Lipid metabolism in helminth parasites. VII. Absorption of cholesterol by Hymenolepis diminuta (Cestoda).

H. diminuta adults which are known not to synthesize cholesterol, efficiently absorbed cholesterol-4-14C from a mixed micellar solution of sodium taurocholate and monoolein. Emulsified cholesterol was also absorbed, but at a much lower rate. A large fraction of the absorbed sterol was converted in 1 hr or less to a single, unidentified metabolite. The results indicated that H. diminuta competes with its host for micellar solutions of cholesterol, just as it does for micellar solutions of fatty acids and monooleins. Acetate, hydroxymethylglutarate, and mevalonate are converted to two isomers of famesol by H. diminuta (Frayha and Fairbairn, 1969) but the farnesols (or their pyrophosphate derivatives) are not converted to squalene, and synthesis of cholesterol does not occur. As this cestode contains considerable amounts of cholesterol (Fairbairn et al., 1961) it must therefore absorb it from the rat intestinal contents. Bailey and Fairbairn (1968) reported that H. diminuta readily absorbs fatty acids and monooleins if these are presented to it in the form of mixed bile salt micelles such as occur naturally in the rat intestine, but only slightly if they are presented as emulsions. In the present investigation, it was found that cholesterol is also freely absorbed from micellar solutions, and that a considerable proportion of it is quickly converted to a more polar but otherwise unidentified metabolite.