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Pharmacology > Adrenergic Agonists > Flashcards

Adrenergic Agonists Flashcards

1
Q

Describe the following characteristics of the sympathetic system:

  • anatomy and chemistry
  • origin
  • pathway
  • NTs released from pre-ganglionic cells
  • NTs released from post-ganglionic cells
A

ANATOMY

  • aka thoracolumbar division
  • fight or flight
  • IML => short pre-ganglionic cells => sympathetic chain => long post-ganglionic cells => effector organs

NTs

  • pre-ganglionic cells release ACh onto nicotinic receptors
  • post-ganglionic cells release NE onto alpha- and beta-adrenergic receptors
  • NOTE: sympathetics innervating the sweat glands will release ACh onto muscarinic receptors
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2
Q

Describe the following characteristics of the parasympathetic system:

  • anatomy and chemistry
  • origin
  • pathway
  • NTs released from pre-ganglionic cells
  • NTs released from post-ganglionic cells
A

ANATOMY

  • aka craniosacral division
  • rest and digest
  • originate from cranial nerves or pelvic nerves (S1-3)
  • long pre-ganglionic cells and short post-ganglionic cells

NTs

  • pre-ganglionic cells release ACh onto nicotinic receptors
  • post-ganglionic cells releases ACh onto muscarinic receptors
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3
Q

Describe the somatic system.

A
  • pre-ganglionic cell releases ACh on nicotinic receptors of skeletal muscles
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4
Q

List the major organs innervated by the parasympathetic systems and their functional responses.

A

EYE

  • miosis: pupillary sphincter constriction
  • accommodation: ciliary body muscle constriction

HEART

  • SA node; reduces heart rate
  • AV node; slows conduction

BRONCHIOLES
- constriction of smooth muscle

GI TRACT
- promotes secretions and motility

BLADDER
- contraction of detrusor muscle; bladder emptying

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5
Q

Describe the basic distribution of the adrenergic receptor subtypes in the following organs and their functional response:

  • eye
  • heart
  • bronchiole smooth muscle
  • kidney
  • vascular smooth muscle
  • splanchnic vaculature
A
  • eye: alpha-1, dilation of pupil via contraction of dilator
  • heart: beta-1, stimulates rate and force of heartbeats
  • bronchiole smooth muscle: beta-2, relaxation
  • kidney: beta-1; stimulates RAAT
  • vascular smooth muscle: alpha-1; constriction causes increased vascular resistance
  • splanchnic vasculature: dopamine-1; relaxation causes decreased vascular resistance
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6
Q

List the 4 main subtypes of adrenergic receptors, their associated second messenger system, and functional response.

A

ALPHA-1

  • Gaq => PhosphoLipase C => increases IP3 and DAG
  • increased Ca (Ca-calmodulin-dependent kinase activation) and PKC activation respectively

ALPHA-2
- Gi => inhibits adenylyl cyclase => inhibits cAMP formation => reduction of PKA activity => reduced activation of N-type calcium channels => prevents NT release

BETA-1

  • Gas => activates adenylyl cyclase => increases cAMP formation
  • increased PKA activation => phosphorylation and activation of downstream signals

BETA-2
- Gas => activates adenylyl cyclase => increases cAMP formation

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7
Q

List the following in order of their affinity for the adrenergic receptors:

  • epi
  • norepi
  • isoproterenol
A

ALPHA receptors: epi > NE&raquo_space; Iso
BETA-1 receptors: iso > epi = NE
BETA-2 receptors: iso > epi&raquo_space; NE

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8
Q

Categorize the adrenergic receptor agonists according to their affinity for the different receptors.

A
  1. dopamine binds to D1 > B1 > alpha as concentration increases
  2. epinephrine binds to all; prefers B2 at low conc.
  3. norepinephrine binds to all but B2;
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9
Q

List 4 commonly used indirect acting sympathomimetics.

A
  • amphetamine
  • methylphenidate
  • ephedrine
  • pseudo-ephedrine

(others: methamphetamine, tyramine)

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10
Q

Describe the most important toxic side effects and therapeutic uses of indirect acting sympathomimetic drugs. (only bold)

A 
toxicity = tachycardia, anxiety
therapeutics = ADD, narcolepsy, nasal decongestants
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11
Q

Describe the enteric system. What does innervation by sympathetic and parasympathetic provide?

A
  • ENS innervates GI, pancreas, and gallbladder
  • functions autonomously, but is moderated by symp/para
  • moderation by sympathetic/parasympathetic provides
    => second level of control over digestion
    => override in times of stress or emergency (fight or flight)
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12
Q

Describe adrenal sympathetic innervation.

A
  • adrenal medulla acts as a modified sympathetic ganglion
  • short pre-ganglionic cells arise from IML
  • pre-ganglionic cells release ACh onto nicotinic receptors directly on chromaffin cells
  • chromaffin cells then secrete NE and Epi directly into bloodstream (no post-ganglionic cells)
  • NE is converted to Epi via phenylethanolamine-N-methyltransferase
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13
Q

List the major organs innervated by the sympathetic nervous system and their functional responses.

A

EYE

  • mydriasis; activation of dilator muscle; pupil dilates
  • ciliary epithelium regulates production of aqueous humor

HEART
- increases SA node depolarization; increased HR

BRONCHIOLES
- relaxation of smooth muscle

BLOOD VESSELS

  • contraction and relaxation
  • depends on adrenergic receptor subtype and ligand

GI TRACT

  • decreased motility
  • overrides ENS during fight or flight

BLADDER

  • contraction of urethral sphincters
  • relaxation of detrusor muscle
  • inhibits emptying

METABOLISM
- increased BG (glycogenolysis, glycolysis, lipolysis)

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14
Q

What currents contribute to SA node pacemaker activity? Which of these currents is affected by sympathetic innervation?

