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Related Experiment Videos

Triiodothyronine generation from thyroxine in human thyroid: enhanced conversion in Graves' thyroid tissue.

H Ishii, M Inada, K Tanaka

    The Journal of Clinical Endocrinology and Metabolism
    |June 1, 1981
    PubMed
    Summary

    Thyroid tissue converts thyroxine (T4) to triiodothyronine (T3) enzymatically. This conversion is significantly increased in Graves

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    Area of Science:

    • Endocrinology
    • Thyroidology
    • Biochemistry

    Background:

    • Thyroid hormones, thyroxine (T4) and triiodothyronine (T3), play crucial roles in metabolism.
    • The conversion of T4 to T3 is a key regulatory step in thyroid hormone action.
    • Understanding this conversion process in different thyroid conditions is essential for diagnosis and treatment.

    Purpose of the Study:

    • To investigate the enzymatic conversion of T4 to T3 in normal, Graves', and neoplastic thyroid tissues.
    • To characterize the kinetics and influencing factors of T4 to T3 conversion in thyroid tissue.

    Main Methods:

    • Thyroid tissue homogenates and cellular fractions were incubated with labeled or unlabeled T4.
    • T3 formation was quantified using paper chromatography and radioimmunoassay (RIA).

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  • Enzyme kinetics (Km, Vmax) and factors like pH, temperature, and inhibitors were analyzed.

    • Main Results:

    • T4 to T3 conversion was confirmed to be an enzymatic process in normal, Graves', and neoplastic thyroid tissues.
    • T3 generation was dependent on incubation time, tissue amount, DTT concentration, temperature, and pH.
    • Conversion was significantly enhanced in Graves' thyroid tissues compared to normal thyroid tissues.
    • Propylthiouracil inhibited T3 formation, while methimazole had no effect.

    Conclusions:

    • T4 is enzymatically converted to T3 in normal thyroids, Graves' thyroids, and differentiated thyroid neoplasms.
    • Graves' thyroid tissue exhibits a markedly enhanced capacity for T4 to T3 conversion.
    • The findings highlight the role of local thyroidal T4 to T3 conversion in thyroid pathophysiology.