bluuebunny/crossref_metadata_2025 huggingface dataset:
Differential effects of (±)‐dobutamine and human α‐CGRP on cardiac and on regional haemodynamics in conscious Long Evans rats
Authors: Gardiner S.M. , Compton A.M. , Kemp P.A. , Bennett T. , Hughes B. , Foulkes R.
Published: July 2012

Comparisons were made of the full haemodynamic profiles of the known cardiostimulant, (±)‐dobutamine, and the putative inotropic peptide, human α‐calcitonin gene‐related peptide (human α‐CGRP), in conscious, chronically‐instrumented Long Evans rats. Both substances were administered continuously i.v. for 60 min at two doses ((±)‐dobutamine, 2 and 10 μmol kg−1h−1; human α‐CGRP, 0.15 and 1.5 nmol kg−1 h−1).

In spite of their similar (small) effects on mean arterial blood pressure, the low doses of (±)‐dobutamine and human α‐CGRP influenced cardiac haemodynamics differently. Thus, (±)‐dobutamine caused an increase in cardiac index (due to a tachycardia), accompanied by rises in peak aortic flow, maximum rate of rise of aortic flow (dF/dtmax) and total peripheral conductance. However, the latter waned during the infusion, and after the infusion there was a significant systemic vasoconstriction and reductions in peak aortic flow, dF/dtmax and stroke index. Such ‘off’ effects following dobutamine infusion have not been described previously. The infusion of the lower dose of human α‐CGRP caused only a transient fall in central venous pressure.

The rise in total peripheral conductance during infusion of the lower dose of (±)‐dobutamine was associated with increases in hindquarters and common and internal carotid vascular conductances. The fall in total peripheral conductance after infusion was associated with renal vasoconstriction. Although there was no significant change in total peripheral conductance during the infusion of the lower dose of human α‐CGRP there were hindquarters and carotid vasodilatations together with mesenteric vasoconstriction.

Infusion of the higher dose of (±)‐dobutamine had greater effects than the lower dose on all cardiac haemodynamic variables and additionally, increased stroke index. However, the negative cardiac haemodynamic effects following the offset of infusion were also enhanced in association with marked renal and mesenteric vasoconstrictions. While infusion of the higher dose of human α‐CGRP increased cardiac index, peak aortic flow, dF/dtmax and total peripheral conductance, stroke index fell together with central venous pressure.

(±)‐Dobutamine caused greater cardiostimulation and increases in hindquarters blood flow than did human α‐CGRP. However, the latter at the higher dose caused substantially greater common and internal carotid hyperaemia than did (±)‐dobutamine, possibly indicating a selective and additional effect of human α‐CGRP on cranial blood flow. Furthermore, there were no adverse cardiovascular effects following infusion of human α‐CGRP.
The effect of cetirizine on antigen‐dependent leucopenia in the guinea‐pig
Authors: Coyle Anthony J. , Lefort Jean , Vargaftig B. Boris
Published: July 2012

Intravenous administration of ovalbumin (1 mg kg−1) to guinea‐pigs that had previously been injected with 3.5 × 109 platelets from actively sensitized animals induced an approximately 40% decrease in the number of circulating leucocytes 30–60 min later, whereas the number of platelets was not affected.

In contrast, there was no change in the leucocyte number following antigen challenge of guinea‐pigs that had received platelets from non‐immunised animals.

This platelet‐dependent leucopenia was inhibited by prior treatment of the recipient animal with cetirizine (10–30 mg kg−1, i.v.). Terfenadine (50 mg kg−1, p.o.) and mepyramine (2 mg kg−1, i.v.) were completely inactive in this respect. All doses of anti‐histamines were used at concentrations which completely inhibited the bronchoconstriction to an i.v. injection of 5 μg kg−1 of histamine.

The site of action of cetirizine is most likely to be the platelet as leucopenia induced by the neutrophil agonists leukotriene B4 (LTB4) (30 ng kg−1) and platelet activating factor (PAF) (30 ng kg−1) were not modified by cetirizine treatment.

In these experiments, we failed to support a role for lipoxygenase products as mediators of the platelet‐dependent leucopenia, as the selective lipoxygenase inhibitor BWA4C (50 mg kg−1, p.o.) was ineffective.

Our present results confirm and extend previous data demonstrating that antigen stimulated platelets can induce leucopenia in non‐immunised animals and this can be inhibited by the anti‐allergic agent, cetirizine, by an action which is probably unrelated to its anti‐histamine properties. The precise nature of the platelet derived factor(s) and their target of action remains to be determined.
Early and late contraction induced by ouabain in human umbilical arteries
Authors: Sato Koichi , Aoki K.
Published: July 2012

Ouabain (3 × 10−7–10−4 m) evoked a biphasic contraction in human umbilical artery that consisted of an early and a late contraction. The Ca2+‐antagonists, verapamil (10−7–10−5 m), diltiazem (10−7–10−5 m) and nifedipine (10−9–10−7 m) inhibited the early but not the late contraction. Caffeine (5 mm) changed neither the magnitude of the peak of the biphasic contraction nor the time needed to reach it.

Sodium concentration reduction (140 to 0 mm, replaced by N‐methyl‐d‐glucamine, NMG) produced dose‐dependent contraction of the arterial strip in 2.5 mm Ca2+ solution after the first treatment with verapamil (10−5 m) and caffeine (5 mm), but not in Ca2+‐free solution.

After prior treatment with verapamil and caffeine, the amplitude of the ouabain (10−4 m)‐induced late contraction varied, depending on the concentration of Ca2+ (0–2.5 mm) in the medium.

Amiloride (5 × 10−5 m–5 × 10−4 m), an inhibitor of the Na+–Ca2+ exchange system, produced dose‐dependent inhibition of the late contraction induced by ouabain (10−5 m) after prior treatment with verapamil and caffeine.

The time needed to reach the peak tension induced by monensin (5 × 10−7 m) together with ouabain (10−6 m) was less than that with ouabain alone, but the magnitude of the peak tension was not changed.

