Biological activity of the unique variants of human chorionic gonadotropin in choriocarcinoma tissue.

Human chorionic gonadotropin (hCG) in sera and placentae from normal pregnant women separated into 7 variants on analysis by an isoelectric focusing technique and determined by radioimmunoassay. The pIs ranged from 3.9 to 7.0. Three additional acidic variants were found in the sera and tumor tissues of patients with choriocarcinoma with pIs of 3.2, 3.5 and 3.7. The biological activity of each variant was determined by measuring testosterone production by rat Leydig cells in vitro. The pI 4.1 fraction corresponding to placental hCG possessed the highest biological activity while those focusing further afield from pI 4.1 showed decreasing activities. All 3 tumor unique acidic variants possessed biological activity with the fraction focusing at pI 3.7 having the greatest potency.