bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanical and electrical aspects of the relaxant action of aminophylline in guinea‐pig isolated trachealis
Authors: Allen S.L. , Cortijo J. , Foster R.W. , Morgan G.P. , Small R.C. , Weston A.H.
Published: July 2012

Aminophylline (1–1000 μmol 1−1) suppressed the spontaneous tone of guinea‐pig isolated trachealis in a concentration‐dependent manner.

In Krebs solution containing acetylcholine (1 mmol 1−1), histamine (200 μmol 1−1) or K+ (120 mmol 1−1) isolated trachealis muscle developed near‐maximal tension. The log concentration‐effect curve for aminophylline was shifted 20 fold, 3 fold and 4 fold to the right, respectively, in the presence of these spasmogens.

Three K+‐channel inhibitors were tested: tetraethylammonium (TEA, 8 mmol 1−1) did not modify the action of aminophylline, procaine (5 mmol 1−1) shifted the log concentration‐effect curve for aminophylline 2 fold to the left and 4‐aminopyridine (5 mmol 1−1) shifted the curve 2.5 fold to the right.

Intracellular electrophysiological recording showed that aminophylline 10 μmol 1−1 could cause relaxation in the absence of electrical changes. Higher concentrations of aminophylline (100–1000 μmol 1−1) suppressed spontaneous slow waves and hyperpolarized the trachealis cells.

In the presence of procaine (5 mmol 1−1) or TEA (8 mmol 1−1), the hyperpolarization induced by aminophylline (1000 μmol 1−1) was significantly reduced but its relaxant effect was unchanged.

In trachealis skinned of its plasma membranes, tension development induced by Ca2+ (20 μmol 1−1) was unaffected either by aminophylline (1000 μmol 1−1) or by isoprenaline (1 μmol 1−1).

In studies of the efflux of 86Rb+ from muscle‐rich strips of trachea, aminophylline (100–1000 μmol 1−1) was without effect whereas nicorandil (100 and 1000 μmol 1−1) increased the efflux rate constant.

It is concluded that aminophylline does not directly reduce the sensitivity of the contractile proteins to cytosolic Ca2+. In low concentration (1–10 μmol 1−1) its relaxant action is not accompanied by membrane potential change but towards the upper end of its effective concentration range, aminophylline evokes hyperpolarization. This hyperpolarization may involve the opening of K+‐channels which are inhibited by procaine and (to a lesser extent) by TEA. These K+‐channels may be impermeable to 86Rb+.
Dissociation constants and relative efficacies of acetylcholine, (+)‐ and (‐)‐methacholine at muscarinic receptors in the guinea‐pig ileum
Authors: Ringdahl Björn
Published: July 2012

Dissociation constants (KA) and relative efficacies of acetylcholine, (+)‐methacholine and (‐)‐methacholine at muscarinic receptors in the guinea‐pig isolated ileum were determined in the absence and presence of the cholinesterase inhibitor diisopropylfluorophosphate. The method used involved analysis of dose‐response data before and after fractional inactivation of receptors with propylbenzilylcholine mustard.

The KA values, estimated after cholinesterase inhibition, of acetylcholine, (+)‐ and (‐)‐methacholine were 1.7, 2.0 and 620 μM, respectively.

The large (730 fold) difference in spasmogenic activity between (+)‐ and (‐)‐methacholine is due primarily to a difference in affinity for ileal muscarinic receptors although differences in efficacy (2 to 4 fold) also contribute.

It is suggested that the methyl group at the chiral centre of (+)‐methacholine has no apparent effect on the binding to muscarinic receptors, whereas the corresponding methyl group of (‐)‐methacholine interferes with binding, presumably by stabilizing a conformation of the drug which does not fit the receptor very well.
In vivo and in vitro activity of selective 5‐hydroxytryptamine2 receptor antagonists
Authors: Conolan Sean , Quinn Michael J. , Taylor David A.
Published: July 2012

The abilities of ketanserin, ritanserin, R56413 and LY53857 to inhibit 5‐hydroxytryptamine (5‐ HT) and noradrenaline‐induced vasoconstrictor responses both in vitro and in vivo and to lower blood pressure in the rat, were compared.

In the isolated perfused mesenteric artery preparation of the rat all of the compounds tested were found to be potent inhibitors of 5‐HT‐induced vasoconstrictor responses. Ritanserin was the most potent compound, producing more than 50% inhibition of a near maximal response to 5‐HT at a concentration of 10−11 M. All four compounds were found to be competitive antagonists of noradrenaline; ketanserin being the most potent with a pA2 value of 7.64 ± 0.06.

5‐HT‐induced pressor responses in the pithed rat were inhibited by low doses (0.3–10 μg kg−1) of the four compounds. Ketanserin, at doses of 0.1–3.0 mg kg−1, resulted in rightward shifts of the control dose‐response curve to noradrenaline in the pithed rat. None of the other compounds had any significant effect on the noradrenaline‐induced pressor responses.

Ketanserin (0.1–1 mg kg−1) produced a dose‐dependent decrease in the mean arterial blood pressure of anaesthetized rats. The maximum decrease in blood pressure observed following a dose of 1 mg kg−1 ketanserin was 73.7 ± 4.7 mmHg. The other compounds at doses of 1.0–3.0 mg kg−1 produced a decrease in blood pressure of a lesser magnitude than that following ketanserin. In addition, this effect did not appear to be dose‐dependent.

It is suggested that the acute hypotensive effect of ketanserin results predominantly from α1‐adrenoceptor blockade. The involvement of antagonism of 5‐HT2 receptors in the hypotensive effect of the other compounds tested cannot be excluded.
Electrophysiological analysis of neurogenic vasodilatation in the isolated lingual artery of the rabbit
Authors: Brayden J.E. , Large W.A.
Published: July 2012

The nature of neurogenic vasodilatation was investigated in isolated segments of rabbit lingual artery. In separate experiments membrane responses to nerve stimulation were studied by use of microelectrodes.

