bluuebunny/crossref_metadata_2025 huggingface dataset:
Actions of tachykinins on the rabbit mesenteric artery: substance P and [Glp6,L‐Pro9]SP6–11 are potent agonists for endothelial neurokinin‐1 receptors
Authors: Stewart‐Lee Anne , Burnstock Geoffrey
Published: July 2012

Identification of the subtype of neurokinin receptor on the endothelium of the rabbit mesenteric artery was demonstrated by comparing the relative potencies of the naturally occurring tachykinins, substance P, neurokinin A and neurokinin B and the highly selective agonists [Glp6,L‐Pro9]SP6–11 (L‐Pro), [Glp6,D‐Pro9]SP6–11 (D‐Pro) and N‐succinyl‐[Asp6,MePhe8]SP6–11 (senktide).

Relaxations of the rabbit mesenteric artery to substance P, neurokinin A and neurokinin B were concentration‐dependent and were abolished by the removal of the endothelium.

Substance P was more potent than neurokinin A or neurokinin B and L‐Pro was more potent than D‐Pro or senktide.

Substance P, neurokinin A and neurokinin B all significantly reduced the nerve‐mediated contractile response in the presence of the endothelium at a concentration of 0.1 μm, with a rank order of potency substance P > neurokinin A > neurokinin B.

At a concentration of 0.1 μm, L‐Pro also significantly reduced the nerve‐mediated contractile response, unlike D‐Pro and senktide.

It is concluded that the relaxation of the rabbit mesenteric artery produced by substance P is mediated by neurokinin‐1 receptors (NK‐1) located on the endothelium. Furthermore, of the analogues, L‐Pro was particularly potent for these receptors.
Microelectrode study on the ionic mechanisms which contribute to the noradrenaline‐induced depolarization in isolated cells of the rabbit portal vein
Authors: Amédée T. , Large W.A.
Published: July 2012

Experiments were carried out to determine the identity of the ionic mechanisms which contribute to the noradrenaline‐evoked depolarization recorded with microelectrodes in freshly dispersed rabbit portal vein cells.

In normal physiological salt solution with microelectrodes containing 1 m NaCl the reversal potential (Er) of the noradrenaline‐induced response was −7.6 ± 2.9 mV. When the external NaCl was replaced by equipmolar concentrations of NaI, NaBr and NaNO3, Er was −33 ± 3.5 mV, −29.1 ± 5.2 mV and −18.4 ± 1.1 mV, respectively.

In physiological salt solution Er of noradrenaline‐evoked responses recorded with electrodes filled with 1m NaI or 1m NaNO3 was + 16.3 + 3.9mV and +10.0 ± 7.6 mV, respectively. These results suggest that an increase in anion conductance contributes to the depolarization to noradrenaline.

Data from experiments with organic anions indicated that glutamate behaves as a less permeant anion but that benzenesulphonate blocks the anion conductance to unmask another conductance mechanism activated by noradrenaline.

When external NaCl was substituted by choline Cl and Tris Cl Er was −21.3 ± 3.7 mV and −20.5 ± 2.8 mV, respectively. These results suggest that noradrenaline also activates a cation conductance mechanism in freshly dispersed rabbit portal vein cells. It is concluded that the depolarization to noradrenaline recorded with a microelectrode is produced by the simultaneous activation of an anion channel and a separate cation channel.
Presence of T‐kininogen and kinins in sponge‐induced exudates in rats
Authors: Damas J. , Adam A. , Bourdon V. , Remade‐Volon G.
Published: July 2012

The content of kinins and T‐kininogen (the third kininogen) in exudates induced by the subcutaneous implantation of saline‐soaked sponges have been measured by radioimmunoassay in normal Wistar rats and in Brown Norway rats from a strain which is deficient in high and low molecular weight kininogens.

In both strains, sponge implantation induced a rise of T‐kininogen in plasma with subsequent accumulation in the sponge exudate. This accumulation correlated with the extravasation of plasma proteins during the first 6 h. Bioassays showed that the T‐kinin moiety was retained in T‐kininogen.

In Wistar rats, a large release of immunoreactive kinins up to a mean value of 6.4 ng ml−1 was observed during the first 6 h and on the second day after the implantation. In Brown Norway rats, the kinin level in the exudates did not exceed 0.53 ng ml−1.

Of the kinins present during the first 6 h in the exudates withdrawn from Wistar rats, 60% were identified by high performance liquid chromatography as bradykinin.

The volume of the exudate induced by the implantation of dry sponges was smaller in Brown Norway rats than in Wistar rats.

We conclude that the role of T‐kininogen in this kind of exudate was mainly the inhibition of thiol proteinases and not the release of T‐kinin. In Wistar rats, bradykinin acts as a pro‐inflammatory factor during the first hours and may play a role during the healing process.
Lorazepam discontinuation promotes ‘inverse agonist’ effects of benzodiazepines
Authors: Schatzki Andrew , Lopez Fred , Greenblatt David J. , Shader Richard I. , Miller Lawrence G.
Published: July 2012

The effects of lorazepam discontinuation on responses to benzodiazepine agonists and antagonists were studied in mice.

The convulsant dose of pentylenetetrazol was decreased after an acute dose of lorazepam (0.5 mg kg−1) at 4 days after drug discontinuation, compared to 1 or 7 days after discontinuation or to vehicle treatment.

The percentage of mice undergoing convulsions after an acute dose of FG 7142 (40 mg kg−1) was increased at 4 days after lorazapam discontinuation, compared to 1 or 7 days after discontinuation or to vehicle treatment.

After an acute dose (0.5 mg kg−1), lorazepam concentrations in cortex tended to be greater in lorazepam‐treated compared to vehicle‐treated mice at 4 days after discontinuation compared to 1 and 7 days.

These data indicate a shift toward reduced agonist sensitivity and increased inverse agonist sensitivity in mice 4 days after lorazepam discontinuation.
Inhibition of agonist‐stimulated inositol lipid metabolism by the anticonvulsant carbamazepine in rat hippocampus
Authors: McDermott Elaine E. , Logan S.D.
Published: July 2012

The effect of the anticonvulsant, anti‐manic drug carbamazepine was examined on inositol lipid signalling in rat hippocampus in vitro.

