Effect of phorbol esters on the hormonal responsiveness of isolated white fat cells.

Phorbol 12-myristate 13-acetate (PMA) did not alter the basal cyclic AMP accumulation or lipolysis in isolated rat fat cells. Similarly, PMA was unable to modify the cyclic AMP accumulation induced by isoprenaline and forskolin or the inhibition of cyclic AMP accumulation and lipolysis induced by prostaglandin E2 and phenylisopropiladenosine. PMA inhibited the alpha 1-adrenergic increase in the labeling of phosphatidylinositol in a dose-dependent fashion. By itself, PMA was without significant effect on the labeling of phosphatidylinositol and phosphatidylethanolamine but increased the labeling of phosphatidylcholine and its precursor phosphatidic acid.