Metabolic and cardiorespiratory responses to "the lactate clamp"

Area of Science:

• Exercise Physiology
• Metabolic Regulation
• Sports Science

Background:

• Gluconeogenesis (GNG) is crucial for maintaining blood glucose during prolonged exercise.
• The role of precursor supply, particularly lactate, in regulating GNG during exercise remains debated.
• Training adaptations can alter substrate utilization and metabolic responses during physical activity.

Purpose of the Study:

• To investigate if precursor supply limits gluconeogenesis during exercise.
• To examine training-induced changes in glucose kinetics, oxidation, and recycling.
• To determine the effect of exogenous lactate infusion on glucose metabolism at rest and during exercise.

Main Methods:

• Utilized a combination of control and lactate-clamped trials (LC) at rest and during submaximal exercise.
• Measured glucose kinetics, including rates of appearance (R(a)), disappearance (R(d)), oxidation (R(ox)), and recycling (R(r)).
• Assessed responses before and after a training intervention at absolute and relative exercise intensities.

Main Results:

• Exogenous lactate infusion did not alter glucose R(a) or R(d) in any condition.
• Glucose recycling (R(r)) remained unchanged with lactate clamping at rest and during exercise.
• Lactate clamping significantly decreased glucose R(ox) during post-training exercise at absolute intensity and rest, indicating increased reliance on other carbohydrate sources.

Conclusions:

• Increased arterial lactate availability does not stimulate glucose production or recycling during rest or exercise post-training.
• Glucose disposal and production are not limited by precursor supply under these conditions.
• Exogenous lactate infusion leads to a reduction in glucose oxidation, favoring alternative carbohydrate utilization.