Exchange of methyl hydrogens in ethanol during incorporation in bile acids in vivo.

[2,2,2-2H]Ethanol was administered continuously to bile fistula rats for 72 h, with or without (--)-hydroxycitrate. The deuterium labelling of biliary bile acids was determined by GC-MS and 13C NMR. Difference spectra between 2H,1H- and 1H-decoupled 13C NMR spectra showed the presence of partly deuterated methyl and methylene groups in methyl cholate, indicating exchange of deuterium in [2,2,2-2H]ethanol for protium prior to or during incorporation of acetate into the bile acid. The extent of exchange was 20--30% as calculated from the isotopic composition of a fragment ion containing one methyl and one methylene group derived from C-2 of acetate. The exchange was unaffected by (--)-hydroxycitrate, indicating that it was not due to reversible incorporation of deuterated acetate into citrate. About 60% of the acetyl-CoA serving as precursor of cholic and chenodeoxycholic acids were derived from ethanol. This value was not changed by administration of (--)-hydroxycitrate. The half-life time of cholesterol molecules acting as precursors of both bile acids was about 50 h in the presence of (--)-hydroxycitrate, which is about the same as previously found in the absence of the inhibitor.