Analysis of chorionic gonadotrophin secreted by cultured human blastocysts

Embryos produced in an in-vitro fertilization (IVF) programme, but which were unsuitable for transfer to patients because they originated from one (1PN) or three pronuclear (3PN) oocytes or because they originated from two pronuclear (2PN) oocytes but cleaved normally, were maintained in tissue culture. The embryos that progressed to blastocytes were cultured to day 14 of development in order to study their daily output of human chorionic gonadotrophin (HCG). Blastocysts that released large amounts of immunoreactive HCG, which continued to increase daily during the study period, provided the culture supernatants used in the present studies. The heterogeneity of HCG released by blastocyst tissues on days 11 and 14 of development was studied by a chromatofocusing method which separates the isoforms of the gonadotrophin based on differences in their isoelectric points. It was found that the secreted HCG was composed of several molecular forms and that this heterogeneity changed from day 11 to 14 of development. The early blastocyst tissues 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 isoforms secreted either on day 11 or day 14 of development. These results suggest that the bioactivity of the HCG secreted by blastocytes may change with time and with differentiation of the trophectoderm. In addition, the results suggest that the ploidy of early blastocytes does not influence the nature of the HCG secreted.