Renal lactate elimination is maintained during moderate exercise in humans

Reduced hepatic lactate elimination initiates blood lactate accumulation during incremental exercise. In this study, we wished to determine whether renal lactate elimination contributes to the initiation of blood lactate accumulation. The renal arterial-to-venous (a-v) lactate difference was determined in nine men during sodium lactate infusion to enhance the evaluation (0.5 mol . L-1 at 16 +/- 1 mL . min(-1); mean +/- s) both at rest and during cycling exercise (heart rate 139 +/- 5 beats . min(-1)). The renal release of erythropoietin was used to detect kidney tissue ischaemia. At rest, the a-v O-2 (CaO2-CvO(2)) and lactate concentration differences were 0.8 +/- 0.2 and 0.02 +/- 0.02 mmol . L-1, respectively. During exercise, arterial lactate and CaO2-CvO(2) increased to 7.1 +/- 1.1 and 2.6 +/- 0.8 mmol . L-1, respectively (P < 0.05), indicating a similar to 70% reduction of renal blood flow with no significant change in the renal venous erythropoietin concentration (0.8 +/- 1.4 U . L-1). The a-v lactate concentration difference increased to 0.5 +/- 0.8 mmol . L-1, indicating similar lactate elimination as at rest. In conclusion, a similar to 70% reduction in renal blood flow does not provoke critical renal ischaemia, and renal lactate elimination is maintained. Thus, kidney lactate elimination is unlikely to contribute to the initial blood lactate accumulation during progressive exercise.