The effect of exogenous estradiol-17β on cytoplasmic progesterone and estrogen receptors in the ovine endometrium during the midluteal phase of the estrous cycle was studied. Mature ewes received a single i.m. injection of 500 μg estradiol-17β on Day 11 and/or Day 12 of the cycle and were necropsied on Day 13. Total cytoplasmic progesterone and estrogen receptors were determined by exchange assay using a synthetic [3H]-progestin and [3H]-estradiol. Jugular blood serum was quantified for progesterone by radioimmunoassay, and in vitro incorporation of [3H]-thymidine into DNA was used as a corollary measure of the response of the endometrium to exogenous estradiol. The equilibrium dissociation constant (K(d)) for the progesterone-receptor complex was found to range from 1.30 to 1.87 nM and the maximum concentration of receptors in endometrial cytosol of ewes was estimated to be 1130 fmole/mg DNA. Although a single injection of estradiol provoked an increase (P<0.01) in cytoplasmic estrogen receptors by 48 hr post-treatment, two sequential injections of hormone were necessary to stimulate increases (P<0.01) in cytoplasmic progesterone receptors and DNA synthesis. No change in cytoplasmic steroid receptors was detected by 24 hr after a single injection of estradiol. Serum concentrations of progesterone did not differ among control and treated ewes. It appears from the present study that exogenous estradiol can provoke significant increases in endometrial cytoplasmic estrogen and progesterone receptors in the presence of relatively high concentrations of endogenous progesterone but not within 24 hr after initial treatment.
|Original language||English (US)|
|Number of pages||9|
|Journal||Biology of reproduction|
|State||Published - 1980|
ASJC Scopus subject areas
- Reproductive Medicine
- Cell Biology