It is proposed that prostaglandin E 2 (PGE 2), secreted by the fetal placenta of the sheep,
acts as a circulating regulator of the physiological function of many fetal organs (tissues) in a
way analogous to catecholamines in the adult. The specificity of PGE 2 action in different
tissues is determined by three different receptor subtypes which regulate intracellular
calcium concentrations via the IP 3 pathway, or cyclic AMP concentrations via the
adenylcyclase system. The placenta, by secreting PGE 2 (and possibly other factors such as …