Regulation of uterine and conceptus secretory activity in the pig

Evidence is presented for the involvement of a number of specific uterine- and conceptus-derived proteins in endometrial differentiation and conceptus or fetal development. These secretory proteins include mitogens (insulin-like growth factor-I and -II, epidermal growth factor, uterine luminal fluid mitogen), binding and transport proteins (uteroferrin, insulin-like growth factor and retinol binding proteins, respectively), protease inhibitors (antileukoproteinase, plasmin/trypsin inhibitor), and trophoblastic specific proteins. Using immunological reagents and specific complementary DNA (cDNA) probes, the tissue origins of several of these proteins have now been identified. In addition, the temporal regulation of messenger RNA (mRNA) production for a number of these proteins has been elucidated. The results suggest that although circulating and locally produced steroid hormones may be involved in regulating the synthetic abilities of these tissues during pregnancy, other, as yet undefined, factors may also mediate these activities. In this paper we present a review of the current knowledge pertaining to the identity, physiological regulation and potential functions of pig maternal and conceptus secretory proteins during pregnancy.