LUTEAL-PHASE OVARIAN ESTROGEN IS NOT ESSENTIAL FOR IMPLANTATION AND MAINTENANCE OF PREGNANCY FROM SURROGATE EMBRYO-TRANSFER IN THE RHESUS-MONKEY

The aim of this study was to investigate whether luteal phase ovarian oestrogen is required for blastocyst implantation and pregnancy maintenance in the rhesus monkey. Preimplantation embryos were retrieved from naturally ovulated, mated embryo donor monkeys. In group I, developmentally normal, age- and stage-matched embryos were transferred to recipient monkeys showing naturally synchronized ovulatory cycles. Immediately prior to embryo transfer, recipients were subjected to bilateral ovariectomy, and following transfer they were treated with i.m. injections of either progesterone (group Ia, n = 4), or oestradiol + progesterone (group Ib, n = 2). Recipient monkeys of group Ic (n = 4) were subjected to sham ovariectomy and vehicle injection. In group Ia, progesterone supplementation alone led to three pregnancies and live births. In group Tb, there was one live birth. In the control group Ic, four transfers resulted in two live births and one abortion on cycle day 58. Analysis of serum progesterone and oestradiol profiles showed that oestradiol had declined to undetectable levels within 3-5 days after ovariectomy in group Ia recipients, and the area under the curve of serum oestrogen concentrations during the periimplantation period (days 10-20 after ovulation) were less (P < 0.001) in group Ia compared with group Ic. There were no changes in the area under the curve among serum progesterone concentrations in all the subgroups. In group II, long-term ovariectomized embryo recipients (n = 4) were primed with oestradiol till cycle day 11 of simulated transfer cycle, and received progesterone treatment from cycle day 10 till the end of the experiment. Of four transfers, live births were recorded in two cases, while in one case abortion occurred on cycle day 66. Serum oestradiol concentrations were undetectable during the presumptive peri-implantation period of pregnancy cycles in group II recipient monkeys. Noyes' dating of endometrial samples collected from both groups on days 5-7 after the oestrogen rise revealed that endometrial histology synchronized well with those found during days 3-5 after ovulation in normal menstrual cycle. We conclude that luteal phase ovarian oestrogen is not essential for progesterone-dependent endometrial receptivity and responses leading to implantation and pregnancy maintenance in the rhesus monkey.