Uterine endocrinology and paracrinology: insulin-like growth factor binding protein-1 and placental protein 14 revisited.

A large number of proteins and peptides have been identified in the endometrium where they are likely to exert local biological effects. These substances may be enzymes, their inhibitors, proteinases, proteinase inhibitors, hormones, or bioactive peptides with diverse functions. Endometrial function and embryo-endometrial interactions require synchronized actions between endocrine and local factors. As examples of local factors recent studies on the insulin-like growth factor (IGF) system and placental protein 14 (PP14) are reviewed. IGF binding protein-1 (IGFBP-1) and PP14 are products of the secretory phase endometrium: IGFBP-1 is produced by decidualized stromal cells and PP14 by glandular epithelial cells. IGFBP-1 may inhibit the action of IGFs at the endometrial-trophoblastic interphase, and it may also have a role in stromal-epithelial interaction. PP14 has immunosuppressive properties, and recent findings indicate that it may play a part in the fertilization process by inhibiting binding of spermatozoa to the zona.