Preimplantation embryo morphology following early luteal phase anti-nidatory treatment with mifepristone (RU486) in the rhesus monkey

The ultrastructural characteristics of peri-implantation stage embryos reco vered on day 6 after ovulation from rhesus monkeys with or without mifepris tone (RU486) treatment during the early luteal phase were examined in the p resent study. Monkeys were randomly allocated to two groups; group 1 animal s were injected s.c. with 2 ml vehicle (1:4, benzyl benzoate: olive oil, v/ v, n = 21) and group 2 animals received a single dose of mifepristone (2 mg /kg body n eight, w/v, n = 30) in the same volume of vehicle on day 2 after ovulation in mated cycles, On day 6 after ovulation, female monkeys of bot h groups were laparotomized and their reproductive tracts were hushed to re trieve preimplantation stage embryos. Embryos that showed frank degeneratio n or desynchrony on gross microscopical examination were not included in th e present study. Preimplantation embryo growth on day 6 after ovulation was significantly (P < 0.05) affected in the morula-blastocyst transition stag e in mifepristone-treated monkeys compared with that in the control group o f monkeys, Ultrastructurally, administration of mifepristone on day 2 after ovulation depressed preimplantation stage embryo development, characterize d by loss of cell polarity, lack of mitochondrial maturity, and lack of dif ferentiation in trophoblast cells. Furthermore, preimplantation embryos fro m mifepristone-treated animals displayed a higher occurrence of inter-blast omere space, intra-cytoplasmic vacuoles, myelinoid bodies, accumulation of lipid droplets, lysosomes, lipofuscins, autophagosomes and multivesicular b odies. Collectively, it appears that the developmental potential of preimpl antation embryos was significantly compromised in mifepristone-treated cycl es.