POSTPRANDIAL PLASMA VITAMIN-A METABOLISM IN HUMANS - A REASSESSMENT OF THE USE OF PLASMA RETINYL ESTERS AS MARKERS FOR INTESTINALLY DERIVED CHYLOMICRONS AND THEIR REMNANTS

We investigated postprandial vitamin A metabolism by measuring retinyl ester, triglyceride, and apolipoprotein (apo)B-48 in the plasma lipoproteins of human subjects before and after fat-feeding. Following a 14-hour fast, eight healthy subjects (two men, six women, 28 to 79 years) were given a fat-rich meal (1 g fat/kg body weight) containing vitamin A (40 retinol equivalents per kilogram body weight). Blood was collected every 3 hours for 12 hours and lipoproteins were isolated by sequential ultracentrifugation. Mean plasma retinyl ester concentration peaked 6 hours after the fat-rich meal, whereas mean plasma triglyceride peaked at 3 hours. Data obtained from hourly samples in 3 subjects showed that changes in the postprandial plasma concentration of retinyl ester occurred 1 to 2 hours after changes in the plasma triglyceride concentration. In triglyceride-rich lipoproteins (TRL) of d<1.006 g/mL, retinyl ester similarly peaked at 6 hours, whereas triglyceride as well as apoB-48 peaked at 3 hours. Although retinyl esters were found mainly in TRL in the initial postprandial period (84%, 3 hours; 83%, 6 hours), in fasting and postprandial plasma, particularly 9 or more hours after fat-feeding, a large percentage of plasma retinyl esters were in low-density lipoproteins (LDL) (44%, fasting; 9%, 3 hours; 9%, 6 hours; 19%, 9 hours; 32%, 12 hours). A small percentage of retinyl esters were also found in postprandial high-density lipoproteins (HDL) (2% to 7%). ApoB-48 was not detected in LDL of fasting or postprandial plasma. We conclude from these data that retinyl esters do not always serve as markers for intestinal apoB-48-containing TRL in fasting or postprandial plasma. © 1990.