Release of Human Chorionic Gonadotropin (hCG) and its Alpha-subunit (hCG-α) from Perifused Human Placenta

Abstract

The release of human chorionic gonadotropin (hCG) and its α-subunit (hCG-α) from the normal human placenta and the effect of some stimulatory agents on their release were studied in vitro using a perifusion system. Each perifusate was assayed for hCG and hCG-α in its own homologous radioimmunoassay systems.
Both hCG and hCG-α were released from the placenta at any stage of gestation in our perifusion system. Much more hCG than hCG-α was released from the placenta in early gestation. By comparison, however, hCG-α increased gradually with the gestational age. The amount of hCG-α released was almost equal to that of hCG in the placenta in the 17th gestational week. After the 22nd gestational week, hCG-α was released in larger quantities than hCG, and about 10times more hCG-α than hCG was released from the term placenta.
These results were also confirmed by gel filtration of perifusates on a Sephadex G-100 column. hCG-α, compared with hCG, was present in excess in gel filtrated perifusates in the last two trimesters.
By adding 1mM dibutyryl cyclic AMP to the perifusion medium, the release of both hCG and hCG-α was stimulated significantly. Synthetic luteinizing hormone releasing hormone (LH-RH) at concentrations of 10ng/ml and 100ng/ml had no effect, but at a high concentration (1μg/ml), LH-RH stimulated the release of them. Moreover, mouse epidermal growth factor (EGF) stimulated not only the release of hCG and hCG-α but also their production, because both hCG and hCG-α levels rose progressively with the time course in the presence of EGF.
The present studies demonstrate that the perifusion system of chorionic tissues is a useful method for investigating the release of hCG and its subunits in vitro.