To study the metabolic fate of chylomicron phospholipid and apoproteins, 15 mg of doubly labeled ([3H]leu, [32P]phospholipid) rat mesenteric lymph chylomicrons were injected as an intravenous bolus into conscious rats. The specific radioactivity, composition, pool size, and morphology of the plasma lipoproteins were determined after 2-60 min. After injection of chylomicrons, there was a rapid transfer of radioactivity into high density lipoproteins (HDL). At peak specific activity in HDL (2-5 min), 35% of injected apoprotein and 25% of phospholipid radioactivity were recovered in HDL (d 1.063-1.21 g/ml), with smaller recoveries in other lipoproteins and liver. There was an initial rapid rise of 32P specific activity in HDL and d 1.02-1.063 lipoproteins (low density lipoproteins [LDL]), but whereas LDL specific activity subsequently converged with that of d < 1.02 lipoproteins, HDL specific activity decayed more rapidly than LDL or d < 1.02 lipoproteins.
Alan R. Tall, Peter H. R. Green, Robert M. Glickman, John W. Riley