bluuebunny/crossref_metadata_2025 huggingface dataset:
The effect of E. coli STa enterotoxin on the absorption of weakly dissociable anti‐malarial drugs from rat intestine in vivo
Authors: Rawlings J.M. , Lynch J. , Lucas M.L.
Published: July 2012

The effect of E. coli heat stable (STa) enterotoxin on the absorption of radiolabelled anti‐malarial weak bases and their appearance in peripheral blood was assessed in vivo by a recirculation procedure in rat intestinal loops.

Enterotoxin increased the jejunal disappearance of quinine (P < 0.05), trimethoprim (P < 0.05), proguanil (P < 0.05) and chloroquine (P < 0.001) and left pyrimethamine disappearance unaltered. Peripheral blood levels of trimethoprim (P < 0.02) and proguanil (P < 0.05) were higher after STa exposure.

In the ileum, enterotoxin increased the luminal disappearance (P < 0.05) and peripheral blood appearance (P < 0.001) of chloroquine. The luminal disappearance rate of trimethoprim was reduced (P < 0.05) and that of pyrimethamine unchanged.

The increased jejunal absorption of the anti‐malarial drugs occurred despite STa causing a reduction in the amount of net fluid absorption. It seems likely that the enhanced absorption with STa exposure is related to the effect of STa on the microclimate pH. An elevation in the microclimate pH would increase the amount of undissociated weak base available for non‐ionic diffusion.

The favourable elevation of microclimate pH by STa seemed to be outweighed by the reduced fluid absorption in the ileum. Only chloroquine still showed enhanced absorption in the ileum and this may have been because unlike the other antimalarial drugs, chloroquine has two dissociable groups likely to be affected by the mucosal surface pH changes.
Evidence that acetylcholine‐mediated hyperpolarization of the rat small mesenteric artery does not involve the K+ channel opened by cromakalim
Authors: McPherson Grant A. , Angus James A.
Published: July 2012

Acetylcholine causes a concentration‐dependent hyperpolarization of the rat small mesenteric artery (diameter at 100 mmHg, 200–400 μm). In the absence of tone the average potential change was from approximately −60 to −75 mV. In the presence of tone induced by endothelin‐1 (20 nm), acetylcholine caused vasorelaxation in association with a marked hyperpolarization; from approximately −32 to −71 mV.

A number of compounds known to antagonize the actions of cromakalim were tested for their ability to block responses to acetylcholine. Glibenclamide (0.1–3 μm), phentolamine (10–100 μm) and alinidine (1–30 μm) caused a concentration‐dependent depolarization of the rat small mesenteric artery which was not dependent on an intact endothelium. Glibenclamide was approximately 10 times more potent than either phentolamine or alinidine, a similar ratio to their potency as antagonists of cromakalim.

In the presence of concentrations of the cromakalim antagonists which functionally inhibited responses to cromakalim, only phentolamine and alinidine had a significant effect on the hyperpolarization and functional responses to acetylcholine. Glibenclamide was without effect at the concentrations used.

Experiments on pig coronary artery, where acetylcholine causes vasoconstrictor responses, showed that phentolamine and alinidine have some anti‐muscarinic activity which could account for their ability to affect vasorelaxant/hyperpolarization responses to acetylcholine in the rat small mesenteric artery.

The results suggest that the acetylcholine‐mediated hyperpolarization observed in the rat small mesenteric artery does not involve K+ channels opened by cromakalim. This finding differs from other studies performed on the rabbit middle cerebral artery which show hyperpolarizing responses to acetylcholine to be glibenclamide‐sensitive. It is likely therefore that the hyperpolarization response observed to acetylcholine can be initiated through a number of mechanisms, only one of which utilizes K+ channels opened by cromakalim.
Facilitatory effects of tachykinins and guanethidine on the acetylcholine output stimulated by nicotine from guinea‐pig bladder
Authors: Shinkai Michiko , Takayanagi Issei , Kato Teruko
Published: July 2012

Contractile responses and acetylcholine release evoked by nicotine in guinea‐pig detrusor strips were determined by isotonic transducer and radioimmunoassay, respectively. Nicotine stimulated acetylcholine release and a contractile response in guinea‐pig detrusor strips treated with the cholinesterase inhibitor, methanesulphonyl fluoride (MSF). Both actions evoked by nicotine were antagonized by the nicotinic receptor antagonist, hexamethonium but were insensitive to tetrodotoxin.

A sympathetic nerve blocker, guanethidine and a tachykinin antagonist, [d‐Arg1, d‐Pro2, d‐Trp7,9, Leu11]‐substance P (rpwwL‐SP) partially inhibited the acetylcholine release evoked by nicotine to much the same degree. The inhibitory effects of guanethidine and rpwwL‐SP on acetylcholine release were significantly greater than corresponding effects on the contraction evoked by nicotine.

In preparations treated with rpwwL‐SP to block the tachykinin receptors, guanethidine had no effect on the response to nicotine. Conversely, after treatment with guanethidine to block release of a mediator from sympathetic nerve endings, nicotine‐induced responses were not affected by rpwwL‐SP.

Nicotine‐induced contraction was reduced to 30% by the muscarinic cholinoceptor antagonist, atropine and completely abolished after desensitization of P2‐purinoceptors with α,β‐methylene ATP in the presence of atropine.

A concentration‐contractile response curve to neurokinin A (NKA) was shited to the left after cholinesterase inhibition with MSF. Atropine abolished the facilitatory effect of MSF and partially inhibited contractions induced by NKA at 100 nm to 1 μm. The contractile responses to substance P methyl ester (SPOMe) and Tyro‐neurokinin B (Tyro‐NKB) were not influenced by MSF or atropine.

After desensitization of NR1 tachykinin receptors with SPOMe or preincubation with senktide, the cholinergic component of the nicotine‐induced contraction was the same as the control value (100%).

