| Summary: | A means of quantifying the two major pathways of cholesterol elimination from the body, bile acid production and neutral sterol excretion, has been devised for use in the intact rat. Utilizing an isotopic “steady state” for blood cholesterol (which has been attained by the subcutaneous implantation of capsules containing cholesterol-4-C14) and the measurement of C14 appearance in the bile acid and sterol fractions of feces, it is possible to measure the amounts of these two excretion products. With this method the increase in bile acid formation following cholesterol feeding has been demonstrated directly; this increase has been shown to be sufficient in magnitude to account for the entire positive balance for neutral sterol which occurs in the cholesterol-fed animal after equilibrium has been attained. Finally, utilizing a double isotopic steady state in animals fed cholesterol-7α-H3 and implanted with cholesterol-4-C14, it has been possible to demonstrate that the major portion of fecal cholesterol of endogenous origin is derived from or is in equilibrium with that of the blood. In these animals the measurement of dietary cholesterol absorption has also been possible.
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