These results suggest that the early and late contractions caused by ouabain respectively produce a Ca2+ influx through voltage‐sensitive Ca2+ channels and Ca2+ entry through sodium‐calcium (Na+ — Ca2+) exchange.
Identification and characterization of histamine H1‐ and H2‐receptors in guinea‐pig left atrial membranes by [3H]‐mepyramine and [3H]‐tiotidine binding
Authors: Hattori Yuichi , Endou Masayuki , Gando Satoshi , Kanno Morio
Published: July 2012

Histamine receptors in the membranes prepared from guinea‐pig left atria were characterized with [3H]‐mepyramine and [3H]‐tiotidine binding.

The binding of the H1‐antagonist, [3H]‐mepyramine, was saturable and of high affinity with a maximum binding capacity of 307 ± 27 fmol mg−1 protein (n = 14) and with an equilibrium dissociation constant (KD) of 1.5 ± 0.2 nm (n = 14). The binding was rapid and readily reversible.

The competition curve for [3H]‐mepyramine binding by histamine was biphasic and revealed high and low affinity states of binding. The addition of 5′‐guanylylimidodiphosphate (GppNHp) (100 μm) converted this heterogeneous binding into homogeneous binding of low affinity.

The competition curves of H1‐antagonists with [3H]‐mepyramine had Hill coefficients not significantly different from unity, consistent with competition with [3H]‐mepyramine at a single site. GppNHp did not shift the competition curves.

Dissociation constants for H1‐antagonists determined from inhibition of [3H]‐mepyramine binding correlated well with the constants derived from inhibition of the positive inotropic response of guinea‐pig left atria to histamine.

The H2‐antagonist, [3H]‐tiotidine, labelled an apparently homogeneous population of recognition sites with a maximum binding capacity of 41 ± 8 fmol mg−1 protein (n = 6) and a KD of 10.8 ± 1.2 nm (n = 6).

Although histamine competed for [3H]‐tiotidine binding in a concentration‐dependent manner, the curve was monophasic and was not shifted by GppNHp.

It is concluded that both H1 and H2‐receptors exist in guinea‐pig left atria. H1‐receptors probably couple to intracellular effector(s) through a guanine nucleotide‐dependent transducing mechanism. On the other hand, H2‐receptors seem unlikely to be linked to guanine nucleotide regulatory proteins in guinea‐pig left atria, which may explain the failure of histamine to cause an increase in cyclic AMP in spite of the presence of H2‐receptors.
Functional changes in GABAA receptor stimulation during the oestrous cycle of the rat
Authors: Westerling Peter , Lindgren Silvana , Meyerson Bengt
Published: July 2012

Slices of rat cuneate nucleus were used to study whether or not gonadal steroids influence the γ‐aminobutyric acid (GABA) system in vivo. Females in different stages of the oestrous cycle as well as steroid‐treated (oestrogen, progesterone or both) ovariectomized animals were used.

Functional changes in the GABAA receptors were assayed using the effects of potentiators (benzodiazepine, barbiturate) and antagonists (picrotoxin) on the muscimol control dose‐response curves.

The potentiating effect of the benzodiazepine, flurazepam was unchanged during the oestrous cycle, and the hormone treatments did not alter this effect.

During oestrus, an increase was seen in the potentiating effect of the barbiturate (pentobarbitone). This suggests a synergistic effect between barbiturates and gonadal steroids. Progesterone treatment also increased the effect of pentobarbitone.

The antagonistic action of picrotoxin was unaffected during the oestrous cycle. However, progesterone (or progesterone and oestrogen) treatment reduced the potency of picrotoxin.

This study supports the idea that endogenous steroids (presumably progesterone) affect the GABAA receptors during the oestrous cycle by a mechanism associated with the barbiturate site of the GABAA receptor complex.
The effect of drugs acting on cholinoceptors and mucosal chloride on luminal bicarbonate transport by rat caecum under in vitro conditions
Authors: Canfield Paul , Abdul‐Ghaffar Tarik
Published: July 2012

The transport of ĤO−3 (Jsm) from a ĤO−3‐buffered serosal to an unbuffered mucosal saline solution has been studied in rat caecum in vitro.

Carbachol, bethanechol and acetylcholine (ACh) caused a concentration‐dependent fall in Jsm with similar maximum effects. 1,1‐Dimethyl‐4‐phenyl‐piperazinium iodide (DMPP) also inhibited Jsm but the effect was less than with the other drugs. Maximum cholinoceptor inhibition was less than that obtained with anoxia.

Responses were blocked by atropine (10−5 m) but hexamethonium (2 × 10−4 m) significantly altered the response only to DMPP.

Physostigmine (10−5 m) shifted the ACh response curve to the left but physostigmine itself caused inhibition of Jsm which was blocked by atropine.

Substitution of mucosal Cl− by NO−3 reduced Jsm to a similar extent to maximum cholinoceptor effect and abolished responses to bethanecol. Anoxia further reduced Jsm in the presence of NO−3.

Mucosal SITS and DIDS (1 mm) reduced Jsm but this was less than the maximum inhibition seen with drugs acting on cholinoceptors or mucosal Cl− removal. Serosal DIDS caused a similar inhibition.

We conclude that cholinoceptor agonists inhibit but do not abolish luminal bicarbonate transport by an action on muscarinic receptors.
Differences between the effects of cromakalim and nifedipine on agonist‐induced responses in rabbit aorta
Authors: Bray K.M. , Weston A.H. , Duty S. , Newgreen D.T. , Longmore J. , Edwards G. , Brown T.J.
Published: July 2012

The effects of cromakalim on endothelium‐denuded rabbit aortic strips were compared with those of the calcium (Ca2+) entry blocking agent, nifedipine.

Pre‐incubation with cromakalim or nifedipine had no significant effect on the initial phasic component of noradrenaline (NA)‐induced responses.

Cromakalim (0.3–10 μm), but not nifedipine, inhibited the maintained tonic contractions produced by NA. The effects of cromakalim were antagonized by raising extracellular [K+] or by glibenclamide.

Nifedipine inhibited contractions produced by KCl (40 mm) whereas cromakalim had no effect.

In Ca2+‐free physiological salt solution (PSS), cromakalim produced a significant inhibition of both the refilling of and the release of Ca2+ from NA‐releasable Ca2+ stores, whereas nifedipine was ineffective.

