bluuebunny/crossref_metadata_2025 huggingface dataset:
Differential regulation of 5‐lipoxygenase and cyclo‐oxygenase pathways of arachidonate metabolism in rat peritoneal leukocytes
Authors: Moroney M.A. , Forder R.A. , Carey F. , Hoult J.R.S.
Published: July 2012

Simultaneous activation of the 5‐lipoxygenase and cyclo‐oxygenase pathways of arachidonate metabolism in rat peritoneal mixed leukocytes in response to A23187, chemoattractant N‐formyl‐methionineleucine‐phenylalanine (FMLP) and arachidonic acid (AA) was studied by radioimmunoassay of leukotriene B4 (LTB4) and thromboxane B2 (TXB2) respectively.

FMLP and AA preferentially activated cyclo‐oxygenase and A23187 preferentially activated 5‐lipoxygenase. Release of TXB2 preceded that of LTB4. A threshold amount of A23187 enhanced FMLP‐and AA‐induced LTB4 production but not that of TXB2.

Phorbol myristate acetate (PMA) abolished LTB4 generation in response to FMLP with much less effect on TXB2, but did not inhibit the formation of either eicosanoid caused by A23187 or AA. Instead, PMA caused a dose‐dependent but modest stimulation of TXB2 generation either on its own or when added with A23187 or AA.

These results show that the 5‐lipoxygenase and cyclo‐oxygenase pathways in rat peritoneal leukocytes are regulated differently and that functional compartmentalisation of the stimulus‐generation sequence operates in these cells.
Volatile anaesthetics inhibit a cyclic AMP‐dependent sodium‐potassium current in cultured sensory neurones of bullfrog
Authors: Tokimasa T. , Sugiyama K. , Akasu T. , Muteki T.
Published: July 2012

Cultured dorsal root ganglion cells of the bullfrog were voltage‐clamped in the whole‐cell configuration.

An adenosine 3′:5′‐cyclic monophosphate (cyclic AMP)‐dependent cationic inward rectifier (IH) was inhibited by bath application of enflurane (0.2‐0.8 mm) and halothane (0.2‐0.5 mm), which thereby induced an outward current at the resting potential, and a membrane hyperpolarization in undamped cells.

The main effect of enflurane (0.5 mm) was to displace the steady‐state IH activation curve to a hyperpolarizing direction by about 10 mV, as well as to reduce the maximum H‐conductance to about 20%.

Forskolin (1–10 μm), which enhances IH by producing a depolarizing shift in the IH activation curve and increasing the maximum H‐conductance, recruited IH even when the current had already been eliminated by enflurane (1 mm).
Contractile and relaxant responses of the canine isolated spinal artery to vasoactive substances
Authors: Shirai K. , Kawai Y. , Ohhashi T.
Published: July 2012

Effects of vasoactive substances were investigated in the canine isolated spinal branch of the intercostal artery (SBICA).

Addition of angiotensin II (AII), vasopressin, noradrenaline (NA), adrenaline, 5‐hydroxytryptamine (5‐HT), and dopamine each produced concentration‐dependent contraction in the SBICA, whereas prostaglandin F2α, histamine, and tyramine caused only slight contraction. The decreasing order of the potency of contractile agents was AII ≫ vasopressin = NA > 5‐HT > adrenaline ≫ dopamine.

Although the pD2 value for phenylephrine (5.31 ± 0.36) was smaller than that for NA (6.48 ± 0.13), there was no significant difference in Emax value between these two agonists in the SBICA. On the other hand, xylazine produced only a slight contraction, the pD2 value being 3.59 ± 0.08. Phentolamine (10−8–10−6m) and prazosin (10−8–10−6m) competitively inhibited the NA‐induced contraction, while yohimbine (10−8–10−6m)did not.

Acetylcholine (ACh), sodium nitroprusside (SNP), ATP, ADP, and adenosine caused concentration‐dependent relaxations in SBICA following contraction with NA. On the other hand, isoprenaline up to 10−4m did not produce any relaxation. The decreasing order of potency of the relaxant agents was ACh > SNP ≫ ATP = ADP = adenosine.

The ACh‐induced relaxation was competitively inhibited by atropine and was abolished by mechanical removal of the endothelium. Aspirin (5 × 10−5m) did not affect the relaxant response to ACh, while oxyhaemoglobin (10−5m) and methylene blue (10−5m) produced significant attenuation.

These results suggest that NA produces contraction of the isolated canine SBICA which is mainly mediated via α1‐adrenoceptors and that ACh causes a relaxation of the SBICA due to release of endothelium‐derived relaxing factor (EDRF) from the endothelial cells.
Haemodynamic alterations in anaesthetized and acutely intoxicated newborn piglets
Authors: Chandler Cara J. , Ong Bill Y. , Sitar Daniel S.
Published: July 2012

We investigated the haemodynamic alterations in 2‐day old anaesthetized piglets after acute ethanol intoxication using the microsphere technique.

After ethanol infusion, mean arterial blood pressure (MABP) decreased by 6%, cardiac output (CO) decreased by 26%, heart rate (HR) increased by 20% and systemic vascular resistance (SVR) increased by 36%.

Arterial perfusion to the kidneys, gastrointestinal (GI) organs and carcass decreased by 39%, 34% and 26%, respectively.

In piglets pretreated with 4‐methylpyrazole (4‐MP), an alcohol dehydrogenase inhibitor, the decrease in MABP and increase in HR were not observed after ethanol infusion, but the reduction in CO and increase in SVR were maintained.

Arterial blood flow to the GI organs and carcass, but not the kidneys, remained at significantly reduced levels.

These observations indicate that ethanol can adversely affect CO and arterial perfusion to GI and musculoskeletal structures while metabolites of ethanol, such as acetaldehyde, affect MABP and HR. Therefore, the clinical effects observed after acute ethanol intoxication in neonates may vary with their rate of ethanol metabolism.
Inhibition of human platelet activation by polymorphonuclear leukocytes
Authors: Schattner Mirta A. , Geffner Jorge R. , Isturiz Martin A. , Lazzari Maria A.
Published: July 2012

The effect of unstimulated human polymorphonuclear leukocytes (PMNs) on platelet activation was examined.

