Influence of niridazole and chloroquine on arterial and myometrial prostacyclin synthesis.

1. The effects of niridazole and chloroquine on rat arterial and myometrial prostacyclin (PGI2) synthesis in vitro were investigated by use of a rat platelet antiaggregatory bioassay. Niridazole (233 microM) and chloroquine (97 microM) inhibited PGI2 synthesis in both tissues. 2. Niridazole-induced inhibition in the myometrium was not reversed by exogenous arachidonic acid (33 microM) indicating a direct effect of the compound on PGI2 synthesizing enzymes. 3. Chloroquine-induced inhibition in the myometrium was significantly reversed by exogenous arachidonic acid (33 microM) indicating a direct effect of the compound on arachidonic acid releasing enzymes (e.g. phospholipases A2 and C). 4. Niridazole and chloroquine also inhibited prostaglandin E2 synthesis in the myometrium. 5. Chloroquine- and niridazole-induced inhibition of prostaglandin synthesis may contribute towards a better understanding of some of their actions in vivo.