Distribution of 22:6n-3 newly synthesized from 18:3n-3 into glycerolipid classes from tissues of rainbow trout (Oncorhynchus mykiss).

The distribution of D5-22:6n-3 following ingestion of a pulse of D5-18:3n-3 was measured quantitatively by GC-negative chemical ionization MS in lipid classes from liver, cecal mucosa, and brain from rainbow trout to further our understanding of the processes determining accretion and turnover of 22:6n-3 in fish. The accretion of D5-22:6n-3 was expressed in two ways, as percent enrichment and as ng D5-22:6n-3/microg 22:6n-3/ mg D5-18:3n-3 eaten. In cecal mucosa at 2 d post-dose, PC was the most enriched lipid class followed by PE and then TAG. Enrichment fell in all lipid classes in cecal mucosa from 2 to 7 d post-dose of D5-18:3n-3. In liver, PC was also the most enriched lipid class at 2 d, but in this tissue all lipid classes were more enriched in D5-22:6n-3 by 7 d. When expressed in terms of the 22:6n-3 content of the different lipid classes, TAG became relatively less important in cecal mucosa and more important in liver. Over a time course of 3 to 35 d, the percent enrichment of D5-22:6n-3 in liver peaked at 7 d in PC, PE, PS, and PI and fell rapidly in TAG from 3 d. PC from liver was the most enriched lipid class at 3 and 7 d, and thereafter PE was the most enriched lipid class. However, TAG had the highest specific activity at all times except 7 d. In brain, the enrichment of D5-22:6n-3 was very low in all lipid classes at 3 d and increased progressively to 35 d with PC and PE similarly enriched. TAG from brain had the highest specific activity at all times. This study is the first to present quantitative information on rates of accretion and depletion of newly synthesized 22:6n-3 into the main lipid classes of fish tissues.