Compartmentation of Glycerides in Adipose Tissue Cells

Isolated adipose tissue cells were prelabeled by incubation with radioactive fatty acids or radioglucose and subsequently transferred to a medium containing serum albumin and epinephrine. The specific activity of the fatty acids released during the first 15 min exceeded that of the bulk glycerides by a factor of over 10, and then dropped rapidly. Cellular free fatty acids could be excluded as the source of these high activity fatty acids. The specific activity of the diglyceride fraction in the prelabeled cells was 3 times that of the fatty acid released and dropped considerably during incubation with epinephrine. The absolute amount of diglyceride did not decrease. Diglycerides accounted for part of the fatty acids released. The rest was derived from a pool of triglycerides of high specific activity, which replenished the diglyceride pool and equilibrated with the bulk triglycerides in 1 hour. Equilibration of the triglyceride pools was very slow in the absence of epinephrine.