bluuebunny/crossref_metadata_2025 huggingface dataset:
Identification of selective, high affinity [125I]‐angiotensin and [125I]‐bradykinin binding sites in rat intestinal epithelia
Authors: Cox Helen M. , Munday Kenneth A. , Poat Judith A.
Published: July 2012

Specific [125I]‐angiotensin II (AII) and [125I]‐bradykinin (Bk) binding sites have been identified within epithelial membranes from rat jejunum and descending colon.

These high affinity intestinal sites exhibited KD values of 0.64 ± 0.16 nM for [125I]‐AII and 0.69 ± 0.13 nM for [125I]‐Bk, which were similar to those for [125I]‐AII (0.85 nM) and [125I]‐Bk binding sites (1.03 nM) previously identified in renal cortex epithelia.

Specific [125I]‐AII binding capacity was only 19.77 ± 2.74 fmol mg−1 in small intestine and 11.31 ± 2.66 fmol mg−1 in descending colon epithelia while a larger population, 332.0 ± 72.9fmol‐mg−1 of specific [125I]‐Bk sites were identified in epithelial membranes from small intestine.

Significant hydrolysis of both free [125I]‐AII and [125I]‐Bk was observed while membrane bound peptides remained relatively resistant to degradation. Whilst no corrections have been made to the observed values of KD and Bmax quoted above, one may assume that the calculated reductions in the free hormone concentration will result in a decrease of the KD value for both peptides. Loss of membrane bound peptide, particularly of [125I]‐AII, may indicate that the calculated Bmax value is an underestimation.

Despite the rapid degradation of unbound [125I]‐AII and [125I]‐Bk during incubations the kinetics of specific peptide binding were reversible and highly selective. The order of potency for specific [125I]‐AII binding was [Sar1, Leu8]‐AII > [Sar1, Thr8]‐AII > AII > [Sar1, Ile8]‐AII > [Des, Asp1, Ile8] AII > AIII. Specific [125I]‐Bk binding was also highly selective, the order of potency being Phe8‐Bk>Tyr8‐Bk>Lys‐Bk>Des, Arg1‐Bk. AII exhibited an IC50 of > ImM for specific [125I]‐Bk binding and likewise Phe8‐Bk for specific [125I]‐AII binding.
The determination of receptor constants for histamine H2‐agonists in the guinea‐pig isolated right atrium using an irreversible H2‐antagonist
Authors: Rising T. J. , Steward A.
Published: July 2012

From measurements of chronotropy in the guinea‐pig isolated right atrium, a compound (E1309) was found which behaved as an irreversible antagonist at the histamine H2 receptor.

E1309 was used to block irreversibly a proportion of the H2 receptors and the dissociation constants, relative efficacies and receptor reserves of four H2‐agonists were determined.

The calculated dissociation constants were similar to the Ki values reported from H2‐radioligand binding studies but different from the observed EC50 values.

The order of potency for the four H2‐agonists was impromidine > > histamine > dimaprit> 4‐methylhistamine.

The order of relative efficacy was 4‐methylhistamine > dimaprit > histamine > impromidine, the natural agonist not being the most efficacious. This atypical finding is discussed in relation to other receptor classes.
Studies on the receptor mediating cyclic AMP‐independent enhancement by adenosine of IgE‐dependent mediator release from rat mast cells
Authors: Church Martin K. , Hughes Philip J. , Vardey Christopher J.
Published: July 2012

Adenosine produced a concentration‐related enhancement of antigen‐induced 5‐hydroxytryptamine (5‐HT) release from rat serosal mast cells. This potentiation was maximal following the simultaneous addition of adenosine with antigen.

Enhancement of 5‐HT release was accompanied by potentiation of the adenosine 3′:5′‐cyclic monophosphate (cyclic AMP) response to challenge. The cyclic AMP response, which was antagonized by 8‐phenyltheophylline, was characterized as an A2‐purinoceptor‐mediated effect by the use of 5′‐N‐ethylcarboxamideadenosine (NECA) and L‐N6‐phenylisopropyladenosine (L‐PIA).

Enhancement of 5‐HT release, conversely, was not blocked by 8‐phenyltheophylline suggesting it to be mediated by a cyclic AMP‐independent mechanism.

The effect of adenosine on 5‐HT release was not reduced by the inhibition of the facilitated uptake of adenosine with dipyridamole, hexobendine or p‐nitrobenzylthioguanosine, therefore, suggesting it to be mediated by a cell surface receptor.

The receptor mediating enhancement of 5‐HT does not appear to belong to the P2‐purinoceptor subtype as adenosine was more potent than both adenosine monophosphate (AMP) and adenosine diphosphate (ADP) and α,β‐methylene ATP was inactive. Furthermore, the effects of AMP were blocked by α,β‐methylene ADP, which inhibits the conversion of AMP to adenosine.

Adenosine, NECA, L‐ and D‐PIA were all of equal potency in enhancing 5‐HT release. Inosine and 3‐deazaadenosine were also active. The rank order of potency of these adenosine analogues is not consistent with an effect at A1‐ or A2‐purinoceptors.

There appear to be two adenosine receptors on rat mast cells, an A2‐purinoceptor which stimulates adenylate cyclase and a separate purinoceptor, stimulation of which produces enhancement of mediator release by an unknown mechanism. The effects mediated by these receptors appear to be independent of each other.
Anaesthesia abolishes the effect of valproate on extracellular 5‐HIAA, DOPAC and ascorbate as measured in rat striatum by differential pulse voltammetry
Authors: Crespi F. , Keane P.E. , Morre M.
Published: July 2012

The effect of sodium valproate (VPA, 400 mg kg−1, i.p.) on extracellular ascorbate, 3,4‐dihydroxyphenylacetic acid (DOPAC) and 5‐hydroxyindoleacetic acid (5‐HIAA) in the striatum was examined by differential pulse voltammetry in anaesthetized and freely‐moving rats.

