Recombinant human 5-HT3A receptors in outside-out patches of HEK 293 cells: basic properties and barbiturate effects.

Barann M, Meder W, Dorner Z, Bruss M, Bonisch H, Gothert M, Urban BW.

Institut fur Pharmakologie und Toxikologie, Universitat Bonn, Germany. barann mailer.meb.uni-bonn.de

The patch-clamp technique was used on excised (outside-out) patches to characterize h5-HT3A receptors stably transfected in HEK 293 cells and to compare the effects of the barbiturate anaesthetics methohexital and pentobarbital on this ligand-gated cation channel. At negative membrane potentials 5-HT induced inward currents in a concentration-dependent manner (EC50=8.6 microM, Hill coefficient =1.5). The mean peak current induced by 30 microM 5-HT was -110 pA at -100 mV. The 5-HT3A receptor antagonist ondansetron (0.3 nM) reversibly inhibited the 5-HT (30 microM) signal by 70% and at 3 nM it abolished the response. Methohexital and pentobarbital inhibited 5-HT-induced (30 microM) currents in a concentration-dependent manner. The maximal inhibition with a given methohexital or pentobarbital concentration was reached when the respective drug was applied 45 s prior to and during the 2-s 5-HT pulse (IC50 values=95 microM and 127 microM, Hill coefficient = -1.0 and -1.6, respectively). Although the barbiturates were, thus, equipotent, their effects differed substantially with respect to the dependence on the time schedule of application to the patches: the potency of methohexital was virtually maximal when the drug was applied exclusively 45 s before the agonist pulse, but its inhibitory potency decreased considerably when it was exclusively applied during the 2-s 5-HT pulse (IC50=380 microM). Conversely, pentobarbital was almost maximally potent in inhibiting the 5-HT signal when it was exclusively coapplied with this agonist, but its inhibitory potency was considerably lower (IC50 approximately 500 microM) when applied exclusively 45 s before 5-HT. Another difference between both barbiturates involves the rate of inactivation of 5-HT3 receptor-mediated currents: whereas high concentrations of methohexital (> or = 300 microM) were necessary to induce moderate (< or = twofold) acceleration of this parameter, pentobarbital produced such an effect at all concentrations and the extent of acceleration increased with increasing concentration (1.5- to fivefold). In conclusion, two barbiturates, chemically closely related but of different lipophilicity, clearly differ with respect to the kinetics of their effect on 5-HT3 receptor channels; one possible explanation involves drug access to an amphipathic site of action via both an aqueous and a hydrophobic pathway. Pentobarbital, in contrast to methohexital, inhibits hS-HT3A receptor-mediated currents at anaesthetic concentrations (approximately 90 microM).

Source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10997728&dopt=Abstract barbiturate Butalbital Fioricet





Psychopharmacological screening of Pfaffia glomerata Spreng. (Amarathanceae) in rodents.

de-Paris F, Neves G, Salgueiro JB, Quevedo J, Izquierdo I, Rates SM.

Centro de Memoria, Departamento de Bioquimica, Instituto de Ci encias Basicas da Saude (ICBS), Universidade Federal do Rio Grande do Sul (UFRGS), RS, Porto Alegre, Brazil.

