The origin of dolichol in the liver of the rat. Determination of the dietary contribution.

Commercial laboratory rat chow was found to contain 8.3 micrograms/g of dolichol and 2.1 micrograms/g of polyprenol; each was 14-18 isoprenes in length. The chain length and relative concentration of rat fecal dolichol and polyprenol were approximately the same as in chow, indicating that there was no preferential absorption of a particular chain length or a particular class of prenols. To quantitate the absorption of these compounds, rats were intubated with either [3H]dolichol or [3H]polyprenol or, as a control, [3H]cholesterol. After 30 h, the amount of radioactivity accumulated in the liver of the [3H]cholesterol-fed rat averaged 6% of the total administered. In contrast, the amount of radioactivity present in the livers of the [3H]dolichol- or [3H]polyprenol-fed rats was 0.05% of the total. From these data the maximum hepatic accumulation of the dietary prenols was calculated to be 0.06 micrograms/30 h. When compared with the values obtained for hepatic de novo synthesis (Adair, W. L., Jr., and Keller, R. K. (1982) J. Biol. Chem. 257, 8990-8996), we conclude that the contributions of the diet to the liver dolichol pool is negligible.