Adrenoceptor Agonists Flashcards
Drugs that mimic the actions of epinephrine or norepinephrine have traditionally been termed
sympathomimetic drugs
indirect agonists because their actions are dependent on their ability to enhance the actions of endogenous catecholamines by:
- inducing the release of catecholamines by displacing them from adrenergic nerve endings
- decreasing the clearance of catecholamines by inhibiting their neuronal reuptake
- preventing the enzymatic metabolism of norepinephrine
Adrenoceptors are typical ___ receptors
G protein-coupled
Alpha1 receptors are coupled via G proteins in the G_ family to
phospholipase C.
q
Alpha2 receptors are coupled to the inhibitory regulatory protein G_ that inhibits adenylyl cyclase activity and causes intracellular cyclic adenosine monophosphate (cAMP) levels to decrease
i
Activation of all three receptor subtypes (β1, β2, and β3) results in:
stimulation of adenylyl cyclase and increased cAMP
a selective β3 agonist, is approved for the treatment of symptoms
of overactive bladder
Mirabegron
means that a drug may preferentially bind to one subgroup of
receptors at concentrations too low to interact extensively with
another subgroup.
Selectivity
After a cell or tissue has been exposed for a period
of time to an agonist, that tissue often becomes less responsive to
further stimulation by that agent
desensitization
refers to loss of responsiveness exclusively of the receptors
that have been exposed to repeated or sustained activation by an
agonist
Homologous
refers to the process by
which desensitization of one receptor by its agonists also results
in desensitization of another receptor that has not been directly
activated by the agonist in question
Heterologous
A major mechanism of desensitization that occurs rapidly involves phosphorylation of receptors by members of the
__
G protein-coupled receptor kinase (GRK) family
Recognition that G protein-coupled receptors can signal through both G protein-coupled and G protein-independent pathways has raised the concept of developing ___that selectively activate these arrestin-coupled signaling pathways
biased agonists
distinct polymorphisms occur in specific combinations termed
haplotypes
90% of released norepinephrine is removed by the
NET
may be considered the parent compound from
which sympathomimetic drugs are derived
Phenylethylamine
Alpha1 receptors are widely expressed in vascular beds, and their
activation leads to ___
arterial and venous vasoconstriction.
Intravenous administration of dopamine promotes ___ of renal, splanchnic, coronary, cerebral, and perhaps other
resistance vessels, via activation of D1 receptors
vasodilation
Activation of β2 receptors in bronchial smooth muscle leads
to __
bronchodilation
In the eye, the radial pupillary dilator muscle of the iris
contains α receptors; activation by drugs such as phenylephrine causes ___
mydriasis
___ increase
the outflow of aqueous humor from the eye and can be used
clinically to reduce intraocular pressure.
Alpha2 agonists
___ antagonists decrease the production of
aqueous humor and are used in the treatment of glaucoma
β
Activation of β adrenoceptors in fat cells leads
to
increased lipolysis
the immediate precursor in the synthesis of
norepinephrine
Dopamine
It
is an important neurotransmitter in the CNS and is involved in
the reward stimulus relevant to addiction.
Dopamine
The primary indication for midodrine is the
treatment of
hypotension
used as a centrally
acting muscle relaxant.
tizanidine
is a direct-acting α agonist used as a topical
decongestant because of its ability to promote constriction of the
vessels in the nasal mucosa and conjunctiva
Oxymetazoline
