Metabolism of Dibutyryl Cyclic Adenosine 3',5'-Monophosphate during Its Regulation of Lipolysis and Glucose Oxidation in Isolated Rat Epididymal Adipocytes

The metabolism of N6,O2'-(2',3'-3H)-dibutyryl adenosine 3',5'-cyclic monophosphate (3H-DBcAMP) was studied in isolated rat epididymal adipocytes. 3H-Butyric acid, isolated from incubation mixtures after stimulation by 3H-DBcAMP of lipolysis or after stimulation or inhibition of glucose oxidation by 3H-DBcAMP, represented less than 4% hydrolysis of the butyryl groups of DBcAMP during up to 2 hours of incubation; this hydrolysis appeared to be nonenzymatic in nature. Of the butyric acid produced, less than 10% was lost by oxidation to CO2 and by volatilization. Only two nucleotides were found following incubation of 3H-DBcAMP, with or without adipocytes, for up to 2 hours—the original 3H-DBcAMP and a radioactive compound with the chromatographic mobility of N6-monobutyryl cyclic AMP (MBcAMP). The molar ratio of 3H-MBcAMP to 3H-DBcAMP in the isolated material, although greater than that of the substrate prior to incubation, was not significantly different in incubations with or without adipocytes. 3H-MBcAMP, although similar to 3H-DBcAMP in lipolytic potency, could not, in the amounts (4 to 8%) present as contaminant in preparations of 3H-DBcAMP, be responsible for the effects ascribed to 3H-DBcAMP. It is concluded that, under the experimental conditions used, DBcAMP exerted several regulatory effects on the metabolism of adipocytes without the necessity for prior removal of one or both butyryl groups from the nucleotide. This implies that free 6-amino and 2'-hydroxyl groups of cyclic AMP are not required for its biological activities in this tissue.