bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of lisinopril on electromechanical properties and membrane currents in guinea‐pig cardiac preparations
Authors: Valenzuela Carmen , Pérez Onésima , Casis Oscar , Duarte Juan , Pérez‐Vizcaino Francisco , Delpón Eva , Tamargo Juan
Published: July 2012

The effects of the angiotensin‐converting enzyme inhibitor, lisinopril, were studied in guinea‐pig atria and papillary muscles and in single isolated ventricular cells.

In isolated right atria, lisinopril (0.001–10 μm) decreased the amplitude and rate of the spontaneous contractions. In electrically driven left atria this negative inotropic effect was accompanied by a shortening of the time to peak tension and time for total contraction.

Lisinopril did not modify the electrophysiological characteristics of the ventricular action potentials recorded in papillary muscles perfused with normal Tyrode solution or elicited by isoprenaline in papillary muscles perfused with 27 mm K Tyrode solution.

In single ventricular cells, lisinopril (10 μm) had no effect on the inward L‐type Ca2+ (ICa,L), the inward rectifier (IK1) or the delayed rectifier K+ currents (IK). However, it abolished the stimulation‐dependent facilitation of the L‐type Ca2+ current.

These results indicate that the negative inotropic effect of lisinopril cannot be explained by a decrease in Ca2+ entry through L‐type channels and suggest that lisinopril may possibly act at an intracellular site to reduce contractile force.
Antagonist effects of seglitide (MK 678) at somatostatin receptors in guinea‐pig isolated right atria
Authors: Dimech J. , Feniuk W. , Humphrey P.P.A.
Published: July 2012

Somatostatin (SS) exerts a negative inotropic effect in isolated atria. Here we report that in guinea‐pig isolated right atria, seglitide, a potent cyclic hexapeptide somatostatin agonist, behaves as a competitive somatostatin receptor antagonist with pA2 values against SS14, SS25 and SS28, of 6.50 ± 0.40, 6.24 ± 0.08 and 6.09 ± 0.06, respectively. Seglitide had little or no effect on the negative inotropic action of carbachol or N6‐cyclohexyladenosine. Our findings indicate that the receptor‐response coupling characteristics of guinea‐pig atria are such that in this preparation seglitide has low intrinsic activity and behaves specifically as a somatostatin receptor antagonist.
Antagonism of the inhibitory action of neuropeptide Y (NPY) in guinea‐pig trachea by the C‐terminal fragment NPY (2–36)
Authors: Benchekroun M. Taoudi , St‐Pierre S. , Fournier A. , Cadieux A.
Published: July 2012

The C‐terminal fragment of neuropeptide Y (NPY), NPY(2–36) was used as a means of discriminating between two differently located NPY receptor sites in guinea‐pig trachea. Both NPY and NPY(2–36) reduced the maximal relaxation elicited by vasoactive intestinal peptide (VIP). In contrast, the C‐terminal fragment did not mimic the inhibitory action of NPY on the noradrenaline‐(NA) evoked response. However, pretreatment of the trachea with 30 nm NPY(2–36), 5 min before generating NA and VIP concentration‐response curves in the presence of NPY, abolished the inhibitory effect of NPY on NA‐elicited response but did not affect the modulatory action of NPY on VIP‐induced relaxation. These results suggest that the two differently located NPY receptor sites in guinea‐pig trachea are of two distinct subpopulations.
Inositol 1,4,5‐trisphosphate and inositol 1,3,4,5‐tetrakisphosphate binding sites in smooth muscle
Authors: Zhang Lubo , Bradley Michael E. , Khoyi Mohammad , Westfall David P. , Buxton Iain L.O.
Published: July 2012

We have previously demonstrated that activation of M3 muscarinic receptors increases inositol 1,4,5‐trisphosphate (InsP3) and inositol 1,3,4,5‐tetrakisphosphate (InsP4) accumulation in colonic smooth muscle.

In the present study, we demonstrate the existence of InsP3 and InsP4 binding sites in colonic circular smooth muscle by use of radioligand binding methods. Both [3H]‐InsP3 and [3H]‐InsP4 bound rapidly and reversibly to a single class of saturable sites in detergent‐solubilized colonic membranes with affinities of 5.04 ± 1.03 nm and 3.41 ± 0.78 nm, respectively. The density of [3H]‐InsP3 binding sites was 335.3 ± 19.3 fmol mg−1 protein which was approximately 2.5 fold greater than that of [3H]‐InsP4 sites (127.3 ± 9.1 fmol mg−1 protein).

The two high affinity inositol phosphate binding sites exhibited markedly different pH optima for binding of each radioligand. At pH 9.0, specific [3H]‐InsP3 binding was maximal, whereas [3H]‐InsP4 binding was only 10% that of [3H]‐InsP3. Conversely, at pH 5.0, [3H]‐InsP4 binding was maximal, while [3H]‐InsP3 binding was reduced to 15% of its binding at pH 9.0.

InsP3 was about 20 fold less potent (K1 = 50.7 ± 8.3 nm) than InsP4 in competing for [3H]‐InsP4 binding sites and could compete for only 60% of [3H]‐InsP4 specific binding. InsP4 was also capable of high affinity competition with [3H]‐InsP3 binding (K1 = 103.5 ± 1.5 nm), and could compete for 100% of [3H]‐InsP3 specific binding.

[3H]‐InsP3 binding in subcellular fractions separated by discontinuous sucrose density gradients followed NADPH‐cytochrome c reductase activity, suggesting an intracellular localization for the majority of InsP3 receptors in this tissue, whereas [3H]‐InsP4 binding appeared to be equally distributed between plasma membrane and intracellular membrane populations.

