Invitro uptake of estradiol and progesterone in the hamster uterus relative to the time of embryo transfer and stage of development

The normal time for cleavage to the 2- and 8-cell stages of development of naturally ovulated hamster embryos is 25–27.5 and 59–61 h respectively, after ovulation and mating. The corresponding values for PMS-hCG treated hamsters were 33–35.5 and 62–64 h respectively. When 2-cell embryos, obtained by this timing method, were transferred to the oviductal bursa on Day 2 of the cycle, and when 8-cell embryos were transferred to the uterus on Day 3 of the cycle, implantation rates of 61.5 and 64.0% respectively, were obtained. The current study was conducted to determine the effects of transfer on estradiol and progesterone uptake by the uterine tissue on Day 14 after mating. A 2-fold increase in estradiol uptake was observed in superovulated, nonpregnant uteri when compared with nonsuperovulated animals. This level was also significantly higher than with nonsuperovulated pregnant animals and of animals receiving 2-cell embryo transfers. Estradiol uptake increases of 3.2 and 1.2-fold were noted for animals receiving 8-cell embryo transfers in naturally and superovulated groups respectively. Superovulation resulted in increased progesterone uptake. Transfer of 2- and 8-cell embryos resulted in a 15.8 and 109.9% increase in progesterone uptake respectively in naturally ovulated hamsters. Similar values for superovulated hamsters were 16.2 and 87.6% respectively. The 8-cell embryos, however, were transferred about four hrs prior to the time for normal 8-cell cleavage and this, coupled with increased estradiol uptake by the embryos themselves, resulted in an elevated estradiol and progesterone uptake in the uterine tissue even when measured on Day 14 of pregnancy. The degree of increase was less with superovulated animals receiving 8-cell embryos, reflecting higher levels of estradiol and progesterone uptake in control tissues. This could account for the slight delay in development of superovulated embryos.