Inhibition by human embryos of mouse granulosa cell progesterone production: development of a sensitive bioassay

Reproduction technologies could be improved by the development of methods to evaluate oocyte or embryo quality in a non-invasive, quantitative manner. Since human embryos secrete a factor that inhibits granulosa cell progesterone production, an interspecies bioassay was established to investigate whether the presence of this progesterone-inhibitory factor (PIF) in human embryo-conditioned (HEC) media is related to the health and developmental capacity of the embryos. Oocytes were microsurgically removed from oocyte-cumulus complexes isolated from superovulated mouse ovaries, and the oocytectomized complexes were cultured in HEC media in the presence of follicle stimulating hormone and testosterone. Progesterone accumulation in the media was determined by radioimmunoassay. Despite the potential limitations of very small volumes of HEC media to evaluate, and the need to freeze these media at the source, the bioassay was able to detect PIF activity in HEC media. Most embryos produced PIF activity, but the degree of inhibition was not correlated with the ability of oocytes to be fertilized, nor with embryo morphology or ability to cleave and develop after transfer. These results demonstrate that secretion of PIF by human embryos can be measured by this bioassay and that human PIF can inhibit murine granulosa cell steroidogenesis; however, PIF activity is not correlated with human embryo quality or developmental competence.