Human platelet aggregation and adenosine 5′‐triphosphate (ATP) release induced by collagen (1–2 μg ml−1); thrombin (0.01–0.02 u ml−1) or arachidonic acid (AA) (0.1–0.2 mm) were markedly inhibited when conducted in the presence of unstimulated PMNs.

Platelet inhibition induced by PMNs was dependent on the number of PMNs and on the incubation time of the mixed cell suspension.

Platelet inhibition was not reversed in time when PMNs were depleted from the mixed‐cell suspension.

PMN‐mediated platelet‐inhibition was not mediated by AA metabolites, oxygen reactive intermediates, nitric oxide or proteases.

The factor(s) accounting for the platelet inhibition mediated by PMNs are not yet characterized.
Role of epithelium in agonist‐induced contractile responses of guinea‐pig trachealis: influence of the surface through which drug enters the tissue
Authors: Iriarte C.F. , Pascual R. , Villanueva M.M. , Román M. , Cortijo J. , Morcillo E.J.
Published: July 2012

A method has been used in guinea‐pig isolated tracheal rings to achieve selective drug entry from the adventitial or mucosal surface. A study has been made of the effects of epithelium removal on responses to spasmogens entering the tissue solely from the adventitial or the mucosal surface.

Cumulative concentration‐response curves for KCl (1 to 100 mm), acetylcholine (0.1 μm to 10 mm) and histamine (1 μm to 1 mm) were constructed in intact and epithelium‐denuded tracheal rings in circumstances where drug entry was unrestricted or restricted to the adventitial or mucosal surface.

Epithelium removal did not alter the responsiveness or sensitivity of tracheal rings to KCl either when drug entry was unrestricted or when drug entry was restricted to the adventitial or mucosal surface.

When acetylcholine entered from the mucosal or adventitial surfaces of intact tracheal rings its concentration‐response curve was displaced to the right with respect to that obtained for unrestricted drug entry. A greater rightward shift was observed for mucosal drug entry than for adventitial drug entry. Epithelium removal potentiated acetylcholine entering from the mucosal surface to a greater extent (27.5 fold) than it potentiated acetylcholine entering from both surfaces (4 fold). Epithelium removal did not potentiate effects of acetylcholine entering from the adventitial surface alone.

In intact tracheal segments, concentration‐response curves for histamine entering from the mucosal surface were displaced to the right compared with those for histamine entering in an unrestricted fashion or from the adventitial surface alone. This displacement was absent in epithelium‐denuded preparations. Epithelium removal potentiated (2–3 fold) histamine entering from the mucosal surface or entering in an unrestricted way. It did not potentiate histamine entering from the adventitial surface alone.

Our findings suggest that the epithelium does not modulate tracheal responses to KCl. Its ability to modulate responses to acetylcholine and histamine is observed when these spasmogens enter the tissue from the mucosal surface but not when they enter from the adventitial surface. The mechanism by which epithelium removal preferentially potentiates acetylcholine and histamine entering from the mucosal rather than the adventitial surface remains to be determined.
Effects of morphine, H‐Tyr‐d‐Arg‐Phe‐Lys‐NH2 (DALDA) and B‐HT920 on non‐cholinergic nerve‐mediated bronchoconstriction in pithed guinea‐pigs
Authors: Rechtman M.P. , Boura A.L.A. , King R.G. , Olley J.E. , Schiller P.W.
Published: July 2012

Electrical stimulation (1 ms, 5 Hz, 80 V) for 5 or 15 s at the level of C4‐T1 in the spinal canal of artificially respired pithed guinea‐pigs (which had received intravenously (i.v.) (+)‐tubocurarine chloride 2 mg kg−1, atropine sulphate 2 mg kg−1 and pentolinium tartrate 5 mg kg−1) caused constriction of airways, indicated by increased insufflation pressure.

This non‐cholinergic constriction was inhibited by morphine (1–3 mg kg−1, i.v.), the peripherally acting μ‐receptor agonist, H‐Tyr‐d‐Arg‐Phe‐Lys‐NH2 (DALDA, 0.1–1 mg kg−1, i.v.) or the α2‐adrenoceptor agonist B‐HT920 (1–3 mg kg−1, i.v.)

The effects of either morphine (3 mg kg−1, i.v.) or DALDA (1 mg kg−1, i.v.) were inhibited by naloxone (3 mg kg−1, i.v.). Idazoxan (3 mg kg−1, i.v.) inhibited the anti‐constrictor effect of B‐HT920 (3 mg kg−1, i.v.), but not that of DALDA (0.1 mg kg−1, i.v.).

Thus activation of peripheral μ‐opioid receptors or α2‐adrenoceptors inhibits airways constriction induced by non‐cholinergic nerve stimulation in the pithed guinea‐pig. This preparation therefore provides a further method for the in vivo examination of the effects of drugs on non‐cholinergic tracheobronchial constrictor nerve function.
Effects of diltiazem on calcium concentrations in the cytosol and on force of contractions in porcine coronary arterial strips
Authors: Hirano Katsuya , Kanaide Hideo , Abe Shimako , Nakamura Motoomi
Published: July 2012

Using front‐surface fluorometry with fura‐2‐loaded porcine coronary arterial strips, we simultaneously measured effects of a Ca2+ antagonist, diltiazem, on cytosolic Ca2+ concentrations ([Ca2+]i) and on tension development.

In the presence of extracellular Ca2+ (1.25 mm), histamine concentration‐dependently induced abrupt (the first component) and then sustained (the second component) elevations of [Ca2+]i. In the absence of extracellular Ca2+, histamine induced transient elevations of [Ca2+]i, and the time course was similar to that of the first component observed in the presence of extracellular Ca2+. Histamine caused a greater contraction for a given change in [Ca2+]i than did potassium, at [Ca2+]i over 300 nm.

