Endocrine Questions/Exercises and Notes 1. List a) most common steroid hormones, b) where their receptors are located, c) when they are synthesized, and d) which one is the only one not attached to a protein carrier. a. Steroid Hormones (are lipid soluble): Glucocorticoids, Mineralocorticoids, Androgens, Estrogens, Progestagens, and Vitamin D (close relative b/c of sterol component) b. Receptors are located Intracellular, usually in the nucleus c. Synthesized as needed, not pre-formed (cannot be preformed if you are lipid-soluble, since you’d cross the membrane of a pre-formed vesicle) d. All attached to protein carrier except Adrenal Androgens 2. List a) lipid soluble hormones, b) half-life is proportional to, c) which one has longest half-life, d) which ones can be measured in urine as diagnostic tests, and e) which lipid soluble hormone is the only one that is stored (and it’s not stored in a vesicle, but covalently-bound)? a. Steroid hormones, Vitamin D, Thyroid hormones b. Half-life is directly proportional to the affinity of the hormone for its protein carrier c. Longest half-life is T4 b/c its affinity is very high (99% of it is bound, too) d. The ones that can be measured in urine, especially if being overproduced, are steroid hormones with large percentages that are NOT bound to protein carriers, but free in the blood. As you’ll learn in renal, substances bound to protein carriers cannot be filtered b/c either they are too large or carry a negative charge (unless there is basement membrane damage in the glomeruli, causing proteins to spill in urine). So, the steroid hormone with the largest percentage unbound is cortisol, one of the glucocorticoids. You’ll occasionally see mentioned a urine test called the 24-hour urinary free cortisol. This test is used for diagnosing either underproduction of cortisol (Addison’s) or overproduction (Cushing’s). Remember, the active form of hormone is the free portion, so this test produces an accurate picture of the activity in the blood of cortisol. e. Thyroid hormone is stored covalently-bound 3. List a) water-soluble hormones (proteins and peptides), b) location of their receptors, c) what they activate to do their job, d) storage form, e) form of transport in blood, and f) half-life determinant a. Some examples are Insulin and Glucagon b. Receptors are on cell surface (like Insulin’s Tyrosine Kinase receptor and Glucagon’s G protein-coupled receptor / 7-transmembrane spanning receptor) c. Act through second messengers, like Glucagon with cAMP and Insulin through the tyrosine kinase receptor that autophosphorylates…they start cascades that activate and/or deactivate many other substances. d. Storage form is pre-formed stored in vesicles ready to be exocytosed. Insulin is stored as a prohormone with an enzyme to cleave it to activate it once it’s needed. Once it’s cleaved, C-peptide is released in an equal amount as Insulin. e. Free, unbound dissolved in plasma is the transport form f. Short half-lives that are proportional to molecular weight 4. The free form (unbound) of lipid-soluble hormones is associated with all of the following except: a. Active/available for tissues b. Determines plasma activity c. Is not filtered through glomeruli d. Creates negative feedback Answer: c, the free unbound form is the portion that is filterable through the kidney’s glomeruli 5. Because the free form of lipid soluble hormones is the portion that creates negative feedback, it is the form that is precisely regulated. Which organ/organ system produces more binding protein to carry the lipid-soluble hormones if it is stimulated to or it is necessary to produce them? a. Liver b. Kidney c. Skeletal Muscle d. Small Intestine e. Heart Answer: a, liver. One very common way to stimulate the production of excess binding proteins is through Estrogen. Estrogen – whether exogenous like Hormone Replacement Therapy or high amounts during pregnancy/endogenous – stimulates the liver to produce not only binding proteins, but clotting factors, and other proteins produced in the liver. 6. In accordance with question #5, we know that because lipid-soluble hormones have a bound fraction (bound to protein carriers). Since the liver produces these protein carriers, we can also conclude that the bound fraction (and thus the unbound fraction) varies with liver function, or the plasma concentration of protein. So, in cirrhosis, would you expect the bound fraction of hormone to be lower or higher? Lower. But remember, because the bound fraction would be lower, the free portion would be higher, thus creating negative feedback and stabilizing the amount of active hormone in the blood (but decreasing the total amount of hormone). 