The metabolism and nuclear migration of estrogen in porcine uterus throughout the implantation process.

Abstract

Gilts and sows were inseminated at estrus and sacrificed from 0 to 25 days later. Minced uterine samples were incubated for 2 h with 17β-[6, 7-3H]-estradiol ([6, 73H]-E2), 3 × 10−9 M and Na235SO4 (∼l × 10−4 M) and the labeled metabolic products were extracted and analyzed. At the same time, endometrial samples were taken for E2 nuclear receptor assays. It was found that sulfurylation, insignificant at the time of insemination (Day 0), rose to a plateau by Day 5 (average 49.2 ± 7.6%) and continued at that level for at least 25 days of pregnancy. During and after implantation, the proportions of estrone, estrone sulfate and E2-3-sulfate were essentially the same as those seen in the cycling animal at diestrus: i.e., 18.7 ± 7.2%, 32.6 ± 6.4% and 16.6 ± 9.5%, respectively. The E2 nuclear receptor level averaged 0.32 pmoles/mg DNA from the day of insemination to Day 8 of pregnancy then dropped to 0 where it remained until Day 17. However, instead of increasing to 1.00–1.50 pmoles/mg DNA as it would at the next estrus (Pack et al., 1978a), only a slight increase then occurred (average 0.09 pmoles/mg DNA), which was maintained at least until Day 25 of pregnancy. Therefore, the combined conditions of a high level of estrogen sulfotransferase and E2 dehydrogenase activities with a low E2 nuclear receptor level are characteristic of implantation and early pregnancy in the pig.