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 mainte nance in the rhesus monkey. Preimplantation embryos were retrieved fro m naturally ovulated, mated embryo donor monkeys. In group I, developm entally normal, age- and stage-matched embryos were transferred to rec ipient monkeys showing naturally synchronized ovulatory cycles. Immedi ately prior to embryo transfer, recipients were subjected to bilateral ovariectomy, and following transfer they were treated with i.m. injec tions of either progesterone (group Ia, n = 4), or oestradiol + proges terone (group Ib, n = 2). Recipient monkeys of group Ic (n = 4) were s ubjected to sham ovariectomy and vehicle injection. In group Ia, proge sterone 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 5 8. Analysis of serum progesterone and oestradiol profiles showed that oestradiol had declined to undetectable levels within 3-5 days after o variectomy in group Ia recipients, and the area under the curve of ser um oestrogen concentrations during the periimplantation period (days 1 0-20 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 seru m progesterone concentrations in all the subgroups. In group II, long- term ovariectomized embryo recipients (n = 4) were primed with oestrad iol till cycle day 11 of simulated transfer cycle, and received proges terone treatment from cycle day 10 till the end of the experiment. Of four transfers, live births were recorded in two cases, while in one c ase 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 endom etrial samples collected from both groups on days 5-7 after the oestro gen rise revealed that endometrial histology synchronized well with th ose found during days 3-5 after ovulation in normal menstrual cycle. W e conclude that luteal phase ovarian oestrogen is not essential for pr ogesterone-dependent endometrial receptivity and responses leading to implantation and pregnancy maintenance in the rhesus monkey.