Linoleic acid kinetics and conversion to arachidonic acid in the pregnant and fetal baboon

Linoleic acid plasma kinetics in pregnant baboons and its conversion to lon g chain polyunsaturates (LCP) in fetal organs is characterized over a 29-da y period using stable isotope tracers, pregnant baboons consumed an LCP-fre e diet and received [U-C-13]linoleic acid (18:2*) in their third trimester of gestation, In maternal plasma, 18:2* dropped to near baseline by 14 days post-dose, while labeled arachidonic acid (20:4*) plateaued at 10 days at about 70% of total labeled fatty acids. After 2-5 days, total tracer fatty acids decreased in visceral organs, but increased in the fetal brain, Maxim al fetal incorporation of 18:2* was 1-2 days post-dose; thereafter it dropp ed while 20:4* increased reciprocally, Labeled 20:4 replaced 18:2" in neura l tissues by 5 days post-dose, In liver, kidney, and lung, 20:4* became dom inant by 12 days, but in heart the crossover was >29 days. Fetal brain 20:4 * plateaued by 21 days at 0.025% of dose, while fetal liver 20:4* was const ant from 1 to 29 days at 0.006% of dose. Under these dietary conditions we estimate that the fetus derives about 50% its 20:4 requirement from convers ion of dietary 18:2, with the balance from maternal stores, and conclude th at 1) fetal organs accumulate 18:2 within a day of a maternal dose and conv ert much of it to 20:4 within weeks, 2)modest dietary 18:2 levels may suppo rt fetal brain requirements for 20:4, and 3) the brain retains n-6 fatty ac ids uniquely compared with major visceral organs.