Identification and origin of oestradiol-binding protein in immature rat skin. Demonstration of oestrophilic alpha-foetoprotein synthesis and secretion by developing rat skin explants in culture.

Oestrophilic alpha-foetoprotein (alpha FP) is found in high concentrations in developing rat skin cytosol. Elevated levels of alpha FP observed in foetal-rat skin decreased during development, and the protein became undetectable after 3 weeks of postnatal life. The developmental profile of alpha FP in skin is different from that in foetal blood. alpha FP in skin arises as a result of its synthesis in situ in the epidermal cells. Synthesis of alpha FP in skin is demonstrated by linear incorporation of [14C]leucine into immunoprecipitable, intracellular alpha FP by skin explants during 6 h in culture. Secretion is demonstrated by incorporation into alpha FP in culture medium. The rate of alpha FP synthesis in skin also declined with age and its synthesis is completely switched off 2 weeks after birth. The skin alpha FP level during development is regulated by controlling the rate of its synthesis in skin. alpha FP synthesized and secreted by skin is immunologically, electrophoretically and, with respect to molecular weight and oestradiol-binding properties, similar to that found in foetal serum. alpha FP was also identified as the major oestradiol-binding protein present in newborn-rat skin or secreted by newborn-rat skin explants in culture.