In the presence of guanethidine to block constrictor responses and noradrenaline to induce tone, field stimulation with trains of pulses (8 Hz for 0.5 to 4 s) produced vasodilatation. Atropine (10−6 M) reduced the relaxations to about 50% of the control values while the induced vasodilatations were potentiated by physostigmine. Tetrodotoxin (TTX, 10−7 M) blocked all nerve‐evoked responses. These data suggest that there is a cholinergic and a non‐cholinergic component of the vasodilatation produced by nerve stimulation in the rabbit lingual artery.

Single stimuli did not evoke electrophysiological responses. With parameters similar to those used in the mechanical studies, periarterial stimulation in the presence of guanethidine evoked membrane hyperpolarizations which achieved amplitudes of up to 11 mV. The ionophoretic application of acetylcholine (ACh) produced hyperpolarization.

The inhibitory junction potentials (i.j.ps) but not the ionophoretic‐induced responses were blocked by TTX. The nerve‐evoked and the ACh‐induced hyperpolarizations were potentiated by physostigmine (5 × 10−7 M) and totally blocked by atropine (10−7 M).

I.j.ps and hyperpolarization to ionophoresis of ACh were recorded from arteries in which the endothelium had been removed by mechanical rubbing. Mechanical relaxation to field stimulation and ACh was observed in preparations without endothelium.

These data suggest that the cholinergic component of the neurogenic vasodilatation in the rabbit lingual artery is accompanied by hyperpolarization. The non‐cholinergic component does not appear to possess an electrophysiological correlate. In addition, it seems that the action of nerve‐released ACh is mediated by muscarinic receptors which are situated directly on the vascular smooth muscle cells.
Biphasic actions of L‐DOPA on the release of endogenous noradrenaline and dopamine from rat hypothalamic slices
Authors: Goshima Yoshio , Kubo Takao , Misu Yoshimi
Published: July 2012

Effects of L‐DOPA on the release of endogenous noradrenaline and dopamine from rat hypothalamic slices evoked by electrical field stimulation at 5 Hz were investigated in the absence and presence of p‐bromobenzyloxyamine (NSD‐1055), a DOPA‐decarboxylase inhibitor.

In the absence of NSD‐1055, L‐DOPA produced a facilitation of impulse‐evoked release of noradrenaline at 0.1 μM but not at 1 and 10 μM, and had no effect on the spontaneous release. On the other hand, L‐DOPA 0.1 to 10 μM dose‐dependently increased the spontaneous release of dopamine and the highest concentration only increased the evoked release and tissue content of dopamine.

In the presence of NSD‐1055 10 μM, the increase in the spontaneous release of dopamine was prevented and L‐DOPA produced biphasic regulatory effects on the evoked release of noradrenaline and dopamine, a facilitation at 0.1 μM and an inhibition at 1 μM. The facilitation was antagonized by (‐)‐propranolol 0.1 μM, but not by the (+)‐isomer, whereas the inhibition was antagonized by S‐sulpiride 1 nM, but not by the R‐isomer.

In conclusion, L‐DOPA appears to produce biphasic actions on the release of endogenous noradrenaline and dopamine from rat hypothalamic slices, not through its conversion to dopamine but through presynaptic regulatory mechanisms, an inhibition via dopamine receptors at a micromolar concentration and a facilitation via β‐adrenoceptors at the lower concentration.
Bremazocine is an agonist at K‐opioid receptors and an antagonist at μ‐opioid receptors in the guinea‐pig myenteric plexus
Authors: Corbett A.D. , Kosterlitz H.W.
Published: July 2012

The agonist and antagonist activity of bremazocine at opioid receptors in the guinea‐pig myenteric plexus preparation was determined in untreated tissues and in tissues in which either μ‐ or k‐opioid receptors were blocked preferentially.

After pretreatment of the tissue with β‐funaltrexamine for 90 min followed by washing out, the IC50 value of the selective μ‐ligand [D‐Ala2,MePhe4,Gly‐ol5]enkephalin was increased 67 fold whereas the IC50 values of the selective k‐ligand U‐69,593 and of the non‐selective k‐ligand bremazocine were not significantly changed. In this experimental design bremazocine acted only on k‐receptors.

After pretreatment of the tissue with β‐chlornaltrexamine and 10 μM of the μ‐ligand for 30 min followed by washout, the IC50 value of the μ‐ligand was increased 2 fold whereas the IC50 value of the selective k‐ligand was increased 32 fold and that of bremazocine 62 fold. Under these experimental conditions, it was shown that bremazocine is an antagonist against [D‐Ala2,MePhe4,Gly‐ol5]enkephalin at the μ‐receptor (Ke. = 1.6 nM). The residual agonist activity of bremazocine is at the k‐receptor.

In naive myenteric plexus preparations the μ‐antagonist activity of bremazocine cannot be demonstrated because its potency at the k‐receptor is very high. This dual action may be of importance for the responses of bremazocine in other peripheral and central tissues.
Activation and desensitization of presynaptic α2‐adrenoceptors after inhibition of neuronal uptake by antidepressant drugs in the rat vas deferens
Authors: García‐Sevilla J.A. , Zubieta J.K.
Published: July 2012

The isolated field‐stimulated vas deferens of the rat (0.1 Hz, 3 ms, 30–40 V) was used to study the relationship between the in vivo inhibition of neuronal uptake of noradrenaline (NA) by cyclic antidepressant drugs and the subsequent activation/desensitization of presynaptic α2‐adrenoceptors. Receptor activation was indirectly measured by quantifying the ability of each drug to inhibit basal twitch responses after their acute administration. Receptor desensitization was also indirectly measured by quantifying the ability of the drugs to reduce the inhibitory effects of selective α2‐adrenoceptor agonists on the electrically‐induced twitch responses after their long‐term administration.

