Combinations of palytoxin or 12-O-tetradecanoylphorbol-13-acetate and recombinant human insulin growth factor-I or insulin synergistically stimulate prostaglandin production in cultured rat liver cells and squirrel monkey aorta smooth muscle cells

In the presence of 12-O-tetradecanoylphorbol-13-acetate (TPA) or the non-TPA-type tumor promoter, palytoxin, recombinant human insulin growth factor-I (IGF-I) and insulin synergistically stimulate prostaglandin production in rat liver cells (the C-9 cell line). Combinations fo palytoxin or TPA with recombinant human IGF-I or insulin also synergistically stimulate deesterification of c ellular lipids in C-9 cells prelabelled with ³H]arachidonic acid. With both types of stimulations, prostaglandin production or deesterification, the synergistic response of the IGF-I and insulin is greater with palytoxin than with TPA. Production of prostaglandin E₂ and F_2α by squirrel monkey smooth muscle cells incubated in the presence of TPA and insulin also is greater than the sum of the effects taken independently.