bluuebunny/crossref_metadata_2025 huggingface dataset:
Peripheral α2‐adrenoceptor‐mediated sympathoinhibitory effects of mivazerol
Authors: Richer C. , Gobert J. , Noyer M. , Wülfert E. , Giudicelli JF
Published: August 2009

Summary—Mivazerol is a new compound that could potentially reduce perioperative cardiovascular morbidity and mortality in patients with or at risk of coronary disease and submitted to surgery. This action of mivazerol depends on a well documented centrally mediated reduction in sympathetic nerve activity, but a direct peripheral decrease in sympathetic neurotransmitter release induced by activation of prejunctional α2‐adrenoceptors located on sympathetic nerve endings could also contribute. To investigate this issue, the effects of mivazerol on the pressor, systemic and regional hemodynamic (pulsed Doppler technique) as well as on the cardiac responses to electrical stimulation of the spinal cord (SCS) were measured in pithed rats in the absence and in the presence of mivazerol. Mivazerol exerted strong sympathoinhibitory effects: SCS‐induced increases in blood pressure, total peripheral resistance and heart rate were dose‐dependently reduced by mivazerol, but among the regional vascular beds investigated, only the hindlimb vasoconstrictor responses were significantly drug‐affected. All these sympathoinhibitory effects of mivazerol were abolished by prior yohimbine administration. Simultaneously, mivazerol did not induce any postjunctional adrenoceptor blockade as it did not affect noradrenaline cardiac and hemodynamic effects. On the contrary, through postjunctional α2‐adrenoceptor stimulation, mivazerol, in this pithed preparation, dose‐dependently increased blood pressure, total peripheral and hindlimb vascular resistances, but heart rate was not affected. We conclude that, in the pithed rat, mivazerol exerts strong peripheral sympathoinhibitory effects. The mechanism involved is prejunctional α2‐adrenoceptor activation as i) mivazerol does not display any postsynaptic α‐adrenoceptor blocking effect — it even behaves as a postsynaptic α2‐adrenoceptor agonist — and ii) yohimbine abolishes mivazerol's sympathoinhibitory effects. Thus, direct peripheral together with central mechanisms contribute to mivazerol's sympathoinhibitory effects and ultimately to its cardioprotective action.
Modulation by alcohol and methadone of 2‐deoxyglucose‐stimulated pancreatic secretion in the rat
Authors: Nagain‐Domaine C. , Tsocas A. , Presset O. , Rozé C. , Vaille C.
Published: August 2009

Summary— Alcohol intake is a major problem in drug addicts, and it is not clear whether the effects of alcohol and opiates are additive or potentiating. Vagally stimulated pancreatic secretion in rats is potently inhibited by opiates acting centrally at μ‐receptors. In the present experiments, we determined the effects of methadone on 2‐deoxyglucose (2DG)‐stimulated pancreatic secretion in rats treated with acute (1.9 g/kgṁ3 h, intravenously) or chronic (1 or 3 month drinking) ethanol. In both acute and 1 month chronic alcoholic rats, methadone administered at its 50% inhibitory dose (ID50) reduced by about 50% 2DG‐stimulated pancreatic secretion of sodium, bicarbonate and protein, and ethanol had only faint, nonsignificant inhibitory effects. In 3 month chronic alcoholic rats, similar results were obtained, but methadone inhibited 2DG‐stimulated pancreatic secretion by 60 to 90% in these older rats. No significant interaction was found in any condition between ethanol and methadone, suggesting that they had only additive, but not potentiating effects in this model.
Pharmacological manipulation of human gastrointestinal blood flow
Authors: Mathias CJ
Published: August 2009

Summary— The splanchnic circulation is one of the largest vascular regions in man. In the past, this has been difficult to study because of methodological problems. The adapting of noninvasive Doppler techniques has made it possible to develop reproducible measurements of coeliac and superior mesenteric artery blood flow, which are the main contributors to the gastrointestinal vasculature. This has resulted in the further understanding of neurogenic and humoral control of this region in a number of physiological and pathophysiological states, and has contributed towards the knowledge of its pharmacological control. These studies are of relevance to cardiovascular homeostasis and, in particular, systemic blood pressure control which depends upon various factors including responses in different vascular regions. In this review the key physiological factors which influence pharmacological studies on this circulation will be discussed. Examples will be provided, in subjects with cardiovascular and neurological disorders, of how administration of endogenous and exogenous substances, including drugs with specific pharmacological effects, alter human gastrointestinal blood flow. These will include insulin, alcohol, the somatostatin analogue octreotide, the central acting sympatholytic clonidine and the angiotensin H‐converting inhibitor captopril. The relevance of these studies to subjects with postural hypotension due to sympathetic denervation and to primary hypertension, in particular, will be discussed.
Antioxidant action of Vaccinium myrtillus extract on human low density lipoproteins in vitro: initial observations
Authors: Laplaud PM , Lelubre A. , Chapman MJ
Published: August 2009

Summary— Oxidative modifications of low density lipoproteins (LDL) are now recognised as one of the major processes in atherogenesis. Various drugs, as well as a number of natural products, have been proposed to inhibit such processes. Among the naturally‐occurring constituents of plants which appear to possess antioxidant activity are polyphenolic compounds such as flavonoids. The aqueous extract of Vaccinium myrtillus is rich in such molecules. In this report, we describe the in vitro antioxidative potential of this extract on human LDL. The copper‐induced oxidative modification of these lipoproteins was assessed using 1) measurement of oxidative resistance as determined by the lag‐phase preceding conjugated diene formation; 2) quantification of the amount of lipoperoxides and thiobarbituric acid‐reactive substances generated, and measurement of the modification in the net negative electrical charge of the lipoproteins, over a 7‐hour time course experiment. Trace amounts of V myrtillus extract (15 to 20 μg/mL) induce statistically significant changes in the oxidation behaviour of LDL, which include 1) prolongation of the lag‐phase of conjugated diene production (P < 0.01); 2) reduction in the formation of lipoperoxides and of thiobarbituric acid‐reactive substances up to 7 hours and especially between 1 and 5 hours (P < 0.01); and 3) inhibition of modification in the net negative charge of LDL. These results demonstrate that V myrtillus extract exerts potent protective action on LDL particles during in vitro copper‐mediated oxidation. Calculation of IC50 values indicates that, on a molar basis, this extract may indeed be more potent than either ascorbic acid or butylated hydroxytoluene in the protection of LDL particles from oxidative stress.
Combination of aspirin and metoclopramide produces a synergistic antithrombotic effect in a canine model of coronary artery thrombosis
Authors: Duval N. , Grosset A. , O'Connor SE
Published: August 2009

