bluuebunny/crossref_metadata_2025 huggingface dataset:
Calcium antagonistic and antiarrhythmic actions of CPU‐23, a substituted tetrahydroisoquinoline
Authors: Dong Hui , Sheng Jian‐Zhong , Lee Chi‐Ming , Wong Tak Ming
Published: July 2012

The effects of CPU‐23 (1‐{1‐[(6‐methoxyl)‐naphth‐2‐yl]}‐propyl‐2‐(1‐piperidine)‐acetyl‐6,7‐dimethyoxy‐1,2,3,4‐tetra‐hydroisoquinoline) were studied on mechanical and electrical activities, and intracellular free calcium ([Ca2+]i) of isolated cardiac tissues in order to investigate its spectrum and mechanisms of action in the heart. Its antiarrhythmic and haemodynamic effects in pentobarbitone‐anaesthetized rats subjected to coronary artery ligation were also evaluated.

CPU‐23 at 10−6‐10−4 m markedly inhibited slow action potential characteristics in guinea‐pig papillary muscles and pace‐maker action potential of rabbit sinoatrial node. It affected fast action potential only at 10−4 M. None of the effects of CPU‐23 was reversed by washout for up to 2 h.

Like nifedipine and diltiazem, CPU‐23 decreased the heart rate of the isolated perfused heart of the rat. However, in contrast to these two classical calcium antagonists which dose‐dependently inhibited the force of contraction, CPU‐23 inhibited and stimulated the force of contraction at 10−7‐3 × 10−6 m and 10−5 m, respectively.

CPU‐23 at 10−6‐10−5 m inhibited the KCl‐induced [Ca2+]i increase in the Ca2+ medium, but did not affect the caffeine‐induced [Ca2+]i increase in the Ca2+‐free medium in isolated ventricular myocytes.

CPU‐23 at 1–5 mg kg−1 reduced dose‐dependently ventricular arrhythmias including ventricular ectopic beats, VT and VF as well as mortality during coronary artery ligation. At 2.5–5 mg kg−1 it even abolished VF, which was accompanied by 100% survival.

It is suggested that CPU‐23 has calcium antagonistic properties in cardiac tissues. It selectively blocks the transmembrane influx of extracellular Ca2+ through Ca2+ channels, thus reducing the heart rate and developed tension, altering the slow action potential characteristics and producing antiarrhythmic effect against ischaemic arrhythmias.
Whole cell and single channel analysis of the kinetics of glycine‐sensitive N‐methyl‐D‐aspartate receptor desensitization
Authors: Parsons Chris G. , Zong Xiangang , Lux Hans D.
Published: July 2012

The kinetics of glycine‐sensitive, N‐methyl‐d‐aspartate (NMDA) receptor desensitization were investigated in cultured neurones with the patch clamp technique.

The degree of fast NMDA‐receptor desensitization was inversely related to glycine concentration. Thus, increasing concentrations of glycine from 30 nm to 2.5 μm potentiated desensitized NMDA responses (873% ± 101%) to a greater degree than peak responses (260% ± 27%).

The desensitization was due to a decrease in the affinity of glycine for the strychnine‐insensitive, glycine modulatory site (glycineB site) following activation of the NMDA‐receptor complex. Thus, the A50 for glycine in potentiating peak responses (77 nm, 95% confidence limited 58–104 nm) was five fold lower than that for plateau responses (399 nm, 340–468 nm).

The rate of desensitization was related to glycine concentration such that a reciprocal plot of desensitization rate (1/τ S−1) against glycine concentration had a slope of 9.5* 106 M−1 S−1.

Recovery from desensitization following step increases in glycine or l‐alanine concentration in the continuous presence of NMDA (200 μm) reflected the association kinetics of the glycineB agonist used.

The rate and degree of NMDA receptor desensitization was independent of holding potential.

NMDA receptor desensitization was also evident at the single channel level.

The glycineB antagonist 7‐chlorokynurenic acid (7‐Chl‐Kyn 3 and 10 μm) concentration‐dependently induced an identical form of desensitization in the presence of 1 μm glycine.

In contrast, the competitive NMDA antagonist (±)‐amino‐phosphonovaleric acid (APV 30 to 300 μm) concentration‐dependently antagonized and slowed the onset kinetics of NMDA responses.
Peripheral endotoxin induces hypothalamic immunoreactive interleukin‐1β in the rat
Authors: Hillhouse E.W. , Mosley K.
Published: July 2012

Interleukin‐1 (IL‐1) is a polypeptide produced by a variety of cells and contributes to the general host response to inflammation. It displays a wide spectrum of inflammatory, metabolic, physiological, haematopoietic and immunological activities. Brain cells, including neurones, microglia, endothelial cells and astrocytes can all produce IL‐1β in response to various physiological and pathological stimuli. In this report we show that peripherally administered endotoxin stimulates the appearance of immunoreactive IL‐1β (IL‐1β) in the rat hypothalamus as measured by an ultrasensitive, highly specific enzyme amplified immunometric assay for rat IL‐1β.
Characterization of propranolol‐resistant (−)‐[125I]‐cyanopindolol binding sites in rat soleus muscle
Authors: Roberts Susan J. , Molenaar Peter , Summers Roger J.
Published: July 2012

The characteristics of a propranolol‐resistant (−)‐[125I]‐cyanopindolol (CYP) binding site in rat soleus muscle were determined.

Saturation studies performed on homogenates of rat soleus muscle showed two phases of (−)‐[125I]‐CYP binding, a high affinity site (KD1 30.5 ± 16.3 pm, Bmax 9.4 ± 1.38 fmol mg−1 protein) and a lower affinity site (KD2 522.5 ± 29.1 pm, Bmax 62.19 ± 11.76 fmol mg−1 protein, n = 4).

In rat soleus muscle homogenates labelled with (−)‐[125I]‐CYP (500 pm), (−)‐propranolol competition curves were biphasic with pKD values of 8.30 ± 0.19, and 5.33 ± 0.08, n = 7.

