Progesterone-Receptor Complex in the Nuclear Fraction of the Bovine Endometrium1

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Abstract
A nuclear exchange assay was used to characterize and quantitate the progesterone-receptor complex (PR) of bovine endometrium. Bos taurus cows (15) were observed twice daily for estrus and were assigned to experimental groups at the time of estrus. Endometrium was removed on the day of estrus, day 4, day 10 or 11, and day 18 of the estrous cycle. Scatchard analysis of the nuclear exchange assay resulted in a nonlinear fit which could be linearized by the inclusion of 100-fold excess of cortisol. The number of binding sites per endometrial cell from the uterine horn ipsilateral to the corpus luteum was 34,900 .+-. 2900, from the contralateral horn it was 17,000 .+-. 4400 (P < 0.02). Data on the nuclear PR varied between individuals at estrus, day 4 and day 18 of the cycle.