Absorption of cholesterol esters in the lymph-fistula rat.

VAHOUNY, GEORGE V. AND C. R. TREADWELL. Absorption oj cholesterol esters in the lymph-fistula rat. Am. J. Physiol. 195(z): 516520. rg#.-Free and esterified cholesterol fractions in thoracic duct lymph of rats were determined after the administration of emulsions containing saline, albumin, taurocholate, oleic acid and free cholesterol, or fatty acid esters of cholesterol. Total lymph cholesterol increased within 3 hours after feeding free cholesterol or the natural cholesterol esters. Cholesterol butyrate was absorbed as well as free cholesterol, while the esters of oleic and linoleic acids, were absorbed slower and less efficiently. Saturated acid esters, laurate and stearate were absorbed slowly and inefficiently. Administration of cholesterol trimethylacetate, which is resistant to the hydrolytic action of pancreatic cholesterol esterase, did not result in any increase in lymph cholesterol above the control level. Throughout all groups in which absorption of cholesterol occurred, the absorbed cholesterol in lymph was esterified from 87 yO to 95 7&. The data are in agreement with the concept that dietary cholesterol esters are hydrolyzed in the intestinal lumen prior to absorption of the cholesterol moiety as free cholesterol. I T HAS LONG BEEN KNOWN that the cholesterol of dietary cholesterol esters is absorbed from the intestinal lumen, and that part of the subsequent increase in blood cholesterol is due to an elevation of the free fraction (I). Mueller (2), in 1915, suggested that dietary cholesterol esters underwent partial hydrolysis in the intestine, with absorption of both free and esterified cholesterol in approximately the same ratio as found in lymph. In an attempt to determine the absorbed form of ingested cholesterol, Schonheimer and Hummel (3) fed cholesterol oxalate in addition to various natural cholesterol esters. From the large deposition of cholesterol in the liver, with no trace of oxalate ester, it was suggested that a complete saponification of the oxalate ester had occurred in the intestinal lumen prior to absorption. More recently, Peterson and co-workers (4), using blood and hepatic cholesterol levels as indicators of cholesterol absorption in chicks, and Swell et al. (s), using a similar approach in rats, studied the comReceived for publication June 25, 1958. 1 Supported in part by grants from the National Heart Institute (H-2033), and the Life Insurance Medical Research Fund. parative absorption of various dietary cholesterol esters, and obtained comparable results in these two species. In general dietary free cholesterol led to higher levels of this alcohol in blood than did dietary esters. Among the esters, those of short-chain fatty acids were absorbed in amounts comparable to the free sterol, while the administration of cholesterol esters of long-chain, unsaturated fatty acids resulted in lower blood cholesterol levels. The long-chain, saturated esters were poorly absorbed, if at all, in these studies. The authors suggested the possibility that alterations in tissue cholesterol levels following the ingestion of cholesterol esters reflected the degree and rate of hydrolysis of these esters prior to absorption from the intestinal lumen. The reports that conditions in the intestinal lumen favor the hydrolysis of cholesterol esters rather than the esterification of free cholesterol with fatty acid (6, 7) are also consistent with the concept that the esters are hydrolyzed prior to intestinal absorption. Since cholesterol is transported almost entirely via the lymphatic channels following absorption (8, 9), it was desirable to reinvestigate the question of dietary cholesterol ester 516 by 10.0.33.4 on A ril 4, 2017 http://ajple.physiology.org/ D ow nladed fom ABSORPTION OF CHOLESTEROL ESTERS s7 absorption using the thoracic duct fistula technique in rats. In addition to a comparative study of the rate and extent of free cholesterol and cholesterol ester absorption, it was of additional interest to investigate the absorption of an unnatural ester of cholesterol which has been reported to be resistant to the action of hydrolytic cholesterol esterase preparations