The acute in vivo administration of desipramine and other antidepressants (0.5–10 mg kg−1; i.p.; 2 h) resulted in dose‐dependent inhibitions of the basal twitch responses which were rapidly reversed to control values by idazoxan (10−5 M). In vitro, desipramine and other antidepressants also inhibited in a concentration‐dependent manner (10−9 − 10−5 M) the twitch responses. In rats pretreated 12 h earlier with reserpine (1 mg kg−1; i.p.) or oxypertine (4 mg kg−1; i.p.), desipramine (10 mg kg−1; 2 h) did not induce inhibition of the basal twitch responses or it induced a smaller effect, respectively.

For the various antidepressants the degree of inhibition of the basal twitch responses (desipramine > protriptyline > nortriptyline > maprotiline = imipramine > amitriptyline > viloxazine > iprindole > zimelidine) was highly correlated (r = 0.914) with the potency for blockade of [3H]‐NA uptake into rat brain synaptosomes.

Clonidine and xylazine inhibited in a concentration‐dependent manner (10−9 − 10−6 M) the twitch responses. The long‐term (7–14 days) administration of antidepressants or cocaine (10 mg kg−1, i.p.) resulted in significant decreases in sensitivity to clonidine or xylazine. Short‐term (3 days) treatment with desipramine did not reduce the sensitivity to clonidine.

The results indicate that the acute in vivo inhibition of NA neuronal uptake by antidepressants leads to the activation (through endogenous NA) of presynaptic inhibitory α2‐adrenoceptors which results in inhibition of the twitch responses. In contrast, prolonged in vivo inhibition of NA reuptake is followed by a slow desensitization process of the same receptors which results in a reduction of sensitivity to clonidine.
The role of the sympathetic nervous system in oestrogen‐induced hypertension in rats
Authors: Bhatt J.D. , Gulati O.D.
Published: July 2012

Albino rats of either sex received chronic ethinyl oestradiol (EO) treatment (1.5 mg kg−1 daily, i.m.) for 3 weeks. Untreated control rats received arachis oil vehicle alone.

Chronic EO treatment resulted in elevation of blood pressure in both sexes. Female rats exhibited significantly greater elevation in blood pressure than males.

In chronic EO‐treated rats pressor responses to low doses (0.5 μg kg−1) of noradrenaline were significantly increased, while those to angiotensin II, acetylcholine and isoprenaline were unaltered. Chronic EO treatment also sensitized the vascular bed of the rats' hindquarters to noradrenaline.

EO‐induced hypertension was associated with significant increase in dopamine‐β‐hydroxylase activity of adrenal glands.

Complete bilateral adrenalectomy or chemical sympathectomy prevented the development of EO‐induced hypertension.

It is suggested that chronic treatment of rats with EO induces and maintains hypertension. The peripheral sympathetic system plays an important role in this phenomenon.
Nerve membrane sodium channels as the target site of brevetoxins at neuromuscular junctions
Authors: Atchison William D. , Luke Virginia Scruggs , Narahashi Toshio , Vogel Stephen M.
Published: July 2012

Actions of two structurally related toxins, T‐17 and brevetoxin‐B, isolated from the red‐tide dinoflagellate, Ptychodiscus brevis, were studied on the giant axon of the squid and the neuromuscular junctions of the frog and rat.

T‐17 toxin caused a large increase in the frequency of miniature endplate potentials at nanomolar concentrations. In one typical case with a frog endplate, the frequency increased from 1.9 s−1 before application of 3.5 nM T‐17 to 69.3 s−1 within 5 min after application. In the rat muscle, the mean frequency increased from 1.39 s−1 in control to 11.93 s−1 after application of 23.2 nM T‐17.

The increase in miniature endplate potential frequency was reversed by the addition of 1 μM tetrodotoxin, and was not observed in a solution containing elevated Mg2+ and reduced Ca2+ concentrations.

External or internal application of T‐17 toxin (2–5 μM) or brevetoxin‐B (10–30 μM) to intact or internally perfused squid axons caused a depolarization of the membrane. This depolarization was abolished by the removal of external Na+ or by addition of tetrodotoxin to the external solution.

In voltage clamped squid giant axons, exposure to T‐17 toxin or brevetoxin‐B increased the non‐ inactivating component of the tetrodotoxin‐sensitive sodium current. The sodium current was activated at potentials 15 to 40 mV more negative than control.

It is proposed that these toxins modify a fraction of the sodium channels to a form which opens at potentials more negative than normal and which inactivates to a lesser extent. This mechanism would predict a depolarization of the nerve membrane at the neuromuscular junction, thus explaining the increased discharge of transmitter.
The relationship between noradrenaline‐induced contraction and 45Ca efflux stimulation in rabbit mesenteric artery
Authors: Leijten Paul A.A. , van Breemen Cornelis
Published: July 2012

Cellular Ca2+ recycling in a branch of the rabbit mesenteric artery was investigated by measuring the time‐ and concentration‐dependent effects of noradrenaline (NA) on contraction and 45Ca efflux in Ca2+‐free solution.

When NA was present continuously (15 min), both force development and 45Ca efflux stimulation consisted of a fast and a slow (often oscillatory) component. These components were sensitive to caffeine and are probably both related to Ca2+ release from the intracellular Ca2+ store, presumably sarcoplasmic reticulum (s.r.).

