Essential fatty acid deficiency in the pig: Effects on eicosanoid basal levels and in vitro synthesis by the small intestine

Abstract

The influence of nutritional essential fatty acid (EFA) deficiency on arachidonate metabolism by porcine small intestine has been studied. Great care was exercised in the manipulation of the jejunal wall to avoid artefactual metabolism of arachidonate. Thus, jejunal wall was frozen in liquid nitrogen after organ removal and washing, and subsequently lyophilized. This lyophilized tissue was used as starting material for all experiments, including organic solvent extractions (for basal level determinations) and reconstitution in aqueous buffer (for neosynthesis experiments). Feeding pigs with a low linoleate diet for 12 weeks resulted in a 36% diminution in the % of arachidonate in jejunal phospholipids. Basal levels of 6-keto prostaglandin F 1α (6-keto PGF 1α), thromboxane B 2 (TXB 2), PGF 2α, PGE 2, PGD 2 and leukotriene B 4 (LTB 4) were not altered in the EFA-deficient state. However, we observed a significant lowering of the synthesis of each of these eicosanoids (except LTB 4) by the EFA-deficient jejunum during brief (15s) in vitro neosynthesis experiments. The origin of arachidonate as a substrate of PG endoperoxide synthase, also named PGH synthase or cyclooxygenase (Cox) in these neosynthesis experiments is probably a non-esterified fatty acid pool since, (1) neosynthesis was not inhibited by the phospholipase A 2 (PLA 2) inhibitor parabromophenacylbromide, and (2) substantial amounts of arachidonic acid were found in the jejunum, frozen or lyophilized. Cox activity of the lyophilized jejunum and Cox content of liver and intestine microsomes were not modified in the EFA-deficient state. A [1- 14C] arachidonic acid metabolic profile of the porcine jejunal mucosa was established: PGE 2 and PGF 2α were the major PGs synthesized, together with another metabolite which was identified as 12-hydroxyeicosatetraenoic acid (12-HETE) due to its chromatographic retention time.