272. Decreased expression of oestrogen receptor β in the reproductive tract of pregnant relaxin-deficient (Rlx–/–) mice

Abstract

The peptide hormone relaxin (RLX) is reported to directly affect uterine oestrogen receptors (ERs) in the rat (1). Treatment of immature ovariectomised rats with porcine RLX causes a decrease in uterine ERβ mRNA levels within 6 h. However, RLX has no effect on ERα expression. As both ERβ1 and ERβ2 inhibit ER-mediated transcriptional activity, this RLX-induced downregulation in ERβ could be a prerequisite for oestrogen to exert its effects on target tissues. The aim of the current study was to use relaxin-deficient (Rlx–/–) pregnant mice to investigate if relaxin deficiency results in alterations in either ERβ or ERα mRNA expression in reproductive tissues. Cervix and vagina tissues were obtained from adult C57/Blk6J wild-type mice at five stages of gestation (Days 7.5, 10.5, 14.5, 17.5, 18.5 pc) and Rlx–/– littermates on Days 7.5, 14.5 and 18.5 pc. Q-PCR with TaqMan probes in the Opticon 2 thermal cycler (MJ Research, GeneWorks) was used to quantify ERα and ERα gene expression. ERα mRNA levels were significantly (P < 0.05; ANOVA) increased in the cervix/vagina on Days 17.5 and 18.5 pc in Rlx+/+ mice. The increase in ERα in Rlx+/+ mice was negatively correlated with a significant decrease in ERβ expression from Day 14.5 pc. In contrast, there was no decrease in ERβ expression in the cervix/vagina of Rlx–/– mice; ERβ mRNA levels were significantly (P < 0.05) higher compared to Rlx+/+ mice on Days 14.5 or 18.5 pc. However, there was no corresponding reduction in ERα expression in the cervix/vagina of the Rlx–/– mice, so that ERα mRNA levels were still elevated at term despite the maintenance of high ERα expression. In summary, these data show changes in ERα expression in the cervix/vagina of relaxin-deficient mice, which may subsequently affect ERα-mediated transcriptional activity.

(1) Pillai et al. (2002) Biol. Reprod. 67, 1919–1926.