Die Harnstoffbildung der menschlichen Placenta

The Distribution and Metabolism of Carbon-Labeled Urea in Pregnant Primates*

“…To date investigators reporting on the subject (2,13,14) have employed methods that depend upon the demonstration of concentration gradients on either side of the placental barrier or on differences in the concentration of umbilical arterial and venous blood (15).2 In the former instance, a gradient must 2As shown in the body of this report the metabolic rate of urea production is probably less than 0.2 mmole UREA EXCHANGE IN PREGNANT PRIMATES be produced artificially by raising the maternal urea concentration above physiologic levels; the latter approach is based on the premise that the placenta is inert. Actually the placenta is metabolically quite active (16), and Brandstrup (14) has shown that its permeability to urea has certain limitations. For these reasons no convincing evidence exists to demonstrate that under normal physiologic conditions a transfer or exchange of urea takes place.…”