Diltiazem, 10−8 m to 10−5 m, concentration‐dependently inhibited the second component of [Ca2+]i elevation and tension development induced by histamine (10−5 m). Only at higher concentrations (over 10−5 m) did diltiazem inhibit the first component of increases in [Ca2+]i and tension development induced by histamine, both in the presence and absence of extracellular Ca2+.

Diltiazem (10−6 m) inhibited increases in [Ca2+]i and tension development induced by cumulative applications of extracellular Ca2+ during K+‐depolarization. The curve of [Ca2+]i against tension of these Ca2+‐induced contractions obtained in diltiazem‐treated strips overlapped with that obtained in untreated strips. This suggests that diltiazem has no direct effects on contractile elements.

In contrast, the histamine‐induced Ca2+‐tension curve (second component) was shifted in parallel to the left by diltiazem.

We conclude that diltiazem, at therapeutic concentrations, specifically inhibits extracellular Ca2+‐dependent increases in [Ca2+]i, with no effects on the release of Ca2+ from intracellular store sites or on Ca2+‐sensitivity of the contractile elements involved in the contractions induced by elevations of [Ca2+]i.
Zacopride and BRL 24924 induce an increase in EEG‐energy in rats
Authors: Boddeke Hendrik W.G.M. , Kalkman Hans O.
Published: July 2012

The substituted benzamides, zacopride and BRL 24924 induced dose‐dependent increases of the total EEG‐energy of rats when applied intracerebroventricularly (i.c.v.) with ED50 values of 8.0 ± 0.6 and 3.6 ± 0.9 μg, respectively. Not only the energy of the low frequency hippocampal theta rhythm but also that of the other frequency bands was increased.

In contrast to i.c.v. application intraperitoneal administration of zacopride or BRL 24924 (1 and 10 mg kg−1) did not lead to an increase in EEG‐energy.

The increase in EEG‐energy induced by zacopride (10 μg, i.c.v.) was blocked by ICS 205–930 (1 μg, i.c.v.). Neither the 5‐HT3 receptor agonist 2‐methyl‐5‐hydroxytryptamine (30 μg, i.c.v.) nor the selective 5‐HT3 receptor antagonist MDL 72222 (30 μg, i.c.v.) had any effect upon rat EEG.

Scopolamine (0.01 μg and 0.1 μg, i.c.v.) dose‐dependently antagonized the effect of zacopride (10 μg, i.c.v.).

An agonist action of zacopride and BRL 24924 and inhibition of these effects by ICS 205–930 but not by MDL 72222 was recently described in isolated colliculi neurones from neonatal mice. The receptor involved was described as ‘5‐HT4’. The present results indicate that the central effects of zacopride and BRL 24924 may be due to activation of such a 5‐HT receptor.
High‐ and low‐affinity binding sites for [3H]‐α,β‐methylene ATP in rat urinary bladder membranes
Authors: Bo Xuenong , Burnstock Geoffrey
Published: July 2012

The characteristics of [3H]‐α,β‐methylene adenosine 5′‐triphosphate ([3H]‐α,β‐MeATP) binding to membrane preparations of rat urinary bladder detrusor were studied.

The rat bladder membrane preparation was obtained by multiple centrifugation. [3H]‐quinuclidinyl benzilate ([3H]‐QNB) binding to this preparation demonstrated that the muscarinic receptor density was 4.32 times higher than that in the homogenate. [3H]‐α,β‐MeATP binding was increased 3.88 times.

Saturation analysis revealed that the rat bladder membrane contained a high density of [3H]‐α,β‐MeATP binding sites, which could be divided into a high‐affinity component (Kd = 8.1–8.9 nm) and a low‐affinity component (Kd = 67.0–119.8 nm).

Magnesium ions inhibited the maximum binding in a concentration‐dependent manner. The maximum high‐affinity binding was reduced from 10.32 pmol mg−1 protein in magnesium‐free buffer to 4.62 pmol mg−1 protein with 25 mm MgCl2, while the maximum low‐affinity binding was reduced from 58.84 pmol mg−1 protein to 14.24 pmol mg−1 protein. Kd values were not greatly affected.

The binding was a rapid reversible process. The association rate constants were 7.64 × 107 m−1 min−1 for high‐affinity binding, and 7.31 × 106 m−1 min−1 for low‐affinity binding. The dissociation rate constants were 0.2896 min−1 for high‐affinity binding, and 0.6348 min−1 for the low‐affinity binding.

Displacement experiments with unlabelled purinoceptor ligands confirmed that [3H]‐α,β‐MeATP mainly binds to P2X‐purinoceptors. The potency order was: α,β‐methylene ATP > β,γ‐methylene ATP > suramin > ATP > ADP > 2‐methylthio ATP ≫ adenosine.

The results indicate that [3H]‐α,β‐MeATP is a radioligand for the P2X‐purinoceptor, which satisfies the basic criteria for use in radioligand binding assay.
Binding of [125I]‐endothelin‐1 to rat cerebellar homogenates and its interactions with some analogues
Authors: Hiley C. Robin , Jones C. Richard , Pelton John T. , Miller Robert C.
Published: July 2012

[125I]‐endothelin‐1, over the concentration range 6 pm–10 nm, bound to a single site in homogenates of rat cerebellum with high affinity (Kd = 2.8 ± 0.6 × 10−10 m). The site was present in a concentration of 321 ± 58 fmol mg−1 protein.

The rates of association and dissociation of [125I]‐endothelin‐1 with the binding site were slow (at 25°C, k+1 = 8.0 ± 1.3 × 105m−1 s−1; k−1 = 2.6 × 10−4 s−1) and, on addition of a maximally displacing concentration of endothelin‐1 (100 nm), 94.0 ± 8.4% of the [125I]‐endothelin‐1 was still bound after 14h.

[125I]‐endothelin‐1 binding was inhibited by a number of naturally occurring or genetically encoded members of the endothelin/sarafotoxin family of peptides. The order of potency was endothelin‐3 = sarafotoxin S6b > endothelin‐2 = endothelin‐1 ≫ porcine proendothelin1–39.

