Intrathyroidal effect of Lycopus europaeus, phenolic acids, potassiumiodide and lithiumiodide

Abstract: The inhibitory effect which extracts of leaves of Lycopus europeaus exert upon thyroidal activity has been explained by a thyrotropin (TSH)-inactivating influence of the plant extract. it was the aim of this study to check if a direct intrathyroidal attack exists which reduces thyroidal secretion in addition. In order to prove this assumption, male Wistar rats received an injection of test substances after TSH. Thus an influence of this plant extract on secretion of thyroid hormones could be shown, as the number of colloid droplets transporting the thyroid hormones to the periphery was clearly decreased.This activity of Lycopus extract was compared to that of the known antithyroidal substances LiC1 and KJ. The plant extract reduces endocytosis at a distinct and quicker rate than it is done by KJ or LiCl. Phenolic acids and related compounds were tested in the same experimental model. Some antithyroid activity, especially the transisomer of p-coumaric acid, showed distinct antithyroidal activity, but isoferulic acid, sinapic acid and syringic acid proved to be active too.Furthermore in an inverse experimental design the reaction upon a TSH-stimulus following pretreatment with test substances was investigated. Lycopus extract as well as KJ and LiC1 were effective in this model, too, though the activity of the latter was reduced following repeated application, whereas the phenolic compounds exerted only low efficacy.The above mentioned results demonstrate that the plant extract is capable to suppress thyroid hormone secretion by a direct intrathyroidal attack. The plant constituents investigated show a clearly reduced activity as compared to the plant extract.

Keyword(s): Lycopus europaeus

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