Epidermal growth factor binding to neonatal mouse skin explants and membrane preparations--effect of triiodothyronine

Daily treatment of newborn Swiss-Webster mice with triiodothyronine (T3, 500 ng/day) increased epidermal growth factor (EGF) content in whole skin (epidermis + dermis). Separation of the epidermis using 0.01 M dithiothreitol followed by processing for radioimmunoassay measurement reveals levels of EGF 2-to 3-fold higher in epidermis than in whole skin. In vitro flotation of circular skin sections from control and T3 treated neonatal mice in medium containing [I125]EGF showed increased uptake of label following 5 days of in vivo T3 treatment. Mouse skin membrane preparations exhibit saturable, specific binding of [I125]EGF. T3 treatment for 5 days in vivo significantly increased EGF binding capacity in skin membrane preparations but did not alter EGF receptor affinity (Kd 4.5 nM). Protein, RNA, and DNA concentrations were significantly increased in whole neonatal mouse skin following T3 administration. These results suggest one mechanism by which thyroid hormones increase skin EGF concentration is augmentation of skin EGF receptor binding.