Journal of Lipid Research, Vol. 19, 359-369, March 1978
Copyright © 1978 by Lipid Research, Inc.

Effect of different dietary triglycerides on 7-hydroxylation of cholesterol and other mixed-function oxidations

Ingemar Björkhem , Rolf Blomstrand , and Lennart Svensson

Department of Clinical Chemistry, Huddinge University Hospital, Karolinska Institutet, Stockholm, Sweden

The effect of a diet containing triglycerides of different fatty acid composition on hepatic 7-hydroxylation of cholesterol was studied. 7-Hydroxylation of exogenous as well as endogenous cholesterol was significantly lower in the liver of rats fed trilinolein and triolein than in those fed tripalmitin and trierucin. The concentration of cytochrome P-450 in liver microsomes was significantly lower in the rats fed tripalmitin and trierucin than in those fed triolein and trilinolein. The inhibitory effect of triolein and trilinolein on 7-hydroxylation of cholesterol and the stimulatory effect of these triglycerides on the concentration of cytochrome P-450 was not due to the small amounts of peroxides present in the unsaturated triglycerides. Thus addition of the antioxidant butylated hydroxyanisol did not change the general pattern with respect to 7-hydroxylation and concentration of cytochrome P-450. However, a diet consisting of peroxidized linoleic acid further decreased 7-hydroxylation of cholesterol. The difference between the effect obtained with triolein and trilinolein on the one hand and trierucin and tripalmitin on the other was observed also in experiments with lower concentrations of fat in the diet and in experiments with different lighting conditions and feeding patterns. The inverse relation between cytochrome P-450 and 7-hydroxylation of cholesterol, as well as results obtained with substrates for mixed-function oxidation other than cholesterol suggest that most of the changes observed due to the different diets are specific for 7-hydroxylation of cholesterol. The level of cholesterol 7-hydroxylase activity was found to be better related to the degree of absorption of fat than to total amount of absorbed fat or degree of unsaturation of the fat. The results are discussed in relation to previous knowledge concerning mechanisms regulating biosynthesis of bile acid.

Supplementary key words bile acids • lipid peroxides • fat absorption • mass fragmentography

Submitted on June 25, 1977
Accepted on November 21, 1977

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