Changes with age in protein-bound iodine (PBI) and body temperature in the mouse.

Protein-bound iodine (PBI), body temperature, and the response of the thyroid gland to different doses of thyrotropin (TSH) were examined in males of two inbred strains of mice at different ages. Results indicate persistent decline in PBI with advancing age that is significantly greater in DBA/2J than C57BL/6J mice. The magnitude of the PBI response to TSH diminishes in both strains with advancing age but is significantly greater in strain DBA/2J than C57BL/6J. Body temperature was found to decline with advancing age and was highly correlated with thyroid function. Although additional research is needed, a tentative conclusion is that advancing age imparts a diminished response of the thyroid gland to endogenous thyrotropin. This is the first report of age-related changes and particularly correlation between PBI and body temperature in genetically controlled mouse strains. The indications are that such thyroid-temperature relationships are genotype dependent.