Competition between (−)‐[125I]‐CYP (500 pm) and (±)‐tertatolol, (±)‐nadolol, (±)‐alprenolol, (±)‐CYP, and (−) and (+)‐pindolol showed that these compounds competed for binding at the propranolol‐resistant site with affinities lower than those displayed at typical β‐adrenoceptors. The atypical β‐adrenoceptor agonists BRL 37344, SR58611A and ICI D7114 and the partial agonist (±)‐CGP 12177 also competed for (−)‐[125I]‐CYP binding.

Stereoselectivity was demonstrated for the stereoisomers of alprenolol and tertatolol. The (−)‐isomers of alprenolol and tertatolol had higher affinity than their corresponding (+)‐isomers (3.1 and 2.6 fold respectively). These low stereoselectivity values are a characteristic of atypical β‐adrenoceptors.

The β‐adrenoceptor agonists, (−)‐adrenaline, (−)‐isoprenaline and (−)‐noradrenaline, all showed lower affinity than the atypical β‐adrenoceptor agonists and competition curves appeared biphasic in nature.

These results confirm the presence of a propranolol‐resistant (−)‐[125I]‐CYP binding site in rat soleus muscle. The affinities of the tested compounds at the propranolol‐resistant (−)‐[125I]‐CYP binding site show similarities to their affinities at ‘atypical’ β‐adrenoceptors in adipocytes and gastrointestinal tissues and at the cloned β3‐adrenoceptor.
Excitatory amino acid receptor‐stimulated phosphoinositide turnover in primary cerebrocortical cultures
Authors: Birrell Graham J. , Marcoux Frank W.
Published: July 2012

Characterization of excitatory amino acid‐induced accumulation of [3H]‐phosphoinositides was carried out in primary cerebrocortical cultures isolated from foetal rats.

All of the excitatory amino acid receptor agonists examined caused concentration‐dependent enhancement of phosphoinositide (PI) formation. The most potent excitatory amino acid receptor agonists were quisqualate, (1S,3R)‐1‐aminocyclopentane‐1,3‐dicarboxylic acid ((1S,3R)‐ACPD), ibotenate and glutamate with mean EC50 values of 0.9 ± 0.4 μm, 15 ± 5 μm, 15 ± 3 μm and 41 ± 8 μm respectively.

The selective ionotropic receptor antagonists kynurenic acid (1 mm), 2,3‐dihydroxy‐6‐nitro‐7‐sulphamoyl‐benzo(F)quinoxaline (NBQX, 10 μm) and (±)‐4‐(3‐phosphonopropyl)‐2 piperazinecarboxylic acid (CPP, 100 μm), failed to block responses to quisqualate, (1S,3R)‐ACPD or glutamate. d,l‐2‐Amino‐3‐phosphonopropionate (d,l‐AP3) did not block 1S,3R‐ACPD or quisqualate‐induced PI turnover, but had an additive effect with quisqualate or (1S,3R)‐ACPD.

Exposure of cultures to agonists in the absence of added extracellular calcium reduced the maximal quisqualate response by approximately 45%, revealing a two‐component concentration‐response curve. Concentration‐response curves to ibotenate and glutamate became flattened by omission of extracellular calcium, whereas (1S,3R)‐ACPD‐stimulated PI turnover was unaffected.

Pretreatment of cultures with pertussis toxin markedly inhibited PI responses evoked by (1S,3R)‐ACPD.

These results suggest that excitatory amino acid‐stimulated PI turnover in cerebrocortical cultures is independent of ionotropic receptor activation and is mediated via specific G‐protein‐linked metabotropic receptors. The partial dependence of the responses to quisqualate, ibotenate and glutamate on the presence of extracellular calcium suggests that the effects of these agonists may be mediated by more than one receptor subtype.
Modulation of vasodilatation to levcromakalim by hypoxia and EDRF in the rabbit isolated ear: a comparison with pinacidil, sodium nitroprusside and verapamil
Authors: Randall Michael D. , Griffith Tudor M.
Published: July 2012

We have used an isolated buffer‐perfused preparation of the rabbit ear to investigate the effects of hypoxia and inhibition of endothelium‐derived relaxing factor (EDRF) synthesis on the vasodilator responses to the potassium channel opener, levcromakalim (the active (−)‐enantiomer of cromakalim). The results obtained with levcromakalim have been compared with those for pinacidil, sodium nitroprusside and verapamil.

Levcromakalim relaxed preconstricted preparations with an EC50 = 343 ± 41 nm and Rmax = 80.3 ± 6.4%. Under hypoxic conditions the concentration‐response curve was significantly (P < 0.01) shifted to the left with an EC50= 118 ± 16 nm and Rmax = 89.9 ± 2.7%. Hypoxia did not influence relaxation to either pinacidil, sodium nitroprusside or verapamil.

Inhibition of EDRF synthesis with 100 μm NG‐nitro‐l‐arginine methyl ester (l‐NAME) also significantly (P < 0.001) increased the vasodilator potency of levcromakalim (EC50 = 56 ± 5 nm), and caused a similar shift in the concentration‐response curve to sodium nitroprusside. It did not influence vasodilatation to either verapamil or pinacidil. The potentiation of vasodilator responses to levcromakalim by l‐NAME was reversed by an excess of l‐arginine.

Impairment of oxidative phosphorylation with 400 nm carbonyl cyanide m‐chlorophenylhydrazone significantly (P < 0.05) increased the potency of levcromakalim (EC50 = 120 ± 20 nm) but did not influence vasodilatation to pinacidil or endothelium‐dependent relaxations to acetylcholine.

