Oxytocin and arginine vasopressin do not alter vascular resistance in the fetoplacental circulation of the dual-perfused human placenta
Abstract Number: OP1-6
Abstract Type: Original Research
Introduction: In non-pregnant animals, high dose vasopressin constricts uterine resistance vessels more than oxytocin!. Physiologic oxytocin concentrations have no effect on pregnant and non-pregnant rat uterine vessels2. In contrast, the effects of these drugs on the fetoplacental circulation have not been well studied. Oxytocin has little effect on umbilical artery Doppler velocity3 and while vasopressin has no effect on overall myometrial blood flow in pregnant animals4, its fetoplacental circulatory effects are unreported.
Methods: With IRB approval and informed written patient consent, placentae from healthy women at term delivered by elective cesarean section were rapidly transported to our laboratory. A fetal chorionic artery and vein serving a discrete cotyledon were quickly cannulated, needles were inserted on the maternal side of the cotyledon, and Krebs Ringers buffer (KRB) was infused at constant pH(7.4) and temperature(37ᵒC). The open (non-recirculating) model was employed and fetal perfusion rates were held constant. Flow rate (Q) was assumed proportional to FAP and inversely related to arteriolar vascular resistance (FVR). Fetal perfusion pressures (FAP) were recorded every 5 minutes and the FAP recordings made just before every step interval were used for data analysis. Each cotyledon was perfused for a control period of 1 hour to allow pressures to stabilize. Arginine vasopressin was added to the fetal reservoir in increasing concentrations [10-11 to 10-6M in 5(10-N+1)] increments (n=5). Similarly, oxytocin was studied over a range of concentrations (10-9 to 10-6M) (n=6). After each study, 5-hydroxytryptamine (5HT) was infused. Wilcoxon rank sum test compared percentage changes from baseline for each concentration.
Results: Two placentas were discarded since 5-HT failed to increase FAP. FAP did not change in response to any concentration of either vasopressin (n=4) or oxytocin (n=5). (Table 1)
Discussion: Our results support umbilical artery Doppler findings showing that oxytocin has minimal effect on FAP3and thus fetal vascular resistance. Although fetal concentrations of vasopressin have been noted to rise substantially during labor4, this would be expected to have little effect on fetal circulation.
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2.Miller.et al. Am J Physiol Heart Circ 2002;282:H1223
3.Olofsson.et al. Ultrasound Obstet Gynecol 1996;8:247
4.Sjoquist.et al. Acta Pharmcaol Toxicol 1978;43:190