Oxytocin and vasopressin increase blood pressure but do not affect uterine perfusion in midpregnant rats

Abstract

UTERINE PERFUSION IN MIDPREGNANT RATS CHRISTIAN VULPESCU, YURI VEDERNIKOV, HOLGER MAUL, SOHN CHRISTOF, GEORGE SAADE, ROBERT GARFIELD, Medizinische Hochschule Hannover, Zentrum fur Frauenheilkunde, Abteilung I fur Pranatalmedizin, allgemeine Gynakologie und Geburtshilfe, Hannover, Germany, Germany, University of Texas Medical Branch at Galveston, Obstetrics & Gynecology, Galveston, Texas OBJECTIVE: To determine if oxytocin (OT) and vasopressin (VP) affect systemic blood pressure and uterine microcirculatory perfusion (UMP) in midpregnant Sprague Daley rats. STUDY DESIGN: Anesthetized animals were positioned on thermo-pads, catheters were placed in the femoral artery and vein for blood pressure (BP, Radnotti pressure transducer) registration and agent injections, respectively. A needle ultrasonic probe (18 Gauge, BLF 21, Transsonic Systems Inc.) was positioned on the surface of the uterine horn after abdominal wall incision and UMP was measured as Tissue Perfusion Units (TPU). After BP and UMP stabilized 30, 100 and 300 mmol of OT were injected stepwise as 0.1 ml bolus treatments at 10 min intervals (n = 5 rats). After a period of rest, 10, 30 and 100 mmol of VP were injected (n = 4). The data registered 2 min before and after agonists were stored on a PC using a DI-220 data acquisition system and Windaq/200 software (Data Q Instruments Inc., Akron, Ohio). RESULTS: OT, 30 mmol significantly (P ! .05) augmented BP by 30.8 G 6.1 %, while at 100 and 300 mmol the increase in BP by 55.1 G 28.1% and 43.3 G 19.4%, respectively did not reach significant levels due to high variations in the responses. UMP did not significantly change after injection of any dose of OT. At the doses of 30 and 100 mmol VP significantly (P ! .05) augmented BP by 77.5 G 13.3% and 135.6 G 29.1 %, while no significant changes in the UMP were registered. Thus, both OT and VP increased systemic BP, but did not significantly affect UMP. CONCLUSION: OT and VP have profound effects on maternal blood pressure but do not simultaneously influence uterine or fetal perfusion. This may represent adaptive mechanisms of maternal/uterine circulation to the peptides during pregnancy in order to maintain adequate uterine perfusion and fetal blood supply. 466 MARKERS OF CHRONIC HYPOXIA IN PREGNANCIES COMPLICATED BY NUCHAL CORD ROBERT L. ANDRES, MICHELLE S. LEWANDOWSKI, MORGAN R. PELTIER, University of Utah, Obstetrics and Gynecology, Salt Lake City, Utah OBJECTIVE: The reported incidence of nuchal cord varies from 20-40%. This common finding has been associated with adverse perinatal outcomes including spastic cerebral palsy. It has been theorized that chronic intermittent hypoxia during pregnancy may predispose to the fetus to development of spastic quadriplegia. Hypoxia provides a physiological signal to increase angiogenesis and the production of erythrocytes. Therefore we hypothesized that chronic intermittent hypoxia associated with a nuchal cord would be associated with alterations in the production of vascular endothelial growth factor (VEGF), placenta growth factor (PlGF) and erythropoietin (EPO) in cord blood. STUDY DESIGN: Cord blood was collected after delivery as a part of our universal sampling procedures with IRB oversight. Samples from fetuses with a nuchal cord (n = 13) and those without (n = 15) were collected into EDTA tubes and plasma was harvested by centrifugation and stored at -85(C until assay for EPO, VEGF and PlGF. Data were evaluated using t tests. RESULTS: No significant differences were detected between VEGF, PlGF and EPO concentrations in cord blood between babies born with nuchal and normal cords (Table). CONCLUSION: The presence of a nuchal cord has no effect on cord blood concentrations of VEGF, PlGF or EPO. This observation does not support the concept that long-term fetal hypoxia is present in pregnancies complicated by nuchal cord. Future prospective investigation is planned focusing on the same markers of hypoxia and angiogenesis in fetuses who are identified sonographically as having a nuchal cord in the antenatal period, rather than limiting the study group to those with a nuchal cord at delivery.