Binding was also inhibited by analogues in which either one or both of the cystine disulphide bridges had been replaced by substitution with 2 or 4 alanine residues. The tetra‐alanyl substituted analogue, [Ala1,3,11,15]endothelin‐1, was equipotent with endothelin‐1 at inhibiting the binding of [125I]‐endothelin‐1. [Ala3,11]endothelin‐1 and [Ala1,15]endothelin‐1, analogues which each contained one of the disulphide bridges from the parent peptide, were respectively 3 and 14 times less potent than the parent peptide. An analogue in which the Glu10 residue had been anisylated was 25 fold less potent than endothelin‐1.

It is concluded that the structural requirements for binding to the cerebellar sites for [125I]‐endothelin‐1 do not require the presence of the disulphide bridges characteristic of the endothelin/sarafotoxin family. Rather, the binding may be more sensitive to the presence of bulky side chain substituents, at least in the smaller intramolecular loop.
Characterization of the l‐arginine: nitric oxide pathway in human platelets
Authors: Radomski M.W. , Palmer R.M.J. , Moncada S.
Published: July 2012

The activation of the l‐arginine:nitric oxide (NO) pathway during aggregation of human platelets by adenosine 5′‐diphosphate (ADP), arachidonic acid, thrombin and the calcium ionophore A23187 and its inhibition by NG‐monomethyl‐l‐arginine (l‐NMMA), NG‐nitro‐l‐arginine methyl ester (l‐NAME) and N‐iminoethyl‐l‐ornithine (l‐NIO) were studied. The inhibition of the cytosolic platelet NO synthase by these compounds was also examined.

Platelet aggregation induced by ADP (1–10 μm) and arachidonic acid (0.1–10 μm), but not that induced by thrombin (1–30 mu ml−1) or A23187 (1–10 nm), was inhibited by l‐, but not d‐arginine (1–30 μm). However, in the presence of a subthreshold concentration of prostacyclin (0.1 nm) or of M & B 22948 (1 μm), a selective inhibitor of guanosine 3′:5′‐cyclic monophosphate (cyclic GMP) phosphodiesterase, l‐arginine caused concentration‐dependent inhibition of aggregation induced by all of these aggregating agents.

l‐NMMA, l‐NAME and l‐NIO (all at 1–30 μm), but not their d‐enantiomers, enhanced to the same extent platelet aggregation induced by ADP, arachidonic acid and thrombin without affecting that induced by A23187.

In the presence of 300 μm l‐arginine, the NO synthase in platelet cytosol was inhibited by l‐NMMA, l‐NAME and l‐NIO with IC50s of 74 ± 9, 79 ± 8 and 8.5 ± 1.5 μm (n = 3), respectively.

These results indicate that the l‐arginine: NO pathway in human platelets plays a role in the modulation of platelet aggregation.
Bradykinin‐induced vasoconstriction of rat mesenteric arteries precontracted with noradrenaline
Authors: Fasciolo Juan C. , Vargas Leonor , Lama M. Cristina , Nolly Héctor
Published: July 2012

Administration of bradykinin caused dose‐dependent vasoconstriction in rat isolated perfused mesenteric arteries precontracted with noradrenaline.

The vasoconstrictor response was not mediated by BK1‐bradykinin receptors.

Inhibition of cyclo‐oxygenase with indomethacin, aspirin or meclofenamate abolished the vasoconstrictor effect of bradykinin, showing that a member of the arachidonic acid cascade may be involved.

Inhibitors of thromboxane synthesis (imidazole and UK 38485) did not affect or only reduced the bradykinin‐induced vasoconstriction.

The endoperoxide H2/thromboxane A2 receptor antagonist SQ 29548 significantly reduced the vasoconstrictor effect of bradykinin, but did not affect the vasoconstrictor response to noradrenaline, adrenaline, vasopressin, 5‐hydroxytryptamine or prostaglandins.

The eicosanoid(s) that mediate bradykinin‐induced vasoconstriction appear to be synthesized outside the arterial endothelium.

The data suggest that the vasoconstrictor effect of bradykinin in the rat isolated mesenteric artery is mediated by vasoconstrictor arachidonic acid metabolites including the cyclic endoperoxides and/or the thromboxanes.
Effects of organophosphorus anticholinesterases on nicotinic receptor ion channels at adult mouse muscle endplates
Authors: Tattersall John E.H.
Published: July 2012

The effects of a range of organophosphorus anticholinesterases on the nicotinic acetylcholine receptor ion channel at the adult mouse muscle endplate were investigated by use of single‐channel recording techniques. Diisopropylfluorophosphate (DFP), sarin and soman had no effect on open times at concentrations of up to 100 μm, but ecothiopate (Eco) and O‐ethyl S‐[2‐(diisopropylamino)ethyl]methyl phosphonothiolate (VX) were found to have voltage‐ and concentration‐dependent open channel‐blocking actions at concentrations of 1–50 μm. In addition to its channel‐blocking action, Eco (50 μm) had a weak agonist effect: it is suggested that this may be attributable to thiocholine produced by hydrolysis of Eco.

Rate constants for blockade by Eco and VX were determined according to a sequential model. The greater voltage‐dependence of the block by Eco was due to a greater voltage sensitivity of the blocking rate constant compared to VX: the voltage‐dependence of the unblocking rate constant was similar for both compounds.

In control recordings, the frequency of channel opening declined exponentially with time after formation of the gigaseal. Sarin and soman both increased the rate of this decline, indicating that they accelerated the rate of desensitization of the receptors. Eco and VX reduced the initial frequency of opening, which may have been due to enhancement of a fast phase of desensitization during gigaseal formation, or to blockade of closed channels.

It is concluded that the direct actions of organophosphates on nicotinic receptor ion channels are of little importance for their toxicity under normal conditions, since they occur only at much higher concentrations than those which cause inhibition of acetylcholinesterase. Such actions may become apparent, however, when therapies against the anticholinesterase effects of organophosphates increase their lethal dose sufficiently. These direct actions should also be taken into account when the effects of organophosphates on cholinergic transmission are studied.
Positive inotropic effect of porcine left ventricular extract on canine ventricular muscle
Authors: Navaratnam S. , Chau T. , Agbanyo M. , Bose D. , Khatter J.C.
Published: July 2012

We previously isolated an extract from porcine left ventricle that possessed digitalis‐like properties such as inhibition of cardiac and kidney Na+, K+‐ATPase, displacement of [3H]‐ouabain from its binding sites and cross reactivity with digoxin antibodies. The extract also had a positive inotropic effect on the guinea‐pig heart.

