SPECIFIC STIMULATION OF ADIPOSE-TISSUE BE TA(3)-ADRENOCEPTORS BY OCTOPAMINE

A new subtype of beta-adrenoceptor (beta3) has been recently character ized in human and rodent genoma. This receptor can be stimulated with catecholamines or selective pharmacological beta3-adrenoceptor agonist s and it fulfils similar function of norepinephrine in rodent and dog adipose tissue. Octopamine but not tyramine or phenylethylamine activa ted lipolysis in dog fat cells as well as BRL 37344 (a beta3-adrenocep tor agonist) or norepinephrine. In human fat cells, norepinephrine was lipolytic whereas BRL 37344 or octopamine were without effect. The li polytic effect of octopamine did not depend on beta1-/beta2-adrenocept or stimulation since it was not supressed by beta1- or beta2-antagonis ts. These results suggest that octopamine is a specific endogenous lig and for beta3-adrenoceptors in mammals.