We tested the hypothesis that prostaglandin (PGs), PGE2, and PGF2 alpha, stimulate labor and delivery in women, in part, by inducing functional progesterone withdrawal in myometrial cells by increasing the progesterone receptor (PR)-A/PR-B expression ration. PHM1-31 cells (an immortal pregnant human myometrial cell line) were exposed to PGE2, PGF2 alpha, cyclic-8-bromoadenosine monophosphate (8-Br-cAMP) and phorbol 12-myristate 13-acetate (PMA) at various concentrations for 24h. Effects on PR-A and PR-B expression were then assessed by quantitative RT-PCR. PGF2 alpha dose dependently increased PR-A mRNA and the PR-A/PR-B expression ration but did not effect PR-B mRNA. PGE2 dose-dependently increased mRNAs encoding PR-A and PR-B. The PGE2 dose-threshold for PR-A (0.01 nM) was lower than that for PR-B (0.1 nM), which resulted in an initial rise then a gradual fall in PR-A/PR-B expression ration to basal levels in response to PGE2. Activation of the protein kinase (PK)-A signaling pathway with 8-Br-cAMP coordinately increased expression of PR-A and PR-B and therefore did not alter the PR-A/PR-B expression ration. In contrast, activation of the PKC signaling pathway with PMA increased expression of PR-A without affecting PR-B and therefore significantly (P<0.05) increased the PR-A/PR-B expression ration. These data demonstrate differential control of myometrial PR-A and PR-B expression by PGE2 and PGF2 alpha and by specific intracellular signaling pathways. We conclude that PGs acting via the PKC pathway facilitate functional progesterone withdrawal by increasing the myometrial PR-A/PR-B expression ratio.

We have demonstrated that hTrpC1 and hTrpC4 are the most abundant TrpC mRNAs in human myometrium, with TrpC6 being the next most abundant. There was no increase in TrpC mRNA or protein in fundal myometrium with the onset of labor. Nonetheless, these isoforms may play significant roles in signal regulated calcium entry in human myometrium.

External Ca2+ entry into myometrial smooth-muscle cells is important to uterine contraction and hence to labor progression and parturition. Proteins of the transient receptor potential (Trp) channel family are putative capacitative Ca2+ entry channels that respond to contractant-generated signals and intracellular Ca2+ store depletion. Quantitative reverse transcription-polymerase chain reaction was used to examine the relative expression of TrpC mRNAs in rat myometrium and determine their expression pattern during pregnancy and labor. rTrpC1, rTrpC2, rTrpC4, rTrpC5, rTrpC6, and rTrpC7 mRNAs, but not rTrpC3 mRNA, were expressed in nonpregnant rat myometrium. With the exception of rTrpC7, the resulting products were sequenced and found to be identical with published sequences; new rTrpC7 sequence exhibited >88% homology to mouse and human TrpC7 coding regions. Relative to beta-actin mRNA, rTrpC4 mRNA was expressed in the greatest abundance. rTrpC1, 5, and 6 mRNAs were expressed at lower levels, whereas rTrpC2 and 7 mRNAs were barely detectable. This relative expression pattern was also observed throughout the course of gestation. There were no major differences in expression of rTrpC1, 2, 4, or 7 mRNAs between Day 13 and Day 21 of gestation or labor. Rat TrpC5 and TrpC6 mRNA expression decreased in pregnancy but was not altered between Day 13 and Day 21 or in labor. Western blot analysis generally confirmed these observations with respect to protein expression. These data suggest that rTrpC4 may play a major role in regulated Ca2+ entry in myometrial cells and throughout pregnancy but do not rule out contributions from other Trp proteins.

Some members of the CYP3A subfamily show gender-dependent expression. Using quantitative real-time polymerase chain reaction, we report that female rats have 28-fold higher CYP3A9 mRNA levels than males in liver and 3.8-fold higher in lung. Furthermore, the CYP3A9 expression profile in kidney exhibits a regio-specific distribution, i.e., a 10-fold higher expression in cortex compared with medulla. Also, we observed tissue-specific estrogen regulation of the CYP3A9 message. Estrogen treatment caused a significant up-regulation in liver and a marked down-regulation both in the cortex and medulla of the kidney. Upon ovariectomy, hepatic and brain CYP3A9 expression were reduced significantly, but a modest increase in kidney expression was observed. The effects of ovariectomy on CYP3A9 gene expression were reversed upon exogenous estrogen treatment. CYP3A protein levels and hepatic microsomal activity toward benzphetamine after various treatments showed changes parallel to CYP3A9 mRNA levels. We report for the first time that CYP3A9 levels change dramatically during the course of pregnancy.

Expression of PKA, PP2B, and AKAP79 is consistent with the presence of a functional AKAP-mediated signaling complex in pregnant human myometrial membranes. A small but significant decrease in PKA, AKAP79, and PP2B in myometrial tissues from women in labor may contribute to a decrease in negative feedback on and enhancement of contractant signals at term.