Octopamine

Octopamine is an organic chemical closely related to norepinephrine. In many types of invertebrates it functions as a neurotransmitter. Octopamine is known to exert adrenergic effects in mammals although specific octopamine receptors have been cloned only in invertebrates. It has been shown that octopamine can stimulate alpha(2)-adrenoceptors (ARs) in Chinese hamster ovary cells transfected with human alpha(2)-ARs. Octopamine stimulates lipolysis through beta(3)-rather than beta(1)-or beta(2)-AR activation in white adipocytes from different mammalian species. Octopamine activates only beta(3)-ARs and is devoid of alpha(2)-adrenergic agonism. Thus, octopamine could be considered as an endogenous selective beta(3)-AR agonist. In humans Octopamine is a trace amine found endogenously in the human brain where it interacts with signalling of catecholamines; it is structurally similar to synephrine and tyramine, being a metabolite of the latter (via dopamine β-hydroxylase) and substrate for the synthesis of the former (via phenethanolamine N-methyltransferase³) while being perhaps the closest in structure to noradrenaline.