RESUMEN
OBJECTIVE: Neuropeptide FF (NPFF) and its receptors (NPFF1 R and NPFF2 R) are differentially distributed throughout the central nervous system. NPFF reduces cortical excitability in rats when administered intracerebroventricularly (i.c.v.), and both NPFF and NPFF1 R antagonists attenuate pilocarpine-induced limbic seizures. In this study, our aim was to determine whether NPFF exerts anticonvulsant or anti-epileptogenic effects in the rat amygdala kindling model for temporal lobe seizures. METHODS: Male Wistar rats were implanted with a recording/stimulation electrode in the right amygdala and a cannula in the left lateral ventricle. In a first group of animals, the afterdischarge threshold (ADT) was determined after a single i.c.v. infusion of saline (n = 8) or NPFF (1 nmol/h for 2 h; n = 10). Subsequently, daily infusion of saline (n = 8) or NPFF (1 nmol/h for 2 h; i.c.v.; n = 9) was performed, followed by a kindling stimulus (ADT+200 µA). Afterdischarge duration and seizure severity were evaluated after every kindling stimulus. A second group of rats (n = 7) were fully kindled, and the effect of saline or a high dose of NPFF (10 nmol/h for 2 h, i.c.v.) on ADT and the generalized seizure threshold (GST) was subsequently determined. RESULTS: In naive rats, NPFF significantly increased the ADT compared to control (435 ± 72 µA vs 131 ± 23 µA [P < 0.05]). When rats underwent daily stimulations above the ADT, NPFF did not delay or prevent kindling acquisition. Furthermore, a high dose of NPFF did not alter ADT or GST in fully kindled rats. CONCLUSIONS: I.c.v. administration of NPFF reduced excitability in the amygdala in naive, but not in fully kindled rats, and had no effect on kindling acquisition.
Asunto(s)
Amígdala del Cerebelo/efectos de los fármacos , Anticonvulsivantes/farmacología , Epilepsia del Lóbulo Temporal/tratamiento farmacológico , Excitación Neurológica/efectos de los fármacos , Oligopéptidos/farmacología , Convulsiones/tratamiento farmacológico , Animales , Anticonvulsivantes/administración & dosificación , Modelos Animales de Enfermedad , Masculino , Oligopéptidos/administración & dosificación , Ratas , Ratas WistarRESUMEN
gamma-Hydroxybutyrate (GHB) is a putative neurotransmitter in brain. We have already demonstrated that it is transformed into gamma-aminobutyrate (GABA) by rat brain slices incubated under physiological conditions. This conversion occurs via a GABA-transaminase reaction. Therefore, succinic semialdehyde, the oxidative derivative of GHB, appears to be the primary catabolite of GHB degradation. Apparently, the kinetic characteristics and pH optimum of GHB dehydrogenase (high Km aldehyde reductase) in vitro do not favor a role for this enzyme in endogenous brain GHB oxidation. However, in the presence of glucuronate, glutamate, NADP and pyridoxal phosphate, pure GHB dehydrogenase, coupled to purified GABA-transaminase does produce GABA from GHB at an optimum pH close to the physiological value and with a low Km for GHB.
