Hormonal Response to Exercise 1

The Endocrine System A communication system – Nervous system = electrical communication – Endocrine system = chemical communication Slower responding, longer lasting than nervous system Maintains homeostasis via hormones – Chemicals that control and regulate cell/organ activity – Act on target cells 2

The Endocrine System Coordinates integration of physiological systems during rest and exercise Maintains homeostasis during exercise – Controls substrate metabolism – Regulates fluid, electrolyte balance 3

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1. Steroid Hormones Derived from cholesterol Lipid soluble, diffuse through membranes Secreted by four major glands – Adrenal cortex (cortisol, aldosterone) – Ovaries (estrogen, progesterone) – Testes (testosterone) – Placenta (estrogen, progesterone) 5

2. Non-steroid Hormones Not lipid soluble, cannot cross membranes Divided into two groups – Protein/peptide hormones Most nonsteroid hormones From pancreas, hypothalamus, pituitary gland – Amino acid-derived hormones Thyroid hormones (T 3, T 4 ) Adrenal medulla hormones (epinephrine, norepinephrine) 6

Hormone Secretion Secreted in bursts – Plasma concentrations fluctuate over minutes/hours – Concentrations also fluctuate over days/weeks *What triggers or regulates hormone bursts?  Secretion regulated by negative feedback 7

Neuroendocrinology Blood Hormone Concentration Determined by: 1. Rate of secretion of hormone from endocrine gland Magnitude of input Stimulatory versus inhibitory input 2. Rate of metabolism or excretion of hormone At the receptor and by the liver and kidneys 3. Quantity of transport protein Steroid hormones 4. Changes in plasma volume 8

Hormone Activity Plasma concentration: – Cells change sensitivity to hormones – Number of receptors on cell surface can change Downregulation:  number of receptors during high plasma concentration = desensitization Upregulation:  number of receptors during high plasma concentration = sensitization 9

Hormone Receptors Hormone effects are limited by hormone- specific receptors No receptor on cell surface = no hormone effect – Hormone only affects tissues with specific receptor – Hormone exerts effects after binding with receptor – Typical cell has 2,000 to 10,000 receptors Hormone binds to receptor: hormone–receptor complex 10

3. Prostaglandins Third class of (pseudo)hormones Derived from arachidonic acid Act as local hormones/ immediate area – Inflammatory response (swelling, vasodilation) – Sensitize nociceptor free nerve endings (pain) 11

Hormonal Regulation of Metabolism During Exercise Major endocrine glands responsible for metabolic regulation: – Anterior pituitary gland – Thyroid gland – Adrenal gland – Pancreas Hormones released by these glands affect metabolism of carbohydrate and fat during exercise 12

Endocrine Regulation of Metabolism: Anterior Pituitary Gland Pituitary gland attached to inferior hypothalamus Three lobes: anterior, intermediate, posterior Secretes hormones in response to hypothalamic hormone factors – Releasing factors & inhibiting factors – Exercise  secretion of all anterior pituitary hormones 13

Hormones: Regulation and Action Posterior Pituitary Gland Antidiuretic hormone (ADH) – Reduces water loss from the body to maintain plasma volume Reabsorption of water from kidney tubules to capillaries – Release stimulated by low plasma volume Due to sweat loss without water replacement = less water in urine – Increases during exercise >60% VO 2 max To maintain plasma volume 14

Endocrine Regulation of Metabolism: Anterior Pituitary Gland Releases growth hormone (GH) – Potent anabolic hormone – Builds tissues, organs – Promotes muscle growth (hypertrophy) – Stimulates fat metabolism 15

Growth Hormone 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 Hormones: Regulation and Action 16

Growth Hormone Slow-acting hormone Exercise effect: – Increase in plasma GH with increased intensity – Greater response in trained runners *GH release proportional to exercise intensity Hormonal Control of Substrate Mobilization During Exercise 17

Growth Hormone and Performance GH increases protein synthesis in muscle and long bone growth – Used to treat childhood dwarfism – Also used by athletes and elderly More adverse effects than benefits No evidence that GH promotes strength gains Difficult to detect usage by athletes Hormones: Regulation and Action 18

Endocrine Regulation of Metabolism: Thyroid Gland Secretes triiodothyronine (T 3 ), thyroxine (T 4 ) T 3 and T 4 lead to increases in – Metabolic rate of all tissues – Protein synthesis – Number and size of mitochondria – Glucose uptake by cells – Rate of glycolysis, gluconeogenesis – FFA mobilization 19

Thyroid Hormones Act in a permissive manner to allow other hormones to exert their full effect & maintain metabolic rate – T 3 enhances effect of epinephrine to mobilize free fatty acids from adipose tissue No significant change in T 3 and T 4 during exercise Hormonal Control of Substrate Mobilization During Exercise 20

Thyroid Gland Calcitonin – Regulation of plasma Ca +2  bone building – When Ca +2 levels are high = stimulates Ca +2 excretion by kidneys  expelled in urine – Protects against calcium loss from skeleton during periods of calcium mobilization  pregnancy & lactation Hormones: Regulation and Action 21

Parathyroid Gland Parathyroid hormone (opposes effects of calcitonin) – Primary hormone in plasma Ca +2 regulation – When Ca +2 levels are low = stimulates reabsorption of Ca +2 by kidneys Hormones: Regulation and Action 22

Endocrine Regulation of Metabolism: Adrenal Medulla Releases catecholamines (fight or flight) –  Exercise   sympathetic nervous system   epinephrine and norepinephrine Catecholamine release increases: – Heart rate, contractile force, blood pressure – Glycogenolysis, FFA – Blood flow to skeletal muscle – Fast acting hormone 23

