Physiologic hyperinsulinemia stimulates lactate extraction by heart muscle in the conscious dog

The effect of physiologic hyperinsulinemia on the net balance of lactate, glucose, and free fatty acids across the heart was studied in eight normal postabsorptive conscious dogs. After obtaining basal measurements of myocardial substrate balance, arterial plasma insulin was increased from 8 +/- 1 to 68 +/- 14 microU/mL while blood glucose was maintained constant (64 +/- 1 mg/dL) using the hyperinsulinemic euglycemic clamp. Myocardial lactate uptake increased nearly fourfold, from 5.8 +/- 1.8 to 22.4 +/- 2.9 mumol/min (P less than .005). Despite a small increase in arterial lactate concentration from 0.46 +/- 0.08 to 0.79 +/- 0.11 mmol/L (P less than .02), the lactate extraction fraction increased from 23% +/- 7% to 54% +/- 2% (P less than .001) indicating an increased efficiency of lactate extraction. Euglycemic hyperinsulinemia led to a comparable increase in myocardial glucose uptake (6.7 +/- 2.3 to 18.2 +/- 3.7 mumol/min, P less than .05). Arterial free fatty acid concentrations fell from 1.06 +/- 0.13 to 0.35 +/- 0.06 mmol/L (P less than .001) with a concomitant decline in the myocardial uptake of free fatty acids from 18.5 +/- 5.3 to 5.8 +/- 2.9 mumol/min (P less than .05). These results indicate that physiologic hyperinsulinemia increases lactate as well as glucose uptake in normal heart muscle.