Our findings give further support to our previous results: nicotine stimulates acetylcholine release in a tetrodotoxin‐resistant manner in guinea‐pig bladder and acetylcholine release evoked by nicotine is increased by the coordinated action of sympathetic nerves and tachykinin(s). It is suggested that the tachykinin receptor subtype involved in acetylcholine release is NK2.
Endothelium‐dependent and endothelium‐independent vasodilatation of the hepatic artery of the rabbit
Authors: Brizzolara Antonia L. , Burnstock Geoffrey
Published: July 2012

The isolated hepatic artery of the rabbit contracted to exogenously applied noradrenaline (NA). There was no significant difference in the maximal contraction or the EC50 value in vessels where the endothelium was present and in endothelium‐denuded preparations.

Acetylcholine (ACh) induced a vasodilatation of vessels preconstricted with NA which was entirely dependent on the endothelium.

Adenosine 5′‐triphosphate (ATP), 2‐methylthio ATP, adenosine and sodium nitroprusside induced concentration‐dependent, sustained relaxations of vessels in which tone had been induced with NA. The relaxation responses were not reduced after removal of the endothelium. 8‐Phenyltheophylline antagonized the relaxation response produced by adenosine, but not that due to ATP at lower concentrations. The maximum response to ATP was reduced in the presence of 8‐phenyltheophylline.

α,β‐Methylene ATP produced further contraction of vessels preconstricted with NA in both endothelium‐denuded preparations and in vessels where the endothelium remained intact.

Immunohistochemical analysis was used to show the presence of nerve fibres containing substance P (SP), calcitonin gene‐related peptide (CGRP) and vasoactive intestinal polypeptide (VIP) in the hepatic artery. Application of SP induced a concentration‐dependent relaxation which was entirely dependent on the presence of an intact endothelium. CGRP and VIP, however, elicited concentration‐dependent relaxations which were independent of the endothelium.

It is concluded that in the rabbit hepatic artery, responses to ACh are dependent on the presence of intact endothelium. P1‐, P2x‐ and P2y‐purinoceptors, mediating relaxation to adenosine, vasoconstriction to ATP and vasodilatation to ATP respectively, are located on vascular smooth muscle. Furthermore, CGRP and VIP mediate a direct vasodilatation of smooth muscle both in the absence and the presence of the endothelium, whereas SP produces a relaxation via receptors located on the endothelium.
Demethoxyviridin and wortmannin block phospholipase C and D activation in the human neutrophil
Authors: Bonser R.W. , Thompson N.T. , Randall R.W. , Tateson J.E. , Spacey G.D. , Hodson H.F. , Garland L.G.
Published: July 2012

The fungal metabolite, wortmannin, has recently been shown to inhibit fMet‐Leu‐Phe‐stimulated superoxide production and phospholipase D (PLD) activation in the human neutrophil.

We have found that a close structural analogue of wortmannin, demethoxyviridin, has a similar inhibitory profile but in addition blocks phosphatidylinositol 4,5‐bisphosphate‐specific phospholipase C and hence inositol 1,4,5‐trisphosphate (IP3) formation.

Inhibition of fMet‐Leu‐Phe‐stimulated PLD by demethoxyviridin was characteristically non‐competitive (IC50 = 31 ± 10 nm).

Inhibition of fMet‐Leu‐Phe‐stimulated IP3 formation required concentrations almost 10 times higher (IC50 = 250 ± 130 nm).

Surprisingly, demethoxyviridin only inhibited fMet‐Leu‐Phe‐induced intracellular calcium mobilization at concentrations 100 times greater than those needed to block IP3 formation.

Demethoxyviridin also inhibited PLD activation induced by sodium fluoride or phorbol myristate acetate (PMA) but the concentrations required were 100 times those needed to block fMet‐Leu‐Phe‐stimulated PLD.

These observations support the contention that PLD plays an important role in signal transduction in the human neutrophil and indicate that wortmannin and demethoxyviridin inhibit PLD activation at a common step in the signalling pathway.

Furthermore, these results suggest that demethoxyviridin may block the interaction between the chemotactic peptide receptor and a GTP‐binding protein that is intimately involved in PLD activation.
Endothelin modulates calcium channel current in neurones of rabbit pelvic parasympathetic ganglia
Authors: Nishimura T. , Akasu T. , Krier J.
Published: July 2012

The effects of endothelin were studied, in vitro, on neurones contained in the rabbit vesical pelvic ganglion by use of intracellular and single‐electrode voltage clamp techniques under conditions where sodium and potassium channels were blocked.

In the current‐clamp experiments, endothelin (1 μm) caused a depolarization followed by a hyperpolarization of the membrane potential. In the voltage‐clamp experiments, endothelin (0.01–1 μm) caused an inward current followed by an outward current in a concentration‐dependent manner.

Membrane conductance was increased during the endothelin‐induced depolarization and inward current. Membrane conductance was decreased during the endothelin‐induced hyperpolarization and outward current.

The endothelin‐induced inward and outward currents were not altered by lowering external sodium concentration or raising external potassium concentration.

The endothelin‐induced inward current was depressed (mean 72%) in a Krebs solution containing nominally zero calcium and high magnesium. These results suggest that a predominent component of the endothelin‐induced inward current is mediated by calcium ions.

The calcium‐insensitive component of the inward current was abolished by a chloride channel blocker, 4‐acetamide‐4′‐isothiocyanostilbene‐2,2′‐disulphonic acid. The mean reversal potential for the calcium‐insensitive component of the inward current was −18 mV. This value is near the equilibrium potential for chloride. Thus, it is presumed that the calcium‐insensitive component of the inward current is carried by chloride ions.

Endothelin caused an initial depression followed by a long lasting facilitation of both rapidly and slowly decaying components of high‐threshold calcium channel currents (N‐ and L‐type).