A
  1. inward calcium current
  2. funny current (hyperpolarization-induced)
  3. outward K+ current

SYMPATHETICS

  • increases inward calcium and funny currents
  • promotes faster depolarization during phase 4
  • lowers threshold for activation
  • greater contractile force (calcium influx in myocytes)
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15
Q

Describe the mechanisms and steps of adrenergic neurotransmission (5).

A
  1. NT SYNTHESIS
    - tyrosine is converted to L-DOPA via tyrosine hydroxylase
    - L-DOPA is metabolized to dopamine via dopa decarboxylase
  2. VESICULAR STORAGE
    - dopamine is transported into vesicles via Vesicle MonoAmine Transporter (VMAT)
    - storage vesicles contain ATP
    - DA is converted to NE by dopamine beta-hydroxylase (found in vesicles)
  3. RELEASE
    - voltage-gated calcium channels open to allow influx of calcium
    - vesicular and synaptic membrane SNAREs interact and exocytose NT inside
  4. BINDING
    - depends on receptor type, second messenger system, and machinery of cell type
  5. TERMINATION
    - reuptake
    - diffusion out of synaptic cleft
    - metabolic transformation via MAO (intracellular, after reuptake) and COMT (circulation)
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16
Q

List the tissue and actions associated with alpha-1 adrenergic receptors.

A

TISSUES => ACTIONS

  • vascular smooth muscle => contracts to increase vascular resistance
  • pupillary dilator muscle => contracts => dilates the pupil
17
Q

List the tissue and actions associated with alpha-2 adrenergic receptors.

A

TISSUES => ACTIONS

  • platelets => aggregation
  • nerve terminals => inhibits NT release
18
Q

List the tissue and actions associated with beta-1 adrenergic receptors.

A

TISSUES => ACTIONS

  • heart => stimulates rate and force
  • juxtaglomerular cells => stimulates renin release
19
Q

List the tissue and actions associated with beta-2 adrenergic receptors.

A

TISSUES => ACTIONS

  • bronchiole smooth muscle => relaxation
  • uterine smooth muscle => relaxation
  • vascular smooth muscle => relaxation
  • somatic nerve terminals => tremor of voluntary muscles
20
Q

List the tissue and actions associated with beta-3 adrenergic receptors.

A

TISSUES => ACTIONS

- fat cells => lipolysis

21
Q

List the tissue and actions associated with dopamine-1 adrenergic receptors.

A

TISSUES => ACTIONS

- renal/splanchnic blood vessels => relaxation => reduces vascular resistance

22
Q

Describe the mechanism by which alpha-1 receptors mediate vascular smooth muscle contraction.

A
  1. Gaq => PLC => IP3 and DAG
  2. IP3 activates IP3 receptor that acts as a calcium channel of the sarcoplasmic reticulum (SR)
  3. IP3R releases stored calcium => increases free calcium in cytoplasm
  4. increased calcium stimulates smooth muscle contraction
23
Q

Describe the mechanism by which beta-1 receptors stimulate force and rate of heart muscle contractions.

A
  1. Gas => AC => cAMP => PKA
  2. PKA => phosphorylation of N-type calcium channels => increased inward Ca current
  3. faster SA node depolarization
24
Q

Describe the mechanism by which beta-1 receptors stimulate increased contractility of heart muscle.

A
  1. Gas => AC => cAMP => PKA
  2. PKA => phosphorylation of L-type calcium channels
  3. larger trigger signal for calcium release from SR
  4. trigger calcium also enters the SR => increased calcium storage for the next contraction
25
Q

Describe the mechanism by which beta-2 receptors stimulate bronchiole vascular smooth muscle relaxation. How does this relate to the function of alpha-2 receptors?

A
  1. Gas => AC => cAMP => PKA
  2. phosphorylation and INactivation of myosin light chain kinase (MLCK)
  3. reduced affinity of MLCK for Ca-calmodulin
  4. reduced MLCK enzymatic activity => no phosphorylation of myosin light chain => no myosin-actin cross-bridging => no contraction
  5. reduced smooth muscle contraction

ALPHA-2
1. Gi => no AC => no cAMP => no PKA => MLCK => phosphorylation of MLC => vascular constriction

26
Q

What are the endogenous ligands for adrenergic receptors?

A
  • NE
  • Epi
  • DA
27
Q

Define direct-acting sympathomimetics.

A

interact directly with adrenergic receptors

28
Q

Describe the structure of catecholamines and how it relates to degradation and specificity.

A

Structure = phenyl ring with 2 OH + ethylamine with side chain

  • prone to degradation
  • can be made more or less specific by altering amino side chain
  • can be made more or less lipophilic by altering OH groups on phenyl
  • can be made more or less susceptible to degradation
29
Q

Define isoproterenol structure.

A
  • has large amino group substitution

- selective for beta-adrenergic receptors

30
Q

Describe which factors of mean arterial pressure are most affected by adrenergic receptors:
MAP = CO x TPR

A
  • adrenergic receptors in the vasculature have more of an effect on TPR and diastolic pressure, since it is mediated by vascular arterial vasoconstriction
    => alpha-1, beta-2
  • adrenergic receptors in the cardiac tissue have more of an effect on CO and systolic pressure, since that is determined by contractility
    => beta-1
31
Q

Define indirect-acting sympathomimetics.

A
  • increase concentration of endogenous catecholamines in synapse and circulation leading to INdirect activation of adrenergic receptors
  • mechanism
    1. release of cytoplasmic catecholamines
    2. blockade of reuptake transporters

Pharmacology (22 decks)

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