These results suggest the existence of distinct and specific InsP3 and InsP4 binding sites which may represent the physiological receptors for these second messengers; differences in the subcellular distribution of these receptors may contribute to differences in their putative physiological roles.
Modulation of opioid antinociception by CCK at the supraspinal level: evidence of regulatory mechanisms between CCK and enkephalin systems in the control of pain
Authors: Noble Florence , Derrien Muriel , Roques Bernard P.
Published: July 2012

Much evidence in the literature supports the idea that cholecystokinin (CCK) interacts with opioids in pain mechanisms. In this work, we have investigated the supraspinal interactions between enkephalins and CCK, using the hot plate test in mice.

Intracerebroventricular (i.c.v.) administration of BDNL (a mixed CCKA/CCKB agonist) induced dose‐dependent antinociceptive responses on both paw lick and jump responses. In contrast, using the same test, the i.c.v. injection of BC 264 (a selective CCKB agonist) induced a hyperalgesic effect, which was restricted to paw licking and occurred only at a high dose of 2.5 nmol.

In addition, i.c.v. administration of BDNL potentiated the antinociceptive effects of the mixed inhibitor of enkephalin degrading enzymes, RB 101 and of the μ‐agonist, DAMGO, while BC 264 reduced these effects.

Furthermore, at a dose where it interacts selectively with δ‐opioid receptors, the opioid agonist BUBU reversed the hyperalgesic responses of BC 264 (2.5 nmol) but was unable to modify the effects induced by BDNL.

Taken together, these results suggest the existence of regulatory mechanisms between CCK and enkephalin systems in the control of pain. These regulatory loops could enhance the antinociceptive effects of morphine allowing the opiate doses used to be reduced and thus, possibly, the side‐effects to be minimized.
A novel metabotropic glutamate receptor agonist: marked depression of monosynaptic excitation in the newborn rat isolated spinal cord
Authors: Ishida M. , Saitoh T. , Shimamoto K. , Ohfune Y. , Shinozaki H.
Published: July 2012

Neuropharmacological actions of a novel metabotropic glutamate receptor agonist, (2S,1′R,2′R,3′R)‐2‐(2,3‐dicarboxycyclopropyl)glycine (DCG‐IV), were examined in the isolated spinal cord of the newborn rat, and compared with those of the established agonists of (2S,1′S,2′S)‐2‐(carboxycyclopropyl)glycine (l‐CCG‐I) or (1S,3R)‐1‐aminocyclopentane‐1,3‐dicarboxylic acid ((1S,3R)‐ACPD).

At concentrations higher than 10 μm, DCG‐IV caused a depolarization which was completely blocked by selective N‐methyl‐d‐aspartate (NMDA) antagonists. The depolarization was pharmacologically quite different from that caused by l‐CCG‐I and (1S,3R)‐ACPD.

DCG‐IV reduced the monosynaptic excitation of motoneurones rather than polysynaptic discharges in the nanomolar range without causing postsynaptic depolarization of motoneurones. DCG‐IV was more effective than l‐CCG‐I, (1S,3R)‐ACPD or l‐2‐amino‐4‐phosphonobutanoic acid (l‐AP4) in reducing the monosynaptic excitation of motoneurones.

DCG‐IV (30 nm–1 μm) did not depress the depolarization induced by known excitatory amino acids in the newborn rat motoneurones, but depressed the baseline fluctuation of the potential derived from ventral roots. Therefore, DCG‐IV seems to reduce preferentially transmitter release from primary afferent nerve terminals.

Depression of monosynaptic excitation caused by DCG‐IV was not affected by any known pharmacological agents, including 2‐amino‐3‐phosphonopropanoic acid (AP3), diazepam, 2‐hydroxysaclofen, picrotoxin and strychnine.

DCG‐IV has the potential of providing further useful information on the physiological function of metabotropic glutamate receptors.
Effects of NG‐nitro‐l‐arginine methyl ester on the cardiovascular system of the anaesthetized rabbit and on the cardiovascular response to thyrotropin‐releasing hormone
Authors: Seligsohn Eva E. , Bill Anders
Published: July 2012

The effects of 300 mg kg−1 of the nitric oxide (NO) inhibitor NG‐nitro‐l‐arginine methyl ester (l‐NAME) on the regional blood flow, on the flow response to 1 mg kg−1 of thyrotropin‐releasing hormone (TRH) and on cerebral blood flow autoregulation were studied in urethane anaesthetized rabbits subjected to unilateral sectioning of the cervical sympathetic chain. The blood flow measurements were performed by the tracer microspheres method.

The cerebral arteriovenous difference in oxygen saturation (CAVOD) was measured before and after the administration of l‐NAME and TRH in order to ascertain whether the effects on cerebral blood flow that were observed were secondary to changes in cerebral metabolism.

l‐NAME caused a significant decrease in blood flow in several cerebral regions; CBFtot decreased to 72 ± 4% of control (P < 0.001). An increase in blood pressure and a concurrent decrease in heart rate and cardiac output were noted.

In the eye, l‐NAME caused a reduction in uveal blood flow which was more pronounced on the sympathetically intact side; in the retina the blood flow decreased to 50% of control on both sides.

The administration of TRH in animals pretreated with l‐NAME caused a significant increase in blood pressure and cerebral blood flow.

In l‐NAME‐treated animals the CBF was not affected when the mean arterial blood pressure was increased by ligation of the abdominal aorta.

The CAVOD increased from 56.0 ± 5.2 to 73.6 ± 3.5%, 20 min after the administration of l‐NAME. In animals given 1 mg kg−1 TRH after l‐NAME the CAVOD decreased to 54.6 ± 4.6%, 5 min after the injection of TRH.

The results of the present study indicate that endogenous NO is involved in the regulation of regional blood flow and blood pressure in the anaesthetized rabbit. The reduction in cerebral blood flow that was caused by l‐NAME was not due to a reduction in cerebral metabolism. An interaction between the NO synthesis/release/effect and the sympathetic nervous system was found in the uvea. There was no evidence for a major involvement of NO in the cardiovascular responses to TRH and autoregulation of cerebral blood flow was not abolished by l‐NAME.
Effects of heparin on the vasodilator action of protamine in the rabbit mesenteric artery
Authors: Akata Takashi , Kodama Kenji , Takahashi Shosuke
Published: July 2012

The effects of protamine on the rabbit isolated small mesenteric artery were investigated both in the presence and in the absence of heparin, by the isometric tension‐recording method.