Adrenal Cortex Secretes steroid hormones – Derived from cholesterol Mineralcorticoids – Aldosterone – Maintenance of plasma Na + and K + Glucocorticoids – Cortisol – Regulation of plasma glucose Sex steroids – Androgens and estrogens – Support prepubescent growth Hormones: Regulation and Action 24

Hormones: Regulation and Action Cortisol Maintenance of plasma glucose – Promotes protein breakdown for gluconeogenesis – Stimulates FFA mobilization from adipose tissue – Stimulates glucose synthesis – Blocks uptake of glucose into cells:  Promotes use of free fatty acids as fuel Stimulated by: – Stress – Exercise 25

Cortisol Slow-acting hormone Effect of exercise: – Decrease during low-intensity exercise – Increase during high-intensity exercise Above ~60% VO 2 max Hormonal Control of Substrate Mobilization During Exercise 26

Adipose Tissue Is an Endocrine Organ In addition to storing triglycerides, adipose tissue also secretes hormones – Leptin Influences appetite Enhances insulin sensitivity and fatty acid oxidation – Adiponectin Increases insulin sensitivity and fatty acid oxidation With increased fat mass (obesity) – Higher leptin levels and lower adiponectin – Leads to type 2 diabetes and low-grade inflammation Hormones: Regulation and Action 27

Testes and Ovaries Testosterone – Released from testes – Anabolic steroid Promotes tissue (muscle) building Performance enhancement – Androgenic steroid Promotes masculine characteristics Estrogen and Progesterone – Released from ovaries – Establish and maintain reproductive function – Levels vary throughout the menstrual cycle Hormones: Regulation and Action 28

Anabolic Steroids and Performance Taken: 10 to 100 times the recommended dosage Also associated with negative side effects – Revert to normal after discontinuation Widespread use has led to testing of competitive athletes Most users are not competitive athletes – Take more than one steroid in megadoses Hormones: Regulation and Action 29

Hormones: Regulation and Action Pancreas Both exocrine and endocrine functions Secretes: – Insulin (from  cells) Promotes the storage of glucose, amino acids, and fats Lack of insulin is called diabetes mellitus – Glucagon (from  cells) Promotes the mobilization of fatty acids and glucose – Somatostatin Controls rate of entry of nutrients into the circulation – Digestive enzymes and bicarbonate Into the small intestine 30

Endocrine Regulation of Metabolism: Pancreas Insulin: lowers blood glucose – Counters hyperglycemia, opposes glucagon –  Glucose transport into cells –  Synthesis of glycogen, protein, fat – Inhibits gluconeogenesis Glucagon: raises blood glucose – Counters hypoglycemia, opposes insulin –  Glycogenolysis, gluconeogenesis 31

Regulation of Carbohydrate Metabolism During Exercise Glucose must be available to tissues Glycogenolysis (glycogen  glucose) Gluconeogenesis (FFAs, protein  glucose) 32

Regulation of Carbohydrate Metabolism During Exercise Adequate glucose during exercise requires – Glucose release by liver – Glucose uptake by muscles Hormones that  circulating glucose: – Glucagon – Epinephrine – Norepinephrine – Cortisol 33

Regulation of Carbohydrate Metabolism During Exercise Circulating glucose during exercise also affected by – GH:  FFA mobilization,  cellular glucose uptake – T 3, T 4 :  glucose catabolism and fat metabolism Amount of glucose released from liver depends on exercise intensity & duration 34

Regulation of Carbohydrate Metabolism During Exercise As exercise intensity increases: – Catecholamine release  – Glycogenolysis rate  (liver, muscles) – Muscle glycogen used before liver glycogen As exercise duration increases – More liver glycogen used –  Muscle glucose uptake   liver glucose release – As glycogen stores , glucagon hormone levels  35

Blood Glucose Homeostasis During Exercise Plasma glucose maintained through four processes: 1. Mobilization of glucose from liver glycogen stores 2. Mobilization of FFA from adipose tissue Spares blood glucose 3. Gluconeogenesis from amino acids, lactic acid, and glycerol 4. Blocking the entry of glucose into cells Forces use of FFA as a fuel Hormonal Control of Substrate Mobilization During Exercise 36

Regulation of Carbohydrate Metabolism During Exercise Glucose mobilization = only half the story Insulin: enables glucose uptake in muscle During exercise – Insulin concentrations  – Cellular insulin sensitivity  – More glucose uptake into cells, use less insulin 37

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Hormonal Control of Substrate Mobilization During Exercise Role of insulin & Glucagon: 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 & glucagon secretion influenced by catecholamines 39

Epinephrine and Norepinephrine Also Fast-acting hormones Maintain blood glucose during exercise – Muscle glycogen mobilization – Increasing liver glucose mobilization – Increasing FFA mobilization – Alter glucose uptake Plasma E and NE increase during exercise – Also related to increased heart rate and blood pressure during exercise Decreased plasma E and NE after training Hormonal Control of Substrate Mobilization During Exercise 40

Regulation of Fat Metabolism During Exercise FFA mobilization and fat metabolism critical to endurance exercise performance – Glycogen depleted  need fat for energy = release hormones accelerate fat breakdown (lipolysis) Triglycerides  FFAs + glycerol – Fat stored as triglycerides in adipose tissue – Broken down into FFAs  transported to muscle – Rate of triglyceride breakdown into FFAs = determine rate of cellular fat metabolism 41

Regulation of Fat Metabolism During Exercise Lipolysis stimulated by: – (Decreased) insulin – Epinephrine – Norepinephrine – Cortisol – GH Stimulate lipolysis via lipase 42