Sympathomimetics

Sympathomimetic drugs are substances whose effect comes about through the activation of adrenal receptors. A distinction is made between:

• directly acting sympathomimetics (adrenoreceptor agonists)
• and
• indirectly acting sympathomimetics. These act indirectly by releasing noradrenalin from the noradrenergic stores.

Direct-acting sympathomimetic drugs(adrenergic receptor agonists)

• Direct-acting sympathomimetic drugs act as adrenergic receptor agonists by activating the adrenergic receptors. The typical representative is the physiological transmitter adrenalin. Adrenaline acts on both alpha-receptors and beta-receptors. This dual functionality has led to the discovery of the different adrenoreceptors (alpha and beta receptors). There is a large number of drugs that act selectively on single or multiple receptor types and thus induce different effects. All alpha- and beta-receptor agonists are interactively influenced by a number of other drugs. Directly acting sympathomimetics are enhanced by tricyclic antidepressants, thyroid hormones, MAO inhibitors, etc. They are attenuated by alpha-receptor antagonists and even reduce the blood sugar-lowering effect of all antidiabetics.

Indirectly acting sympathomimetics

• Indirectly acting sympathomimetics release noradrenaline from noradrenergic stores. The two most important representatives are amphetamine and methyl penidate. Furthermore, ephedrine, tyramine and norephedrine (see figure). Some direct-acting sympathomimetic drugs also have an indirect sympathomimetic effect, such as dopamine.
• Indirectly acting sympathomimetics are also found as natural substances, such as tyramine (cheese), norephedrine (leaves of the catatrine shrub), ephedrine (in the herb of Ephedra sinica.) Tyramine, ephedrine and norephedrine are of no great importance as pharmaceuticals. Ephedrine is offered together with other drugs as an influenza drug, norephedrine as an appetite suppressant.

1. Graefe KH (2016) Sympathetic nervous system. In: Graefe KH et al (Ed.) Pharmacology and Toxicology. Georg Thieme Publisher Stuttgart S. 85-103
2. Rasmussen N et al (2016) History full circle: 'Novel' sympathomimetics in supplements. Drug Test Anal 8(3-4):283-286.