STIMULATION AND INHIBITION OF ANGIOGENESIS BY PLACENTAL PROLIFERIN AND PROLIFERIN-RELATED PROTEIN

In many mammalian species, the placenta is the site of synthesis of pr oteins in the prolactin and growth hormone family. Analysis of two suc h proteins, proliferin (PLF) and proliferin-related protein (PRP), rev ealed that they are potent regulators of angiogenesis; PLF stimulated and PRP inhibited endothelial cell migration in cell culture and neova scularization in vivo. The mouse placenta secretes an angiogenic activ ity during the middle of pregnancy that corresponds primarily to PLF, but later in gestation releases a factor that inhibits angiogenesis, w hich was identified as PRP. Incubation of placental tissue with PLF le d to the specific binding of this hormone to capillary endothelial cel ls. Thus PLF and PRP may regulate the initiation and then the cessatio n of placental neovascularization.