Prefertilization treatment of mice with platelet activating factor affects pregnancy.

Embryo-derived platelet activating factor (EPAF) is thought to be either biologically similar to platelet activating factor (PAF) or responsible for PAF liberation in vivo. We have previously shown that premating PAF treatment in the mouse renders the platelets nonresponsive to EPAF, leading to a reduced implantation rate in these animals. In this study, we have shown that females, injected with PAF before mating, show altered embryo development invivo on day 4 postfertilization. This is manifested as an interruption of compaction, a reduced cell number per embryo, and reduced embryo number per mouse. Results suggest that EPAF represents an early pregnancy signal that supports embryo development. The most likely mechanism is via platelet activation, since only those mice that showed thrombocytopenia after fertilization were found to have normal embryos on day 4 postmating.