RAT PLACENTAL LACTOGEN-I BINDS TO THE CHOROID-PLEXUS AND HYPOTHALAMUSOF THE PREGNANT RAT

Recent findings suggest that placental lactogen has a role in the regu lation of hypothalamic function during pregnancy. To explore the mecha nisms by which placental hormones may exert effects in the maternal ce ntral nervous system, we have examined the binding of rat placental la ctogen-I (rPL-I) to brain slices from pregnant rats at mid- and late g estation. The binding of rPL-I to maternal rat brain was compared with that of human GH (hGH). Radiolabelled rPL-I bound specifically to epe ndymal cells of the choroid plexus in the lateral ventricles and in th e roof of the third ventricle. The binding of I-125-labelled rPL-I was inhibited by unlabelled rPL-I, hGH or rat prolactin but not by rat GH , indicating that rPL-I and rat prolactin interact with a common bindi ng site in maternal rat brain. Radiolabelled hGH bound to the choroid plexus and to ependymal cells lining the third ventricle in the region of the arcuate nucleus. In addition, hGH bound specifically to the ve ntromedial nuclei and to the medial preoptic area of the hypothalamus. The binding of radiolabelled hGH to all brain regions was inhibited b y unlabelled rPL-I as well as hGH, indicating that rPL-I competes for lactogenic binding sites in the hypothalamus as well as the choroid pl exus of the pregnant rat. These findings suggest potential mechanisms by which placental hormones may exert direct effects on the maternal c entral nervous system during pregnancy. The precise functions and role s of the PL-I binding sites in maternal choroid plexus and hypothalamu s remain to be explored.