CORTICOSTEROID-BINDING GLOBULIN (CBG) IN FETAL DEVELOPMENT

In fetal sheep the prepartum increase in plasma cortisol concentration is associated with an increase in high affinity corticosteroid bindin g activity in plasma. This appears to reflect an increase in corticost eroid-binding globulin (CBG) biosynthesis from the fetal liver, and ev idence is presented that hepatic CBG gene expression is increased by e xposure to glucocorticoids in the fetus. Immunoreactive CBG is found i n other fetal tissues, and CBG mRNA is present in fetal pituitary. CBG reduces the ability of cortisol to exert negative feedback on basal o r CRH-stimulated ACTH output by fetal sheep pituitary cells in culture . We suggest that CBG interacts with cortisol in a manner that maintai ns a low negative feedback on the pituitary, and perhaps hypothalamus. This constitutes a component of the cascade of events that is associa ted with hypothalamic-pituitary-adrenal activation in the late gestati on fetus, and with the onset of parturition.