Effects of dipyrone on prostaglandin production by human platelets and cultured bovine aortic endothelial cells.

Dipyrone and its metabolites 4-methylaminoantipyrine, 4-aminoantipyrine, 4-acetylaminoantipyrine and 4-formylaminoantipyrine inhibited the formation of thromboxane A2 (TXA2) during in vitro platelet aggregation induced by ADP, epinephrine, collagen, ionophore A23187 and arachidonic acid. Inhibition occurred after a short incubation (30--40 sec) and depended on the concentration of the drug or its metabolites and the aggregating agents. The minimal inhibitory concentration of dipyrone needed to completely block aggregation varied between individual donors, and related directly to the inherent capacity of their platelets to synthesize TXA2. Incubation of dipyrone with cultured bovine aortic endothelial cells resulted in a time and dose dependent inhibition of the release of prostacyclin (PGI2) into the culture medium. However, inhibition was abolished when the drug was removed from the culture, or when the cells were stimulated to produce PGI2 with either arachidonic acid or ionophore A23187. These results indicate that dipyrone exerts its inhibitory effect on prostaglandins synthesis by platelets or endothelial cells through a competitive inhibition of the cyclooxygenase system.