Decreased circulating arginine in ALF mice does not compromise whole body NO production

Abstract

In fulminant hepatic encephalopathy (HE), the plasma level of the precursor of nitric oxide (NO) Arginine is reduced. In contrast, nitric oxide (NO) production, measured as plasma NOx is increased. This contradiction could be due to failure of plasma NOx to represent NO production. Therefore, we studied whole body (Wb) ARG (precursor of NO) and NO metabolism using stable isotope technology in a newly developed acetaminophen (APAP) induced acute liver failure (ALF) mouse model with pre-coma HE after 20h. Method: In post absorptive C57Bl6/J mice, an oral dose of 200+200 mg/kg of APAP or drinking water (control) was given at t=0+1 h. At T=20 h, Wb ARG and Arginine to NO and Urea/Ornithine conversion was measured in carotid artery/jugular vein catherized mice under anaesthesia using a primed-continuous infusion of 15N-CIT, 15N2-2H2-ARG and 13C-UREA stable isotopes. At plasma steady state, arterial (art) plasma was collected. Whole body rate of appearance (WbRa), NO production, de novo ARG and rate of urea converted from ARG (ARG-UREA) were calculated. Statistics: t-test, sign p<0.05, data as mean ± SEM. Results Twelve of the 17 APAP animals had ALT>1000 IU/l (ALF group) and showed behaviour changes at a level of pre coma. Art ARG was decreased in the ALF group (65 ± 15 vs. 134 ± 6 μM). Art ORN (190 ± 19 vs. 84 ± 7 μM) and ARG-UREA conversion (19 ± 3 vs. 13 ± 1 nmol/10 gr bw/min) were increased. WbRa of ARG, Wb NO production and de novo ARG were unchanged compared to control animals. Conclusion Reduced plasma ARG is probably caused by release of the enzyme arginase from the injured liver and subsequent ARG to ORN/UREA conversion. Reduced Arginine availablity, however, did not affect NO production at this early stage of HE.