In rats anaesthetized with chloral hydrate (400 mg kg−1, i.p.), pentobarbitone (50 mg kg−1, i.p.) or phenobarbitone (60 mg kg−1, i.p.), VPA produced no significant changes in peak 1 (extracellular ascorbate) or peak 2 (extracellular DOPAC), but produced a slight but statistically significant reduction in the height of peak 3 (extracellular 5‐HIAA).

In contrast, in freely‐moving rats the same dose of VPA greatly reduced extracellular ascorbate and DOPAC concentrations, and increased that of 5‐HIAA.

These results suggest that VPA may reduce the release or turnover of dopamine, and increase that of 5‐hydroxytryptamine in conscious rats. Our data also suggest that caution may be required in the interpretation of the effects of VPA in anaesthetized animals, as the results obtained may not always reflect the situation in the absence of anaesthesia.
Naloxone inhibits arrhythmias induced by coronary artery occlusion and reperfusion in anaesthetized dogs
Authors: Huang X.D. , Lee A.Y.S. , Wong T.M. , Zhan C.Y. , Zhao Y.Y.
Published: July 2012

The intravenous administration of naloxone 2 min before coronary artery occlusion in anaesthetized dogs reduced the incidence and severity of cardiac arrhythmias during coronary occlusion (20 min) and reperfusion (120 min) in a dose‐related manner. It also reduced the mortality. At a dose of 1 mg kg−1 (the maximum dose used in this study) naloxone abolished the appearance of the life threatening ventricular fibrillation (VF) and ventricular tachycardia (VT) and as a consequence all dogs in this group survived. The results suggest a possible involvement of endogenous opioid peptides in arrhythmogenesis during coronary occlusion and reperfusion in the dog.
The effect of enalapril (MK421), an angiotensin converting enzyme inhibitor, on the conscious pregnant ewe and her foetus
Authors: Pipkin Fiona Broughton , Wallace Carol P.
Published: July 2012

The effects of enalapril, an angiotensin converting enzyme (ACE) inhibitor, on maternal and foetal blood pressure, heart rate and components of the renin‐angiotensin‐aldosterone system were studied in 9 chronically‐cannulated pregnant ewes and their foetuses.

Six ewes received 1 mg kg−1 enalapril i.v. while 3 were given 2 mg kg−1. Although the initial fall in blood pressure was slightly greater in the higher dose group, there was substantial overlap of data. The pressor response to angiotensin I, assessing ACE activity, was abolished within 10 min of administration, and did not recover during 3 h of observation. Maternal systolic and diastolic pressures reached a nadir 90 min after administration (P < 0.001, P < 0.002 respectively). The maximum tachycardia was seen at 60 min (P < 0.05).

The foetuses of the ewes given 1 mg kg−1 enalapril showed no change in systolic or diastolic blood pressure or heart rate. Those of the ewes given the higher dose showed late‐onset hypotension, coincident with the lowest maternal blood pressures.

Maternal plasma renin concentration (PRC) had risen significantly by 30 min (P < 0.02), reaching a maximum at approximately 90 min. Maternal plasma angiotensin II and aldosterone concentrations both fell initially (P < 0.05) but were almost at basal levels by the end of the experiment.

Foetal plasma renin, angiotensin II and aldosterone concentrations were unchanged throughout the experiment.

Peak values of enaprilic acid, the active principle, were recorded in maternal plasma 65–90 min after administration of 1 mg kg−1, and 25–30 min after the administration of 2 mg kg−1. A trace amount of the active principle was recorded in the foetal plasma of one lamb, whose mother had been given the higher dose. None was recorded in the plasma from three other lambs.

Maternal plasma ACE concentrations fell by an average of 84%; in 4 of the 6 ewes in which concentrations were measured they were undetectable after treatment. Foetal plasma ACE concentrations were unchanged throughout.

Enalapril at 1 mg kg−1 thus exerts a depressor effect on the pregnant ewe which is probably related to its blockade of the renin‐angiotensin system. Both direct measurement of the drug and foetal observation suggest that it does not cross the sheep placenta at this dose. This is consistent with its failure to cross the blood‐brain barrier. Foetal effects were noted at 2 mg kg−1, and there was an unexpected foetal death in this group.
Evidence against the formation of 13,14‐dihydro‐15‐keto‐prostaglandin F2α following inhalation of prostaglandin D2 in man
Authors: Hardy Christopher C. , Holgate Stephen T. , Robinson Clive
Published: July 2012

There is evidence that an important step in the metabolism of prostaglandin D2 (PGD2) involves 11‐keto‐reduction and that such a conversion might account for the reported increase in plasma concentrations of 13,14‐dihydro‐15‐keto‐PGF2α in allergic asthmatic subjects challenged with inhaled allergen.

Plasma concentrations of immunoreactive 13,14‐dihydro‐15‐keto‐PGF2α were measured by specific radioimmunoassay both before and after inhalation of PGD2 and PGF2α in 7 normal and 7 asthmatic men.

In both groups of subjects, PGF2α produced an approximate two fold increase in plasma concentrations of 13,14‐dihydro‐15‐keto‐PGF2α that was maximal 5–7 min after inhalation. There was no significant difference in response between the normal and asthmatic subjects.

In contrast, PGD2 failed to produce a change in plasma 13,14‐dihydro‐15‐keto‐PGF2α concentration in either group.

These results provide evidence that the conversion of PGD2 to PGF2α with subsequent metabolism to 13,14‐dihydro‐15‐keto‐PGF2α is unlikely to occur when PGD2 is released from mast cells in the airways.
Mechanisms of intrinsic tone in bullfrog lung: relaxant effects of indomethacin, ouabain and potassium
Authors: Downes Hall , Edelstein Robert A. , Taylor Stephen M.
Published: July 2012

Bullfrog hemilungs showed minimal relaxation (9 ± 2% of the maximal relaxant effect of theophylline, Imax) after a 16 h incubation in 10−5 M indomethacin, indicating that prostaglandin synthesis plays little or no role in the high intrinsic tone characteristic of this preparation.