7. So, in summary, the two things decreasing the circulating level of binding proteins are liver dysfunction and androgens (testosterone), and the main substance increasing the level of binding proteins is estrogen. But, remember, for example, that with Estrogen the transient decrease in free hormone takes away negative feedback and stimulates the production of more hormone and thus restoration of free hormones back to normal level…but there will be a slight increase in the level of total hormone. So, slightly increased total thyroid hormone, for instance, during pregnancy, is nothing to worry about b/c the free fraction remains the same (the active form). 8. While ACTH only affects cells with receptors for it (adrenal cortex zona fasiculata/reticulate) and LH only affects/stimulates gonadal tissue, both increase secretion of steroid hormones. ACTH adrenal androgens and LH ovarian or testicular sex hormones. 9. We already mentioned that the free hormone level is what dictates hormonal activity. There are some exceptions. For example, there are some conditions in which the number of functioning receptors or post-receptor mechanism function will dictate hormonal activity: a. Type II Diabetes Mellitus: the chronic high circulating levels of insulin downregulate the receptors…so, you have a high circulating/free level of insulin, but its activity does not match! There is insulin resistance. b. Also, with SIADH, we have high ADH, but we may not form a concentrated urine, as is expected, due to downregulation of receptors, once again…this would only happen after a long time. 10. All hormones of the Hypothalamus-Anterior Pituitary System are: water soluble, synthesized in the cell body of the neuron, and packed in vesicles and released from nerve terminals. 11. The only hypothalamic-anterior pituitary system hormone not synthesized in the arcuate or paraventricular nuclei is: GnRH in the preoptic nucleus. 12. The name of where all nerve endings of hypothalamus come together to secrete hormones into the anterior pituitary is: median eminence. 13. The two hypothalamic hormones that inhibit anterior-pituitary system hormones: GHIH/Somatostatin inhibits GH and Prolactin Inhibiting Factor/Dopamine inhibits Prolactin. 14. The only hormone that will increase its secretion from the anterior pituitary if the pituitary stalk (connection between hypoth and anterior pituitary) is damaged (Sheehan’s syndrome, head trauma) is: Prolactin. You may think, why wouldn’t growth hormone also increase if GHIH is decreased, or goes away…well, the truth is that growth hormone would decrease b/c the MAIN factor regulating growth hormone is GHRH, not GHIH. 15. All hormone release from hypothalamic-anterior pituitary system is pulsatile except: Thyroid Hormone system. This prevents downregulation of the sensitive anterior pituitary receptors. For instance, if GnRH were constant, the target receptors on anterior pituitary for GnRH would stop responding to GnRh after about a week, and therefore, stop releasing LH and FSH. 16. ACTH controls and regulates all adrenal cortex hormones except: Aldosterone (which is regulated mainly and directly by Angiotensin II and is regulated slightly by high potassium concentration and is regulated indirectly by Renin levels, since Angiotensin II levels directly correlate with Renin levels. 17. Why do we see amenorrhea in women and decreased libido and impotence in men with hyperprolactinemia? Because Prolactin suppresses the normal pulsatile pattern of GnRH and therefore prevents the positive feedback effects of Estrogen on the gonadal tissue that creates the LH surge necessary for ovulation; and LH drives testosterone secretion by the testes…if the GnRH receptors of the anterior pituitary are downregulated, then, we’ll have no LH to drive this testosterone secretion. Lab values in this hyperprolactinemia usually show decreased estradiol and testosterone (b/c of no LH or FSH) 18. If we have an increased LH but a decreased testosterone, where is the problem? At the level of the testis (you could say, a primary problem), b/c circulating testosterone provides negative feedback to hypothalamus and anterior pituitary to regulate LH secretion. 