In summary, the data show that for neurones in the vesical pelvic ganglia, endothelin causes membrane depolarization and activates an inward current. The ionic mechanisms involve receptor‐operated calcium and chloride currents. Also, endothelin causes an initial depression followed by a long‐lasting facilitation of the voltage‐dependent calcium current.
Specific neurokinin receptors mediate plasma extravasation in the rat knee joint
Authors: Lam F.Y. , Ferrell W.R.
Published: July 2012

Plasma extravasation in the rat knee joint was induced by intra‐articular injection of neurokinins and specific neurokinin receptor agonists.

Pronounced plasma extravasation was produced by substance P (SP, 4–185 μm) and to a lesser extent by neurokinin‐B (NKB, 83–413 μm), whereas neurokinin‐A (NKA, 88–440 μm) and calcitonin gene‐related peptide (CGRP, 26–130 μm) had no significant effect.

The specific neurokinin1 receptor agonist [Sar9, Met(O2)11]‐substance P (NR1 agonist) in doses of 0.4–70 μm appeared to be more potent than SP in eliciting plasma extravasation. The neurokinin2 receptor agonist [Nle10]‐neurokinin A4–10 (NK2 agonist) was not effective at 70 μm but produced a small and significant effect at 330 μm, whereas the neurokinin3 receptor agonist [MePhe7]‐neurokinin B (NK3 agonist) was without effect at 40 μm or 400 μm.

Injections of SP or NKA into the synovial cavity of the rat knee were equally effective in producing marked plasma extravasation in remote sites such as the forelimb and hindlimb paws.

Co‐administration experiments showed that the effects of SP were synergistic with NKA or the NK1 receptor agonist, but not with CGRP or the NK2 receptor agonist.

The rank order of potency was NK1 agonist ≥ SP > NKB > NK2 agonist suggesting that NK1 receptors mediate plasma extravasation in the rat knee joint.
Kinetic studies on stereospecific recognition by the thromboxane A2/prostaglandin H2 receptor of the antagonist, S‐145
Authors: Kishino Junji , Hanasaki Kohji , Nagasaki Tohru , Arita Hitoshi
Published: July 2012

The mechanism for the stereospecific recognition of the antagonist S‐145 by the thromboxane A2 (TXA2)/prostaglandin H2 (PGH2) receptor was examined by ligand‐binding techniques in rat vascular smooth muscle cells (VSMCs) and in human platelet membranes.

Scatchard analysis revealed the existence of a single class of binding sites with the same maximum number for both [3H]‐(+)‐S‐145 and [3H]‐(−)‐S‐145 in both cell types. The dissociation constants (Kd) for the binding of the (+)‐isomer in rat VSMCs and human platelet membranes were, respectively, 0.40 ± 0.03 and 0.20 ± 0.02 nm, each value being lower than that for the (−)‐isomer (3.57 ± 0.74 and 2.87 ± 0.08 nm, respectively).

The rank orders of potency (Ki) for a series of TXA2/PGH2 ligands at inhibiting [3H]‐(+)‐S‐145 binding were highly correlated with those determined for [3H]‐(−)‐S‐145 binding in both cell preparations.

Kinetic analysis of the binding of both radioligands revealed a much lower dissociation rate constant (k−1) and a slightly greater association rate constant (k1) for the (+)‐isomer compared to those for the (−)‐isomer.

These results suggest that it is at the stage of dissociation from the TXA2/PGH2 receptor that the stereochemistry of the optical isomers of S‐145 confers their difference in affinity for these receptors in rat VSMCs and human platelet membranes.
Nitroglycerin relaxes coronary artery of the pig with no change in glutathione content or glutathione S‐transferase activity
Authors: Sakanashi Matao , Matsuzaki Toshihiro , Aniya Yoko
Published: July 2012

The role of glutathione content and glutathione S‐transferase activity in vascular relaxant responses to nitroglycerin was evaluated in potassium (30 mm)‐contracted coronary artery strips of the pig by measuring changes in tension, glutathione content and glutathione S‐transferase activity.

Prior exposure of coronary artery strips to nitroglycerin (10−5 m or 10−4 m for 20 min) resulted in tachyphylaxis to subsequent relaxation to nitroglycerin (10−8–10−5 m).

The glutathione content and glutathione S‐transferase activity of the arterial strips rendered tachyphylactic by prior exposure to nitroglycerin (10−5 m for 20 min or 10−3 m for 120 min) were not significantly different from those of control strips.

Treatment with diethyl maleate (10−4 m or 10−3 m for 60 min) markedly depleted arterial glutathione content in a concentration‐dependent manner with no change in glutathione S‐transferase activity.

The relaxant response of coronary artery strips to nitroglycerin (10−8–10−5 m) was completely unaffected following treatment with diethyl maleate (10−4 m or 10−3 m for 60 min).

The results suggest that vascular glutathione content does not play an important role in vascular relaxation or tolerance development to nitroglycerin, at least in pig isolated coronary artery.
Inhibitory effects of guanosine 3′: 5′‐cyclic monophosphate on the synthesis of dopamine in the rat kidney
Authors: Soares‐da‐Silva P. , Fernandes M. Helena
Published: July 2012

In the present study the effects of M&B 22,948, a guanosine 3′: 5′‐cyclic monophosphate (cyclic GMP) selective phosphodiesterase inhibitor and of 8‐bromo cyclic GMP were examined on the synthesis of dopamine from l‐3,4‐dihydroxyphenylalanine (l‐DOPA) in rat cortical slices and in whole kidney homogenates. The deamination of newly‐formed dopamine into 3,4‐dihydroxyphenylacetic acid (DOPAC) was also studied. The assay of l‐DOPA, dopamine, noradrenaline and DOPAC was performed by high performance liquid chromatography (h.p.l.c.) with electrochemical detection.

Incubation of renal slices and homogenates of whole kidney with exogenous l‐DOPA (0.1–10.0 μm) resulted in a concentration‐dependent formation of both dopamine and DOPAC.

