Human Placental-Lactogen Promotes Cell-Proliferation, Dna-Synthesis, And Somatomedin Release By Isolated Human-Fetal Connective Tissues

Since placental lactogens have been implicated in the control of fetal metabolism, and in the release of somatomedins (SM) by fetal tissues, we examined the actions of human placental lactogen (HPL) on the growth of isolated human fetal myoblasts, fibroblasts and cartilage explants, and on their release of immunoassayable SM-C. Myoblasts were derived from skeletal muscle and fibroblasts from the skin of abortuses delivered between 12 to 17 weeks after prostaglandin induction. Costal cartilage explants were obtained from one hemithorax. After myoblasts and fibroblasts were plated at low density (0.3 × 105 cells per well) HPL (50-1000 ng ml−1) caused a dose-dependent increase in cell number over a 7 day incubation, becoming statistically significant between 50 and 250 ng/ml with individual experiments. After sub-confluent mycblasts and fibroblasts were growth-restricted by exposure to medium containing 1% fetal calf serum, HPL caused a significant increase in [3H] thymidine uptake during a subsequent exposure at similar concentrations. Human growth hormone (HGH) failed to increase thymidine incorporation by myoblasts or fibroblasts, while neither HPL or HGH affected isotope uptake by cartilage explants. Culture medium conditioned for 44 h by exposure to myoblasts or fibroblasts was assayed for SM-C by RIA after extraction with acid-ethanol. The SM-C present in conditioned medium was significantly elevated after exposure of cells to HPL (250 ng ml−1) but not HGH. The results show that HPL is mitogenic for cultured human fetal myoblasts and fibroblasts and that this may be due partly to an increase in SM-C release by the cells.