| Summary: | Although endogenous synthesis of conjugated linoleic acid (CLA) in the mammary gland of lactating cows has been already well documented, no study has determined so far as to which tissue and/or organ is involved in CLA synthesis in the growing ruminant except one study showing that CLA synthesis does not occur in ruminant liver. In this context, adipose tissue appears to be a good candidate for endogenous synthesis of CLA in the growing ruminant. The aim of this study was to compare the respective metabolisms of 11trans 18:1 (vaccenic acid, VA) and 9cis,11trans 18:2 (rumenic acid) to that of stearic acid (the preferential substrate of Δ9 desaturase) in adipose tissues (subcutaneous, SC and intermuscular, IM) of six Charolais steers by using the in vitromethod of incubated tissue slices. Samples of SC and IM adipose tissues were incubated at 37°C for 16 h under an atmosphere of 95% O2/5% CO2 in a medium supplemented with 0.75 mM of fatty acid (FA) mixture (representative of circulating non-esterified FA) and 186 μM [1-14C]-18:0 or 58.6 μM [1-14C]-VA or 56 μM [1-14C]-9cis,11trans CLA. Viability of explants was verified by measuring metabolic functions (glucose uptake and glucose-6-phosphate dehydrogenase activity). After 16 h of incubation, FA uptake was similar for all FA (18:0, VA and 9cis,11trans 18:2) in both SC and IM adipose tissues (around 40%). Once in adipose tissue, all FA were preferentially esterified (>80% of cell FA) favouring neutral lipid synthesis (around 90% of esterified FA). Stearic acid was highly (27%) desaturated into oleic acid in SC adipose tissue whereas this desaturation was much lower (6.8%) in IM adipose tissue (P < 0.0001). VA was desaturated into 9cis,11trans CLA at a low extent of about 2.5% to 4.4% in both adipose tissues probably because of a limited affinity of Δ9 desaturase for VA. 9cis,11trans CLA was itself converted by desaturation into 6cis, 9cis,11trans 18:3 at the intensity of 10.8% and 14.5% of cell 9cis,11trans CLA in SC and IM adipose tissues, respectively. In conclusion, bovine adipose tissues of the growing ruminant were especially involved in the endogenous synthesis of CLA from VA and in its desaturation into conjugated derivative, mainly 6cis, 9cis,11trans 18:3, of which biological properties need to be elucidated.
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