Chylomicron formation and composition in unanaesthetised rabbits

Emulsified lipid was infused steadily into the upper small intestine of unanaesthetised rabbits for 6 h and 24 h periods. Lymph was collected from a thoracic duct cannula, the output of infused lipids was measured and the lymph chylomicrons were isolated. Recovery of infused triacylglycerol was 63 +/- 6.4% and recovery of infused radioactive cholesterol was 24 +/- 4.2% during a 24 h period. There was considerable dilution of radioactive exogenous cholesterol with endogenous cholesterol. Provided that absorption was well-established most exogenous lipid was present in the lymph in the form of chylomicrons, and there was a close relationship between lipid content of the lymph and the presence of chylomicrons. During absorption of fats of differing fatty acid composition chylomicrons remained the predominant transport form in the lymph. Chylomicrons obtained during absorption of several fats have been analysed in detail. The protein, phospholipid, free and esterified cholesterol content of these chylomicrons varies within narrow limits. The fatty acid composition of chylomicron triacylglycerols reflects the type of fat in the test meal but the composition of chylomicron phospholipids and cholesteryl esters shows clear discrimination. During absorption of coconut oil there is a strong negative discrimination towards lauric acid both for cholesteryl esters and for phospholipids.