Factors Involved in Maintenance of Pregnancy in the Rat. The Temporal Need for Estrogen, Pituitary Prolactin and the Ovary1

The roles of the anterior pituitary, ovary and placenta were examined in pregnant rats. All experiments were timed from Day 1 when sperm were observed in the vaginal lavage. Animals were hypophysectomized (APX) with or without subsequent autograft (APtr) or homograft of the pituitary to the kidney capsule. Estradiol benzoate (EB), Estradiol-17j3 (E-17(3) or diethylstilbestrol (DES) in sesame oil were injected s.c. When APX was done on Days 8, 9 or 10 and EB was given in doses of 0.25 or 0.5 #g/day from the day before APX through Day 12, most sites had resorbed by Day 12. Rats receiving anterior pituitary homografts on Days 4, 5 or 6 were subsequently APX on Day 8 and given E-17(3 (0,1 �zg/day) on Days 8-12. Ten of 11 rats resorbed theirimplantationsites. Only 1 of6 rats APtr on Day 8 and givenE-1713(0.1ug/day)on Days 8-12 retainedsitesbeyond Day 12.RatsAPtr on Day 2 and given E-17p (0.1 ug/day) Days 8-12 (equivalent to Days 4-8 of normalpregnancy because of the 4 day delay of implantation inherent in the model) exhibited fetal resorption on Day 16 (equivalent to Day 12). However, if the E-17(3 treatment was extended to Day 14 or 16, live fetuses were observed on Day 20 or beyond; Diethylstilbestrol (0.2 Mg/day) can replace E-1713 (0.1 Mg/day). Ovariectomy on Days 12, 16 or 18 (equivalent to Days 8, 12 or 14), in rats APtr on Day 2 and given E-1 7(3 from Day 8-16, resulted in fetal resorption. Removal of the pituitary autograft by nephrectomy on Day 10 (equivalent to Day 6) resulted in total fetal resorption by Day 16 (equivalent to Day 12).Similarly, ratsoperated on Days 12-16 (equivalent to Days 8-12) retained viable fetuses. The results suggest that during normal rat pregnancy: 1) an estrogenic source is required for implantation and must be present through Day 10-12; 2) the ovary is required for progesterone secretion beyond Day 14 and 3) pituitary prolactin is not required beyond Day 8.