Adrenergic Pharmacology
Sympathetic Nervous System
Dilates pupils, increases heart rate, increases respiration, inhibits digestion, releases adrenaline, vasodilation
Dopamine is the precursor of adrenaline and noradrenaline (both are catecholamines)
Tyrosine > DOPA > Dopamine > Noradrenaline > Adrenaline
Fight or flight
Adrenoreceptors are all G-coupled. They are: Alpha-1, alpha-2
Beta-1, beta-2, beta-3
Noradrenaline is the neurotransmitter
Alpha
Alpha-1
Alpha-2
Stimulation of alpha-2 inhibits insulin, adrenaline and ACh release. Causes vasoconstriction
Stimulation of alpha-1 causes vasoconstriction, pupil dilation and bladder contraction
Adrenaline is an alpha-1 agonist. It causes vasoconstriction
Coupled with Gq protein and phospholipase C
The drug clonidine is an alpha-2 agonist. It inhibits noradrenaline release so is an anti-hypertensive
Coupled with Gi protein, inhibits adenyl cyclase
Beta
Beta-1
Beta-2
Stimulation of beta-1 causes increased force of heart contraction (+ve inotropic effect), increased heart rate (+ve chronotropic effect), increased electrical conduction in heart, increased renin release from kidney, increased BP
Stimulation of beta-2 causes bronchodilation, vasodilation, reduced GI motility and promotes insulin release
Adrenaline and the drug dobutamine are agonists for beta-1 - they cause a +ve inotropic effect
Coupled with G protein and adenyl cyclase
Adrenaline and the drug salbutamol are agonists for beta-2 - they cause bronchodilation - used in asthma patients
Coupled with G protein and adenyl cyclase
Beta-3
Coupled with G protein and adenyl cyclase
Stimulation of beta-3 causes increased lipolysis and relaxation of bladder
Atenolol is a beta blocker. It results in a reduced cardiac output for patients with hypertension, angina and arrhythmia
Tamsulosin is an alpha-1 antagonist - it relaxes the bladder which helps men with prostatic hypertrophy to urinate
Yohimbine is an alpha-2 antagonist - it prevents inhibition of noradrenaline release so there is an increase in noradrenaline
Beta 3 agonists reduce overactive bladder symptoms
Propranolol is non selective - it works on all beta receptors and is used to treat arrhythmias
Do not use beta blockers in asthmatics as these patients will be on beta-2 agonists
Some beta-blockers are partial agonists - they can stimulate beta receptors as well as acting as antagonists e.g. penbutolol