The dissociation constant for the binding of heparin to protamine has never been previously reported, so in order to minimize the effects of protamine, known to have a vasodilator action, and to examine only the effects of a heparin‐protamine complex, the experiments with heparin were performed in the presence of high concentrations of heparin (21–700 u ml−1), concentrations at which heparin itself does not affect the vascular tone.

Protamine (15–500 μg ml−1), in the absence of heparin, was found to inhibit (P < 0.05) noradrenaline (1 μm)‐induced contractions both in endothelium‐intact and in endothelium‐denuded tissues.

Such vasodilator action of protamine in either endothelium‐intact or ‐denuded tissues continued, even in the presence of excess heparin at a heparin/protamine (H/P) ratio of 1.4 uμg−1, but was almost completely blocked in the presence of a much greater excess of heparin (H/P ratio ≥ 4.7 u μg−1): heparin was present both before and during the application of protamine.

The vasodilator action of protamine in the absence of heparin was prolonged both in the endothelium‐intact and ‐denuded tissues after protamine had been washed out from the bath with Krebs solution. Although this washing out with a Krebs solution containing excess heparin (4.7 u ml−1) readily reversed such prolonged vasodilator action of protamine both in the endothelium‐denuded strips and in the endothelium‐intact strips which had been pretreated with inhibitors of the endothelium‐derived relaxing factor (EDRF) pathway, it did not affect the prolonged vasodilator action of protamine in the endothelium‐intact strips which received no pharmacological intervention.

These results suggest that: (1) only protamine, not a heparin‐protamine complex, exerts vasodilator action in vitro; (2) the vasodilator action of protamine presumably has an EDRF‐mediated component; and (3) protamine probably exerts its direct vasodilator action without entering the smooth muscle cell.
Vascular mode of action of kinin B1 receptors and development of a cellular model for the investigation of these receptors
Authors: Levesque Luc , Drapeau Guy , Grose John H. , Rioux Francis , Marceau François
Published: July 2012

Kinins exert a contractile effect on rabbit aortic rings via the stimulation of B1 receptors. Des‐Arg9‐bradykinin (BK) is more potent than BK on this receptor type. The mode of action of des‐Arg9‐BK on rabbit aortic tissue has been studied by both the aortic ring contractility assay and a cellular model using cultured aortic smooth muscle cells (SMCs).

The des‐Arg9‐BK‐induced contractions in rabbit aortic rings were unaffected by pretreatments with nifedipine, indomethacin, REV‐5901 (a 5‐lipoxygenase blocker) and LY‐83583 (a guanylyl cyclase inhibitor); however, the protein kinase inhibitors H‐7 and H‐9 significantly reduced the maximal effect of des‐Arg9‐BK.

The contractile responses to des‐Arg9‐BK in calcium‐free Krebs solution were slightly but not significantly attenuated in amplitude, as compared to paired control tissues bathed in Krebs solution, and sustained plateaus of contraction were observed in the absence of Ca2+. However, Ca2+ replenishment further increased the kinin‐induced contraction measured in Ca2+‐free bathing fluid.

Despite the lack of evidence of a mediating role for prostaglandin in the mechanical response to des‐Arg9‐BK, the kinin stimulated the release of prostacyclin from rabbit aorta rings measured as immunoreactive 6‐keto‐prostaglandin F1α (6‐keto‐PGF1α).

Smooth muscle cells (SMCs) derived from the rabbit aorta exhibit functional responses to des‐Arg9‐BK in acute release of 6‐keto‐PGF1α and of inositol phosphate turnover which were inhibited by pretreatment with the B1 receptor antagonist, Lys[Leu8]des‐Arg9‐BK, but not by the B2 receptor antagonist, Hoe‐140. Preincubation of the cells with interleukin‐1 (IL‐1) 20 h before stimulation with the kinin had no effect on basal inositol phosphate turnover, but potentiated the acute effect of des‐Arg9‐BK.

These results suggest that second mesengers derived from the action of phospholipase C are produced by SMCs when B1 receptors are activated in rabbit aortic tissue. Intracellular calcium stores are primarily mobilized by des‐Arg9‐BK, although receptor‐controlled calcium influx has not been ruled out, and may contribute to initiate the contractile responses. The maintenance of the contractile state involves protein kinase C activity and is consistent with a current model of SMC function. The cell model retains some of the cardinal properties of B1 receptor‐mediated vascular responses: endothelium‐independent PGI2 release and up‐regulation by the cytokine IL‐1. PGI2 is not involved in the mechanical response, possible because the rabbit aorta is refractory to this prostaglandin.
The effects of α‐adrenoceptor agonists on intracellular Ca2+ levels in freshly dispersed single smooth muscle cells from rat tail artery
Authors: Li Xiao‐Fang , Kargacin Margaret E. , Triggle Christopher R.
Published: July 2012

The presence of functional α‐adrenoceptors in freshly dispersed single smooth muscle cells from rat tail arteries was investigated by use of selective α‐adrenoceptor agonists and antagonists.

Cirazoline, a selective α1‐adrenoceptor agonist, caused a prazosin‐sensitive, rapid but transient increase in intracellular Ca2+, which was partially inhibited by the voltage‐dependent Ca2+ channel blocker, nifedipine.

TL99, an α2‐adrenoceptor agonist, in the presence of prazosin, initiated a slow and sustained increase in intracellular Ca2+ which was partially inhibited by yohimbine and almost completely blocked by nifedipine.

