title: Age related changes in serum throxine and 125I-triiodothyronine resin sponge uptake in the young dog.
abstract: Serum thyroxine (T4) concentrations and 125I-labelled 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 microgram 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 five times the adult value in the 1st month 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 first 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.
mesh_terms: D000367:Age Factors; D000818:Animals; D004285:Dogs / Q000097:blood*; D005260:Female; D008297:Male; D013974:Thyroxine / Q000097:blood*; D014284:Triiodothyronine / Q000378:metabolism*
chemical_list: D014284:Triiodothyronine; D013974:Thyroxine