Endothelial cell chemotaxic activity expressed in rat placenta is not associated with prolactin-like proteins B and C

Conditioned medium from gestation day 18 rat placental cultures showed pote nt stimulation of the directional migration of human retinal endothelial ce lls. To examine the role of major secreted placental proteins in this chemo taxic activity, prolactin-like proteins (PLPs)-B and C were purified from r at placenta using immune-affinity chromatography. In contrast to conditione d medium, native PLP-B and PLP-C preparations failed to show any significan t stimulation of endothelial cell migration. This study further examined th e ability of PLP-B to bind to rat receptors for growth hormone (GH-R) and p rolactin (PRL-R). In competitive binding assays with [I-125]-hGH, neither n ative nor recombinant PLP-B preparations showed significant high affinity b inding to the transfected rat GHR or PRL-R. In summary, neither PLP-B nor P LP-C exhibit the potent chemotaxis stimulatory activity of placental condit ioned media, nor does PLP-B show evidence of ability to act via rat GH or P RL receptors.