bluuebunny/crossref_metadata_2025 huggingface dataset:
Identification of the human and animal hepatic cytochromes P450 involved in clonazepam metabolism
Authors: Seree EJ , Pisano PJ , Placidi M. , Rahmani R. , Barra YA
Published: August 2009

Summary— This report characterizes the cytochrome P450 isozyme involved in clonazepam metabolism. This study was undertaken using a library of liver microsomal fractions prepared from untreated rabbits or those treated with drugs known to specifically induce various cytochrome P450 isozymes (ie P450 2B4 by phenobarbital, P450 1A1 and P450 1A2 by 3‐methylcholanthrene and β‐naphthoflavone, P450 2E1 by acetone and ethyl alcohol, and P450 3A6 by erythromycin). Only microsomes obtained from phenobarbital‐treated rabbits exhibited a type II binding spectrum upon addition of clonazepam (Ks(app) = 31.4±3.8 μM) and significantly metabolized clonazepam to 7‐aminoclonazepam. Benzphetamine, which is a known substrate for P450 2B1 was also extensively metabolized by microsomes prepared from phenobarbital treated rabbits. This indicates that the same isozyme (P450 2B subfamily) was involved in the biotransformation of both substrates. Experiments performed on 14 human liver microsomal preparations showed a wide inter‐individual variability (from 1–4) and a good correlation (r = 0.70) between benzphetamine and clonazepam metabolism. Since P450 3A4 (nf25) was involved in benzphetamine metabolism, clonazepam was probably nitroreduced by the same isozyme. An oligonucleotide specific for the P450 3A4 gene subfamily was synthetized and used for hybridization on total RNA from human liver samples. Two transcripts of 2.2 and 3.0 kb were detected and the level of the 2.2 kb mRNA expression was significantly correlated (r = 0.61) with the intensity of clonazepam nitroreduction by the corresponding microsome batches.
Differential response of hypertrophied rat hearts to various α1‐adrenoceptor agonists
Authors: Mertens MJF , Pfaffendorf M. , van Zwieten PA
Published: August 2009

Summary— With respect to the heart, the prolonged existence of hypertension, both in man and in experimental animals is predominantly characterized by an increase in left ventricular myocardial mass. In this process, the autonomic nervous system plays an important role. Although endogenous catecholamine stimulation of the heart is mainly exerted via the β‐adrenoceptors, in several mammalian species, the stimulation of cardiac α‐adrenoceptors also mediates positive inotropic actions. We investigated the functional responses of isolated hypertrophied hearts taken from spontaneously hypertensive rats (SHR) and rats with an induced aortic stenosis (ASR) to various α1‐adrenoceptor agonists and compared them with those from age matched Wistar Kyoto (WKY) and “sham” operated controls. Accordingly, we studied the functional response to: methoxamine (α1), cirazoline (α1) and phenylephrine (α1 > β1). The inotropic response to the α1‐adrenoceptor agonists cirazoline and methoxamine proved to be significantly weaker in hypertrophied hearts from SHR and ASR than in non‐hypertrophied hearts from WHY and “sham” operated controls (p < 0.05). The inotropic response to phenylephrine remained intact in hypertrophied myocardial tissue. However, it was significantly reduced when the hearts were pre‐treated with the intracellular Ca2+‐antagonists ryanodine and TMB‐8. These findings show that the mechanism of sarcolemmal Ca2+ release, activated by phenylephrine, is still intact in the hypertrophied myocardial cell. In conclusion, these data show that cardiac hypertrophy, be it of genetical or mechanical origin, leads to a reduced response of the isolated heart to α1‐adrenoceptor stimulation.
Neurotensin modulates differently potassium, veratridine and 4‐aminopyridine‐evoked release of dopamine in rat striatal slices
Authors: Boireau A. , Miquet JM , Olivier V.
Published: August 2009

Summary—We have studied the effects of neurotensin (NT) on the release of [3H]dopamine ([3H]DA) evoked by terminal depolarization with either K+, veratridine or 4‐aminopyridine (4‐AP). NT (1–1000 nM) induced a net potentiation (up to 170%) of the K+ (25 mM) ‐evoked release of [3H]DA. The capacity of NT to potentiate the effect of K+ ions decreased as the K+ concentration rose from 25 to 50 mM and totally disappeared at this high K+ concentration. NT (100 nM; 1000 nM) had no significant effect on the veratridine (1.5; 5μM) or 4‐AP (20 μM) ‐evoked release of [3H]DA. The relevance of these experimental models of DA release to physiological transmitter release remains to be established. Those data highlight the complexity of the modulation of evoked neurotransmitter release by pharmacological agents.
Dopamine agonists in Parkinson's disease: a look at apomorphine
Authors: Lees AJ
Published: August 2009

