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

Abstract

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 μU/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 μmol/min ( P < .005). Despite a small increase in arterial lactate concentration from 0.46 ± 0.08 to 0.79 ± 0.11 mmol/L ( P < .02), the lactate extraction fraction increased from 23% ± 7% to 54% ± 2% ( P < .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 μmol/min, P < .05). Arterial free fatty acid concentrations fell from 1.06 ± 0.13 to 0.35 ± 0.06 mmol/L ( P < .001) with a concomitant decline in the myocardial uptake of free fatty acids from 18.5 ± 5.3 to 5.8 ± 2.9 μmol/min ( P < .05). These results indicate that physiologic hyperinsulinemia increases lactate as well as glucose uptake in normal heart muscle.