Tolerance of perinidatory primate embryos to RU 486 exposure in vitro and in vivo.

Monkey embryos were exposed to RU 486 both in vitro and in vivo (with and without progesterone therapy) in the perinidatory interval. These primate embryos were highly tolerant of RU 486, except when RU 486 alone terminated early pregnancy. There were no indications of teratogenicity in this limited trial when the embryos were exposed to RU 486 either before implantation (10(-7)M in 24-hour cultures) or during the immediate post-implantation interval (50 mg orally/day; days 32 to 39 LMP).