When NA was applied for shorter time periods, both tension and stimulated 45Ca efflux decreased similarly.

Repetitive short (30 s) NA applications resulted in repeated contractions and stimulations of 45Ca efflux.

The NA‐stimulated 45Ca efflux was not inhibited when external Ca2+ was present or in Na+‐free medium.

Loading the cell with Ca2+ (with physiological salt solution for 3 h or with a high K+ depolarizing solution) increases the number of subsequent NA‐induced repeated contractions in Ca2+‐free solution.

The Ca2 + content of the sarcoplasmic reticulum (s.r.) in the smooth muscle cells of this small artery was estimated to be at least 50 μmol kg−1 wet weight, corresponding to an s.r. Ca2+ concentration of about 3.1 mM.

These results indicate that the NA‐induced increase in cytosolic free Ca2+ (as measured by force development) is accompanied by an increase in Ca2+ extrusion (as measured by stimulation of 45Ca efflux). This suggests that at least part of the activator Ca2+ cycles through the extracellular space during hormone‐induced activation of vascular smooth muscle.
Interactions between noradrenaline and α2‐adrenoceptor agonists in the superior mesenteric arterial bed of the rat
Authors: Hiley C. Robin , Nichols Andrew J. , Thomas G. Roger
Published: July 2012

Interactions between α2‐agonists and noradrenaline vasoconstrictor responses were studied in the superior mesenteric arterial bed of the rat by use of perfusion both in situ with blood and in vitro with Krebs‐Henseleit solution.

Xylazine (1.9 × 10−6 mol) administered into the perfusion circuit reduced the maxium response to noradrenaline in the in situ preparation by 35% and decreased the pD50 for noradrenaline from 8.5 ±0.01 to 7.9 ±0.13 (n = 7). Yohimbine (1 mg kg−1, i.v.) gave a small parallel shift in the noradrenaline log dose‐response curve and prevented the reduction in the maximum response by subsequent administration of xylazine.

In vitro, xylazine (1.9 × 10−6 mol) also gave a long‐lasting reduction of 37% in the maximum response but did not affect the mid‐point sensitivity to noradrenaline. Yohimbine (10−6 M) did not change either of these effects.

Clonidine (1.9 × 10−6 mol) did not affect the maximum response to noradrenaline in vitro but did reduce the pD50 from 7.72 ± 0.17 to 6.9 ± 0.17 (n = 6). Yohimbine did not change these effects.

Guanfacine (1.8 × 10−6 mol) had no effect on the sensitivity of the in vitro preparation to noradrenaline but did reduce the maximum response by 20%. Yohimbine (10−6 M) prevented the depression of the maximum response.

It is concluded xylazine and clonidine interfere with noradrenaline induced vasoconstriction only to a limited extent through their interaction with α2‐adrenoceptors and that some other, as yet uncharacterised mechanism which may be activated by their aryl amidine structure, is responsible for their in vitro effects.
Effect of somatostatin on 45Ca fluxes in guinea‐pig isolated atria
Authors: Díez Juan , Tamargo Juan
Published: July 2012

The effect of somatostatin (SS, 10−6 m and 5 × 10−6 m) was studied on 45Ca fluxes in guinea‐pig isolated atria.

SS produced a dose‐dependent decrease in 45Ca uptake, this effect being dependent on the stimulation rate and Ca concentration in the bathing media.

The decrease in 45Ca uptake was more evident at faster (60 and 180 beats min−1) than at slower frequencies (15 beats min−1) and was less evident in high Ca (5.4 mm).

SS had no effect on 45Ca efflux.

These results suggest that SS inhibits the slow inward Ca current in guinea‐pig atrial fibres.
Sodium‐dependence of the non‐specific desensitization of the guinea‐pig ileum induced by acetylcholine and histamine
Authors: Aboulafia J. , Capocci H. , Paiva A.C.M. , Paiva T.B.
Published: July 2012

The isometric maximal responses of the guinea‐pig ileum to acetylcholine and to histamine (but not those to prostaglandin E2 and to high K+) exhibited a secondary transient increase in tonus during the tonic component of the contraction.

After desensitizing treatment with acetylcholine or histamine, the isometric responses to either agonist showed decreased phasic and enhanced tonic components, whereas both components of the response to prostaglandin E2 were markedly depressed.

During the desensitizing treatment the degree of desensitization went through a maximum that coincided with the occurrence of the secondary tonic increment.

In low‐Na+ medium, or in ouabain‐treated tissues, the responses to the three agonists were similar to the respective responses in the desensitized state.

It is concluded that the non‐specific desensitization is due to changes in Na+ translocation and that the increased tonic component of the isometric response is due to a reduced Na+ gradient across the cell membrane and consequent increase in Ca2+ loading.
P2‐purinoceptors of two subtypes in the rabbit mesenteric artery: reactive blue 2 selectively inhibits responses mediated via the P2y‐ but not the P2x‐purinoceptor
Authors: Burnstock Geoffrey , Warland Jennifer J.I.
Published: July 2012

α,β‐Methylene ATP and ATP both produced concentration‐dependent contractions of the isolated mesenteric artery of the rabbit that were not inhibited by reactive blue 2.

In preparations where the tone had been raised with noradrenaline, ATP and 2‐methylthio ATP, but not α,β‐methylene ATP, produced relaxations of the vessel. These relaxations were inhibited in the presence of reactive blue 2.

Reactive blue 2 did not inhibit the contractions to noradrenaline, and only slightly inhibited relaxations to adenosine and acetylcholine.

The rank order of potency of purine nucleotide analogues in contracting the vessel was: α,β‐methylene ATP > β,γ‐methylene ATP = 2‐methylthio ATP > ATP, and in relaxing the vessel at raised tone was: 2‐methylthio ATP > ATP > β,γ‐methylene ATP > α,β‐methylene ATP.

