Prior exercise and postprandial substrate extraction across the human leg.

Prior exercise decreases postprandial plasma triacylglycerol (TG) concentrations, possibly through changes to skeletal muscle TG extraction. We measured postprandial substrate extraction across the leg in eight normolipidemic men aged 21-46 yr. On the afternoon preceding one trial, subjects ran for 2 h at 64 +/- 1% of maximal oxygen uptake (exercise); before the control trial, subjects had refrained from exercise. Samples of femoral arterial and venous blood were obtained, and leg blood flow was measured in the fasting state and for 6 h after a meal (1.2 g fat, 1.2 g carbohydrate/kg body mass). Prior exercise increased time averaged postprandial TG clearance across the leg (total TG: control, 0.079 +/- 0.014 ml.100 ml tissue(-1).min(-1) ; exercise, 0.158 +/- 0.023 ml.100 ml tissue(-1).min(-1), P <0.01), particularly in the chylomicron fraction, so that absolute TG uptake was maintained despite lower plasma TG concentrations (control, 1.53 +/- 0.13 mmol/l; exercise, 1.01 +/- 0.16 mmol/l, P < 0.001). Prior exercise increased postprandial leg blood flow and glucose uptake (both P < 0.05). Mechanisms other than increased leg TG uptake must account for the effect of prior exercise on postprandial lipemia.