Inhibition of the lipolytic action of beta-adrenergic agonists in human adipocytes by alpha-adrenergic agonists

The aim of this study was to define the role of the alpha-adrenergic receptor in the regulation of lipolysis by human adipocytes. Glycerol production by isolated human adipocytes was stimulated by the pure beta-adrenergic agonist isoproterenol in a dose-dependent fashion. This stimulation of lipolysis was inhibited by the alpha-adrenergic agonists methoxamine, phenylephrine, and clonidine. Epinephrine-stimulated lipolysis was potentiated by the alpha-adrenergic antagonists, dihydroergocryptine, phentolamine, phenoxybenzamine, and yohimbine. Whereas the attenuation of beta-adrenergic agonist-stimulated lipolysis by alpha-adrenergic agonists was reversed completely by the alpha 2-adrenergic antagonist yohimbine, the alpha 1-antagonist prazosin did not reverse such attenuation. It is concluded that alpha-adrenergic agonists act as antilipolytic agents in human adipocytes and that this action may result from the interaction of these compounds with a population of alpha 2-adrenergic receptors.