A higher concentration of indomethacin (10−4 M) produced greater relaxation (23 ± 3% of Imax), but also markedly potentiated isoprenaline‐induced relaxation. The interaction with isoprenaline was similar to that previously found for papaverine, a phosphodiesterase inhibitor.

Ouabain (10−5 and 10−4 M) produced an initial contraction followed by marked relaxation (50% of Imax), indicating that a ouabain‐sensitive mechanism is of major importance in the maintenance of intrinsic tone.

Ouabain‐treated hemilungs showed (a) reversal (relaxation) of the normal contractile response to 26 mM potassium and (b) marked impairment of the contractile response to calcium in calcium‐depleted preparations. These effects suggest that ouabain‐induced relaxation reflects a drug action on calcium movements.

The marked relaxation (30 to 40% of Imax) produced by 26 mM potassium in ouabain‐treated hemilungs is of particular interest in that it indicates a mechanism of potassium‐induced relaxation distinct from stimulation of sodium‐potassium ATPase.
Acetylcholine output and foetal vascular resistance of human perfused placental cotyleda
Authors: Bourn A.L.A. , Gude N.M. , King R.G. , Walters W.A.W.
Published: July 2012

The foetal villous vessels of single cotyleda of human placentae have been perfused with a constant flow of Krebs solution, recording inflow pressure and passing the venous perfusate in cascade over guinea‐pig ileum and rat stomach strip preparations in vitro.

Each cotyledon released for at least 4 h a substance that was probably acetylcholine. The perfusate caused contractions of both preparations which were inhibited by atropine or hyoscine and potentiated by physostigmine. Contractile activity was destroyed after incubation at 37°C of perfusate with acetylcholinesterase but not with acetylcholinesterase plus physostigmine.

When the perfusion temperature was lowered to 34°C or below, acetylcholine output was reduced, the extent depending on the fall in temperature.

No change in resistance of the villous vessels occurred during the changes in temperature or in the presence at 37°C of atropine, hyoscine, hexamethonium, (+)‐tubocurarine, hemicholinium‐3 or bretylium.

Submaximal vasoconstrictor responses of the villous vessels to the thromboxane A2‐mimetic U46619 were not affected by reduction of the perfusion temperature to 30°C, which lowered acetylcholine‐like output by approximately 70%. Responses to U46619, at 37°C, were unchanged during the presence of atropine or hyoscine.

Acetylcholine is released into the foetal circulation of the human placenta but no evidence could be obtained that it affects villous vascular smooth muscle tone or vasoconstrictor responses.
Morphine attenuates cholinergic nerve activity in human isolated colonic muscle
Authors: Burleigh David E. , Trout Stephen J.
Published: July 2012

The action of morphine on cholinergic nerves in human sigmoid taenia coli muscle strips (taenia) was investigated using a radiolabelling technique.

Basal release of tritiated material from taenia was increased by electrical field stimulation (EFS). This increase was tetrodotoxin (3.14 μM)‐sensitive and calcium‐dependent. Analysis of basal and stimulated release of tritiated material indicated that evoked release (i.e. stimulated minus basal) is almost entirely due to an increase in [3H]‐acetylcholine ([3H]‐ACh) output.

Evoked release of [3H]‐ACh was dependent on the current strength and could be greatly reduced by exposing taenia to hemicholinium (34.8, 87.0 μM) before and during incubation with [3H]‐choline (4 μCi ml−1, 15 Ci mmol−1).

Spontaneous activity, muscle tone and the motor response of taenia to EFS were unaffected by morphine.

Evoked, but not basal, release of tritiated material was inhibited by morphine (1.32‐13.20 μM) in a concentration‐dependent manner. The inhibition of release was frequency‐dependent and naloxone (0.28 μM)‐sensitive.

The possible relationship between the effects of morphine on cholinergic nerves in taenia muscle and its actions in vivo are discussed.
Binding of a radioiodinated 13‐azapinane thromboxane antagonist to platelets: correlation with antiaggregatory activity in different species
Authors: Narumiya Shuh , Okuma Minoru , Ushikubi Fumitaka
Published: July 2012

Binding of a 125I‐labelled derivative of the 13‐azapinane thromboxane antagonist (ONO‐11120), [125I]‐9,11‐dimethylmethano‐11,12‐methano‐16‐(3‐iodo‐4‐hydroxyphenyl)‐13,14‐dihydro‐13‐aza‐15‐β‐ω‐tetranor‐thromboxane A2 ([125I]‐PTA‐OH), to washed platelets of human, dog and rabbit was studied. Results were compared with the in vitro inhibitory potency of ONO‐11120 on platelet aggregation induced by arachidonate and a thromboxane agonist, 9,11‐epithio‐11,12‐methanothromboxane A2 (STA2).

[125I]‐PTA‐OH bound to washed human platelets in a reversible, saturable and temperature‐dependent manner, and specific binding displaced by 20 μM ONO‐11120 constituted about 40% of the total binding. Scatchard analyses revealed a single class of specific binding and the equilibrium dissociation constant (KD) and maximal concentration of binding sites (Bmax) were 22 nM and 390 fmol per 108 platelets (about 2,300 sites per platelet), respectively. In addition to ONO‐11120, STA2 and another thromboxane receptor agonist, (15S)‐hydroxy‐11,9‐epoxymethano‐prosta‐5Z,13E‐dienoic acid (U‐46619), effectively displaced the binding with IC50 values of 44 and 125 nM respectively. Prostaglandin D2 (PGD2) partially displaced the binding only at a concentration above 1 μM. PGE1 and thromboxane B2 (TXB2) were without effect up to 100 μM.

