Week 2 Pituitary Hormones PDF

Week 2 Pituitary Hormones GH, ADH and Prolactin Assoc Prof Cyril Mamotte Curtin Medical School Curtin University  Learning Outcomes Knowledge and understanding of: Regulation and roles of pituitary hormones, with an emphasis on GH, ADH and prolactin. C...

Week 2 Pituitary Hormones GH, ADH and Prolactin Assoc Prof Cyril Mamotte Curtin Medical School Curtin University  Learning Outcomes Knowledge and understanding of: Regulation and roles of pituitary hormones, with an emphasis on GH, ADH and prolactin. Causes and presentations of deficiencies and excess of pituitary hormones including -Pan-hypopituitarism -Isolated deficiencies/excess Diagnosis of pituitary hormone excess and deficiency -use physiological responses as the basis for diagnosis -the concept of dynamic testing/provocative testing Methodological issues in measurement of pituitary hormones  Examples of Questions — Describe the regulation of pituitary hormones. — How are physiological responses be used in the investigation of pituitary hormone disturbances? — When/why/how do we investigate for defects in GH, ADH and prolactin secretion? How do disturbances present, and what is the pathophysiological basis? — Compare the approach to investigation of disturbances for two of the following: -GH, ADH and prolactin secretion — Detail some of the methodological issues in measurement of complex molecules using prolactin as an example. E.g. Lack of “harmonization” or standardization. — How are GH, prolactin measured- what are the principles of assays for these hormones — What is macroprolactin, why and how is it measured?  Properties of Hormones Present at low concentrations, and very potent Generally of four types a) steroids; b) proteins and peptides; c) fatty acid derivatives; d) those derived from amino acids (amines) Hydrophobic hormones circulate bound to a carrier protein, but free form is the active free form Plasma t1/2: Steroids: 30-100 min; aa derived varies; T4 t1/2: 1 week (protein bound) vs adrenalin < 1 min (circulates freely) Effects are mediated by binding to receptors  Pituitary Gland © Springer 2009. Produced by Current Medicine Group Ltd, a part of Springer Science+Business Media  Blood supply and Innervation Hypothalamus Neuroendocrine cells Superior hypophyseal artery Pituitary Hypophyseal portal vein Stalk Anterior Pituitary Posterior Pituitary Hypophyseal efferent vein  Abbreviations and Definitions Antidiuretic Hormone Trophins or tropins- hormones that stimulate the secretion of hormones by other tissues ACTH= adrenocorticotrophin = Corticotrophin TSH= Thyroid stimulating hormone =thyrotrophin FSH= Follicle stimulating hormone, a Gonadotrophin LH= Luteinizing hormone, a Gonadotrophin Prolactin (PRL) TSH=Thyroid stimulating hormone GH= Growth Hormone Pan-hypopituitarism: of and affecting all of the pituitary or pituitary hormones Differential diagnosis -possible causes  Hormone characteristics Hormone Mol Weight Type Number of a.a. ADH ~1,000 Nonapeptide 9 Oxytocin ~1,000 Nonapeptide 9 ACTH ~4,500 Peptide 39 TSH ~25,000 Glycoprotein 89+112 LH ~26,000 Glycoprotein 89+112 FSH ~30,000 Glycoprotein 89+115 PRL ~23,000 Protein 198 GH ~22,000 Protein 191 Secretion of hormones is often pulsatile  Cortisol ACTH From: Twenty-Four-Hour ACTH and Cortisol Pulsatility in Depressed Women Elizabeth A Young MD, Nichole E Carlson MS & Morton B Brown Ph.D Neuropsychopharmacology volume 25, pages 267–276 (2001)  Example of hormone action -ADH receptor activation- Adapted from Boone and Deen, 2008* Ways by which AVP increases Aquaporin 2 (AQP2) expression on the Apical Cell Surface (luminal side, top side)) Binding of ADH (=AVP) to the V2 receptor on the basolateral membrane activates adenylate cyclase (AC) and increases intracellular cAMP levels> activates protein kinase A (PKA)> induces translocation of AQP2-bearing vesicles to the apical membrane, rendering this membrane water permeable. PKA also increases AQP2 synthesis by phosphorylation of the cAMP-responsive