Rat placental lactogen-I binds to the choroid plexus and hypothalamus of the pregnant rat.
Recent findings suggest that placental lactogen has a role in the regulation of hypothalamic function during pregnancy. To explore the mechanisms by which placental hormones may exert effects in the maternal central nervous system, we have examined the binding of rat placental lactogen-I (rPL-I) to brain slices from pregnant rats at mid- and late gestation. The binding of rPL-I to maternal rat brain was compared with that of human GH (hGH). Radiolabelled rPL-I bound specifically to ependymal cells of the choroid plexus in the lateral ventricles and in the roof of the third ventricle. The binding of 125I-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 binding 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 ventromedial nuclei and to the medial preoptic area of the hypothalamus. The binding of radiolabelled hGH to all brain regions was inhibited by unlabelled rPL-I as well as hGH, indicating that rPL-I competes for lactogenic binding sites in the hypothalamus as well as the choroid plexus of the pregnant rat. These findings suggest potential mechanisms by which placental hormones may exert direct effects on the maternal central nervous system during pregnancy. The precise functions and roles of the PL-I binding sites in maternal choroid plexus and hypothalamus remain to be explored.
Pihoker, C; Robertson, MC; Freemark, M
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