Independent regulation of thromboxane and prostaglandin synthesis in liver macrophages.

Incubation of liver macrophages with zymosan, phorbol ester and calcium ionophore A 23187 led to the formation of thromboxane, prostaglandin E2 and prostaglandin D2, whereas after external addition of arachidonic acid prostaglandin E2 and prostaglandin D2 only were found. This was confirmed by the use of labeled arachidonic acid given together with the stimuli. When the liver macrophages were prelabeled with [3H]arachidonic acid, and zymosan and [14C]arachidonic acid were added simultaneously, [3H]-label only was found in thromboxane whereas both [3H]- and [14C]-labeled PGE2 and PGD2 were detected in the cell medium. These data suggest that in cultured rat liver macrophages externally added arachidonic acid is accessible to the cyclooxygenase supplying prostaglandin H2 for prostaglandin E2 and D2 synthesis but not for thromboxane synthesis.