Control of urea synthesis in fetal rat liver slices.

Urea synthesis in fetal rats was studied using a liver slice system with ammonium chloride as nitrogen source. In term fetuses, the rate of urea formation increases with ammonium chloride concentration up to 100 microM and is enhanced by the addition of ornithine. The developmental pattern for urea synthesis is very similar to that found in the enzyme activity studies: urea production increases slightly during fetal life and then rises rapidly at birth. It is found that fetal liver has an absolute requirement for glucocorticosteroids to develop a normal urea synthesis. The accordance with argininosuccinate synthetase activity measured in liver homogenate is discussed.