Sympathomimetics: Direct agonists

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Sympathomimetics: Direct agonists

Prerequisite basic sciences

Prerequisite basic sciences

Prerequisite basic sciences

Prerequisite basic sciences


Sympathomimetics: Direct agonists


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Sympathomimetics: Direct agonists

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A 56-year-old is admitted to the hospital for management of severe, symptomatic hypertension. In the emergency department, the patient was noted to have a blood pressure of 225/105 mmHg, severe headache, and was ultimately found to have an intraparenchymal hemorrhage. The patient was provided with a medication that acts selectively on D1 receptors, decreases blood pressure, and increases heart rate and cardiac output. Which of the following medications is described in this vignette?  

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Amphetamines p. 243

as noradrenergic drug p. 240

norepinephrine and p. 240

Cocaine p. 571

as noradrenergic drug p. 240


serotonin-norepinephrine reuptake inhibitors (SNRIs) for p. 599

Dopamine p. 243, 334

in noradrenergic drugs p. 240

Ephedrine p. 243

as noradrenergic drug p. 240

Generalized anxiety disorder (GAD) p. 585, 586

serotonin-norepinephrine reuptake inhibitors (SNRIs) for p. 599


norepinephrine for p. 243


norepinephrine vs p. 244

Noradrenergic drugs p. 240

Norepinephrine (NE)

adrenal medulla secretion p. 332

amphetamines and p. 240

bupropion effect on p. 600

changes with disease p. 512

circadian rhythm p. 513

direct sympathomimetic p. 243

isoproterenol vs p. 244

male sexual response p. 651

MAO inhibitor effects p. 599

in nervous system p. 237

opioid effect on p. 572

phenoxybenzamine and p. 231

pheochromocytoma secretion p. 345

REM sleep and p. 513

tramadol effects p. 572

tyrosine catabolism p. 81

vitamin B6 and p. 65

Phenoxybenzamine p. 245

norepinephrine and p. 231


as noradrenergic drug p. 240

Septic shock

norepinephrine for p. 243

Serotonin-norepinephrine reuptake inhibitors (SNRIs)

Shock p. 319

norepinephrine for p. 243

SNRIs (serotonin-norepinephrine reuptake inhibitors ) p. 599

Tricyclic antidepressants (TCAs) p. 599

as noradrenergic drug p. 240


as noradrenergic drug p. 240


Alpha agonists and beta agonists are two types of adrenergic medications that stimulate their respective receptors and mimic the effect of endogenous catecholamines, like norepinephrine and epinephrine.

The nervous system is divided into the central nervous system and the peripheral nervous system.

The peripheral nervous system can be further divided into the somatic nervous system, which controls voluntary movement of our skeletal muscles; and the autonomic nervous system, which controls the involuntary movement of the smooth muscles and glands of our organs; this system is then further divided into the sympathetic and parasympathetic nervous systems.

Now, the autonomic nervous system is made up of a relay that includes two neurons.

We’ll focus on just the sympathetic nervous system.

Signals for the autonomic nervous system start in the hypothalamus, at the base of the brain.

Hypothalamic neurons have really long axons that carry signals all the way down to the thoracic and lumbar spinal cord nuclei, where they synapse with preganglionic neuron cell bodies.

From there, the signal goes from the preganglionic neurons down its relatively short axon, exits the spinal cord, and reaches the nearby sympathetic ganglion, which is made up of lots of postganglionic neuron cell bodies.

The postganglionic neurons are also called adrenergic neurons, because they release the neurotransmitter norepinephrine, which is also called noradrenalin; and to a much lesser degree, epinephrine also known as adrenaline.


Sympathomimetics are drugs that act on the sympathetic nervous system to produce their effects. They include classes of drugs like alpha agonists and beta-agonists. Both alpha agonists and beta-agonists bind to receptors in the body and activate them.

Alpha agonists activate alpha receptors, which are found primarily in the smooth muscles of the blood vessels and lungs. Alpha agonists are divided into alpha-1 agonists, like phenylephrine and midodrine; and alpha-2 agonists, like clonidine. Phenylephrine is used to treat hypotension, but it can also be used as a decongestant to treat rhinitis, or as a topical agent to cause mydriasis. Midodrine is used to treat orthostatic hypotension; while intravenous and nasal administration of clonidine causes vasoconstriction.

On the other hand, beta-agonists activate beta receptors, which are found in the heart, lungs, and other organs. Beta-agonists are subdivided into non-selective beta agonists like isoproterenol; and selective beta-2 agonists, like albuterol, salmeterol, and terbutaline. Isoprenaline is used to stimulate the heart in individuals with bradycardia or heart block, while albuterol, salmeterol, and terbutaline are used in the treatment of asthma, chronic obstructive pulmonary disease, and hyperkalemia.


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  6. "Mechanism of action of agents used in attention-deficit/hyperactivity disorder" J Clin Psychiatry (2006)
  7. "Pharmacological treatment of COPD – New evidence" Pulmonology (2019)
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