Hippocampal miniprisms were labelled with [3H]‐inositol before stimulation with a variety of neuroactive agents that increase phosphoinositide turnover.

The presence of carbamazepine (0.1–100 μm) during labelling caused a dose‐related reduction of basal and carbachol‐evoked [3H]‐inositol phosphate accumulations. The effect of the drug on basal inositol phosphate levels was lost when slices were labelled with [3H]‐inositol before incubation with carbamazepine.

Incubation of slices with carbamazepine after labelling with [3H]‐inositol and before stimulation showed the inhibitory effect of the drug to be selective according to the agonist used. Responses to carbachol, histamine and the sodium‐channel agent veratrin were reduced by carbamazepine whilst the responses to 5‐hydroxytryptamine, noradrenaline and substance P were unaffected.

Inhibition of carbachol, histamine and veratrin‐induced stimulation by carbamazepine share a similar dependence on length of pre‐incubation time with the drug. However, the effect of carbamazepine (100 μm) on the respective dose‐response curves suggests that the mechanism of inhibition of the carbachol response differs from the inhibition of the histamine and veratrin responses. These effects may be significant in the mechanism of action of carbamazepine as an anticonvulsant and in its effectiveness against manic depression.
Multiple mechanisms in the motor responses of the guinea‐pig isolated urinary bladder to bradykinin
Authors: Maggi Carlo Alberto , Patacchini Riccardo , Santicioli Paolo , Geppetti Pierangelo , Cecconi Roberto , Giuliani Sandro , Meli Alberto
Published: July 2012

Bradykinin (1 nM‐1 μm) produced a contraction of bladder strips excised from the dome of the guinea‐pig urinary bladder, an effect which was greatly enhanced by removal of the mucosal layer or by thiorphan (10 μm). All subsequent experiments were performed in mucosa‐free strips and in the presence of thiorphan.

In carbachol (5 μm)‐contracted strips, bradykinin produced a concentration (1 nM‐1 μm)‐dependent transient relaxation.

Kallidin was slightly more potent than bradykinin in producing a contraction and a relaxation of the carbachol‐induced tone. By contrast, [des‐Arg9]‐bradykinin, a selective B1 receptor agonist was barely effective up to 1 μm.

The contractile response to bradykinin was: (a) unaffected by either tetrodotoxin (1 μm), in vitro capsaicin desensitization (10 μm for 30 min) or apamin (0.1 μm); (b) antagonized by indomethacin (5 μm), the prostaglandin receptor antagonist SC‐19220 (100 μm) or the B2 receptor antagonist [D‐Arg0, Hyp3, Thi5,8, Phe7]‐bradykinin (10 μm) and (c) almost abolished by nifedipine (1 μm).

The antagonism of the contractile response to bradykinin produced by indomethacin and SC‐19220 was non‐additive while that produced by indomethacin and the B2 receptor antagonist was additive.

The relaxant response to bradykinin was unaffected by tetrodotoxin, in vitro capsaicin desensitization or indomethacin but antagonized in a competitive manner by the B2 receptor antagonist. Further, this response was abolished by apamin (0.1 μm) but unaffected by glibenclamide (1 μm).

Bradykinin (10 μm) produced a consistent release of calcitonin gene‐related peptide‐like immunoreactivity (CGRP‐LI) but not substance P‐LI from the guinea‐pig bladder muscle. CGRP‐LI release by bradykinin was greatly reduced in bladders exposed to indomethacin. [des‐Arg9]‐bradykinin (10 μm) was ineffective.

We conclude that: (a) bradykinin‐induced contraction involves activation of both B2 receptors and prostanoid synthesis, via distinct mechanisms which act by inducing calcium influx via nifedipine‐sensitive channels; (b) bradykinin‐induced relaxation involves activation of B2 receptors and opening of apamin‐sensitive potassium channels; (c) bradykinin stimulates sensory nerves in this tissue largely via prostanoid production.
Selective inhibition by vasocortin of histamine release induced by dextran and concanavalin‐A from rat peritoneal cells
Authors: Carnuccio Rosa , Di Rosa Massimo , Ialenti Armando , Iuvone Teresa , Sautebin Lidia
Published: July 2012

Vasocortin, a glucocorticoid‐induced anti‐inflammatory protein, has been purified from the peritoneal lavage fluid of dexamethasone‐treated rats. Vasocortin inhibited the release of histamine from rat peritoneal cells stimulated by dextran or concanavalin A but did not alter the release induced by calcium ionophore A23187 or compound 48/80. This selective effect exhibited by vasocortin mimics the glucocorticoid inhibition of histamine release from rat mast cells.
Inhibition by neuropeptides of interleukin‐1β‐induced, prostaglandin‐independent hyperalgesia
Authors: Follenfant R.L. , Nakamura‐Craig M. , Henderson B. , Higgs G.A.
Published: July 2012

The cytokine interleukin‐1β (IL‐lβ) is a potent hyperalgesic agent in the rat whereas IL‐1α is relatively inactive (Ferreira et al., 1988). IL‐1β induced a dose‐dependent increase in the sensitivity of rat paws to mechanical stimulation following intra‐plantar injection but this effect was not reduced by indomethacin (1.0 mg kg−1, p.o.), at a dose known to inhibit completely prostaglandin synthesis in the rat (Salmon et al., 1983). Prostaglandin (PG)E2 enhanced sensitivity to both mechanical pressure and increased temperature but IL‐1β enhanced only sensitivity to pressure. These observations indicate that IL‐1β sensitized pressure‐sensitive but not temperature‐sensitive sensory neurones, through a prostaglandin‐independent mechanism. Hyperalgesia induced by IL‐1β but not PGE2, was inhibited by the neuropeptide melanocyte‐stimulating hormone (αMSH) and its analogue [Nle4, D‐Phe7] αMSH which are known to antagonize IL‐1 responses in other systems (Holdeman & Lipton, 1985; Cannon et al., 1986). IL‐1β induced hyperalgesia was also reduced by the putative IL‐1β antagonist Lys‐D‐Pro‐Thr (Ferreira et al., 1988) but αMSH and its analogue were 10–50 times more potent.
Evidence for tonic activation of prejunctional β‐adrenoceptors in guinea‐pig pulmonary arteries by adrenaline derived from the adrenal medulla
Authors: Misu Yoshimi , Kuwahara Misako , Amano Hiro , Kubo Takao
Published: July 2012

