Cerebral lactate uptake during exercise is driven by the increased arterial lactate concentration

Area of Science:

• Exercise Physiology
• Neuroscience
• Metabolism

Background:

• The brain utilizes lactate as an alternative fuel source during exercise.
• Previous studies suggested beta-adrenergic pathways control cerebral lactate uptake.
• Propranolol's effect on cerebral lactate uptake was previously attributed to beta-adrenergic blockade.

Purpose of the Study:

• To investigate whether propranolol reduces cerebral lactate uptake by decreasing arterial lactate concentration.
• To differentiate between passive diffusion and active transport mechanisms for cerebral lactate uptake during exercise.

Main Methods:

• Nine healthy males underwent incremental cycling exercise to exhaustion.
• Arterial and internal jugular venous blood lactate concentrations were measured.
• Fractional extraction of lactate (FE_Lac) was calculated, accounting for arterial lactate levels.

Main Results:

• Propranolol significantly reduced arterial lactate concentration during exercise.
• Arterio-jugular venous lactate difference (AV_Lac) and FE_Lac increased with exercise intensity.
• Neither AV_Lac nor FE_Lac were affected by propranolol, irrespective of workload or arterial lactate concentration.

Conclusions:

• Propranolol's reduction in cerebral lactate uptake is due to decreased arterial lactate, not direct beta-adrenergic inhibition.
• Cerebral lactate uptake during exercise is primarily driven by passive diffusion, influenced by arterial lactate concentration.
• The brain's lactate uptake during exercise is not mediated by a beta-adrenergic mechanism.