The effect of dietary
phosphatidylcholine on the assimilation and distribution of ingested free
oleic acid (18:1n-9) in gilthead seabream (Sparus aurata)
larvae
E. Hadas, W. Koven, D. Sklan, A. Tandler-2002
Aquaculture, 217(1-4)
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] 18:1n-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.