The effects of (+)‐carteolol 10−8 m to 10−6 m, a non‐selective β‐antagonist, applied cumulatively, on stimulation‐evoked 3H‐release at 1 Hz were studied in pulmonary arteries isolated from guinea‐pigs. The guinea‐pigs were subjected to either bilateral adrenalectomy, adrenalectomy followed by injections of deoxycorticosterone acetate (DOCA) and hydrocortisone, bilateral adrenodemedullation or a sham operation, and then loaded in vitro with [3H]‐noradrenaline.

Carteolol inhibited 3H‐output in arteries from sham‐operated animals in a concentration‐dependent manner. This inhibitory effect was not found in pulmonary arteries from animals subjected to adrenalectomy or adrenodemedullation. However, DOCA and hydrocortisone pretreatment, did not prevent the disappearance of the carteolol‐induced inhibition of 3H‐release.

Adrenalectomy and adrenodemedullation depleted or markedly reduced the endogenous contents of adrenaline in pulmonary arteries without altering the levels of dopamine and noradrenaline.

It is concluded that adrenaline, mainly derived from the adrenal medulla, acts as an endogenous agonist for tonically functioning prejunctional β‐adrenoceptors in guinea‐pig pulmonary arteries, probably by being taken up and co‐released with noradrenaline.
Alveolar macrophages and eicosanoids but not neutrophils, mediate bronchoconstriction induced by FMLP in the guinea‐pig
Authors: Boukili M. Abdelhakim , Bureau Michel‐Francis , Lellouch‐Tubiana Arielle , Lefort Jean , Simon Marie‐Thérèse , Vargaftig B. Boris
Published: July 2012

N‐formyl‐methionyl‐leucyl‐phenylalanine (FMLP), when administered by aerosol to guinea‐pigs, induced a dose‐dependent bronchoconstriction (BC) with no overt effect on platelet and leukocyte blood counts. Repeated administration of FMLP by aerosol was followed by desensitization.

Electron microscopy studies showed that administration of FMLP by aerosol is accompanied by alveolar macrophage activation, accumulation and aggregation in the alveolar lumens. Non‐degranulated eosinophils were observed in the lungs and a few platelet micro‐aggregates in the pulmonary microvasculature.

No significant accumulation of 131I‐labelled albumin, 111In‐labelled neutrophils or 111In‐labelled platelets was detected in the lungs after the administration of FMLP by aerosol, whereas the intravenous administration was accompanied by an increase of extravascular albumin and significant neutrophil sequestration in the lungs.

Aspirin administered intravenously or by aerosol reduced significantly the BC induced by an aerosol of FMLP. By contrast, intravenous indomethacin reduced only BC induced by the sub‐maximal dose of FMLP as an aerosol whereas, when administered by inhalation, it inhibited BC induced by FMLP administered either intravenously or by aerosol at all the concentrations tested.

FMLP induced a dose‐dependent contraction of the guinea‐pig trachea, which was not inhibited by indomethacin.

The dual cyclo‐oxygenase/lipoxygenase inhibitor compound BW755C suppressed the BC induced by an aerosol of FMLP at all the concentrations used, whereas the histamine H1‐antagonist mepyramine was inactive.

Leukocyte depletion with vinblastine failed to reduce BC induced by intravenous or an aerosol of FMLP.

Our studies indicate that: (a) FMLP administered by aerosol induces dose‐dependent BC followed by desensitization, indicating that local mechanisms account for BC; (b) BC induced by i.v. FMLP, but not by its inhalation, is accompanied by albumin extravasation and neutrophil sequestration in the lungs; (c) BC by either i.v. or an aerosol of FMLP is not due to neutrophil activation; (d) inhalation of FMLP induces BC accompanied by accumulation of activated alveolar macrophages, non‐degranulated eosinophils and a few platelet microaggregates in the lung; (e) both cyclo‐oxygenase and lipoxygenase metabolites are involved in the BC induced by an aerosol of FMLP.
Reversal of haemorrhagic shock in rats by cholinomimetic drugs
Authors: Guarini Salvatore , Tagliavini Simonetta , Ferrari William , Bertolini Alfio
Published: July 2012

In an experimental model of haemorrhagic shock resulting in the death of all rats within 20–30 min, the intravenous (i.v.) injection of the tertiary amine cholinesterase inhibitor physostigmine (17–70 μgkg−1) induced a prompt, sustained and dose‐dependent improvement of cardiovascular and respiratory function, with marked increase in the volume of circulating blood and survival of all treated animals, at least for the 2 h of observation.

Similar results were obtained with the i.v. injection of the cholinoceptor agonist oxotremorine (5–25 μg kg−1), while neostigmine (54 or 70 μgkg−1), a quaternary cholinesterase inhibitor which cannot cross the blood‐brain barrier, had negligible effects.

The anti‐shock activities of oxotremorine and physostigmine were blocked by the intracerebroventricular injection of either of the combined nicotinic and M2‐muscarinic receptor antagonists gallamine and pancuronium, or of the nicotinic antagonist mecamylamine. They were also blocked by intraperitoneal injection of the adrenergic neurone blocking agent guanethidine, but they were not antagonized by either the combined M1‐ and M2‐muscarinic receptor antagonist atropine, the M1‐muscarinic receptor antagonist pirenzepine, or the M2‐muscarinic receptor antagonist 4‐diphenylacetoxy‐N‐methylpiperidine methobromide.

