| Abstract: | Recently, the metabolism of arachidonic acid to two unidentified products (Peak 1 and Peak 2) by a cytochrome P-450 dependent mixed function oxidase has been described in canine polymorphonuclear leukocytes (PMNs). This study assessed the biologic activity of one of these metabolites, Peak 2, on PMN function. Peak 2 was formed biologically following addition of exogenous arachidonic acid to canine PMNs pretreated with BW755c to inhibit lipoxygenase and cyclooxygenase enzymes, and purified by high performance liquid chromatography following separation by column chromatography. Peak 2 (20-200 ng/ml) inhibited calcium ionophore A23187-induced aggregation and the second phase of LTB4-induced aggregation. Additionally, Peak 2 inhibited A23187-induced PMN adhesion to columns of Sephadex G-25. BW755c (94 microM), which increased the formation of Peaks 1 and 2 by almost 300%, also inhibited A23187-induced PMN adhesion. In contrast, Peak 2 did not inhibit the release of superoxide anions or immunoreactive LTB4, after stimulation of the PMNs with A23187. Thus, Peak 2 may modulate some activities of canine PMNs. Because the biologic activity of Peak 2 is opposite to that of LTB4, which promotes PMN aggregation and adhesion, and because LTB4 may be metabolized by a cytochrome P-450-dependent mixed function oxidase to less active metabolites, this enzyme system may play a central role in the control of PMN function. |
