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Hepatic Fuel Metabolism During Exercise • Introduction 1. Since 1961, numerous studies show in hepatic glucose output with exercise 2. Blood glucose stays the same or until liver glycogen depletion thus mechanisms other than just feedback regulation must be occurring. glucose production during exercise 40 umol/min/kg x 70 kg = 3 mmol/min 25 mmol in blood volume Feedback Control of Blood Glucose at rest. Hepatic Fuel Metabolism During Exercise (cont.) – 3. Glucose output : Glycogenolysis vs. Gluconeogenesis A.) Intensity Glycogenolysis SBF Gluconeogenesis B.) Duration Gluconeogenesis (after 1 hr accounts for 30%, 4hr50%) Hepatic Fuel Metabolism During Exercise (cont.) C.) Absorptive State Gluconeogenesis (in fasted subjects) D.) Training liver glycogen stores Rest 10% Gluconeogenesis 1 hr 25% 3-4 hr 50% Hepatic Fuel Metabolism During Exercise (cont.) – 4. Regulation of hepatic glucose output A. Feedback systems unlikely No change or in blood glucose B. Feedforward system Curare model (fig 3.4) Epidural block/electrical stimulation glucose uptake glucose output blood glucose Hepatic Fuel Metabolism During Exercise (cont.) – 4. Regulation of hepatic glucose output (cont.) C. EPI insulin (which would inhibit glycogenolysis) Glycogenolysis via c-AMP Glucagon Glycogenolysis in liver via c-AMP Gluconeogenesis Cortisol Plasma AA glucose production during exercise 40 umol/min/kg x 70 kg = 3 mmol/min 25 mmol in blood volume Liver Contributes Glucose via Glycogenolysis and Gluconeogenesis at Different Times @ 40 min: Glycogen 75% Gluconeogenesis 25% @ 4hr: Glycogen 55% Gluconeogenesis 45% Wahen, et., al., Splanchnic and leg metabolism of glucose, free fatty acids and amino acids during prolonged exercise in man, In Metabolic Adaptations to Prolonged Physical Exercise, Eds. Howald andPoortmans, Birkhauser Verlag Basel, pp. 144-153, 1975.