It is concluded that cholinomimetic drugs can reverse hypovolaemic shock through central activation (seemingly mediated by nicotinic receptors) of sympathetic tone, with mobilization and redistribution of the residual blood.
Kallikrein‐kinin system in the plasma of the snake Bothrops jararaca
Authors: Abdalla F.M.F. , Hiraichi E. , Picarelli Z.P. , Prezoto B.C.
Published: July 2012

Bothrops jararaca venom (BJV) caused a fall in the carotid artery blood pressure of the anaesthetized snake. This effect was tachyphylactic and was potentiated by captopril, a kininase II inhibitor; it was partially antagonized by promethazine plus cimetidine and was not affected by atropine.

Similar hypotensive effects were obtained by administration of trypsin or a partially purified BJV kininogenase to the snake.

Incubation of Bothrops jararaca plasma (BJP) with trypsin released a substance (or substance(s) that produced hypotension in the snake but not in the rat; this hypotensive effect was also potentiated by captopril.

The trypsinised plasma contracted Bothrops jararaca isolated uterus, a pharmacological preparation weakly sensitive to bradykinin. Trypsinised plasma was inactive on pigeon oviduct and rat uterus and displayed a weak action on the guinea‐pig ileum. Similar effects were observed with incubates of a fraction of BJP, containing globulins, with a partially purified BJV kininogenase.

Like mammalian kinins, the substance(s) was(were) dialysable, thermostable in acid but not in alkaline pH, and inactivated by chymotrypsin but not by trypsin. Its(their) inactivation by BJP or BJP kininase II was inhibited by captopril.

These findings strongly suggest that, besides releasing histamine, BJV or trypsin release a kininlike substance (or substances) from the snake plasma.

Since BJV and other kininogenases active on mammalian plasmas were shown to be unable to release kinins from BJP, in experiments conducted on pharmacological preparations suitable for the assay of mammalian kinins, these data also suggest that the snake Bothrops jararaca, like birds, may have developed its own kallikrein‐kinin system.
Chronotropic and inotropic actions of amrinone, carbazeran and isobutylmethyl xanthine: role of phosphodiesterase inhibition
Authors: Shahid M. , Rodger I.W.
Published: July 2012

The chronotropic and inotropic effects of amrinone, carbazeran and 3‐isobutyl‐1‐methyl xanthine (IBMX) were examined in isolated preparations of papillary muscle and right atria from rabbit heart. The effects of the drugs on cardiac phosphodiesterase and cyclic nucleotide content were also examined.

Amrinone (2.4 × 10−4 M‐2 × 10−3 M), carbazeran (9.1 × 10−6 M‐1.2 × 10−3 M), and IBMX (1.8 × 10−5 M‐4.5 × 10−4 M) produced concentration‐dependent positive inotropic responses of papillary muscle preparations, the rank order of potency being carbazeran = IBMX > amrinone. Sub‐threshold positive inotropic concentrations of all three compounds potentiated the positive inotropic effects of isoprenaline; leftward shifts in the concentration‐effect curves were 5 fold (IBMX), 11 fold (amrinone) and 46 fold (carbazeran).

Amrinone and IBMX produced concentration‐dependent positive chronotropic responses in isolated right atria and showed a similar rate selectivity to isoprenaline, but carbazeran elicited a decrease in beating frequency. None of these drugs potentiated the positive chronotropic effects of isoprenaline.

Concentrations of amrinone, carbazeran and IBMX that produced similar positive inotropic responses were associated with different increases in papillary muscle cyclic AMP and cyclic GMP concentrations.

All three compounds inhibited right atrial and ventricular phosphodiesterase, with amrinone being the least potent. There was, however, a marked difference between the IC50 and EC50 values for phosphodiesterase inhibition and positive inotropy. In contrast the positive chronotropic effects of amrinone and IBMX were observed in the same concentration ranges that produced phosphodiestrease inhibition.

The results indicate that amrinone possesses a similar rate/force selectivity to isoprenaline and IBMX. In contrast, carbazeran exerts both positive inotropic and negative chronotropic effects. Phosphodiesterase inhibition and elevation of intracellular cyclic AMP concentration may be involved, at least in part, in the cardiac effects of these drugs.
Comparison of the effects of isobutylmethylxanthine and milrinone on ischaemia‐induced arrhythmias and platelet aggregation in anaesthetized rabbits
Authors: Holbrook Mark , Coker Susan J.
Published: July 2012

The aim of this study was to compare the effects of the non‐selective phosphodiesterase (PDE) inhibitor, isobutylmethylxanthine (IBMX) and the selective PDE III inhibitor, milrinone, in a rabbit model of acute myocardial ischaemia.

Coronary artery occlusion caused changes in the ST‐segment of the ECG and ectopic activity in all control rabbits. Ventricular fibrillation occurred in 10 out of 14 (71%) of these animals. Pretreatment with IBMX 100 μg kg−1 plus 10 μg kg−1 min−1, starting 10 min before coronary artery occlusion, reduced ischaemia‐induced ST‐segment changes and ventricular fibrillation occurred in only 10% of this group (n = 10). A similar dose of milrinone had no antiarrhythmic activity, whereas with a lower dose of milrinone, 30 μ g kg−1 plus 3 μgkg−1 min−1 (n = 10), only 30% of rabbits fibrillated and ST‐segment changes were attenuated.

Acute administration of both IBMX and milrinone reduced arterial blood pressure. With the higher dose of milrinone a significant effect was still present after 10 min of drug infusion. A greater hypotensive response to the higher dose of milrinone was observed in the rabbits which subsequently fibrillated during ischaemia. A marked tachycardia was also observed after administration of the higher dose of milrinone.

At the end of the experiment platelet aggregation was studied ex vivo. ADP‐induced aggregation was reduced by pretreatment of the rabbits with milrinone but not IBMX. Both PDE inhibitors enhanced the ability of isoprenaline to inhibit ADP‐induced platelet aggregation but milrinone was more effective, particularly at the higher dose.

