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 ea rlier than unfertilized eggs in cycling females. The hypothesis that a substance derived from eicosanoids is released by the embryos, but no t by oocytes, to hasten their transport to the uterus was tested by ex amining the effects of indomethacin, nordihydroguaiaretic acid (NDGA), platelet-activating factor (PAF), and PAF antagonists on egg transpor t in the hamster. Administration of indomethacin had no effect on embr yo transport, whereas administration of NDGA delayed the transport of eggs to the uterus in pregnant but not in cycling hamsters. The PAF an tagonists 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 ute rus. 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 b y PAF. Thrombocytopenia was detected in early-pregnant hamsters, and P AF-like activity was detected in spent media of two-cell through morul a stage hamster embryos. These results suggest that preimplantation ha mster embryos produce PAF-like activity that mediates embryonic signal ing to the oviduct as well as pregnancy-associated thrombocytopenia.