Asunto(s)
Oxidorreductasas de Alcohol/metabolismo , Química Encefálica , Hidroxibutirato Deshidrogenasa/metabolismo , Hidroxibutiratos/metabolismo , Oxibato de Sodio/metabolismo , 4-Aminobutirato Transaminasa/metabolismo , Animales , Concentración de Iones de Hidrógeno , Cinética , Oxidación-Reducción , Ratas , Especificidad por Sustrato , Ácido gamma-Aminobutírico/biosíntesisRESUMEN
The effects of derivatives of gamma-hydroxybutyrate (GHB) and gamma-butyrolactone were examined in Wistar rats from a strain in which spontaneous spike-and-wave discharges can be recorded electroencephalographically. For each compound, the effects were compared to those obtained in rats from a strain without spontaneous seizures. Administration of GHB (62.5-375 mg/kg, i.p.) increased, in a dose-dependent manner, the duration of spontaneous spike-and-wave discharges. In non-epileptic rats, this compound (250 and 375 mg/kg) induced bursts of spikes of a lower frequency and smaller amplitude than spontaneous spike-and-wave discharges. Similar results were obtained in both strains, respectively, after injection of gamma-butyrolactone (85-170 mg/kg, i.p.). This latter compound, however, showed greater potency in its epileptogenic effects than GHB. Administration of trans gamma-hydroxycrotonic acid (up to 1000 mg/kg, i.p.), a semi-rigid analogue of GHB was without any effect in both strains of rats. Injection of gamma-crotonolactone (42.5-170 mg/kg, i.p.), suppressed the spike-and-wave discharges in epileptic rats and had no effect in non-epileptic animals. These results confirm the similarities between seizures induced by GHB and spontaneous spike-and-wave discharges in the rat. The neural mechanism of the epileptogenic effect of GHB is discussed.
Asunto(s)
4-Butirolactona/farmacología , Epilepsia/fisiopatología , Furanos/farmacología , Hidroxibutiratos/farmacología , Oxibato de Sodio/farmacología , Animales , Electroencefalografía , Masculino , Ratas , Ratas EndogámicasRESUMEN
Substituted 4-hydroxybutyric (GHB) or trans-4-hydroxycrotonic acids (T-HCA) and structurally related compounds were synthesized and submitted to [3H]GHB binding. Structure-activity relationships studies highlighted for [3H]GHB binding (a) the necessity of a nonlactonic, relatively extended conformation of the gamma-hydroxybutyric chain, (b) the existence of some bulk tolerance in the vicinity of the hydroxyl group, and (c) the high sensitivity toward isosteric replacements of the carboxyl or the hydroxyl groups. T-HCA has been recently identified as a naturally occurring substance in the central nervous system (CNS) and shows a better affinity than GHB. Our findings are in favor of the presence in the CNS of specific GHB binding sites, which are different from the GABA and the picrotoxin binding sites, and for which T-HCA may be an endogenous ligand.
Asunto(s)
Hidroxibutiratos/síntesis química , Animales , Sitios de Unión , Encéfalo/metabolismo , Hidroxibutiratos/metabolismo , Técnicas In Vitro , Ratas , Relación Estructura-ActividadRESUMEN
Rolipram [(R,S)-4-[3-(cyclopentyloxy)-4-methoxyphenyl]-2-pyrrolidone] has been shown to inhibit selectively the cAMP phosphodiesterase (PDE) of vascular smooth muscle. In order to further explore the structural requirements for selective PDE inhibition, we synthesized a series of rolipram derivatives differently substituted either at the pyrrolidinone or at the aromatic ring. Among these compounds, rolipram was the most active compound. Semirigid analogues were prepared and used for an evaluation of the active conformation of rolipram. Structural comparison with two other potent and chemically different smooth muscle cAMP-PDE inhibitors, trequinsin and Ro 20-1724, allows us to propose a first topological model of the smooth muscle cAMP-PDE pharmacophore.
