Activation of adenosine 3‘,5‘-monophosphate-dependent protein kinase and its relationship to cyclic AMP and lipolysis in hamster adipose tissue.

Abstract

The interrelationships among cAMP-dependent protein kinase activity, lipolysis, and cellular concentrations of cAMP were investigated in hamster epididymal adipose tissue. Isoproterenol, norepinephrine, and theophylline increased the protein kinase activity assayed in tissue extracts with no added cAMP, but not in the presence of added cyclic nucleotide. The maximum rate of lipolysis was associated with a nearly three-fold increase in cAMP levels and a protein kinase activity ratio of 0.8 (the ratio of activity assayed without cAMP to that assayed with cAMP). Rates of lipolysis less than maximum were associated with lesser degrees of protein kinase activity and lower levels of cAMP. The relatively pure alpha-adrenergic agent phenylephrine partially suppressed the isoproterenol-stimulated protein kinase activity, lipolysis, and cAMP levels. Conversely, the alpha-adrenergic blocking agent phentolamine increased the activity of protein kinase and cAMP levels in adipose tissues exposed to norepinephrine. These data are consistent with the primary role for cAMP and its dependent protein kinase in control of lipolysis in adipose tissue. Moreover, our data are consistent with the view that the antilipolytic action of alpha-adrenergic agents is mediated by a decrease in activity of protein kinase, caused by a decrease in cellular cAMP concentrations.