In rat tail artery, the effects (dose‐response and time‐response curves) of cirazoline and TL99 on intracellular Ca2+ levels in freshly dispersed single smooth muscle cells were comparable with those obtained with organ bath studies of ring preparations of artery.

In freshly dispersed single smooth muscle cells, the time‐course response curves induced by the selective α1‐adrenoceptor agonist, phenylephrine and the selective α2‐adrenoceptor agonist, UK14304, were similar to those observed with cirazoline and TL99, respectively.

These results indicate that: (a) functional α1‐ and α2‐adrenoceptors are present in freshly dispersed single smooth muscle cells from rat tail artery and (b) α1‐ and α2‐adrenoceptors are coupled to different cellular processes that lead to an increase in intracellular Ca2+.
Lack of effect of L‐687,414 ((+)‐cis‐4‐methyl‐HA‐966)5 an NMDA receptor antagonist acting at the glycine site, on cerebral glucose metabolism and cortical neuronal morphology
Authors: Hargreaves R.J. , Rigby M. , Smith D. , Hill R.G.
Published: July 2012

N‐methyl‐d‐aspartate (NMDA) receptor ion channel antagonists have been reported to cause pronounced increases in cerebral glucose metabolism (CMRglc) and transient reversible vacuolation within pyramidal cortical neurones. The present studies examined in rats the effects of the NMDA receptor antagonist, L‐687,414 (R‐(+)‐cis‐4‐methyl‐3‐amino‐l‐hydroxypyrolid‐2‐one; (+)‐cis‐4‐methyl‐HA‐966) on regional CMRglc and cortical neuronal morphology.

L‐687,414 was given as a steady state intravenous infusion for 4 h in a neuroprotective dose regime of 17.5 mg free base kg−1 bolus followed by 225 μg kg−1 min−1 (n = 8) or at the higher dose rate of 35 mg kg−1 bolus followed by 440 μg kg−1 min−1 (n = 10). Data were compared to a parallel series of experiments in rats given the NMDA receptor ion channel antagonist, dizocilpine for 4 h in the optimum intravenous neuroprotective dose‐regime of 0.12 mg kg−1 bolus followed by 1.8 μg kg−1 min−1 (n = 8) or at the higher dose rate of 0.4 mg kg−1 bolus followed by 6 μg kg−1 min−1 (n = 4; morphology only studied). A saline‐infused group of rats (n = 8) were used as controls.

CMRglc was studied by use of [14C]‐2‐deoxyglucose and autoradiography (n = 4 each group) whilst plasma drug levels were in a steady state during the final 45 min of the 4 h drug infusion. Effects on cortical neuronal morphology were assessed at the end of the 4 h infusion period using light microscopic techniques (n = 4–6 each group).

The results showed a selective activation of limbic CMRglc by dizocilpine at optimal neuroprotective dose levels and showed that this dose was at the threshold for the neuronal vacuolation response as 1 of 4 rats showed morphological changes in the pyramidal neurones in the posterior cingulate and retrosplenial cortices. At the higher dose rate of dizocilpine, all 4 animals showed extensive morphological changes in these cortical neurones. In contrast, L‐687,414 did not increase limbic CMRglc nor evoke vacuolation when given in the neuroprotective dose‐regime or at the higher dosage rate.

The findings of the present study suggest that neuroprotection mediated through the NMDA receptor complex can be achieved without changes in CMRglc or cortical neuronal morphology by antagonism at the glycine modulatory site.
Effect of heparin and a low‐molecular weight heparinoid on PAF‐induced airway responses in neonatally immunized rabbits
Authors: Sasaki Masahiro , Herd Caroline M. , Page Clive P.
Published: July 2012

We have investigated the effect of an unfractionated heparin preparation, a low‐molecular weight heparinoid (Org 10172) and the polyanionic molecule polyglutamic acid against PAF‐induced airway hyperresponsiveness and pulmonary cell infiltration in neonatally immunized rabbits in vivo.

Exposure of neonatally immunized rabbits to aerosolized platelet activating factor (PAF) (80 μg ml−1 for 60 min) elicited an increase in airway responsiveness to inhaled histamine 24 h and 72 h following challenge which was associated with an infiltration of inflammatory cells into the airways, as assessed by bronchoalveolar lavage (BAL).

A significant increase in the total numbers of cells recovered from BAL fluid was associated with significantly increased cell numbers of neutrophils, eosinophils and mononuclear cells 24 h following PAF exposure. The numbers of eosinophils and neutrophils in the airways remained elevated 72 h after challenge.

The intravenous administation of an unfractionated preparation of heparin (100 units kg−1) or Org 10172 (100 μg kg−1) 30 min prior to PAF exposure significantly inhibited the airway hyperresponsiveness induced by PAF, 24 h and 72 h following challenge. PAF‐induced hyperresponsiveness was not significantly affected by prior intravenous administration of polyglutamic acid (100 μg kg−1).

The intravenous administration of unfractionated heparin (100 units kg−1), Org 10172 (100 μg kg−1) or polyglutamic acid (100 μg kg−1) 30 min prior to PAF exposure significantly inhibited the expected increase in total cell infiltration.

This study shows that unfractionated heparin and a low‐molecular weight heparinoid, Org 10172, are capable of inhibiting both the airway hyperresponsiveness and pulmonary cell infiltration induced by PAF in the rabbit.
The effect of platelet‐activating factor on the responsiveness of the human nasal airway
Authors: Austin C.E. , Foreman J.C.
Published: July 2012

The effects of inhaled platelet‐activating factor (PAF) on responsiveness of the human nasal airway were examined in normal subjects by measuring nasal airway resistance in response to histamine and bradykinin at 2, 6, 24, 48 h and 7 d after PAF administration. Eosinophil cationic protein (ECP) in nasal secretions was also measured.

Intranasal aerosol administration of PAF, 30 or 60 μg per nostril to normal human subjects induced an increased responsiveness to inhaled histamine, 50 to 400 μg and bradykinin, 100 μg per nostril at 2, 6 and 24 h following PAF treatment. However the effect was not apparent at 48 h or 7 days after PAF administration.

