bluuebunny/crossref_metadata_2025_split huggingface dataset:
Spinal antinociceptive actions of μ‐ and κ‐opioids: the importance of stimulus intensity in determining ‘selectivity’ between reflexes to different modalities of noxious stimulus
Authors: Parsons Chris G. , Headley P. Max 
Published: July 2012

In electrophysiological experiments in spinalized rats, μ‐ and κ‐opioids were tested intravenously on the responses of single motoneurones to electronically controlled, alternating noxious heat and noxious pinch stimuli. The effects of μ‐ and κ‐opioids were compared with those of the general anaesthetic α‐chloralose and the dissociative anaesthetic/PCP ligand ketamine.
The κ‐opioids U‐50,488 (0.5–16 mg kg−1 i.v.) and tifluadom (0.05‐1.6 mg kg−1 i.v.) had very similar actions to the μ‐opioid fentanyl (0.5–16 μg kg−1 i.v.). Thus all three agonists reduced thermal and mechanical nociceptive reflexes in parallel and in a dose‐dependent manner, but only so long as neuronal responses to the alternating stimuli elicited similar excitability levels in the neurone under study. Ketamine (0.5–16 mg kg−1 i.v.) had similar actions to the opioids whereas α‐chloralose (20 mg kg−1 i.v.) had very little effect on neuronal responsiveness.
Apparently ‘selective’ depressions by both μ‐ and κ‐opioids could be orchestrated by a deliberate mismatch of the intensities of alternating noxious heat and pinch stimuli; as measured by neuronal firing rate, the weaker of the responses to either type of stimulus was invariably reduced to a greater degree.
Similar ‘selectivity’ could be demonstrated for both μ‐ and κ‐ligands when the weaker and stronger responses were of the same modality, being applied by the same pincher device but with alternating applied force.
It is concluded that the ‘selective’ spinal actions of κ‐opioids seen in non‐thermal over thermal behavioural models of nociception is likely to be related to the relative intensities, rather than the modalities, of the noxious stimuli used. The validity of the interpretation of results obtained in such behavioural studies is discussed.
Inhibitory effect of a toxin okadaic acid, isolated from the black sponge on smooth muscle and platelets
Authors: Karaki Hideaki , Mitsui Minori , Nagase Hiromi , Ozaki Hiroshi , Shibata Shoji , Uemura Daisuke 
Published: July 2012

Effects of okadaic acid, a toxin isolated from marine sponges, on smooth muscle contraction and platelet activation were examined.
Contractions in rabbit aorta induced by high concentrations of K+ and noradrenaline were inhibited by 0.1–1 μm okadaic acid in a concentration‐dependent manner. Spontaneous rhythmic contractions as well as high K+‐induced contraction in guinea‐pig taenia caeci were also inhibited by 1 μm okadaic acid.
High K+‐induced contraction in rabbit aorta was accompanied by increased Ca2+ influx measured with 45Ca2+ and increased cytosolic Ca2+ ([Ca2+]cyt) measured with fura‐2‐Ca2+ fluorescence. Okadaic acid inhibited the contraction without inhibiting Ca2+ influx and produced only a small decrease in [Ca2+]cyt.
In a saponin‐skinned taenia, Ca2+‐induced contraction was not inhibited but rather potentiated by okadaic acid.
Okadaic acid, 1 μm, inhibited aggregation, ATP release and increase in [Ca2+]cyt induced by thrombin in washed rabbit platelets. Okadaic acid itself did not change the platelet activities.
Okadaic acid did not change the cyclic AMP content of rabbit aorta although the inhibitory effects of okadaic acid were similar to those of cyclic AMP.
Although the mechanism of the inhibitory effect of okadaic acid was not clarified in the present experiments, it is suggested that okadaic acid acts by inhibiting protein phosphatases resulting in an indirect activation of cyclic AMP‐dependent protein phosphorylation.
Enhancement of leukotriene C4 release from primate airway macrophages by cellular interactions
Authors: Campbell A.M. , Harper S.T. , Hallam C. , Wells E. , Mann J. , Robinson C. 
Published: July 2012