In the present study the positive inotropic response of the extract was characterized in canine right ventricular trabeculae. Maximum inotropic response (501 ± 20%) was produced by 300 μl and the half maximal increase occurred with 125 μl of the extract.

Ouabagenin produced aftercontractions in rapidly paced trabeculae. Equipotent and even greater amounts of the extract did not produce aftercontractions.

The extract increased the amplitude of the delayed component (P2) of biphasic contractions produced by replacing about 92–96% of the external Ca with Sr. A smaller increase in the size of the early component (P1) was also seen.

The extract decreased post‐rest potentiation after rest for 30 s and 2 min. After 8 min of rest, post‐rest potentiation was converted to post‐rest depression.

The extract (20 μl) produced a decrease in the amplitude of the post‐rest rapid cooling contracture (RCC) at all rest intervals. The steady state RCC, although greater than that in the control muscle, was increased to a lesser extent than the size of the steady state electrically driven contractions.

It is suggested that the extract from porcine left ventricle produces a positive inotropic response by increasing the trans‐sarcolemmal influx of Ca. It also has additional effect(s) on the sarcoplasmic reticulum in that it may facilitate the loss of Ca from the sarcoplasmic reticulum and/or inhibit the uptake of Ca by the organelle.
The effects of ryanodine and caffeine on Ca‐activated current in guinea‐pig ventricular myocytes
Authors: White Edward , Terrar Derek A.
Published: July 2012

Action potentials from guinea‐pig single ventricular myocytes were interrupted by application of a 300 ms voltage clamp to −40 mV in order to evoke the Ca‐activated tail current which is thought to be carried by Na: Ca exchange. Stimulation frequency was 1 Hz and temperature 36°C.

The actions of ryanodine (1 μm and 10 μm) and caffeine (1 mm and 10 mm) on Ca‐activated tail currents were investigated.

Exposure to 10 mm caffeine and ryanodine reduced tail currents associated with very abbreviated (12 ms duration) action potentials and greatly reduced the difference between first and steady‐state tail currents at this action potential duration. These observations were interpreted in terms of suppression of Ca release from the sarcoplasmic reticulum (SR) stores.

Tail current decay during the voltage clamp is thought to reflect the fall in [Ca]i which accompanies muscle relaxation. Current decay is dependent on Ca extrusion via Na:Ca exchange and on Ca accumulation by the SR stores. Time constants of tail current decay were seen to decrease with increasing action potential duration. This relationship was not affected by 1 mm caffeine or 1 μm ryanodine. Ryanodine at 10 μm and 10 mm caffeine abolished this relationship and increased the time constants of current decay. An increase in the time constant of tail current decay was thought to reflect a reduction in the rate of Ca accumulation by the sarcoplasmic reticulum.

The actions of caffeine and ryanodine on the Ca‐activated tail currents are consistent with a dose‐dependent leakage of Ca from the SR Ca stores. The Ca‐activated tail current appears to be a useful tool in the study of Ca homeostasis.
Inhibitory effect of streptozotocin‐induced diabetes on non‐cholinergic motor transmission in rat detrusor and its prevention by sorbinil
Authors: Luheshi G.N. , Zar M.A.
Published: July 2012

Non‐cholinergic motor transmission in the urinary bladder of streptozotocin (STZ)‐diabetic rats was studied by recording contractile activity of strips of detrusor in vitro.

The neurogenic contractile responses to electrical field stimulation (EFS) of atropine‐treated detrusor strips were decreased in 4, 8 and 12 week STZ‐diabetic rats. The decrease was most marked in 12 week diabetic rats and least in 4 week ones.

Concentration‐response curves showed no change in sensitivity of the detrusor to acetylcholine (ACh) in diabetic rats. The maximum tension generated by ACh was similar in diabetic and non‐diabetic animals.

The contractile responses to EFS at frequencies ≥ 1 Hz were not maintained during stimulation. The ‘fade’ was significantly greater in detrusor strips of diabetic rats.

The contractile response of detrusor to EFS was significantly greater in 12 week diabetic rats treated with the aldose reductase inhibitor sorbinil, than in untreated 12 week diabetic rats. The sensitivity to ACh was similar in the two groups.

It is concluded that the reduction of the neurogenic non‐cholinergic responses of detrusor to EFS in STZ‐diabetic rats is probably caused by a reduction in the release of the non‐cholinergic motor transmitter. The results are discussed in relation to bladder dysfunction in human diabetes mellitus.
Impairment of relaxations to acetylcholine and nitric oxide by a phorbol ester in rat isolated aorta
Authors: Morrison Keith J. , Pollock David
Published: July 2012

This study compared the abilities of acetylcholine (ACh) (endothelium‐dependent) and nitric oxide (NO) (endothelium‐independent and which may be the active component of the endothelium‐derived relaxing factor) to relax rat isolated aortic rings contracted with equi‐effective concentrations of noradrenaline (NA) or phorbol 12‐myristate 13‐acetate (PMA).

ACh and NO induced concentration‐dependent relaxations of aortic rings contracted with NA (EC70 value: 0.2 μm). However, relaxations to both ACh and NO were markedly reduced in rings contracted with PMA (EC80 value: 0.5 μm). NO‐induced relaxations of tissues were not affected by removal of the endothelium, but ACh‐induced relaxations were confirmed to be endothelium‐dependent.

ACh (10 μm) induced a 10 fold increase in guanosine 3′:5′‐cyclic monophosphate (cyclic GMP) levels above control values in aortic rings contracted with NA (0.2 μm), but did not affect cyclic GMP levels in rings contracted with PMA (0.5 μm).

NO (3 μm) induced a 100 fold increase in cyclic GMP levels above control values in aortic rings contracted with NA (0.2 μm), but only an 11 fold increase in tissues contracted with PMA (0.5 μm).

