Cerebral lactate uptake during exercise is driven by the increased arterial lactate concentration.
Level 3 - non-randomized controlled study
Small non-randomized/unspecified crossover physiological trial in healthy humans
PubMed 34734784 · doi:10.1152/japplphysiol.00505.2021
What was done
Nine healthy males performed incremental cycling exercise to exhaustion with and without intravenous non-specific β-adrenergic blockade (propranolol, 18.7 ± 1.9 mg). Arterial and internal jugular venous lactate concentrations were measured at the end of each workload. Researchers calculated the arterio-jugular venous lactate difference (AV Lac) and fractional extraction (FE Lac, defined as AV Lac divided by arterial lactate concentration) to evaluate whether β-adrenergic blockade influences cerebral lactate uptake independently of arterial supply.
What was found
Propranolol significantly decreased arterial lactate concentration across all workloads (P < 0.05), reaching 11 ± 3 mmol·l⁻¹ during maximal exercise compared to 14 ± 3 mmol·l⁻¹ without blockade. Both AV Lac and FE Lac increased with exercise (both P < 0.05), but neither metric was significantly altered by propranolol at any workload (P = 0.68 and P = 0.26) or for any matched arterial lactate concentration (P = 0.78 and P = 0.22).
Why it matters
These results clarify that cerebral lactate uptake during exercise is a passive process dictated by the concentration gradient from circulating arterial lactate, resolving prior speculation that β-adrenergic signaling directly modulates brain lactate transport.
Limits
The study included a very small sample (n = 9) limited exclusively to healthy males. The abstract does not specify whether the condition order was randomized or blinded. Cerebral blood flow was not reported in the abstract, relying on fractional extraction rather than total volumetric flux.
Cited by
- supports Human studies show that lactate generated from vigorous exercise crosses into the brain.