Summary— Apomorphine is a D1 and D2 dopamine receptor agonist with anti‐parkinsonian properties qualitatively similar to those seen with l‐dopa. It was first used in the treatment of Parkinson's disease by Schwab in the 1950s but owing to its short duration of action, the need for parenteral administration, and adverse reactions including nausea, vomiting, postural hypotension and sedation, it was not widely prescribed. In the early 1970s, Cotzias confirmed its potent anti‐parkinsonian effects and that some of its secondary effects were diametrically opposite to those seen with l‐dopa. The advent of peripheral dopamine receptor antagonist drugs, which counteract the unwanted effects of apomorphine, and the development of new drug delivery systems including insulin pens and ambulatory mini pumps have led to the resurrection of apomorphine for the treatment of Parkinson's disease. Over the last five years in Europe, the drug has proved to be a major advance in the treatment of refractory “on‐off” oscillations in Parkinson's disease. It has also been used as a diagnostic test for dopaminergic responsiveness in Parkinson syndromes and tremors of uncertain aetiology. The drug has also proved particularly useful in dealing with certain “off‐period” disabilities, including pain, bladder dysfunction, dystonia and gastro‐intestinal symptoms. Continuous steady state infusion of apomorphine by mini‐pump may reduce the severity of “on” phase dyskinesias over time. The drug has also proved useful in the clinical pharmacological investigation of the pathophysiology of the motor response to dopaminergic drugs in Parkinsons's disease and the occurrence of involuntary movement sequences. Neuropsychiatry side‐effects are relatively infrequent when compared with ergolene dopamine agonists. Studies with apomorphine raise the hope that it may be possible to develop a long acting, orally active dopamine receptor agonist with therapeutic effect comparable to that observed with l‐dopa and with fewer long term adverse reactions.
Effect of famotidine on renal transplant patients treated with ciclosporine A
Authors: Morel D. , Bannwarth B. , Vinçon G. , Penouil F. , Elouaer‐Blanc L. , Aparicio M. , Potaux L.
Published: August 2009

Summary—The influence of a 7‐day course of 40 mg famotidine administered orally on the pharmacokinetics of ciclosporine A at steady‐state has been investigated in 10 renal transplant patients. Famotidine did not appear to significantly alter the pharmacokinetics of ciclosporine A. This might be ascribed to the limited potential of famotidine for inhibiting microsomal enzyme function. Moreover, plasma creatinine concentrations and creatinine clearance remained stable. Our results suggest that famotidine has no noticeable interaction with ciclosporine A.
Dopamine formation, from its immediate precursor 3,4‐dihydroxyphenylalanine, along the rat digestive tract
Authors: Vieira‐Coelho MA , Soares‐da‐Silva P.
Published: August 2009

Summary—The formation of dopamine, from L‐3,4‐dihydroxyphenylalanine (l–dopa), in fragments of non‐glandular and glandular stomach, duodenum, jejunum, ileum and proximal and distal colon of the rat was examined. The deamination of newly‐formed dopamine into 3,4‐dihydroxyphenylacetic acid (dopac) was also studied. The synthesis of dopamine in tissues incubated with 500 μMl–dopa for 20 min in conditions of catechol‐O‐methyltransferase (Comt) inhibition was found to be in the duodenum, jejunum and ileum 2‐fold that in the proximal colon, 6‐fold that in the glandular stomach and 120‐fold that in the non‐glandular stomach and distal colon. The formation of dopac in these tissues followed the pattern of amine formation. In the jejunum, the formation of dopamine and dopac was found to be dependent on the concentration ofl–dopa (50 to 5000 μM) used. In another set of experiments, it was found that the formation of dopamine in jejunal segments loaded with increasing concentrations ofl–dopa (50, 100 and 500 μM) was a time‐dependent process. The rate constant (k) of formation of dopamine as a function of time was found to be similar (0.050 ± 0.005) with either concentration ofl–dopa; the rate constant of dopac formation in these experiments was, in contrast, found to be greater at the highest concentrations ofl‐dopa (100 and 500 μM). Aromaticl–amino acid decarboxylase (Aaad) activity determined in homogenates of the jejunal mucosa was found to be twice that observed in homogenates of the remaining jejunal wall (muscular). The Vmax(nmol/g/h) and Km(μM) of Aaad was, respectively, in the jejunal mucoase 1324 ± 206 and 124 ± 13 and in the jejunal muscular wall 680 ± 35 and 136 ± 25. The results presented here show that the formation of dopamine along the digestive tract of the rat presents a heterogeneous pattern, the small intestine and the proximal colon being the areas where this reaction appears to be more important.
Bronchopulmonary responses to endothelin‐1 in sensitized and challenged guinea‐pigs: role of cyclooxygenase metabolites and platelet‐activating factor
Authors: Boichot E. , Lagente V. , Mencia‐Huerta JM , Braquet P.
Published: August 2009

Summary— The effect of phosphoramidon on the increase in pulmonary inflation pressure (PIP) induced by endothelin‐1 (ET‐1) administered by aerosol in ovalbumin (OA)‐sensitized and challenged guinea‐pigs was investigated after pretreatment or not of the animals with the neutral endopeptidase inhibitor, phosphoramidon, the cyclooxygenase inhibitor, indomethacin or the platelet activating factor (PAF) antagonist, BN 50730. When guinea‐pigs were pretreated by phosphoramidon (0.1 mM, aerosol for 15 min), a significant enhancement of PIP was observed after administration of ET‐1 (1 or 3 μg ml−1, aerosol for 2 min), whereas these doses of the peptide were only slightly active in control animals. In sensitized and unchallenged guinea‐pigs, ET‐1 (1 or 3 μg·ml−1, aerosol for 2 min) induced, as in controls, a moderate increase in PIP. In contrast, aerosol exposure of OA in sensitized guinea‐pigs developed an increased PIP following ET‐1 (1 and 3 μg·ml−1, aerosol for 2 min) administration, that was non significantly affected by pretreatment of the animals with phosphoramidon after the dose of 3 μg ml−1 ET‐1. Guinea‐pigs exposed to phorphoramidon and treated with indomethacin (10 mg kg−1, iv) or BN 50730 (25 mg kg−1, per os) significantly reduced the increase in PIP upon administration of ET‐1 (3 μg·ml−1, aerosol for 2 min). No inhibitory effect of indomethacin was noted when ET‐1 (3 μg·ml−1, aerosol for 2 min) was administered to sensitized and OA‐exposed guinea‐pigs, pretreated or not with phosphoramidon. In contrast, BN 50730 significantly reduced the increase in PIP induced by ET‐1 observed in sensitized and OA‐exposed guinea‐pigs. Moreover, this drug was moderately active in reducing the increase in PIP induced by ET‐1, when the animals were pretreated by phosphoramidon. These results suggest that a phosphoramidon‐sensitive endopeptidase‐like enzyme, present in the airway tissue modulates the effect of ET‐1. Furthermore, the increase in PIP to ET‐1 observed in aerosol‐sensitized and antigen‐exposed guinea‐pigs appears to be mediated by PAF rather than cyclooxygenase metabolites, even though the participation of other mediators in this process is open.
Physiological roles of dopamine and neuropeptides in the retina
Authors: Denis P. , Nordmann JP , Elena PP , Dussaillant M. , Saraux H. , Lapalus P.
Published: August 2009

