AGE-RELATED CHANGES IN SERUM THYROXINE AND TRIIODOTHYRONINE-I-125 RESIN SPONGE UPTAKE IN YOUNG DOG

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  • 1 January 1977
    • journal article
    • research article
    • Vol. 27  (5) , 646-650
Abstract
Serum thyroxine (T4) concentrations and 125I-labeled triiodothyronine resin sponge uptakes (T3-RSU) were determined in young dogs every 10 days between 3 and 103 days of age. When compared to the adult mean of 1.7 .mu.g T4/100 ml serum, the T4 in young dogs was elevated throughout the ages studied. The serum T4 concentration was twice the adult value at 3 days of age, rose to over 5 times the adult value in the 1st mo. of life, and declined again to twice the adult mean by 103 days of age. Serum T3-RSU values decreased from 52% at 3 days (approximately equal to the adult mean) to about 30% from 13 to 23 days, indicating an increase in the thyroid hormone binding capacity of serum proteins in the 1st few weeks of life. Thereafter, T3-RSU rose to near 50% again. The change in binding capacity appeared to explain, at least in part, the apparent hyperthyroid-like T4 concentrations of the young dog.