Summary—We compared the antithrombotic properties of low doses of aspirin (0.03, 0.1 mg kg−1intravenously [iv]) and metoclopramide (0.1, 0.3 mg kg−1iv) alone or in combination. The animal model chosen for this study involved the generation of cyclic flow variations (CFV) in the circumflex coronary artery of anaesthetized dogs as a result of a critical coronary stenosis associated with a controlled arterial lesion at the site of stenosis. Subsequent regular CFV represent sequential thrombus formation and embolization in the damaged vessel. Neither aspirin nor metoclopramide alone demonstrated antithrombotic properties at the doses tested. However, the combination of aspirin 0.1 mg kg−1iv and metoclopramide 0.3 mg kg−1iv produced a significant antithrombotic effect, reducing the frequency of large CFV from 6.7 ± 0.5 to 0.8 ± 0.4 cycles h−1(P< 0.01) and increasing minimum mean coronary blood flow from 5.0 ± 1.1 to 23.7 ± 2.6 mL min−1(P< 0.01). This result apparently reflects an antithrombotic synergism between aspirin and metoclopramide since the effects of the combination were greater than the combined effects of the individual treatments. The antithrombotic influence of metoclopramide could be due to its 5HT2‐antagonist or α2‐antagonist properties, both of which would inhibit platelet aggregation. This demonstration of a synergistic antithrombotic action of the combination of aspirin and metoclopramide is of interest since these two agents are often combined in clinical use. Its therapeutic relevance, however, remains to be established.
Further biochemical characterization of imidazoline binding sites from the human brainstem
Authors: Greney H. , Dontenwill M. , Vonthron C. , Bousquet P.
Published: August 2009

Summary—Biochemical characteristics of imidazoline specific binding sites from the human brainstem were further investigated using [3H]idazoxan as radiolabeled ligand. The study of the interaction of [3H]idazoxan binding sites with heparin and lectins (soybean and lentil lectin) confirm the heterogeneity of these sites in the human brain. In fact, about 10–15% of [3H]idazoxan binding sites were retained by each of the three supports used, leading to the hypothesis that two populations of sites, with different biochemical characteristics, coexist in this tissue. A small proportion of [3H]idazoxan binding sites was retained on an affinity chromatography support consisting of a clonidine‐derived Pharmalink column. The binding activity of these clonidine‐eluted sites was markedly and dose‐dependently improved by the addition of ‘treated fall‐through’ fraction from the same column. On the other hand, this ‘treated fall‐through’ fraction inhibited the binding activity detected in the solubilized human brainstem membranes. These results also suggest the existence of heterogeneous imidazoline specific binding sites in the human brainstem and the existence of endogenous factors able to discriminate between them.
Oxidative degradation of cholesteryl esters in low‐density lipoproteins: analysis by liquid chromatography‐light scattering and protection by a new synthetic antioxidant, S20478
Authors: Arborati M. , Benchorba D. , Lesieur I. , Bizot‐Espiard JG , Guardiola‐Lemaitre B. , Chapman MJ , Ninio E.
Published: August 2009

Summary—Cholesteryl esters in the hydrophobic core of low‐density lipoprotein (LDL) particles constitute a major molecular target during copper‐mediated oxidation. To facilitate the rapid analysis and quantitation of the oxidative degradation of LDL cholesteryl esters, we describe a new approach based on light scattering detection following separation by HPLC. We have applied this approach to the evaluation of the protective capacity of a new synthetic antioxidant, S20478, during oxidation of LDL in the presence of copper ions. HPLC separation of cholesterol and the four major molecular species of cholesteryl esters (C16:0, C18:1, C18:2 and C20:4) of LDL was achieved in a single run of 20 min with high sensitivity (50 ng) and low background. Time course studies of the oxidative modification of LDL (ratio LDL protein: copper, 100 μg/mL: 1μM) revealed that the content of unsaturated cholesteryl esters (C20:4 and C18:2) decreased (–30% and –15%, respectively) within 90 min of copper‐mediated oxidation, while only minor degradation (up to 15%) of monounsaturated (C18:1) and saturated (C16:0) esters occurred. At 24 hours of oxidation, only traces (< 5%) of the C20:4 and C18:2 esters were detectable; whereas 52% of the C18:1 ester remained (P< 0.01). Of the saturated esters, only minor proportions (35% or less) underwent oxidative modification. In addition, some 81% of free cholesterol was conserved as the native sterol. The synthetic antioxidant, S20478 (50 μM) was capable of inhibiting the initiation and the propagation of copper‐mediated LDL oxidation as determined by the time‐ and dose‐dependant inhibition of the formation of conjugated dienes and thiobarbituric acid‐reactive substances, as well as the conservation of the net electrical charge of LDL; indeed S20478 conserved cholesteryl esters in their native form up to 24 hours. However, after prolonged exposure to copper ions (48 hours), only 47% of the unsaturated esters remained (C18:2,P< 0.05). Nonetheless, S20478 (10 μM) was more efficient in inhibiting copper‐mediated LDL oxidation as compared to probucol at the same concentration. These findings suggest that S20478 may be of potential interest in a new antioxidant approach to therapeutic stabilisation and regression of atherosclerotic plaques. Moreover, this method should prove useful in the assessment of the integrity of native LDL, and provides a new chemical marker of the degree of LDL oxidation.
Response of large and small vessels to α and β adrenoceptor stimulation in heart failure: effect of angiotensin converting enzyme inhibition
Authors: Mulder P. , Compagnon P. , Devaux B. , Richard V. , Henry JP , Elfertak L. , Wimart MC , Thibout E. , Comoy E. , Macé B. , Thuillez C.
Published: August 2009

