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Related Experiment Videos

Sequential deiodination of thyroxine in human thyroid gland.

H Ishii, M Inada, K Tanaka

    The Journal of Clinical Endocrinology and Metabolism
    |November 1, 1982
    PubMed
    Summary

    Thyroid tissues from Graves' disease patients show accelerated conversion of thyroxine (T4) to 3,3'-diiodothyronine (3,3'-T2). This study demonstrates enhanced iodothyronine deiodination in Graves' thyroids, impacting thyroid hormone metabolism.

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    Area of Science:

    • Endocrinology
    • Biochemistry
    • Thyroidology

    Background:

    • Thyroid hormones, thyroxine (T4) and triiodothyronine (T3), are crucial regulators of metabolism.
    • Iodothyronine deiodinases are key enzymes that activate or inactivate thyroid hormones.
    • Alterations in deiodinase activity are implicated in thyroid disorders like Graves' disease.

    Purpose of the Study:

    • To investigate and characterize iodothyronine deiodinase activities in human thyroid tissues.
    • To compare deiodination pathways in normal thyroid glands versus those from patients with Graves' disease.
    • To elucidate the specific roles of 5-deiodinase and 5'-deiodinase in thyroid hormone metabolism in Graves' disease.

    Main Methods:

    • Incubation of human thyroid tissues (normal and Graves' disease) with iodothyronines (T4, T3, rT3).

    Related Experiment Videos

  • Measurement of deiodination products (rT3, T3, 3,3 2) using radioimmunoassays (RIAs).
  • Kinetic analysis (Km, Vmax) and determination of optimal reaction conditions (pH, temperature, cofactors, inhibitors).

    • Main Results:

    • Both inner ring (5-deiodination) and outer ring (5'-deiodination) monodeiodination activities were identified in human thyroids.
    • Deiodination reactions were dependent on time, tissue volume, temperature, pH, and dithiothreitol concentration.
    • Graves' disease thyroid tissues exhibited significantly higher conversion rates of T4 to rT3 and overall T4 to 3,3 2 compared to normal thyroids.
    • Specific kinetic parameters (Km, Vmax) were determined for T3 and rT3 conversion to 3,3 2.

    Conclusions:

    • Human thyroid glands possess both 5-deiodinase and 5'-deiodinase activities.
    • Graves' disease is associated with accelerated iodothyronine deiodination, particularly the conversion of T4 to 3,3 2 via T3 or rT3.
    • These findings highlight altered thyroid hormone metabolism in Graves' disease, potentially contributing to the hyperthyroid state.