bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of 5‐HT‐receptor and α2‐adrenoceptor ligands on the haemodynamic response to acute central hypovolaemia in conscious rabbits
Authors: Evans Roger G. , Haynes John M. , Ludbrook John 
Published: July 2012

We set out to elucidate the pharmacological mechanisms by which α2‐adrenoceptor and 5‐HT‐receptor ligands affect the haemodynamic response to acute central hypovolaemia in conscious rabbits.
Acute central hypovolaemia was produced by inflating an inferior vena caval cuff so that cardiac output fell at a constant rate of ∼8.5% of its baseline level per min.
Drugs were administered into the fourth cerebral ventricle in either 154 mm NaCl (saline) or 20% w/v 2‐hydroxypropyl‐β‐cyclodextrin (β‐CDX). After vehicle treatments, the haemodynamic response to acute central hypovolaemia had the usual two phases. During Phase I, systemic vascular conductance fell in proportion to cardiac output so that mean arterial pressure fell by only 8 mmHg. Phase II commenced when cardiac output had fallen to ∼60% of its baseline level, when vascular conductance rose abruptly and arterial pressure fell to ≤ 40 mmHg. The haemodynamic response was not dependent on the vehicle used (saline or β‐CDX).
Methysergide delayed the occurrence of Phase II in a dose‐dependent manner, and prevented it at a dose of 30– 600 nmol (geometric mean = 186 nmol). The effects and potency of methysergide were not dependent on the vehicle used, indicating that β‐CDX can be used as a vehicle for fourth ventricular administration of lipophilic drugs to conscious rabbits. Clonidine (10 nmol) reversed the effects of a critical dose of methysergide.
Phase II was also prevented by 8‐hydroxy‐2‐(di‐n‐propylamino)tetralin (5‐HT1A‐selective agonist, geometric mean critical dose (range) = 13.1 (10–30) nmol), sumatriptan (5‐HT1D‐selective agonist, 72.1 (10–300) nmol), mesulergine (5‐HT2/1c‐selective antagonist, 173 (30–1000) nmol), idazoxan (α2‐adrenoceptor‐selective antagonist, 548 (100–3000) nmol), and mianserin (5‐HT2/1c‐selective antagonist, 548 (100– 3000) nmol). It was not affected by MDL 72222 (5‐HT3‐selective antagonist, 300 nmol) or ketanserin (5‐HT2/1c‐selective antagonist, 3000 nmol).
To characterize the nature of α2‐adrenoceptors in rabbit brainstem, we examined the binding of [3H]‐rauwolscine to membrane homogenates of whole brainstem. [3H]‐rauwolscine bound to a population of sites with the characteristics of α2A‐adrenoceptors.
From these results we suggest that activation of 5‐HT1A receptors in the brainstem can prevent Phase II of the response to acute central hypovolaemia in conscious rabbits. Our results do not support the notion of an endogenous 5‐hydroxytryptaminergic mechanism mediating Phase II. The mechanism by which the α2‐adrenoceptor antagonists yohimbine and idazoxan prevent Phase II remains to be elucidated. However, their potency relative to other 5‐HT‐receptor ligands indicates that an agonist action at 5‐HT1A‐receptors is more likely than an antagonist action at α2‐adrenoceptors.
Radioligand and functional estimates of the interaction of the 1,4‐dihydropyridines, isradipine and lacidipine, with calcium channels in smooth muscle
Authors: Salomone Salvatore , Godfraind Théophile 
Published: July 2012

