Chapter 5 Hormonal Responses to Exercise. Objectives. Objectives

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1 Chapter 5 Hormonal Responses to Exercise Objectives 1. Describe the concept of hormone-receptor interaction. 2. Identify the four factors influencing the concentration of a hormone in the bld. 3. Describe the mechanism by which steroid hormones act on cells. 4. Describe the 2 nd messenger hypothesis of hormone action. 5. Describe the role of hypothalamus-releasing factors in the control of hormone secretion from the anterior pituitary gland. Objectives 6. Describe the relationship of the hypothalamus to the secretion of hormones from the posterior pituitary gland. 7. Identify the site of release, stimulus for release, & the predominant action of the following hormones: epinephrine, norepinephrine, glucagon, insulin, cortisol, aldosterone, thyroxine, growth hormone, estrogen, & testosterone. 8. Discuss the use of testosterone (an anabolic steroid) & growth hormone on muscle growth & their potential side effects. 1

2 Objectives 9. Contrast the role of plasma catecholamines w/ intracellular factors in the mobilization of muscle glycogen during exercise. 10.Briefly discuss the following four mechanisms by which bld glu homeostasis is maintained: mobilizing glu from liver glycogen stores, mobilizing plasma FFAs from adipose tissue, synthesizing glu from AAs & glycerol in the liver, & blocking glu entry into cells. Objectives 11.Describe the Δs in the hormones insulin, glucagon, cortisol, growth hormone, epinephrine, & norepinephrine during graded & prolonged exercise & discuss how those Δs influence the four mechanisms s used to maintain the [bld glu]. 12.Describe the effect of changing hormone & substrate levels in the bld on the mobilization of FFAs from adipose tissue. Neuroendocrinology Neuroendocrinology Neuroendocrine system Endocrine glands Hormones 2

3 Neuroendocrinology [Bld Hormone] Neuroendocrinology Factors That Influence the Secretion of Hormones Figure 5.1 Hormone-Receptor Interactions Neuroendocrinology 3

4 Mechanisms of Hormone Action Neuroendocrinology Mechanism of Steroid Hormone Action Neuroendocrinology Figure 5.2 Neuroendocrinology Cyclic AMP 2 nd Messenger Mechanism Figure 5.3 4

5 Calcium & Phospholipase C 2 nd Messenger Mechanisms Neuroendocrinology Figure 5.4 Insulin Receptor Neuroendocrinology Figure 5.5 In Summary Neuroendocrinology The hormone-receptor interaction triggers events at the cell; changing the concentration of the hormone, the number of receptors on the cell, or the affinity of the receptor for the hormone will all influence the magnitude of the effect. Hormones bring about their effects by modifying mb transport, activating/suppressing genes to alter pro synthesis, & activating 2 nd messengers (cyclic AMP, Ca ++, inositol triphosphate, & diacylglycerol). 5

6 Hormones: Regulation & Action Hypothalamus & 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) Hypothalamus Stimulates release of hormones from anterior pituitary gland Releasing hormones or factors Provides hormones for release from posterior pituitary gland 6

7 Anterior Pituitary Gland Adrenocorticotropic hormone (ACTH) Stimulates cortisol release form adrenal glands Follicle-stimulating hormone (FSH) Luteinizing hormone (LH) Stimulates production of testosterone & estrogen Melanocyte-stimulating hormone (MSH) Thyroid-stimulating hormone (TSH) Controls thyroid hormone release from thyroid gland Prolactin Growth hormone (GH) Growth Hormone Influences on Growth Hormone Release Figure 5.6 7

8 A Closer Look 5.1 Growth Hormone & Performance In Summary The hypothalamus controls the activity of both the anterior pituitary & posterior pituitary glands. GH is released from the anterior pituitary gland & is essential for normal growth. GH s during exercise to mobilize FFAs from adipose tissue & to aid in the maintenance of bld glu. Posterior Pituitary Gland 8