The addition of M&B 22,948 (10 μm) to the incubation medium resulted in a marked reduction in the accumulation of both newly‐formed dopamine and DOPAC in kidney slices; the inhibitory effect of M&B 22,948 on DOPAC formation was greater than that on dopamine. 8‐Bromo cyclic GMP (250 μm) produced only a slight decrease in the tissue levels of newly‐formed dopamine (5–13% reduction), but was found to decrease significantly (51–68% reduction) the formation of DOPAC in kidney slices. The addition of 8‐bromo cyclic GMP plus M&B 22,498 to the incubation medium resulted in similar effects to those described for M&B 22,948 alone.

In kidney homogenates, in contrast to results observed in kidney slices, M&B 22,948 (10 μm) and 8‐bromo cyclic GMP (250 μm) were found to affect neither the formation of dopamine nor its deamination to DOPAC.

In conclusion, the results presented here suggest that cyclic GMP may be involved in the regulation of dopamine synthesis, probably through the control of the entry of l‐DOPA into the tubular epithelial cells.
In vitro vascular effects of cicletanine in pregnancy‐induced hypertension
Authors: Ebeigbe A.B. , Cabanie M.
Published: July 2012

The vascular effects of cicletanine have been studied in vitro on ring preparations of inferior epigastric arteries from normotensive human females and human females with pregnancy‐induced hypertension (preeclampsia).

Cicletanine (10−7–10−3 m) elicited concentration‐dependent relaxation of vessels precontracted with 10−7 m noradrenaline (NA) or 60 mm K+ but was more potent in the former. Relaxation was significantly greater in rings from preeclamptic patients and was uninfluenced by endothelium removal.

The intracellular Ca‐dependent contractile responses to 10−5 m NA in Ca‐free medium as well as the subsequent extracellular Ca‐dependent contractions (on restoration of external Ca) were significantly attenuated dose‐dependently by cicletanine (10−5 m, 3 × 10−4 m) in arterial rings from both normotensive and preeclamptic patients. Cicletanine also relaxed rings precontracted by 25 mm K+ but was ineffective against 80 mm K+‐induced contractions.

The inhibition of intracellular Ca‐dependent contractions was significantly greater in rings from preeclamptic than from normotensive patients whereas extracellular Ca‐dependent contractions were comparably inhibited in both groups. Nifedipine, on the other hand, had little effect on the intracellular Ca‐dependent contractions but significantly depressed extracellular Ca‐dependent contractions.

Cicletanine‐induced relaxation was uninfluenced by pretreatment with propranolol, ouabain, tetraethylammonium, procaine, indomethacin, cimetidine or tetrodotoxin but was antagonized by glibenclamide.

The results show that cicletanine inhibits contractile responses of human isolated inferior epigastric arteries by a mechanism unrelated to endothelial factors but associated with inhibition of calcium metabolism. An action of cicletanine on glibenclamide‐sensitive K+ channels is also suggested. Cicletanine‐induced inhibition was significantly greater in arteries from preclamptic patients.
Pharmacology of the putative M4 muscarinic receptor mediating Ca‐current inhibition in neuroblastoma × glioma hybrid (NG 108–15) cells
Authors: Caulfield M.P. , Brown D.A.
Published: July 2012

We have assessed the potency of a range of agonists and antagonists on the muscarinic receptor responsible for inhibiting the Ca‐current (ICa) in NG 108–15 hybrid cells.

Acetylcholine (ACh), oxotremorine‐M and carbachol were potent ‘full’ agonists (EC50 values were 0.11 μm, 0.14 μm and 2 μm, respectively). Maximum inhibition of peak high‐threshold ICa by these agonists was 39.5%. (±)‐Muscarine, methylfurmethide and arecaidine propargyl ester (APE) were ‘partial’ agonists, with EC50 values of 0.54 μm, 0.84 μm and 0.1 μm, respectively.

Atropine, pirenzepine and himbacine were potent antagonists of muscarinic inhibition of ICa, with apparent pKB values of 9.8, 7.74 and 8.83, respectively. Methoctramine was relatively weak (pKB = 7.63). Atropine and pirenzepine depressed maximum responses to agonists, probably because these antagonists have relatively slow dissociation rates.

The characteristic pharmacological profile found for the M4 receptors in these functional experiments (himbacine high affinity, pirenzepine moderate to high affinity, methoctramine low affinity) corresponds well with data from earlier binding experiments (Lazareno et al., 1990). Since mRNA hybridising to probes for the m4 receptor genotype can be detected in these cells, it is suggested that these pharmacological characteristics identify the equivalent expressed receptor subtype M4.
The antimigraine drugs ergotamine and dihydroergotamine are potent 5‐HT1C receptor agonists in piglet choroid plexus
Authors: Brown Anthony M. , Patch Tracey L. , Kaumann Alberto J.
Published: July 2012

Fozard & Gray (1989) proposed that migraine is mediated by stimulation of 5‐HT1C receptors. We have examined the interaction of two effective anti‐migraine agents, ergotamine and dihydroergotamine (DHE), with these receptors. Binding (inhibition of labelling by [3H]‐mesulergine) and agonist activity (phosphoinositide hydrolysis) were measured in piglet choroid plexus, a tissue rich in 5‐HT1C receptors.

The pKD for [3H]‐mesulergine binding was 8.4. Ergotamine and DHE both inhibited [3H]‐mesulergine binding with a pKD of 7.1. This was similar to the potency of m‐chlorophenylpiperazine (m‐CPP) (pKD 7.4) and rather less than that of 5‐hydroxytryptamine (5‐HT) (pKD 8.1).

Both ergotamine and DHE were full agonists (pEC50s 7.5 and 7.6 respectively) with potencies similar to that of 5‐HT (pEC50 7.7) and greater than that of m‐CPP (pEC50 7.1). Mesulergine 10−7m produced near‐parallel rightward shifts of the concentration‐response curves for all these agents of 1.8–2.2 log units, consistent with an action of the agonists at the same receptor.

