Treatment of the neonatal rat with epidermal growth factor: differences in time and organ response.

The ability of exogenous mouse epidermal growth factor (EGF) (500 ng/g body weight/day) to retard somatic growth and to alter the timing of integumental maturation was investigated in the newborn rat. The immediate postnatal period (days 0-3) was identified as the critical time for elicitation of EGF effects. Somatic growth retardation produced by EGF persisted through weaning (day 20) and was asymmetric with maximal organ growth retardation present in liver and kidney and with relative sparing of heart and brain. Treatment of newborn rats with EGF on postnatal days 0-3 advanced the mean time of eyelid opening by 146 versus 31 h for tooth eruption. In contrast, EGF delayed opening of the external ear canal by approximately 48 h. EGF-treated pups thus exhibited a rearrangement in the normal sequence of craniofacial development. In summary, these data provide new information on the critical time of EGF response in the rat, the existence of an asymmetric pattern of organ growth retardation following perinatal EGF exposure, and the ability of EGF to retard morphogenesis of the external ear.