Hormonal Responses to Exercise Powers, Chapter 5 Hormonal Responses to Exercise

Neuroendocrinology 神經內分泌學 Sense information, organize appropriate responses, deliver messages to proper organs or tissues Endocrine glands 腺體 release hormones directly into the blood Hormones alter the activity of tissues that possess receptors to which the hormone can bind The plasma hormone concentration determines the magnitude of the effect at the tissue level

Blood Hormone Concentration Determined by: Rate of secretion of hormone from endocrine gland Rate of metabolism or excretion of hormone Quantity of transport protein Changes in plasma volume

Control of Hormone Secretion Rate of insulin secretion from the pancreas is dependent on: Magnitude of input Stimulatory vs. inhibitory

Factors That Influence the Secretion of Hormones

Hormone-Receptor Interactions Trigger events at the cell Magnitude of effect dependent on: Concentration of the hormone Number of receptors on the cell Affinity of the receptor for the hormone Down-regulation of receptor number decreased when exposed to chronically elevated hormone concentrations Up-regulation of receptor number Chronic exposure to low hormone concentrations

Hormone-Receptor Interactions Hormones bring about effects by: Altering membrane transport Stimulating DNA to increase protein synthesis Activating second messengers Cyclic AMP (cAMP) Ca++ Inositol triphosphate Diacylglycerol

Mechanism by Which Steroid Hormones Act on Target Cells

The Cyclic AMP “Second Messenger” Mechanism

Ca++ and Phospholipase C Second Messenger Systems

Hormones: Regulation and Action Hormones are secreted from endocrine glands Hypothalamus 下視丘 and pituitary glands 腦下垂體 Thyroid 甲狀腺 and parathyroid glands 副甲狀腺 Adrenal glands (adrenal medulla and adrenal cortex) 腎上腺 Pancreas 胰臟 Testes 睪丸 and Ovaries 卵巢

Hypothalamus Controls activity of the anterior and posterior pituitary glands Influenced by positive and negative input

Positive and Negative Input to the Hypothalamus

Anterior Pituitary Gland 腦下垂體前葉

Growth Hormone 生長激素 Secreted from the anterior pituitary gland Essential for normal growth Stimulates protein synthesis and long bone growth Increases during exercise Mobilizes fatty acids from adipose tissue Aids in the maintenance of blood glucose

Posterior Pituitary Gland 腦下垂體後葉 Secretes antidiuretic hormone (ADH) 抗利尿激素 Reduces water loss from the body to maintain plasma volume Stimulated by: High plasma osmolality and low plasma volume due to sweating Exercise

Change in the Plasma ADH Concentration During Exercise

Thyroid Gland Triiodothyronine (T3) & thyroxine (T4) 甲狀腺素 Important in maintaining metabolic rate and allowing full effect of other hormones Calcitonin 抑鈣素, 降血鈣素 Regulation of plasma Ca++ Parathyroid Hormone 副甲狀腺素 Also involved in plasma Ca++ regulation

Adrenal Gland Adrenal medulla 腎上腺髓質 Adrenal cortex 腎上腺皮質 Secretes catecholamines: Epinephrine 腎上腺素 and norepinephrine 正腎上腺素 Adrenal cortex 腎上腺皮質 Secretes steroid hormones: Mineralcorticoids 礦物性皮質素, glucocorticoids 糖皮質素

Adrenal Medulla Part of the sympathetic nervous system Secrete catecholamines Epinephrine (E) and norepinephrine (NE) Bind to receptors on effector organs Alpha () and beta () receptors Bring about changes in cellular activity via second messengers

Response to Catecholamines: Role of Receptor Type Effect of E/NE Membrane-bound enzyme Intracellular mediator Effects on Various Tissues 1 E=NE Adenylate cyclase  cAMP  Heart rate  Glycogenolysis  Lipolysis 2 E>>>NE  Bronchodilation  Vasodilation 1 ENE Phospholipase C  Ca++  Phosphodiesterase  Vasoconstriction 2 cAMP Opposes action of 1 & 2 receptors