Summary—The increased sympathetic drive in chronic heart failure (CHF) might provoke vascular adrenoceptor desensitization, which, together with endothelial dysfunction, could contribute to the altered vasomotor tone seen in CHF. We investigated 1) whether CHF alters the responses mediated by α and β adrenoceptors in small and large peripheral arteries, and 2) the effect of angiotensin‐converting enzyme (ACE) inhibition. Rats with CHF (coronary artery ligation) were treated with placebo or the ACE inhibitor lisino‐pril (10 mg/kg/d) starting 7 days after ligation. Responses to phenylephrine (α, agonist), salbutamol (β2agonist) as well as acetylcholine (endothelium‐dependent), were assessed after 3 months in isolated and pressurized segments of the abdominal aorta, the femoral and the mesenteric arteries. In animals with hemodynamic signs of CHF, neither the vasoconstrictor responses to phenylephrine nor the vasodilator response to salbutamol were affected. In contrast, the dilator response to acetylcholine of both small arteries, but not that of the aorta, was impaired. Furthermore, CHF did not modify vessel structure. While lisinopril did not modify the responses to adrenergic agonists, it normalized the response to acetylcholine. Furthermore, ACE inhibition reduced vascular media cross sectional area and collagen density. Thus, the unchanged arterial responsiveness to adrenoceptor agonists does not indicate any vascular adrenoceptor desensitization, while endothelial dependent vasodilation of small arteries is impaired in CHF. ACE inhibition does not modify the response to adrenergic stimuli, prevents endothelial dysfunction and induces both cardiac and vascular remodeling, which probably contribute to the effect ACE inhibitors have on exercise tolerance and survival.
Tachykinin antagonist FK224 inhibits neurokinin A‐, substance P‐ and capsaicin‐induced human bronchial contraction
Authors: Honda I. , Kohrogi H. , Yamaguchi T. , Hamamoto J. , Hirata N. , Iwagoe H. , Fujii K. , Goto E. , Ando M.
Published: August 2009

Summary— To determine the roles of endogenously released tachykinins (substance P [SP] and neurokinin A [NKA]) in the human bronchial tissues, we studied the effects of tachykinin antagonist FK224 on bronchial smooth muscle contraction induced by SP, NKA and capsaicin in an organ bath. FK224 (10−6 M and 10−5 M, respectivly) significantly inhibited NKA‐induced contraction and 10−5 M FK224 shifted the dose‐response curve to more than one log unit higher concentration. Because SP‐ and capsaicin‐induced contractions were small, we pretreated the tissues with the neutral endopeptidase inhibitor phosphoramidon (10−5 M), which inhibits degradation of exogenous tachykinins in order to potentiate the contractions. FK224 (10−5 M) significantly inhibited SP‐induced contraction and it shifted the dose‐response curves to about one log unit higher concentration. FK224 (10−5 M) also significantly inhibited capsaicin‐induced contraction and it shifted the dose‐response curves to more than one log unit higher concentration. In contrast, FK224 (10−5 M) did not affect on acetylcholine‐, histamine‐, and leukotriene D4‐induced contraction. These results suggest that FK224 is a tachykinin receptor antagonist in the human bronchial smooth muscle, and that capsaicin‐induced contraction is due to endogenously released tachykinin‐like substances in the human bronchus.
Efficacy of huperzine in preventing soman‐induced seizures, neuropathological changes and lethality
Authors: Lallement G. , Veyret J. , Masqueliez C. , Aubriot S. , Burckhart MF , Baubichon D.
Published: August 2009

Summary— Huperzine A (HUP) is a potent reversible inhibitor of acetylcholinesterase (AChE) that crosses the blood‐brain barrier. Its ability to prevent seizures and subsequent hippocampal neuropathological changes induced by the organophosphate soman was studied in guinea pigs. Results were compared to guinea pigs treated with pyridostigmine (PYR, 0.2 mg/kg, subcutaneously). HUP pretreatment at 0.5 mg/kg, intraperitoneally, totally prevented seizures and ensured the survival of all animals for 24 h after intoxication. Hippocampal tissue was then free of any neuronal damage. Comparatively, all animals pretreated with PYR exhibited epileptic activity after soman poisoning and five of six animals died. Examination of the hippocampus of the only surviving guinea pig pretreated with PYR showed extensive neuropathological changes. Although HUP or PYR induced similar inhibitions of blood AChE activity, only HUP pretreatment led to a decrease in central AChE activity. In binding studies on guinea‐pig brain homogenates, HUP had no affinity for muscarinic, alpha‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazole propionic acid (AMPA) and gamma‐aminobutyric acid (GABA)A receptors and only a very low one for N‐methyl‐D‐aspartate (NMDA) receptors. In conclusion, HUP, unlike PYR, protects against soman‐induced convulsions and neuropathological changes in the hippocampus. This efficacy seems to be related to a protection by HUP of both peripheral and central stores of AChE.
Protective effects of trimetazidine on hypoxic cardiac myocytes from the rat
Authors: Fantini E. , Athias P. , Demaison L. , Grynberg A.
Published: August 2009

