The action of cyclic 3′,5′-adenosine monophosphate on lipolysis in rat adipose tissue

Abstract

1. 1. Stimulation of lipolysis in fat cells or intact adipose tissue by cyclic 3',5'-AMP, 1 mM, was readily demonstrated in simple phosphate-saline (all Na +) medium. Adenine, 1 mM, also to a lesser extent stimulated lipolysis in this medium but unlike cyclic 3',5'-AMP its effect was not diminished by the presence of K + in the incubation medium. Adenosine, 5'-AMP, ADP, or ATP did not enhance lipolysis. 2. 2. In phosphate-saline medium with K + (7 mequiv/1) cyclic 3',5'-AMP stimulated lipolysis when the basal rate was low (tissue from fasted-refed rats, tissues preincubated with glucose and insulin) and inhibited lipolysis when the basal rate was high (tissues from fasted rats, tissues incubated with epinephrine). 3. 3. In Krebs-Ringer phosphate medium cyclic 3',5'-AMP alone had no effect on production of glycerol by fat cells and decreased the elevated rate of glycerol production associated with the presence of theophylline. In Krebs-Ringer phosphate medium without Ca 2+ and Mg 2+, cyclic 3',5'-AMP alone stimulated glycerol production and did not decrease glycerol production when theophylline was present. 4. 4. EDTA (5 mM) increased glycerol production in medium without Ca 2+ and Mg 2+. Alone, it had no effect in medium with Ca 2+ and Mg 2+ but inhibited the effect of epinephrine. Stimulation of lipolysis by EDTA (no Ca 2+ or Mg 2+) was much greater in all Na + medium than it was in the presence of K +. The composition of free fatty acids released into the medium was similar whether lipolysis was stimulated by epinephrine, cyclic 3',5'-AMP or EDTA. 5. 5. Stimulation of lipolysis by cyclic 3',5'-AMP (all Na + medium) was not observed in the absence of phosphate which itself in high concentration (>20 mM) increased release of free fatty acids.