Differences between in vivo and in vitro production of eicosanoids following long-term dietary fish oil supplementation in the rat.

The effects of different lipid supplements on endogenous and exogenous production of eicosanoids were investigated in the rat following a 12-month pre-feeding period. The urinary excretion of tetranorprostanemonoic (TPM) and tetranorprostanedioic (TPD) acids was measured as an index of endogenous production whilst myocardial release of PGI2 and TXA2 was estimated under in vitro conditions. Compared to the reference group, n-3 PUFA rich tuna fish oil (TFO) fed rats displayed a near doubling of endogenous (TPM + TPD) synthesis; however, myocardial production was reduced by 32% (PGI2) and 55% (TXA2). Sheep fat supplementation also caused a 62% rise in urinary tetranor metabolites but in contrast to TFO feeding, myocardial production in vitro also showed a significant increase (P less than 0.05). Considerable changes in PUFA profile of plasma, heart and kidney occurred as a result of dietary lipid treatment and in addition a high tissue specificity was also noted with regard to the incorporation and conversion of dietary n-3 PUFA. For example, the heart showed a low EPA (1.2%) and high DHA (28.0%), whereas their proportions in the kidney were near equal (6-7%). As only the TFO diet exerted a significant effect on the proportion of AA, the changes in eicosanoid production cannot be fully explained on the basis of precursor/inhibitor availability. The results probably reflect the complex interactions between fatty acid substrates, release mechanisms and biosynthetic enzymes.