| Abstrakt: |
Black cohosh (Actaea racemosa) is a frequently used herbal remedy for the treatment of mild climacteric symptoms. In the present study, the modulation of γ-aminobutryic acid (GABA)-induced chloride currents (IGABA) through GABA type A (GABAA) receptors by black cohosh extracts and isolated compounds was investigated. GABAAreceptors, consisting of α1, β2, and γ2Ssubunits, were expressed in Xenopus laevisoocytes, and potentiation of IGABAwas measured using the two-microelectrode voltage clamp technique. In a bioactivity-guided isolation procedure the positive modulation of IGABAcould be restricted to the plant terpenoid fractions, resulting in the isolation of 11 cycloartane glycosides, of which four significantly (p< 0.05) enhanced IGABA. The most efficient effect was observed for 23-O-acetylshengmanol 3-O-β-d-xylopyranoside (4, 100 μM), enhancing IGABAby 1692 ± 201%, while actein (1), cimigenol 3-O-β-d-xylopyranoside (6), and 25-O-acetylcimigenol 3-O-α-l-arabinopyranoside (8) were significantly less active. In the absence of GABA, only 4induced small (not exceeding 1% of IGABA-max) chloride inward currents through GABAAreceptors. It is hypothesized that the established positive allosteric modulation of GABAAreceptors may contribute to beneficial effects of black cohosh extracts in the treatment of climacteric symptoms. |
