Differential regulation of 5-lipoxygenase and cyclo-oxygenase pathways of arachidonate metabolism in rat peritoneal leukocytes.

1. Simultaneous activation of the 5-lipoxygenase and cyclo-oxygenase pathways of arachidonate metabolism in rat peritoneal mixed leukocytes in response to A23187, chemoattractant N-formyl-methionine-leucine-phenylalanine (FMLP) and arachidonic acid (AA) was studied by radioimmunoassay of leukotriene B4 (LTB4) and thromboxane B2 (TXB2) respectively. 2. FMLP and AA preferentially activated cyclo-oxygenase and A23187 preferentially activated 5-lipoxygenase. Release of TXB2 preceded that of LTB4. A threshold amount of A23187 enhanced FMLP-and AA-induced LTB4 production but not that of TXB2. 3. Phorbol myristate acetate (PMA) abolished LTB4 generation in response to FMLP with much less effect on TXB2, but did not inhibit the formation of either eicosanoid caused by A23187 or AA. Instead, PMA caused a dose-dependent but modest stimulation of TXB2 generation either on its own or when added with A23187 or AA. 4. These results show that the 5-lipoxygenase and cyclo-oxygenase pathways in rat peritoneal leukocytes are regulated differently and that functional compartmentalisation of the stimulus-generation sequence operates in these cells.