NONGLUCOSE SUBSTRATES INCREASE GLYCOGEN-SYNTHESIS IN-VIVO IN DOG HEART

The effects of circulating nonglucose substrates on insulin-stimulated cardiac glycogen synthesis were studied in the dog heart in vivo usin g C-13-nuclear magnetic resonance (-NMR) and arteriovenous difference techniques. [1-C-13]glycogen was monitored in hearts during an intrave nous infusion of 20 mU/min insulin and glucose while [1-C-13]glucose ( 10 mg/min) was infused into the left anterior descending coronary arte ry. When 1 mmol/ min of lactate, pyruvate, or P-hydroxybutyrate was ad ded to the venous infusion, the measured rate of glycogen synthesis wa s increased, on average, sixfold. It was not increased further after a subsequent 10-min infusion of 5 mu g/min epinephrine. Lactate extract ion increased from 0.18 +/- 0.05 to 0.62 +/- 0.11 mu mol . min(-1) . g wet wt(-1) during lactate infusion, whereas glucose extraction did no t change significantly (0.15 +/- 0.05 mu mol . min(-1) . g wet wt(-1) at 45 min of insulin and glucose infusion to 0.09 +/- 0.02 mu mol . mi n(-1) g wet wt(-1) at 45 min of the lactate infusion). Therefore, the uptake and oxidation of circulating nonglucose substrates redirects th e fate of extracted glucose from glycolysis to glycogen synthesis in t he dog heart in vivo.