Summary— The electrophysiological effects of the antianginal drug trimetazidine (TMZ) were investigated in cultured rat ventricular myocytes using a substrate‐free hypoxia model of ischemia. The transmembrane potentials were recorded with glass microelectrodes and the contractions were simultaneously monitored with a video motion detector. The cardiomyocytes were treated with TMZ (1–5.10−4 M final concentration) in the bath. The untreated and the drug‐treated cells were submitted either to 150 min normoxia or to 150 min hypoxia followed by 90 min reoxygenation in the absence of oxidizable substrate. In normoxic conditions, TMZ did not affect the maximal diastolic potential (MDP) but significantly lowered the plateau potential level (OS) and decreased the upstroke velocity (Vmax) and the spontaneous action potential rate (APR). Conversely, TMZ significantly increased action potential duration at 80% repolarization (APD80). Under substrate‐free hypoxia, the untreated cells displayed a progressive contractile failure and an important decrease in OS and APD. In parallel, early postdepolarizations triggering high rate spikes were observed. Prolonging oxygen depletion led to the cessation of the spontaneous electrical activity and thereafter to a gradual decrease in MDP. Near normal rhythmic action potentials and contractions resumed after reoxygenation. Comparatively, the treatment by 5.10−4 M TMZ almost completely prevented the decrease in plateau amplitude, resting membrane potential, Vmax, APD80, and rate caused by substrate‐free hypoxia. Moreover, the hypoxia‐induced arrhythmias and the cessation of spontaneous electromechanical activities did not occur in the presence of TMZ (5.40−4 M). After reoxygenation, the TMZ‐treated cells exhibited a higher action potential amplitude than that of the untreated cells, although the TMZ‐induced depressive effects on the spontaneous frequency and the Vmax persisted. In conclusion, this study shows that TMZ (5.10−4 M) is efficient in protecting the isolated cardiac myocytes against the functional alterations induced by substrate‐free hypoxia and led thus to a better recovery upon reoxygenation. This cytoprotective action may be linked, at least in part, to apparent ion channel blocking effects of the drug, which appeared in basal conditions at concentrations used in this study.
Comparison of the effects of cyclosporine A and trimetazidine on Ca2+‐dependent mitochondrial swelling
Authors: Elimadi A. , Morin D. , Sapena R. , Chauvet‐Monges AM , Crevat A. , Tillement JP
Published: August 2009

Summary—Cyclosporine A (CsA) is a known potent inhibitor of pro‐oxidant‐induced mitochondrial swelling. In the present study we show that CsA's effect is only transient when the liver mitochondrial swelling is induced by Ca2+plustert‐butylhydroperoxide (t‐BH). After an initial inhibition, swelling is worsened by CsA as evidenced by an extent of mitochondrial swelling that exceeds that of the control. Unlike CsA, trimetazidine (TMZ), an anti‐ischemic drug decreases both the extent and the rate of the swelling with an IC50value of 214 ± 24 μM. Its inhibition effect on the initial swelling rate mimicks that of CsA but the mechanism may be independent. During long‐term swelling, TMZ counteracts the worsening effect of CsA. The inhibition of swelling induced by TMZ is assessed by the fact that TMZ significantly increases the EC50of Ca2+‐induced mitochondrial swelling (46.6 ± 6.0 to 85 ± 10 μM,P< 0.01), without affecting its cooperativity. Apparently, TMZ seems to behave like trifluoperazine (TIT), a phospholipase A2inhibitor that, under our experimental conditions, inhibits the mitochondrial swelling induced by Ca2+andt‐BH with an IC50value of 25 ± 10 μM. Both drugs are able to protect mitochondria from both phases (early and late) of the swelling, especially the late, which is enhanced in the presence of CsA. TFP and other phospholipase A2inhibitors were able to displace [3H]TMZ from its mitochondrial binding sites whereas CsA was ineffective. We suggest that TMZ, like TFP, inhibits the CsA insensitive mechanism involved in the swelling process which is responsible for the worsening effect observed in the presence of CsA when the swelling is generated by Ca2+andt‐BH.
Serum bupivacaine concentrations and transplacental transfer following repeated epidural administrations in term parturients during labour
Authors: Decocq G , Brazier M , Hary L , Hubau C , Fortaine MR , Gondry J , Andréjak M
Published: August 2009

Summary— Bupivacaine is the most widely used local anaesthetic in obstetrics for epidural analgesia. Nineteen women (mean age 26.9 ± 5.3 years) who underwent epidural analgesia during labour were included in this study. All parturients received a first injection of 21.8 ± 2.5 mg 0.25% plain bupivacaine. The following administrations were given on request: 0.25% concentration was used when cervix uteri was supple, and a 0.375% concentration when it was tonic. Blood samples were collected 5 min after the first injection and then every 30 min until delivery. At delivery blood samples were collected from the infant umbilical cord vein and from the arm vein of the mother. Bupivacaine was assayed by high pressure liquid chromatography. Serum data were analyzed for each patient using a non‐compartmental model. Bupivacaine was rapidly detected in serum, and maximal concentration was reached between 5 and 35 min. Pharmacokinetic parameters were estimated in 17 women after the first injection: 87 ± 35 min for elimination half‐life, 60 ± 19 L for apparent volume of distribution and 0.5 ± 0.3 L/min for plasmatic clearance. For a mean total duration of labour and total dose administered of respectively 222 ±115 min and 57.1 ± 28.7 mg, the mean value of the foeto‐maternal ratio was 0.29 ±0.10. The infant maximal serum concentration was 0.26 μg/mL. No side effects were spontaneously reported by the parturients and all infants had an Apgar score of 10 at 5 min after the delivery. We confirm the fast systemic absorption and rapid elimination of bupivacaine which may be used without risk of acute toxicity both in mother and child, even when it is used in a 0.375% concentration.
Effect of different ozone concentrations on the neurogenic contraction and relaxation of guinea pig airways
Authors: Sommer B , Vargas MH , Segura P , Bazán‐Perkins B , Carbajal V , Chávez J , Gustin P , Montaño LM
Published: August 2009