Vasodilatation to levcromakalim was augmented both by hypoxia and by inhibition of EDRF activity. Since impairment of oxidative phosphorylation increased the potency of levcromakalim but did not alter EDRF activity then the mechanism responsible for hypoxic facilitation of responses to levcromakalim is likely to be due to reduced ATP levels in hypoxic smooth muscle cells rather than a change in EDRF activity. These results suggest that levcromakalim may selectively dilate both hypoxic vessels and vessels with impaired EDRF activity. The results also point to important differences in the pharmacology of levcromakalim and pinacidil.
Selective MPP+ uptake into synaptic dopamine vesicles: possible involvement in MPTP neurotoxicity
Authors: Del Zompo M. , Piccardi M.P. , Ruiu S. , Quartu M. , Gessa G.L. , Vaccari A.
Published: July 2012

In the present study we provide evidence for a saturable, Mg2+/ATP‐ and temperature‐dependent, tetrabenazine‐, dopamine‐, and amphetamine‐sensitive uptake of 1‐methyl‐4‐phenylpyridinium ion (MPP+) in synaptic vesicles from mouse striatum.

Similarity in the properties of the vesicular uptake suggests that in the striatum dopamine and MPP+ share the vesicular carrier.

The presence of MPP+ vesicular uptake in dopamine‐rich regions such as striatum, olfactory, tubercles and hypothalamus, as well as its absence in cerebellum, cortex and pons‐medulla, suggest that monoamine vesicular carriers differ between highly and poorly dopamine‐innervated regions.

The restriction of active MPP+ uptake to the dopaminergic regions, which reflects the previously shown distribution of [3H]‐MPP+ binding sites in mouse brain membranes, indicates MPP+ as a marker of the vesicular carrier for dopamine in dopaminergic neurones.

A role in MPP+ neurotoxicity is suggested for this region‐specific, vesicular storage of the toxin.
Changes in [3H]‐PK 11195 and [3H]‐8‐OH‐DPAT binding following forebrain ischaemia in the gerbil
Authors: Kenny B.A. , MacKinnon A.C. , Spedding Michael , Brown Christine M.
Published: July 2012

A high density of [3H]‐PK 11195 binding sites was present in gerbil cortical membranes (Bmax [3H]‐PK 11195 1360 ± 71 fmol mg−1 protein) in comparison to rat cortical membranes (254 ± 21 fmol mg−1 protein). This effect was species‐specific as similar findings were obtained with hippocampal membranes (Bmax 1430 ± 111 fmol mg−1 protein in gerbil, compared to 196 ± 31 in rat).

RO 5–4864, also a peripheral type benzodiazepine compound, displayed low affinity for the [3H]‐PK 11195 site in the gerbil (pKi 6.57 ± 0.02 and 6.70 ± 0.12 in hippocampus and cortex respectively) compared to rat (pKi 8.16 ± 0.07 and 8.48 ± 0.02). Central benzodiazepine compounds, diazepam and flunitrazepam, also displayed this trend.

RO 5–4864 displaced [3H]‐PK 11195 binding from gerbil and rat cortical membranes through a competitive interaction with Hill slopes close to unity. In both tissues, saturation isotherms of [3H]‐PK 11195 binding indicated that the presence of RO 5–4864 caused changes in Kd without any effect on Bmax. In kinetic experiments, the presence of RO 5–4864 failed to modify the rate of dissociation of [3H]‐PK 11195 from equilibrium in both rat and gerbil cortical membranes.

Forebrain ischaemia in the Mongolian gerbil (5 min bilateral carotid artery occlusion) with 7 days recovery caused a significant (P < 0.05) decrease in the density of hippocampal 5‐HT1A binding sites labelled by [3H]‐8‐OH‐DPAT (Bmax control, 393 ± 33 fmol mg−1 protein; ischaemic, 289 ± 21 fmol mg−1 protein) and an increase (P < 0.01) in [3H]‐PK 11195 binding sites (Bmax control, 1430 ± 111 fmol mg−1 protein; ischaemic, 2160 ± 170 fmol mg−1 protein). Ischaemia and recovery had no effect on the affinity of either ligand.

Autoradiography experiments in gerbil brain sections revealed that the ischaemia‐induced increase in [3H]‐PK 11195 binding was consistent and significant in the CA1 subfield on the hippocampus (control, 152 ± 42 fmol mg−1 tissue; ischaemic; 314 ±; 43 fmol mg−1 tissue).
A comparison of the effects of polyarginine and stimulated eosinophils on the responsiveness of the bovine isovolumic bronchial segment preparation
Authors: Omari Taher , Sparrow Malcolm P. , Church Martin K. , Holgate Stephen T. , Robinson Clive
Published: July 2012

The bovine isovolumic bronchial segment preparation has been used to study the sensitivity and responsiveness of bronchial smooth muscle after various manipulations.

Addition of acetylcholine (ACh) to the lumen of the segments elicited an increase in intraluminal pressure as a result of contraction of the airway smooth muscle. However, the increases in intraluminal pressure were greater when the ACh was added to the adventitial surface of the preparation.

Addition of polyarginine to the bronchial lumen for 60–120 min resulted in an increased magnitude of response and greater than 100 fold increase in sensitivity to ACh administered into the lumen. Depolarizations induced by KCl were similarly enhanced when the solution was added into the lumen. In contrast, the sensitivity and responsiveness to ACh or K+‐induced depolarization administered adventitially was unchanged.

The mechanical disruption of the epithelium produced a 32 fold increase in sensitivity to ACh introduced via the lumen, whereas the sensitivity to ACh added adventitially remained unaltered.

Addition of polyarginine to the adventitial bathing medium resulted in no change in the responsiveness or sensitivity to ACh, irrespective of whether the ACh was given intraluminally or adventitially.

Histological examination revealed that polyarginine caused extensive disordering of the normal architecture of the bronchial epithelium. Taken together with the unaltered responsiveness to adventitial ACh (i.e. lack of change in intrinsic muscle sensitivity) these observations suggest that the effect of polyarginine was most likely due to disruption of a diffusion barrier.

