Maturation of cytokine receptors in preparation for birth

The elucidation of the tissue-specific profile of expression of the prolact in (PRL) and growth hormone (GH) receptors during embryonic and fetal devel opment in a range of species has provided a new impetus for the delineation of the specific roles of the hormone ligands for these receptors in develo pment. During late gestation, there is a requirement to shift from a phase of predominant cellular proliferation, where placental nutrient supply is a dominant influence on organ and body growth, to one of functional differen tiation, which is required for independent homoeostasis after birth. In thi s review we discuss the interactions between the pre-partum increases in co rtisol and thyroid hormones and the synthesis, secretion and actions of fet al PRL and GH. We also review the changes that occur in the tissue-specific expression of the PRL and GH receptors before birth which may play an impo rtant role in precocial species in the successful transition of the fetus t o extra-uterine life.