DIRECT MEASUREMENT OF CHOLESTEROL ABSORPTION VIA THE THORACIC DUCT IN MAN

The route of absorption of steroids from the gastrointestinal tract seems to l)e largely deter-minedl bv the chemiiical nature of the comiipounds. AMethyl testosterone (1), 17a-methvl estradiol (2), and cortisone acetate (3) are al)sorl)ed in the rat by way of the portal circulation. Stu(lies fromii this lal)oratory in lhtumiian sul)jects showedI that testosterone, cortisol. cortisone acetate, and corti-costerone are also absorbed in this miianner and are virtually absent fromii the lymph (4). In con-trast, absorption of cholesterol into lymph of the rat (5, 6) and(I dog (7) accounts for essentially all of the sterol that eniters these species fromii the diet. Although it miiight be anticipated fromii these ani-miial studies and fronm the nonpolar nature of the nmolecule that cholesterol woould be absorbed via the lymiiph in hutmiian subjects, it was of interest to test this directly, since somiie aspects of steroid metabolism in the laboratory animiial are different fromii those observed in miian (8-10). By miieans of cannulation of the thoracic duct andI the admin-istration of labeled cholesterol. it has been possible for the first tinme to study directlv the absorption and esterification of cholesterol in mlan. These stutlies have demlonistrated that dietary cholesterol is largely absorbed throtugh the lymphatics an(d that the miiajor l)ortion is esterifiedI (luring the ab-sorp)tive parocess. MATERIAL AND METIIODS The clinical data concerninig the subjects are given in Table I. A polyethylenie catheter was inserted into the left thoracic duct at operation as described previously (4). The lymplh was continiuously collected from the thoracic duct cannlula at predeterminied time intervals anid blood samples were withdrawn periodically. The p)a-* This inivestigation was supported by a grant from th