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-to-pyruvate (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 ∼65% of maximal voluntary contraction force, and during 20 min of recovery in seven healthy male volunteers during control and a ∼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 p.mol/l (LIP 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; r² = 0.79; P < 0.01). Hyperglycemia increased arterial lactate and pyruvate to 1.9 ± 0.2 mmol/l and 115 ± 4 μmol/1, 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 LIP ratio modulates cerebral blood flow during cerebral activation independently from the plasma glucose concentration. [ABSTRACT FROM AUTHOR]