Effects of steroid hormones on calcitonin gene-related peptide receptors in cultured human myometrium

Abstract

Objective: This study was designed to examine whether, with the use of human myometrial explants in culture, calcitonin gene-related peptide B receptors are regulated by steroid hormones. Study design: Myometrial tissues were obtained from the lower uterine segments from women in a nonpregnant state and pregnant women who were not in labor undergoing cesarean delivery (39.1 ± 0.2 weeks of gestation). Tissues were incubated in Dulbecco's modified Eagle's medium without phenol red, with either 17β-estradiol (10−9, 10−8, 10−7 mol/L), progesterone (10−8, 10−7, 10−6 mol/L), or in a combination of 17β-estradiol (10−8 mol/L) and progesterone (10−7 mol/L). Reverse transcriptase-polymerase chain reaction was performed to examine the expression of estrogen receptor-α, progesterone receptor, and Western blotting was used for calcitonin gene-related peptide B receptor protein measurement in the myometrium. Results: We found that (1) messenger RNA expression for both estrogen receptor-α and progesterone receptor in nonpregnant myometrium significantly declined within 48 hours explant culture; (2) estrogen receptor-α messenger RNA levels in the pregnant myometrium were 98.6%, 95.3%, and 89.8% at 12, 24, and 48 hours of incubation, respectively; (3) the levels of messenger RNA for progesterone receptor in the pregnant myometrium were 96.2%, 93.3%, 90.1%, at 12, 24, and 48 hours of incubation, respectively; (4) the 17β-estradiol dose dependently inhibited calcitonin gene-related peptide B receptor protein in pregnant myometrium explant culture; (5) the progesterone dose dependently increased calcitonin gene-related peptide B receptor expression in pregnant myometrium explant culture; (6) the combined treatment with 17β-estradiol (10−8 mol/L) and progesterone (10−7 mol/L) further enhanced myometrial calcitonin gene-related peptide B receptor protein expression. Conclusion: We conclude from this study that (1) the messenger RNA expression of estrogen receptor-α and progesterone receptor in pregnant myometrium were maintained at relatively high levels (>89%) within 48 hours incubation and that this may be useful for in vitro studies that are designed to evaluate the effects of sex steroids on the human myometrium during pregnancy and that (2) estrogen inhibits and progesterone stimulates the expression of calcitonin gene-related peptide B receptors in cultured pregnant myometrial explants. We suggest that steroid hormone-regulated calcitonin gene-related peptide B receptor expression could underlie differential myometrial sensitivity to calcitonin gene-related peptide-induced relaxation. (Am J Obstet Gynecol 2003;188:466-72.)