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Discordant Secretion of Placental Protein Hormones in Differentiating Trophoblasts in Vitro

Department of Medicine, Cedars-Sinai Medical Center-UCLA School of Medicine Los Angeles, California 90048

Address requests for reprints to: Glenn D. Braunstein, M.D., Cedars- Sinai Medical Center, Department of Medicine, 8700 Beverly Boulevard, Room B118, Los Angeles, California 90048.

The regulation of trophoblast secretion of the placental proteins CG (hCG), placental lactogen (hPL), and pregnancy specific-β-1-glycoprotein (SP-1) has not been fully elucidated. We therefore studied the secretion of hCG, hCG-β subunit, hCG- subunit, hPL, and SP-1, both in the basal state and after exposure to 8-bromo-cAMP, during the in vitro differentiation of cytotrophoblasts to syncytiotrophoblasts. Term placental tissue was enzymatically digested and cytotrophoblasts purified by Percoll density gradient centrifugation. At the time of seeding of 4–6 x 10⁶ cells/ml in 35-mm flasks all of the cells were mononuclear and 48% contained hCG-, but none contained hCG or hCG-β by the avidin-biotin-peroxidase immunohistochemical method. After 3 days in culture, hCG- and hCG or hCG-β were present in multinucleated syncytiotrophoblasts and in the mononuclear cytotrophoblasts. During the 5 days in culture, the secretion of hCG, hCG-, hPL and SP-1 into the media increased and reached a maximum on day 4 followed by a decrease on day 5. Basal hCG-β secretion was very low and did not change during culture. The ratio of hCG-/hCG decreased from days 1–4 of culture. Incubation with 8-bromocAMP for 24 h stimulated the secretion of hCG and hCG-, whereas hCG-β and hPL levels did not change. The secretion of SP-1, however, was inhibited by 8-bromo-cAMP.

These results indicate that the cytotrophoblasts secrete hCG, hCG-β and hCG- during in vitro differentiation into syncytiotrophoblasts. Since the basal ratio of hCG to hCG- secretion changed during 5 days in culture and a cAMP analogue differentially modulated the secretion of the different placental protein hormones, the physiological regulation of secretion of each of the proteins also may differ.

Received September 26, 1988.

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