Studies on the formation of C7-oxygenated cholesterol and β-sitosterol metabolites in cell-free preparations of rat liver

Abstract

The microsomal fraction and the 18,000 g supernatant fluid obtained from livers from normal rats, cholestyraminetreated rats, or from rats with a bile fistula have been used to compare the 7α-hydroxylation of [4-14C]cholesterol and β-[4-14C]sitosterol (24α-ethyl-cholesterol). It was not possible to increase the specific formation of 7α-hydroxy-β-sitosterol above 0.05% with any of the preparations. This conversion was less than 1% of that found for cholesterol. The inhibitory effect of added 7-oxo- and 7β-hydroxy-β-sitosterol on the 7α-hydroxylation of cholesterol was found to be much less than that of the corresponding cholesterol compounds. 7α-Hydroxy-β-sitosterol was without effect. It is concluded that the activity of the cholesterol 7α-hydroxylase is dependent upon the structure of the steroid side chain.

Keywords

• 7α-hydroxylation
• cholestyramine
• diurnal variations
• bile fistula
• phenobarbital
• inhibition by C7-oxygenated sterols