Intranasal administration of lyso‐PAF, 60 μg by aerosol did not increase the reactivity of the nasal airway in response to histamine, 200 μg.

There was no difference in the time course of the PAF‐induced hyperresponsiveness to histamine or bradykinin.

PAF‐induced nasal hyperresponsiveness at 2 and 6 h was associated with increases in the ECP concentration of the nasal lavage fluid.

Vitamin E pretreatment of subjects resulted in the attenuation of the PAF‐induced hyperresponsiveness to histamine, and a decrease in ECP levels of the nasal lavage fluid.

The results suggest that in the human nasal airway, PAF induces a non‐specific hyperresponsiveness which is accompanied by eosinophil activation in the nasal cavity. Free radical production induced by PAF may contribute to the hyperresponsiveness and the activation of eosinophils.
Relation between α1‐adrenoceptor subtypes and noradrenaline‐induced contraction in rat portal vein smooth muscle
Authors: Sayet Irène , Neuilly Ghislaine , Rakotoarisoa Lala , Mironneau Chantal , Mironneau Jean
Published: July 2012

In vascular smooth muscle, α1‐adrenoceptors have been classified recently into two or three subtypes. We examined which α1‐adrenoceptor subtypes are involved in the noradrenaline‐induced contraction of rat portal vein smooth muscle.

Binding studies with [3H]‐prazosin in membranes from equine portal vein smooth muscle revealed the presence of two distinct affinity binding sites. The high‐affinity site for [3H]‐prazosin was also identified in intact strips of rat portal vein. Prazosin, HV723 (α‐ethyl‐3,4,5‐trimethoxy‐α‐(3‐((2‐(2‐methoxyphenoxy)ethyl)‐amino)‐propyl) benzene‐acetonitrile fumarate), WB4101 (2‐(2,6‐dimethoxyphenoxyethyl)aminomethyl‐1,4‐benzodioxane), 5‐methylurapidil, phentolamine and yohimbine antagonized [3H]‐prazosin binding at both types of sites. Pretreatment with 50 μm chloroethylclonidine (CEC) eliminated the high‐affinity sites for prazosin but had no effect on the low‐affinity sites.

Noradrenaline produced a concentration‐dependent contraction in the rat portal vein. Pretreatment with 50 μm CEC induced a slight rightward displacement of the concentration‐response curve but the maximal contraction was not significantly affected suggesting that the CEC‐sensitive α1‐adrenoceptors played a minor role in the noradrenaline‐induced contraction. Prazosin, WB4101 and HV723 produced a concentration‐dependent inhibition of noradrenaline‐induced contractions. The inhibition curves were little affected by CEC‐pretreatment and yielded a relative order of potency of WB4101 > prazosin > HV723.

In the presence of 0.1 μm isradipine to block voltage‐dependent Ca2+ channels, the noradrenaline‐induced contraction is due to release of Ca2+ ions from agonist‐sensitive intracellular Ca2+ stores. Under these conditions, the noradrenaline‐induced contraction was not significantly affected by pretreatment with 50 μm CEC but was inhibited by the antagonists mentioned above with affinities different from those in the absence of isradipine. The rank order of potency became HV723 ≥ WB4101 > prazosin.

The present results indicate the existence of two distinct α1‐adrenoceptor subtypes in rat portal vein smooth muscle, which show high‐ and low‐affinities respectively for each of prazosin, WB4101 and HV723 and correspond to α1H‐ and α1L‐adrenoceptor subtypes. According to recent α1‐adrenoceptor subclassifications, the α1H‐adrenoceptor subtype which is sensitive to inactivation by CEC may correspond to the α1B‐adrenoceptor subtype. The contraction induced by noradrenaline seems to be predominantly mediated through the α1L‐adrenoceptor subtypes which may include the α1N‐adrenoceptor subtype, as recently proposed.
Effect of adrenoceptor agonists on striated muscle strips of the canine oesophagus
Authors: Tokuhara Taigo , Meulemans Ann L. , De Ridder Walter J.E. , Higashino Masayuki , Kinoshita Hiroaki , Schuurkes Jan A.J.
Published: July 2012

Acute psychological stress, which could be related to the release of a large amount of catecholamines, may cause oesophageal motility disorders. Therefore, the aim of our study was to elucidate the influence of adrenoceptor agonists on the striated muscle portion of the oesophagus by use of isolated strips from dogs.

Contractions were evoked in isolated striated muscle strips by electrical field stimulation (1 pulse min−1, 1 ms/pulse, submaximal voltage). The effects induced by administration of adrenoceptor agonists alone or in the presence of antagonists were tested to determine the nature of the adrenoceptors on this muscle preparation.

The administration of both the natural adrenoceptor agonists, adrenaline and noradrenaline, and the synthetic β‐adrenenoceptor agonists, isoprenaline (β1 + β2), dobutamine (β1) or ritodrine (β2), enhanced the amplitude of the contractions induced by electrical stimulation in a concentration‐dependent manner. The maximum responses were 82.6 (adrenaline), 66.2 (noradrenaline), 86.2 (isoprenaline), 34.6 (dobutamine) and 80.8% (ritodrine). The EC20 values obtained were respectively 2 nm, 0.2 μm, 0.91 nm, 3 μm and 80 nm. The administration of the α1‐adrenoceptor agonist, phenylephrine, also enhanced the contractile response in a concentration‐dependent manner (EC20 value = 0.3 μm) and the maximum response was 64.6%, but the administration of the α2‐adrenoceptor agonist, clonidine, did not influence the contractile response. These data suggest the involvement of β2‐ and possibly α1‐adrenoceptors in the responses of these adrenoceptor agonists.