The results demonstrate that IBMX was antiarrhythmic but that this activity was not directly related to inhibition of platelet aggregation. Adverse haemodynamic effects may explain the failure of milrinone to have similar activity during myocardial ischaemia.
Niguldipine discriminates between α1‐adrenoceptor‐mediated second messenger responses in rat cerebral cortex slices
Authors: Robinson J.P. , Kendall D.A.
Published: July 2012

The effect of both isomers of niguldipine, a highly selective α1‐adrenoceptor antagonist and dihydropyridine calcium channel blocker, on noradrenaline‐stimulated inositol phosphate (IP) accumulation and adenosine 3′:5′‐cyclic monophosphate (cyclic AMP) potentiation was examined. Both isomers inhibited noradrenaline‐stimulated IP accumulation. (+)‐Niguldipine was 100 fold more potent than (−)‐niguldipine. Potentiation of β‐adrenoceptor‐stimulated cyclic AMP by noradrenaline was only partially inhibited by both isomers. The dihydropyridine, israpidine, did not inhibit either second messenger response. This study provides further evidence that the α1‐adrenoceptors mediating IP accumulation and cyclic AMP potentiation are different.
Calcium antagonizes the magnesium‐induced high affinity state of the hepatic vasopressin receptor for the agonist interaction
Authors: Wang Hao , Gopalakrishnan Venkat , McNeill J. Robert , Sulakhe Prakash V. , Triggle Chris R.
Published: July 2012

The present study describes the role of Ca2+ in the regulation of the hepatic vasopressin V1 receptor. With low concentrations of Ca2+, there was a small increase in [3H]‐arginine vasopressin ([3H]‐AVP) binding, but above 10 mm, Ca2+ decreased the binding of this agonist. In contrast, low concentrations of Mg2+ were associated with a dramatic concentration‐dependent increase in [3H]‐AVP binding, reaching a maximal effect of 650% above control at concentrations ranging between 1–5 mm. At higher concentrations of Mg2+, the stimulatory effect of this cation was less pronounced, falling to 210% of control at 100 mm Mg2+. Strikingly, Ca2+‐inhibited the stimulatory effect of Mg2+ in a concentration‐dependent fashion.

Saturation binding data revealed that Ca2+ (2 to 10 mm) per se promotes the high affinity conformation of the V1 receptor for the agonist binding with the KD decreased from a control value of 2.3 nm to 0.5 nm in the presence of 10 mm Ca2+. This effect was attenuated with an increase in Ca2+ above 10 mm. With an increase in Ca2+ to 20 mm, however, the Bmax for [3H]‐AVP binding was decreased. Ca2+ also decreased the high affinity/high capacity state (KD 100 pm) of the receptor induced by 1 mm Mg2+ for agonist interaction.

[3H]‐V1 antagonist binding was inhibited by both Ca2+ and Mg2+. The IC50 values (mean ± s.e.mean) for Ca2+ and Mg2+ were 32 ± 8 and 53 ± 9 mm respectively. Maximal inhibition achieved at 100 mm was 29% for Ca2+ and 42% for Mg2+. Both cations decreased the affinity and increased the capacity of the V1 receptor for the antagonist.

The results suggest that the divalent metal ion binding site(s) modulated by Mg2+ is also accessible to Ca2+. Although Ca2+ opposes the powerful stimulatory effects of Mg2+ on agonist binding, the effects of Ca2+ and Mg2+ on the Bmax of [3H]‐AVP binding were different, suggesting that the divalent cations may bind to two different sites, thereby regulating the affinity and the capacity characteristics of the V1 receptor.
Demonstration of extrapulmonary activity of angiotensin converting enzyme in intact tissue preparations
Authors: Lembeck F. , Griesbacher T. , Eckhardt M.
Published: July 2012

The activity of angiotensin converting enzyme (ACE) has been studied on functional parameters of intact isolated preparations of extrapulmonary tissues. The conversion of angiotensin I (A I) to angiotensin II (A II) and the cleavage of bradykinin (BK) were used as indicators of ACE activity. Captopril was employed as a specific inhibitor of ACE.

Captopril augmented the BK‐induced contractions of the rat isolated uterus, the BK‐ and substance P‐induced contractions of the guinea‐pig ileum, and the BK‐induced venoconstriction in the isolated perfused ear of the rabbit. Degradation of BK by ACE was calculated to be 52% in the rat uterus and 75% in the rabbit perfused ear.

Captopril inhibited the A I‐induced contractions of the rat isolated colon, the A I‐induced vasoconstriction in the isolated perfused ear of the rabbit and the rise in blood pressure induced by i.a. injections of A I in pithed rats. Conversion of A I to A II was calculated to be 13% in the rat colon and 26% in the rabbit perfused ear.

From estimations of the A II activity (bioassay on the rat colon) in the effluent of the perfused ear of the rabbit after injections of A I into the arterial inflow cannula it was calculated that approximately one tenth of A I was converted to A II during a single passage through the ear (less than 15 s).

The present experiments suggest that the high activity of ACE in endothelium of blood vessels of extrapulmonary tissues may provide an additional (endothelium‐dependent) local vasoconstrictor mechanism by the rapid formation of A II and inactivation of BK. The ACE activity in non‐vascular smooth muscles, other than those of blood vessels, may also affect the physiological functions of these tissues.
Interactions between adenosine and phorbol esters or lithium at the frog neuromuscular junction
Authors: Sebastião A.M. , Ribeiro J.A.
Published: July 2012

Interactions between the effects of adenosine or 2‐chloro‐adenosine (CADO) and the effects of substances that interfere with the phosphoinositides/protein kinase C transducing system or with the adenylate cyclase transducing system, on endplate potentials (e.p.ps), were investigated. The preparation used was the innervated sartorius muscle of the frog in which twitches had been prevented with high magnesium concentrations.

The activator of protein kinase C, 4β‐phorbol‐12,13‐diacetate (PDAc), reversibly increased the amplitude and the quantal content of e.p.ps and attenuated the inhibitory effects of adenosine and CADO on e.p.p. amplitude. The affinity of the adenosine receptor antagonist, 8‐phenyltheophylline, was not modified by PDAc.

