The effect of dietary phosphatidylcholine on the assimilation and distribution of ingested free oleic acid (18:1 n−9) in gilthead seabream ( Sparus aurata) larvae

Abstract

Two separate studies investigated the effect of dietary phosphatidylcholine (PC) on the assimilation of ingested free fatty acid (FFA) into the tissues of 28-day-old gilthead seabream larvae. Two squid meal based microdiets (MD), labeled with free [1- 14C] 18:1 n−9, were prepared that were identical in their nonlipid fractions and total lipid levels but differed in their lipid compositions. The control MD contained, by dry weight (DW), 10% capelin oil while the treatment MD comprised of 7.5% capelin oil and 2.5% di-stearylphosphatidylcholine. In the first study, the MDs were fed to seabream larvae over 14 h followed by 10 h of food deprivation in the dark. Larval samples were taken after 1, 8, 14 and 24 h and the resultant distribution of radioactivity in whole body lipid fractions was determined. Starting at 8 h and reaching a maximum after 14 h of feeding, larvae fed the PC diet demonstrated higher ( P<0.05) levels of radioactivity compared to the control larvae, in their polar (1179±72 and 595±70 dpm larva −1, respectively) and free fatty acid fractions (460±66 and 201±40 dpm larva −1, respectively). This suggested that both the assimilation and ingestion rate in the PC larvae increased over the control fish after 8 h of feeding. During the 10 h of food deprivation, radioactivity in the triacylglycerol (TAG) fraction of the PC larvae decreased by 37% while radioactivity in the control fish TAG decreased by only 16%. Apparently, a considerable amount of this 14C-label was mobilized for membrane lipid synthesis as evidenced by increases of 14C-label in the PL class of the PC and control larvae that reached 1447±62 and 737±49 dpm larva −1, respectively. The second experiment examined the influence of dietary PC on the mobilization of ingested 14C-oleic acid from the digestive tract to the body. The levels of 14C-label in the PL, TAG and cholesterol ester (CE) lipid classes in the body were significantly ( P<0.05) greater in larvae fed the PC diet (156±48, 49±28 and 97±14 dpm larva −1, respectively) compared to fish ingesting the control treatment (85±32, 26±12 and 36±33 dpm larva −1, respectively). Conversely, control larvae exhibited 57% (141±41 dpm larva −1) of its 14C-label in the TAG fraction of the gut while PC larva only accumulated 14% (15±11 dpm larva −1) of their total 14C-label in this region. The results clearly suggest that PC fed larvae, compared to the PC deficient control, were more rapidly transporting dietary FFA to the tissues as evidenced by their accumulating levels of radioactivity in the PL class of the body as feeding continued.