TRANSFUSION SYNDROME CORRECTED AFTER LASER COAGULATION OF CHORIONIC PLATE ANASTOMOSES AND AMNIOREDUCTION ILINCA GUSSI, JACKY NIZARD, LYDIA MALAGRIDA, MASSAMI YAMAMOTO, ROMAINE ROBYR, YVES VILLE, University of Versailles Saint-Quentin-en-Yvelines, Department of Obstetrics and Gynecology, Poissy, France, University of Versailles SaintQuentin-en-Yvelines, Department of Biology, Poissy, France OBJECTIVE: To observe changes in the renin-angiotensin-aldosterone system following the treatment of twin-to-twin transfusion syndrome (TTTS). STUDY DESIGN: Twenty consecutive cases of monochorionic diamniotic pregnancies complicated by severe TTTS at 20–28 weeks of gestation were investigated prospectively. Patients were treated by placental surgery followed by amnioreduction. Tocolysis consisted of one dose of 100 mg intrarectal indomethacin. Maternal venous blood was collected before, 6 and 12-24 hours after surgery. Aldosterone, renin, angiotensine II, ANP and vasopressin were measured by RIA. Simultaneous full blood count and ionograms were performed. Results are expressed as mean G SEM, range intervals as 25 and 75 percentiles. Wilcoxon test was used for statistical analysis. RESULTS: Twenty patients were investigated at 21.5 G 1 weeks with severe TTTS. The mean amniotic fluid volume drained was 1500 G 175 mL. Within 12 hours of treatment, hemoglobin levels decreased by a mean of 1.2 g/dL (0.4–1.6), and this was not explained by perioperative complications. Plasma sodium and potassium levels remained stable and there was maternal hyperaldosteronism, with a mean aldosterone level of 1131.6 G 206 pg/mL (337-1732) for a normal range !355 pg/mL. Aldosterone levels decreased 12 hours after laser and amnioreduction (P = .023). ANP increased as early as 6 hours following amnioreduction (P = .025). Mean renin and angiotensin II levels did not decrease significantly following treatment (P > .05). Vasopressin levels remained within normal ranges (!8 pg/ml) following amnioreduction. CONCLUSION: Marked maternal hyperaldosteronism in TTTS is rapidly corrected following amnioreduction showing that rapid and efficient maternal hormonal adaptive mechanisms succeed in maintaining sodium balance and subsequent volemic homeostasis. 454 LOCALIZATION OF CONTRACTILE PROSTAGLANDIN E2 RECEPTORS IN RAT CERVICAL TISSUE ANDREA HINTON, PETA GRIGSBY, BRAD PITZER, DIANE BROCKMAN, LESLIE MYATT, University of Cincinnati, Obstetrics and Gynecology, Cincinnati, Ohio OBJECTIVE: Preterm labor remains a significant problem in obstetrics. Application of progesterone is emerging as a preventative measure for preterm labor, although the mechanism of action remains unclear. Prostaglandin E2 (PGE2) plays a role in cervical ripening and is mediated by changes in the relaxatory and contractile PGE2 receptors. We hypothesize that cervical PGE2 receptors are hormonally regulated by progesterone throughout gestation and labor. The purpose of our study was to investigate the localization of the contractile PGE2 receptors (EP1 and EP3) in the rat cervix during RU486induced labor and progesterone treatment. STUDY DESIGN: Pregnant rats received either RU486 (10 mg/kg, IP; n = 5) or vehicle on day 16 of gestation. Animals were euthanized on day 18 of gestation. A second group received progesterone (2.5 mg/day, IP; n = 18) or vehicle. Animals were sacrificed on days 21, 22, and 23 of gestation (treated; n = 6, vehicle; n = 5, respectively). Cervical tissue was collected and sectioned (8mm) for immunostaining using anti-human EP1 and EP3 polyclonal antibodies. Slides were evaluated for receptor localization and intensity of staining as a reflection of the number of receptors. RESULTS: EP1 receptors were not present in cervical smooth muscle in RU486-treated or control animals, but were localized to the cervical smooth muscle in progesterone-treated and control animals. In contrast, EP3 receptors were localized to the smooth muscle cells in all animal groups. The RU486induced labor increased EP1 and EP3 expression throughout all layers of the cervical epithelium, whereas EP1 and EP3 receptors were present only in the apical layer of the epithelium in both the progesterone-treated and control animals. Progesterone treatment decreased EP1 and EP3 expression when compared to control animals. CONCLUSION: Progesterone appears to differentially regulate expression of contractile EP receptors in the cervix. Understanding the hormonal regulation of the PGE2 receptors in the cervix is important in developing improved management of preterm labor.