The influence of environmental temperature on membrane fluidity, fatty acid composition and lipoxygenase product generation in head kidney leucocytes of the rainbow trout, Oncorhynchus mykiss

Abstract

The adaptive responses of leucocytes isolated from the head kidney of rainbow trout, Oncorhynchus mykiss, to temperature changes were studied. Membrane fluidity measurements showed that these cells underwent an adaptive response to reduced environmental temperature. This was mediated, at least in part, by changes in the fatty acid profiles of these cells. The unsaturated to saturated fatty acid ratio of total lipid extracted from leucocytes isolated from summer (14.5°C) and winter (6.5°C) temperature-acclimated fish was increased at the lower temperature. This alteration was as a result of reduced saturated fatty acid and increased polyunsaturated fatty acid content of these cells. The eicosanoid generating capacity of leucocytes from winter-and summer-acclimated trout showed a significant reduction in leukotriene B 4 and B s synthesis in the winter, whereas lipoxin A 4 and A s biosynthesis was unaffected. There was no difference in the ratio of 4-to 5-series lipoxins or leukotrienes derived from 20:4(n-6) and 20:5(n-3), respectively, synthesised by head kidney leucocytes between these two periods. Investigations of the time course of the acclimation to a reduction in temperature showed an increase in the membrane fluidity of leucocytes from fish after 5–10 days maintenance at low (4°C) temperature. This correlated with a progressive increase in the unsaturated to saturated fatty acid ratio in the lipids of these cells. This in turn was as a result of a significant decrease in the relative amounts of 16:0 and increases in 18:2, 18: 3 and 20: 2. Overall, this study shows that rainbow trout leucocytes undergo progressive changes in their membrane fluidity and fatty acid composition following short-term and long-term changes in environmental temperature.