Rat neutrophil activation and effects of lipoxygenase and cyclooxygenase inhibitors

Activation (defined as lysosomal enzyme secretion and generation of O(2) of rat neutrophils has been measured with the use of varying doses of soluble stimuli (phorbol myristate acetate (PMA); calcium ionophore A23187; and N-formyl-methionyl-leucyl-phenyl-alanine (FMLP] and particulate agents (immune complexes and zymosan particles). With either the calcium ionophore or the chemotactic peptide (FMLP), substantial enzyme release occurred, but the amount of O(2) produced was very small. Cytochalasin B greatly enhanced the enzyme release response to the chemotactic peptide but had little effect on neutrophil responses to other soluble stimuli. The cell response to PMA resulted in the greatest production of O(2) with significant enzyme secretion. When cell stimulation with insoluble stimuli (immune complexes or zymosan particles) was studied, significant amounts of enzyme release occurred in parallel with the generation of substantial amounts of O(2). The presence of cytochalasin B enhanced the cell responses to immune complexes but had an inhibitory effect on zymosan-induced responses. As expected, the amount of lysozyme secreted by stimulated rat neutrophils tended to exceed the amount of beta-glucuronidase released from the same cells. Neutrophil responses were investigated in the presence of drugs that were demonstrated in the rat neutrophil to inhibit either the lipoxygenase or the cyclooxygenase pathway. Inhibitors of the cyclooxygenase pathway (indomethacin, piroxicam, ibuprofen, BW755C), with few exceptions, consistently enhanced the enzyme secretion response, while effects on O(2) generation were less clear-cut but tended to be predominantly inhibitory. Drugs with inhibitory effects on the lipoxygenase pathway (nordihydroguaiaretic acid and nafazatrom) had significant inhibitory effects on both enzyme secretion as well as generation of O(2). These data suggest that activation responses (enzyme secretion and O(2) generation) of rat neutrophils may be dissociated (ie, one not always accompanying the other). Further, it appears that neutrophil activation, as defined by enzyme secretion, is enhanced by products of the lipoxygenase pathway and suppressed by products of the cyclooxygenase pathway. Generation of O(2) is not affected in such a clear-cut manner. Taken together the data suggest that enzyme release and O(2) production by activated rat neutrophils may be under separate control.