Effect of inhibitors of eicosanoid biosynthesis on the immune reactivity of the rainbow trout, Oncorhynchus mykiss

Abstract

The effect of nordihydroguaiaretic acid (NDGA), a lipoxygenase inhibitor, and indomethacin, a cyclo-oxygenase inhibitor, on the immune reactivity of rainbow trout was examined. While NDGA had a dose-dependent inhibitory effect on antibody synthesis against Aeromonas salmonicida , indomethacin had a variable effect ranging from inhibition to stimulation. Further experiments with NDGA demonstrated that following administration of this compound via the peritoneal cavity there was no apparent effect on the biosynthesis of lipoxygenase products, such as leukotrienes and lipoxins by head kidney macrophages. Injection of A. salmonicida vaccine in the presence of NDGA into the peritoneal cavity had no significant effect on the total number of leucocytes present in this site 3 and 7 days post-vaccination compared with vaccine-only controls. However, NDGA caused significant reductions in the macrophage and neutrophil ratios and an increase in the proportion of lymphocytes/immature leucocytes in the peritoneal cavity at both 3 and 7 days post-immunisation. The phagocytic ability of head kidney leucocytes (mainly macrophages) was also significantly depressed in fish previously injected with NDGA compared with the control.