Characterization of hepatic epidermal growth factor receptors in the developing rat

Binding of ¹²⁵I-labeled epidermal growth factor (EGF) was characterized in basolateral plasma membranes prepared from the livers of 21-day gestation fetuses, 14-day-old sucklings and adult Sprague-Dawley rats using a self-generating Percoll gradient method. The membrane preparations employed have been previously assayed in terms of plasma membrane protein yield, enrichment of various marker enzymes and sodium-dependent bile acid and amino acid transport. ¹²⁵I-EGF binding was saturable and time and temperature dependent. Equilibrium analyses showed that the suckling period is characterized by a marked decrease in overall hepatic EGF binding capacity (460 ± 50 fmol/mg protein) compared to either the fetal period (1290 ± 160 fmol/mg) or to adults of either sex (males = 1540 ± 230, females 1010 ± 130 fmol/mg). Treatment of the suckling rat with parenteral EGF resulted in a 78% reduction in the observed binding capacity when assessed 2 h after growth factor administration. Comparison of binding affinities revealed no significant difference between the suckling and adult preparations (K_d = 0.40 ± 0.03 vs. 0.39 ± 0.02 nM, respectively); however, both preparations differed significantly from the fetal group which exhibited a decreased affinity of binding with a higher overall dissociation constant (K_d = 0.68 ± 0.06 nM). Thus, it appears that major ontogenetic changes occur in the rat hepatic ligand/receptor system for epidermal growth factor. These changes are discussed in the context of transitional events in mammalian development such as birth and weaning.