1.Names of adrenergic agonists 2. Synthesis of acetylcholine 3. ⁠adverse effects of NM BLOCKERS 4. ⁠ADVERSE EFFECTS OF SUCCNYLE CHOLINE 5. ⁠USES OF TIMOLOL 6. ⁠WHY CATECHOLEAMINE DO NOT ENTER TO CNS 7. ⁠MECHANISM OF NMJ BLOCKERS 8. ⁠ ROUTES OF DRUG ADMINISTRATIONS 9. ⁠LOCATIONS OF B2 RECEPTORS 10. ⁠SYNTHESIS,STORAGE ,RELEASE AND LYSIS OF EPINEPHRINE Answer all these questions

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Comprehensive Pharmacology Answers

Sources: Lippincott Illustrated Reviews: Pharmacology, Goodman & Gilman's Pharmacological Basis of Therapeutics, Barash's Clinical Anesthesia, Katzung's Basic & Clinical Pharmacology

1. Names of Adrenergic Agonists

Adrenergic agonists (sympathomimetic amines) are classified into three groups based on their mechanism:

A. Direct-Acting (act directly on adrenergic receptors):

Catecholamines: Epinephrine (adrenaline), Norepinephrine (NE), Dopamine, Isoproterenol, Dobutamine
Non-catecholamines: Phenylephrine (α1), Clonidine (α2), Salbutamol/Albuterol (β2), Terbutaline (β2), Salmeterol (β2), Formoterol (β2), Metaproterenol (β2)

B. Indirect-Acting (trigger NE release from nerve terminals):

Amphetamine, Tyramine, Cocaine (blocks reuptake)

C. Mixed-Acting (both direct + indirect):

Ephedrine, Pseudoephedrine, Metaraminol

Goodman & Gilman's, Figure 14-1: Classification of adrenergic receptor agonists

2. Synthesis of Acetylcholine

ACh synthesis and neurotransmission involves 6 sequential steps:

Step 1 - Synthesis:

Choline is transported from extracellular fluid into the cytoplasm of the cholinergic neuron via a sodium-cotransport carrier system
Choline has a quaternary nitrogen (permanent positive charge) so it cannot diffuse through the membrane
Uptake of choline is the rate-limiting step
The enzyme choline acetyltransferase (ChAT) catalyzes the reaction:

Choline + Acetyl-CoA → Acetylcholine (ACh)
This reaction occurs in the cytosol of the presynaptic terminal

Step 2 - Storage: ACh is packaged into presynaptic vesicles by active transport along with ATP (cotransmitter) and proteoglycan

Step 3 - Release: An action potential opens voltage-sensitive Ca²⁺ channels → ↑ intracellular Ca²⁺ → vesicle fusion with presynaptic membrane → ACh released into synaptic cleft (blocked by botulinum toxin; caused to dump by black widow spider venom)

Step 4 - Receptor Binding: ACh binds to muscarinic or nicotinic receptors on target cells

Step 5 - Degradation: Acetylcholinesterase (AChE) rapidly cleaves ACh into choline + acetate in the synaptic cleft

Step 6 - Recycling: Choline is taken back up into the presynaptic terminal to be reused

Lippincott Pharmacology, Figure 4.3

3. Adverse Effects of NM (Neuromuscular) Blockers

Non-depolarizing NMB Adverse Effects:

Drug	Key Adverse Effects
Pancuronium	Tachycardia, hypertension (vagolytic effect)
Vecuronium / Rocuronium	Minimal cardiovascular effects; rocuronium slightly increases heart rate
Cisatracurium	Laudanosine accumulation (CNS excitation at high doses)
Atracurium	Histamine release → hypotension, bronchospasm
Mivacurium	Histamine release; prolonged block in patients with pseudocholinesterase deficiency

Class-wide effects:

Skeletal muscle paralysis including respiratory muscles (diaphragm last affected, first to recover)
Apnea/respiratory failure if not reversed
No CNS penetration - NMBs do not cross the blood-brain barrier (do not cause sedation or analgesia - must always be paired with anesthetic)
Drug interactions: Enhanced blockade with halogenated anesthetics (isoflurane, sevoflurane), aminoglycosides, magnesium; reversed by neostigmine/sugammadex

Lippincott Pharmacology; Fuster & Hurst's The Heart

4. Adverse Effects of Succinylcholine

Succinylcholine is a depolarizing NMB with several unique and serious adverse effects:

a. Malignant Hyperthermia - Most serious; triggered especially with concurrent halothane. Leads to a hypermetabolic crisis (treat with dantrolene)

b. Hyperkalemia - Depolarization at NMJ causes efflux of K⁺ from muscle cells. Under normal conditions this is tolerable, but in:

Burn patients
Trauma / crush injury
Immobilized/paralyzed patients
Patients with myopathies
Denervation injuries

...massive upregulation of nicotinic receptors leads to life-threatening hyperkalemia → cardiac arrhythmia or arrest. Succinylcholine is contraindicated in these patients.

c. Prolonged Paralysis - Patients with plasma cholinesterase deficiency (qualitative or quantitative) cannot hydrolyze succinylcholine, resulting in prolonged neuromuscular blockade

d. Muscle Fasciculations & Myalgias - Initial brief fasciculations (visible muscle twitching) cause postoperative muscle soreness in up to 30% of patients

e. Increased Intraocular Pressure (IOP) - Risk in penetrating eye injuries

f. Increased Intragastric Pressure - Risk of regurgitation

g. Increased Intracranial Pressure (ICP) - Caution in head injury

h. Bradycardia - Especially with repeat dosing or in children (due to muscarinic stimulation)

i. Masseter Spasm - Rare, especially in children; may precede malignant hyperthermia

Lippincott Pharmacology; Miller's Anesthesia; Rosen's Emergency Medicine

5. Uses of Timolol

Timolol is a non-selective β-blocker (blocks both β1 and β2 receptors), more potent than propranolol.

Primary Uses:

1. Glaucoma (main use):

Topically applied timolol reduces intraocular pressure (IOP) by decreasing the production of aqueous humor by the ciliary body
Used for chronic open-angle glaucoma
Onset ~30 minutes; effects last 12-24 hours
Unlike cholinergic drugs, does NOT affect pupil size or near-vision focusing
Note: For acute angle-closure glaucoma, pilocarpine is still the emergency drug of choice

2. Hypertension

3. Angina Pectoris

4. Post-Myocardial Infarction - Reduces mortality and risk of reinfarction

5. Migraine Prophylaxis - Oral timolol reduces frequency of migraines

6. Infantile Hemangioma - Topical timolol (ophthalmic preparation) used off-label for pediatric hemangiomas

Contraindications: Asthma, obstructive airway disease, bradycardia, congestive heart failure

Lippincott Pharmacology, Figure 7.8; Fitzpatrick's Dermatology

6. Why Catecholamines Do NOT Enter the CNS

Catecholamines (epinephrine, norepinephrine, dopamine) cannot cross the blood-brain barrier (BBB) for these reasons:

1. Polar/Hydrophilic Nature:

Catecholamines have a catechol ring with two hydroxyl groups (-OH) and a charged amine group
This makes them highly polar and water-soluble
The BBB requires lipid-soluble substances to pass by passive diffusion

2. Blood-Brain Barrier Structure:

The BBB consists of tight junctions between brain capillary endothelial cells
Polar molecules are blocked from paracellular passage
Catecholamines lack sufficient lipid solubility to cross by transcellular diffusion

3. Active Transport Exclusion:

There are no specific active transport carriers for catecholamines at the BBB
They are not substrates for the transporters that allow CNS entry

Clinical Consequence:

Catecholamines present in the brain are synthesized locally (not derived from circulation)
Only at the highest infusion rates do very minor CNS effects occur ("nervousness," "adrenaline rush")
In contrast, non-catecholamines like amphetamine (lipid-soluble, lacking hydroxyl groups) readily penetrate the BBB and produce marked CNS stimulation

Barash's Clinical Anesthesia; Katzung's Basic & Clinical Pharmacology

7. Mechanism of NMJ Blockers

A. Non-Depolarizing (Competitive) Blockers

(Cisatracurium, Rocuronium, Vecuronium, Pancuronium, Mivacurium)

Competitively bind to nicotinic (Nm) receptors at the motor endplate of skeletal muscle
They compete with ACh at the receptor without stimulating it
This prevents depolarization of the muscle cell membrane
Result: muscle is unable to contract → flaccid paralysis
Reversal: by cholinesterase inhibitors (neostigmine, edrophonium) that increase ACh concentration, outcompeting the blocker; or by sugammadex (encapsulates rocuronium/vecuronium)
Order of muscle paralysis: Face/eyes → fingers → limbs → neck/trunk → intercostals → diaphragm (last)
Recovery: reverse order (diaphragm first)

B. Depolarizing Blockers

(Succinylcholine - the only one in clinical use)

Structurally resembles ACh (two linked ACh molecules)
Binds to nicotinic receptors and causes persistent depolarization
Phase I: Initial fasciculations then flaccid paralysis (membrane remains depolarized; cannot respond to further ACh)
Succinylcholine is not metabolized at the NMJ - it must redistribute to plasma to be hydrolyzed by plasma cholinesterase
Cannot be reversed by neostigmine (actually worsens Phase I block)

Lippincott Pharmacology, Figures 5.9 & 5.12

8. Routes of Drug Administration

Route	Key Features
Oral	Most common, convenient, economical; affected by gastric pH, first-pass metabolism; enteric-coated and ER preparations available
Sublingual / Buccal	Under tongue / between cheek and gum; rapid absorption, bypasses first-pass metabolism
IV (Intravenous)	Fastest onset; 100% bioavailability; no absorption phase; used in emergencies and unconscious patients
IM (Intramuscular)	Slower absorption than IV; good for depot preparations; moderate pain
SC (Subcutaneous)	Slowest parenteral route; good for insulin, heparin; constant slow absorption
Intradermal	Into dermis; used for allergy testing and desensitization
Inhalation	Rapid onset (nearly as fast as IV); ideal for respiratory diseases (asthma, COPD); minimizes systemic effects
Nasal	Topical to nasal mucosa; used for allergic rhinitis, some systemic drugs
Topical	Local effect on skin/mucosa
Transdermal (patch)	Systemic effect via skin; slow sustained release; avoids first-pass; e.g., nicotine, fentanyl patches
Rectal	50% bypasses portal circulation (reduces first-pass); useful when patient vomiting or unconscious; absorption erratic
Intrathecal / Intraventricular	Direct into CSF; bypasses BBB; for CNS infections or cancer

Three major categories:

Enteral - oral, sublingual, buccal, rectal
Parenteral - IV, IM, SC, intradermal
Other - inhalation, nasal, topical, transdermal, intrathecal

Lippincott Pharmacology, Figure 1.2 & Table 1.5

9. Locations of β2 Receptors

β2 receptors are found in:

Location	Effect of β2 Stimulation
Bronchial smooth muscle	Bronchodilation (main therapeutic target in asthma)
Uterine smooth muscle (myometrium)	Relaxation (tocolysis - stops preterm labor; e.g., terbutaline)
Vascular smooth muscle (skeletal muscle vessels)	Vasodilation → ↓ peripheral resistance
Gastrointestinal smooth muscle	Decreased motility and tone
Skeletal muscle	Increased K⁺ uptake (↓ plasma K⁺); tremor with excess
Liver (hepatocytes)	Glycogenolysis → ↑ blood glucose
Pancreas (β-cells)	↑ Insulin secretion
Mast cells	Inhibition of mediator release
Heart (minor role)	Slight positive inotropic/chronotropic (mostly β1)
Kidney (juxtaglomerular cells)	↑ Renin release (β1 primarily, some β2 contribution)
Eye (ciliary muscle)	Relaxation