Cells were obtained from the lungs of Macaque monkeys by bronchoalveolar lavage in order to study the role of cellular interactions in the release of leukotriene C4 (LTC4).
In normal monkeys, macrophages were the most abundant cell type recovered, whereas in monkeys sensitized with Ascaris suum there was an increase in the numbers of eosinophils and mast cells recovered.
Challenge of cells from both groups of animals with an optimal concentration of opsonized zymosan (OPZ) resulted in the time‐dependent release of LTC4 from macrophages. However, release was significantly greater in cells obtained from sensitized donors compared to normal donors.
Density‐gradient centrifugation of cells lavaged from sensitized donors was used to prepare fractions containing both eosinophils and mast cells. Addition of these cells to macrophage populations obtained from non‐sensitized donors caused a significant enhancement of OPZ‐induced LTC4 release. In the absence of macrophages no significant release of LTC4 was detected from eosinophil/mast cell‐containing fractions stimulated with OPZ, despite the fact that the zymosan had been phagocytosed by the eosinophils.
There was a significant correlation between the percentage enhancement of LTC4 release and the number of eosinophils added. However, there was not a significant correlation with the number of mast cells added.
These results suggest that a cellular interaction between macrophages and eosinophils may be important in the regulation of mediator synthesis and release. The precise mechanism of this effect remains to be elucidated.
Effect of acute and subchronic nicotine treatment on cortical acetylcholine release and on nicotinic receptors in rats and guinea‐pigs
Authors: Nordberg A. , Romanelli L. , Sundwall A. , Bianchi C. , Beani L. 
Published: July 2012

The effect of acute and chronic (16 days) administration of nicotine on cortical acetylcholine (ACh) release, gross behaviour and brain nicotinic binding sites was investigated in rats and guinea‐pigs.
The drug, injected either subcutaneously (0.45‐0.90 mg kg−1) or intracerebroventricularly (1, 3 and 5 μg) increased the cortical ACh release, in a dose‐dependent manner, through mecamylamine‐sensitive receptors for 1–2 h in both species.
Chronic treatment significantly increased basal ACh release in the rat and slightly lowered it in the guinea‐pig, but the response to a challenging dose of nicotine was proportionally maintained in both species.
The number of nicotinic receptors was four times higher in the rat than in the guinea‐pig and was not dependent on the radioligand used ([3H]‐nicotine or [3H]‐ACh, in the presence of atropine) to determine this. The nicotinic binding sites showed an apparent increase in chronically treated rats but no change in guinea‐pigs.
Tolerance to the inhibitory effect of the drug, assessed with the T maze test, was found in the rat. No apparent change in gross behaviour was detected in the guinea‐pig.
It is concluded that chronic nicotine treatment causes evident tolerance to its inhibitory effect on behaviour in the rat, but no adaptation to its excitatory properties on the cholinergic brain structures in rats and guinea‐pigs.
Intracellular platelet‐activating factor regulates eicosanoid generation in guinea‐pig resident peritoneal macrophages
Authors: Stewart Alastair G. , Phillips Wayne A. 
Published: July 2012

The role of intracellular platelet‐activating factor (Paf) in arachidonic acid (AA) mobilization from guinea‐pig peritoneal macrophages has been investigated by use of the potent and selective Paf receptor antagonists, WEB 2086 and CV 6209.
Adherent macrophages contained cell‐associated Paf which was increased by exposure to formyl‐methionyl‐leucyl‐phenylalanine (fMLP), endotoxin and the ionophore, A23187. However, only endotoxin and A23187 caused release of detectable amounts of Paf into the extracellular medium.
Exogenous Paf and each of the above stimuli mobilized previously incorporated [14C]‐AA and increased the generation of prostacyclin (PGI2) in resident macrophages.
WEB 2086 (10–100 μm) and CV 6209 (0.1–10 μm) reduced both basal and stimulated PGI2 generation and WEB 2086 inhibited the mobilization of [14C]‐AA. In addition, WEB 2086 (10 μm) inhibited fMLP‐ and Paf‐induced superoxide anion generation. Responses to A23187 were not inhibited by either antagonist.
Activation of macrophages by fMLP caused a short burst of intracellular Paf generation but none was detected in the supernatants. The time‐course of PGI2 synthesis followed closely that of Paf.
These data suggest that intracellular Paf generation is important for subsequent AA mobilization and may have a wider role in signal transduction processes.
Different time courses of the blockade of sodium current by lignocaine and SUN 1165 in single myocytes isolated from guinea‐pig atrium
Authors: Inomata Norio , Ishihara Takafumi , Akaike Norio 
Published: July 2012