In tissues preloaded with 42K+ cromakalim (0.3–10 μm) produced a concentration‐dependent increase in the 42K+ efflux rate coefficient. NA (0.3 μm) also produced an increase in the rate of efflux of 42K+, an effect which was not antagonized by nifedipine (0.3 μm).

When microelectrodes were used, cromakalim (1–10 μm) produced a maintained concentration‐dependent membrane hyperpolarization. However, low concentrations of cromakalim (<1 μm) which relaxed the aorta had no effect on membrane potential. NA had no significant effect on membrane potential.

It is concluded that the ability of cromakalim to relax NA‐induced contractions in rabbit aorta is not exerted by the indirect closure of nifedipine‐sensitive Ca2+ channels. Instead, cromakalim may exert a direct inhibitory action on Ca2+ uptake into and release from Ca2+ stores and additionally inhibit the pathway through which Ca2+ passes from the extracellular fluid to intracellular Ca2+ stores.
The differential contribution of endogenous prostaglandins to the release of acetylcholine from the myenteric plexus of the guinea‐pig ileum
Authors: Takeuchi Tadayoshi , Okuda Miho , Yagasaki Osamu
Published: July 2012

Prostaglandin E (PGE) may be essential for maintaining the sensitivity of the myenteric plexus of guinea‐pig ileum to nicotine. The contributions of prostaglandins to nervous activity evoked by different stimuli have now been investigated by measuring the amount of acetylcholine (ACh) released from the myenteric plexus of the guinea‐pig ileum.

The amount of ACh released in response to dimethylphenylpiperazinium (DMPP) or substance P was depressed to about 40% of control by 2.8 μm indomethacin (Ind), whereas the release of ACh induced by 5‐hydroxytryptamine (5‐HT) was not affected. The inhibitory effects of Ind were oyercome by 14.3 nm PGE2.

Mepacrine 5 μm, an inhibitor of phospholipase A2, depressed the release of ACh in response to DMPP and substance P to the same extent as Ind. These inhibitory effects of mepacrine were overcome by arachidonic acid (10 μm), but not by arachidonic acid plus Ind. The release of ACh evoked by 5‐HT or electrical field stimulation (EFS) was also inhibited to about 60% of control by mepacrine but these inhibitions were overcome by arachidonic acid (10 μm) either in the absence or the presence of Ind.

The results suggest that endogenous prostaglandins and arachidonic acid contribute to the maintenance of the excitability of the myenteric plexus by DMPP and substance P. By contrast, the release of ACh induced by 5‐HT and EFS may be regulated by arachidonic acid and not by prostaglandins.
Adenosine‐ and α,β‐methylene ATP‐induced differential inhibition of cholinergic and non‐cholinergic neurogenic responses in rat urinary bladder
Authors: Parija S.C. , Raviprakash V. , Mishra S.K.
Published: July 2012

The effects of adenosine and α,β‐methylene adenosine triphosphate (α,β‐Me ATP) on single pulse‐induced neurogenic responses and contractions caused by exogenously applied acetylcholine (ACh) and adenosine triphosphate (ATP) were examined in rat urinary bladder.

Application of single pulse stimulation (1 ms; 80 V) evoked a biphasic contractile response (abolished by tetrodotoxin, 0.5 × 10−7 m) consisting of a fast (time to peak: 1.02 ± 0.07 s) and a slow component (time to peak: 4.92 ± 1.6 s). The selective inhibition of the slow component by atropine (3 × 10−6 m) suggests the participation of both cholinergic and non‐cholinergic neurotransmitters.

α,β‐Me ATP (5 × 10−6 m) abolished ATP (10−4 m)‐induced contractions without altering those to ACh (10−6 m). Further, the selective inhibition of the fast component of the neurogenic response by α,β‐Me ATP is suggestive of the contribution of endogenous ATP to the non‐cholinergic component.

Adenosine (10−8 m to 10−4 m) caused dose‐related differential inhibition of the fast (IC50, 1.04 ± 0.25 × 10−5 m) and slow (IC50, 2.18 ± 0.69 × 10−6 m) components, thereby further supporting two modes of neurotransmission in bladder.

Theophylline (10−4 m) antagonized the inhibitory effects of adenosine on the non‐cholinergic component, thereby implicating the participation of P1‐purinoceptors in neuromodulation. In contrast, theophylline at this concentration enhanced the adenosine‐induced inhibition of the cholinergic component.

The magnitude of ATP (10−4 m)‐ and ACh (10−8 m)‐induced contractions were almost identical to those of the fast and slow components of the neurogenic response, respectively. Comparable reduction of ATP (30.2 ± 3.4%) and ACh (100%) contractions to those of fast (44.2 ± 6.5%) and slow (88.2 ± 5.5%) components suggests the involvement of a postjunctional mechanism in adenosine‐induced differential inhibition of neurogenic responses.

The lack of effect of erythro‐6‐amino‐9‐(2‐hydroxy‐3‐nonyl) adenosine hydrochloride (10−6 m) and dipyridamole (10−6 m) suggests that endogenous adenosine plays little part in modulation of single pulse‐induced neurogenic response.

The results of the present study suggest that fast and slow components of neurogenic response are mediated through ATP and ACh, respectively, possibly co‐released from the same neurone in the rat bladder.
Very high affinity interaction of DPI 201‐106 and BDF 8784 enantiomers with the phenylalkylamine‐sensitive Ca2+‐channel in Drosophila head membranes
Authors: Glossmann Hartmut , Zech Christina , Striessnig Jörg , Staudinger Robert , Hall Linda , Greenberg Robert , Armah Benjamin I.
Published: July 2012

Piperazinylindoles (DPI 201‐106, BDF 8784), drugs known to act on voltage‐dependent Na+‐channels, bind with very high affinity to a Ca2+‐channel‐associated phenylalkylamine receptor in Drosophila melanogaster head membranes. These compounds and (+)‐tetrandrine, a naturally occurring Ca2+‐antagonist, were the most selective inhibitors for phenylalkylamine‐labelled Drosophila Ca2+‐channels compared to mammalian L‐type Ca2+‐channels.

