Chapter 5 Hormonal Responses to Exercise

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Chapter 5Hormonal Responses to Exercise

• EXERCISE PHYSIOLOGY
• Theory and Application to Fitness and
  Performance, 6th edition
• Scott K. Powers Edward T. Howley

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Neuroendocrinology

• Neuroendocrine system
• Endocrine system releases hormones
• Nervous system uses neurotransmitters
• Endocrine glands
• Release hormones directly into the blood
• Hormones
• Alter the activity of tissues that possess
  receptors to which the hormone can bind

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Blood Hormone Concentration

• The free plasma hormone concentration determines
  the magnitude of the effect at the tissue level
• Determined by
• Rate of secretion of hormone from endocrine gland
• Magnitude of input
• Stimulatory vs. inhibitory input
• Rate of metabolism or excretion of hormone
• At the receptor and by the liver and kidneys
• Quantity of transport protein
• Steroid hormones
• Changes in plasma volume

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Factors That Influence the Secretion of Hormones
Figure 5.1
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Hormone-Receptor Interactions

• Hormone affect only tissue with specific
  receptors
• Magnitude of effect dependent on
• Concentration of the hormone
• Number of receptors on the cell
• Affinity of the receptor for the hormone
• Downregulation
• Decrease in receptor number in response to high
  concentration of hormone
• Upregulation
• Increase in receptor number in response to low
  concentration of hormone

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Mechanisms of Hormone Action

• Altering membrane transport
• Insulin
• Stimulating DNA to increase protein synthesis
• Steroid hormones
• Activating second messengers via G protein
• Cyclic AMP
• Ca2
• Inositol triphosphate
• Diacylglycerol

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Mechanism of Steroid Hormone Action
Figure 5.2
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Cyclic AMP Second Messenger Mechanism
Figure 5.3
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Calcium and Phospholipase C Second Messenger
Mechanisms
Figure 5.4
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Hormones Regulation and Action

• Hormones are secreted from endocrine glands
• Hypothalamus and pituitary glands
• Thyroid and parathyroid glands
• Adrenal glands
• Pancreas
• Testes and Ovaries

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Hypothalamus and Pituitary Gland

• Hypothalamus
• Controls secretions from pituitary gland
• Anterior Pituitary Gland
• Adrenocorticotropic hormone (ACTH)
• Follicle-stimulating hormone (FSH)
• Luteinizing hormone (LH)
• Melanocyte-stimulating hormone (MSH)
• Thyroid-stimulating hormone (TSH)
• Growth hormone (GH)
• Prolactin
• Posterior Pituitary Gland
• Oxytocin
• Antidiuretic hormone (ADH)

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Hormones Released From the Anterior Pituitary
Gland
Figure 5.5
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Growth Hormone

• Secreted from the anterior pituitary gland
• Stimulates release of insulin-like growth factors
  (IGFs)
• Essential growth of all tissues
• Amino acid uptake and protein synthesis
• Long bone growth
• Spares plasma glucose
• Reduces the use of plasma glucose
• Increases gluconeogenesis
• Mobilizes fatty acids from adipose tissue

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The Influence of the Hypothalamus on Growth
Hormone Secretion
Figure 5.6
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Antidiuretic Hormone

• Reduces water loss from the body to maintain
  plasma volume
• Favors the reabsorption of water from the kidney
• Stimulated by
• High plasma osmolality and low plasma volume
• Due to sweat loss without water replacement

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Change in Plasma ADH Concentration During Exercise
Figure 5.7
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Thyroid Gland

• Stimulated by TSH
• Triiodothyronine (T3) and thyroxine (T4)
• Maintenance of metabolic rate
• Allowing the full effect of other hormones
• Calcitonin
• Regulation of plasma Ca2
• Parathyroid Hormone
• Primary hormone in plasma Ca2 regulation

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Adrenal Medulla

• Secretes the catecholamines
• Epinephrine (E) and norepinephrine (NE)
• Bind to adrenergic receptors
• Alpha (?)
• Beta (?)
• Effects depend on hormone used and receptor type

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Adrenal Cortex

• Aldosterone (mineralcorticoid)
• Control of Na reabsorption and K secretion
• Na/H2O balance
• Regulation of blood volume and blood pressure
• Part of renin-angiotensin-aldosterone system
• Stimulated by
• Increased K concentration
• Decreased plasma volume

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Change in Renin, Angiotensin II, and Aldosterone
During Exercise
Figure 5.8
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Adrenal Cortex

• Cortisol (glucocorticoid)
• Promotes protein breakdown for gluconeogenesis
  and tissue repair
• Stimulates FFA mobilization
• Stimulates glucose synthesis
• Blocks uptake of glucose into cells
• Promotes the use of free fatty acids as fuel
• Stimulated by
• Stress, via ACTH
• Exercise

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Control of Cortisol Secretion
Figure 5.9
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Pancreas

