A comparison of the effects of bile salts on the absorption of cholesterol from the intestine of the rat

Abstract 1. 1. A comparison of the effectiveness of free and conjugated bile salts on the appearance of free and esterified cholesterol into the rat lymph was made using a modification of Bollman's technique for the cannulation of the thoracic duct. 18 to 24 h after operation an emulsion, containing protein, carbohydrate, monoolein and a trace dose of [4- 14 C ] cholesterol , was administered by stomach tube. The influence of natural bile or individual bile salts on the absorption of cholesterol was studied. 2. 2. The data collected included radioactive measurements of free cholesterol, as well as cholesteryl palmitate, cholesteryl oleate, cholesteryl linoleate and cholesteryl arachidonate in lymph. 3. 3. Evidence is presented indicating that the quantity of bile salt used and/or its chemical specificity are factors which produce different rates of absorption and esterification of cholesterol. A significant amount of cholesterol is absorbed without esterification. 4. 4. The free-cholesterol pool of the intestinal wall first becomes enriched (3–4 h after emulsion administration) after which this free-cholesterol pool is drawn upon for esterification. 5. 5. At the hour of peak absorption, about 80% of the total cholesterol is esterified when the rats are given natural bile. 6. 6. A high dose (269 mg) of taurocholate produces a pattern of absorption and esterification of cholesterol very similar to that of natural bile. On the other hand, 269 mg of taurodeoxycholate produces absorption of cholesterol mainly in the free form. 7. 7. Taurochenodeoxycholate is the most effective bile salt when tested at the moderate level of 100 mg; it gives 40% or less esterification. At this dosage level, taurocholate, taurodeoxycholate and cholate are borderline in stimulating absorption of cholesterol and less than 40% is esterified. Glycocholate, deoxycholate, glycodeoxycholate, chenodeoxycholate, glycochenodeoxycholate, lithocholate, glyco- and taurolithocholate, dehydrocholate, glyco- and taurodehydrocholate are not effective at this level. These findings are explicable either by failure of the bile salt to form micelles ( i.e. free and conjugated dehydrocholate) to facilitate absorption or by its failure to activate the esterification mechanism ( i.e. chenodeoxycholate) or both, at this concentration of bile salt. 8. 8. Administration of low dose levels of conjugated bile salts (up to 35 mg) promotes very poor absorption of free cholesterol, none of which is esterified; a finding which results from the concentration of the bile salt being too low to reach its critical micellar concentration.