Katzung's Basic & Clinical Pharmacology; Lippincott Pharmacology

10. Synthesis, Storage, Release, and Lysis (Inactivation) of Epinephrine

Synthesis (Catecholamine Pathway):

Phenylalanine / Tyrosine → (Tyrosine Hydroxylase) → L-DOPA → (DOPA Decarboxylase) → Dopamine → (Dopamine β-Hydroxylase†) → Norepinephrine → (PNMT‡) → Epinephrine*

* Tyrosine Hydroxylase = rate-limiting step; subject to feedback inhibition by NE
† Dopamine β-Hydroxylase occurs inside vesicles of postganglionic neurons and adrenal medulla
‡ PNMT (phenylethanolamine-N-methyltransferase) converts NE → EPI; found only in adrenal medulla chromaffin cells; stimulated by glucocorticoids from adrenal cortex

EPI is primarily synthesized in the adrenal medulla (80-85% of adrenal medullary catecholamine content is EPI; 15-20% is NE)

Storage:

EPI is synthesized outside vesicles (PNMT is cytoplasmic), then re-enters vesicles for storage
Stored in chromaffin granules (secretory vesicles) in adrenal medulla
Vesicles also contain ATP, chromogranins, and dopamine β-hydroxylase
Reserpine depletes vesicular stores by blocking vesicular uptake

Release:

Sympathetic nerve stimulation → acetylcholine released at preganglionic endings → nicotinic receptor activation on chromaffin cells → membrane depolarization → Ca²⁺ influx → exocytosis of vesicle contents into bloodstream
EPI acts as a circulating hormone (unlike NE which acts as a neurotransmitter locally)
Release is inhibited by presynaptic α2-receptor stimulation (negative feedback)

Lysis / Inactivation (Three Mechanisms):

1. Reuptake (Uptake-1) - Most important for NE at local synapses; active, energy-dependent, temperature-dependent, stereospecific transport back into presynaptic terminal; blocked by cocaine and tricyclic antidepressants

2. Enzymatic Degradation:

MAO (Monoamine Oxidase) - located on mitochondria; oxidatively deaminates catecholamines
COMT (Catechol-O-Methyltransferase) - located extraneuronally; methylates the catechol ring
Final metabolite: Vanillylmandelic Acid (VMA) - measured in urine to diagnose pheochromocytoma

3. Diffusion - Small amounts diffuse into circulation and are metabolized by liver and kidney (predominant pathway for exogenously administered catecholamines, explaining their longer duration of action)

Barash's Clinical Anesthesia, Figures 14-7 & 14-8; Goodman & Gilman's

Quick Reference Summary:

Topic	Key Point
Adrenergic agonists	Direct (Epi, NE, phenylephrine), Indirect (amphetamine), Mixed (ephedrine)
ACh synthesis	Choline + Acetyl-CoA → ChAT → ACh; choline uptake is rate-limiting
NMB adverse effects	Histamine release, cardiovascular effects, apnea, no CNS effects
Succinylcholine adverse effects	Hyperkalemia, malignant hyperthermia, prolonged paralysis, fasciculations
Timolol uses	Glaucoma (topical), HTN, angina, MI, migraine prophylaxis
Catecholamines & CNS	Too polar/hydrophilic; no BBB transporters; synthesized locally in brain
NMJ blocker mechanism	Non-depolarizing: competitive block of nicotinic receptor; Depolarizing: persistent depolarization
Drug administration routes	Enteral, parenteral, inhalation, topical, transdermal, intrathecal
β2 receptor locations	Bronchi, uterus, vascular SM, liver, skeletal muscle, mast cells
Epinephrine synthesis	Tyrosine → DOPA → Dopamine → NE → EPI (via PNMT in adrenal medulla)

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