bluuebunny/crossref_metadata_2025 huggingface dataset:
Cardiotoxicity of emetine dihydrochloride by calcium channel blockade in isolated preparations and ventricular myocytes of guinea‐pig hearts
Authors: Lemmens‐Gruber R. , Karkhaneh A. , Studenik C. , Heistracher P.
Published: July 2012

The cardiotoxic effects of emetine dihydrochloride on mechanical and electrical activity were studied in isolated preparations (papillary muscles, sinoatrial and atrioventricular nodes, ventricular myocytes) of the guinea‐pig heart.

Force of contraction was measured isometrically, action potentials and maximum rate of rise of the action potential were recorded by means of the intracellular microelectrode technique. Single channel L‐type calcium current (Ba2+ ions as charge carrier) was studied with the patch‐clamp technique in the cell‐attached mode.

Emetine dihydrochloride (8–256 μm) reduced force of contraction in papillary muscles and spontaneous activity of sinoatrial and atrioventricular nodes concentration‐dependently; the negative inotropic effect was abolished when the extracellular Ca2+ concentration was increased.

Maximum diastolic potential, action potential amplitude, maximum rate of rise of the action potential and the slope of the slow diastolic depolarization were decreased by emetine in sinoatrial as well as atrioventricular nodes, while action potential duration was prolonged in both preparations (1–64 μm).

The amplitude of the L‐type calcium single channel current was not altered by emetine dihydrochloride, while average open state probability was decreased concentration‐dependently (10, 30 and 60 μm).

The most prominent effect of emetine dihydrochloride on single channel current was an increase of sweeps without activity.

At 60 μm, emetine dihydrochloride caused a decrease of the mean open time and an increase of the mean closed time. The number of openings per record and number of bursts per record were reduced.

It is concluded that emetine dihydrochloride produces an L‐type calcium channel block which might contribute to its cardiac side effects.
Binding and competitive inhibition of amine uptake at postsynaptic neurones (transport‐P) by tricyclic antidepressants
Authors: Al‐Damluji S. , Kopin I.J.
Published: July 2012

We have provided evidence for a novel amine uptake process for which prazosin is a substrate in postsynaptic neurones, characterized by a paradoxical increase in accumulation of the radioligand when the concentration of the unlabelled drug is increased above 10−7 m. This increase is due to activation of a proton‐dependent, vacuolar type‐ATPase‐linked uptake process which is blocked by desipramine but is resistant to reserpine. We have now examined the effects of tricyclic antidepressants on this uptake system in a cell line derived from hypothalamic peptidergic neurones, known to be innervated by noradrenergic nerve terminals in vivo.

[3H]‐imipramine bound to the cells and was displaced by unlabelled imipramine, desipramine, amitriptyline and nortriptyline. The data fitted a single binding site model. This is the first demonstration of antidepressant binding sites in postsynaptic neurones.

There was no increase in the binding of [3H]‐imipramine at high concentrations of unlabelled imipramine, suggesting that antidepressants inhibit uptake but are not themselves accumulated by peptidergic gonadotrophin releasing hormone neurones.

Accumulation of prazosin was competitively inhibited by antidepressants. Tertiary amines were slightly more potent than secondary amines and the presence of a nitrogen atom in the heterocyclic ring enhanced blocking activity.

The affinities of the antidepressants for the uptake process are within the range of plasma concentrations that are observed during therapeutic use of these compounds. Since it is likely that this uptake process has a physiological function, its inhibition by antidepressants may provide a new avenue for investigating the mechanism of action of these compounds.
Effects of a selective adenosine A1 receptor antagonist on the development of cyclosporin nephrotoxicity
Authors: Balakrishnan V.S. , von Ruhland C.J. , Griffiths D.F.R. , Coles G.A. , Williams J.D.
Published: July 2012

The clinical application of cyclosporin as an immunosuppressive agent is limited by its nephrotoxicity.

The effect of FK453, a selective A1‐receptor antagonist, administered twice daily to rats at a dose of 100 mg kg−1 was assessed on the development of nephrotoxicity induced by cyclosporin (10 mg kg−1 i.p. daily) administered for 14 days. The effects of nifedipine administered twice daily (0.3 mg kg−1 s.c.) for 14 days, on cyclosporin nephrotoxicity were also studied.

Cyclosporin induced a 46.58% and 35.78% decline in glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) respectively and a reduction of 16.69% in filtration fraction (FF). Co‐administration of FK453 resulted in falls of 30.5%, 18.59% and 14.7% in GFR, ERPF and FF respectively, the former two significantly less than the falls seen with cyclosporin (CyA) alone (P < 0.05 vs CyA, ANOVA).

Nifedipine appeared to have a more pronounced protective effect resulting in a decline of only 20.91% in GFR, with no significant change in ERPF (increase of 0.93%) when co‐administered with CyA.

These observations indicate adenosine plays a minor role in the pathophysiology of CyA nephrotoxicity.
Role of nitric oxide in the induction and expression of morphine tolerance and dependence in mice
Authors: Dambisya Yoswa M. , Lee Tat‐Leang
Published: July 2012

The possible involvement of nitric oxide (NO) in the induction and expression of morphine tolerance and dependence was studied in mice. A two‐day repeated injection regimen was used to induce morphine tolerance and dependence. Tolerance was assessed by the tail flick test and physical dependence by naloxone challenge, on the third day.

Two days pretreatment with L‐arginine (20 mg kg−1, twice daily) or D‐NG‐nitro arginine methyl ester (D‐NAME, 20 mg kg−1, twice daily) alone had no effect on subsequent morphine antinociception. L‐NG‐monomethyl arginine (L‐NMMA, 10 mg kg−1, twice daily) for two days led to a slight increase (not statistically significant) in morphine antinociception; while L‐NG‐nitro arginine methyl ester (L‐NAME, 10 mg kg−1, twice daily) for two days led to attenuation of morphine analgesia. None of the animals treated with these drugs alone showed signs characteristic of the opioid withdrawal syndrome upon naloxone challenge.

Induction phase L‐arginine slowed the development of opioid tolerance and physical dependence, while L‐NAME and L‐NMMA led to a higher degree of tolerance but had no effect on the development of physical dependence.

