Endometrial development and adenogenesis in the neonatal pig: Effects of estradiol valerate and the antiestrogen ICI 182,780

In the pig, appearance of endometrial glands between birth (postnatal day [ PND] 0) and PND 14 involves development of estrogen receptor-alpha-positive (ER+) phenotype by,and increased DNA synthesis in, nascent glandular epith elium (GE). To determine whether ER activation is required for this process , gilts were treated daily with either vehicle, the antiestrogen ICI 182,78 0 (ICI), estradiol-17 beta valerate (EV), or both ICI and EV. Treatments be gan on PND 0, before onset of adenogenesis, or on PND 7, after onset of gla nd proliferation. Uteri obtained on PNDs 7 and 14 (study one) or on PND 14 (study two) were weighed; uterine histology was evaluated; DNA synthesis in luminal epithelium and GE was characterized by determining 5-bromo-2'-deox yuridine (BrdU) labeling index; and patterns of ER mRNA expression were eva luated in situ (study one). Gland genesis was inhibited by ICI, which decre ased gland penetration depth by PND 14 in study one, both endometrial thick ness and BrdU-labeling index in CE in study two, and increased stromal cell compaction in both studies. Uterotropic effects of EV included increased g land development and epithelial BrdU labeling and decreased stromal compact ion. These effects were inhibited by coadministration of ICI. Treatments di d not alter ER mRNA expression, which remained limited to stroma and GE. Da ta indicate that endometrial maturation and adenogenesis in the neonatal pi g require expression and activation of a functional ER system.