Axis CRH-ACTH-adrenal glands CRH, corticotropin-releasing hormone Characteristics - CNS stress response modulation (anxiety, food intake) - Functions on periphery (BP, immune system, heart) - a part of system of related peptides - CRH-1R – neocortex, cerebellar cortex, subcortical structures of limbic system, amygdala, ovaries, endometrium, skin - CRH-binding protein Hypothalamo-hypophyseal axis - Fast ACTH secretion Clinical significance - Potential treatment of obesity - CRH-R1 antagonists – anxiety and depression treatment Regulation of secretion - Neural control – various stressors - Hypothalamo-hypophyseal axis activation - Sympathoadrenal axis activation - ADH and oxytocin binding - Ensuring requirements in emergency situations - Inflammation and cytokines - IL-1B and hypothalamohypophyseal axis activation - Circadian rhythms - diurnal rhythms Proopiomelanocortin - POMC Characteristics -Adenohypophysis - short transcript -CNS -Placenta -Skin -Gonads -GIT -Liver -Kidneys -Adrenal medulla -Lungs -Lymphocytes Stimulation of expression -CRH, cytokines, ADH, catecholamines, VIP Posttranslational modification - Role of prohormone convertases (PCs) long transcript with synthesis of products regulating energy metabolism Functions of POMC-derived peptides Adrenal glands - ACTH - the only POMC hormone with effect on adrenal glands - MC2R receptor for melanocortin) - Glucocorticoids, androgens, (mineralocorticoids) - Mitogennic effect on adrenal glands (N terminal peptide) Skin pigmentation – ACTH, b-LPH, g-LPH - MC1R - Paracrine regulation (melanocytes, keratinocytes) Regulation of appetite – a-MSH - Inhibition of inhibitory effect of leptin - Activation of MC3R and MC4R (hypothalamus) Immune functions – a-MSH - Inhibition of leukocyte migration - Inhibition of macrophage functions - Modulation of antigen-presenting and T cells Analgesia – b-endorphin - Circulating probably without effect on CNS Placental POMC - 2nd trimester - Decrease 3 days after birth - No correlation to ACTH/cortisol of mother - Unknown physiological function Ectopic synthesis of POMC/ACTH - Mainly tumors with ability of posttranslational changes MSH – melanotropins α-MSH: Ac-Ser-Tyr-Ser-Met-Glu-His-Phe-Arg-Trp-Gly-Lys-Pro-Val β-MSH: Ala-Glu-Lys-Lys-Asp-Glu-Gly-Pro-Tyr-Arg-Met-Glu-His-Phe-Arg-Trp-Gly-Ser-Pro-Pro-Lys- Asp γ-MSH: Tyr-Val-Met-Gly-His-Phe-Arg-Trp-Asp-Arg-Phe-Gly - Pregnancy (+) - Adrenal glands (hypofunction) Clinical significance -Synthetic analogues -Afamelanotide – photoprotection -Melanotan II – increased libido -Bremelanotide – aphrodisiac effect (MC3R and MC4R) ACTH Secretion -Circadian and ultradian rhythms -Rise from 16:00 with peak before 19:00 -Lowest levels between 23:00 and 3:00 -Pulsatile secretion (ca 40/day, higher in males) ACTH and stress - Complex – peripherial and central stress adaptors - Vasovagal and sympathetic activation (catecholamines), cytokine secretion - Pain, infection, inflammation, bleeding, hypovolemia, trauma, hypoglycemia, psychological stress - Higher amplitude of ACTH pluses Secretion regulation - Very complex - neuroendocrine control of stress response and homeostasis - Regulatory molecules – CNS, hypothalamus (CRH, ADH, dopamine) – corticotropic cells - Cytokines (IL-6, LIF), growth factors – adenohypophysis – local control (paracrine) - Glucocorticoids - Negative feedback mechanism – inhibition of CRH secretion, decrease of basal ACTH secretion - Modulation of somatostatin inhibitory effect (downregulation of R) - Dopamine - Physiological regulation of secretion – exercise (athletes – hypercortisolism) Function - Adrenal glands size, structure and function - Steroidogenesis stimulation Clinical significance - Deficiency ACTH - Hypersecretion of ACTH - Testing - insulin Adrenal glands Adrenal cortex - Steroid hormones - Glucocorticoids - Mineralocorticoids - Androgens Adrenal medulla - Catecholamines - Epinephrine (adrenaline) - Norepinephrine (noradrenaline) - Dopamine Corticomedullary portal system Function - Stress response - Na+, K+, ECT - Blood pressure Adrenal gland hormones Functional architecture of adrenal gland allows transport of steroid hormones into medulla and influences activity of enzymes connected to catecholamine synthesis. ERLipiddroplets 15 % 75 % 10 % Adrenal medulla Adrenaline secerning cells (90 %) Noradrenaline secerning cells (10 %) Dopamine secerning cells (?) Secretory vesicles contain apart from catecholamines also ATP, neuropeptides – adrenomedullin, ACTH, VIP, calcium, magnesium and chromogranines. Medulla - NA Cortex Adrenal medulla Preganglionic sympathetic neurones Sympathetic nervous ganglion – medulla acetylcholine Cholinergic receptors of chromaffin cells (feochromocytes) Catecholamines release Catecholamine synthesis is regulated by negative feedback loop through effect of noradrenaline. Adrenaline synthesis is influences by steroid hormone production in adrenal cortex. Noradrenaline conversion takes place in cytoplasm. It is then transported into vesicles by ATP-controlled transport (monoamine transporter VMAT1). Catecholamines secretion Is determined by direct sympathetic stimulation: 1. Binding of Ach on nicotinic cholinergic receptors (ligand-gated ion channels) 2. Rapid Na+ influx and depolarization 3. Activation of voltage-gated Ca2+ ion channels 4. Influx of Ca2+ ions 5. Secretory vesicles associated with voltage-gated Ca2+ ion channels 6. Exocytosis – intersticium 7. Modulation of NA release by NA itself through a2-AR (inhibition) 8. Transport to target organs Constitutive secretion - Spontaneous - Ca2+ independent Regulated secretion - Ca2+ dependent - Complex system of sorting and „packaging“ Transport and metabolization of catecholamines - Very short half-life in circulation (cca 2 min) - Binds to albumin (50 %) with very low affinity - Reuptake (up to 90 % - nerve endings, 10 % uptake extraneuronal tissues) and degradation - Catechol-O-methyltransferase (COMT) – metadrenaline, normetadrenaline - Monoaminooxidase (MAO) – deamination - Aldehyde dehydrogenase - Direct filtration (kidneys) - Final degradation product is vanillylmandelic acid (A, NA) and homovanillic acid (DOP) Physiological effects of catecholamines Physiological effects of catecholamines are mediated through G-protein-coupled adrenergic receptors. Catecholamines from adrenal medulla cannot cross HEB and affect peripherial tissues. Adrenergic receptor G protein Secondary messenger Ligand a1-adrenergic a1A, a1B, a1D Mainly GQ/11 Activation of PLCa, PKC, increased concentration of intracellular Ca2+ ions Noradrenaline > adrenaline >> (isoprenaline) a2-adrenergic a2A, a2B, a2C Mainly Gai and G0 Decreased activity of AC (antagonistic effect to k b-AR). Activation of K+ ICH, inhibition of Ca2+ ICH. Activation of PLCb or PLA2. adrenaline = noradrenaline >> isoprenaline b1-adrenergic Gas Activation of AC and increased cAMP concentration Isoprenaline > adrenaline = noradrenaline b2-adrenergic Gas Activation of AC and increased cAMP concentration Isoprenaline > adrenaline >> noradrenaline b3-adrenergic Gas Activation of AC and increased cAMP concentration Isoprenaline = noradrenaline > adrenaline D1 family D1, D5 Gas GOlf Activation of AC and increased cAMP concentration dopamine D2 family D2, D3, D4 Gai Inhibition of AC and decreased cAMP concentration dopamine Main effects of catecholamines - overview Mediated by a-AR