ONTOGENY OF EPIDERMAL GROWTH-FACTOR, TRANSFORMING GROWTH FACTOR-ALPHA, EPIDERMAL GROWTH-FACTOR RECEPTOR, AND THYROID-HORMONE RECEPTOR RNA LEVELS IN RAT-KIDNEY AND CHANGES IN THOSE LEVELS INDUCED BY EARLY THYROXINE TREATMENT

Ontogenic changes in the mRNA levels of epidermal growth factor (EGF), transforming growth factor-alpha, EGF receptor, and thyroid hormone r eceptor (r-erbA) were examined in developing rat kidneys. The mRNA lev els of both EGF and thyroid hormone receptor rose dramatically during the postnatal period with the rise in thyroid hormone receptor message preceding the rise in EGF message. In addition, we examined renal mRN A levels in 1-wk-old rats treated with thyroxine (T4) from birth throu gh d 6. Neonatal T4 treatment augmented the renal mRNA levels of EGF b ut decreased the levels of EGF-receptor and transforming growth factor -alpha. T4 treatment did not significantly affect the levels of renal mRNA for thyroid hormone receptor. Although the EGF and transforming g rowth factor-alpha peptides are similar and interact with the same rec eptor, our findings indicate that these homologous growth factors are regulated differently during development. In addition, hormones that i nfluence growth and development, such as T4, may function both as posi tive and negative regulators of growth factor expression.