Octopamine

Octopamine (β,4-dihydroxyphenethylamine) is an endogenous biogenic amine that is closely related to norepinephrine, and has effects on the adrenergic and dopaminergic systems. It is also found naturally in numerous plants, including bitter orange. Biosynthesis of the D -(–)-enantiomer of octopamine is by β-hydroxylation of tyramine via the enzyme dopamine β-hydroxylase. Under the trade names Epirenor, Norden, and Norfen, octopamine is also used clinically as a sympathomimetic agent.

Role in invertebrates
Octopamine was first discovered by Italian scientist Vittorio Erspamer in 1948 in the salivary glands of the octopus and has since been found to act as a neurotransmitter, neurohormone and neuromodulator in invertebrates. It is widely used in energy-demanding behaviors by all insects, crustaceans (crabs, lobsters, crayfish), and spiders. Such behaviors include flying, egg-laying, and jumping.

The best-understood role for octopamine is in the locust jump. Here it modulates muscle activity, making the leg muscles contract more effectively. This is at least in part due to an increase in the rate of contraction and of relaxation.

In the honey bee and fruit fly, octopamine has a major role in learning and memory. In the firefly, octopamine release leads to light production in the lantern.

Octopamine also plays a role in mollusks, though the role of octopamine has been examined only in the central nervous system of the model organism, the pond snail.

Heberlein et al. have conducted studies of alcohol tolerance in fruit flies; they found that a mutation that caused octopamine deficiency also caused lower alcohol tolerance.

The emerald cockroach wasp stings the host for its larvae (a cockroach) in the head ganglion (brain). The venom blocks octopamine receptors and the cockroach fails to show normal escape responses, grooming itself excessively. It becomes docile and the wasp leads it to the wasp's den by pulling its antenna like a leash.

Role in vertebrates
In vertebrates, octopamine replaces norepinephrine in sympathetic neurons with chronic use of monoamine oxidase inhibitors. It may be responsible for the common side effect of orthostatic hypotension with these agents, though there is also evidence that it is actually mediated by increased levels of N-acetylserotonin.

In mammals, octopamine may mobilize the release of fat from adipocytes (fat cells), which has led to its promotion on the internet as a slimming aid. However, the released fat is likely to be promptly taken up into other cells, and there is no evidence that octopamine facilitates weight loss. Octopamine may also increase blood pressure significantly when combined with other stimulants, as in some weight loss supplements.

Owing to lack of research, much is not known about octopamine or its role in humans.