It is concluded from this study that in the isolated mesenteric artery of the rabbit, purine nucleotides act via P2y‐purinoceptors to cause the muscle to relax and via P2x‐purinoceptors to cause the muscle to contract. The results also suggest that reactive blue 2 selectively inhibits responses mediated via the P2y‐purinoceptor, at least within a limited concentration range.
Uptake inhibitors potentiate γ‐aminobutyric acid‐induced contractile responses in the isolated ileum of the guinea‐pig
Authors: Ong Jennifer
Published: July 2012

The γ‐aminobutyric acid (GABA)‐induced contractile responses in the guinea‐pig isolated ileum, maintained in Krebs‐bicarbonate solution (pH 7.4, 37°C), were significantly potentiated by inhibitors of GABA uptake, with a greater potentiation of the responses in the presence of (±)‐cis‐3‐aminocyclohexane‐carboxylic acid (ACHC) > l‐2,4‐diaminobutyric acid (DABA) > (±)‐nipecotic acid > β‐alanine, whilst simultaneous addition of DABA with β‐alanine caused a greater potentiation of the GABA‐induced responses than did nipecotic acid with β‐alanine, or any of the uptake blockers applied alone.

The concentration‐response curves for the GABA‐induced ileal contraction were shifted to the left in the presence of the uptake inhibitors, this shift being more prominent over the lower concentration range of GABA (1–20 μm). By contrast, contractile responses to muscimol or 3‐amino‐1‐propanesulphonic acid (3APS) were not potentiated by the uptake blockers, neither were their concentration‐response curves altered.

Bicuculline methochloride shifted the GABA concentration‐response curve to the right, whilst picrotoxinin both shifted the concentration‐response curve for GABA to the right and depressed the maximum response. In the presence of the uptake inhibitors, the rightward shift of the concentration‐response curves for GABA induced by bicuculline was less than that induced by bicuculline alone. The rightward shift with picrotoxinin was similarly reduced in the presence of the uptake inhibitors, without altering the depression of the maximum by picrotoxinin.

Bicuculline caused a rightward shift of the concentration‐response curves for 3APS and muscimol, with the curve for 3APS most affected. Picrotoxinin similarly shifted the concentration‐response curves for 3APS and muscimol but depressed the maximum, with the curve for 3APS again being most affected. None of the inhibitors of GABA uptake influenced the concentration‐response curves for 3APS or muscimol in the presence of bicuculline or picrotoxinin.

In conclusion, a saturable GABA uptake system is present in the enteric nervous system of the guinea‐pig intestine, where neuronal GABA uptake appears to predominate over glial uptake.
Effect of omeprazole on eicosanoid formation in and release from guinea‐pig gastric mucosal cells
Authors: Hell M. , Sewing K.‐Fr.
Published: July 2012

Guinea‐pig gastric mucosal cells isolated by collagenase and pronase digestion were used to study the release of prostanoids prostaglandin I2 (PGI2; measured as 6‐keto PGF1α), PGE2, PGF2α and thromboxane A2 (TXA2; measured as TXB2). Lysophosphatide acyltransferase (LAT) and phospholipase A2 (PLA2) were measured in the microsomal fraction of isolated but not separated gastric cells and isolated and enriched parietal and mucous cells.

In all cell preparations PLA2 activity was approximately 5 times higher than that of LAT.

Acid‐activated omeprazole inhibited LAT in a concentration‐dependent manner with similar IC50 values in gastric, parietal and mucous cells. It had no effect on PLA2.

Gastric cells constantly produced PGI2, PGE2, PGF2α and TXA2. The main prostaglandins released were PGI2 and PGE2. PGF2α and TXA2 were released in smaller quantities.

Omeprazole dissolved in polyethylene glycol 400 (PEG) pH 2 inhibited spontaneous PGI2 release in a concentration‐dependent manner with an IC50 of 14.3 ± 4.8 μm. Only concentrations as high as 100 μm produced a significant reduction in PGE2 release by 60%. No significant changes could be detected in the spontaneous release of PGF2α and TXA2.

Omeprazole dissolved in PEG pH 7 had no effect on PGI2 release except at 100 μm which led to an insignificant decrease by 40%.

These data suggest that omeprazole beyond its inhibitory effect on parietal cell K+/H+‐ATPase also affects gastric mucosal prostanoid formation and release. The inhibitory effect on PGI2 does not support the view that omeprazole protects the gastric mucosa by increasing prostanoid formation.
Nifedipine effects in severe myocardial ischaemia in the dog due to left anterior descending coronary occlusion with left circumflex coronary artery constriction
Authors: Szekeres L. , Udvary Éva , Végh Ágnes
Published: July 2012

The effects of nifedipine were studied in a model of local myocardial ischaemia, comprising anaesthetized thoracotomized dogs in which a critical constriction of the left circumflex coronary artery (LCX) was combined with sudden occlusion of the left anterior descending coronary artery (LAD). Since more than one coronary artery is involved in ischaemic heart disease, the model seems to reflect the clinical situation very closely.

In this model, infusion of 1 μg kg−1 min−1 nifedipine increased myocardial blood flow within the stenosed area served by the LCX as well as in the myocardial region supplied by the LAD, mainly in the subepicardium. Accordingly, the drug reduced ischaemic ST‐segment elevation only in the epicardium.

It is suggested that nifedipine directed flow to the sub‐epicardium of the ischaemic area by improving the collateral circulation. This redistribution of flow resulted in a decrease in the endo/epicardial flow ratio.