The phorbol ester 4α‐phorbol‐12,13‐didecanoate, which does not activate protein kinase C, did not modify either e.p.p. amplitude or the inhibitory effect of adenosine on e.p.ps.

The inhibitor of protein kinase C, polymyxin B, reversibly decreased the amplitude and the quantal content of e.p.ps, prevented the enhancement caused by PDAc on e.p.p. amplitude, but did not modify the inhibitory effect of adenosine on e.p.ps. H‐7, another inhibitor of protein kinases, also decreased e.p.p. amplitude but did not modify the effect of PDAc on the amplitude of e.p.ps.

Lithium chloride, which alters phosphoinositide signal transduction by inhibiting the breakdown of inositol phosphates, reversibly increased the amplitude and the quantal content of the e.p.ps. In the presence of adenosine or CADO the effect of lithium on e.p.p. amplitude was markedly attenuated.

The activator of adenylate cyclase, forskolin, reversibly increased the amplitude and the quantal content of the e.p.ps. MDL 12,330A, an inhibitor of adenylate cyclase, irreversibly decreased e.p.p. amplitude, an effect which was prevented by forskolin. Neither forskolin nor MDL 12,330A modified the inhibitory effect of adenosine on e.p.ps.

The results suggest that the phosphoinositides/protein kinase C transducing system, but not the adenylate cyclase transducing system, might be involved in the inhibitory effect of adenosine on neuromuscular transmission.
Pharmacological properties of FPL 63547, a novel inhibitor of angiotensin‐converting enzyme
Authors: Carr R.D. , Higgs L. , Killingback P.G. , Nicol A.K. , O'Connor S.E. , Robson A. , Wells E. , Simpson W.T.
Published: July 2012

FPL 63547, in its active diacid form, was a potent inhibitor of rabbit lung angiotensin converting enzyme (ACE) in vitro (IC50 0.51 nm).

In conscious normotensive dogs, FPL 63547 (10–300 μg kg−1 i.v.) produced prolonged, dose‐related inhibition of plasma ACE activity and angiotensin I pressor responses, without affecting basal blood pressure, heart rate or pressor responses to angiotensin II.

In anaesthetized dogs, FPL 63547 diacid (3–300 μg kg−1 i.v. cumulatively) produced dose‐related increases in cardiac output accompanied by falls in total peripheral resistance indicative of vasodilatation. Mild stimulation of cardiac rate and contractility was also observed. Enalapril diacid had a similar profile.

FPL 63547 was a highly effective antihypertensive agent after oral administration to spontaneously hypertensive rats (SHR) pretreated with a diuretic. It lowered systolic blood pressure (SBP) on acute administration over the range 3 × 10−7–10−5 mol kg−1 p.o. (⋍ 0.13–4.5 mg kg−1 p.o.). FPL 63547 was more potent than other ACE inhibitors tested, threshold active doses for lisinopril, enalapril and captopril being 10−6, 10−6 and 3 × 10−5 mol kg−1 p.o., respectively. The antihypertensive effects of FPL 63547, unlike those of enalapril and captopril, were of long duration.

The antihypertensive efficacy of FPL 63547 was also observed following chronic oral administration. A dose of 0.5 mg kg−1 day−1 once daily for 23 days produced a sustained reduction of SBP. By the end of the treatment period, SBP was significantly lowered both pre‐ and post‐dose, i.e. effective 24 h control had been achieved.

The profile of FPL 63547 is consistent with it being a potent, selective and long‐acting ACE inhibitor. As an antihypertensive agent in SHR it compared favourably with other members of this class with respect to potency and duration of action.
Ryanodine facilitates calcium‐dependent release of transmitter at mouse neuromuscular junctions
Authors: Nishimura Masakazu , Tsubaki Kikuko , Yagasaki Osamu , Ito Katsuaki
Published: July 2012

Quantal release of transmitter was measured intracellularly at mouse neuromuscular junctions in the presence and absence of ryanodine (Rnd).

Rnd at concentrations up to 1 μm did not significantly alter the frequency of miniature endplate potentials (m.e.p.ps) in the presence or absence of Ca2+, suggesting that Rnd is unlikely to alter the internal concentration of Ca2+ ([Ca2+]i) at rest.

In a high‐K+ (10 mm) bathing solution, Rnd further potentiated the facilitatory effect of Ca2+ on the frequency (F, s−1) of m.e.p.ps. Rnd shifted the relationship between ln(F) and ln[Ca2+]o to lower concentrations.

In a high‐Mg2+ bathing solution, Rnd did not affect the frequency of m.e.p.ps at any value of [Ca2+]o. However, Rnd slightly but significantly increased the quantal content (m) of e.p.ps. It shifted the relationship between ln(m) and ln[Ca2+]o to lower concentrations. These results suggest that Rnd potentiates the quantal release of transmitter after depolarization of the membrane or nerve impulse, in keeping with the cooperativity of Ca2+ at the active site.

A series of two closely spaced nerve impulses produced a facilitation of transmitter release, as judged by the quantal content (m2) of the second response in relation to that of the first one (m1), m2/m1. Rnd did not change the ratio m2/m1. Thus Rnd is unlikely to affect the rapid phase of the sequestration of Ca2+ inside the nerve terminal.

High levels of K+ (5 mm) and caffeine (2 mm) potentiated both modes of transmitter release, in a manner dependent on [Ca2+]o. Caffeine did not potentiate facilitation of transmitter release.

These results indicate that Rnd facilitates the quantal release of transmitter presumably via an increase in [Ca2+]i by a manner different from that of high‐K+ or caffeine. The results suggest that Rnd probably affects calcium turnover in neuronal cells.
Hexocyclium derivatives with a high selectivity for smooth muscle muscarinic receptors
Authors: Micheletti R. , Schiavone A. , Cereda E. , Donetti A.
Published: July 2012

The affinity of a number of derivatives of the muscarinic antagonist, hexocyclium, containing an amidine cationic head, for guinea‐pig cardiac and ileal receptors was investigated.