Mediated by b-AR Vasoconstriction Vasodilatation (+) inotropy (+) chronotropy Smooth muscle relaxation (GIT) (+) dromotropy Sphincter contraction (GIT) (+) inotropy Mydriasis Smooth muscle relaxation (GIT) Stimulation of saliva and tear secretion Musculus detrusor relaxation Bronchoconstriction Bronchodilatation Ejaculation Calorigenesis, thermogenesis Gluconeogenesis (liver) Glycogenolysis (-) insulin secretion Lipolysis Thrombocytes aggregation (+) renin secretion (+) Na+ reabsorption (kidneys) (+) glucagon secretion Pilomotor muscle contraction Accommodation of distance vision Clinical relevance - Antagonistic effect of various a2AR subtypes - A – decresed blood pressure - B – increased blood pressure (vasoconstriction) - Wide use of agonists and antagonists in clinical practice: - Cardiology - Ophthalmology - Internal medicine Physiological effects of catecholamines Catecholamine secretion stimuli - Sympathetic stimulation (generally) - Stress response (physical, psychical stress) - Bleeding and blood loss - Hypoglycemia - Trauma - Surgery - Fear - „fight or flight“ Acute response to stress stimuli - e.g. bronchodilatation, sphincter contraction, tachycardia, peripherial vasoconstriction and increased peripherial resistance, inhibition of motility (GIT) Ensuring energy requirements - Mobilisation of substrates – liver, muscles, adipose tissue - Glycogenolysis, lipolysis - Effect – increased glycemia, concentration of glycerol, FFA Regulation of adrenergic receptors - Chronic stimulation = changes in sensitivity (biological response) of target tissues - Desensitization of AR (phosphorylation) - Internalization of AR - Upregulation: - Glucocorticoids - Thyroid hormones - Different upregulation of various AR receptors! Clinical relevance - Changes in target tissue sensitivity during chronic administration of agonists/antagonists - Chronic application of b-agonists – asthma - Chronic application of a-agonists – tachyphylaxis (intranasal decongestants) - Feochromocytom Biochemical aspects - Monitoring of catecholamine secretion - urine Dopamine Functions of dopamine outside of CNS : - Hormone, paracrine and autocrine factor - Cannot cross HEB! - Regulation of ECF volume and ion balance - increased GFR - natriuretic effect - Immune function - (-) lymphocyte activation - Endocrine pancreas - (-) insulin secretion - Heart - (+) inotropy - (+) systolic blood pressure - (0) diastolic blood pressure Clinical relevance - i.v. application in newborns - Treatment of acute kidney damage? - Cardiogenic shock - Septic shock DR Family D1 Family D2 D1 D5 D2 D3 D4 (-) ion transport in GIT (-) Na+ and water in kidneys Relaxation of smooth muscle (-) sympathetic n.s. (CNS) Blood pressure regulation Chromogranin A Characteristics - Acidic glycoprotein - Precursor protein for: - Vasostatin-1 - Vasostatin-2 - Pancreastatin - Catestatin - Parastatin - Chromaffin cells of AM − b-cells of pancreas - Paraganglia - ECL cells eNOS Functions and relevance - Cardioprotective effect (catecholamines) - Autoantigen – DM1 - Hormone secerning CgA - marker Adrenomedullin - AMD Characteristics - Hormone, neuromodulator, neurotransmitter - Peptide (partial homology with CGRP) - Receptors – combination of CALCR + RAMP2/3 – AM1/2 - Found in: - CNS - Blood vessels - Myocardium - Tumour tissue Functions - Vasodilatation (cAMP, NO) - Cardioprotection - Protection during oxidative stress - Protection from hypoxic damage - angiogenesis Hormones of adrenal cortex Hormones of adrenal cortex = cholesterol derivates ⁻ C21 steroids with two carbon chain in position C17 ⁻ Mineralocorticoids ⁻ Glucocorticoids ⁻ C19 steroids with keto- or hydroxyl group in position C17 ⁻ Androgens ⁻ C18 steroids with 17-keto or hydroxyl group without angular methyl group in position C10 Source of cholesterol – cholesterol esters or plasma membrane STAR (Steroid Acute Regulatory) proteins - Transfer of cholesterol into inner mitochondrial membrane Regulation of synthesis - Acute (minutes) versus chronic Synthesis and secretion of steroid hormones Glucocorticoids - pulsatile character under ACTH stimulation (cortisol – 10 – 20 mg/day) Mineralocorticoids – ACTH only basal secretion, RAAS – angiotensin II (aldosterone – 100 – 150 mg/day) Androgens – ACTH (DHEA, DHEAS, androstenedione – 100 – 150 mg/day) Different expressions of enzymes catalyzing steps in steroid conversions are responsible for synthesis of various steroid hormones in individual zones of adrenal cortex. Regulation of synthesis and secretion Glucocorticoids - ACTH – GaS – activation of AC and PAK - Phosphorylation of cholesterol ester hydrolase - Increased availability of cholesterol - Increased STAR synthesis Mineralocorticoids - Angiotensin II and extracellular K+ - ACTH (only basal and acute secretion) - RAAS system - Renin (juxtaglomerular cells) - Conversion of angiotensinogen - Angiotensin II stimulates aldosteron synthesis and secretion - Inhibition also by somatostatin and dopamine Glucocorticoid metabolism - Lipophilic - Conjugates - Binding to CBG proteins (transcortin, cortisol-binding globulin) and albumin - Half-life 70 – 90 min Cortisol- CBG - Up to 80 % Free cortisol - Up to 10 % Cortisol- albumin - 20 – 50 % estrogens cirrhosis Detoxication - Liver - Kidney - Reduction, oxidation, hydroxylation and conjugation - Glucuronides and sulphates Local glucocorticoid metabolism - Tissues with different expression of isoforms of 11bhydroxysteroid dehydrogenase type I (conversion cortisone to cortisol) - Liver, adipose tissue, lungs, skeletal muscle, smooth muscles of blood vessels, gonads, CNS - Tissues with different expression of isoforms of 11bhydroxysteroid dehydrogenase type II - Tubular system Conversion of cortisol to cortisone is essential for prevention of cortisol binding to mineralocorticoid receptor. Effects of glucocorticoids All tissues express glucocorticoid receptors, which causes their wide array of effects. 1. Binding of GC on corresponding receptor 2. Conformational change and dissociation of receptor from complex HSP70 and HSP90 3. Migration to nucleus 4. Binding on GRE together with activating protein (AP1) Glucocorticoids affect intermedial metabolism, stimulate proteolysis and gluconeogenesis, inhibit proteosynthesis (mainly in muscles) and stimulate mobilization of FFAs. Specific effects of glucocorticoids System Induced gene expression Suppressed gene expression Immune system Inhibitor of NF-κB, haptoglobin, TCR, p21, p27, p57, lipocortin Interleukins, TNF-α, interferon-g, Eselectin, COX-2, iNOS Metabolism PPAR-g, glutamine synthase, glycogen synthase, Glu-6-phosphatase, leptin, gfibrinogen, cholesterol 7a-hydroxylase Tryptophan hydroxylase, metalloproteases Bone tissue Androgene receptor (AR), calcitonin receptor (CTR), alcalic phosphatase, IGFBP6 Osteocalcin, collagenase Ion channels and transporters ENaC-α, -β a –g, SGK, aquaporin 1 Endocrine system Basic FGF, VIP, endothelin, RXR, GHRH receptor, receptors for natriuretic peptides GCR, prolactin, POMC/CRH, PTHrP, ADH Growth and development Surfactant proteins A, B, C Fibronectin, a-fetoprotein, NGF, erythropoietin, G1 cyclins and CDKs Effects of glucocorticoids - overview Cardiovascular system: - Increased sensitivity to catecholamines (a2-AR) - Increased sensitivity to angiotensin II - Inhibition of NO-mediated vasodilatation - Stimulation of angiotensinogen