Similar binding of [125I]‐PTA‐OH was observed on dog platelets. The KD and Bmax were 12 nM and 110 fmol per 108 platelets (about 680 sites per platelet), respectively, and these values did not change significantly after adrenaline treatment which potentiated arachidonate‐induced aggregation of platelets in this species. On the other hand, no specific binding of [125I]‐PTA‐OH was found on rabbit platelets.

Consistent with the results from binding studies, ONO‐11120, 0.5 μM, completely suppressed arachidonate‐induced aggregation of human platelets, whereas, at concentrations up to 5 μM, this agent did not significantly inhibit aggregation of rabbit platelets induced by the same stimulus. STA2‐induced aggregation of rabbit platelets also showed less sensitivity to ONO‐11120. When a similar extent of irreversible aggregation was induced by STA2 and the inhibitory potency of ONO‐11120 was compared in human and rabbit platelets, about one hundred times greater concentration of ONO‐11120 was required to suppress aggregation of rabbit platelets than that of human platelets.

These results suggest that [125I]‐PTA‐OH binds to a platelet thromboxane receptor, and that the structure of the binding site(s) on the receptor may vary between species.
The sulphoxide moiety of substituted benzimidazoles is essential for inhibition of parietal cell K+/H+‐ATPase
Authors: Beil W. , Eltze M. , Heintze K. , Klemm K. , Riedel R. , Schudt C. , Sewing K.‐Fr. , Simon A.
Published: July 2012

The antisecretory action of the benzimidazole sulphoxide derivative B 823‐10, 2[(4‐methoxy‐3‐methyl‐2‐pyridylmethyl)‐sulphinyl]‐5‐trifluoromethyl(1H)‐benzimidazole, was compared with the effect of the corresponding sulphide B 823‐08 in several in vivo and in vitro test systems.

The sulphide B 823‐08 and the sulphoxide B 823‐10 were found to be equipotent in the Shay rat. The sulphide was found to inhibit H+ secretion in intact rabbit gastric glands and enriched guinea‐pig parietal cells with lower potency than the corresponding sulphoxide. The relative potency in antisecretory activity (sulphide/sulphoxide) decreased in the following rank order: Shay rat: gastric glands: parietal cells.

Purified K+/H+‐ATPase was not blocked by the sulphide, whereas the sulphoxide inhibited the overall as well as the partial reactions of this enzyme.

In all in vitro systems tested, inhibition of H+ secretion and enzyme activity by the sulphoxide, but not by the sulphide, was antagonized by SH‐compounds such as dithiothreitol.

It is concluded that in vivo sulphoxidation of the sulphide plays an important role in acid inhibition. In vitro an additional inhibitory mechanism of the sulphide has to be considered.
β‐Adrenoceptor‐mediated modulation of calcium ionophore activated polymorphonuclear leucocytes
Authors: Mack James A. , Nielson Christopher P. , Stevens Dennis L. , Vestal Robert E.
Published: July 2012

β‐Adrenoceptor‐mediated modulation of calcium‐mediated stimulus‐response coupling was studied using calcium ionophore (A23187) activation of polymorphonuclear leucocytes (PMNL). Oxygen metabolite generation was measured with luminol‐ and lucigenin‐dependent chemiluminescence in both whole blood and isolated PMNL.

Isoprenaline reduced PMNL response by 53% in a dose‐dependent fashion. The effect was saturable, stereoselective, antagonized by propranolol and significant at isoprenaline concentrations as low as 0.01 nM. Fifty % maximal response was induced by 0.26 nM, 3 nM, and 125 nM isoprenaline, adrenaline and noradrenaline respectively.

Because the effects of β‐adrenoceptor agonists in PMNL have not consistently correlated with measurements of cyclic AMP, alternative means of increasing cyclic AMP were studied. Forskolin and dibutyryl cyclic AMP inhibited PMNL with significant effects at 1.0 μM and 10 μM respectively.

The effects of β‐adrenoceptor agonists were much greater when PMNL were activated by calcium ionophore compared with opsonized zymosan. Isoprenaline had no effect upon l‐oleoyl‐2‐acetylglycerol activated PMNL.

Because catecholamine modulation of oxygen metabolite generation can be characterized pharmacologically, PMNL activation by calcium ionophore is an excellent model for study of β‐adrenoceptor function in viable human cells.

In contrast to previously described β‐adrenoceptor agonist modulation of PMNL function, inhibition of calcium‐mediated activation is significant at physiological concentrations. The clinical consequences of such catecholamine effects are dependent upon the mechanism of PMNL activation in a specific circumstance.
Apomorphine‐induced inhibition of histamine release in rat peritoneal mast cells
Authors: Battistella Antonio , Boarato Elena , Bruni Alessandro , Mietto Lucia , Palatini Pietro , Toffano Gino
Published: July 2012

The apomorphine‐induced inhibition of histamine release in rat peritoneal mast cells was studied by means of secretagogues stimulating different pathways of mast cell activation.

Apomorphine inhibited the mast cell response to all releasing agents (lysophosphatidylserine plus nerve growth factor, compound 48/80, substance P, ATP, tetradecanoylphorbolacetate, melittin). The IC50 ranged from 4 μM to 24 μM at concentrations of secretagogues releasing 30–50% of mast cell histamine. However, the potency of the drug decreased at higher segretagogue concentrations.

Mast cells, pretreated with apomorphine and washed, released little histamine upon stimulation. The secretory response could be partially restored on increasing the concentration of secretagogues.

The results suggest that apomorphine affects a regulatory step controlling the terminal sequence of mast cell secretory activity. As indicated by the reduced potency of the drug, the control by the apomorphine‐sensitive reaction loses efficiency under conditions of massive histamine release.
The depolarizing action of 5‐hydroxytryptamine on rabbit vagal afferent and sympathetic neurones in vitro and its selective blockade by ICS 205–930
Authors: Round Alison , Wallis D.I.
Published: July 2012

Depolarizing responses to 5‐hydroxytryptamine (5‐HT) were recorded from rabbit nodose (NG) and superior cervical (SCG) ganglia using the sucrose‐gap technique. The antagonist potency and selectivity of ICS 205–930 ([3α‐tropanyl]‐1H‐indole‐3‐carboxylic acid ester) were investigated.