It is concluded that the action (s) of EDRF (NO) are impaired in the presence of PMA by a mechanism that may involve the stimulation of protein kinase C in vascular smooth muscle cells.
Distinct antinociceptive actions mediated by different opioid receptors in the region of lamina I and laminae III‐V of the dorsal horn of the rat
Authors: Hope P.J. , Fleetwood‐Walker S.M. , Mitchell R.
Published: July 2012

In view of the presence of μ, δ and κ opioid receptors in the spinal dorsal horn and their apparent involvement in behavioural analgesia, the present experiments addressed the action of selective agonists ionophoresed in the vicinity of rat dorsal horn neurones which were located either in lamina I or in laminae III‐V.

In laminae III‐V, κ agonists (U50488H and dynorphin A) caused a selective inhibition of the nociceptive responses of multireceptive cells, whilst μ and δ agonists ([d‐Ala2,MePhe4,Gry‐ol]enkephalin and [d‐Pen2,d‐Pen5]enkephalin respectively) failed to alter either the spontaneous activity or the responses to noxious and innocuous cutaneous stimuli and to d,l‐homocysteic acid or glutamate. Nocispecific neurones were encountered too rarely in laminae III‐V to study their properties.

In lamina I, agonists had no effects on either nocispecific or multireceptive neurones. In contrast, the μ agonist [d‐Ala2,MePhe4,Gly‐ol]enkephalin consistently inhibited nociceptive responses of both multireceptive and nocispecific lamina I cells. The δ agonist [d‐Pen2,d‐Pen5]enkephalin consistently caused selective inhibition of the nociceptive responses of multireceptive cells but had a mixed profile of action on nocispecific cells.

These results suggest that μ, δ and κ opioid receptors mediate different antinociceptive actions in both laminae III‐V and lamina I. The study reveals a distinct physiological role for δ receptors in modulating nociceptive inputs to lamina I neurones. In contrast to μ and κ receptor actions, δ receptors heterogeneously influence subpopulations of neurones.
The anti‐adrenergic effect of adenosine and its blockade by pertussus toxin: a comparative study in myocytes isolated from guinea‐pig, rat and failing human hearts
Authors: Brown L.A. , Humphrey S.M. , Harding S.E.
Published: July 2012

In intact ventricular preparations, adenosine has been shown to reduce the β‐adrenoceptor‐induced increase in contraction (the anti‐adrenergic effect). In the present study we have investigated this effect of adenosine on isolated ventricular myocytes from failing human heart and normal guinea‐pig and rat heart.

Adenosine in the absence of β‐adrenoceptor‐mediated stimulation had no effect on contraction in human and guinea‐pig myocytes but produced a variable effect in rat myocytes.

8‐Cyclopentyl 1,3‐dipropylxanthine (CPX), a selective A1‐receptor antagonist, antagonised the anti‐adrenergic effect of adenosine in guinea‐pig myocytes.

The anti‐adrenergic effect of adenosine was greater in guinea‐pig than rat myocytes and even more pronounced in cells isolated from failing human heart.

Pertussis toxin‐pretreatment at 35°C of guinea‐pig and human myocytes abolished the anti‐adrenergic effect of adenosine. Longer exposure to higher concentrations of pertussis toxin was required for complete abolition in human compared to guinea‐pig cells.

These results support the suggestion that the adenosine receptors mediating the anti‐adrenergic effect of adenosine are of the A1 subtype and are coupled to the inhibitory guanine nucleotide binding protein, Gi/Go.

Pertussis toxin pretreatment increased the sensitivity of guinea‐pig myocytes to isoprenaline in the absence of adenosine; the EC50 value was decreased by a factor of 10. This suggests that Gi may exert a tonic inhibitory effect on the β‐adrenoceptor/adenylate cyclase interaction in normal myocardium.
α‐Methyldopa induces a naltrexone‐insensitive antinociception and hypomotility in rats
Authors: van Giersberge Paul L.M. , van Duinkerken Elizabeth , Sweep C.G.J. (Fred) , Wiegant Victor M. , van Ree Jan M. , de Jong Wybren
Published: July 2012

This study served to investigate whether endogenous opioid peptides play a role in the putative antinociceptive and the sedative actions of α‐methyldopa.

In conscious normotensive rats, α‐methyldopa induced hypotension, starting around 1 h and reaching a maximum 3–4 h after administration. Pretreatment with naltrexone resulted in an inhibition of α‐methyldopa‐induced hypotension.

α‐Methyldopa dose‐dependently increased hot plate latency which became evident after a 4 h lag period and reaching a maximum effect at 6 h. The antinociceptive effect of α‐methyldopa was not affected by naltrexone.

In a small open field, α‐methyldopa dose‐dependently suppressed locomotion and sniffing behaviour. These effects of α‐methyldopa were apparent 1 h after administration and were naltrexone‐insensitive.

No changes in the level of β‐endorphin‐like immunoreactivity in plasma and cerebrospinal fluid were observed after administration of α‐methyldopa.

The results indicate that endogenous opioid peptides are involved in the hypotensive action of α‐methyldopa but not in α‐methyldopa‐induced hypomotility and antinociception.
Heterogeneity of α2‐adrenoceptors in rat cortex but not human platelets can be defined by 8‐OH‐DPAT, RU 24969 and methysergide
Authors: Brown C.M. , MacKinnon A.C. , McGrath J.C. , Spedding M. , Kilpatrick A.T.
Published: July 2012

Saturation experiments indicated that [3H]‐yohimbine binding was specific, saturable and labelled a single population of sites in rat cerebral cortex (Kd 5.3 ± 0.9 nm, Bmax 121 ± 10 fmol mg−1 protein) and human platelets (Kd 0.7 ± 0.1 nm, Bmax 152 ± 10 fmol mg−1 protein).

The α2‐adrenoceptor antagonists, yohimbine, rauwolscine, WY 26703, idazoxan and BDF 6143 displaced [3H]‐yohimbine binding to each tissue in a simple manner, with high affinity and Hill slopes close to unity.

