Characterization of the Synthesis and Release of Human Placental Lactogen and Human Chorionic Gonadotropin by an Enriched Population of Dispersed Placental Cells*

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Abstract
An enriched fraction of human placental cells that synthesize and release both placental lactogen (hPL) and hCG was obtained by isopycnic centrifugation of collagenase/ hyaluronidase-clispersed cells through a density gradient of 40% Percoll. The enriched cells, which banded at a density of approximately 1.01 g/ml, comprised 10-15% of the total DNA. During the first 24 h after attachment, the cells released 50-250 ng hPL and 4-10 mlU hCG/106 cells. Thereafter, the rate of hPL release decreased, while the rate of hCG and [35S]trichloroacetic acid-precipitable protein release remained constant. The enriched cells responded to phospholipase A2, low extracellular calcium, and (Bu)2cAMP in a manner similar to that of placental explants. Phospholipase A2 (0.1 and 1 U/ml) stimulated hPL release by 270% and 568%, respectively, and low extracellular calcium (0–0.18 mM) stimulated hPL release by 48%. (Bu)2 cAMP (1 mM) stimulated hCG release by 42%, but had no effect on hPL. Estradiol (10−5–10−12m) and progesterone (10−5–10−10m) had no effect on the synthesis and release of either hPL or hCG over a 6-day period. In addition, insulin (8.3 × 10−7m) and changes in medium glucose content (0–5 mg/ml) had no effect on hPL release over a 72-h period. Since the enriched trophoblast cells respond to provocative stimuli in a manner similar to that of explants and placental fragments, this cell population is a useful model system for investigations of the cellular mechanisms of hPL and hCG release.