In contrast to the effects of polyarginine, the only effect of stimulated eosinophils was to produce a small diminution in the responsiveness to ACh that had been added adventitially.
Induction by endothelin‐1 of epithelium‐dependent relaxation of guinea‐pig trachea in vitro: role for nitric oxide
Authors: Filep János G. , Battistini Bruno , Sirois Pierre
Published: July 2012

The purpose of the present experiments was to study the underlying mechanisms responsible for the relaxant action of endothelin‐1 (ET‐1) in the guinea‐pig trachea in vitro.

In tracheal strips precontracted (60–70% of the maximum) with carbachol, ET‐1 (1–100 nm) evoked slowly developing concentration‐dependent relaxations. Preincubation of the tissues with the thromboxane A2/prostaglandin H2 receptor antagonist, BM 13505 (5 μm) significantly potentiated the relaxant response to ET‐1.

Removal of the epithelium changed the response of precontracted tracheal preparations to ET‐1 from a relaxation to a sustained contraction.

ET‐1‐induced relaxations were abolished by methylene blue (10 μm) and were almost completely attenuated by oxyhaemoglobin (5 μm) and NG‐monomethyl‐l‐arginine (l‐NMMA, 100 μm), an inhibitor of nitric oxide synthesis, but were not altered by indomethacin (10 μm).

In tracheal strips under passive tension, ET‐1 (1–100 nm) elicited dose‐dependent contractions. The sensitivity of tissues to ET‐1 was significantly enhanced by removal of the epithelium (apparent EC50 values were 28.1 ± 4.1 and 12.5 ± 0.8 nm in intact and rubbed trachea, respectively, n = 7, P < 0.01).

Preincubation of intact tracheal strips with methylene blue, oxyhaemoglobin or l‐NMMA did not mimic the effect of epithelium removal on ET‐1‐induced contractions.

There was a concentration‐dependent increase in thromboxane A2 but not in PGE2 and prostacyclin release from intact tracheal strips following stimulation with ET‐1 (5–100 nm).

These results show that ET‐1 exerts a dual action on guinea‐pig isolated trachea: it evokes contractions at low resting tone, whereas it induces relaxations at higher resting tone. The relaxant action of ET‐1 may be mediated by nitric oxide released from epithelial cells and resultant activation of smooth muscle guanylate cyclase.
In vivo microdialysis of noradrenaline overflow: effects of α‐adrenoceptor agonists and antagonists measured by cumulative concentration‐response curves
Authors: van Veldhuizen M.J.A. , Feenstra Matthijs G.P. , Heinsbroek Rob P.W. , Boer Gerard J.
Published: July 2012

The purpose of the present study was to compare the effects of several α‐adrenoceptor agonists and antagonists on cerebral cortical overflow of endogenous noradrenaline (NA) in freely moving rats. One or two days after the implantation of transcerebral dialysis tubes in the frontoparietal cortex, extracellular NA levels were monitored on‐line with high performance liquid chromatography and electrochemical detection. The drugs were applied locally via the dialysis membrane, and effects on NA overflow were determined in cumulative concentration‐response curves.

The average basal cortical NA overflow of all experiments was 0.25 pg min−1. The α2‐adrenoceptor agonists caused a concentration‐dependent decrease in NA levels. UK‐14,304 was the most potent and B‐HT 933 the least potent agonist. The maximal decrease in NA overflow was to 10–15% of control levels after UK‐14,304 or moxonidine, to 30% after clonidine and to 50% after B‐HT 933 administration. Continuous activation of the presynaptic α2‐adrenoceptor with 10−6 m UK‐14,304 caused a decrease in NA levels to 40–50% of basal levels. This decrease was reached within 1 h and remained stable for the entire 3 h measurement period. The α1‐adrenoceptor agonists, phenylephrine and methoxamine, induced an increase in NA levels to 225% and 300%, respectively, at a concentration of 10−3 m.

Local application of α2‐adrenoceptor antagonists caused an increase in NA levels, with idazoxan being more potent than piperoxan. Yohimbine did not cause any significant change.

All drugs used in these in vivo experiments had in vitro recoveries across the dialysis membrane between 10 and 20%.

We conclude that microdialysis with local drug application is suitable for the comparison of the pharmacological effects of drugs with affinity for α‐adrenoceptors on cortical NA overflow in vivo, provided that the passage across the membrane is equal for the different drugs.
Endothelin receptors mediating contraction in goat cerebral arteries
Authors: Salom Juan B. , Torregrosa Germán , Barberá María D. , Jover Teresa , Alborch Enrique
Published: July 2012

The aim of the present study was to identify the subtype of receptor mediating contraction to endothelin‐1 and sarafotoxin S6b in goat isolated middle cerebral arteries.

Endothelin‐1, endothelin‐2 and endothelin‐3 contracted cerebral arteries in a concentration‐dependent manner. Although the three peptides were full agonists, the order of potency was endothelin‐1 = endothelin‐2 > endothelin‐3, with a relative potency of endothelin‐1 and endothelin‐2 versus endothelin‐3 of ∼280. Sarafotoxin S6b induced concentration‐dependent contractions with lower potency than endothelin‐1/endothelin‐2, higher potency than endothelin‐3 and a higher maximum response than the three endothelins.

The selective ETA‐receptor antagonist, BQ‐123, did not induce changes in either the resting tension or in the active tone developed by depolarization. In contrast, BQ‐123 produced concentration‐dependent relaxations of endothelin‐1‐precontracted cerebral arteries, and to a greater extent of sarafotoxin S6b‐precontracted arteries.

Concentration‐response curves to endothelin‐1 and sarafotoxin S6b were competitively antagonized by BQ‐123 (pA2 of 7.43 ± 0.12 and 8.41 ± 0.09, respectively). In contrast, BQ‐123 had no effect on 5‐hydroxytryptamine‐elicited contractions even at 10−6 M.

