305 CARDIOVASCULAR EFFECTS AND CLEARANCE OF EXO-GENOUS ARGININE VASOPRESSIN (AVP) IN THE FETAL LAMB

Abstract

The concentration of AVP has been shown by us to be elevated in the human and lamb fetus during perinatal stress, especially hypoxia and asphyxia, with levels being greatest in association with meconium in the amniotic fluid (AF). The role of AVP in these instances is unclear; thus, we studied in fetal lambs the cardiovascular effects and clearance of infused AVP. AVP was infused into the vena cava of fetal lambs, 129-137 days gestation, at doses of 1.94, 3.88, and 7.76 mU/min for 75 min (n=5) while monitoring fetal and maternal mean arterial pressure (MAP), heart rate (HR), and umbilical and uterine blood flows. Samples were obtained for serial determinations of fetal plasma and AF AVP in 3 studies. Fetal plasma AVP rose from 2.0 ± .02 μU/ml (Mean ± SE) to 12 to 67 μU/ml at 60 min without changes in arterial blood gases. AF AVP increased at 60 and 120 min post-infusion, but did not correlate with plasma levels. Fetal MAP at 60 min rose 16 to 24%* while HR fell 9 to 43%*; both responses were dose dependent. Umbilical and uterine blood flows and maternal MAP and HR did not change. Of note, meconium stained AF occurred in association with intermediate and high rates of AVP infusions. The T1/2 of AVP in fetal plasma was 14 ± 2.5 min and the clearance was 51 ± 10 ml/min.kg. We conclude that AVP 1) causes a rise in MAP and fall in HR that relates to circulating levels of AVP, suggesting AVP may mediate these changes during episodes of fetal stress, and 2) may be responsible for the expulsion of meconium into the AF during such episodes. *p < .01