Summary—Prejunctional and postjunctional effects of several ozone (O3) concentrations, including those found in highly polluted cities, were evaluated in guinea pig airways. Animals bred in O3‐free conditions were exposed to air or O3(0.3, 0.6 or 1.2 ppm) during 4 h, and studied 16–18 h later. Tracheal and bronchial rings were studied in organ baths. Electrical field stimulation (EFS) (100 V, 2 ms, 10 s) was given at increasing frequencies (0.25–16 Hz). Some tissues received atropine (2 μM) and/or propranolol (10 μM). Concentration‐response curves to carbachol, isoproterenol, nitroprusside, and substance P were constructed. In tracheas, almost all O3concentrations decreased the relaxation at low EFS frequencies, but had no effect on the propranolol‐resistant (i‐NANC) relaxation, suggesting that only adrenergic relaxation was affected. This was a prejunctional effect, since O3did not modify the responses to isoproterenol. Relaxation induced by a nitric oxide (NO) donor, nitroprusside, was not affected by O3, which agrees with the lack of O3‐effect on i‐NANC system. O3did not modify the EFS‐induced e‐NANC contraction in atropine‐treated bronchi, nor the contraction caused by exogenous substance P. By contrast, in bronchi without atropine, 1.2 ppm O3increased the e‐NANC contraction induced by the highest EFS (16 Hz). O3increased the maximum responses to carbachol in tracheas (1.2 ppm) and bronchi (0.6 and 1.2 ppm). In conclusion, we found that: a) O3decreased adrenergic relaxation in guinea pig tracheas at low EFS frequencies through a prejunctional alteration; b) O3did not modify the i‐NANC relaxation in tracheas, at least the NO‐mediated; c) O3added a cholinergic component to the bronchial slow‐phase (e‐NANC) contraction evoked by EFS; and d) O3enhanced the cholinergic responses in trachea and bronchi by a postjunctional mechanism.
The effects of levcromakalim and pinacidil on the human internal mammary artery
Authors: Bukarica L Gojkovic , Kazic T , Sajic Z , Djukanovic B , Panic G , Peric M , Bojic M
Published: August 2009

Summary— The present study was undertaken to examine the effects of pinacidil and levcromakalim, two potassium channel openers, on human internal mammary artery (HIMA) obtained from patients undergoing coronary artery bypass surgery, and to clarify the contribution of different K+ channel subtypes in pinacidil and levcromakalim action in this blood vessel. Pinacidil and levcromakalim induced a concentration‐dependent relaxation of the precontracted arterial segments (pEC50 = 5.77 ± 0.05 and 6.89 ± 0.03, respectively). 4‐Aminopyridine (3 mM), a non‐selective blocker of K+ channels, induced significant shifts to the right of the concentration‐response curves for pinacidil and levcromakalim. Tetraethylammonium (6 mM), charybdotoxin (0.4 μM) and apamin (0.1 μM), blockers of Ca2+‐sensitive K+ channels, had no effect on the pinacidil‐ and levcromakalim‐evoked relaxation. Glibenclamide (0.1–10 μM), a selective blocker of adenosine triphosphate (ATP)‐sensitive K+ channels, competitively antagonized the response to levcromakalim (pKB = 7.92 ± 0.07). In contrast, glibenclamide, in significantly higher concentrations (3–30 μM), non‐competitively antagonized the response to pinacidil. High concentrations of pinacidil (> 10 μM) relaxed arterial rings bathed by a medium containing 100 mM K+ with maximum response 83 ± 6%. Under the same conditions, the maximum levcromakalim‐induced relaxation on HIMA was almost abolished (15 ± 2%). It is concluded that pinacidil and levcromakalim do not relax the HIMA through the same subtype of K+ channel. ATP‐sensitive K+ channels are probably involved in levcromakalim‐ but not in a pinacidil‐induced relaxation in the HIMA. In addition, in pinacidil‐induced relaxation of the HIMA, K+ channel‐independent mechanisms seem to be involved.
Effects of yohimbine, an α2‐adrenoceptor antagonist, on experimental neurogenic orthostatic hypotension
Authors: Verwaerde P , Tran MA , Montastruc JL ,   JM Senard with the technical collaboration of G Portolan
Published: August 2009

Summary—Yohimbine has been proposed for the treatment of neurogenic orthostatic hypotension; however, no controlled trial has been performed in experimental models of orthostatic hypotension or in patients with autonomic failure. The aim of the present study was to compare the effects of yohimbine (0.05 mg/kg, intravenously [iv]) and placebo (saline) in a new model of neurogenic orthostatic hypotension obtained by sinoaortic denervation (SAD) in chloralose‐anaesthetized dogs. Blood pressure, heart rate, noradrenaline plasma levels and systolic blood pressure and heart rate short‐term variabilities (calculated on low frequency [40–50 MHz] and high frequency [390–490 MHz] bands) were measured in supine position and after a 10 min 80° head‐up tilting. The drugs were administered in a double‐blind cross‐over randomized fashion. The head‐up tilting performed in normal animals increased diastolic blood pressure (+12 ± 4 mmHg), heart rate (+39 ± 12 beats per minute [bpm]), the low frequency band of systolic blood pressure and noradrenaline plasma level, without changing systolic blood pressure or heart rate variability. In SAD dogs, a marked fall in systolic (‐80 ± 11 mmHg) and diastolic (‐43 ± 4 mmHg) blood pressures was observed within 1 min after placebo, without modification in heart rate, systolic blood pressure and heart rate short‐term variabilities and noradrenaline plasma levels. In SAD dogs, yohimbine (0.05 mg/kg, iv) delayed the blood pressure fall elicited by head‐up tilting, but failed to modify its magnitude. These results show that, in the model of orthostatic hypotension obtained by SAD, yohimbine, at an α2‐adrenoceptor selective dose (0.05 mg/kg), delays the fall in blood pressure elicited by head‐up tilting. The effect of yohimbine can be explained by an increase in sympathetic tone.
Prospects of glutamate antagonists in the therapy of Parkinson's disease
Authors: Blandini F , Greenamyre JT
Published: August 2009

