Estrogen and Progesterone Regulation of Proliferation, Migration, and Loss in Different Target Cells of Rabbit Uterine Epithelium*

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Abstract
The possibility that estrogens and progesterone could have different target uterine cell populations according to their cell cycle stage and localization in glands vs. lumen was explored. Experiments were carried out in which rabbits were injected with [3H]thymidine for 3 days to label nuclei of dividing cells, then either 17.beta.-estradiol, progesterone or vehicle were administered. 17.beta.-Estradiol induced a decrease in the percentage of cells with labeled nuclei or labeling index of either luminal or glandular epithelium. Since this steroid had a significant proliferative effect on glands, the data suggest that its effect is exerted on unlabeled quiescent cells, which are then recruited into the cell cycle. Progesterone induced a significant increase in labeling index of both luminal and glandular epithelium. Dividing cells are a target for this hormone. Analysis of the number of nuclear grains according to cell location in luminal vs. glandular epithelia and the effect of hormone administration confirmed that each ovarian hormone acts on different target cell populations. Short and long term administration of estrogens resulted in a larger internal circumference of the uterus due to an increase in the number of luminal cells; the number of glands and glandular cells per section did not appear to change. Apparently, endometrial gland cells migrate towards the lumen and estrogen administration decreases the rate of cell loss in the luminal epithelium. The concept of cell migration is supported by experiments in which single administration of [3H]thymidine to rabbits was followed by determination at different times of the geographical distribution of cells with labeled nuclei. There was observed, as a function of time, a decrease in the number of labeled cells in the bottom of the glands with a concomitant increase in the same parameter in the upper part of the glands and luminal epithelia. Estradiol administration changed these kinetics.

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