Pharm Overview of CV Autonomic Nervous System Flashcards
(109 cards)
α1 effect on CV
Vasoconstriction leading to increased BP
α2 effect on CV
Negative feedback - Can limit vasoconstriction by preventing further norepinephrine release from synapse
α1 mechanism
POSTSYNAPTIC, downstream signaling via DAG/IP3 leading to increased calcium
α2 mechanism
PRESYNAPTIC, “autoreceptors” that perform feedback inhibition of adenylate cyclase to decrease levels of cAMP
What receptors do epinephrine target? What is the effect on vessels?
Targets ALL alpha and beta receptors. Therefore, it creates a limited increase in blood pressure (vasoconstriction caused by alpha activation overcomes vasodilation from beta activation)
How do alpha-blockers affect epinephrine’s effects?
Allow only the vasodilatation effects due to epinephrine-stimulated beta-receptors to be seen, so you get a decrease in BP!
How do beta-blockers affect epinephrine’s effects?
Allow only the vasoconstriction effects due to epinephrine-stimulted alpha-receptors to be seen, so see further increase in blood pressure
What receptors do norepinephrine target? What is the effect on vessels?
Selectively targets alpha receptors (but can target beta1 receptors). Therefore, it creates an increase in BP due to vasoconstriction from alpha activation.
How do alpha-blockers affect norepinephrine’s effects?
Prevents vasoconstriction due to alpha activation and (since no beta effect really significant) does NOT cause vasodilation
How do beta-blockers affect norepinephrine’s effects?
Does NOT affect the vasoconstriction effects due to norepinephrine-stimulted alpha-receptors to be seen, so see no change in the increased blood pressure
Which alpha blockers are α1»>α2 ?
doxazosin, terazosin, and prozosin
Which alpha blockers are α1>α2 ?
phenoxybenzamine
Which alpha blockers are α1=α2 ?
phentolamine
Which alpha blocker has the longest half-life?
doxazosin
Which alpha blocker has the shortest half-life?
prozosin (take every 8 hours)
MOA of α1 specific blockers? 3 main pharmacological effects.
1) blocking the binding of norepinephrine to post-synaptic nerve endings (so you do NOT get vasoconstriction, leading to decreased peripheral resistance, which decreases BP)
2) Relieve symptoms of benign prostatic hyperplasia
3) Increase HDL, lower LDL
What is a consequence of starting alpha 1 blockers to control blood pressure?
Reflex tachycardia due to drop in blood pressure!
Orthostatic hypotension also occurs because you are blocking the alpha receptors (and vessels in legs cannot contract well to send blood back to brain)–worse with prazosin!
MOA of Nonspecific alpha-blockers?
Causes presynaptic α2-receptors to increase norepinephrine release (by blocking the negative feedback inhibition), resulting in increased cardiac output—which tempers the BP lowering action you get from α1 blockers.
Small doses of phentolamine have what affect on BP?
increase in BP (inotropic effect)
Large doses of phentolamine have what affect on BP?
decrease in BP (peripheral vasodilation)
Which is better for hypertension, diuretics or alpha blockers?
DIURETICS!
β receptor activity on heart?
Accelerates SA node, Accelerates ectopic pacemaker, Increase in contractility (beta1)
β receptor activity on vascular?
relaxes skeletal muscle vessels (beta2)
β receptor activity on kidney JG cells?
beta1 receptors stimulate renin release