Temporal and regional expression of placental lactogen-II messenger ribonucleic acid and protein in the hamster placenta

The purpose of this investigation was to identify the cell types synthesizing hamster placental lactogen-II (haPL-II) in the chorioallantoic placenta. In addition, temporal changes in haPL-II mRNA expression, in placental mass, and in the proportion of haPL-II-containing cells per unit area were examined. Hamster PL-II mRNA expression was assessed by in situ hybridization and Northern and slot-blot analyses. Cells containing haPL-II protein were identified by immunocytochemical techniques. Placentae were recovered in the morning on Days 6, 8, 10, 12, and 14 of gestation and in the afternoon on Day 15. A single 1-kb haPL-II transcript was first detected on Day 10 of gestation. Hamster PL-II message increased to Day 14 and remained elevated on Day 15. Giant trophoblast cells (GTC) located in the trophospongium were the major source of haPL-II mRNA and protein, although GTC along the periphery of the placenta and in the labyrinth expressed haPL-II as well. Placental weight, trophospongium portion of placental weight, and number of haPL-II-immunostained GTC per unit of placental area increased between Days 12 and 14 and remained elevated to Day 15. These observations indicate that an increased number of haPL-II-producing GTC is a major factor contributing to increased maternal haPL-II serum levels during pregnancy.