There was no effect of prazosin, spiperone, mepyramine or atropine on the phosphoinositide hydrolysis induced by ergotamine, ruling out an action via α1‐adrenoceptors, 5‐HT2, histamine H1, or muscarinic receptors.

It is concluded that, together with 5‐HT, ergotamine and DHE are the most potent 5‐HT1C agonists reported so far. These findings do not support the theory that 5‐HT1C receptor activation causes migraine.
Effects of adenosine 3′: 5′‐cyclic monophosphate and guanine nucleotides on calcium‐evoked ACTH release from electrically permeabilized AtT‐20 cells
Authors: Guild Simon
Published: July 2012

The mouse AtT‐20/D16–16 anterior pituitary tumour cell line was used as a model system for the investigation of adenosine 3′:5′ ‐cyclic monophosphate (cyclic AMP)‐mediated enhancement of calcium‐evoked adrenocorticotrophin (ACTH) secretion.

AtT‐20 cells were permeabilized by subjecting the cells to intense electric fields. Exposure of permeabilized cells to calcium (1 mm) in the external medium significantly stimulated ACTH secretion over the first 20 min of exposure. This calcium‐stimulated ACTH secretion was dependent upon the presence of MgATP (5 mm).

The amount of ACTH secreted, in a 20 min incubation at 37°C, from permeabilized cells depended upon the free calcium concentration in the permeabilization medium. Calcium stimulated ACTH secretion from permeabilized cells in the concentration range of 10−7–10−5m (half maximal = 7 × 10−7m). Cyclic AMP(10−4m) increased the amount of ACTH secreted at each effective concentration of calcium. However, cyclic AMP did not alter the potency of calcium as a stimulant of ACTH secretion.

Guanosine 5′‐0‐(3‐thio triphosphate) (GTP‐γ‐S, 10−4m) stimulated ACTH secretion from permeabilized cells in the absence of calcium and was additive with calcium‐evoked ACTH secretion up to a maximum which could be stimulated by calcium acting singly. Guanosine 5′‐O‐(2‐thiodiphosphate) (GDP‐β‐S, 10−4m) inhibited calcium‐evoked ACTH secretion from permeabilized cells.

GTP‐γ‐S stimulated ACTH secretion from permeabilized cells in a concentration‐dependent manner. The nucleotide significantly stimulated ACTH secretion at concentrations of 10−5m and above. Cyclic AMP (10−4m) increased the amount of ACTH secretion evoked by effective concentrations of GTP‐γ‐S.

The results of the present study support the hypothesis that, in AtT‐20 cells, cyclic AMP is acting at some site, distal to calcium entry, which modulates the ability of an increase in cytosolic calcium concentration to stimulate ACTH secretion. One such site may be a GTP‐binding protein which the present study suggests may mediate the effects of calcium upon the secretory apparatus. These GTP‐binding proteins may be a target for regulation by cyclic AMP.
Endothelium‐derived relaxing factor inhibits the endothelin‐1‐induced increase in protein kinase C activity in rat aorta
Authors: Lang D. , Lewis M.J.
Published: July 2012

Particulate and cytosolic protein kinase C (PKC) activity was measured in rat aortae with and without endothelium, following exposure to endothelin‐1 (10−8m) for various time intervals.

Endothelin‐1 induced two peaks of particulate PKC activity, occurring at 30s and 10 min exposure times in both endothelium‐intact and endothelium‐denuded preparations. Cytosolic PKC activity fell below baseline at all incubation times studied.

In endothelium‐denuded preparations, elevation of guanosine 3′:5′‐cyclic monophosphate (cyclic GMP) levels with sodium nitroprusside (10−6m) or atrial natriuretic peptide (10−6m) and, in endothelium‐intact preparations with the calcium ionophore A23187 (10−6m), inhibited the activation of particulate PKC activity seen after incubation with endothelin‐1 for 30 s. The inhibitory effect of A23187 was prevented by prior incubation of the endothelium‐intact vessels with the nitric oxide synthetase inhibitor, l‐NG‐nitro arginine (5 × 10−5m).

These results indicate that EDRF acting via cyclic GMP can inhibit the activation of PKC induced by endothelin‐1 in rat aorta.
1‐O‐hexadecyl‐2‐acetyl‐sn‐glycero‐3‐phospho (N,N,N trimethyl) hexanolamine: an analogue of platelet‐activating factor with partial agonist activity
Authors: Grigoriadis George , Stewart Alastair G.
Published: July 2012

During studies of the role of platelet‐activating factor (PAF) in macrophage superoxide anion generation (O2−1), we identified an agonist action of the putative PAF receptor antagonist 1‐O‐hexadecyl‐2‐acetyl‐sn‐glycero‐3‐phospho (N,N,N‐trimethyl) hexanolamine (hexanolamine PAF) in guinea‐pig macrophages. The 1‐O‐octadecyl form of this compound has specific antagonist actions at PAF receptors.

The agonist properties of hexanolamine PAF were examined in rabbit washed platelets (aggregation) and in guinea‐pig peritoneal macrophages (O2−generation).

Hexanolamine PAF induced significant platelet aggregation (50% of the PAF maximum). However, the omission of bovine serum albumin (BSA) from the Tyrode buffer resulted in a diminution of the response of washed platelets during storage for 24 h at 4°C (7% of PAF maximum), whereas the maximum response to PAF was unaffected by storage for this period, irrespective of the presence of BSA.

Platelet aggregation induced by hexanolamine PAF was not accompanied by a detectable increase in intracellular calcium [Ca2+]i, whereas the aggregation response to PAF was preceded by a large rise in [Ca2+]i.