19. Since LH drives the secretion of testosterone by the Leydig cells, can you think of a time(s) that LH may need to be high? Fetus, where LH stimulates Wolffian duct development and the development of the prostate and other external structures via DHT. And, during puberty, when we re-stimulate the Leydig cells in preparation for reproduction. 20. The enzyme converting testosterone to DHT: 5 alpha reductase (peripherally-converts testosterone to DHT) 21. While there are many hormones controlled by ACTH and released from the cortex, the ONLY thing providing negative feedback on ACTH is Cortisol! 22. Along the same lines as question #21, if the anterior pituitary stalk gets damaged, what system will not be affected (from the lack of ACTH)? The mineralocorticoid system, that responds to Angiotensin II. 23. A board question: will you show signs of loss of regional adrenal function with a kidney donation? NO, b/c a patient must have 80-90% loss of adrenal glands before he/she even starts to show symptoms. 24. Absence of mineralocorticoids leads to: decreased ECF/decreased cardiac output, low BP, possible circulatory shock and possible death (pharm treatment is fludrocortisone) 25. Absence of glucocorticoids leads to: possible circulatory failure b/c without cortisol, we lose the permissive effect on catecholamines to exert their normal vasoconstrictive action in stressful situations or with normal BP or blood volume fluctuations, and we also lose the ability to readily mobilize glucose and free fatty acids, since cortisol also exerts permissive action on Glucagon and catecholamines during stressful (metabolically-stressful) situations, like fasting and exercise. 26. The rate-controlling enzyme/step in adrenal cortex hormone synthesis is: Cholesterol to Pregnenolone through Desmolase. 27. 21 Carbon substances are Aldosterone, Cortisol; 19 Carbons are Androgens (DHEA and Testosterone) and 18 Carbons are Estradiol (through Aromatase conversion of Testosterone) 28. If a woman has hirsutism, it may be a result of excess androgens at the adrenal OR the ovary level. Elevation of which form of DHEA says it’s an adrenal excess? DHEA-Sulfate (the sulfated form), and this would be the form elevated, for instance, in a 21-Beta OH Deficiency (CAH) 29. 21 Carbon Steroid with an OH at position 17 is Cortisol … so, if you see “Elevated 17 OH (hydroxy) steroids in the urine,” think cortisol excess. 30. Although DHEA is the major androgen secreted by the adrenal cortex, it’s very weak. So, it only masculinizes in females when in excessive amounts, and it only masculinizes (precocious puberty) in males with they are prepubertal! 31. All androgens, testicular and adrenal, are 17-KetoSteroids (19 carbon steroids with Ketone group on position 17) because whenever testosterone is metabolized to its lipid-soluble form, it’s converted to a 17-ketosteroid. So, urinary 17-ketosteroids are an index of both testicular and adrenal androgens 32. When may urinary 17-ketosteroid only be an index of adrenal androgens? Female and prepubertal males 33. A normal ACTH/anterior pituitary response to low-dose dexamethasone is: suppresses ACTH and therefore decreases cortisol. 34. The levels of renin and AGII in CAH (21-beta OH deficiency) are VERY HIGH, b/c lack of negative feedback from aldosterone. 35. The only difference in 21-Beta OH def and 11-Beta OH def is that in 11-Beta OH deficiency, we have hypertension b/c of 11-DOC having mineralocorticoid effects…just so happens, this increased blood pressure inhibits renin and thus renin and AGII levels are LOW. 11-DOC released in excess amounts b/c its synthesis and release is controlled by ACTH on the zona fasiculata. 36. Interesting pharm/concept question: When would an AGII block (ACE inhibitor, AGII receptor blocker) be insignificant in decreasing blood pressure? In 11-Beta OH deficiency, because the BP increase comes from 11-DOC release from the zona fasiculata, not from aldosterone released from zona glomerulosa…ACTH drives the 11-DOC. Even if Angiotensin II is working or available, the enzyme necessary to make aldosterone is absent! 37. Elevated levels of growth hormone, glucagon in starvation…what stress hormone is not elevated in starvation? Cortisol. 