Urea concentration and ornithine decarboxylase in liver of female rats.

In virgin female rats thioacetamide administration (1 mg/100 g body wt) induced a 16-fold increase in liver ornithine decarboxylase (ODC) activity and a significant decrease (19%) in hepatic urea concentration. The ornithine-metabolizing enzymes, ornithine-oxo-acid aminotransferase and ornithine carbamoyltransferase, were not modified by the treatment; only carbamoyltransferase, were not modified by the treatment; only carbamoyl-phosphate synthetase I activity was significantly reduced. In 19-day pregnant rats DL-alpha-difluoromethylornithine treatment inhibited the expression of enhanced ODC activity occurring normally at this stage of pregnancy. Concomitantly an inhibition of the usual decrease in hepatic urea was observed. This increase of ureagenesis occurred without any increase in liver N-acetylglutamate or ornithine concentrations, which remained as low as in normal pregnant rats.