Vitamin D-Dependent Calcium Binding Protein in Rat Uterus: Differential Effects of Estrogen, Tamoxifen, Progesterone, and Pregnancy on Accumulation and Cellular Localization*

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Abstract
The present studies were undertaken to characterize the expression of calcium binding protein (CaBP or calbindin-D9k) in uterine tissues. Using immunohistochemical techniques, calbindin-D9k was localized to the uterine (luminal) epithelium of pregnant rats, but was not present in the uterine epithelium of nonpregnnat rats. Calbindin was found also in the uterine smooth muscle and endometrial stromal cells of pregnant animals. The latter localizations were reproduced in uteri of 21-day-old nonpregnant rats by administration of tamoxifen or physiological doses of estrogen. Estrogen and tamoxifen produced half-maximal increases of uterine calbindin at daily doses of 0.1 and 10 .mu.g, respectively, and maximal responses at 0.3 and 40 .mu.g/day. Testosterone and progesterone, at doses which increased the growth of the uterus, did not induce calbindin-D, and both hormones blocked estradiol''s effect on uterine calbindin-D appearance. The epithelial localization of calbindin in pregnant uteri was not reproduced in nonpregnant animals by either estradiol (3 .mu.g/day) or progesterone (1 mg/day). The localization of calbindin in uterine epithelium during pregnancy appears to be dependent upon an as yet unknown factor. In view of the large surface area of the luminal epithelium in pregnant animals, and the pregnancy-related expression of calbindin in these cells, we propose that uterine epithelium plays an important role in transport of calcium during pregnancy.

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