Adrenergic blocking agents: Lect 7 Flashcards
function of adrenergic antagonists depends on
- selectivity for alpha and beta receptors
- degree to which a tissue is innervated by alpha and beta
- if alpha is blocked, beta will dominate and vice versa
Effects of alpha receptor blocker on the cardiovascular system
- decreases vasoconstriction (arteries and veins)
- lowers peripheral vascular resistance and decreases blood pressure
- decreased BP activates baroreflex
Are the effects of alpha receptor blocker on the cardiovascular system more pronounced when a person is standing or lying down?
- Alpha blockade lowers peripheral vascular resistance and decreases blood pressure
- This effect is greater when the patient is standing than supine, as the prevailing sympathetic tone will be higher when standing
how do alpha blockades result in reflex tachycardia
- decreased blood pressure -> stimulate the baroreceptors to increase sympathetic stimulation and decrease vagal tone
- if the drug also blocks α2 receptors, NE release may increase and cause further stimulation of β receptors in the heart
how can alpha blockades lead to postural hypotension
- Postural hypotension may occur due to blockade of α1 receptors in venous smooth muscle: when the patient stands up the veins don’t contract enough, filling pressure decreases, and the blood pressure drops
Explain why alpha blockades are used to reverse the response to epinephrine
- epinephrine stimulates alpha, beta1, and beta2 receptors and normally causes an increase in systolic pressure and an increased heart rate
- Blocking the alpha effect allows the beta receptor mediated vasodilation to be dominant, so that blood pressure is decreased, rather than increased.
- The effects of epinephrine now resemble those of isoproterenol.
pulse pressure
difference between the systolic and diastolicpressure readings.
diastolic pressure is created by tone of what receptor
alpha 1 receptor
pulse pressure is created by tone of what receptor
beta
what drugs are used to treat BPH benign prostatic hyperplasia
alpha blockers
- cause decreased resistance to urine flow
- prostate, sphincters, and base of bladder relax
alpha blockers have what effect on eye
- miosis
- iris radial muscles of the pupil relax
alpha blockers have what effect on nose
- nasal stuffiness
- vasodilation in nasal mucosa
What drug class is Phentolamine in?
- competitive alpha1 and alpha 2 antagonist
Phentolamine has what cardiovascular effects
- Decreases peripheral resistance and blood pressure (especially diastolic) due to blockade of α1 receptors
- Baroreceptor reflex as well as increased NE release in the heart (α2 blockade) may cause cardiac stimulation
- NE stimulates beta receptors which increase HR
side effects of Phentolamine
- tachycardia
- arrhythmia, MI
- hypotension
clinical use of Phentolamine
- used rarely
- hypertensive crisis due to pheochromocytoma or in patients on monoamine oxidase (MOA) inhibitors
- prevent necrosis after local infusion of alpha agonists
which drug class is Phenoxybenzamine (Dibenzyline) in?
- Irreversible αlpha blocker
- Effects last several days until new receptors are formed
effect of Phenoxybenzamine (Dibenzyline) on CV system? What makes this effect more pronounced?
- Tachycardia may occur from beta 1 stimulation and increased sympathetic stimulation due to lowered blood pressure
- α-receptor blockade decreases vasoconstriction produced by sympathetic stimulation
- Effect is small when the person is lying down and sympathetic tone is low, but increases if the person stands, or if sympathetic tone is increased due to reduced blood volume
clinical use of Phenoxybenzamine (Dibenzyline)
pheochromocytoma: hormone-secreting tumor that can occur in the adrenal glands that can cause life-threatening HTN
side effects of Phenoxybenzamine (Dibenzyline)
- postural hypotension
- tachycardia
- nasal congestion
- inhibit ejaculation
What is pheochromocytoma? How does it manifest?
- tumor that releases NE and epinephrine
- often indicated by sudden-onset severe HTN, tachycardia, and arrhythmia
- *measure 24-hr urine NE and VMA
which drug class is Prazosin (Minipress) in?
- α1 receptor antagonist
cardiovascular effects of Prazosin (Minipress)
- relaxes both arterial and venous smooth muscle through α1 blockade
- decreases peripheral vascular resistance and venous return, so blood pressure drops
- lack of α2 blockade reduces likelihood of reflex tachycardia, as NE release is not increased
- decreases sympathetic outflow from the CNS, and may inhibit the baroreceptor reflex in hypertensive patients, again contributing to the lack of tachycardia
clinical use of Prazosin (Minipress)
- treatment of hypertension • treatment of benign prostatic hyperplasia (BPH)
- very useful in men who have both hypertension and BPH
- has beneficial effect on lipids
- **must be given twice daily