Asunto(s)
3',5'-AMP Cíclico Fosfodiesterasas/antagonistas & inhibidores , Músculo Liso Vascular/enzimología , Inhibidores de Fosfodiesterasa , Pirrolidinonas/farmacología , Tetrahidroisoquinolinas , Animales , Bovinos , Fenómenos Químicos , Química , GMP Cíclico/metabolismo , Hidrólisis , Imidazoles/farmacología , Técnicas In Vitro , Isoquinolinas/farmacología , Conformación Molecular , Músculo Liso Vascular/efectos de los fármacos , RolipramRESUMEN
A conformational analysis, performed on muscarinic M1 agonists, identified four structural features characteristic of the muscarinic M1 pharmacophore: (i) a protonable basic or quaternary nitrogen acting as a cationic head; (ii) an electronegative dipole usually part of a planar mesomeric ester, amide, or amidine function which can be replaced by an ether (muscarine) or a dioxolane (AF 30); (iii) an intercharge distance of 5 +/- 0.5 A between the cationic head and the electronegative atom of the dipole; (iv) an elevation of 0.5 +/- 0.03 A of the cationic head over the plane containing the electronegative dipole. During a reinvestigation of the conformational behavior of published structures of 5-HT3 antagonists, similar features were observed for the 5-HT3 pharmacophore. However many 5-HT3 antagonists possess additional aromatic planes not present in the muscarinic M1 agonists. These observations brought us to predict the chemical modifications that would change muscarinic M1 agonists into 5-HT3 antagonists. Four of the predicted aminopyridazines were actually synthesized and submitted to testing. The observed IC50 values for 5-HT3 receptor binding ([3H] BRL 43694) ranged from 10 to 425 nM, whereas the affinities for the muscarinic receptor preparations ([3H] pirenzepine) layed over 10,000 nM. In electrophysiological studies the two most active compounds 10 and 13 produced antagonist-like effects on the 5-HT receptor channel complexes responsible for the generation of the rapidly desensitizing ionic currents, and agonist-like effects on those responsible for the slowly desensitizing components.
Asunto(s)
Agonistas Muscarínicos/química , Piridazinas/química , Receptores de Serotonina/efectos de los fármacos , Antagonistas de la Serotonina/síntesis química , Animales , Tronco Encefálico/efectos de los fármacos , Tronco Encefálico/metabolismo , Hipocampo/efectos de los fármacos , Hipocampo/metabolismo , Técnicas In Vitro , Modelos Moleculares , Miocardio/metabolismo , Conformación Proteica , Ratas , Receptores Muscarínicos/metabolismo , Receptores de Serotonina/química , Receptores de Serotonina 5-HT3 , Antagonistas de la Serotonina/farmacologíaRESUMEN
Following the discovery of the weak, competitive and reversible acetylcholinesterase (AChE)-inhibiting activity of minaprine (3c) (IC50 = 85 microM on homogenized rat striatum AChE), a series of 3-amino-6-phenylpyridazines was synthesized and tested for inhibition of AChE. A classical structure-activity relationship exploration suggested that, in comparison to minaprine, the critical elements for high AChE inhibition are as follows: (i) presence of a central pyridazine ring, (ii) necessity of a lipophilic cationic head, (iii) change from a 2- to a 4-5-carbon units distance between the pyridazine ring and the cationic head. Among all the derivatives investigated, 3-[2-(1-benzylpiperidin-4-yl)ethylamino]-6-phenylpyridazine (3y), which shows an IC50 of 0.12 microM on purified AChE (electric eel), was found to be one of the most potent anti-AChE inhibitors, representing a 5000-fold increase in potency compared to minaprine.1
Asunto(s)
Acetilcolinesterasa/metabolismo , Inhibidores de la Colinesterasa/síntesis química , Piperidinas/síntesis química , Piridazinas/síntesis química , Animales , Butirilcolinesterasa/metabolismo , Inhibidores de la Colinesterasa/química , Inhibidores de la Colinesterasa/farmacología , Humanos , Técnicas In Vitro , Neostriado/enzimología , Piperidinas/química , Piperidinas/farmacología , Piridazinas/química , Piridazinas/farmacología , Ratas , Relación Estructura-ActividadRESUMEN
We have recently shown that an arylaminopyridazine derivative of GABA, SR 95103 [2-(3-carboxypropyl)-3-amino-4-methyl-6-phenylpyridazinium chloride], is a selective and competitive GABA-A receptor antagonist. In order to further explore the structural requirements for GABA receptor affinity, we synthesized a series of 38 compounds by attaching various pyridazinic structures to GABA or GABA-like side chains. Most of the compounds displaced [3H]GABA from rat brain membranes. All the active compounds antagonized the GABA-elicited enhancement of [3H]diazepam binding, strongly suggesting that all these compounds are GABA-A receptor antagonists. None of the compounds that displaced [3H]GABA from rat brain membranes interacted with other GABA recognition sites (GABA-B receptor, GABA uptake binding site, glutamate decarboxylase, GABA-transaminase). They did not interact with the Cl- ionophore associated with the GABA-A receptor and did not interact with the benzodiazepine, strychnine, and glutamate binding sites. Thus, these compounds appear to be specific GABA-A receptor antagonists. In terms of structure-activity, it can be concluded that a GABA moiety bearing a positive charge is necessary for optimal GABA-A receptor recognition. Additional binding sites are tolerated only if they are part of a charge-delocalized amidinic or guanidinic system. If this delocalization is achieved by linking a butyric acid moiety to the N(2) nitrogen of a 3-aminopyridazine, GABA-antagonistic character is produced. The highest potency (approximately equal to 250 times bicuculline) was observed when an aromatic pi system, bearing electron-donating substituents, was present on the 6-position of the pyridazine ring.
