The effect of vasopressin on fetal oxygenation in sheep

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Abstract
To examine the effects of vasopressin on fetal oxygenation, the hormone was infused i.v. for 1 h (1.4-3.5 mU .cntdot. min-1 .cntdot. kg fetal wt-1) to chronically catheterized fetal lambs in utero (113-137 days gestation). Arterial pressure rose (48.3-59.6 mm Hg) (1 mm Hg = 133.322 Pa [pascal]) and heart rate fell (185.3-141.0 beats/min) during the infusion. There was a significant increase in fetal arterial PO2 [partial pressure] (20.0-23.1 mm Hg) and significant declines in pH (7.414-7.381) and base excess. Umbilical blood flow rose, and the percentage increase in flow (23%) was identical to the proportional rise in arterial pressure. Accompanying ths rise in umbilical blood flow was a rise in umbilical O2 delivery. But as there was no change in fetal O2 consumption, fractional O2 extraction by the fetus fell significantly (0.31-0.25). The vasopressin-induced rise in fetal vascular PO2 results from an increase in umbilical O2 delivery and concomitant fall in fractional extraction. Fetal vasopressin levels are greatly elevated during hypoxia, and under conditions of reduced O2 supply, the effects of the hormone on umbilical O2 delivery and vascular PO2 could have definite survival value.