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Hormonal regulation of oestrogen and progesterone receptors in cultured bovine endometrial cells

Changes in the number of progesterone and oestradiol receptors in the endometrium are thought to play a role in the induction of luteolysis. The effect of oestradiol and progesterone on the regulation of their receptors in cultured bovine uterine epithelial and stromal cells was examined to determine the mechanisms involved in this process. Cells were obtained from cows at days 1–3 of the oestrous cycle and were cultured for 4 or 8 days in medium alone (RPMI medium + 5% (v/v) charcoal–dextran stripped newborn calf serum) or with oestradiol, progesterone or oestradiol and progesterone. At the end of culture, receptor binding was measured by saturation analysis. Specific binding of both [³H]ORG 2058 (16-ethyl-21-hydroxy-19-nor (6,7-³H) pregn-4-ene-3,20-dione) and [³H]oestradiol to epithelial and stromal cells showed high affinities (K_d = 1.1 x 10^–9 and 6 x 10^–10 mol l^–1, respectively, for progesterone receptors; K_d = 5.5 x 10^–9 and 7 x 10^–10 mol l^–1 respectively, for oestradiol receptors). In the stromal cells, oestradiol (0.1-10 nmol l^–1 increased the number of oestradiol receptors from 0.21 ± 0.06 to 0.70 ± 0.058 fmol µg^–1 DNA and the number of progesterone receptors from 1.4 ± 0.83 to 6.6 ± 0.70 fmol µg^–1 DNA in a dose-dependent manner after 4 days of culture (P < 0.01). After culture for 8 days, the stimulatory effect of oestradiol increased. Progesterone (50 nmol l^–1) had no effect on the number of oestradiol or progesterone receptors (P > 0.05). However, progesterone inhibited the stimulatory effect of oestradiol. In epithelial cells, the lower concentrations of oestradiol (0.1 and 1 nmol l^–1) stimulated the number of progesterone receptors (P = 0.05) after 4 days culture, whereas the highest concentration of oestradiol (10 nmol l^–1), progesterone (50 nmol l^–1) and progesterone (50 nmol l^–1) plus oestradiol (1 nmol l^–1) had no effect. After culture for 8 days, the stimulatory effect of oestradiol decreased. In contrast to progesterone receptors, the number of oestradiol receptors increased with oestradiol concentration (P < 0.01). These data show that the number of progesterone receptors was higher in the stromal cells than in epithelial cells, whereas the number of oestradiol receptors was higher in the epithelial cells than in stromal cells. Oestradiol upregulates its own receptor and increases the number of progesterone receptors in both cell types in vitro, whereas progesterone has little effect, but inhibits the effects of oestradiol on progesterone receptors.