The Effects of Insulin on Lipolysis Evoked by Cyclic AMP and Its Dibutyryl Analog ∗

Summary

Glycerol production by segments of epididymal fat from normal rats was used as a measure of lipolysis. Theophyl-line (0.3 mg/ml) produced a striking increase in lipolysis. Further addition of cyclic adenosine 3′, 5′-monophosphate (CAMP) at a concentration of 10^-2 M caused an even greater increase in glycerol production. Insulin (1 mU/ml) slightly reduced the lipolytic effects of theophylline and completely abolished lipolysis in response to CAMP. The dibutyryl analog of CAMP (10^-3 M) also increased lipolysis and its effects were also potentiated by theophylline. Insulin failed to reduce and in some experiments even enhanced the lipolytic action of dibutyryl CAMP. Imidazole reduced lipolysis in response to both nucleotides. The findings indicate that CAMP and its dibutyryl analog may behave quite differently under some circumstances and underscore the need for caution in drawing physiological conclusions based on findings with DBCAMP alone.