Gluconeogenesis in humans with induced hyperlactatemia during low-intensity exercise

Area of Science:

• Human Physiology
• Metabolic Regulation
• Exercise Science

Background:

• Gluconeogenesis (GNG) is crucial for maintaining blood glucose homeostasis, especially during fasting and exercise.
• The role of lactate as a substrate for GNG during exercise in humans requires further elucidation.

Purpose of the Study:

• To investigate the contribution of lactate to gluconeogenesis during low-intensity exercise in untrained, fasting humans.
• To determine the effect of exogenous lactate administration on glucose production and blood glucose levels during exercise.

Main Methods:

• Seven untrained subjects underwent a 4-hour cycle exercise at 33-34% maximal O(2) uptake.
• Subjects received either sodium lactate or sodium bicarbonate infusion during the final hour.
• Deuterium labeling of body water and [6,6-(2)H(2)]glucose dilution were used to quantify GNG and glucose rate of appearance (R(a)).

Main Results:

• Lactate infusion increased plasma lactate concentration and abolished the exercise-induced decrease in blood glucose.
• Glucose R(a) was significantly higher with lactate infusion compared to bicarbonate.
• Lactate infusion increased the contribution of lactate to GNG and overall GNG, sustaining blood glucose levels.

Conclusions:

• Lactate infusion during low-intensity exercise in fasting humans increases gluconeogenesis from lactate and enhances overall glucose production.
• This demonstrates that gluconeogenic capacity is available post-fasting and can be utilized to sustain blood glucose levels when lactate is elevated.
• Lactate serves as a significant precursor for glucose production during exercise in humans.