Hepatic glycerol flux was examined in dogs after the administration of Escherichia coli endotoxin (0.4 mg/kg) to determine the contribution of the liver to the previously observed decline in the metabolic clearance rate of glycerol. Hepatic glycerol flux was estimated by determining hepatic arterial and portal venous blood flows with electromagnetic flow probes and by measuring arteriovenous difference of glycerol across the liver. Administration of endotoxin significantly decreased total hepatic blood flow (by approximately 20%) but did not alter hepatic arterial blood flow. Hepatic glycerol clearance decreased by 25–30% after endotoxin administration. Hepatic glycerol extraction also decreased. Under control conditions, 60% of the metabolic clearance rate of glycerol was attributable to the liver, whereas in the postendotoxin state approximately 72% of the glycerol clearance could be accounted for by hepatic clearance. Thus changes in transhepatic glycerol flux are only partially responsible for the previously observed alterations in glycerol clearance after endotoxin administration. Although hepatic glycerol clearance decreased, net hepatic glycerol, as well as lactate and alanine, uptake did not decrease, indicating that gluconeogenic precursor availability to the hepatocytes was not diminished. Hepatic glucose output was elevated after endotoxin administration. Changes in hepatic glucose output and gluconeogenic precursor uptake help explain the endotoxin-induced alternations in the fluxes of these metabolites.
The Renin-Angiotensin System in Conscious Newborn Sheep: Metabolic Clearance Rate and Activity