The postprandial lipoprotein metabolism is important since it determines the circulation of potentially atherogenic particles and influences the metabolism of high-density lipoproteins (HDL) in a complex manner that is at present not completely understood. Therefore, the short-term (24-h) changes in postprandial lipoprotein metabolism, including retinyl palmitate (RP), apolipoprotein A-I (apo A-I), and apolipoprotein B, were studied in relation to postheparin lipolytic activities in six healthy normolipidemic men after an oral RP fat tolerance test. The fat load (98 g) was cleared in 7 h, because the triglyceride (TG) concentrations had returned to initial values (0.72 +/- 0.31 mmol/l) at that time. RP showed a peak in plasma at 4 and 5 h but remained present in chylomicron (remnants) in low concentrations after 8 and 24 h. After the fat load, HDL cholesterol and HDL-associated apo A-I showed a significant decrease in concentration of 35 and 29%, respectively. The decrease coincided with the increase in chylomicron remnants and the transient appearance of TG-enriched HDL. Hepatic lipase was correlated to both the initial HDL cholesterol concentration as well as the peak concentration of TG in chylomicron remnants, suggesting that it could be one of the regulating common physiological pathways in postprandial HDL and TG metabolism. In the subjects studied, the atherogenic potential of plasma increased in response to an oral fat load, characterized by a decrease in HDL cholesterol and HDL-associated apo A-I.
