ANALYSIS OF CHORIONIC-GONADOTROPIN SECRETED BY CULTURED HUMAN BLASTOCYSTS

Embryos produced in an in-vitro fertilization (IVF) programme, but whi ch were unsuitable for transfer to patients because they originated fr om one (1PN) ok three pronuclear (3PN) oocytes or because they origina ted from two pronuclear (2PN) oocytes but cleaved normally, were maint ained in tissue culture. The embryos that progressed to blastocysts we re cultured to clay 14 of development in order to study their daily ou tput of human chorionic gonadotrophin (HCG). Blastocysts that released large amounts of immunoreactive HCG, which continued to increase dail y during the study period, provided the culture supernatants used in t he present studies. The heterogeneity of HCG released by blastocyst ti ssues on days 11 and 14 of development was studied by a chromatofocusi ng method which separates the isoforms of the gonadotrophin based on d ifferences in their isoelectric points. It was found that the secreted HCG was composed of several molecular forms and that this heterogenei ty changed from day 11 to 14 of development. The early blastocyst tiss ues produced more acidic HCG isoforms than the more advanced embryonic tissues. Differences in the apparent ploidy of the blastocyst tissues studied did not affect significantly the distribution of the HCG isof orms secreted either on day 11 or day 14 of development. These results suggest that the bioactivity of the HCG secreted by blastocysts may c hange with time and with differentiation of the trophectoderm. In addi tion, the results suggest that the ploidy of early blastocysts does no t influence the nature of the HCG secreted.