Download Hepatic Fuel Metabolism During Exercise

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%, 4hr50%)
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.