Effect of thyroxine administration on the expression of epidermal growth factor in the kidney and submandibular gland of neonatal mice. An immunocytochemical and in situ hybridization study.

The effect of T4 administration on epidermal growth factor (EGF) expression in kidney and submandibular glands (SMG) was studied in newborn mice. EGF messenger RNA (mRNA) abundance and EGF immunoreactivity were assessed by in situ hybridization and immunohistochemical techniques, respectively. T4 treatment on days 0-6 augmented both the in situ hybridization and immunocytochemical signals in kidney but not in SMG on day 7. By contrast, T4 injections on days 7-14 did not alter the in situ hybridization or immunocytochemical signals in kidney but increased both signals in SMG on day 15. Thus, neonatal T4 treatment augments the levels of EGF mRNA as well as EGF immunoreactivity in both kidney and SMG. The T4 effect is manifested during the first week in kidney whereas the SMG responds to T4 treatment only during the second week of life.