The blood lactate/pyruvate equilibrium affair.

Area of Science:

• Biochemistry
• Physiology
• Metabolic Research

Background:

• The Lactate Shuttle hypothesis explains lactate transport and utilization.
• Mass spectrometry with carbon-labeled tracers is used to study metabolic fluxes.
• Controversy exists regarding whether lactate tracers reflect lactate or pyruvate turnover.

Purpose of the Study:

• To review analytical errors and methodological limitations in using carbon-labeled lactate tracers.
• To clarify whether these tracers accurately measure lactate (L) or pyruvate (P) turnover.
• To validate the use of lactate tracers for quantifying lactate fluxes.

Main Methods:

• Review of analytical errors, tissue/animal models, and sampling sites.
• Consideration of lactate and pyruvate pool sizes in modeling.
• Support from magnetic resonance spectroscopy (MRS) and immunocytochemistry.

Main Results:

• Identified analytical errors, inappropriate models, and sampling issues.
• Highlighted the importance of considering L and P pool sizes and heart/lung interactions.
• Demonstrated that carbon-labeled lactate tracers can accurately quantify lactate fluxes.

Conclusions:

• Carbon-labeled lactate tracers are valid tools for quantifying lactate fluxes.
• Addressing methodological challenges ensures accurate interpretation of tracer data.
• The Lactate Shuttle hypothesis can be reliably studied using these techniques.