Abstract
The levels of nuclear and uncharged cytoplasmic estrogen receptors were determined in gilt endometrium throughout the estrous cycle. Nuclear estrogen receptor was found to reach its highest level of 1.3 (range, 1.0-1.5) pmol/mg DNA on day 1 of the cycle just before ovulation (day 2), after which the values dropped sharply to 0.3 (range, 0.1-0.4) pmol/mg DNA. This level of nuclear receptor was consistently found through day 9. Between days 9-14, the estrogen receptor present in the nucleus decreased to zero, where it remained until the return of estrus (day 1). The dissociation constant (Kd +/- SD) for the nuclear estrogen receptor was 1.6 (+/- 1.4) x 10(-9) M. Initially, the nuclear estrogen receptor peak at day 1 was preceded by elevation (0.04-0.05 pmol/mg DNA) in cytoplasmic receptor at day 19, which declined when the receptor appeared in the nucleus. There was an even larger peak (range of maximal values, 0.07-0.26 pmol/mg DNA) of uncharged receptor in the cytosol near day 5. Throughout the rest of the cycle the values ranged from 0.01-0.03 pmol/mg DNA. Kd( +/- SD) for the cytoplasmic estrogen receptor was 2.4 (+/- 1.5) x 10(-9) M. The fluctuations of these two pools of endometrial estrogen receptor are discussed in relation to the previously observed cyclic variations in porcine uterine oxidation and sulfurylation of 17 beta-estradiol (Pack and Brooks, Endocrinology 95: 1680, 1974).
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