Estrogen and antiestrogen effects on neonatal ovine uterine development.

Postnatal development of the ovine uterus between birth and Postnatal Day (PND) 56 involves differentiation of the endometrial glandular epithelium from the luminal epithelium followed by tubulogenesis and branching morphogenesis. These critical events coincide with expression of estrogen receptor alpha (ERalpha) by nascent endometrial glands and stroma. To test the working hypothesis that estrogen and uterine ERalpha regulate uterine growth and endometrial gland morphogenesis in the neonatal ewe, ewes were treated daily from birth (PND 0) to PND 55 with 1) saline and corn oil as a vehicle control (CX), 2) estradiol-17 beta (E2) valerate (EV), an ERalpha agonist, 3) EM-800, an ERalpha antagonist, or 4) CGS 20267, a nonsteroidal aromatase inhibitor.