Comparison of isotopic equilibrium and dual isotope blood ratio methods for measurement of cholesterol absorption in rats.

The dual isotope plasma ratio method (IRM) was applied to eight 3-month-old rats fed a semipurified diet. 1 month later, the isotopic equilibrium method (IEM) was substituted and was continued for 2 months. The animals were therfore 6 months old at the end of the isotope experiment. The IRM was then applied to a second group of eight 6-month-old rats. No difference was seen between the absorption coefficient of cholesterol measured by the IRM in rats of the first (73 +/- 2%) and of the second groups (72 +/- 4%) or by the IEM (69 +/- 1%). A critical discussion of both techniques is presented.