Hormonal regulation of cell death in rabbit uterine epithelium

It is known that estrogen (E) and progesterone (P) play important roles in the regulation of endometrial growth. In the rabbit endometrial epithelium, a balance is maintained between cell proliferation and cell death which seems to be under ovarian hormonal control. In this study the authors determined cell proliferation by quantitating the mitotic index (MI) and cell death by quantitating the death index (DI) in uterine histologic sections from whole animals that were hormone treated versus control rabbits. E caused proliferation of uterine epithelial cells and decreased the DI transiently, while P also increased proliferation but decreased the DI dramatically. In a time course study, after a single injection of human chorionic gonadotropin to induce pseudopregnancy, there was transient decrease in the DI and an increase in the MI between Days 2 and 5. In pseudopregnant animals, hormones had no effect in intact animals, but after ovariectomy there was about a 124-fold increase in the DI, which could be prevented by P administration. The predominant type of cell death observed in this system is apoptosis (97.5%), as opposed to necrosis (2.5%). Thus, it is proposed that cell death may be as important as cell proliferation in the regulation of normal uterine epithelial growth.