principles of endocrine functions UNI ED Hormones • Starling 1905 - secretin Definition? • Glandotropic hormones Aglandotropic hormones Hypothalamus Releasing hormones: GHRH, CRH, TRH, GnRH Inhibitory hormones: somatostatin, dopamine, vasopressin oxytocin Thyroid gland T3, T4, & calcitonin Adrenal glands Cortisol Aldosterone Adrenal androgens Epinephrine Norepinephrine Ovaries Estrogens Progesterone Pituitary gland Growth hormone, Prolactin. ACTH, MSH. TSH. FSH. & LH Parathyroid glands Parathyroid hormone Pancreas Insulin Glucagon Somatostatin Testes Testosterone Source: Molina PE: Endocrine Physiology, 4th Edition: www.accessmediclne.com Copyright c The McGraw-Hill Companies, Inc. All rights reserved. How do cells communicate? • Intracrine • Autocrine • Paracrine • Neurocrine • Endocrine • Neuroendocrine source environment target cell 1. INTRACRINE ((^^) IJ 2. AUTOCRINE 3. PARACRINE TARGET CELLS ^ 0 SIGNALING CELL f 1 4. NEUROCRINE ) T // \V *^®) /® a) NEURONS 5. ENDOCRINE ^^^^^^^^^^^^SSEL ENDOCRINE CELLS **— M ^^^^^^ TARGET CELLS 6. NEUROENDOCRINE J\. NEUROSECRETORY ~"S «» V NEURON ^„ ,„-»„,-, ^y^*^^^^^^^^^ BLOOD VESSEL ^^^^^^^^ ANTERIOR PITUITARY CELLS source synthesis/secretion no influence on specificity of effect - synthesis/secretion - main determinant of target eel (determined by localization) environment blood - universal environment - dilution and interactions r matrix/interstitial fluid diffusion binding proteins proteases components of extracellular matrix - receptor = specificity - cell response - number of receptors - signaling pathways - other ligands - metabolisation of ligand/receptor specificity and sensitivity diffusion barrier determinants of gradient inhibition signaling pathways effect of other ligands binding proteins Chemical nature of hormones DERIVED FROM AMINOACIDS -Adrenaline -Noradrenaline -Dopamine -Melatonine -T3/T4 T o STEROID -Cortisol -Aldosterone -Testosterone -Progesterone -Estradiol -Calcitriol PEPTIDES AND PROTEINS -Hypothalamic hormones -Adenohypophyseal hormones -Insulin, glucagon, somatostatin -Gastrin, cholecystokinin, secretin -Natriuretic peptides -Erythropoietin, thrombopoietin -PTH,PHrP -etc HO > O H2N O NH N- NH 0= P. -NH HN—' \ V- NH i O V) / HN^/ 0^-NH H JiN.^-^ 0 N-^0 SNH ' ~"C o-vNH2 -NH \ N J.. . u O^NH 0 = HN Chemical nature of hormones Hormone-characteristics Peptides -proteins Catecholamines Steroid hormones Thyroid hormones Ph-CH properties hydrophilic hydrophilic lipophilic lipophilic synthesis proteosynthesis Tyr modification CH precursors Tyr modifications storage secretory granules secretory granules not present colloid secretion controlled exocytosis controlled exocytosis diffusion diffusion transport free free/weakly bound bound bound elimination half-life short (4-40-170min) very short (2-3 min) moderate (up to 180 min) long (20 hours - 7 days) receptors membrane membrane cytosol nuclear effect short-term very short-term long-term long-term cell response quick very quick slow slow CHEMICAL STRUCTURE OF HORMONES DETERMINES THEIR BIOSYNTHESIS, STORAGE, RELEASE, TRANSPORTATION, ELIMINATION HALF-LIFE, WAY OF ELIMINATION AND THE MECHANISM OF EFFECT ON TARGET CELLS aldosterone Hormones • Pleiotropic effects Multiplicity Permissive effect Kidneys Salivary glands 1*1 Arterioles- a2 receptors Complement factors (adipsin) Blood pressure factors (angiotensinogen] Endocrine organs specialised cells - specialised organs („endocrine") „secretory" cells - organs with endocrine function cells without specialised secretory function cells converting hormone precursors Cytoki (IL-6# TP adipose tissue Adipokines Clinical aspects • Production of hormones by tumors - PARANEOPLASTIC SYNDROMES Lung tumors Liver and kidney tumors GIT tumors - ADH (hyponatremia) - erythropoietin - ACTH (Cushing syndrome) - ACTH (Cushing syndrome) (polycythemia) - PTHrP (hypercalcaemia) Secretion of hormones and its regulation • Neuronal control • hypothalamus • sympathetic/parasympathetic nervous system • Hormonal control • Regulation od secretion by ions or substrates (Glu, AA) INSULIN Hormone secretion is controlled by feedback system NEGATIVE FEEDBACK POSITIVE FEEDBACK 0 Short loop Hypothalamus J ^> 0 I © Anterior pituitary © * 0 "*J Long I loops Endocrine gland (e.g.. testis) © Hormone (e.g.. testosterone) © Target tissue (e.g.. muscle) Hypothalamus J ^ © Anterior pituitary 4 I. Endocrine gland (e.g.. ovary) J. Hormone (e.g., estradiol) Target tissue SCN: - Afferent - retina - Efferent - hypothalamic nucleus Melatonin GHRH/GHIH ADH ACTH Insulin Ghrelin Adiponectin Leptin Cyclic changes in hormone secretion External 24 h light-dark cycle Endogenous circadian rhythm SCN (Master clock) Entrainment Photic Zeitgeber Synchronization I Nonphotic Zeitgeber ■ Sleep-wake cycle Peripheral oscillators ■ Physical activity ■ Social time ■ Meals Cellular oscillators Neuronal/hormonal = SNC-dependent Satiety/fasting ^ Body temperature Hormone transport • Physico-chemical properties • Transport protein(s) • Albumin • Globulins • Specific proteins - TBG, SHBG, CBG • Bond strength • „Alternative" binding - TBG versus transthyretin •Protection • Reservoir •Ubiquitous distribution •Transport across plasmatic membrane (SHBG-megalin) DYNAMIC BALANCE BETWEEN HORMONE AND TRANSPORT PROTEIN Hormone elimination Different length of time in circulation Metabolisation by • Target cells • Enzymatic systems in blood • Organs - mainly liver Elimination • Liver • Kidneys PHASE I Hydroxylation, decarboxylation Oxidation, reduction PHASE II Glucuronidation Sulphatation Methylation Conjugation with glutathione \7 Vascular system bile urine Hormones and cell response Target cells Specificity High affinity Selectivity hormone O QO #°o0o°o' MECHANISMS Conformation changes Phosphorylation/dephosphorylation + protein recruitment GTP binding (G proteins) cAMP binding (efector proteins) Precursor molecule generation in PM Non-covalent Ca2+ bond SIGNALING PATHWAYS I CELL RESPONSE Receptor binding Signal amplification and transduction efector molecules % of occupied receptors conformation change synergy antagonism possible loss of sensitivity feedback-loop regulation CELL RESPONSE IS MEDIATED BY RELEVANT RECEPTORS Regulation of cell response at receptor level Downregulation versus upregulation upregulation downregulation Regulation of cell response at receptor 1fiX/ß1 Homologous desensitization („with ligand") X Heterologous desensitization („without ligand") Hormones - proteins and peptids Signal (26) □ Preproopiomelanocortin (265) (146) N terminal pcplide (76) □ ACTH (39) (13) CLIP p-Lipolropin (91) y-Lipotropin (5$) ß-Endorphin (31) + ß ( ) Peptide length in amino acids MSH sequences Koeppen & Stanton: Berne and Levy Physiology, 6th Edition, Copyright © 2006 by Mosby, an imprint of Elsevier, Inc. All rights reserved Nucleus Capillary lumen —m Secretory vesicles ' O n o ° ° Immature secretory granules (4) Mature secretory granules Plasma membrane SER/Golgi Lysosome preprohormone - prohormone - hormone (+ fragments) G protein-coupled receptors (GPCR) •G0 (2, brain) •Gt (2, photorec. - cAMP-PDE) •Gz (inhibition of K+ channels) Peptide and protein: Glucagon, Angiotensin, GnRH, SS, GHRH, FSH, LH, TSH, ACTH Amino acid derived: * Epinephrine, norepinephrine Example - G-protein coupled receptors and smooth muscle NO Receptor tyrosinkinases Receptors associated with cytosolic TK GH Prolactin Leptin erythropoietin Hormone/cytokine signal transducers and activators of transcription SOCS proteiny STAT regulation of gene expression Receptor serine/threonine protein kinases Anti-Müllerian hormone inhibitin SMAD = „latent transcription factors" TGF-ß-related RII/RI dimer hormones ' RH* ■ojj Ĺ (smad) Cytoplasm Co-SMAD active SMAD) Co-SMAD Nucleus Regulation of specific gene expression gamma-activated sequence-like elements (GLEs, promotor region of some genes) Receptor guanylate cyclase O Natriuretic peptide Signal transduction - system of second messengers HORMONE = FIRST MESSENGER INTRACELLULAR SIGNALING MOLECULE GENERATED AFTER HORMONE-RECEPTOR BONDING = SECOND MESSENGER • CAMP • TSH, glucagon, ACTH, hypothalamic hormones, ADH etc. • Proteinkinase A • Modulation of signaling pathways by compartmentalization (A-kinase anchoring proteins (AKAPs)) cGMP • ANP, BNP, CNP • NO (sGC) • Proteinkinase G DAG and IP • PIP2 - phospholipase C system Ca2+ • Ca2+/Ca2+-calmodulin EXTRACELLULAR SIGNAL MUST BE CONVERTED TO INTRACELLULAR RESPONSE AC-cAMP system PLC - DAG and IP3 system Ca2+ - calmodulin system Calcium •* * Intracellular (.II' <.1»1- Calcium- calmodulin I Kinase complex Protein kinase phosphorylation of target enzyme