Nifedipine did not change the inhomogeneity of electrical activation indicating that it has no effect on the ischaemia‐induced conduction delay. At the same time nifedipine was not able to reduce either the number of extrasystoles appearing in the early postocclusion and reperfusion phase or the incidence of ventricular fibrillation occuring mainly during reperfusion.
Binding of thromboxane A2/prostaglandin H2 agonists to human platelets
Authors: Halushka Perry V. , Kochel Pamela J. , Mais Dale E.
Published: July 2012

The competition of [125I]‐9,11 dimethylmethano‐11,12 methano‐16‐(3‐iodo‐4‐ hydroxyphenyl)‐13, 14‐dihydro‐13‐aza 15αβ‐ω)‐tetranor‐thromboxane A2 ([125I]‐PTA‐OH), a thromboxane A2/prostaglan‐din H2 receptor antagonist, with a series of thromboxane A2/prostaglandin H2 (TXA2/PGH2) mimetics for binding to the putative TXA2/PGH2 receptor in washed human platelets was studied.

The rank order potency for the series of mimetics to compete with [125I]‐PTA‐OH for binding was compared with their rank order potency for induction of platelet aggregation. The rank order potency for the mimetics to compete with [125I]‐PTA‐OH for binding was ONO‐11113>SQ‐26655>U44069>U46619 = 9, 11‐azo PGH2>MB28767. This rank order potency was highly correlated with their rank order potency for inducing platelet aggregation (r = 0.992).

Changes in the intra or extracellular concentrations of Na+ did not have a significant effect on the competition between U46619 and [125I]‐PTA‐OH for binding to the putative receptor.

In summary, it appears that these TXA2/PGH2 mimetics activate human platelets through the putative TXA2/PGH2 receptor.
Dose‐related effects of pharmacological mediators on tracheal vascular resistance in dogs
Authors: Laitinen Lauri A. , Laitinen M. Annika , Widdicombe J.G.
Published: July 2012

Various doses of mediators were tested on tracheal vascular resistance in dogs anaesthetized with pentobarbitone. Tracheal vascular resistance was determined by perfusing the cranial tracheal arteries at constant flows and measuring inflow pressures.

All drugs produced dose‐related changes in vascular resistance.

The peptides bradykinin, substance P and vasoactive intestinal peptide (VIP) each had similar vasodilator potencies and were much more powerful than histamine, methacholine and salbutamol.

Platelet activating factor (Paf) was a weaker dilator than the peptides. Prostaglandins D2, E1 and F2α had wide dilator potency ranges, PGE, being very effective even at low concentrations.

Phenylephrine, an α‐adrenoceptor agonist, was the only drug tested that always increased vascular resistance.

All the drugs studied also had effects on the contralateral tracheal vascular resistance.
Effects of local anaesthetics on short‐term desensitization of guinea‐pig taenia caecum to histamine
Authors: Hishinuma Shigeru , Uchida Masaatsu K.
Published: July 2012

Short‐term desensitization to histamine was induced by incubating guinea‐pig taenia caecum with 10−4 m histamine for 30 min (desensitizing incubation) in normal Locke‐Ringer solution or Ca‐free Locke‐Ringer solution containing 0.2 mm EGTA. This desensitization was measured as a reduction of the maximal contractile response.

The effects of the presence of local anaesthetics during the desensitizing incubation were examined. Results showed that tetracaine, procaine, procainamide, oxybuprocaine and lignocaine inhibited the desensitization, whereas dibucaine, benzocaine and mepivacaine did not.

The inhibitory effects of these drugs on the desensitization were not correlated with their lipid solubility nor with the potency of their known effects, such as membrane stabilization, Ca channel blockade, calmodulin antagonism, or inhibition of C‐kinase.

It is concluded that the inhibitory effects of local anaesthetics on the desensitization are not due to their non‐specific membrane‐stabilizing effects per se, but to some other action.
Pharmacological differences between two muscarinic responses of the rat superior cervical ganglion in vitro
Authors: Newberry N.R. , Priestley T.
Published: July 2012

Pharmacological differences have been observed between the muscarinic agonist‐induced depolarizing and hyperpolarizing responses of the rat isolated superior cervical ganglion.

Pirenzepine (0.3 μm) selectively reduced the depolarizing response and unmasked the hyperpolarizing response. No such selectivity was observed with a concentration of N‐methylatropine which was equipotent with pirenzepine in antagonizing the depolarizing response.

The neuromuscular blocking agents gallamine (10 μm) and pancuronium (3 μm) exhibited the oppositive selectivity to pirenzepine, both dramatically reduced the hyperpolarization but only slightly antagonized the depolarization.

The potencies of a range of agonists in evoking the depolarizing and hyperpolarizing responses, the latter in the presence of 0.3 μm pirenzepine, have been determined. Methylfurmethide failed to hyperpolarize the ganglion at concentrations which evoked maximal depolarizations.

The muscarinic hyperpolarization did not appear to be mediated by the secondary release of catecholamines.

It was concluded that the two muscarinic responses on the rat superior cervical ganglion, the slow depolarization and faster hyperpolarization, are mediated by different muscarinic receptor subtypes.
Effects of reserpine and 6‐hydroxydopamine on the adrenergic and purinergic components of sympathetic nerve responses of the rabbit saphenous artery
Authors: Warland Jennifer J.I. , Burnstock Geoffrey
Published: July 2012

The effects of reserpine and of 6‐hydroxydopamine on the contractions of the rabbit isolated saphenous artery produced by stimulation of the sympathetic nerves were studied.

In vessels exposed to reserpine, substantial contractions to nerve stimulation were recorded despite a 95.7% reduction in the noradrenaline content of the tissue. These responses of the vessel were not significantly affected by the α1‐antagonist, prazosin, whereas after desensitization of the P2‐purinoceptor with α,β‐methylene ATP, no response to nerve stimulation remained.

