Effects of Administration of Hydrocortisone, Actinomycin D and Puromycin on Carbamoylphosphate Synthetase-I and Ornithine Carbamoyltransferase Activities in Fetal Rat Liver

Abstract

The administration of hydrocortisone (0.1 mg) to intact fetuses <i>in utero</i> on day 16.5, 17.5 and 18.5 caused a marked increase in the activity of carbamoylphosphate synthetase-I 48 h later. This increase can be abolished 48 h later by simultaneous administration of actinomycin D (2 μg). No change in the activity of ornithine carbamoyltransferase was found with administration of hydrocortisone <i>in utero</i> during the same period. The normal increase of the activity of carbamoylphosphate synthetase-I during the late fetal period is not abolished by administration of actinomycin D, while this treatment on day 18.5 <i>in utero</i> stimulates the activity of ornithine carbamoyltransferase. The normal increase of carbamoylphosphate synthetase-I activity during the late fetal period is not associated with an enzyme synthesis, while its hydrocortisone-induced increase seems to be due to an enzyme synthesis. The nature of the increase in ornithine carbamoyltransferase activity with actinomycin D remains to be identified.