ESTERIFICATION OF INTRA- AND EXTRA-CELLULAR FREE FATTY ACIDS BY RAT ADIPOSE TISSUE

The esterification of intracellular and extracellular FFA by rat adipose tissue in vitro was investigated. The rate of incorporation of FFA into neutral lipids was proportional to the FFA concentration in the incubation medium. Both in the presence and absence of a lipolytic agent (epinephrine), heptadecanoate-1-C14, which is not specifically diluted by tissue fatty acids, was esterified in the same manner as palmitate-9,10-H3. Stearate, palmitate, and oleate were esterified at similar rates by adipose tissue taken from fed animals and incubated with glucose. The rate of esterification of one fatty acid was not significantly affected by the presence of another. Similar results were obtained when tissues were taken from fasted animals and incubated in the absence of glucose, except that the overall rate of esterification was diminished and FFA accumulated in the tissue. It is concluded that long-chain fatty acids do not compete for esterification or entry into the adipose tissue cell.In some experiments tissue FFA esterification was studied by measuring the incorporation of glucose-U-C14 carbons into glyceride–glycerol. Esterification, assayed in this manner, increased when albumin was present in the incubation medium and allowed FFA to diffuse from the tissue. However, pre-incubation of adipose tissue in medium containing labelled FFA indicates that much of the intracellular FFA may be esterified without its mixing with the extracellular FFA pool.