Transpulmonary lactate shuttle.
Level 5 - mechanism / opinion, no new human data
Preclinical animal model in anesthetized rats (CEBM Level 5)
PubMed 22031785 · doi:10.1152/ajpregu.00402.2011
What was done
Transpulmonary lactate kinetics were evaluated in an anesthetized rat model using a primed-continuous infusion of [U-13C]lactate. Mixed central venous ([v]) and arterial ([a]) lactate concentrations, transpulmonary lactate gradients ([v] - [a]), and tracer-measured fractional extractions were measured across three conditions: baseline control (Con), exogenous lactate load via lactate clamp (LC), and epinephrine (Epi) stimulation.
What was found
Net transpulmonary lactate uptake occurred in all conditions: Con 1.2 (SD 0.7), LC 1.9 (SD 2.5), and Epi 1.9 (SD 3.5) mg/min. Lactate clamp increased mixed central venous lactate to 4.7 (SD 0.4) vs. 1.9 (SD 0.5) mM in Con, and arterial lactate to 4.1 (SD 0.6) vs. 1.6 (SD 0.4) mM (P < 0.05). Transpulmonary lactate gradient was highest in LC [0.6 mM (SD 0.7)] and lowest in Epi [0.2 mM (SD 0.5)] (P < 0.05). Tracer-measured lactate fractional extraction was 16.6% (SD 15.3) for Con and 8.2% (SD 15.3) for LC, but negative during Epi stimulation [-25.3% (SD 45.5)], reflecting transpulmonary production via conversion of mixed central venous pyruvate to arterial lactate.
Why it matters
This study demonstrates that the lungs actively participate in dynamic whole-body lactate shuttling rather than serving as passive transit conduits. It shows that simple arteriovenous concentration differences mask substantial concurrent parenchymal uptake and release, especially during adrenergic stress.
Limits
The study was conducted entirely in anesthetized rats, limiting direct translation to human physiology or awake states. The abstract does not report the total sample size (n). Several outcome parameters exhibited large standard deviations indicating high measurement variability.
Cited by
- supports When pyruvate is infused intravenously, red blood cells and the lungs convert it to lactate within seconds to a minute in one circulatory passage.