Epidermal growth factor in mouse ocular tissue: effects of thyroxine and exogenous epidermal growth factor

Using a specific and sensitive epidermal growth factor (EGF) radioimmunoassay, we identified radioimmunoassayable EGF both in developing and adult mouse ocular tissues. In neonatal animals ocular EGF concentrations increase during the first 4-9 days and then decline between 9 and 15 days. Thyroxine (T4) administration (0.4 micrograms/g body weight/day from day 0) increased local EGF concentrations in eye and skin of 7-day-old neonatal mouse pups. However, this treatment did not affect submandibular gland EGF concentrations during the 1st wk of life. Both EGF and T4 are known to accelerate eye opening in the neonatal mouse. Exogenous EGF administration (2 micrograms/g body weight/day) during the first 8 days of life elicited precocious eyelid opening as expected but did not alter the serum T4 concentration, suggesting that EGF does not mediate eye opening by T4 dependent mechanism(s). Tissue EGF measurements revealed that the exogenous EGF was localized in skin and eye; however, other tissues including lung, liver, heart and submandibular gland also contained exogenous EGF. Kidney-EGF concentrations did not rise while brain-EGF levels were significantly decreased after exogenous EGF, suggesting that different EGF uptake and regulatory mechanism(s) exist in different tissues during the neonatal period. T4 administration (0.4 micrograms/g body weight/day) for 10 days to adult mice also increased ocular-EGF concentrations. However, this increase was abolished by sialoadenectomy, suggesting in contrast to the newborn, that submandibular gland is an important source of ocular-EGF in adult mice. These studies indicate that ocular EGF in the mouse is thyroxine responsive only during the neonatal period.