In NG, 5‐HT (5 to 80 nmol) evoked depolarizations of graded amplitude. The ED50 was 18.2 (10.9–30.5) nmol (geometric mean, 95% confidence limits). Responses were blocked surmountably by ICS 205–930, 10−11 and 10−10 M, the threshold for blockade being below 10−11 M. Parallel, rightward shifts in dose‐response curves were seen with these concentrations of antagonist, but at higher concentrations (10−9 and 10−8 M) there was a further rightward shift with reduction in slope and maximum of the curves.

In SCG, where 5‐HT (20 to 320 nmol) evoked depolarizations of graded amplitude and the ED50 was 55.8 (22.3–139.6) nmol (geometric mean, 95% confidence limits), ICS 205–930 had a similar inhibitory effect to that observed in NG.

The apparent pA2 values for the surmountable blockade produced by ICS 205–930 at concentrations of 10−11 and 10−10 M were 10.2 ± 0.2 for NG and 10.4 ± 0.1 for SCG (means ± s.e. mean).

ICS 205–930 was selective in its action since it had no effect on dimethylphenylpiperazinium (DMPP) responses in either ganglion or on GABA responses in NG.

This study provides quantitative evidence on the blocking action of ICS 205–930 at neuronal 5‐HT receptors using a technique that allows the depolarizing responses evoked by the amine to be directly recorded.
Inhibition of the excitatory junction potential in the guinea‐pig saphenous artery by ANAPP3
Authors: Cheung D.W. , Fujioka M.
Published: July 2012

Electrical stimulation of the perivascular nerves of the guinea‐pig saphenous artery elicited excitatory junction potentials (e.j.ps) in the smooth muscle cells. These e.j.ps were inhibited by arylazido aminopropionyl adenosine triphosphate (ANAPP3), a specific antagonist for the P2‐purinoceptor, suggesting that ATP may be the neurotransmitter.
An investigation into the α‐adrenoceptor mediating renal nerve‐induced calcium reabsorption by the rat kidney
Authors: Johns Edward J. , Manitius Jacek
Published: July 2012

An investigation was undertaken in pentobarbitone‐anaesthetized rats to determine the sub‐type of α‐adrenoceptor responsible for the renal nerve‐induced increases in the reabsorption of calcium and sodium by the tubules of the kidney.

Stimulation of the renal nerves at low frequencies (0.8‐1.5 Hz) did not change either renal blood flow or glomerular filtration rate but significantly reduced urine flow by 32%, calcium excretion by 36% and absolute and fractional sodium excretions by 36% and 22%, respectively.

In the presence of the selective α1‐adrenoceptor antagonist prazosin, renal nerve stimulation (2–3 Hz) caused a significant reduction in renal blood flow of 7% but did not change either glomerular filtration rate, urine flow, calcium excretion or absolute and fractional sodium excretions.

During administration of the selective α1‐adrenoceptor antagonist, idazoxan, renal nerve stimulation (1.0–1.5 Hz) significantly reduced renal blood flow by 4% and glomerular filtration rate by 7%; at the same time there were significant falls in urine flow of 43%, calcium excretion of 43% and absolute and fractional sodium excretions of 41% and 37%, respectively.

These results show that low frequency renal nerve stimulation causes an anticalciuresis, independent of renal haemodynamics, which represents an increase in tubular reabsorption of calcium. This effect was blocked by prazosin but not idazoxan which is consistent with the mediation of α1‐adrenoceptors. The neurally‐induced antinatriuresis also appeared to be dependent on the activation of α1‐adrenoceptors.
Vasoactive intestinal peptide in bovine pulmonary artery: localisation, function and receptor autoradiography
Authors: Barnes Peter J. , Cadieux Alain , Carstairs Jill R. , Greenberg Barry , Polak Julia M. , Rhoden Kerry
Published: July 2012

The role of vasoactive intestinal peptide (VIP) in the control of pulmonary vascular tone was investigated by functional response, immunocytochemical localisation and receptor autoradiography in bovine pulmonary arteries.

VIP‐immunoreactive nerve fibres were present at the adventitial‐medial junction and in the media of the vessels.

Exposure of precontracted bovine pulmonary artery segments to VIP in vitro resulted in almost complete (86 ± 3%; mean ± s.e.mean) relaxation, the concentration needed for 50% relaxation being 4.47 ± 0.37 × 10−9 M. VIP effects did not depend on the presence of intact endothelial cells.

The distribution of VIP receptors was studied by autoradiography using [125I]‐VIP. A high density of VIP receptors was found in arterial vascular smooth muscle, with a gradient of density from adventitia to luminal surface. There were no receptors on endothelial cells.

These data show that VIP is a potent vasodilator of bovine pulmonary arteries, via direct activation of VIP receptors in vascular smooth muscle. VIP‐immunoreactive nerves may influence pulmonary vascular tone directly and could, therefore, be important in regulating pulmonary blood flow.
Stimulation and suppression of renin release from incubations of rat renal cortex by factors affecting calcium flux
Authors: May Clive N. , Peart W.S.
Published: July 2012

Inhibition of renin secretion from incubations of rat kidney cortex by angiotensin II (AII), ouabain and K+ depletion, depended on the presence of external Ca2+.

AII inhibition of isoprenaline‐stimulated renin secretion was only partially dependent on external Ca2+.

Ouabain and K+ depletion inhibited isoprenaline‐stimulated renin release but only in the presence of external Ca2+. Since, in Ca2+‐free medium, isoprenaline stimulated renin release when the Na+/K+‐ATPase was blocked, isoprenaline probably does not act through the Na+/K+‐ATPase.

Lanthanum blocked the stimulation of renin release by isoprenaline.

