The physiology and pharmacology of adrenaline

Author: Brian Wu PhD. MD Candidate, Keck School of Medicine, Los Angeles, USA. Chief Editor: Dr Amanda Oakley, Dermatologist, Hamilton, New Zealand, August 2015.

Physiology of adrenaline

What is adrenaline/epinephrine and how does it differ from noradrenaline/norepinephrine?

Adrenaline is a hormone derived from tyrosine, an amino acid. Adrenaline is also spelled adrenalin, and in North America is known by the name epinephrine. Adrenaline/epinephrine, noradrenaline/norepinephrine and dopamine are classified as catecholamines.

Epinephrine and norepinephrine are stress hormones and function as part of the “fight or flight” response.

Where and how is adrenaline produced and released in the body?

Adrenaline is produced by the chromaffin cells in the medulla of the adrenal glands and is released in response to a stressor or perceived threat. This stressor can be emotional, physical or environmental.

The steps to the adrenaline response and release are as follows:

  1. A stressor is perceived
  2. This stimulates signals to the brain
  3. The brain sends signals to the chromaffin cells of the adrenal glands
  4. Adrenaline is released

What happens to the body when adrenaline is released?

The release of adrenaline activates specific physiological reactions, which are intended to prepare the body to respond to the perceived stressor or threat.

The responses include:

Pharmacology of adrenaline

What is adrenaline used for pharmacologically?

Adrenaline is a first-line treatment for anaphylaxis, an IgE-mediated, severe allergic reaction caused by release of mediators from mast cells that have been previously sensitised to a specific allergen. Anaphylaxis is characterised by:

Due to its physiological effects, adrenaline is able to reverse anaphylaxis by:

Other uses of adrenaline include its use in local anaesthetic to enhance the duration of anaesthesia and to reduce the chance of haemorrhage. It is also used as an adrenergic receptor stimulant during cardiopulmonary resuscitation (CPR).

What are the risks of use of adrenaline?

While adrenaline is considered to be a life-saving medication, there are risk involves with its use, especially if it is administered intravenously or in high dosages. These risks are of particular concern in the following circumstances:

Prolonged or repeated use of adrenaline has the potential to cause cardiac hypertrophy due to stimulation of mitogen-activated proteins and an increase in myocardial cells.

Adrenaline self-treatment for anaphylaxis

Knowledge of self-administration of adrenaline to treat anaphylactic shock is critical for those with a history of severe allergic reactions. The procedure of self-administering adrenaline using the Epipen® device is as follows:

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