Changes in the activities of the enzymes of urea synthesis caused by dexamethasone and dibutyryladenosine 3′:5′-cyclic monophosphate in foetal rat liver maintained in organ culture

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Abstract
Liver explants from 19 day fetal rats were maintained in organ culture, in a defined medium, for up to 48 h. Both 6-N,2''-O-dibutyryl cyclic AMP, in the presence of theophylline and dexamethasone increased the activities of carbamoyl phosphate synthase, argininosuccinate synthetase, argininosuccinate lyase and arginase. These increases were abolished by simultaneously incubating the explants with cycloheximide. No change in the activity of ornithine transcarbamoylase was found with either hormone. In previous work injection of corticosteroids into 19.5 day fetal rats in utero did not increase the arginine synthetase system. This lack of effect is probably not due to any incompetence of the fetal rat liver at this stage to respond to this agent. The observations on ornithine transcarbamoylase activity suggest that this enzyme is induced in the liver of the perinatal rat by neither corticosteroids nor hormones acting via cyclic AMP. All the enzymes of the urea cycle may be induced physiologically by an agent or agents as yet unidentified.