Effects of immunization with gonadal steroids on pregnancy and on the estrous and menstrual cycle in rodents and primates.

The roles of estrogen and progesterone in the control of nidation the maintenance of pregnancy and of the midcycle ovulatory surge of gonadotropins was investigated in vivo in rodents and primates via passive and active immunization against the steroids. For example when antibodies are administered on Days 3-5 of pregnancy in rats intrauterine ova are still detectable on Day 6 or 7 whereas in untreated rats nidation has already occurred by Day 6 and no free intrauterine ova can be found. Furthermore in rats in which nidation is delayed by administration of antibodies there is a greatly increased rate of resorption of the implanted ova and mean number of viable fetuses delivered is about 1/2 that seen in controls. Administration of anti-progesterone on Day 11 of pregnancy resulted in complete resorption of all fetuses. The causal relationship between ovarian steroids and LH surge as ascertained in rodents passively immunized with antiestrogen or antiprogesterone; when administered 12-15 hours before expected LH surge ovulation was suppressed but only transiently without additional antibody injections. The estradiol-immunized monkey is suggested as a model for the study of ovarian-pituitary relationships; its advantages over pharmacological and surgical approaches to the study of antibody-steroid interaction are noted.