Study Set Content:
Blockade of a receptors in other tissues elicits () (small pupils) and nasal stuffiness. > Alpha 1 receptors are expressed in the base of the bladder and the prostate, and their blockade decreases
mosis, resistance to the flow of urine.
Alpha blockers, therefore, are used therapeutically for the treatment of urinary retention due to
prostatic hyperplasia.
binds covalently to a1 receptors, causing irreversible blockade of long duration (14-48 hours or longer).
Phenoxybenzamine
Blocks histamine (H 1), acetylcholine, and serotonin receptors as well as
a eceptors.
The most significant effect is attenuation of
catecholamine-induced vasoconstriction
causes relatively little fall in blood pressure in normal supine individuals, it reduces blood pressure when sympathetic tone is high, eg, as a result of upright posture or because of reduced blood volume.
Phenoxybenzamine
It works by non-competitively blocking the a,-postsynaptic receptor and
a₂ presynaptic receptors
Phenoxybenzamine is given orally, starting with dosages of () and progressively increasing the dose until the desired effect is achieved
10 mg/d
A dosage of less than ____ is usually sufficient to achieve adequate a-receptor blockade
100 mg/d
Use in the treatment of
pheochromocytoma.
Most adverse effects:
➢ orthostatic hypotension
➢ tachycardia.
and inhibition of ejaculation Since it enters the central nervous system, it may cause less specific effects, including fatigue, sedation, and nausea.
Nasal stuffiness
Is a potent competitive antagonist at both a 1 and a 2 receptors.
PHENTOLAMINE
Reduces peripheral resistance, blockade of a 1 receptors and possibly a 2 receptors on vascular smooth muscle.
PHENTOLAMINE
Its cardiac stimulation is due to antagonism of () (leading to enhanced release of norepinephrine) and sympathetic activation from baroreflex mechanisms
presynaptic a 2 receptors
Has minor inhibitory effects at serotonin receptors and agonist effects at muscarinic and
H 1 and H 2 histamine receptors.
Adverse effects related to cardiac stimulation, which cause severe tachycardia, arrhythmias, and
myocardial ischemia.
used in the treatment of pheochromocytoma
PHENTOLAMINE
used to reverse local anesthesia in soft tissue sites; local anesthetics are often given with vasoconstrictors that slow their removal. Local phentolamine permits reversal at the
end of the procedure.
is a piperazinyl quinazoline effective in the management of hypertension.
Prazosin
