Adrenergic Pharmacology

Question 1

Synthesis of catecholamines

Answer 1

Tyrosine is taken up into the nerve terminal when it is hydroxylated to dihydrocyphenylalanine (DOPA) by tyrosine hydroxylase [note: this is the rate limiting step]. DOPA is decarboxylated to dopamine (DA) by aromatic L-amino acid decarboxylase.

Question 2

Storage of catecholamines

Answer 2

DA actively transported into vesicle by vesicular monoamine transporter 2 (VMAT2) [promiscuous for all monoamines, susceptible to reserpine]. In the vesicle DA is hydroxylated to NE by dopamine beta-hydroxylase.
In the adrenal medulla NE is further N-methylated to epinephrine by phenylethanolamine-N-methyltransferase (PNMT)

Question 3

Release of catecholamines

Answer 3

Influx of calcium causes vesicles to fuse with membranes. Guanethidine blocks

Question 4

Presynaptic regulation of NE release

Answer 4

NE along with cotransmitters, neuropeptide Y and ATP, feedback on prejunctional receptors [alpha2, y2 and p1 respectively] to inhibit transmitter release. NE binding to beta2 results in enhanced neurotransmitter release

Question 5

Termination of actions of catecholamines

Answer 5

Metabolism of catecholamines does not occur in synaptic cleft. Reuptake and dilution are responsible. [Note: reuptake via NET or DAT is blocked by cocaine, SSRIs, SNRIs and TCAs (imipramine)]

Question 6

Catecholamine metabolism in nerve terminal

Answer 6

MAO is associated with the mitochondrial surface. Two subgroups: MOA-A preferentially metabolizes NE and 5-HT (serotonin). MAO-B like DA and phenylethylamine best. Both are found in the brain. A is also present in GI, liver, placenta and skin. B is in platelets and lymphocytes. Vanyllylmandelic acid is the major end product, renally excreted, ultra high levels present in pheochromocytoma.

Question 7

alpha-methyltyrosine

Answer 7

blocks the synthesis of NE by inhibiting TH

Question 8

methyldopa

Answer 8

inhibits AAADC and forms “false neurotransmitter,” alpha-methylnorepinephrine.

Question 9

Bretylium and guanethidine

Answer 9

prevent release of NE

Question 10

Tyramine, ephedrine and amphetamine

Answer 10

rapid, brief NE liberation both by displacing NE in extracellular fluid, and by facilitated exchange diffusion for the outward transport of NE. They also mobilize NE in vesicles by competing for vesicular uptake processes.

Question 11

Alpha adrenergic receptors

Answer 11

epinephrine > norepinephrine&raquo_space; isoproterenol.
alpha1 has a higher affinity for phenylephrine. Postsynaptic, constricts smooth muscle by Gq activation (PIP3 -> DAG and IP3 -> activation of protein kinase C and release of Ca++ resepectively.)
alpha2 selectively binds clonidine. Presynaptic, feedback inhibition, mediated by Gi and decreased cAMP levels. [Note: tamsulosin selectively treats BPH because it binds only alpha2A which is present in the urinary tract and not alpha2B in the blood vessels]

Question 12

Beta adrenergic receptors

Answer 12

isoproterenol > epinephrine > norepinephrine.
Beta1 equal affinity for NE and E.
Beta2 higher affinity for E than NE (make it particularly responsive to circulating E)
Beta3 involved in lipolysis, detrussor muscle
All beta receptors are mediated by Gs to increase intracellular cAMP

Question 13

Blood pressure control mechanisms

Answer 13

Cardiac output - dependent on venous return and heart rate (thus CO is under the control of RAAS and SANS)
Blood volume - dependent on renin-angiotensin-aldosterone system
Peripheral vascular resistance - dependent on RAAS and SANS

Question 14

Baroreceptor reflex

Answer 14

A drop in blood pressure (as measured by the aortic arch and the carotid sinus) results in SANS firing which causes: increased heart rate, increase ventricular contractility, increase total peripheral resistance, and vascular tone.
An increase in blood pressure results in PANS firing causing a decrease in heart rate.
Reflex can be blocked by ganglion blocking drugs - hexamethonium. Reflex tachycardia can be blocked with beta1 antagonist. Reflex bradycardia can be blocked with muscarinic antagonist

Question 15

Anti-hypertensive drugs

Answer 15

Can trigger ANS and endocrine feedback loops, resulting in tachycardia and salt and water retention. Beta blockers and diuretics are often part of anti-hypertensive regimens.

