bluuebunny/crossref_metadata_2025_split huggingface dataset:
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.
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.