In vessels exposed to 6‐hydroxydopamine, no nerve‐mediated responses were observed.

Noradrenaline‐containing nerves were observed by fluorescence histochemistry in control tissues, but were not observed in tissues treated with reserpine or 6‐hydroxydopamine.

The potencies of ATP and histamine were not significantly affected by reserpine or 6‐hydroxydopamine treatment. However, there was a slight supersensitivity to noradrenaline in reserpine‐treated and 6‐hydroxydopamine‐treated vessels compared with that of control vessels. Prazosin was selective for α‐adrenoceptors, while α,β‐methylene ATP was selective for P2‐purinoceptors.

These results substantiate the finding that ATP and noradrenaline are sympathetic cotransmitters in the rabbit isolated saphenous artery, and demonstrate that ATP can act as a transmitter independently of noradrenaline in this vessel.
Bradykinin‐stimulated prostaglandin synthesis in conscious rabbits
Authors: Warren J.B. , Ritter J.M. , Hickling N.E. , Barrow S.E.
Published: July 2012

Bradykinin was infused intravenously into conscious rabbits to determine its effect on the concentration of prostaglandins in plasma. 6‐Oxo‐prostaglandin (PG) F1α, the stable hydrolysis product of prostacyclin, and 13,14‐dihydro‐15‐oxo‐PGF2α, a metabolite derived from PGE2 and PGF2α, were measured by gas chromatography‐electron capture mass spectrometry.

Incremental infusions of bradykinin (0.4‐3.2 μg kg−1 min−1) increased plasma concentrations of both 6‐oxo‐PGF1α and 13,14‐dihydro‐15‐oxo‐PGF2α.

Aspirin (10 mg kg−1, i.v.) inhibited bradykinin‐stimulated 6‐oxo‐PGF1α and 13,14‐dihydro‐15‐oxo‐PGF2α synthesis at 30 min and 6 h. At 24 h, the mean bradykinin‐stimulated 13,14‐dihydro‐15‐oxo‐PGF2α concentration was 66% of its original value, whilst 6‐oxo‐PGF1α remained substantially inhibited.

The different rates of recovery of bradykinin‐stimulated production of the two prostaglandins after inhibition by aspirin suggests that intravenous bradykinin stimulates prostacyclin and PGE2/PGF2α production in distinct cell populations which synthesize cyclo‐oxygenase at different rates.
Purinergic and non‐purinergic innervation in the cerebral arteries of the dog
Authors: Muramatsu Ikunobu , Kigoshi Shigeru
Published: July 2012

Possible involvement of sympathetic purinergic transmission in the neurogenic response of dog cerebral and basilar arteries was examined with the use of α,β‐methylene ATP and adrenoceptor, cholinoceptor blocking agents.

In the isolated basilar arteries, electrical transmural stimulation produced a transient contraction which was frequently followed by a relaxation. This transient contraction was abolished after desensitization of P2‐purinoceptors with α,β‐methylene ATP or by treatment with guanethidine. The relaxant response induced by electrical stimulation was also attenuated but was not abolished by such treatments. Prazosin, propranolol and atropine had no significant effect on the responses to electrical stimulation. Yohimbine augmented both the contractile and relaxant responses.

In most preparations of the dog middle cerebral arteries, electrical transmural stimulation produced only a relaxation. This relaxation was little affected after treatment with α,β‐methylene ATP or guanethidine, and was not inhibited by the other adrenoceptor and cholinoceptor blocking agents.

Tetrodotoxin abolished the responses induced by electrical transmural stimulation in both the basilar and middle cerebral arteries.

Exogenous ATP (10−6 and 10−5 m) produced a transient contraction followed by a relaxation of the basilar arteries and a relaxation of the middle cerebral arteries. Desensitization of P2‐purinoceptors abolished the contractile response to ATP without affecting the amplitude of relaxation.

In the basilar and middle cerebral arteries preincubated with [3H]‐noradrenaline, electrical transmural stimulation evoked an increase in 3H‐efflux and this response was markedly inhibited by guanethidine or tetrodotoxin but was not affected by α,β‐methylene ATP. Yohimbine increased the evoked 3H‐efflux.

These findings indicate that cerebral arteries of the dog are innervated by sympathetic purinergic nerves and non‐sympathetic nerves which liberate unknown vasodilator substance(s), and that the former nerves are more dominant in the neurogenic response to electrical stimulation of the dog basilar artery than in the middle cerebral artery.
Pharmacological profile of PD 117302, a selective κ‐opioid agonist
Authors: Leighton G.E. , Johnson M.A. , Meecham K.G. , Hill R.G. , Hughes J.
Published: July 2012

PD 117302, a new nonpeptide opioid compound shown in in vitro studies to be a selective κ‐opioid agonist, has been evaluted in vivo for antinociceptive activity and other effects characteristic of κ‐receptor activation.

Dose‐related long lasting antinociception was produced by PD 117302 against a mechanical noxious stimulus in rats following intravenous, subcutaneous or oral administration.

PD 117302 was effective in raising the nociceptive threshold to mechanical and chemical but not to thermal noxious stimuli in the mouse. This effect was attenuated in animals pretreated with the opioid antagonist naloxone.

In addition to producing antinociception, PD 117302 also caused naloxone‐reversible locomotor impairment and diuresis, effects that are typical of κ‐agonists.

PD 117302 did not cause respiratory depression, inhibition of gastrointestinal motility or naloxone‐precipated withdrawal jumping in mice, effects that are associated with actions at the μ‐opioid receptor.

