Abstract

PIP: A method for assaying, directly, cyclic 3',5'-adenosine (AMP) in isolated adipose cells is described which consists of measuring formation and accumulation of cyclic AMP-8 which is radiolabeled by 14C. This assay helped confirm known effects of cyclic AMP and adipose tissue. It showed that 1) cyclic AMP formation, stimulated by catecholamines, is evident before lipolysis if theophylline is also present; 2) without theophylline, catecholamine-induced lipolysis occurred without elevating cyclic AMP levels; 3) in the absence of norepinephrine, theophylline also induced lipolysis without elevating cyclic AMP levels; and 4) the synergistic effect of theophylline and norepinephrine on lipolysis induction was less marked than the corresponding synergism of theophylline and norepinephrine on elevating cyclic AMP levels. The assay was also used to confirm the decrease in cyclic AMP levels in adipocytes induced by insulin and prostaglandin E1. The data confirmed an hypothesis that cyclic AMP exists in different intracellular compartments, only 1 of which, comprising a small fraction of total cellular cyclic AMP, is involved in activation of the hormone-sensitive lipase. Also found was that polyene antibiotics lowered cellular cyclic AMP levels and markedly increased the levels observed in the medium.