It is concluded that both the order of potency of endothelin isopeptides and the antagonism of BQ‐123 point to the existence of ETA receptors mediating vasoconstriction to endothelin‐1 and sarafotoxin S6b in the goat middle cerebral artery. The different antagonistic potency of BQ‐123 against endothelin‐1 and sarafotoxin S6b suggests the existence of subtypes of ETA receptors.
Effects of beraprost on the transmembrane potentials of guinea‐pig ventricular muscles during normoxia and hypoxia‐reoxygenation
Authors: Ueno Yuji , Shigenobu Koki , Nishio Shintaro
Published: July 2012

The present study was performed to determine whether beraprost, a new stable analogue of prostacyclin, may exert beneficial effects on the transmembrane action potentials during normoxia and hypoxia‐reoxygenation in isolated right ventricular muscles of the guinea‐pig.

Under normal oxygenation, beraprost (0.01–100 μmol−1) had no effects on the electrophysiological parameters.

Hypoxic conditions induced a decrease in action potential duration (APD) without affecting other action potential parameters. Beraprost inhibited this hypoxia‐induced decrease in APD. However, beraprost had no effect on the decrease in contractile force induced by hypoxia, whereas it significantly improved the recovery of contractile force after reoxygenation.

Pinacidil‐induced shortening of APD was not antagonized by beraprost.

Hypoxia significantly decreased the myocardial adenosine triphosphate (ATP) level, which was also prevented by beraprost.

These results suggested that beraprost may inhibit the hypoxia‐induced shortening of APD by some mechanisms which contribute to the maintenance of muscle ATP level.
Existence of rolipram‐sensitive phosphodiesterase in rat megakaryocyte
Authors: Akaike Norio , Uneyama Hisayuki , Kawa Kazuyoshi , Yamashita Yoshiro
Published: July 2012

The effect of rolipram (ME3176) on ADP‐ and IP3‐induced repetitive IK(Ca) in rat megakaryocyte was investigated by use of the nystatin perforated patch and conventional whole‐cell patch‐clamp techniques.

The ADP‐induced IK(Ca) was depressed by treatment with rolipram in a concentration‐dependent manner. The inhibition by rolipram disappeared after treatment with a cyclic nucleotide‐dependent protein kinase inhibitor, H‐8. The inhibition of IK(Ca) was also observed in the presence of cyclic AMP accumulating agents such as forskolin and isobutylmethylxanthine (IBMX).

Rolipram enhanced the inhibitory action of forskolin, suggesting that rolipram facilitates the accumulation of cyclic AMP by blocking its breakdown. Similar results was obtained with adenosine, an endogenous adenylate cyclase activator.

Intracellular application of inositol trisphosphate (IP3) induced repetitive IK(Ca) in megakaryocytes. The induced IK(Ca) was also inhibited by rolipram and by other cyclic AMP accumulating agents.

It was concluded that megakaryocytes possess rolipram‐sensitive phosphodiesterase (PDE), which was not detected in platelets, but plays a distinct modulatory role in megakaryocytes for generating ADP‐induced IK(Ca).
Mechanism of carbachol‐evoked contractions of guinea‐pig ileal smooth muscle close to freezing point
Authors: Blackwood A.M. , Bolton T.B.
Published: July 2012

The effect of lowering the temperature to near freezing‐point upon the contractions and [3H]‐inositol phosphate responses to carbachol were investigated in longitudinal smooth muscle from the guinea‐pig ileum.

The peak amplitude of the contraction to a single application of 100 μm carbachol was the same at 37°C and temperatures near freezing‐point. However, the sensitivity to carbachol was reduced upon lowering the temperature and the time to peak contraction was increased from 5–10 s to 2–10 min. Even when the temperature was maintained near freezing‐point, washing off carbachol produced a relaxation and eventual return of tension to basal levels.

Incubating the tissue in 140 mm K+, calcium‐free solution or in calcium channel antagonists significantly reduced the carbachol‐induced contraction to 10–30% of the control at 37°C and also at 3°C. Thus the majority of the activator calcium required for contraction entered the tissue via voltage‐dependent calcium channels (VDCs) at both 37°C and 3°C.

The contractions produced by high potassium solutions were less at temperatures close to freezing‐point than those at 37°C suggesting that voltage‐dependent calcium entry was inhibited as the temperature was lowered.

A small part of the contractile response to 100 μm carbachol was resistant to the removal of extracellular calcium at both 37°C and 3°C and this component was increased under depolarizing conditions. This suggests that the release of stored calcium contributes to a minor degree to contraction at both 37°C and 3°C.

Although 100 μm carbachol produced a statistically significant rise in several [3H]‐inositol phosphate isomers at both 37°C and 3°C, the production of [3H]‐inositol phosphates was less at 3°C than at 37°C and the increase in their production caused by carbachol was much slower.

These results suggest that the carbachol‐induced contraction at 3°C utilizes both calcium entry through VDCs and calcium release from intracellular stores, as at 37°C. The components of the responses dependent upon intracellular calcium release at 37°C and at temperatures near freezing‐point were similar. However, the production of [3H]‐inositol phosphates, including the calcium‐mobilizing second messenger inositol (1,4,5) trisphosphate (Ins(1,4,5)P3), is reduced at such low temperatures.
Effects of cromakalim on the electrical slow wave in the circular muscle of guinea‐pig gastric antrum
Authors: Katayama N. , Huang S.‐M. , Tomita T. , Brading Alison F.
Published: July 2012

In circular muscle strips of the antrum of guinea‐pig stomach, the effects of cromakalim were studied on mechanical activity and intracellular membrane potential.

Cromakalim inhibited mechanical activity at concentrations higher than 1 μm, accompanied by membrane hyperpolarization and a decrease in membrane resistance. The hyperpolarization was markedly potentiated in K+‐free solution and was still observed in the absence of Na+.

Slow wave electrical activity was relatively resistant to cromakalim. Changes in its amplitude and frequency were not consistent but blockade of slow waves was never observed. In many preparations cromakalim induced spike‐like potentials at the top of slow waves, or when spike‐like potentials already existed they were potentiated. However, mechanical activity was always inhibited.