Hexanolamine PAF induced O2−generation in adherent macrophages, with a maximum response 45% of that to PAF. Hexanolamine PAF (100 nm), at a concentration equi‐effective with PAF (1 nm) for stimulation of O2−generation in macrophages, induced an increase in [Ca2+]i which was significantly less than that induced by PAF.

PAF concentration‐response curves were constructed in platelets or macrophages following pretreatment with hexanolamine PAF (0.1 and 1 μm). The interaction between PAF and the putative partial agonist (hexanolamine PAF) had the characteristics expected of a partial agonist interacting with a full agonist.

Platelet aggregation induced by hexanolamine PAF was antagonized non‐competitively by the PAF receptor antagonist, WEB 2086, whereas antagonism of PAF‐induced aggregation by WEB 2086 was competitive. Macrophage O2−generation induced by hexanolamine PAF or PAF was antagonized by WEB 2086.

These data indicate that hexanolamine PAF is a partial agonist at PAF receptors in macrophages and platelets. The inability of hexanolamine PAF to increase [Ca2+]i in platelets suggests that PAF receptors may be coupled to platelet aggregation by both Ca2+‐dependent and ‐independent pathways.
Effects of paracetamol and aspirin on neural activity of joint mechanonociceptors in adjuvant arthritis
Authors: McQueen D.S. , Iggo A. , Birrell G.J. , Grubb B.D.
Published: July 2012

The effects of paracetamol and lysine acetylsalicylate (L‐AS) on high‐threshold mechanonociceptors have been investigated by recording neural activity from the inflamed ankle joint in anaesthetized rats with mild adjuvant‐induced monoarthritis.

Paracetamol (50 mg kg−1, i.v.) and L‐AS (100 mg kg−1, i.v., equivalent to 50 mg kg−1 aspirin) both caused a maximal reduction of about 40% in mechanically‐evoked discharge and of 30% in ongoing (spontaneous) activity by about 15 min after the injection: a second dose of either drug did not have any significant additional effect on discharge.

The prostanoid IP receptor agonist, cicaprost (0.1–0.5 μg), increased both mechanically‐evoked and ongoing discharge to pre‐paracetamol levels when injected close‐arterially 30–50 min after paracetamol, whereas prostaglandin E2 (PGE2) was relatively ineffective at restoring activity.

The results suggest that prostacyclin (PGI2) contributes to the sensitization of high‐threshold joint mechanonociceptors in adjuvant‐induced monoarthritis, and that paracetamol and L‐AS both act to reduce discharge by inhibiting the synthesis of prostacyclin in the joint capsule.

Paracetamol has a direct peripheral action affecting joint capsule mechanonociceptors in rat adjuvant‐induced arthritis which is very similar to that of the soluble aspirin preparation, L‐AS. These findings, together with the existing literature concerning the anti‐arthritic effects of paracetamol, are relevant to the treatment of chronic inflammatory disorders such as rheumatoid arthritis.
Carotid vascular effects of ergotamine and dihydroergotamine in the pig: no exclusive mediation via 5‐HT1‐like receptors
Authors: den Boer Marinus O. , Heiligers Jan P.C. , Saxena Pramod R.
Published: July 2012

Though it is well known that the antimigraine drugs ergotamine and dihydroergotamine reduce carotid arteriovenous anastomotic shunting, it is uncertain whether a 5‐HT1‐like receptor is responsible for this effect. Using a high dose of methiothepin (3 mg kg−1), which completely blocks the carotid vascular effects of sumatriptan, we have attempted to study the role of 5‐HT1‐like receptors in the carotid vascular effects of ergotamine as well as dihydroergotamine in anaesthetized pigs.

Both ergotamine and dihydroergotamine increased arterial blood pressure and decreased heart rate.

The ergot alkaloids reduced dose‐dependently total carotid blood flow and conductance as a result of a selective decrease in the arteriovenous anastomotic fraction. The nutrient fraction increased, particularly to bones, tongue and salivary glands with ergotamine and to ears, head skin, bones and salivary glands with dihydroergotamine. In contrast, dural vascular conductance tended to decresae.

Methiothepin (3 mg kg−1) partially antagonized the decrease in total carotid and arteriovenous anastomotic blood flow and conductance by the ergot alkaloids; the ED30 for ergotamine and dihydroergotamine (agonist dose eliciting a 30% decrease in arteriovenous anastomotic conductance) was raised by 3.1 and 5.2 fold respectively.

These results indicate that the effects of ergotamine and dihydroergotamine are partly mediated by methiothepin‐sensitive receptors, which may probably belong to either 5‐HT1‐like or α2‐adrenoceptor category. However, an important part of the effect of ergot alkaloids is left after methiothepin and this could be mediated by other, perhaps novel, receptors.
Inositol 1,4,5‐trisphosphate‐stimulated calcium release from permeabilized cerebellar granule cells
Authors: Whitham Emma M. , Challiss R.A. John , Nahorski Stefan R.
Published: July 2012

Muscarinic cholinoceptor stimulation of phosphoinositide hydrolysis in rat cultured cerebellar granule cells results in a rapid, transient accumulation of inositol 1,4,5‐trisphosphate (Ins(1,4,5)P3), which has been implicated in the release of non‐mitochondrial intracellular Ca2+stores. In the present study, the release of Ca2+from intracellular stores and the Ins(1,4,5)P3 receptor responsible for this process have been investigated.

Monolayers of saponin‐permeabilized granule cells accumulate 45Ca2+in an ATP‐dependent manner and the sequestered 45Ca2+can be concentration‐dependently released by Ins(1,4,5)P3 by a stereospecific and heparin‐sensitive mechanism. The EC50 for Ins(1,4,5)P3‐stimulated 45Ca2+release was 80 ± 3 nm.

Radioligand binding studies performed on a crude granule cell membrane fraction indicated the presence of an apparently homogeneous population of stereo‐specific Ins(1,4,5)P3 receptors (KD 54.7 ± 2.0 nm; Bmax 1.37 ± 0.29 pmol mg−1 protein).

