KINETICS OF RETINYL ESTERS DURING POSTPRANDIAL LIPEMIA IN MAN - A COMPARTMENTAL MODEL

Orally ingested vitamin A (retinol) is incorporated into intestinal ch ylomicrons (CHYLO) in the form of retinyl esters (RE) along with newly absorbed dietary triglycerides (TG). As the intestinal lipoproteins u ndergo hydrolysis in the circulation, the majority of the RE remain wi th the secreted intestinal particles and have been used as a marker fo r intestinally derived lipoproteins during the early phase of the post prandial state. A multicompartmental model was developed for the kinet ics of RE during postprandial lipemia in individuals with normal lipid levels (n=16) and in patients with hyperlipidemia (n=44). The assumpt ions used in the development of the model are presented in this report . Some of the key findings include (1) as much as 50% of the newly syn thesized RE may be secreted by the intestine as very-low-density lipop rotein (VLDL)-sized particles of St 20 to 400 following consumption of a test meal containing a moderate amount of fat (20 to 30 g); (2) in most individuals, approximately 50% of the RE secreted in S-f greater than 400 are converted to smaller, less buoyant fractions, and 50% are irreversibly removed directly from the plasma; (3) as much as 5% to 2 0% of the ingested retinol may be secreted as smalt intestinal lipopro teins with the buoyance of low-density lipoprotein (LDL) in some indiv iduals; and (4) less than 5% of RE flux through St 20 to 400 is conver ted to Sc less than 20, and the primary catabolic pathway for RE in th is fraction is direct uptake, Comparable estimates can be obtained for the kinetic parameters when repeat studies are made in the same subje cts under comparable conditions. Copyright (C) 1997 by W.B. Saunders C ompany.