Plasma oxytocin concentrations in the foetal sheep

Fetal plasma oxytocin has been measured by bioassay in samples taken from 6 chronically catheterized sheep fetuses between 128 days gestation and term. In 10 plasma samples, from five fetuses taken more than 50 hr before delivery, oxytocin was not measurable. Sensitivity of the assay varied with the volume of plasma extracted but was usually about 2 μU/ml. In the two animals in which samples were taken in the last few hr before the delivery of a live lamb, fetal plasma oxytocin concentrations were high.