Serum thyroxine concentration before and after administration of thyrotropin-stimulating hormone decreases with chronological age in the dog

Thyroid function in the dog was evaluated as a function of increasing chronological age. Ninety-one dogs between the ages of 14.6 and 160.8 months were evaluated. Basal serum triiodothyronine (T/sub 3/) concentration, basal serum thyroxine (T/sub 4/) and serum T/sub 4/ concentration following stimulation by thyrotropin were found to decrease with age. The results suggested that age may be an important factor in interpreting thyroid profiles in the dog. 17 refs., 4 figs., 1 tab.