Hormonal Responses to Exercise III – Hormonal Regulation of Metabolism
I.
Review: HOW hormones work
A. Hormones bring about effects
by:
1. Altering membrane transport
2. Activating DNA transcription
to increase protein synthesis
3. Activating second messengers
• Cyclic AMP
• Ca++
• Inositol
triphosphate
• Diacylglycerol
II. Blood Glucose Homeostasis During Exercise
A. Fast-acting hormones
1. Norepinephrine and
epinephrine
Increase linearly during exercise
Favor the mobilization of FFA and maintenance of plasma glucose
E/NE Control of Insulin and Glucagon
Secretion During Exercise
Effect of aerobic training on norep and ep during exercise
2. Insulin and glucagon
Plasma insulin decreases during exercise
Prevents rapid uptake of plasma glucose
Favors mobilization of glucose and FFA
B. Maintenance of plasma glucose
1. Mobilization of glucose from
liver glycogen stores
2. Mobilization of FFA from
adipose tissue
3. Gluconeogenesis from amino
acids, lactic acid, and glycerol
4. Block entry of glucose into
non-CNS cells
C. Permissive and slow-acting
hormones
1. Thyroxine
2. Cortisol
Control of cortisol secretion
Role of cortisol in maintenance of
plasma glucose
3. Growth hormone
Role of GH in mainenance of plasma
glucose
4. Act to support actions of
other hormones
D. Muscle Glycogen Utilization
1. Glycogen breakdown is related
to exercise intensity
- High-intensity exercise
results in greater and more rapid glycogen depletion
2. Control of Glycogenolysis
- Breakdown of muscle glycogen
is under dual control
- Epinephrine-cyclic AMP
- Ca++-calmodulin
•
Delivery of
glucose parallels activation of muscle contraction
- Glycogenolysis can still occur in presence of b-blocking agent
- Changes in Muscle Glycogen With and
Without b-Blockade
E. Free Fatty Acid Mobilization During Exercise
1. FFA mobilization decreases
during heavy exercise
2. This occurs in spite of persisting hormonal
stimulation for FFA mobilization
3. Could be due to high levels
of lactic acid
– Promotes resynthesis of triglycerides