Introduction Hepatic Fuel Metabolism During Exercise 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.

Hepatic 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%, 4hr  50%)

Hepatic Fuel Metabolism During Exercise (cont.) C.) Absorptive State  Gluconeogenesis (in fasted subjects) D.) Training  liver glycogen stores Rest1 hr3-4 hr 10% Gluconeogenesis25%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

–4. Regulation of hepatic glucose output (cont.) Hepatic Fuel Metabolism During Exercise (cont.) C. EPI  insulin (which would inhibit glycogenolysis)  Glycogenolysis via c-AMP Glucagon  Glycogenolysis in liver via c-AMP  Gluconeogenesis Cortisol  Plasma AA

Hepatic 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 4hr: Glycogen 55% Gluconeogenesis 40 min: Glycogen 75% Gluconeogenesis 25% 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 , 1975.