element-binding (CREB) protein and its binding to the AQP2 promoter. The basolateral side has AQP3 and AQP4 water channels *Boone and Deen 2008, Physiology and pathophysiology of the vasopressin-regulated renal(bottom side) water reabsorption Pflügers Archiv - European Journal of Physiology September 2008, 456:1005  Cell Surface Receptors & Second Messenger Systems* Hormone Second Messenger System for Hormone ADH, TSH, LH, FSH, PTH cyclic AMP (cAMP) Glucagon Adrenaline, noradrenaline calcitonin GH, Prolactin, oxytocin Protein kinase activity Insulin Erythropoietin ADH, GnRH, TRH, angiotensin II Calcium and/or phosphoinositides Adrenaline, noradrenaline Atrial natriuretic peptide, nitric oxide cGMP *Steroid and Thyroid Hormones operate differently; principle receptors belong the nuclear receptor family, and intracellular.  Anterior Pituitary Hormone Regulation Target Tissue  Posterior Pituitary Hormones Synthesized in neuronal cells of hypothalamus. Packaged into secretory granules ADH Oxytocin Migrate down nerve axon and stored in posterior pituitary ADH Oxytocin Release from secretory granules into portal circulation Kidney Uterus/Mammary gland Increased permeability Muscle contraction Of collecting ducts to -uterine contractions water -milk ejection High Pituitary Hormone Concentrations Physiological FHS/LH in postmenopausal women GH increase in response to exercise Elevated prolactin in breast feeding Iatrogenic Drugs Increases due to Pathological causes Examples Tumours –prolactin, ACTH, GH. – AUTONOMOUS secretion Pituitary Stalk lesion (elevated prolactin, others not, more likely low) ………….not subject to regulation………….  Hypopituitarism Partial or complete failure to secrete one, several (usual) or all pituitary hormones If all affected (rare): termed pan-hypopituitarism -Several or all pituitary hormones affected Can be due to hypothalamic disease, damage to pituitary stalk, or pituitary disease Causes Primary or secondary tumour Commonly of breast or bronchial origin If of pituitary origin; secretion one hormone may be high &others low. Infarction (e.g. Sheehan's syndrome- post-partum blood loss) Iatrogenic: radiation therapy/surgery Head injury, infections Idiopathic, especially in isolated deficiencies can be idiopathic (e.g. GH deficiency). Presentation of Pan Hypopituitarism (rare) Usually present with: – Infertility, impotence, loss of body hair – Adrenocortical insufficiency, i.e. diminished cortisol reserves (e.g. may present as hyponatremia). – Evidence of a tumour (clinical or by imaging) – GH and gonadotrophins usually affected first. no so evident in an adult  Assessment of Suspected Hypopituitarism Extent of investigation depends on presentation and level of suspicion e.g. infertility/hypogonadism etc. Baseline hormone levels are often not sufficient to make a diagnosis Growth Hormone  Anterior Pituitary Hormone Regulation Neural Control (E.g. Emotional, Physical Somatostatin GHRH Stress) -ve +ve Ghrelin IGF (from liver and some target tissues) GH Liver and Stimulates Stimulates other organs growth growth  Anterior Pituitary Hormone Regulation Neural Control (E.g. Emotional, Physical Somatostatin GHRH Stress) -ve +ve Ghrelin IGF (from liver and some target tissues) GH Liver and Stimulates Stimulates other organs growth growth  GH Regulation Stimulation Suppression Somatostatin Deep sleep (any time of day); IGF-1 ( lost in GH excess/deficiency) Hyperglycaemia Exercise Cortisol Hypoglycaemia & fasting stimulates Obesity Some aa, eg Arginine (adrenergic Hypothyroidsim effect) Stress, physical & emotional (but high levels of glucocorticoids suppress) From: Muller et al. PHYSIOLOGICAL REVIEWS Vol. 79, No. 2, April 1999 Printed in U.S.A.  GH- General effects General Effects Promotes growth of soft tissue, cartilage & bone. Similar anabolic effects to insulin in relation to protein metabolism Promotes protein synthesis and transport of aa into peripheral cells Opposite effects to insulin in relation to glucose Chronic elevation antagonises glucose uptake by cells* Hyperglycaemia decreases GH secretion Clinical Investigations Investigation of growth hormone deficiency/excess. More general assessment of pituitary/hypothalamic function.  