Estrogen receptors (ERα/ERβ) in normal and pathological growth of the human myometrium:: pregnancy and leiomyoma

The distributions of the mRNAs for estrogen receptors (ER alpha and ER beta) and their binding properties in myometria of pregnant and nonpregnant women and in leiomyoma were studied. RT-PCR analysis indicated that the term pregnancy myometria had little ER alpha mRNA, whereas the amounts of ER beta mRNAs in pregnant or nonpregnant myometria appeared to be similar. Both ER alpha and ER beta mRNA were greater in certain leiomyoma than in normal nonpregnant myometria. The binding kinetics revealed that two specific binding sites (with high or low affinity) for 17 beta-estradiol were present in the nonpregnant myometrium. Only the low-affinity binding sites were detectable in late-pregnancy myometria and in leiomyoma, and their capacities were increased two- to threefold (P < 0.001) in leiomyoma. The pregnancy- and leiomyoma-related changes in myometrial ER status, especially the low concentration of ER alpha. mRNA and the lack of high-affinity ER in pregnant women, plus the increased ER alpha and ER beta mRNAs and the increased low-affinity ER in some leiomyoma, suggest that the redistribution of ER subtypes is associated with the pathological and/or normal growth of the myometrium.