Summary— The retina is a highly complex nervous tissue that converts light into patterns of electrical action potentials in order to process visual information. To carry out its function as a transducer and processor of visual information, the retina must be structurally and biochemically organized to send a coherent signal to the visual areas of the brain. In recent years, a number of biologically active substances have been demonstrated to be located within neurons in the retina. Most of them are thought to be involved in the modulation of the signal and its transmission to the brain through the optic nerve. The present paper attempts to summarize the immunocytochemical distribution and physiology of some neuronally localized substances in the mammalian retina, namely dopamine and neuropeptides.
Metabotropic glutamate receptors: an original family of G protein‐coupled receptors
Authors: Bockaert J. , Pin J. , Fagni L.
Published: August 2009

Summary—In 1985, we discovered a new glutamate receptor which was coupled to phospholipase Cviaa G protein and which was later termed metabotropic glutamate receptor (mGluR). In this review, both the diversity of mGluRs and the cellular events they control are discussed, as well as their roles in physiological regulation and brain function.
MHC class II antigen expression by ocular cells in proliferative diabetic retinopathy
Authors: Baudouin C. , Fredj‐Reygrobellet D. , Brignole F. , Lapalus P. , Gastaud P.
Published: August 2009

Summary— An immunohistological study was performed on ciliary biopsies of the pars plana obtained surgically in 10 patients suffering from diabetic retinopathy and on 15 surgical specimens of pre‐retinal neovascularized membranes. Using immunofluorescence and immunoperoxidase procedures, linear deposits of IgG, IgA and complement components were found in the 8 pars plana from patients with proliferative diabetic retinopathy, at the basal pole of the pigment epithelial cells and within the stroma. In contrast, these deposits were absent from normal pars plana and from the cases of background retinopathy. Moreover, pigment and non‐pigment epithelial cells were found to express HLA DR and DQ determinants, in six of the eight patients with proliferative retinopathy. Immunohistological examination of pre‐retinal membranes showed deposition of immunoglobulins and complement components within the connective stroma and along the new blood vessels. Endothelial cells of the newly formed vascular walls strongly expressed class II antigens on their membrane, as well as scattered stromal cells. As neither pigment epithelial cells nor retinal vascular endothelial cells normally express class II determinants, our results suggest the involvement of immunological phenomena in intraocular proliferative diseases and eventual interactions between the immune system and peptide growth factors. However, whether or not this immune reaction plays a role in the initiation or extension of intra‐ocular proliferation remains to be determined.
Nitric oxide: an ubiquitous messenger
Authors: Berdeaux A.
Published: August 2009

Summary—During the last decade, a multitude of experimental arguments have led to the concept that EDRF is nitric oxide (NO), a messenger not only involved in the control of vasomotor tone but also in vascular homeostasis, neuronal and immunological functions. Regardless of its origin, endogenous NO is produced through the conversion of L‐arginine to L‐citrulline by NO‐synthase (NOS) from which several isoforms have recently been isolated, purified and cloned. NOS‐type I (isolated from brain) and type III (isolated from endothelial cells) are termed “constitutive‐NOS” and produce picomolar levels of NO from which only a small fraction elicits physiological responses. These isoforms are regulated by Ca2+‐calmodulin with NADPH, FAD/FMN and tetrahydrobiopterin as co‐factors and reveal a high degree of homology with the amino‐acid sequence of cytochrome P450 reductase within the C‐terminal domain. Functionally, neuronal‐NOS type I is important in neurotransmission (modulation of NMDA receptor), the central control of vascular homeostasis and possibly learning and memory. In the peripheral nervous system, NOS appears to be linked to nonadrenergic noncho‐linergic (NANC) neuronal pathways. Endothelial‐NOS type III is essential for the control of vascular tone in response to the release of endogenous mediators, although shear stress is the major trigger of endothelial‐NOS activity under physiological conditions. NOS‐type III also contributes to the prevention of abnormal platelet aggregation. NOS‐types II and IV (isolated from macrophages) are Ca2+‐calmodulin independent and are termed “inducible‐NOS” since their activation is only promoted under pathophysiological situations where macrophages exert cytotoxic effects in response to cytokines. In contrast with NOS‐types I and III, activation of NOS‐type II in these cells induces the formation of nanomolar levels of NO which act as a defense mechanism of the immune system. Dysfunctions of the L‐arginine‐NO pathway have been characterized in multiple diseases (atherosclerosis, hypertension, diabete, sepsis, cerebral ischemia, etc) and the design of more selective activators/inhibitors of NOS isoforms is a new challenge for the understanding of their pathophysiology and treatment.
Fever‐induced changes in theophylline pharmacokinetics in rats
Authors: Bruguerolle B. , Dubus JC
Published: August 2009