Asunto(s)
Antagonistas del GABA , Piridazinas/síntesis química , Ácido gamma-Aminobutírico/análogos & derivados , Animales , Encéfalo/metabolismo , Membrana Celular/metabolismo , Indicadores y Reactivos , Espectroscopía de Resonancia Magnética , Piridazinas/farmacología , Ratas , Receptores de GABA-A/efectos de los fármacos , Receptores de GABA-A/metabolismo , Relación Estructura-Actividad , Ácido gamma-Aminobutírico/síntesis químicaRESUMEN
Minaprine [3-[(beta-morpholinoethyl)amino]-4-methyl-6-phenylpyridazine dihydrochloride] is active in most animal models of depression and exhibits in vivo a dual dopaminomimetic and serotoninomimetic activity profile. In an attempt to dissociate these two effects and to characterize the responsible structural requirements, a series of 47 diversely substituted analogues of minaprine were synthesized and tested for their potential antidepressant, serotonergic, and dopaminergic activities. The structure-activity relationships show that dopaminergic and serotonergic activities can be dissociated. Serotonergic activity appears to be correlated mainly with the substituent in the 4-position of the pyridazine ring whereas the dopaminergic activity appears to be dependent on the presence, or in the formation, of a para-hydroxylated aryl ring in the 6-position of the pyridazine ring.
Asunto(s)
Antidepresivos/síntesis química , Dopaminérgicos/síntesis química , Piridazinas/síntesis química , Receptores de Serotonina/efectos de los fármacos , Animales , Fenómenos Químicos , Química , Femenino , Ratones , Piridazinas/farmacología , Receptores Dopaminérgicos/efectos de los fármacos , Relación Estructura-ActividadRESUMEN
The synthetic-computational approach to the study of the binding site of peripheral benzodiazepine receptor (PBR) ligands related to 1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)-3-isoquinolinecarboxamide (PK11195, 1) within their receptor (Cappelli et al. J. Med. Chem. 1997, 40, 2910-2921) has been extended. A series of carboxamide derivatives endowed with differently substituted planar aromatic or heteroaromatic systems was designed with the aim of getting further information on the topological requisites of the carbonyl and aromatic moieties for interaction with the PBR binding site. The synthesis of most of these compounds involves Weinreb amidation of the appropriate lactone as the key step. The most potent compound, among the newly synthesized ones, shows a nanomolar PBR affinity similar to that shown by 1 and the presence of a basic N-ethyl-N-benzylaminomethyl group in 3-position of the quinoline nucleus. Thus, it may be considered the first example of a new class of water soluble derivatives of 1. Several computational methods were used to furnish descriptors of the isolated ligands (indirect approaches) able to rationalize the variation in the binding affinity of the enlarged series of compounds. Sound QSAR models are obtained by size and shape descriptors (volume approach) which codify for the short-range contributions to ligand-receptor interactions. Molecular descriptors which explicitly account for the electrostatic contribution to the interaction (CoMFA, CoMSIA, and surface approaches) perform well, but they do not improve the quantitative models. Moreover, useful hints for the identification of the antagonist binding site in the three-dimensional modeling of the receptor (direct approach) were provided by the receptor hypothesis derived by the pharmacophoric approach. The ligand-receptor complexes obtained provided a detailed description of the modalities of the interaction and interesting suggestions for further experiments.