The present experiments were undertaken in order to characterize further the apparently irreversible inhibition of the contraction of depolarized rat aorta caused by lacidipine, a 1,4‐dihydropyridine calcium antagonist.
We studied the effect of lacidipine on contraction evoked by 100 mm KCl solution in rat aorta, treated by Nω‐nitro‐l‐arginine (0.1 mm), an inhibitor of nitric oxide (NO) synthesis. We compared the effect of prolonged depolarization on lacidipine and (+)‐isradipine inhibition and the reversal of this inhibition after washout in the absence of dihydropyridines. Assuming that the onset of lacidipine‐evoked inhibition was a pseudo‐first order association kinetics, we estimated the dissociation rate constant (k−1 = 0.031 min−1), the association rate constant (k1 = 2.70 × 108 m−1 min−1) and the dissociation constant (KD = k−1/k1 = 115 pm) which was close to the IC50 value in steady‐state conditions (160 pm).
The inhibitory effects of lacidipine and (+)‐isradipine on rat aorta contraction were reversibly enhanced after preincubation with the drug in a 40 mm KCl‐solution. Washout with drug‐free 40 mm K+‐depolarizing solution reversed inhibition in the (+)‐isradipine‐treated preparations, but not in the lacidipine‐treated ones.
Radioligand binding studies were performed with [3H]‐lacidipine and [3H]‐isradipine in microsomes from rat aorta and rat ileum. Both ligands bound to a homogeneous population of binding sites (for [3H]‐lacidipine: KD = 23 ± 2.6 pm, Bmax = 380 ± 21 fmol mg−1 protein in membranes from aorta; KD = 23 ± 3.1 pm, Bmax = 790 ± 60 fmol mg−1 protein in membranes from ileum; for [3H]‐isradipine: KD = 140 ± 46 pm, Bmax = 350 ± 64 fmol mg−1 protein in membrane from aorta; KD = 68 ± 14 pm, Bmax = 760 ± 75 fmol mg−1 protein in membranes from ileum). After isotopic dilution, [3H]‐lacidipine and [3H]‐isradipine dissociated according to a monoexponential kinetics. In membranes from ileum, the calculated dissociation rate constants (k−1) were 0.0257 min−1 and 0.0595 min−1, for [3H]‐lacidipine and [3H]‐isradipine, respectively.
The non specific binding of [3H]‐lacidipine and [3H]‐isradipine, was measured in intact rat aorta preparations incubated under the conditions of the functional experiments, in the presence of nifedipine (1 μm). After incubation with [3H]‐lacidipine 77.6 ± 1.9 pm for 2 h the concentration of drug in the tissue was 15.15 ± 1.18 fmol mg−1 w.wt. and still amounted to 7.24 ± 0.61 fmol mg−1 w.wt. after 3.5 h washout in drug‐free solution. After incubation with [3H]‐isradipine 47.2 ± 0.4 pm for 2 h it was 2.26 ± 0.07 fmol mg−1 w.wt. and was undetectable after 3.5 h washout in a drug‐free solution.
It is concluded that lacidipine interacts reversibly with dihydropyridine binding sites and that the apparent irreversible inhibition of contraction in depolarized preparations could be related to a non specific binding in a tissue compartment different from the plasma membrane.
Effects of cicletanine on whole‐cell currents of single smooth muscle cells from the guinea‐pig portal vein
Authors: Noack Thomas , Deitmer Petra 
Published: July 2012

Smooth muscle cells of the guinea‐pig portal vein were dispersed by enzymatic treatment and recordings of membrane currents were made in the whole‐cell mode by the patch‐clamp technique. The effects of extracellular application of cicletanine‐hydrochloride on the whole‐cell currents of isolated smooth muscle cells from the guinea‐pig portal vein were studied in solutions containing a normal concentration of calcium (2.5 mm).
Cicletanine, 10 to 100 μm, reduced the voltage‐dependent inward calcium current with an IC50 of 250 μm. These effects of cicletanine were reversible.
The action of cicletanine on calcium currents can be interpreted as a decrease of the availability of calcium channels but not by an alteration of the time course or voltage‐dependency of inactivation. 3 The control calcium current was enhanced by application of Bay K 8644. On this enhanced inward current, cicletanine also exerted inhibitory effects which were not use‐dependent.
Cicletanine, 1 to 100 μm, did not enhance outward potassium currents.
It is concluded that at least one component of the vasorelaxant effects of cicletanine is produced by inhibition of calcium currents.
The effect of lifarizine (RS‐87476), a novel sodium and calcium channel modulator, on ischaemic dopamine depletion in the corpus striatum of the gerbil
Authors: Brown C.M. , Calder C. , Alps B.J. , Spedding M. 
Published: July 2012

Unilateral ligation of the right common carotid artery in the anaesthetized gerbil for 3 h caused a 62.7% decrease in ipsilateral dopamine in the corpus striatum from 1.40 (± 0.13, n = 27) μg g−1 in the non‐ischaemic hemisphere to 0.47 (± 0.07, n = 27) μg g−1 in the ischaemic hemisphere (all results are expressed as mean ± s.e.mean). In sham‐operated animals there were no differences in the dopamine levels (1.31 ± 0.14 μg g−1, n = 11, left; 1.27 ± 0.13 μg g−1, n = 11 in the right hemisphere). Animals with intact communicating arteries in the circulus arteriosus were excluded.
Lifarizine (RS‐87476; 250, 500, but not 50, μg kg−1, i.p.) protected against this dopamine depletion showing only a 9.2% decrease at 250 μg kg−1, i.p. (P < 0.01) and no decrease at 500 μg kg−1, i.p. (P < 0.01).
Nicardipine (250 μg kg−1, p.o.) was effective when administered chronically once daily for 10 days (26.6% decrease, P < 0.05) but not when administered acutely at 50 μg kg−1, i.p.
Induction by endotoxin of nitric oxide synthase in the rat mesentery: lack of effect on action of vasoconstrictors
Authors: Mitchell Jane A. , Kohlhaas Kathy L. , Sorrentino Raffaella , Warner Timothy D. , Murad Ferid , Vane John R. 
Published: July 2012