The time course of the blockade of sodium currents (INa) by the antiarrhythmic agents, lignocaine and SUN 1165, was studied in single myocytes isolated enzymatically from guinea‐pig atrium, by a new concentration‐jump termed as a ‘concentration‐clamp’ technique. This technique combines an intracellular perfusion and a rapid exchange of external solution surrounding the voltage‐clamped myocyte within 2 ms.
Lignocaine (3.7 × 10−5 m to 3.7 × 10−4 M) inhibited the peak amplitude of INa in a concentration‐dependent fashion. It took 2 to 5 s to reach apparent steady‐state inhibition at the concentrations used. Complete recovery from the inhibition also took 2 to 5 s after washing out the agent. In contrast, the inhibitory effect of SUN 1165 (1 × 10−5 M) on the peak INa gradually progressed and reached a steady‐state level about 2 min after the start of drug‐application. The recovery required more than 10 min after washing out of the agent.
In cardiomyocytes treated with scorpion toxin (5 μg ml−1), the inactivation of INa was greatly inhibited, resulting in the relatively persistent Na inward current (persistent INa) during the depolarizing pulse. Lignocaine (1.1 × 10−4 M) applied during the depolarizing pulse, reduced in a single‐exponential fashion the amplitude of the persistent INa in milliseconds. On the other hand, lignocaine applied several tens of milliseconds before the depolarizing pulse induced only a small reduction of the peak amplitude of the first persistent INa. When SUN 1165 (1 × 10−5 M) was applied during the depolarizing pulse, there was only a small instantaneous reduction of the amplitude of the persistent INa, although it did inhibit time‐dependently, the peak INa. Both agents accelerated the decay phase of the persistent INa in a time‐dependent manner.
These results suggest that lignocaine and SUN 1165 may preferentially interact with the open‐state of the sodium channel rather than with the rested one, although SUN 1165 does so much more slowly.
The modulation by chlormethiazole of the GABAA‐receptor complex in rat brain
Authors: Cross Alan J. , Stirling Janet M. , Robinson Timothy N. , Bowen David M. , Francis Paul T. , Green A. Richard 
Published: July 2012

The interactions of chlormethiazole with γ‐aminobutyric acid (GABA) synthesis and release, and with ligand binding to sites associated with the GABAA‐receptor complex and the GABAB‐receptor have been studied in the rat. The GABAA‐receptor was studied using [3H]‐muscimol, [3H]‐flunitrazepam was used to label the benzodiazepine modulatory site, and [35S]‐butylbicyclophosphorothionate ([35S]‐TBPS) to label the chloride channel.
Chlormethiazole had no effect on GABA synthesis in the cortex, hippocampus and striatum or on GABA release from cortical slices in vitro. Chlormethiazole did not displace [3H]‐baclofen binding to the GABAB‐receptor.
Chlormethiazole (IC50 = 140 μm) and pentobarbitone (IC50 = 95 μm) both inhibited [35S]‐TBPS binding by increasing the rate of [35S]‐TBPS dissociation. In addition, chlormethiazole caused an apparent decrease in the affinity of [35S]‐TBPS binding.
Chlormethiazole enhanced the binding of [3H]‐muscimol but had no effect on [3H]‐flunitrazepam binding. In contrast, the sedative barbiturate pentobarbitone enhanced both [3H]‐muscimol and [3H]‐flunitrazepam binding.
It is concluded that the sedative and anticonvulsant effects of chlormethiazole are probably mediated through an action at the GABAA‐receptor. However, chlormethiazole does not interact with the GABAA‐receptor complex in an identical manner to the sedative barbiturate pentobarbitone.
Differences in regional vascular sensitivity to endothelin‐1 between spontaneously hypertensive and normotensive Wistar‐Kyoto rats
Authors: Wright Christine E. , Fozard John R. 
Published: July 2012