Asunto(s)
Quinolinas/síntesis química , Receptores de GABA-A/química , Secuencia de Aminoácidos , Animales , Unión Competitiva , Corteza Cerebral/metabolismo , Técnicas In Vitro , Isoquinolinas/química , Isoquinolinas/metabolismo , Ligandos , Masculino , Modelos Moleculares , Conformación Molecular , Datos de Secuencia Molecular , Relación Estructura-Actividad Cuantitativa , Quinolinas/química , Quinolinas/metabolismo , Ensayo de Unión Radioligante , Ratas , Receptores de GABA-A/metabolismo , Alineación de SecuenciaRESUMEN
To investigate further the structural requirements for benzodiazepine (BZD) receptor ligands, we synthesized SR 95195, [7-phenyl-3-methyl-1,2,4-triazolo-(4,3-b) pyridazine], a positional isomer of the 6-phenyl-triazolo-pyridazines, which were the first non-BZD derivatives to exhibit high affinity for the BZD receptor and BZD-like activity in vivo. In vitro, SR 95195 displaced specifically bound [3H]-flunitrazepam from rat cerebellar and hippocampal membranes with respective IC50 values of 4 and 8 microM. In vivo, SR 95195 lacked BZD-like activity. At high doses SR 95195 induced clonic seizures in mice (threshold convulsant dose: 150 mg kg-1; CD50: 160 mg kg-1 i.p.) which were antagonized by Ro 15-1788. At non-convulsant doses (25 mg kg-1 i.p. and 100 mg kg-1 i.p.) SR 95195 significantly decreased punished responding in an operant conflict procedure in the rat, suggesting SR 95195 has intrinsic anxiogenic activity. SR 95195, in mice, reversed the anticonvulsant and myorelaxant actions of diazepam 3 mg kg-1, orally (respective ED50 values: 45 mg kg-1 i.p. and 44 mg kg-1 i.p.). In an operant-conflict test in rats, SR 95195 at non-anxiogenic doses, antagonized the disinhibitory action of diazepam 4 mg kg-1, i.p. (ED50: 8.6 mg kg-1, i.p.), but not that of pentobarbitone 15 mg kg-1, i.p. It is concluded that SR 95195 has the pharmacological profile of an inverse BZD agonist and that displacing the phenyl from the 6- to the 7-position in the triazolopyridazine series causes a shift from agonist to inverse agonist type activity at the BZD receptor site.
Asunto(s)
Convulsivantes , Piridazinas/farmacología , Receptores de GABA-A/metabolismo , Animales , Unión Competitiva , Encéfalo/metabolismo , Condicionamiento Operante/efectos de los fármacos , Diazepam/antagonistas & inhibidores , Femenino , Flumazenil/metabolismo , Flumazenil/farmacología , Flunitrazepam/metabolismo , Técnicas In Vitro , Masculino , Ratones , Piridazinas/metabolismo , Ratas , Ratas Endogámicas , Relación Estructura-ActividadRESUMEN
Previous data have shown that HEPES, a taurine structural analog, inhibits the uptake of taurine by cultured cells differently, depending on its addition either to the culture medium or to the Krebs-Ringer buffer used for cell incubation during taurine uptake measurements (Lleu and Rebel, J Neurosci Res 23: 78-86, 1989). An extensive study of the effect of numerous other taurine structural analogs on taurine uptake by cultured glial cells was carried out. Our results show that taurine uptake modulation by structural analogs follows two different mechanisms. For the first mechanism, observable after the simultaneous presence of taurine and of its analog during the incubation time of the uptake experiment (10 min), the amine function on the molecule is essential. The sulfonate group could be replaced either by a sulfinic group or by a carboxylic group. beta-Alanine, hypotaurine, acetyltaurine, guanidinoethanesulfonate and guanidinopropionate are the most potent inhibitors in this first mechanism. For the second mechanism, which requires the presence of the analog in the culture medium during the 48 hr preceding the taurine uptake measurement, the simultaneous presence of an amine and of a sulfonate group or of an amine and a sulfinate group is required. Carboxylates are ineffective in modulating taurine uptake in this mechanism. The sulfonate buffers synthesized by Good et al. (Biochemistry 5: 467-477, 1966) also affect taurine uptake in both mechanisms.
