THE EFFECT OF DIETARY FAT LOAD ON THE SIZE AND COMPOSITION OF CHYLOMICRONS IN THORACIC DUCT LYMPH

¹ Department of Experimental Pathology, John Curtin School of Medical Research, Australian National University, Canberra, Australia

Chylomicrons of Sf 400 and lipoproteins of Sf 12-400 were separated by ultra-centrifugation from samples of thoracic duct lymph collected from rabbits fed for 1 to 2 weeks previously on diets containing 5 per cent and 30 per cent corn oil or butter and from rats given a single intragastric dose of 0·5 ml. corn oil.

The size of these particles after corn oil was determined by electron microscopy following fixation in osmium tetroxide. In rabbits on the low fat diet the mean diameter of chylomicrons was 960 Å with half the triglyceride in particles of diameter greater than 1400 Å; on the high fat diet the mean diameter was 1435 Å with half the triglyceride in particles of diameter greater than 2700 Å. In rats the mean chylomicron diameter was 1094 Å in the early phase of fat absorption with half the triglyceride in particles of diameter greater than 1320 Å. These figures increased to 2105 Å and 3600 Å respectively at the peak of fat absorption.

The relationship between the chemical composition of these complexes and their actual size suggests that phospholipid is uniformly distributed on the surface, each phospholipid molecule occupying approximately 65 Ų.

Although meaningful electron micrographs of butter chylomicrons could not be obtained, determinations of the triglyceride : phospholipid ratios indicate that, as with the corn oil-fed animals, the chylomicrons from the rabbits fed 30 per cent butter are on the average larger than those from the animals fed 5 per cent butter.