The origin and glyceride distribution of fatty acids in rat adipose tissue.

Abstract

To study the contribution of fatty acid synthesis to the content and composition of fatty acids in rat adipose tissue, fatty acids were synthesized in rat epididymal fat by in vivo incubation in a medium containing uniformly labelled glucose. Immediately after incubation 80% of the fatty acid radioactivity was in saturated acids; this proportion was virtually unchanged 13 days later. Over this interval, the lipid content of the pads increased 60% and the total fatty acid composition remained unaltered at 40% saturated, 40% monounsaturated and 20% diunsaturated acids. Due to the preponderance of saturated acids in the synthesized components, the absence of extensive desaturation or preferential mobilization of these acids, and the maintenance of the predominantly unsaturated character of the tissue over the experimental interval, it is evident that the process of in situ systhesis followed by direct incorporation of the synthesized acids, had not provided the major portion of the lipid which accrued in the tissue. It is thus concluded that in rats maintained on a mixed diet, plasma triglyceride rather than plasma glucose may be the predominant precursor of adipose tissue fatty acids. The distribution of the newly synthesized acids amongst a variety of triglycerides and diglycerides was also explored. Radioactive saturated acids were recovered in triglycerides containing 3 or more double bonds and diglycerides containing 2 double bonds; hence acids synthesized in the tissue and dienoic acids derived from bulk lipid or plasma triglyceride had mixed, probably as free acids, prior to diglyceride formation.