L‐Arginine and D‐NAME had no effect on the expression of morphine tolerance and physical dependence. Expression phase L‐NAME and L‐NMMA, on the other hand, attenuated morphine tolerance and reduced the incidence of withdrawal signs.

NO may, therefore, play a role in both phases of morphine tolerance and dependence: elevation of NO levels during the induction phase delays the development of opioid tolerance/dependence, while inhibition of NO synthase accelerates the development of tolerance. Inhibition of NO attenuates the expression of both tolerance and physical dependence.
Potentiation by cadmium ion of ATP‐evoked dopamine release in rat phaeochromocytoma cells
Authors: Ikeda Makoto , Koizumi Schuichi , Nakazawa Ken , Inoue Kaori , Ito Kanako , Inoue Kazuhide
Published: July 2012

The effects of cadmium ion (Cd2+) on release of dopamine and on an inward current evoked by extracellular ATP were investigated in rat phaeochromocytoma PC12 cells.

Cd2+ (100 μm‐3 mM) potentiated the dopamine release evoked by 30 μm ATP from the cells. Cd2+ (100 μm) shifted the concentration‐response curve of ATP‐evoked dopamine release to the left without affecting the maximal response.

Suramin (30 μm) completely abolished the dopamine release evoked by 30 μm ATP but only partially inhibited the release evoked by 100 μm ATP consistent with its role as a competitive antagonist. The response evoked by 30 μm ATP in the presence of Cd2+ (300 μm) was comparable to that observed with 100 μm ATP alone; however, only the former was almost completely inhibited by suramin.

Cd2+ (100 μm) potentiated an inward current activated by 30 μm ATP alone. A higher concentration of Cd2+ (300 μm) had a smaller effect on amplitude potentiation but significantly prolonged the duration of the current.

The time‐course of the ATP‐evoked dopamine release was investigated using a real‐time monitoring system for dopamine release. Although Cd2+ (300 μm) had little effect on the time‐course of activation the ATP‐evoked dopamine release, it produced a long‐lasting dopamine release which slowly returned to the baseline.

Taken together, these observations suggest that Cd2+ enhances ATP‐evoked dopamine release by affecting P2‐purinoceptor/channels. The enhancement may be attributed to a Cd2+‐dependent increase in sensitivity to ATP.
Micturition in conscious rats with and without bladder outlet obstruction: role of spinal α1‐adrenoceptors
Authors: Ishizuka Osamu , Persson Katarina , Mattiasson Anders , Naylor Alasdair , Wyllie Michael , Andersson Karl‐Erik
Published: July 2012

In normal rats and rats with bladder hypertrophy secondary to outflow obstruction, undergoing continuous cystometry, we examined the responses to the selective α1‐adrenoceptor antagonist doxazosin given intrathecally (i.t.) and intra‐arterially (i.a.). In addition, we investigated the effects of the drug on L‐dopa‐induced bladder hyperactivity in normal, unobstructed rats.

Doxazosin 50 nmol (approximately 60 μg kg−1), given i.t., decreased micturition pressure in normal rats and in animals with post‐obstruction bladder hypertrophy. The effect was much more pronounced in the animals with hypertrophied/overactive bladders. Doxazosin did not markedly affect the frequency or amplitude of the unstable contractions observed in obstructed rats. In contrast, however, doxazosin reduced L‐dopa‐induced bladder overactivity. When tested, the enantiomers of doxazosin produced qualitatively similar effects to doxazosin, but there was no evidence of stereoselectivity.

The results suggest that in addition to the well documented action on prostatic and lower urinary tract smooth muscle, and an effect on the sympathetic outflow to the bladder, bladder neck, prostate, and external urethral sphincter, doxazosin may have an action at the level of the spinal cord and ganglia, thereby reducing activity in the parasympathetic nerves to the bladder. This effect is more pronounced in rats with bladder hypertrophy than in normal rats.
Blockade of swelling‐induced chloride channels by phenol derivatives
Authors: Gschwentner Martin , Jungwirth Andreas , Hofer Sabine , Wöll Ewald , Ritter Markus , Susanna Alex , Schmarda Andreas , Reibnegger Gilbert , Pinggera Germar M. , Leitinger Markus , Frick Julian , Deetjen Peter , Paulmichl Markus
Published: July 2012

. In NIH3T3 fibroblasts, the chloride channel involved in regulatory volume decrease (RVD) was identified as ICln, a protein isolated from a cDNA library derived from Madin Darby canine kidney (MDCK) cells. ICln expressed in Xenopus laevis oocytes gives rise to an outwardly rectifying chloride current, sensitive to the extracellular addition of nucleotides and the known chloride channel blockers, DIDS (4,4′‐diisothiocyanatostilbene‐2,2′‐disulphonic acid) and NPPB (5‐nitro‐2‐(3‐phenylpropylamino)‐benzoic acid). We set out to study whether substances structurally similar to NPPB are able to interfere with RVD.

. RVD in NIH3T3 fibroblasts and MDCK cells is temperature‐dependent.

. RVD, the swelling‐dependent chloride current and the depolarization seen after reducing extracellular osmolarity can be blocked by gossypol and NDGA (nordihydroguaiaretic acid), both structurally related to NPPB.

. The cyclic AMP‐dependent chloride current elicited in CaCo cells is less sensitive to the two substances tested while the calcium‐activated chloride current in fibroblasts is insensitive.

. The binding site for the two phenol derivatives onto ICln seems to be distinct but closely related to the nucleotide binding site identified as G × G × G, a glycine repeat located at the predicted outer mouth of the Icln channel protein.
Inhibition of NO‐mediated responses by 7‐ethoxyresorufin, a substrate and competitive inhibitor of cytochrome P450
Authors: Li C.G. , Rand M.J.
Published: July 2012

. The effects of 7‐ethoxyresorufin (7‐ER), which is a substrate for and competitive inhibitor of cytochrome P450, were studied on responses to nitric oxide (NO), the NO donors sodium nitroprusside (SNP) and glyceryl trinitrate (GTN), acetylcholine‐induced endothelium‐dependent relaxations of rat and rabbit aortic rings and nitrergic nerve stimulation‐induced relaxations of rat anococcygeus muscles.