The systemic and regional haemodynamic effects of porcine endothelin‐1 (endothelin) have been measured in anaesthetized spontaneously hypertensive (SH) rats rendered areflexic by ganglion blockade; comparisons were made with age‐matched Wistar‐Kyoto (WKY) control animals.
In both SH and WKY rats endothelin (0.1–1 nmol kg−1 i.v.) elicited an initial, short‐lived (<2 min), fall in blood pressure which was associated with substantial increases in hindquarter and carotid vascular conductances. Both the blood pressure falls and the peripheral vasodilator responses were greater in SH than in WKY rats.
The initial depressor effects of endothelin were followed by marked and sustained increases in blood pressure associated with constriction in carotid, hindquarter, renal and mesenteric vascular beds. Vasoconstrictor responses were quantitatively similar in the two rat strains.
Pretreatment with indomethacin (5 mg kg−1 i.p. or i.v.) did not alter the responses to endothelin, 1 nmol kg−1, in SH rats.
The regional haemodynamic effects of intravenously administered acetylcholine (0.01–1 μg kg−1), nitroprusside (0.3–10 μg kg−1) and angiotensin II (0.01–0.1 μg kg−l) were similar in SH and WKY rats.
Endothelin (10−10−3 × 10−8 m) contracted aortic rings from both SH rats and WKY control animals. Removal of the endothelium enhanced significantly the sensitivity of tissues from both WKY and SH rats to endothelin; the increase in sensitivity was greater in tissues from SH than WKY rats.
The results demonstrate qualitative similarities in the complex haemodynamic effects of endothelin in SH rats and WKY control animals. However, the SH rats display substantially greater vasodilator responses to endothelin than WKY. Eicosanoid generation is not the mechanism of the vasodilator action of endothelin in SH rats under the conditions of our experiments.
Microionophoretic study with milacemide, a glycine precursor, on mammalian central nervous system cells
Authors: Godfraind Jean‐Marie 
Published: July 2012

The effect of milacemide, a glycine percursor known to increase γ‐aminobutyric acid (GABA) and glycine content in the brain, and to have anticonvulsant properties, was tested by ionophoresis on 247 neurones situated in the cerebral cortex and in deeper structures of cats and rats anaesthetized with urethane.
Virtually all the neurones, either firing spontaneously or exogenously driven by the excitatory amino acids, glutamate, N‐methyl‐d‐aspartate (NMDA), kainate and quisqualate or by acetylcholine, were reversibly depressed in a dose‐dependent fashion. The same depressant effect was observed in animals pretreated with the monoamine oxidase B inhibitor (IMAO‐B) deprenyl which is known to reduce milacemide metabolism into glycinamide and glycine. Intravenous administration of milacemide (10 to 100 mg kg−1) also depressed the firing induced by glutamate, NMDA and acetylcholine.
When compared to GABA, milacemide was a weaker depressant. However, its effect could still be observed in the presence of the reversible GABAA antagonist, SR 95531, and thus milacemide is unlikely to act through GABA receptors. In addition, on cells unaffected by glycine, milacemide also had a depressant effect, and on cells inhibited by glycine, it was still capable of depressing cell firing during reversible blockade by strychnine of the glycine inhibitory action; thus milacemide is unlikely to act through glycine receptors. Simultaneous release of milacemide and GABA or of milacemide and glycine, did not show potentiation of the inhibitory amino acid action. However, the depressant effect of milacemide was additive with that of GABA and glycine.
No consistent depression of glutamate‐induced firing was obtained by ionophoresis of glycinamide, the first metabolite of milacemide.
It is concluded that milacemide by itself is a depressant agent and that its depressant effect does not necessarily require its metabolism into glycine, or its stimulator effect on the production of GABA.
Modulation of cholinergic neurotransmission in guinea‐pig airways by opioids
Authors: Belvisi M.G. , Stretton C.D. , Barnes P.J. 
Published: July 2012