Summary— Our aim was to document possible alterations of theophylline pharmacokinetics in rats during fever. Two groups (group A = normothermic controls, group B = fever‐induced animals) of Wistar AF IOPS male rats were injected at 19 30 h either with 2 g/kg of brewer's yeast subcutaneously (20% w/v) or with the equivalent volume of saline. Twelve hours later at 07 30 h the two groups received a single 12 mg/kg/IP dose of theophylline. Blood samples were obtained by retro‐orbital sinus puncture 0, 0.25, 0.5, 1, 2, 4, 8, 12, 16 and 24 hours after administration. A third group of 10 male IOPS rats (group C) were used under the same experimental conditions in order to determine the influence of brewer's yeast‐induced fever on biological parameters. Cmax, Tmax, Cmax/Tmax, T 1/2, Cl, Vd and AUC were determined according to a one‐compartment open model. Our results confirm the fever‐induced decrease in total plasma proteins and albumin but do not demonstrate any significant change in theophylline pharmacokinetic parameters.
Involvement of endothelium‐derived NO in the basal tone and in the vasodilator responses to muscarinic agonists in the rat isolated mesenteric arterial bed
Authors: Baisch AL Muccillo , Larrue J. , Freslon JL
Published: August 2009

Summary—To investigate the involvement of nitric oxyde (NO) derived from endothelial cells in the control of vascular tone in the rat mesenteric vascular bed, the effects of different procedures known to interfere with the NO‐cyclic GMP pathway were evaluated both on the basal tone and on the vasodilatory responses to four muscarinic agonists. To this aim, rat isolated mesenteric vascular beds were perfused at constant pressure. Water infusion significantly increased the resting perfusion pressure whereas L‐NOARG, L‐NAME and methylene blue were devoid of effect. In noradrenaline‐preconstricted vascular bed, the perfusion pressure was significantly increased after water or L‐NAME infusion. The vasodilator response induced by subsequent addition of acetylcholine in bolus was not significantly modified by pre‐treatment with indomethacin but was significantly reduced by water infusion. Reponses to acetylcholine and to three other muscarinic agonists ‐carbachol, oxotremorine or McNeil A 343‐ were assessed. Incubation with L‐NAME did not modify the initial peak falls of the agonists except for Mc Neil A 343, whereas it significantly reduced the area under the pressure trace for all the substances. The latter effect was reversed after a subsequent incubation with L‐Arginine. Finally, L‐NAME strongly and significantly increased the drop in perfusion pressure and the area under the pressure trace following bolus of glyceryl trinitrate. These results suggest that in the mesenteric arterial bed of the rat, which can be considered as a resistant arteries preparation, basal tone appears to be controlled by a factor other than NO. Moreover, the vasodilator responses of muscarinic agonists are affected by L‐NAME in their second late sustained phase only, which probably relies on ade novosynthesis of endothelium derived‐NO. Finally, endothelium derived‐NO exerts inhibitory effects both on the sensitivy of the vascular smooth muscle to glyceryl trinitrate and on the magnitude of its contraction in the presence of noradrenaline, two types of effects which are sensitive to L‐NAME.
Cardiac β‐adrenoceptors and adenylyl cyclase activity in human left ventricular hypertrophy due to pressure overload
Authors: Galinier M. , Sénard JM , Valet P. , Arias A. , Daviaud D. , Glock Y. , Bounhoure JP , Montastruc JL
Published: August 2009

Summary—The effect of left ventricular hypertrophy (LVH) due to chronic pressure overload on right atrial (RA) and left ventricular (LV) myocardial β‐adrenergic receptor (β‐AR) density and subtypes, adenylyl cyclase (AC) activity and ADP‐pertussis toxin ribosylated proteins was investigated in humans with LVH due to aortic stenosis and in patients without LVH undergoing heart surgery for mitral stenosis or coronary artery disease taken as controls. Both groups presented normal systolic function or plasma catecholamine levels. In LVH and controls, β‐AR density was similar in RA (62 ± 6vs77 ± 12 fmol·mg−1protein) and LV (39 ± 7vs32 ± 2 fmol·mg−1protein). In LVH, β1‐AR percentage was < than in controls in LV (35 ± 11vs73 ± 5%,P< 0.05) but not in RA (79 ± 5vs73 ± 8%). Basal AC activity in RA (19 ± 4vs21 ± 6 pmol·;mg−1protein) and LV (22 ± 5vs27 ± 3 pmol·mg−1protein) was similar in LVH and in controls. Isoprenaline‐induced stimulation of AC in RA was similar in LVH and in controls (51 ± 18vs36 ± 18%) but < in LV of LVH (7 ± 6vs45 ± 6%,P< 0.05). In the presence of ICI‐118,551 (a β2‐adrenoceptor antagonist), isoprenaline failed to induce any increase in cAMP in LVH. The quantification of ADP‐pertussis toxin ribosylated proteins indicated a lower concentration of substrates in LV myocardial membranes from LVH. These data indicate that in LVH due to pressure overload, there is a down‐regulation of β1‐AR and an increase in β2‐AR density. This is associated with alterations of the transmembrane signalling marked by a decreased capacity of isoprenaline to stimulate AC and an impaired expression of Gi proteins.
Molecular biology of voltage‐gated K+ channels in heart
Authors: Honoré E. , Lesage F. , Romey G.
Published: August 2009

