Rat uterine oxytocin receptor and estrogen receptor α and β mRNA levels are regulated by estrogen through multiple estrogen receptors

Abstract

Estrogen action is mediated through several types of receptors (ERs), such as ERα, ERβ and putative membrane ERs. Oxytocin receptor (OTR) and ER expression levels in the rat uterus are regulated by estrogen; however, which types of ERs are involved has not been elucidated. This study examined OTR, ERα and ERβ levels in ovariectomized rats treated with 17β-estradiol (E2), an ERα agonist (PPT), an ERβ agonist (DPN) or estren (Es). E2 and PPT increased OTR mRNA levels and decreased ERα and ERβ mRNA levels 3 and 6 h posttreatment. DPN decreased ERα and ERβ mRNA levels at 3 and 6 h, while OTR mRNA levels increased at 3 h and decreased at 6 h. OTR mRNA levels increased 3 h after the Es treatment and then declined until 6 h. ERα and ERβ mRNA levels decreased by 3 h and remained low until 6 h posttreatment with Es. The ER antagonist ICI182,780 (ICI) suppressed the increases in OTR mRNA levels induced 3 h after the Es treatment. However, ICI and tamoxifen (Tam) had no significant effect on ERα and ERβ mRNA levels in the Es-treated or vehicle-treated group. In intact rats, proestrus-associated increases in OTR mRNA levels were antagonized by both ICI and Tam. However, decreases in ERα and ERβ mRNA levels were not antagonized by Tam and ICI, respectively. Therefore, uterine OTR gene expression is upregulated by estrogen through the classical nuclear (or non-nuclear) ERs, ERα and ERβ, while the levels of these ERs are downregulated by estrogen through multiple pathways including Es-sensitive nonclassical ERs.

Fig. 1.

Effects of 17β-estradiol (E2) on OTR, ERα and ERβ mRNA levels in the uteri of OVX rats. Rats were given a subcutaneous injection of 17β-estradiol (0.5, 2.5 or 12.5 μg) or vehicle (cont) (A) and 17β-estradiol (12.5 μg) (B) at 1100–1120 h and were euthanized 24 h (A) and 1, 2, 3, 4, 5, 6, 7, 8 and 9 h (B) after the injection. Uteri were extracted, and the gene expression levels of OTR, ERα and ERβ were determined by real-time PCR. Data are expressed as means ± SEM (n=5). The value in the vehicle-treated control group was defined as 100%. a, vs. vehicle-treated group (cont); b, vs. group treated with 0.5 μg E2; c, vs. groups at 0 h, 7 h and 9 h; d, vs. groups at 0–6 h and 8 h; e, vs. groups at 0 h and 1 h; P < 0.05, by Tukey’s test.

Fig. 2.

Effects of PPT and DPN on OTR, ERα, and ERβ mRNA levels in the uteri of OVX rats. Rats were given a subcutaneous injection of PPT (200 μg) or DPN (200 μg) at 1100–1200 h and were euthanized 3 h (A) and 6 h (B) after the injection. Uteri were extracted, and the gene expression levels of OTR, ERα and ERβ were determined by real-time PCR. Data are expressed as means ± SEM (n=5). The value in the vehicle-treated control group was defined as 100%. * vs. vehicle-treated group (cont); P < 0.05, by Dunnett’s test.

Fig. 3.

Effects of estren (Es) on ERα and ERβ mRNA levels in the uteri of OVX rats. Rats were given a subcutaneous injection of Es (800 μg) at 1100–1120 h and were euthanized 1, 3 and 6 h after the injection. Uteri were extracted, and the gene expression levels of OTR, ERα and ERβ were determined by real-time PCR. Data are expressed as means ± SEM (n=5). The value in the group at 0 h was defined as 100%. * vs. group at 0 h; a, vs. group at 1 h; b, vs. group at 3 h; P < 0.05, by Tukey’s test.

Fig. 4.

Effects of ER antagonists on Es-induced changes in OTR, ERα and ERβ mRNA levels in the uteri of OVX rats. Rats were given a subcutaneous injection of ICI (250 μg) (A) or Tam (250 μg) (B) 30 min prior to an injection of Es (800 μg). Es was injected at 1100–1120 h, and rats were euthanized 3 h after the injection. Uteri were extracted, and the gene expression levels of OTR, ERα and ERβ were determined by real-time PCR. Data are expressed as means ± SEM (n=4). The value in the vehicle-treated control group was defined as 100%. a, vs. vehicle- and vehicle-treated group; b, vs. vehicle- and ICI-treated group; c, vehicle- and Es-treated group; P < 0.05, by Tukey’s test.

Fig. 5.

Effects of ER antagonists on OTR, ERα and ERβ mRNA levels in the uterus of rats in proestrus. Rats were given a subcutaneous injection of ICI (250 μg) or Tam (250 μg) during diestrus (1100–1130 h) and were euthanized at 1030–1200 h the next day (proestrus). Uteri were extracted, and the gene expression levels of OTR, ERα and ERβ were determined by real-time PCR. Data are expressed as means ± SEM (n=4). The value of intact rats at metestrus (Met) was defined as 100%. * vs. the vehicle-treated control group; P < 0.05, by Dunnett’s test.