Question 16

sympathomimetic drugs - direct acting agonist

Answer 16

Responses are not reduced by prior treatment with reserpine or guanethidine. Actions of direct-acting amines may actually increase after transmitter depletion because the loss of the endogenous neurotransmitter induces compensatory changes that up-regulate receptors

Question 17

Sympathomimetic drugs - indirect-acting agonist

Answer 17

Act by releasing or displacing NE from vesicles, blocking reuptake of NE, blocking MAO or COMT. The response is abolished if there is prior treatment with reserpine or guanethidine

Question 18

Sympathomimetic drugs - mixed-action agonist

Answer 18

Effects are blunted, but not abolished by prior treatment with reserpine or guanethidine

Question 19

Epinephrine

Answer 19

Interacts with alpha and beta receptors (B>A). Effects are dose-dependent: low dose = beta effects (vasodilation). high dose = alpha effects (vasoconstriction).
Cardiovascular effects: Increase contractility and rate of contraction (positive ionotrope: beta1). Constricts arterioles in the skin, mucous membranes and viscera (alpha). Dilates liver and skeletal muscle vessels (beta2). Renal blood flow decreases. Increased systolic blood pressure with slightly decreased diastolic
Respiratory: powerful bronchodilator (beta2) and inhibits histamine release.
Hyperglycemia: glucose liberation (Beta2) and decreased insulin release (alpha2)
Lipolysis: beta2 on adipose tissue
Used to treat anaphylaxis, acute asthma, cardiac arrest, adjunct to local anesthetics.
Rapidly metabolized by MAO and COMT, metanephrine and vanillylmandelic acid excreted in urine.
Adverse effects include restlessness, tremor, tension, headache, and palpitation. Can induce cerebral hemorrhage and cardiac arrhythmia, diabetic patients may need to increase insulin doses

Question 20

Norepinephrine

Answer 20

Direct acting catecholamine. Stimulates alpha1 > alpha2 > beta1
Cardiovascular effects include rise in peripheral resistance from vasoconstriction in most beds including kidney. Increase in systolic and diastolic BP. Does not induce compensatory vasodilation in skeletal muscle, weak B2 activity.
Baroreceptor reflex: NE increases BP, inducing rise in vagal activity causing reflex bradycardia. Preadministration of atropine blocks vagal transmission and NE stimulation of the heart can be seen as tachycardia.
Therapeutic use in treating shock.
Given IV, duration 1-2 minutes, MAO and COMT metabolism, excretion in urine.
Adverse Effects are similar to epinephrine with additional blanching, sloughing off of skin and necrosis associated with injection site due to extreme vasoconstriction. Impaired circulation can be treated with phentolamine

Question 21

Isoproterenol

Answer 21

Direct-acting synthetic catecholamine, stimulates beta1 and 2, rarely used therapeutically,
Cardiovascular actions - intense stimulation of the heart, dilate skeletal muscle arterioles, greatly reduces mean arterial and diastolic blood pressure.
Potent bronchodilator, may still be useful intreating AV block.
Adverse effects similar to epinepthrine

Question 22

Dopamine

Answer 22

direct-acting natural catecholamine, stimulates D1, beta1 and alpha1. Effects are dose dependent. low dose = just D1, high dose = D1, beta1, and alpha1.
Cardiavascular effects - positive inotropic and chronotropic effects, at very high dose stimulates alpha1 causing vasocontriction.
Renal and visceral effects - dilates renal and splanchnic arterioles
Therapeutic drug of choice for cardiogenic and septic shock, especially in the context of oliguria. Also used to treat hypotension and severe heart failure in patients with low or normal peripheral vascular resistance or oliguria.
Adverse effects - same as sympathetic stimulation, rapidly metabolized by MAO and COMT so effects are short lived.

Question 23

Fenoldopam

Answer 23

Agonist of periperal dopamine D1 receptors. Used as a rapid active vasodilator to treat sever hypertension in hospitalized patients, acts of coronary arteries, kidney arterioles and mesenteric arteries
Adverse effects - headache, flushing, dizziness, nause, vomiting and tachycardia

Question 24

Dobutamine

Answer 24

Synthetic direct-acting catecholamine, beta1 receptor agonist. Increases cardiac rate and output with few vascular effects. Used to increase CO in acute heart failure and MI, inotropic effect after cardiac surgery because it does not significantly increase O2 demands on myocardium.
Adverse effects - used with caution in atrial fibrillation, because it increases AV conductance, others similar to epinephrine. Tolerance may develop with prolonged use.

