Parathyroid hormone-related protein (PTHrP) gene expression in the pregnant rat uterus has been shown to be dependent on occupancy of the uterus by the fetus. To further test the hypothesis that the synthesis of PTHrP in smooth muscle tissue is regulated by mechanical stretch, we conducted experiments using the rat urinary bladder as a model of an expansible hollow organ. The results indicate that PTHrP mRNA levels do change in response to the stretch of the bladder wail. Under normal conditions PTHrP mRNA levels in the bladder correlated with the urine volume-namely, the extent of bladder distension. When bladders were maintained empty in vivo, PTHrP mRNA levels decreased gradually. Conversely, when bladders were distended by the accumulation of urine, levels of PTHrP mRNA increased dramatically with time. When distension was limited to one-half of the bladder, the increase in PTHrP mRNA was observed only in the distended portion. Histochemical studies performed on distended bladder tissue indicated the presence of PTHrP immunoreactivity in smooth muscle cells. Isolated organ bath studies were used to examine the possible physiological role of PTHrP in smooth muscle tonicity. In vitro responsiveness of bladder muscle strips to exogenous PTHrP was dependent on the in vivo condition of the bladder. In muscle strips obtained from bladders kept empty in vivo, PTHrP-(1-34)-NH2 relaxed carbachol-induced contraction in a dose-dependent manner but failed to relax the contraction in muscle strips from distended bladders that had high endogenous PTHrP expression. These results and the previous findings in the rat uterus suggest a physiological role ofPTIHrP in bladder smooth muscle function.

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.

Administration of 17 beta-estradiol (E2) induces a mitogenic response in the rat uterus. Previous studies have shown that this effect involves the transient activation of c-fos and c-myc expression, followed by significant increases in both DNA synthesis and cell proliferation. Zif268 is a zinc finger-containing, DNA-binding transcription factor that has been implicated in the regulation of cell growth and development and has been shown to be coregulated with c-fos in a number of systems. To determine whether Zif268 is also a target for estrogen regulation, we measured the effects of E2 on Zif268 mRNA expression in the uterus of the ovariectomized rat. In this report we demonstrate that although low levels of Zif268 mRNA expression are detectable in the uteri from ovariectomized control rats, treatment with E2 (4, 40, or 400 micrograms/kg BW) induces a rapid and transient 45- to 50-fold increase in the level of Zif268 mRNA 2 h after E2 treatment. The elevated levels of Zif268 mRNA returned to basal 6 h after hormone treatment. Lower doses of E2 (0.004, 0.04, and 0.4 micrograms/kg) had little or no effect on Zif268 mRNA expression, while higher doses of E2 (4-400 micrograms/kg) resulted in maximal increases in Zif268 expression. Dexamethasone, 5 alpha-dihydrotestosterone, and progesterone had no effect on uterine Zif268 mRNA expression, and the induction of Zif268 by E2 was abolished by pretreating the animals with the RNA synthesis inhibitor actinomycin-D. In addition, stimulation of Zif268 mRNA expression was observed with the short-acting estrogen estriol, suggesting that the response may be specific for estrogenic steroids.(ABSTRACT TRUNCATED AT 250 WORDS)