Intestinal absorption of biliary and exogenous cholesterol in the rat

Non-starved rats (fed a cholesterol-free diet prior to the experiments) with common bile fistula were infused intraduodenally with rat bile labelled with [1,2-³H]cholesterol at a constant rate (0.6 ml/h) and a nutritive mixture containing, in particular, olive oil and 1 μmol [4-¹⁴C]cholesterol per ml at rates of 1 ml/h (group B) or 2.3 ml/h (group A) for 5 h. Control rats (group C) were prepared as group B rats but the nutritive mixture was free of cholesterol. 1 h after the end of infusions, the animals were killed. Biliary and exogenous cholesterol were absorbed in the upper two-thirds of the small intestine; a large proportion of ³H and ¹⁴C radioactivity was present in the mucosa, but cholesterol from exogenous origin went across the mucosa more rapidly than cholesterol from biliary source. These observations suggest the existence of a non-homogeneous luminal mixture of molecules of cholesterol from different sources. The luminal dilution of [³H]- and [¹⁴C]sterols by non-labelled sterols increased from the proximal to the distal part of the small intestine. Precursor sterols and coprosterol were present in the stomach contents and in the lumen of caecum, colon and feces.