Conjugated Linolenic Acid Is Slowly Absorbed in Rat Intestine, but Quickly Converted to Conjugated Linoleic Acid

We showed previously that α-eleostearic acid (α-ESA; 9Z11E13E-18:3) is converted to 9Z11E-conjugated linoleic acid (CLA) in rats through a Δ13-saturation reaction. To investigate this further, we examined the absorption and metabolism of α-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 α-ESA, α-linolenic acid (LnA; 9Z12Z15Z-18:3), CLA, and punicic acid (PA; 9Z11E13Z-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 ¹³C-NMR, respectively; the product was confirmed to be 9Z11E-CLA. A part of α-ESA and PA was converted to 9Z11E-CLA 1 h after administration; therefore the lymphatic recoveries of α-ESA and PA were modified by the amount of recovered CLA. Cumulative recovery of CLA, α-ESA, and PA was lower than that of LnA only during h 1 (P < 0.05), and cumulative recovery of α-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 > α-ESA = PA. The conversion ratio of α-ESA to 9Z11E-CLA was higher than that of PA to 9Z11E-CLA over 24 h (P < 0.05). These results indicated that α-ESA and PA are slowly absorbed in rat intestine, and a portion of these fatty acids is quickly converted to 9Z11E-CLA.