FEMALE REPRODUCTIVE TRACT - B
Wednesday, August 4, 2004
10:30 AM–12:30 PM
(816) INHIBITION OF PROSTAGLANDIN F2 SYNTHESIS AND OXYTOCIN RECEPTOR BY MIFEPRISTONE IN BOVINE ENDOMETRIAL CELLS.
Goff, Alan1, Aimé, Kombé1, 1 Université de Montréal, St-Hyacinthe, QC, Canada
ABSTRACT- Progesterone (P4) and estradiol (E2) are the hormones responsible for increasing oxytocin receptor (OTR) on the endometrial epithelial cells during luteolysis, but it is still not understood exactly how they act. The OTR, which appears to be constitutively expressed, is suppressed by progesterone during the luteal phase and then increases at the time of luteolysis even in the presence of high P4. The time of luteolysis is directly related to the time at which P4 increases, but the mechanisms involved are unknown. In vitro studies have been used to try to elucidate the action of P4 on prostaglandin synthesis and OTR in isolated endometrial cells. However, these kinds of studies are confounded by the fact that OTR is spontaneously up-regulated when the endometrium is cultured and attempts to down regulate OTR in vitro have met with limited success. The objective of this study was to investigate the effect of P4 and its antagonist mifepristone on OTR and PGF2 secretion from endometrial epithelial cells in vitro. In the first experiment, confluent epithelial cells were treated with P4 (0 and 10ng/ml) and mifepristone (0 and 5 M) for 24, 48 and 72 h. At the end of culture the cells were incubated for 6h with OT (0 and 20 ng/ml) for the measurement of PGF2 by RIA. Results showed that P4 increased PGF2 secretion. Mifepristone had no significant effect after 24h but by 72h it decreased basal PGF2 secretion (2.5 ± 0.3 vs. 0.6 ± 0.2 ng/ protein, P < 0.01) and abolished the response of the cells to OT (P < 0.01). To begin to determine the mechanism of action of mifepristone, cells were cultured for 3 days with or without mifepristone and then COX was measured by Western blotting and OTR measured by saturation analysis. The results showed that mifepristone did not affect levels of either COX-1 or COX-2. Mifepristone did however decrease OTR number (0.03 ± 0.01 vs. 0.012 ± 0.004 nmol/ protein, P < 0.05). These data demonstrate that OTR and the response to OT can be downregulated in endometrial epithelial cells in vitro via a mechanism involving the P4 receptor. Since mifepristone can act as a partial agonist in some tissues further studies are underway using a more specific antagonist.
KEY WORDS: prostaglandin, oxytocin, luteolysis, endometrium