Male Sprague‐Dawley or Wistar rats were injected with bacterial lipopolysacharride (LPS; 5 mg kg−1, i.p.) and killed after 1, 3, 6, 15, and 24 h. The brains, mesenteries, spleens, lungs, livers, kidneys, hearts, aortae and diaphragms were removed and frozen immediately. Control rats were injected with sterile saline and killed after 6 h.
The organs were homogenized in a semi‐frozen state and NO synthase (NOS) activity measured in tissues from both LPS‐treated and saline‐treated groups by the ability of homogenates to convert [3H]‐l‐arginine to [3H]‐l‐citrulline in a NADPH‐dependent manner.
The NOS activity in all organs taken from control animals was found to be calcium‐dependent, with the highest activity being in the brain. After LPS‐treatment an induced calcium‐independent NOS was detected in all tissues tested, with the exception of the brain. The spleen, lung, mesentery and liver had the highest amounts of LPS‐induced NOS activity. No induction of calcium‐dependent NOS was detected.
Induction of NOS was maximum 6 h after administration of LPS and had returned to control levels in 24 h.
The constitutive NOS in brain and mesentery and the LPS‐induced activities in the spleen, lung, liver and mesentery were inhibited by NG‐monomethyl‐l‐arginine (l‐NMMA) or NG‐nitro‐l‐arginine methyl ester (l‐NAME) according to concentration. The IC50 for l‐NAME was 2.5 μm against the constitutive NOS from brain, and 20–25 μm against the inducible NOS. For l‐NMMA the IC50 was 20–25 μm against either NOS isoform.
The vascular responses to endothelin‐1 (ET‐1), the thromboxane A2‐mimetic 11α,9α‐epoxymethano prostaglandin F2α (U46619), phenylephrine (PE) or 5‐hydroxytryptamine (5‐HT) were measured in the simultaneously perfused arterial and venous mesenteric vascular beds from both control and LPS‐treated (6 h) rats. Vasoconstrictor responses to all agonists tested were unaffected by LPS treatment. In the presence of l‐NAME (100 μm) vasoconstrictor responses were potentiated in both the arterial and venous portion of the mesenteric beds from both control and LPS‐treated rats. The potentiation of responses to U46619 was significantly greater in beds from LPS‐treated rats.
Injection of LPS i.p. is associated with induction of NOS in all organs tested, except for the brain. In the mesentery this is not accompanied by a hyporesponsiveness to constrictor agents suggesting an increased sensitivity, particularly to U46619. This may explain the poor perfusion and tissue damage in the splanchnic circulation associated with sepsis.
Differential effects of cocaine and cocaethylene on intracellular Ca24+ and myocardial contraction in cardiac myocytes
Authors: Qiu Zhihua , Morgan James P. 
Published: July 2012

Isolated cardiac myocytes of the ferret were used to investigate the influence of cocaine and cocaethylene on the intracellular Ca2+ transient indicated by the indo‐1 405/480 nm ratio signal, and peak cell shortening.
Both cocaine and cocaethylene produced significant decreases in peak intracellular Ca2+ and peak cell shortening in a dose‐dependent manner. Of interest, (1) the minimally effective dose of cocaethylene was ten fold lower (10−8 m versus 10−7 m) than that of cocaine; (2) the log EC50 of cocaethylene was −5.99 ± 0.13 (1.0 × 10−6 m), which was about ten fold lower than that of cocaine (−5.02 ± 0.11, 9.6 × 10−6 m); and (3) 1 × 10−4 m cocaethylene decreased the contraction amplitude by 71 ± 7%, while the same concentration of cocaine decreased the amplitude only by 55 ± 5%, indicating that cocaethylene is more potent than cocaine.
The negative inotropic effects of either cocaine or cocaethylene could be overcome by noradrenaline (∼ 5 μm) or calcium.
In contrast to cocaine, cocaethylene shifted the peak [Ca2+]i‐peak shortening relationship downward, indicating that cocaethylene decreased myofilament Ca2+‐responsiveness.
These data indicate that both cocaine and cocaethylene act directly on cardiac myocytes to produce a negative inotropic effect that is due to decreased Ca2+ availability. In contrast to cocaine, cocaethylene produces more potent inhibition by an additional action to decrease myofilament Ca2+‐responsiveness.
High‐affinity uptake of noradrenaline in postsynaptic neurones
Authors: Al‐Damluji S. , Krsmanovic L.Z. , Catt K.J. 
Published: July 2012

