Adrenergic Agonists & Antagonists Flashcards
(36 cards)
From where is norepinephrine released?
post-ganglionic sympathetic fibers at end organ tissues (except in eccrine sweat glands and some blood vessels)
From where is acetylcholine released?
Preganglionic sympathetic fibers and all parasympathetic fibers
How is the action of NorEpi terminated
Primarily reuptakeinto postganglionic nerve ending; also diffusion from receptor sites or via metabolism by monoamine oxidase
Where are alpha1-receptors located
smooth muscle throughout the body
What is occurs with activation of alpha1-receptors
contraction of smooth muscle
- midriasis, bronchoconstriction, vasoconstriction, uterine contraction, constriction of sphincters
- myocardium has alpha1-receptors –> positive inotropic effect
- most important clinical effect is vasoconstriction
What occurs with activation of peripheral alpha2-receptors
Inhibits NorEpi release
Vasoconstriction
What occurs with activation of CNS alpha2-receptors
Sedation and reduced sympathetic outflow –peripheral vasodilation and lower BP
Where are most B1 receptors located and what occurs with activation of these receptors?
Heart
+ Chronotropy
+ Dromotropy (conduction)
+ inotropiy
What occurs with activation of B2 receptors?
Smooth muscle relaxation: bronchodilation, vasodilation, uterus relaxation, bladder and gut
What occurs with activation of dopamine receptors - D1 and D2?
D1: mediates vasodilation in kidney, intestine and heart
D2: antiemetic properties (e.g., as in droperidol)
What are the naturally occurring cathecolamines and what is unique about their structure
Epinephrine, Norepi, Dopamine
All have a 3,4-dihydroxybenzene structure
What receptors does phenylephrine act on and what is its primary effect?
Selective alpha1-agonist
Peripheral vasoconstriction
Why does phenylephrine cause bradycardia?
Reflex bradycardia is mediated by the vagus nerve and can reduce cardiac output
Can tachyphylaxis occur with phenylephrine infusions? what is a typical infusion rate (mcg/kg/min)?
YES
0.25-1mcg/kg/min
What receptors does dexmedetomidine act on?
alpha-2 (200:1 alpha2:alpha1)
What is the half life of dexmedetomidine?
2-3 hours
What is the recommended dose of dexmed?
loading dose 1mcg/kg over 10 minutes, followed by infusion 0.2-0.7mcg/kg/hour
What can occur with abrupt cessation of dexmed after >48h of adminstration?
Withdrawal: hypertensive crisis
Where is epinephrine synthesized
Adrenal medulla
What is a typical range for an epinephrine infusion?
2-20mcg/min
On which receptors does NorEpi act?
Alpha-1 and 2; Beta-1
What receptors does dopamine act on at low doses (0.5-3mcg/kg/min)? What effect does this have?
Dopamine receptors (DA1) Vasodilates renal vasculature and promotes diuresis and natruiresis No beneficial effect on renal function
What receptors does dopamine act on at moderate doses (3-10mcg/kg/min)? What effect does this have?
Beta-1
Increased myocardial contractility, rate, SBP, CO
Myocardial oxygen demand increases disproportionately to supply
What receipts does dopamine act on at high doses (10-20 mcg/kg/min):? what effect does this have?
Alpha-1
increase in peripheral vascular resistance (fall in renal blood flow)
