EFFECT OF METHOXYCHLOR ON IMPLANTATION AND EMBRYO DEVELOPMENT IN THE MOUSE

Methoxychlor (MXC) has been shown to have adverse effects on reproduct ive functions, However, it has not been fully determined whether the e ffects of MXC on reproduction are due to its estrogenic or antiestroge nic effects, Therefore, to further elucidate the estrogenic action of this pesticide in the mouse, we studied the effect of MXC on implantat ion and embryo development, MXC was found to initiate implantation in most delayed implanting mice at 400 mu g/g body weight, However, at th e higher dose of 800 mu g/g body weight, MXC initiated implantation in only 50% of animals and the number of embryos implanting was signific antly decreased (P < 0.05), It was determined that MXC inhibited impla ntation in intact pregnant mice only when given on Day 1 or Day 2 at 8 00 mu g/g but not at lower doses or later in the preimplantation perio d, Embryonic development and transport were delayed on Days 3 and 4 in these animals, Finally, reciprocal embryo transfers with donor embryo s recovered from MXC-treated animals (800 mu g/g body weight on Day 1) transferred to untreated recipients resulted in no implantation compa red to 79% implantation when donor embryos were treated with vehicle, These data indicate that MXC acts as an estrogen agonist at the level of the uterus and oviduct but as an antiestrogen in the ovary, In addi tion, MXC appears to alter normal preimplantation embryonic developmen t, These results suggest the need for further studies to assess the me chanism of action of MXC in preimplantation embryos. (C) 1997 Elsevier Science Inc.