HuBio 543 September 25, 2007 Neil M. Nathanson K-536A, HSB 3-9457 nathanso@u.washington.edu Introduction to the Sympathetic Nervous System

Catecholamines + HO Catechol Plus Amine NH 2 OH C H Norepinephrine 3 CH Isoproterenol Dopamine

Adrenergic Innervation of Vasculature

ADRENERGIC TRANSMISSION DOPA Dopamine Tyrosine Ca ++ AdR TH DDC DA NE DßH MAO Transp. COMT

SYNTHESIS OF EPINEPHRINE IN THE ADRENAL MEDULLA Tyrosine DOPA DDC Ca ++ Dopamine PMNT DA NE EPI DßH NE EPI EPI

TERMINATION OF SYNAPTIC TRANSMISSION Ch + AcCoA ACh + CoA CAT NE NE ACh NE ACh ACh NE ACh Re-Up NE ACh Ch +Ac AdR AChR AChE

Metabolism of Catecholamines OH HO C H NH 2 Norepinephrine H3CO Normetanephrine COMT MAO O 3,4- Dihydroxymandelic acid Metabolism of Catecholamines

ADRENERGIC TRANSMISSION DOPA Dopamine Tyrosine Ca ++ AdR TH DDC DA NE DßH MAO Transp. COMT

Drugs that act on adrenergic terminals Inhibit reuptake of NE into terminal- cocaine, tricyclic antidepressants Induce release of NE from terminal- amphetamine, tyramine Inhibit uptake of DA & NE into vesicle- reserpine Block release of NE- bretylium Displace NE from vesicle- guanethidine Inhibit TH activity- a-methyltyrosine Inhibit DDC activity- carbidopa Inhibit MAO activity- pargyline (Inhibit COMT activity- tolcapone)

Presynaptic Receptors Inhibit NE Release From Terminals ß1- AdR NE X X NE NE a2- AdR NE

The Subtypes of Adrenergic Receptors a: EPI > NOR >>ISO ß: ISO > EPI > NE

Beta- Adrenergic Receptors Mediate Positive Chronotropic Effect 80 Isoproterenol Norepinephrine 60 Change in HR. BPM 40 20 Dose, µg/kg 0.001 0. 01 0.1 1 10 100

Even More Subtypes of Adrenergic Receptors a: EPI > NOR >>ISO ß: ISO > EPI > NE a1: contraction of smooth muscle (incl. VSM) a2: presynaptic receptors ( decrease NE release) ß1: in heart and juxtaglomerular cells (and some fat cells) ß2: relaxation of smooth muscle (and in heart) ß3: some fat cells NOTE ON ß2: (1) mediate relaxation of skeletal muscle vasculature (2) P’cologically administered NE is not effective

Specificity of Agonists at Targets and Receptors NE I Contraction of VSM (a1-AdR) I Relaxation of Airways (ß2-AdR) E NE I E NE Increase in HR (ß1-AdR) Concentration of Drug

Hormone/Transmitter Effector BANG Receptors G-Proteins Effectors GTP BANG GDP Receptors G-Proteins Effectors 9 adrenergic R 20 a 4 PLC-ß 5 mAChR 5 ß 10 AC 12 g PDE (≥ 100?) K channels (GIRK ) Na, Ca channels IP3 Receptors PI-3-kinases Rho-GEF, Ras-GEF Tyrosine Kinases (src)

Regulator of G-protein Signaling

The basic functions of G-proteins as family: mediates stimulation of adenylyl cyclase (ß-AdR) ai family: mediates inhibition of adenylyl cyclase activates GIRK (M2, M4 mAChR; 2-AdR) aq family: activate certain forms of PLC (M1, M3, M5 mAChR; 1-AdR) (and others as well)

Beta-adrenergic receptors stimulate adenylyl cyclase Norepinephrine Adenylyl Cyclase G-protein ATP (Gs) cAMP cAMP-dependent protein kinase (PKA) Increased phosphorylation

Regulation of Receptor Signaling by G-protein- Coupled Receptor Kinase (GRK) and ß-Arrestin Iso g b a ß- ARR GRK Ad. Cyc. Iso P g b a ß- ARR Ad. Cyc. Receptor is uncoupled from G-protein and targeted for internalization and down-regulation

Chronic Isoproterenol Decreases Cardiac Beta-AdR # 10 20 30 40 Control ISO- Treated ISO, Withdrawn ß-Receptors In Heart

Chronic Isoproterenol Decreases Cardiac Beta-AdR Functional Responsiveness Increase In Contractile Force Control Isoproterenol, Withdrawn (OR) Increase In Adenylyl Cyclase Isoproterenol Treated Concentration of Isoproterenol

Thyroid Hormones Increase Cardiac Beta-AdR # 50 100 150 200 Control T3- Treated T4- ß-Receptors In Heart

Decreased number of cardiac ß-AdR in ventricles of patients with heart failure Controls Heart Failure (Receptor #)

Decreased function of cardiac ß-AdR in ventricles of patients with heart failure

Differential coupling of ß1 and ß2- AdR ß1-AdR only couple to the stimulatory G-protein Gs ß2-AdR can couple to both Gs & the inhibitory G-protein Gi In heart failure, levels of ß1-AdR decrease and levels of Gi increase Therefore, ß2-AdR has less stimulatory and more inhibitory effects in a failing heart than in a non-failing heart Failing heart has increased expression and activity of GRK, which increases ß1 desensitization and degradation and also increases coupling of ß2 to Gi The decreased level of ß1-AdR and increased ß2-AdR coupling to Gi both contribute to decreased ß-adrenergic stimulation of contractility in failing heart