Adrenal Cortex Mineralcorticoids (aldosterone 醛固酮) Promote reabsorption of Na+ and K+ in kidney, Involved in maintaining plasma Na+ and K+ Part of the renin-angiotensin-aldosterone system of blood pressure regulation

Adrenal Cortex Glucocorticoids (Cortisol) 可體松 Stimulated by exercise and long-term fasting Promotes the use of free fatty acids as fuel Stimulates glucose synthesis Promotes protein breakdown for gluconeogenesis and tissue repair

Pancreas Insulin 胰島素 Secreted by the  cells of the islets of Langerhans Promotes the storage of glucose, amino acids, and fats Diabetes mellitus is characterized as a lack of insulin (Type 1) or a lack of insulin receptors (Type 2) Results in high blood glucose levels Considered a significant health risk Glucagon 升糖激素 Released from the  cells of the islets of Langerhans Promotes the mobilization of fatty acids and glucose

Testes Release testosterone 睪固酮 Anabolic steroid Androgenic steroid Promotes tissue (muscle) building Performance enhancement Androgenic steroid Promotes masculine characteristics

Estrogen 女性荷爾蒙 Establish and maintain reproductive function Levels vary throughout the menstrual cycle

Muscle Glycogen Utilization Breakdown of muscle glycogen is under dual control Epinephrine-cyclic AMP Fig 5.13, 5.14 Ca++-calmodulin Delivery of glucose parallels activation of muscle contraction Glycogenolysis can still occur in presence of -blocking agent Propranolol, fig 5.15

Control of Glycogenolysis

Muscle Glycogen Utilization Glycogen breakdown is related to exercise intensity High-intensity exercise results in greater and more rapid glycogen depletion

Plasma Epinephrine Concentration During Exercise

Maintenance of Plasma Glucose During Exercise Mobilization of glucose from liver glycogen stores Mobilization of FFA (free fatty acid 游離脂肪酸) 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

Blood Glucose Homeostasis During Exercise Permissive and slow-acting hormones Thyroxine 甲狀腺素 Cortisol Growth hormone Act in a permissive manner to support actions of other hormones

Cortisol Stimulates FFA mobilization from adipose tissue Mobilizes amino acids for gluconeogenesis Blocks entry of glucose into cells

Plasma Cortisol During Exercise At low intensity: ↓plasma cortisol At high intensity: ↑plasma cortisol

Growth Hormone Important in the maintenance of plasma glucose ↓ glucose uptake, ↑FFA mobilization, ↑gluconeogenesis

Growth Hormone During Exercise: Trained vs. Untrained

Growth Hormone During Exercise: Effect of Intensity

Blood Glucose Homeostasis During Exercise Fast-acting hormones Norepinephrine and epinephrine Insulin and glucagon Maintain plasma glucose Increasing liver glucose mobilization Increased levels of plasma FFA Decreasing glucose uptake Increasing gluconeogenesis

Role of Catecholamines in Substrate Mobilization

Epinephrine & Norepinephrine During Ex Increase linearly during exercise Favor the mobilization of FFA and maintenance of plasma glucose

Epinephrine & Norepinephrine Following Training Decreased plasma levels in response to exercise bout Parallels reduction in glucose mobilization Physical training, stimulates the sympathetic nervous system, increases the capacity to respond to extreme challenges

Plasma Catecholamines During Exercise Following Training

Effect of Insulin and Glucagon on FFA Uptake and Oxidation

Insulin During Exercise Plasma insulin decreases during exercise Prevents rapid uptake of plasma glucose Favors mobilization of glucose and FFA

Effect of Training on Plasma Insulin During Exercise

Effect of Training on Plasma Glucagon 升糖激素 During Exercise

Control of Insulin and Glucagon Secretion During Exercise

Effect of SNS 交感神經系統 on Substrate Mobilization

Hormonal Responses to Exercise

Free Fatty Acid Mobilization During Exercise FFA mobilization decreases during heavy exercise This occurs in spite of persisting hormonal stimulation for FFA mobilization Could be due to high levels of lactic acid Promotes resynthesis of triglycerides

Effect of Lactic Acid on FFA Mobilization