This study provides evidence for Ins(1,4,5)P3‐sensitive intracellular Ca2+stores in primary cultures of cerebellar granule cells and suggest that these cells provide an excellent model neuronal system in which to study the relative functional roles of Ca2+release from intracellular stores and Ca2+‐entry in neuronal Ca2+homeostasis.
The behavioural properties of CI‐988, a selective cholecystokininB receptor antagonist
Authors: Singh Lakhbir , Field Mark J. , Hughes John , Menzies Richard , Oles Ryszard J. , Vass Caroline A. , Woodruff Geoffrey N.
Published: July 2012

The behavioural effects of a selective cholecystokininB (CCKB) receptor antagonist CI‐988 were investigated in rodents.

In three rodent tests of anxiety (rat elevated X‐maze, rat social interaction test and mouse light/dark box) CI‐988 over the dose range 0.001–10.0 mg kg−1, (i.p.) produced an anxiolytic‐like action. The magnitude of this effect was similar to that of chlordiazepoxide (CDP). In contrast, the selective CCKA receptor antagonist, devazepide, was inactive. CI‐988 also showed anxiolytic‐like action in the rat conflict test but the magnitude of this effect was about 2.5 fold less than that of CDP.

Central but not peripheral administration of the selective CCKB receptor agonist, pentagastrin, like FG 7142, produced an anxiogenic‐like action.

The pentagastrin‐induced anxiety was dose‐dependently antagonized by CI‐988, whereas devazepide was inactive. However, ten times higher doses of CI‐988 were required to block a similar action of FG 7142.

In contrast to CDP, CI‐988 up to 3000 fold higher doses than those inducing anxiolysis was inactive in tests measuring sedation and ataxia. It also failed to antagonize pentylenetetrazol‐induced tonic seizures. Furthermore, CI‐988 did not interact with alcohol or barbiturates. Thus, CI‐988 appears to be an anxioselective compound.

The anxiolytic‐like action of CDP in the rat elevated X‐maze was dose‐dependently antagonized by flumazenil. In contrast, the benzodiazepine receptor antagonist failed to block a similar effect of CI‐988.

Thus, CI‐988 shows anxiolytic‐like activity in several animal models of anxiety. The anxiolytic‐like effect of CI‐988 involves a novel mechanism of action, that is likely to be mediated by selective antagonism of the brain CCKB receptor. It is suggested that CI‐988 should have a better side‐effect profile in man than the benzodiazepines.
Effects of cromakalim on neurally‐mediated responses of guinea‐pig tracheal smooth muscle
Authors: Burka J.F. , Berry J.L. , Foster R.W. , Small R.C. , Watt A.J.
Published: July 2012

The ability of cromakalim to modulate several different types of neuroeffector transmission has been assessed in guinea‐pig isolated trachea.

In trachea treated with propranolol (10−6m) and indomethacin (2.8 × 10−6m), stimulation of the extrinsic vagal nerves evoked contractions which were blocked by hexamethonium (5 × 10−4m) or by tetrodotoxin (TTX; 10−6m). Cromakalim (10−5m) caused a two fold rightward shift of the frequency‐response curve.

In carinal trachea treated with propranolol and indomethacin, transmural stimulation evoked an initial, rapid contraction followed by a more sustained secondary contraction. The initial, rapid contractile response was virtually ablated by atropine (10−6m) or by TTX but was resistant to hexamethonium. Cromakalim (10−8–10−5m) caused a concentration‐dependent rightward shift of the frequency‐response curve for the initial contraction.

In carinal trachea treated with atropine, propranolol and indomethacin, transmural stimulation evoked only the secondary (non‐adrenergic, non‐cholinergic (NANC)) contractile responses. These were markedly reduced by TTX but were resistant to hexamethonium. Cromakalim (10−8–10−5m) suppressed the NANC contractile responses in a concentration‐dependent manner. This action could be offset by glibenclamide (10−6m).

In trachea treated with atropine, histamine (10−4m), propranolol and indomethacin, transmural stimulation evoked NANC relaxant responses. Cromakalim (up to 10−5m) was without effect on the frequency‐response curve for the stimulation of NANC inhibitory nerves.

Tested on trachea bathed by drug‐free Krebs solution, cromakalim (10−7–10−5m) caused concentration‐dependent suppression of tracheal tone. In trachea treated with propranolol and indomethacin, cromakalim (10−7–10−5m) caused concentration‐dependent antagonism of acetylcholine (ACh). In trachea treated with atropine, propranolol and indomethacin, cromakalim (up to 10−5m) failed to antagonize effects of either histamine or substance P.

It is concluded that cromakalim can inhibit cholinergic (excitatory) neuroeffector transmission in the trachea but only at a concentration having demonstrable inhibitory activity against the action of exogenous ACh and the spontaneous tone of the airways smooth muscle. In contrast, cromakalim may depress NANC excitatory (putative peptidergic) neuroeffector transmission at a concentration below that exerting inhibitory activity on airways smooth muscle. Cromakalim does not concurrently depress NANC inhibitory neuroeffector transmission. Depression of NANC excitatory neuroeffector transmission could explain the ability of cromakalim to suppress airway hyperreactivity or bronchial asthma at doses lacking direct relaxant effect on airways smooth muscle.
The effects of lectins on the release of EDRF from rabbit aorta
Authors: Kleha Joseph F. , Devesly Pierre , Johns Anthony
Published: July 2012

The effects of the lectins, wheat germ agglutinin (WGA) and concanavalin A (Con A) on endothelium intact pre‐contracted rabbit aorta were investigated. WGA (8.3 μm) produced endothelium‐dependent relaxations, while Con A (4.3 μm) produced a partially endothelium‐dependent relaxation. The endothelium‐dependent relaxations to WGA were completely reversed by N‐acetylglucosamine, haemoglobin and methylene blue and were partially reversed by NG‐monomethyl‐l‐arginine (l‐NMMA). It is suggested that WGA works as an agonist in releasing endothelium‐derived relaxing factor (EDRF) from the endothelium of rabbit aorta by interacting with a glycosylated receptor on endothelial cells.
Effects of okadaic acid and ATPγS on cell length and Ca2+‐channel currents recorded in single smooth muscle cells of the guinea‐pig taenia caeci
Authors: Lang R.J. , Ozolins I.Z. , Paul R.J.
Published: July 2012

The effects of inhibiting phosphatase activity on Ca2+‐channel currents and cell shortening in single cells of the guinea‐pig taenia caeci were investigated by whole‐cell voltage clamp and video recording techniques.

