• 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%, 4hr50%)

Hepatic Fuel Metabolism During Exercise (cont.)C.) Absorptive State

Gluconeogenesis (in fasted subjects)

D.) Training liver glycogen stores

Rest 1 hr 3-4 hr 10% Gluconeogenesis 25% 50%

Hepatic Fuel Metabolism During Exercise (cont.)

– 4. Regulation of hepatic glucose output

A. Feedback systems unlikelyNo 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 Times

@ 4hr:Glycogen 55%Gluconeogenesis 45%

@ 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. 144-153, 1975.