Excessive NO production does not account for the inhibition of hepatic gluconeogenesis in endotoxemia

The pattern of inhibition of gluconeogenesis in hepatocytes was compared between endotoxemia in vivo and nitric oxide (NO) exposure in vitro. Fasted rats were injected with lipopolysaccharide (LPS; 12 mg/kg) or with vehicle alone. After 2-24 h, hepatocytes were isolated, placed in suspension, and incubated for 1 h with various gluconeogenic substrates that enter at different sites of the gluconeogenic pathway. Hepatocytes from LPS-treated rats exhibited up to a 50% decrease in gluconeogenesis for substrates that enter proximal to glyceraldehyde-3-phosphate dehydrogenase (GAPDH) beginning at 6 h, followed by a nadir at 12 h after LPS. Although hepatocytes exposed to exogenous NO (S-nitroso-N-acetylpenicillamine) also exhibited a depressed gluconeogenesis, the pattern was not the same with inhibition in gluconeogenesis for substrates that enter the pathway both before and after GAPDH. Furthermore, when rats injected with LPS were subjected to a constant portal infusion (Alzet pump) of the NO synthase (NOS) inhibitors, N(G)- monomethyl-L-arginine or aminoguanidine, no changes in the LPS-induced gluconeogenesis suppression were seen. In addition, no difference in LPS- induced inhibition of gluconeogenesis was detected when hepatocytes from inducible NO synthase (NOS-2) knockout mice were compared with cells obtained from wild-type mice. Minimal decreases in GAPDH activity were measured in hepatocytes from the LPS-treated rats, whereas the activity of phosphoenolpyruvate carboxykinase (PEPCK) declined up to 40%, independent of NO synthesis. These data indicate that NO does not account for the inhibition of gluconeogenesis in endotoxemia, and they provide support for NO- independent reduction in PEPCK activity as a more plausible explanation.