Ethylenediamine tetra‐acetic acid (EDTA) and ethyleneglycol‐bis‐(β‐amino‐ethyl ether) N,N'‐tetra‐acetic acid (EGTA) increased renin secretion to a similar degree in Ca2+‐ and Mg2+‐free buffer. When Mg2+ was present the effect of EGTA, but not EDTA, was considerably reduced.

Verapamil reduced the fall in basal renin secretion in normal but not Ca2+‐free buffer. Verapamil did not block the inhibitory effects of AII or ouabain and did not alter the stimulation of renin secretion by isoprenaline.

Bay K 8644 inhibited renin secretion from cortex incubated in medium containing 15 mM K+ and this was dependent on extracellular Ca2+. In normal buffer (5.9 mM K+) Bay K 8644 increased renin secretion.
The effect of mepyramine and ranitidine on the oestrogen and anti‐oestrogen stimulated rat uterus
Authors: Marshall K. , Senior J.
Published: July 2012

The aims of this study were to elucidate further the role of histamine in the rat uterotrophic response and to investigate the differences between the oestrogen and the anti‐oestrogen induced uterine responses.

The parameters examined were uterine blood flow (measured by the microsphere technique), uterine wet and dry weights.

17β‐Oestradiol and the anti‐oestrogen, tamoxifen, were used to stimulate the ovariectomised rat uterus and the antihistamines mepyramine (H1) and ranitidine (H2) were employed to modify these responses.

The uterine changes evoked by oestradiol proved to be more susceptible to modification by the antihistamines than the tamoxifen‐stimulated responses.

The results suggest that histamine is involved in the early uterine response to oestradiol but histamine does not appear to play a major role in the uterine response to tamoxifen.
Feline endotoxin shock: effects on tissue histamine and histidine decarboxylase activity
Authors: Parratt James R. , Saleh Samira , Waton N. Graham
Published: July 2012

Tissue histamine levels as well as specific and non‐specific histidine decarboxylase were examined before and at various times (5 and 10 min) after the intravenous injection of a lethal dose (2 mg kg−1) of E. coli endotoxin in anaesthetized cats.

Histamine levels were increased 5 min after endotoxin, especially in the skin, liver, lung and stomach.

There was evidence, in most of the cats, for a rapid and substantial activation of specific histidine decarboxylase especially in the lungs, liver, heart and gastrointestinal tract 5–10 min after endotoxin administration.

It is suggested that endotoxin induces the local formation of histamine and that this formation and local release may contribute to the pathophysiology of endotoxin shock in this species.
A further search for selective antagonists at M2‐muscarinic receptors
Authors: Barlow R.B. , Shepherd M.K.
Published: July 2012

In an attempt to obtain more selective antagonists acting at muscarinic M2‐receptors, analogues of 4‐diphenylacetoxy‐N‐methylpiperidine methobromide (4‐DAMP methobromide) have been synthesized. These were tested, along with silabenzhexol, procyclidine, sila‐procyclidine and AFDX‐116, in dose‐ratio experiments with guinea‐pig isolated atria at 30°C and ileum at 30°C and 37°C. The agonist was carbachol and the selectivity was assessed from the difference between log K for receptors in ileum and log K for receptors in atria.

The selectivity was not related to the affinity and some weakly active compounds retained appreciable selectivity but no compound had greater selectivity than 4‐DAMP methobromide or pentamethylene bis‐(4‐diphenylacetoxy‐N‐methylpiperidinium) bromide.

Structure‐activity relations are discussed. There seem to be steric limits to affinity but there are no obvious indications of the structural features associated with selectivity. It is suggested that more selective drugs may be obtained by introducing groups which may reduce affinity.
Stimulation of receptors of γ‐aminobutyric acid modulates the release of cholecystokinin‐like immunoreactivity from slices of rat neostriatum
Authors: Conzelmann Ute , Meyer Dieter K. , Sperk Günter
Published: July 2012

Slices of rat dorsal neostriatum were incubated in Krebs‐Henseleit medium and the release of cholecystokinin‐like immunoreactivity (CCK‐IR) was induced by veratridine or high concentrations of K+. It was investigated whether drugs which act at receptors for γ‐aminobutyric acid (GABA) affected the release.

The GABAA‐receptor agonists muscimol and isoguvacine enhanced the veratridine‐induced release of CCK‐IR. This effect was abolished by the GABAA‐receptor antagonist, bicuculline. When used alone, bicuculline decreased the release.

The GABAB‐receptor agonist, (‐)‐baclofen, decreased the veratridine‐induced release of CCK‐IR. The stereoisomer (+)‐baclofen, which has low intrinsic activity, had no effect when used alone, but antagonized the effect of (‐)‐baclofen as did δ‐amino‐n‐valeric acid, another antagonist at GABAB‐receptors.

When the release of CCK‐IR was stimulated by K+ (40 mM) in the presence of tetrodotoxin, it was no longer affected by GABAA‐receptor agonists or antagonists. Thus, their sites of action were probably not in the immediate vicinity of the nerve‐endings which release CCK‐IR.

Under these conditions, stimulation of GABAB‐receptors still reduced the release of CCK‐IR. Therefore, it is concluded that these receptors are in the immediate vicinity of or even on the terminals which release CCK‐IR.
Feedback control of arterial smooth muscle tone: the role of prostacyclin
Authors: Hadházy P. , Magyar K.
Published: July 2012

Indomethacin potentiated noradrenaline (NA)‐induced contractions of rabbit isolated mesenteric arteries. Mechanical removal of the endothelium did not influence its potentiating effect.

Prostacyclin (PGI2) synthesis was stimulated by NA (0.1‐1.0 μmol 1−1) and inhibited by indomethacin in a concentration‐dependent manner.

There was a positive correlation between the indomethacin‐induced inhibition of PGI2 formation and the indomethacin‐evoked potentiation of contractile responses to NA.

