Partial purification of a chorionic gonadotropin-like protein from bovine cotyledons

The presence of placental gonadotropin activity in early pregnancy was studied in the cow. Cotyledons from the first trimester of gestation were used to isolate a chorionic gonadotropin-like (CG-like) protein by means of ammonium sulfate precipitations (0.17-4.5 M) and gel filtration on Sephadex G-100 and DEAE-Sephadex. The CG-like activity was measured by a radioreceptor assay (RRA) specific for human chorionic gonadotropin (hCG). Luteotrophic activity was also assessed in two separate in vitro bioassays using cultures of bovine granulosa and rat Leydig cells. It was found that the 3 M ammonium sulfate precipitate of cotyledon extracts contained a CG-like activity of 179 mIU/mg protein as measured by RRA. The precipitate inhibited 125I-hCG binding in a linear fashion. A ninefold increase in specific activity was achieved by further purification on Sephadex G-100 (800 mIU/mg protein) and Sephadex-DEAE (1600 mIU/mg). In experiments with cell cultures, it was found that 20 micrograms of protein eluted from Sephadex-DEAE (equivalent to 16 mIU of hCG as determined by RRA) added to the culture medium significantly enhanced (P less than 0.05) progesterone production by the granulosa cells and testosterone production by the Leydig cells. We conclude that the bovine placenta contains a chorionic gonadotropin which may serve to maintain the corpus luteum of pregnancy.