Sterol metabolism. 5. The uptake of sterols by organelles of intestinal mucosa and the site of their esterification during absorption

Abstract

Sterol esters are absent from the intestinal mucosal cells of fasting guinea pigs and occur only occasionally in the groundplasm fraction of cells from animals dosed with cholesterol. In the rat, sterol esters were found sporadically in the mucosa of both fasting animals and animals dosed with 7-dehydrocholesterol, mainly in the groundplasm and F-layer fractions. The results imply that esterification is not directly involved in the absorption of sterols across the outer-cell membrane. By contrast, a single dose of vitamin A is mainly (approximately 75%) esterified during absorption across the intestinal mucosa of the guinea pig. The vitamin becomes associated with each cell fraction. A comparison of the sterol/nitrogen ratios for the cell fractions of fasting animals with those of sterol-dosed animals indicates that additional sterol can be taken up by the organelles. The latter therefore appear to play an important part in sterol absorption. It is postulated that in these two species esterification of single doses of cholesterol occurs mainly in the connective tissue before its entry into the lymph vessels, and that the action of esterase, although not obligatory for absorption, greatly accelerates the process.