The transport of carotenoids, vitamin A and cholesterol across the intestines of rats and chickens

Abstract

Chickens kept on a low-carotenoid diet and normal adult rats were starved for 24 hours and dosed with oily solutions of vitamin A alcohol, its acetate or palmitate, free cholesterol, its acetate or palmitate, [beta]-carotene, lycopene or lutein. The rats were killed 60-90 minutes later and the chickens after 150-180 minutes. The intestinal contents were washed out and, after being separated from the intestinal muscles, the mucosal cells were homogenized and fractionated into nuclear, mitochondrial, microsomal and supernatant (cell sap) fractions. In all trials with vitamin A the latter was present mostly as ester in both the intestinal muscles and in the mucosal cells, and this ester could be recovered almost completely from the supernatant fraction of the cell homogenate. It was immaterial whether no cholesterol, free cholesterol, its acetate or palmitate was fed; cholesterol was present predominantly as the free compound both in the muscles and in the mucosal cells, and the microsomal fraction of the mucosal cells contained most of the free cholesterol. The concentration of free cholesterol in the microsomal fraction could not be changed, whereas that in the muscles increased slightly after heavy dosing. Except for lutein in chickens, all carotenoids were found only in traces in both intestinal muscles and in mucosae. In chickens lutein was found in high concentration in the intestinal muscles and in the mucosal cells; in the latter it was concentrated in subcellular particles such as mitochondria and microsomes. The role of stereospecific binding by lipoproteins in the absorption, transport and storage of carotenoids is discussed with special reference to species differences in the selective absorption of different carotenoids.