Desaturation and elongation of unsaturated fatty acids in hepatocytes from thermally acclimated rainbow trout

Abstract

Hepatocytes isolated from 5- and 20 °C-acclimated rainbow trout ( Salmo gairdneri) were incubated with [1- 14C]oleic, -linoleic, or -linolenic acid to investigate the role of desaturation and elongation pathways in cold adaptation. Cells from both acclimation groups demonstrated a substrate preference in the order: 18:3 > 18:2 > 18:1. When assayed at 5 °C, cells from cold-acclimated trout were more efficient at producing derivatives of linolenic acid than cells from warm-acclimated trout. Cold acclimation resulted in degrees of compensation of desaturation and elongation rates that depended on the fatty acid family and specific reaction in the sequence. In the oleic acid family, reaction rates showed no compensation; partial compensation was observed in the linoleic acid family, and perfect (e.g., Δ6 desaturation) to overcompensation (e.g., Δ4 desaturation) in the linolenic acid family. Cells from cold-acclimated trout had higher rates of production of linolenic-derived acids when assayed at 5 than 20 °C. The proportion of the product of a given desaturation or elongation reaction that continued to the next reaction in the sequence was higher when assayed at 5 than 20 °C, increasing the probability of producing polyunsaturates. The results suggest that the substrate preference of the desaturation and elongation enzymes, the compensation of reaction rates, and the possible “link” between certain reactions in the metabolic sequence may ensure the production of poly-unsaturated fatty acids in cold-adapted trout.