9 Δ in Plasma [ADH] during Exercise Figure 5.7 Thyroid Gland Stimulated by TSH Triiodothyronine (T 3 ) & thyroxine (T 4 ) Establishment of metabolic rate Permissive hormones Permit full effect of other hormones Calcitonin Regulation of plasma Ca +2 Blocks release from bone, stimulates excretion by kidneys Parathyroid Hormone 1 hormone in plasma Ca +2 regulation Stimulates release from bone, stimulates reabsorption by kidneys In Summary Thyroid hormones T 3 & T 4 are important for maintaining the metabolic rate & allowing other hormones to bring about their full effect. 9

10 Parathyroid Gland Parathyroid hormone 1 hormone in plasma Ca +2 regulation Stimulates Ca +2 release from bone Stimulates reabsorption of Ca +2 by kidneys Converts vitamin D 3 into a hormone that Ca +2 absorption from GI tract Adrenal Medulla Effects of E &N 10

11 In Summary The adrenal medulla secretes the catecholamines epinephrine (E) & norepinephrine (NE). E is the adrenal medulla s 1 secretion (80%), while NE is primarily secreted from the adrenergic neurons of the sympathetic nervous system. Epinephrine & norepinephrine bind to α- & β-adrenergic receptors &bring about Δs in cellular activity (e.g., d HR, mobilization of FAs from adipose tissue) via 2 nd messengers. Adrenal Cortex Secretes steroid hormones Derived from cholesterol Mineralcorticoids Aldosterone Maintenance of plasma Na + &K + Glucocorticoids Cortisol Regulation of plasma glu Sex steroids Androgens & estrogens Support prepubescent growth Aldosterone Control of Na + reabsorption & K + secretion Na + /H 2 O balance Regulation of bld volume &bld pressure Part of renin-angiotensin-aldosterone system Part of renin angiotensin aldosterone system All three hormones during exercise Stimulated by: d [K + ] d plasma volume 11

12 Δ in Renin, Angiotensin II, &Aldosterone during Exercise Figure 5.8 Cortisol Control of Cortisol Secretion Figure

13 In Summary The adrenal cortex secretes aldosterone (mineralcorticoid), cortisol (glucocorticoid), &estrogens &androgens (sex steroids). Aldosterone regulates Na + &K + balance. Aldosterone secretion s w/ strenuous exercise, driven by the reninangiotensin system. Cortisol responds to a variety of stressors, including exercise, to ensure that fuel (glu &FFAs) is available, &to make AAs available for tissue repair. A Closer Look 5.2 Adipose Tissue Is an Endocrine Organ Pancreas 13

14 In Summary Insulin is secreted by the β cells of the islets of Langerhans in the pancreas &promotes the storage of glu, AAs, &fats. Glucagon is secreted by the α cells of the islets of Langerhans in the pancreas &promotes the mobilization of glu &fats. Testes &Ovaries Testosterone Released from testes Anabolic steroid Promotes tissue (muscle) building Performance enhancement Androgenic steroid Promotes masculine characteristics Estrogen &Progesterone Released from ovaries Establish &maintain reproductive function Levels vary throughout the menstrual cycle Control of Testosterone Secretion Figure

15 Control of Estrogen Secretion Figure 5.11 Δ in FSH, LH, Progesterone, & Estradiol during Exercise Figure 5.12 A Closer Look 5.3 Anabolic Steroids &Performance 15

16 In Summary Testosterone & estrogen establish &maintain reproductive function & determine secondary sex characteristics. Chronic exercise (training) can testosterone levels in males & estrogen levels in females. The latter adaptation has potentially negative consequences related to osteoporosis. Muscle Glycogen Utilization Glycogen Depletion during Exercise Figure

17 Plasma [EPI] during Exercise Figure 5.14 Control of Muscle Glycogen Utilization Δs in Muscle Glycogen Before & After Propranolol Administration Figure