synthesis - HSD11B2-activity-dependent increase in Na+ retention in distal tubulus and increased K+ excretion - Increased GFR - Increased resorption of Na+ in proximal tubulus Increasedbloodpressure Immune system: - Decrease in lymphocyte count (T more than B) based on redistribution to spleen, lymphatic nodes and bone marrow - Increased number of neutrophils - Decreased number of eosinophils and basophils - Inhibition of monocyte-macrophage differentation - Inhibition of immunoglobulin synthesis - Inhibition of cytokine synthesis - Inhibition of histamine and serotonin secretion from mast cells - Inhibition of prostaglandine synthesis Anti-inflammatoryand immunosuppressiveeffect Glucocorticoids – clinical aspects Field Utilization Endocrinology Substitution therapy Dermatology Dermatitis Haematology, hematooncology Leukemia, lymphoma, haemolytic anemia, immune thrombocytopenic purpura Gastroenterology Ulcerative colitis, Crohn’s disease Internal medicine, Infectious diseases Chronic active hepatitis, transplantation, nephrotic syndrome, vasculitis Neurology Cerebral edema, increased intracranial pressure Pneumology Asthma, angioedema, anaphylaxis, sarcoidosis, obstructive pulmonary diseases Rheumatology Systemic lupus erythematosus, arteritis, rheumatoid arthritis Glucocorticoids are characteristic by not only glucocorticoid, but also mineralocorticoid activity and by ability to affect axis CRHACTH-GC by feedback loop. Long-term glucocorticoid application: - Steroid diabetes - Secondary osteoporosis - Dexamethasone test - Metyrapone test - CRH stimulation test Glucocorticoids – clinical aspects Cushing syndrom Addison disease Mineralocorticoids – regulation of aldosteron secretion Effects of mineralocorticoids Main effects of aldosterone - Stimulation of epithelial Na transport - Distal tubulus and collecting duct - Distal colon - Salivary glands Mechanism of effect - (+) synthesis of Na+ IK - (+) synthesis of Na+/K+-ATPase - (+) activity of Na+/K+-ATPase - (+) synthesis of H+-ATPase - (+) synthesis of Cl-/HCO3 - exchanger Receptors - Limited distribution - Keratinocytes - Neurons (CNS) - Myocytes - Smooth muscle cells in large blood vessels Adrenal gland androgens Androgens produced in adrenal glands represent more than 50 % of circulating androgens in premenopausal women. In men dominates the testicular production. - DHEA is important precursor for sex hormones synthesis - Conversion by enzymes from b-hydroxysteroid dehydrogenase group and aromatase in peripherial tissues - Possible presence of CASH (cortical androgenstimulating hormone) Possible functions of adrenal gland androgens - Libido and its „regulation“ - Cardioprotective effects in men - Possible protective role from ovarial and breast carcinoms in premenopausal women - Neuroprotection - Effect on synthesis and secretion: - IGF-1 - Testosterone and dihydrotestosterone - Estradiol Clinical aspects - Congenital adrenal hyperplasia (CAH) - prenatal virilization (high androgen concentration in utero) - Deficit of 21b-hydroxylase, „salt wasting form“ - Deficit of 11β-hydroxylase, „hypertensive form“ - Deficit of 3β-hydroxysteroid dehydrogenase II - Deficit of 17α-hydroxylase - Congenital lipoid adrenal hyperplasia - Defective conversion of cholesterol to pregnenolone - Adrenogenital syndrome - Hyperaldosteronism - Primary hyperaldosteronism - Secondary hyperaldosteronism with increased renin level - Secondary adrenal insufficiency (ACTH) - Tertiary adrenal insufficiency (CRH) - Hyporeninemic hypoaldosteronism - Pseudohypoaldosteronism Apparent mineralocorticoid excess syndrome - Inhibition or absence of 11β-hydroxysteroid dehydrogenase II Watch out for liquorice ☺