Ca2+‐channel currents were isolated by use of pipette solutions containing Cs, tetraethylammonium and adenosine triphosphate (ATP) (3 mm). Ca2+or Ba2+(7.5 mm) in the bathing solution acted as the charge carrier during inward current flow.

Ca2+‐channel currents in 7.5 mm Ba2+(IBa) were recorded at potentials positive to −40mV, were maximal near 0mV and reversed near +60mV. Both the inward and outward flow of current was blocked by 100 μm Cd2+.

Addition of the ATP analogue, adenosine 5′‐O(3‐thio triphosphate) (ATPγS) (1 mm) to the pipette solution (containing 3 mm ATP) caused cell shortening to 23 ± 2% (n = 5) of their initial length within 5 min. Control cells (containing 4 mm ATP) did not contract during recording periods up to 60 min in duration.

IBa recorded 1–2 min after membrane rupture, was 134 ± 19 (n = 13) pA, compared with 209 ± 25 (n = 5) pA in control cells, otherwise there were no significant time‐dependent effects of ATPγS. In particular, ATPγS did not prevent the decrease in amplitude, nor the acceleration of inactivation when Ca2+(7.5 mm) replaced Ba2+as the permeating ion.

Okadaic acid (OA) (50 μm), a chemical inhibitor of phosphatase activity, produced similar effects when applied intracellularly. When OA (25 μm) was applied extracellularly the rate of rundown of IBa was slowed.

Isoprenaline (1 μm) alone had no effect on IBa, but induced a small increase in IBa in the presence of OA(25 μm).

Thus, our results indicate that (1) the contractions in ATPγS and OA may well arise from the activation of a kinase which phosphorylates myosin at low concentrations of Ca2+, and (2) changes in the state of phosphorylation of Ca2+channels, or associated proteins, in the taenia caeci modulate their function, but probably not via mechanisms involving cyclic AMP‐dependent protein kinases.
Vasodilator response of coronary smooth muscle to the sympathetic co‐transmitters noradrenaline and adenosine 5′‐triphosphate
Authors: Corr Laura , Burnstock Geoffrey
Published: July 2012

Vasodilator and vasoconstrictor responses to noradrenaline (NA), adenosine and adenosine 5′‐triphosphate (ATP) were examined in isolated ring segments of the left anterior descending coronary artery of the rabbit in the absence of endothelium.

NA caused dose‐dependent relaxation of potassium‐constricted vessels in the absence of β‐adrenoceptor blockade, with a pD2 of 5.96 ±0.21. This was inhibited by 1 μm propranolol. Constrictor responses of vessels at baseline tension were only seen at concentrations greater than 1 mm, and reached a maximum of 6% of the contraction to 30 mm KCl.

ATP caused relaxation of the potassium‐constricted ring segments in a dose‐dependent manner, although a transient constriction often preceded the relaxation. Adenosine was equipotent with ATP in producing relaxation; this was significantly inhibited by the P1‐purinoceptor antagonist, 8‐phenyltheophylline (8‐PT). The responses to ATP were little affected by 8‐PT, indicating that ATP was not acting through breakdown to adenosine. At basal tone, ATP produced transient vasoconstriction only at concentrations greater than 0.1 mm, reaching a maximum of 38% of the contraction to 30 mm KCl.

We conclude that in the rabbit coronary artery both NA and ATP produce vasodilatation by a direct action on the smooth muscle.
Renovascular hypertension impairs formation of endothelium‐derived relaxing factors and sensitivity to endothelin‐1 in resistance arteries
Authors: Dohi Yasuaki , Criscione Leoluca , Lüscher Thomas F.
Published: July 2012

Endothelium‐dependent vascular regulation was investigated in mesenteric resistance arteries of Goldblatt two kidney‐one clip (2K1C) renovascular hypertensive rats.

Third order branches of mesenteric arteries were dissected free and mounted on glass cannulae in an organ chamber. Changes in vascular diameter were measured in pressurized and perfused arteries with a video dimension analyzer.

Acetylcholine evoked endothelium‐dependent relaxations that were much more pronounced with intraluminal than with extraluminal application. In 2K1C rats the relaxation induced by intraluminal, but not extraluminal acetylcholine was decreased compared to normotensive Wistar Kyoto rats (WKY). Increased duration of hypertension further decreased the response to intraluminal but not extraluminal acetylcholine.

Endothelin‐1 and noradrenaline caused contractions which were augmented by removal of the endothelium. This augmentation was reduced in 2K1C rats compared to WKY; the difference was small with noradrenaline but more pronounced with endothelin‐1.

In arteries without endothelium the sensitivity, but not the maximal contraction to endothelin‐1 was lower in 2K1C rats, while the response to noradrenaline was not different in 2K1C rats and WKY. The sensitivity to the peptide was not further affected by increasing the duration of hypertension.

Thus, renovascular hypertension leads to an impaired intraluminal, but not extraluminal activation of the release of endothelium‐derived relaxing factor and a decreased inhibitory effect of the endothelium against endothelin‐1‐ and noradrenaline‐induced contractions in mesenteric resistance arteries. Furthermore, the sensitivity, but not the maximal response of vascular smooth muscle to endothelin‐1 was reduced.