Summary— The recent cloning of numerous voltage‐activated K+ channels provides new information concerning the architecture of K+ channel proteins. The combination of molecular genetic and biophysical methods gives us a new insight into the molecular mechanisms of K+ channel pharmacology.
Analysis of the cAMP response on liver‐specific gene expression in transgenic mice
Authors: Montoliu L. , Blendy JA , Cole TJ , Schütz G.
Published: August 2009

Summary— Expression of many genes is modulated by intracellular variations of cyclic AMP (cAMP) levels in response to different signals from the environment. This regulation is mediated via a cAMP‐response element (CRE). This report addresses the role of cAMP in the physiological activation of a subset of liver‐specific genes which are perinatally activated. The tyrosine aminotransferase (TAT) gene and other genes such as phosphoenolpyruvate carboxyquinase (PEPCK) and glucose‐6‐phosphatase, involved in gluconeogenesis, belong to this category. CRE elements derived from the rat TAT −3.6 kb enhancer have been positioned in chimeric constructs, such that the activity of the reporter gene LacZ is dependent on cAMP. The tissue‐specificity of these constructs is guaranteed by the presence of the liver‐specific enhancers of the alpha fetoprotein gene. These constructs have been tested in cells and transgenic mice demonstrating cAMP regulation, liver‐specific expression and perinatal activation of the reporter gene. The CRE is recognized by a number of related proteins of which the cAMP‐response element‐binding factor (CREB) has been best studied. To assess the role of CREB in the in vivo transduction of cAMP signalling, mice deficient in CREB protein have been generated by homologous recombination in embryonic stem (ES) cells. Homozygous mutant mice, although recovering at a lower ratio than expected, do not display impairment of growth or development. The cAMP‐dependent LacZ transgenic mice in a CREB mutant genetic background also show perinatal activation of the reporter gene. Compensation with other members of the family of CRE‐binding proteins, such as cAMP‐response element modulator (CREM) or activating transcription factor‐1 (ATF‐1), may explain the lack of an obvious phenotype in CREB mutant mice.
Transduction of the light message: from the photon to the optic nerve
Authors: Doly M.
Published: August 2009

Summary— Retinal transduction consists of the conversion of a physical stimulus, light, into an electrophysiological signal. This conversion takes place in several stages. First of all, at the photoreceptor level, via a sequence of molecular activations and deactivations, the detection of light results in an hyperpolarization of the cell membrane. This initial electrical signal is then relayed onto the functional cells of the retina. The bipolar cells are the first associated neurons, responding to the light stimulus by either hyperpolarization (OFF), or depolarization (ON). The second associated neurons are the ganglion cells where the ON‐OFF duality also operates and whose fibers make up the optic nerve. In coloured photopic vision, the photoreceptor — bipolar cell — ganglion cell circuit is direct. For the cone‐bipolar cell transmission, horizontal cells delimit excitatory (center) and inhibitory (surround) zones at the origin of the receptive field. In scotopic vision, however, i) there is only a single class of bipolar cells, that depolarize in response to light, and ii) the bipolar‐ganglion cell connection is not direct. Here, the All amacrine cells are responsible for the inhibition of the OFF ganglion cells directly connected to them or for the excitation of the ON ganglion cells via ON bipolar cells of the cone circuit. Finally, in mesopic vision, the sensory message originates in rods, and is subsequently relayed by the cone circuit via gap junctions between photoreceptors.
Agonist desensitisation of α1 adrenoceptors and endothelin‐1 receptors coupled to phosphatidylinositol metabolism
Authors: Hamilton CA , Boyle JJ , Huang YT , McCulloch J. , Nixon GF , Pryadarshi S.
Published: August 2009

Summary— Agonist desensitisation of responses coupled to phosphatidylinositol metabolism were studied. Responses mediated by two different agonists, endothelin‐1 and noradrenaline were investigated. In vivo pressor responses were examined in conscious male New Zealand white rabbits, while effects on inositol phosphate formation were studied in rings of freshly isolated aorta and in cultured aortic vascular smooth muscle cells. No desensitisation of responses to noradrenaline were observed in vivo despite a 10‐day infusion under conditions which cause desensitisation of α2 and β‐adrenoceptor mediated responses. In contrast, responses to endothelin‐1 were attenuated within 5 min of commencing endothelin‐1 infusions. No reduction in noradrenaline stimulated inositol phosphate was observed in cultured vascular smooth muscle cells after pre‐incubation with noradrenaline up to 10−4M, whereas with endothelin‐1 pre‐incubation a dose and time‐related reduction in endothelin‐1 stimulated inositol phosphate formation was observed. Thus, differences in the pattern of desensitisation of both pressor responses and phosphatidylinositol metabolism were observed for noradrenaline and endothelin‐1 suggesting that the nature of the 2nd messenger involved in signal transduction is not the only determinant of agonist desensitisation. In addition, differences in the rate of desensitisation and sensitivity to endothelin‐1, but not noradrenaline, were observed when responses in cultured cells were compared with in vivo responses or responses to freshly isolated tissues. These differences are discussed in relation to possible modifications of the endothelin receptor or its coupling to phosphatidylinositol metabolism during culture.
Comparison of the “zero crossing” method in derivative spectroscopy and ultrafiltration for the determination of free and bound fractions of mitoxantrone
Authors: Maia MBS , Tufenkji AE , Rochas MA , Saivin S. , Houin G.
Published: August 2009