. In rat and rabbit aortic rings, 7‐ER (2 μm) inhibited the relaxations to acetylcholine in endothelium‐intact preparations and the relaxant action of NO in endothelium‐denuded preparations. Relaxant responses to SNP and GTN were inhibited by 7‐ER in the rat but not rabbit aortic rings. However, the relaxant actions of papaverine and 8‐bromo‐cyclic GMP were not affected by 7‐ER.

. In rat anococcygeus muscles, 7‐ER (2 μm) inhibited the relaxant action of NO, but relaxations elicited by nitrergic nerve stimulation were only partly inhibited by a higher concentration of 7‐ER (10 μm).

. After inhibition by 7‐ER, superoxide dismutase (100 u ml−1) restored NO‐induced relaxations of the rat aortic rings, but not acetylcholine‐, SNP or GTN‐induced relaxations, and restored NO‐ and nitrergic nerve stimulation‐induced relaxations of anococcygeus muscles.

. Another cytochrome P450 inhibitor, troleandomycin (10–30 μm), had no effect on NO‐ or acetylcholine‐induced relaxations of rat aortic rings and NO‐ or nitrergic nerve stimulation‐induced relaxations of anococcygeus muscles. However, resorufin, an analogue of 7‐ER, inhibited responses to acetylcholine, NO and GTN in rat aortic rings.

. The results suggest that 7‐ER inhibited responses to NO and nitrergic nerve stimulation through generation of superoxide radicals. However, an additional mechanism may be involved in the reduction in acetylcholine‐induced responses in aortic rings.

. A 7‐ER sensitive P450 system may be involved in the bioactivation of GTN and SNP in rat aortic rings, but not in rabbit aorta or rat anococcygeus muscles.
Blockade of porcine carotid vascular responses to sumatriptan by GR127935, a selective 5‐HT1D receptor antagonist
Authors: De Vries Peter , Heiligers Jan P.C. , Villalón Carlos M. , Saxena Pramod R.
Published: July 2012

. It has previously been shown that the antimigraine drug, sumatriptan, a putative 5‐HT1D receptor agonist, decreases porcine common carotid and arteriovenous anastomotic blood flows, but slightly increases the arteriolar (capillary) blood flow to the skin and ears. Interestingly, such responses, being mediated by 5‐HT1‐like receptors, are resistant to blockade by metergoline, which, in addition to displaying a very high affinity for (and occasionally intrinsic efficacy at) the 5‐HT1D receptor subtypes, blocks (with lower potency than methiothepin) some 5‐HT1D receptor‐mediated vascular responses. These findings raise doubts whether sumatriptan‐sensitive 5‐HT1‐like receptors mediating changes in the distribution of porcine carotid blood flow are identical to cloned 5‐HT1D receptors. With the recent advent of the potent and selective 5‐HT1D receptor antagonist, GR127935, we have examined in the present study whether the carotid vascular effects of sumatriptan in the pig are amenable to blockade by GR127935.

. In animals pretreated with saline, sumatriptan (30, 100 and 300 μm kg−1, i.v.) reduced the total carotid and arteriovenous anastomotic blood flows in a dose dependent manner. In contrast, sumatriptan increased blood flow to the skin, ears and fat, although the total capillary fraction was not significantly affected.

. While GR127935 pretreatment (0.25 and 0.5 mg kg−1) itself slightly reduced the total carotid and arteriovenous anastomotic blood flows, carotid vasoconstrictor responses to sumatriptan were either partly (0.25 mg kg−1) or completely (0.5 mg kg−1) blocked by the compound. In GR127935 pretreated animals, the sumatriptan‐induced increases in blood flow to the skin, ears and fat were also attenuated.

. Taken together, the results suggest that arteriovenous anastomotic constriction and, possibly, arteriolar dilatation in the skin, ears and fat by sumatriptan are mediated by 5‐HT1D receptors. Therefore, vascular 5‐HT1‐like receptors in the porcine carotid bed appear to be identical to 5‐HT1D receptors.
Baroreflex resetting but no vascular tolerance in response to transdermal glyceryl trinitrate in conscious rabbits
Authors: Serone Adrian P. , Angus James A. , Wright Christine E.
Published: July 2012

. We investigated whether acute (5 h) and chronic (3 days) transdermal glyceryl trinitrate (GTN) patches could cause the development of tolerance in terms of haemodynamics and vascular reactivity in the conscious rabbit. The effects of haemodynamic tolerance were assessed on arterial pressure, heart rate and the baroreflex control of heart rate, while hindquarter vascular reactivity in response to dilator and constrictor drugs and reactive hyperaemia were used to assess vascular tolerance.

. Seven days prior to experiments, an inflatable cuff, a pulsed Doppler flow probe and an indwelling intra‐aortic catheter (for i.a. agonist infusions) were implanted around the lower abdominal aorta.

. In acute experiments, the effects of 0–5 h treatment with transdermal GTN (0 Sham), 10 or 20 mg 24 h−1) on MAP, HR and the baroreflex were examined. Chronic experiments were performed on three separate days (days 0 ‐ before, 4 ‐ with GTN patch and 8 ‐ recovery). On each day, the baroreflex, reactive hyperaemic responses and hindquarter vascular dose‐response curves to i.a. GTN, adenosine, acetylcholine, S‐nitroso‐N‐acetylpenicillamine (SNAP) and methoxamine were assessed. On days 1–4, GTN was administered transdermally via a patch(es) (10 mg 24 h−1(low dose) or 20 mg 24 h−1(high dose); renewed every 24 h).

. Acute treatment with 20 mg GTN 24 h−1, but not with 0 (n= 4) or 10 mg GTN 24 h−1(n= 4), caused a significant fall in MAP (−8±1 mmHg;n= 4) and resetting of the baroreflex by 5 h. Chronic GTN caused a significant fall in MAP of 8±2 and 8±2 mmHg on day 4 with low (n= 8) and high dose (n= 8), respectively, with no change in HR. There was no significant change to hindquarter vascular reactivity to i.a. infusion of GTN, nor were there any significant differences in the reactivity to i.a. adenosine, acetylcholine, SNAP or methoxamine with either low or high doses of GTN.

