Effect of saturated and unsaturated fats on fecal excretion of end products of cholesterol-4-C¹⁴ metabolism in the rat

¹ Department of Internal Medicine, The University of Texas Southwestern Medical School, Dallas, Texas

The influence of fat on the excretion into feces of the end products of cholesterol-4-C¹⁴ metabolism was studied in rats fed diets which were either fat-free or contained lard or corn oil at the 20% or 30% level. Total recovery of injected C¹⁴ was consistently higher in rats fed corn oil and lard than in rats fed fat-free diets. No consistent differences were noted among the three groups in the excretion of C¹⁴ in either bile acids or digitonin-precipitable neutral sterols. However, in rats fed corn oil there was a marked increase in the excretion of C¹⁴ in nondigitonin-precipitable neutral sterols, amounting in these animals to as much as 54% of the excreted C¹⁴. These data are interpreted as demonstrating that the excretion of nondigitonin-precipitable neutral sterols may under some circumstances be a major pathway for cholesterol excretion. Furthermore, the marked acceleration in the excretion of nondigitonin-precipitable sterols may account in part for the cholesterol-lowering effect of unsaturated fats.