The ultrastructure of chylomicra and of the particles in an artificial fat emulsion

Abstract

Chylomicra collected from the cannulated thoracic duct of rats fed corn oil or olive oil, and particles of an artificial fat emulsion (Intralipid), were examined with the electron microscope after osmium fixation and Epon embedding. In section, corn oil chylomicra and Intralipid particles show a pale core and an electrondense surface layer; these two zones are thought to represent the triglyceride and phospholipid components respectively. The surface layer measures 50 to 100 Å in width when sectioned transversely. It shows minute interruptions and may be laminated in focal areas. Corn oil chylomicra fixed after storage in a solution of sodium citrate for several days do not differ morphologically from those fixed in the fresh state. In section, olive oil chylomicra show a paler core and a less well-defined surface layer. When fixed in the fresh state, the more electron-dense material is located just beneath the surface of the chylomicron; after storage in citrate the electron-dense material is scattered more peripherally. The findings are discussed in relation to the composition of chylomicra and the changes which the lipids undergo during processing for electron microscopy.