These results suggest that endogenous PGI2 plays a part in the feedback control of vascular smooth muscle tone.
Effect of exogenous 5, 8, 11, 14, 17‐eicosapentaenoic acid on cardiac anaphylaxis
Authors: Juan H. , Peskar B.A. , Simmet Th.
Published: July 2012

The effects of infusions of eicosapentaenoic acid (EPA) (6 × 10−8 mol min−1 and 15 × 10−8 mol min−1) on the coronary constriction and the release of immunoreactive sulphidopeptide‐leukotrienes (SP‐LT), thromboxane B2(TXB2) and 6‐keto‐prostaglandin F1α(PGF1α) from perfused anaphylactic guinea‐pig hearts were investigated.

EPA dose‐dependently inhibited the profound early coronary flow reduction after antigen injection. The less pronounced late phase of anaphylactic coronary flow reduction was, however, not significantly affected. EPA (15 × 10−8 mol min−1) significantly shortened the average duration of antigen‐induced arrhythmias.

EPA dose‐dependently decreased release of immunoreactive TXB2 and 6‐keto‐PGF1α from anaphylactic guinea‐pig hearts.

Release of immunoreactive SP‐LT was dose‐dependently increased after antigen challenge in the presence of EPA. Inhibition of the release of SP‐LT by the lipoxygenase inhibitor esculetin (1 × 10−7 mol min−1) was accompanied by a significant attenuation of flow reduction during the late phase of anaphylactic vasoconstriction.

Reversed phase h.p.l.c. of perfusates from anaphylactic guinea‐pig hearts revealed immunoreactivity comigrating with authentic leukotriene C4 (LTC4), LTD4 and LTE4. In perfusates from hearts treated with EPA infusions, additional immunoreactivity was detected comigrating with LTC5, LTD5 and LTE5. In addition to immunoreactivity migrating with LTB4, as observed in control heart perfusates, in perfusates from EPA‐treated hearts, a second peak was observed, which coincides with the retention time described for LTB5.

Exogenous LTC5 (1 × 10−12 mol min−1 and 20 × 10−12 mol min−1) induced dose‐dependent reductions of coronary flow and was found to be a slightly weaker constrictor than LTC4, but no significant differences were observed. Coronary vasoconstriction elicited by infusion of exogenous LTC4 (20 × 10−12 mol min−1) was dose‐dependently inhibited by infusions of EPA. However, the negative inotropic effect of LTC4 remained unaffected.

Thus, in the isolated anaphylactic heart of the guinea‐pig exogenous EPA was effectively metabolized via the 5‐lipoxygenase pathway whereas the cyclo‐oxygenase pathway of polyunsaturated fatty acid metabolism was found to be inhibited. The results are in agreement with the suggestion that cyclo‐oxygenase products are mediators of the early phase of the anaphylactic coronary constriction, while vasoconstrictor SP‐LT are involved in the later phase. However, in spite of enhanced release of SP‐LT, EPA infusion did not result in increased coronary constriction. Considering the fact that EPA antagonizes LTC4‐induced coronary constriction, it seems possible, that EPA might act as a functional antagonist of vasoconstrictor eicosanoids including EPA‐derived SP‐LT.
Failure of prostaglandin E2 and its 16,16‐dimethyl analogue to prevent the gastric mucosal damage induced by Paf
Authors: Steel Graham , Wallace John L. , Whittle Brendan J.R.
Published: July 2012

Intravenous and orally administered prostaglandin E2 (PGE2) and 16,16‐dimethyl PGE2 (dm PGE2) protect the rat gastric mucosa from injury induced by oral administration of acidified 40% ethanol. The effects of pretreatment with these prostaglandins on platelet activating factor (Paf)‐induced gastric damage has now been investigated in the rat.

A 10 min infusion of Paf (50 or 100 ng kg−1 min−1, i.v.) resulted in dose‐related vasocongestion of the gastric mucosa.

Intravenous pretreatment with dmPGE2 (20 μg kg−1) failed to prevent the gastric damage induced by the higher dose of Paf. Pretreatment with PGE2 (10–100 μg kg−1) or dmPGE2 (1–20 μg kg−1), either orally or intravenously, also failed to prevent the gastric vasocongestion induced by the lower dose of Paf. On the contrary, significant augmentation of Paf‐induced damage was observed with several of the doses of PGE2 and dmPGE2.

These studies demonstrate that the protective properties of PGE2 and dmPGE2 in the gastric mucosa do not extend to damage induced by Paf.
Crystal‐induced inflammation in the rat subcutaneous air‐pouch
Authors: Brooks P.M. , Burton D. , Forrest M.J.
Published: July 2012

Monosodium urate (MSU) and calcium pyrophosphate dihydrate (CPPD) crystals initiated acute inflammatory reactions characterized by increased plasma extravasation and polymorphonuclear leukocyte (PMNL) accumulation in the rat subcutaneous air‐pouch.

Pretreatment of rats with colchicine (1 mg kg−1, s.c.) inhibited PMNL accumulation induced by either crystal type but had a greater inhibitory effect on MSU‐induced plasma extravasation compared with that induced by CPPD crystals.

Colchicine (1 mg kg−1, s.c.) did not reduce histamine‐induced plasma extravasation in the air‐pouch.

The lipoxygenase product of arachidonic acid metabolism, leukotriene B4 (LTB4), was detected in MSU‐induced exudates but not in CPPD‐induced exudates.

Pretreatment of rats with colchicine (1 mg kg−1, s.c.) inhibited LTB4 production in MSU‐induced exudates.
Inhibition of IgE‐dependent histamine release from human dispersed lung mast cells by anti‐allergic drugs and salbutamol
Authors: Church Martin K. , Hiroi Jun
Published: July 2012

The ability of the anti‐allergic drugs, sodium cromoglycate (SCG), lodoxamide, traxanox, RU31156 and the β‐adrenoceptor agonist sulbutamol to inhibit IgE‐dependent histamine and prostaglandin D2 (PGD2) release was assessed using human dispersed lung mast cells.

