Relationship between intracellular cyclic AMP and lipolysis in human adipose tissue

Human subcutaneous adipose tissue has been incubated in vitro in the presence and absence of isoprenaline (ISNA). The tissue concentration of cyclic AMP (cAMP) and the release of glycerol into the incubation medium were measured after various incubation periods. In the presence of ISNA (6 X 10(-5) mol/l), the tissue concentration of cAMP reached a peak after around 10 min and then declined to a level significantly lower than that at the start of the incubation. In contrast, the ISNA-induced rate of lipolysis was a linear function of the incubation time. The addition of propranolol (13 mumol/l) at different times after ISNA did not influence the rate of lipolysis, although it resulted in a decrease in the tissue level of cAMP. There was a positive correlation between the maximal increase in tissue cAMP and the rate of lipolysis in adipose tissue exposed to ISNA, both in individual experiments and in a group of 23 persons. No correlation was found between the rate of lipolysis and the tissue level of cAMP in adipose tissue incubated under basal conditions. The findings are compatible with the theory that the beta-adrenergic-induced lipolysis by human adipose tissue is a function of the maximal rise in the concentration of tissue cAMP. It is concluded that this peak level of cAMP represents single compartment of the nucleotide.