Fatty acid and glucose utilization in isolated, working newborn pig hearts

The effects of exogenous fatty acids on glucose uptake were assessed in isolated, working newborn pig hearts in which great vessel pressures were controlled (mean 55 mmHg) and oxygenated nutrient buffer was recirculated through the heart for 30 or 60 min. When palmitate (1.5 mM) or octanoate (1.0 mM) were added to buffer containing 10 mM glucose and 100 mU insulin/ml, glucose uptake, as measured by 3H2O production from D-[2-3H]glucose, was suppressed to less than one-half that observed when glucose alone was present. Increased tissue levels of glucose 6-phosphate, fructose 6-phosphate, and citrate following perfusion in the presence of exogenous fatty acids were consistent with decreased glycolytic activity due to inhibition of phosphofructokinase. Measurements of carnitine in perfused and unperfused hearts indicated that total carnitine levels in neonatal hearts are similar to those of adult pigs. Increased tissue levels of long-chain acyl carnitine, acetyl carnitine, and citrate in hearts perfused with palmitate and glucose in combination with extensive fatty acid uptake and marked suppression of glycolysis indicated that the newborn pig heart is capable of utilizing fatty acids as a primary energy source.