. Chronic GTN treatment with low and high dose patches caused a parallel leftward shift (‘resetting’) of the baroreflex on day 4. By day 8, the baroreflex had still not recovered from this leftward shift.

. In the rabbit, chronic exposure to clinical nitrate patches caused haemodynamic compensation and baroreflex resetting but no evidence of vascular reactivity tolerance. Novel NO donor drugs and delivery regimens which provide intermittent dosing may prevent the development of haemodynamic resetting rather than preventing vascular tolerance, a commonly perceived difficulty in chronic nitrate therapy.
Inhibition of nitrergic relaxations by a selective inhibitor of the soluble guanylate cyclase
Authors: Cellek Selim , Kasakov Lubomir , Moncada Salvador
Published: July 2012

. The actions of 1H‐[1,2,4]oxadiazolo[4,3,‐a]quinoxalin‐1‐one (ODQ), a specific inhibitor of the soluble guanylate cyclase (SGC), were investigated in the rabbit anococcygeus muscle.

. ODQ (1 nM‐1 μm) inhibited in a concentration‐dependent manner the relaxations induced by electrical field stimulation (EFS; 50 V, 0.3 ms duration, 1 Hz, for 5 s, every 120 s).

. ODQ (1 μm) also inhibited the relaxations elicited by EFS (50 V, 0.3 ms duration, 1, 2.5, 5, 10 Hz, for 5 s) and sodium nitroprusside (SNP; 1 μm) without affecting those induced by isoprenaline (1 μm), atrial natriuretic peptide (ANP; 100 nM) or an analogue of cyclic GMP (8‐pCPT‐cyclic GMP; 500 μm).

. ODQ (1 μm) inhibited the elevations in the concentration of cyclic GMP induced by SNP or EFS, but not by ANP. ODQ did not affect the concentrations of cyclic AMP.

. Nitrergic relaxation in this tissue appears, therefore, to be mediated via activation of SGC.
Nitric oxide as a mediator of cocaine‐induced penile erection in the rat
Authors: Chan Julie Y.H. , Huang Chian‐Ling , Chan Samuel H.H.
Published: July 2012

. The effect of local application of cocaine to the corpus cavemosum on intracavemous pressure (ICP), an experimental index for penile erection, was examined in Sprague‐Dawley rats anaesthetized with chloral hydrate. The potential involvement of dopamine, noradrenaline or nitric oxide as the chemical mediator in this process, and the pharmacological action of cocaine as a local anaesthetic in the induced increase in ICP, were also investigated.

. Intracavemous (i.e.) administration of cocaine (40, 80 or 160 μg) to the corpus cavemosum resulted in a dose‐related increase in both amplitude and duration of ICP.

. The elevation in ICP induced by cocaine (160 μg, i.e.) was not significantly influenced by prior injection into the corpus cavemosum of either the D1 or D2 dopamine receptor antagonist, R‐(+)‐SCH 23390 (250 pmol) or (—)‐sulpiride (250 pmol).

. Similarly, penile erection promoted by cocaine (160 μg, i.e.) was not appreciably affected by i.e. pretreatment with the α1, α2‐, or β‐adrenoceptor antagonist, prazosin (50 pmol), yohimbine (50 pmol) or propranolol (5 nmol).

. Whereas lignocaine (4 μmol, i.e.) depressed penile erection induced by papaverine (400 μg, i.e.), local application of cocaine (160 μg) into the corpus cavemosum still elicited significant elevation in ICP in the presence of lignocaine or papaverine.

. The increase in ICP induced by cocaine (160 μg, i.e.) was attenuated dose‐dependently by prior cavemosal administration of the NO synthase inhibitor, Nω‐nitro‐L‐arginine methyl ester (1‐NAME, 0.5, 1 or 5 pmol) or NG‐monomethyl‐L‐arginine (L‐NMMA, 2.5, 5 or 10 pmol). The blunting effect of L‐NAME or L‐NMMA was reversed by co‐administration of the NO precursor, L‐arginine (1 nmol, i.e.).

. Pretreatment by local application into the corpus cavemosum of methylene blue (2.5 μmol), an inhibitor of cytosolic guanylyl cyclase, antagonized cocaine‐induced penile erection.

. Direct i.e. administration of a NO donor, nitroglycerin (10 or 20 nmol), mimicked the local action of cocaine by promoting a significant increase in ICP.

. It is concluded that cocaine may induce penile erection by increasing ICP via a local action on the corpus cavemosum. This process did not appear to involve either dopamine or noradrenaline as the chemical mediator, nor the pharmacological action of cocaine as a local anaesthetic. On the other hand, it is likely that initiation and maintenance of penile erection elicited by cavemosal application of cocaine engaged an active participation of NO and subsequent activation of guanylyl cyclase in the corpus cavemosum.
Deficient nitric oxide responsible for reduced nerve blood flow in diabetic rats: effects of L‐NAME, L‐arginine, sodium nitroprusside and evening primrose oil
Authors: Omawari Nagashige , Dewhurst Mark , Vo Phuong , Mahmood Salina , Stevens Elizabeth , Tomlinson David R.
Published: July 2012

. This study examined the potential role of impaired nitric oxide production and response in the development of endoneurial ischaemia in experimental diabetes. Rats were anaesthetized (Na pentobarbitone 45 mg kg−1, diazepam 2 mg kg−1) for measurement of sciatic nerve laser Doppler flux and systemic arterial pressure. Drugs were administered into the sciatic endoneurium via a microinjector attached to a glass micropipette.

. In two separate studies comparing diabetic rats (streptozotocin‐induced; 8–10 wk duration) with controls, nerve Doppler flux in diabetic rats (Study 1, 116.6±40.4 and Study 2, 90.1±34.7 (s.d.) in arbitrary units) was about half that measured in controls (219.6±52.4 and 212.8±95.5 respectively; P<0.005 for both). There were no significant differences between the two in systemic arterial pressure.

. Inhibition of nitric oxide production by microinjection of 1 nmol L‐NAME into the endoneurium halved flux in controls (to 126.3±41.3 in Study 1 and 102.1±38.9 in Study 2; both P<0.001), with no significant effect in diabetic rats, indicating markedly diminished tonic nitric oxide production in the latter. D‐NAME was without effect on nerve Doppler flux.

