Evidence for a human chorionic gonadotropin-like material in the rabbit blastocyst

Extracts from (1) 300 day 6 rabbit blastocysts, (2) 300 day 2 unfertilized ova, and (3) uteri from the nonpregnant does were analyzed in the following assays in order to determine the presence of a chorionic gonadotropin: (1) in vitro bioassay for testosterone production by decapsulated rat testes, (2) in vitro bioassay for progesterone production by porcine granulosa cells, (3) in vitro determination of adenylyl cyclase-stimulating activity in rabbit Graafian follicles, (4) gel filtration in a Sephadex G-150 column and assay of the elutions in a radioimmunoassay (RIA) specific for the beta-subunit of human chorionic gonadotropin (hCG), (5) parallelism with hCG standard preparations in beta-hCG RIA, and (6) concanavalin A-column chromatography. The rabbit blastocyst extracts showed an hCG-like material in all of the systems tested. None of the other two extracts presented hCG-like activity in any of the assay. The immunoreactive material in the beta-hCG RIA of the blastocyst extracts after gel filtration presented a profile different from that of pure hCG; this may represent heterogeneity due to a species difference or a slightly different molecular weight. These results confirmed previous findings of several investigators and those from our laboratory in that the preimplanted rabbit embryo contains a gonadotropin with characteristics similar to hCG.