Inhibition of adenylate cyclase activity in human fat cells by alpha-adrenergic agonists

The effects of the alpha 1-adrenergic agonist methoxamine and the alpha 2-adrenergic agonist clonidine on isoproterenol stimulated adenylate cyclase activity were examined in plasma membranes prepared from female human subcutaneous adipose tissue. It was found that in the presence of 10 microM GTP and 100 mM NaCl increasing concentrations of both agonists inhibited basal and isoproterenol-stimulated adenylate cyclase activity. The inhibitory action of 5 x 10(-7) M clonidine could not be overcome by increasing concentrations of isoproterenol. These results suggest both alpha 1- and alpha 2-adrenergic agonists inhibit beta-agonist-stimulated adenylate cyclase activity in human adipose tissue.