The impact of physiological insulin concentration and depletion on the metabolism of glucose, endogenous glycogen, and triglycerides in the isolated perfused heart

In isolated nonworking hearts perfused with substrate-free medium for 90 min, 2000 microU insulin.mL-1 reduced the rates of glycogenolysis and lipolysis, whereas 50 microU insulin.mL-1 reduced the rate of lipolysis with no significant effect on glycogenolysis. Glycogen and triglycerides were the chief energy sources during the course of depletion in the presence and absence of insulin. In hearts perfused with medium containing 5 mM glucose for 3 h, glycogen and triglycerides contributed to the heart energy requirement, but in the presence of insulin (50 or 2000 microU.mL-1) endogenous triglycerides contributed to the heart energy requirement with net glycogen synthesis. In hearts preperfused with substrate-free medium for 90 min and perfused for another 90 min with medium containing 5 mM glucose, the depletion of endogenous glycogen and triglycerides stimulated the utilization of glucose and the synthesis of glycogen and triglycerides. In hearts preperfused with substrate-free medium for 90 min and perfused for another 90 min with medium containing glucose (5 mM) and insulin (50 or 2000 microU.mL-1), insulin enhanced the utilization of glucose and the synthesis of glycogen and triglycerides. Glucose utilization, glycogenolysis, lipolysis, and synthesis of glycogen and triglycerides were sensitive to the physiological insulin concentration and were also affected by the heart content of glycogen and triglycerides, in the isolated nonworking perfused rat heart.