Effects of Prostaglandins on Adenosine 3’ , SMonophosphate Levels in Fat and Other Tissues*

The action of prostaglandins on cyclic AMP levels in rat epididymal fat pads, isolated fat cells, and other tissues was studied. Fat pads incubated with prostaglandin El (PGE1) contained higher levels of cyclic AMP than controls but lipolysis was not stimulated. However, PGEr did not cause increased cyclic AMP levels in isolated fat cells, suggesting that the stimulatory action occurred in another cell type. PGEl at very low concentrations antagonized the action of epinephrine on cyclic AMP levels in both intact fat pads and isolated fat cells. PGEl was considerably more effective as an inhibitor of epinephrine than PGFl,, an d PGFrp was without effect. PGEl lowered cyclic AMP levels in isolated fat cells very rapidly, and was effective against adrenocorticotropic hormone, glucagon, and thyroid-stimulating hormone as well as the catecholamines. Incubation of intact cell preparations of lung, spleen, diaphragm, kidney, and other tissues with 2.8 pM PGEr resulted in increased levels of cyclic AMP.