Conjugated linolenic acid is slowly absorbed in rat intestine, but quickly converted to conjugated linoleic acid

We showed previously that [alpha]-eleostearic acid ([alpha]-ESA; 9Z11 E13 E-18:3) is converted to 9Z11 E-conjugated linoleic acid (CLA) in rats through a [DELTA] 13-saturation reaction. To investigate this further, we examined the absorption and metabolism of [alpha]-ESA in rat intestine using a lipid absorption assay in lymph from the thoracic duct. In this study, we used 4 test oils [tung oil, perilla oil, CLA-triacylglycerol (TG), and pomegranate seed oil, containing [alpha]-ESA, [alpha]-linolenic acid (LnA; 9Z12 Z15Z-18:3), CLA, and punicic acid (PA; 9Z11 E13Z-18:3), respectively]. Emulsions containing the test oils were administered to rats, and lymph from the thoracic duct was collected over 24 h. The positional and geometrical isomerism of CLA produced by PA metabolism was determined using GC-electron impact (EI)-MS and [sup.13]C-NMR, respectively; the product was confirmed to be 9Z11 E-CLA. A part of [alpha]-ESA and PA was converted to 9Z1 1E-CLA 1 h after administration; therefore the lymphatic recoveries of [alpha]-ESA and PA were modified by the amount of recovered CLA. Cumulative recovery of CLA, [alpha]-ESA, and PA was lower than that of LnA only during h 1 (P < 0.05), and cumulative recovery of [alpha]-ESA and PA was significantly lower than that of LnA and CLA for 8 h (P < 0.05). Therefore, the absorption rate was LnA > CLA > [alpha]-ESA = PA. The conversion ratio of [alpha]-ESA to 9Z11 E-CLA was higher than that of PA to 9Z11 E-CLA over 24 h (P < 0.05). These results indicated that [alpha]-ESA and PA are slowly absorbed in rat intestine, and a portion of these fatty acids is quickly converted to 9Z11 E-CLA.