The absorption and competition kinetics of the essential fatty acids (EFAs)
, linoleic acid (LA), alpha-linolenic acid (alpha LnA) and arachidonic acid
(AA) in vivo were studied in the perfused rat jejunum. Uptake of each EFA
on its own followed saturable kinetics at low luminal concentrations, sugge
sting a facilitative transport process, the affinity of which increased wit
h chain length and degree of unsaturation. Absorption of one EFA was enhanc
ed by low, whilst competitively inhibited by high, concentrations of a seco
nd EFA. Whereas LA and aLnA each interfered with the absorption of one anot
her, both had little effect on AA. There was a strong inverse correlation b
etween the relative unsaturation of an EFA and the change in Km of its abso
rption observed upon inhibition with another EFA. Overall, the results indi
cated a specific absorptive mechanism, probably involving a transport prote
in, the affinity of which increased with the degree of unsaturation of the
EFA. (C) 2000 Harcourt Publishers Ltd.