Inhibition by cromakalim of the phasic contractions associated with the slow waves, could not be reversed by increasing the external K+ concentration (12–30 mm).

The results suggest that in guinea‐pig stomach muscle mechanical suppression by cromakalim does not simply result from membrane hyperpolarization or from inhibition of slow waves. A clear dissociation was found between the mechanical and electrical activities. Slow waves, particularly their frequency, are relatively insensitive to membrane hyperpolarization.
The effect of endothelins on nitric oxide and prostacyclin production from human umbilical vein, porcine aorta and bovine carotid artery endothelial cells in culture
Authors: White David G. , Mundin Jason W. , Sumner Michael J. , Watts Ian S.
Published: July 2012

This study has investigated the effects of the endothelin isopeptides, endothelin‐1 (ET‐1), ET‐2 and ET‐3 on the production of the endothelium‐derived relaxing factors, nitric oxide (NO) and prostacyclin (PGI2) from primary cultures of endothelial cells obtained from human umbilical vein (HUVECS), porcine aorta (PAECS) and bovine carotid artery (BCAECS).

NO generation was assessed indirectly by measuring production of cyclic GMP and PGI2 formation was measured by radioimmunoassay of 6‐keto PGF1α.

In HUVECS, histamine (1 μm) increased cyclic GMP and 6‐keto PGF1α production by 12.6 ± 2.0 and 4.9 ± 0.7 fold respectively over the corresponding basal values. Haemoglobin (10 μm) and the NO synthase inhibitor NG‐monomethyl‐l‐arginine (10 μm) significantly inhibited the increase in cyclic GMP formation in response to histamine but had no effect on 6‐keto PGF1α production. In contrast to histamine, the endothelin isopeptides (ET‐1, ET‐2 and ET‐3; 0.01–1000 nm) produced no significant change in either cyclic GMP or 6‐keto PGF1α production in HUVECS.

In a separate series of experiments, ET‐3 (0.01–1000 nm) also failed to produce any significant change in cyclic GMP or 6‐keto PGF1α production from primary cultures of PAECS and BCAECS. In contrast, bradykinin (0.1 μm) and sodium nitroprusside (1 mm) were used as positive control agents and increased cyclic GMP production in these cells.

In conclusion, the endothelin isopeptides do not release NO and PGI2 from primary cultures of HUVECS, PAECS and BCAECS. This suggests that endothelin receptors are either absent from these cells or are not coupled to NO or PGI2 production.
Characterization of the 5‐hydroxytryptamine receptor mediating the positive inotropic response in guinea‐pig isolated left atria
Authors: Lattimer Norman , Gupta Paul , Rhodes Keith F.
Published: July 2012

5‐Hydroxytryptamine (5‐HT), in the presence of propranolol (1 μm), atropine (3 μm) and ketanserin (1 μm), induced a positive inotropic response of guinea‐pig isolated electrically paced left atria (pEC50 = 7.52). The positive inotropic response was mimicked by α‐methyl‐5‐HT (pEC50 = 7.26) and 5‐carboxamidotryptamine (5‐CT; pEC50 = 6.56) but not by sumatriptan or 1‐(m‐chlorophenyl) piperazine (m‐CPP).

The 5‐HT induced positive inotropic response was competitively antagonized by both mesulergine (pA2 = 7.68) and methiothepin (pA2 = 6.67). Methysergide was a surmountable antagonist at 3 nm producing a rightward shift in the 5‐HT concentration‐response curve giving an apparent pA2 = 9.2 with no significant reduction in the maximum. At higher concentrations, methysergide behaved as an insurmountable antagonist, significantly reducing the maximum response to 5‐HT as well as producing rightward shifts in the 5‐HT concentration‐response curves.

The 5‐HT‐induced positive inotropic response was not antagonized by either tropisetron (10 μm) or yohimbine (10 μm).

The guinea‐pig atrial 5‐HT receptor does not satisfy the criteria for any of the currently recognised 5‐HT receptor subtypes and appears to have some similarities to the atypical 5‐HT receptors previously described in other peripheral tissues.
Induction by endogenous noradrenaline of an α1‐adrenoceptor‐mediated positive inotropic effect in rabbit papillary muscles
Authors: Hattori Yuichi , Takeda Youji , Nakaya Haruaki , Kanno Morio
Published: July 2012

The possible involvement of α1‐adrenoceptors in the inotropic and electrophysiological responses to endogenous noradrenaline released by tyramine was examined in rabbit papillary muscles.

A concentration‐dependent positive inotropic effect was produced by tyramine. This effect of tyramine was not observed in muscles from rabbits pretreated with reserpine.

The positive inotropic effect of tyramine was greatly inhibited by propranolol, but not altered by prazosin. However, when β‐adrenoceptors were blocked by pretreatment with propranolol, tyramine still produced a positive inotropic effect, an effect which was antagonized by prazosin.

Tyramine caused a decrease in action potential duration (APD) and an increase in action potential amplitude in a concentration‐dependent manner. Isoprenaline also produced the same electrophysiological effects. These electrophysiological effects of both agents were inhibited by propranolol.

When β‐adrenoceptors were blocked by propranolol, the observed prazosin‐sensitive positive inotropic effect of tyramine was not accompanied by any change in APD. In contrast, APD was markedly prolonged by α1‐adrenoceptor stimulation with phenylephrine in the presence of propranolol, in association wh the positive inotropic effect.