All the compounds studied displayed a greater affinity for muscular than for cardiac muscarinic receptors.

The 5 fold ileal selectivity of hexocyclium was increased by a number of chemical substitutions. The largest discrimination between receptors (about 200 fold) was found for the formamidine derivative.

The selectivity displayed by the hexocyclium derivatives stemmed from a greater decrease in affinity towards cardiac as compared to ileal receptors.
ω‐Conotoxin GVIA is a potent inhibitor of sympathetic neurogenic responses in rat small mesenteric arteries
Authors: Pruneau D. , Angus J.A.
Published: July 2012

We have investigated the effects of the N‐type calcium channel blocker, ω‐conotoxin GVIA, on contractile responses to nerve stimulation, noradrenaline and KCl in rat small mesenteric arteries. In separate experiments, single and summated excitatory junctional potentials (e.j.ps) evoked by nerve stimulation were recorded with an intracellular electrode in the absence and presence of ω‐conotoxin.

Electrical field stimulation of intramural sympathetic nerves (30 V; 0.25 ms pulse width; 3 s train length; 4–24 Hz) caused frequency‐dependent contractions. Cumulative concentration‐response curves for the contractions induced by noradrenaline and KCl were constructed in the same preparations. Stimulation at 0.2 Hz and 10 Hz induced respectively single e.j.ps without contractions and summated e.j.ps associated with a contractile response.

ω‐Conotoxin (0.1 to 3 nm) inhibited markedly and in a concentration‐dependent manner both the contractions and e.j.ps to electrical field stimulation. The concentration‐response curves to exogenous noradrenaline and KCl remained unaffected.

The time‐course for the effects of ω‐conotoxin (0.3 to 3 nm) indicated a slow onset of action with at least one hour to achieve an equilibrium.

The experiments indicate that ω‐conotoxin acts prejunctionally to inhibit sympathetic neurotransmission in rat small arteries presumably by inhibition of noradrenaline release. We suggest that ω‐conotoxin could be a useful tool to study the control of vascular tone through the autonomic nervous system.
Bay K 8644, modifier of calcium transport and energy metabolism in rat heart mitochondria: a new intracellular site of action
Authors: Baydoun Anwar R. , Markham Anthony , Morgan Rae M. , Sweetman Alan J.
Published: July 2012

The dihydropyridine Ca2+ channel agonist Bay K 8644 (10–200 μm) produced a concentration‐dependent increase in State 4 respiration in the rat heart mitochondria with the highest concentration (200 μm) increasing the rate from 33.1 ± 0.7 to 187.0 ± 13.3 ng atoms O2 consumed min−1 mg−1 protein.

Bay K 8644 (200 μm) reduced State 3 respiration from 247.2 ± 11.7 to 174.4 ± 0.06 ng atoms O2 min−1 mg−1 protein, reduced the respiratory control index (RCI) from 5.3 ± 0.45 to 1.1 ± 0.03 and reduced the ADP:O ratio from 2.75 ± 0.03 to 1.3 ± 0.15.

A similar, but smaller, stimulation of State 4 respiration was seen with nitrendipine (25–200 μm), the rate increasing from 22.6 ± 1.0 to 33.1 ± 1.8 ng atoms O2 consumed min−1 mg−1 protein in the presence of 200 μm nitrendipine.

Bay K 8644 (10–60 μm) increased the total Ca2+ uptake into rat heart mitochondria, the total increasing from 248.8 ± 8.4 to 406.9 ± 17.6 ng Ca2+ mg−1 protein at 60 μm Bay K 8644 (EC50 = 18.9 ± 1.4 μm).

Bay K 8644 (10–60 μm) produced a concentration‐dependent reduction in the Ca2+ influx rate (IC50 = 52.5 ± 2.8 μm). Similar effects were seen with (+)‐Bay K 8644 and (−)‐Bay K 8644.

Nitrendipine (40–120 μm) stimulated Ca2+ efflux from mitochondria preloaded with the ion; the efflux rate increasing from 2.9 ± 0.05 to 114.2 ± 6.2 nmol Ca2+ min−1 mg−1 protein (EC50 = 57.3 ± 1.3 μm).

These data indicate dihydropyridine‐induced changes in the activity of the mitochondrial Na+/Ca2+. antiporter pathway; nitrendipine causing stimulation and Bay K 8644 causing inhibition.
The effects of (−)‐daurisoline on Ca2+ influx in presynaptic nerve terminals
Authors: Lu Y. Ming , Liu G. Qing
Published: July 2012

The effects of (−)‐daurisoline on 45Ca2+ uptake and [3H]‐γ‐aminobutyric acid ([3H]‐GABA) release from synaptosomes of rat cerebral cortex and on contractile activity of rat aorta were examined.

Application of (−)‐daurisoline (1–100 μm) produced concentration‐related inhibition of high K+‐stimulated 45Ca2+ uptake and [3H]‐GABA release (IC50 = 7.7 ± 0.9 μm and 10.0 ± 1.5 μm, respectively) in synaptosomes but verapamil was only weakly active.

Neither (−)‐daurisoline (100 μm) nor verapamil (100 μm) modified 45Ca2+ uptake in control medium (5 mM K+, resting uptake) and [3H]‐GABA release in Ca‐free medium (45 mM K+ basal release).

High K+ and noradrenaline‐evoked contractions of rat aorta were inhibited by both (−)‐daurisoline and verapamil.

In conclusion, (−)‐daurisoline, which differed from verapamil in its mode of blocking Ca2+ influx may be a potent Ca2+ antagonist of Ca2+ channels in neurones.
The role of Na+ in muscarinic receptor‐mediated catecholamine secretion in the absence of extracellular Ca2+ in cat perfused adrenal glands
Authors: Teraoka Hiroki , Yamada Yutaka , Nakazato Yoshikazu , Ohga Akira
Published: July 2012

The role of Na+ in muscarinic receptor‐mediated catecholamine secretion, which is independent of extracellular Ca2+, was investigated by observing the effect of veratridine and ouabain in perfused adrenal glands of the cat.

