Regulation of the Estrogen Receptor in the Decidua Basalis of the Pregnant Rat1

Abstract

This study examines the distribution of the estrogen receptor (ER) in the mesometrial decidua basalis (DB) and the chorioallantoic placenta between Days 8 and 21 of pregnancy (Day 1 = presence of vaginal sperm) and its regulation by estradiol and progesterone. Immunocytochemistry revealed that ER was localized within nuclei of cells of the DB but not in trophoblastic cells (Day 10) or in cells of the junctional zone (JZ) or labyrinth zone (LZ). Western blot analysis and estradiol binding assays of DB, JZ, and LZ also revealed that only DB expressed ER. Native ER (66 kDa) was most abundant on Days 8 and 9, and declined 67% on Day 11 (p < 0.01), becoming barely detectable by Day 17. A truncated ER moiety (49 kDa) gradually increased, becoming the dominant form on Day 13. The effects of estradiol and progesterone on ER were studied during periods of growth and decline of DB (i.e., Days 8-10 and 12-14, respectively). Rats were ovariectomized on Day 8 or 12 and treated with estradiol daily (0.2, 0.75, or 2 micrograms, s.c.), with a progesterone pellet, or with both, for 48 h. Progesterone, but not estradiol, stimulated the 66-kDa ER moiety and ER binding activity (p < 0.01). Estradiol administered with progesterone antagonized progesterone action, at least in part, by enhancing expression of the 49-kDa ER at the expense of the native form (p < 0.01). Thus, progesterone up-regulated ER whereas estradiol down-regulated ER in rat DB.

Regulation of the Progesterone Receptor and Estrogen Receptor in Decidua Basalis by Progesterone and Estradiol during Pregnancy1

“…On Day 14 the nuclei of many stromal cells were negative for ER, and positive cells were only weakly stained, which is consistent with earlier findings that ER protein decreased to very low levels after Day 10 [14,15]. Nuclear staining was restricted to the periphery of the nuclear envelope (Fig.…”

“…We previously reported the serum levels of P 4 and E 2 produced by these regimens to be consistent with those found in normal pregnancy except that 2 ag of E 2 induced pharmacologic levels (about 3-fold higher than in normal pregnancy on Days 10 and 14 of gestation) [14,18].…”

“…Ogle, 1120 15th Street, Medical College of Georgia, Augusta, GA 30912-3000. FAX: (706) 721-7299; e-mail: togle@mail.mcg.edu tein expression [14]. We expect that P 4 also has a trophic effect on P 4 receptor (PR) regulation; however, this aspect of P 4 action has not come under close scrutiny.…”

“…We have shown recently that PR and ER proteins and their mRNAs are expressed in stromal cells of the decidua basalis (DB) but not in chorioallantoic tissues [14,15]. In an effort to understand regression of the DB that occurs during the last half of pregnancy [15][16][17] in spite of high levels of circulating P 4 , we hypothesized that changes in the relative composition of PR isoforms play a role in modulating P 4 action.…”

Regulation of prostaglandin D synthase and prostacyclin synthase in the endometrium of cyclic, pregnant, and pseudopregnant rats and their regulation by sex steroids

“…Additionally, the DB began to regress on day 14 and became too thin to reliably dissect after day 17. The protocol for DB isolation was described previously by Ogle & George (1995).…”