Question 25

Oxymetazoline

Answer 25

Direct-acting synthetic adrenergic agonist that stimulates both alpha1 and alpha2 receptors. Actions at the vessels supplying the nasal mucosa and conjunctiva causing vasoconstriction and decreasing congestion. Found in many over the counter short term nasal spray decongestants and in ophthalmic drops for eye redness relief. Adverse effects from systemic circulation (inevitable) include nervousness, headaches, and trouble sleeping. Local effects include irritation, sneezing, rebound congestion and dependence with long term use.

Question 26

Phenylephrine

Answer 26

direct-acting, synthetic adrenergic, binds to alpha1 receptor. vasoconstrictor - raise both systolic and diastolic pressure, no effect on heart itself, induces reflex bradycardia Used to treat hypotension in hospitalized or surgical patients, especially those with rapid heart. Acts as a nasal decongestant when applied topically or taken orally. Ophthalmic solution for myadriasis. Can cause hypertensive headache and cardiac irregularities

Question 27

Clonidine

Answer 27

alpha2 agonist, acts presynaptically to decrease sympathetic outflow to the periphery. Used for the treatment of hypertension, minimize withdrawal from opiates, tobacco and benzodiazepines. Adverse effects commonly include lethargy, sedation, constipation, and xerostomia, abrupt discontinuance can cause rebound hypertension

Question 28

Albuterol and terbutaline

Answer 28

short-acting beta2 agonist. Used as bronchodilators and administered by a metered-dose inhaler, management of acute asthma symptoms. Terbutaline is also used off label as a uterine relaxant to suppress premature labor. Adverse effects include tremor, restlessness, apprehension, and anxiety. If administered orally, may cause tachycardia or arrhythmia especially in underlying cardiac disease. MAOI increase risk of cardiovascular effects and concomitant use should be avoided

Question 29

Salmeterol and formoterol

Answer 29

Long-acting beta2 agonists, single metered-dose inhalation device. Prolonged bronchodilation of 12 hours, has delayed onset, not for monotherapy but highly effective with a corticosteroid. Used to treat nocturnal asthma in symptomatic patients taking other asthma medications. Increase the risk of asthma related death.

Question 30

Amphetamine

Answer 30

NET substrate, reuptake inhibitors, reverse transport of NE, NE mobilizer. Also acts as an alpha1 agonist in vasculature and beta1 simulatory effect in the heart. Uses are as a CNS stimulant in the treatment of children with ADHD, narcolepsy, and for appetitie control. Adverse effects include aggressiveness, paranoid hallucinations, panic states, hypertension and arrhythmias, major potential for abuse, drug interation with MOA-A inhibitors causing hypertensive crisis.

Question 31

Tyramine

Answer 31

found in fermented foods, normally oxidized by MOA-A in gut and liver, but if patient in on MOAI, tyramine can precipitate a hypertensive crisis.

Question 32

Cocaine

Answer 32

unique among local anesthetic, block sodium-chloride-dependent norepinephrine transport to uptake NE, NE acculumates in the synaptic space. Potentiation of E and NE actions

Question 33

Ephedrine

Answer 33

Mixed-action adrenergic agents. Release stored NE and directly stimulate alpha and beta receptors, actions are similar to epinephrine, but less potent. Not catecholamines, poor MAO and COMT substrates so long duration of action. Raise S and D blood pressures by vasoconstriction and cardiac stimulation. Used to treat asthma and hypotention, but has been replaced by more effective drugs. Ephedrine produces a mild stimulation of the CNS - increases alertness, decreases fatigue, and prevents sleep. Pseudoephedrine is used orally to treat nasal and sinus congestion. Excellent oral absorption and BBB penetration, Ephedrine is eliminated largely unchanged in urine, while pseudoephedriun is incompletely metabolized by the liver before being excreted into the urine.

Question 34

phenoxybenzamine

Answer 34

Nonselective, covalently linking antagonizt of alpha1 and alpha2 receptors. Irreversible and non-competitive. Duration 24 hours after few hour delay Cardiovascular effects: prevents vasocontriction, decreased TPR causes reflex tachycardia. alpha2 blocking can contribute to increased cardiac output. Epinephrine reversal. Treatment uses include pheochromocytoma and Reynaud disease and frostbite. Adverse effects: postural hypotension, nasal congestion, nausea and vomiting, inhibit ejaculation, reflex tachycardia so caution should be used in patients with cerbrovascular or cardiovascular disease.