The selective β2‐adrenoceptor antagonist ICI 118551 (3–100 nm) shifted the concentration‐effect curves for noradrenaline, phenylephrine and ritodrine to the right in a concentration‐dependent manner. ICI 118551 (3 nm) also shifted the concentration‐effect curves for adrenaline and isoprenaline to the right, but increasing the concentration of ICI 118551 did not cause any further antagonist activity until a concentration of 100 nm, when a further rightward shift was obtained.

The selective α1‐adrenoceptor antagonist, prazosin (30–300 nm), did not affect the increased contractile responses induced by adrenaline, noradrenaline, phenylephrine, isoprenaline or ritodrine.

In conclusion, it appears that β2‐adrenoceptors are present in the striated muscle portion of the canine oesophagus, where they mediate an enhancement of contractile responses evoked by electrical stimulation. The α1‐agonist, phenylephrine, appears to interact with β2‐adrenoceptors on this preparation. β3‐Adrenoceptors have already been demonstrated in smooth muscle from various parts of the gastrointestinal tract, and our study does not exclude the possibility that there is an additional population of β3‐receptors in the canine striated muscle part of the oesophagus.
Effects of excitatory neurotransmitters on Ca2+ channel current in smooth muscle cells isolated from guinea‐pig urinary bladder
Authors: Nakayama S.
Published: July 2012

A whole‐cell voltage clamp technique was used to examine the effects of purinoceptor and muscarinic receptor agonists on voltage‐sensitive Ca2+ channels in guinea‐pig isolated urinary bladder cells.

When the cell membrane was clamped at the holding potential, rapid application of ATP elicited a large inward current in normal solution containing 2.5 mm Ca2+, and reduced the subsequent Ca2+ channel current evoked by a depolarizing pulse (0 mV). Carbachol (CCh) elicited little membrane current, but similarly reduced the Ca2+ current.

When purinoceptor agonists were rapidly applied during conditioning depolarizations at +80 mV, an outward current was elicited, and the Ca2+ channel current evoked by the subsequent test potential of 0 mV was not affected. Application of CCh at +80 mV also elicited an outward current, but it reduced the subsequently evoked Ca2+ current.

The inhibitory effect of muscarinic agonists on the Ca2+ channel current was attenuated by caffeine (10 mm).

In Ca2+‐free, low‐Mg2+ solution, a Na+ current flowing through voltage‐dependent Ca2+ channels was evoked by depolarization. This current was not reduced by bath application of purinoceptor agonists (ATP and α,β‐methylene ATP).

These results suggest that the main effect of purinoceptor stimulation is opening of non‐selective cation channels, and that muscarinic stimulation triggers Ca2+ release from intracellular stores. Voltage‐sensitive Ca2+ channels are inactivated through an increase in intracellular Ca2+ induced by either activation of purinoceptor or muscarinic receptors.
Post‐receptor pathway of the ATP‐induced relaxation in smooth muscle of the mouse vas deferens
Authors: Gailly Ph. , Boland B. , Paques C. , Himpens B. , Casteels R. , Gillis J.M.
Published: July 2012

The post‐receptor pathway of the ATP relaxant effect in K+‐precontracted vas deferens smooth muscle (VD) was examined.

The relaxation to ATP was not antagonized either by 10 μm methylene blue, a cyclic GMP inhibitor, by 10 μm indomethacin, an inhibitor of prostaglandin synthesis or by 100 μm NG‐nitro‐l‐arginine, an inhibitor of NO production.

The Rp‐diastereomer of adenosine 3′:5′‐cyclic monophosphorothioate (Rp‐cAMPS) 200 μm, a competitive inhibitor of cyclic AMP significantly diminished the relaxant response to ATP.

Isoprenaline 10 μm, a β‐adrenoceptor agonist, produced a sustained relaxation, inhibited by Rp‐cAMPS, without a significant change in [Ca2+]i, thereby mimicking the ATP‐induced relaxant effect.

The level of the phosphorylated myosin light chain in the precontracted VD was significantly lowered by 1000 μm ATP.

ATP (1000 μm) and isoprenaline (10 μm) produced the same increase (+ 50%) of [cyclic AMP] when applied to a resting VD.

The effect of simultaneous increases of [Ca2+]i and of [cyclic AMP] produced by externally applied ATP are discussed.

These results suggest that ATP‐induced relaxation in K+‐precontracted VD is mediated by the activation of adenylyl cyclase.
Evidence for sympathetic neurotransmission through presynaptic N‐type calcium channels in human saphenous vein
Authors: Fabi Fulvia , Chiavarelli Mario , Argiolas Livio , Chiavarelli Roberto , del Basso Paola
Published: July 2012

The specific type(s) of voltage‐sensitive calcium channels (VSCCs) involved in sympathetic neurotransmission have not yet been characterized in human vascular tissues. We therefore examined the functional role of the N‐ and L‐type VSCCs in human saphenous veins.

Contractile response curves for transmural nerve stimulation (TNS) and for exogenously administered noradrenaline (NA) were obtained in superfused saphenous vein rings. The contractions induced by TNS, but not by NA, were inhibited by 1 μm tetrodotoxin and by 10 μm guanethidine. Both responses were substantially reduced by 1 μm phentolamine, indicating that the contractions evoked by TNS were mediated by endogenous NA released from noradrenergic nerves.

In the presence of 2 μm ω‐conotoxin GVIA (omega Conus Geographus toxin, fraction VI A; ω‐CgTx), a polypeptide with specific inhibitory activity on N‐ and L‐type calcium channels, the neurally evoked contractions were almost completely abolished. In contrast, the responses induced by exogenous NA were not affected by the neurotoxin, thus providing evidence of the exclusive presynaptic action of ω‐CgTx.

In the presence of the calcium antagonist verapamil (10 μm), which selectively blocks L‐type VSCCs, the contractions induced by both TNS and NA were diminished to the same extent, suggesting that the organic calcium blocker is active only at the postjunctional level.