Neurotransmitters released from nerve endings are inactivated by re‐uptake into the presynaptic nerve terminals and possibly into neighbouring glial cells. While analysing the functional properties of α1‐adrenoceptors in the hypothalamus, we observed a high‐affinity uptake process for noradrenaline in postsynaptic peptidergic neurones.
In primary hypothalamic cell cultures and in a hypothalamic neuronal cell line, [3H]‐prazosin bound with high affinity and was displaced by unlabelled prazosin in concentrations of 10−10 to 10−7 m. However, at concentrations of unlabelled prazosin above 10−7 m, there was a paradoxical increase in apparent [3H]‐prazosin binding.
Methoxamine, an α1‐adrenoceptor ligand that is not subject to significant neuronal uptake, displaced [3H]‐prazosin but did not cause the paradoxical increase in the apparent binding of [3H]‐prazosin. Cooling the cells to 4°C reduced the total amount of prazosin associated with the cells; under these conditions, methoxamine almost completely inhibited [3H]‐prazosin binding to the cells.
In the presence of desipramine (DMI), unlabelled prazosin displaced [3H]‐prazosin as before, but no paradoxical increase in apparent binding was seen above 10−7 m.
The paradoxical increase of [3H]‐prazosin binding was not observed in membrane preparations of hypothalamic neurones. These findings indicated that the paradoxical increase in apparent [3H]‐prazosin binding was due to a cellular uptake process that becomes evident at high concentrations of the ligand.
DMI (10−5 m) had no effect on the specific binding of [3H]‐prazosin. The presence of α1‐adrenoceptors was confirmed by binding of [125I]‐HEAT, but [3H]‐idazoxan (an α2‐ ligand) did not bind to the cells.
The uptake of prazosin obeyed the Michaelis‐Menten model, with similar Km and Vmax values in both types of cultures.
Noradrenaline was taken up with high affinity by both types of cultures. (±)‐[3H]‐noradrenaline uptake was reduced by DMI and by excluding sodium from the medium, indicating that this process has some of the properties of uptake1. (±)‐[3H]‐noradrenaline uptake in the cell line was unaffected by testosterone.
The measured uptake of (−)‐noradrenaline in the cell line was considerably increased by blockade of catechol‐O‐methyl‐transferase and monoamine oxidase, suggesting that (−)‐noradrenaline is metabolized to lipophilic products that escape across the plasma membrane.
Studies in rats, in which the noradrenaline isomer 6‐hydroxydopamine was used, suggested that the postsynaptic uptake process is operative in hypothalamic CRH and vasopressin neurones in vivo.
The Km for (−)‐noradrenaline was within the range for the high affinity uptake1 process in noradrenergic neurones. Uptake takes place in concentrations at which noradrenaline activates α1‐adrenoceptors. Removal of noradrenaline from the vicinity of the receptors may prevent desensitization, thus maintaining the responsiveness of postsynaptic neurones to the actions of the neurotransmitter.
Effects of potassium channel openers and their antagonists on rat locus coeruleus neurones
Authors: Finta E.P. , Harms L. , Sevcik J. , Fischer H.‐D. , Illes P. 
Published: July 2012

Intracellular recordings were obtained from a pontine slice preparation of the rat brain containing the locus coeruleus (LC). Two openers of ATP‐sensitive potassium (KATP) channels, RO 31–6930 (10 μm) and cromakalim (100 μm) decreased the spontaneous discharge of action potentials without altering their amplitude or duration. Neither compound changed the resting membrane potential.
Of two KATP channel blockers, tolbutamide (300 μm) increased the firing rate, while glibenclamide (3 μm) only tended to do so. In addition, both compounds antagonized the effect of RO 31–6930 (10 μm). Neither glibenclamide (3 μm) nor tolbutamide (300 μm) altered the resting membrane potential.
Tetrodotoxin (0.5 μm) depressed the firing, but did not influence the inhibitory action of RO 31–6930 (10 μm). The excitatory amino acid antagonist, kynurenic acid (500 μm), did not change the spontaneous discharge of action potentials.
Small shifts (2–4 mV) of the membrane potential by hyper‐ or depolarizing current injections markedly decreased and increased the firing rate, respectively.
Noradrenaline (100 μm) hyperpolarized the cells and decreased their input resistance. This effect was not antagonized by glibenclamide (3 μm) or tolbutamide (300 μm). Ba2+ (2 mm), a blocker of both ATP‐sensitive and inwardly rectifying potassium channels, abolished the effects of RO 31–6930 (10 μm) and noradrenaline (100 μm).
These data suggest that KATP channels are present on the noradrenergic LC neurones, but are not coupled to α2‐adrenoceptors.
Nitric oxide and arachidonic acid modulation of calcium currents in postganglionic neurones of avian cultured ciliary ganglia
Authors: Khurana G. , Bennett M.R. 
Published: July 2012