The α1‐adrenoceptor agonist, oxymetazoline and the antagonist prazosin inhibited the binding of [3H]‐yohimbine to rat cortex in a complex manner consistent with an interaction at more than one site. However, indoramin and WB 4101 only appeared to interact with one site. In contrast, in human platelets, all antagonists gave rise to monophasic displacement curves with Hill slopes close to unity suggesting a single site of interaction.

The 5‐hydroxytryptamine (5‐HT) receptor ligands, 8‐hydroxy‐2‐(di‐n‐propylamino)‐tetralin (8‐OH‐DPAT), RU 24969, and methysergide inhibited the binding of [3H]‐yohimbine to rat cortex with high and low affinity, consistent with an interaction with two populations of binding sites. However, inhibition of [3H]‐yohimbine binding to human platelets suggested a single site of interaction. The low affinity of 5‐HT, 5‐carboxyamidotryptamine (5‐CT) and dipropyl‐5‐CT indicated that [3H]‐yohimbine was not labelling a 5‐HT1‐like site in rat cortex.

The ability of 8‐OH‐DPAT, RU 24969 and methysergide in addition to prazosin and oxymetazoline to differentiate [3H]‐yohimbine binding provides additional pharmacological evidence for heterogeneity within rat cortical α2‐adrenoceptors. However, if the two sites in rat cortex that are differentiated by the 5‐HT ligands represent α2A‐ and α2B‐adrenoceptor subtypes as defined by prazosin and oxymetazoline, then they do not correspond to the population of sites in human platelets. As receptor classification should be linked to affinity of drugs rather than tissue distribution, the current classification of α2‐adrenoceptor subtypes does not appear to be satisfactory.
Effects of pinacidil, RP 49356 and nicorandil on ATP‐sensitive potassium channels in insulin‐secreting cells
Authors: Dunne M.J.
Published: July 2012

The whole‐cell patch‐clamp technique has been used to investigate the effects of pinacidil, RP 49356 and nicorandil on membrane potential and adenosine 5′‐triphosphate (ATP)‐sensitive K+ channel currents in the insulin‐secreting cell line RINm5F. Interactions between pinacidil, RP 49356, nicorandil, diazoxide and ATP have been studied in excised outside‐out membrane patches and open‐cells.

In RINm5F whole‐cells (current‐clamp mode) continually exposed to glucose, pinacidil, RP 49356 and nicorandil, at concentrations greater than 100 μm, consistently reversed the effects of the sugar by repolarizing the membrane and terminating voltage‐gated Ca2+ spike‐potentials.

The actions of pinacidil, RP 49356 and nicorandil on membrane potential may be explained by their effects on the opening of ATP‐sensitive K+ channels, since all three compounds activated channels in whole‐cells (voltage‐clamp mode), excised outside‐out membrane patches and open‐cells, at concentrations greater than 100 μm. Below 100 μm the actions of pinacidil, RP 49356 and nicorandil were weak and inconsistent.

The mechanism of channel activation appears to depend on the presence of cytosolic ATP, since in its absence, pinacidil, RP 49356 and nicorandil (> 100 μm) had either no effects or inhibited K+ channels.

Pinacidil, nicorandil and RP 49356 (200–500 μm) also appeared to open K+ channels inhibited by quasi‐physiological concentrations of ATP (4 mm) and ADP (1 mm). However, in comparison to diazoxide their effects were weak.

Since pinacidil, RP 49356 and nicorandil have been shown to have effects on smooth muscle preparations at concentrations of 30 μm and below, the data presented in this study may have important implications for any prospective therapeutic application of the drugs, since at the concentrations required to relax smooth muscle cells, hyperglycaemia will be avoided.
Opioid receptor ligands in the neonatal rat spinal cord: binding and in vitro depression of the nociceptive responses
Authors: James I.F. , Bettaney J. , Perkins M.N. , Ketchum S.B. , Dray A.
Published: July 2012

Opioid receptors in the neonatal rat spinal cord have been characterized by measurements of ligand binding to crude membrane fractions and by functional tests on the nociceptive spinal response in a spinal cord‐tail preparation in vitro.

There were high affinity binding sites for [3H]‐[d‐Ala2, MePhe4, Gly(ol)5]enkephalin (DAGOL), [3H]‐U69593, and [3H]‐ethylketocyclazocine (EKC) on spinal cord membranes from neonatal rats. Hill slopes for binding of [3H]‐DAGOL and [3H]‐U69593 were close to unity. The Hill slope for binding of [3H]‐EKC was less than unity, even after its interactions at μ‐receptors had been blocked with 100 nm unlabelled DAGOL. Binding sites for [3H]‐[d‐Pen2, d‐Pen5]enkephalin (DPDPE) could not be detected.

In competition assays U50488 was as potent as PD117302 and U69593 in competition for either [3H]‐U69593 or [3H]‐EKC binding sites. Hill slopes for a range of competing ligands at [3H]‐DAGOL or [3H]‐U69593 sites were close to unity. Hill slopes for competition at [3H]‐EKC sites were less than one.

In the spinal cord‐tail preparation from neonatal rats, opioid receptor agonists depressed spinal nociceptive responses evoked by application of capsaicin or heat to the tail. The order of potency was DAGOL > U69593 = PD117302 > morphine > U50488 = [d‐Pen2, l‐Pen5]enkephalin (DPLPE).

The antagonist naloxone was about equally potent against DAGOL, morphine and DPLPE, and about ten times less potent against U69593 and PD117302. The effects of U50488 were much less sensitive to blockade by naloxone than the effects of PD11703 or U69593. The κ antagonist, nor‐binaltorphimine was equipotent against all three κ agonists.

The absence of δ‐binding sites, and the low potency and relatively high sensitivity to naloxone suggest that DPLPE could be working at μ‐receptors in the neonatal rat spinal cord.

