Adrenergic Agonists 2 Flashcards
Norepinephrine inactivation by
neuronal uptake of COMT and MAO (uptake 1)
PK of NE:
POLAR, found in urine, poorly absorbed in gut
Receptor selectivity of NE
a1=a2; B1»_space; B2
Receptor selectivity of E
a1=a2; B1 = B2
Receptor selectivity of Phenylephrine, Methoxamine
a1>a2»_space;» B (alpha agonists)
Receptor selectivity of Clonidine, Methyldopa
a2>a1»_space;» B (alpha agonists)
alpha 2 agonists decrease sympathetic outflow –> decreased TPR and HR
Receptor selectivity of Dobutamine
B1»_space; B2»_space;» a (beta agonist)
Receptor selectivity of Isoproterenol
B»_space;» a (strong beta agonist)
Receptor selectivity of Terbutaline, Albuterol
B2»_space; B1»_space;» a (beta agonists)
Receptor selectivity of Dopamine
D1=D2»_space; B»_space; a
Receptor selectivity of Fenoldopam
D1»_space; D2
Norepinephrine CVS effects?
Increased PVR –> Increased SP/DP
Increased SV
CO variable
Which has the greater effect on BP? NE or E? Why?
Norepinephrine because of increase in PVR (predominant alpha receptor activation–NE does not at on B2 which is responsible for vasodilation)
Why does NE result in reflex bradycardia but not E?
Epi will not cause a tremendous increase in BP because it acts on B2 receptors responsible for vasodilation. Norepi will act on alpha 1 receptors (blood vessels) and beta 1 (heart) but not beta 2. The increase in blood pressure evokes a baroreceptor vagal reflex in bradycardia.
How can NE cause tissue necrosis and sloughing when extravasated through IV?
Vasoconstriction
Impaired circulation due to NE can be relieved by what?
phentolamine (alpha receptor antagonist)
What is the metabolic precursor of NE and E?
Dopamine
What are the effects of low doses of Dopamine on CVS?
Vasodilation (D1 receptors at renal, mesenteric, and coronary beds)
Cardiogenic shock is treated with?
DA > isoproterenol
What are the effects of moderately high doses of Dopamine on CVS?
Beta 1 receptor activation (heart) –> +inotropy with MINIMAL TACHYCARDIA
Alpha 1 activation (vascular) –> vasoconstriction
What can dopamine cause the release of at nerve terminals?
NE
What are the effects of low doses of Dopamine on renal system?
D1 stim –> natriuresis –> diuresis
This is a benzazepine derivative and agonist for peripheral D1 receptors with moderate affinity for a2 receptors.
Fenoldopam
Which drug has dopamine receptor affinity and is used as a vasodilator in severe HTN?
Fenoldopam
Synthetic analog of dopamine:
Dopexamine
This has D1 and D2 affinity and inhibits catecholamines uptake.
Dopexamine (also B2 activity)
Therapeutic uses of Dopexamine:
severe CHF, cardiogenic and septic shock (similar to dopamine)
Powerful beta receptor agonist. Acts on all beta receptors.
Isoproterenol
Administration of isoproterenol?
Parenteral or aerosol
Metabolism of isoproterenol?
In liver by COMT.
POOR substrate for MAO
What are the effects of isoproterenol on the CVS?
Decrease DP –> Decrease BP (SP varies)
+inotropic/chronotropic effects (B1) –> increase CO
Vasodilation (B2) –> decreased PVR
What are the effects of isoproterenol on smooth muscles?
Bronchodilation (B2)
Vasodilation in skeletal muscles (B2)
B2 agonists are effective in asthmatics because of two reasons. What are they?
1) bronchodilation
2) inhibition of antigen-induced release of histamine and other inflammatory mediators
Therapeutic uses of isoproterenol:
1) Emergency bradycardia or heart block, in anticipation of cardiac pacemaker insertion or in patients with ventricular arrythmias
2) Replaced in treatment of asthma, COPD, and shock