Lactate, glucose and O₂ uptake in human brain during recovery from maximal exercise

Abstract

The metabolic activity of the brain has not been evaluated during physical exercise. In six volunteers substrate uptake by the brain was determined during graded exercise and recovery from maximal exercise by measuring the arterial‐internal jugular venous concentration differences(a–v differences). The a–v difference for lactate increased from 0.02 ± 0.08 mmol l−1 at rest to 0.39 ± 0.13 mmol l−1 during exercise and remained positive during 30 min of recovery (P < 0.05). The a–v difference for glucose (0.55 ± 0.06 mmol l−1 at rest) did not change significantly during exercise, but during the initial 5 min of recovery it increased to 0.83 ± 0.10 mmol l−1 (P < 0.05). The O2 a–v difference at rest of 3.11 ± 0.30 mmol l−1 remained stable during exercise, then increased during the initial 5 min of recovery (3.77 ± 0.52 mmol l−1) and remained high during the subsequent 30 min recovery period (3.62 ± 0.64 mmol l−1; P < 0.05). Thus the O2/glucose uptake ratio did not change during exercise (pre‐exercise 5.95 ± 0.68; post‐exercise 6.02 ± 1.39) but decreased to 4.93 ± 0.99 during the initial 5 min of recovery (P < 0.05). When lactate uptake was included, the resting O2/carbohydrate uptake ratio of 5.84 ± 0.73 was reduced to 4.42 ± 0.25 during exercise and decreased further during the recovery phase (to 3.79 ± 0.30; P < 0.05). In contrast, in the resting and immobilised rat, lactate infusion to a level similar to that obtained during maximal exercise in humans did not affect the a–v difference for lactate. The large carbohydrate uptake by the brain during recovery from maximal exercise suggests that brain glycogen metabolism is important in the transition from rest to exercise, since this would explain the significant post‐exercise decrease in the O2/carbohydrate uptake ratio.

Neurohumoral responses during prolonged exercise in humans

“…The reduced cerebral oxygen-to-carbohydrate uptake ratio during recovery from the hyperthermic trial was established via a marked increase in the a-vD glucose , whereas there was no net uptake of lactate by the brain. Reductions in the oxygen-to-carbohydrate uptake ratio are observed after exhaustive, high-intensity exercise (29) and during recovery from exercise in which the "mental effort" associated with exercise is enhanced by partial neuromuscular blockade (11) or by obstructing blood flow to the exercising legs (12). In those studies, the arterial lactate concentration increased severalfold during exercise, and the reduced oxygen-to-carbohydrate ratio during the recovery was associated with a relatively large lactate uptake by the brain.…”

“…40 for review). Dopamine transport across the brain-blood barrier may be limited (2, 26), but dopamine from several hypothalamic nerve tracts is released into the hypophysial portal blood (23), and increased dopaminergic activity could result in dopamine spillover from the brain.In addition to neurotransmitter alterations, central fatigue could relate to depletion of brain glycogen stores (11,29). This hypothesis is based on the observation that, during recovery from exercise involving a maximal effort, the cerebral oxygen-to-carbohydrate uptake ratio becomes low as the cerebral glucose and lactate uptake increase out of proportion to the cerebral oxygen uptake.…”

“…In addition to neurotransmitter alterations, central fatigue could relate to depletion of brain glycogen stores (11,29). This hypothesis is based on the observation that, during recovery from exercise involving a maximal effort, the cerebral oxygen-to-carbohydrate uptake ratio becomes low as the cerebral glucose and lactate uptake increase out of proportion to the cerebral oxygen uptake.…”

Brain Lactate Metabolism: The Discoveries and the Controversies

“…During strenuous physical work, human plasma lactate increases from B0.5 to 1 mmol/L to 20 to 30 mmol/L, and whole-brain studies of metabolic activity during exercise reveal progressive increases in brain lactate uptake and metabolism as work load and plasma lactate levels increase (Ide et al, 1999(Ide et al, , 2000. Blood lactate is oxidized in the brain and more glucose is also consumed during exhaustive exercise, (Cremer et al, 1983;Hargreaves et al, 1986), lactate release and its use as a blood flow regulator need not be a 'waste' of fuel, because lactate can be used by peripheral tissues as fuel or as a gluconeogenic substrate.…”

“…During strenuous physical work, human plasma lactate increases from B0.5 to 1 mmol/L to 20 to 30 mmol/L, and whole-brain studies of metabolic activity during exercise reveal progressive increases in brain lactate uptake and metabolism as work load and plasma lactate levels increase (Ide et al, 1999(Ide et al, , 2000. Blood lactate is oxidized in the brain and more glucose is also consumed during exhaustive exercise, Brain lactate metabolism GA Dienel but there is also a decline in the oxygen/(glucose + 1 2 lactate) utilization ratio from B6 to as low as 1.7, and there is a large, unexplained excess carbohydrate taken up into brain that is not accounted for by oxidative metabolism or tissue metabolite accumulation or release (Dalsgaard, 2006;Quistorff et al, 2008;van Hall et al, 2009).…”