Steady-state kinetics of serum bile acids in healthy human subjects: single and dual isotope techniques using stable isotopes and mass spectrometry.

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Techniques have been developed for the measurement of the complete steady-state kinetics of both chenodeoxycholic (CDCA) and cholic (CA) acid and the pool size of deoxycholic acid (DCA) from the serum of healthy subjects using stable isotopes and capillary gas-liquid chromatography-mass spectrometry (GLC-MS). Serum bile acids were purified by a method employing a C18 chromatographic cartridge, acid solvolysis, enzymic hydrolysis, methylation, a C8 chromatographic cartridge, and TMS-ether derivatization. Fifty mg each of [24-13C]CDCA and [24-13C]CA was given to five healthy subjects and kinetics were measured from serum and bile. In each case, the measurements from serum (S) equalled those from bile (B) (CDCA (S vs. B): fractional turnover rate (FTR) (d-1) 0.17 +/- 0.03 vs. 0.18 +/- 0.04; pool (g) 0.64 +/- 0.1 vs. 0.68 +/- 0.14, synthesis (g d-1) 0.12 +/- 0.03 vs. 0.1 +/- 0.03; CA (S vs. B): FTR (d-1) 0.28 +/- 0.05 vs. 0.29 +/- 0.07, pool (g) 0.84 +/- 0.29 vs. 0.82 +/- 0.29, synthesis (g d-1) 0.24 +/- 0.10 vs. 0.25 +/- 0.12). In addition, a dual isotope technique for measuring the steady-state kinetics of CDCA was developed using [11,12-2H]CDCA, [24-13C]CDCA, and a single sample of serum. In ten subjects, the FTR, pool and synthesis of CDCA measured from serum was similar to that measured from bile. Finally, a technique for estimating the deoxycholic acid (DCA) pool from serum using the ratio of the 370 ion of DCA to that of CDCA was developed. In summary, these data demonstrate that the steady-state kinetics of CDCA and CA and the pool size of DCA can be measured from the serum of healthy subjects.