Replacement of the cyano group by a methyl group in (+)‐DPI 201‐106 ((+)‐BDF 8784) increases the IC50 value for inhibition of phenylalkylamine labelling of Drosophila Ca2+‐channels from 0.29 to 2.1 nm but decreases the IC50 value for inhibition of phenylalkylamine labelling of mammalian skeletal muscle Ca2+‐channels from 3480 to 49 nm.

DPI 201‐106 enantiomers completely block (at 0.1 μm) phenylalkylamine photolabelling of a 136 K polypeptide in Drosophila head membranes whereas 10 μm aconitine or lidocaine are without effect.

Assessment of the Ca2+‐antagonist effects of the substituted DPI 201‐106 enantiomers in K+‐depolarized taenia strips from guinea‐pig caecum yielded pA2 values of 6.33 ± 0.07 for (−)‐BDF 8784 and 6.99 ± 0.17 for (+)‐BDF 8784, respectively.

Piperazinylindoles, previously believed to act nonspecifically on voltage‐dependent mammalian L‐type Ca2+‐channels, therefore have stereoselectivity for a novel binding site and chemical selectivity unrelated to local anaesthetic activity.

It is proposed that a very high affinity piperazinylindole‐selective site is coupled to the phenylalkylamine receptor of Drosophila Ca2+‐channels. These sites are still present on mammalian L‐type Ca2+‐channels but have lower affinity and/or are less tightly coupled to phenylalkylamine receptors on the α1‐subunit.
Pharmacological evidence for the possible involvement of repetitive action potentials in facilitation by GABA of catecholamine secretion in bovine adrenal chromaffin cells
Authors: Kitayama Shigeo , Nakatsukasa Yoichi , Morita Katsuya , Dohi Toshihiro , Tsujimoto Akira
Published: July 2012

γ‐Aminobutyric acid (GABA) evokes catecholamine (CA) secretion and enhances the stimulation‐evoked CA secretion via facilitation of Ca2+ entry in a Cl−‐dependent manner. The present study was designed to investigate further the ionic mechanism of modulation by GABA of CA secretion from adrenal medulla, using a primary culture of bovine chromaffin cells.

Tetrodotoxin (TTX), a voltage‐sensitive Na+ channel blocker, reduced GABA‐evoked CA secretion.

Inhibition of the sodium pump by ouabain or removal of extracellular K+ enhanced GABA‐evoked CA secretion in a TTX‐sensitive manner.

Tetraethylammonium (TEA) and cesium, which are known to block some types of K+ channels, markedly enhanced GABA‐evoked CA secretion in a concentration‐related fashion. TEA‐induced enhancement of the GABA‐evoked CA secretion was attenuated by TTX or replacement of extracellular Na+ by choline. On the other hand, ouabain accelerated the effect of TEA.

TEA and ouabain also enhanced GABA‐induced Ca2+ influx and accumulation of cytosolic Ca2+, assessed with 45Ca2+ uptake and quin2 fluorescence.

Veratridine increased accumulation of cytosolic Ca2+ in a TTX‐sensitive manner. GABA facilitated the veratridine‐induced elevation of cytosolic Ca2+ even when the GABA‐induced rise of cytosolic Ca2+ levelled off.

These results suggest the involvement of repetitive action potentials in modulation of GABA by Ca2+ mobilization and, as a consequence, of the CA secretion in chromaffin cells.
Changes in neurotransmitter sensitivity in the mouse neocortical slice following propranolol and theophylline administration
Authors: Mally Judit , Connick J.H. , Stone T.W.
Published: July 2012

The mouse neocortical slice has been used to examine the sensitivity of neurones to isoprenaline, 5‐hydroxytryptamine (5‐HT) and adenosine acutely and following chronic treatment of animals with propranolol or theophylline.

While having little effect alone, all three agonists enhanced the d.c. depolarizing potential produced by N‐methyl‐d‐aspartate (NMDA). The effect of (−)‐isoprenaline (0.2 μm) was shared by (+)‐isoprenaline at the much higher concentration of 10 μm.

Superfusion of slices with theophylline or 8‐phenyltheophylline blocked responses to adenosine with evidence of selectivity. A single injection of theophylline 24 h before slice preparation did not alter agonist sensitivity, but when administered daily at 100 mg kg−1 for 14 days, the xanthine caused a loss of sensitivity to adenosine and (−)‐isoprenaline but not 5‐HT. The lower dose of theophylline, 10 mg kg−1 daily, also led to a loss of adenosine responses but no change of sensitivity to the amines.

Following the 14 day treatment with theophylline at 100 mg kg−1 daily in two groups of mice, responses to adenosine recovered to control levels after 20 days.

Propranolol superfusion blocked responses to both isomers of isoprenaline and 5‐HT but did not affect sensitivity to adenosine.

Chronic treatment with propranolol at 25 mg kg−1 daily for 14 days induced a loss of sensitivity to (−)‐isoprenaline and 5‐HT but not adenosine. A lower dose of 5 mg kg−1 daily caused no change in responses to adenosine or 5‐HT, but yielded an increased sensitivity to (−)‐isoprenaline.

The results are discussed with respect to reports of receptor up‐regulation in binding studies; caution is clearly required in extrapolating from such work to receptor activity in a functional system, especially in the case of theophylline and adenosine.
Alkylation with β‐funaltrexamine suggests differences between μ‐opioid receptor systems in guinea‐pig brain and myenteric‐plexus
Authors: Franklin T.G. , Traynor J.R.
Published: July 2012

The effects of pre‐incubation with β‐funaltrexamine (β‐FNA) on the binding of [3H]‐[d‐Ala2, MePhe4, Gly‐ol5]enkephalin ([3H]‐DAMGO) to homogenates of guinea‐pig brain and myenteric‐plexus longitudinal muscle have been studied.

β‐FNA pretreatment of brain homogenates in Tris‐HCl buffer reduced the amount of [3H]‐DAMGO binding. This was principally due to a reduction in the maximal number of binding sites measurable. However, approximately 30% of sites labelled by 1 nm [3H]‐DAMGO were insensitive to 1 μm β‐FNA. Similar findings were obtained when the alkylation was performed in brain homogenates prepared in Krebs solution buffered with HEPES.

