Diurnal variation in biliary lipids and serum VLDL before and during treatment with cloribrate

Biliary lipid composition and serum VLDL triglyceride (VLDL-TG) level were determined intermittently over 24 h in 5 previously cholecystectomized hypertriglyceridaemic patients. The study was repeated when the patients had been treated with clofibrate for 2 months. Before and during treatment the molar cholesterol concentration in duodenal bile showed marked diurnal variations. It dropped after the first meal in the morning, remained depressed until the end of the evening, increased early at night and dropped back slightly between 2 and 8 a.m. A diurnal variation was also recorded for bile acid composition, as the contribution of cholic acid (C) increased in 4 of the subjects at night. During treatment with clofibrate, the molar concentration of cholesterol remained unchanged during the day but was significantly elevated in samples obtained at night. The contribution of C increased during both the day and the night. As a general tendency, changes in the curve representing the molar level of cholesterol in bile were mirrored by reversed changes in the VLDL level in plasma. The possibility of a causal relationship between these two parameters is discussed.