. L‐Arginine (100 nmol), injected after L‐NAME, markedly increased flux in controls (by 65.8% (P<0.03) and 97.8% (P<0.01) in the two studies) and by proportionally similar amounts in diabetic rats [75.8% (P<0.001) and 60.2% (P<0.02)]. The nitro‐donor, sodium nitroprusside (SNP; 10 nmol) had similar effects to L‐arginine in both groups (increases of 66.0% in controls and 77.5% in diabetics; both P<0.002).

. A second diabetic group, treated with evening primrose oil performed exactly like control rats in respect of responses to L‐NAME, L‐arginine and SNP.

. These findings implicate deficient nitric oxide in nerve ischaemia of diabetes and suggest correction thereof as a mechanism of action of evening primrose oil.
Effects of the endothelin receptor antagonist, SB 209670, on circulatory failure and organ injury in endotoxic shock in the anaesthetized rat
Authors: Ruetten Hartmut , Thiemermann Christoph , Vane John R.
Published: July 2012

. This study investigates the effects of the non‐selective ETA/ETB receptor antagonist, SB 209670, on systemic haemodynamics, renal function, liver function, acid‐base balance and survival in a rat model of endotoxic shock.

. Injection of E. coli lipopolysaccharide (LPS, 10 mg kg−1, i.v.) resulted in increases in the serum levels of tumour necrosis factor‐α (TNF‐α, maximum 60 min after LPS), endothelin‐1 (ET‐1; maximum 120 min after LPS), and interferon‐γ (IFN‐γ, maximum 180 min after LPS).

. Injection of LPS also resulted in a fall in blood pressure from 113 ± 3 mmHg (time = 0) to 84 ± 4 mmHg at 360 min (n = 15) as well as a hyporeactivity to the vasoconstrictor responses elicited by noradrenaline (NA, 1 μg kg−1, i.v.). Pretreatment of rats with a continuous infusion of SB 209670 (3 mg kg−1, i.v. bolus + 100 μg kg−1, i.v. infusion commencing 15 min prior to LPS) significantly augmented the hypotension as well as the vascular hyporeactivity to NA caused by endotoxaemia.

. Pretreatment of LPS‐rats with SB 209670 (3 mg kg−1, i.v. bolus given 15 min prior to LPS) or infusion of SB 209670 (bolus dose and infusion as above) resulted in a reduction in 6 h‐survival from 71% (control) to 30% and 13%, respectively.

. Endotoxaemia for 4 h resulted in rises in the serum levels of urea and creatinine (indicators of renal failure), but not in the serum levels of bilirubin, GPT and GOT (indicators of liver dysfunction and/or hepatocellular injury). Pretreatment of LPS‐rats with SB 209670 (3 mg kg−1, i.v. bolus 15 min prior to LPS) significantly augmented the serum levels of creatinine, bilirubin, GPT and GOT caused by endotoxin. In addition, endotoxaemia caused, within 15 min, an acute metabolic acidosis (falls in pH, HCO3− and base excess) which was compensated by hyperventilation (fall in Paco2). Pretreatment of LPS‐rats with SB 209670 (3 mg kg−1, i.v. bolus) significantly augmented the metabolic acidosis caused by LPS.

. Thus, the non‐selective ETA/ETB receptor antagonist, SB 209670, augments the degree of (i) hypotension, (ii) vascular hyporeactivity to noradrenaline, (iii) renal dysfunction and (iv) metabolic acidosis caused by endotoxin in the anaesthetized rat. In contrast to rats treated with LPS alone, LPS‐rats treated with SB 209670 exhibited liver dysfunction and hepatocellular injury. We propose that the release of endogenous ET‐1 serves to maintain blood pressure and subsequently organ perfusion in septic shock.
Functional correlation between allopregnanolone and [35S]‐TBPS binding in the brain of rats exposed to isoniazid, pentylenetetrazol or stress
Authors: Concas Alessandra , Mostallino Maria Cristina , Perra Chiara , Lener Raffaela , Roscetti Gianna , Barbaccia Maria Luisa , Purdy Robert H. , Biggio Giovanni
Published: July 2012

The relation between changes in the cerebral cortical concentration of allopregnanolone and γ‐aminobutyric acid (GABA) type A receptor function after intracerebroventricular injection of this neurosteroid was investigated in male rats.

Intracerebroventricular administration of allopregnanolone (1.25 to 15 μg) produced a maximal increase (100 fold at the highest dose) in cortical allopregnanolone concentration within 5 min; the concentration remained significantly increased at 15 and 30 min, before returning to control values by 60 min.

The same treatment induced a rapid and dose‐dependent decrease in the binding of t‐[35S]‐butylbicyclophosphorothionate ([35S]‐TBPS) to cerebral cortical membranes measured ex vivo, an effect mimicked by the benzodiazepine midazolam but not by the 3β‐hydroxyepimer of allopregnanolone. The time course of changes in [35S]‐TBPS binding paralleled that of brain allopregnanolone concentration.

In a dose‐dependent manner, allopregnanolone both delayed the onset of convulsions and inhibited the increase in [35S]‐TBPS binding to cortical membranes induced by isoniazid. The potency of allopregnanolone in inhibiting [35S]‐TBPS binding in isoniazid‐treated rats was approximately four times that in control animals.

The ability of allopregnanolone to decrease [35S]‐TBPS binding in isoniazid‐treated rats also correlated with its anticonvulsant activity against pentylenetetrazol‐induced seizures as well as its inhibitory effect on the increase in [35S]‐TBPS binding induced by foot shock.

The results indicate that the in vivo administration of allopregnanolone enhances the function of GABAA receptors in rat cerebral cortex and antagonizes the inhibitory action of stress and drugs that reduce GABAergic transmission.
Effects of cyclopiazonic acid and thapsigargin on electromechanical activities and intracellular Ca2+ in smooth muscle of carotid artery of hypertensive rats
Authors: Sekiguchi F. , Shimamura K. , Akashi M. , Sunano S.
Published: July 2012

The effects of cyclopiazonic acid (CPA) and thapsigargin (TG), both of which are known to inhibit sarcoplasmic reticular Ca2+‐ATPase, on the mechanical activities, intracellular Ca2+ level and electrical activities of smooth muscle of the carotid artery of stroke‐prone spontaneously hypertensive rats (SHRSP) and Wistar Kyoto rats (WKY) were compared.