β‐FNA pretreatment of whole myenteric‐plexus longitudinal muscle strips caused an increase in the IC50 values of μ‐agonists, but not of κ‐agonists. However, the binding of [3H]‐DAMGO to homogenates of myenteric‐plexus longitudinal muscle was not altered by pre‐incubation with β‐FNA in Tris‐HCl buffer. On the other hand when the pretreatment was carried out in whole tissue in Krebs solution, or in homogenates in the presence of NaCl and Gpp(NH)p, a marked reduction in [3H]‐DAMGO binding was observed.

These results suggest that a low affinity form of the μ‐opioid receptor is the physiologically relevant site for β‐FNA alkylation in the myenteric‐plexus and that differences exist between μ‐receptor systems in guinea‐pig myenteric plexus and brain.
Modification of the rat uterine response to oestrogen and tamoxifen by thromboxane antagonists
Authors: Kerr M.B. , Marshall K. , Senior J.
Published: July 2012

The thromboxane receptor antagonists EP092, AH23848 and BM 13.505 were used to investigate the role of thromboxane in the uterotrophic response to oestradiol and tamoxifen.

The parameters examined were uterine blood flow (measured by the microsphere technique), uterine wet and dry weights and the concentrations of cytosolic and nuclear oestrogen receptors.

Only EP092 potentiated the hyperaemic response to oestrogen but all three thromboxane antagonists inhibited oestradiol‐stimulated uterine growth. This inhibition was accompanied by a decrease in nuclear oestrogen receptor concentration.

The uterotrophic response to tamoxifen was unaffected by the thromboxane antagonists.

The mechanism by which the thromboxane antagonists may be exerting their growth inhibitory effect is discussed, although, whether this effect can be attributed to blockade of thromboxane receptors or to some other mechanism is not clear from this study.
Pinacidil inhibits the ryanodine‐sensitive outward current and glibenclamide antagonizes its action in cells from the rabbit portal vein
Authors: Xiong Zhiling , Kajioka Shunichi , Sakai Takeshi , Kitamura Kenji , Kuriyama Hirosi
Published: July 2012

Pinacidil, a potassium‐channel opener, inhibited the ryanodine‐sensitive oscillatory outward potassium current induced by Ca released from an intracellular store. Glibenclamide, a blocker of the ATP‐sensitive K‐channel, prevented the action of pinacidil, suggesting the presence of an additional site (to K channels) for the vasodilator actions of pinacidil at which glibenclamide can act as an antagonist.
Enhanced contractility of the rat stomach during suppression of angiotensin converting enzyme by captopril in vitro
Authors: Rani R. , Rao K.S.
Published: July 2012

Intragastric pressure (IGP) was used as an index, of the effect of serosal application of captopril (SQ 14,225; d‐3‐mercapto‐2‐methylpropanoyl‐l‐proline) on the contractility of rat stomach in vitro.

Captopril, at concentrations > 0.3 μm, enhanced the spontaneous gastric motility (GM) in a concentration‐dependent manner whereas concentrations < 0.3 μm selectively potentiated 4 nm bradykinin (BK)‐evoked gastric contractions without significantly affecting the spontaneous GM.

The kallikrein inhibitor, aprotinin (100 u ml−1), markedly antagonized the enhanced GM to 1.4 μm captopril and BK (4 nm)‐evoked contractions, without affecting the contractions evoked by angiotensin 1 (10 nm) and acetylcholine (0.4 μm). The angiotensin II antagonist, saralasin (50 μm) failed to mimic aprotinin.

The enhanced GM to captopril was markedly inhibited by tetrodotoxin (1 μm), and partially inhibited by atropine (1 μm).

These results indicate that in vitro, captopril (> 0.3 μm) enhances gastric contractility through kininase/ACE inhibitory action, presumably by increasing the concentration of undegraded tissue kinins and substance P. This motor response seems to be predominantly due to activation of the cholinergic neurones but non‐cholinergic excitatory neurones are also involved.
Influence of acute and chronic chlorimipramine treatment on the 5‐HT receptor‐mediated modulation of acetylcholine release from the cerebral cortex of freely moving guinea‐pigs
Authors: Siniscalchi Anna , Bianchi Clementina , Beani Lorenzo
Published: July 2012

Acetylcholine (ACh) release from the cerebral cortex of freely moving guinea‐pigs, implanted with epidural cups, was studied.

A single dose of chlorimipramine (Cl‐Imip, 10 mg kg−1, s.c.), reduced the cortical ACh release both in normal and in chronically (10 mg kg−1 daily, s.c., for 14 days) Cl‐Imip‐treated guinea‐pigs; the 5‐HT3 antagonist MDL 72222 (1 mg kg−1, s.c.) antagonized this effect.

A single dose of Cl‐Imip significantly reduced the effect of the 5‐HT1A agonist 8‐hydroxy‐2‐(di‐n‐propylaminotetralin) (8‐OH‐DPAT, 0.1 mg kg−1, s.c.), which nearly doubled the cortical ACh release in control animals. MDL 72222 restored to normal the response to 8‐OH‐DPAT reduced by the antidepressant.

A single dose of Cl‐Imip did not change the inhibitory, MDL 72222‐sensitive, effect induced by the 5‐HT3 agonist 2‐methyl‐5‐hydroxytryptamine (2‐methyl‐5‐HT, 500 μg, i.c.v.).

In chronically Cl‐Imip‐treated guinea‐pigs, the facilitatory effect of 8‐OH‐DPAT was no longer present, while the inhibitory, MDL 72222‐sensitive, effect of 2‐methyl‐5‐HT was maintained.

These results indicate that the 5‐HT1A receptor‐mediated increase in ACh release is reduced by prolonged Cl‐Imip treatment, while the 5‐HT3 receptor‐mediated inhibition of ACh release is unaffected. The relevance of these findings to the antidepressant mechanism of Cl‐Imip is discussed.
A comparison of excitotoxic lesions of the basal forebrain by kainate, quinolinate, ibotenate, N‐methyl‐d‐aspartate or quisqualate, and the effects on toxicity of 2‐amino‐5‐phosphonovaleric acid and kynurenic acid in the rat
Authors: Winn Philip , Stone Trevor W. , Latimer Mary , Hastings Michael H. , Clark Andrew J.M.
Published: July 2012

It has been suggested that an NMDA1 receptor subtype might be activated by N‐methyl‐d‐aspartate (NMDA) and ibotenate and an NMDA2 subtype by NMDA or quinolinate, and that the NMDA2 site might be more susceptible to blockade by kynurenic acid.

