronchoconstriction induced by electrical stimulation of the cervical vagus nerves; (+)‐tubocurarine and suxamethonium lacked this effect.

The bronchoconstriction produced by intravenous injection of acetylcholine or histamine, however, was not potentiated by gallamine.

Vagally‐induced bradycardia was abolished by gallamine, confirming antagonism of the effect of acetylcholine on muscarinic receptors in the heart.

The muscarinic receptor agonist pilocarpine, had the opposite effect to gallamine in the lung as it inhibited vagally‐mediated bronchoconstriction.

Pretreatment of guinea‐pigs with either guanethidine or propranolol did not affect the gallamine‐induced potentiation of vagally‐mediated bronchoconstriction.

The potentiating effect of gallamine in the lung can be explained by blockade of inhibitory, muscarinic receptors located in the parasympathetic nerves supplying the lungs.
Histamine is an antagonist of the acetylcholine receptor at the frog endplate
Authors: Ariyoshi M. , Hasuo H. , Koketsu K. , Ohta Y. , Tokimasa T.
Published: July 2012

The effects of histamine on the acetylcholine (ACh) receptor‐channel complex were examined by means of voltage‐clamp at the frog endplate. ACh was ionophoretically applied to the endplate. Histamine was added to the perfusate.

Histamine (100 nM − 1 mM) reversibly depressed the peak amplitude of the ACh‐induced inward current in a dose‐dependent manner.

The double reciprocal plot of the dose‐response relationship between the peak ACh current and the amount of ACh applied suggested that histamine (100 μM) depressed the ACh‐induced current in a competitive manner.

Histamine prevented the specific ACh binding site within the receptor‐channel complex from binding erabutoxin, a sea‐snake venom, which binds irreversibly to the specific ACh binding site.

Histamine had no detectable effects on the equilibrium potential of the endplate current but shortened the half‐decay time of the endplate current in a voltage‐dependent manner.

It was therefore concluded that histamine blocks not only the specific ACh binding site but also interacts with the ACh‐channel site.

The present experiments strongly suggest that histamine can act as an antagonist to modulate nicotinic cholinergic transmission.
The effect of nedocromil sodium and sodium cromoglycate on antigen‐induced bronchoconstriction in the Ascaris‐sensitive monkey
Authors: Eady R.P. , Greenwood B. , Jackson D.M. , Orr T.S.C. , Wells E.
Published: July 2012

Nedocromil sodium inhibited the bronchoconstriction caused by antigen challenge in Ascaris‐sensitive monkeys and in addition it prevented the release of histamine from mast cells lavaged from sensitive monkeys. Sodium cromoglycate was relatively inactive in both these systems. It is suggested that nedocromil sodium can stabilize both mucosal and connective tissue mast cells and may represent a new type of drug.
Subcellular localization of [3H]‐nitrendipine binding sites in guinea‐pig ileal smooth muscle
Authors: Godfraind T. , Wibo M.
Published: July 2012

The binding of [3H]‐nitrendipine was studied in microsomal fractions isolated from guinea‐pig ileal smooth muscle.

Only one class of specific binding sites was detected, with a KD of 0.4 nM. For various dihydropyridine derivatives, including the stereoisomers of nimodipine and the ‘Ca agonist’ Bay K 8644, the potency for inhibition of [3H]‐nitrendipine binding correlated well with the reported pharmacological potency in smooth muscle preparations.

To establish the subcellular localization of [3H]‐nitrendipine binding sites, untreated and digitonin‐treated microsomal fractions were subfractionated by isopycnic density gradient centrifugation. The density distribution of [3H]‐nitrendipine binding was markedly shifted by digitonin towards higher densities, as were the distributions of 5′‐nucleotidase and [3H]‐ouabain binding, whereas the distributions of NADPH:cytochrome c reductase and NADH:cytochrome c reductase were hardly modified by digitonin.

It is concluded that most, if not all, [3H]‐nitrendipine binding sites in guinea‐pig ileal smooth muscle are present in the plasma membrane, in agreement with the postulated mode of action of dihydropyridines as inhibitors of plasmalemmal Ca channels.