The composition and structure of lymph chylomicrons in dog, rat, and man.

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Abstract
Thoracic duct chyle was collected from one patient and several dogs and rats fed corn oil and cream. Washed chylomicrons were frozen and thawed to prepare an oil phase and a membrane fraction. The oil phase contained, in addition to triglyceride, all of the esterified cholesterol, about 25-35% of the free cholesterol, and none of the phospholipid. Chylomicron "ghosts" or "membranes" were demonstrated by electron microscopy in a fraction sedimented by centrifugation. These membranes consisted mostly of phospholipids with small amounts of protein, free cholesterol and triglyceride. GLC analysis showed large differences in chylomicron triglyceride fatty acids due to changes in dietary fat wnereas the phospholipid fatty acids were subjected to much less variation. Triglycerides of membranes prepared by freezing contained a much higher proportion of saturated fatty acids than the oil phase. Various interpretations of this finding are discussed. Sphingo-myelin from dog chylomicrons contained little or no fatty acids of chain lengths greater than 18 carbons whereas up to 25% of dog plasma sphingo-myelin fatty acids were of longer chain variety. After cream feeding the percentage of chylomicron cholesterol in the esterified form varied from 32 to 45% whereas after corn oil feeding the percentage of esterified cholesterol was, except in one instance, between 16 and 33 percent. Lymph, freed from chylomicrons by centrifugation, showed higher percentages of its cholesterol in the esterified form. On the basis of analytical data it is suggested that chylomicron membrane is a mosaic of small amounts of protein, free cholesterol, and saturated triglyceride in a monolayer of phospholipid.