Abstract
Plasma LCAT activity was assessed in cebus and squirrel monkeys fed diets containing either corn or coconut oil with or without 0.1% cholesterol. In vitro enzyme activity was determined by measuring the incorporation of [1,2-
3H] cholesterol into cholesteryl ester. Three assay conditions were used to assess overall enzyme activity and to differentiate between the concentration of enzyme and substrate effects. LCAT activity was affected primarily by species and dietary fat and to a lesser extent by dietary cholesterol in squirrel monkeys. Specifically, plasma from both species of monkeys fed corn oil diets had comparable overall rates of LCAT activity (percent esterification and mass esterified/h). In all monkeys fed the coconut oil diets percent esterification was lower than in those monkeys fed the corn oil diets, and was lowest in squirrel monkeys, particularly those fed cholesterol. Coconut oil feeding also resulted in lower substrate activity in all monkeys, whereas cholesterol feeding had no significant effect on substrate activity. Squirrel monkeys always had lower substrate activity than cebus for any diet group. Coconut oil feeding resulted in a lower p]S ratio of HDL phospholipid fatty acids in both species, but the decrease was greater for cebus monkeys. In terms of the mass of cholesterol ester formed (molar rate) during the in vitro assay, plasma from cebus monkeys fed coconut oil diets had greater activity than plasma from other groups. Evaluation of enzyme activity indicated that the greater esterification in cebus monkeys fed the coconut oil diet was associated with the ability of cebus, but not squirrel monkeys, to increase their enzyme activity. In essence, cebus monkeys maintained greater LCAT substrate and enzyme activities than squirrel mon keys when made hypercholesterolemic with coconut oil feeding.