Asunto(s)
HEPES/farmacología , Neuroglía/metabolismo , Taurina/metabolismo , Animales , Células Cultivadas , Medios de Cultivo , HEPES/química , Ratas , Relación Estructura-Actividad , Taurina/análogos & derivados , beta-Alanina/metabolismoRESUMEN
CGS 15943A is the first reported nonxanthine adenosine antagonist and it shows high affinity towards A1 and A2 receptors. The present data show that CGS 15943A increased in a dose-dependent manner locomotor activity of mice confronted with a free exploratory test without markedly modifying rears or, at low or medium doses, novelty seeking responses. In the light/dark choice procedure, which is especially appropriate for revealing anxiolytic and anxiogenic drug-effects, CGS 15943A decreased the time spent by mice in the lit box and increased the number of transitions. By contrast, the highly selective adenosine A1 receptor, DPCPX, did not significantly modify the behavior of mice except at high doses, which decreased it in the free exploratory test. It is suggested that the present findings confirm the hypothesis that the behavioral effects of adenosine antagonists are linked to their actions at adenosine A2 receptors.
Asunto(s)
Adenosina/antagonistas & inhibidores , Conducta Animal/efectos de los fármacos , Antagonistas Purinérgicos , Quinazolinas/farmacología , Triazoles/farmacología , Animales , Relación Dosis-Respuesta a Droga , Conducta Exploratoria/efectos de los fármacos , Masculino , Ratones , Actividad Motora/efectos de los fármacos , Xantinas/farmacologíaRESUMEN
Activated glia (astrocytes and microglia) and their associated neuroinflammatory sequelae have been linked to the disease progression of several neurodegenerative disorders, including Alzheimer's disease. We found that the experimental anti-inflammatory drug K252a, an inhibitor of calmodulin regulated protein kinases (CaMKs), can block induction of both the oxidative stress related enzyme iNOS and the proinflammatory cytokine IL-1 beta in primary cortical glial cultures and the microglial BV-2 cell line. We also found that the profile of CaMKIV and CaMKII isoforms in primary cortical glial cultures and BV-2 cells is distinct from that found in neurons. Knowledge of cellular mechanisms and high throughput screens of a pharmacologically focused chemical library allowed the discovery of novel pyridazine-based compounds that are cell permeable ligand modulators of gene regulating protein kinases involved in the induction of iNOS and IL-1 beta in activated glia. Pyridazine-based compounds are attractive for the development of new therapeutics due to the retention of the remarkable pharmacological properties of K252a and related indolocarbazole alkaloids, and presence of enhanced functional selectivity in a comparatively simple structure amenable to diverse synthetic chemistries.
Asunto(s)
Carbazoles/farmacología , Inhibidores Enzimáticos/farmacología , Interleucina-1/antagonistas & inhibidores , Neuroglía/fisiología , Óxido Nítrico Sintasa/antagonistas & inhibidores , Proteínas Serina-Treonina Quinasas/antagonistas & inhibidores , Animales , Proteína Quinasa Tipo 2 Dependiente de Calcio Calmodulina , Proteína Quinasa Tipo 4 Dependiente de Calcio Calmodulina , Proteínas Quinasas Dependientes de Calcio-Calmodulina/metabolismo , Células Cultivadas , Corteza Cerebral/citología , Corteza Cerebral/metabolismo , Inducción Enzimática/efectos de los fármacos , Alcaloides Indólicos , Isoenzimas/metabolismo , Ligandos , Microglía/enzimología , Neuroglía/enzimología , Óxido Nítrico Sintasa de Tipo II , Ratas , Ratas Sprague-DawleyRESUMEN
Gamma-hydroxybutyrate (GHB) at low doses (5-10 mg/kg i.p.) increased and at high doses (160-320 mg/kg i.p.) decreased the spontaneous firing rate of prefrontal cortex (PFC) neurons recorded in urethane-anesthetized rats. Only excitations were blocked by NCS-382, a specific GHB receptor antagonist; this suggests that the excitatory effect of low doses of GHB is mediated by a GHB receptor whereas the inhibitory effect of high doses of GHB involves a more complex mechanism.
