Determination of Fetal, Placental and Neonatal Blood Volumes in the Sheep

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Abstract
A sheep preparation was developed for studying fetoplacental and neonatal blood volumes using isotope dilution techniques. Fetoplacental blood volume was measured in 46 fetal lambs (gestational age 112 to 146 days) using radioactive iodinated human serum albumin (125I-RISA). In 28 of the 46 animals, blood volume was also computed using 125I-RISA and maternal red cells labeled with radiochromium (51Cr). Blood volume averaged 156.1 ml/kg of fetal weight with the single-label method and 134.7 ml/kg with the double-label method. Blood volumes measured in 17 neonatal lambs with the single-label technique averaged 110.0 ml/kg, and with the double-label technique in 10 animals averaged 104.0 ml/kg. Placental blood volume, determined by subtracting the neonatal blood volume from the fetoplacental blood volume, although varying from animal to animal, was independent of fetal weight and remained relatively constant during the last fourth of gestation.