Hordenine (N,N-dimethyltyramine) is a protoalkaloid related to tyramine (known as 4-hydroxyphenethylamine and derived from L-Tyrosine) that came to light after it appeared in the serum or horses fed sprouted barley (containing Hordenine) and indirectly acted as an adrenergic drug, although the doses found in their feed did not mimick the clear stimulant effects following injections. Other related structures include N-methyltyramine (a lone methyl group on the nitrogen atom) and Candicine, with three methyl groups on the nitrogen atom.
Hordenine can be found as a component of:
Hordenine is subject to metabolism (deamination) via Monoamine Oxidase subset B (MAOB) with minimal metabolism by the MAO-A subset. This selective metabolism by MAO-B rather than MAO-A lessens the possible risk that is seem with the related structure Tyramine and Monoamine Oxidase inhibitors (known as the cheese effect, which leads to hypertensive crisises) which is more MAO-A dependent.
Hordenine has been found to interact with Morphine testing drug kits, which extended to oxymorphone, hydromorphone and apomorphine with less reactivity to tests for etorphine- and buprenorphine; the authors suggested that high dose Hordenine can cause a false positive for Morphine and related structures.
One study in isolated rat vas deferas muscles noted that Hordenine was able to augment adrenaline-induced contractions without inherently inducing contractions, suggesting it worked via acting as a noradrenaline reuptake inhibitor. This may be related to the clear adrenaline-like effects found after injections of 2mg/kg into horses (to reach serum levels of 1mcg/mL) which include a doubling of heart rate and induction of respiratory rate.