Acylation of lyso platelet‐activating factor by splenocytes of the rainbow trout, Oncorhyncus mykiss

In mammalian systems, platelet‐activating factor, 1‐ O ‐alkyl‐2‐acetyl‐ sn ‐glycero‐3‐phosphocholine, (PAF) is rapidly inactivated by a deacetylation/reacylation system that produces 1‐ O ‐alkyl‐2‐acyl‐ sn ‐glycero‐3‐phosphocholine which is highly enriched in arachidonic acid. There is some evidence that n−3 fatty acids may have an impact on this system in humans but the nature of this impact is unclear. In rainbow trout, n−3 fatty acids are known to be essential dietary components which are derived through the food chain. Substantial quantities of n−3 fatty acids are found in trout membrane phospholipids. We show here that in sharp contrast to mammalian cells, trout cells acylate lyso platelet‐activating factor, alkyl‐GPC, 1‐ O ‐alkyl‐2‐lyso‐ sn ‐glycero‐3‐phosphocholine, (lyso‐PAF) with a high degree of specificity for n−3 fatty acids. When [ 3 H]lysoPAF was incubated with these cells, only three molecular species of alkylacylglycerophosphocholine were produced, and 92% contained n−3 fatty acids. Since isolated membranes yielded similar results, it appears that the acylation proceeds via a coenzyme A‐independent transacylase as found in mammalian systems.