The binding assays show that U50488 has the same affinity as PD117302 and U69593 for κ‐receptors, yet it was less effective in the depression of nociceptive responses. This may be because U50488 has a relatively low efficacy at κ‐receptors. It is possible that at high concentrations U50488 activates receptors not affected by other κ‐ligands. These additional receptors may be non‐opioid receptors (hence the insensitivity to naloxone), or they could be a subtype of κ‐opioid receptor.
Effects of B‐HT 920 on nigrostriatal and mesolimbic dopamine systems in normosensitive and supersensitive rats
Authors: Clarke Paul B.S. , Wyder Kathleen J. , Jakubovic Alexander , Fibiger Hans C.
Published: July 2012

B‐HT 920, a D2 dopamine receptor agonist, was tested for its ability to exert presynaptic actions in normosensitive rats, and for possible postsynaptic actions in rats made ‘supersensitive’ to apomorphine.

In normosensitive rats, B‐HT 920 (0.01–0.3 mg kg−1, i.p.) increased dopamine concentrations and lowered metabolite levels to a similar extent in all four terminal regions examined (medial prefrontal cortex, olfactory tubercle, nucleus accumbens, caudate‐putamen). Analogous effects were seen for 5‐hydroxytryptamine and its metabolite 5‐hydroxyindoleacetic acid.

Rats which received bilateral 6‐hydroxydopamine (6‐OHDA) infusions into the caudate‐putamen showed signs of postsynaptic dopamine receptor activation (stereotyped behaviour) in response to B‐HT 920 (0.1 and 1.0 mg kg−1, i.p.) and to apomorphine (0.2 mg kg−1, s.c.). Similarly, B‐HT 920 (0.1 mg kg−1) induced contralateral circling in rats that had received unilateral 6‐OHDA infusions into the medial forebrain bundle; the rate of circling increased gradually over several weeks.

In contrast, bilateral 6‐OHDA infusions into the nucleus accumbens resulted in a supersensitive (locomotor stimulant) response to a low dose of apomorphine (0.1 mg kg−1, s.c.), but not to B‐HT 920 (0.01 and 0.1 mg kg−1).

In intact rats, withdrawal of chronic haloperidol treatment induced behavioural supersensitivity to apomorphine but not to B‐HT 920.
The involvement of 5‐hydroxytryptaminergic and dopaminergic mechanisms in the eating induced by buspirone, gepirone and ipsapirone
Authors: Fletcher Paul J. , Davies Michael
Published: July 2012

The roles of 5‐hydroxytryptamine (5‐HT) and dopamine systems in mediating the increased feeding induced by buspirone, gepirone and ipsapirone were investigated.

All three compounds induced dose‐dependent increases in food intake when administered subcutaneously to free feeding rats. Buspirone was effective over a narrower dose range than either gepirone or ipsapirone, and the maximal effect observed was smaller than the effects elicited by gepirone and ipsapirone.

Depletion of brain 5‐HT with parachlorophenylalanine (PCPA) prevented the effects of equi‐effective doses of gepirone (2.5 mg kg−1) and ipsapirone (2.5 mg kg−1), but failed to prevent buspirone (1 mg kg−1)‐induced eating. Thus buspirone does not appear to interact with 5‐HT systems to elicit feeding.

Gepirone (0.2 μg) and ipsapirone (0.04 and 0.2 μg) increased food intake when injected into the dorsal raphé nucleus (DRN), presumably by inhibiting the activity of DRN 5‐hydroxytryptaminergic afferents. Buspirone (0.04–5 μg) was ineffective when injected into the DRN.

Pretreatment with haloperidol (0.1 mg kg−1, 30 min) significantly attenuated the effects of equi‐effective doses of buspirone, gepirone and ipsapirone, indicating that these drugs interact with dopaminergic systems to increase feeding.

Previously it has been shown that each of these drugs increases striatal dopamine activity. Increased dopaminergic neurotransmission in the striatum induces a general behavioural activation, which under certain conditions facilitates feeding. It is possible that this mechanism underlies the behavioural effects of buspirone, gepirone and ipsapirone. The effects of gepirone and ipsapirone probably involve an indirect action to inhibit the activity of DRN 5‐hydroxytryptaminergic afferents, whereas buspirone interacts directly with dopaminergic systems.
Release of a neutrophil‐derived vascoconstrictor agent which augments platelet‐induced contractions of blood vessels in vitro
Authors: Sessa William C. , Mullane Kevin M.
Published: July 2012

The effects of neutrophil‐derived products on vascular tone in vitro were examined by adding purified rabbit neutrophils to siliconized organ baths containing rings of rabbit thoracic aorta.

Neutrophil‐derived products induced a concentration‐dependent contraction of the blood vessels generating 3.9 ± 0.2 g of tension at a cell concentration of 2 × 106 ml−1. This contractile response was not dependent on an intact endothelium and was not ameliorated by treatment of the neutrophils with inhibitors of lipoxygenase or cyclo‐oxygenase enzymes, by free radical scavengers or by the use of end organ antagonists to angiotensin II, desArg9‐bradykinin, histamine, catecholamines or acetylcholine.

Neutrophils stimulated with phorbol myristate acetate, formyl methionyl‐leucyl‐phenylalanine or calcium ionophore A23187 released a contractile factor into the supernatant which produced qualitatively similar contractions compared to those elicited by incubation with intact unstimulated neutrophils.

Ten to twenty times more platelets were required to evoke equivalent contractions to those observed with neutrophils. However, neutrophil supernates significantly augmented platelet‐mediated contractions (P < 0.001).

Contractions elicited by neutrophils and supernates derived from activated neutrophils were partially antagonized by 5‐hydroxytryptamine (5‐HT) receptor antagonists, methysergide and ketanserin. However, the inhibition of exogenous 5‐HT‐induced contractions on rabbit aorta and rat stomach strips by both antagonists was greater than the inhibition of contractions produced by neutrophils and neutrophil‐derived supernates.

Extraction of the biologically active material from supernatants of activated neutrophils into acetone, but not chloroform‐methanol or ethyl acetate, suggests the contractile factor may be a protein/peptide. Partial purification on a Sephadex G100 column yields a contractile factor with a molecular weight of less than 4,000 daltons.

This factor may augment vascular tone, either directly or by interactions with platelets, in pathophysiological states associated with neutrophil activation and accumulation.