Patients with nonalcoholic fatty liver disease (NAFLD) have elevated fasting levels of glucagon (gcg) and amino acids (AA) . Gcg regulates hepatic AA catabolism by augmenting ureagenesis. We hypothesized that hepatic steatosis causes gcg resistance and impaired gcg-induced hepatic ureagenesis. To address this, we developed an isolated liver perfusion model in mice and used it to investigate gcg’s direct effect on hepatic glucose production (HGP) and ureagenesis in 9 male mice with hepatic steatosis (NAFLD mice) (B6.Vlepob/ob/JRj) and healthy controls (CON) (C57bl6/JRj) . NAFLD mice had higher body mass (50 vs. 26 g, P<0.0001) and higher hepatic fat triglycerides (1vs. µmol/g, P<0.0001) compared to CON. Catheters were place in the portal vein and the inferior vena cava and the liver was perfused with Krebs Henseleit buffer with and without 5 mM AA mixture (Vamin) , nM gcg or both. Samples were collected every minute and analyzed for urea and glucose concentrations. Results were normalized to liver tissue protein content. AA administration increased hepatic urea production from baseline in both groups within six minutes (NAFLD mice: 2.4 vs. 5.3 mmol/min × µg protein, P=0.01) , (CON: 3.4 vs. 7.4 mmol/min × µg protein, P=0.02) . Gcg increased the AA-stimulated ureagenesis compared to AA administration alone in CON (7.4 vs. 9.4 mmol/min × µg protein, P<0.0001) but not in NAFLD mice (5.3 vs. 5.1 mmol/min × µg protein, P=0.66) . During the gcg administration (50 minutes) the total HGP was far greater in CON compared to NAFLD mice (309.5 vs. 195.5 µmol/min/µg protein, P=0.03) . The difference in glucose output could not be explained by hepatic glycogen content, as the NAFLD mice showed higher glycogen content than CON (1.7 vs. 0.8 µg/mg liver mass, P=0.02) . Our data support
1) that glucagon acutely increases the substrate-induced ureagenesis and
2) that hepatic steatosis causes resistance to the acute metabolic actions of glucagon on ureagenesis.
F.R.Ceutz: None. E.E.Christensen: None. M.Winther-soerensen: None. H.Vilstrup: None. J.J.Holst: Advisory Panel; Novo Nordisk, Board Member; Antag Therapeutics, Bainan Biotech. N.J.Wewer albrechtsen: Research Support; Mercodia AB, Novo Nordisk, Regeneron Pharmaceuticals Inc., Speaker's Bureau; Merck & Co., Inc., Mercodia AB.
Nicolai J. Wewer Albrechtsen were financed by NNF Excellence Emerging Investigator Grant – Endocrinology and Metabolism (Application No. NNF19OC0055001) , EFSD Future Leader Award (NNF21SA0072746) and DFF Sapere Aude.