GH- metabolic effects in different tissues Adipose tissue Stimulates lipolysis Decreases esterification of FA (to triglycerides) Impairs glucose uptake. In skeletal muscle Increased uptake of aa, and protein synthesis. Stimulates uptake of fatty acids for use as fuel Decreases glucose uptake, thus sparing glucose. In liver Stimulates gluconeogenesis and glycogen synthesis. Stimulates fatty acid oxidation to acetyl CoA and ketogenesis.  GH and IGFs IGFs, Insulin Like Growth Factors , also known as somatomedins. Have structural similarity to pro-insulin and have insulin like growth activity. In general, plasma levels of IGF-1 correlates with GH. IGF-1 better marker than GH for GH excess. IGF-1 generally constant. Levels È in childhood; Çin puberty; then È  Other Factors Important to Growth Nutrition, thyroxine, genetic factors, social/emotional/environmental deprivation), systemic disease. At the same time, IGF-I can also be reduced in numerous forms of growth retardation, e.g. in hypothyroidsim, nutritional deficiency (as above). Also reduced in chronic illness, liver disease, poorly controlled diabetes.  GH Deficiency Rare Basal GH levels not useful But finding of a single elevated level excludes deficiency. Deficiency In adults usually asymptomatic Associated with increased morbidity: e.g. influences on bone fracture risk, blood lipids. GH deficiency is cause of reduced growth rate in small percentage of children (~8%): important to identify for Tx with GH. ~15% of children with growth retardation have an endocrine cause. Idiopathic GH deficiency most commonly due to deficiency of GHRH.  Ix of GH Deficiency Basal levels low in children normally low, secretion pulsatile In both children/adults best to sample when levels are expected to be highest: Sleep (60-90 mins, inconvenient) Provocative testing: 20 minutes of vigorous exercise (basal, 2 and 20mins, supervised) IV arginine over 30 min, measure at 60-120 mins Insulin induced hypoglycaemia* -gold standard (45-75 min; supervised, glucose on hand)*. Must demonstrate hypoglycaemia is achieved (eg 20 mU/L (arbitrarily defined; assay dependent) Need to use at least two methods: 30% fail a single test. IGF-I not as useful as in GH excess  Case 1 A 15 year old male of short stature is investigated for GH deficiency. A blood sample was collected at noon and gave the following results. Serum GH 2.5 L water); exclude glycosuria Water deprivation test Differentiation of nephrogenic & hypothalamic/pituitary cause Pitressin stimulation test. Avoid drugs which may influence ADH secretion (nicotine, barbiturates, alcohol). Note : aldosterone secretion will increase!  Causes of Diabetes Insipidus Hypothalamic disease Also called central or neurogenic DI Head injury Pituitary tumour Idiopathic ~30% Nephrogenic Hereditary (rare): vasopressin receptor (X-linked) or aquaporin-2 (Ch 12) defect. Acquired: Chronic renal failure hypokalaemia, hypercalcaemia, amyloidosis  Water Deprivation Test 18:00 07:00 no food or water blood & urine Deprivation of water is normally a powerful stimulus for ADH secretion/action 07:00 If plasma osmolality is low, water depletion/DI unlikely. Urine osmolality of 3 If MRI/CT. Ie diagnosis, is largely by exclusion, and response to therapy Remember stress, even that due to venupuncture, can increase levels eg 2 x increase. Should rest for 30 min prior to sampling. As before, should check for macroprolactinaemia for levels > 700 mU/L. There are no specialised tests that are particularly helpful. Bromocriptine has no influence on pseudoprolactinomas. TRH stimulation fails to stimulate further increases in most causes.  