Cholesterol absorption and turnover in rhesus monkeys as measured by two methods

We compared the absorption of cholesterol in seven rhesus monkeys (four high-responders and three low-responders) as measured by two methods: 1) the dual isotope plasma ratio method of Zilversmit (1972. Proc. Soc. Exp. Biol. Med. 140: 862) and 2) the single isotopic meal feeding technique of Borgström (1969. J. Lipid Res. 10: 331). We also compared the cholesterol pool sizes calculated by kinetic analysis of the plasma cholesterol specific activity decay curves obtained after simultaneous administration of [(3)H]- and [(14)C]cholesterol, one given intravenously and the other orally. The ratio of orally to intravenously administered cholesterol radioactivity in plasma did not attain constancy until 6 weeks after isotope administration. Therefore, the percent absorption of cholesterol was calculated by the Zilversmit method 8 weeks after the administration of isotopes. The mean percent absorption of cholesterol by the Borgström method was 66.3 +/- 5.1 (S.E.) and by the Zilversmit method was 70.3 +/- 7.4. The differences were not statistically significant. However, in two of seven monkeys the percent absorption of cholesterol calculated by the Zilversmit method was higher by 10.4 and 22.6 percentage points than the values obtained by the Borgström method. Cholesterol absorption by either method was higher in the high-responding monkeys than in the low-responding group. The sizes of the rapidly exchangeable pool or the minimum estimate of the total body pool of cholesterol were similar for all monkeys or for either the low-responding or the high-responding animals and were also similar when calculated using the data from either the orally or the intravenously administered radioactive cholesterol. Cholesterol synthesis was significantly higher in the low-responding monkeys (115 mg/day) than in the high-responding (64 mg/day). The present study and our previous studies support the hypothesis that a major factor causing the difference in response of plasma cholesterol to dietary cholesterol between the high- and low-responding rhesus monkeys is a difference in the intestinal absorption of cholesterol.-Bhattacharyya, A. K., and D. A. Eggen. Cholesterol absorption and turnover in rhesus monkeys as measured by two methods.