• Both exocrine and endocrine functions
• Secretes
• Insulin (from b cells)
• Promotes the storage of glucose, amino acids, and
  fats
• Glucagon (from a cells)
• Promotes the mobilization of fatty acids and
  glucose
• Somatostatin (from d cells)
• Controls rate of entry of nutrients into the
  circulation
• Digestive enzymes and bicarbonate
• Into the small intestine

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Testes and Ovaries

• Testosterone
• Released from testes
• Anabolic steroid
• Promotes tissue (muscle) building
• Performance enhancement
• Androgenic steroid
• Promotes masculine characteristics
• Estrogen
• Released from ovaries
• Establish and maintain reproductive function
• Levels vary throughout the menstrual cycle

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Control of Testosterone Secretion
Figure 5.10
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Control of Estrogen Secretion
Figure 5.11
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Change in FSH, LH, Progesterone, and Estradiol
During Exercise
Figure 5.12
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Muscle Glycogen Utilization

• Glycogenolysis is related to exercise intensity
• High-intensity of exercise results in greater and
  more rapid glycogen depletion
• Plasma epinephrine is a powerful simulator of
  glycogenolysis
• High-intensity of exercise results in greater
  increases in plasma epinephrine

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Glycogen Depletion During Exercise
Figure 5.13
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Plasma Epinephrine Concentration During Exercise
Figure 5.14
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Control of Muscle Glycogen Utilization

• Breakdown of muscle glycogen is under dual
  control
• Epinephrine-cyclic AMP
• Via b-adrenergic receptors
• Ca2-calmodulin
• Enhanced during exercise due to Ca2 release from
  sarcoplasmic reticulum
• Evidence for role of Ca2-calmodulin in
  glycogenolysis
• Propranolol (b-receptor blocker) has no effect on
  muscle glycogen utilization

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Control of Glycogenolysis
Figure 5.16
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Changes in Muscle Glycogen Before and After
Propranolol Administration
Figure 5.15
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Blood Glucose Homeostasis During Exercise

• Plasma glucose maintained through four processes
• Mobilization of glucose from liver glycogen
  stores
• Mobilization of FFA from adipose tissue
• Spares blood glucose
• Gluconeogenesis from amino acids, lactic acid,
  and glycerol
• Blocking the entry of glucose into cells
• Forces use of FFA as a fuel
• Controlled by hormones
• Permissive or slow-acting
• Fast-acting

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Permissive and Slow-Acting Hormones

• Thyroid hormones
• Act in a permissive manner to support actions of
  other hormones
• Cortisol and growth hormone
• Stimulate FFA mobilization from adipose tissue
• Enhance gluconeogenesis in the liver
• Decrease the rate of glucose utilization by cells

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Role of Cortisol in the Maintenance of Blood
Glucose
Figure 5.17
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Changes in Plasma Cortisol During Exercise
Figure 5.18
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Role of Growth Hormone in the Maintenance of
Plasma Glucose
Figure 5.19
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Changes in Plasma Growth Hormone During Exercise
Figure 5.20
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Fast-Acting Hormones

• Epinephrine and norepinephrine
• Maintain blood glucose during exercise
• Muscle glycogen mobilization
• Increasing liver glucose mobilization
• Increasing FFA mobilization
• Interfere with glucose uptake
• Plasma E and NE increase during exercise
• Decreased plasma E and NE following training

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Role of Catecholamines in Substrate Mobilization
Figure 5.21
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Change in Plasma Epinephrine and Norepinephrine
During Exercise
Figure 5.22
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Plasma Catecholamines Responses to Exercise
Following Training
Figure 5.23
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Fast-Acting Hormones

• Insulin
• Uptake and storage of glucose and FFA
• Plasma concentration decreases during exercise
• Decreased insulin response following training
• Glucagon
• Mobilization of glucose and FFA fuels
• Plasma concentration increases during exercise
• Decreased response following training
• Insulin and glucagon secretion influenced by
  catecholamines

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Effects of Insulin and Glucagon
Figure 5.24
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Changes in Plasma Insulin During Exercise
Figure 5.25
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Changes in Plasma Glucagon During Exercise
Figure 5.26
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Effect of Epinephrine and Norepinephrine on
Insulin and Glucagon Secretion
Figure 5.27
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Effect of the SNS on Substrate Mobilization
Figure 5.28
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Summary of the Hormonal Responses to Exercise
Figure 5.29
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Hormone-Substrate Interaction

• FFA mobilization decreases during heavy exercise
• This occurs in spite of persisting hormonal
  stimulation for FFA mobilization
• May be due to
• High levels of lactic acid
• Promotes resynthesis of triglycerides
• Inadequate blood flow to adipose tissue
• Insufficient albumin to transport FFA in plasma

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Changes in Plasma FFA Due to Lactic Acid
Figure 5.30
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Effect of Lactic Acid on FFA Mobilization
Figure 5.30