Experiments were carried out to examine the ability of 2‐amino‐5‐phosphonovaleric acid (AP5) and kynurenic acid to antagonize the neurotoxic properties of kainate, ibotenate, NMDA, quinolinate and quisqualate injected into the rat basal forebrain.

Following histological analysis of the injection sites, lesion volume was assessed parametrically. Each of the toxins except quisqualate was found to make lesions of parvocellular neurones within the basal forebrain with a relative order of potency: kainate ≫ quinolinate > ibotenate = NMDA.

Equimolar doses of AP5 abolished the toxicity produced by quinolinate and NMDA; toxicity to kainate and ibotenate was attenuated to ∼40% of the toxin‐alone condition.

The antagonistic properties of kynurenate were dose‐dependent: equimolar kynurenate had no effect on quinolinate but attenuated the actions of ibotenate, kainate and NMDA; 2 × equimolar kynurenate had no effect on quinolinate or ibotenate but attenuated the toxicity of kainate and NMDA; and 3 × equimolar kynurenate had no effect on the toxicity of kainate or ibotenate, attenuated the actions of NMDA and abolished the toxic action of quinolinate.

The results are discussed in terms of the actions of the various toxins at different receptors, differentially sensitive to AP5 and kynurenate.
Effects of tacrine, velnacrine (HP029), suronacrine (HP128), and 3,4‐diaminopyridine on skeletal neuromuscular transmission in vitro
Authors: Braga M.F.M. , Harvey A.L. , Rowan E.G.
Published: July 2012

The effects of tacrine (9‐amino‐1,2,3,4‐tetrahydroacridine), velnacrine (HP029, 9‐amino‐1,2,3,4‐tetrahydroacridin‐1‐ol maleate), suronacrine (HP128, 9‐benzylamino‐1,2,3,4‐tetrahydroacridin‐1‐ol maleate), and 3,4‐diaminopyridine on neuromuscular transmission were compared on isolated nerve‐muscle preparations.

Tacrine, HP029, and 3,4‐diaminopyridine augmented responses of chick biventer cervicis preparations to nerve stimulation, with tacrine and HP029 increasing responses to exogenously applied acetylcholine. HP128 blocked responses to nerve stimulation and to carbachol, but increased responses to acetylcholine.

In mouse diaphragm preparations that were partially paralysed by tubocurarine or low calcium solutions, tacrine, HP029, and 3,4‐diaminopyridine reversed the twitch block. HP128 deepened the block.

In mouse triangularis sterni preparations, tacrine and HP029 prolonged the decay phase of endplate potentials and miniature endplate potentials, but had no effect on quantal content at 36°C; above 10 μm, they reduced endplate potential amplitude. 3,4‐Diaminopyridine increased quantal content without affecting the time course of the endplate potentials. HP128 (1–10 μm) had no effect on amplitude or time course of endplate potentials, but reduced their amplitude at higher concentrations.

Extracellular recording of nerve terminal currents from triangularis sterni preparations revealed that 3,4‐diaminopyridine and HP128 had a selective blocking action on the waveform associated with K+ currents, tacrine reduced and prolonged the K+‐related waveform, and HP029 had nonselective blocking actions only seen at high concentrations.

Tacrine and HP029 behave predominantly as anticholinesterase agents, while HP128 has weaker anticholinesterase actions that are masked by cholinoceptor blockade. Tacrine and HP128, but not HP029, have some blocking actions on K+ currents of mouse motor nerve terminals.
Characterization of Gaddum's substance R
Authors: Douglas G.J. , Williams K.I. , Flower R.J.
Published: July 2012

When the isolated small intestine of the rat is perfused via the mesenteric artery, an oxytocic principle (Gaddum's substance R) is released which is detectable in the perfusate after 30 min and is present in samples collected 8 h later.

The oxytocic activity of substance R is lost after boiling but is unaffected by treatment with thioglycolate. Furthermore, atropine, methysergide and indomethacin failed to antagonize uterine contractions to substance R.

Neither substance R nor urinary kallikrein alone induce a contraction of the guinea‐pig isolated ileum. However, in the presence of kininogen both substance R and urinary kallikrein produce a slow and prolonged contraction of the guinea‐pig ileum.

The oxytocic and kininogenase properties of both substance R and urinary kallikrein are inhibited by Trasylol.

Soy bean trypsin inhibitor (SBTI) selectively inhibited both the oxytocic and the kininogenase activities of substance R but not those of urinary kallikrein.

Gel filtration of substance R resolved a single peak of oxytocic activity with an estimated molecular weight of 40 kDa.

We conclude that substance R is a kininogenase enzyme which may be distinguished from plasma kallikrein by its molecular weight and from urinary kallikrein by its susceptibility to SBTI. The exact nature of this enzyme remains to be elucidated.
Effect of hyperosmolarity on human isolated central airways
Authors: Jongejan R.C. , de Jongste J.C. , Raatgeep R.C. , Stijnen T. , Bonta I.L. , Kerrebijn K.F.
Published: July 2012

We studied the effect of hyperosmolarity on human isolated airways because a better understanding of the effect of hyperosmolarity on the human airway wall may improve insight into the pathophysiology of hyperosmolarity‐induced bronchoconstriction in asthma.

In cartilaginous bronchial rings dissected from fresh human lung tissue, hyperosmolar Krebs‐Henseleit buffer (450 mosm, extra sodium chloride added) evoked a biphasic response: a rapid relaxation phase (peak after 5.0 ± 0.3 min) followed by a slow contraction phase (peak after 25.4 ± 0.8 min).

With the histamine (H1) receptor antagonist mepyramine, the contraction phase was reduced to 41.2% of the control value (P < 0.001), with atropine to 50.0% (P < 0.01), with the local anaesthetic lignocaine to 48.7% (P < 0.05) and with mepyramine together with atropine to 19.2% (P < 0.001).

With the inhibitor of neutral metalloendopeptidase, phosphoramidon, the contraction phase increased to 128.0% of the control value (P < 0.05) and after removal of the epithelium to 131.8% (P < 0.05).

