Estrogen receptors (ER alpha/ER beta) in normal and pathological growth ofthe 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 wom en and in leiomyoma were studied. RT-PCR analysis indicated that the term p regnancy 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 no npregnant myometria. The binding kinetics revealed that two specific bindin g sites (with high or low affinity) for 17 beta-estradiol were present in t he nonpregnant myometrium. Only the low-affinity binding sites were detecta ble in late-pregnancy myometria and in leiomyoma, and their capacities were increased two- to threefold (P < 0.001) in leiomyoma. The pregnancy- and l eiomyoma-related changes in myometrial ER status, especially the low concen tration of ER alpha. mRNA and the lack of high-affinity ER in pregnant wome n, plus the increased ER alpha and ER beta mRNAs and the increased low-affi nity ER in some leiomyoma, suggest that the redistribution of ER subtypes i s associated with the pathological and/or normal growth of the myometrium.