A study has been made of the modulation of high‐voltage activated transient and sustained calcium currents in cultured neurones of avian ciliary ganglia by nitric oxide (NO) and arachidonic acid.
Sodium nitroprusside (100 μm) reduced the transient calcium current (ICa) on average by 31% and the sustained ICa by 32% during a test depolarization to + 20 mV from a holding potential of −100 mV. This reduction was maintained for at least 30 min following a single application of sodium nitroprusside.
l‐Arginine (270 μm) reduced the transient ICa on average by 28% and the sustained ICa by 22% and these effects were prevented by the presence of the NO‐synthase competitive blocker NG‐nitro‐l‐arginine methylester (l‐NAME; 100 μm) in the bathing solution.
Arachidonic acid (50 μm) reduced the transient ICa on average by 28% and the sustained ICa by 33%. When added together, arachidonic acid (50 μm) and l‐arginine (270 μm) produced the same effects as arachidonic acid alone.
Blocking the conversion of arachidonic acid to prostaglandins by addition of indomethacin (20 μm) to the bathing solution did not prevent the depression of either the transient or the sustained calcium current during application of arachidonic acid (50 μm). The effects of arachidonic acid were also not occluded by l‐NAME (100 μm) when present in the bathing solution.
Inhibiting the biosynthesis of leukotrienes by applying L‐663,536 (MK‐886; 3 μm) to the bathing solution prevented the depression of both components of ICa during application of arachidonic acid (50 μm).
These results indicate that endogenous NO and arachidonic acid pathways are present in parasympathetic ciliary neurones, and that both act to depress high‐voltage, gated, calcium channel activity.
Induction of endothelium‐dependent relaxation in the rat aorta by IRL 1620, a novel and selective agonist at the endothelin ETB receptor
Authors: Karaki Hideaki , Sudjarwo Sri Agus , Hori Masatoshi , Takai Michihiro , Urade Yoshihiro , Okada Toshikazu 
Published: July 2012

The effects of a novel and selective agonist at the endothelin ETB receptor, IRL 1620 (Suc‐[Glu9, Ala11,15] endothelin‐1 (8–21)), were examined in the isolated aorta of the rat.
IRL 1620 (1–300 nm) changed neither the resting tone nor the cytosolic Ca2+ level ([Ca2+]i) of the aorta without endothelium. In the presence of endothelium, however, IRL 1620 increased endothelial [Ca2+]i with little effect on the muscle tone. In the absence of external Ca2+, IRL 1620 still induced a transient increase in endothelial [Ca2+]i.
Noradrenaline (100 nm) increased both muscle [Ca2+]i and tension. IRL 1620 (1–300 nm) relaxed the muscle with an increase in endothelial [Ca2+]i only in the presence of endothelium. An inhibitor of nitric oxide synthase, 100 μm NG‐monomethyl‐l‐arginine, inhibited the relaxant effect of IRL 1620 but not the increase in endothelial [Ca2+]i.
In resting and noradrenaline‐stimulated aorta, the effects of IRL 1620 were inhibited by a selective antagonist of the ETB receptor, IRL 1038 (0.3–3 μm), although a selective antagonist of the ETA receptor, BQ‐123 (3 μm), was ineffective. Verapamil (10 μm) did not alter the effects of IRL 1620.
A muscarinic receptor agonist, carbachol (1 μm), also induced endothelium‐dependent relaxation with an increase in endothelial [Ca2+]i. However, the effects of carbachol were not inhibited by the ETB antagonist, IRL 1038 (3 μm).
These results suggest that IRL 1620 is a selective agonist at the ETB receptor which increases endothelial [Ca2+]i by releasing Ca2+ from storage sites and by opening non‐L type Ca2+ channels, activates nitric oxide synthase, releases nitric oxide, and relaxes vascular smooth muscle.