Alpha 1 agonists

Characteristics

-weak β effects

- not metabolized by COMT so longer 1/2 life

Uses

- nasal decongestant

- hypotension: increases BP w/ little cardiac effect at normal doses

- shock

Effects

- dilates pupils

- induces reflex bradycardia

α1 agonist

Characteristics

- no β effects

- not a substrate for MAO of COMT

Uses

- hypotension

Effects

- induces reflex bradycardia

α2 agonist

Characteristics

- acts at α2 receptors in brainstem to lower sympathetic outflow and lower BP

- causes acute rise in BP followed by prolonged hypotension

Uses

- antihypertensive agent

Effects

- rebound hypertension possible so patient must be weaned off slowly

 β1 agonist

Characteristics:

- inotropic: raises HR and contractility

- also acts on α1 and β2 receptors 

Uses:

-CHF

Side effects

- α1 action causes vasoconstriction and could be potentially harmful in kidneys but β2 action causes vasodilation and counteracts 

Terbutaline

Albuterol

β2 agonists

Characteristics:

- selective β-agonist, doesn't affect heart (β1)

Uses:

- bronchodilator for asthma or COPD-related bronchoconstriction

- may be used to induce labor

Side effects:

- inhibits mast cell secretion (?)

- Not metabolized by MAO or COMT = long 1/2-life

Amphetamines

- Dexedrine

- Methamphetamine

Indirect agonist - promotes NE release = α and β1

Characteristics

- Similar to NE effects but is a CNS stimulant b/c it can cross BBB unline NE

Uses:

- increases alertness, decreases fatigue, enhances physical and mental performance

Side effects:

- increased systolic and diastolic BP

- can also lead to appetite suppression but tolerance is reached

Mixed acting agonist - direct and indirect effects

Characteristics:

- Direct - stimulates α1 receptors and weak β-effect

- Indirect - false neurotransmitter that replaces NE in storage granules

Uses:

- treatment for hypotension (e.g. shock)

Side effects:

- effects similar to NE = increased BP

Mixed-acting agonist - direct and indirect effects

Characteristics:

- Direct - stimulates α and β receptors

- Indirect - induces NE release like amphetamines and stimulates CNS

Uses:

- appetite supressant - more effective w/ caffeine

- pseudoephedrine used as nasal decongestant due to α effects

α antagonist

Characteristics:

- irreversible block, esp α1 which has more effect on smooth muscle

Uses:

- Pheochromocytoma: prevents HTN crisis from α receptor overstimulation; preoperative

- autonomic hyperreflexia

- Benign prostatic hypertrophy: relieves urine obstruction

Side effects:

- orthostatic hypotension

- reflex tachycardia

- nasal congestion

- side effects of impaired smooth muscle contraction 

α antagonist

Characteristics:

- non-selective, competitive α1 & 2 antagonist

Uses:

- ED

- Pheochromocytoma

- induced hypertention - not a general anti-HTN due to s/e

Side effects:

- orthostatic hypotension

- reflex tachycardia

- nasal congestion

- limited clinical use due to action on other receptors like serotonin, K channels

- histamine release from mast cells

Prazosin

Terazosin

α-antagonist

Characteristics:

- selective for α1 antagonism and inhibition of cyclic phosphodiesterase (PDE)

- direct vasodilatory effect via α1 antagonism

- decreased peripheral resistance due to PDE inhibition

Uses:

- treat hypertension

- improved urinary flow in BPH (esp terazosin)

Side effects:

- first dose phenomenon: dizziness and postural syncope -take before bedtime 

β-antagonist

Characteristics:

- competitive antagonists of both β1 and β2 receptors

- decreases HR, contractility, and peripheral vascular resistance

Uses:

- treat hypertension

- MI and post-MI patients (reduces O2 requirement)

- glaucoma: decreased aqueous humor secretion

- hyperthyroidism- reduces symptoms caused by

Side effects:

- lead to bronchoconstriction in patients with COPD, asthma

- hypoglycemia in diabetics

β-antagonists

Characteristics:

- competitive antagonists of β1 receptor

- decreases HR, contractility and peripheral vascular resistance

Uses:

- Hypertension

- ischemic heart disease

Side effects:

- less tendency for bronchoconstriction due to lack of β2 block

Inhibit NE release and storage

Characteristics:

- depletes NE from presynaptic neuron and inhibits its release

- does not cross BBB

Uses:

- hypertension: dilates arterial and venous beds

Side effects:

- orthostatic hypotension

- GI problems: diarrhea due to decreased sympathetics = parasympathetic hypermotility

- male sexual disturbances (retrograde ejaculation)

Inhibits NE release and storage

Characteristics:

- irreversible inhibition of dopamine and NE uptake into storage vesicles which blocks NE storage and synthesis but not NE release; MAO/COMT degrade NE and Dopamine in cytosol

Uses:

- mild to moderate hypertension

Side effects:

- less orthostatic hypotension

- crosses BBB --> CNS effects:

   ~depression, sedation, nightmares, suicidal thoughts

Acts as a "false-neurotransmitter"

Characteristics:

- creates false NE - mimics DOPA and is incorporated during NE synthesis

Uses:

- Hypertension but due to CNS action rather than peripheral action

  ~good for pregnant women and renal disease patients

Side effects:

- due to CNS action

   ~ sedation, drowsiness, orthostatic hypotension, nasal congestion

Inhibits NE synthesis

Characteristics:

- inhibits tyrosine hydroxylase to stop synthesis of catecholamines

Uses:

- pheochromocytoma

Inhibits Uptake 1

Characteristics:

- inhibition of Uptake 1 causese NE accumulation in synaptic cleft and overstimulation of postsynaptic receptor

Uses:

- local anesthetic

Side effects:

- many but will be covered in neuroscience lectures

Phenylephrine

Methoxamine

- cause vasoconstriction

Dobutamine

-increases myocardial contractility

Terbutaline

Albuterol

-smooth muscle dilators

Amphetamines

- Dexedrine

- Methamphetamine

-cause release of NE

Metaraminol

Ephedrine

- have both direct and indirect agonistic effects

Phenoxybenzamine

Phentolamine

Prazosin

Propranolol

Metoprolol

Guanethidine

Reserpine