Cholesterol absorption and transport in thoracic duct lymph lipoproteins of nonhuman primates. Effect of dietary cholesterol level

Abstract

The effect of dietary cholesterol level on cholesterol absorption and its subsequent transport in thoracic duct lymph lipoproteins was studied in two species of nonhuman primates, namely the African green monkey (Cercopithecus aethiops) and the cynomolgus macaque (Macaca fascicularis). Each animal served as its own control because each received sequential, intraduodenal infusions of two fat-rich liquid diets that differed only in the amounts of cholesterol. The percentage of dietary cholesterol absorbed was calculated by dividing the rate of appearance of exogenous cholesterol radioactivity in lymph by the rate of infusion of dietary cholesterol radioactivity at a time when lymph cholesterol specific activity was constant relative to that of diet. The percentage of dietary cholesterol absorbed was similar during both diet infusions in African green monkeys but was significantly decreased during the high cholesterol diet infusion in cynomolgus macaques. Rates of appearance of lymph total cholesterol mass were significantly increased during infusion of high cholesterol diets due to a statistically significant increase in cholesteryl ester transport rates. This increase was due in large part to the preferential esterification of exogenous cholesterol that was incorporated into lymph chylomicrons and VLDL. The rate of appearance in lymph of exogenous cholesterol significantly increased during the high cholesterol diet infusion while that of endogenous cholesterol decreased. This decrease or compensation in endogenous cholesterol transport occurred during absorption of increased levels of dietary cholesterol and apparently was due to an approximate 50% decrease in the absorption of lumenal cholesterol. Our data demonstrated that there was not a simple one-to-one relationship between the amount of isotopic dietary cholesterol absorbed from the intestinal lumen and the mass of cholesterol moved into lymph via the intestine. Rather, the amount of sterol transported into the body depends on the degree of the decrease in endogenous cholesterol transport and probably on the efficiency of cholesterol esterification during absorption.