The pharmacological profile of PD 117302 in vivo is consistent with in vitro data suggesting that PD 117302 is a selective agonist at the κ‐opioid receptor.
Muscarinic receptors mediating suppression of the M‐current in guinea‐pig olfactory cortex neurones may be of the M2‐subtype
Authors: Constanti A. , Sim J. A.
Published: July 2012

Guinea‐pig olfactory cortical neurones in vitro were voltage clamped by means of a single intracellular microelectrode technique. Hyperpolarizing voltage commands from holding potentials between −40 to − 50 mV produced slow inward current relaxations reflecting deactivation of the M‐current (IM). IM was reversibly suppressed by 30 μm muscarine or carbachol; this suppression was insensitive to pirenzepine (up to 300 nm) but was inhibited by gallamine (10–20 μm) or 4‐diphenyl‐acetoxy‐N‐methylpiperidine (100, 500 nm), suggesting the involvement of the M2‐type muscarinic receptor.
A comparison between the pattern of dopamine and noradrenaline release from sympathetic neurones of the dog mesenteric artery
Authors: Soares‐da‐Silva P.
Published: July 2012

The release of dopamine and noradrenaline (NA), from the main trunk of the mesenteric artery and its proximal branches elicited by electrical nerve stimulation and K+, has been measured by using high pressure liquid chromatography with electrochemical detection.

Both stimuli released dopamine and NA. With the main trunk of the mesenteric artery, dopamine represented 8% of the NA tissue content; the dopamine/N A ratio in the catecholamine overflow caused by nerve stimulation or K+‐induced depolarization also averaged 8%. For the proximal branches the tissue dopamine/NA ratio was significantly greater than that observed to occur in the overflow caused by nerve stimulation and K+.

When the perifusion with a K+‐enriched medium was extended to 120min the amount of NA released from both the main trunk and the proximal branches progressively declined. The same pattern of release was observed for dopamine in the main trunk, whereas for the proximal branches dopamine overflow did not decline throughout the perifusion period. The addition of α‐methyl‐p‐tyrosine did not change the pattern of amine overflow.

Our interpretation of these results is that both dopamine and NA are derived from the same sympathetic neurone. In the proximal branches of the mesenteric artery dopamine and NA appear to be in two different storage structures, whereas in the main trunk both dopamine and NA are located in only one storage structure.
Protein kinase C and presynaptic modulation of acetylcholine release in rabbit hippocampus
Authors: Allgaier Clemens , Daschmann Beate , Huang Hua Yu , Hertting Georg
Published: July 2012

The involvement of protein kinase C in the presynaptic modulation of stimulated acetylcholine release was investigated in rabbit hippocampus.

Slices of the rabbit hippocampus, labelled with [3H]‐acetylcholine, were superfused with medium and stimulated electrically during superfusion.

The protein kinase C activating phorbol ester 4β‐phorbol 12,13‐dibutyrate (4β‐PDB) enhanced the electrically evoked tritium overflow in a concentration‐dependent manner. Its biologically inactive 4α‐isomer was without any effect on transmitter release.

The protein kinase C inhibitor polymyxin B decreased the stimulation‐evoked tritium overflow and counteracted the enhancement of release caused by 4β‐PDB.

The stimulation‐evoked tritium overflow was facilitated when the muscarine receptor antagonist atropine was present. The effects of both atropine and 4β‐PDB, given in combination, were additive.

The net inhibition of the evoked tritium overflow caused by the muscarine receptor agonists carbachol and oxotremorine was similar, irrespective of whether 4β‐PDB was present or not.

Similar results to those for muscarine autoreceptor‐mediated inhibition, were obtained for inhibition of the stimulated tritium overflow caused by the adenosine receptor agonist (−)‐N6‐(R‐phenylisopropyl)‐adenosine ((−)‐PIA) and the opioid receptor agonist ethylketocyclazocine (EKC). The net inhibition of both agonists was independent of the presence of the phorbol ester.

The above results provide further evidence for participation of a presynaptically located protein kinase C in the modulation of acetylcholine release. However, the modulatory mechanisms which are coupled to presynaptic receptors and mediate inhibition of release seem not to be directly affected by protein kinase C.
κ‐Opioid agonists produce antinociception after i.v. and i.c.v. but not intrathecal administration in the rat
Authors: Leighton G.E. , Rodriguez R.E. , Hill R.G. , Hughes J.
Published: July 2012

Nociceptive thresholds to noxious mechanical (paw pressure) and thermal (tail flick) stimuli were recorded in conscious rats. The effects of three selective κ‐opioid receptor agonists on the responses to these stimuli were determined following intravenous, intracerebroventricular or intrathecal administration. Results were compared with those obtained with morphine.

Following intravenous administration PD117302, U50488, U69593 and morphine produced steep parallel dose‐response curves indicating antinociceptive activity when evaluated in the paw pressure test. When U50488 and U69593 were tested at a single dose of 3.3 mg kg−1 no effect was seen in the tail flick test.

When given by the intrathecal route only morphine was effective at increasing the nociceptive threshold. PD117302, U50488 and U69593 were without effect in either the paw pressure or tail flick tests when tested at doses up to 100 μg per rat. PD117302 caused flaccid paralysis of the hindlimbs following intrathecal administration at the top dose tested. This effect was not reversible by naloxone.

All three κ‐opioid receptor agonists produced naloxone‐reversible antinociception in the paw pressure test, and to a lesser extent in the tail flick test, when injected directly into the third cerebral ventricle with the maximum effect occurring between 5 and 10 min after administration and declining back to control levels by 60 min. Morphine had a much slower onset of action with the peak effect being observed 30 min after dosing.

It is concluded that, under our experimental conditions in the rat, the antinociceptive effects of κ‐agonists are likely to be operated via an action at a supraspinal rather than a spinal site.