Opioid receptors have been localised on sensory fibres in the vagus nerve and opioids have previously been shown to inhibit non‐adrenergic, non‐cholinergic (NANC) neurotransmission in guinea‐pig bronchi in vitro and in vivo. We have now investigated whether an inhibitory effect could be demonstrated on cholinergic neurotransmission.
Electrical field stimulation (EFS) (8 Hz, 0.5 ms, 40 V for 20 s) produced only a rapid, cholinergic response in the upper trachea but in the lower trachea and main bronchi a cholinergic response which was atropine‐sensitive and a longer lasting NANC contraction that was atropine‐insensitive was demonstrated. This slow contraction could be blocked by tetrodotoxin and capsaicin pretreatment.
[d‐Ala2, NMePhe4, Gly‐ol5]enkephalin (DAMGO), a selective μ‐opioid receptor agonist, inhibited the cholinergic response to EFS at 8 Hz in a dose‐dependent manner in main bronchi (IC50 = 113 nm with a maximal inhibition of 35.7 ± 5.6% 10 μm, n = 5). In the lower trachea, DAMGO inhibited the cholinergic response to a similar extent (inhibition of 35.8 ± 3.5% at 10 μm, n = 5). However, DAMGO had no effect on the contractile response to exogenously applied acetylcholine in the main bronchi. By contrast, opioids had no inhibitory effect on cholinergic neurotransmission in the upper trachea. DAMGO (1 μm) inhibited the cholinergic response to EFS in a frequency‐dependent manner in the main bronchi with greater inhibition at lower frequencies of stimulation.
The δ‐opioid receptor agonist [d‐Pen2, d‐Pen5]enkephalin (DPDPE) significantly inhibited the cholinergic component of the constrictor response to EFS at 8 Hz in the bronchi but at the highest dose used (10 μm). U‐50,488H, a κ‐receptor agonist, had no inhibitory effect on the cholinergic constrictor component in the main bronchi (10 μm).
DAMGO also inhibited the NANC responses to EFS in the main bronchi in a dose‐dependent manner (with an IC50 = 36 nm and a maximal inhibition of 63.4 ± 8.3%, at 1 μm, n = 5). DAMGO had no effect on contractile responses to exogenously applied substance P (SP). DPDPE (10 μm) was less effective in inhibition of the NANC bronchoconstriction with a maximal inhibition of 29.2 ± 4.2% (n = 7), and U‐50,488H (10 μm) had no inhibitory effect.
After capsaicin pretreatment, which depleted sensory nerves of neuropeptides, the inhibitory effect of DAMGO (1 μm) on cholinergic constriction in main bronchi at 8 Hz was only 13.4 ± 1.9% (n = 13) compared with 32.9 ± 4.0% (n = 9) inhibition in vehicle‐treated controls (P < 0.001).
Opioids may reduce the cholinergic neural responses in airways partly via an inhibitory action on excitatory NANC nerves and partly by a direct effect on cholinergic neurotransmission. The opioid receptor involved is of the μ‐opioid receptor subtype.
Evidence that pinacidil may promote the opening of ATP‐sensitive K+ channels yet inhibit the opening of Ca2+‐activated K+ channels in K+ ‐contracted canine mesenteric artery
Authors: Masuzawa Kaoru , Matsuda Tomohiro , Asano Masahisa 
Published: July 2012

