THE EFFECT OF FASTING ON THE ESTERIFICATION OF PALMITATE BY RAT EPIDIDYMAL ADIPOSE TISSUE IN VITRO

Abstract

The effect of 48-h fasting on the in vitro esterification of fatty acids by rat epididymal adipose tissue was investigated. Fat pads from fed and fasted animals were incubated with palmitate-9,10-3H and glucose-U-14C. Fasting diminished the incorporation of both isotopes into glycerides. The decrease in glucose incorporation after fasting was found both in the glycerol and fatty acid moieties. The effect of fasting was not altered by the presence of insulin. Since lipotysis, which is increased after fasting, results in the preferential hydrolysis of newly synthesized triglycerides, the amount of labeled free glycerol after incubation was determined. It was insufficient to account for the decrease in glucose incorporation into lipids following fasting. The decrease in esterification of palmitate-9,10-3H could also be detected in free adipocytes and fat-free homogenates, but to a less extent than in intact tissue. Esterification by adipose-tissue homogenates from fasted animals was diminished in spite of optimum concentrations of substrates and coenzymes. The decrease in esterification was reflected in both neutral lipids and phosphatidic acid.