Early Pregnancy in the Ewe: Effects of Oestradiol and Progesterone on Uterine Metabolism and on Embryo Survival

Abstract

The hormonal regulation of embryo development during early pregnancy in the ewe has been examined. Ovariectomized ewes received injections of oestradiol (E2) and progesterone (P) according to schedules designed to simulate endogenous ovarian secretion during the luteal phase of the previous oestrous cycle (priming P), around the time of oestrus (oestrous E2 ) and during early pregnancy (maintenance P, maintenance E2)' Embryos were transferred to the ewes on the 4th day after induced oestrus, and ewes were killed at 6 or 13 days after transfer to assess embryo development. Cytosol concentrations of oestradiol 'and progesterone receptors and RNA and protein metabolism in the endometrium and amounts of protein in uterine flushings were examined on the day of embryo transfer and 6 days after transfer.Twenty one of 27 ewes which received maintenance P, oestrous E2 and priming P carried normal embryos at the time of killing. Omitting maintenance E2 had no effect on the proportion of ewes in which embryos developed normally. When either priming P or oestrous E2 was omitted embryos ceased to develop normally within 1-2 days of the time of transfer. Omitting oestrous E2 reduced the amount of protein in the uterine lumen and the RNA: DNA ratio, rate of synthesis of protein and amounts of oestradiol and progesterone receptors in the endometrium at the time of embryo transfer. Omitting priming P caused a small decrease in the concentration of progesterone receptor but no other significant changes in the endometrium or uterine flushings at the time of transfer. It is suggested that oestrous E2 controls embryo development by regulating endometrial sensitivity to the progesterone of pregnancy. The mechanism by which priming P affects embryo development remains unknown.

Effects of Progesterone on the Oestrogen-Stimulated Uterus: a Comparative Study of the Mouse, Guinea Pig, Rabbit and Sheep

“…When ovariectomized ewes receive P together with large doses of E2 the P does not interfere with oestrogen-induced increases in uterine weight and endometrial RNA: DNA ratios (Miller 1976;Miller et al 1977a). In these studies P caused only a small decrease in the cytosol concentration of E2 receptor in whole uterus.…”

Relationship of follicle size and concentrations of estradiol among cows exhibiting or not exhibiting estrus during a fixed-time AI protocol

“…Concentrations of estradiol peak approximately 36 h before ovulation [5] and increased preovulatory concentrations of estradiol resulted in increased fertilization success, improved embryo quality and viability [6,7], and a >60% improvement in pregnancy success [8]. Preovulatory concentrations of estradiol also have been reported to influence sperm transport [9], embryo survival [10], and the uterine environment [11][12][13].…”

From Germ Cell Preservation to Regenerative Medicine: An Exciting Research Career in Biotechnology

“…They had systematically supplied hormones via daily injection to ovariectomized ewes before transferring embryos to these ewes to assess uterine function (5). There was a need for priming with progesterone to mimic a previous luteal phase, estradiol equivalent to that at estrous, and then an increasing dose of progesterone to mimic the changes seen after ovulation.…”