It is concluded that N‐type calcium channels are the main pathway of calcium entry controlling the functional responses induced by activating sympathetic nerves; the role of L‐type channels appears to be limited to the postjunctional level, modulating smooth muscle contractions.
The effect of ions and second messengers on long‐term potentiation of chemical transmission in avian ciliary ganglia
Authors: Scott T.R.D. , Bennett M.R.
Published: July 2012

The effects of tetanic stimulation of the oculomotor nerve on transmission through the avian ciliary ganglion have been determined by use of the amplitude of the compound action potential recorded in the ciliary nerve, in the presence of hexamethonium (300 μm), as a measure of synaptic efficacy.

Tetanic stimulation for 20 s at 30 Hz potentiated the chemical phase of the compound action potential by at least 100% of its control level. This potentiation, reflecting an increase in synaptic efficacy, decayed over two distinct time courses: firstly, a rapid decay with a time constant in the order of minutes, and secondly, a slower decay, representing a smaller potentiation, with a time constant in the order of an hour. The large increase in synaptic efficacy is attributed to post‐tetanic potentiation (PTP) whereas the smaller but longer lasting increase is attributed to long‐term potentiation (LTP).

Higher frequencies of tetanic stimulation gave increased PTP and LTP.

In order to test whether the influx of calcium ions into the nerve terminal during the tetanus is likely to be involved in potentiation, facilitation was measured during PTP and LTP. Facilitation was reduced to approximately zero during PTP but recovered to normal values about 15 min into LTP. A requirement for the induction of LTP was shown to be the presence of calcium in the bathing solution. However, blocking synaptic transmission with a high concentration of hexamethonium (3 mm) during the tetanic stimulation did not block the induction of LTP.

Application of the muscarinic inhibitor, atropine (2 μm), did not affect the magnitude of PTP or LTP.

The activator of protein kinase C, phorbol 12,13‐dibutyrate (2 μm) potentiated synaptic transmission and reduced the potentiation due to PTP although it did not affect that due to LTP, but the inhibitor of this kinase, staurosporine (0.5 μm), partially blocked the appearance of LTP without affecting PTP after the tetanus.

An inhibitor of calmodulin, W‐7 (5 μm), reversibly blocked the appearance of LTP significantly after a tetanus although the size of PTP was not affected.

The results presented here suggest that the initiation of LTP in the ciliary ganglion is due to an influx of calcium ions into the calyciform nerve terminal during the tetanus and that the mechanism for LTP involves a calcium‐calmodulin‐dependent process.
The paradoxical vascular interactions between endothelin‐1 and calcitonin gene‐related peptide in the rat gastric mucosal microcirculation
Authors: Lopez‐Belmonte J. , Whittle B.J.R.
Published: July 2012

The interactions between local intra‐arterial infusion of endothelin‐1 (ET‐1) and rat α‐calcitonin gene‐related peptide (α‐CGRP) on gastric mucosal damage and blood flow have been investigated in the pentobarbitone‐anaesthetized rat.

Close‐arterial infusion of ET‐1 (2–200 pmol kg−1 min−1) induced a significant and dose‐dependent increase in gastric mucosal haemorrhagic injury.

Close‐arterial infusion of the higher doses of ET‐1 (100 and 200 pmol kg−1 min−1) resulted in a biphasic effect on mucosal blood flow, as determined by laser Doppler flowmetry (LDF). This consisted of an initial transient increase followed by a pronounced and sustained fall in LDF.

Local microvascular constriction may thus contribute to the mechanisms underlying the gastric injury induced by these higher doses of ET‐1.

However, close‐arterial infusion of lower doses of ET‐1 (2–50 pmol kg−1 min−1), that also provoked substantial mucosal damage, induced only a sustained and significant mucosal hyperaemia, which may be secondary to microvascular injury.

Concurrent close‐arterial administration of rat α‐CGRP (50 pmol kg−1 min−1) significantly inhibited the extent of gastric mucosal injury induced by ET‐1 (5 pmol kg−1 min−1).

Furthermore, concurrent close‐arterial infusion of this dose of α‐CGRP, which itself increased mucosal LDF, significantly inhibited the hyperaemic response induced by close‐arterial infusion of ET‐1 (5 pmol kg−1 min−1).

These results indicate a damaging action on the gastric mucosa by low doses of ET‐1 which is independent of local vasoconstriction, that may involve a direct injury of the microvascular endothelium. The protective action of α‐CGRP thus seems unlikely to be due to a local vasodilator effect but may reflect protective actions on the microvascular endothelium
Effects of ω‐conotoxin on adrenergic, cholinergic and NANC neurotransmission in the rabbit urethra and detrusor
Authors: Zygmunt P.M. , Zygmunt P.K.E. , Högestätt E.D. , Andersson K.‐E.
Published: July 2012

The effects of ω‐conotoxin GVIA (an inhibitor of N‐type voltage‐operated calcium channels; VOCCs) were compared on adrenergic, cholinergic and non‐adrenergic, non‐cholinergic (NANC) responses induced by electrical field stimulation (EFS) in the rabbit urethra and detrusor.

EFS induced a relaxation in urethral smooth muscle and lamina propria precontracted by arginine vasopressin (AVP). The relaxation was abolished by tetrodotoxin (TTX) or the nitric oxide (NO) synthase inhibitor Nω‐nitro‐l‐arginine. ω‐Conotoxin inhibited the relaxation induced by EFS, but not that elicited by the NO donor 3‐morpholino‐sydnonimin. The inhibition, however, decreased with increasing frequencies of stimulation. Nimodipine, tetramethrin and nickel did not affect the ω‐conotoxin‐resistant relaxation in lamina propria, suggesting that neuronal L or T VOCCs were not involved in the response.

EFS contracted urethral smooth muscle at resting tension. The contractions were virtually abolished by TTX or prazosin. ω‐Conotoxin effectively inhibited the contractile responses to EFS, but not those to exogenous noradrenaline. An ω‐conotoxin‐resistant contraction was, however, observed at high frequencies of stimulation.

