3.2 - Sympathetic Drugs Flashcards
Biosynthesis of Catecholamines
- Location
- Steps
- Fate of NE in the cleft
- Drugs that interfere in the biosynthesis, storage, release and fate of Catecholamines
Catecholamines
- NE
- EPI
- Dopamine
Locations
- Sympathetic, post-ganglionic neurons — NE
- Adrenal Medulla — EPI
- CNS — Dopamine
Steps
Tyrosine ➡️1️⃣ L-DOPA ➡️2️⃣ Dopamine ➡️ vesicular transport via VMAT ➡️ formation of NE (DA ➡️3️⃣ NE) ➡️ formation of EPI (NE ➡️4️⃣ EPI)
REMEMBER ‼️
- Tyrosine — Precursor
* L-DOPA — L-dihydroxyphenylalanine)
Prevent premature metabolism by pre-synaptic enzymes
VMAT
– Vesicular Monoamine Transporter
1️⃣
Tyrosine Hydroxylase
— rate-limiting step
2️⃣
L-DOPA decarboxylase
3️⃣
Dopamine-B-hydroxylase
4️⃣
Phenylethanolamine-N-methyltransferase
Fate of NE in the cleft
- Binding to post-synaptic ®
- Metabolism by MAO & COMT
- Reuptake Process
– Major mechanism of excess NE in the cleft (loss)
– Transporter:
— NET (NE Transporter/ Uptake-1 Transporter
Reuptake Process
Drugs that Interfere in the Biosynthesis, Storage, Release and Fate of Catecholamines
- Formation of L-Dopa
- Vesicular Transport via VMAT
- Release of NE
- Reuptake Process
Formation of L-DOPA: INHIBITOR
Metyrosine
— Inhibits tyrosine hudroxylase
Vesicular transport via VMAT: INHIBITOR
Reserpine
Release of NE (exocytosis): STIMULATORS
— TEAAA
- Tyramine
- Ephedrine
- Amphetamine
- Angiotensin II
- a-latrotoxin
Release of NE (expcytosis): INHIBITORS
- Guanethidine
- Guanabenz
- Bretylium
Reuptake Process: INHIBITORS
• TCAs - Inhibits reuotake of NE > 5-HT • Cocaine - Vasoconstriction • NERI (Reboxitine)
Receptors
- Alpha
- Beta
- Dopamine
Alpha
- Alpha 1
* Alpha 2
Alpha 1 Receptors
– Gq linked — CONTRACTION
— Locations & Effects
Alpha 1: Locations & Effects
- Vascular SM
- Bladder Trigone & Sphincter
- Prostatic SM
- Radial Muscle of the 👀
- Pilomotor SM
Vascular SM
Vasoconstriction
— ⬆️ BP
Bladder Trigone & Sphincter
Contraction
— Urinary Retention
Prostatic SM
Contraction
— URinary Retention
Radial Muscle of the 👀
Contraction
— MYDRIASIS
Pilomotor SM
Piloerection
— Goosebumps
Alpha 2 Receptors
- Pre-synaptic a2
* Post-synaptic a2
Pre-synaptic a2
– Gi-linked— ⬇️ CAMP
— Location
— Effect
— Consequencs
Location
Vasomotor Center (Brain) — momentary regulation of BP
Effect
Autoregulation
— stimulation will INHIBIT further release of NE
Consequences
- Central
* Peripheral
Central
Sedation & Depression
Peripheral
Vasodilation
Post-synaptic a2
– Gq-linked — CONTRACTION
— Location
— Effects
Location
Peripheral Blood Vessels
Effect
VasoCONSTRICTION
Beta
– Gs-linked — ⬆️cAMP
- Beta 1
- Beta 2
- Beta 3
Beta 1 Receptors
• Locations & Effects
Heart
- (+) Inotropy — force
- (+) Chronotropy — rate
- (+) Dromotropy — conduction velocity
Kidneys (Juxtaglomerular Apparatus)
Release of the enzyme renin = HTN
Beta 2 Receptors
• Locations & Effects
Locations
- Bronchial SM
- Uterine SM
- Vascular SM
- Skeletal Muscle Cell Membrane
- Neuromuscular End Plates
Bronchial SM
Bronchodilation
Uterine SM
Uterine Relaxation (Tocolysis)
Vascular SM
- Blood vessels that supply skeletal muscles
VasoDILATION
Skeletal Muscle Cell Membrane
⬆️ inward conductance of K ions = HYPOkalemia
Neuromuscular End Plates
Contraction (Tremors)
Beta 3 Receptors
• Location
- Adipose Tissues
• Effect
- LIPOLYSIS
Dopamine
– Gs-linked
- D1 Receptors
* D2 Receptors
D1 Receptors
- Location
* Effect
Renal & Splanchic Blood Vessels
Renal Vasodilation = ⬆️ GFR = ⬆️ diuresis
D2 Receptors
- Peripheral GIT
* CNS
Peripheral GIT
Loss of Peristalsis (Ileus)
— Relaxation
** Antagonist: Metoclopramide
CNS
- Modulates motor activity
* Perception & behavior
Sympathomimetics
— aka Adrenergic Agonists
- Direct-acting
- Indirect-acting
- Centrally-acting
Direct-acting Sympathomimetics
– directly binds & stimulates adrenergic receptors
- Non-selective
* Selective
Non-selective
Directly bind & activate MORE THAN 1 general type of adrenergic receptors (a, B, DA)
Examples:
- Natural catecholamines
- NE
- EPI
- DA
Pharmacodynamics
⬆️ affinity at B receptors than A receptors
• Low Dose: B effect
• Hugh Dose: A effect
Pharmacodynamics
Specific:
• NE: B1 ➡️ A1
• EPI: B2 = B1 ➡️ A1 (anaphylaxis)
• DA: D1 ➡️ B1 ➡️ A1
Pharmacokinetics
- ✖️oral preparations available
* Undergo extensive first pass effect
Route of Administration
- IV
- SQ
- Inhalational