Hormone regulation during exercise Flashcards
What are the sizes of the different stores of energy in the body?
Triglyceride= 400mj
Usable protein = 100mj
Liver glycogen= 2.4mj
Blood glucose= 0.16mj
Daily needs= 12mj
What are the factors that are affecting fuel use?
- Fat is more dense, 10 times as much energy per gram (wet weight), best long term store
- Fats can ONLY be metabolised aerobically, ATP production is intrinsically slow, can’t meet high energy demands
- Fats power gentle “routine” physical activity, shift towards aerobic oxidation of carbohydrates as work rate rises.
- Anaerobic glycolysis is used at the highest work rates, but these can only be sustained for very short times.
What are the main hormones involved in the control of energy use?
Insulin, glucagon/adernaline, growth hormone, cortisol, TNF-a and IL-1
How is AMP made?
ADP + ADP —> ATP +AMP
What does increased levels of AMP indicate?
[AMP] is a sensitive indicator of cellular energy stress, activates AMPK
How is cAMP made?
ATP –> cAMP +PP
What is the reaction that created cAMP catalysed by?
This is catalysed by adenylate cyclase and is a second messenger for some G-protein coupled receptors, activates PKA
What is the role of AMP kinase?
It controls fuel use
How does cyclic AMP work?
Cyclic AMP is a Second Messenger
Hormone binding activates a G-protein
G-protein activates adenylate cyclase
[cAMP] rises
Protein Kinase A activated and activates other proteins
Glucagon and β-adrenergic receptors act in this way
What is the effect of inulin on the muscle, adipose tissue and liver?
MUSCLE Enhances -glucose uptake by GLUT 4 -Glycogen synthesis -glycogenesis -amino acid uptake -enhance protein synthesis
Inhibits
- gluconeogenesis (protein degradation)
- glycogenolysis
ADIPOSE Increase glucose uptake but GLUT 4 Increase lipogenesis decrease lipolysis Decreases FFA release
LIVER Increase glycogen synthesis Increase Lipogenesis Increases protein synthesis Decrease gluconeogenesis Decreases glucose release Decreases glycogenolysis
What is the effect of glucagon on the muscle, adipose tissue and liver?
MUSCLE
No effect
ADIPOSE
Increased lipolysis
LIVER
Decreased glycogen synthesis
Increased glycogenolysis
Increase gluconeogenesis
What is the effect of epinephrine on the muscle, adipose tissue and liver?
MUSCLE
Increased glycogenolysis
ADIPOSE TISSUE
increased lipolysis
LIVER
decreased glycogen synthesis
increased glycogenolysis
increased gluconeogenesis
How does the uptake of glucose controlled?
Exercise increases insulin sensitivity, and independently stimulates vesicle recycling.
What is the action of glucagon?
Binds to the glucagon receptor in the liver and adipose tissue.
Activates second messenger signalling via cAMP.
Activates protein kinase A.
What two pathways does glucagon act to control?
- Stimulates breakdown of hepatic glycogen.
2. Activates hepatic gluconeogenesis
How does glucagon work?
Glucagon binds to a receptor causing GTP exchange which activated AMP cyclase which creates cAMP which creates protein kinase A which leads to gluconeogenesis and glycogen breakdown
When are catecholamines secreted?
Secreted from the medulla of the adrenal gland in response to sympathetic nervous system stimulation
Secreted in response to low blood glucose, exercise and fear. Relative exercise has to be >50% VO2 max.
What effects do catecholamines have on the body?
Systemic effects throughout the body, including stimulation of heart rate contractility and alteration of blood vessel diameter.
What is the overall action of adrenaline?
Stimulates use of glucose in the muscles but production of glucose in the liver
Stimulates lipolysis and fat uptake by muscles
Large range of physiological effects all supportive of exercise
Two different receptors which act via different mechanisms
Suppresses the release of insulin and stimulates the release of glucagon
Dominant hormone during intense exercise
How is fat released as a fuel source?
Cannot be made available through anaerobic metabolism at high rates but is released fairly slowly in the process of being converted to CO2 and H2O.
