The successful pregnancy requires careful orchestratation of fetal development and maternal physiology. Many of these changes may be coordinated by placental hormones, which are in a unique position to alter both maternal and fetal physiology. The bovine placenta secretes a family of placental prolactin-related hormones which may assist or replace the pituitary hormones during pregnancy. Despite the obvious relationship of these hormones to prolactin, the placental hormones are very distinct from the pituitary hormones and one another in amino acid sequence, differing by 50-65%. These include bovine placental lactogen (bPL), which was identified by binding to prolactin and growth hormone receptors, and a diverse subfamily which does not interact with these characterized recepors, including bPRCl. As part of a long term effect to investigate the function and mechanism of action of these placental hormones in this bovine model system, attention will be focused of bPL and bPRCI. Specific high affinity binding sites for each these hormones have been identified. The plan is to characterize bPL receptor protein(s) and localize their target cells. The copy DNAs corresponding to the receptor proteins from a model target tissue will be isolated and cloned. These will then be used to investigate other target tissues. Taken together, these studies will increase understanding of the hormone and tissue specific actions of this gene family, and provide the tools to begin to examine the function of these placental hormones in the controlled proliferation and maternal adaptions which occur during pregnancy.
