adrenergic receptors Flashcards
Alpha receptors generally mediate
Excitation
except in GI
Beta receptors generally mediate
Inhibition
except in heart
Alpha 1
Radial muscle - contracts
vascular smooth muscle, skin, splanchnic vessels - contracts
skeletal muscle vessels - contracts
GI - contracts sphincters
Alpha 2
GI - walls relax
Beta 1
SA node - accelerates
Ectopic pacemakers - accelerates
contractility - increases
renin release
Beta 2
ciliary muscle - relaxes (lens thins) skeletal muscle - relaxes bronchiolar smooth muscle - relaxes GI smooth muscle - relaxes walls GU smooth muscle - bladder wall relaxes uterus - relaxes
What tissues have alpha receptors?
vascular smooth muscle, skin, splanchnic vessels - contracts skeletal muscle vessels - contracts enteric NS - inhibits uterus - contracts Ejaculation pilomotor smooth muscle - contracts apocrine (stress) - increases liver gluconeogenesis and glycogenolysis
In general, Alpha 1 receptors are found on
postsynaptic sympathetic effector sites
In general, Alpha 2 receptors are found on
presynaptic neurons (some postjunctional sites)
In general, Beta 1 receptors are found on
adipocytes and the heart
In general, Beta 2 receptors are found on
smooth muscle (some presynaptic neurons)
In general, Beta 3 receptors are found on
adipocytes but has a low affinity for endogenous catecholamines
what type of receptors are alpha and beta adrenergic receptors?
G protein coupled
What effector systems does alpha 1 activate?
stimulates PLC-IP3-DAG-PKC pathway via the Gq protein
=similar to M1, M3,M5
pathway stimulates intracellular calcium signaling mechanisms (contraction of smooth muscle)
What effector systems does alpha 2 activate?
inhibit adenylylcyclase activity via Gi protein
what effector systems do Beta receptors activate?
all subtypes stimulate activity of adenylyl cyclase via Gs protein
though B1 also does increase L type Ca+2 channel activation
Alpha 1 agonists
phenylephrine
methoxamine
phenylephrine
potent vasoconstrictor
increases both systolic and diastolic pressure with little cardiac effect
induce reflex bradycardia
nasal decongestant (long term can damage mucosa)
mydriatic agent
not a substrate for COMT
Methoxamine
potent vasoconstrictor
used to treat hypotensive states (shock, spinal anesthesia)
induces reflex bradycardia
longer duration of action then Phenylephrine
not substrate for COMT or MAO
Alpha 2 agonists
clonidine
Clonidine
IV infusion causes acute increase in BP due to a2 stimulation in vascular beds. Hypertensive response is transient
followed by prolonged hypotension - due to stimulation of a2 in the CNS which depresses sympathetic outflow to periphery
Beta 1 agonists
dobutamine
Dobutamine
similar to dopamine in structure but has higher affinity for beta 1 receptors
Inotropic agent to tx CHF
greater affect on contractility than HR
dilates renal vasculature to preserve kidney function
beta 2 agonists
terbutaline
Terbutaline
bronchodilator with minimal cardiac effects at normal doses
inhaled to relieve bronchospasm
given orally, delay of 1 to 2 hours in effect, can be long term for Asthma, emphysema, bronchitis
inhibit premature labor
not metabolized by COMT or MAO and not taken up into adrenergic terminals
What drug is Albuterol similar to?
Terbutaline
Indirect adrenergic agonists
Amphetamine
Dextroamphetamine
methamphetamine
promote the release of NE from adrenergic nerve terminals