Whole-body DHA synthesis-secretion kinetics from plasma eicosapentaenoic acid and alpha-linolenic acid in the free-living rat

Whole body docosahexaenoic acid (DHA, 22:6n-3) synthesis from α-linolenic acid (ALA, 18:3n-3) is considered to be very low, however, the daily synthesis-secretion of DHA may be sufficient to supply the adult brain. The current study aims to assess whether whole body DHA synthesis-secretion kinetics are different when comparing plasma ALA versus eicosapentaenoic acid (EPA, 20:5n-3) as the precursor. Male Long Evans rats (n = 6) were fed a 2% ALA in total fat diet for eight weeks, followed by surgery to implant a catheter into each of the jugular vein and carotid artery and 3 h of steady-state infusion with a known amount of 2H-ALA and 13C-eicosapentaenoic acid (EPA, 20:5n3). Blood samples were collected at thirty-minute intervals and plasma enrichment of 2H- and 13C EPA, n − 3 docosapentaenoic acid (DPAn-3, 22:5n-3) and DHA were determined for assessment of synthesis-secretion kinetic parameters. Results indicate a 13-fold higher synthesis-secretion coefficient for DHA from EPA as compared to ALA. However, after correcting for the 6.6 fold higher endogenous plasma ALA concentration, no significant differences in daily synthesis-secretion (nmol/day) of DHA (97.6 ± 28.2 and 172 ± 62), DPAn-3 (853 ± 279 and 1139 ± 484) or EPA (1587 ± 592 and 1628 ± 366) were observed from plasma unesterified ALA and EPA sources, respectively. These results suggest that typical diets which are significantly higher in ALA compared to EPA yield similar daily DHA synthesis-secretion despite a significantly higher synthesis-secretion coefficient from EPA.