Human Reproduction, Vol. 9, No. 7, pp. 1300-1307, 1994
© 1994 European Society of Human Reproduction and Embryology
research-article |
Fertilization and early embrology: The secretion of gonadotrophin-releasing hormone by peri-implantation embryos of the rhesus monkey: comparison with the secretion of chorionic gonadotrophin
1Wisconsin Regional Primate Research Center 1223 Capitol Court 2Department of Physiology, University of Wisconsin Madison, WI 53715–1299, USA 3Center for Reproductive Biology and Molecular Endocrinology, Indian Institute of Science Bangalore 560012, India
Correspondence: 4To whom correspondence should be addressed
Chorionic gonadotrophin (CG) is the first clear embryonic signal during 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 mechanism of CG secretion in primate embryos, we examined the production and timing of secretion of GnRH in peri-implantation embryos of the rhesus monkey. In-vivo fertilized/developed morulae and early blastocysts, recovered from non-superovulated, naturally-bred rhesus monkeys by non-surgical uterine flushing, were cultured in vitro to hatched, attached and post-attached blastocyst stages using a well-established culture system. We measured GnRH and CG in media samples from cultured embryos 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 stage to 0.70 ± 0.08 at 6–12 days and 1.30 ± 0.23 at 
13 days of hatched blastocyst attachment and proliferation of trophoblast cells. GnRH concentrations in culture media obtained from embryos (n = 5) that failed to hatch and attach were mostly undetectable (
0.1). Samples that did not contain detectable GnRH failed to show detectable CG. Immunocytochemical studies, using a specific monoclonal anti-GnRH antibody (HU4H) as well as polyclonal antisera (LR-1), revealed that immunopositive GnRH cells were localized in pre-hatching blastocysts (n = 4), in blastocysts (n = 2) after 5–10 days of attachment and in monolayer cultures (n = 4) of well-established embryonic trophoblast cells. GnRH positive staining was seen only in cytotrophoblasts but not in syncytiotrophoblasts. Similarly, cytotrophoblast, but not syncytiotrophoblast, cells of the rhesus placenta were immunopositive. In controls, either in the absence of antibody or in the presence of antibody pre-absorbed with GnRH, these cells failed to show stain. These observations indicate, for the first time, that an immunoreactive GnRH is produced and secreted by blastocysts during the peri-attachment period and by embryo-derived cytotrophoblast cells in the rhesus monkey.
Key words: chorionic gonadotrophin/GnRH/primate blastocyst/trophoblast cells
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