The effects of cromakalim and pinacidil on contraction and 86Rb efflux were investigated in strips of canine mesenteric artery.
Cromakalim and pinacidil relaxed arterial strips precontracted with 20.9 mm K+ with pD2 values of 6.56 and 5.88, respectively.
High (above 10 μm) concentrations of pinacidil, but not cromakalim, relaxed arterial strips bathed by a medium containing 65.9 mm K+, and inhibited Ca2+‐induced contractions in strips bathed by a medium containing 80 mm K+. These findings suggested that pinacidil may act as an inhibitor of Ca2+ influx.
In arterial strips preloaded with 86Rb, cromakalim and pinacidil increased the basal 86Rb efflux.
When the effects of cromakalim and pinacidil on 86Rb efflux were determined in arterial strips contracted with 65.9 mm K+, both drugs increased 86Rb efflux. The increase in 86Rb efflux induced by pinacidil was much smaller than that induced by cromakalim. Under the same conditions, nifedipine decreased 86Rb efflux.
After the addition of nifedipine to arterial strips contracted with 65.9 mm K+, pinacidil produced a greater increase in 86Rb efflux than in the absence of nifedipine, whereas the effects of cromakalim were the same for the two conditions. Therefore, the effects of pinacidil on 86Rb efflux may be the resultant of two opposing effects: an increased 86Rb efflux due to the opening of ATP‐sensitive K+ channels, and a decreased efflux due to the closing of Ca2+‐activated K+ channels.
In causing relaxation, cromakalim was competitively antagonized by glibenclamide with a pA2 value of 7.16. However, glibenclamide antagonism of pinacidil was not of the simple competitive type, suggesting that inhibition of Ca2+ influx may contribute to the relaxant action of pinacidil.
It may be concluded that although the ability of pinacidil to increase 86Rb efflux via ATP‐sensitive K+ channel opening was similar to that of cromakalim, the inhibition of Ca2+ influx by pinacidil may reduce the opening of Ca2+‐activated K+ channels in K+‐contracted arterial strips.
Separate [3H]‐nitrendipine binding sites in mitochondria and plasma membranes of bovine adrenal medulla
Authors: Ballesta J.J. , Garcia A.G. , Gutierrez L.M. , Hidalgo M.J. , Palmero M. , Reig J.A. , Viniegra S. 
Published: July 2012

Two binding sites for the 1,4‐dihydropyridine (DHP) derivative [3H]‐nitrendipine have been found in the bovine adrenal medulla. The high‐affinity site (Kd = 0.48 nM and Bmax = 128 fmol mg−1 protein) was specifically located in purified plasma membranes. The low‐affinity site (Kd = 252nM and Bmax = 169 pmol mg−1 protein) was located only in mitochondria. Chromaffin granule membranes lacked specific binding sites for [3H]‐nitrendipine.
Kinetic analysis of the rates of association and dissociation of [3H]‐nitrendipine, saturation isotherms and displacement experiments with unlabelled nitrendipine and PN200‐110 revealed single, homogeneous populations of high‐ and low‐affinity sites in plasma and mitochondrial membranes, respectively.
The high affinity site was sensitive to Ca2+ deprivation and heating; it was practically unaffected by changes in ionic strength of the medium and its optimal pH was slightly alkaline. This site exhibited a strong DHP stereoselectivity; diltiazem increased and verapamil decreased the affinity of [3H]‐nitrendipine.
In contrast, binding of [3H]‐nitrendipine to the low affinity site was more heat resistant and less affected by Ca2+ removal. Its optimal pH was slightly acid and the increase in ionic strength enhanced the number of available sites. The site had no DHP stereoselectivity. Verapamil decreased the dissociation constant of [3H]‐nitrendipine acting in a non‐competitive manner; diltiazem did not affect equilibrium binding parameters of [3H]‐nitrendipine.
These results suggest that both binding sites reflect different receptor entities. The high‐affinity binding site corresponds to the dihydropyridine receptor associated with the L‐type calcium channel. The function of the mitochondrial, low‐affinity binding site is, at present, unknown.