Both CPA and TG induced elevation of tension of the smooth muscle, which was composed of a phasic and a tonic component. The level of tension attained, especially the tonic component, was greater in the preparation from SHRSP.

The elevation of tension was associated with an increased intracellular Ca2+ level. Both the elevation of tension and the increase in intracellular Ca2+ were diminished by the removal of extracellular Ca2+ or by the application of verapamil.

The resting membrane potential of the preparations from SHRSP were depolarized to a greater extent than those from WKY. CPA depolarized the smooth muscle from both SHRSP and WKY, and the final level was also more depolarized in the preparation from SHRSP.

These results indicate that the elevation of tension induced by these drugs is mainly due to increased Ca2+ influx through voltage‐dependent Ca2+ channels, and the difference in the action between the preparation from SHRSP and that from WKY can be explained mainly by the changes in the channels.

Thus, differences in the action of these drugs on the tension of smooth muscle between preparations from WKY and SHRSP can mainly be explained by the difference in the membrane potential which is related to the difference in voltage‐dependent Ca2+ influx.
Nitric oxide, a possible mediator of 1,4‐dihydropyridine‐induced photorelaxation of vascular smooth muscle
Authors: Lovren Fina , O'Neill Sean K. , Bieger Detlef , Igbal Nadeem , Knaus Ed E. , Triggle Chris R.
Published: July 2012

In rat aortic tissues pre‐contracted with phenylephrine, certain 1,4‐dihydropyridines (DHPs) such as Bay K 8644 (0.1 μm), PN 202791 (1 μm), RK 30 (1 μm), NI 104 (1 μm) and NI 105 (1 μm) enhanced photoactivated relaxations (photorelaxation or PR) whereas NI 72, NI 85, NI 99, NI 102, amlodipine, felodipine, nifedipine and nimodipine were inactive.

The PR inducing effects of Bay K 8644 were mimicked by the diabetogenic agent, streptozotocin (STZ).

Solutions of Bay K 8644 which had been irradiated for various periods of time initiated light independent transient relaxations followed by contractile responses in aortic tissue partially contracted with phenylephrine. With exposure times to light of 30 to 120 min, the intensity of the relaxation response to irradiated Bay K 8644 increased from 26±3.3 to 71±3.7% of the maximum contractile response to phenylephrine (n = 5). Conversely the contractile responses decreased, from 84.2±4.1 to 19.8±10.4% of the maximum contractile response to phenylephrine (n = 5).

Superoxide ions, generated by incubation of xanthine (2 mM) plus xanthine oxidase (10 mu ml−1) in physiological saline solution (PSS) NaCl 118, KCl 4.7, CaCl2 2.5, KH2PO4 1.2, MgSO4 1.2, NaHCO3 12.5 and glucose 11.1 (mM) for 1 h, reduced the PR induced by DHPs, STZ, and also NO‐induced relaxations of rat aortic preparations.

Direct measurements of NO indicate that, following exposure to a polychromatic light source, equimolar concentrations (0.1 mM) of the DHP compounds that enhance PR, as well as STZ, photodegrade to release NO (25±2‐40.3±5.9 nmol min−1, n = 6).

Structure‐activity studies indicate that a nitro group at the −3 position of the dihydropyridine ring is essential for DHPs to support PR.

These data suggest that the photodegradation of DHPs and STZ leading to the release of NO provides the primary cellular process underlying the PR response.
Involvement of nitric oxide and eicosanoids in platelet‐activating factor‐induced haemodynamic and haematological effects in dogs
Authors: Noguchi Katsuhiko , Matsuzaki Toshihiro , Shiroma Noboru , Ojiri Yoshihiko , Sakanashi Matao
Published: July 2012

Platelet‐activating factor (PAF) is a phospholipid mediator with potent cardiovascular and haematological actions. But its mechanisms of action in vivo have not been fully elucidated, probably due to difficulties arising from previous findings that the effects of PAF are largely mediated by the release of a variety of other autacoids. In the present study, the roles of nitric oxide and eicosanoids in the effects of PAF (0.01‐0.25 μg kg−1 i.v.) on systemic and pulmonary vasculatures and circulating blood cell count were pharmacologically evaluated in anaesthetized dogs.

Higher doses of PAF (>0.1 μg kg−1) produced a biphasic systemic hypotension. The first hypotension seen 30 s after the injection was accompanied by a decrease in systemic vascular resistance, thrombocytopenia and leukopenia, while the second hypotension seen 1–2 min after PAF was accompanied by a marked rise in pulmonary vascular resistance and decreases in aortic blood flow and cardiac contractility. Lower doses of PAF (0.01‐0.05 μg kg−1) caused only the first responses in a dose‐dependent manner.

Pretreatment with indomethacin inhibited the second responses to PAF without affecting the first responses. The thromboxane A2/prostaglandin H2 (TP)‐receptor antagonist vapiprost blocked the PAF‐induced rise in pulmonary vascular resistance. AA‐861, a 5‐lipoxygenase inhibitor, attenuated the PAF‐induced cardiac depression. The nitric oxide synthase inhibitor NG‐nitro‐l‐arginine methyl ester inhibited the PAF‐induced early decrease in systemic vascular resistance.

All observed changes in haemodynamics and blood cell count after PAF were almost abolished by TCV‐309, a PAF‐receptor antagonist.

Reproducible hypotension and thrombocytopenia produced by a lower dose of PAF (0.05 μg kg−1) were respectively attenuated and potentiated by pretreatment with NG‐nitro‐l‐arginine, another nitric oxide synthase inhibitor. Administration of l‐arginine reversed the effects of the nitric oxide synthase inhibitor.

These results indicate that PAF‐receptor‐mediated production of not only eicosanoids but also nitric oxide may contribute to the cardiovascular and haematological responses to PAF in the dog.
Electrophysiological actions of GABAB agonists and antagonists in rat dorso‐lateral septal neurones in vitro
Authors: Bon Christelle , Galvan Martin
Published: July 2012

The actions of GABAB‐receptor agonists and antagonists on rat dorso‐lateral septal neurones in vitro were recorded with intracellular microelectrodes.

