Squalene and sterol synthesis in isolated small-intestinal cells of the rat

To compare the synthesis rate of cholesterol in different cells of the small intestine, isolated villous and crypt cells were incubated with a mixture of 14C-acetate and 3H-mevalonate in the presence of unlabeled carriers. The synthesis rate of squalene (includes the portion converted to sterols) from acetate was tenfold higher in the crypt than villous cells. The synthesis rate of squalene from mevalonate and the cyclization rate of squalene (the portion found in sterols) were about twofold higher in crypt than in villous cells. The conversion of acetate to squalene was correlated with that to fatty acids in the crypt cells only (r = 0.823), and the ratio of the two synthesis rates (squalene/fatty acids) was threefold higher in crypt than in villous cells. Despite the significant differences in the synthesis rates of squalene and sterols the concentrations of squalene and methyl sterols were similar in the two cell types. THe cholesterol content was, however, consistently higher in villous than in crypt cells, but the concentration was not correlated with the synthesis of squalene in the two cell types. The appearance of labeled squalene was clearly lower than that of labeled sterols in the lipoprotein-free incubation medium, but no differences were found between villous and crypt cells.