2. Adrenergic Agonists (Sympathomimetics) Flashcards
What is the Rate Limiting Step in the mechanism of adrenergic agonists (synthesis of NE)?
Hydroxylation of tyrosine
How is NE stored?
- Dopamine enters a vesicle and is converted to NE
- NE is protected from degradation in the vesicle
- Transport in the vsicle is inhibited by reserpine
What is the release of NE blocked by?
- guanethidine
- bretylium
What inhibits the reuptake of NE into the neuron?
- Cocaine
- Imipramine
How is NE metabolised?
- NE is methylated by COMT
- Oxidized by MAO
Alpha adrenoceptors response to isoproterenol?
Weak
Beta adrenoceptors response to isoproterenol?
Strong
Alpha adrenoceptors response to Epi + NE?
Strong
Beta adrenoceptors response to Epi + NE?
Less responsive
Rank order of catecholamine potency for alpha adrenoceptors?
Epi > NE >> isoproterenol
Rank order of catecholamine potency for beta adrenoceptors?
Isoproterenol > Epi > NE
What is the location of α1 adrenoceptors?
Mainly POST-synaptic
What is the location of α2 adrenoceptors?
Mainly PRE-synaptic
What is the location of β1 adrenoceptors?
Heart
What is the location of β2 adrenoceptors?
Smooth Muscle
What is the location of β3 adrenoceptors?
Adipocytes
What drug has a selective afinity for α1 adrenoceptors?
Phenylephrine
What drug has a selective afinity for α2 adrenoceptors?
Clonidine
What is the potency of endogenous ligands for β1 adrenoceptors?
Epi = NE
What is the potency of endogenous ligands for β2 adrenoceptors?
Epi > NE
What is the mode of action of α1 adrenoceptors?
Activate phospholipase C
What is the mode of action of α2 adrenoceptors?
Inhibit adenylyl cyclase
What is the mode of action of all β adrenoceptors?
Activate adenylyl cyclase to inc cAMP
What is the distribution of α1 adrenoceptors?
- Heart
- Vasc. smooth muscle
What is the distribution of α2 adrenoceptors?
- Kidneys
- CNS
What is the distribution of β1 adrenoceptors?
Heart
What is the distribution of β2 adrenoceptors?
Smooth muscle
What is the distribution of β3 adrenoceptors?
Adipocytes
What are the effects of α1 adrenoceptors?
- Vasoconstriction
- Inc peripheral resistance
- Inc BP
- Mydriasis
- Inc closure of bladder’s internal sphincter
What are the effects of α2 adrenoceptors?
- Inhib NE release
- Tx HTN
- Inhib ACh release
- Inhib insulin release
What are the effects of β1 adrenoceptors?
- Tachycardia
- Inc lipolysis
- Inc myocardial contractility
- Inc release of renin
What are the effects of β2 adrenoceptors?
- Vasodilation
- Dec peripheral resistance
- Bronchodilation
- Inc muscle + liver glycogenolysis
- Inc release of glucagon
- Relaxed uterine smooth muscle
What are the pharmacological effects of low doses of Epi?
Predom β-effects = vasodilation
What are the pharmacological effects of high doses of Epi?
Predom α-effects = vasoconstriction
What are the overall cardiovascular effects of Epi?
- Net increase in systolic BP
- Slight decrease in diastolic BP
What are the cardiac effects of Epi?
Increased CO
What is Epi’s effect on vascular smooth muscle?
Decreased renal BF
What are the respiratory effects of Epi?
Bronchodilation = β2
How does Epi cause Hyperglycemia?
- Inc glycogenolysis = β2
- Inc glucagon release = β2
- Dec insulin release = α2
What are the therapeutic uses of Epi?
- Bronchospasms
- Anaphylactic shock
- Cardiac arrest
- Local anesthetics
What are the pharmacokinetics of Epi?
- Not effective orally
- Absorp more rapid with IM injection
- In emergencies = IV
What are pt contraindications for Epi?
- Hyperthyroidism (inc adrenoreceptors)
- Pts taking digoxin
- DB pts
What can have drug interactions with Epi?
- Inhalation anesthetics
- Cocaine
- β - blockers
What are the cardiovascular effects of NE?
- Inc SBP and DBP
- Inc TPR
- CO unchanged or dec
What are the therapeutic uses for NE?
- Raises or support BP in ICU
- Tx shock
What is an adverse affect from NE?
Causes necrosis at site of injection (due to vasoconstriction)
What does the stimulation of dopaminergic receptors cause?
vasodilation
What are the cardiovascular effects of Dopamine?
- Stimulate β1 - adrenoceptors
- At very high doses stimulates α1 - adrenoceptors
What are the Renal effects of Dopamine?
- Dilates renal and splanchnic arterioles
- Inc renal BF (opposite of Epi)
What are the therapeutic uses for Dopamine?
- Tx cardiogenic and septic shock
- Raises BP via β1 stimulation
- Vasoconstriction via α1
- And inc renal perfusion via D1 and D2
- Tx hypotension
- Tx severe CHF
Non-selective α adrenergic agonist
oxymetazoline
α1 selective agonists
phenylephrine
α2 selective agonists
Clonidine, guanabenze, guanafanecine
Non-selective β agonists
isoproterenol, dobutamine
β1 - selective agonists
dobutamine
β2 - selective agonists
terbutaline
What is clonidine used to tx?
HTN
What is the therapeutic use of Dobutamine?
Acute cardiac insufficiency
What are the adverse effects of Dobutamine?
- Contraindicated in A-fib
- May inc AV conductance
What are the therapeutic uses for short acting β2 - selective agonists (albuterol)?
- Bronchodilation
- Pre-mature labor (terbutaline)
What are the therapeutic uses for long acting β2 - selective agonists?
Chronic managment of asthma
(salmeterol, formoterol, carmoterol, ritodrine, indacaterol)