It is concluded that in rabbit papillary muscles, endogenous noradrenaline causes a positive inotropic effect predominantly mediated by β‐adrenoceptors, but can still evoke a positive inotropic effect through α1‐adrenoceptors when β‐adrenoceptor stimulation is eliminated. This suggests that the α1‐adrenoceptor‐mediated positive intropic mechanism(s) may be masked by simultaneous activation of β‐adrenoceptors. In addition, this study indicates that APD prolongation is not involved in the α1‐adrenoceptor‐mediated inotropic responses to endogenous noradrenaline.
Release‐regulating dopamine autoreceptors in human cerebral cortex
Authors: Fedele Ernesto , Andrioli Gian Carlo , Ruelle Antonio , Raiteri Maurizio
Published: July 2012

Slices from fresh specimens of human neocortex which had to be removed during neurosurgery to reach subcortical tumours were labelled with [3H]‐dopamine and stimulated electrically. Quinpirole, a selective dopamine D2 receptor agonist, inhibited the stimulated tritium overflow (EC50 = 25 nm; maximal inhibition: about 80% at 10 μm). The selective D1 receptor agonist, SKF 38393, was inactive up to 10 μm. Quinpirole was antagonized by the D2 receptor antagonist (−)‐sulpiride (apparent pA2 = 8.26). Thus dopaminergic axon terminals in the human mesocortical pathway possess autoreceptors of the D2 type.
Effects of LY274614, a competitive NMDA receptor antagonist, on the micturition reflex in the urethane‐anaesthetized rat
Authors: Yoshiyama M. , Roppolo J.R. , Thor K.B. , de Groat W.C.
Published: July 2012

The effects of 3 competitive N‐methyl‐d‐aspartate (NMDA) receptor antagonists, LY274614, LY233536 and LY235723, on the micturition reflex and external urethral sphincter EMG activity, were examined either under isovolumetric conditions or during continuous filling cystometry in urethane‐anaesthetized (1.2 g kg−1, s.c.) rats.

Intravenous administration of LY274614 (3–30 mg kg−1) inhibited in a dose‐dependent fashion both bladder and sphincter activity in the intact rats. In addition, the volume threshold for inducing micturition was increased and voided volume was decreased.

Intrathecal administration of LY274614 (0.06–30 μg) similarly inhibited bladder and sphincter activity during cystometry in intact rats.

In chronic spinal cord (T6−T8) transected rats LY274614 (0.1–30 mg kg−1, i.v.) did not alter bladder activity under isovolumetric conditions but decreased the amplitude of micturition contractions and sphincter EMG activity during cystometry at a dose of 10–30 mg kg−1.

The inhibitory effects of i.v. administration of LY274614, on bladder and sphincter activity induced by infusion of chemical irritant (0.1 % acetic acid) or saline, were similar; except that a slightly larger dose was needed to inhibit sphincter activity during acetic acid infusion.

Peak amplitude of micturition contractions recovered to 50% of control 3 h following i.v. (30 mg kg−1) or i.t. (6 μg) administration of LY274614.

Two other chemically related NMDA antagonists, LY233536 and LY235723 produced similar but less potent effects than LY274614 when given i.v.

These data indicate that glutamatergic transmitter mechanisms at the level of the spinal cord are important in modulating bladder activity in the intact animal, but that these mechanisms do not contribute to bladder reflexes in the chronic spinal rat. These mechanisms may, however, contribute to sphincter activity in both intact or chronic spinal rats.
Effects of hydroxyethylrutosides on the permeability of microvessels in the frog mesentery
Authors: Kendall S. , Towart R. , Michel C.C.
Published: July 2012

We have investigated the effects of a standardised mixture of hydroxyethylrutosides (HR, Venoruton), a mixture of five of its main components (M) and each of the five components separately (7‐mono‐HR, 7,4′‐di‐HR, 7,3′,4′‐tri‐HR, 5,7,3′,4′‐tetra‐HR and 7,3′4′‐tri HQ) upon the permeability of single perfused capillaries and venules in the mesenteries of pithed frogs.

In each experiment, the hydraulic permeability (Lp) of a single perfused microvessel and the effective osmotic pressure (σΔπ) exerted by macromolecules across its walls were estimated by a microcclusion technique, first during control perfusion and then in the presence of a known concentration of test substance.

HR, M and 7,4′‐di‐HR reduced Lp in a similar concentration‐dependent manner over the range of 1 μg ml−1 to 1 mg ml−1 (maximum reduction was to 40% of control Lp at 1 mg ml−1). At perfusate concentrations greater than 1 mg ml−1, these substances reduced Lp to a lesser extent. While the four other test substances reduced Lp significantly when their perfusate concentrations equalled or exceeded 100 μg ml−1, they were all less potent than 7,4′‐di‐HR.

The reduction in Lp induced by the mixture of flavonoids was only slightly reversed by subsequent perfusion with flavonoid‐free solutions.

When permeability was increased by perfusing with protein‐free solutions, both HR and 7,4′‐di‐HR reduced and then reversed the increase in Lp in a concentration‐dependent manner over the range of 1 μg ml−1 to 100 μg ml−1. None of the other component flavonoids was effective in restoring Lp under these conditions.
Inhibition of rat cerebellar nitric oxide synthase by 7‐nitro indazole and related substituted indazoles
Authors: Babbedge R.C. , Bland‐Ward P.A. , Hart S.L. , Moore P.K.
Published: July 2012

7‐Nitro indazole (7‐NI) produces potent inhibition of rat cerebellar nitric oxide synthase (NOS) with an IC50 of 0.9 ± 0.1 μm (n = 6). NOS activity is dependent on the presence of both exogenous CaCl2 and NADPH. The inhibitory potency of 7‐NI remained unaltered in the presence of different concentrations of either CaCl2 (0.75–7.5 mm) or NADPH (0.05–5.0 mm).

Kinetic (Lineweaver‐Burke) analysis of the effect of 7‐NI on rat cerebellar NOS revealed that inhibition was of a competitive nature with a Ki value of 5.6 μm. The Km of cerebellar NOS with respect to L‐arginine was 2.5 μm.