Veratridine (10−4m) markedly enhanced catecholamine secretion evoked by acetylcholine (ACh, 10−4m) during perfusion with Ca2+‐free Locke solution containing hexamethonium (10−3m). The enhancement tended to be larger for noradrenaline secretion than for adrenaline secretion. Qualitatively the same result was obtained in the response to pilocarpine (5 × 10−4m).

Ouabain (10−4m) also enhanced ACh‐ and pilocarpine‐induced catecholamine secretions, especially noradrenaline secretion in the absence of extracellular Ca2+.

Tetrodotoxin (10−6m) blocked the enhancing effect of veratridine on ACh‐induced catecholamine secretion, but not that of ouabain in the absence of extracellular Ca2+.

When NaCl was replaced with sucrose, there was no secretory response to ACh regardless of the presence or absence of veratridine or ouabain. However, when ouabain, but not veratridine, was infused with Na+ before the replacement of NaCl, the response to ACh was substantially augmented.

These results indicate that Na+ is essential in the initiation of muscarinic receptor‐mediated catecholamine secretion and its enhancement by veratridine and ouabain in the absence of extracellular Ca2+. Both drugs seem to increase the intracellular concentration of Na+ through different mechanisms and result in increases in the efficiency of Ca2+ mobilization from intracellular Ca2+ pools linked to muscarinic receptors.
The effect of peptidase inhibitors on bradykinin‐induced bronchoconstriction in guinea‐pigs in vivo
Authors: Ichinose Masakazu , Barnes Peter J.
Published: July 2012

Bradykinin (BK) instilled directly into the airway lumen caused bronchoconstriction in anaesthetized, mechanically ventilated guinea‐pigs in the presence of propranolol (1 mg kg−1 i.v.) The geometric mean dose of BK required to produce 100% increase in airway opening pressure (PD100) was 22.9 nmol (95% c.i. 11.7–44.6 nmol).

The dose‐response curve for the effect of instilled BK was significantly shifted to the left by the angiotensin converting enzyme (ACE) inhibitor, captopril (5 and 50 nmol instillation, PD100 = 3.0, 95% c.i. 0.98–8.9, and 2.0 nmol, 95% c.i. 0.65–6.2 nmol, respectively).

The neutral endopeptidase (NEP) inhibitor, phosphoramidon (5 and 50 nmol instillation) also shifted the dose‐response curve for the effect of instilled BK; the PD100 values = 2.2 (95% c.i. 0.40–11.7) and 1.8 nmol (95% c.i. 0.87–3.5 nmol), respectively.

After pretreatment with captopril (50 nmol) and phosphoramidon (50 nmol) in combination, the dose‐response curve for the effect of instilled BK (PD100 =1.1 nmol, 95% c.i. 0.37–3.2 nmol) was similar to that obtained in the presence of each inhibitor used alone.

The kininase I inhibitor, dl‐2‐mercaptomethyl‐3‐guanidinoethylthiopropionic acid (50 nmol instillation) failed to alter the dose‐response curve to instilled BK (PD100 = 14.6 nmol, 95% c.i. 6.7–32.0 nmol).

These data suggest that both ACE and NEP degrade BK in the airway lumen, but that kininase I is not involved.
Mode of inhibitory actions of acute and chronic chloroquine administration on the electrically stimulated mouse diaphragm in vitro
Authors: Okwuasaba F.K. , Otubu J.A.M. , Udoh F.V.
Published: July 2012

The effects of bath applied chloroquine (Chlo) and of acute and chronic Chlo administration on skeletal muscle reactivity to electrical stimulation and to drugs have been studied on mouse hemidiaphragm preparations in vitro.

Chlo (0.15–150 μm) produced a concentration‐dependent inhibition of twitch and tetanic contractions due to direct muscle stimulation (MS). Acute and chronic administration of Chlo (45 mg kg−1 i.p. daily, for 3–28 days) progressively shifted the concentration‐response curve to bath‐applied Chlo to the right, with maximum effect occurring from day 14 of Chlo pretreatment.

Acute and chronic administration of Chlo decreased the twitch and tetanus tension, raised the minimal fusion frequency (MFR) for tetanic contraction to occur and did not alter the twitch/tetanus tension ratio. Tetanus tension unlike twitch tension was not significantly decreased on day 3.

Caffeine (5–500 μm) ‐ and isoprenaline (0.001‐0.8 μm)‐induced potentiations of twitch contraction were attenuated in a concentration‐dependent manner by bath‐applied Chlo and by acute and chronic administration of Chlo. Higher concentrations of caffeine (0.1–5 μm) and KCl (10 mM‐130 mm) produced contracture of the muscle which was sensitive to inhibition by Chlo (50–150 μm). Moreover, the spike contractions superimposed on caffeine contracture were more sensitive to the inhibitory effect of Chlo than the contracture.

The inhibitory effects of dantrolene sodium and (+)‐tubocurarine on MS and on indirectly stimulated hemidiaphragm respectively were not significantly altered by acute and chronic administration of Chlo. In contrast, the inhibitory concentration‐response curve to procaine was shifted to the right.

The inhibitory effect of bath‐appled Chlo, or acute and chronic pretreatment on twitch tension (MS) was not significantly antagonized by stepwise increase in extracellular Ca2+ (0.05‐2.5 mm). Sodium thiocyanate (1–5 mm) reversed in a concentration‐dependent manner the inhibitory effects of Chlo.

Complete recovery of twitch contractions occurred after 3 days of stopping daily Chlo administration, with partial recovery to tetanic tension after 28 days and no recovery of MFR. The reactivity of the diaphragm to bath applied Chlo was progressively restored, whereas the tension curve area to caffeine and KCl was still attenuated even 28 days after stopping Chlo pretreatment.

It is concluded that acute and chronic Chlo administration results in changes in reactivity of the hemidiaphragm muscle to electrical stimulation and to drugs such that there is a decrease in muscle strength and tolerance to Chlo in vitro. These effects are dependent on its direct inhibitory action on skeletal muscle and may result from interference with Ca2+ mobilization within the muscle.