Kajer L E, Williams G C, Szczepanik P, Silvis S, Hanson R F
Biochim Biophys Acta. 1979 Jun 21;573(3):430-5. doi: 10.1016/0005-2760(79)90217-0.
The proposed cholic precursor, 3 alpha, 7 alpha, 12 alpha-trihydroxy-5 beta-[3H]cholestan-26-oic acid, and [14C]cholesterol were infused intravenously at a constant rate into two dogs for 25 days. If the specific activities of trihydroxy[3H]cholestanoic acid and [3H]cholic acid will be equal after an isotopic steady-state is achieved. The specific activities of [14C]deoxycholic acid (formed from [14C]cholic acid) isolated in the stool of these two dogs were equal the last four days of the infusion indicating that labeled deoxycholic acid (and presumably labeled cholic acid) was in an isotopic steady-state. However, the specific activities of trihydroxy[3H]cholestanoic acid were 3.3 and 5.7 times greater than the specific activities of [3H]cholic acid, respectively. These data suggest that either an alternate route of cholic acid synthesis exists exclusive of trihydroxycholestanoic acid or that an isotopic steady state of trihydroxycholestanoic acid cannot be reached during an infusion of labeled trihydroxycholestanoic acid.
将拟议的胆酸前体3α,7α,12α - 三羟基 - 5β - [3H]胆甾烷 - 26 - 酸和[14C]胆固醇以恒定速率静脉内输注到两只狗体内，持续25天。如果在达到同位素稳态后，三羟基[3H]胆甾烷酸和[3H]胆酸的比活度将相等。在这两只狗粪便中分离出的[14C]脱氧胆酸（由[14C]胆酸形成）的比活度在输注的最后四天相等，这表明标记的脱氧胆酸（可能还有标记的胆酸）处于同位素稳态。然而，三羟基[3H]胆甾烷酸的比活度分别比[3H]胆酸的比活度大3.3倍和5.7倍。这些数据表明，要么存在一条独立于三羟基胆甾烷酸的胆酸合成替代途径，要么在输注标记的三羟基胆甾烷酸期间无法达到三羟基胆甾烷酸的同位素稳态。
