Transpulmonary pyruvate kinetics.
Level 5 - mechanism / opinion, no new human data
Animal model physiology study
PubMed 21677271 · doi:10.1152/ajpregu.00206.2011
What was done
Transpulmonary pyruvate kinetics were evaluated in an anesthetized rat model under three experimental conditions: unstimulated control (Con), lactate clamp (LC), and epinephrine infusion (Epi). A primed-continuous infusion of [U-¹³C]pyruvate was used to quantify transpulmonary extraction, net balance, and release across the pulmonary circulation. Monocarboxylate transporter (MCT) isoforms in whole lung homogenates were evaluated using Western blot analysis.
What was found
Lactate clamp significantly increased mixed central venous and arterial pyruvate concentrations compared to Con and Epi (P < 0.05). Transpulmonary net pyruvate balance was positive in all three conditions, indicating net uptake, and was significantly greater during Epi than Con (P < 0.05). Tracer-measured pyruvate fractional extraction averaged 42.8 ± 5.8% across all conditions and was significantly higher during Epi compared to Con or LC (P < 0.05). Pyruvate total release was significantly higher during Epi (400 ± 100 μg/min) compared to Con (30 ± 20 μg/min) (P < 0.05). Western blot analysis detected MCT1, MCT2, and MCT4 in lung tissue.
Why it matters
These findings show that the pulmonary circulation is an active site of simultaneous pyruvate uptake and release, indicating that lungs contribute substantially to whole-body carbohydrate intermediary metabolism rather than serving as passive transit conduits.
Limits
The study was conducted entirely in an anesthetized rat model, limiting direct extrapolation to conscious human physiology. The abstract does not specify the sample size (n) or exact animal numbers, nor does it detail the intracellular metabolic fate of the extracted pyruvate.
Cited by
- partial When pyruvate is infused intravenously, red blood cells and the lungs convert it to lactate within seconds to a minute in one circulatory passage.