Lecture 8: Sympatholytics Flashcards
a1 receptor ANTAGONIST
-phenoxybenzamine
-phentoalmine
-prazosin
-terazosin
-doxazosin
a1 ANTAGONIST side effects
-orthostatic HTN
-inhibit ejaculation
-nasal stiffness
-tachycardia
non-selective a receptor ANTAGONISTs
-B-Haloalkylamines
-imidazolines
B-haloalkylamines
-non selective a ANTAGONIST
-also blocks Acetylcholine, histamine, and serotonin receptors
-IRREVERSIBLE (form covalent bond)
B-haloalkylamines example
-phenoxybenzamine
B-haloalkylamines mechanism
Slide 13
Imidazolines
-non selective a ANTAGONIST
-also blocks 5-HT receptors
-also muscarinic and histmaine AGONIST
-reversible
Imidazoline effects
-vasodilator BUT induces tachycardia
-blocks presynaptic a2 receptors may promote release of NE
Imidazoline medication
-phentolamine
a1 vs non selective a blockers
slide 15
Reversible vs irreversible a antagonism
slide 16
Phenoxybenzamine action
-IRREVERSIBLE
-a1 and a2 ANTAGONIST
-new receptors must be synthesized in order to restore receptor function leading to a long drug effect
Phentolamine action
-competitive (REVERSIBLE)
-a1 and a2 ANTAGONIST
Phenozybenzamine and phentolamine use
-perioperative management of pheochromocytoma (tumor of adrenal medulla that results in excessive epinephrine and NE synthesis and release)
Phenozybenzamine and phentolamine problems
-not useful in treatment of HTN due to a2 effects
Effect of blocking a2
-greater release of NE at the heart
-increase HR
a1 ANTAGONISTS
-vary in half life
-undergo high metbaolism
-excreted in bile
-“-osins”
-quinazolines
a1 ANTAgonist effects
-vasoDILATION
-relax smooth muscle in enlarged prostate and bladder base
Quinizolines
-a1 ANTAGONIST
-prazosin, terazosin, doxazosin
-produce vasodilation without causing tachycardia or increased Cardiac Output
Prazosin mechanism
=decrease TPR
-activate baroreceptor reflex
-increase NE release to heart
-increase HR via B2
-negative feedback via a2 receptors in myocardia mitigates NE release
Tamsulosin (Flomax)
-a1a ANTAgonist
-very selective to prostate (rich in a1a receptors)
-less prone to induce fall in BP compared to a1 blockers
Benign Prostatic Hyperplasia (BPH)
-problem with voiding leads to overactive bladder
-stimulation of a1a makes bladder resist pissing
-treat with a1 blocker (tamulosin)
a2 ANTAgonists
-yohimbine
yohimbine
-indole alkaloid
-found in Rubaceae and other trees
-block a2
-increase sympathetic discharge
-might treat male impotence