Adrenergic Stimulants Flashcards
Formation of adrenergic molecules
tyrosine –> L-Dopa –> Dopamine (ends here orrr) –> NE –> E
Where is NE converted to E
adrenal medulla
Rate limiting step and what is it blocked by
Tyrosin –> L-dopa;
blocked by metyrosine
Increase release of NE at presynaptic terminal
Tyramine and amphetamine (only have effect if noradrenergic innervation is intact)
What blocks reuptake of NE
antidepressant and cocaine
metabolize NE
monoamine oxidase (MAO) and catechol-O-methyl transferase (COMT)
MAO
on outer surface of mitochondria, breaks down NE in presynatptic terminal
COMT
found throughout body, especially in liver, breaks down circulating NE and EPI
How to measure NE and EPI concentrations
measure VMA (mandelic acid) and HVA (homovanillic acid) in 24 hour urine sample
Alpha receptor order
EPI > NE»_space; Isoproterenol
beta-1 order
Iso > EPI = NE
Beta-2 order
Iso > EPI»_space; NE
Beta-3 Order
Iso = NE > EPI
alpha 1 agonist
phenylephrine
alpha 2 agonist
clonidine
Clonidine actions
aggregation of platelets
some smooth muscle contraction
decrease insulin secretion
NE has little effect on what receptors
B2
What has a greater effect on beta3 receptors, NE or EPI?
NE
Beta1 agonst
Dobutamine
Dobutamine effects
increase contraction and HR
increase AV conduction
Increase renin secretion
Beta 2 receptor agonist
ALbuterol
Albuterol effects
Relax respiratory, uterine, GI smooth muscle
Relax blood vessels to skeletal muscle
promote potassium uptake in skeletal muscle
increase glycogenolysis
Beta-3 receptor effects
increase lipolysis
DA receptor location
brain, renal and splanchnic vasculature
D1
stimulate adenylyl cyclase and causes dilation of renal blood vessels (increasing RBF)
D2
inhibits adenylyl cyclase, open potassium channels, and decrease Ca influx, which generally inhibits release of transmitters from nerve terminals
Atherosclerosis and alpha 1 receptors
baroreceptor response may be impaired, so alpha agonist effect on BP will be magnified
Norepinephrine effects what receptors
alpha stimulation causes vasocontriction, increases BP
B1 stimulation increases HR, overcome by baroreceptor reflex
Norepinephrine facts
must be injected
increase PR, increased BP, PP unchanged
Dec. blood flow to kidney, spleen, liver
HR increases, reversed by baroreceptor reflex
CO unchanged or decreased
Atropine prior to NE will block vagal reflex, HR will increase
Short action, vasoconstriction at infusion site, used to reverse hypotension; necrosis if poor blood flow
NE clinical use
RARE; hypotensive crisis!
Epinephrine receptors
alpha: vasocontriction, initially increases diastolic pressure
Beta1- increases HR, contraciton (increased PP)
beta 2- dilate blood vessels to skeletal muscle, decrease diastolic
PP increases MAP doesn’t change much
CO and O2 consumption increase
Beta-2 more sensitive to EPI than alpha!!!
Dose dependence of epinephrine
low dose: B2 (vasodilation of skeletal muscle- dec. diastolic)
High dose: alpha receptors (vasoconstriciton, BP increases - inc. diastolic)
Other effects of epinephrine
increased glycogenolysis (blood sugar increases) increased lipolysis dec. insulin secretion (a2) renin increases bronchodilation
Difference between NE and EPI receptor stimulation
NE does not stimulate B2 (bronchodilation, dilation to skeletal mm. vessels)
alpha block + epi
take away vasoconstriction, now only have vasodilation – no BP increase anymore, diastolic decreases