IP3«timulated release of Ca"* from endoplasmic reticulum Protein Phosphoprotein Lumen of endoplasmic reticulum Ca2+ • - • NO as a signalling molecule - cGMP Clinical aspects • Syndromes of resistance to hormones (i.e. IR, IGF-1, TR(3) • Syndromes caused by CPCRs and G proteins mutations • ADH - nephrogenic diabetes insipidus • ACTH-familiar ACTH resistance • GnRH - hypogonadotrophic hypogonadism • FSH - hypergonadotrophic ovarial dysgenesis • LH - male pseudohermaphroditism • Melanocortin 4-obesity • PTH/PTHrP - Blomstrand lethal chondrodysplasia Hormones acting through nuclear receptors HORMONES -Thyroid hormones - TRa/ß <^ i heterodimers -Estrogens - ERa/ß -Testosterone - AR -Progesterone - PR homodimers -Aldosterone - MR -Cortisol - GR VITAMINS -1,25-[0H]2D3 - VDR -All-trans-retinoic acid - RA receptors a, ß, y -9-c/s-retinoic acid - retinoid X receptor RXR a, ß, y PRODUCTS OF METABOLISM AND XENOBIOTICS -Fatty acids- PPAR a, P, y -Oxysterols - liver X receptor LXR a, P -Bile acids - BAR -Hem - RevErb a, P -Phospholipids - homologue of liver receptor LRH-1, SF-1 -Xenobiotics - pregnane X receptor PXR - constitutive androstane receptor CAR -Orphan receptors -Variable receptors Explanation of some effects and pathologies General mechanism of effect of hormones acting through nuclear receptors Prohormone (ligand precursor) Hormone (ligand) -High affinity of ligand bond = due to R structure -Recognition of specific promotor region -Dimerisation of receptors (homodimers, heterodimers) -Remodelation of chromatin for gene expression (HDAC) -Gene expression at the end decreased or increased WHY ONLY NUCLEAR RECEPTORS? -Synthesis in cytoplasm -Stay until ligand binding or until transport to nucleus -Regulation mechanism - modification, count of receptors -Important parameter - selectivity of target cells -Tissue-specific factors, coactivators and corepressors Nuclear receptors ATD DBD LBD (amino terminus domain) (DNA binding domain) (ligand binding domain) -Coregulatory proteins binding (independent on ligand) - Phosphorylation sites -DNA binding (zinc fingers) -Dimerisation -ERE, PRE, GRE, MRE, ARE -Ligand binding (agonist, antagonist) -Coregulatory proteins binding (dependent on ligand) -Dimerisation -Nuclear translocation -Chaperone association (HSP) Example - steroid hormones X thyroid hormones Pathway 1 (Steroid hormones) (-) Hormone Pathway 2 (Thyroid hormones, vitamin D. PPARs) (-) Hormone HRE Gene Blocking general transcription factor Gene (+) Hormone (+) Hormone Repressed transcription Dissociation of cc-repressors Gene T Basal transcription Recruitment of co-activators Recruitment of activation of ^ general transcription factors Chromatin structure stimulated transcription T Stimulated transcription Termination of hormone action Receptor-mediated endocytosis and subsequent lysosome degradation Phosphorylation/ dephosphorylation of receptor or proteins of signaling pathway Ubiquitination and proteosomal degradation Binding of regulatory factor on corresponding protein (enzyme) Inner enzymatic activity and its regulation J i Clinical aspects Hormone overproduction Hormone underproduction Changes in sensitivity of target tissues and/or change in cell response Higher rate of inactivation or degradation of hormones Insufficient production or higher degradation of transport proteins Changes of transport hormones production during physiological conditions (pregnancy) Clinical aspects A. Decreased hormone responsiveness u 100 QJ 3= 0) c o X SO 0 Maximal response-^ ff -> B. Decreased hormone sensitivity Í 100 o o 50 0 / 4 Hormone / * concentration /■ required to elicit half- /Y maximal response. * s • Vjl-> Log [hormone] Log [hormone] Source: Molina PE: Endocrine Physiology, 4th Edition: Yvww.acoessmedicine.com Source: Molina pe: Endocrine Physiology, 4lh Edition: vjww.acce&sniedicine.com Copyright & Tlie McGraw-Hill Companies, Inc. All rights reserved. Copyright & The McGraw-Hill Companies, Inc. All rights, reserved. Decreased number of receptors Decreased concentration of hormone-activating enzyme(s) Increased concentration of non-competitive inhibitor Decreased number of target cells Decreased affinity of hormone to receptor Decreased number of receptors Increased rate of hormone degradation Increased concentration of antagonists/competitive inhibitors