The following indazole derivatives (IC50 values shown in parentheses, all n = 6) caused concentration‐related inhibition of rat cerebellar NOS in vitro: 6‐nitro indazole (31.6 ± 3.4 μm), 5‐nitro indazole (47.3 ± 2.3 μm), 3‐chloro indazole (100.0 ± 5.5 μm), 3‐chloro 5‐nitro indazole (158.4 ± 2.1 μm) and indazole (177.8 ± 2.1 μm). The IC50 values for 5‐amino indazole, 6‐amino indazole and 6‐sulphanilimido indazole were in excess of 1 mm; 3‐indazolinone was inactive.

7‐NI (10 mg kg−1) administered i.p. to rats produced 60 min thereafter a significant inhibition of NOS activity in cerebellum (31.1 ± 3.2%, n = 6), cerebral cortex (38.2 ± 5.6%, n = 6), hippocampus (37.0 ± 2.8%, n = 6) and adrenal gland (23.7 ± 3.0%, n = 6). NOS activity in olfactory bulb and stomach fundus were unchanged.

These results indicate that 7‐NI is a potent and competitive inhibitor of rat brain NOS in vitro and also inhibits NOS in different brain regions and in the adrenal gland in vivo. Inhibition of NOS is a characteristic property of the indazole nucleus. Nitration of the indazole ring at positions 5, 6 and 7 results in a graded increase in inhibitory potency. Indazole‐based inhibitors of NOS may prove useful tools with which to evaluate the biological roles of nitric oxide in the central nervous system.
Centrally administered ouabain aggravates rapid‐eye‐movement‐sleep‐related bradyarrhythmias in freely moving rats
Authors: Sato Takayuki , Seto Katsuo
Published: July 2012

The effects of continuous infusions of ouabain on bradyarrhythmias (cardiac pauses for 0.5 s or longer) during sleep were examined in freely moving Wistar‐Kyoto rats.

In a control group (n = 7), saline was infused into both the lateral ventricle and the femoral vein. In an intracerebroventricular (i.c.v.) ouabain group (n = 7), ouabain was infused centrally, such that each rat received three stepped doses of 1, 10, and 100 ng kg−1 h−1 for 3 days at each dose, while saline was infused systemically. In an intravenous (i.v.) ouabain group (n = 7), ouabain was infused systemically at the same doses as the i.c.v. ouabain received, while the simultaneous i.c.v. infusion of saline was carried out.

Three‐day i.c.v. infusions of the three stepped doses of ouabain caused a dose‐dependent increase in the frequency of bradyarrhythmias during rapid‐eye movement (REM) sleep without affecting the time spent in REM sleep, arterial pressure, average heart rate, or the frequency of bradyarrhythmias during non‐REM sleep. Intravenous ouabain or i.c.v. saline had no effects on the frequency of bradyarrhythmias.

Intrinsic CNS activity during REM sleep may be involved in the centrally mediated arrhythmogenic properties of ouabain during sleep.
Functional evidence for multiple receptor activation by κ‐ligands in the inhibition of spinal nociceptive reflexes in the rat
Authors: Herrero Juan F. , Headley P. Max
Published: July 2012

The evidence for κ‐receptor heterogeneity is equivocal. We have now investigated this question by comparing the effects of five putatively selective κ‐agonists. The parameters examined were: the relative potencies in depressing hindlimb flexor muscle reflexes to noxious pinch stimuli in both spinalized and sham‐spinalized rats; the reversibility of these effects by naloxone; and the effects on blood pressure.

Two types of drug effect was discriminated. One drug group, represented by U‐50,488, U‐69,593 and PD‐117,302, had a potency ratio between sham and spinalized rats approximately 10 fold lower than the other group, which comprised GR103545 and CI‐977.

Under sham‐spinalized conditions, CI‐977 and GR103545 at high doses caused only sub‐maximal reductions of spinal reflexes. U‐50,488 was still active when superimposed on these high doses of GR103545.

Naloxone reversed all effects, but different doses were required between compounds, with GR103545 taking some 20 times higher doses of naloxone to cause reversal than did U‐50,488.

The effects on mean arterial pressure were opposite between groups.

The results imply that more than one type of naloxone‐sensitive non‐μ opioid receptor must be involved in mediating these complex actions of ligands that have been claimed to be selective for κ‐receptors.
The effects of single and repeated anorectic doses of 5‐hydroxytryptamine uptake inhibitors on indole levels in rat brain
Authors: Caccia Silvio , Anelli Marina , Codegoni Anna Maria , Fracasso Claudia , Garattini Silvio
Published: July 2012

The effects of acute and repeated equiactive anorectic doses (ED50) of recently marketed 5‐hydroxytryptamine (5‐HT) uptake inhibitors on the content of brain indoles were compared in rats in relation to the brain regional concentrations of unchanged drug and its known active metabolite.

Single intraperitoneal (i.p.) doses of the anorectic ED50 of fluoxetine (35 μmol kg−1), fluvoxamine (60 μmol kg−1), paroxetine (20 μmol kg−1) and sertraline (49 μmol kg−1) slightly reduced brain 5‐hydroxyindoleacetic acid (5‐HIAA), with regional differences, this being compatible with 5‐HT uptake blockade. Only fluvoxamine and sertraline significantly enhanced the content of 5‐HT in the cortex.

The regional sensitivity to the acute effect of a given drug was not related to any preferential drug distribution, as these compounds distributed almost uniformly in the brain areas considered (cortex, striatum and hippocampus).

Repeating the same doses twice daily, i.p. for 14 days, however gave a different picture, fluvoxamine having little or no effect on the content of indoles and fluoxetine, paroxetine and sertraline lowering both 5‐HT and 5‐HIAA in all the brain regions compared to pair‐fed control animals, 1 h after the last dose.

One week later only fluoxetine‐treated animals still had reduced brain 5‐HT, this probably being related to the accumulation of its main metabolite norfluoxetine in rat brain after chronic dosing.

Further studies on the relationship between the long‐term neurochemical changes and anorectic activity are required but it appears from these results that anorectic drugs with similar acute effects on 5‐HT uptake may differ in their long‐term effects on 5‐HT mechanisms.