On the Antigonadotropic Activity of Lithospermum and Lycopus Species and Some of their Phenolic Constituents¹

Abstract

The active principle responsible for the antigonadotropic activity of Lithospermum, Lycopus, and related species is formed from phenolic precursors. For its formation, an oxidation step was found to be essential. It could be shown that several phenolic plant ingredients like caffeic acid, chlorogenic acid, and rosmarinic acid as well as luteolin-7β-glucuronide represent precursors of compounds with such efficacy. During the preparation of aqueous plant extracts, an enzymatical oxidation occurs. This oxidation step can be substituted by treatment with KMnO₄.

The activity of aqueous plant extracts clearly exceeds the effects expected from its content in phenolic ingredients, e .g. 10 µg FDE of Litospermum off. (77) was found to be more active than 36 µg (0.05 µmol) rosmarinic acid, the most active plant constituent. An evident augmentation in the biological efficacy of such oxidized plant ingredients can be achieved by addition of either Mn²⁺ ions or unoxidized diphenols. Furthermore, the oxidation carried out during the extraction of plant extracts by a very active phenoloxidase of these plants may cause an increased activity. The lack of such auxiliary reactions clearly improving the antigonadotropic activity may explain the poor results gained with plant ingredients till now.