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Abstract
The antihormonal activity of Lithospermum officinale (Boraginaceae) and Lycopus virginicus and other Lamiaceae has been investigated in the rat. L. officinale cold water freeze dried extracts (FDE) significantly lowered thyroid hormone content in the serum whereas an inactivated extract exhibited a considerable loss of biological activity. The efficacy of different plant extracts greatly depended on the extraction procedure: extraction of powdered leaves with boiling water or ethanol yielded FDEs without thyroid hormone-lowering capacity. The chemical oxidation of a hot-water (100°C) extract by KMnO4 served to reintroduce the antihormonal effectiveness. In a goiter suppression test, the chronic administration of L. officinale FDE greatly suppressed TSH-levels and consequently goiter weight. The antithyrotropic and antithyroidal activity of a variety of plant extracts was accompanied by an additional prolactin diminution. Lithospermum officinale exhibited a strong antigonadotropic effectiveness and completely inhibited the PMS-stimulated growth of ovaries and uteri by as little as 100 μg of FDE. As to the mechanism of action there are different possibilities:
1. inactivation of the circulating hormone (TSH, Prolactin, PMS), the so-called hypophysealhormone-blocking effect.
2. inhibition of hypophyseal hormone secretion (TSH, Prolactin).
3. inhibition of thyroidal secretion (T4 and T3).