Summary— It has been suggested that the excitatory amino acid glutamate, acting as both a neurotoxin and a neurotransmitter, might play a central role in the pathophysiology of Parkinson's disease (PD). Intrinsic energetic defects of the neurons of the substantia nigra pars compacta, the brain area where the degenerative process of PD takes place, may render nigral neurons highly vulnerable to the effects of glutamate, which acts as a neurotoxin in the presence of impaired cellular energy metabolism. Degeneration of dopamine nigral neurons and striatal dopaminergic denervation cause a cascade of functional modifications in the activity of basal ganglia nuclei. Due to the close relationship that links dopaminergic and glutamatergic neurotransmission, glutamate is directly involved in the functional alterations of basal ganglia circuitry that lead to the development of parkinsonian motor symptoms. Drugs counteracting the effects of glutamate might therefore provide new protective and symptomatic strategies for therapy of PD.
Experimental and clinical methods in the development of anti‐Alzheimer drugs
Authors: Allain H , Bentué‐Ferrer D , Zekri O , Schück S , Lebreton S , Reymann JM
Published: August 2009

Summary— Methodology used for the development of anti‐Alzheimer's disease (AD) drugs raises specific problems which are rarely examined in the literature. While the general development scheme is similar to that required for most drugs, some specific aspects must be analyzed, highly dominated by the dual goal of pharmacology, ie, to obtain both symptomatic and etiopathogenic drugs. During preclinical studies, aged or lesioned animals are mainly useful for symptomatic drugs, whereas transgenic models or neurodegeneration‐induced techniques would probably lead to etiopathogenic drugs potentially slowing down the process of AD. The first administrations of a new compound to human beings raise the question of the activity measurement techniques. Psychometry remains the most informative procedure to detect and analyze the activity of the drugs on the different components of cognition. Electrophysiology and neuroimaging need some complementary studies before they can be proposed as surrogate criteria in phase III trials. At this stage of development, American and the recently published European guidelines are of great help while insisting on long‐term (6 months) placebo controlled trials with the use of the triple efficacy criterion: an objective cognition scale, a global assessment, and the opinion of the caregiver. In the long term, pharmacoepidemiology and pharmacoeconomy will have to confirm the rationale of this recent progress in the methodology of anti‐AD drug development.
Effect of activation of protein kinase A and of protein kinase C on the kinetics of the renal basolateral PAH transporter
Authors: Stärk U , Bergh H Vanden , Rover N , Greven J
Published: August 2009

Summary— The aim of the present study was to examine the effect of activation of the protein kinase A (PKA) and protein kinase C (PKC) pathways on 3H‐p‐aminohippurate (PAH) uptake of isolated S2 segments of proximal tubules, microdissected from rabbit kidneys without the use of enzymatic agents. Because the tubules were not perfused, and hence were collapsed, the tubular uptake of 3H‐PAH reflects transport across the basolateral membrane. The phorbol ester phorbol 12‐myristate 13‐acetate (PMA) (10 7 M), an activator of PKC, significantly increased tubular 3H‐PAH uptake with steady state conditions (by 115%), whereas dibutyryl cyclic adenosine monophosphate (db‐cAMP) (10‐4 M) and forskolin (10‐4 M) significantly inhibited it (by 42% and 52%, respectively). Kinetic data, which were based on 15 sec PAH uptake measurements, revealed that PMA, after a 10 min incubation period, significantly enhanced Km and Vmax of the PAH transporter (Km from 174 ± 22 to 447 ± 91 μM, Vmax from 2.76 ± 0.24 to 16.67 ± 1.85 pmol nL‐1 min‐1), whereas db‐cAMP significantly decreased Vmax (from 2.76 ± 0.24 to 1.82 ± 0.19 pmol nL‐1 min‐1). The Km value was also numerically lowered by dibutyryl‐cAMP (from 174 ± 22 to 139 ± 21 μM), but this change did not reach statistical significance. The data provide evidence that short time activation of the PKC pathway 1) enhances the effectiveness of PAH transport into proximal S2 segments across the basolateral cell membrane, 2) increases the maximum transport rate of the PAH transporter and 3) decreases its affinity for PAH. Activation of the cAMP/PKA pathway induces the opposite effects.
Studies on the possible mechanism of the gastric mucosal protection by Calotropis procera— involvement of 5‐lipoxygenase pathway
Authors: Sen T , Basu A , Chaudhuri AK Nag
Published: August 2009

Summary— The role of chloroform fraction of Calotropis procera root extract on different experimental ulcer models in rats was investigated. The extract demonstrated significant anti‐ulcer activity against aspirin, indomethacin, ethanol, indomethacin + ethanol, or stress‐induced ulcerations. Significant inhibition of gastric secretory volume and total acidity in pylorus ligated rats were observed to occur with the extract. It was also observed that the root extract significantly inhibited arachidonic acid metabolism induced by soyabeian lipoxygenase. The results suggest that the anti‐ulcer activity of the extract might be attributable to the inhibition of 5‐lipoxygenase (5‐LO).
Effects of SR140333, a selective non‐peptide NK1 receptor antagonist, on trigemino‐thalamic nociceptive pathways in the rat
Authors: Michaud JC , Alonso R , Gueudet C , Fournier M , Calassi R , Brelière JC , Le Fur G , Soubrié P
Published: August 2009

