Distribution and turnover of cholesterol in humans

Abstract

The relationships between some parameters of cholesterol metabolism and body weight were studied in 22 subjects. Cholesterol-4-(14)C, complexed with plasma lipoprotein, was injected intravenously and from the resultant specific activity-time curves a number of indexes of cholesterol turnover were calculated. These were based on the two-pool model previously described by Goodman and Noble and included estimates of the sizes of the two pools, the production rate of cholesterol in the system, the rate constants for cholesterol removal from the two pools and transfer between the pools, and the metabolic clearance of cholesterol. Single and multiple regression analysis was used to define the relationships between the turnover and distribution of cholesterol and the total weight and fat content of the body. The amount of cholesterol in the more rapidly turning over pool A, which probably includes cholesterol in liver, plasma, erythrocytes, and part of the viscera such as intestine, varied from 14.9 to 32.7 g. The mean value for the extraplasma part of pool A was 17.9 g. Making certain assumptions it was possible to derive estimates of the probable lower and upper values for size of pool B (exchangeable cholesterol in tissues other than in pool A), which were, on average, 35 and 60 g. The daily production rate of cholesterol (assumed to be equivalent to total turnover rate) varied between 0.73 and 1.68 g/day. The production rate of cholesterol and the size of pool B were significantly related to total body, and particularly to excess body, weight. When the plasma content was excluded, the amount of cholesterol in pool A was not related to weight. For a body of ideal weight the production rate was 1.10 g/day and the size of pool B between 32 and 53 g. For each kilogram of excess weight the expected increments were 0.0220 g/day and 0.90 g, respectively. The plasma cholesterol concentration was not related to the production rate or to the amount of cholesterol in the two pools. It was, however, inversely related to the fractional rate of removal from pool A and to the metabolic clearance rate of cholesterol which suggests that inadequate excretion could be of importance in the development of hypercholesterolemia.