Stimulation of development in vitro by platelet-activating factor receptor ligands released by mouse preimplantation embryos.

Previous reports have demonstrated that culture of mouse preimplantation embryos at high density stimulates their rate of development. The molecular basis of this phenomenon was investigated. Culture of embryos from the four-cell stage at high density in normal medium, or at low density either in embryo-conditioned medium or medium containing platelet-activating factor (PAF), significantly advanced the timing of compaction, initiation of cavitation and/or completion of zona hatching, and also increased the number of cells in blastocysts. In contrast, Lyso-PAF, an inactive metabolite of PAF, and Enantio-PAF, an enantiomer of PAF, did not have a stimulatory effect at low embryo density, but did not inhibit the stimulation of development at high embryo density. The stimulatory effect of culture at high density was inhibited in the presence of either CV-3988 or SDZ 64-412, two structurally distinct competitive PAF-receptor antagonists, while the development rate at low density was not affected. We conclude that an embryo-derived factor related to PAF is secreted by blastomeres during in vitro culture and acts in a receptor-mediated manner to stimulate the rate of development.