Indomethacin, the leukotriene C4/D4 (LTC4/D4) antagonist FPL 55712 or the blocker of nerve conduction, tetrodotoxin, had no effect on the contractile phase.

The relaxation phase was not altered by any of these drugs nor by epithelial denudation. The relaxation phase was also unchanged in the presence of α‐chymotrypsin, which degrades muscle relaxing peptides such as vasoactive intestinal peptide.

Hyperosmolar buffer slightly increased the sensitivity and maximal response to methacholine as well as the cholinergic twitch to electric field stimulation.

We conclude that hyperosmolarity releases acetylcholine, histamine and neuropeptides in the human airway wall in sufficient quantities to contract airway smooth muscle. This release itself or its effect on airway muscle is modulated by the airway epithelium. The mechanism of the relaxation phase may be an unknown smooth muscle relaxing substance or a direct effect on the airway muscle, related to ion fluxes.
The contribution of Rb‐permeable potassium channels to the relaxant and membrane hyperpolarizing actions of cromakalim, RP49356 and diazoxide in bovine tracheal smooth muscle
Authors: Longmore J. , Bray K.M. , Weston A.H.
Published: July 2012

Cromakalim (1 and 10 μm), RP49356 (5 and 50 μm) and diazoxide (100 and 300 μm) produced full relaxation of smooth muscle strips pre‐contracted with 25 mm KCl. These agents caused membrane hyperpolarization and increased 42K and 86Rb efflux. The time taken to achieve the maximum change in each of these parameters (tmax) was less for the higher concentration levels of cromakalim, RP49356 and diazoxide than for the lower concentration levels.

Calculation of permeability (P) changes showed that cromakalim (1 and 10 μm) produced a greater rise in PK than PRb, although the PRb:PK ratio was simiiar at both concentration levels. Similarly RP49356 produced a greater change in PK than PRb. However, in contrast to cromakalim, this difference was more marked at the higher concentration (50 μm) and was reflected by a differential effect of the two concentrations of RP49356 on the PRb:PK ratio. Diazoxide (100 and 300 μm) produced similar changes in PK and PRb.

For cromakalim (1 and 10 μm) the tmax for the electrical and mechanical effects and also the profile of change in these parameters corresponded to changes in both PK and PRb. For RP49356 (5 μm), changes in tension and membrane potential were related to both changes in PK and PRb, whereas at 50 μm these responses more closely corresponded to changes in PK. For diazoxide (100 and 300 μm) the electrical and mechanical effects corresponded to changes in both PK and PRb.

The results show that changes in 42K and 86Rb efflux induced by cromakalim, RP49356 and diazoxide are good indicators of changes in membrane PK and PRb evoked by these agents. Furthermore, it is concluded that the K channels involved in the mechanical and electrical effects of cromakalim are represented by the opening of a single population through which Rb can pass less easily than K, whilst the K channels associated with actions of diazoxide are equally permeable to both K and Rb. In contrast, the relaxant and membrane hyperpolarizing actions of RP49356 may involve the opening of more than one group of K channels which differ in their permeability to Rb.
5‐Hydroxytryptamine‐induced bronchoconstriction in the guinea‐pig: effect of 5‐HT2 receptor activation on acetylcholine release
Authors: Macquin‐Mavier Isabelle , Jarreau Pierre‐Henri , Istin Nathalie , Harf Alain
Published: July 2012

The bronchoconstrictor responses to 5‐hydroxytryptamine (5‐HT) were studied in the guinea‐pig to establish whether they are partly attributable to parasympathetic activation within the airways. 5‐HT dose‐response curves were constructed in anaesthetized and ventilated guinea‐pigs pretreated with saline, or by bilateral cervical vagotomy or vagotomy plus atropine 3 mg kg−1, i.v. Vagotomy had no effect on 5‐HT‐induced bronchoconstriction but vagotomy plus atropine significantly reduced it.

To determine whether parasympathetic activation within the airways resulted from pre‐ or postganglionic stimulation, 5‐HT dose‐response curves were constructed for two groups of vagotomized guinea‐pigs treated with hexamethonium 2 mg kg−1, or hexamethonium 2 mg kg−1, plus atropine 3 mg kg−1. Guinea‐pigs treated with hexamethonium plus atropine experienced significantly less 5‐HT‐induced bronchoconstriction than those treated with hexamethonium alone.

To characterize the subtype of 5‐HT receptors involved in the activation of the parasympathetic system by 5‐HT, dose‐response curves to 5‐HT were constructed for four groups of vagotomized guinea‐pigs treated with saline, 1 mg kg−1 of the 5‐HT3 antagonist ICS 205–930, or either 0.01 or 0.1 mg kg−1 of the 5‐HT2 antagonist ketanserin. ICS 205–930 enhanced 5‐HT‐induced bronchoconstriction but 0.01 mg kg−1 ketanserin inhibited it significantly and 0.1 mg kg−1 ketanserin abolished it. To confirm the involvement of 5‐HT2 receptors in these responses, we studied the effects in vagotomized guinea‐pigs of atropine on the bronchoconstriction induced by the 5‐HT2 agonist, α‐methyl‐5‐HT, infused at rates of 40 and 80 ng kg−1 s−1. At both rates, atropine significantly reduced the bronchoconstrictor responses to α‐methyl‐5‐HT.

The above results indicate that 5‐HT‐induced bronchoconstriction is indeed partly mediated by parasympathetic activation within the airways. This activation is mediated by stimulation of 5‐HT2 receptors which are probably located on the postganglionic parasympathetic nerve endings.
The effects of probucol on the progression of atherosclerosis in mature Watanabe heritable hyperlipidaemic rabbits
Authors: Daugherty Alan , Zweifel Ben S. , Schonfeld Gustav
Published: July 2012

Probucol was administered to mature Watanabe heritable hyperlipidaemic (WHHL) rabbits (≅9 months old). Groups of WHHL rabbits were randomly selected and treated as follows: Group 1 killed at 9 months (n = 9); Group II placed on sham‐treated diet at 9 months and followed for 6 months (n = 8); Group III placed on probucol at 9 months and followed for 6 months (n = 8). Probucol was administered by mixing 1% wt/wt drug with standard laboratory diet.

