Leg and splanchnic arteriovenous differences of plasma citrate in exercising man

Arteriovenous concentration differences of plasma citrate, glucose, lactate, pyruvate, free fatty acids, acetoacetate, and 3-hydroxybutyrate were determined across the leg and the splanchnic vascular bed in six healthy subjects in postabsorptive state, during 30 min of exercise (60--70% work load) and 65 min of recovery. A release of citrate across the leg and an uptake across the splanchnic vascular bed were found. Citrate arterial-femoral venous difference at rest, -19 +/- 2 mumol/l was abolished after 5 min of exercise and rebuilt during continuous work to reach peak value, -30 +/- 3 mumol/l at 20 min recovery. During exercise increasing negative arterial-femoral venous citrate differences were inversely related to fractional glucose extraction across the leg. Arterial-hepatic venous citrate difference at rest, 10 +/- 2 mumol/l, increased twofold during recovery. The results agree with the concept that a citrate inhibition of phosphofructokinase may be of regulatory importance for muscular glycolysis and glucose uptake as well as for hepatic glycolysis and gluconeogenesis in man during exercise.