Messenger RNA levels of estrogen receptors alpha and beta and progesterone receptors in the cyclic and inseminated/early pregnant sow uterus

The aim of the present study was to investigate differences in the expression of mRNAs for ERalpha, ERbeta and PR in the sow uterus at different stages of the estrous cycle as well as in inseminated sows at estrus and during early pregnancy by use of solution hybridization and in relation to plasma levels of estradiol and progesterone. Uterine samples were collected at different stages of the estrous cycle and after insemination/early pregnancy. In the endometrium, the expression of ERalpha mRNA and PR mRNA was similar for cyclic and early pregnant groups. Both were highest at early diestrus/70 h after ovulation and ERalpha mRNA was lowest at late diestrus/d 19 while PR mRNA was lowest at diestrus and late diestrus/d 11 and d 19. The expression of endometrial ERbeta was constantly low during the estrous cycle but higher expression was found in inseminated/early pregnant sows at estrus and 70 h after ovulation. In the myometrium, high expression of ERalpha mRNA and PR mRNA was observed at proestrus and estrus in cyclic sows and at estrus in newly inseminated sows. Higher expression of myometrial ERbeta mRNA was found in inseminated/early pregnant sows compared with cyclic sows, although significant only at estrus. In conclusion, the expression of mRNAs for ERalpha, ERbeta and PR in the sow uterus differed between endometrium and myometrium as well as with stages of the estrous cycle and early pregnancy. In addition to plasma steroid levels, the differences between cyclic and inseminated/early pregnant sows suggest that other factors, e.g. insemination and/or the presence of embryos, influence the expression of these steroid receptor mRNAs in the sow uterus.