Sterol synthesis in intestinal villi and crypt cells of rats and guinea pigs.

The villi of the small intestine of rats and guinea pigs have been demonstrated to be capable of as rapid synthesis of sterols as the crypt cell fractions. This finding is not in agreement with the generally accepted belief that the crypt cells are responsible for essentially all of the synthesis of sterols in the intestine. Three methods of measuring synthesis were used: incubation with [(14)C]-acetate of villi, crypt cell, and muscle fractions obtained by the method of graduated scraping; incubation of whole intestine pieces followed by fractionation into the same fractions; and in vivo studies in rats injected with [(14)C]-acetate and killed 7-40 min later, after which the intestine was fractionated by scraping or by serial sectioning of frozen tissue. All methods were in agreement in showing sterol synthesis in villi to be as active per mg protein as in crypt cells. Measurements of the isotope content of the total nonsaponifiable lipid fractions led to the same conclusions as did the isotope content of the digitonin-precipitable sterol fractions. For a given period of incubation, the ratio of the two values was the same in villi and crypts, ruling out the possibility of synthesis of sterols in crypts prior to transfer to villi. The fractionation into villi, crypts, and muscle fractions by scraping greatly reduced the total sterol synthetic activity in rat but not in guinea pig small intestine, indicating the hazard of using only this in vitro technique to make quantitative estimates of the sterol synthetic capacity of tissue fractions.