Catecholamines
Definition & Biosynthesis
Catecholamines are biogenic amines that share a dihydroxy structure on the phenyl ring. The biosynthesis of the catecholamines norepinephrine and epinephrine begins with the amino acid tyrosine (see figure), which in turn can be synthesized in the body from the essential amino acid phenylalanine.
The following enzymes are involved in biosynthesis (Fig. 1):
- Tyrosine-3-monooxygenase,
- DOPA decarboxylase,
- dopamine-β-monooxygenase
- Phenylethanolamine N-methyltransferase
The synthesis of norepinephrine occurs both in the vesicles of the nerve endings of neurons that release norepinephrine as a neurotransmitter and in the adrenal medulla. The synthesis of epinephrine (through methylation of the nitrogen atom of norepinephrine), however, can only occur in cells of the adrenal medulla, as only these cells possess the enzyme phenylethanolamine N-methyltransferase.
Significance as a doping agent
Of the catecholamines, only epinephrine is specifically listed on the WADA Prohibited List, under Group S6 Stimulants, with the note that local applications (e.g., in nasal sprays or eye drops) are permitted. However, no cases of doping abuse involving epinephrine have been reported to date.
Effect
The catecholamines epinephrine and norepinephrine activate or inhibit target cells via alpha and beta receptors. The release of catecholamines is a consequence of sympathetic activation, and their effects on various organs can be summarized as follows:
| Bronchi | Vasodilation, improved respiration |
| Adipose tissue | Fat breakdown and release of fatty acids |
| Heart | Increased heart rate, increased stroke volume, increased blood pressure |
| Liver | Glycogen breakdown, glucose release |
| Gastrointestinal tract | Constriction of blood vessels |
| Skeletal muscle | Increased blood flow, glycogen breakdown |
| CNS | Drive, alertness |
Sympathetic activation of the autonomic nervous system is the body’s response to achieve peak performance, as required in fight-or-flight situations. Consequently, the body must ensure an increased supply of energy. This includes an increased oxygen supply to muscle cells (improved respiration, increased blood flow) as well as an improved supply of energy substrates such as glucose and free fatty acids (glycogen breakdown, glucose release, and fat breakdown).
Institute of Biochemistry at the German Sport University Cologne, last updated August 27, 2013
