Endocrine Abstracts

Thyroid hormones (TH) regulate (brain) development, growth, body temperature, most pathways involved in energy and structural metabolism as well as anabolic and catabolic reactions. Inadequate availability of essential trace elements (iodine, selenium, iron, zinc) limits TH biosynthesis, metabolism and action. Endocrine-disrupting chemicals (EDC), i.e., exogenous chemicals or their mixtures, can interfere with any aspect of TH synthesis, distribution, transport, metabolism, and action via (non-)canonical T3 receptor mediated signalling. Only a limited number of EDC exert their adverse effects by directly interfering with follicular TH production. Majority of EDC effects occurs by disruption of protein-protected TH distribution via bloodstream, specific TH transport across cellular membranes and/or intracellular (in-)activation and/or TH metabolism. This pre-receptor control of local T3 availability to intracellular T3 receptors, which act as ligand-modulated transcription factors for gene expression, represents the main operation field for EDC in the TH system (THS). Only few EDC modulate functions of T3 receptors, which contrasts adverse EDC actions on the sex steroid dependent reproductive processes, most of which are known to be associated with direct disruption of sex steroid receptor functions. Thus, individual blood TH concentrations only provide limited information about adverse action and consequences for EDC exposed individuals, e.g., mother-child pairs. TH, trace elements and EDC exert their direct and permissive effects in very low, locally regulated, physiological concentrations frequently not reflected at the systemic level as impressively illustrated during TH-regulated amphibian metamorphosis, embryonal development of fish or mammalian species, including humans. Considering that anthropogenic mass recently exceeded our blue planet’s biomass, we must minimize exposure to EDC, contained in and released from anthropogenic products, as EDC interfere already at very low concentrations with the THS. Concomitantly, the THS needs to be fortified and protected by globally adequate supply with those essential trace elements (I, Se, Fe) required for its proper function.