Proteolysis associated with a deficit of peripheral energy fuel substrates in septic man

Sixteen seriously septic patients were studied to determine whether proteolysis occurred to satisfy a deficit of peripheral fuel, as suggested by out previous experimental observations. Concentrations of glucose, lactate, free fatty acids,and alanine were measured in blood samples from the femoral artery and vein to determine extraction (+) and release (-) by the leg. Simultaneously, cardiac index (CI) was determined by thermal dilution, so that an estimate of uptake or production of fuel substrates could be made from the proportional relationship of cardiac index to peripheral blood flow. Due to the antilipolytic effect of elevated levels of insulin (42 +/- 4 muM per milliliter) in those patients with elevated cardiac indices (4.38 +/- 0.33 L. per square meter per minute), free fatty acid uptake (-0.59 +/- 0.021 mM.) was reduced. In low-flow septic shock (CI, 1.66 +/- .41 L. per square meter per minute), the majority of glucose taken up by the limb was converted to lactate (arterial lactate, 3.14 +/- 0.7 mM.; deltaA-V 0.68 +/- 0.17). Free fatty acid uptake also was impaired in low-flow sepsis. As opposed to fasting, arterial levels and uptake of ketone bodies were insignificant in sepsis. These findings suggest that there is a deficit of peripheral fuel with respect to glucose and fat. That protein is oxidized to fill this deficit is substantiated by the increased alanine release (-0.13 +/- 0.01, -0.33 +/- 0.12 mM.) in the high-flow and low-flow septic groups, respectively, whereas alanine production was three- and fourfold greater than that observed in fasting patients. Enhanced release of alanine reflects the magnitude of oxidation of branched-chain amino acids and accounts for the high rates of gluconeogenesis and proteolysis observed in sepsis.