Summary— In vitro mitoxantrone binding to human serum, human serum albumin (HSA, 600 μM) and alpha‐1‐acid glycoprotein (AAG, 15 μM) was investigated by ultrafiltration and the first‐derivative spectrophotometry based on the “zero crossing” method. The binding of mitoxantrone to isolated proteins was studied at eight concentrations whose range depended on the protein used. The results showed that mitoxantrone binding to human plasma and HSA involved a saturable binding. The AAG binding involved a saturable binding followed by a non saturable process. Within the concentration range studied, the percent and binding parameters which characterize the drug‐protein interaction were comparable in both methods.
Iodinated contrast media‐induced nephropathy: pathophysiology, clinical aspects and prevention
Authors: Idée JM , Beaufils H. , Bonnemain B.
Published: August 2009

Summary— Administration of iodinated contrast media (CM) for radiographic purposes is a preoccupying cause of acute renal failure. This review of the literature deals with what is known about physiopathology, clinical course, risk factors and prevention. Factors involved in the pathophysiology of CM‐induced acute renal failure are vasoconstriction, direct tubular cell injury and tubular obstruction by casts. In the case of pre‐existing renal hypoperfusion, CM may disturb the complex interaction between factors which modulate renal haemodynamics by increasing vasoconstrictor factors, notably endothelin peptides. The renal medulla, a zone characterized by a high metabolic activity and a low oxygen tension, may be a specific target for CM‐induced effects. CM‐induced nephropathy (CMN) is essentially observed in patients with one or more associated risk factors (chronic renal failure, dehydration, diabetes mellitus with impaired renal function, multiple myeloma, large CM volume, intra‐arterial rather than intravenous route, etc). There is much debate as to whether newer low osmolar CM (LOCM) are better tolerated than conventional high osmolar CM (HOCM). Most of the animal studies clearly demonstrate the advantages of LOCM over HOCM. Clinical literature is far more confusing, although some recent studies and one meta‐analysis demonstrate that LOCM are better tolerated in patients with impaired renal function. The low number of comparative clinical trials carried out in high risk patients, wide variability in CMN definitions, limited number of patients enrolled and inadequacy of various selected endpoints may explain difficulties experienced in demonstrating this advantage. Furthermore, while hydration is correctly maintained during clinical trials, this is not always true in clinical practice. Such a discrepancy could lead to underestimation of the potential advantage of LOCM over HOCM. Effective prevention should associate the correct hydration of patients, identification and, when possible, optimal correction of risk factors, avoidance of repeated CM injections within a short period of time and temporary disruption of treatment with other nephrotoxic drugs (non steroidal antiinflammatory drugs, aminoglycosides, etc).
Presynaptic modulation of the release of the co‐transmitters noradrenaline and ATP
Authors: von Kügelgen I. , Kurz K. , Bültmann R. , Driessen B. , Starke K.
Published: August 2009

Summary—The release of both sympathetic co‐transmitters, noradrenaline and ATP, is modulatedviapresynaptic receptors. However, the degree of the modulation may differ indicating that the ratio of the released co‐transmitters changes upon presynaptic receptor activation. For example, α2‐autoinhibition affects the release of noradrenaline more markedly than the release of ATP. Some sympathetic axon terminals possess presynaptic P2‐purinoceptors which are activated by endogenous ATP. These receptors are a novel kind of auto‐receptor: they mediate a presynaptic negative feedback mechanism in which released ATP inhibits subsequent co‐transmitter release.
α1‐adrenoceptor subtype(s) mediating noradrenaline‐induced contractions of the guinea‐pig aorta
Authors: Oriowo MA
Published: August 2009

Summary—The effect of α1‐adrenoceptor subtype selective antagonists, WB 4101, SZL‐49 and chloroethylclonidine on noradrenaline‐induced contractions of the guinea‐pig aorta has been studied in an attempt to identify the α1‐adrenoceptor subtype(s) involved in the response. Noradrenaline and SDZ NVI 085 induced contractions of the aorta. Noradrenaline‐induced contractions were competitively antagonised by WB 4101 (pA2= 8.92, slope = 1.05). The contractions were significantly reduced by SZL‐49 but not by chloroethylclonidine, indicating an action on α1A‐adrenoceptor subtype. Noradrenaline‐induced contractions of the aorta were not inhibited by nifedipine (10−6M). The results are interpreted to suggest that α1A‐adrenoceptor subtype mediates noradrenaline‐induced contractions of the guinea‐pig aorta and that activation of α1A‐adrenoceptor subtype in the guinea‐pig aorta is probably linked to intracellular Ca++release.
Epithelium modulates the kinetics of the response to substance P and its intrinsic activity in the guinea‐pig trachea
Authors: Da Silva A. , Bertrand C. , Landry Y.
Published: August 2009

Summary—The contractile response of guinea‐pig tracheal preparations with or without epithelium to substance P has been studied in the presence or absence of thiorphan, an endopeptidase 24.11 inhibitor, paying special attention to the kinetics of the response. Without thiorphan, the response to substance P was greater in tracheal preparations without epithelium than in tracheal preparations with epithelium. The concentration‐response curve was shifted to the left in the absence of the epithelium. In the presence of 10 μM thiorphan, the maximal contractile response induced by single doses of substance P (0.1 to 10 μM) was lower in tracheal preparations without epithelium. The maximal responses required 10 min in tracheal preparations with epithelium and 2 min in tracheal preparations without epithelium. These epithelium‐dependent differences of reactivity remained in the presence of lipoxygenase or cyclooxygenase inhibitors and of selective antagonists of muscarinic, serotoninergic and histaminergic receptors, after the pre‐treatment of tissues with capsaicin or compound 48/80 and in the presence of tetrodotoxin. The profile of the cumulative concentration‐response curves for substance P was largely dependent on the time between two successive doses. When this time was short (2–4 min), curves established with or without the epithelium were parallel and both reached similar maximal values (2696 ± 214 mg and 2780 ± 62 mg, respectively). The curve in tracheal preparations without epithelium was slightly shifted to the left (EC50s: 24 ± 10 nM and 78 ± 19 nM). When this time was longer (10 min,iecorresponding to the time required for a full response to a single dose in intact trachea) the potency of substance P was not modified (EC50s: 13 ± 3 nM and 52 ± 11 nM), but a lower maximal response was observed with tracheal preparations without epithelium (1440 ± 182 mg and 2832 ± 209 mg). Similar results were observed with neurokinin A and neurokinin B. Thus, the removal of the epithelium led to a more rapid contraction and to a decrease of the maximal response to neurokinins,iea decreased intrinsic activity, a property known to be drug‐ and tissue‐dependent. These data suggest that the intrinsic activity of drugs depends on the cellular environment of the target cells in a tissue and is partly related to the diffusion and metabolism of drugs and to drug‐induced hyporeactivity of the target cells.
Dose‐dependence and reversibility of the hemoconcentrating and hypotensive activities of atrial natriuretic peptide in binephrectomized rats
Authors: Valentin JP , Sechi LA
Published: August 2009

