In Vivo Regulation of Parathyroid Hormone-Related Peptide Messenger Ribonucleic Acid in the Rat Uterus by 17β-Estradiol

During pregnancy, elevated levels of PTH-related peptide (PTHrP) persist in the myometrium of the rat uterus. Near term, intrauterine occupancy is correlated with high levels of PTHrP messenger RNA in the gravid horn of the unilaterally pregnant uterus. In nongravid tissue from these same animals the presence of smaller yet significant elevations of PTHrP mRNA suggests that the PTHrP gene also may be regulated by humoral factor(s). To test this hypothesis, we assessed the action of 17 beta-estradiol (E2) on the expression of the PTHrP gene in the uterus of the ovariectomized rat. While low levels of PTHrP mRNA are detected in uteri from ovariectomized rats, a single dose of E2 (4, 40, or 400 micrograms/kg body weight) stimulated a 6- to 8-fold increase in the levels of PTHrP mRNA in the uterus at approximately 2 h after E2 treatment. This increase was transient with levels gradually declining to pretreatment (basal) levels within 24 h. Other steroid hormones tested, including dihydrotestosterone, dexamethasone, and progesterone, failed to stimulate this response. The increase of PTHrP mRNA accumulation required a dose greater than 0.4 micrograms/kg. The magnitude and duration of PTHrP mRNA accumulation were very similar when doses of 40 or 400 micrograms/kg were used. In addition, the stimulation of the PTHrP gene by E2 is neither age dependent nor specific to the rat and is, in part, under transcriptional control. Together, these data indicate that in vivo E2 regulates the levels of PTHrP mRNA in the rat uterus and support a role for E2 in the increased expression of PTHrP mRNA in early gestational tissue, as well as in the nongravid horn of the unilaterally pregnant uterus.