Methodological Aspects Usually measured by immunochemiluminometric assays. Lack of adequate standardization- as for many immunoassays Macroprolactin causes interpretive difficulties  Macroprolactin One of two high molecular mass forms of prolactin. Complex of prolactin and IgG Benign Causes interpretive difficulties when present at high concentrations. Essential that laboratories screen samples with elevated levels for macroprolactin. Most commonly done by precipitation with polyethylene glycol (PEG). PEG can interfere in some assays: may need to use assay specific adjust reference range (PEG RR).  Case Example: Hyperprolactinaemia 35 year old female Not menstruating Not on oral contraceptive pill >Measured, among others, Prolactin, FSH/LH, E2, TFT Low FSH & LH, elevated Prolactin (800 mU/L) Imaging: Adenoma in pituitary How to get a better handle on the prolactin? What other measures? Sourced from: Y.-J. Chen, G.-Z. Song, Z.-N. Wang, Eur Rev Med Pharmacol Sci. 2016 May;20(9):1788-94 http://www.europeanreview.org/wp/wp-content/uploads/1788-1794.pdf Pituitary Hormone Regulation  How about big prolactin Less is known is known about big PRL. A more consistent component of total serum PRL but rarely the cause of hyperprolactinaemia. Both macroprolactin and big prolactin remain subject of further research including possible clinical significance. Reference: Ann Clin Biochem 2005; 42: 175–192  Prolactin Survey- AACB WA QC Sub-committee Prolactin Survey Results 4200 4000 3800 3600 3400 3200 3000 2800 2600 Prolactin mU/L 2400 2200 Lab 1 2000 Lab 2 1800 Lab 3 Lab 4 1600 Lab 5 1400 Lab 6 1200 Lab 7 1000 Lab 8 Lab 9 800 Lab 10 600 Lab 11 400 Lab 12 200 Lab 13 Lab 14 0 1 2 3 4 5 6 7 8 Sample number  WA QC Survey ctd… Methods Used: Prolactin was analysed by two Abbott Axsym, two Abbott Architect, four Centaurs, two Immulite 1000 and four Immulite 2000 instruments. Reference intervals: Laboratories reported results in both mg/L and mIU/L. Eleven laboratories developed their own reference intervals whereas three laboratories reported manufacturer supplied values. The lower limit of the male reference interval range varies from 0 to 105 mIU/L. The upper limit of the male reference interval range varies from 300 to 760 miU/L The lower limit of the female reference interval range varies from 0 to 85 mIU/L. The upper limit of the female reference interval range varies from 370 to 924. Some Factors Contributing to Lack of Harmony in Immunoassays Between Labs/Assays Calibrators Methods The process of value transfer Difficult to know what to No “gold standard” Inaccuracies in assigning use as the gold standard method for high molecular values to calibrators used “reference material or weight/complex by reagent and instrument standard” molecules. manufacturers E.g. Which of the many forms of “hormones” do Differences in antibodies we use? Many hormones used/epitope recognition exist in multiple forms. Issues in value transfer from internationally “agreed” reference materials to “working” standards/calibrators From: Armbruster and Miller, The Joint Committee for Traceability in Laboratory Medicine (JCTLM): A Global Approach to Promote the Standardisation of Clinical Laboratory Test Results. Clin Biochem Rev Vol 28 August 2007 p105  Examples of Questions — Describe the regulation of pituitary hormones. — How can physiological responses be used in the investigation of pituitary hormone disturbances? — List the causes of an excess or deficiency of the following: GH, ADH, Prolactin. — When/why/how do we investigate for defects in GH, ADH and prolactin secretion? How do disturbances present, and what is the pathophysiological basis? — Compare the approach to investigation of disturbances in GH, ADH and prolactin secretion? — Detail some of the methodological issues in measurement of complex molecules using prolactin as an example. — How are GH, prolactin measured- what are the principles of assays for this — What is macroprolactin, why and how is it measured? — E.g. Lack of “harmonization” or standardization  Pan Hypopituitarism 18 y old male Slow onset of puberty Short stature/slightly obese Frequent headaches Glu Cort GH TSH PRL LH Testosterone RR 3.0-5.5 140-160