MCA Vmean and the arterial lactate-to-pyruvate ratio correlate during rhythmic handgrip

Regulation of cerebral blood flow during physiological activation including exercise remains unknown but may be related to the arterial lactate-topyruvate (L/P) ratio. We evaluated whether an exercise-induced increase in middle cerebral artery mean velocity (MCA V-mean) relates to the arterial L/P ratio at two plasma lactate levels. MCA V-mean was determined by ultrasound Doppler sonography at rest, during 10 min of rhythmic handgrip exercise at similar to 65% of maximal voluntary contraction force, and during 20 min of recovery in seven healthy male volunteers during control and a similar to 15 mmol/l hyperglycemic clamp. Cerebral arteriovenous differences for metabolites were obtained by brachial artery and retrograde jugular venous catheterization. Control resting arterial lactate was 0.78 +/- 0.09 mmol/l (mean SE) and pyruvate 55.7 +/- 12.0 mu mol/1 (L/P ratio 16.4 +/- 1.0) with a corresponding MCA V-mean of 46.7 +/- 4.5 cm/s. During rhythmic handgrip the increase in MCA V-mean to 51.2 +/- 4.6 cm/s was related to the increased L/P ratio (23.8 +/- 2.5; r(2) = 0.79; P < 0.01). Hyperglycemia increased arterial lactate and pyruvate to 1.9 +/- 0.2 mmolA and 115 +/- 4 mu mol/l, respectively, but it did not significantly influence the L/P ratio or MCA V-mean at rest or during exercise. Conversely, MCA V-mean did not correlate significantly, neither to the arterial lactate nor to the pyruvate concentrations. These results support that the arterial plasma L/P ratio modulates cerebral blood flow during cerebral activation independently from the plasma glucose concentration.