18 Control of Glycogenolysis Figure 5.16 In Summary Glycogen breakdown to glu in muscle is under the dual control of epinephrine-cyclic AMP &Ca +2 -calmodulin. The latter s role is enhanced during exercise due to the in Ca +2 from the sarcoplasmic reticulum. In this way, the delivery of fuel (glu) parallels l the activation of contraction. Bld Glu Homeostasis during Exercise 18

19 Thyroid Hormones Cortisol Role of Cortisol in the Maintenance of bld glu Figure

20 Δs in Plasma Cortisol during Exercise Figure 5.18 Growth Hormone Role of Growth Hormone in the Maintenance of Plasma glu Figure

21 Δs in Plasma Growth Hormone during Exercise Figure 5.20 In Summary The hormones thyroxine, cortisol, & growth hormone act in a permissive manner to support the actions of other hormones during exercise. Growth hormone & cortisol also provide a slow-acting effect on CHO & fat metabolism during exercise. Epinephrine & Norepinephrine 21

22 Role of Catecholamines in Substrate Mobilization Figure 5.21 Δ in Plasma E & NE during Exercise Figure 5.22 Plasma Catecholamines Responses to Exercise following Training Figure

23 Fast-Acting Hormones Effects of Insulin & Glucagon Figure 5.24 Δs in Plasma Insulin during Exercise Figure

24 Δs in Plasma Glucagon during Exercise Figure 5.26 Effect of E & N on Insulin & Glucagon Secretion Figure 5.27 Effect of the SNS on Substrate Mobilization Figure

25 Summary of the Hormonal Responses to Exercise Figure 5.29 In Summary Plasma glu is maintained during exercise by ng liver glycogen mobilization, using more plasma FFA, ng gluconeogenesis, & ng glu uptake by tissues. The in plasma insulin & the in plasma E, NE, GH, glucagon, & cortisol during exercise control these mechanisms to maintain the [glu]. In Summary glu is taken up 7-to 20-times faster during exercise than at rest even w/ the in plasma insulin. The s in intracellular Ca +2 & other factors are associated w/ an in the number of glu transporters that the mb transport of glu. gu Training causes a reduction in E, NE, glucagon, & insulin responses to exercise. 25

26 Hormone-Substrate Interaction Δs in Plasma FFA Due to Lactic Acid Figure 5.30 Effect of Lactic Acid on FFA Mobilization Figure

27 In Summary The plasma [FFA] s during heavy exercise even though the adipose cell is stimulated by a variety of hormones to triglyceride breakdown to FFA & glycerol. This may be due to: (a) the higher [H + ] inhibiting hormone sensitive s e lipase, (b) the high levels e of lactate a during heavy exercise promoting the resynthesis of triglycerides, (c) an inadequate bld flow to adipose tissue, or (d) insufficient albumin needed to transport the FFA in the plasma. Study Questions 1. Draw & label a diagram of a negative feedback mechanism for hormonal control using cortisol as an example. 2. List the factors that can influence the [bld] of a hormone. 3. Discuss the use of testosterone & growth hormone as aids to muscle size &strength, &discuss the potential long-term consequences of such use. 4. List each endocrine gland, the hormones(s) secreted from that gland, & its (their) action(s). 5. Describe the two mechanisms by which muscle glycogen is broken down to glu (glycogenolysis) for use in glycolysis. Which one is activated at the same time as muscle contraction? Study Questions 6. Identify the four mechanisms involved in maintaining the bld [glu]. 7. Draw a summary graph of the Δs in the following hormones w/ exercise of increasing intensity or duration: epinephrine, norepinephrine, cortisol growth hormone, insulin, & glucagon. 8. What is the effect of training on the responses of epinephrine, norepinephrine, & glucagon to the same exercise task? 9. Briefly explain how glu can be taken into the muscle at a high rate during exercise when plasma insulin is reduced. Include the role of glu transporters. 27

28 Study Questions 10. Explain how FFA mobilization from the adipose cell s during maximal work in spite of the cell being stimulated by all the hormones to break down triglycerides. 11. Discuss the effect of glu ingestion on the mobilization of FFAs during exercise. 28