In the presence of 1 μm tetrodotoxin to prevent indirect neuronal effects caused by action potential‐dependent neurotransmitter release, bath application of baclofen (0.1–30 μm) or SK&F 97541 (0.01–3 μm) evoked concentration‐dependent hyperpolarizations which reversed close to the potassium equilibrium potential; the EC50s were 0.55 and 0.05 μm, respectively. No significant desensitization was observed during prolonged agonist exposure (≤ 10 min).

Hyperpolarizations induced by baclofen were antagonized in a competitive manner by the following GABAB‐receptors antagonists (calculated pA2 values in parentheses): CGP 36742 (4.0), 2‐OH saclofen (4.2), CGP 35348 (4.5), CGP 52432 (6.7) and CGP 55845A (8.3). Responses to SK&F 97541 were also antagonized by CGP 55845A (pA2 = 8.4).

The amplitude of the late, GABAB receptor‐mediated inhibitory postsynaptic potential (i.p.s.p.) was reduced by the GABAB antagonists as follows (means ± s.e.mean): CGP 55845A (1 μm) 91 ± 5%, CGP 52432 (1 μm) 64 ± 5%, CGP 35348 (100 μm) 82 ± 5%, CGP 36742 (100 μm) 76 ± 8%, and 2‐OH saclofen (100 μm) 68 ± 3%.

It is concluded that neurones in the rat dorso‐lateral septal nucleus express conventional GABAB receptors, which are involved in the generation of slow inhibitory postsynaptic potentials. CGP 55845A is the most potent GABAB receptor antagonist described in this brain area.
Possible mechanism of the potent vasoconstrictor actions of ryanodine on femoral arteries from spontaneously hypertensive rats
Authors: Asano Masahisa , Kuwako Miho , Nomura Yukiko , Ito Kaoru M. , Ito Katuaki , Uyama Yoshiaki , Imaizumi Yuji , Watanabe Minoru
Published: July 2012

The Ca2+ buffering function of sarcoplasmic reticulum (SR) in the resting state of arteries from spontaneously hypertensive rats (SHR) was examined. Differences in the effects of ryanodine that removes the function of SR, on tension and cellular Ca2+ level were assessed in endothelium‐denuded strips of femoral arteries from 13‐week‐old SHR and normotensive Wistar‐Kyoto rats (WKY).

The addition of ryanodine to the resting strips caused a concentration‐dependent contraction in SHR. This contraction was extremely small in WKY. In the presence of 10−5 m ryanodine, caffeine (20 mM) failed to cause a further contraction in SHR, but it caused a small contraction in WKY. After washout of the strips with a Krebs solution, the resting tone was greatly elevated in SHR when compared with WKY.

The elevated resting tone in SHR strips was abolished by 10−7 m nifedipine. The ryanodine‐induced contraction was also abolished by 10−7 m nifedipine. Nifedipine itself caused a relaxation from the resting tone of SHR strips, suggesting the maintenance of myogenic tone.

In strips preloaded with fura‐PE3, the addition of 10−5 m ryanodine caused a large and moderate elevation of cytosolic Ca2+ level ([Ca2+]i) in SHR and WKY, respectively. After washout, the resting [Ca2+]i was greatly elevated in SHR. The ryanodine‐induced elevation of [Ca2+]i was decreased by 5 × 10−6 m verapamil in SHR. Verapamil itself caused a decrease in resting [Ca2+]i which was significantly greater in SHR than in WKY, and caused a relaxation only in SHR.

The resting Ca2+ influx in arteries measured by a 5 min incubation with 45Ca was significantly increased in SHR when compared with WKY. The resting Ca2+ influx was not increased by 10−5 m ryanodine in both SHR and WKY. The net cellular Ca2+ uptake in arteries measured by a 30 min incubation with 45Ca was decreased by 10−5 m ryanodine in both strains.

The resting Ca2+ influx was decreased by 10−7 m nifedipine in the SHR artery, but it was unchanged in the WKY artery.

These results suggest that (1) the Ca2+ influx via L‐type voltage‐dependent Ca2+ channels was increased in the resting state of the SHR femoral artery, (2) the greater part of the increased Ca2+ influx was buffered by Ca2+ uptake into the SR and some Ca2+ reached the myofilaments resulting in the maintenance of the myogenic tone, and (3) therefore the functional removal of SR by ryanodine caused a potent contraction in this artery.
Prevention by the 5‐HT3 receptor antagonist, ondansetron, of morphine‐dependence and tolerance in the rat
Authors: Hui Siu‐Chun G. , Sevilla Elenita L. , Ogle Clive W.
Published: July 2012

The effect of ondansetron, a selective 5‐hydroxytryptamine3 (5‐HT3) receptor antagonist, was studied in morphine‐addicted rats. Morphine‐dependence and tolerance, induced by drinking increasing concentrations of morphine sulphate in 5% sucrose solution for 3 weeks, were demonstrated by the naloxone‐precipitated withdrawal syndrome and tail flick response to a thermal noxious stimulus (water at 50°C), respectively.

Morphine‐dependence, assessed by naloxone precipitated withdrawal, was undetectable by the 6th day, when the animals drank only tap water for 7 days after the 3‐week induction period.

When detoxified rats were offered sucrose and morphine solutions for 10 days, the recurrence of opiate solution preference with relapse to dependence and tolerance was observed.

Giving ondansetron (0.1 or 1 μg kg−1; i.p.; twice daily) on the 14th day of, or 7 days prior to, the 3‐week induction period reduced dependence and tolerance seen during the 3‐week morphine induction and the 10‐day drinking preference periods.

5‐Hydroxytryptamine2 (5‐HT2) receptor antagonism by cyproheptadine (100 or 250 μg kg−1; i.p.; twice daily) did not influence morphine‐dependence and tolerance.