Summary— In addition to its blood pressure lowering effect, atrial natriuretic peptide (ANP) infusion, increases hematocrit and decreases plasma volume by inducing a transfer of plasma fluid from the vascular to the interstitial compartment. We explored the dose‐dependence as well as the reversibility of these actions by measuring changes in mean arterial pressure (MAP), hematocrit and plasma protein concentration (PPC) in anesthetized acutely binephrectomized Sprague‐Dawley rats. Infusion of ANP (10, 100 or 1000 ng/kg/min for 45 min) dose‐dependently reduced MAP (+ 2.3 ± 1.8, –5.8 ± 2.5 and –8.6 ± 1.3%) and increased hematocrit (1.7 ± 0.4, 8.1 ± 0.4 and 9.0 ± 0.6%), corresponding to calculated decreases in plasma volume of 3.0 ± 0.6, 13.1 ± 0.6 and 14.4 ± 0.9% repectively. PPC increased significantly less than expected for a plasma volume reduction without proteins extravasation indicating that some loss of plasma proteins occurred in response to ANP. Both the reduction in MAP and plasma volume were reversible within 45 min after discontinuation of ANP infusion. During the recovery period, PPC decreased to values lower than baseline suggesting that the hemodilution was not associated with a detectable return of proteins into the circulation. Thus, in binephrectomized rats, infusion of ANP induced a dose‐dependent and reversible reduction in arterial pressure and plasma volume through an extrarenal mechanism. Moreover, ANP dose‐dependently increased the vascular permeability to proteins; the escaped proteins remained out of the vascular space for at least the duration of the experiment (ie 45 min post‐infusion).
Anti‐IgE induces the opening of non selective cation channels on human basophils
Authors: Beauvais F. , Shimahara T. , Inoué I. , Benveniste J.
Published: August 2009

Summary— Basophils play a major role in allergic reactions — particularly in late phase reactions — by releasing histamine and other mediators of inflammation. Although transmembrane ion fluxes are thought to play an important role in the modulation of histamine release, little is known about ion pathways through the basophil membrane. We thus studied human basophils from normal subjects (n = 25 cells) with the patch‐clamp method. We observed that IgE‐dependent activation of human basophils led to the opening of non selective cation channels with a 20pS conductance. This was obtained when the patch pipette was applied onto the cell surface and sealed onto it in order to measure transmembrane currents on a small surface of intact basophils (cell‐attached configuration). Non selective channels with the same 20pS conductance were also observed when a membrane patch was detached from basophil and its inner side placed in a Ca2+‐containing medium (inside‐out configuration). These data are a first contribution of the patch‐clamp method in the understanding of ion movements in human basophils.
Differential inhibition of the pressor effects of natural pro‐endothelins by phosphoramidon in rats
Authors: Le Monnier de Gouville AC , Thiry C. , Cavero I.
Published: August 2009

Summary—The vasopressor responses of three natural endothelins (ET‐1, ET‐2, ET‐3) and their precursors, pro‐ETs, were studied in a pithed rat preparation, which allows the profile and the potency of vasoconstrictor agents to be determined in the absence of central control of the cardiovascular system. ET‐1 was found to be 4‐ and 8‐fold more potent in raising blood pressure than ET‐2 and ET‐3, respectively. The immediate precursors of these isopeptides, h‐pro‐ET‐1 (human), p‐pro‐ET‐1 (porcine), pro‐ET‐2 and proET‐3, produced significantly smaller pressor responses than their respective ETs, when measured either as peaks or as areas under the time‐effect curve. Hence, the bioavailability of h‐pro‐ET‐1, p‐pro‐ET‐1 and pro‐ET‐2, assessed on the basis of these two parameters, was approximately 50% of that of their corresponding ET, whereas the bioavailability of pro‐ET‐3 was only 25% that of ET‐3. Phosphoramidon inhibits metallopeptidases, the enzymes that convert pro‐ETs to ETs. The approximate iv doses of phosphoramidon reducing by 50% the pressor effects of the pro‐ETs were 2.5, 0.625, less than 2.5 (this dose produced 75% inhibition) and 5 mg/kg iv for h‐pro‐ET‐1, p‐pro‐ET‐1, pro‐ET‐2 and pro‐ET‐3, respectively. In conclusion, these results indicate that the rat may have more than one pro‐ET converting enzyme, each specific for one of the natural pro‐ETs studied, although the alternative explanation, that there is a single enzyme with different affinities for these pro‐ETs, cannot be entirely dismissed.
In vitroelectrophysiological detection of iatrogenic arrhythmogenicity
Authors: Adamantidis MM , Kerram P. , Dupuis BA
Published: August 2009

