Epinephrine (neurotransmitter)

Epinephrine (also known as adrenaline) is a hormone and neurotransmitter that plays a vital role in the body's fight-or-flight response by increasing blood flow to muscles, output of the heart, pupil dilation, and blood sugar. It is produced in some neurons of the central nervous system and by the adrenal medulla from the amino acids phenylalanine and tyrosine.

Production and Release

Epinephrine is synthesized in the adrenal glands, specifically in the adrenal medulla. The process involves multiple steps, starting with the amino acid tyrosine. Tyrosine is first converted to L-DOPA, then to dopamine, and finally to norepinephrine. Norepinephrine is then converted to epinephrine by the enzyme phenylethanolamine N-methyltransferase (PNMT) in the presence of S-adenosylmethionine (SAMe). In the central nervous system, certain neurons also produce epinephrine, which acts as a neurotransmitter.

Function

As a neurotransmitter, epinephrine is involved in regulating attention, mental focus, arousal, and cognition. It can cross the blood-brain barrier, influencing brain function to increase alertness and the ability to respond to stress.

In the peripheral nervous system, epinephrine binds to adrenergic receptors, triggering a series of physiological changes that constitute the fight-or-flight response. These effects include increased heart rate and force of heart contractions, dilation of airways to improve oxygen intake, and breakdown of glycogen to glucose in the liver to provide energy. Additionally, epinephrine causes vasoconstriction in many parts of the body, which leads to increased blood pressure and redirects blood flow to critical areas such as the muscles and brain.

Clinical Use

Epinephrine is used medically in several ways. It is a critical drug in treating anaphylaxis, a severe allergic reaction, by counteracting the massive vasodilation, airway constriction, and other symptoms. It is also used in cardiac arrest to stimulate the heart. In local anesthetics, epinephrine is added to prolong the duration of anesthesia by causing vasoconstriction, which slows the absorption of the anesthetic.

Pharmacology

Epinephrine acts primarily on alpha and beta adrenergic receptors, which are G protein-coupled receptors located throughout the body. The effect of epinephrine on these receptors triggers the various physiological changes associated with the fight-or-flight response.

Metabolism

Epinephrine is metabolized mainly by the enzymes monoamine oxidase (MAO) and catechol-O-methyl transferase (COMT) into inactive metabolites which are then excreted in the urine. The metabolism of epinephrine plays a crucial role in regulating its action and ensuring that the body's response to stress is appropriate and not prolonged.

History

The discovery of epinephrine was a significant milestone in physiology and medicine. It was first isolated and identified as a hormone by Japanese chemist Jokichi Takamine in the early 20th century. This discovery led to the understanding of its role in the fight-or-flight response and its medical applications.

See Also

• Norepinephrine
• Adrenal gland
• Sympathetic nervous system
• Stress (biology)
• Anaphylaxis