The anti‐allergic drugs were weak inhibitors of histamine release, high concentrations (100–1000 μm) producing < 35% inhibition. Salbutamol produced 39% inhibition at 10 μm.

The efficacy of both SCG and salbutamol was inversely related to the concentration of anti‐IgE used for challenge and to the degree of histamine release.

Rapid tachyphylaxis was observed with all anti‐allergic drugs but not with salbutamol.

Cross‐tachyphylaxis was observed between SCG and the other anti‐allergic drugs, suggesting a common mechanism of action. No cross‐tachyphylaxis was observed between SCG and salbutamol.

SCG was significantly (P < 0.001) more effective in inhibiting PGD2 than it was histamine release. Preferential inhibition of PGD2 compared with histamine release was less marked (P < 0.05) with salbutamol and not significant with the other anti‐allergic drugs.

Mast cells dispersed by enzymatic digestion of human lung released more histamine on immunological challenge than mechanically dispersed cells obtained by fine chopping of tissue. Enzyme treatment of mechanically dispersed cells removed this difference. Enzymatically and mechanically dispersed cells responded similarly to the inhibitory effects of SCG and salbutamol.

Our results suggest that salbutamol is a more effective inhibitor of mediator release from human lung mast cells than anti‐allergic drugs. However, with the low levels of mediator release achieved during an allergic reaction in man in vivo, both salbutamol and SCG are likely to be effective inhibitors of both preformed and newly generated mediators.
Influence of derivation on the lipophilicity and inhibitory actions of cardiac glycosides on myocardial Na+‐K+‐ATPase
Authors: Dzimiri Nduna , Fricke Uwe , Klaus Wolfgang
Published: July 2012

Lipophilicity and inhibitory actions on guinea‐pig heart Na+‐K+‐ATPase of twenty‐six digitalis and six strophanthus glycosides comprising the aglycones, mono‐, bis‐, tris‐sugar, alkylated (acylated) tris‐sugar, acyl steroid derivatives and three cardanolides were investigated.

Their octanol/water partition coefficients (P), reversed phase thin layer (r.t.l.c.) and reversed phase high performance liquid chromatography (r.h.p.l.c.) were determined and the viability of these methods as a measure of the lipophilicity of the cardiotonic steroids evaluated.

The influence of lipophilicity and so also structural changes on the inhibitory effects of the cardiac glycosides on myocardial Na+‐K+‐ATPase was then examined.

It is concluded that (a) r.t.l.c. and r.h.p.l.c. are just as effective as the conventional shake‐flask method for estimation of the lipophilicity of cardiac glycosides and (b) the inhibitory potencies of cardiotonic steroids on the myocardial Na+‐K+‐ATPase increase with growing lipophilicity. The relationship between these two parameters is, however, governed by the influence of substitution or derivation of structural components on their inhibitory potencies on the myocardial Na+‐K+‐ATPase.
Failure of allopurinol and a spin trapping agent N‐t‐butyl‐α‐phenyl nitrone to modify significantly ischaemia and reperfusion‐induced arrhythmias
Authors: Parratt James R. , Wainwright Cherry L.
Published: July 2012

The possible role of free radicals in the genesis of occlusion and reperfusion‐induced arrhythmias was studied by determining the effects of the xanthine oxidase inhibitor allopurinol (400 mg p.o. 24 h before experimentation + 25 mg kg−1 i.v.) and the free radical scavenger N‐t‐butyl‐α‐phenyl nitrone (PBN; 50 mg kg−1 i.v.) on these arrhythmias in chloralose anaesthetized greyhounds.

Neither of the drugs had any major effects on haemodynamic variables, although allopurinol caused a significant increase in heart rate.

The mean number of extrasystoles observed during ischaemia in dogs given allopurinol or PBN was not significantly different from those seen in controls. Further, the incidence of ventricular fibrillation during either occlusion or reperfusion was unchanged by either drug and there was thus no improvement in survival.

These results suggest that, in this model of myocardial ischaemia and reperfusion, free radicals may not play a major role in the genesis of life‐threatening arrhythmias.
Circulating [Met]enkephalin and catecholamine responses to acute hypotension and hypertension in anaesthetized greyhounds
Authors: Mason D.F.J. , Medbak S. , Rees Lesley H.
Published: July 2012

The effects of either hypotension induced by sodium nitroprusside or hexamethonium or hypertension produced by angiotensin II or noradrenaline on the circulating levels of methionine enkephalin ([Met]enkephalin)‐like immunoreactivity (MLI), adrenaline and noradrenaline in anaesthetized greyhounds were examined.

Nitroprusside infusions (200 and 400 μg min−1) induced a fall in blood pressure accompanied by significant rises in plasma MLI and catecholamine concentrations.

Concomitant administration of a high dose of naloxone did not alter the fall in blood pressure produced by nitroprusside but was associated with greater rises in circulating MLI and catecholamines when compared to nitroprusside alone, suggesting that [Met]enkephalin is not involved in the hypotensive action of nitroprusside.

Intravenous hexamethonium (2.5 mg kg−1) provoked a fall in blood pressure which was not associated with any changes in plasma MLI. However, it produced a fall in plasma noradrenaline and a rise in plasma adrenaline. Thus it appears that neural mechanisms are required, at least in part, for the release of MLI.

Angiotensin II (1.25 μg kg−1 min−1) and noradrenaline (8 μg kg−1 min−1) infusions produced an elevation in blood pressure without altering the circulating MLI levels.

Study of the molecular forms of circulating MLI, before and during hypotension, revealed that the large molecular weight enkephalin‐containing peptides with approximate molecular sizes of 18kD and 8kD were the predominant forms both in the basal and stimulated states.

It is concluded that circulating [Met]enkephalin is not involved in the tonic control of blood pressure but it may modulate catecholamine release following hypotension as part of the stress response.