38. Cortisol raises blood sugar by 1) decreasing peripheral uptake in most tissues (anti-insulin effect) in periphery and 2) by increasing gluconeogenesis (does not stimulate glycogenolysis; it’s just permissive on glucagon) 39. Corticotrophs synthsize and release the stored form of ACTH that is Pro-opimelanocortin (POMC), which makes ACTH, and B-lipotropin that makes Beta-MSH and Endorphins. 40. Aldosterone increases Na+ Reabsorption and K+ secretion in the principal cells of the collecting duct, while increasing H+ secretion in the intercalated cells of the collecting duct. 41. Two direct actions of aldosterone on the principal cells of the collecting duct are: increased activity of the Na/K ATPase pump (active Na+ reabsorption) and it also puts more Na+ channels in the luminal membrane, to help with passive reabsorption of sodium. 42. Aldosterone tends to produce a metabolic alkalosis b/c it increases H+ secretion, drawn by the increasingly negative luminal charge from increased Na reabsorption. For every H+ secreted, one HCO3 is reabsorbed, so it also creates it this way… In a chronic state of metabolic alkalosis, H+ ions leave the cell to buffer the alkalosis. K+ enters the cell, but with aldosterone it’s low anyway…so we have a hypokalemic metabolic alkalosis. 43. Major difference between chronic and acute acidosis is that at first we have a positive K+ balance, but as acidosis continues, H+ ions enter the cell and K+ exits the cell to buffer the loss of positive ions. Chronic acidosis produces a negative K+ balance. 44. Main cells regulating RAAS are modified smooth muscle cells surrounding afferent arteriole called: Juxtoglomerular cells (Beta 1 receptors)…the macula densa of the distal tubule also senses Na+ delivery and communicates with the JG cells. 45. Main thing stimulating renin release from JG cells is decrease in blood/perfusing pressure, but an increase in SANS and decreased NaCl to macula densa also stimulate. 46. Causes of secondary hyperaldosteronism are: CFH, vena cava constriction, Hepatic cirrhosis (fluid goes into intersitium from plasma), renal artery stenosis a. Lab values are: renin and AGII levels are INCREASED, which drives the secondary hyperaldosteronism (versus primary, which the levels are decreased); renin and AGII levels are increased due to decreased CO and BP sensed by afferent arteriole JG cells 47. In islets of langerhans, delta and alpha cells are near periphery, while beta cells are near center…blood enters centrally and goes peripherally, so glucagon cannot act locally on insulin, but insulin can act locally on glucagon. 48. C-peptide is a better marker for endogenous insulin production than insulin itself, b/c all Cpeptide is delivered to the peripheral circulation – none is delivered to and removed by the liver, like insulin. 49. Adipose tissue and resting skeletal muscle require insulin to uptake glucose through GLUT 4 transporters; Insulin accelerates but is not required by liver for glucose uptake; CNS tissue does not require insulin for glucose uptake, nor do red blood cells, Beta cells of pancreas, kidney PT or intestinal mucsosa (both of which uptake glucose through secondary active transport coupled to sodium). 50. Insulin accelerates glucose uptake by the liver not by inserting transporters but by enhancing glucose metabolism (PFK-2, which forms fructose 2, 6 bisphosphate, which stimulates PFK-1, the rate-limiting step enzyme of glycolysis). 51. Anabolic hormones include: insulin, GH/IGF-1, Thyroid (euthyroid only**), and sex steroids (androgens). Because they are anabolic, they conserve proteins and do not increase their excretion, thus promoting a positive nitrogen balance. 52. Insulin promotes glycogen synthesis through stimulating glucokinase in liver and hexokinase in muscle and glycogen synthetase. It also decreases glycogen phosphorylase and glucose-6phosphatase (liver only) 53. Insulin stimulates TG uptake by stimulating LPL in endothelial cells of capillaries, which clears VLDL and chylomicrons from blood, and it stimulates TG synthesis by stimulating the ratelimiting step: carboxylation of acetyl CoA to malonyl CoA. 54. HSL breaks down TG into free fatty acids and glycerol; insulin inhibits HSL. 55. What can be used/given as an acute/fast K+ regulator, by stimulating the Na/K ATPase pump to take up K+? Insulin. In hyperkalemia of renal failure, insulin and glucose may be given!