Asunto(s)
Anticonvulsivantes/farmacología , Benzocicloheptenos/farmacología , Conducción Nerviosa/efectos de los fármacos , Corteza Prefrontal/efectos de los fármacos , Oxibato de Sodio/farmacología , Animales , Relación Dosis-Respuesta a Droga , Electrofisiología , Masculino , Corteza Prefrontal/fisiología , Ratas , Ratas Sprague-Dawley , Factores de TiempoRESUMEN
NCS-382 possesses antagonistic properties at gamma-hydroxybutyrate receptor sites. Its effect on the sedative/cataleptic behaviour observed in rats after gamma-hydroxybutyrate administration was investigated. NCS-382 diminished, in a dose-dependent manner, the sedative and/or cataleptic effects of gamma-hydroxybutyrate, as revealed by a variety of sensorimotor tests. These results indicate that the well-known sedative/anaesthetic effects induced by gamma-hydroxybutyrate administration are provoked via stimulation of a specific class(es) of gamma-hydroxybutyrate receptors which exist in the rat brain and which could mediate a local stimulation of opiate synthesis and release.
Asunto(s)
Anticonvulsivantes/farmacología , Benzocicloheptenos/farmacología , Catalepsia/prevención & control , Hipnóticos y Sedantes/antagonistas & inhibidores , Oxibato de Sodio/antagonistas & inhibidores , Animales , Catalepsia/inducido químicamente , Relación Dosis-Respuesta a Droga , Haloperidol/farmacología , Masculino , Desempeño Psicomotor/efectos de los fármacos , Ratas , Ratas Endogámicas , Oxibato de Sodio/farmacología , Sulpirida/farmacología , NataciónRESUMEN
The effects of a potent P2Y1 receptor antagonist, N6-methyl-2'-deoxyadenosine-3',5'-bisphosphate (MRS2179) on adenosine-5'-diphosphate (ADP)-induced platelet aggregation in vitro, ex vivo and on the bleeding time in vivo were determined. In suspensions of washed platelets, MRS2179 inhibited ADP-induced platelet shape change, aggregation and Ca2+ rise but had no effect on ADP-induced inhibition of adenylyl cyclase. Binding studies using the new radioligand [33P]MRS2179 showed that washed human platelets displayed 134+/-8 binding sites per platelet with an affinity (Kd) of 109+/-18 nM. Finally, intravenous injection of MRS2179 resulted in inhibition of rat platelet aggregation in response to ADP and prolonged the bleeding time, in rats or mice, as compared to controls. These results suggest this potent P2Y1 receptor antagonist to be a promising tool to evaluate the in vivo effects of pharmacologically targeting the P2Y1 receptor with a view to antithrombotic therapy.
