THE SECRETION OF GONADOTROPIN-RELEASING-HORMONE BY PERIIMPLANTATION EMBRYOS OF THE RHESUS-MONKEY - COMPARISON WITH THE SECRETION OF CHORIONIC-GONADOTROPIN

Chorionic gonadotrophin (CG) is the first clear embryonic signal durin g early pregnancy in primates. CG has close structural and functional similarities to pituitary luteinizing hormone (LH) which is regulated by gonadotrophin releasing hormone (GnRH). To study the regulatory mec hanism of CG secretion in primate embryos, we examined the production and timing of secretion of GnRH in peri-implantation embryos of the rh esus monkey. In-vivo fertilized/developed morulae and early blastocyst s, recovered from non-superovulated, naturally-bred rhesus monkeys by non-surgical uterine flushing, were cultured in vitro to hatched, atta ched and post-attached blastocyst stages using a well-established cult ure system. We measured GnRH and CG in media samples from cultured emb ryos with a sensitive radioimmunoassay and bioassay, respectively. The secretion of GnRH (pg/ml; mean +/- SEM) by embryos (n = 20) commenced from low levels (0.32 +/- 0.05) during the pre-hatching blastocyst st age to 0.70 +/- 0.08 at 6-12 days and 1.30 +/- 0.23 at greater than or equal to 13 days of hatched blastocyst attachment and proliferation o f trophoblast cells. GnRH concentrations in culture media obtained fro m embryos (n = 5) that failed to hatch and attach were mostly undetect able (less than or equal to 0.1). Samples that did not contain detecta ble GnRH failed to show detectable CG. Immunocytochemical studies, usi ng a specific monoclonal anti-GnRH antibody (HU4H) as well as polyclon al antisera (LR-1), revealed that immunopositive GnRH cells were local ized in pre-hatching blastocysts (n = 4), in blastocysts (n = 2) after 5-10 days of attachment and in monolayer cultures (n = 4) of well-est ablished embryonic trophoblast cells. GnRH positive staining was seen only in cytotrophoblasts but not in syncytiotrophoblasts. Similarly, c ytotrophoblast, but not syncytiotrophoblast, cells of the rhesus place nta were immunopositive. In controls, either in the absence of antibod y or in the presence of antibody pre-absorbed with GnRH, these cells f ailed to show stain. These observations indicate, for the first time, that an immunoreactive GnRH is produced and secreted by blastocysts du ring the peri-attachment period and by embryo-derived cytotrophoblast cells in the rhesus monkey.