Summary— Trigeminal stimulation of C‐fibers increased c‐fos expression within the trigeminal nucleus caudalis (NtV) and thalamic neuronal activity which both reflect the transmission of a nociceptive message. We examined the effects on both these phenomena of the selective NK, and NK2 receptor antagonists, SR140333 and SR48968. SR140333 (0.3, 1 and 3 μg/kg intravenously [iv]) dose‐dependently, reversibly and stereoselectively antagonized the increase of contralateral thalamic activity. This compound, when given iv (30 μg/kg) or orally (10 mg/kg), also reduced the number of Fos‐like immunoreactive cells particularly at the medial and caudal level of the NtV. In contrast, SR48968 did not exert any antagonistic effect either on thalamic activity or on Fos‐like immunoreactivity. The data strongly suggest a preferential involvement of NK, vs NK2 receptors in nociceptive transmission following trigeminal ganglion stimulation. Taken together, our results indicate that SR140333 could provide a potent drug for the relief of pain occurring under excessive activity of sensory trigeminal fibers.
Effects of α1‐acid glycoprotein in different rodent models of shock
Authors: Muchitsch E‐M , Auer W , Pichler L
Published: August 2009

Summary— It was the aim of the present study to investigate the effects of the acute phase protein α1‐acid glycoprotein in different models of shock. The human plasma preparation used was without effect on mortality in lipopolysaccharide‐injected mice when administered in two different doses (1 or 0.33 g/kg iv) and according to different treatment schedules. The same preparation significantly increased survival rate (48 h) in rats with septic peritonitis. This effect was seen when α1‐acid glycoprotein (200 mg/kg iv) was given 15 min prior to and 24 h after cecal puncture. All other dose regimes tested were without significant effect on survival rate. A hemorrhagic/hypovolemic shock model (including a defined trauma) in rats resuscitated with 200 mg/kg α1‐acid glycoprotein resulted in significantly higher values of mean arterial blood pressure, cardiac output and stroke volume when compared to corresponding values obtained after resuscitation with Ringer's solution or 200 mg/kg albumin iv (free of α1‐acid glycoprotein; placebo formulation). Taking all other possible mechanisms of α1‐acid glycoprotein into consideration, the partially protective effects of the preparation are explained by enhancing the capillary barrier function and thereby maintaining perfusion of vital organs.
Calcium antagonist properties of the bisbenzylisoquinoline alkaloid cycleanine
Authors: Martínez JA , Bello A , Rubio LL , Rodríguez C , Galán L , Caudales E , Alvarez JL
Published: August 2009

Summary—The alkaloid cycleanine ([12aR‐(12aR,24aR)]‐2,3,12a,13,14,15,24,24a‐octahydro‐5,6,17,18‐tetramethoxy‐1,13‐dimethyl‐8,11: 20,23‐dietheno‐1H,12H [1,10]dioxacyclooctadecino[2,3,4‐ij: 11,12,13‐i′j′]diisoquinoline) was extracted from the bulbs ofStephania glabra (Roxb) Miersand its effects on cardiac and smooth muscle preparations were studied and compared to those of nifedipine (1,4‐dihydro‐2,6‐dimethyl‐4‐(2‐nitrophenyl)‐3,5‐pyridine dicarboxylic acid dimethylesther). Cycleanine inhibited the KCl‐induced contraction of rabbit aortic rings with higher potency than nifedipine. IC50s for cycleanine and nifedipine were 0.8 and 7·10−9M respectively. Cycleanine had minor effects on the norepinephrine‐induced contraction of rabbit aortic rings. Cycleanine and nifedipine also depressed the contraction of rat ventricular preparations but with lower potency (IC50 = 3 and 0.03·10−6M respectively). Action potential duration of rat right ventricular strips was decreased by both compounds. L‐type Ca‐current (ICaL) of single rat ventricular cardiomyocytes was inhibited by cycleanine in a voltage‐ and frequency‐dependent manner. With a higher potency nifedipine inhibited ICaLin a tonic and almost frequency‐independent manner. The results suggest that cycleanine can act as a potent vascular selective Ca‐antagonist.
Effect of WIN 64338, a B2bradykinin receptor antagonist on guinea‐pig tracheal smooth muscle cells in culture
Authors: Scherrer D , Schmidlin F , Lach E , Da Silva A , Landry Y , Gies J‐P
Published: August 2009

Summary—This study investigated the effect of the non‐peptidic B2bradykinin (BK) receptor antagonist WIN 64338 on BK binding and BK‐induced inositol phosphate formation on guinea‐pig tracheal smooth muscle cells in culture. The presence of specific and saturable binding sites for BK was demonstrated using [3H]BK. Scatchard analysis indicates a single population of binding sites for [3H]BK with a maximal density (Bmax) of 245.4 ± 71 fmol/mg of protein and an equilibrium dissociation constant (Kd) of 87.7 ± 0.12 pM. The order of potency of B2BK receptor ligands was Hoe 140 = NPC 17731 > BK > WIN 64338 > D‐ Arg0[Hyp3, D‐Phe7]‐BK > > des‐Arg9‐BK, while the B1BK receptor antagonist, des‐Arg9‐[Leu8]‐BK, was without effect on [3H]BK binding. These results demonstrate the presence of B2BK receptors on cultured tracheal smooth muscle cells. The cells were stimulated by BK, and inositol phosphate formation was determined by anion exchange chromatography. The stimulating effect of BK on inositol phosphate formation was concentration dependent (1 nM to 10 μM). The B1BK agonist des‐Arg9‐BK did not induce inositol phosphate formation. The order of potency of B2antagonists to inhibit BK‐induced inositol phosphate formation was Hoe 140 = NPC 17731 > WIN 64338 > D‐Arg0[Hyp3, D‐Phe7]‐BK. This study demonstrates that WIN 64338 is able to displace [3H]BK binding and to inhibit B2‐BK‐induced inositol phosphate formation on cultured guinea‐pig tracheal smooth muscle cells.
In vitro interactions between fluoxetine or fluvoxamine and methadone or buprenorphine
Authors: Iribarne C , Picart D , Dréano Y , Berthou F
Published: August 2009

