FEMALE REPRODUCTIVE TRACT - B
Wednesday, August 4, 2004
10:30 AM–12:30 PM
(809) RAPID PROGESTERONE ACTION INHIBITS OXYTOCIN-INDUCED SECRETION OF PROSTAGLANDIN F2 BY OVINE ENDOMETRIAL EXPLANTS.
Bishop, Cecily1, Stormshak, Fredrick1, 1 Departments of Biochemistry/Biophysics and Animal Sciences, Corvallis, OR
ABSTRACT- Progesterone (P4) regulates the expression of ovine uterine oxytocin receptor (OTR) mRNA via a genomic mechanism. However, recent research has demonstrated that P4 also acts nongenomically via a putative plasma membrane receptor to inhibit binding of oxytocin in the ovine endometrium. Oxytocin (OT) stimulates the release of prostaglandin F2 (PGF2) from ovine uterine endometrium during proestrus. Therefore, the objective of the present research was to determine whether a rapid action of P4 in vitro would suppress OT-induced secretion of PGF2 in ovine endometrial explants. Five ewes were injected im with 250 g PGF2 analogue (cloprostenol) on Day 14 to hasten onset of luteal regression and reduce systemic levels of P4. On Day 15 intercaruncular endometrial tissue was collected via midventral laparotomy. Explants (50-200 mg) were then cultured in Eagle's MEM in the absence or the presence of arachidonic acid [AA] (20 M) and cultured in 6-well plates for 2 h at 37°C in a humidified atmosphere (95% air, 5% CO2). Explants were then subjected to a change of medium (3 ml) containing vehicle or 2.5 ng/ml P4, and cultured an additional hour at 37°C. The treatment regimen resulted in a 2×2 factorial arrangement of groups. All wells containing explants were then challenged with OT (5M) and cultured for an additional hour. A fifth group of explants was exposed only to medium for the entire experiment to serve as a negative control and establish basal PGF2 release. After the final hour of culture, media were collected and analyzed for PGFM by RIA. Intra- and interassay coefficients of variation were 5.27 and 7.85 %, respectively. Prostaglandin F2 secretion was expressed as pg PGFM/100l/mg tissue. Data on medium concentrations of PGFM were analyzed statistically by two-way ANOVA. Treatment of explants with AA increased PGF2 compared to that of controls (P=0.06). Brief exposure to P4 significantly decreased OT-induced PGF2 secretion (P<0.01) in explants previously exposed to medium or AA. Results of this experiment demonstrate a rapid, presumably nongenomic, effect of P4 in inhibiting OT-induced PGF2 secretion by ovine endometrial explants.
KEY WORDS: endometrium, prostaglandin F2, progesterone, oxytocin