These findings suggest that ondansetron may be useful for treating opiate addiction and lowering the recidivism rate.
Effect of lignocaine in myocardial contusion: an experiment on rabbit isolated heart
Authors: Pu Qian , Mazoit Jean Xavier , Cao Lin Sen , Mao Wieke , Samii Kamran
Published: July 2012

The reported incidence of myocardial contusion after blunt chest trauma varies from 16 to 76%. Of these patients, about 6% present a severe, life threatening contusion. We used an isolated heart preparation to examine the effect of lignocaine on myocardial performance after contusion.

Thirty hearts obtained from male New Zealand rabbits were perfused at constant flow according to the Langendorff technique and were divided into four groups. The following parameters were measured at frequent intervals for 60 min: mean coronary perfusion pressure (CPP), left ventricular diastolic pressure (LVDP), developed pressure (DP), dP/dtmax, dP/dtmin.

Group 1 (n = 6) served as control, group 2 (n = 7) received lignocaine for 20 min (15 μm for the first 10 min and 30 μm for the following 10 min), group 3 (n = 9) had a contusion leading to a 30–50% decrease in dP/dtmax and group 4 (n = 8) had the contusion and the lignocaine infusion was started 10 min after the contusion and stopped after 30 min. Lignocaine concentration was measured in the effluent.

Lignocaine alone moderately decreased contractility in group 2. In group 3, after contusion, DP, dP/dtmax, and dP/dtmin were markedly decreased during the 60 min recording period. In group 4, lignocaine infusion rapidly restored contractility. DP, dP/dtmax and dP/dtmin returned towards their basal values. This improvement of contractility remained stable, even after lignocaine infusion was discontinued.

In our rabbit isolated heart preparation, lignocaine at a low therapeutic concentration was able to restore contractility after contusion. These results need to be confirmed by other studies but this may lead to promising therapeutic intervention.
Inositol hexakisphosphate binding sites in rat heart and brain
Authors: Rowley Kevin G. , Gundlach Andrew L. , Cincotta Marion , Louis William J.
Published: July 2012

. Inositol 1,4,5‐trisphosphate (Ins(1,4,5)P3) and inositol hexakisphosphate (InsP6) are produced in response to stimulation of cardiac α1‐adrenoceptors. While the role of Ins(1,4,5)P3 and Ins(1,4,5)P3 receptors is well‐defined in many tissues including brain, the functional role of the putative InsP6‐InsP6 receptor system in cardiac function is less clear. Using quantitative autoradiography, this study examined the characteristics and regional localization of [3H]‐InsP6 binding sites in rat heart and compared the affinity of a range of inositol polyphosphates for [3H]‐InsP6 and [3H]‐Ins(1,4,5)P3 binding sites in heart and brain.

. [3H]‐InsP6 bound to a single, high affinity site in sections of rat heart (KD ranging from 22 ± 1.9 nM in right atria to 35 ± 2.6 nM in the interventricular septum, n = 7). The maximal number of binding sites (Bmax) ranged from 5.1 ± 0.48 to 12 ± 1.8 pmol mg−1 protein in left atrium and left ventricle, respectively. Inositol phosphates inhibited binding of [3H]‐InsP6 with the order of potency: InsP6 > Ins(1,4,5)PS3 > inositol 1,3,4,5‐tetrakisphosphate ≥ inositol pentakisphosphate > Ins(1,4,5)P3 > > inositol mono‐ and bisphosphates, consistent with the labelling of an InsP6 binding site.

. The Ins(1,4,5)P3 analogue, Ins(1,4,5)PS3, originally investigated as a putative selective radioligand for the Ins(1,4,5)P3 receptor, was a potent inhibitor of [3H]‐InsP6 binding in all heart regions (KI = 170–260 nM). The KI of Ins(1,4,5)PS3 for the inhibition of [3H]‐Ins(1,4,5)P3 binding in rat brain (60–220 nM) was similar to that observed for the inhibition of [3H]‐InsP6 binding in heart, suggesting that Ins(1,4,5)PS3 is not a specific ligand for either Ins(1,4,5)P3 or InsP6 receptor binding sites.

. Previous studies have detected [3H]‐InsP6 binding in mitochondrial and sarcoplasmic reticulum fractions of heart and links between InsP6 and cardiac mitochondrial Ca2+ regulation have been proposed, suggesting further studies are warranted to determine the functional role(s) of InsP6 and InsP6 receptor binding sites in cardiac tissue.
Inhibition by tetranactin of interleukin 1β‐ and cyclic AMP‐induced nitric oxide synthase expression in rat renal mesangial cells
Authors: Kunz Dieter , Walker Gaby , Wiesenberg Irmgard , Pfeilschifter Josef
Published: July 2012

. We have investigated whether tetranactin, a cyclic antibiotic produced by Streptomyces aureus with a molecular structure related to cyclosporin A, influences inducible nitric oxide synthase (iNOS; EC 1.14.13.39) induction in rat glomerular mesangial cells.

. Previously we have shown that iNOS is expressed in renal mesangial cells in response to two principal classes of activating signals comprising inflammatory cytokines such as interleukin 1 (IL‐1) or tumour necrosis factor α and agents that elevate cellular levels of cyclic AMP. Treatment of mesangial cells with IL‐1β or the membrane‐permeable cyclic AMP analogue, N6, 0–2′‐dibutyryladenosine 3′,5′‐phosphate (Bt2 cyclic AMP) for 24 h induces iNOS activity measured as nitrite levels in cell culture supernatants by 44 fold or 33 fold, respectively. Incubation of mesangial cells with tetranactin inhibits IL‐1β‐ and cyclic AMP‐dependent production of nitrite in a dose‐dependent fashion with IC50 values of 50 nM and 10 nM, respectively.

. Western‐blot analyses of mesangial cell extracts reveal that the inhibition of nitrite synthesis by tetranactin is due to a suppression of iNOS protein levels. This effect is preceded by a reduction of iNOS mRNA steady state levels as demonstrated by Northern blot analyses of total cellular RNA isolated from stimulated mesangial cells.

. Thus, tetranactin is a potent inhibitor of iNOS expression in cytokine‐ and cyclic AMP‐stimulated mesangial cells and represents a new class of iNOS inhibitors with IC50s in the low nanomolar range. This compound may be useful in the therapy of diseases associated with pathological NO overproduction due to iNOS expression.