The alcoholic extract of Pfaffia glomerata roots (100, 500, 1000 mg/kg, intraperitoneally (i.p.), and 500, 1000, 1500 mg/kg, per os) was studied in several behavioral animal models for the evaluation of central activity: open field, barbiturate sleeping time, pentilenotetrazole (PTZ)-induced convulsions, elevated plus-maze, step-down inhibitory avoidance and forced swimming test. The acute treatment (500 mg/kg, i.p.) interfered with the open-field habituation, decreased sleep latency and increased barbiturate-induced sleeping time, protected partially the animals of PTZ-induced convulsions, decreased the memory retention in step-down inhibitory avoidance, and did not have an important effect in the elevated plus-maze test and forced swimming test. The same extract at 1000 mg/kg per os did not cause any effect in barbiturate sleeping time and pentilenotetrazole-induced convulsions models. Thus, the effect on the memory was deeper evaluated in the step-down inhibitory avoidance task. When administered by intraperitoneal route, the extract showed a dose-dependent effect causing full amnesia at 1000 mg/kg. On the other hand, when it was given by oral route at 500, 1000 and 1500 mg/kg, no influence on the memory retention was observed. These results suggest that the alcoholic extract of P. glomerata roots presents different effects depending on the route of administration: by i.p route, it seems to be a central nervous system depressant agent; by oral route, it seems to be ineffective, at least in the tested doses.

Source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11025164&dopt=Abstract barbiturate Butalbital Fioricet





Evaluation of Emit tox benzodiazepine and barbiturate assays on the Vitalab Viva analyser and FPIA on the Abbott ADx analyser.

Charlier CJ, Plomteux GJ.

Laboratory of Clinical Toxicology, CHU Sart-Tilman, Liege, Belgium. C.CHARLIER chu.ulg.ac.be

We evaluated the performance of the Emit tox benzodiazepine and barbiturate assays (Dade Behring) and fluorescence polarisation immunoassay (FPIA) (Abbott) for use with serum determinations in preliminary therapeutic drug monitoring or acute drug intoxication detection. Performance, as indicated by CVs, of the Emit tox benzodiazepine and barbiturate assays and FPIA showed that both immunochemical techniques are precise and have good reproducibility. For within-run studies, results from benzodiazepine determinations showed maximum CV values of 1.91% for the Emit method and 2.65% for FPIA; results from barbiturate determinations showed maximum CV values of 2.01% for the Emit method and 1.89% for FPIA. For between-run studies, results from benzodiazepine determinations showed maximum CV values of 1.79% for the Emit method and 1.12% for FPIA; results from barbiturate determinations showed maximum CV values of 2.09% for the Emit method and 2.02% for FPIA.

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EEG burst suppression is not necessary for maximum barbiturate protection in transient focal cerebral ischemia in the rat.

Schmid-Elsaesser R, Schroder M, Zausinger S, Hungerhuber E, Baethmann A, Reulen HJ.

Department of Neurosurgery, Klinikum Grosshadern, Ludwig-Maximilians-University, Munich, Germany. schmid-elsaesser nc.med.uni-muenchen.de

Barbiturates have been demonstrated to reduce the cerebral metabolic rate (CMR) in a dose-dependent manner but investigations of a dose-response relationship for their neuroprotective efficacy are scant. It has been suggested that barbiturates possess other mechanism of action that may be critical to their protective effect. If so, it is conceivable that the peak effect of such mechanisms does not parallel the reduction in CMR. Thus, maximal neuroprotection may be achieved with a substantially lower dose of the drug. Thirty Sprague-Dawley rats were subjected to 2 h of middle cerebral artery occlusion while either anesthetized with (1) halothane (control) or (2) intravenous thiopental titrated to cause mild EEG suppression or (3) thiopental titrated to maintain EEG burst suppression. Cortical blood flow was recorded by continuous bilateral laser Doppler flowmetry (LDF). Infarct volume was assessed after 3 h of reperfusion. Low-dose thiopental decreased blood flow to 80% of baseline and high-dose thiopental to 70% of baseline. LDF did not indicate improvement of blood flow by thiopental in the ischemic area. Compared to controls, low-dose thiopental significantly decreased infarct volume by 28% and high-dose thiopental by 29%. The results of this study and a review of literature indicate that barbiturates provide cerebral protection but that the magnitude of this effect has been overestimated. Other mechanisms than CMR reduction seem to contribute to their beneficial effects, and high doses administered to the point of burst suppression may not be required to obtain maximal protection.

Source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10064163&dopt=Abstract barbiturate Butalbital Fioricet