Summary—Cardiac arrhythmias and sudden death have been associated with both therapeutic and toxic doses of a number of cardiotropic and non‐cardiac drugs. Generally the drug‐induced electrocardiographic (ECG) alterations have been well described, whereas corresponding cellular electrophysiological effects are poorly documented or lacking. Taking into account the recent advances in the understanding of the mechanisms underlying arrhythmias and antiarrhythmic effects, suitable relationships can be established between ECG alterations and drug effects on cardiac action potential. Thus, a decrease in maximal upstroke velocity (Vmax) and membrane depolarisation leading to cellular inexcitability may slow conduction, prolong QRS interval duration and result in incessant wide QRS ventricular tachycardia. On the other hand, lengthening of the repolarisation phase and early afterdepolarisations (EADs) have been proposed as a mechanism for prolonged QT interval and subsequentTorsades de Pointes.A representative study aimed at detecting the arrhythmogenic potentiality of a drug is given, by examining carefully the concentration‐ and frequency‐dependent effects of four neuroleptics (sultopride, droperidol, thioridazine and clozapine) on Purkinje fibers and comparing them with the reported iatrogenic arrhythmias. The results showed that 10 to 100 μM sultopride and 0.01 to 1 μM droperidol exerted “pure” class III effects. In addition, higher concentrations (3 to 30 μM) of droperidol reversed the prolonging effect on repolarisation concomitantly with a dose‐ and frequency‐dependent decrease in Vmax, action potential amplitude and resting membrane potential (class I effects) resulting in cellular inexcitability at 30 μM. Similar class I effects were induced by thioridazine and clozapine concomitantly with a slight prolonging effect on final repolarisation (class la effects). In the presence of sultopride (30 and 100 μM) and droperidol (0.3 to 3 μM), EADs developed at plateau level. Their incidence, amplitude and number were influenced by extracellular K or Mg concentration, stimulation frequency, modification of Ca entry (by nifedipine or isoproterenol). These experimental results fit well with clinical data although they need further development to precise underlying ionic mechanisms. Therefore,in vitrostudies should be considered before clinical prospects for future drug development.
Influence of ischaemia and reperfusion on cardiac signal transduction. G protein content, adenylyl cyclase activity, cyclic AMP content, and forskolin and dibutyryl cyclic AMP‐induced inotropy in the rat Langendorff heart
Authors: van den Ende R. , Batink HD , Michel MC , van Zwieten PA
Published: August 2009

Summary—We investigated whether post‐receptor alterations contribute to the diminished β‐adrenergic inotropic effects in the rat Langendorff heart following ischaemia (I) and reperfusion (R). We quantitated immunodetectable Gsand Giprotein α‐subunit content, basal and stimulated adenylyl cyclase activity and cyclic AMP (cAMP) content in normoxic, ischaemic (30 min) and ischaemic reperfused (30 min) hearts. In addition, we measured the inotropic response of normoxic and reperfused Langendorff hearts to forskolin and dibutyryl cAMP (db‐cAMP). Immunodetectable Gsand Giα‐subunits were unaltered by I or R. Basal adenylyl cyclase activity was decreased during I, but recovered during R. In membranes from normoxic hearts, isoprenaline, GTP, Gpp(NH)p, NaF, forskolin or Mn2+enhanced adenylyl cyclase activity. This increase in activity was diminished in ischaemic hearts, but could be restored by R. cAMP content decreased time‐dependently during I and did not recover by R, indicating ATP depletion. Forskolin and db‐cAMP induced an inotropic response in normoxic hearts, which was virtually abolished after I and R. We conclude that adenylyl cyclase responsiveness is impaired during I. Since adenylyl cyclase responsiveness recovers during R, whereas inotropic responses to forskolin and db‐cAMP are virtually absent in reperfused hearts, an additional mechanism downstream of cAMP formation appears to be defective during R, which prevents recovery of inotropic responses to hormonal stimulation.
Effects of dipyridamole, soluflazine and related molecules on adenosine uptake and metabolism by isolated human red blood cells
Authors: Ferrandon P. , Barcelo B. , Perche JC , Schoffs AR
Published: August 2009

Summary— The suggestion that adenosine may have beneficial effects on post reperfusion survival following cardiac ischaemia has led to the search for agents which increase the concentration of this substance in the ischemic region as a possible therapeutic approach to the treatment of angina and myocardial infarction. In the present study, dipyridamole, soluflazine and lidoflazine, known inhibitors of the nucleotide exchange system, have been shown using an HPLC method to prevent the decrease in the concentration od added adenosine outside human red blood cells in vitro. However, the results suggest that this effect was due to inhibition of adenosine deaminase rather than inhibition of nucleotide exchange as had previously been suggested. The selective inhibitor of adenosine deaminase erythro‐9‐(2 hydroxy‐3‐nonyl adenosine) exhibited the same profile of activity in the human red blood cell assay. pIC50 values for the four compounds named above were found to be 6.80 ± 0.09, 6.95 ± .03, 6.10 ± 0.14 and 7.39 ± 0.05 vs adenosine disapearance observed in the extracellular incubation medium respectively. Thus, as the disappearance of adenosine outside the cells was not due to its uptake but to its catabolism, this in vitro method does not appear to be predictive for the ability of compounds to act on adenosine uptake into cardiac myocytes. Any antiischemic action of these agents is more readily explained by an inhibition of the catabolism of adenosine and not by the inhibition of its transport across the membrane of cardiac myocytes.