JBC, Vol. 251, Issue 9, 2709-2715, May, 1976
Metabolism of bile alcohols in the perfused rabbit liver
B. I. Cohen, T. Kuramoto, M. A. Rothschild and E. H. Mosbach
The mechanism and sequence of side chain hydroxylation of cholesterol in
bile acid synthesis was studied in the isolated perfused rabbit liver. A
comparison was made between the importance of 26- and 25-hydroxylation in
cholic acid biosynthesis in the rabbit. The formation of [G-3H]cholic acid
was observed when the liver was perfused with
5beta-[G-3H]cholestane-3alpha, 7alpha-diol, 5beta-[G-3H]cholestane-3alpha,
7alpha-12alpha-triol, and 5beta-[G-3H]cholestane-3alpha, 7alpha, 26-triol.
No [G-3H]chenodeoxycholic acid was detected in the bile. These findings
indicate that potential precursors of chenodeoxycholic acid were
hydroxylated at position 12alpha either subsequent to or before
hydroxylation of the cholesterol side chain. In addition, no other
intermediates (tetrahydroxy or pentahydroxy bile alcohols) were found in
the bile when these compounds were perfused in the liver. Bile acid
precursors were detected in bile when the rabbit liver was perfused with
5beta-[24-14C]cholestane-3alpha, 7alpha, 25-triol. The
5beta-[24-14C]cholestane-3alpha, 7alpha, 25-triol was hydroxylated in the
liver at the 12alpha position to yield the corresponding
5beta-cholestane-3alpha, 7alpha, 12alpha, 25-tetrol. The tetrol was further
metabolized to a series of pentols (5beta-cholestane-3alpha, 7alpha,
12alpha, 22, 25-pentol; 5beta-cholestane-3alpha, 7alpha, 12alpha, 23,
25-pentol; 5beta-cholestane-3alpha, 7alpha, 12alpha, 24, 25-pentol; and
5beta-cholestane-3alpha, 7alpha, 12alpha, 25, 26-pentol). The major bile
acid obtained from the perfusion of the 5beta-cholestane-3alpha, 7alpha,
25-triol was cholic acid. The experiments indicated that in the rabbit
liver 12alpha-hydroxylation can occur after hydroxylation of the
cholesterol side chain at either C-25 (5 beta-cholestane-3alpha, 7alpha,
25-triol) or C-26 (5beta-cholestane-3alpha, 7alpha-26-triol). Apparently,
the rabbit can form cholic acid via the classical 26-hydroxylation pathway
as well as via 25-hydroxylated intermediates.