Inhibition of urea synthesis by pent-4-enoate associated with decrease in N- concentration in isolated rat hepatocytes

Pent-4-enoate at 0.1 to 1.0 mM strongly inhibited urea synthesis in isolated rat hepatocytes. Pent-4-enoate at the same concentrations markedly decreased concentrations of N-acetyl-L-glutamate, an essential activator of carbamoyl-phosphate synthase-I (EC 2.7.2.5), and the decrease was well in parallel with the inhibition of urea synthesis by pent-4-enoate. This compound also lowered cellular concentrations of acetyl-CoA, a substrate of acetylglutamate synthase (EC 2.3.1.1). Pent-4-enoate in a dose of 1 mM did not significantly affect cellular concentrations of ATP, and had no direct effect on acetylglutamate synthase activity. These results suggest that the inhibition of urea synthesis by pent-4-enoate is due to decrease in N-acetyl-L-glutamate concentration and that the decrease is probably brought about by decreased rate of its synthesis due to the lowered concentration of cellular acetyl-CoA.