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

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Abstract
The administration of hydrocortisone (0.1 mg) to intact fetuses in utero 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 in utero 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 in utero 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.