Asunto(s)
Adenosina Difosfato/farmacología , Plaquetas/efectos de los fármacos , Inhibidores de Agregación Plaquetaria/farmacología , Agregación Plaquetaria/efectos de los fármacos , Antagonistas del Receptor Purinérgico P2 , Transducción de Señal/efectos de los fármacos , Adenosina Difosfato/análogos & derivados , Alprostadil/farmacología , Animales , Apirasa/farmacología , Plaquetas/metabolismo , Calcio/metabolismo , AMP Cíclico/metabolismo , Relación Dosis-Respuesta a Droga , Humanos , Ratones , Ensayo de Unión Radioligante , Ratas , Transducción de Señal/fisiología , Tionucleótidos/farmacologíaRESUMEN
In order to design a selective M1 muscarinic agonist, we synthesized SR 95639A (morpholinoethylamino-3-benzocyclohepta-(5,6-c)-pyridazine, dihydrochloride), a semi-rigid analogue of the aminopyridazine antidepressant drug minaprine. SR 95639A displaced [3H]pirenzepine from its binding sites in rat hippocampal membranes with an IC50 value of 0.27 microM. It only weakly displaced [3H]N-methylscopolamine from cerebellar, cardiac and ileal membranes (10-48 microM), and, up to 100 microM, did not interact with the main other receptors of the rat brain. In rat isolated sympathetic ganglia, SR 95639A induced dose-dependent depolarizations which were antagonized by pirenzepine, and dose dependently suppressed the M current. These latter effects were also pirenzepine-sensitive. After i.p. or oral treatment in mice, SR 95639A never induced the classical cholinergic syndrome, up to lethal doses. Finally, SR 95639A (i.p. and p.o.) antagonized contralateral rotations induced by intrastriatal injection of pirenzepine, in mice. These results suggest that SR 95639A is a selective agonist at central muscarinic M1 receptors and may represent a useful tool for further characterization of the nature and function of muscarinic receptor subtypes.
Asunto(s)
Morfolinas/farmacología , Parasimpaticomiméticos/farmacología , Piridazinas/farmacología , Animales , Conducta Animal/efectos de los fármacos , Cisterna Magna , Relación Dosis-Respuesta a Droga , Electrofisiología , Cobayas , Técnicas In Vitro , Inyecciones , Masculino , Relajación Muscular/efectos de los fármacos , N-Metilescopolamina , Pirenzepina/antagonistas & inhibidores , Pirenzepina/farmacología , Ratas , Ratas Endogámicas , Receptores Muscarínicos/efectos de los fármacos , Receptores Muscarínicos/metabolismo , Derivados de Escopolamina/farmacología , Conducta Estereotipada/efectos de los fármacosRESUMEN
Trans-gamma-hydroxycrotonate (THCA), a compound naturally present in rat brain, possesses high-affinity binding sites with a heterogeneous distribution which are superimposable with those for gamma-hydroxybutyrate (GHB). Binding studies of THCA on rat brain membranes revealed two binding components, one of high affinity (Kd1, 7 nM, Bmax1 42 fmol/mg protein) and the other of low affinity (Kd2, 2 microM, Bmax2 13 pmol/mg protein). Displacement curves of [3H]THCA by THCA and GHB or of [3H]GHB by THCA are in favour of the existence of a specific high affinity site for THCA. Quantitative autoradiography with image analysis of [3H]THCA binding in rat brain slices indicated that [3H]THCA high affinity binding was displaced at a lower potency by GHB. THCA showed also some selectivity in displacing [3H]GHB from its high affinity binding site (Kd = 95 nM). This mutual overlap favours a subpopulation of GHB receptors, which have THCA as a natural ligand, showing partial agonistic properties compared to GHB. The functional significance of this result remains unknown.
Asunto(s)
Encéfalo/metabolismo , Hidroxibutiratos/metabolismo , Receptores de Neurotransmisores/metabolismo , Oxibato de Sodio/metabolismo , Animales , Masculino , Ratas , Ratas EndogámicasRESUMEN
The existence of a specific synthesizing enzyme for gamma-hydroxybutyric acid in rat brain has recently been reported. Here, for the first time, we demonstrate the presence of a high affinity, apparently specific binding site for this compound in the same tissue. This binding does not require Na+ and takes place optimally at pH 5.5. The bound gamma-hydroxybutyric acid is not displacable by GABA or baclofen. We report here on some structurally related compounds of GHB with a similar or better binding capacity than GHB itself. The number of binding sites increases with age up to adulthood and differs depending on the brain region. In primary tissue cultures of pure chicken neurones and glia, gamma-hydroxybutyric acid binding occurs exclusively in the neuronal preparations.