Determination of cholesterol absorption in man by intestinal perfusion

In this study a technique is described for estimating net absorption of total cholesterol (endogenous + exogenous) that enters the intestine. The method employs intubation of patients with a 3-lumen tube that contains a 10-cm mixing segment in the duodenum and a 100-cm absorption segment in the jejunum. A liquid formula diet containing varying amounts of exogenous cholesterol is infused continuously into the upper duodenum for a period of several hours; the formula diet stimulates constant contraction of the gallbladder and thus provides for continous secretion of biliary cholesterol sitosterol as a marker, the input of endogenous + exogenous cholesterol can be measured at the end of the 10-cm mixing segment. Net cholesterol absorption is estimated from the disappearance of cholesterol relative to beta-sitosterol over the next 100-cm of jejunum. When radioactive cholesterol was also used as a marker, radioactivity usually disappeared more rapidly than the mass of choleesterol over the absorption segment; this suggests that a significant amount of isotope exchange occurs in the upper intestine. Using beta-sitosterol as a marker, the extent of exchange can be determined. In six patients, cholesterol inputs ranged from 51 to 118 mg/hr, and net percentage absorption was 34-56%. When inputs of cholesterol were acutely increased by enhancing exogenous cholesterol, absolute absorption was uniformly increased, but percentage absorption either remained the same or was decreased somewhat. Changine inputs of beta-sitosterol had a striking effect on cholesterol absorption, and relatively small increments of beta-sitosterol almost always produced corresponding reductions in uptake of cholesterol. The intestinal perfusion method appears to provide certain advantages over previous techniques for estimating total cholesterol entering the upper intestine, including that derived from both endogenous and exogenous sources. Measurements can be made over short periods of time, and the method allows for determination of effects of acute changes in the intestinal milieu on cholesterol absorption. Finally, the technique defines the extent of isotope exchange between cholesterol in the intestinal mucosa and in the lumen.