Plasma concentrations of probucol increased to 93 ± 11 μg ml−1 in Group III during the initial 2 weeks and increased further to 149 ± 24 μg ml−1 at the end of the treatment period.

Plasma concentrations of total cholesterol, unesterified cholesterol and phospholipids were significantly reduced overall by probucol, while triglycerides were not affected.

No statistically significant differences were observed in the presence of oxidized products in low density lipoproteins (LDL) isolated from plasma of controls compared to probucol‐treated rabbits. However, LDL from probucol‐treated animals was resistant to oxidation in the presence of Cu2+ (3 μm).

Group I had aortic atherosclerosis covering 70 ± 5% of intimal area of thoracic aortae, that increased to 91 ± 3% in Group II. This was associated with cholesterol contents of aortae increasing from 1.4 ± 0.2 μg mg−1 in Group I to 2.7 ± 0.3 μg mg−1 in Group II. Probucol administration did not produce a statistically significant reduction of atherosclerotic lesion area (78 ± 7%). However, probucol treatment reduced cholesterol content to 1.9 ± 0.3 μg mg−1 (P < 0.01). Collagen content of aortae was not affected by probucol treatment.

Thus, while probucol did not promote regression, the drug did retard the continued deposition of cholesterol esters into atherosclerotic lesions of mature WHHL rabbits.
Separation of two pathways for calcium entry into chromaffin cells
Authors: Gandía Luis , Casado Luis‐Felipe , López Manuela G. , García Antonio G.
Published: July 2012

The effects of various drugs on 45Ca + 40Ca uptake into cultured bovine adrenal chromaffin cells evoked by 1,1‐dimethyl‐4‐phenylpiperazinium (DMPP) or high K, were studied. In the presence of 1 mm external 40Ca, with 45Ca as a radiotracer, unstimulated cells took up an average of 0.13 fmol/cell 40Ca and 772 c.p.m./106 cells of 45Ca (n = 76). Upon stimulation with DMPP (100μm for 60s) or K (59 mm for 60s), Ca uptake increased to 0.92 and 1 fmol/cell, respectively.

Flunarizine behaved as a potent blocker of both DMPP‐ and K‐evoked Ca uptake (IC50 of 1.76 and 1.49 μm, respectively for DMPP and K). A similar picture emerged with Cd ions, though Cd exhibited an IC50 against K (1.86 μm) slightly lower than the IC50 against DMPP (8.14 μm).

Clear cut differences were observed with amiloride, guanethidine, nimodipine and nisoldipine which behaved as selective blockers of DMPP‐mediated Ca uptake responses: IC50 values to block DMPP effects were 290, 27, 1.1 and 1.63 μm respectively for amiloride, guanethidine, nimodipine and nisoldipine. Amiloride blocked K‐evoked Ca uptake by only 35% and guanethidine did not affect it. Nisoldipine inhibited K‐evoked Ca uptake only partially at low concentrations (about 30%); a second blocking component was observed at the highest concentration used (10 μm). At 10 μm, nimodipine blocked K‐evoked Ca uptake by 50%.

Thus, it seems that the nicotinic receptor mediated Ca uptake pathway can be pharmacologically separated from the K‐activated pathway. The results are compatible with the hypothesis that in cultured bovine adrenal chromaffin cells, stimulation of nicotinic receptors recruits a single type of Ca channel which is sensitive to flunarizine, Cd, amiloride, guanethidine, nimodipine and nisoldipine. The results also suggest that K depolarization might be recruiting in addition to this channel, another Ca channel which is highly sensitive to Cd and flunarizine, resistant to nisoldipine, nimodipine and amiloride, and insensitive to guanethidine.
Effects of brevetoxin‐B on motor nerve terminals of mouse skeletal muscle
Authors: Tsai M.C. , Chen M.L.
Published: July 2012

The effects of brevetoxin‐B, a red tide toxin, on motor nerve terminal activity were assessed on mouse triangularis sterni nerve‐muscle preparations. The perineural waveforms were recorded with extracellular electrodes placed in the perineural sheaths of motor nerves.

At 0.11 μm, brevetoxin‐B increased the components of waveforms associated with sodium and potassium currents while it decreased the calcium activated potassium current and the slow calcium current of the nerve terminal. The fast calcium current and slow potassium current were not affected.

At 1.11 μm, brevetoxin‐B decreased all of the components of waveforms associated with sodium, potassium and calcium currents.

It is concluded that brevetoxin‐B affects sodium, potassium as well as calcium currents in the nerve terminal. The effects may contribute to its pharmacological actions on synaptic transmission.
Rapid decrease in neuropeptide Y gene expression in rat adrenal gland induced by the α2‐adrenoceptor agonist, clonidine
Authors: Higuchi Hiroshi , Iwasa Atsushi , Miki Naomasa
Published: July 2012

The mechanism of regulation of the neuropeptide Y (NPY) gene by pharmacological treatment with the α2‐adrenenoceptor agonist, clonidine, was investigated by quantitative Northern blot analysis of the effects of this drug on the NPY mRNA levels in rat adrenal gland and medulla oblongata/pons.

In the adrenal gland, clonidine‐treatment (50 μg kg−1, s.c., once daily) resulted in decrease in the amount of NPY mRNA to 44 ± 10% of the control level in 24 h and then its increase to 162 ± 16% of the control level after 5 days. Concomitant changes in putative NPY pre‐mRNA species (7.0 and 3.3 kb) were observed, probably due to changes at the level of NPY gene transcription.

The short‐term (24 h) effect of clonidine was blocked by yohimbine (5 mg kg−1, i.p., once daily). Yohimbine alone tended to increase the NPY mRNA level after 24 h.

The recovery/increase in the NPY mRNA level in the adrenal gland after 5 days treatment with clonidine was similar to its increase after treatment with reserpine (0.5 mg kg−1, i.p., once daily).

NPY gene expression in the medulla oblongata/pons was not changed by short‐ or long‐term treatment with clonidine.

These results suggest that clonidine suppresses NPY gene expression in the adrenal gland, probably at the level of transcription, by activation of the α2‐adrenoceptor.