Metabolism of glucose-U-C14 in perfused rat heart

A closed perfusion system was designed to study C 14 O 2 formation during uptake of glucose-U-C 14 by the isolated, beating rat heart. An initial period of 5 min of preperfusion with oxygenated buffer allowed stabilization of the heart before 30 min of perfusion in the closed recirculation system. Oxygenation was adequate as judged by cardiac rate and force, the pattern of glucose metabolism, the rate of glycogenolysis, and the perfusate oxygen content. Glucose uptake increased sharply with increasing perfusate glucose concentrations over the range 1.25– 5 mm glucose, with a lesser rise in the 5–10 mm range and very little rise from 10–40 mm. Glucose oxidation, which accounted for 60% of the glucose uptake at 1.25 mm glucose concentration, reached a maximal rate at 5–10 mm. This maximal rate accounted for only 24% of the glucose uptake at 40 mm, indicating the increasing importance of nonoxidative fates of glucose with increasing glucose uptake. Lactate and net glycogen formation, and incorporation of glucose carbon into glycogen, were least at lowest glucose concentrations and increased irregularly as the glucose concentration rose. Uptake and oxidation of fructose-U-C 14 (5 mm) was much less than that of glucose.