Splanchnic removal of lactate and pyruvate during prolonged exercise in man

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Abstract
To determine the time course of hepatic-splanchnic lactate and pyruvate uptake during exercise, estimated hepatic blood flow (EHBF) was determined in 6 normal men by constant infusion of indocyanine green during prolonged (60-70 min.) treadmill exercise requiring 48-70% of maximum Vo2. Arterial and hepatic venous lactate and pyruvate concentrations peaked by the 10th min. of exercise and decreased thereafter (tl/2 - 22-33 min.). EHBF was reduced 50-70%; nevertheless, splanchnic Vo2 increased with time while splanchnic lactate uptake averaged 0.77 [plus or minus] 2.5% of estimated total body lactate/minute, or 46% of the lactate removed in 60 min. Splanchnic CO2 productin could account for oxidation of only a small fraction of lactate removed by this region, making gluconeogenesis a likely major pathway. Arterial lactate/pyruvate ratios and "excess" lactate (Huckabee) decreased with time while hepatic venous values increased. During milder exercise one man showed proportionally smaller splanchnic lactate removal rate. We conclude that the lactate-O2 debt relationship during exercise is time dependent while O2 debt is not.