What is lipolysis?
The breakdown of triglycerides into fatty acids and glycerol components.
What controls lipolysis and how is it activated?
Initial reaction is catabolised by a hormone sensitive lipase.
Adrenaline and glucagon raise cAMP levels, activating protein kinase A, which phosphorylates and activates hormone sensitive lipase.
Insulin signalling counteracts this to lower levels of cAMP – to inhibit lipase activity.
What is released under extended stress?
Cortisol
What is the biochemistry of cortisol?
-Steroid hormone produced by the adrenal cortex when stimulated by the polypeptide ACTH from the anterior pituitary
-Acts upon the nucleus of cells in response to stressful situations, exercise, injury, infection, lack of food
Immunosuppressive
What is the effect of cortisol?
– Stimulate FFA mobilization from adipose tissue
– Enhance gluconeogenesis in the liver
– Decrease the rate of glucose utilisation by cells
-Mobilizes tissue amino acids
-Blocks entry of glucose into tissues
- Leads to an increased level of glucose and FFA in the blood
What is the exercise effect of cortisol?
– Decrease during low-intensity exercise
– Increase during high-intensity exercise
-Above ~60% VO2 max
Where and when is somatotropin secreted??
Somatotropin is a polypeptide hormone secreted by specific cells in the anterior pituitary, in response to signals from the hypothalamus
What is somatotropin?
A growth hormone
What is the effect of exercise on somatotropin?
increase in plasma GH with increased intensity
greater response in trained runners
How do growth hormones work?
Growth hormone stimulates tissues to produce insulin-like growth factor (IGF) which mediates the direct effects
Main effects are anabolic, supporting muscle growth and repair
Decreases glucose uptake increases fatty acid mobilisation
Increases amino acid uptake and protein synthesis (opposite to cortisol)
Complementary to cortisol
What are the 2 forms of IGF?
IGF-1 Released in response to Growth Hormone stimulation
IGF-2 stimulates embryonic growth and is secreted in adults but function unknown
What is myostatin?
Myostatin is a cytokine produced by muscle which autoregulates muscle mass by inhibiting mesenchymal stem cell proliferation and differentiation.
Myostatin-null animals have increased bone density and double the normal muscle mass, heterozygotes may show enhanced athletic performance.
What is the effect of anabolic steroids?
Steroid hormones such as testosterone (and, allegedly, its precursor androstenedione) increase muscle mass in response to training against a resistive load.
They may also increase aggression and the “will to win”.
Testosterone forms part of a negative feedback loop which regulates the secretion of pituitary gonadotropins such as FSH and LH. These peptide hormones from the anterior pituitary are important for normal sexual function in both men and women.
What is a side effect of anabolic steroids?
One side-effect of anabolic steroid abuse is a marked reduction in FSH and LH, which paradoxically reduces testicular volume and sperm counts.
What does IL-6 cause?
IL-6 causes the liver to secrete a number of “acute phase proteins” such as C-reactive protein, which are inflammatory markers.
Where is IL-6 released from?
IL-6 is secreted by exercising muscle independent of muscle damage
What happens in IL-6 deficient mice?
IL-6 deficient mice become obese in adulthood relieved by IL-6
Appears to help mobilise fat, glucose and cortisol during exercise
Overall what are the fast acting hormones>
plasma glucose is regulated during exercise through the actions of insulin, glucagon and adrenaline.
glucagon and adrenaline have similar properties but act on different tissues.
Glucagon results in release of glucose to the blood from the liver. Adrenaline retains glucose in the muscle.
adrenaline and noradrenaline both aid and control the actions of insulin and glucagon.
Overall what are the slow acting hormones?
The actions of cortisol and growth hormone act in a permissive manner to support the actions of other hormones during exercise.
Growth hormone and cortisol also provide a “slow acting” effect on carbohydrate and fat metabolism during exercise.
Anabolic Steroidal hormones and Growth hormone promote growth and repair in response to exercise
Myostatin limits muscle growth
