Possible role of platelet-activating factor in embryonic signaling during oviductal transport in the hamster

Hamster embryos enter the uterus in pregnant females nearly one day earlier than unfertilized eggs in cycling females. The hypothesis that a substance derived from eicosanoids is released by the embryos, but not by oocytes, to hasten their transport to the uterus was tested by examining the effects of indomethacin, nordihydroguaiaretic acid (NDGA), platelet activating factor (PAF), and PAF antagonists on egg transport in the hamster. Administration of indomethacin had no effect on embryo transport, whereas administration of NDGA delayed the transport of eggs to the uterus in pregnant but not in cycling hamsters. The PAF antagonists TCV-309 and BN 52021 delayed significantly the transport of eggs to the uterus in pregnant animals, but not in cycling animals; i.e., they retarded the passage of embryos but not of oocytes to the uterus. Administration of PAF to cycling hamsters hastened the oviductal transport of ova. These data suggest that, in the hamster, the earlier passage of embryos to the uterus as compared to oocytes is mediated by PAF. Thrombocytopenia was detected in early-pregnant hamsters, and PAF-like activity was detected in spent media of two-cell through morula stage hamster embryos. These results suggest that preimplantation hamster embryos produce PAF-like activity that mediates embryonic signaling to the oviduct as well as pregnancy-associated thrombocytopenia.