In the present study, the lipoxygenase activity in polymorphonuclear (PMN) leukocytes of rats was characterized, and the change in lipoxygenase activity in peritoneal and peripheral PMN leukocytes challenged by caseinate was investigated. Peritoneal PMN leukocytes produced 5-HETE and LTB4 as the major 5-lipoxygenase metabolites from arachidonic acid. The 5-lipoxygenase activity was calcium dependent. Caseinate treatment in rats significantly stimulated the 5-lipoxygenase activity in peripheral and peritoneal PMN leukocytes. Although it also stimulated the cyclooxygenase metabolic pathway, the effect was not as evident as that on the 5-lipoxygenase pathway. Since LTB4 is a potent chemotactic factor for PMN leukocyte migration, the present results might explain the mechanism on the PMN leukocyte infiltration caused by caseinate treatment.
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