Endocrine Abstracts

Iodine (I) and selenium (Se) are two essential trace elements for regular thyroid gland functioning and thyroid hormone metabolism. Most Europeans are only marginally supplied with both elements through their daily nutrition. The mammalian organism has developed efficient and highly complex mechanisms to control I and Se uptake, metabolism and recycling. The thyroid gland is equipped with the necessary transporters and metabolizing enzymes for I uptake and bioconversion into thyroid hormones. In addition, it appears extremely efficient in controlling its exceptionally high Se status by as yet poorly defined pathways. Se in the thyroid gland is pivotal for its defense against highly toxic peroxides generated continuously during thyroid hormone biosynthesis, and for the expression of active deiodinase isozymes which control thyroid hormone activation and inactivation. A number of genetically or chemically modified mouse models have been generated to study thyroid gland physiology and thyroid hormone biosynthesis. Until now, quantification of Se and I concentrations in the thyroid gland, peripheral tissues or murine serum samples has been hampered by the small amounts of material which is available from single mice. To circumvent these limitations, we have tested total reflection X-ray fluorescence (TXRF) spectroscopy as a very sensitive method to measure the elementary composition of a single murine thyroid lobe (approx. 2 mg wet weight). In a first group of animals, we found an average content of 223 ppb (Se) and 543 ppm (I) which is inside the expected physiological ranges. As a proof of concept, we compare Se concentrations in small (thyroid, pituitary, adrenals) and large (liver, kidney, spleen) organs from Se-deficient and regular mice with their serum Se concentrations. Our results indicate that the TXRF-spectroscopy represents a fast and reliable method to determine trace element status from minute amount of tissue or serum and might become an important technique for mouse experiments.