Question 35

Phentolamine

Answer 35

competitive alpha1 and 2 block that last approximately 4 hours. Causes epinephrine reversal. Causes reflex cardiac stimulation and tachycardia. Therapeutic uses are for short term management of pheochromocytoma, prevent dermal necrosis after norepinephrine extravasation, and to treat hyoertensive crisis due to clonidine withdrawal or MOAI patients who ate tyramine.

Question 36

Prozosin, terazosin, doxazosin, tamsulosin, and alfuzosin

Answer 36

selective competitive alpha1 blockers useful in hypertension treatment or the treatment of benign prostatic hyperplasia. All are excreted in urine except doxazosin which is excreted fecally. Cardiovascular effects: decrease TPR, lower BP, minimal changes in cardiac output, renal blood flow or GFR. Tamsulosin is most selective for SM at bladder neck and prostate. When treating hypertension with these agents, beware first dose effect orthostatic hypotension. alpha1 antagonists are not used as monotherapy. Adverse effects: dizziness, lack of energy, nasal congestions, headache, drowsiness, and orthostatic hypotension, inhibition of ejaculation and retrograde ejaculation and floppy iris syndrome during eye surgery

Question 37

Yohimbine

Answer 37

Competitive alpha2 blocker, has been sexual stimulant but doesn't work, contraindicated in cardiovascular disease, psychiatric and renal dysfunction because it may worsen these conditions

Question 38

Propranolol

Answer 38

Prototype beta-adrenergic antagonist, blocks beta1 and 2 with equal affinity. Cardiovascular effects, diminishes CO, HR, SV, and renin release. Attenuate the expected increase in heart rate. Non-selective blockade prevents B2 skeletal muscle vasodilation. Decreased blood pressure, in patients with hypertension, TPR returns to normal with long term use. Can exacerbate bronchoconstriction in COPD or asthma. Decreases glycogenolysis and glucogenesis and decreased glucagon secretion. Hypoglycermia may occur after insulin injection. Blocks the action of isoproterenol. Used to treat hypertension, angina pectoris, myocardial infarction (protective effect on myocardium and decreased incidence of sudden arrhythmic death), Migraine (BBB penetration due to lipophlic nature) and hyperthyroidism. Pharmacokinetics - good oral absorption, but first-pass effect brings only 25% to circulation. Volume of distribution is large. Extensively metabolized in liver (CYP450 - rifampin can decrease effects), metabolites excreted in urine. Adverse effects: Bronchoconstriction with asthma, arrhythmias if stopped abruptly, sexual impairment reported - mechanism unknown, metabolic disturbance (hypoglycemia and increased LDL with decreased HDL), CNS effects (depression, dizziness, lethargy, fatigue, weakness, visual disturbances, hallucinations, short-term memory loss, emotional lability and vivid dreams)

Question 39

Nadolol and timolol

Answer 39

Same as propranolol but more potent, nadolol has longer duration of action. Timolol reduces aqueous humor production in the eyes. Does not affect near vision of change pupil size, onset in 30 minutes, effects last 12-24 hours

Question 40

Atenolol, betaxolol, bisoprolol, esmolol, metoprolol and nebivolol

Answer 40

Selective beta1 antagonists, minimizes unwanted bronchoconstriction - but asthma patients should still be monitored Lowers BP in hypertension and increases exercise tolerance in angina - first line therapy for stable angina. Esmolol has short half-life and is used to control blood pressure or heart rhythm during surgery. Bisoprolol is the extended release formulation of metoprolol and is used for congestive heart failure.

Question 41

Acebutolol and pindolol

Answer 41

not pure antagonists, weakly stimulate B1 and 2 receptors, said to have intrinsic sympathomimetic activity. Diminished effect on cardiac rate and cardiac output compared to beta-blocker without ISA. Therapeutic uses: particularly effective in hypertensive patients with moderate bradycardia (these agents do not further decrease heart rate)

Question 42

Labetalol and carvedilol

Answer 42

nonselective beta and alpha1 blocking agents the produce peripheral vasodilation. Difference with beta-blockers that increase TPR initally Uses: labetalol is an alternative to methyldopa in pregnancy-induced hypertension, used in hypertensive emergencies. Beta-blockers cannot be given to patients in acute exacerbation of heart failure, but, carvedilol, metoprolol and bisoprolol are beneficial in patient with stable chronic failure. Adverse effects are orthostatic hypotension and dizziness.