Summary—Methadone and buprenorphine, widely used in the treatment of opioid abuse, are metabolized by cytochrome P450 3A4, while fluoxetine and fluvoxamine, both selective serotonin reuptake inhibitors, are known to be P450 2D6 and 3A4 inhibitors in vitro. This study deals with the in vitro interactions between methadone or buprenorphine and fluoxetine or fluvoxamine. Fluoxetine inhibited methadoneN‐demethylation (Ki= 55 μM), but conversely did not inhibit buprenorphine dealkylation. Norfluoxetine inhibited the metabolism of both methadone and buprenorphine metabolisms (Ki13 and 100 μM, respectively). Fluvoxamine inhibited methadoneN‐demethylation with a Kiof 7 μM and buprenorphine dealkylation, uncompetitively, with a Kiof 260 μM. Finally, these results suggest that care should be taken when selective serotonin reuptake inhibitors are administered in the treatment of drug craving. This is particularly true in the case of fluvoxamine which is more potent than fluoxetine in inhibiting methadone and buprenorphine metabolism.
In vitro antioxidant properties of calcium dobesilate
Authors: Brunet J , Farine JC , Garay RP , Hannaert P
Published: August 2009

Summary— Calcium dobesilate, a vascular protective agent, was tested in vitro for its scavenging action against oxygen free radicals. Calcium dobesilate was as potent as rutin to scavenge hydroxyl radicals (ICW = 1.1 vs 0.7 μM, respectively). It was also able to scavenge superoxide radicals, but with 23 times less potency than rutin (IC50 = 682 vs 30 μM, respectively). Calcium dobesilate significantly reduced platelet activating factor (PAF)‐induced chemiluminescence in human PMN cells and lipid peroxidation by oxygen free radicals in human erythrocyte membranes, although these actions required calcium dobesilate concentrations ≥ 50 μM. Finally, in cultured bovine aortic endothelial cells, magnesium dobesilate reduced the increase in cytosolic free calcium induced by hydrogen peroxide and inhibited phenazine methosulfate‐induced cell potassium loss. In conclusion, calcium dobesilate was effective in scavenging hydroxyl radicals in vitro, at therapeutically relevant concentrations. Conversely, higher concentrations of the compound were required to scavenge superoxide radicals or to protect the cells against the deleterious effects of intracellular reactive oxygen species. Further studies in vivo are required to determine if these antioxidant properties of calcium dobesilate can play a role in its vascular protective mechanisms.
Alteration of lipid composition of hepatic membranes associated with manganese‐bilirubin induced cholestasis
Authors: Duguay A , Yousef IM , Tuchweber B , Plaa GL
Published: August 2009

Summary— One hypothesis concerning the pathogenesis of manganese‐bilirubin (Mn‐BR)‐induced cholestasis is that the molecular organization of the bile canalicular membrane is altered. The purpose of the present study was to evaluate lipid composition and fluidity of hepatic membranes during cholestasis in male Sprague‐Dawley rats. To induce cholestasis, manganese (Mn, 4.5 mg/kg, intravenously [iv]) was given IS min before bilirubin (BR, 25 mg/kg, iv). The rats were killed 30 min after BR injection, at which time bile flow was decreased by approximately 40% compared to control values. Liver cell plasma membranes enriched in canalicular fractions (BCM) and plasma membranes enriched in sinusoidal and lateral fractions (PM), microsomes, mitochondria and cytosol were isolated by differential centrifugation. Total lipids were extracted and measured colorimetrically. To assess fluidity, membranes were incubated in vitro with fluorescent probes [1,6‐diphenyl‐1,3,5‐hexatriene and 1‐(4′‐trimethyl‐ammonium‐phenyl)‐6‐phenyl‐1,3,5‐hexatriene]. After Mn‐BR treatment, BCM cholesterol incorporation increased markedly (about 3‐fold) accompanied by a decrease in fluidity. BCM phospholipid content was unaltered by the cholestatic challenge. In PM‐enriched fractions, the changes in cholesterol and phospholipid content after Mn‐BR treatment were not statistically significant (P > 0.05) compared to controls. Furthermore, the biochemical alterations in PM were not accompanied by changes in membrane fluidity. These results support the hypothesis that altered lipid composition and fluidity of BCM are involved in the pathogenesis of Mn‐BR cholestasis.
Identification of human and rabbit cytochromes P450 1A2 as major isoforms involved in thiabendazole 5‐hydroxylation
Authors: Coulet M , Dacasto M , Eeckhoutte C , Larrieu G , Sutra JF , Alvinerie M , Macé K , Pfeifer AMA , Galtier P
Published: August 2009

Summary—This report characterized one of the major cytochrome P450 isozyme involved in thiabendazole metabolism. This study was undertaken by using both cultured rabbit hepatocytes treated or not with drugs known to specifically induce various cytochromes P450 isoenzymes (ie, P450 1A1/2 by β‐naphthoflavone, P450 2B4 by phenobarbital, P450 3A6 by rifampicine and P450 4A by clofibrate) and human liver (THLE‐5) and bronchial (BEAS‐2B) epithelial cells expressing or not the major constitutive human cytochromes P450 (ie, CYP1A2, 2A6, 2B6, 2C9, 2D6, 2E1 or 3A4). Only hepatocytes exposed to β‐naphthoflavone and clofibrate significantly metabolized thiabendazole to 5‐hydroxythiabendazole. Extensive biotransformation of this anthelmintic only occurred in human cells expressing CYP1A2. Moreover, experiments performed on rabbit preparations showed good correlations between thiabendazole 5‐hydroxylase activity and both ethoxyresorufin and methoxyresorufinO‐dealkylase activities. Thus, CYP1A2 is a major isoenzyme involved in thiabendazole 5‐hydroxylation.