The detrusor responded with frequency‐dependent contractions upon EFS. A TTX‐resistant contraction less than 10% of controls remained at 30 Hz stimulation. At a stimulation frequency of 10 Hz, scopolamine reduced the EFS‐induced contraction by 71%. ω‐Conotoxin inhibited the responses in both the absence and presence of scopolamine. The inhibition decreased with increasing frequencies of stimulation (examined in the absence of scopolamine). ω‐Conotoxin did not affect the contractile responses to carbachol or adenosine 5′‐triphosphate.

The adrenergic contraction (25 Hz) and NANC relaxation (10 Hz) in the urethra, and cholinergic and NANC contractions (10 Hz) in the detrusor were inhibited concentration‐dependently by ω‐conotoxin. The adrenergic contraction in the urethra was 10 times and the cholinergic contraction in the detrusor was three times more sensitive to ω‐conotoxin than the NANC responses.

These results suggest that NANC neurotransmission is less inhibited by ω‐conotoxin than transmission mediated by adrenergic and cholinergic nerves in the rabbit lower urinary tract. In the urethra a marked ω‐conotoxin‐resistant component of the NANC relaxation was observed which increased with increasing stimulation frequencies and was unaffected by inhibitors of L and T type VOCCs. This raises the question whether VOCCs of a type other than L, T, and N is involved in the mediation of this response.
The action of Hoe 140 on the bradykinin‐induced splenic pressor reflex of the anaesthetized cat
Authors: Louttit J.B. , Coleman R.A.
Published: July 2012

Intrasplenic injection of bradykinin (BK) induced a dose‐dependent pressor response in the anaesthetized cat, with an ED50 of 0.98 ± 0.43 nmol. In contrast, intrasplenic administration of desArg9bradykinin (desArg9K) was without significant effect at doses of up to 200 nmol.

Intravenously administered BK induced a dose‐dependent depressor response in the anaesthetized cat, with an ED50 of 0.86 ± 0.09 nmol kg−1. desArg9BK was again without significant effect in this system at doses of up to 200 nmol kg−1.

Both the pressor and depressor responses to BK were antagonized to a similar degree in a dose‐dependent manner by Hoe 140 (10 and 100 nmol kg−1, i.v.).

At these doses, Hoe 140 appears to be a specific BK antagonist as it was ineffective against pressor responses to intrasplenic injection of capsaicin (5 nmol), while blocking those to an approximately equieffective dose of BK (1 nmol) in a dose‐dependent fashion.

Both the pressor response to intrasplenic BK and the depressor response to intravenous BK in the anaesthetized cat appear to be mediated by B2‐receptors. This model may be useful in the quantitative determination of the antinociceptive potency of BK antagonists.
Inhibition by hydrochlorothiazide of insulin release and calcium influx in mouse pancreatic β‐cells
Authors: Sandström Per‐Erik
Published: July 2012

The effect of hydrochlorothiazide on insulin release, 36Cl− fluxes and 45Ca2+ uptake was tested in β‐cell‐rich mouse pancreatic islets.

At high glucose concentrations (10 and 20 mmol l−1), low concentrations of hydrochlorothiazide (0.1–1.0 μmol l−1) reduced insulin release by 22–42%. At lower glucose concentrations (3–8.5 mmol l−1) insulin release was not affected by the drug.

Neither short‐term influx (3 min) nor net accumulation (60 min) of 36Cl− in the islets was affected by hydrochlorothiazide (0.1–500 μmol l−1).

Glucose‐stimulated 45Ca2+ uptake was significantly reduced by hydrochlorothiazide (1–10 μmol l−1).

The data suggest that the diabetogenic effect of hydrochlorothiazide, at least in part, can be mediated by direct inhibition of insulin release from the pancreatic β‐cells. The inhibition is not mediated by reduced chloride fluxes but may rather be caused by inhibition of calcium uptake.
Effects of atrial natriuretic peptide and nitroprusside on isolated pulmonary resistance and conduit arteries from rats with pulmonary hypertension
Authors: Wanstall Janet C. , Thompson Justine S. , Morice Alyn H.
Published: July 2012

The relaxant effects of atrial natriuretic peptide (ANP) and nitroprusside were studied on prostaglandin F2α (PGF2α)‐contracted preparations of pulmonary resistance vessels (internal diameter 200–500 μm) and main pulmonary arteries taken from rats with pulmonary hypertension induced by monocrotaline (105 mg kg−1, s.c., 4 weeks previously). Control rats received saline.

In preparations from monocrotaline‐treated rats, the potencies (negative log EC50) of ANP on resistance vessels (8.45) and main pulmonary arteries (8.25) were similar to those obtained in vessels from control rats (8.78 and 8.53 respectively), whereas those of nitroprusside were significantly less than in controls in both resistance vessels (7.13 compared with 7.63 in controls; three fold decrease in potency) and main pulmonary arteries (6.92 compared with 8.17 in controls; 18 fold decrease in potency).

On pulmonary resistance vessels from monocrotaline‐treated rats, the maximum relaxant responses to ANP and nitroprusside, and also to pinacidil, were increased compared with controls, and reversal of the PGF2α‐induced contraction by these drugs was greater than 100%. In contrast, on main pulmonary arteries from monocrotaline‐treated rats, the maximum relaxations to ANP and nitroprusside were not increased relative to controls, and reversal of PGF2α was not greater than 100%.

Since the high potency of ANP on pulmonary resistance and conduit arteries is retained in vessels from rats with pulmonary hypertension, whether induced by monocrotaline (this study) or by chronic hypoxia (previous findings), it is postulated that elevation of plasma levels of ANP by use of drugs that inhibit the breakdown of this endogenous peptide, may be one approach to the pharmacological treatment of pulmonary hypertension.