text: In contrast to diethylcarbamazine, piriprost (U-60,257; << 6,9-deepoxy-6,9-(phenylimino)-delta 6,8-prostaglandin I1 >>), which inhibits the formation of sulfidopeptide leuktrienes in RBL cells at the [[ 5-lipoxygenase ]] step (EC50 5 microM), did not inhibit the leukotriene synthetase of these cells.