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The mode of action of the anxiolytic medicinal plant Souroubea sympetala was investigated to test the hypothesis that extracts and the active principle act at the pharmacologically important [GABA.SUB.A]-benzodiazepine ([GABA.sub.A]-BZD) receptor. Leaf extracts prepared by ethyl acetate extraction or supercritical extraction, previously determined to have 5.54 mg/g and 6.78 mg/g of the active principle, betulinic acid, respectively, reduced behavioural parameters associated with anxiety in a rat model. When animals were pretreated with the [GABA.sub.A]-BZD receptor antagonist flumazenil, followed by the plant extracts, or a more soluble derivative of the active principle, the methyl ester of betulinic acid (MeBA), flumazenil eliminated the anxiety- reducing effect of plant extracts and MeBA, demonstrating that S. sympetala acts via an agonist action on the [GABA.sub.A]-BZD receptor. An in vitro [GABA.sub.A]-BZD competitive receptor binding assay also demonstrated that S. sympetala extracts have an affinity for the [GABA.sub.A]-BZD receptor, with an [EC.sub.50] value of 123 p.g/mL (EtOAc leaf extract) and 154 µg/mL (supercritical CO2 extract). These experiments indicate that S. sympetala acts at the [GABA.sub.A]-BZD receptor to elicit anxiolysis. Key words: natural health product, anxiety, pharmacology, betulinic acid, methyl ester of betulinic acid. Le mode d'action de la plante medicinale anxiolytique Souroubea sympetala a ete etudie afin de verifier l'hypothese que les extraits et le principe actif de la plante agissent sur le recepteur [GABA.SUB.A]-benzodiazepine ([GABA.sub.A]-BZD), un recepteur d'importance clinique. Des extraits de feuilles prepares par extraction a l'acetate d'ethyle ou par extraction supercritique, dont on a determine qu'ils contenaient respectivement 5,54 mg/g et 6,78 mg/g de principe actif, l'acide betulinique, reduisaient les parametres comportementaux associes a l'anxiete chez le rat utilise comme modele. Lorsque les animaux etaient pretraites avec un antagoniste du recepteur [GABA.sub.A]-BZD, le flumazenil, et des extraits de la plante ou d'un derive plus soluble du principe actif, l'ester de methyle de l'acide betulinique (MeBA), le flumazenil eliminait l'effet anxiolytique des extraits de la plante, demontrant ainsi que S. sympetala agit par une action agoniste du recepteur [GABA.sub.A]-BZD. Un test de competition de liaison du recepteur [GABA.sub.A]-BZD realise in vitro a aussi demontre que les extraits de S. sympetala ont une affinite pour le recepteur [GABA.sub.A]-BZD, avec des valeurs de [EC.sub.50] de 123 pg/mL (extrait de feuilles a l'acetate d'ethyle) et 154 pg/mL (extrait supercritique au C[O.sub.2]). Ces experiences indiquent que S. sympetala agit sur le recepteur [GABA.sub.A]-BZD pour provoquer un effet anxiolytique. [Traduit par la Redaction] Mots-cles: produit de sante naturel, anxiete, pharmacologie, acide betulinique, ester de methyle d'acide betulinique., Introduction The major neurotransmitter implicated in the etiology of anxiety disorders is 7-amino butyric acid (GABA) (Treiman 2001; Lydiard 2003). GABA is the major inhibitory neurotransmitter in the central nervous [...]

The mode of action of the anxiolytic medicinal plant Souroubea sympetala was investigated to test the hypothesis that extracts and the active principle act at the pharmacologically important GABAA-benzodiazepine (GABAA-BZD) receptor. Leaf extracts prepared by ethyl acetate extraction or supercritical extraction, previously determined to have 5.54 mg/g and 6.78 mg/g of the active principle, betulinic acid, respectively, reduced behavioural parameters associated with anxiety in a rat model. When animals were pretreated with the GABAA-BZD receptor antagonist flumazenil, followed by the plant extracts, or a more soluble derivative of the active principle, the methyl ester of betulinic acid (MeBA), flumazenil eliminated the anxiety-reducing effect of plant extracts and MeBA, demonstrating that S. sympetala acts via an agonist action on the GABAA-BZD receptor. An in vitro GABAA-BZD competitive receptor binding assay also demonstrated that S. sympetala extracts have an affinity for the GABAA-BZD receptor, with an EC50 value of 123 μg/mL (EtOAc leaf extract) and 154 μg/mL (supercritical CO2 extract). These experiments indicate that S. sympetala acts at the GABAA-BZD receptor to elicit anxiolysis. [ABSTRACT FROM AUTHOR]