[Specific stimulation of adipose tissue adrenergic beta 3 receptors by octopamine]

A new subtype of beta-adrenoceptor (beta 3) has been recently characterized in human and rodent genome. This receptor can be stimulated with catecholamines or selective pharmacological beta 3-adrenoceptor agonists and it fulfils similar function of norepinephrine in rodent and dog adipose tissue. Octopamine but not tyramine or phenylethylamine activated lipolysis in dog fat cells as well as BRL 37344 (a beta 3-adrenoceptor agonist) or norepinephrine. In human fat cells, norepinephrine was lipolytic whereas BRL 37344 or octopamine were without effect. The lipolytic effect of octopamine did not depend on beta 1-/beta 2-adrenoceptor stimulation since it was not suppressed by beta 1- or beta 2-antagonists. These results suggest that octopamine is a specific endogenous ligand for beta 3-adrenoceptors in mammals.